implants

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implants
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implants spring 2014
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  1. Define osseointegration.
    • • Direct structural and functional contact between ordered, living bone and the surface of a load carrying implant
    • • No fibrous CT interface between the surface of the implant and the adjacent bone
    • o Epithelial migration along this interface is prevented
    • • Titanium does not corrode and TiO2 increases Ca and P deposition on implant surface, thus increasing bone deposition around the implant.
    • • Bone appositional index varies from 35-75% with the anterior mandible being highest and posterior maxilla being lowest.
    • • Biologic process of osseointegration (4 mos)
    • o Blood clot
    • o Neovascularization
    • o Osteoprogenitor cell migration
    • o Woven bone formation
    • o Deposition of lamellar bone
    • o Secondary remodeling of woven bone with lamellar bone
  2. List those clinical factors which are critical if a titanium screw shaped implant placed into a favorable bone site is to achieve osseointegration. (6 points, 1/2 page)
    • • Uncontaminated implant sufaces
    • • Non-traumatized implant site
    • o Temp below 47C
    • o Gap between implant and surrounding bone should be as small as possible (<1mm)
    • o Narrower implants
    • • Primary stability
    • o Prevents micromotion of implant
    • o No relative movement during the healing phase
    • • Attached keratinized tissue available at the exit site of the implant
  3. Define A-P spread. Why and when is it important? (6 points, 1/2 page)
    • • AP spread is the distance between a line drawn through the center of the anterior most implant(s) and a line drawn connecting the distal end of the most posterior implants.
    • • Minimums required for implant-supported prosthetses to avoid overloading
    • o Max: 6 implants, AP spread >/= 2cm
    • o Mand: 4 implants, AP spread >/= 1cm
    • • Cantilever prevents overloading
    • o Max: cantilever o Mand: cantilever </= 2 x AP spread
  4. Osseointegrated implants used to retain and support single teeth restorations have had mixed success. Please discuss their use for each of the following sites and provide the following information: (1) prognosis, (2) special surgical considerations if any, (3) other prosthetic options, and (4) your recommendation.
    • a. Maxillary central incisor site. (4 points, 1/4 page)
    • • Prognosis: Anterior max bone is thinner than ant mand bone and trabecular bone is not as dense. However, due to ¼ of the loading of posterior teeth, anterior maxilla is still a relatively predictable implant site with a good prognosis
    • • SSC: Loss of crestal bone, labial plate, soft tissue contours for esthetics
    • • Other Options: FPD, RPD
    • • Recommendations: Implant>FPD>RPD
    • b. Mandibular first bicuspid site. (4 points, 1/4 page)
    • • Prognosis: Location of mental foramen, B/L bone width and crestal bone height can all decrease prognosis if in unfavorable locations. Bone quality is good in this area, so if you can achieve a 10x4mm implant, good prognosis.
    • • SSC: Mental foramen location, bone augmentation not typically successful in this area due to high loads. Nerve repositioning is an issue with high morbidity
    • • Other Options: FPD, RPD
    • • Recommendaitons: Implant (10x4)>FPD>RPD>Small Implant
    • c. Mandibular first molar site. (4 points, 1/4 page)
    • • Prognosis: Same as mandibular first premolar except that you don’t have to worry about the mental foramen, but the IA nerve and canal. Bone appositional index is 50-90% for posterior mandible, which gives a good prognosis if you can get the adequate length and width.
    • • SSC: IA canal, bone augmentation not that successful due to high loads, nerve repositioning not that successful.
    • • Other Options: FPD, RPD
    • • Recommendations: Implant (10x4 or 5)>FPD>RPD>Small implant
    • d. Mandibular central incisor site. (4 points, 1/4 page)
    • • Prognosis: anterior mandible has the best prognosis for single implants due to the fact that there are no nerves to worry about, the bone is the densest and crestal bone is the thickest (bone appositional index of 60-90%).
    • • SSC: No major considerations other than maybe soft tissue augmentation if inadequate keratinized tissue.
    • • Other options: FPD, RPD
    • • Recommendations: Implant>FPD>RPD
  5. 5. Subperiosteal implants are reasonably successful for the first 4 to 5 years of use. However, after this period the incidence of local infections and implant failures increase dramatically. Please explain. (6 points, 1/2 page)
    • • Subperioosteal implants were originally made out of CrCo, which is subject to corrosion and release of metallic ions which elicit an inflammatory response and lead to bone loss.
    • • Peri-implant pocketing, further inflammation and epithelial migration result
    • • Without immaculate OH, peri-implantitis is imminent and further infection will lead to bone resorption and eventually implant failure.
    • • This especially occurs in the maxilla where severe bony defects have been seen 4-5yrs after placement of these implants.
  6. 6. Dental cantilevers have been incorporated into the design of many types of implant retained and supported prostheses for edentulous patients. Discuss (1) their feasibility and (2) the methods of determining cantilever length for the following situations:
    • a. Edentulous mandible. (4 points, 1/3 page)
    • • Feasibility: Implant retained and supported dentures are highly successful in the edentulous mandible due to the thick cortical bone in the anterior mandible and relatively thick cortical bone and dense trabeculation of the posterior mandible. You must place 2 implants for implant assisted and 4 implants in a curvilinear manner for implant supported dentures.
    • • Cantilever: The AP spread for mandibular implant supported prostheses must be a minimum of 1cm. Therefore, the cantilever can be up to 2x the AP spread=2cm, with a high feasibility.
    • b. Edentulous maxilla. (4 points, 1/3 page)
    • • Feasibility: Maxillary implant-supported prostheses are less successful than mandibular due to stringent requirements for the placement of the implants. Due to the poorer quality bone in the maxilla, 6 implants must be placed for implant-supported and a minimum AP spread of 2cm must be achieved. The implants must be at least 10mm (13 is better) and 4-5mm wide to support the loading.
    • • Cantilever: Due to the poorer quality of bone, cantilevering can only be ½ the AP spread and therefore is a minimum of 1cm. It has been found that implant-retained prosthetses are better for the maxilla by using 4 implants in a curvilinear fashion and placing ERAs on the distal most implants to allow for mucosal support of some of the loading. Palatal coverage is not required when doing this.
    • c. Posterior quadrant of the mandible in a partially edentulous patient. (4 points, 1/3 page)
    • • The feasibility of cantilevering unilaterally in the posterior maxilla is very poor due to the fact that you cannot obtain the proper AP spread through curvilinear placement of the implants. This drastically decreases the prognosis of a cantilevered crown due to implant overloading, neck fractures and possible peri-implant bone loss.
    • • If you MUST cantilever, minimize the BL and MD dimension of the cantilever by decreasing the width of the occlusal plane, flattening cusp angles, use light centric contacts and do not have any contacts in excursives. Do not allow the MD cantilever to exceed the diameter of the implant.
    • In the edentulous maxilla, implant assisted overlay prostheses are best suited for most patients, as compared to fixed restorations. Explain. (10 points, full page)
    • • Implant assisted overlay prostheses are more predictable, simpler to fabricate, well-liked by the patients, less costly and typically better for phonetics, esthetics, and lip support.
    • • Only 4 implants are required for the implant assisted denture compared to 6 required for the implant supported denture.
    • • The anterior two implants should be placed a minimum of 12mm apart to ensure enough room for the hadar bar clips and attachments.
    • • The posterior two implants should be placed as far distally as possible to maximize the AP spread.
    • • Implant supported dentures often see failure of the distal most implants within 3-5years due to excessive cantelivering and posterior overloading. Also, implant supported dentures do not provide the lip support like the acrylic does with the implant assisted. This can cause poor esthetics and patient do not accept it.
    • • Cantelivering the edentulous maxilla can only support up to ½ the AP spread, thus leaving little room for distal teeth without placing additional implants, which increase cost and decrease prognosis.
  7. 8. The success rates for the “Branemark” system in the anterior mandible exceed 95% after 10 years. This rate of success has not been duplicated in the posterior quadrants of partially edentulous patients. Please explain. Please address both the mandible and maxilla during your discussion. (12 points, full page)
    • • The anterior maxilla has significant anatomical factors which lends itself to a higher prognosis than the posterior quadrants. The anterior maxilla has dense trabecular bone with thick cortical plates and a good amount of bone. In addition, the bone appositional index ranges from 60-90% thus increasing the prognosis of the implant significantly. Furthermore, the load-bearing requirements of implants placed in the anterior mandible are significantly less than the posterior quadrants (1/4 the occlusal load experienced), thus putting less stress on the implant and leading to a higher success rate.
    • • The posterior mandible has the IA canal, which can lead to the need for bone augmentation, grafting or nerve repositioning, all of which are not that successful and can have a high morbidity rate. In addition, the bone appositional index for the posterior mandible is 50-90%, which is less, but not significantly less than the anterior mandible.
    • • The posterior maxilla has the worst prognosis for implant placement due to both anatomical reasons and bone quality. The bone appositional index is 30-60% which is significantly less than either the anterior mandible or posterior mandible. Furthermore, the posterior maxilla is often tainted by pneumatized sinuses which require sinus lifting or grafting procedures to increase the amount of bone available for implant placement. These procedures further decreases the success rates of implants in this area.
  8. 9. Define “combination” syndrome. (4 points, 1/4 page)
    • • Patient has edenulated maxilla and edentulated POSTERIOR mandible (remaining anterior mandibular teeth). In addition, the patient either doesn’t wear their lower RPD or their dentures are unbalanced and forces are not evenly distributed between remaining teeth and mucosal-bearing surfaces.
    • • Patients often experience “Combination Syndrome”
    • o Loss of bone in the pre-maxilla
    • o Overgrowth of the maxillary tuberosities
    • o Fibrous hyperplasia of the maxillary tuberosities
    • o Extrusion of the mandibular anterior teeth
  9. 10. Describe the periimplant soft tissues histologically from the crest of the periimplant gingiva down to area of the implant that is osseointegrated. (8 points, 1/2 page)
    • • 3 Major Layers
    • o Long Junctional Epitheliumcuboidal basal cells and flat suprabasal cells
    • o Connective tissue zonenonattached collagen fibers that run parallel to the implant surface. Because there is no cementum on the implant surface, fibers cannot connect directly to the implant surface. Instead, epithelial cells attach by means of the basal lamina and numerous hemidesmosomes of the JE.
    • o Alveolar bone crest
  10. 11. In evaluating a patient for an implant in the maxillary anterior region, what are the clinical parameters that need to be taken into consideration. (12 points, 3/4 page) Evaluate these clinical parameters:
    • 1. Biomechanical considerations: occlusal analysis is required to understand the functioning canines and their mutual protection of posterior and other anterior teeth.
    • 2. Esthetic considerations:
    • • Can’t place implants too close together or will get “black triangle disease”
    • • 1.5mm from implant to adjacent tooth and 3mm from implant to implant minimum
    • A. Edentulous tissues
    • a. Need to ensure proper amount of keratinized tissue for esthetic purposes around the neck of the implant.
    • b. Interdental papilla height and buccal plate deficiencies may lead to deficiencies in the functional and esthetic outcome of the implant.
    • B. Residual edentulous space
    • a. Interarch space must be a minimum of 2mm in anterior sites and 4mm in posterior sites
    • b. Need a MD distance of at least 7mm
    • c. Ridge position may dictate the implant placement to be more lingual than desired, be careful of B cantilevering.
    • d. Size of the contralateral tooth must be taken into account for proper matching and esthetics.
    • C. Adjacent teeth
    • a. Rotations, tilts, extrusions or intrusions, position of proximal contacts can all affect the prognosis of a single anterior implant. Functional considerations need to be taken into account
    • b. Study the wear facets on the teeth to understand any bruxing patterns or occlusal functional patterns.
    • c. Soft tissue contours need to be taken into account to determine any deficits that may have adverse esthetic outcomes.
    • d. Restorations and materials on adjacent teeth will assist in designing the optimal implant restoration for esthetic matching
    • D. Opposing teeth
    • a. Plane of occlusion must be taken into consideration when designing the implant restoration
    • i. Need to ensure no contacts during excursive movements and limited interocclusal contact
    • b. Fixed restorations transmit more forces to the opposing than removable ones.
    • i. Prognosis of opposing compromised teeth may decrease due to the increased load placed upon them.
