3Evolution of Cavity Preparation Design for Posterior Composite Taking into consideration the differences in the physical properties between the two materials (amalgam vs composite); and based on the rationale of the cavity preparation design for amalgamQuestions were asked: Do we need convergent walls? retention grooves? Worry about unsupported enamel? Extension for prevention? Do we need bulk?New cavity preparation design for posterior composite was created; it was based on specific characteristic of the material.
4Why are we talking about amalgam/composite Example of utilizing the skill/knowledge we acquired in using a specific material/procedure (amalgam restoration) and applying it on a new material/procedure (composite restoration)Preparation skills should be easily transferable.Knowledge on the rationale of cavity preparation will allow us to adapt to the new material based on the material’s specific characteristic.Answer to your question on “why are we still teaching cast gold inlay/onlay”? - when only a few dentists are doing these kinds of procedures in their offices.
6Differences between gold and porcelain restorations Physical properties - porcelain more brittleMode of retention - bonding vs mechanical retentionConcept of marginBased on these differences, can we design a cavity preparation for using porcelain intra-coronally??Starting with cavity preparation design for cast gold inlay/onlay, what features do we have to modify for porcelain????
7Physical PropertiesWhat cavity preparation features do we need to modify?Bulk - more occlusal clearanceReinforcement - bondingBevels contraindicated
8Mode of RetentionCast gold preparation rely on 6 to 7 degree of divergent walls and sharp internal line angles.Porcelain rely on the bonding process, no need for 6 to 7 degree divergent wall and sharp internal line anlges.
9Marginal AdaptationCast gold - rely on close adaptation (20u); lack of adhesion between tooth structure/cement/gold interfacePorcelain - rely on the adhesion between tooth structure/resin cement/procelain to create a gap free continuous margin.No gingival bevels needed to minimize the gap.
10Empress Procelain System All procelain restoration used for inlay, onlay, full crownCastableAdequate marginal fitBetter wear characteristic than conventional procelainSimilar to cast gold inlay/onlay in terms of cavity preparation design
11Porcelain Fused to Metal Crown vs Empress: Similarities Highly estheticWearBrittle - reinforced through the bonding process
12Composite vs Empress: Similarities Mode of retention - dentinal bonding agentApply skills you learn for composite on the bonding process.
13Mechanism of AdhesionPorcelain etched with hydrofluoric acid (micromechanical)Bond between etched tooth and DBA - identical to composite/toothSilane coupling agent - chemical bond
14Summary of Characteristics Highly estheticAcceptable marginal fitConservation of tooth structureLess occlusal wearHighly technique sensitive
15Indications High esthetic demand Replace moderate to large existing restorationFractured tooth/restorationModerate to large primary cariesContraindiationsUnable to adequately isolate the fieldParafunctional habits - bruxing, clenching, excessive wear
16Empress vs Gold Inlay/Onlay Empress AdvantagesESTHETICConservation of tooth structure (gold onlay vs porcelain inlay)Less complicated cavity design??DisadvantagesExpensiveTechnique sensitive - bonding processAbrasive to occluding dentition
17Empress vs PFM Empress Advantages Conservative cavity preparation Foundation restoration may not be necessaryLess abrasive to occluding dentitionNo metal collarDisadvantagesExpensiveTechnique sensitive
19Cavity Preparation Design 3. DrawDegree of draw = approximately 12 to 15 degree4. BevelNo bevel
20Mn first premolar- DO amalgam with fractured lingual cusp, deep pulpal floor Existing amalgam removed, making all walls divergent, smoothed all cavosurface margins
21Mx first molar - MOD amalgam with deep pulpal floor (4mm) Existing amalgam removed
22Proximal walls and gingival seats extended, occlusal wall divergent, clinical judgement was made to cover DL cusp (with shoulder)No cavosurface bevel on shoulder
23MOB amalgam on Mx first molar with deep pulpal floor Existing amalgam removed, make all walls divergent and smoothed all cavosurface margins
24Occl amalgam on Mn first molar, normal pulpal depth; patient complaining about pain on function- Dx: DB cusp fracturedPatient’s occlusion
25Existing amalgam removed, DB cusp reduced by 2mm, all walls divergent No shoulder on DB cusp - WHY???
26MOD amalgam on Mn second molar with fractured Li cusp MOD amalgam on Mn second molar with fractured Li cusp. Normal pulpal depth; all amaglam removedProximal box divergent, Li cusp - smoothed cavosurface margin
27MOD amalgam on Mn first molar - occlusal fractured Shade selection BEFORE rubber dam; need dentin shade (match shade at gingival third) and overall shade
28Finished preparation; rubber dam removed; ready for impressioning; proximal box divergent, cusp reduction, buccal cusp with heavy bevel (no shoulder)Buccal view
29Wax up on working castSpecial die for shade matching/staining - reason for taking the dentin shade