Removable Prosth

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emm64
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Removable Prosth
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2014-03-19 03:03:54
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Removable Prosth
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Removable Prosth
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  1. pre-prosth considerations
    • tori: major connector contours
    • tuberosity & teeth/crown length: occlusal plane
    • frenulae, attached tissues: retainers
  2. What is the effect of reduced periodontal support on RPD abutment load distribution?
    • Biomechanical factors
    • – 50/50 crown-root ratio results in a 20% reduction in support
    • – 60/40 crown-root ratio results in a 35% reduction in support
  3. Loading vector toward abutment
    • increased levels of stress concentration along the PDL
    • Periodontal bone loss further increased stress concentration both at the tooth/bone interface as well as within the tooth root
  4. PD compromised abutments clinical implications
    • – Splinting of abutments
    • – Stabilization of multiple abutments with RPD framework
    • – Attention to occlusion: Anterior guidance
  5. Endodontically treated teeth with compromised periodontal support adjacent to extension bases may be poor candidates for RPD abutments
    • – Higher susceptibility to fracture
    • – Higher stress levels within the root
    • – Avoid occlusal rests on these teeth if possible
  6. I-Bar retainers in mandibular bilateral distal extension cases with diminished periodontal support
    • Conclusions
    •  Highest stress concentration with the largest defect
    •  Splinting improves the distribution of load
    •  Stress reduction not proportional to number of splinted abutments
    • Clinical Implications
    •  Consider splinting abutments adjacent to extension
    • bases with poor periodontal support or poor residual
    • ridges
  7. The RPD and Periodontal Stabilization
    • Periodontal considerations: RPD design objectives
    • - Uniting and controlling the entire arch
    • - Control individual tooth movement
    • - Hygienic contouring at the tooth/tissue junction
    • - Flexibility to accommodate variable treatment situations
  8. Disclosing wax for
    • Coronoid interferences
    • – Side to side movements
    • • Flanges overextensions
    • – Pull on the cheeks, lips, patient
    • move tongue
    • Temp the disclosing wax
    • in the water bath before insertion!
    • • Tight pterygomandibular raphe
    • - mouth open wide
  9. CD Reline can only solve ___ problems related to inadequate denture base adaptation
    retention
  10. RPD Reline will only improve ________ of RPD, not retention.
    • mucosal support and stability
    • Retention provided by active retainers and parallel proximal plates
  11. Reline steps
    • record VDO to maintain
    • Border relief (2mm) and general tissue surface (1mm) of base
    • Border mold: compound, cutback w/scalpel, apply adhesive
    • Rubber base (or ZOE or PVS) impression
    • close mouth: CD, mainain occlusion, VDO
    • open mouth: RPD, fingers to fully seat framework
  12. Resilient Attachment:
    • Allows movement to take place between the matrix and patrix when fully seated, thus having a stress-breaking
    • function.
    • The movement is usually that of a hinge and serves to distribute potentially harmful forces away from abutment teeth in distal extension situations and where there are long edentulous spans
  13. NON-RESILIENT/RIGID ATTACHMENTS Indications:
    •  No vertical movement is anticipated
    •  Only for tooth supported appliances
    •  Strong abutments
    •  Functioning against complete denture or resilient overdenture
    •  Large well fitting denture base to distribute or dissipate forces of occlusion
    •  Intraocclusal space is limited
  14. RESILIENT ATTACHMENTS Indications:
    •  Tissue-tooth supported appliance
    •  Very weak abutments, when maximum tissue support is required
    •  Only a few abutments
    •  Functioning opposite natural dentition
    •  Functioning against non-resilient appliance
    •  Multi-directional action is desired
    •  With minimal denture base
  15. Active Attachment:
    • the retention between the matrix and the patrix can be adjusted- this means that the
    • attachment can be reactivated when wear takes place
  16. Passive Attachment:
    The retention between the elements cannot be increased or decreased. Passive attachments are used mainly to overcome minor alignment problems of abutment teeth or as stress breakers in fixed restorations
  17. ERA-Extracoronal Resilient Attachment
    • SPLINTING ABUTMENTS helps distribute the forces
    • ERA vertically resilient attachment
    • Best used with:
    • -light retention (white, orange)
    • -supporting rests
    • -adjacent teeth splinted
    • •ERA(rests & splints)
    • compares favorably to
    • I-bar (rests, no splints)
  18. OVERDENTURES Advantages:
    • • Preservation of the alveolar ridge
    • • Conservation of the remaining abutments
    • • Prosthesis stability, more stable occlusion
    • • Improved retention
    • • Esthetics & speech
    • • Open palates
    • • Proprioceptive response
    • • Distribution of forces of mastication
    • • Easily modified to a complete denture
    • Disadvantages:
    • •Cost
    • •Overdenture bulk
    • •Increased maintenance
  19. Implant-retained partial overdentures with _______ are a predictable and cost-effective treatment option for partially edentulous patients.
