Dental restoration Study Guide

📖 Core Concepts Dental restoration – replaces lost tooth structure to restore function, integrity, and shape. Direct vs. indirect – Direct: material placed & cured in the mouth in one visit. Indirect: restoration fabricated outside the mouth (lab or CAD/CAM) then cemented. Cavity classification (G.V. Black) – Classes I–V describe location & extent of caries; helps choose preparation design & material. Bonding principle – Composite, GIC, and compomer rely on micromechanical/chemical adhesion; amalgam relies on mechanical retention. Fluoride release – Glass ionomer and compomer release fluoride, lowering secondary‑caries risk. --- 📌 Must Remember Amalgam – ≥ 65 % Ag, 29 % Sn, < 6 % Cu; indicated for load‑bearing posterior cavities; contraindicated when aesthetics or mercury sensitivity matter. Composite resin – Light‑cured (camphorquinone, 460–480 nm); placed in increments to control shrinkage. Glass ionomer cement (GIC) – Acid‑base set, chemically bonds to enamel/dentine, releases fluoride, expands like dentine. Compomer – Composite + polyacid; requires bonding agent; fluoride release > composite, strength < composite. Ceramics – Zirconia = high strength; lithium disilicate = high translucency + fracture resistance. Lifespan – Avg. ≈ 12.8 yr for amalgam, 7.8 yr for composite. Preparation – Remove all decay, unsupported enamel, and create appropriate retention form (intracoronal vs. extracoronal). Matrix choice – Sectional matrices → better proximal contacts for composites; circumferential matrices = alternative but less precise. --- 🔄 Key Processes Tooth preparation Diagnose extent of decay → determine amount of tooth to remove. Use rotary handpiece/burrs → create cavity walls, depth, and convergence for retention. Protect pulp (liner/base if deep). Take impression (direct or digital) if indirect restoration needed. Direct restoration placement Etch enamel (if needed) → apply primer/bonding agent. Place composite in 2 mm increments → light‑cure each layer (≈ 20 s). Finish & polish to restore anatomy and aesthetics. Indirect restoration workflow Prepare tooth → take optical or conventional impression. Laboratory/CAD‑CAM fabricates restoration (inlay, onlay, crown, etc.). Place provisional restoration while lab work proceeds. Try‑in, adjust, and cement final restoration. CAD/CAM (CEREC) process Intra‑oral scanner → 3‑D model. Software designs restoration, selects tool paths. 5‑axis milling → ceramic block (zirconia, lithium disilicate) → sinter/ glaze → cement. --- 🔍 Key Comparisons Amalgam vs. Composite Retention: Amalgam = mechanical; Composite = adhesive. Aesthetics: Amalgam = none; Composite = tooth‑colored. Lifespan: Amalgam > Composite (average). Glass Ionomer vs. Composite Bond: GIC = chemical; Composite = micromechanical (bonding agent). Fluoride: GIC = high release; Composite = none. Strength/Wear: Composite > GIC. Compomer vs. GIC Aesthetics: Compomer = better. Mechanical strength: Compomer > GIC but < Composite. Zirconia vs. Lithium Disilicate Strength: Zirconia > Lithium disilicate. Translucency: Lithium disilicate > Zirconia. Sectional vs. Circumferential Matrix Contact quality: Sectional = superior for composites. Ease of placement: Circumferential = simpler but may leave open contacts. --- ⚠️ Common Misunderstandings “Amalgam expands, composites shrink” – Amalgam’s slight expansion occurs over many years; composite shrinkage is immediate during polymerization and must be managed with incremental placement. “All GICs are moisture‑sensitive” – Modern resin‑modified GICs tolerate moisture better, but conventional GIC still requires a dry field during initial set. “Zirconia can be bonded like composite” – Zirconia requires special primers (e.g., MDP‑based) for reliable adhesion; conventional composite bonding agents are insufficient. “Larger cavity always needs indirect restoration” – Direct composites can manage moderate‑size Class II/III lesions; indirect indicated when extensive tooth loss, high stress, or aesthetic demand exceeds direct material capabilities. --- 🧠 Mental Models / Intuition “Retention = Form + Bond” – Mechanical retention (undercuts, grooves) + chemical adhesion = durable restoration. “Shrink‑wrap model for composites” – Think of each incremental layer as a thin film that pulls inward; cure from deepest to superficial to minimize gap formation. “Fluoride shield” – GIC’s fluoride release creates a protective halo around the restoration, reducing secondary caries risk. “Strength‑vs‑Transparency trade‑off” – Zirconia = steel‑like strength (low translucency); lithium disilicate = glass‑like translucency (moderate strength). --- 🚩 Exceptions & Edge Cases Amalgam in high‑esthetic zones – Rarely used; if unavoidable, consider a veneer over the amalgam (requires adequate thickness). Deep cavities with little remaining dentine – May need a calcium hydroxide liner or glass ionomer base to protect pulp before any direct restoration. Patients with metal allergies – Avoid nickel‑chromium or certain amalgam formulations; choose ceramic or gold‑based alloys. Heavy bite forces (bruxism) – Prefer high‑strength ceramics (zirconia) or metal‑based indirect restorations over composites. --- 📍 When to Use Which Small–moderate posterior Class I/II → Composite (direct) for aesthetics; amalgam if cost/ durability priority. Large posterior restoration, high stress → Indirect onlay/crown (ceramic or metal‑ceramic). Cervical lesions, root‑surface caries → GIC or resin‑modified GIC for chemical bond & fluoride. Pediatric fissure sealing → Compomer or sealant (high fluoride release, easy placement). Full‑coverage aesthetic crown → Lithium disilicate (anterior) or zirconia (posterior) via CAD/CAM. Implant‑supported crown → Titanium implant anchor + zirconia or lithium disilicate crown (choose based on occlusal load & aesthetics). --- 👀 Patterns to Recognize “Class I‑III = intracoronal, Class IV‑V = extracoronal” – Guides whether a crown/onlay is needed. “Moisture‑sensitive stage = early set of GIC/ resin‑modified GIC” – Protect with a rubber dam. “Shade matching difficulty = layered ceramic vs. monolithic” – Multi‑layered lithium disilicate can better mimic natural gradients. “Composite marginal discoloration = polymerization shrinkage or inadequate bonding” – Look for open contacts or over‑etching. --- 🗂️ Exam Traps Trap: “Amalgam has the highest wear resistance of all materials.” Why wrong: While durable, high‑strength ceramics (zirconia) exhibit superior wear resistance under heavy occlusal loads. Trap: “All GICs bond chemically to dentine without any pretreatment.” Why wrong: Moisture control is critical; some formulations require a conditioner to optimize the acid‑base reaction. Trap: “Composite shrinkage is negligible with modern bulk‑fill composites.” Why wrong: Bulk‑fill reduces but does not eliminate shrinkage; incremental technique still recommended for large cavities. Trap: “Sectional matrices are only for anterior teeth.” Why wrong: They are preferred for posterior composites to achieve tight proximal contacts. Trap: “Zirconia crowns are always the best choice for aesthetics.” Why wrong: Zirconia’s opacity limits translucency; lithium disilicate offers superior aesthetics in the smile zone. ---