TOPIC: FINISHING AND CEMENTATION
🎯 KEY POINTS:
🔹In Chronic Xerostomic patient, cervical caries and periodontitis are prime reasons for FPD failure.
🔹Beilby layer is a microscopic surface layer produced during polishing of gold crowns.
🔹Metamerism is a phenomenon of an object appearing of different colours when viewed under different light source.
🔹The use of dissimilar metallic restorations in the same mouth may result in the creation and flow of galvanic currents.
🔹Sandblasting is recommended on the internal surface so that it becomes more conducive to nonadhesive cement.
🔹Kieselguhr is a mild abrasive and polishing agent.
🔹Sand or other forms of quartz called flint are coated on discs and are available in various grits.
🔹Emery is a mixture of aluminium oxide and iron oxide, called corundum.
🔎 CLASSIFICATION OF FAILURES IN FPD BY BERNARD G. SMITH
(i) Loss Of Retention
(ii) Mechanical Failure of Crown or Bridge Components:
💠This is Subclassified as follows:
🔸Porcelain fracture
🔸Failure of solder joints
🔸Distortion
🔸Occlusal wear and perforation
🔸Lost facings
(iii) Changes In Abutment Tooth
🔸Periodontal diseases
🔸Problems with the pulp
🔸Caries
🔸Fracture of the prepared natural crown or root
🔸Movement of the tooth
(iv) Design Failures:
💠 This is Subclassified as follows:
🔸Underprescribed bridges
🔸Overprescribed bridges
(v) Inadequate Clinical or Laboratory Technique:
💠 This is subclassified as follows:
🔸Positive ledge
🔸Negative ledge
🔸Defect
🔸Poor shape and contour
(vi) Occlusal Problems
🔷 FACTORS RESPONSIBLE FOR FPD FAILURES
👉 The factors can be of three types:
(i) Biological factors
(ii) Mechanical factors
(iii) Aesthetic factors
📢 ABRASIVES CAN BE CLASSIFIED AS FOLLOWS:
(i) Finishing abrasives
(ii) Polishing abrasives
(iii) Cleansing abrasives
⭐ COMMONLY USED ABRASIVES & POLISHING AGENTS:
🔺 SILICONE CARBIDE: Commonly used in the laboratory; formed into grinding wheels or discs.
🔺 DIAMOND: Hardest abrasive, used on enamel or porcelain; ineffective on soft materials like gold.
🔺ALUMINIUM OXIDE: Made from bauxite; coarse-grit for metal–ceramic finishing, fine-grit for polishing (e.g., poly stones).
🔺EMERY: Mixture of aluminium and iron oxide; used for porcelain or gold finishing.
🔺GARNET: Red abrasive, used for cutting metal and ceramic.
🔺TIN OXIDE: Fine powder for final intraoral polishing of metal restorations.
🔺TRIPOLI: Siliceous polishing powder with wax binder, used for initial polishing of gold.
🔺ROUGE: Fine red iron oxide powder in cake form; excellent for gold polishing.
🔺SAND: Quartz-based abrasive on discs, used for finishing and polishing gold.
🔺PUMICE: Siliceous material for polishing dentures and smoothing teeth.
🔺KIESELGUHR: Mild abrasive and polishing agent.
🔺CUTTLE: Made from cuttlefish shells, used for fine polishing via paper discs.