    resilient attachments
  20. Natural occlusion Maximum Intercuspation usually occurs
    • 0.5 to 1.0 mm anterior to the Centric Relation position
    • CR=ICP in Complete dentures
  21. Natural Dentition
    • Retained in PDL
    • Units move independently
    • Malocclusion effects not immediate
    • Non-vertical forces affect only teeth involved and usually well tolerated
    • Incising doesn’t affect posteriors
    • Bilateral balance is rare
    • Tactile sensitivity
  22. Denture “Dentition”
    • Mobile bases on mucosa
    • Teeth move as an unit
    • Malocclusion affects entire base immediately
    • Non-vertical forces affect all teeth and is traumatic
    • Incising affects all teeth attached to base
    • Bilateral balance is often desired for base stability
    • Decreased tactile sense
  23. Retromolar Pad
    • Glandular tissue
    • Fibrous connective tissue
    • Buccinator
    • Superior constrictor
    • Pterygomandibular raphe
  24. Requirements for RPD occlusion will be dependent upon the requirements for the “weakest arch”
    • Bilateral balance vs. anterior guidance
    • the type of guidance established is dependent upon the condition, number and position of any remaining anterior teeth (sometimes including the first pre-molar in the case of anterior extension bases)
  25. Principles of RPD design
    • Extension base RPD designs must anticipate and accommodate the movements of the prosthesis during function, without exerting pathologic stresses on the abutment teeth
    • Major connectors must be rigid.
    • Occlusal rest must direct occlusal forces along the long axis of the teeth.
    • Guide planes are employed to enhance stability and bracing.
    • Retention must be within the limits of physiologic tolerance of the periodontal ligament.
    • Maximum support is gained from the adjacent soft tissue denture bearing surfaces.
    • Designs must consider the needs of cleansibility.
  26. anterior rests
    • positive: long axis, NO lateral/inclines
    • center deepest
    • round line angles
    • half circle especially for extensions
    • close to gingiva/bone to reduce leverage
    • doesn't interfere w/occlusion
  27. incisal rests
    • 1/3-1/2 width of edge
    • concave MD
    • convex BL
  28. posterior rests
    • Provide rigid prosthetic support
    • Restore occlusion
    • Direct occlusal forces along the long axis of the teeth
    • Provide reciprocation and stabilization
  29. proximal plates Function
    • Protect against food impaction
    • Prevent tissue hypertrophy between tooth and prosthesis
    • Resist dislodgement of the prosthesis by frictional contact with the teeth (retention)
    • Maintain arch integrity by anterior-posterior bracing action, which controls tooth movement
    • Act with other connectors in reciprocation opposite retainers
  30. Major connectors
    • unites the rests and other parts of the prosthesis across the arch.
    • should be free of movable tissues
    • They should avoid impinging upon gingival tissues
    • Boney and soft tissue prominences such as tori should be avoided
    • Relief should be provided beneath the major connector to prevent its settling into tori or elevated mid palatal sutures
    • Major connectors should be rigid
  31. Lingual plate
    • Used when floor mouth contours are insufficient to accommodate a lingual bar
    • Used to splint periodontally compromised teeth together
    • Provides indirect retention and bracing
    • Enables replacement of anterior teeth
  32. connector design
    • minor connector is designed to cross the tooth tissue junction at right angles
    • The major connector should be at least 4mm away from the gingival margin to minimize food impaction
  33. I bar
    • Minimal tooth contact
    • Placement of retention contact is more exact
    • Minimal Interference with natural tooth contour
    • Maximum natural cleansing action
    • Allows for passive functional movement of an extension prosthesis
    • Better esthetics
    • I” bar should cross tooth tissue junction at right angles parallel to long axis of tooth.
    • Horizontal portion of the I bar is placed on unattached tissue whenever possible
    • Connection of I-bar to prosthesis should be in planned interproximal area between denture teeth.
