Optimal photoactivation time and thermal behavior of gingival barriers used in in-office dental bleaching

To evaluate the influence of exposure time and curing distance on the degree of conversion (DC) and temperature change of light-cured gingival barrier materials.

An in vitro study was conducted with 576 disk-shaped specimens, divided into 72 groups (n = 8) based on three factors: gingival barrier type (SDI Gingival barrier, DMC Lase Protect, Ultradent OpalDam, PHS Potenza Blocco, FGM Top Dam, DFL Total Blanc Protetor Gengival), irradiation time (3, 5, 10, 15, 20, and 30 s), and curing distance (Valo, Standard Mode: 1 mm [900 mW/cm²] or 10 mm [450 mW/cm²]). DC was assessed by micro-Raman spectroscopy. Thermal changes were assessed using a T-type thermocouple on simulation model. Light characteristics of the LED curing unit were determined using spectroradiometer and integrating sphere. Data were analyzed using ANOVA and Tukey's test (α = 0.05).

At 1 mm, the LED delivered 657.31 mW of power and 908.57 mW/cm² of irradiance; at 10 mm, the values were 326.25 mW and 450.95 mW/cm². Radiant exposure increased with time and was significantly higher at 1 mm (p < 0.01). Longer exposure improved DC, with significant variations among materials (p < 0.01). The highest DC (93 %) was achieved with 1 mm distance after 30 s. Temperature rise also varied by material and increased with irradiance and time (p < 0.01).

Gingival barrier polymerization is influenced by material type, curing distance, and exposure time. Most materials reached adequate conversion with 10 s at 1 mm. However, prolonged curing (30 s) led to temperature increases above 50 °C in some materials. At 10 mm, at least 20 s was required for safe and effective polymerization.

Gingival barriers should be light-cured for a minimum of 10 s at 1 mm. At 10 mm, exposure time should be extended to at least 20 s to ensure sufficient polymerization while minimizing thermal risk.