Fundamentals of Cavity Preparation 3 PDF

5. Removal of remaining carious dentin or old restorative material: Teeth with frank deep carious lesion Elimination of any infected dentin, old faulty restorative material after initial tooth preparation Floor of the cavity may be composed of: I. Hard sound healthy dentin  Free from latera...

5. Removal of remaining carious dentin or old restorative material: Teeth with frank deep carious lesion Elimination of any infected dentin, old faulty restorative material after initial tooth preparation Floor of the cavity may be composed of: I. Hard sound healthy dentin  Free from lateral spread of decay or discoloration  CP depth is 0.2 mm beyond the DEJ  No more deepening should be made II. Hard but discolored dentin Stained dentin is not considered as carious dentin it is stained from pigments produced by chromogenic bacteria III. Carious dentin In dentin caries progress: area of decalcification precedes the penetration of microorganisms often appears discolored in comparison with undisturbed dentin, but it has no soft texture of caries This dentin condition may be termed affected dentin differs from infected dentin in that it has been significantly invaded by microorganisms The outer layer (infected dentin) is softened and contaminated with bacteria. It includes the superficial, granular necrotic tissue and the softened dry leathery dentin. It can be selectively stained in vivo by caries detection dyes (1% acid red in propylene glycol) that stains the irreversibly denatured collagen The inner layer (affected dentin) is slightly softened demineralized dentin not invaded by bacteria. Not stained by the dye as it contains reversibly denatured collagen  Clinically carious dentin is formed of two distinct layers infected dentin affected dentin - Outer -inner - soft texture of caries - structural integrity maintained - discolored - slightly - bact. Invasion - Few - Non vital, no pain - Vital, painful - Removed (unreminerizable) - Not (reminerizable)  It is accepted and appropriate practice to leave affected dentin to remain in finished CP  The use of color alone to determine how much dentin to remove is unreliable?????  It may lead to over-cut remineralizable dentin or leave infected dentin in prepared cavity  A clinical description of exactly where infected dentin stops and affected dentin begins is practically impossible. It is an empirical decision enhanced by practical knowledge and experience, although some chemical, caries- disclosing" dyes may aid that decision Recent rotary instruments as carbide bur, ceramic bur, CMCR Techniques: Moderate, Deep, extensive Caries ???????? SOFT, HARD Caries???? Tools: Hand: (soft) The direction of movement for sharp spoon excavator with light force parallel to recessional lines of the pulp to avoid pulp exposure Rotary: (hard) Round carbide burs at low speed water cooling and intermittent strokes (complete control, adequate vision) or round carbide burs at high speeds with light pressure Removal of old restoration: the same with high- volume evacuation ( removal old ama to prevent mercury vapor inhalation) Caries-control procedure 6. Pulp Protection: Deep dentin is very porous and susceptible to desiccation The thin remaining dentin provides little protection from: heat generated by rotary instruments during subsequent steps, noxious ingredients of various restorative materials, thermal changes conducted through restorative materials, forces transmitted through materials to the dentin, the ingress of bacteria and toxins  Placement of liners and bases is not a step in tooth preparation, it is a step in adapting the preparation for receiving the final restorative material  As a general rule, it is desirable to have approximately 2-mm between pulp and any restorative material include remaining dentin, liner, and base Deep caries management strategy 7. Secondary Retention and Resistance Features: Sometimes, additional retention features must be incorporated in final stage of preparation for non-bonded restoration Because many preparation features that improve retention form also improve resistance form, and the reverse is true, they are presented together I. Proximal axial grooves (locks):  Prepared at the axio-buccal and axio-lingual line angles in extensive cavity preparations  Cutting of proximal retention grooves at the expense of buccal and lingual walls not axial II. Axial coves: Prepared with No ¼ round bur III. Horizontally oriented axial retention grooves: Are prepared in most Class V preparations for amalgam and in some root surface tooth preparations for composite IV. Skirt:  are preparation features used in extensive Class IV, cast gold restorations that extend the preparation around some or all of the line angles of the tooth  When properly prepared, skirts provide additional, opposed vertical walls for added retention  The placement of skirts also significantly increases resistance form by enveloping the tooth, and resisting fracture of the remaining tooth from occlusal forces V. Horizontal Slots: is a retentive groove in dentin With a No. 33 1/2 bur, prepared approximately 0.6 mm deep and 0.5 to 1 mm inside DEJ VI. Pins: Pin retention used in preparation with few or no vertical walls Pins improve retention but negatively affect the resistance to fracture of both the restoration and tooth VII. Beveled enamel margins: The bevels for cast metal slightly improve retention form when there are opposing bevels, but are used primarily to afford a better junctional relationship between the metal and the tooth Many enamel margins of RC restorations have a beveled or flared configuration to increase both the surface area of etchable enamel and to maximize the effectiveness of the bond by etching more enamel rod ends 8. Finishing External Walls and margins of CP: Is developing specific cavosurface design, smoothness or roughness to ensure maximium restoration effectiveness durability Objectives: 1. Create the best marginal seal possible between the restorative material and the tooth structure 2. Afford a smooth marginal junction 3. Provide maximum strength of both the tooth and the restorative material at and near the margin Ideal finished enamel wall is gained by: 1. Removal of undermined enamel 2. Adjust CSA according to the physical properties of restoration 3. Smoothening of walls for better adaptation 4. Make the outline in sweeping curves 5. Roundation of line and point angles Features: 1. amalgam and ceramics have low edge strength, 90 CSA produces maximal strength (no bevels) 2. beveling for intra-coronal cast gold, and composite restorations for: marginal seal and gingival adaptation easy polishing of margins. Methods of enamel wall Finishing:  Hand cutting instruments:  Enamel hatchet, chisel  Gingival margin trimmer  angle former  Rotary instruments:  Abrasive points Objectives of cleaning:  Removal of bacteria, loose caries debris after using sharp excavator, temporary restoration, saliva  To improve adaptation and avoid caries recurrence around restoration  Prepare tooth surface to receive the selected restorative material Technique of cleaning:  Scrap the cavity walls and floors with a hand instrument.  Flush the cavity with air–water spray  Dry the cavity with cotton pellets then gentle dryness with oil free air blowing Contraindications  Use of chemicals to clean or sterilize the cavity  Excessive dryness with air blast to avoid dentin dehydration with subsequent post- operative hypersensitivity (solution contains 5% glutaraldehyde and 35% hydroxyethyl methacrylate HEMA) restrict tubular fluid movement and sensitivity HOW: crosslink to dentin collagen fibers (Pr) forming plug. THANKS