    • A space is created between the I bar and the mucosa (it is crossing over) to prevent tissue hypertrophy.
    • Ideally “I” bar will terminate in gingival 1/3 of the tooth.
    • An active I-Bar requires only 0.010 “ undercut.
    • Reciprocation provided by the minor connector
  34. An active I bar retainer must be reciprocated by one of the following:
    • Opposing reciprocating clasp at 0” (I bar or C clasp)
    • A combination of rest, minor connector and guide plane.
    • A lingual or palatal plate
  35. Circumferential Clasp (Akers Clasp)
    • Suprabulge clasp
    • The flexible retentive arm originates from a minor connector or a proximal plate and its terminal 1/3 crosses the height of contour into the undercut
    • The rigid reciprocating arm stays above the height of contour
    • Advantages
    • Improved stability and bracing
    • Useful in patient with severe boney undercuts
    • Disadvantages
    • Food trap
    • Poor esthetics anteriorly
    • Potential for torquing the abutment tooth in extension situations
    • Useful
    • Posterior molars with unfavorable angulations
    • RPD’s with unilateral dentition where additonal bracing is required
  36. mesial vs distal rest I-bar effects
    • distal: up and anterior into undercut = bad
    • mesial: down, forward away from undercut
  37. RPI design
    • Rest on mesial in distal extension defects
    • Rest on distal in anterior extension defects
    • Retentive portion of the retainer should not engage an undercut anterior to the axis of rotation
    • From occlusal view, the retainer is placed at the point of greatest mesial-distal curvature of the tooth
  38. ERA should not be used unless a
    positive occlusal stop is present on the defect side, either from a tooth or an implant.
  39. (combination syndrome)
    • premaxilla undergoes severe resorption and is
    • usually accompanied by the development of fibrous
    • hyperplasia of the maxillary tuberosity.
  40. window impression
    custom tray window for ZOE for flabby tissue
  41. Hanau’s Quint
    • Condylar Guidance (CG)
    • Incisal Guidance (IG)
    • Occlusal Plane Orientation (OP)
    • Compensating Curve (CC)
    • Cuspal Inclination (CH)
    • Theilmans Formula:
    • Balanced Occlusion= (IG*CG)/ (OP*CC*CH)
  42. Implant supported overlay dentures are preferred to a fixed prosthesis. However, 6 or more implants with at least 2 cm of anterior spread must be used to achieve a predictable result. Occlusionis bilateral balanced.
    • Advantages:
    • 1) Lip support
    • 2) Speech articulation
    • 3) Cost
  43. 1. List the basic principles of partial denture design. (12 points)
    • • Major connectors must be rigid.
    • • Occlusal rest must direct occlusal forces along the long axis of the teeth.
    • • Guide planes are employed to enhance stability and bracing.
    • • Retention must be within the limits of physiologic tolerance of the periodontal ligament.
    • • Maximum support is gained from the adjacent soft tissue denture bearing surfaces.
    • • Designs must consider the needs of cleansibility.
    • • Extension base RPD designs must anticipate and accommodate the movements of prosthesis during function, without exerting pathologic stresses on the abutment teeth
  44. 2. Describe some of the problems commonly encountered that complicate partial denture design for patients with large maxillary defects. (10 points).
    • • Multiple axis of rotation
    • • Compromised support on the defect side
    • • Lack of cross arch stabilization due to loss of palatal structure on one side
    • • Long lever arms
    • • Forces of gravity become more significant.
  45. 3. In RPD’s used to restore large maxillary defects, why are “positive” rests absolutely necessary on the teeth adjacent to the defect? (4 points)
    • • Abutment teeth adjacent to maxillary defect are subject to more vertical & lateral forces & are more frequently lost than abutments in other positions b/c the defect offers little support & the long lever arms magnify the occlusal forces.
    • • Anterior teeth adjacent to the defect must have "positive" cingulum rests to direct occlusal forces along the long axis of the teeth.
  46. 4. Discuss the two most common factors that lead to distortion of a cast made with an alginate impression in a stock tray? (4 points)
    • o Impression material separated from the tray - Provide for mechanical locking of impression material to the tray. Spray alginate adhesive onto the inner surface of the tray. When removing excess alginate that extends beyond the back of the tray cut carefully and towards the tray to avoid pulling the alginate away from the tray.
