class 13 - Class IV cavity prepartion for composite materials - indications, stages of cavity preparation

what is class IV cavity?

• proximal surfaces of anterior teeth that involve the incisal edge

indications of Class IV cavity preparations for composite materials

• fractures

• ideal for composite restoration to preserve remaining tooth structure

• previously treated with porcelain crowns - composie offers a more conservative alternative

• good isolation possible

• aesthetics is of concern

contraindications of Class IV cavity preparations for composite materials

• same as class III: poor isolation, or margin on root surfaces

Stages of preparation of class IV cavity for composite material

Initial stage

1. Outline form and initial depth - shape dictated by caries/defect extent

2. Primary resistance form - preserve strong tooth structure

3. Primary retention form - bonding to etched enamel/dentin; grooves rarely needed

4. Convenience form - allow adequate access for instruments

Final stage

5. Remove remaining caries or old materials

6. Pulp protection, if needed

7. Secondary resistance/retention - retention grooves only if on the root surface

8. Finishing walls - create smooth transitions

9. Final cleaning and inspection

Modified type of Class IV preparation (for small defects)

• no defined shape - ‘scooped’ out with minimal extension

• Done with a small round or flame-shaped bru (roughens enamel surface)

Bevelled conventional type of Class IV preparation (for large restorations)

• 45 degree bevels on all accessible enamel margins using flame-shaped or round diamond

• Bevels width: 0.25 to 2mm, depending on amount of tooth structure missing and retention required

• May include gingival retention grooves or incisal coves in large restorations

• Bevels provide retention for large restorations by increasing the surface area for etching and bonding

Conventional type of Class IV preparation

• used only when margins extend onto root surfaces

• Treated like amalgam slot only preparation form with butt joints, 90 degree cavosurface, retention grooves in dentin, 0.2mm in dentin initial depth

• Coronal portion may be done in a modified manner or beveled conventional manner while the portion extending onto the root surface must be prepared as conventional

Avoid pin retention unless a large amount of tooth structure is missing!!!!

Pins risk perforation, discolouration, do not strengthen composite and can corrode