Fragment-bonded Teeth: Effect of Preservation Environment on Shear Bond Strength

Materials & Methods: Seventy-two mandibular incisors were collected and divided into 6 groups of 12. The samples in 5 groups were fractured at the middle one-third, and the apical parts of the rest of the teeth were dipped in normal saline. The environments where the fractured parts were kept in the first to fifth groups were normal saline, water, milk, saliva, and a dry environment, respectively. Healthy teeth, or the sixth group, were regarded as the positive control group. After the fractured portion of the tooth had been kept in the intended environment for 24 hrs, all parts were bonded to the apical parts of the related groups by a bonding agent (Single Bond) and a flowable composite resin. The force required for fracture was measured by a universal testing machine, and analyzed by ANOVA and Tukey statistical tests.

Results: The forces required to fracture the teeth in the first to sixth groups were 239.4, 231.2, 347.2, 328.6, 205.4, and 693.3 Newtons, respectively. Statistical analyses indicated that, among the various groups under study, there was a significant difference (p value < 0.001). The highest and the lowest required forces for fracture were related to the sixth and fifth groups, respectively. The forces required for fracture in the third and fourth groups were significantly higher than those for the first, second, and fifth groups, and the sixth group had the highest fracture force of all, with a significant difference.

Conclusion: This study indicated that the force required to fracture restored teeth is affected by placing the fractured parts in various environments before bonding.