Effect of access design on angle, radius and location of the primary canal curvature in Type IV mandibular molars

Aims This study assessed the effect of access design on angle, radius, and location of primary canal curvature in mesial roots of Type IV mandibular molars at different phases of root canal preparation. Methodology Twenty-four teeth were selected radiographically and via μCT and accessed with contracted (CEC; n = 12) or traditional endodontic cavity (TEC; n = 12) designs. Angle, radius, and location were determined at: pre-instrumentation (PI), glide path (GP) and after final instrumentation (FI). GP was established with #1 and #2 PathFiles. FI was performed to a 30.04 Profile Vortex. Irrigation was performed using 8.25% NaOCl and 17% EDTA. Time required for complete instrumentation was recorded. A standardized apparatus was used to reposition samples at each phase and a radiograph was taken in maximum curvature view. Changes in the angle, radius, and location were measured with ImageJ. Data was analysed with two-way repeated-measures ANOVA (α < 0.05) and Tukey HSD tests. Results The mean angle decreased at the different phases (P < 0.001) for both CEC (PI: 42.57 ± 8.00; GP: 36.27 ± 4.50; FI: 32.61 ± 5.17) and TEC (PI: 38.80 ± 7.15; GP: 33.76 ± 7.83; FI: 30.08 ± 6.99). Curvature location moved apically at GP and FI (P < 0.001). The changes in angle and location were greater from PI to GP than GP to FI (P < 0.0001). The radius of curvature increased at GP and FI (P < 0.0001). Time required for root canal instrumentation in the CEC group (83.17 ± 6.71 min) was significantly longer than for the TEC group (33.18 ± 9.20 min; P < 0.0001). Access design did not show a significant difference in the evaluated canal curvature parameters (P > 0.05). Conclusions The angle, radius, and location changed at glide path and after instrumentation independent of the access design for the type of teeth and instrumentation protocol used in this study. Instrumentation through CEC took 2.5 times longer than TEC designs.