CLASS III CAVITY
Restorations on the proximal surfaces of the anterior teeth that do not involve the incisal angle.
LINE ANGLES:-
Axiolingual (al), Axiogingival (ag), Faciogingival (fg), Axiofacial (af), Incisal (i).
POINT ANGLES:-
Axiolinguogingival (alg), Axiofaciogingival (afg), Axioincisal (ai)
INITIAL TOOTH PREPARATION
(for maxillary canine) * A no. 2 bur is used for the entry cut on the distolingual marginal ridge. * The bur is positioned so that it will penetrate into the carious lesion, which is usually gingival to the contact area. This conserves the marginal enamel. * Penetration should be at limited axial depth (0.5 to 0.6mm). * The lingual outline blends with the incisal and gingival margins in a smooth curve creating a very little or no lingual wall. * Cavosurface angle should be 90` at all the margins. * The facial, incisal, gingival walls should meet the axial wall at approx. right angles. * The axial wall should be uniformly deep and flat. * A triangular wedge is placed in the gingival embrasure to depress and protect the soft tissues and the rubber dam. * The internal line angles should be slightly rounded. This permits more complete condensation of amalgam. * Smoothening of any roughened, undermined enamel produced at the gingival and facial Cavosurface margins is done. * The boxlike preparation form provides primary retention form.
FINAL TOOTH PREPARATION * Remove any remaining infected carious dentin on the axial wall. * Secondary retention form is provided by a gingival groove, an incisal cove and sometimes a lingual dovetail. * Place the gingival groove starting from afg moving continuously upto alg. * The direction of the gingival groove is slightly more gingival than axial. * Alternatively, if less retention form is needed; two gingival coves can be given, as opposed to a continuous groove (each on placed in the afg and alg point angles). * Prepare an incisal retention cove at the afi point angle. * The lingual dovetail should be conservative, generally not extending beyond the mesiodistal midpoint of the lingual surface. * The axial depth of the dovetail should be approx. 1mm and the axial wall should be parallel to the lingual surface of the tooth. * The lingual convergence of the dovetail’s external walls usually provides sufficient retention form. * Careful assessment should be made that all the caries are been removed, depths are proper along with all the angles.
RESTORATIVE TECHNIQUEMATRIX PLACEMENT:
The wedged, compound-supper-supported matrix may be used for the class III amalgam restoration.
Insertion of the amalgam into the class III tooth preparation is usually lingual.
CONDENSATION AND CARVING:
Insertion of the amalgam, initial carving, matrix removal, wedge removal, and final carvings are similar to the techniques for the posterior teeth.
FINISHING AND POLISHING:
They are similar to that of other restorations.
ADVANTAGES:
* Easier to place * Less expensive * Because of its metallic color, can be easily differentiated from the surrounding tooth structure * Easier to finish and polish.
DISADVANTAGES:
* Metallic and unaesthetic * Typically requires 90’ Cavosurface margins, specific and uniform axial depths, and incorporated retentive features. * The potential for mercury contamination is another disadvantage.