Critical Instrumentation Area: Influence of Root Canal Anatomy on the Endodontic Preparation

Abstract

The aim of this study was to evaluate the root canal anatomy of mandibular incisors before and after endodontic instrumentation, identifying regions inaccessible to the action of files (Critical instrumentation Area - CA) in a three-dimensional perspective. Thirty human mandibular central incisors were selected, assigned to two groups (n=15) and instrumented using ProTaper Universal rotary files. In the RX group, longitudinal digital radiographic images were obtained in the buccolingual (BL) and mesiodistal (MD) views. In the CT group, cross-sectional micro-computed tomography (µCT) images were obtained at 3, 9 and 15 mm from the apex. The canal area of the specimens was evaluated before and after instrumentation using digital images from each group. Data were analyzed using t-test, one-way ANOVA with subdivided parcels and Tukey's test (α=0.05). The canal area found in the MD radiographs was larger than in the BL radiographs, which was also confirmed in the transversal images (p<0.01). The CA was only detected in the MD radiographs and µCT scans. On the root canal configuration, a continuous reduction in the canal conicity was observed in BL radiographs, while in MD view there was a constriction at the cervical third and subsequent increase at the middle third (p<0.01). The conical shape of the root canal was observed only in the BL view. The canal enlargement in BL radiographs was not indicative of homogeneous instrumentation, since unprepared areas (CA) were also verified on the buccal and lingual walls in different images.

Analysis of the presence of filling material in oval root canals using computed microtomography after endodontic retreatment performed by different techniques

“…Consequently, non-instrumented areas may remain on the lingual wall of the root canal. The non-instrumented regions reported in the previous study 18 , correspond to the critical instrumentation area formerly described 15 , and to the zones presenting remaining filling material found in our study. These anatomical interferences are not present only in mandibular incisors, but in all teeth with roots presenting oval shaped canals, as the distal root of mandibular molars 11 .…”

“…The interference of anatomical complexities in the capacity of instrumenting root canals was evidenced by a previous study that analyzed human mandibular incisors before and after biomechanical preparation using digital radiographs taken in the buccolingual and mesiodistal direction and micro-computed tomography sections 15 . This study has reported that after instrumentation, the canal remained without action of files in a region described as critical instrumentation area 15 .…”

“…It was clearly possible to observe that the filling remained in the areas where the canal has not been instrumented during the retreatment procedure ( Figures 3A and 3B). This fact probably occurred when trying to remove the filling material during retreatment, which was probably, pressed to these areas which are inaccessible to files or where the instruments had limited action 15 .…”

The prevalence of oval‐shaped root canals: A morphometric study using cone‐beam computed tomography and image analysis software

“…Oval-shaped canals (including oval, long oval and flat) are described as root canals whose longest diameter on the horizontal cross section is greater than the shortest diameter (3,4). Oval canals, and especially long oval and flat, are challenging for shaping and they have been the focus of many previous studies regarding the techniques for their instrumentation (2,(5)(6)(7)(8)(9)(10). In order to choose adequate instruments or shaping techniques, clinicians need to be familiar with the expected shapes of root canals (11).…”

Response to comments on to our published article entitled: ‘Comparison of ProTaper, RaCe and Safesider instruments in the induction of dentinal microcracks: a micro‐CT study’

“…Evaluation of microcracks at 1 mm intervals can give satisfactory and comparable results. Several micro-CT studies evaluated shaping effects of various instrumentation systems only on particular sections (Ceyhanli et al 2014, de Oliveira et al 2014, Vallaeys et al 2014. Observation of 700-900 slices per tooth is time consuming and expensive.…”