  11. 12. What are the most important factors to be considered if osseointegration is to be achieved consistently? (relative to preparation of bone sites and placement of implants) (10 points, 1/2 page)
    • A. Uncontaminated implant surface
    • B. Non-traumatic implant placement
    • a. No hotter than 47C
    • b. Creation of congruent implant site with drills of increasing size
    • C. Primary implant stability for proper blood clot formation and osseointegration
    • a. Depends on bone quality and quantity
    • D. No relative movement during the healing phasefibrous encapsulation can occur if implant is moved immediately after placement
  12. 13. Describe the layers in the bone-implant interface zone of a pure titanium implant. Start from the center of the implant and proceed outward. (8 points, 1/2 page)
    • 1) Titanium layer
    • 2) Titanium dioxide layer
    • 3) Surface film of complex phosphates of titanium and calcium
    • 4) Noncollagenous bone matrix proteins (osteopontin, osteocalcin, and bone sialoprotein, ie cement line)
    • 5) Osteoid and mineralized bone matrix
  13. 14. List the possible morbidities associated with skin graft vestibuloplasty when applied to the edentulous mandible. (8 points, 1/2 page)
    • Morbidities associated with skin graft vestibuloplasty in edentulous mandible:
    • 1. detachment of the mentalis muscle (leading to chin droop/change in facial contours)
    • 2. granulation tissue formation
    • 3. callus formation (because it's skin, not mucosa)
    • 4. scar tissue at mucosa-skin graft junction
    • 5. fungal infestation
    • 6. perforation of the periosteum during dissection leading to exposure of bone
    • 7. temporary or permanent anesthesia/paresthesia of lower lip
  14. 15. Various implant surfaces are commercially available which claim to achieve a state of osseointegration as defined by “Branemark.” The two major categories are pure titanium and hydroxyl apatite coated titanium. Discuss the arguments in favor and against the use of each of these surfaces. (8 points, 1/2 page)
    • Pure Titanium
    • Positives:
    • 1. no epithelial migration
    • 2. resistant to corrosion
    • 3. spontaneously forms coating of titanium oxide (biocompatible)
    • 4. strong and easily machined
    • Negatives
    • 1. takes longer for implant-bone interface to complete
    • Hydroxyl apatite-coated Titanium
    • Positives:
    • 1. more bio-reactive, thus more rapid osseointegration and healing
    • Negatives:
    • 1. greater incidence of cracks and fissures, & loss of entire HA coating
    • 2. heavier colonization by microorganisms
    • 3. problem with long-term predictability
    • The informations above are from the following: ppt 1 “Biologic Basis for Osseointegrated Implants” slide: 10
    • Properties of titanium oxide
    • Many minerals form surface oxides. However, most are not suitable as biomaterials because corrosion of these metals result in continuous release of metal ions into adjacent tissues. The presence of these ions cause acute and chronic inflammatory responses which eventually result in fibrous encapsulation of the offending material. Epithelial migration then follows if the material extends through the skin or mucosa.
    • Titanium is resistant to corrosion and spontaneously forms a coating of titanium dioxide, which is stable, biologically inert and promotes the deposition of a mineralized bone matrix on its surface. In addition, it is strong, and easily machined into useful shapes.
    • However, compare to HA, titanium is less bioreactive and leads to longer healing time after implant placement.
    • Side: 28-29, 31
    • Coatings of hydroxyl apatite, because of their chemical similarity to bone, were thought to be advantageous. The HA surface is more bioreactive than titanium and this leads to more rapid healing following implant placement.
    • The bioreactive surface leads to more rapid osseointegration. At six weeks following placement the bone appositional index is close to 70% for HA coated implants compared to 30-50% for original titanium surfaces (machined and TPS).
    • However, HA coated implants removed from patients demonstrate cracks and fissures and in some cases entire loss of the HA coating. They also demonstrate a heavier colonization by microorganisms. These factors predispose to a higher rate of implant failure than seen with titanium implants (Wheeler, 1997).
    • Reason for HA failure: mostly composed of tricalcium phosphates (up to 85% of some implants) as opposed to HA. The tricalcium phosphates are resorbed and this leads to loss of the coating and contributed to implant failures.
    • Giant cells and macrophages are seen phagocytizing the HA surfaces further degrading the HA coating.
  15. 16. List those factors that affect the mastication efficiency of a patient with a well made complete denture. (10 points, 1/2 page)
    • Efficient mastication requires pt factors to be favorable such that the fabricated denture may optimize retention, stability, & support.
    • Factors include:
    • • Neuromuscular control and denture wearing experience
    • • Sensorimotor fxn
    • • Tongue Posture (retruded tongue is very undesirable)
    • • Integrity of support areas
    • o Primary:
    •  Mx: hard palate & max tuberosity
    •  Md: B shelf & Retromolar pad
    • o Secondary: Residual Ridges
    • • Bearing mucosa: amt and quality of attached keratinized mucosa
    • • Salivary flow rates and quality
    • • Oral hygiene
    • • Degree of parafunction
    • • Vestibular depth
  16. 17. With reference to the previous question describe how each of these is affected with the addition of two implants to the anterior mandible and the fabrication of mandibular overlay denture opposed by a maxillary complete denture. (10 points, 1/2 page)
    • The answer on the notes seemed okay but I also found the following slides that answered the question (Slides 4-12 on Lecture 6: Restoration of the edentulous mandible). Slides 11 & 12 answer the question but 4-12 are relevant. Also attached the slides for convenience. Take care and good luck.
    • Mandibular dentures retained with osseointegrated implants:
    • Results:
    • 1. improved retention: denture snaps onto tissue bar
    • 2. improved stability: from the implants and the tissue bar
    • 3. improved support: anteriorly
    • 4. better control of the bolus: tongue no longer must position denture and control bolus simultaneously
    • 2-implant assisted overlay denture with conventional complete denture:
    • 1. predictability: implant failure rates for this application are virtually zero
    • 2. patient acceptance is very favorable
    • 3. cost effective
    • 4. simplicity
  17. 18. List the possible difficulties associated with cementing crowns on commercially fabricated abutments? (6 points, 1/3 page)
    • Although the cement-retained crowns are more esthetic especially in posterior sites, and clinical procedures are less technique sensitive, however:
    • a. Retrievability is a problem – if for whatever reason you need to service any component of the implant system (i.e. screw loosens between fixture and abutment), it requires crown removal procedures (drill of the crown) and cost of replacement
    • b. Commercial implant abutments may not correct for poor implant position and may not produce natural emergence profiles with natural gingival contours. Custom abutment such as the UCLA abutment would allow to correct for these problems.
    • c. Many times it is difficult to remove the cement completely after seating, and this excess cement can lead to inflammatory reactions leading to fistula formation. This can affect the soft tissues and can also lead to implant failure in the future if not corrected.
    • d. Hydraulic pressure may make seating the crown more difficult and increased need for space to accommodate 2 piece restoration
  18. 19. List those factors which have lead to a high failure rate for osseointegrated implants used to restore the posterior quadrant of the maxilla. (8 points, 1/2 page)
    • - pneumatized sinus
    • - load bearing capacity of implants in grafted bone (in re sinus lift) may be compromised
    • - may lead to placement of short implants more susceptible to failure
    • -Increased porosity of bone in the interface zone secondary to remodeling
    • -Implants placed in the posterior maxilla enjoy much less effective anchorage because the cortical bone is thin and the
    • trabecular bone is not very dense.
    • -The bone appositonal index decreases from the premaxillary segment to posterior maxilla where it is 30-60%. The load carrying capacity of implants positioned in the maxilla is therefore much less.
    • -Implant overload through
    • a) cantilever forces (mesially & distally, B&L)
    • b) insufficient implants per dental unit replaced in extension cases.
  19. 20. Success rates for implants used to restore edentulous spaces in the posterior quadrant of the mandible have been lower than those reported in the anterior mandible. Explain.
    • (8 points, 1/2 page)
    • 1. Posterior Mandible Limiting Factors (PPT 8, slide 20)
    • * Insufficient height of bone over the Inferior Alveolar Nerve (arrow) to permit placement of a 10 mm or longer implant.
    • * Insufficient width of bone.
    • * Non-ideal positioning of implant for axial loading due to inadequate bone volume.
    • * Single cortical anchorage
    • * Many patients present with severe alveolar resorption requiring a technique sensitive bone graft and/or displacement of the inferior alveolar nerve if implants are to be placed in the posterior quadrant
    • * Possible IA Nerve Displacement: Although the risk of nerve injury is relatively small the morbidities associated with nerve injury may be severe.
    • 2. Crestal Augmentation (PPT 8, slide 23)
    • * Augmentation of vertical defects in the posterior quadrants with free autogenous bone grafts has been unpredictable.
    • * Historically such grafts are subject to resorption particularly upon occlusal loading.
    • * The careful use of GBR (guided bone regeneration) and sufficient numbers of implants has greatly improved predictability.
    • 3. Use of Short / Wide Diameter Implants in the Posterior Mandible (PPT 8, slide 24)
    • * This practice has not been predictable.
    • * The short implants are particularly prone to occlusal overload and bone loss.
    • 4. Anchorage - Anterior Mandible (PPT 1, slide 89)
    • * Implants placed in the anterior mandible enjoy excellent anchorage because the cortical bone is thick and the trabecular bone is very dense, particularly in older edentulous patients. The density of the trabecular bone in this specimen is particularly good.
    • * After complete healing under physiologic load conditions the bone appositional index is maintained at a level of from 65-90% at this site and therefore the load carrying capacity of implants placed in this region is very great.
    • 5. Implant Angulations - Posterior vs Anterior Quadrants (PPT 1, slide 11)
    • * Implants should be placed so that occlusal loads can be directed axially in the posterior quadrants.
    • * In the anterior region, anatomic necessity precludes implant placement perpendicular to the occlusal plane. However, the forces used to incise the bolus are only about ¼ of those used posteriorly to masticate the bolus. For this and other reasons implant overload is rarely seen in the anterior regions.
    • 6. Bone quality and quantity
    • • Posterior max: bone appositional index averages: 30-50%
    • • Anterior mand: bone appositional index averages: 60-90%
  20. 21. Define “implant assisted restoration.” (4 points, 1/4 page)
    • Dictated by biomechanical considerations:
    • The forces of occlusion are shared between the implants and the mucoperiosteum/hard tissue. Always removable overlay dentures.
    • - good lip support (better with a removable)
    • - Hygienic
    • - better phonetics than non-removable implant supported prostheses
    • - requires less implants than impl supported prostheses
    • - cheaper than impl supp prosth
    • Implants: anterior 2 implants should be 12-20 mm apart for 2 Hader bar clips
  21. 22. Define “implant supported restoration.” (4 points, 1/4 page)
    • Dictated by biomechanical considerations:
    • All the forces of occlusion are borne by the implants. Can be either fixed partial dentures or removable overlay dentures.
    • Distal implant must be at least 10 mm in length
    • Maxilla: 6 or more implants required;
    • AP spread: 2 cm or more
    • Mandible: 4 or more implants required
    • AP spread: 1 cm or more
  22. 23. In the edentulous maxilla most patients are best fitted with implant assisted restorations. Explain. (6 points, 1/3 page)
    • Anatomic limitations secondary to the pneumatization of the maxillary sinus limit the number of implants able to be placed in the maxilla to four. This is not a sufficient number to bear the occlusal loads in most patients if the prosthesis is designed to be implant supported. (There needs to be a minimum of 6 implants to be implant supported). Instead, a four implant assisted overlay denture is the preferred choice in most patients to minimize the possibility of implant overload.
    • Poor quality of bone and limited quantity of bone tends to make one favor implant assisted overlay dentures.
  23. 24. An implant assisted palateless, overlay denture is planned for this patient. Indicate the minimum number of implants you would use, the tooth positions you would favor for placement into the edentulous ridge and your reasons for selecting these positions.