    • o Air inclusion in impression that distorts when stone is poured - To avoid bubbles use a syringe filled with alginate to apply impression material to rests, guide planes, occlusal surfaces and the gingival margins. Load trays making sure so as not overlap alginate and entrap air pockets.
  47. 5. The surface of your master cast is soft and chalky. Explain reasons why this occurs. (6 points)
    • • Saliva in the impression when cast was poured
    • • Improper water powder ratio used
    • • Water from rinsing remains in impression
  48. 6. Describe how the clinician can avoid difficulty when removing an altered cast impression from the master cast. (4 points)
    • • heat compound before separating
    • • Place undercuts in the impression tray
  49. 7. Describe how a clinician can ensure proper seating of an RPD framework when making the wash impression component of an altered cast impression. (6 points)
    • When the RPD framework is seated, the clinician needs to make sure that pressure is only applied on the rest areas and not on the edentulous areas as this may dramatically distort the wash impression. In addition, there should be no impression material left in the rest areas. Basically, the pressure should be applied on the teeth and not on the edentulous areas to ensure proper seating of the framework.
  50. 8. When making impressions, what strategies can the clinician employ to prevent the patient from gagging? (6 points)
    • • thicker mix of alginate
    • • mandible--contact with tongue can be unavoidable. Proper fit of tray, shorten un-necessary areas
    • • maxilla--Bend head forward: this causes lift of soft palate. Beading wax to reduce alginate posterior flow
    • • tell pt, please do not move your tongue
    • • Tell pt to breath through their nose
    • • Distraction method
  51. 9. Under what circumstances would you establish fully balanced occlusion with removable partial dentures? (4 points)
    • When RPD opposes complete denture to protect the weaker arch: bilateral balanced occlusion to resist tipping forces of the complete denture.
  52. 10. List the 6 requirements of a clasp, (12 points)
    • • Retention
    • • Bracing
    • • Support
    • • Reciprocation
    • • Encirclement of the tooth over 180 degrees
    • • Passivisity
  53. 11. Discuss why a clinician would choose to fabricate a crown to serve as a RPD abutment. (6 points)
    • • Crowns are necessary as RPD abutments to:
    • o establish the proper guide plane if abutment has previous crown
    • o reposition the clinical crown
    • o restore a badly broken down clinical crown
    • o also, a proper rest could be incorporated into the crown which is not normally present on the tooth, such as a cingulum rest on a mandibular canine
  54. 12. Describe three potential methods of establishing the correct occlusal plane and centric contacts in a situation where an abutment tooth exhibits mesial angulation and mesial drifting such as a mandibular 2nd molar. (6 points)
    • • Occlusal plane is determined after VDO is determined. Occlusal plane is determined by
    • o Camper’s line
    • o position of anterior teeth by esthetics and phonetics
    • o middle third of retromolar pad.
    • • In the case where the abutment tooth is malpositioned
    • o gross modification is required(crown)
    • o occasional removal of the malpositioned tooth in order to achieve the satisfactory occlusal plane.
    • o Occlusal rest that will correct the angulation
  55. 13. What are the clinical implications of Caputo and Berg’s finding with regards the use of abutments that are endodontically and periodontally compromised? Please discuss in detail. (12 points)
    • • Abutments adjacent to extension bases with compromised periodontal support may require special consideration
    • o Splinting of abutments
    • o Stabilization of multiple abutments with RPD framework
    • o Attention to occlusion: Anterior guidance
    • • Endodontically treated teeth with compromised periodontal support adjacent to extension bases may be poor candidates for RPD abutments
    • o Higher susceptibility to fracture
    • o Higher stress levels within the root
    • o Avoid occlusal rests on these teeth if possible
  56. 14. What objectives do you hope to accomplish with an RPD framework when attempting to stabilize a periodontally compromised dentition? (6 points)
    • • Periodontal considerations: RPD design objectives
    • - Uniting and controlling the entire arch
    • - Control individual tooth movement
    • - Hygienic contouring at the tooth/tissue junction
    • - Flexibility to accommodate variable treatment situations
  57. 15. What is the definition of centric relation? (4 points)
    • The relation of the mandible to the maxillae when the condyles are in their most anterior/superior position in the glenoid fossa from which unstrained lateral movements can be made at the occluding vertical dimension normal for the individual.
