Preheating and “snow‐plow” composite application technique affect double bond conversion but not bond strength to dentine

Abstract

ObjectiveTo measure degree of conversion (DC) of a flowable composite, microtensile bond strength (MTBS) to dentine in the snow‐plow technique with/without preheating and temperature in the preheated composite.Materials and MethodsFor DC, snow‐plow specimens of Filtek Ultimate Flowable (Flow) and Filtek Bulk Fill (Bulk) (3M) were prepared by light‐curing composites simultaneously in standardized molds while in control groups light‐curing was separate. DC of Flow was measured using micro‐Raman spectroscopy. For MTBS, specimens were prepared on dentine of human extracted molars by simultaneous (snow‐plow) or separate (control) light‐curing. MTBS was measured using a universal testing machine after 24 h and 6 months. Data were analyzed using ANOVA with Tukey's post hoc (α = 0.05).ResultsIncreased curing time significantly increased DC in snow‐plow from 13.4% ± 11.6% (10 s) to 31.8% ± 4.4% (40 s) albeit significantly lower than controls (p < 0.05). Preheated Bulk improved conversion in snow‐plow (44.3% ± 1.7%) and control (50.5% ± 2.6%) (p < 0.05). No significant differences occurred in MTBS between groups (p > 0.05). MTBS values ranged between 66.7 ± 8.4 MPa (snow‐plow group_21°C_baseline) and 54.1 ± 15.8 MPa (control_21°C_long‐term). Temperature in the preheated Bulk dropped to ~38°C after 30 s.ConclusionsSnow‐plow technique, irrespective of preheating, resulted in lower DC of Flow than separate light‐curing of composite increments. Snow‐plow, irrespective of preheating, resulted in similar initial and long‐term MTBS to dentine.Clinical SignificanceClinicians with preference for flowable composite liners in Class II restorations should be aware that the snow‐plow technique of simultaneous light‐curing of flowable and bulk‐fill composite increments affects monomer‐to‐polymer conversion, albeit no effect on immediate, and long‐term bonding to dentine was detected. Preheating sculptable bulk‐fill composite improves conversion of the flowable liner in the snow‐plow technique but has no detectable effect on bond strength to dentine.