Percentage of root canal wall surfaces touched by rotary nickel-titanium instruments: a systematic review and a preliminary experimental evaluation of a new instrument

Introduction Adequate mechanical debridement of the root canal system is a prerequisite for successful endodontic therapy. However, a well-documented limitation of rotary nickel-titanium (NiTi) instruments is their inability to contact all canal wall surfaces during instrumentation. This systematic review aimed to evaluate the percentage of root canal wall surfaces contacted by rotary NiTi instruments and to identify factors that influence this parameter. Methods Electronic databases (PubMed/MEDLINE, Scopus, Web of Science, and Cochrane Library) were searched up to December 2023. Studies reporting the percentage of instrumented canal wall surface using micro-computed tomography (micro-CT) or other volumetric methods were included. Risk of bias was assessed using the Joanna Briggs Institute (JBI) critical appraisal checklist for quasi-experimental studies. Results Forty-three studies met the inclusion criteria. Across all rotary NiTi systems, the mean percentage of untouched canal wall surface ranged from 35% to 82%, with most studies reporting values between 50% and 75%. Single-file systems and reciprocating instruments showed similar or marginally superior canal wall contact compared to multi-file sequences. Oval and irregular canal cross-sections, apical thirds, and isthmus areas were consistently associated with higher percentages of untouched dentin. Conclusions Rotary NiTi instrumentation inherently leaves a substantial portion of the root canal wall unprepared, regardless of the system used. These findings underscore the critical complementary role of irrigant activation, adjunctive sonic/ultrasonic techniques, and novel shaping approaches in achieving thorough canal disinfection. Future instrument designs should prioritize adaptive contact with complex canal anatomies.