    • (6 points, 1/2 page)
    • min. of 4 implants for maxilla
    • * implants should exit at the ridge crest - this is ideal angulation b/c the bar fabricated will not distort the palatal contours
    • * 2 anterior implants = minimum of 12 mm apart - need sufficient distance for the implants for the placement of 2 clips,
    • * denture will be more stable and the rate of clip wear will be reduced
    • * posterior implants should be placed as posteriorly as possible to maximize A-P spread
  24. 25. What is the difference between fibrous-encapsulated and osseointegrated implants? Which one is clinically more predictable and why? (10 points, 1/2 page)
    Fibrous encapsulated implants were made of chrome cobalt or similar alloys which were susceptible to corrosion and metallic ions were released into surrounding tissues triggering acute and chronic inflammatory responses. This led to fibrous connective tissue encapsulation of the implant which allows epithelial migration between the recipient bone site and the surface of the implant. Osseointegrated implants are made of titanium which is resistant to corrosion and spontaneously forms a coating of titanium dioxide, which is stable, biologically inert, and promotes deposition and mineralization of bone matrix on the surface of implants. This facilitates direct structural and functional contact between ordered living bone and the surface of the implant. Osseointegrated implants are more predictable because bone is deposited on the surface of the implant which firmly anchors it to the surrounding bone. There is no fibrous connective tissue interface between the surface of the implant and the surrounding bone which prevents epithelial migration into the interface. Epithelial migration, development of extended peri-implant pockets, and chronic infections which often developed around fibrous encapsulated implants, led to exposure of the implant and its eventual failure.
  25. 26. Which surface (machined, titanium plasma spray, hydroxyl apatite) gives the highest bone to implant contact? Does this relate to the clinical results? Explain. (8 points, 1/2 page)
    • Reference: Power point 1 Biol Basis of OsseoIntegration Slides 28 - 32
    • Hydroxyl apatite gives the highest bone to implant contact. At six weeks following placement the bone appositional index(amount of bone contact with the surface of the implant) is close to 70% for HA coated implants compared to 30-50% for original titanium surfaces (machined and TPS-Titanium Plasma Spray).
    • In summary, HA coated systems have provoked great interest and enthusiasm because of their bioreactivity. However, at present there remain significant problems associated with their long term predictability.
    • Coatings of hydroxyl apatite, because of their chemical similarity to bone, were thought to be advantageous. The HA surface is more bioreactive than titanium and this leads to more rapid healing following implant placement. The bioreactive surface leads to more rapid osseointegration. At six weeks following placement the bone appositional index is close to 70% for HA coated implants compared to 30-50% for original titanium surfaces (machined and TPS Titanium Plasma Spray). In animals studies,
    • several investigators have shown an increased bone appositional index for HA coated implants 6 weeks post insertion as compared to machined titanium or plasma sprayed titanium surfaces (Weinlander et al,1993. ) However, HA coated implants removed from patients demonstrate cracks and fissures and in some cases entire loss of the HA coating. They also demonstrate a heavier colonization by microorganisms. These factors predispose to a higher rate of implant failure than seen with titanium implants (Wheeler, 1997). In addition, the coatings of the HA implants marketed in the late 80’s and early 90’s was mostly composed of tricalcium phosphates (up to 85% of some implants) as opposed to HA (Weinlander et al, 1993). The tricalcium phosphates are resorbed and this presumably leads to loss of the coating and contributed to implant failures. In addition, in animal studies giant cell and macrophages are seen phagocytizing the HA surfaces further degrading the HA coating. These data have lead most clinicians to switch to the titanium surfaces.
    • However, new methods of applying the HA coating employing nanotechnologies are evolving which result in better bonding between titanium and the hydroxyl apatite layer creating a pure HA crystalline coating.
  26. 27. What are the advantages of roughening the surface of an implant by acid etching or some similar method? (6 points, 1/3 page)
    • • More rapid osseointegration
    • o Takes 4 mo to load a machined surface
    • o Takes 4-6 wks to load roughened surfaces
    • • Increase bone implant interface by ~ 50%
    • • Able to achieve greater bone apposition compared to machined surfaces as was tested in the torque removal studies
    • • Dr Davies (1998) hypothesized that rough surfaces retain the fibrin clot and thereby facilitates the initial events of OI more rapidly (clot formation  angiogenesis  osteoprogenitor cell migration  woven bone deposition  deposition of lamellar bone  secondary remodeling of woven bone to lamellar)
    • • Excessively rough & irregular surfaces have been known to trigger a macrophage and giant cell response on the surface of the implant
    • • Resorption and remodeling of bone deposited on acid etched surfaces appears to be different on machined surfaces.
    • • A different combination of collagenous and non-collagenous proteins make up the mix of osteoid like material deposited on the surface of a dual acid etched titanium surface as compared to a machined surface.
    • • Achieve higher osseointegration: Ogawa and Nishimura have suggested that surface topography influences gene expression.
    • o Implant anchorage data obtained with a push out test which tested the strength of implant tissue interface rather than the strength of surrounding bone. It showed a slear superiority of souble acid etched surfaces. Bone formed on the surface of acide etched surfaces much more quickly and achieve better anchorage than on machined surfaces. Osteopontin and osteocalcin were both upregulated. There was an enhanced gene expression of prolyl 4-hydroxylase. Double acid etched surfaces evoked an additional activation of selected bone genes, which may be associated with enhanced interfacial strength and accelerated bone formation.
  27. 28. Why is attached keratinized soft tissue preferable to unattached nonkeratinized tissue around implants. (6 points, 1/2 page)
    • A: If the implant emerges through attached keratinized mucosa, the residual circumferential gingival fibers promote close adaptation of the mucosa around the implants resulting in the formation of cuffs similar to those seen around dentition. With an adequate zone of attached keratinized soft tissue, oral hygiene is more comfortable, plaque control is facilitated, and soft tissues are more likely to remain healthy. An inadequate zone of keratinized attached soft tissue may contribute to a hyperplastic response and formulation of granulation tissue. Unattached mucosa is movable, easily displaced, susceptible to trauma, and it does
    • not provide an adequate seal or barrier which can lead to peri-implant pockets, recession and implant failure.
  28. 29. Describe the biologic processes that take place associated with the bony tissues next to the surface of a titanium implant immediately following placement until complete healing has taken place. (10 points, 1/2 page)
    • lecture 1 (principles of osseointegration, slide 15)
    • same as other answer
    • 1. Blood clot formation and release of growth factors in space between
    • bone and surface of implant.
    • 2. Angiogenesis: formation of new blood vessels to the area.
    • 3. Osteoprogenitor cell migration to the bone implant interface zone.
    • 4. Woven bone formation (1st few weeks)
    • 5. Deposition of lamellar bone
    • 6. Secondary remodeling of woven bone with lamellar bone (6-20 weeks)
  29. 30. How long does this process take in humans ? (2 points, 1/4 page)
    • • Machined surface: 4 months
    • • Roughened surface: 4-6 weeks
  30. 31. What strategies can be employed to avoid implant overload when restoring single molar defects in the mandible (6 points, 1/3 page)
    • 1) Place implants perpendicular to the occlusal plane
    • - note: curve of Wilson and curve of Spee
    • - often implants in posterior mandible are lingually and slightly mesially inclined
    • 2) Place implants in tooth positions
    • 3) When in doubt, always add an additional implant
    • 4) Avoid M-D & B-L cantilevers
    • 5) If required to attach to natural dentition, do so with a rigid attachment system
    • 6) Control occlusal factors (cusp angles, width of occlusal table)
    • 7) Avoid use of short implants (less than 10mm) and implants of less than 4mm in diam
    • - wide diameter implant
    • - occlusal anatomy
    • - narrow occlusal table
    • - flat cusp angles
    • - lingualize or buccalize
    • - occlusion: minimize lateral forces
    • - anterior guidance with centric only contact
    • - mutually protected occlusion (distribute lateral loads as widely as possible in order to reduce overload)
  31. 32. What factors determine the load carrying capacity of an implant supported prosthesis? (10 points, 1/2 page)
    • 1. Quality of bone site
    • Three dimensional volume of the proposed sites
    • –lengths of implants that can be accommodated?
    • Thickness of pertinent cortices
    • Density of the trabecular bone
    • Most favorable: anterior mandible
    • Least favorable: posterior maxilla
    • Vascularity
    • 2. Quality of bone implant interface (anchorage)
    • - bone quantity: most volume in anterior mandible and anterior maxilla
    • Least volume in the posterior mandible and posterior maxilla
    • - nature of the implant surface: bone deposited on acid etched surfaces is 2-3 times more dense than the bone deposited on machined surface
    • - bone appositional index: surface are of implant covered with bone
    • 3. Implant micro surface -
    • Machined vs rough surfaces
    • 4. Implant
    • Number
    • - maxilla (6 or more implants)
    • - mandible (4 or more implants)
    • Arrangement: curvilinear arrangements show increase load bearing capacity
    • - cross arch stabilization
    • - AP spread required: maxilla 2cm or more, mandible 1 cm or more
    • Length and width
    • Angulations: load magnification
  32. 33. Brunski et al (2000) has proposed a possible mechanism of implant failure associated with implant overload and bone resorption. Please describe in detail (10 points, 3/4 page)
    • Implant Overload and Bone Resorption Proposed Mechanisms of Implant Failure
    • * Excessive occlusal loads
    • * Resulting microdamage (fractures, cracks, and delaminations)
    • * Resorption remodeling response of bone
    • * Increased porosity of bone in the interface zone secondary to remodeling
    • * Vicious cycle of continued loading, more microdamage, more porosity until failure
    • Also if Implants are placed at wrong angle--> Subject to significant lateral forces.
    • With rougher surfaces, probably won’t see as much failure.
    • Resorptive remodeling response provoked by excessive occlusal loads
    • Nonaxial loads --> load magnification --> Micro fractures, delaminations particularly affecting the cortical bone around the neck of the implant --> Osteocytes signal the marrow --> Resorptive remodeling response is provoked --> Increased porosity of bone at the interface --> Vicious cycle of continued loading, more microdamage and more porosity until failure
  33. 34. The magnitude of occlusal loads delivered to the bone through a three unit implant-supported fixed bridge restoring a posterior quadrant is controlled by many factors. What are they? (12 points, 1/2 page)
    • - Biting forces during normal function (best if force is distributed along long axis of implant and minimized by use of multiple implants to share occlusal load)
    • - Biting forces during parafunction (bruxism)
    • - BL width of occlusal table (best to make the occlusal table narrow)
    • - Cusp angles (avoid steep cusp angles)
    • - Presence and length of cantilevers (in max, cantilever must be less than 1/2 of the AP spread; in mand, cantilever must be less than 2X the AP spread in implant supported; eliminate cantilever by using: wide diameter and multiple implants)
    • - Angulation of implants relative to the occlusal plane (don't make them flat, make them perpendicular to the plane of occlusion according to the Curve of Spee and Wilson)
    • From Dr. B's #1 ppt - (slide 131 and 87)
  34. 35. In edentulous patients (both maxilla and mandible) what strategies would you use to avoid implant overload when planning for and designing implant supported prostheses? (8 points, 1/2 page)
    • * Edentulous maxilla
    • o Use a minimum of 6 implants
    • o Design A-P spread to be at least 2 mm, maximize
    • o The distal implant must be at least 10mm
    • o Cantilever length should not exceed ½ times the A-P spread
    • o should have a balanced occl scheme
    • * Edentulous mandible
    • * Use a minimum of 4 implants
    • * Design A-P Spread of at least 1 cm, maximize
    • * All implants must be at least 10 mm in length
    • * Cantilever length should not exceed 2 times the A-P spread
    • * Should have a balanced occl scheme
  35. 36. When restoring an edentulous posterior quadrants of a partially edentulous patients what strategies would you use to avoid implant overload when planning for and designing an implant supported fixed partial denture. (14 points, 3/4 page)
    • • Use implants at least 10mm in length- enhanced roughened surface for better anchorage- increased length to better with stand the forces of occlusion
    • • Use implants at least 4mm in diameter- to decrease cantilever forces
    • • Use direct axial loading (NOT transverse such as buccally or lingually placed implants or cantilevers). Do NOT angle implants in any direction except that which is down the long axis perpendicular to the occlusal plane. Also consider the curve of spee and wilson. Implant should exit at the crest of ridge
    • • Position teeth as close to ideal tooth positions as possible.
    • • Use non-linear configurations (curvo-linear configuration) to resist buccal & ling cantilevers
    • • provide anterior guidance or group function to decrease load on posterior implant sites
    • • In the posterior max – one implant for each dental unit and at least three in distal extension areas. Consider multiple implants per unit to prevent mesial-distal lingual cantilever forces.
    • • In posterior mand – two is sufficient for most pts, but force may alter this #. Three implants are recommended when bone quality is poor, there is only room for short implants, when loads are predictably high, or when restoring four units in that area
    • • Absolutely no mesial or distal cantilevers.
    • • If required to attach to natural tooth structures, use a rigid attachment system.
