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Influence of Heat Treatment on the Shaping Ability of Rotary Instruments in Severely Curved Root Canals: A Stepwise
Jeronimo Careaga1, Ana Flávia Almeida Barbosa1, Graziela Dos Santos Massa1
1Rio de Janeiro State University, Rio de Janeiro, Brazil.
Objective:
This study aimed to assess the shaping ability of 2 preparation systems with similar designs but different heat treatments during the progressive enlargement of severely curved mesiobuccal and mesiolingual canals in mandibular molars.
Methods:
Twenty-two mandibular molars with mesial canals curved >25º were scanned, pair-matched and divided into 2 groups (n=11) for preparation using austenitic (Genius) or martensitic (Genius Proflex) heat-treated instruments. Phase transformation temperatures of the instruments were determined via differential scanning calorimetry. Mesiobuccal and mesiolingual canals were first instrumented with a 17/.05 file and then sequentially enlarged using instruments sized 25/.04-40/.04, with scans taken after each enlargement step. Pre- and postoperative datasets were analysed for volume, surface area, unprepared canal areas, removed dentine volume, transportation and dentine thickness reduction. Statistical analyses included Student's t-test, Generalized Linear Model (GLM) multivariate model and independent t-tests (significance: P < .05).
Results:
Genius displayed an austenitic structure, while Genius Proflex exhibited an R-phase structure at both 20ºC and 36ºC. Instrument size increase (P=.001) and heat treatment (P < .001) significantly affected shaping outcomes without interaction effects (P=.882). Size increases impacted canal volume (P=.023), unprepared areas (P=.005), removed dentine (P < .001) and dentine thickness reduction (P < .001), but not surface area (P=.390). Heat treatment significantly influenced unprepared canal areas (P < .001). Martensitic instruments caused less transportation (P < .05) and preserved more distal dentine (P < .001) compared to austenitic instruments.
Conclusions:
In severely curved mesial canals of mandibular molars, martensitic instruments result in fewer unprepared areas, reduced transportation and better dentine preservation at the distal root canal wall compared with austenitic instruments.
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