  58. 16. What are four objectives to be accomplished when modifying the contours of teeth selected to serve as RPD abutments? (4 points)
  59. • Develop acceptable path of insertion
    • • Promote favorable biomechanical properties
    • • Improve esthetics
    • • Enhance comfort
  60. 17. What are the purposes served by physiologic adjustment of an RPD framework? (4 points)
    • • To establish a safety factor for abutment teeth to minimize the torquing or binding force due to bone resorption or poor edentulous area support.
    • • allow for the movement of the prosthesis. This adjustment keeps the axis of rotation within the planned rest rotation axis, with forces in the long axis of the abutment teeth.
  61. 18. When making an altered cast impression for a posterior extension base mandibular partial denture, what two prime support areas must be engaged in the edentulous extension area? (4 points)
    • • buccal shelf and the retromolar pad.
    • o Buccal Shelf- bordered externally by the external oblique line and internally by the slope of the residual ridge. This region of very dense bone is oriented perpendicular to the forces of occlusion and thus becomes a primary stress bearing area in the mandibular arch.
    • o Retromolar Pad- pear shaped area containing glandular tissue, loose areolar connective tissue, the lower margin of the pterygomandibular raphe, fibers of the buccinator and superior constrictor muscles, along with fibers from the temporal tendon. Primary support area of the mandibular denture.
  62. 19. Why will RPD’s be needed in the future?
    • • Numbers of pts continues to expand
    • • Unmet needs continue to increase
  63. 20. Bassi et al (1996) screened 40 patients who were deemed suitable for implant supported fixed partial dentures. Almost all these patients were eventually restored with RPD’s. Please explain why? (8 points)
    • • Barriers to receiving implants
    • i. Economic concerns
    • ii. Poor patient compliance
    • iii. Patient satisfied with the RPD
    • iv. Fearful or skeptical of the result
  64. 21. When a patient is restored with a well designed and properly fabricated RPD, what factors are most important for ensuring a favorable long-term prognosis? (4 points)
    • • Patient compliance
    • • Close follow-up
  65. 22. Kapur et al (1993) compared treatment outcomes of implant supported fixed partial dentures with distal extension RPD’s. What were their conclusions? (8 points)
    • • Both RPD and FPD treatments were successful in approximately 80% of the pts over 5 years
    • • Both treatments were equally effective in improving chewing function
    • • A large number of pts in both groups expressed satisfaction with the prosthesis. Improvement with FPD was more frequent than with RPD for several perceptions.
    • • Despite the slight superiority of the FPD in terms of pt satisfaction, lack of functional differences and success rates do not support the selection of implant-supported FPD over RPD, without consideration of other factors.
  66. 23. What anatomic limitations may preclude the use of implants in restoring posterior extension defects in the maxilla? (4 points)
    • • Pneumatized sinus: Not enough bone between the alveolar crest and the floor of the sinus. There must be at least 4mm of existing bone in this area because it is not possible to place an implant in bone graft material alone (following sinus lift). This is a major limitation.
    • • Major ridge &/or tuberosity undercuts that would lead to implant dehiscence (difficult to eliminate this problem w/ a graft)
  67. 24. What anatomic structure precludes the use of implants for restoring posterior extension defects in the mandible and mandates that a RPD must be employed? (4 points)
    • • Inferior alveolar nerve
    • • Insufficient bone over the nerve to permit placement of a 10mm or longer implant
    • • Unicoritcal anchorage
  68. 25. Name the parts of an RPD (12 points)
    • 1. rests
    • 2. major connectors
    • 3. minor connectors
    • 4. proximal plates
    • 5. denture base connector
    • 6. retainers
  69. 26. What is meant by the concept of the so-called “positive” occlusal rest? (4 points)
    - Basic principle is: the rest must be positive and must direct functional forces in the long axis of the tooth. Must provide a position or connection between prosthesis and tooth that does not allow tooth and prosthesis to separate as increasing masticatory force or occlusal pressure and functions are applied. To provide most ideal support position, the rest is placed as close to the
  70. 27. Why is it so important that rests on anterior abutments be “positive”? (4 points)
    • • Occlusal forces are directed along the long axis of the abutment
    • • If not,
    • i. Tooth displacement
    • ii. Bone loss around the abutment
    • iii. Tissue displacement and destruction
    • iv. Disruption of occlusion
  71. 28. Name three methods for creating “positive” rests on anterior abutments. (6 points)
    • • Complete and Three Quarter Crown
    • • Light cured composite resin (unpredictable)
    • • Reshape existing cingulum (maxillary cuspids)
  72. 29. Name the three types of “positive” rests that can be used on anterior abutments. (6 points)
    • (1) Cingulum rest –
    • • Crescent-shaped
    • • As center as possible when viewed from all directions
    • • The center is deeper buccal-lingually (positive rest)
    • (2) Insisal rest- concave mesiodistally and convex buccolabially.
