Identification of Enamel Cracks during Cavity Preparation

Abstract

Purpose: It was revealed by dental microscope that there were a large number of cracks not only in tooth roots but also in tooth crowns. These cracks occurred or progressed because of cavity preparation, premature contact, injury and aging. Cracks that occur during preparation may cause postoperative pain, falling-off of the restorative materials, pulpitis, secondary caries and tooth fracture. In this study, we analyzed enamel cracks when extracted human tooth cavities were prepared by various instruments. Methods: Before all extracted teeth were used in this study, the enamel surface without cracks was observed by laser microscope (Olympus 1100). Four kinds of preparation apparatus and five kinds of burs and tips were used for cavity preparation and were compared and evaluated. The four preparation apparatuses were as follows: air turbine, micromotor, Er. Cr: YSGG laser (Waterlase C100; Biolase Technology) and supersonic wave (P-max; with each cutting apparatus made by Satelec). In all extracted teeth, a standard cavity was formed in the labial side under water to avoid the influence of quantity of water, and the influence of fever when preparing the cavity, and the generation of enamel cracks was evaluated after cavity preparation. Furthermore, to evaluate the influence of the shape of the bur (round type or cylinder type) on crack generation, a diamond bur, carbide bur and laser tips were used for preparing enamel cavities and the influence of the bur type and apparatus on crack generation around the cavity was evaluated. The burs and tips used for cavity preparation are shown below. ・Laser tip S (cylinder type, 750μm diameter), Biolase Japan ・Carbide round bur #4 (1.4 mm diameter), SS White ・Diamond fissure bur 835-012 (cylinder type, 1.4 mm diameter), Diatec ・Diamond round bur F-012XL (round type, 1.2 mm diameter), Hinatawada seimitsu MFG ・Carbide fissure bur #1557 G (cylinder type, 1.4 mm diameter), CEI All prepared cavities were observed by the Olympus 1100 laser scanning microscope and the frequency and pattern of cracks and chipping were analyzed. Results: The enamel margin of the cavity was occurred the microcrack formed by rotary preparation appliance and supersonic wave apparatus, but was not induced by the preparation with the laser apparatus. As the cavity preparation was performed by the diamond fissure burs, It was showed that was hard to produce a microcrack than a diamond round burs, and this tendency was also seen by usage of the carbide bar. Conclusion: The usage of the preparation appliance was shown to cause pulpitis and fracture of a tooth because a microcrack was generated at the cavity margin of the enamel. From this study, it was shown when we prepared with the laser appliance+laser tip and the micromotor+diamond fissure burs with the rotary preparation appliance controlled the occurrence of the microcrack.