    • • do not use steep cusp angles and fabricate narrow (B-L) restorations
  36. 37. Describe clinical situations where immediate or early loading of osseointegrated implants would be feasible. (6 points, 1/2 page)
    • • Success is dependent upon absence of movement during the healing phase
    • • Requires good initial bone anchorage
    • o Site specific, long implants in anterior mand & max work well
    • o Bicortical stabilization can be achieved with long implants
    • • Nature of Occl Loads
    • o Posterior loads = 4 x Anterior Loads
    • • Implant supported or assisted prosthesis
    • o Assisted has a much better prognosis (predictable) than supported
    • • Surface texture of the implant
    • o Better initial anchorage can be ontained with rough surfaces as opposed to machine surfaces
    • • Are there sites available for additional implants.?.. if so, place additional implants
    • Note: surface of implant is important: sand blasted acid etched are most desirable (double acid etched are actually not desired for this purpose b/c torque removal studies showed a low value for this surface)
  37. 38. Describe some of the potential problems associated with placing implants into fresh extraction sites. (6 points, 1/2 page)
    • This is generally not recommended in most clinical situations. Some problems may include:
    • 1) Size of the extraction site larger than the size of the implant. With a large gap between the bone of the extraction site and the neck of the implant, a fibrous connective tissue interface results followed by epithelial migration and lengthening of the peri-implant pockets.
    • 2) Infected, poorly vascularized, necrotic bone at the implant site. This will lead to poor osteointegration and potential failure.
    • 3) Inability to control implant position and angulations. May lead to restoration difficulties.
    • From Lecture 1 slide 146
    • Also, for specifically for immediate loading implants:
    • - bone quality concerns. Bone must be type 1, 2, or 3 w/roughen implant surface.
    • o Type 1: almost all jaw bone is composed of homogenous compact bone
    • o Type 2: thick layer of compact bone surrounding a core of dense trabecular bone
    • o Type 3: a thin layer of contrical bone surrounding a core of dense trabecular bone of favorable strength w/ roughen implant surfaces
    • - extraction trauma
    • o adequate bone quantity/quality/strength
    • o may need bone augmentation procedures for correction
    • - lack of primary stability
  38. 39. Compare the bone quality and quantity of the edentulous posterior maxilla and anterior mandible with respect to their suitability as implant sites. (8 points, 1/2 page)
    • Anterior mand - excellent anchorage for implants due to thick cortical bone and dense trabecular bone, especially in older edentulous patients. This area also has a higher bone appositional index (60-90%), therefore it has great load carrying capacity, and also the greatest quantity of bone. Anterior mandible has the best quality of bone and the most quantity.
    • Mandibular arch - typically denser bone would result in greater initial implant stability.
    • Posterior Max – The cortical bone is thin and the trabecular bone is not very dense. The bone appositional index is much lower (30-50%), therefore its load bearing capacity is diminished. This area also has the least quantity due to the pneumatized sinus, reducing the width. The pneumatization of sinuses does not allow the placement of implants in some patients. The posterior maxilla has the least quantity and worst quality of bone.
  39. 40. What factors influence the implant anchorage in bone? (6 points, 1/2 page)
    • 1. Quality of bone site: areas where cortical bone is thick and the trabecular bone is very dense such as the anterior mandible will help increase anchorage whereas anchorage may be less in areas where the cortical bone is thin and trabecular bone is not very dense (mx).
    • 2. Bicortical stabilization will also increase bone anchorage, or bone appositional index
    • 3. Length of implant: longer implants in the mx and md will increase implant anchorage.
    • 4. 2 implants is better than one in the posterior md to achieve better bone anchorage
    • 5. Roughened surfaces and acid-etched surfaces (rather than machined) clearly improve the anchorage of osseointegrated implants.
    • 6. The amount of occlusal load on the implant: it takes 2-4 months to repair the trauma caused by preparation of the implant site and develop sufficient bone anchorage to withstand occlusal loads without provoking a resorption remodeling response of the investing bone.
    • 7. Atraumatic surgical sites as in immediate placement of implant following extraction of an incisor.
    • 8. Bioreactivity of the implant surface
    • 9. Bone quantity:
    • Biologic Basis for Osseointegrated Implants: slides 89, 90, 91, 98, 102, 142, 143.
    • Restoring Posterior Quadrants: slides 33-35.
  40. 41. What are the advantages of implant assisted overlay dentures in the maxilla as opposed to fixed implant supported prosthesis? (8 points, 1/2 page)
    • • Bone quality and quantity and sinus architecture
    • o Pneumatized sinuses do not allow for implant-supported prosthesis unless posterior sites are enhanced with a sinus life and graft
    • • Resorptive patterns and maxillomandibular relations
    • • Esthetics/lip support
    • • Phonetics
    • • Patient acceptance
    • • Simple to fabricate
    • • Predictability
    • • Less Cost (less implants needed and less expensive prosthesis)
    • • More hygienic (removable so can be cleaned easier esp for pts w/ limited motor control or vision)
    • • No hygienic gap b/w prosthesis and mucoperiosteum
    • o More esthetic
    • • Better phonetics (air escapes and causes a lisp)
    • • More lip support (better esthetically)
    • o Removable appliances (assisted or supported) provide better lip support and restore facial contours more effectively.
    • • Decreased chance of overloading implants
    • o Anterior maxilla the bone is not as ideal as in the anterior mand
    • o Load is shared b/w implants (anterior) and mucoperiosteum/max tuberosity & possibly the hard palate (posterior)
  41. 42. What are the minimum requirements for an implant supported prosthesis in the mandible with respect to number, length and arrangement? (6 points, 1/2 page)
    • - Length of implant should be at least 10mm long
    • - In the mand, you should place at least 4 implants and the min AP spread should be 1cm
    • - Also, cantilever length should not be 2 times the A-P spread
  42. 43. What are the minimum requirements for an implant supported prosthesis in the maxilla with respect to number, length and arrangement. (6 points 1/3 page)
    • The minimal Biomechanical Requirements
    • Number: Minimum of 6 implants
    • Length: Distal Implant must be at least 10 mm in length
    • Arrangement: Minimum of 2 cm A-P spread
    • Reference: Lec#5, Slides 4-6
  43. 44. What factors should be taken into account when you are deciding between restoring an edentulous mandible with a fixed hybrid prosthesis vs. an implant assisted overlay denture? (10 points, 2/3 page)
    • 1. Esthetic demands
    • -denture flange needed sometimes to establish proper lip contours
    • 2. Psychological demands
    • 3. Need for hygiene access
    • 4. Oral compliance
    • -impaired vision or impaired motor skills -> removable overlay dentures
    • 5. Quality of the soft tissues
    • - ample keratinized tissue: fixed
    • - inadequate keratinized tissue: removable to have access to hygiene
    • 6. Cost: most bang for the buck: two implant assisted overlay denture
    • -----------------------------------
    • Treatment Planning - Edentulous Maxilla
    • 1. Bone quantity and quality
    • 2. Resorptive patterns
    • 3. Maxillomandibular relations
    • 4. Sinus architecture
    • 5. Esthetics/lip support
    • 6. Phonetics
    • 7. Hygiene access and patient compliance
    • 8. Cost
    • 9. Predictability of surgical interventions
  44. 45. When restoring posterior quadrants of partially edentulous patients with osseointegrated implants, how do you minimize the buccal or lingual cantilever effect?
    • (6 points, 1/3 page)
    • Buccal and lingual cantilever effects lead to prosthesis failures, screw fractures, and implant overload and bone loss
    • 1) When in doubt add the 3rd implant in posterior quadrant cases
    • 2) minimize length and width of the occlusal table (lingualize or buccalize occlusion)
    • - molars should be no wider than premolars
    • - when too narrow, the implant may not withstand the occlusal load and cause screw loosening
    • 3) use curvelinear formation
    • 4) flat cuspal angles
    • 5) place implants in ideal tooth position, access screw channels should exit central fossa
    • 6) implant perpendicular to occlusal plane
    • 7) if required to attach to natural dentition, do so with a rigid attachmend system
  45. 46. When considering patients for implants in the edentulous mandible, describe some of the common problems that are encountered and need to be considered before embarking a specific course of treatment. (6 points – 1/2 page)
    • ***The answer is a combination of the 2 RP answers. Just hit all the major points!
    • General Problems:
    • • Lack of stability
    • • Lack of retention
    • • Poor support
    • • Poor neuromuscular control
    • Other Common Problems
    • • Support tissues: the more keratinized mucosa, the better support provided for the complete denture. The buccal shelf and retromolar pad are prime support areas.
    • • Floor of mouth posture and tongue position (depth of retromylohyoid space): these affect stability and retention. Favorable anatomy would be one that permits development of a longer lingual flange. Patients with unfavorable floor of mouth posture would be those that had a retruded tongue position, the tip of tongue losing its definition, and floor of mouth elevated. The result is that the lingual flange of the denture would be limited, compromising retention and stability, as well as the ability of the pt to control the lower denture. The solution for pt with this problem would be to have a denture retained with osseointegrated implants. (IE: implant assisted overlay denture)
    • • Neuromuscular control: some patients have the ability to manipulate their lower denture and control the bolus simultaneously, regardless of the quality of the design and construction of the denture. Those with poor neuromuscular control will benefit from a mandibular implant assisted overlay denture.
    • Implants in the Edentulous Mandible : Common Problems
    • 1. Severe resorption
    • *Buccal-lingual dimension most important. Less than 5-6 mm requires bone augmentation
    • 2. Lack of attached keratinized tissue
    • *Hygiene compromised when the implants are surrounded by poorly keratinized
    • unattached mucosa
    • *Palatal grafts are favored over skin grafts
    • 3. Lack of interocclusal space
    • *Limits design choices
    • *Compromises prosthodontic procedures
    • *Commonly encountered when a patient still retains residual dentition in either the maxilla
    • or mandible
    • *Seen in some recently edentulated patients
    • 2. Set margin with impression cap
    • 3. Prepable
    • 1. Titanium
    • 2. Ceramic
    • 4. Procera
    • 1. titanium
    • 2. alumina
    • 3. zirconia
    • 5. Provisional to fixture (acrylic/composite)
    • 3. Gold cylinders
    •  Incorporated into the final restoration and screwed onto the abutment with the gold set screw
    •  Different cylinders for different abutments
    •  Cylinders become incorporated into the final restoration
    •  Since its pre-made and with a machined interface toward the abutment, the consistency of fit is improved over a custom casting
    •  Standard abutment gold cylinder
    •  Estheticone abutment gold cylinder
    • 4. Analogs / Replicas: allow the accurate transfer of a facsimile of the intraoral component to a working model
    •  Stainless steel or other alloy
    •  Abutment
    • 1. allows creation of a model with the same characteristics as a given intraoral abutment
    •  Fixture
    • 1. allows creation of a model with the same characteristics as a given intraoral fixture
    • 5. Impression copings
    •  Stainless steel or other alloy
    •  Facilitates transfer of the intraoral location of the fixture or abutment to the lab cast during the impression procedure
    • 6. Connection Armamentaria
    •  Screw drivers
    •  Guide pins: gold and abutment screw size
  46. 48. Explain how the UCLA abutment is different from a standard abutment and what problems it can solve. (6 points – 1/2 page)
    • Custom abutment
    • Allows connection of the restoration directly the fixture.
    • Combines abutment, gold cylinder and restoration into one.
    • Uses: Esthetics: now margin can be placed subgingival
    • Limited interocclusal space (less room is needed since the abutment, gold screw and restoration are all incorporated into one)
    • Angulation correction (can be waxed to provide for ideal angulation of the final restoration using a 2 piece UCLA abutment)
    • Custom substructures
    • Soft tissue problems (allows for abutment to follow the contours of the soft tissue)
    • Can be used for both screw and cement-retained options
  47. 49. Explain the difference between an implant and an abutment level impression and describe two techniques for making the impression. (8 points – 1/2 page)
    • There are two types of impression copings:
    •  Abutment level and Fixture level
    • Both can utilize either the pick-up or transfer technique.
    • Abutment level
    • 1. Square / Pick-up
    • Square coping is “locked” into the impression due to shape
    • Screwed to abutment with guide pin
    • Impression is made with “open tray”
    • Analogs are attached before pouring master model.
