Mehmet DÜNDAR
Middle Black Sea Journal of Health Science - 2026;12(2):181-200
Objective: Nickel -titanium (NiTi) endodontic instruments have improved the efficiency of root canal treatment due to their flexibility and shape memory properties. However, instrument separation remains an important clinical complication mainly associated with cyclic fatigue and torsional stress. Although canal curvature, instrument design, alloy type, and motion kinematics have been widely investigated, the effect of canal access angle on the cyclic fatigue resistance of NiTi instruments has received limited attention. This scoping aimed to map and evaluate the biomechanical influence of canal access angle on the cyclic fatigue resistance of NiTi endodontic instruments in accordance with the PRISMA -ScR framework. Methods: This scoping was conducted following the PRISMA -ScR guidelines. A systematic electronic search was performed in PubMed/MEDLINE and Web of Science from database inception to January 2026. In vitro or ex vivo experimental studies evaluating the effect of canal access angle or coronal angulation on the cyclic fatigue resistance of NiTi endodontic instruments were included. Studies that did not assess access angulation as an experimental variable, did not report cyclic fatigue outcomes, or represented inappropriate publication types such as reviews, case reports, and editorials were excluded. A total of 126 records were identified; after removing 24 duplicates, 102 records were screened, 18 full -text articles were assessed for eligibility, and 5 studies were included in the study. Results: Most included studies reported that increasing canal access angle reduced the cyclic fatigue resistance of NiTi instruments. Four of the five studies demonstrated a decrease in the number of cycles to failure as access angulation increased. In particular, a 30 derece access angle was generally associated with lower fatigue resistance compared with straight access configurations. This effect may be attributed to the formation of an additional coronal bending segment, which increases stress concentration along the instrument. Conclusion: Limited available evidence suggests that canal access angle may be an important biomechanical factor affecting the fatigue behavior of NiTi endodontic instruments. Increased access angulation may generate additional coronal bending stress and contribute to earlier fatigue failure. Therefore, optimizing access cavity design and achieving a straighter instrument trajectory may help reduce mechanical stress during root canal preparation; however, further experimental and clinical studies are required to confirm its direct clinical impact on instrument separation.
