Planning Protocol for Apical Preparation Maximizing Root Canal Wall Instrumentation and Preserving Root Dentin Structural Integrity.

Abstract

Introduction: This study developed a personalized root canal instrumentation planning protocol designed to minimize uninstrumented canal walls while preserving a remaining dentin thickness (RDT) of at least 0.5 mm and compared it with the best available planning protocol.

Methods: One hundred maxillary lateral incisors were scanned by microcomputed tomography, and 400 cross-sections were analyzed at 1, 2, 3, and 4 mm from the apical foramen. Canal diameters, aspect ratio, and minimum RDT were measured. Virtual preparation was planned using 5 nickel titanium systems (ProTaper Ultimate, Reciproc Blue, SRF Sequence MKLife, HyFlex EDM, and WaveOne Gold) individually and a new hybrid protocol allowing instruments from multiple systems and hand K-files when necessary. The primary outcomes were uninstrumented canal surfaces and an RDT <0.5 mm. Paired risk ratios, exact McNemar tests, and Bayes factors were calculated.

Results: The mean canal taper was 0.08 mm/mm, and the mean aspect ratio was 1.40 ± 0.59. Among single-system protocols, ProTaper Ultimate produced the lowest frequency of uninstrumented surfaces (215/400; 53.8%). The new protocol reduced this frequency to 52 of 400 (13.0%), corresponding to a 76% reduction versus ProTaper Ultimate (risk ratio of 4.13; 95% confidence interval, 3.20-5.34; P < .001). The hybrid protocol was also the only strategy with no sections presenting RDT <0.5 mm (0/400), whereas single-system protocols ranged from 1.8% to 4.5%. The protocol significantly outperformed every tested single-system strategy for both primary outcomes.

Conclusions: The new personalized hybrid instrumentation planning substantially reduced uninstrumented canal surfaces while preventing critical dentin thinning compared with existing customized single-system protocols.