A study on the fracture strength of collarless metal-ceramic fixed partial dentures

Abstract

Purpose: The objective of this study was to evaluate fracture strength of collarless metal-ceramic FPDs according to their metal coping designs.

Materials and methods: Four different facial margin design groups were investigated. Group A was a coping with a thin facial metal collar, group B was a collarless coping with its facial metal to the shoulder, group C was a collarless coping with its facial metal 1 mm short of the shoulder, and group D was a collarless coping with its facial metal 2 mm short of the shoulder. Fifteen 3-unit collarless metal-ceramic FPDs were fabricated in each group. Finished FPDs were cemented to PBT (Polybutylene terephthalate) dies with resin cement. The fracture strength test was carried out using universal testing machine (Instron 4465, Instron Co., Norwood MA, USA) at a cross head speed of 0.5 mm/min. Aluminum foil folded to about 1 mm of thickness was inserted between the plunger tip and the incisal edge of the pontic. Vertical load was applied until catastrophic porcelain fracture occurred.

Results: The greater the bulk of unsupported facial shoulder porcelain was, the lower the fracture strength became. However, there were no significant differences between experimental groups (P > .05).

Conclusion: All groups of collarless metal-ceramic FPDs had higher fracture strength than maximum incisive biting force. Modified collarless metal-ceramic FPD can be an alternative to all-ceramic FPDs in clinical situations.

Keywords: Collarless metal-ceramic fixed partial denture; Fracture strength; Modified collarless coping; Porcelain margin.

Fig. 1

The prepared specimen and copper anodes. A: Abutments fixed in stone, B: Copper anodes.

Fig. 2

Fabricated injection mold. A: Abutment part of mold, B: Assembled mold, C: Base part of mold.

Fig. 3

A: Group A, B: Group B, C: Group C, D: Group D, E: Duplicated PBT resin die, F: Four groups of metal-ceramic FPDs.

Fig. 4

A: Fabricated 60 metal-ceramic FPDs, B: Cemented FPDs.

Fig. 5

Fracture strength test. A: Load stylus, B: Stabilizing jig, C: Specimen with jig, D: Loading test.

Fig. 6

Fracture strength of metal-ceramic fixed partial dentures when subjected to vertical load application on the middle pontic.

Fig. 7

Fractured metal-ceramic fixed partial dentures. A: Group A, B: Group B, C: Group C, D: Group D.

Fig. 8

Fracture patterns of FPDs. A: Group A, B: Group B, C: Group C, D: Group D.

Fig. 9

Variants of fractures. A: Group A, B: Group B, C: Group C, D: Group D.

Fig. 10

Graphs during fracture test.