Influence of conservative endodontic access cavities on instrumentation of oval-shape straight root canals.

Aim To evaluate the influence of the design of endodontic access cavity on the percentage of unprepared areas of canal walls and flexural fatigue of the instrument activated by reciprocating movement in oval-shaped straight canal. Methodology Forty two mandibular incisors with oval canals were scanned by a computerized microtomography (MicroCT) device for homogeneous selection and distribution of the samples. Then, the teeth were divided into two groups (n = 21) according to the design of access cavity being tested: ultraconservative endodontic access cavity (UltraAC) and traditional access cavity (TradAC). The canals were accessed with the aid of a surgical microscope, instrumented with the WaveOne Gold Medium system, and irrigated with 2.5% NaOCl and 17% EDTA. The unprepared areas of the canal wall were analyzed by overlaying images before and after instrumentation and expressed as percentages. MicroCT data were analyzed using T-test, Mann-Whitney, and Wilcoxon tests. The endodontic instruments used in the instrumentation were subjected to static flexural fatigue testing using an artificial stainless steel canal with a 60 ° angle of curvature and a radius of 5 mm, located 5 mm from the tip of the instrument. The instruments were activated until a fracture occurred, and the time in seconds for the fracture was recorded using a digital timer. The number of cycles to fracture (NCF) was calculated and analyzed statistically. For flexural fatigue data, an ANOVA test complemented by a Tukey's range test was used. The significance level of 5% was used for all analyses. Results There was no significance difference between the groups related to unprepared areas by the instrument during canal preparation (p> 0.05). The difference in flexural fatigue resistance between the groups were not significant. Conclusion The use of UltraAC did not interfere with the canal instrumentation of mandibular incisors with straight and oval canals. There was no difference in the flexural fatigue resistance of the instruments in relation to access cavity design.