5 Cavity preparation stages and steps: Initial stage steps: 1 Cavity preparation stages and steps: Initial stage steps: 1. Out line form and initial depth 2. Primary resistance form 3. Primary retention form 4. Convenience form Final stage steps: 5. Removal of infected dentin and old restoration 6. Pulp protection 7. Secondary resistance and retention form 8. Finishing extrenaal walls 9. Final cleaning,inspecting,varnishing and conditioning.
6 Step 1:( Out line form) - Mental image 1st → depth → rough out line → alter by seeing hidden problems. - Remove weakened enamel - Preserve cusp and marginal ridge strength - ↓ faciolingual extention - Connect two close cavities - ↓ dentin depth mm - Care for D.C extension, esthetic, occlusion and cavosurface margin.
12 Step 2:( Primary resistance form) - Flat floor - ↓ extension - Rounding internal line angels - Cap weak cusps - Provide enough thickness for restorative material - Box shape - Preserve cusps and marginal ridge - Care for occlusion, remaining tooth structure amount and restorative material type.
16 Step 7: ( Secondary resistance and retention form ) - Cavity wall conditioning by etch enamel and dentin bonding agents - Mechanically: * Retention grooves and locks * Pins, slots and steps * Bevel enamel margins
17 Step 8: (Finishing extrenal walls ) - Create: Step 8: (Finishing extrenal walls ) - Create: * Good marginal seal between tooth and the filling material *Smooth marginal junction * Maximum strength to tooth and the filling material - Care for * Enamel rod direction and support ADJ and laterally. * Margin location * Filling material type → cavo surface angel: a. Amalgam: 90˚ → maximum strength of tooth and Amalgam b. Gold: bevel provide marginal metal ease burnishing and adaptation
18 Step 9: (Final cleaning,inspecting,varnishing and conditioning) Step 9: (Final cleaning,inspecting,varnishing and conditioning). Cleaning by remove debris and smear by citric or polycarboxilic acid
20 Box only preparation - Small D Box only preparation - Small D.C - Facial a lingual proximawalls occlusal convergence - Locks 0.5 mm depth in gingival point angels then decrease occlusally - ( ↓ retention )
21 Tunnel preparation - Proximal D Tunnel preparation - Proximal D.C - Marginal ridge intact - ↓ access and visibility
22 Slot preparation: - At root - Approach facial and lingual - High speed bur 2 , 4 - Out line form : limited pulpal depth 0.75 – 1 mm gingivally and 1 – 1.25 mm occlusaly ( enamel ) - In facial approach : * Lingual wall face facially as much as possible * Provide access, visibility and convenience * Help in Amalgam condensation - Remove remaining D.C by bur 2 , 4 - External walls 90 ˚ cavosurface angel - Retention grooves by bur 1/4 in occlusal and gingival walls at axial line angels, with 0.25 mm depth
24 Sandwich technique: - G. I. C under composite - G. I Sandwich technique: - G.I.C under composite - G.I.C bond to tooth and composite → ↑ retention and seal. - F → ↓ D.C
25 Bonded amalgam: - Same preparation - Retain ↑ weakened remaining tooth structure - Need special adhesive materials
26 Adjoining restorations: - Can repair or replace existing Amalgam filling defective part if the remaining Amalgam filling is good - Adjoining restoration on occlusal surface coz new restoration dove tail can be prepare without eliminating existing restoration dove tail - May prepare Amalgam filling in two or more phases ( eg. Cl ΙΙ lesion continued with Cl V , so 1st prepare and restore Cl ΙΙ before Cl V )
29 cavity preparation designs: - Conventional - Beveled conventional - Modified - Combination of the above three
30 Conventional : - Past design - Out line form : Conventional : - Past design - Out line form : * Extend external walls to initial limited uniform dentin depth * External walls follow enamel rod direction * External walls on root meet root surface at right angel - Dentin retention grooves - For materials like ( Amalgam , silica , porcelain ) ( brittle and ↓ edge strength ) - Not preferred for composite - For composite if lesion at root ( non enamel areas )
31 Beveled conventional : - Similar to conventional but with beveled enamel margins - To replace existing filling with conventional ( in enamel area ) - For resin filling with ↑ thermal expansion coefficient ( acrylic resin , microfilled composite ) - Filling bled esthetically with surrounding tooth color ( not like in conventional that a white line appear between tooth and filling " coz marginal enamel racture during fininshing ) - Bevel : * By flame diamond bur ( 45˚to external tooth surface ) * Rods are exposed → ↑ etched * ↑ etched surface area → ↑ enamel resin bond → ↑ retention and ↓ marginal leakage and discoloration * Width 0.25 – 0.5 mm
