The biomechanical role of periodontal ligament in bonded and replanted vertically fractured teeth under cyclic biting forces / 国际口腔科学杂志·英文版

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.

Effect of curing modes on knoop hardness and microtensile bond strength of two dentin adhesives / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluated the effect of curing modes and light-cure times on knoop hardness (KH) and microtensile bond strength (µTBS) of dentin adhesives in vitro.</p><p><b>METHODS</b>Twenty molars were made into 80 dentin slices (about 1 mm thick). The dentin slices were prepared with an etch&rinse adhesive A (ONE-STEP PLUS) and a self-etch adhesive B (Clearfil SE Bond), and light-cured respectively under fast mode, i.e.1250 mW/cm(2) light intensity for 10 s, 15 s, 20 s, and ramp mode (soft start curing mode), i.e.initial 0 mW/cm(2) gradually increasing to 1250 mW/cm(2) in first 10 s, then steady for the next 10 s. The prepared dentin slices were kept in dark dry room for 24 h at 37°C, and KH were tested. The other 40 molars were flattened to expose coronal dentin, prepared with adhesives as above. Then the prepared teeth were restored with resin composites incrementally and cured under fast mode. The restored teeth were stored in water for 24 h at 37°C, and slowly sectioned to obtain multiple bonded beams. After 7 d water-storage, the samples received microtensile bond test, and the failure models of beams were observed under a stereomicroscope. Data were analyzed by ANOVA and LSD test (α = 0.05).</p><p><b>RESULTS</b>No statistical difference in KH [(28.20 ± 5.36), (29.13 ± 5.60), (28.13 ± 4.40), (27.06 ± 3.77) MPa] and µTBS [(22.30 ± 5.07), (22.73 ± 6.59), (26.32 ± 6.17), (25.67 ± 4.31) MPa] of adhesive A were found between four curing conditions (fast mode for 10 s, 15 s, 20 s and ramp mode for 20 s) (P > 0.05). In adhesive B, KH of Fast 20 s [(28.23 ± 3.67) MPa] were significantly higher than those of Fast 10 s [(14.15 ± 2.24) MPa] and Fast 15 s [(17.63 ± 2.17) MPa] (P < 0.05). The µTBS of Fast 20 s [(42.52 ± 3.59) MPa] were significantly higher than those of Fast 10 s [(24.21 ± 3.60) MPa], Fast 15 s [(22.25 ± 4.16) MPa] and Ramp 20 s [(31.12 ± 5.40) MPa] (P < 0.05). In Fast 20 s and Ramp 20 s modes, there were no statistical difference in KH of adhesive A and B, while µTBS of adhesive B were higher than that of adhesive A(P < 0.05).</p><p><b>CONCLUSIONS</b>As for different type dentin adhesives, the appropriate curing time in fast mode is different, and ramp mode (soft start curing mode) has no advantage over fast mode.</p>