Class III & IV Cavity Preparation for Composite Restoration PDF

CLASS III & IV CAVITY PREPARATION FOR COMPOSITE RESTORATION Dr. Ahmed Holiel BDS, MSc, PhD Lecturer of Conservative Dentistry Faculty of Dentistry - Alexandria University ‫‪To the memory‬‬ ‫‪of my Brother‬‬ ‫ي ﷺ‪ :‬إذا مات ابنُ آدم انقطع عملُه إال من ثالث‪ :‬صدقة جارية‪ ،‬أو علم يُنتفع به‪،‬‬ ‫يق...

CLASS III & IV CAVITY PREPARATION FOR COMPOSITE RESTORATION Dr. Ahmed Holiel BDS, MSc, PhD Lecturer of Conservative Dentistry Faculty of Dentistry - Alexandria University ‫‪To the memory‬‬ ‫‪of my Brother‬‬ ‫ي ﷺ‪ :‬إذا مات ابنُ آدم انقطع عملُه إال من ثالث‪ :‬صدقة جارية‪ ،‬أو علم يُنتفع به‪،‬‬ ‫يقول النب ُّ‬ ‫أو ولد صالح يدعو له‬ Class III tooth preparations: are located on proximal surfaces of anterior teeth Indications: ✓ ✓ ✓ Esthetic prominent areas Operating area can be adequatly isolated to attain an effective bond Tooth preparation have all – enamel margins (best scenario) Cavity designs: • Conventional cavity preparation • Beveled conventional • Minimal invasive (modified) Conventional cavity preparation Indication • preparation is necessary on the root surface Cavity forming features: • Box shape • depth: 0,75mm on root, 0,2mm in dentin • 90° cavosurface margin is required • Groove retention can be prepared ✓ 0,25mm into the dentin of the axiogingival line and incisoaxial line • dovetail extension Large Class III tooth preparation extending onto root surface. A, Facial view. B, Lingual view. C, Mesial view showing gingival and incisal retention, which is only used when deemed necessary to increase retention. The tooth preparation is now ready for beveling of the enamel walls. Beveled conventional cavity preparation Indication • replacing an existing defective restoration in the crown Cavity forming features: • Similar to conventional, but beveled enamel margin • Box shape • 0,75- 1,25 mm depth • 0,2 mm in the dentin • axial wall in convex, following the external contour of the tooth Reason of beveling is the microretention • The end of enamel rods are more effectively etched producing deeper „microundercuts” than when only the sides of enamel rods are etched • The composite filling has stronger adhesion to the tooth structure • Better esthetic • Use diamond bur 45 degrees to the external tooth surface • Width should be 0,25-0,5mm Minimal invasive (Modified) Indication • small and moderate lesions or faults Cavity forming features: • Most used type of cavity preparation • designed to be as conservative as possible • walls extent only of the fault or defect no specific shapes or forms • preparation design appears to be scooped or concave • no groove retention • but bevel the enamel 1. Use a 1/2, 1, 2 round bur, point of entry is within the incisogingival dimension of the lesion, perpendicular to the enamel surface. 2. Remove all remaining caries or defect. 3. No attempt is made to create a uniform axial wall. 4. Place cavosurface bevel or flare at the enamel except at the gingival margin area. 5. Use a flame shape or round bur resulting in a 45 degrees angle to the external tooth surface. 6. Bevel width should be 0.25 to 0.5mm. 7. Clean the preparation of any debris and inspect final preparation A small, scoop-shaped Class III tooth preparation. -If possible, the outline form should not: (1) include the entire proximal contact area (2) extend onto the facial surface (3) or be extended subgingivally. Facial or lingual approach ??? The lingual approach is preferable due to : • The facial enamel is conserved for enhanced aesthetics. • Some unsupported enamel may be left on the facial wall • Color matching of the composite is not as critical • Discoloration of the restoration is less visible Beginning Class III tooth preparation (lingual approach). A, The bur or diamond is held perpendicular to the enamel surface, and an initial opening is made close to the adjacent tooth at the incisogingival level of the caries. B, The correct angle of entry is parallel to the enamel rods on the mesiolingual angle of the tooth. C, Incorrect entry overextends the lingual outline. D, The same bur or diamond is used to enlarge opening for caries removal and convenience form while establishing the initial axial wall depth. Ideal initial axial wall preparation depth. A, Incisogingival section showing axial wall 0.2 mm into dentin. B, Faciolingual section showing facial extension and axial wall following the contour of the tooth. The facial approach is used when : • The carious lesion is positioned facially • The teeth are irregularly aligned, making lingual access undesirable • An extensive carious lesion extends onto the facial surface\ • A faulty restoration on facial surface Retention form micromechanical bond from acid-etching and resin bonding, so no additional preparation retention form is usually necessary. Using diamond stones for the tooth preparation leaves the prepared surfaces rougher, thereby increasing the surface area and the micromechanical retention. Sometimes a groove or cove may be necessary for Class III restorations that either extend onto the root surface or are very large. Usually, however, additional needed retention form can be achieved simply by increasing the surface area with a wider enamel bevel or flare along the margin. Large Class III tooth preparation. A, Beveling. The cavosurface bevel is prepared with a flame-shaped or round diamond, resulting in an angle approximately 45 degrees to the external tooth surface. B, Completed cavosurface bevel (arrowhead). Class IV tooth preparations: located on proximal surfaces of anterior teeth and involve the incisal edge Causes of class IV • Dental caries • Fracture/trauma ✓ Incisal edge involving Enamel only ✓ Fracture involving Enamel & Dentin ✓ Fracture involving Enamel , Dentin &Pulp preoperative assessment of occlusion (margins placed in noncontact areas) shade selection is very important still difficult preparation extends to the incisal angles Class IV cavity design Box like class IV cavity • The conventional design with the 90 degree cavo surface angle has very few indications • It is indicated when there is root extension Beveled conventional class IV cavity • To provide additional retention in high stress area, a wide bevel is necessary for better retention Modified class IV cavity preparation • The treatment of teeth with minor traumatic fractures requires less preparation then the beveled conventional • The retention is obtained primarily from the bonding strength of composite to enamel and dentin. Indicated for small to moderate lesions or traumatic defects Bevelled cavosurface mrgins Objective: removing as little as possible tooth structure , while removing the fault and providing for appropriate retention and resistance forms Axial depth depends upon extent of the lesion ,previous restoration or fracture but still not deeper than 0.2mm below ADJ Why to place a bevel ? • To expose max no of enamel rods for etching and bonding • To increase the surface substrate area needed for bonding • To remove the fluoride rich low surface energy enamel • Color blending at tooth/restoration marginal area (gradual change in thickness of restoration and tooth substance • Better esthetics (no white halo characteristic of butt joint) When NOT to place a bevel ? Areas of centric contact (brittle composite will easily break in high stresses) At gingival area where thin or no enamel is found ( retention will be made on bonding dentin and gingival groove made in dentin ) Bevelling In composite restoration In supported enamel Following enamel rods ▪ Short bevel (1/3-1/2 enamel thickness) ▪ Long bevel (entire enamel wall is bevelled, when not enough thickness of enamel is found to offer retention) ▪ Full bevel (entire enamel) ▪ Hollow ground (inaccessible gingival areas to avoid overhangs , enamel is ground in a concave manner) ▪ Scalloping (in short and long bevels to increase the surface area and retention ) ▪ chamfer with bevel/ skirting/circumferential bevel (best, excellent retention , chamfer finish line with a bevel in all surfaces all around– better esthetics and blending of the material)