The effect of combination of mechanical and chemical enlargement through the root canal on sealability of vertical root fracture gap using 4-META/MMA-TBB resin

The basic conservative treatment of a vertical root fracture is bonding and sealing the gap of the root fracture. It is difficult to seal the gap completely from the root canal side. Grinding the gap wall using an ultrasonic endodontic file from the root canal side improves sealability of the gap However, there may be excessive and insufficient grinding. It is possible that dissolving the root canal wall with 10% citric acid 3% ferric chloride solutions （10-3） and 10% sodium hypochlorite （NC） enlarge a region that is difficult for mechanical expansion. The purpose of this study was to evaluate the sealability after enlarging the gap of a root fracture with a chemical method and together with an ultrasonic endodontic filing and chemical agents. In the first experiment, 1 millimeter thick dentin pieces were cut out from extracted human teeth, fractured in the direction of tooth axis, restored to the original position, and held. The gaps were treated by 10-3 for five minutes and NC for two minutes one time （one time group）, three times （three time group） and no time （control group）. In all groups, gaps were bonded using 4META/MMA-TBB resin （Super Bond） to seal the fractured gaps. All pieces were then tested by dye penetration tests and the gaps were microscopically measured. In the second experiment, extracted human teeth were fractured vertically and restored. The gaps were treated by the following methods. 1） not treated （control group）, 2） ground from the root canal wall side with an ultrasonic endodontic file, until the Root ZX reading showed 1.0 （grinding group）, 3） treated by 10-3 for 5 minutes and NC for 2 minutes three times （chemical group）, 4） treated by 3rd method after grinding by 4th method （combination group）. In all groups, gaps were sealed using Super Bond, tested by dye leakage tests, and microscopically measured. In the first experiment, enlarged width was significantly larger in the three times group than in the control and one time group. The rate of dye penetration was significantly smaller in the three times group than in the control and one time group. In the second experiment, the rate of dye penetration was significantly statistically smaller in the combination group than the other groups. These findings indicate that the combination of a chemical method and a mechanical method with the ultrasonic endodontic file in the gap of root fractures is effective to enhance the sealability of the fractured gap while preventing over grinding.