Fracture strength of fragment-bonded teeth. Effect of calcium hydroxide lining before bonding

To measure, in vitro the strength of intact teeth, fracture-bonded teeth, and fracture-bonded teeth bonded after a preliminary calcium hydroxide lining of the dentin part of the remaining tooth.

The study used 30 young, similarly aged sheep incisors. Twenty incisors were fractured 2.5 mm from the incisal edge and another 10 incisors remained non-fractured and served as control (Group 1). Group 2 comprised 10 fractured incisors, which after 3 weeks water storage were bonded by use of acid etching and a dentin bonding agent. In Group 3, the root part of 10 fractured incisors were lined with calcium hydroxide and kept in water for 3 weeks. Then the lining was removed with a hand instrument before bonding as above. The strength of the teeth in Groups 1-3 was measured and the mean fracture strengths representing the three groups were compared by Newman-Keuls' multiple range tests at a 5% level of significance.

The mean fracture strength of the lined teeth (9.6 MPa) was significantly different from that of intact teeth (17.8 MPa) as well as from that of the bonded but unlined teeth (15.8 MPa). The latter two means were not significantly different. It is concluded that the use of calcium hydroxide on the fracture surfaces of fractured teeth before bonding lowers the fracture strength of the restored teeth.