Rotary First: A Technique for Simultaneous Root Canal Negotiation and Glide Path Establishment—An In Vitro Study

Objectives: This preliminary in vitro study compared active instrumentation time and instrument fracture between the rotary first technique, which combines engine-driven canal negotiation and glide path establishment, and conventional manual instrumentation. Methods: Thirty freshly extracted human maxillary molars (103 canals) with canal curvatures ≤ 30° were randomised at tooth level to the rotary first or manual group. Active instrumentation time was compared separately in palatal (P), distobuccal (DB), mesiobuccal (MB) and second mesiobuccal (MB2) canals using 2-sided Mann–Whitney U-tests with Holm–Bonferroni adjustment. Overall canal-level fracture frequencies were compared exploratorily using a 2-sided Fisher’s exact test. Results: Median active instrumentation time was lower with rotary first in every canal type. After multiplicity adjustment, the difference remained statistically significant only in MB canals (6.3 vs. 55.0 s; adjusted P = .004; rrb = 0.70). Differences in P (adjusted P = .087), DB (adjusted P = .100) and MB2 canals (adjusted P = .354) were not statistically significant. Fractures occurred in 7/53 rotary first canals (13.2%) and 2/50 manual canals (4.0%); the difference was not statistically significant (P = .162). Conclusions: Under the restricted anatomical conditions evaluated, rotary first reduced active instrumentation time significantly only in MB canals after adjustment. The fracture comparison was underpowered and did not account for within-tooth clustering; therefore, neither equivalent procedural safety nor the overall superiority of either protocol can be inferred.