Direct Fall 2012
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cervical, wedge-shaped defects resulting from heavy eccentric occlusal force
abnormal tooth surface loss resulting from direct friction forces between the teeth and external objects or from frictional forces between contacting teeth components in the presence of an abrasion medium
amalgam containing alloys of different shape and composition
mechanical wear of the incisal or occlusal surface as a result of functional or parafunctional movements of the mandible
: the angle created by the intersection of the prepared cavity wall and the unprepared surface of the tooth. the vertex of this angle is the cavosurface margin
the wear or loss of tooth surface by chemicomechanical actions
gradual dimensional change that occurs under cyclical loads such as chewing
Modified Law of Mixtures
: the whole is equal to the sum of their parts plus their interface (interface factors include bonding, arrangement, and defects)
the angle created by the intersection of the prepared cavity wall with the surface of the completed restoration
layer of microcrystalline and organic particle debris, which are compacted unavoidably into a layer on the cut surface
combination of dissimilar metals in direct physical contact causing a potential difference, causing a driving force for galvanic current flow
Preventive Resin Restoration:
an ultraconservative, modified preparation design allowing for restoration of lesions of defects with minimal removal of tooth structure and often may be combined with the use of composite or sealant to seal radiating noncarious fissures or pits that are at high risk for subsequent caries activity
the initiator for visible light-cured dental acrylic composite materials and primers
- the slope of the linear portion of the stress-strain curve that represents the amount of strain produced in response to each amount of stress. It is essentially a measure of the stiffness of an elastic material
- Coefficient of Thermal Expansion and Contraction:
- The relative rate of change of a solid that undergoes contraction during temperature decreases. Thermal expansion and contraction differences between a restorative material and adjacent tooth structure causes percolation/margin defects, so you would want to use restorative material with similar COTE to tooth.
an alloy particle in dental amalgam that can dissolve into mercury, has low mechanical strength, and is prone to corrosion. Placement of dental amalgam in small increments, as well as proper condensation and carving, can help remove the gamma 2, thus reducing the mercury content and increasing the overall strength of the amalgam
the ratio of bonded surfaces to the unbounded, or free, surfaces in a tooth preparation. The higher the C-factor, the greater is the potential for bond disruption from polymerization effects
Silane Coupling Agent:
used to provide a stable bond between two otherwise nonbonding and incompatible surfaces. In reinforced and filled plastics, the improved bond between the fibrous or particulate inorganic component and the organic matrix polymer results in greater composite strength and longer service life.
Define outline form and identify the criteria that address it in the class II cavity preparation for amalgam.
- Outline form is the preparation extension primarily dictated by the amount of caries, old restorative material, or defect present. Adequate extension is needed to provide access for the tooth preparation, caries removal, matrix placement, and insertion of the restorative material.
- Five (5) main criteria are involved in the overall class II cavity prep:
- • Occlusal outline form
- • smooth-flowing from dovetail thru isthmus to box
- • shape of dovetail, fishtail, s-curve as needed
- • Occlusal outline size
- • 0.9-1.3 mm isthmus width and occlusal groove extensions
- • 0.25 – 0.5 mm dovetail
- • 0.8 -1.0 mm fishtail extension (distal cusp)
- • 0.5 mm proximal clearance (0.25 – 0.75 mm)
- • 0.5 mm gingival clearance (0.5 – 1.0 mm)
- • Buccoproximal and linguoproximal walls
- • extended to provide 0.5 mm (0.25-0.75 mm) clearance from adjacent tooth
- • extensions parallel proximal embrasures to allow conservative access for:
- • finishing and polishing to refine margins
- • brushing & flossing to reduce caries recurrence
- • Gingival wall
- • horizontal buccolingually, 0.5 mm clearance (0.25 – 0.75 mm)
- • Quality of cavosurface margins
- • smooth-flowing, defined, supported enamel
Describe the “s-curve” and its role in the occlusal outline form for class II preparations.
The “s-curve” is an outline form feature in class II preparations and is the connecting point between the isthmus and the box. “S-curves” are incorporated because most proximal contacts occur in the buccal third. Instead of simply having a solid straight line connect the isthmus to the box, a “s-curve” is incorporated to allow for the conservation of tooth structure when connecting the isthmus to the box while still maintaining 90 degree exit angles.
Define resistance form and identify the criteria that address it in the class II cavity preparation for amalgam.
