Evaluation of Preheating Methods for Bulk-Fill Thermoviscous Composite in Non-Carious Cervical Lesions: A 24-month Randomized Controlled Trial

Abstract

This 24-month, double-blind, split-mouth randomized equivalence clinical trial compared the retention rates of a bulk-fill thermoviscous composite resin using two different preheating methods for the restoration of non-carious cervical lesions (NCCLs). A total of 120 NCCLs were randomized into two groups (n = 60 each). In one group, a bulk-fill thermoviscous composite resin (VisCalor bulk, Voco GmbH) was preheated using a dispenser heater (DH, VisCalor Caps dispenser/warmer), while in the other group, the same resin was preheated with a bench heater (BH, Caps Warmer). In the BH group, the composite underwent preheating at 68°C using a heating bench for 3 min while in the DH group, the composite was preheated at the same temperature for 30 s using a dispenser heater. Subsequently, the preheated bulk-fill thermoviscous composite resin was directly applied to the NCCLs. The restorations were evaluated at baseline, and after 6, 12, 18, and 24 months of clinical service using the FDI criteria. The total working time was recorded. The study used TOST-P to assess groups equivalence, Kaplan-Meier analysis for retention/fracture rate, log-rank test for secondary outcomes' survival distributions, and paired t-tests for comparing time per clinical step between groups (α = 0.05). After 24 months, 106 restorations were evaluated. Four restorations were lost-two from the DH group and two from the BH group-resulting in similar retention rates for both groups (96.1%, 95% CI 86.8 - 98.9, p > 0.05). The hazard ratio was 0.83 (95% CI 0.26 to 2.72), indicating no significant difference between the groups (p > 0.05). All other FDI parameters were deemed clinically acceptable. However, the total working time for the BH group was significantly longer than that for the DH group (p < 0.001). Both preheating protocols employed for the bulk-fill thermoviscous composite resin demonstrated high and equivalent retention rates after 24 months, the other FDI parameters were deemed clinically acceptable over the same period. Clinicians can choose either method for heating the thermoviscous composite resin for restoration of non-carious cervical lesions, as they do not impact important clinical outcomes after 24 months. The total working time for the bench heater is higher than that for the dispenser heater due to the need for preheating of the bench heater.