Thermal impact of dental adhesive photopolymerization: effects of adhesive volume, air application, and material composition

Objective To evaluate pulp-chamber temperature rise (ΔT) during photopolymerization of dental adhesive systems, considering the influence of adhesive volume, air application, and adhesive type. Materials and methods One hundred and twenty bovine incisors ( n = 120) received standardized buccal cavity preparations using a new diamond bur under water cooling. The teeth were sectioned approximately 2 mm below the cementoenamel junction to provide access to the pulp chamber. Pulp tissue remnants were removed, and a type-J thermocouple (AerOpak®, Okazaki Manufacturing Company, Kobe, Japan) was positioned in contact with the pulpal roof and connected to a digital data acquisition system. Thermal paste was applied between the thermocouple and the pulpal roof to improve thermal coupling. The specimens were embedded in acrylic resin and kept under laboratory conditions (24°C and 50% relative humidity), without incubation or water-bath temperature control. Two universal adhesive systems [Single Bond Universal (3M, Maplewood, MN, USA) and Ambar Universal (FGM, Joinville, SC, Brazil)] were evaluated in a 2 × 2 × 2 factorial design according to adhesive type, air application (with or without), and adhesive volume (1/4 or 1/16 drop). Adhesives were actively rubbed for 20 s. When applicable, air was applied for 10 s from a standardized distance of 10 cm. Photoactivation was performed using an light emitted diode (LED) curing unit at 1,100 mW/cm 2 for 10 s. ΔT was calculated as the difference between peak and baseline temperatures. Data were analyzed using three-way analysis of variance (ANOVA) ( α = 0.05). Results All experimental groups showed an increase in pulp-chamber temperature during adhesive photopolymerization, with ΔT values ranging from 6.35°C to 14.32°C. ANOVA test revealed significant effects of adhesive type ( p < 0.001), air application ( p < 0.001), and adhesive volume ( p < 0.001), whereas none of the two-way or three-way interactions was significant ( p ≥ 0.160). Higher temperature increases were associated with the larger adhesive volume (1/4 drop) and the absence of air application. The highest ΔT was observed for Single Bond Universal without air application and with 1/4 drop (14.32 ± 1.37°C), whereas the lowest ΔT was observed for Ambar Universal with air application and 1/16 drop (6.35 ± 1.40°C). Single Bond Universal produced higher ΔT values than Ambar Universal. Conclusion Adhesive volume, air application, and adhesive type influenced ΔT during photopolymerization. Larger adhesive volumes and omission of air application were associated with greater temperature increases. Under the present in vitro conditions, all experimental groups exceeded the 5.5°C temperature-rise threshold historically associated with pulpal injury in an animal model; however, this comparison should be interpreted cautiously because the present model did not reproduce living pulpal tissue or physiological blood flow.