    • 2. Transfer/ Tapered
    • Screw to abutment
    • Take impression with closed tray
    • Remove impression
    • Unscrew copings
    • Attach to analogs
    • Replace copings into impression and pour.
    • Fixture level impression is made directly to fixture (no abutment is in place), x-rays are always needed to verify seating.
    • 1. Pick-up
    • Registers both position of fixture and orientation of fixture hex.
    • Becomes locked into final impression so open tray is needed.
    • After the tray is removed a fixture analog is connected and model is poured.
    • 2. Transfer
    • Shape allows it to remaining mouth when impression is removed- use flat head screw
    • Two piece coping will still allow registration of hex.
    • Single piece coping is only for bridges (no hex registration)
    • Note: pick-up can be changed into transfer coping:
    •  by utilizing the flat-head screw instead of guide-pin, the same impression coping can be used as a transfer impression coping.
  48. 50. Describe a technique for improving a final impression and/or verifying a master model making the impression. (6 points) 1/2 page)
    • LINKED COPINGS
    • These are useful in impression taking to improve the accuracy of the impression (accuracy is limited by materials used). How they work is that they directly connect the coping intraorally with triad or flowable composite. The copings are then sectioned and reluted as necessary. They behave as a PICKUP IMPRESSION coping. Once the impression is taken, the index is removed from the mouth and a registration poured in quickset intraoral plaster type II before taking final impressions.
    • IMPRESSION TECHNIQUE 2 (Advanced technique)
    • For this technique and custom tray can be made around any model, preferably one that shows the healing abutments. It should be kept close to the tissue in the area that the holes for the impression copings are made. In the patient’s mouth, the healing abutments are replaced with the pick-up style fixture level impression copings. When seating the tray, make sure that the tray will seat without touching these impression copings. Take a regular final impression, but remove any impression material from the copings. The copings are luted to the tray using GC pattern resin. You then carefully unscrew the tray from the mouth and add the analogs, and carefully pour the master model.
    • Abutment level
    • 1. Screw impression coping to abutment
    • 2. take impression w/ closed tray
    • 3. remove impression
    • 4. unscrew copings
    • 5. attach to analogs
    • 6. replace coping into impression and pour
    • 1. make a custom tray preferably around a model that shows the healing abutments
    • 2. replace the healing abuments w/ the pick up style fixture level impression copings
    • 3. Make sure the tray will seat w/o touching the impression copings
    • 4. Take a regular final impression but remove any impression material from the copings
    • 5. lute the copings to the tray w/ GC pattern resin
    • 6. carefully unscrew tray from mouth and add analogs
    • 7. carefully pour master model
  49. 51. Draw an implant assisted bar and identify its axis of rotation. (4 points – 1/2 page)
    • The axis of rotation is thru the center of the Hader bar in an implant assisted prosthesis.
    • Arrow rotates into page.
  50. 52. Explain what is meant by an AP spread and what is it used for? (4 points – 1/2 page)
    • A-P spread = The distance b/w a line drawn thru the center of the most anterior implant(s) and a line drawn the distal end of the most posterior implants in a curvelinear arrangement of multiple implants. Concept required for implant-supported prosthesis. If these can not be met, implant-assisted prosthesis is indicated.
    • • AP spread serves to increase the amount of posterior support provided by the implants.
    • • Especially important in re: Implant Supported Prostheses (ISP)
    • o Mx: req 6 implants w/ an AP Spread of 2 cm or more
    • o Md: req 4 implants w/ an AP spread of 1 cm or more
    • • Dictates the amount of posterior cantilever that can be used w/o overloading the implants
    • o Mx: cantilever ≤ ½ x AP spread
    • o Md: cantilever ≤ 2 x AP spread
    • o When overloaded the distal implants are typically lost
  51. 53. Describe a Fixed Bone Anchored Bridge and identify the main issues when considering its use. (6 points – 1/2 page)
    • Fixed is double to triple the cost of implant assisted removable overlay dentures. It is requires more implants and is more time consuming and costly to manufacture.
    • Minimum requirements
    • 1. Mandible
    • a. Minimum length= 10 mm
    • b. Minimum # of implants = 4
    • c. AP spread = 1cm
    • 2. Main issues
    • a. Psychological demands- only case where fixed has advantage over removable prosthesis
    • b. Esthetics
    • i. low lip line is better as to hide the IP contacts
    • c. Need for hygiene access
    • i. older designs that allowed for hygiene access created air escape through spaces which adversely affected speech articulation
    • d. Amount of keratinized tissue/- fixed bridge requires sufficient amounts of tissue
    • i. oral hygiene procedures are much easier to perform when the implants are surrounded by keratinized attached mucosa
    • e. Anatomic concerns:
    • i. Placing implants posterior to Mental foramen will hit mandibular canal causing paraesthesia
    • f. Maxillo-mandibular relationships
    • i. less lip support with fixed and they don’t restore contours as effectively
    • ii. normal patterns of resorption result in pseudo class III jaw relations
    • iii. causes labial surfaces of anterior teeth to be pushed as far anterior to the labial contours of the alveolar ridge
    • a. will lead to buccal cantilever and implant overload
    • g. Insufficient interocclsual space
    • i. need 15 mm from implant head to occlusal surface
    • ii. 3-4 mm space between bottom of bridge and gingival tissue
  52. 54. What are the factors necessary to allow opening the palate on an implant assisted overdenture? When should you cover the palate? (6 points –1/2 page)
    • If A-P spread is adequate, length of implants is adequate and bone's quality and vol is good, a palateless denture is permitted. advantage: pt comfort, better speech, and improved taste.
    • cover palate: a:)Lack of A-Spread
    • b:)Short implants
    • c:)Poor quality bone sites
    • d:) bruxer
    • E: only 2 implants can be used
    • F: failure of one or more implants to osseointegrate
    • source: Restoration of the Edentulous Maxilla with Osseointegrated Implants slides #46
  53. 55. What factors affect load distribution of an implant supported fixed partial denture designed for the posterior quadrants of the maxilla or mandible? (10 points – 1/2 page)
    • 1. Bone factors
    • a. QUALITY of bone/implant interface - Thin cortical layers and poor quality trabecular bone make it difficult to achieve anchorage at surgery and leads to a poor bone implant interface
    • b. QUANTITY of bone - Limited quantity of bone may lead to the placement of short implants and/or poorly angled implants. In the mandible, nless bone sites are available that will accept implants 10 mm or longer the patient should be considered for a removable partial denture.
    • 2. Implant factors
    • a. number - One implant for each dental unit; At least three in distal extension areas
    • b. length - The short implants are particularly prone to occlusal overload and bone loss. Longer implants distribute stresses much more favorably. Machined style Implants of at least 13 mm in length should be used in the Posterior Maxilla.
    • c. width - It is recommend that with original threaded implants of at least 4 mm in diameter be used in posterior quadrants.
    • d. arrangement - Linear configurations of implants are particularly vulnerable to the effects of non-axial loading. Tooth positions typically increase potential that occlusal loads will be directed axially. Implants should be placed in ideal tooth positions.
    • e. angulation - Perpendicular to the occlusal plane.
    • 3. Prosthodontic factors
    • a. Occlusal factors
    • i. Cusp angles - Flat cusp angles are preferred.
    • ii. Width of occlusal table - Reduce width of occlusal table
    • -Lingualized or buccalized occlusion
    • b. Guidance type - minimize lateral forces to the implants.
    • i. Anterior guidance - Anterior guidance on natural teeth with centric only contact for the implant supported posterior occlusion.
    • ii. Group function
    • c. Cantilevers - Avoid the use of cantilevers with linear configurations.
    • d. Connection to natural dentition
    • i. Semi-precision attachments: intrusion of natural tooth; cantilever effect.
    • ii. Rigid attachment system: If required to attach to natural dentition do so with a rigid attachment system.
    • e. Interocclusal space
    • i. need 15 mm between implant head and occlusal plane
    • ii. 3-4 mm between bottom of fixed bridge and gingiva
    • 4. Para-functional Factors i.e. bruxism
    • Chronic bruxism predisposes to:
    • 1. Implant fractures
    • 2. Fracture of retaining screws
    • 3. Implant overload with resorption of bone around the implant
  54. 56. What purposes are served by the use of provisional implant restoration in partially edentulous patients? (8 points 1/2 page)
    • Lecture: 8 - Restoring Post. Quads I.ppt
    • Slides: 86-87
    • Primary Uses:
    • Esthetic Issues
    • -form the most ideal gingival contours for definitive crown
    • -Tooth shape / form.
    • - gain patient’s approval
    • - soft tissue development by progressive alteration of provisional
    • Prosthesis design issues.
    • -Identify angulation problems that may affect the definitive restoration.
    • - helps to test and reevaluate the restorative plan
    • - long term evaluation if the osseointegration of the implant is questionable
    • restoring post quads I
  55. 57. What factors (anatomic and implant) influence the effectiveness of implant anchorage in bone? (6 points – 1/2 page)
    • • Uncontaminated implant surface
    • • Preparation of Congruent, Non-traumatic implant sites
    • • Primary Implant Stability
    • • No movement during the healing phase
    • • Thickness of Cortical bone
    • • Density of trabecular bone
    • • Length of the implant
    • • Width of the implant
  56. 58. When restoring the edentulous maxilla, what are the advantages of overlay dentures over fixed prostheses?
    • Removable overlay dentures:
    • 1) provide better lip support and facial contours
    • 2) biomechanics: Relationship between posterior occlusal surfaces and alveolar ridge (due to resorptive patterns) result in buccal cantilevers which could lead to implant overload if posterior implants of fixed prosthesis are short or bone quality is poor
    • 3) better hygiene access
    • 4) phonetics- seals up spaces so that air cannot escape during speech and alter speech
    • 5) Cost (overlay dentures are cheaper because less implants needed)
    • 6) High predicatability
    • 7) High pt acceptance
    • 8) Simple to fabricate
    • Source: "Restoration of Edentulous Pts (Pt Selection and Tx Planning) by Buemer and Parvizpour. Slides 13-21 and 41.
  57. 59. When restoring an edentulous maxillary and mandibular arch with a fixed implant supported prosthesis, how is the cantilever length determined? (4 points – 1/4 page)
    • Basically, you always want to reduce the cantilever length as much as you can (place implants as far posteriorly as possible, while still being mindful of implant length, bone density, sinus/IA position, etc…). However, the cut off for cantilever length is as follows:
    • Mandible- 2 times the A-P spread
    • Maxilla- ½ times the A-P spread
  58. 60. In the edentulous mandible, what factors influence the treatment choices available (fixed vs. removable)? In each factor indicate whether you would favor fixed or removal and explain the reason for your choice. (20 points – whole page)
    • (from the lecture about Tx planning the edentulous pt--slide 34 and on--and my own thoughts)
    • Fixed vs. removable in the edentulous mandible is dictated by (1) esthetics, (2) psychological demands, (3) hygiene access, and (4) cost.
    • 1. Esthetics: The pattern of jaw resorption results in a loss in the bucco-lingual dimension of the mandible so a fixed prosthesis may not provide adequate lip support. If there is a lot of resorption, then using a fixed prosthesis to reproduce proper lip support may result in a buccal cantilever and unfavorable forces on the implants. Thus, in severe mandibular resorption, a removable overlay denture would be the preferred choice because the patient will require the presence of a properly contoured denture flange in order to establish proper lip contours.
    • 2. Psychological demands: Some pts find it unacceptable to have a removable prosthesis that needs to be removed at night. In these pts, if esthetics, hygiene, and cost permit, a fixed prosthesis may be a better choice. For other pts, a removable overlay denture may be sufficient because their concerns are about the lack of retention, stability, and support in conventional mandibular dentures and their own poor neuromuscular control resulting in embarrassing movements of the denture.
    • 3. Hygiene: Oral hygiene must be maintained meticulously to prevent peri-implant gingival infections which can lead to loss of the implants.
    • a) quality of soft tissue surrounding the implants: when implants emerge through poorly keratinized unattached mucosa, removable overlay dentures are recommended because oral hygiene is easier for the pt. In a fixed prosthesis, oral hygiene will be more difficult to perform because of tissue sensitivity. However, if there is ample keratinized attached mucosa, forming a gingival cuff around the implants, and the pt had good oral compliance, a fixed prosthesis would be a suitable choice. A palatal graft may be necessary to improve the quality of the peri-implant tissue.