    • (3) Circular concave rest
  73. 30. Why are cingulum rests preferred over incisal rests for anterior abutments? (4 points)
    • • esthetics
    • • no interference with occlusion
    • • lesser leverage than with incisal rests
    • • blends more with existing anatomy
  74. 31. Why are concave circular rests rarely used on anterior abutments? (6 points)
    • • Difficult to prepare
    • • Difficult to prepare in the center of the tooth
    • • Difficult to clean
  75. 32. What are the functions of occlusal rests on posterior teeth? (8 points)
    • • Provide rigid prosthetic support- The rest must not flex under occlusal loads. It must be of sufficient size to provide constant, controlled relations among tooth, prosthesis, & mucosa
    • • Restore occlusion- this is most important in cases where
    • i. a tooth is tipped
    • ii. a tooth has not erupted into proper occlusion
    • iii. there is a loss of vertical dimension.
    • • Direct forces in the long axis of the teeth
    • • Provide reciprocation and stabilization- stabilizing abutment teeth against torquing or twisting forces
  76. 33. Kratochvil (1989) believed that guide planes should be incorporated into the contours of abutment teeth and that the tooth-tissue junction should be in contact with the proximal plate. Please explain why? (6 points)
    • • Protect against food impaction
    • • Prevent tissue hypertrophy between the tooth and prosthesis
    • • Prevents accumulation of plaque
  77. 34. A lingual bar for a mandibular RPD should be at least 4 mm away from the tooth tissue junction. Why? (4 points)
    • • To protect from
    • o hypertrophy of tissue over the bar
    • o 2) food impaction and tissue irritation between the bar and tissue
    • Extra: The lingual bar should be placed on Unattached tissue. (Attached tissue will hypertrophy to fill the space). Also, make sure that the placement of the lingual bar doesn't interfere with speech or frenum activity.
  78. 35. What possible functions can be served by a lingual plate when designing and fabricating a distal extension RPD for the mandible? (6 points)
    • • Mobile Anterior Teeth
    • i. Placement of lingual coverage can provide stabilization for the teeth and can buttress them against lateral and distal forces
    • • Recession of Supporting Tissues
    • i. It is possible to restore the contour of missing tissues w/ lingual coverage by contouring the casting to reproduce the anatomical topography of the missing tissues
    • ii. This does not invade the tongue space but will help prevent food impaction
    • • Provides indirect retention
  79. 36. What are the functions served by properly designed and contoured proximal plates? (8 points)
    • • Maintain arch integrity by anterior-posterior bracing action, which controls tooth movement
    • • Act as retainers by frictional contact with the parallel guiding surfaces on the teeth
    • • Protect against food impaction by adaptation of the guide plates at the tooth-tissue junction
    • • maintain soft tissue health at the tooth-tissue junction by eliminating voids, which helps prevent tissue hypertrophy or recession
    • • provide reciprocation action to the RPD retainers.
  80. 37. When designing a mandibular bilateral distal extension RPD why are lingual bars preferred over lingual plates? (8 points)
    • o Lingual bars should be placed on unattached gingival (less chance for hypertrophy), and have the following advantages:
    • - Simple with minimal tissue contact and interference with tooth and tissue contours
    • - prevents tissue hypertrophy and less food/plaque impaction
    • - more normal self-cleansing situation
    • - less potential for lateral force on anterior teeth in extension base situations.
  81. 38. What are the benefits of “I” bar retainers when they are used to engage abutments adjacent to extension denture base areas? (12 points)
    • o Minimal tooth contact.
    • o Exact placement of retention contact.
    • o Minimal interference with natural tooth contour.
    • o Maximum natural cleansing action.
    • o Passive functional movement of an extension prosthesis.
