essay 11 - Class 1 and Class II cavity preparation for composite materials - indications, critical analysis stages of preparation, retention

describe composite

• a material that is sufficient strength for Class I and II restorations. It is insulative and in most cases does not require pulpal protection with bases. Because composite is bonded to the enamel and dentin, tooth preparations for composite can be very conservative. A composite restoration not only is retained well in the tooth, but also strengthens the remaining unprepared tooth structure.

Indications of class I and II preparation for composite materials

1. small to moderate restorations - especially with enamel margins

2. Posterior premolars and first molars - when aesthetics are a concern

3. Restorations without full occlusal contacts - to reduce load

4. Teeth without heavy occlusal stress

5. Cases with good isolation - moisture control is critical for bonding

6. Foundations for crowns - in some cases

7. Large restorations - to strengthen remaining tooth structure (economic/clinical reasons)

Contraindications for class I and II preparation for composite materials

1. Inability to isolate the operating site

2. Heavy occlusal stress or bruxism

3. All occlusal contacts falling solely on the composite

4. Restoration margins extending onto the root surface

The preparations types

1. Conventional - in cases which need increased resistance form, large restorations subjected to heavier occlusal loads

2. Bevelled conventional

3. Modified (most conservative) - for small to moderate restorations

Note: Bevelled conventional is rare for class I/II; more often used for groove extensions.

Prevention of Extensions! Facial and lingual extension and width are dictated by the caries, old restorative material or fault

Conventional Prep (for larger lesions)

• Entry with inverted cone bur, parallel to long axis at the distal pit of the area of faulty occlusal surface (permits better vision for operator)

• Depth: 1.5mm from central groove

• Flat pulpal floor that follows DEJ contours

• Cusp and ridge extensions should be minimal

• Groove extensions should have an axial depth of 0.2mm inside DEJ

• No occlusal bevels, to avoid thin composite margins in areas of heavy occlusal contacts

• Enamel rods are exposed naturally - no need for bevelling

• Retention: occlusal convergence of walls

Only cavitated carious lesion is prepared in the above described manner, the adjacent less involved areas should be included more conservatively with sealants or minimally invasive preparations.

Modified preparation (small lesions)

• Scooped-out, rounded preparation, less specific form

• No defined flat floors or sharp angles

• uses small round or inverted cone burs

• Pulpal depth: 1.5mm or 0.2mm inside DEJ, not always uniform

• Used when caries or defects are minimal

What are some retention features used when using composite?

• Composite is micro mechanically bonded to tooth structure

• Retention is chemical and micromechanical via:

— Etching and bonding agents

— Surface roughness from diamond or carbide burs

• Walls often converge occlusally for mechanical interlock (conventional)

• Bevelling of enamel margins (especially on facial/lingual groove extensions) increases bonding surface

• DO NOT bevel occlusal walls, especially in load-bearing areas

What are some key concepts to remember?

• Prevention of extension: Only the cavitated areas are prepared. Adjacent suspicious fissures are sealed, not cut

• No bevels on occlusal margins; bevelling is only done where it benefits adhesion and aesthetics

• Modified preps are the most conservative, following caries removal

• Proper instrument selection (inverted cone, round, or diamond) affects prep form and retention