Effect of citric acid application on removing three types of calcium hydroxide and adhesiveness to root dentin

Calcium hydroxide （Ca（OH）2） has been generally used for root canal dressing, however, the remnants of calcium hydroxide reduce the sealing ability of resin-based-sealer. The purpose of this study was to investigate the efficacy of 10% citric acid and 3% ferric chlorite （10-3 solution） on removing three types of calcium hydroxide, and adhesion to root dentin. For experiment 1, extracted human teeth were split longitudinally （crown-to-root direction） into halves. After 300μm groove were prepared, those were reconstituted and fixed. The reassembled root canal was filled with Vitapex® （Vitapex group）, Calcipex planeⅡ® （Calcipex group） or Ca（OH）2 mixed with distilled water. （Reagent group） This was stored for 1 or 4 week at 37℃ in 100% humidity and ultrasonically irrigated with ultrasonic file #50 for 60s and the following irrigants, 10-3 solution for 60s and 10% sodium hypochlorite for 30s. The percentage of Ca （OH）2 remnants area was measured microscopically with 40 magnification and was calculated. The dentin surface of the root canal and gap was examined by SEM. For experiment 2, the reassembled root canal was filled with Calcipex planeⅡ®（Calcipex group） or Ca（OH）2 mixed with distilled water （Reagent group）. This was stored for 1 or 4 weeks at 37℃ in 100% humidity and ultrasonically irrigated in the same way. A control group root canal was not dressed. A Micro tensile bond strength （MTBS） test and a dye penetration test were employed to evaluate dentin bond strength and leakage between 4-META/MMA-TBB resin sealer （SBS） and the dentin surface of each group. The results were that the percentage of Ca（OH）2 remnants area in the reagent group was lowest and the Vitapex group was highest among all groups at 1 and 4 weeks. The percentage of Ca（OH）2 remnants area in each groups at 4 weeks were a little higher than at 1 week. MTBS of the Calcipex group was significantly less than each of the Reagent group or the Control group. Dye penetration distances of the Calcipex group was significantly more than in the Reagent group and the Control group. No statistically significant difference was found between the Reagent group and the Control group in the MTBS test and the dye penetration test. The viscosity of agents in Vitapex® and Calcipex planeⅡ® might be influenced by removing calcium hydroxide and adhesion. Therefore, it is suggested that Ca（OH）2 mixed with distilled water can be effectively removed and the adhesiveness to root dentin can be recovered.