- Resistance form refers to preparation features that help the restoration and too resist fracturing as a result of occlusal forces.
- Criteria involved with resistance for class II preparation include:
- 1. Flat pulpal wall
- 2. 1.5 mm minimum pulpal depth
- 3. Divergent dovetail wall
- 4. Axial depth 1.0 mm min (1.5mm max) (0.5 mm into dentin)
- 5. Rounded axiopulpal line angle
- 6. Gingival “bevel” follows enamel rods
- 7. Flat gingival wall (B-L)
Define retention form and identify the features or techniques in (a) amalgam and (b) composite resin preparations that address retention form.
- Retention form means that the design of the preparation must provide for the retention of the restorative material in the tooth.
- I. Prevent occlusal displacement of restorative material
- a. Buccal and lingual walls should converge occlusally. This can be done by holding the 330 bur perpendicular to the occlusal plane. Convergent walls will help retain the amalgam while keeping enamel rods fully supported by dentin.
- b. Convergence of functional cusp wall of proximal box
- II. Prevent proximal displacement
- a. Dovetail and buccal and lingual extensions
- b. Retention grooves at axiobuccal and axiolingual line angles
- i. must be in dentin
- ii. are extensions of the axial wall
- iii. follow curvature of axial wall & DEJ
- iv. 0.25 mm depth buccolingually following axial curvature
- v. Extends from axioproximogingival point angles to axioproximopulpal point angles
- III. Adhesive systems provide some retention by micromechanically bonding amalgam to tooth structure and also reducing or eliminating microleakage.
- I. Bevel enamel margins
- a. 45 degree bevels on accessible margins
- b. 0.5 mm bevel width minimum
- c. DO NOT bevel dentin b/c there is no added retentive value.
- Conserve tooth structure.
- II. Grooves and coves
- a. Margin is in dentin
- b. Dentin bond is ONE THIRD of an enamel bond
- c. Minimize effect of shrinkage
Describe the proper hole placement for the posterior anchor tooth of a rubber dam placement from #18 – 28.
To determine the proper location for the anchor hole when the rubber dam is applied to the mandibular teeth, mentally divide the rubber dam into three vertical sections: left, middle, and right. Although the anchor tooth is tooth #18, the second molar, first consider a situation where the first mandibular molar, or #19, is the anchor tooth. You would punch the hole for this tooth at a point halfway from the superior edge to the inferior edge and at the junction of the right (or left) and middle thirds. However, since the anchor tooth is the second molar, the position for the hole moves toward the inferior border and slightly toward the center of the rubber dam, as compared to the first molar hole just described.
Describe all the requirements for a successful matrix application using the Tofflemire retainer system.
- 1) Select strip of matrix material is long enough to extend from the mesial to the distal corners of the tooth.
- 2) If unburnished, must burnish the band to achieve proper contour and contact. (done prior to placement of band)
- a. Burnishing → metal band has been deformed occlusogingivally with a suitable hand instrument to produce a rounded or convex surface that (when in place around the tooth) will produce a restoration that is symmetric in contour with the adjacent proximal surface.
- 3) Fold band end to end forming a loop.
- 4) Place folded band into Tofflemire retainer
- a. gingival edge → smaller circumference
- b. occlusal edge → wider circumference
- c. occlusal edge should go in first leaving the gingival edge at the bottom of retainer which will be the slotted end
- 5) Place band over tooth
- a. Slotted end (smaller gingival side) should be placed towards gingiva
- b. Band should be placed 1 mm apical to gingiva or deep enough to be engaged by wedge (whichever is lower)
- c. Band should be at least 1 mm above adjacent marginal ridge
- 6) Tighten & Evaluate band
- a. Used explorer to ensure gingival portion of band goes beyond the prep
- b. Make sure it is secured tightly around tooth
- c. Proximal contour or contours of the band should be symmetric with the band and adjacent surface.
- d. Occlusogingival contour should be convex
- e. Height of contour at proper contact level and contacting the adjacent tooth
- f. From an occlusal aspect evaluate the position of the contact area in a faciolingual direction
- 7) Place wedge at gingival embrasure
- a. Insert the pointed tip from the lingual or facial embrasure (whichever is larger), slightly gingival to the gingival margin.
- b. Wedge the band tightly against the tooth and margin as close as possible to the margin without being occlusal to it
- c. Conservative prep → round tooth pick wedge
- d. Deed gingival margin prep → triangular wedge
Describe all the requirements for a successful Barton matrix application using the Tofflemire retainer system.