    • b) oral compliance: it is difficult to manipulate the hygiene aids used in pts with fixed edentulous bridges. If the pt has impaired vision or motor skills, removable overlay dentures are recommended.
    • 4. Cost: Overlay dentures are less expensive than a fixed prosthesis. Furthermore, implant-assisted dentures are less expensive than implant-supported dentures. Thus, in a pt with limited funds, a removable overlay denture will be the most cost effective choice.
  59. 61. What issues need to be considered when deciding whether or not to immediately load an implant retained prostheses? (8 points, 1/2 page)
    • Initial bone anchorage – This is site specific. Good initial anchorage can by achieved and long implants can be used in the anterior maxilla and anterior mandible. In the posterior regions of both the maxilla and mandible shorter implants are generally used and initial bone anchorage is not as good.
    • Nature and magnitude of occlusal loads – Posterior occlusal loads are four times greater than anterior occlusall loads. Immediate loading of posterior quadrant implant supported restorations with linear configurations is quite risky.
    • Regarding edentulous patients, is the prosthesis going to be implant supported or implant assisted - Exposing an implant assisted prosthesis to immediate loading is relatively predictable whereas the opposite is true with regard to implant supported prostheses.
    • Surface texture of the implant – Better initial anchorage can be obtained with rough surfaces as opposed to machined surfaces.
    • Are sites available for placement of additional implants? Since the initial bone anchorage is less than what would be achieved with suitable healing periods, generally more than the usual number of implants would need to be employed.
    • - Acid etched surfaces: blood clot formation, angiogenesis, osteoprogenitor cell migration , cortical bone deposited on implant surface (as opposed to woven bone seen in machined surfaces), and secondary remodeling of the woven bone.
  60. 62. What biologic processes need to be complete before an implant is fully anchored in bone? (12 points, 1/2 page)
    • • Blood clot formation
    • • Angiogenesis
    • • Osteoprogenitor cell migration
    • • Woven bone formation
    • • Deposition of lamellar bone
    • • Secondary remodeling of woven bone.
    • In humans these events take about 4 months. The presence of a rough surface titanium implant will reduce this time by accentuating specific gene expression.
  61. 63. What are the advantages of the two implant assisted overlay denture as compared to fixed prostheses when restoring the edentulous mandible? (8 points – 1/2 page)
    • Advantages of a two implant assisted overlay denture:
    • 1) Predictability - implant failure rates for this application are virtually zero
    • 2) Patient acceptance is very favorable
    • 3) Cost effective
    • 4) Simple to fabricate
    • Lecture #5 Slide 41.
    • 5) Esthetics: provides lip support
    • 6) Easier access for proper hygiene of implants
    • Lecture #5 Slide 34, 39
  62. 64. When designing an implant assisted overlay denture for the mandible, what prime support areas will be used to absorb posterior occlusal loads? (4 points – 1/4 page)
    The anterior, or incisal, loads are borne by the implants while the posterior occlusal loads are born by the primary denture support areas (retromolar pad and the buccal shelf).
  63. 65. When designing a two implant assisted overlay denture for a patient, where are the two most desirable implant locations? Please explain your answer. (4 points – 1/2 page) The answer is in PP#6 Slides 13-18
    When designing a two implant assisted overlay denture, the two most desirable implant locations are the canine positions or between the canine and the 1st premolar. This allows for the bar to be configured parallel to the axis of rotation with little or no anterior cantilever extension. This configuration is far enough anteriorly to minimize the anterior cantilever. The anterior, or incisal, loads are borne by the implants while the posterior occlusal loads are born by the primary denture support areas (retromolar pad and the buccal shelf). They should be 12-20 mm apart. Little benefit is gained by increasing the distance between the implants. If implants are placed too close to one another, there will not be enough room for 2 Hader Bar clips (stability and retention of the denture), Hader bar segment cantilevered anteriorly, occlusal forces are minimal, the bar will serve as the axis of rotation. Placing an additional implant (total of 3) provides no additional benefit.
  64. 66. Prior to processing the two implant assisted overlay denture, the clip housings are secured to the bar via Hader clips and the rest of the bar is blocked out with plaster or stone. Why? (4 points – 1/3 page)
    • This is to guarantee that only the clip housing gets incorporated into the denture base and not the whole clip housing-bar complex. The only thing that touches the bar is the Hader clip. The denture doesn't touch the bar, otherwise the denture will pop out when eating.
    • Answer from going to Dr. Perri's wonderful lecture on Hader bars. ppt 6
  65. 67. What is meant by the phrase “prosthetically-driven” implant placement? (4 points –1/3 page)
    Implant placement is primarily determined by, and related to, the final prosthetic objectives. The type, size, exact location, etc of the fixture is determined by the limitations of the desired prosthesis. A tooth is set or waxed up where the restoration is desired and the implant placement is derived from this information, but without violating the limitations of implants themselves. Often modifications are necessary due to the limitations of implants as load bearing prostheses.
  66. 68. When surgically placing an implant into a bony site, what strategies are used to avoid overheating the bone? (8 points – 1/2 page)
    • -incrementally increase diameter of twist drills to prepare recipient bone site
    • -drilling procedures performed under copious irrigation to minimize generation of heat
    • -all drilling procedures except tapping performed w/ high speed at 2,000 rpm
    • -tapping is performed w/ low speed at 45 rpm
    • -insertion of implant also performed w/ low speed
    • lecture 2 - slide 12-13
  67. 69. List the relative medical contraindications to placing osseointegrated implants in patients with bone sites of quantity and quality volume. (8 points – 1/2 page)
    • -Severe xerostomia
    • -Bruxism
    • -Brachycephalics
    • -Radiation therapy to implant bone sites
    • -Poor oral compliance
    • -Immunologic disorders
    • -Psychic disorders
    • -Patients using medication that affect healing
    • -Medical condition affecting the patient ability to tolerate the surgical procedure.
    • Bruxism and Brachycephalics (implant assisted only)
    • Lec 1-Biol Basic of Osseoin. Slide #147.
  68. 70. List the relative dental contraindications to placing osseointegrated implants in patients with bone sites of appropriate volume. (8 points – 1/2 page)
    • Severe Xerostomia
    • Uncontrolled bruxism
    • Radiation therapy to implant site
    • Poor oral hygeine / compliance
  69. 71. What are the objectives to be accomplished at second stage surgery? (6 points – 1/2 page)
    • EDENTULOUS PTS (AND POSTERIORS)
    • *surgically expose the coverscrew/head of the implant(s)
    • *replace cover screw with a healing abutment
    • *evaluate the surrounding soft tissue contours and quality
    • *create an adequate zone of keratinized-attached mucosa around the implant
    • PARTIALLY EDENTULOUS PTS
    • *same as above and...
    • *esthetic zone: preserve/restore gingival contours (esp the interdental papilla)
    • *implant position is critically important and should be determined by "prosthetically driven" surgical guide.
  70. 72. What impact have the changes in surface microarchitecture had on predictability, anchorage as measured by reverse torque tests, and histomorphometry of titanium implants? (10 points – 1/2 page)
    • Old surface: machined (smooth);
    • New surface microarchitecture changes: electrolytically modified surface; sand blast / acid etch surface; double acid etch surface (rough).
    • The data indicate that rough surfaces appeared to create significantly better initial anchorage of the implant in bone as compared to machined surfaces and may even accelerate the biologic events leading to osseointegration. To test initial anchorage, torque removal studies were performed. Dual acid etch vs. machined: about 4x increased initial anchorage (20 Ncm (dual acid etched) vs ~5 Ncm (machined)). Surface roughness and bone appositional index – all new surfaces tested developed about the same bone contact area.
    • The rougher surfaces on average increase the bone implant interface by about 50% over the machined surfaces in most studies. However, additive surfaces that are excessively rough and irregular may provoke a response of macrophages and giant cells on the surface of the implant. For this reason most of the surfaces used today are modified with acid etching techniques. It has been hypothesized that rough surfaces capture and retain the fibrin clot initially deposited on the implant surface more effectively than machined surfaces and thereby better facilitates the initial events (clot formation, angiogenesis etc) associated with osseointegration.
  71. 73. Describe the sinus lift and graft procedure. List the donor materials available. Which donor material is ideal? Explain!! (12 points – 1/2 page)
    • Sinus lift and graft
    • Purpose bone augmentation
    • 1. to allow placement of implant and prevent perforation into sinus by adding additional bone between sinus and alveolus
    • Procedure:
    • 1. surgical opening in the lateral aspect of the maxillary sinus wall
    • 2. sinus lining is carefully elevated from bony floor of sinus
    • 3. bone graft (autogenous/allogenic/combo) is packed on the floor of the sinus and roof of the alveolus
    • 4. graft healing time=3-6 months
    • 5. first stage of implant placement  after bone is properly healed
    • List the donor materials available:
    • 1. autogenous  PREFERRED
    • a. graft comes from same individual
    • b. fresh autogenous bone IDEAL!!!
    • c. advantages:
    • i. offers viable cells needed for phase1 osteogensis
    • ii. no immunologic response
    • d. disadvantage:
    • i. requires surgical preparation @ 2 sites:
    • e. sources:
    • i. iliac crest
    • ii. tibia
    • iii. calvarium:
    • iv. intra-oral: ramus, chin
    • 2. allogenic
    • a. tissue from another individual (same species)- not self
    • b. advantage:
    • i. does not require 2nd surgical site in host
    • ii. similar type/shape of bone to that being replaced can be obtained
    • c. disadvantage:
    • i. does not offer viable cells for phase 1 osteogenesis
    • 3. xenograft
    • a. tissue from different species
    • b. advantages:
    • i. does not require 2nd surgical site
    • ii. large amts of bone can be harvested
    • c. disadvantages:
    • i. no viable cells available for phase 1 osteogeneis
    • ii. rigorous treatment of bone needed to reduce antigenecity
    • 4. combination: autogenous/allogenic graft
    • a. advantage: allows for both phase 1 and phase 2 osteogenesis
    • b. disadvantage:
    • i. 2nd surgical site required
  72. 74. Why have HA coated implants been less predictable than titanium implants? Please explain in detail. (6 points – 1/3 page)
    • Main point: HA coated systems have great interest and enthusiasm b/c of bioreactivity, but they have problems with long term predictability
    • -Biological basis: HA similar to bone surface, so should be advantageous and more bioreactive than bone
    • -Initial studies show: More rapid osseointegration (at 6 weeks have 70% appositional index vs 30-50% with titanium)
    • -Long term studies show:
    • -HA coatings show cracks, fissures, and entire loss leading to microbial colonization and thus failure
    • -Most early HA marketed implants were actually coated mostly with tricalcium phosphate that resorbs, leading to more loss
    • -Animal studies show macrophages phagocytizing the HA coating
    • -Current attempts: HA coating with nanotechnology to bond titanium to HA better for HA crystalline coating may be a better surface to promote OI while being biocompatible
  73. 75. What are the most common problems patients experience with their mandibular dentures that lead patients to inquire about dental implants? (6 points – 1/3 page)
    • • Lack of stability
    • o Low residual ridges
    • o High muscle attachments/ low vestibular depths
    • • Lack of retention
    • o FOM posture
    • o Tongue position (retruded – unfavorable)
    • o Difficult to establish a gasket seal
    • • Poor Support
    • o Esp anteriorly
    • o Limited attached keratinized mucosa
    • o B shelf and Retromolar pad only provide support posteriorly
    • o Residual Ridge Resorption
    • • Poor neuromuscular control
    • o Denture wearing experience is important
    • o Tongue, buccinator, & orbicularis oris are used to stabilize the denture in pts w/ good neuromuscular control
  74. 76. What impact would the placement of two implants in the symphyseal region and the fabrication of an implant assisted overlay denture have on each of problems cited above?
    • (8 points, 1/2 page)
    • a. Improved retention. Note denture snaps onto retention bar.
    • b. Improved stability (from the implants and the retention bar).
    • c. Improved support (anteriorly). Anterior, or incisal, loads are borne by the implants while the posterior occlusal forces are borne by the primary denture support areas (retromolar pad and buccal shelf).
    • d. Better control of the bolus (tongue no longer must position denture and control bolus simultaneously).
