Class II Amalgam Cavity Preparartion Date: 6/11/2014 Asalaam Alekum Class II Amalgam Cavity Preparartion Dr. Gaurav garg ( M.D.S.) Lecturer, College of Dentistry Al Zulfi, M.U.

Contents Outline form Retention form Secondary retention Resistance form Reverse curve References

Outline form Occlusaly similar to that for the Class I tooth preparation Proximally there is a box shape extension ( Occlusal Step)

No. 245 or no. 330 bur can be used for preparation Enter tooth with punch cut and extend distally along central fissure at uniform depth of 1.5 mm ( 0.5 mm inside DEJ) Bur position for entry- slight lingual tilt

1 2 3 5 4

B Wedging. A, Round toothpick wedge placed in gingival embrasure protects gingiva and rubber dam during preparation of proximal box. B, Triangular wedge is indicated when deep gingival extension of proximal box is anticipated, because wedge's greatest cross-sectional dimension is at its base. Consequently, it will more readily engage the remaining clinical tooth surface

DEJ

Proximal box: Buccolingual extension: there should be 0.2- 0.3mm clearance from adjacent tooth buccaly & lingually Gingivally there should be a clearance of 0.5 mm from adjacent tooth Axial wall should follow the external tooth contour

Removeremaining undermined proximal enamel with enamel hatchet on facial proximal wall (A), lingual proximal wall (B), and gingival wall (C).

Beveling axiopulpal line angle

A, Bevel of enamel portion of gingival wall is established with gingival margin trimmer to ensure full-length enamel rods forming gingival margin. B and C, Sharp angles at linguogingival and faciogingival corners are rounded by rotational sweep with gingival marginal trimmer ( GMT).

Retention form Occlusal convergence of buccal & lingual walls Proximal Dovetail

Secondary Retention Retention Locks ( No. 169L or ¼ round bur can be used) 169L ¼ round

Resistance form Minimal extension, Ideal Isthmus width- 1/4th of Intercuspal distance Smooth outline and smooth walls 90 degree cavosurface angle Flat pulpal & gingival floor Gingival floor should be bevelled ( 15-20 degree), to remove unsupported enamel rods Rounded all internal line angle Bevelled axiopulpal line angle

Final finished cavities ¼ th of ICD Buccal wall Pulpal floor Palatal/ Lingual wall Axiopulpal line angle Axio- buccal line angle Axio-lingual line angle Axial wall Axiogingival line angle Gingival floor

Reverse Curve In case of maxillary teeth, mostly the molars, the contact area is more buccally, i.e.; the lingual embrasures are more than the buccal embrasures In such cases, extending the bucco- proximal wall into the embrasure lead to excessive cutting of the buccal cusps To avoid this, a reverse curve ( S- shaped) is made in the buccal proximal wall so as to have sufficient amount of dentin in that area & also to achieve butt joint with the cavosurface margins Such a curve, though mostly given in maxillary molars, can be given in any tooth where the contact area is deviated or more pronounced on one side.

Advantages of reverse curve Conservation of tooth structure ( preserve cuspal inclines) Creation of 90 degree cavosurface angle Less display of restorative material ( enhance esthetics)

References & Suggested reading Sturdevant's art & science of operative dentistry-2006- Theodore M. Roberson, Harald O. Heymann, Edward J. Swift, Jr. Principles of operative dentistry (2005)- A.J.E. Qualtrough, J.D. Satterthwaite, L.A. Morrow and P.A. Brunton. Fundamentals of Operative Dentistry- 2nd Edition- Summitt & Robbins

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