Class iii cavity preparation

Blacks Class III cavity preparation for amalgam and composite

1. CLASS III CAVITY PREPARATION

2. CONTENT DEFINITION CLASS III AMALGAM RESTORATION CLASS III COMPOSITE RESTORATION

3. DEFINITION Class III Cavity preparation is cavity preparation involving the proximal surface of the anterior teeth.

4. CLASS III AMALGAM RESTORATION

5. Amalgam restoration is used infrequently in Class III cavity preparation due to aesthetic concerns It has been replaced by tooth colored restorative material especially composites which have become increaasingly wear resistant and color stable.

6. INDICATION Distal surface of maxillary and mandibular canines in situations: 1) Extensive prep with minimal facial involvement 2) Gingival margin is primarily in cementum 3) Difficulty in moisture control Any class III not involving the facial surface or undermining the incisal corner.

7. CONTRAINDICATION Areas of aesthetic importance such as mesial surface and preparation involving the facial surface rather than lingual.

8. BUR SELECTION Depending on the anticipated size of the restoration, the bur selection done No. 2 Bur:- Entry cut on Disto-lingual marginal ridge No. 1 or 1/2 Bur:- Tooth or carious lesion is small No. 1/4 Bur:- To place retention grooves. Even diamond points can be used.

9. OUTLINE FORM A lingual access preparation is recommended because of the use of amalgam in that location is more appropriate. Mandibular canine a facial approach may be indicated if the lesion is more facial than lingual.

10. PUNCH CUT The bur is oriented in such a way that it penetrates the carious lesion which is usually gingival to distal contact point. Ideally, the bur is positioned so that its long axis is perpendicular to the lingual surface of the tooth, but directed at a mesial angle as close to the adjacent tooth as possible. This position conserves the marginal ridge enamel

11. FACIAL AND LINGUAL MARGINS For a small lesion, the facial margin is extended 0.2-0.3 mm into the facial embrasure (if necessary), with a curved outline from the incisal to the gingival margin (resulting in a less visible margin). The lingual outline blends with the incisal and gingival margins in a smooth curve, creating a preparation with little or no lingual wall.

12. CAVOSURFACE MARGINS The cavosurface angle should be 90 ° at all margins. The facial, incisal, and gingival walls should meet the axial wall at approximately right angles (although the lingual wall meets the axial wall at an obtuse angle or may be continuous with the axial wall)

13. INCISAL EXTENSION Incisal extension to remove carious tooth structure may eliminate the proximal contact. It is important to conserve as much of the distoincisal tooth structure as possible to reduce the risk for subsequent fracture. When possible, it is best to leave the incisal margin in contact with the adjacent tooth.

14. GINGIVAL PREPARATION When preparing a gingival wall that is near the level of the rubber dam or apical to it, it is beneficial to place a wedge in the gingival embrasure earlier to depress and protect soft tissue and the rubber dam. As the bur is preparing the gingival wall, it may lightly shave the wedge. A triangular (i.e., anatomic) wedge, rather than a round wedge, is used for a deep gingival margin

15. INITIAL AXIAL WALL DEPTH P enetration should be at a limited initial axial depth (i.e., 0.5–0.6 mm) inside the DEJ (see Fig. 15-7, C and D) or at a 0.75-0.8-mm axial depth when the gingival margin is on the root surface (in cementum) . It may be in sound dentin (i.e. shallow lesion), in infected dentin (i.e. moderate to deep lesion) or in existing restorative material (if replacing a restoration).

16. PRIMARY RESISTANCE FORM Primary Resistance form is that shape and placement of the cavity walls to best enable both the tooth and restoration to withstand, without fracture the stresses of Masticatory forces delivered principally along the long axis of the tooth. Features of Primary Resistance Form 1) Cavosurface margin is 90 °. 2) Enamel walls supported by sound dentin. 3) Sufficient bulk of enamel (= 1mm) 4) Slightly rounded internal line angles.

17. PRIMARY RETENTION FORM Primary Resistance form is that shape and placement of the cavity walls to best enable both the tooth and restoration to withstand, without fracture the stresses of Masticatory forces delivered principally along the long axis of the tooth . Primary retention form is provided by box like preparation form.

18. FINAL TOOTH PREPARATION REMOVAL OF ANY INFECTED CARIOUS DENTIN on the axial wall which is done by 1) a slowly revolving no. 2 or 4 round burs 2) spoon excavator

19. SECONDARY RETENTION FORM can be provided by any or all of the following: 1) GINGIVAL GROOVE # This is done by using a No. 1/4 (0.5mm thick) bur rotating at slow speed in the axial wall along the axiogingival line angle. # Depth = 0.25 mm

20. 2) GINGIVAL RETENTION COVES # indicated as an alternative to retentive groove when less amount of retention is needed. # instead of a continuos groove two coves can been placed at axiogingivofacial and axiogingivolingual point angles.

21. 3) INCISAL RETENTION COVES This is placed using a Round No. 1/2 Bur at the gingivoaxio- -facial point angle ut undermining the enamel.

22. 4) LINGUAL DOVETAIL # It is placed on the lingual surface of the teeth in teeth with large preparation, especially those with excessive incisal extension in which additional retention form is needed.

23. FINISHING EXTERNAL WALLS # Finishing of minimally extended margins is recommended by using a hoe. # If the gingival margin is in enamel, a slight bevel is necessary to ensure full length enamel rods (Approx. 20 ° ).

24. CLASS III COMPOSITE RESTORATION

25. CONVENTION CAVITY PREPARATION BEVELED CONVENTIONAL PREPARATION MINIMALLY INVASIVE PREPARATION

26. CONVENTIONAL CAVITY PREP. Indication P reparation is necessery on the root surface Cavity forming features:  Box shape  depth: 0 . 75mm on root, 0 . 2mm in dentin  90° cavosurface margin is requied  Groove retention can be prepared 0 . 25mm into the dentin of the axiogingival line and incisoaxial line  dovetail extension

27. BEVELED CONVENTIONAL PREP Indication R eplacing 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 .

28. MINIMAL INVASIVE PREPARATION INDICATION small and moderate lesions or faults CAVITY FORMING FEATURES  designed to be as conservative as possible  walls extent only of the fault or defect area  no specific shapes or forms  no groove retention but bevel the enamel

29. LINGUAL VS FACIAL APPROACH Lingual approach is preferable  The facial enamel is conserved for enhanced aesthetics.  Some unsupported enamel may be left on the facial wall  Colour matching of the composite is not as critical

30. Indications for a facial approach include  The carious lesion is positioned facially  The teeth are irregularly aligned, making lingual access undesirable  An extensive carious lesion extends onto the facial surface

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