    • Advantages:
    • Predictability – Implant failure rates for this application are virtually zero
    • Patient acceptance is very favorable
    • Cost effective
    • Simplicity
    • The anterior, or incisal, loads are borne by the implants while the posterior occlusal loads or born by the primary denture support areas
    • (retromolar pad and the buccal shelf
  75. 77. As compared to fixed, what are the advantages of restoring the edentulous mandible with an implant assisted overlay denture? (8 points, 1/2 page)
    • Implant Assisted overdentures:
    • o Are predictable & show virtually zero implant failures
    • o Have high pt acceptance
    • o Are cost effective (cheaper than fixed)
    • o Are more simple to fabricate
    • o Support the lip (in re esthetics & phonetics)
    • o Are more hygienic
    • o Better for pts w/ limited motor control or vision problems
    • o Do not need the hygienic gap b/w the mucoperiosteum and the prosthesis
    • o More esthetic & hygienic
    • o No phonetic whistling
    • o Do not require 4 implants, 2 is sufficient
    • o AP spread is favorable but not required
    • o Exert less non-axial forces (fixed often have cantilevers)
  76. 78. When using a “Hader” bar to retain an implant assisted overlay for the edentulous mandible, why are the two implants positioned in the cuspid region? (4 points 1/3 page)
    • Implants are placed at the cuspid positions so that the Hader bar can be configured parallel to the axis of rotation with less cantilever problems.
    • The implants needs to be placed 12-20mm apart (Dr. Perri prefers 16-20mm) to accept 2 Hader clips for stability.
  77. 79. When making implant assisted overlay dentures for the mandible, why is the impression border molded? (4 points, 1/4 page)
    • The answer is from "Complete denture" syllabus Page 16.
    • The forces of occlusion are shared between the implants and the mucoperiosteum. Therefore the impression border is molded to obtain the most ideal denture base. The denture base must have ideal tissue adaptation and flange extension. In addition, the denture base should cover as large area as functionally possible to achieve the maximum retention, stability and resistance to the forces of mastication.
  78. 80. When fabricating an implant assisted overlay denture for the mandible, why does the land of the master cast have to be wider than normal? (2 points, 1/4 page)
    • A silicone template with the denture teeth imbedded within will need to be fabricated and this is supported by the land of the cast.
    • --> In slide 44, there is an example of the silicone template. It serves to record where the teeth are so you know where to wax your
    • tissue bar (see to slide 48). The extra thickness of the land acts to support the silicone template so as to get a repeatable/ stable record.
  79. 81. When designing a Hader bar for a mandibular implant supported denture, describe the configuration of the bar with respect to the occlusal plane, midline and the underlying tissue. Carefully label your drawing. (6 points, 1/3 page)
    • Configuration of the bar
    • -Parallel to the plane of occlusion
    • -Perpendicular to the midline
    • -There should be ample space beneath the bar to provide for proper hygiene access
    • - in cross section it’s a complete circle and permits the denture to rotate around it.
  80. 82. How do you decide whether to restore an edentulous mandible with a fixed or a removable prosthesis? Please explain. (12 points, 1/2 page)
    • 1. Esthetic demands-properly contoured lip contour may require removable
    • 2. Need for hygiene access-removable if poor motor skills to brush and poorly keratinized unattached mucosa
    • 3. Psychological demands-Probably fixed, pt does not want to remove denture at night
    • 4. Cost- Removable overlay denture is less expensive than fixed
    • Removable is predictable, high pt satisfaction, less costly, and simple
    • from Tx planning the edentulous pt--slide 34
  81. 83. What are the most common problems encountered when considering implants for the edentulous mandible? Please explain why each problem you list is significant?
    • (10 points, 2/3 page)
    • 1/ Insufficient height of bone over the IA nerve. These may be caused by severe resorption of mandibular ridge or various anatomy of IA canal in a individual. The bone height over the IA nerve is very important because this area requires implants that are 10mm or longer.
    • 2/ Insufficient bone width, caused by resorption. Implants usually require at least 5 mm buccolingual dimension of the ridge.
    • 3/ Non-ideal positioning of implant for axial loading due to inadequate bone volume
    • 4/ Lack of interocclusal space, commonly seen in pts who retain residual dentition or recently edentulated. This will limit design choices and compromise prosthodontic procedures
    • 5/ Lack of attached keratinized tissue, leading to compromised hygiene.
    • * Each of above problems may cause failure of implants following bone fracture, resorption, or inflammation.
  82. 84. In this patient only 4 implants can be placed in the edentulous maxilla because of pneumatized maxillary sinuses.
    • a. Indicate by drawing, where each of the implants should be positioned with respect to one another. Be specific. (4 points, 1/3 page)
    • PowerPoint: “Restoration of the edentulous maxilla w/ osseointegrated implants”, slide 11.
    • • Implants should exit at the ridge crest
    • . The two ant. implants should be a minimum of 12mm apart (measured from the center of the implants)
    • • The post. Implants should be placed as posteriorly as possible to maximize A-P spread.
    • b. What type of tissue bar would you design for this patient; an implant supported, or implant assisted design? (2 points, 1/8 page)
    • An implant assisted bar is preferred when only four implants are placed b/c:
    • • To minimize the possibility of implant overload
    • • When implant supported designs were used the distal implants often failed after 3-5 years of service.
    • • When implant assisted designs w/ resilient attachments connected to the distal portion of the bar were used in the maxilla the failures after loading were completely eliminated.
    • c. Indicate by drawing, the design of the tissue bar you would recommend. Be specific with respect to the types of attachments you
    • would use. (6 points, 1/2 page)
    • Implant assisted tissue bar is recommended w/ resilient attachments such as ERA connected to the distal of the bar. This attachment permits the overlay prosthesis to be compressed into the mucoperiosteum in the extension areas. As a result, the denture bearing tissues absorb the posterior occlusal forces. The failures after loading were completely eliminated w/ this design.
  83. 85. Why do you need to border mold an impression when fabricating a palateless implant retained overlay denture? (4 points, 1/4 page)
    • Border molded impressions made with a custom tray need to be made in order to record the thickness, contour, and length of the buccal and labial flange of the overlay denture.
    • The posterior palatal seal area need not be displaced and recorded because a palateless denture is being fabricated
  84. 86. Why does a palateless implant retained denture require metal reinforcement?
    • (4 points, 1/4 page)
    • Metal reinforcement - prevents flexure of the prosthesis and crazing and subsequent fracture of the acrylic resin overlying the bar.
    • - adds rigidity
    • Saves interocclusal space --Can also be used to incorporate the metal housings within the metal framework (i.e.. ERA and hader attachments).
    • (source: restoration of the eden max w/osseo impl)
  85. 87. When performing implant surgery, why is it important to use standard sterile surgical technique? (6 points, 1/3 page)
    • - to reduce the risk of contamination of the sterile implant surface
    • - to enhance the success rate of dental implants
    • - to reduce the risk of post-surgical infections
    • straight from the ppt entitled "Stage I Dental Implant Surgery" by Dr Peter Moy; slide 9.
  86. 88. Why are implant assisted tissue bar designs used in the maxilla when the A-P spread is less than 2 cm? (4 points, 1/4 page)
    • Because you can gain further support by having FULL PALATAL COVERAGE OF THE DENTURE.
    • note that: AP spread serves to elongate posterior support provided by the implants. if AP spread is limited, posterior support cannot be provided solely by the implants and the primary support areas of the maxilla (the max tuberosity and hard palate) are utilized for posterior support. hence, an implant assisted overdenture is indicated. full palatal coverage is not necessarily always used w/ implant assisted designs.
  87. 89. What are the possible undesirable outcomes if a fixed implant supported prosthesis in an edentulous patient is designed with excessive cantilevers combined with insufficient A-P spread? (4 points, 1/4 page)
    • 1) Mechanical Failures - recurrent fracture and/or loosening of the prosthesis retaining screws
    • 2) Implant Overload - resorptive remodeling response of the adjacent bone and eventual loss of the distal abutment; Can lead to significant loss of alveolar bone.
  88. 90. Why are ridge lapped prostheses discouraged when restoring the anterior maxilla with implant supported restoration? (6 points, 1/3 page)
    • Following extraction, particularly if traumatic, the labial plate resorbs. Resorption creates a site that dictates a palatal placement and a ridge lapped restoration. Ridge lapped restorations, however, are discouraged in restoring ant max with implant supported prosthesis for the following reasons:
    • • Hygiene is made more difficult; except for removable prosthesis
    • • Esthetics is compromised in pts with a high smile line who display significant amounts of gingival
    • • Psychological factors of the pt
    • • May interfere with phonetics
  89. 91. Why do implant sites in the anterior maxilla in partially edentulous patients frequently need to be augmented with bone grafts? (4 points, 1/3 page)
    • - Buccal plate deficiency in single tooth site
    • - following extraction, particularly if traumatic, the labial plate resorbs
    • - resorption creates a site that dictates a palatal placement and a ridge restoration
    • - need to restore bone and soft tissue contours to enhance the final esthetic result by idealizing implant position
    • - if not augmented, buccal cantilervering will result and might cause overloading due to off-axial loads
    • 1. To improve bone quality and quantity lost due to resorption patterns that result in pseudo class 3 relation
    • 2. To be able to place at least 6 implants in the anterior maxilla for an implant assisted or supported prosthesis
    • 3. To provide an A-P spread of 2cm minimum ?
    • 4. Adequate support for the upper lip
  90. 92. Do implants achieve the same degree of anchorage in grafted sites as in normal bone? Please explain your answer. (4 points, 1/3 page)
    • Only if woven bone are replaced by normal lamellar bone in the grafted sites is the level of anchorarage the same.
    • The INITIAL bone implant interface is compromised in sites with woven bone.
    • In some sites, the woven bone is never replaced with dense lamellar bone.
    • The load bearing capacity of implants in grafted bone may be compromised until normal lamellar bone is developed.
  91. 93. In partially edentulous patients, why do implants in grafted bone sites do better in the anterior maxilla than they do in the posterior mandible? (4 points, 1/4 page)
    • Patients with severe alveolar resorption may require a bone graft before implants are to be placed. Bone graft enables placement of implants of sufficient length with bicortical anchorage. However, bone grafts are technique sensitive, particularly in the posterior mandible since there is risk of inferior alveolar nerve displacement. Although the risk of nerve injury is relatively small, the morbidities associated with nerve injury may be severe. Short or wide diameter implants in the posterior mandible have been used to avoid IA nerve displacement. However, this practice has been unpredictable since shorter implants are particularly prone to occlusal overload and bone loss. (Thus, patients should be considered for a removable partial denture if bone sites are unavailable to accept implants 10 mm or longer.) In addition, augmentation of vertical defects in the posterior quadrants with free autogenous bone grafts has been unpredictable since historically such grafts are subject to resorption particularly upon occlusal loading. Implants in grafted bone sites in the anterior maxilla are more predictable due to minimal loads in the anterior maxilla compared to the posterior mandible.
    • -In the posterior mandible, augmentation of vertical defects with free autogenous grafts have been unpredictable.
    • -The grafts are subject to increased resorption due to heavy occlusal loading in this site.
    • -Due to proximity to the Inferior Alveolar nerve in the posterior mandible, shorter implants are used which are particularly prone to occlusal overload and bone loss.
    • All these factors lead to implant failures in grafted bone sites in the posterior mandible. Implants in grafted bone sites in the anterior maxilla fare better because bone grafts in this site is more predictable due to minimal loads in this region.
  92. 94. There are several ways to supplement soft tissue contour of the peri-implant gingiva around implants in the anterior maxilla. List the choices available and indicate which would be your first choice. Explain your reason. (10 points, 1/2 page).
    • 1. Free palatal graft
    • a. ST augmentation in non-esthetic areas
    • b. To increase the zone of keratinized tissue around implant
    • 2. CT graft
    • a. ST augmentation inesthetic areas due to superior color match and esthetic blending
    • b. To provide a zone of attached non-mobile ST around implants
    • c. The underlying CT will determine the character of the overlying epi
    • d. To enhance ST contours
    • e. To reconstruct missing ST volume defects
    • f. Dual blood supply to support graft revascularization
    • 3. Partial thickness apical repositioning flap
    • Good soft tissue quality and contour can be enhanced by surgical procedures at the time of stage II surgery- implant exposure -
    • However-Some critical soft tissue contours, such as the interproximal papilla, must be preserved because they are difficult to reconstruct if lost.
    • Whenever possible, surgical procedures should be designed to preserve soft tissue contours (esp. interdental papilla)
    • A customized “anatomically-correct” healing abutment can be used to “shape” the gingival tissues.