33 Modified : - No specific pulpal depth - No specific wall configuration - Only remove lesion conservatively - Rely on enamel etching for retention - For lesion ( initial , small , new , surrounded by enamel ) - Bevel enamel margin - Retention by grooves if large lesion
37 Resistance form: - Go around cusps - Don’t go deep pulpally - Depth 1 Resistance form: - Go around cusps - Don’t go deep pulpally - Depth mm ( 1/2 – 2/3 bur cutting portion) ( 0.1 – 0.2 mm into dentin ) - Don’t extend facial and lingual margins more than half way between cusp tip and central groove (1/4 distance between cusp tips ) - Eliminate weak enamel wall by joining two cavities near each other less than 0.5 mm - Enameloblasty: * Conserve tooth *Remaining fissure not deeper than 1/4 – 1/3 enamel thickness *Eliminate developmental fault by open it by flame diamond side →smooth surface *Surface left meet cavity preparation with cavosurface angle not greater than 100˚ ( Amalgam margin not less than 80 ˚) * Remove Amalgam from enameloplasty area. - Bur no. 245 * 3 mm length * 0.8 diameter *Pear shaped * Produce walls occlusal clearance * Produce rounded internal line angels *Long axis rarallel to tooth long axis * Bur no. 330 smaller size - If marginal ridge remaining thickness more than 1.6 mm → occlusal convergence to mesial and distal walls (if 1.6 mm occlusal divergence ) - Isthmus width not more than bur diameter ( not more than 1.5 mm )
40 Retention form: Parallel or slight occlusal convergence of two or more opposing walls.
41 Removing remaining D. C: - Bur no Removing remaining D.C: - Bur no. 245 →deepen floor ( maximum 2 mm ) - Round bur ( slow speed ) - Spoon scavator - Large instruments safe ( ↓ penetration ) - Stop if feel hard firm ( as sound dentin ) before all stained discolored dentin removed
42 Pulp protection: - If ideal depth no need for liner or base - Two layers cavity varnish ( cotton pallet ) → D.T complete seal + ↓ microleakage ( ↓ tooth sensitivity and pulp inflammation ) - Moderately deep lesion ( remaining dentin thickness 1 mm or more → place quick setting ZOE thin layer 0.5 mm ) ( don’t cover all pulp floor with ZOE because it is not strong senough to support Amalgam under ↑ occlusal forces ) - Boded Amalgam to tooth * After acid etch by new dentin bonding agents contain 4-META *↓microleakage * ↑ Amalgam fracture resistance. - Extensive D.C * Distance between infected dentin and pulp less than 1 mm * ↓ D.C removal if pulp exposure expected ( by x-ray or by dentin pinkish hue ) * If exposure occur decide direct pulp capping ( Ca(OH)2 )or R.C.T * Ca (OH)2 ( Dycal ) 0.5 mm base * Spherical Amalgam need ↓ condensational force
43 Cl Ι Composite: Conventional : - After old Amalgam filling removal - Flat floor - Dentin under cuts - 90˚ cavo surface angel Beveled conventional: - After old Amalgam filling removal - If large lesion - Use bur Modified: - For small pits and fissures
51 Occlusal out line form: - Similar to Cl Ι - Dove tail - Stop 0 Occlusal out line form: - Similar to Cl Ι - Dove tail - Stop 0.8 mm before cutting proximal marginal ridge - Proximal box: * Bur 245 move faciolingually *Diverge gingivally * Cavo surface angle 90˚ * Reverse curve * Lingual minimal reverse curve
55 Primary reseistance: - Pulpal and gingival walls flat and perpendicular to tooth long axis - ↓ wall extension - Roundening internal line angels ( ↓ stresses ) - Filling enough thickness
56 Primary retention: - Facial and lingual walls occlusal convergence and occlusal step dove tail for the cavity occlusal portion - Mesiofacial and mesiolingual walls occlusal convergence for the proximal box
57 Remove remaining infected dentin D Remove remaining infected dentin D.C by slow speed round bur or use spoon scavator
58 secondary resistance: Bevel ( roundening ) of the axio pulpal line angel → ↓ stresses concentration and ↑ material bulk there
61 A. Locks: - Against proximal displacement - In axio lingual and axio facial line angels mm depth at axio lingio gingival point angel and then depth decrease gradually - By slow speed bur 1/4 , /2 , ( ↑ control and tactile sensation )