Analysis of isthmus cleaning in mesial canals of mandibular molars after the use of different auxiliary substances and agitation protocols

Abstract

The aim of this study will be to evaluate, through scanning electron microscopy (SEM), the cleaning and remaining material of isthmus in mesial canals of mandibular molars using two solutions, 2.5% NaOCl and 2% chlorhexidine gel, with four different agitation protocols: Passive ultrasonic agitation (PUI) with an ultrasonic insert, with the EQ-S device, with the XPendo Finisher file and with an Easy-Clean file. The fifth group with irrigation of 0.9% saline solution without agitation will be performed as a control (n=10). One hundred permanent human mandibular molar teeth (first and second molars) from patients without distinction of sex and age group between 30 and 60 years will be used, with the following inclusion factors: teeth with no endodontic treatment, without cavities up to the root region and with complete root formation. The collected teeth will be stored in 0.9% saline until the beginning of the tests. To confirm the presence of isthmuses and that they are included in types II,II,V,VI, and VII of the classification of Vertucci (1984), at 2, 4, and 6 mm from the apex, the canals will be previously evaluated by means of computerized microtomography (micro-CT). After the coronary opening, the teeth will be inserted inside an aluminum muffle and filled with transparent epoxy resin until the cement enamel junction. After resin polymerization, the muffle will be opened and the resin block with the tooth will be removed. Then, with the aid of a diamond disk, 0.3mm thick, coupled to a precision cutting machine, 3 cuts will be made in the marks of the samples previously made, corresponding to 2, 4, and 6 mm from the root apex. The sections will be inserted again into the muffle for instrumentation with the Reciproc R25 and Mtwo 35/04 system. Then, the block will be removed from the muffle and the teeth will be randomized and divided into 2 groups: 2.5% NaOCl and 2% Chlorhexidine gel with 4 different types of cleaning protocols plus the control group, all involving irrigation with a syringe and 30-gauge needle. In all groups, the 3 sections in each of the teeth, which correspond to 2, 4, and 6mm from the root apex, will be removed from the muffle and will be analyzed under a scanning electron microscope (SEM) in low vacuum mode. The entire sample will be analyzed at four different times: before instrumentation, after the first, second, and third cycle of agitation, totaling four images for each tooth. The images will be analyzed in the Image J software and the calculation will be made, in percentage, of the total area of debris in the canals and isthmuses after instrumentation and after each process with and without agitation. To verify the normality of the data, the Shapiro-Wilk test will be used, followed by further interpretations using statistical tests for intragroup and intergroup analysis, with a significance level of 5%. (AU)