- o Barton matrix → used with OLs, DOLs & MOLs. (for occlussal-lingual portion of prep)
- o Tofflemire matrix retainer band does not intimately adapt to the lingual groove area of the tooth
- 1) Cut piece of matrix band (.o5mm thick & 8 mm wide)
- 2) Place between lingual surface (lingual box) of tooth and existing band already in place (tofflemire matrix band)
- a. Make sure gingival edge of cut band is placed slightly gingival to the existing matrix band to help secure the cut band
- 3) Break off ½ inch of a round toothpick wedge (we used just a regular wedge) and hold it with cotton pliers
- 4) Heat compound and cover the end of the wedge
- 5) Immediately insert compound coated wedge between Tofflemire band and the cut band
- 6) While compound is still soft press it gingivally to secure the matrix piece tightly against the gingival cavosurface margin and lingual surface of the tooth
- 7) If necessary used a heated instrument to re-contour and reshape the barton matrix band
- Note: Barton matrix is technically in addition to the placing of the universal Tofflemire matrix band…so you cannot really place the Barton matrix without first placing the Tofflemire matrix band….Just pay attention to that little detail in case he gets picky.
Discuss the role of copper in high-copper dental amalgam and its impact on physical and mechanical properties.
High-Copper-Content dental amalgams are made by mixing three ingredients:• Ag-Sn alloy• Ag-Cu alloy• Mercury- There is high reactivity of Copper with Tin.- When Ag-Sn is mixed with Mercury, Ag-Hg and Sn-Hg phases form.- But almost as quickly as Sn-Hg (γ2)phase forms, the phase is eliminated by competitive reaction of Copper with Tin. [Cu6Sn5]• γ2 (Hg-Sn) is more sensitive to corrosion and weaker than γ1 (Ag-Hg)- So, high-copper-content dental amalgam prohibits the formation of more corrosive γ2 (Sn-Hg)- Resulting Properties• Higher compressive strength• More rapid set to full strength• Reduction in creep• Reduced susceptibility to corrosion
Describe all the requirements for a successful matrix application using the bitine ring sectional retainer system.
- [THIS IS NOT PART OF THE ANSWER-MERELY BENEFITS OF SECTIONAL MATRICES]
- - Contoured Bands
- - Anatomically correct contacts
- - Contacts at the height of contour
- - More separate provides tight contacts
- [THIS IS THE TECHNIQUE FOR PLACING A SECTIONAL MATRIX]
- - Prior to placement of bitine ring
- • Curl sectional matrix to conical shape
- • The concave curve is always toward gingival
- - Insert appropriate size wedge to seal gingival margin
- - Place ring adjacent to band when possible (between the matrix band and the wedge)
- • For wide embrasures, place ring on opposite side of wedge
- - Burnish band against adjacent tooth
Describe the proper technique of inserting, condensing, and carving amalgam that maximizes the physical and mechanical properties of the final restoration.
- Before inserting the amalgam the dentist should take a mental note of the prep and the margins. After a matrix is properly placed, an amalgam carrier is used to insert the amalgam into the preparation in small increments. For a class II preparation, the dentist fills the amalgam carrier and transfers into the proximal portion of the tooth prep enough amalgam that when condensed will fill the gingival floor 1 mm. Generally smaller amalgam condensers are used first; this allows the amalgam to be properly condensed into the internal line angles and secondary retention features. Subsequently, larger condensers are used. The dentist condenses the amalgam along the gingival floor to adapt the amalgam to the gingival floor then against the proximal margins of the preparation and into the proximal retention locks. Firm lateral condensation (facial and lingual) and mesial/distal condensation should be done to ensure proximal contact with the adjacent tooth. The dentist continues the procedure of adding amalgam and condensing until the amalgam reaches the level of the pulpal wall. The dentist will then usually change condensers to a larger one and condenses amalgam in the remaining proximal portion of the preparation concurrently with the occlusal portion. When the occlusal margins are approached, the dentist should take care not to injure the enamel margins. The occlusal margins should be overpacked by at least 1 mm. Condensation should be accomplished in 3-4 minutes (depending on the alloy). When condensing amalgam should neither be wet (mercury rich) nor dry and crumbly (mercury poor). Proper condensation should remove as much excess mercury as possible, should be a non-porous final restoration, and have optimal marginal adaptation.