    • o Better esthetics
  82. 39. What methods are used reciprocate active “I” bar retainers? (6 points)
    • • Opposing reciprocating clasp at 0” (I bar or C clasp)
    • • A combination of rest, minor connector and guide plane
    • • A lingual or palatal plate
  83. 40. What are the advantages of suprabulge retainers? (4 points)
    • • Improved stability and bracing
    • • Useful in patient with severe boney undercuts
  84. 41. What are the disadvantages of suprabulge retainers? (6 points)
    • • Food trap
    • • Poor esthetics anteriorly
    • • Potential for torquing the abutment tooth in extension situations
  85. 42. What type of suprabulge retainer do we recommend at UCLA? Why? When do we recommend that such a retainer be used? (6 points)
    • • Recommendation: Circumferential Clasp (aka: Akers Clasp) because
    • o With flexible retentive arm that crosses the height of contour into the undercut and a rigid reciprocating arm that stays above the height of contour
    • o Fulfills the requirements of clasp
    •  Retention
    •  Bracing
    •  Support
    •  Reciprocation
    •  Encirclement
    •  Passivity
    • • Indications for use of a circumferential clasp
    • o Bulbous gingival contours
    • o Lack of access for an I-bar clasp due to a shallow vestibule, a frenum attachment, or a severe gingival undercut
    • o Short teeth with poor or no guide planes
    • o Tilted teeth
    • o Significant recession and/or abfraction
  86. 43. Why are altered cast impressions recommended in extension base situations? (4 points)
    • Alter cast impression gives maximum support possible from edentulous area of the extension partial denture. It provides two or three times greater support and allows less movement then other impression techniques. The objective of altered cast impression is to ensure the best possible relationship between the casting framework properly fitted on the teeth, and the denture base, thereby deriving the greatest support potential from both teeth and edentulous areas
  87. 44. When designing a bilateral distal extension partial denture framework where the 1st premolars are present bilaterally and employing the RPI design philosophy developed by Kratochvil at UCLA, why are the rests placed on the mesial of these premolar abutments rather than on the distal? (6 points)
    • • A mesial rest produces a better load distribution to the abutment tooth (since the adjacent teeth help brace and distribute some of the loads)
    • • A distal rest next to a distal extension base will adversely load the abutment tooth leading to the distal movement of that tooth and bone loss.
  88. 45. Discuss the primary differences between natural and complete denture occlusion. (4 points)
    • • Natural Dentition:
    • 1. retained in PDL
    • 2. units move independently
    • 3. malocclusion effects not immediate
    • 4. non-vertical forces affect only teeth involved and usually well tolerated
    • 5. incising doesn’t affect posteriors
    • 6. bilateral balance is rare
    • 7. tactile sensitivity
    • 8. mutually protective scheme of occlusion
    • • Denture “Dentition”:
    • 1. mobile bases on mucosa
    • 2. teeth move as a unit
    • 3. malocclusion affects entire base immediately
    • 4. non-vertical forces affect all teeth and is traumatic
    • 5. incising affects all teeth attached to base
    • 6. bilateral balance is often desired for base stability
    • 7. decreased tactile sense
  89. 46. Under what conditions is it indicated to splint RPD abutments? (4 points)
    • Consider splinting abutments adjacent to extension bases with poor periodontal support or poor residual ridges
  90. 47. Abutments with compromised periodontal support adjacent to extension bases may require special attention. Please explain! (6 points)
    • • There is an increase in the stress levels when loading on compromised/unstable abutments when compared to sound abutments. The clinical implication is that abutments adjacent to extension bases with compromised periodontal support may require special consideration and extra support. Lack of this extra support may cause the abutment to fail. Some special considerations:
    • i. Splinting of abutments
    • ii. Stabilization of multiple abutments with RPD framework
    • iii. Attention to occlusion: Anterior guidance
  91. 48. Endontically treated teeth with compromised periodontal support adjacent to extension bases may be poor RPD abutments. Please explain!
