This study evaluates how different wavelength ranges emitted by a poly-wave LED curing light violet (405 nm) and blue (445 and 465 nm) affect the microtensile bond strength (μTBS), nanoleakage (NL), and in situ degree of conversion (DC) of universal adhesives applied to dentin.

Eighty caries-free human molars were randomly assigned to four groups according to two variables: (1) Adhesive system (Ambar Universal APS [AMU], Scotchbond Universal [SBU] and (2) application mode (etch-and-rinse [ER] or self-etch [SE]). To control tooth dependency, each tooth quadrant of every tooth was allocated to a different wavelength range (405, 445 and 465 nm) and identified accordingly during light-curing with the Valo unit (1400 mW/cm²). Afterwards, resin composite fillings were placed, and each quadrant was sectioned to obtain resin-dentin bonded beams (0.8 mm²). These beams were tested for μTBS, NL, and DC. Data for μTBS (MPa), NL (%), and DC (%) were analyzed using three-way ANOVA and Tukey's test (α=5%).

For AMU and SBU, no significant differences were observed among the 445-nm and 465-nm wavelength ranges (p > 0.05) for all outcomes. However, light curing SBU with 405-nm LED resulted in significantly lower μTBS and DC values and higher NL values compared with 445 and 465 nm LEDs (p < 0.01). AMU exhibited higher μTBS and DC values than SBU (p = 0.001). No significant differences were found between SE and ER application strategies (p > 0.05).

Bonding to dentin may be locally compromised when universal adhesives relying on the conventional camphorquinone/amine photoinitiator system are light-cured with poly-wave LEDs that exhibit non-uniform spectral distribution.