- Precarve burnishing is a form of condensation. The amalgam should be burnished with a large burnisher with heavy strokes that contact the cusp slopes. Precarve burnishing produces denser amalgam at the margins of occlusal preparations. Carving should begin immediately after condensation with the discoid-cleiod as the instrument of choice. One should use the larger first followed by the smaller. All carving should be done with the blade perpendicular to the margins as the instrument is moved parallel to the margins. Part of the blade should rest on the unprepared tooth surface adjacent to the prep margin. This helps prevent overcarving the amalgam at the margins and produces continuity. Amalgam should be sufficient at the margins and not in excess (flash). The outline of the amalgam margin should reflect the contour and location of the prepared cavosurface margin. Care should be taken around the marginal ridges. Anatomy can be reproduced with the acorn. A damp ball of cotton can be used to improve the smoothness.
Describe the proper technique of 3-step resin bonding and insertion of composite resin into a cavity preparation that maximizes the prognosis of the final restoration.
- If optimal results are to be obtained, one needs to isolate from fluids by using a rubber dam or cotton roll and retraction cord. The proximal surfaces of adjacent unprepared tooth should be protected from inadvertent etching by placement of a polyester strip. Placing the matrix first allows one to assess cavosurface margins, and protect adjacent teeth. Etching enamel affects the prism core and periphery. Etching dentin affects the intertubular and peritubular dentin resulting in enlarging the tubular openings. Most etchants are in concentrations of 32%-37% phosphoric acid. Usually a syringe applicator is used to inject the gel etchant directly onto the prepared tooth surface. The acid should be kept to a maximum of .5mm past the anticipated extent of the restoration. An etching time of 15 s for dentin and enamel is considered sufficient. For enamel preps only, 30 s is considered optimal. The area is rinsed with water for 5s, starting on the adjacent tooth. The area is then lightly dried leaving any dentin exposed moist so that primer and adhesive materials can penetrate the collagen more effectively to form a hybrid layer ( micromechanical bond). Enamel should have a frosted appearance. Any moisten cotton balls should be replaced.
- Primer is applied to all of the prepared tooth structure with a microbrush. The manufacturer’s directions specify how long to apply the primer and how long it should be cured. In all cases, dentin should be uniformly shiny after primer application. Another micobrush is used to place adhesive on the tooth structure that was etched and primed. Every effort should be made to prevent the adhesive from pooling. The adhesive is lightly dried with the air syringe to evaporate any solvent. The adhesive is the light cured as directed.
- The wedge and matrix is then placed. The matrix will reduce excess material and minimize finishing time. The wedge should seal the gingival cavosurface margin and the matrix burnished for proper proximal contour. Composite can be placed with a hand instrument or with a syringe. Resin should be added in increments of 1-2 mm. If the composite thickness exceeds 1.5-2mm, the light intensity can be inadequate and produce incomplete curing of the composite. The camphoroquinone in the composite is the photoinitiator and absorbs photon light energy from the LED light at 474nm. The composite should be cured incrementely for 20-30s. The dentist should limit the ratio of bound-to-unbound surfaces to less than 1.5 to limit the interfacial stresses and shrinkage stresses. Therefore the dentist should not bulk fill but layer the walls with composite.
Describe (1) the role of and (2) the creation of the dentinal hybrid layer in the resin bonding technique for composite resin restorations.
- a. Role of the dentinal hybrid layer
- i. The basic role of the dentinal hybrid layer is to give the resin a surface to bond with in the dentin—resin bonds very well with enamel but much less so with dentin
- ii. Hybrid layer is also known as the resin impregnated layer—it is a diffuse mixture of resin and dentin
- iii. See the “creation of the dentin hybrid layer” below to better understand how the hybrid layer increases the resin’s ability to bond to it
- b. Creation of the dentinal hybrid layer
- i. Etch (34-37% phosphoric acid):
- 1. removes smear layer, enlarge openings—allows for resin tags to form (added retention)
- ii. Rinse (water) and dry: stops etching, cleanses tooth
- iii. Moist dentin (re-wet with water or re-wetting agent):
- 1. permits resin interlacing with dentinal tubules
- iv. Primer (hydrophilic monomer, e.g., HEMA)
- 1. enhances dentin bonding to resin
- v. Adhesive (resin monomer ~ resin matrix)
- 1. completes hybrid layer
Describe both the causes of and preventive techniques to avoid the creation of the white line or “halo” defect around enamel margins of bonded resin restorations.
