Bonding Performance of a Bisphenol A-Free Universal Adhesive to Sound and Caries-Affected Dentin

Current universal adhesives exhibit unreliable bonding to caries-affected dentin and release bisphenol A (BPA). This study compares a BPA-free universal adhesive with its predecessor (bisphenol-based) to assess bonding performance and interfacial characteristics on sound and caries-affected dentin.

Two hundred forty human molars were used in this study: 120 with sound dentin and 120 with caries-affected dentin (CAD). The dentin surfaces were prepared and bonded with Scotchbond Universal Plus (SBUP/BPA-free) or Scotchbond Universal (SBU/BPA-containing) using etch-and-rinse (ER) or self-etching (SE) modes. Resin-dentin bonded specimens (1 mm2) were stored in water for 24 hours and one year and tested for microtensile bond strength (μTBS). The failure images were analyzed through scanning electron microscopy (SEM). Data were submitted to three-way ANOVA and Bonferroni post hoc tests (α < 0.05). Three additional teeth were prepared for each group for evaluation of adhesive diffusion into dentin by dyeing the adhesives with a fluorochrome (Rhodamine B). After longitudinal sectioning, the generated interfaces were stored for 24 hours and one year, immersed in fluorescein dye and examined under confocal laser scanning microscopy (CLSM) and SEM (n = 3).

CAD showed μTBS mean values significantly lower (p < 0.0001) than those of sound dentin for all groups at 24 hours. The SE mode on sound dentin showed no signs of degradation or fluorescein infiltration. SBU in the ER mode (CAD) showed the lowest mean μTBS in both storage periods. The ER mode for both adhesives showed exposed collagen fibrils and fluorescein infiltration underneath the hybrid layer of the sound and CAD over time. Although SBUP showed deeper adhesive diffusion into the CAD, no significant difference in μTBS was found between SBUP (ER and SE) and SBUSE after a year of water storage.

Both the BPA-free and BPA-containing adhesives produced similar short- and long-term μTBS to sound dentin. Bond strengths to CAD varied by material and conditioning mode. Qualitative appearance of SEM images suggests that interfacial diffusion in CAD at 24 hours may be enhanced for the BPA-free adhesive. However, both adhesives exhibited degradation after one year of water storage.