Predictors of Dental Needle Bevel Deformation: Gauge, Insertion Frequency, and Length as Key Determinants

Background/Objectives: Dental needles are used routinely for local anaesthesia, but repeated insertion, needle selection, and operator handling may all compromise tip integrity. This study assessed bevel deformation, biological debris, and manual bending in used dental needles collected during undergraduate clinical practice. Their associations with needle dimensions, insertion frequency, injection technique, and operator seniority were also examined. Methods: 192 discarded needles were collected from fourth-, fifth-, and sixth-year students and dental interns after routine local anaesthesia procedures at an academic dental hospital. Each needle was examined under stereomicroscopy. Needle bevels were classified as intact, outward bending, or inward bending; biological debris and manual bending were also recorded. Predictors of bevel deformation were identified by multivariable logistic regression. Results: Bevel deformation was present in 93 of 192 needles. Thirty-gauge needles showed higher odds of deformation than 27-gauge needles (OR = 2.54, p = 0.004), and each additional insertion further increased the odds (OR = 1.98, p = 0.016); once gauge was accounted for, needle length was not an independent predictor. Intended bone contact showed no association with deformation. Outward bending predominated among deformed tips (63.4% vs. 36.6% inward), and biological debris was detected on 16.1% of needles. Manual bending was more frequent among interns than students (OR = 3.67, p = 0.007). Conclusions: Used dental needles frequently exhibited bevel deformation, particularly with 30-gauge needles and after repeated insertions. The occurrence of deformation even in the absence of intentional bone contact further supports strict single-use practices and careful needle handling during local anaesthesia. Although the higher frequency of manual needle bending observed among interns should be interpreted cautiously, this finding highlights a potential area for targeted operator training and further investigation.