- c. The following factors cause the white line or “halo” defect (microfracture of marginal enamel):
- i. Traumatic contouring or finishing techniques
- ii. Inadequate etching and bonding of that area
- iii. High-intensity light-curing, resulting in excessive polymerization stresses
- d. Potential preventative techniques and solutions include:
- i. Re-etch, prime, and bond the area
- ii. Use atraumatic finishing techniques (e.g., light intermittent pressure)
- iii. Use slow-start polymerization techniques
- iv. Conservatively remove the fault and rerestore
- v. Leave as is
Describe non-surgical treatment recommendations for demineralized but non-cavitated dental lesions.
- e. Non-surgical tx is always preferred over surgical
- f. MI paste, fluoride tx, Rx toothpaste (ie 5000ppm F toothpaste)
- g. OHI and good hygeine
Describe the impact of a restorative material’s coefficient of thermal expansion in the prognosis of any dental restoration.
- h. A challenge to dental restorations is the fact that the mouth is exposed to a large range of temperatures. Teeth have their own expansion and contraction with a given temperature, and the problem is that restorations ideally would mirror this same rate perfectly so as to not stress the restoration, but they don’t.
- i. Thermal cycling causes percolation at margin due to volumetric changes occurring at different rates in tooth and restoration
- ii. Same process causes margins to undergo microleakage
- i. From the book: LCTE (linear coefficient of thermal expansion): the LCTE is the rate of dimensional change of a material per unit change in temperature. The closer the LCTE of the material is to the LCTE of enamel, the less chance there is for creating voids or openings at the junction of the material and the tooth when temperature changes occur. The LCTE of improved composites is approx three times that of tooth structure; that for hybrid glass ionomer is 1.5 to 2x that of tooth structure. Bonding a composite to etched tooth structure reduces the potential negative effects due to the difference between the LCTE of tooth structure and that of the material.
- i. Amalgams LCTE is 2.5 times that of enamel
Describe the clinical indications and contraindications for dental amalgam and composite resin as restorative materials in posterior teeth.
- • when esthetics are of concern
- • small and moderate restorations, preferably with enamel margins
- • restoration that can be properly isolated during the procedure
- • restorations that do not have heavy occlusal contacts or does not provide all of the occlusal contacts
- • restorations that may serve as foundations for crowns
- • large restorations that are used to strengthen remaining weakened tooth structure
- • when operating site cannot be isolated
- • when there are heavy occlusal stresses and when those contacts are on composite only
- • restorations that extend to the root surface
- • moderate to large Class I and II’s, esp with the following:
- • when there is heavy occlusal functioning and when the restoration must restore all of the occlusal contacts of the tooth
- • when isolation is not so critical (minor contamination during the procedure is not too bad)
- • extends into the root surface
- • Class V restorations when:
- • esthetics are not of a concern
- • cannot be well isolated
- • located entirely on root surface
- • temporary caries-control restoration when teeth are badly broken down and require an assessment of pulpal health before a final restoration
- • foundations for badly-broken teeth that require more retention and resistance form before crown or onlay placement
- • when esthetics is of major concern to patient (esp on the premolars)
- • small to moderate defects
- configuration factor (also known as c-factor) refers to the number of bonded to unbonded surfaces in a tooth preparation.
- For instance, in an occlusal class I preparation there would be 5 bonded surfaces and only 1 unbonded surface. The net result would be a C factor of 5. As the C factor increases so too does the possibility of bond disruption when using a composite resin. This effect is caused by a reduction in unbonded surfaces in which the composite can "flow" to relieve polymerization stress. The technique of incremental layering has been suggested to compensate for preparations with high configuration factors
Describe how particle size and percentage of particles in composite resins impacts physical properties and their indications for specific clinical applications.
- small particles: used in low stress, greater polish
- more SA/w resin matrix
- better flexure strength
- better polishability
- greater viscosity
- greater shrinkage
- LARGE PARTICES: greater stress
- more filler loading
- higher fracture resistance
- less shrinkage(resin matrix)
- decreased polishabilty (stick out)
- balance flexure and mechanical
- HIGH FILLER %:
- more packable
- less shrinkage/wear
- less polishability
- inferior margin adaptation
- used in Class I, II
- LOW % FILLER: flowable
- greater flexure strength (resin)
- more shrinkage
- less wear resistance
- less viscous
- cervical, pediatric cases
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