Influence of beam homogenization on bond strength of adhesives to dentin

Objective. This study evaluated the effect of beam homogeneity on the microtensile bond strength (mu TBS) of two adhesive resins to dentin. Methods. One polywave light-emitting-diode (LED) LCU (Bluephase Style, Ivoclar Vivadent AG) was used with two different light guides: a regular tip (RT, 1010 mW/cm(2) emittance) and a homogenizer tip (HT, 946 mW/cm(2) emittance). The emission spectra and beam profiles were measured from both light guides. Extracted third molars were prepared for mu TBS evaluation using two adhesive systems: Excite F (EXF) and Adhese Universal (ADU). Bond strength was calculated for each specimen (n = 10) at locations that correlated with the output of the two LED chips emitting blue (455 nm) and the one chip that emitted violet light (409 nm) after 24-hs and after one-year water-storage. The mu TBS was analyzed using a four-way analysis of variance (factors: adhesive system, light guide, LED wavelength, and storage time) and post-hoc Tukey test (alpha = 0.05). Results. EXF always delivered a higher mu TBS than ADU (p < 0.0001), with the mu TBS of ADU being about 20% lower than EXF. The light guide (p = 0.0259) and storage time (p = 0.0009) significantly influenced the mu TBS. The LED wavelengths had no influence on the mu TBS (p > 0.05). Significance. Homogeneity of the emitted light beam was associated with higher 24-h mu TBS to dentin, regardless of the adhesive tested. Also, differences in the composition of adhesives can affect their compatibility with restorative composites and their ability to maintain bonding over one year. (C) 2020 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.