Fracture resistance of the undermined cavities filled with composite resin

Objectives: The purpose of this study was to compare the fracture resistance of resin restoration of buccally undermined cavity according to the remained thickness of the occlusal tooth structure with non-cavitated natural tooth.

Methods: Forty extracted sound upper molars were randomly divided into four groups. After flattening the occlusal enamel, undermined cavity from the buccal surface was prepared in thirty teeth (Group I~III). Another non-cavitated ten teeth (Group IV) were used as a control group. In Group I, remained occlusal thickness was about 1mm, which was composed of mainly enamel and small amount of dentin. In Group II, remained thickness was about 1.5mm, which was composed of 1mm enamel and 0.5mm dentin. In Group III, thickness was about 2mm in which 1mm of enamel and 1mm of dentin were remained. All the cavity have the 5 mm mesio-distal width and 7 mm bucco-lingual depth. It was tried to keep the remaining dentin thickness about 0.5mm in cavitated groups with a radiographic evaluation.

The cavities were restored with composite resin (Z-250) according to the maunfacturer's instructions and the teeth were embedded in acrylic with occlusal surface horizontally positioned. Then the occlusal surface of the specimen was loaded to the long axis of the tooth in an universal test machine until fracture occurred.

Results: No significant difference in fracture resistance of composite resin restoration was found between groups. The control teeth without cavity showed a greater fracture resistance than cavitated and restored teeth.

Conclusion: The fracture resistance of the undermined cavity filled with composite resin was lower than the control teeth. However, sound tooth structure may be supported and saved by the composite resin filling, even though the remaining area consist of mainly enamel and a little dentin structure.