    • • Higher susceptibility to fracture
    • • Higher stress levels within the root
    • • Avoid occlusal rests on these teeth if possible
  92. 49. The decision to use a lingual bar as opposed to lingual plate is based on two factors. Name them! (4 points)
    • 1. anatomic space available
    • 2. the periodontal situation of the remaining teeth
  93. 50. The contour of a palatal connector of a RPD framework is thickest in the central portion of the casting and tapers to blend smoothly into the mucosa at the margins. Why? (4 points)
    • • To avoid food impaction
    • • To allow for appropriate speech articulation
    • • bulk for connector rigidity, thinness for pt comfort
  94. 51. An RPD framework is best designed using a specific design sequence. Describe the sequence used for maxillary RPD’s. (10 points)
    • • Occlusal rests
    • • Major connectors
    • • Minor connectors (proximal plates)
    • • Denture base connectors
    • • Retainers
  95. 52. When fabricating a maxillary RPD opposing a mandibular RPD, it is recommended that centric occlusion be made coincident with centric relation. Why? (6 points)
    • • Repeatable
    • • Learnable
    • • Recordable
  96. 53. What purposes can be served with treatment partials? (8 points)
    • • Replace missing teeth
    • • Establish posterior occlusion
    • • Test changes in vertical dimension
    • • Trial prostheses: see if patient can adapt to removable prostheses
  97. 54. What type of occlusion (centric contacts and type of guidance) would you develop for a removable partial denture with an anterior extension base (edentulous span from maxillary second premolar to maxillary second premolar)? (4 pts)
    • • Bilateral centric contacts
    • • Bilateral Balanced occlusion
  98. 55. Describe three methods of establishing the correct occlusal plane and centric contacts in a situation where an abutment tooth exhibits mesial drifting? (6 pts)
    • • Tooth modification/crown
    • • Restore occlusion with occlusal posterior rest
    • • Removable periodontal stabilization prosthesis – helps to establishes occlusion (perio prepros powerpoint slide #50)
    • • Ortho?
  99. 56. List three conditions which require preprosthetic tissue modifications prior to fabrication of removable partial dentures. (6 pts)
    • • Tuberosities affecting establishment of proper plane of occlusion
    • • Tooth modification/crownlenthening to enable establishment of plane of occlusion
    • • Tori affecting major connector contours
    • • Frenulae and/or minimal attached tissues affecting retainer design
  100. 57. In studies by Dr. Caputo and Dr. Berg examining distal extension RPDs, what was the effect of periodontal bone loss around RPD abutments? (4 pts)
    • In the study, photoelastic stress analysis was performed in which isochromatic fringe distributions demonstrated relative magnitude and distributions of stress. In periodontally compromised abutment teeth, study showed an increase level of stress concentration along the tooth/bone interface along the PDL when there was a change in the vector of load application.
  101. 58. What are the clinical implications of Dr. Caputo and Dr. Berg’s findings in regards to periodontally compromised, and endodontically treated RPD abutments? (8 pts)
    • • Abutments adjacent to extension bases with compromised periodontal support may require special consideration:
    • i. Splinting of abutments
    • ii. Stabilization of multiple abutments with RPD framework
    • iii. Attention to occlusion: anterior guidance
    • • Endodontically treated teeth with compromised periodontal support adjacent to extension bases may be poor candidates for RPD abutments
    • i. Higher susceptibility to fracture
    • ii. Higher stress levels within the root
    • iii. Avoid occlusal rests on these teeth if possible
  102. 59. List three RPD design objectives with respect to periodontal stabilization. (6 pts)
    • • Uniting and controlling the entire arch.
    • • Control individual tooth movement.
    • • Hygienic contouring at the tooth/tissue junction.
    • • Flexibility to accommodate variable treatment situations.
  103. 61. Are amalgam restorations satisfactory for RPD abutments? Please explain your answer. (4 points)
    • • Yes. However to do so, one must have adequate occlusal reduction, as well as adequate axial reduction.
    • o Adequate occlusal reduction = rest clearance + adequate Amalgam thickness
    • o Adequate Axial reduction = reduction to gain parallel surfac + adequate Amalgam thickness.
  104. 62. Discuss the reasons why we perform a clinical remount when delivering an extension base RPD. (6 points)
    • The rationale for doing a patient articulator remount and equilibration is to obtain a definite, repeatable, proven relationship of the maxillary and mandibular arches prior to final adjustments of the opposing occlusal surfaces. The occlusion developed at this time affects the freedom of mandibular movement and influences the forces delivered to teeth and support tissues. Adjustments on the articulator are easily observed, the movements are repeatable, and refinement can be precise and quick.
  105. 63. What type of occlusion would you develop for a patient when designing and fabricating RPD’s for patients who retain the remaining maxillary and mandibular anterior teeth? (4 points)
    • • Cross-arch even occlusal centric contacts
    • • Anterior guidance (group function or canine guidance) in excursive movements with no posterior interferences/contacts.

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