The biomechanical role of periodontal ligament in bonded and replanted vertically fractured teeth under cyclic biting forces

After teeth are replanted, there are two possible healing responses: periodontal ligament healing or ankylosis with subsequent replacement resorption. The purpose of this study was to compare the fatigue resistance of vertically fractured teeth after bonding the fragments under conditions simulating both healing modes. Thirty-two human premolars were vertically fractured and the fragments were bonded together with Super-Bond C&B. They were then randomly distributed into four groups (BP, CP, CA, BA). The BP and CP groups were used to investigate the periodontal ligament healing mode whilst the BA and CA groups simulated ankylosis. All teeth had root canal treatment performed. Metal crowns were constructed for the CP and CA groups. The BP and BA groups only had composite resin restorations in the access cavities. All specimens were subjected to a 260 N load at 4 Hz until failure of the bond or until 2×106 cycles had been reached if no fracture occurred. Cracks were detected by stereomicroscope imaging and also assessed via dye penetration tests. Finally, interfaces of the resin luting agent were examined by scanning electron microscope. The results confirmed that the fatigue resistance was higher in the groups with simulated periodontal ligament healing. Periodontal reattachment showed important biomechanical role in bonded and replanted vertically fractured teeth. The success of replanting vertically fractured teeth depends on crown restoration and healthy periodontal tissues. Using 40 upper first premolar teeth that had been extracted from adolescents for orthodontic reasons, a team led by Wen-Mei Wang from Nanjing University Medical School, China, split each tooth in two, creating vertical fractures. The researchers rejoined the halves with a bonding resin and applied metal crowns to half the teeth. To simulate the two kinds of replantation that can occur, they either attached a layer of silicone rubber to mimic periodontal ligaments or attached epoxy resin as a stand-in for bone. The researchers then applied cyclic forces to reproduce the repeated stress of chewing and found that crown restoration and repaired periodontal fibers are both important for the long-term health of vertically fractured teeth.