Class II Cavity Preparation PDF

Characters of Caries : ▪ Two opposite cones with their base at the DEJ. ▪ Cone shaped spread in enamel with the base at the DEJ and small opening. ▪ Cone shaped spread in dentin with the base at the DEJ. ▪ Rapid lateral spread at DEJ. * Class II CAVITY PREPARATION FOR AMALGAM...

Characters of Caries : ▪ Two opposite cones with their base at the DEJ. ▪ Cone shaped spread in enamel with the base at the DEJ and small opening. ▪ Cone shaped spread in dentin with the base at the DEJ. ▪ Rapid lateral spread at DEJ. * Class II CAVITY PREPARATION FOR AMALGAM RESTORATION Definition : It is smooth surface lesion occurring on the proximal surfaces of molars and bicuspids at middle- middle third of tooth. Class II Simple Compound Complex Character of Caries : 1. Difficult to detect until it is of a considerable size. 2. A bite-wing x-ray film is necessary for correct diagnosis. 3. It spreads in enamel and dentin in a conical pattern. 4. It tends to spread occlusally along the dento- enamel junction, and to undermine the marginal ridge early. 5. It tends to extend bucco-lingually towards the axial angles and also gingivally. 6. There is a probability for the caries to recurrence at buccal gingival and lingual gingival line angles of the cavity margin. Designs of Class II Cavity Preparation:  Class II compound or complex cavity with proximal step: It is composed of "3" portions: 1. Occlusal portion. 2. Isthmus portion. 3. Proximal portion. a) Outline form : Occlusal portion : The same as occlusal class I cavity. Isthmus portion: Definition : The narrowest connection between the occlusal and proximal portions of the cavity. The outline of the isthmus portion should be extended to: 1. Involve all the carious enamel and dentin. 2. Place the cavity margins in area self-cleansable with freeing of the proximal contact area. The width of the cavity at isthmus should be narrow Bucco-lingually as much as possible about 1/4 the distance. Isthmus outline form: 1. Straight: In case of small contact area. 2. Uniform: In case of normal sized contact area. 3. Reverse curve: In case of broad or wide contact area. Proximal portion : Should be extended enough to ensure: 1.Involvement of all carious enamel and dentin. 2.Freeing the proximal surface out of contact lingually, buccally and gingivally. 3. Placing the cavity margins in the embrasures to be in area self-cleansable. -The buccal wall mid way between the contact area and the buccal axial line angle in direction parallel to the corresponding buccal surface of the tooth. -The lingual wall mid way between the contact area and the lingual axial line angle in a direction parallel to the corresponding lingual surface of the tooth. -The gingival floor is 0.25 - 0.5 mm above the gingival crest and in a direction parallel to the pulpal floor and occlusal plane of the tooth. -The axial wall is about 1.5-2 mm away from the DEJ to provide enough bulk of the restoration. b) Resistance form: Occlusal portion:. Axiopulpal lineangle The same as class I cavity. Isthmus portion: -Minimal width of the cavity Bucco-lingually about ¼ the inter-cuspal distance. This will provide decrease in the surface area of restoration subjected to the occlusal stresses. -Roundation, beveling or saucerization of the axio-pulpal line angle, to provide removal of sharp axio-pulpal line angle that acts as stress concentration area & increased bulk of restoration at isthmus area. -Reverse curve in case of wide proximal contact area will provide maximum conservation of the sound tooth structure during freeing of the contact and removal of all undermined enamel with correct CSA 90°. Proximal portion: Reverse curve approach : -It is placed in the buccal wall of upper premolars to remove all undermined enamel. -CSA 90°. -Gingival floor should be smooth, flat and parallel to the pulpal floor and the occlusal plane. -Axial wall parallel to the external proximal tooth surface and be at 1.5 - 2 mm away from the DEJ, this will provide uniform bulk of the restoration. -Buccal and lingual walls parallel to the direction of the corresponding surfaces. /The proximal portion is in box form. c) Retention form: Axial retention: 1.Mechanical undercuts by preparing the cavity walls slightly converging occlusally. 2.The inverted truncated cone shape of the proximal portion. Lateral retention(refer to assignment secondary retention) 1. Proximal dove tail: In premolars, considered as extension for retention. In molars, considered as extension for prevention that provides retention also. 2. Occlusal lock. 3. Proximal axial grooves. 4. Pin retention in extensive cavities. Proximal axial grooves: -Cut in the axio-buccal and axio-lingual line angles, in the expense of buccal and lingual walls rather than the axial wall to avoid pulp exposure. -Extended from the gingival floor in occlusal direction up to the level of the pulpal floor. -These grooves are wider internally than externally and wider gingivally than occlusally. -These grooves are prepared using small tapered fissure bur.  d) Convenience form: -Cutting an occlusal cavity provides accessibility to the proximal portion. -Accentuation of cavity walls and margins. -Roundation of line angles. -The axial wall should be parallel to the tooth long axis in occluso-gingival direction to allow instrumentation up to the depth of the proximal portion. -Selection of suitable sized instruments. e) Finishing of enamel wall: Occlusal portion: The same as class I cavity. Isthmus portion Following Ingrham's lines will provide: 1. Enamel wall in the direction of enamel rods with CSA 90°. 2. Enamel wall free from any loose, undermined or friable enamel rods. Proximal portion: The buccal and lingual walls are flared slightly to outward to get CSA 90°. The gingival floor is slanted slightly gingivally to get CSA 90°. Reverse curve approach: In the buccal wall of the proximal portion of upper premolars after performing reverse curve outline of the isthmus portion, the enamel of the buccal wall will be undermined. So, Beveling of the enamel of this buccal wall will provide: a) Removal of all undermined enamel. b) CSA 90°. Clinical Considerations: It is preferable to complete the proximal outline before breaking the marginal ridge and proximal enamel plate. This will provide: a) A guide to proximal design. b) Protection of the proximal surface of the adjacent tooth from rotary instrument. c) Save time and effort. d) Reduce heat generation as cutting in enamel produces much more heat generation. Other ways to protect neighboring tooth structure & gingiva: 1) Using a matrix band around the neighboring tooth during cavity preparation. 2) Using rubber dam to protect the gingival tissues. 3) Using circular wedge during gingival floor preparation to protect the gingiva. Class II simple proximal cavity: In cases having enough proximal access due to: -Missing adjacent tooth, which is not to be restored. -Wide embrasure due to senile(old aged) gum recession provided that the corresponding marginal. -Ridge is intact and not undermined by caries