CLASS 2 FEATURES

FEATURE 1

The cavity preparation has the inverted truncated cone form, where the occlusal orifice is narrower than the pulpal and gingival floor.

What is the rationale for feature 1?

for the mechanical retention of the filling in the prepared cavity

FEATURE 2

There is an occlusal and proximal dovetail

What is the Rationale for Feature 2?

For the retention of the filling in both occlusal and proximal surfaces

FEATURE 3

The isthmus is 1/4 of the intercuspal distance (1.7 -2.0 mm for molars); (¼) of

the intercuspal distance 1.6-1.7 mm for premolars

What is the rationale for Feature 3?

to conserve tooth structure and to prevent cusp inclusion or encroachment

FEATURE 4

There is a bevel in the axio-pulpal line angle

What is the rationale for feature 4?

To remove the sharp axio-pulpal line angle which is an area of stress and fracture and to increase the bulk of the restoration in this area and thereby increase the strength of amalgam around the isthmus or neck

FEATURE 5

No bevel of the cavosurface angles or margins for amalgam. A 90° butt-joint is present in all areas.

What is the rationale for feature 5?

This will prevent fracture of the restoration margins and the production of the so called “ditched filling”

FEATURE 6

No undercuts on the existing intact wall (mesial or distal). This wall slightly diverges pulpo-occlusally

What is the rationale for feature 6?

so as not to undermine the intact mesial or distal marginal ridge which is an area subjected to a lot of stresses during the mastication and during closure into centric

FEATURE 7

The internal outline form meets the external outline form at a 90° angle. This is the so called blunt joint or butt joint margin

What is the rationale for feature 7?

To create a definite interface between cavity and restoration. This will prevent knife-edged margins of the restoration. They will fracture (prevent) later on leaving a “ditched” filling.

FEATURE 8

An S-curve or reverse curve on the buccal proximal areas.

What is the rationale of Feature 8?

to avoid undermining the mesio-buccal or disto-buccal cusp and at the same time bring about the creation of a blunt joint margin with the external surface. Provide bulk of restoration at bucco-proximal margin. Avoid feather margin.

FEATURE 9

Tooth out of contact with the adjacent tooth by about 0.5 mm in the proximal area, bucally or facially, lingually and gingivally.

What is the rationale for feature 9?

to bring the proximal areas or margins of the cavity preparation into self-cleansing area.

FEATURE 10

Cavity depth on the occlusal surface is 0.2-0.8 mm beyond the DEJ.

What is the rationale for Feature 10?

To provide adequate bulk or thickness of the restoration for resistance to biting forces and retention of the amalgam filling.

FEATURE 11

There are proximal grooves starting at the bucco-axiogingival and Linguo-axiogingivapoint angles and it goes up to where the axial wall meets the pulpal floor. This groove decreases its depth gradually to the top.

What is the rationale for feature 11?

added retention of the restoration in the proximal area and to prevent restoration creep later on

FEATURE 12

The gingival floor is placed above the crest of the healthy gingiva.

What is the rationale for the feature 12?

To free gingival wall of contact with the adjacent tooth and to bring the gingival margins into self cleansing areas

FEATURE 14

Inclusion of all deep, uncoalesced developmental grooves in the cavity preparation.

What is the rationale for RATIONALE #14?

cutting for immunity or extension For prevention of recurrence of decay

FEATURE 15

No S-curve or Reverse curve on the Linguo-proximal areas.

What is the rationale for feature 15

these areas on the lingual surface presents a wider lingual embrasure compared with the buccal area

FEATURE 16

The gingival floor has a width of about 0.8 mm in premolars and about 0.8 – 1.0 mm in molars.

What is the rationale for feature 16

to create a definite seat for the restoration following the contour or profile of the gingival surface

FEATURE 17

The axial wall is 0.2 – 0.5 mm within the DEJ and the axial wall follows or is parallel to the external contour of the tooth.

What is the rationale for feature 17

to provide sufficient separation and protection for the pulp

FEATURE 18

On upper molars where the occluso-lingual grooves are involved and a lingual extension has to be made, the cut is made at the expense of the mesio-lingual cusp, and not the disto-lingual cusp.

What is the rationale for feature 18

to prevent excessive reduction and weakening of the disto-lingual cusp

FEATURE 20

If a cusp is undermined by caries due to faulty cavity preparation, said cusp must be removed and included as a part of the cavity preparation

What is the rationale for feature 20?

remove unsupported and overhanging tooth structures cannot withstand biting stresses and the resulting strain can cause e overhang to fracture later on