    • Another way to supplement soft tissue contour of the peri-implant gingival around implants is Reconstruction of the Papilla.But Regenerating the interproximal papilla between natural teeth is one of the most challenging and least predictable procedures in periodontics today. Tarnow, et a. (J Perio, 1992) showed that if the distance between the contact point and the interdental crest of bone was less than 5mm, the papilla was present nearly 100 % of the time. However, when this distance was greater than 5mm, the presence of the papilla was less predictable. Reconstructing the inter-implant papilla is an even more challenging problem than that between natural teeth because there is no support from connective tissue fibers .Tarnow, et al.,2000) showed that the distance between the implants was also a critical determinant of whether a papilla was present. The authors concluded that 3 mm of space between implants was optimal
  93. 95. When designing a surgical template for placement of an implant in #8 position, what landmarks or surfaces associated with the proposed definitive restoration need to be incorporated within the design of the template? (4 points, 1/4 page)
    • When designing a surgical template for placement of an impant at #8 position, landmarks and surfaces to be considered are:
    • 1. Inciso-cervical/occlusocervical position is mainly dependent on the locaton of the existing bone. The head of the implant should be 2 to 4 mm below the adjacent gingival marigne. Implant template should represent the CEJ of the proposed restoration for guiding the surgery.
    • 2. Deficencies in Interdental papillae and resorption of the buccal plate after traumatic extraction dictates the palatal placement and a ridge lapped restoration. Compromised aesthetics and difficult hygiene, buccal cantilevering.
    • 3. Interarch distance should be at least 2mm in the anterior sites. (4 mm in posterior sites)
    • 4. M/D Distance about 7mm. If more than 10mm, implant size and number should be carefully considered to avoid overloading.
    • 5. One-to-one crown/implant ratio for sound biomechanics.
  94. 96. What are the disadvantages of the so-called cera-one abutment or similar abutments?
    • (4 points, 1/4 page)
    • Cera-one is an all ceramic implant restoration that is cemented to a zirconia implant abutment for esthetic purposes. The disadvantages include:
    • • No metal reinforcement
    • • Susceptible to fracture
    • • Cannot be used in load-bearing areas
    • • Disadvantages of being cemented:
    • o Run the risk of leaving cement in the sulcus which can lead to inflammation and fistula formation
    • o Non-retrievability – if need to service implant, may need to cut off crown
    • o Cannot correct angulation errors during implant placement
    • o Cannot compensate for limited interocclusal space
    • o Maybe difficult to seat completely due to hydrolic pressure
  95. 97. Why are custom abutments often necessary when restoring anterior maxillary teeth with implants? (4 points, 1/4 page)
    • A customized “anatomically-correct” healing abutment can be used to “shape” the gingival tissues in the anterior esthetic zone. (Klokkevold’s lecture)
    • Abutment Selection (Fanuscu’s lecture)
    • The final restoration can be either screw or cement retained. Various abutments can be used to facilitate the connection between the implant and the final crown. The UCLA abutment is the most versatile abutment since it can be used for both screw and cement retained options.
    • Screw retained restorations are used when retrievability of the restoration is desired and minimum incisocervical/occlusocervical height is available. The single piece restoration uses UCLA abutment and is screwed onto the implant through the access hole in the cingulum or central fossa of the crown. This method is used when the position and the angulation of the implant is ideal. However, a two piece restoration is used when the access hole exits the crown in an undesirable way. In these situations a custom abutment is fabricated to accommodate a crown piece with a lingual set screw. By this way, first piece (custom abutment) gets screwed onto the implant and the second piece (crown) is screwed onto the abutment.
    • Anterior maxillary is the area where esthetic concern plays a major role in determining the treatment plan. Often there is a vertical and/or horizontal ridge deficiency in the area, while the bone volume is sufficient to place implants. In this case a careful treatment planning using Custom abutments (UCLA type abutments) is important in obtaining the ideal esthetic and functional results. Vertically insufficient bone is a major concern especially in people with high smile line since vertical bone augmentation is not predictable.
    • Exact implant positioning is critical in creating natural emergence profile. Implant misplacement would lead to varying widths for the anterior teeth causing esthetic disharmony. In this case custom abutments are indicated. Screw or cement retained implant restorations can be fabricated. Various reasons (retrievability, amount of space, esthetics, occlusion, ease of operation, etc.) can be considered in choosing one over the other option. However, the decision should be made prior to the placement of the implant, since position of the implant might be slightly different in each option.
    • Uses of the UCLA (custom abutmnts) include:
    • Esthetics
    • Limited Interocclusal space
    • Angulation Correction
    • Custom Substructures
    • Custom abutments are used for better esthetic results when interarch space is limited, or when the fixture angulation is not acceptable. They follows contours of the soft tissue leading to better esthetic result than the standard adutments.
  96. 98. What factors contribute to an ideal esthetic result when restoring a single tooth defect in the anterior maxilla? (6 points, 1/3 page)
    • A) Edentulous tissues:
    • -The amount of attached tissue is important in establishing periodontal health around the implant crown.
    • -Interdental papilla and buccal plate should be carefully analyzed for deficiencies, since they might effect functional and esthetic outcome of the implant restoration.
    • B) Residual edentulous space:
    • -Interarch distance should be minimum 2mm in the anterior sites
    • -Mesio-distal distance should be about 7 mm
    • -Size of the missing tooth space in relation to contralateral tooth in the anterior region should be carefully matched for good esthetic results.
    • - Crown/implant ratio should be kept to 1:1 for sound
    • biomechanics.
    • C) Adjacent teeth:
    • -Soft tissue contours and levels should be reviewed to identify any deficits that might have direct impact on the esthetic outcome.
    • -Position of the adjacent teeth (rotated, tilted, out of curve, extruded, intruded) along with position of proximal contacts can cause functional and esthetic problems if not addressed properly.
    • -Restorations and materials in the adjacent teeth would assist in designing the optimal implant restoration
  97. 99. What are the limiting factors to consider when placing implants in the posterior mandible in partially edentulous patients? (8 points, 1/2 page)
    • - Insufficient height of bone over the inferior alveolar nerve to permit placement of a 10mm or longer implant.
    • - less than 7 mm are at risk for fracture during or immediately after implant placement and should be augmented with a bone graft
    • - Insufficient width of bone
    • - less than 5-6 mm requires bone augmentation
    • - Non-ideal positioning of implant for axial loading due to inadequate bone volume
    • - Single cortical anchorage
    • - lack of attached keratinized tissue
    • - hygiene compromised when the implants are surrounded by poorly keratinized unattached mucosa
    • - palatal grafts are favored over skin grafts performed at second stage implant surgery
    • - lack of interocclusal space
    • - limits design choices
    • - compromises prosthodonitc procedures
    • - commonly encountered when a patient still retains residual dentition in either the maxilla or mandible
    • - seen in some recently edentulated patients
    • - patients with supraeruption of anterior teeth prior to extraction: need alveolectomy
    • - need 15 mm from head of implant to plane of occlusion
    • - 3-4 mm of space between the bottom of the bridge and gingival tissues
  98. 100. What anatomical landmarks limit the placement of an implant in the posterior maxilla?
    • - Floor of the maxillary sinus: insufficient height of bone over the sinus
    • - Insufficient width of bone
    • - Decreased quality of bone: increased trabeculation (decrease in dense cortical bone)
  99. 2. What are the critical components of an acceptable clinical trial? (10 points)
    • • well-controlled
    • • double-blinded
    • • randomized
    • • appropriate statistical analysis of data
  100. 3. Compare the masticatory performance of individuals with complete upper and lower dentures with patients using an implant assisted lower denture opposing a completemaxillary denture. (4 points)
    • • Nearly identical
    • • Very small (<10%) difference decreases over time. By 24 months, virtually identical.
    • • Patients reported marginally better chewing ability with implant-assisted denture
    • • Chewing comfort and eating enjoyment also rated better for implant-assisted denture
    • • Most reported differences due to a subset of pts who liked their new conventional denture less than their original one, but this group disappeared after 24 months.
  101. 4. Compare the masticatory performance and chewing strokes required to reach swallowing threshold of a fully dentate individual with a patient wearing upper andlower dentures. (4 points)
    • Masticatory performance Chewing strokes
    • Fully dentate (32 teeth) 88 12
    • Excluding 3rd molars (28 teeth) 78 20
    • Complete dentures 35 86
  102. 5. Compare the masticatory performance of Kennedy Class II patients restored with removable partial dentures vs fixed, implant supported partial dentures. (12points)
    • • There is no significant difference.
    • • FPDs scored slightly higher at delivery
    • • RPDs scored an eensy bit higher given time to adjust
    • • Appx scores for RPD and FPD:
    • Peanuts Carrots
    • At delivery 35 45
    • Later 55 70
    • • FPD group scored significantly better on subjective ratings of chewing comfort and food choices
    • • Both groups scored the same on subjective ratings of chewing ability, ease chewing hard foods, and eating enjoyment
  103. 6. Describe the difference between a resilient and a nonresilient attachment. In your answer provide a clinical example where each of the attachment types could be used.(8 points)
    A resilient attachment allows movement of the prosthesis in relation to the implants. A nonresilient attachment doesn’t allow this, so implant-assisted dentures with a distal nonresilient extension are essentially implant supported rather than implant assisted, which leads to implant failure. Thus, nonresilient attachments should be used only in implant supported dentures, while resilient attachments can be used for implant assisted dentures.
  104. 7. In specific situations attachments are used to connect implants to natural dentition when fabricating fixed partial dentures. Both precision and semi-precisionattachments have been used. Which type is preferred and why. (4 points)
    • Precision attachments are preferred. Semi-precision attachments tend to put more stress on the implants abutment, causing a cantilever effect which leads to bone loss around the implant. The natural tooth often tends to intrude as well when using a semi-precision attachment. Precision attachments lead to approximately even sharing of the occlusal load between the tooth and implant.
    • 8. Patients fitted overdentures assisted by natural tooth abutments chew more effectively
    • than patients fitted with overdentures assisted by osseointegrated implants. Why do
    • you think this is true? (4 points)
    • Patients with natural teeth can better perceive denture pressure/movement
    • Pts anesthetized max and mand score 20 points lower on a masticatory performance test
  105. 22. Describe the difference between a pickup type impression coping and a transfer type impression coping. Which type would you favor? Please explain. (6 points, 1/3page)
    • • Pickup Impression – registers both position and orientation, becomes locked into final impression, and after tray is removed an analog is connected and the model is poured
    • • (Implant Components and Basic Techniques: slide 88)
    • o A square coping is “locked” into the impression due to their shape
    • o Screwed to abutment with guide pin
    • o Impression made with “open” tray
    • o Analogs are attached before pouring the master model
    • (Implant Components and Basic Techniques: slide 84)
    • • Transfer Impression – shape allows it to remain in the mouth when the impression is removed and uses a 2 piece coping that will allow registration
    • (Implant Components and Basic Techniques: slide 90)
    • o Screw to abutment
    • o Take impression with closed tray
    • o Remove impression
    • o Unscrew coping
    • o Attach to analog
    • o Replace coping into impression and pour
    • Pickup is more accurate.
  106. 60. How can labial-buccal plate deficiencies be resolved in single tooth defects in the anterior maxilla? Which of the two methods available would you prefer? Pleaseexplain. (4 points – 1/2 page)
    • • Palatal placement of implant and ridge lapped restoration
    • o Hygiene is made more difficult
    • o Esthetics is compromised in patients with a high smile line who display significant amounts of gingiva
    • o Esthetics is compromised because most such patients lack interdental papilla
    • • Bone augmentation - preferred
    • o Grafting anterior horizontal deficiencies has been relatively predictable due to minimal loads usual in this region
    • o Grafting serves to restore bone and soft tissue contours to enhance the final esthetic result by idealizing implant position
  107. 84. Single tooth implant restorations can be either screw retained or cement retained. Cite arguments in favor of each method. Based on your knowledge to this point,which would your prefer? Please explain. (8 points – ½ page)
    • • Screw retained restoration
    • o Retrievable
    • o Minimum incisocervical/occlusocervical height
    • o Do not have to remove cement
    • o No risk of being able to seat crown due to hydraulic pressure
    • • Cement retained restoration
    • o More esthetic due to lack of screw access hole
    • o Better occlusal control
    • o Lab fabrication is easier
    • o Cementation technique more similar to conventional crown cementation

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