RESUMEN
Objective: To compare the incidences of root cracks after canal instrumentation with HyFlex CM system and the ProTaper Universal system .Methods:Sixty mandibular incisors were mounted in resin blocks with simulated periodontal ligaments , and the apex was exposed .The control group of 20 teeth was not prepared , and the other 40 teeth were divided into 2 experimental groups ( n=20 ) .The 40 root canals of the experimental groups were instrumented using HyFlex CM and ProTaper Universal to the major apical foramen ( AF).The horizontal sections 1 mm, 2 mm, and 3 mm from the apex were observed under an optical stereomicroscope at 25 ×magnification .The presence of cracks was noted . Results:No cracks were found in the control teeth .Cracks were found in 1 of 20 ( 5%) teeth in HyFlex CM group , and 17 of 20 ( 85%) teeth in ProTaper Universal group .The difference between the two experimental groups was statistically significant (P<0.01).Conclusion: The HyFlex CM files caused fewer root cracks than the ProTaper Universal files during the root canal instrumentation .
RESUMEN
OBJECTIVES: The purpose of this study was to compare the cutting efficiency of a newly developed microprojection tip and a diamond-coated tip under two different engine powers. MATERIALS AND METHODS: The apical 3-mm of each root was resected, and root-end preparation was performed with upward and downward pressure using one of the ultrasonic tips, KIS-1D (Obtura Spartan) or JT-5B (B&L Biotech Ltd.). The ultrasonic engine was set to power-1 or -4. Forty teeth were randomly divided into four groups: K1 (KIS-1D / Power-1), J1 (JT-5B / Power-1), K4 (KIS-1D / Power-4), and J4 (JT-5B / Power-4). The total time required for root-end preparation was recorded. All teeth were resected and the apical parts were evaluated for the number and length of cracks using a confocal scanning micrscope. The size of the root-end cavity and the width of the remaining dentin were recorded. The data were statistically analyzed using two-way analysis of variance and a Mann-Whitney test. RESULTS: There was no significant difference in the time required between the instrument groups, but the power-4 groups showed reduced preparation time for both instrument groups (p < 0.05). The K4 and J4 groups with a power-4 showed a significantly higher crack formation and a longer crack irrespective of the instruments. There was no significant difference in the remaining dentin thickness or any of the parameters after preparation. CONCLUSIONS: Ultrasonic tips with microprojections would be an option to substitute for the conventional ultrasonic tips with a diamond coating with the same clinical efficiency.