Class II Cavity Preparation

Question 1

What is class II cavity?

Answer 1

Cavities occurring on the proximal surfaces of posterior teeth

Question 2

Armamentarium?

Answer 2

• no. 245 tungsten carbide bur for the preparation of the occlusal and proximal cavity
• no. 169 L tungsten carbide bur for the placement of the retention lock in the proximal box.

Question 3

Preoperative vidualization of the outline form?

Answer 3

It is important to visualise the outline form including the proximal flare of the proposed cavity preparation keeping in mind the following parameter:

• width and depth of the carious lesion
• position of tooth in relation to the adjacent teeth
• type of contact

Question 4

Draw the preoperative visualisation of tooth preparation extension when caries is present gingival to the medial proximal contact and in the central groove area for
(A) Rotated tooth
(B) open proximal contact
(C) normal relationship

Answer 4

Page 289

Question 5

Preparation steps of Class II cavity?

Answer 5

1. Occlusal step

2. Proximal box

Question 6

Occlusal step?

Answer 6

Basic feature similar to class I cavity. Additional characteristics including

1. Occlusal dovetail
   - given on the non-involved proximal margin
   - enhance retention form
   - prevents displacement of the completed restoration towards the involved proximal side.
2. Proximal flare
   - it is determined by the extend of the caries and the contact with the adjacent tooth
3. Reverse curve
   - the external outline of the occlusal surface where the isthmus joins the buccal proximal flare is often in the form of a straight line. Reverse curve is a concave curve made by offsetting the outline form of the isthmus and proximal outline form in a buccolingual direction.
   - this S-shaped curve helps in conserving the facial cusp structure and is given on the buccal side of the cavity.

Question 7

Proximal box

Answer 7

A. Placement of the bur

• bur is placed over the dentinoenamel junction in the pulpal floor adjacent to the affected proximal margin.
• initial orientation of the bur is maintained.
• bur is placed 2/3rd at the expense of dentin(0.5-0.6mm) and 1/3rd at the expense of enamel (0.2-0.3mm)

B. Creating the ditch out

• pressure on the bur directly gingivally, facially, and lingually along the dentinoenamel junction helps in creating the ditch out.
• the preparation is deepened gingivally until the bur falls into soft carious dentin.

C. Gingival floor location
- this is determined by the gingival extent of carious lesion and /or by the level necessary to provide separation of gingival margin from the adjacent tooth.

Question 8

Outline form?

Answer 8

1. Inclusion of all pits and fissure along with gently flowing curves
2. Circumventing of cusps
3. Appropriate extent of proximal flare

Question 9

Primary resistance form?

Answer 9

1. Flat pulpal and gingival wall
2. Reverse curve
3. Roundening the axiopulpal line angle to reduce stress concentration
4. Providing depth to accommodate sufficient bulk for the restorative material
5. Bevelling of gingival cavosurface margin

Question 10

Primary retention form?

Answer 10

1. Occlusal convergence

2. Dovetail