Elsevier

Journal of Endodontics

Volume 36, Issue 4, April 2010, Pages 703-707
Journal of Endodontics

Basic Research
Preparation of Oval-shaped Root Canals in Mandibular Molars Using Nickel-Titanium Rotary Instruments: A Micro-computed Tomography Study

https://doi.org/10.1016/j.joen.2009.12.020Get rights and content

Abstract

Introduction

This study evaluated the prepared surface areas of oval-shaped canals in distal roots of mandibular molars using four different instrumentation techniques.

Methods

Teeth were prescanned and reconstructed using micro–computed tomography (MCT) scans at low resolution (68 μm). Forty-eight molars with ribbon-shaped/oval distal root canals were selected and randomly assigned to four groups. Distal canals (n = 12 each) were prepared by circumferential filing using Hedström files to apical size #40 (group H/CF); with ProTaper nickel-titanium rotaries to finishing file 4 (F4) considering the distal canal as 1 canal (group PT/1); ProTaper to F4 considering buccal and oral aspects of the distal canal as 2 individual canals (group PT/2); ProTaper to F4 in a circumferential filing motion (PT/CF). Before and after shaping, teeth were evaluated using MCT at 34-μm resolution. The percentage of prepared surface was assessed for the full canal length and the apical 4 mm. Statistical analysis was performed using analysis of variance and Bonferroni/Dunn multiple comparisons.

Results

Preoperatively, canal anatomy was statistically similar among the groups (p = 0.56). Mean (± standard deviation) untreated areas ranged from 59.6% (±14.9, group PT/2) to 79.9% (±10.3, PT/1) for the total canal length and 65.2% to 74.7% for the apical canal portion, respectively. Canals in group PT/1 had greater untreated surface areas (p < 0.01) than groups PT/2 and PT/CF. Among all groups, amounts of treated surface areas were statistically similar in the apical 4 mm.

Conclusions

Preparations of oval-shaped root canals in mandibular molars left a variable portion of surface area unprepared regardless of the instrumentation technique used. However, considering oval canals as two separate entities during preparation appeared to be beneficial in increasing overall prepared surface.

Section snippets

Materials and Methods

From teeth that had been extracted for reasons unrelated to the current study, a total of 200 human mandibular molars were collected. Distal roots were inspected under a stereomicroscope to verify that they had only one main portal of exit. The remaining 100 molars were prescanned using MCT (μCT 20; Scanco Medical, Brüttisellen, Switzerland) at a resolution of 68 μm. Based on a slice-by-slice assessment taking the distal root apex as a reference point, the slice 6-mm coronal of the apex was

Results

Preoperatively, there were no differences regarding overall and apical canal volumes among experimental groups (p = 0.56), indicating adequate randomization. Root canal preparation of distal root canals resulted in increased volumes (p < 0.001) with no significant differences among groups. Neither a ProTaper rotary instrument nor a Hedström file fractured in any of the experimental groups.

Figure 1 shows representative examples of superimposed root canal models before and after canal

Discussion

The main aim of this study was to compare commonly recommended methods to prepare root canals with long-oval cross section based on MCT reconstructions. Distal root canals in mandibular molars represented an adequate model for the present experiment, with a mean diameter ratio of 1:3.91 even at the 6-mm level. The present data suggest that the preparation of nonround canals leaves some canal surface uninstrumented. This finding was not related to the preparation strategy, and its extent was

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