Class I restoration - National University 1 and II amalgam.pdf · Preserve marginal ridge. ... The...

Class I restoration

- Gain access to caries.

- Removal of all carious lesions.

- Cut away all significantly unsupported enamel.

- Extended margins so that they are accessible for

instrumentation and Cleaning.

Obtaining Outline Form

Obtaining Primary Resistance Form

Obtaining Primary Retention Form

Obtaining Convenience Form

Removal of Remaining Carious Dentin

Obtaining Secondary Resistance & Retention Form

Providing Pulp Protection

Finishing of Enamel Walls & Margins

Performing the Toilet of the Cavity

Achieved by:

• Placing the preparation margins in places they

will occupy in the final restoration.

• Preparing an initial depth of 0.2-0.8 mm

pulpally at the DEJ.

• Removal of caries.

Extent of caries. Esthetics. Occlusal relationship.

out line form: Small and conservative.

As narrow as possible: Sufficient width to

include the defect To permit insertion of

small condenser.

Preserve cuspal strength.

Preserve marginal ridge.

Minimize faciolingual extensions.

Connect 2 close lesions.

Restricting the depth into dentine 0.2-0.8 mm.

All weakened enamel should be removed. All faults should be included. All margins should be placed in position to

afford good finishing.

If two pits or fissure preparations in close proximity it is wise to prepare each cavity separately.

Pulpal floor cut at right angle to long axis of the tooth, but where are cusp is shorter than the other e.g. first premolar pulpal floor is sloped to paralleled the cusp heights.

The mesial and distal walls adjacent to the marginal ridges should not undermine the enamel.

Facial and lingual surfaces are prepared so their internal walls will parallel the outer tooth surface.

All internal line angles should be rounded to provide distribution of stresses.

The cavo-surface line angles should be round to remove any unsupported enamel.

The preparation wall should be at right angle to the enamel,

▪ Provide a butt joint

▪ Maintain a maximum edge strength of enamel and amalgam.

A 90-degree enamel margin on the occlusal surface will withstand occlusion

An acute cavosurface margin of enamel has the potential for fracture,

Retention form:

The box form: the preparation walls should be cut nearly at right angle to the flat pulpal floor.

To retain the amalgam restoration, the facial and lingual must be conveying occlusally.

Can be obtained by: The pulpal floor should be flat and cut below the

DEJ (1 mm) to ensure:

Removal of caries

To provide adequate depth for the filling.

Dental amalgam resist compressive forces far better than shear or tension forces.

Removed soft peripheral dentine .

Pulp caries should be removed with excavator, bur should not be used.

No cutting towards the pulp until the preparation is completed to prevent contamination of

exposure to occur.

Hard stained or discolored dentine in the pulpal floor should be left, if is so in close proximity to the pulp.

Deep carious dentine can be left and pulp capping is done.

Convenience form: Finishing of the enamel margin:

Two main factors controls the steps

▪ The direction of enamel rods.

▪ The edge strength at restorative material.

The enamel walls of the preparation must be cut so that all enamel prisms are supported by sound dentine.

Ideal and strongest enamel margin is formed by full-

length enamel rods (a) resting on sound dentin supported

on preparation side by shorter rods, also resting on sound

dentin (b).

Proximal caries, at or gingival to contact area, Not involving occlusal surface (single class II).

Extension from a pit and fissure, considered as compound/ complex preparation.

Class II restorations.

Exceptions for need to involve occlusal surface in single class II preparation:

Where adjacent tooth is missing

Where the lesion is exactly in cementum

As temporary procedure

Class II preparation consists of: Occlusal lock Proximal box▪ Pulpal floor▪ Axial wall▪ Gingival floor▪ Lingual wall▪ Facial wall

Tooth preparations for amalgam filling are best considered under three headings: Position of gingival margin. Position of embrasure wall. Position of occlusal dove tail.

Convergent walls specially in the cusp areas.

Flat pulpal floor/ parallel to occlusal surface.

Pulpal floor below DEJ (1 mm). Rounded line angles. Cutting dovetail or lock to prevent

displacement in the direction of the missing walls.

The gingival dentine floor is slightly inclined in an apical direction: To remove any unsupported enamel. To reduce the stress at the isthmus area

Retentive grooves are cut in the facial and lingual embrasure walls, extend up from gingival floor to level of pulpal floor.

Use taper fissure bur to avoid pulp exposure.

• The use of a "proxitector“ (matrix band) for protection of adjacent tooth during proximal cavity preparation.

Axial wall, cut parallel to long axis of the tooth.

Axio-pulpal line angles, beveled to provide additional bulk of the restorative material

Area joining occlusal lock with proximal box.

Dimensions of the isthmus are balance between adequate depth, without risking pulpal exposure (1.5 mm) and adequate width without weakening the cusp (⅓ - ½ distances between cusps).