Does the absence of HEMA in universal adhesive systems containing MDP affect the bonding properties to enamel and dentine? A one-year evaluation

Objectives: To evaluate the effect of the absence of HEMA in commercial universal adhesives containing MDP on the adhesive properties of dentine and enamel immediately and after one year of water storage. Methods: 144 third molars were used to evaluate bonding to dentine (n = 64) and enamel (n = 80). For each substrate, teeth were divided into eight experimental groups, following the main variables: 1) Adhesives: Scotchbond Universal/SBU; Gluma Bond Universal/GBU; Solare/SUB and Zipbond Universal/ZIP; 2) Adhesive strategies: etch-and-rinse/ER and self-etch/SE; and 3) Time: immediately and after one year of water storage. For both substrates, after restoration, the specimens were sectioned, and the adhesive interfaces tested by bond strength (mu TBS in dentin and mu SBS in enamel) or nanoleakage (NLD = dentin and NLE = enamel). The evaluation of mu TBS, mu SBS, NLD and NLE was performed immediately and after one year of water storage. The data for each substrate and property were subjected to three-way repeated measures ANOVA and Tukey's test (alpha = 0.05). Results: The SBU and ZIP showed the highest mu TBS, mu SBS, and lower NLD values when compared to GBU and SUB for both strategies and storage time (p = 0.001). ER showed higher values of mu TBS and mu SBS when compared to the SE strategy (p = 0.001) for both storage time, except for SBU. For all adhesives and adhesive strategies evaluated, lower NLD was observed in the immediate time when compared to 1 year (p = 0.0002). Conclusion: Considering that two HEMA-free universal adhesives, namely Gluma Universal Bond and Solare Universal Bond, exhibited lower bonding performance compared to one HEMA-free adhesive universal adhesive (ZipBond). Clinicians should also consider additional factors such as the solvent used and pH when choosing between HEMA-free and MDP-containing universal adhesives. Clinical significance: The adhesive efficacy of commercial MDP-containing universal adhesives and HEMA-free alternatives on dentin and enamel appears to be contingent upon the specific material employed, in comparison to a HEMA-containing adhesive.