Evolution 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 amalgam Questions 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.
Why 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.
Differences between gold and porcelain restorations Physical properties - porcelain more brittle Mode of retention - bonding vs mechanical retention Concept of margin Based 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????
Physical Properties What cavity preparation features do we need to modify? –Bulk - more occlusal clearance –Reinforcement - bonding –Bevels contraindicated
Mode of Retention Cast 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.
Marginal Adaptation Cast gold - rely on close adaptation (20u); lack of adhesion between tooth structure/cement/gold interface Porcelain - 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.
Empress Procelain System All procelain restoration used for inlay, onlay, full crown Castable Adequate marginal fit Better wear characteristic than conventional procelain Similar to cast gold inlay/onlay in terms of cavity preparation design
Porcelain Fused to Metal Crown vs Empress: Similarities Highly esthetic Wear Brittle - reinforced through the bonding process
Composite vs Empress: Similarities Mode of retention - dentinal bonding agent Apply skills you learn for composite on the bonding process.
Mechanism of Adhesion Porcelain etched with hydrofluoric acid (micromechanical) Bond between etched tooth and DBA - identical to composite/tooth Silane coupling agent - chemical bond
Summary of Characteristics Highly esthetic Acceptable marginal fit Conservation of tooth structure Less occlusal wear Highly technique sensitive
Indications High esthetic demand Replace moderate to large existing restoration Fractured tooth/restoration Moderate to large primary caries Contraindiations Unable to adequately isolate the field Parafunctional habits - bruxing, clenching, excessive wear
Empress vs Gold Inlay/Onlay Empress Advantages ESTHETIC Conservation of tooth structure (gold onlay vs porcelain inlay) Less complicated cavity design?? Disadvantages Expensive Technique sensitive - bonding process Abrasive to occluding dentition
Empress vs PFM Empress Advantages Conservative cavity preparation Foundation restoration may not be necessary Less abrasive to occluding dentition No metal collar Disadvantages Expensive Technique sensitive
Cavity Preparation Design 1. Occlusal Depth/Cusp Reduction Occlusal Depth = 1.5 to 2.0 mm Cusp Reduction:Functional cusp = 1.5-2.0mm Nonfunction cusp = 1.5 mm 2. Internal/External Line Angles Rounded
Cavity Preparation Design 3. Draw Degree of draw = approximately 12 to 15 degree 4. Bevel No bevel
Mn first premolar- DO amalgam with fractured lingual cusp, deep pulpal floor Existing amalgam removed, making all walls divergent, smoothed all cavosurface margins
Mx first molar - MOD amalgam with deep pulpal floor (4mm) Existing amalgam removed
Proximal walls and gingival seats extended, occlusal wall divergent, clinical judgement was made to cover DL cusp (with shoulder) No cavosurface bevel on shoulder
MOB amalgam on Mx first molar with deep pulpal floor Existing amalgam removed, make all walls divergent and smoothed all cavosurface margins
Occl amalgam on Mn first molar, normal pulpal depth; patient complaining about pain on function- Dx: DB cusp fractured Patient’s occlusion
Existing amalgam removed, DB cusp reduced by 2mm, all walls divergent No shoulder on DB cusp - WHY???
MOD amalgam on Mn second molar with fractured Li cusp. Normal pulpal depth; all amaglam removed Proximal box divergent, Li cusp - smoothed cavosurface margin
MOD amalgam on Mn first molar - occlusal fractured Shade selection BEFORE rubber dam; need dentin shade (match shade at gingival third) and overall shade
Finished preparation; rubber dam removed; ready for impressioning; proximal box divergent, cusp reduction, buccal cusp with heavy bevel (no shoulder) Buccal view
Wax up on working cast Special die for shade matching/staining - reason for taking the dentin shade