Flexure strength of repaired dental composites.

A study was conducted to determine differences in flexure strength between unrepaired and repaired dental composite bars. Four groups, each consisting of 10 samples, were investigated. Group A consisted of unrepaired samples, while groups B-D consisted of samples which had been cut to lengths of 17.5 mm and repaired to a total length of 35.0 mm. The cut surfaces of these samples were washed with water (group B), treated with phosphoric acid, water and bonding agent (group C), or treated with a silane-toluene solution (group D) before new material was added. The samples were stored in distilled water at 37 degrees C, and after 3 and 6 months the flexure strength of samples from each group was determined by "four-point" bending. The results showed that repaired composites were weaker than unrepaired samples. The mean strength of the silane-toluene treated group was superior in strength to that of the other two groups. This group was also least affected by exposure to water. Of the other two groups, specimens treated with the acid etch technique were superior in strength to the other group.