3 DefinitionTooth preparation is the mechanical alteration of a defective, injured, or diseased tooth to receive a restorative material that reestablishes a healthy state for the tooth, including esthetic corrections where indicated and normal form and function.
5 Objectives of cavity preparation For tooth:Remove the defect conservatively.Provide necessary protection to the pulp.Prevent further fracture of tooth..
6 Objectives of cavity preparation For the restoration:Prevent further fracture of restoration under masticatory forcesPrevent displacement of restorationAllow for esthetic and functional placement of restoration.
7 Principles of cavity preparation: Biological principles.Protection of the pulp(thermal, mech, chem, bact.).Prevention of caries recurrence.Aseptic conditions.Mechanical principles.
12 Protection of the pulp AVOID!!! Overcutting of enamel (width). Overcutting of dentin (depth) Cutting of the OP close to the cell body may result in irreversible injuryExcessive pressure application during excavation or use of rotary toolsInjudicious use of small pointed instrument.Avoid use of eccentric rotary tools “Shock-wave” phenomena.Cutting across recessional lines of pulp
15 Thermal irritation:TTZ (thermal tolerance zone) of dentin which ranges between FMinimizing the frictional heat resulting in cavity preparation via, decreasing friction: speed, pressure, area of cutting, mode and time of cutting. Using tools with high cutting efficiency (sharp, suitable, and proper sized).
16 the intentional use of coolants copious in amountMulti directed
17 Air-water spray jet is considered to be the most appropriate (Why?) air drying stream desiccate the dentinwater stream disturbs visibility during work.The temperature of coolant should be that of the mouth i.e.37 C (Why?)Lower temperatures fogging, disturbs vision and may irritate the pulp.Higher temperatures not effective in cooling.
18 Thermal Injury:“Blushing” of teeth during or after cavity prep is attributed to frictional heat• Pink or purple color due to vascular stasisof sub-odontoblastic capillary plexus bloodflow which rupture and release RBC’s.
20 Chemical irritation:Cavity cleansers, cavity sterilizers like phenolic and alcoholic agents proved to have an insignificant role in preventing or decreasing secondary caries and thus their use must be omitted.
21 Chemical irritation to dentine-pulp organ without pulpal bacterial contamination did not produce harmful effects on the pulp in spite the existence of a very thin protective dentin bridge or even in cases of micro- or macroscopic pulp exposures.
23 Bacterial irritation: Sterilization of instruments is essential since bacterial ingress to the pulp can pass through minute undetected exposures in case of thin dentine bridge barrierUse of rubber dam to isolate the field of operation
37 The cavity design should decrease the deleterious and damaging effect of tensile stresses created within the tooth as a result of defect by:ConservationRemoval of weakened tooth structure and undermined enamelProvision of bulk in the brittle restorations for stress distribution so that the destructive forces could not damage the brittle restoration.Provision of adequate means of retention to prevent displacement of restoration under functional forces.