Physicochemical, mechanical and SEM characterization of a new experimental adhesive containing G-IEMA

Abstract

Introduction: Universal dental adhesives are a new versatile and very attractive adhesive family recently introduced in the market [1]. However, they still present limitations that lead to the degradation of the interface between the tooth and the restoration [2]. Moreover, the in vitro performance of universal adhesives has been reported as material-dependent due to the complexity of their chemical composition [3]. Low polymerization shrinkage, high double bond conversion, high resin monomers penetration and high hydrophobicity are important characteristics to be considered for the improvement of dental adhesive’s bonding efficacy [4]. Due to their polymerization characteristics, hyper-branched macromers are promising candidates to be used in dental materials [5]. In this study, a new Bis-GMA (Bisphenol A-glycidyl mathacrylate) free dental adhesive system was prepared, using G-IEMA (G(2)-isocyanatoethyl methacrylate), and its physicochemical properties and dentin adhesion efficacy were investigated. Materials and methods: G-IEMA was synthesized and subsequently incorporated into an experimental adhesive (AE2) formulated without Bis-GMA. Their physicochemical properties, such as double bond conversion (DBC), polymerization shrinkage (PS), and water sorption (WS) and solubility (S) were compared with three control groups: – AE1(formulated with Bis-GMA), SBU (Scotchbond Universal, 3M ESPE, St. Paul, USA) and FUT (Futurabond M+, VOCO GmbH, Cuxhaven, Germany). Micro-tensile bond strength (µTBS) tests were used to study dentin adhesion, and values obtained were compared among groups. Additionally, the bonding interfaces were characterized by SEM. Results: AE2 presented a significantly higher DBC than SBU (p < 0.001) and FUT (p = 0.004); no significant differences were observed between AE2 and AE1 (p = 0.403) with 60 s of light-curing. Regarding mechanical properties, AE2 presented the highest µTBS when Etch-and-rinse protocol was applied. AE1 presented significant higher µTBS than SBU (p = 0.019) and no other differences between adhesives were observed. No significant interaction between the adhesives and protocols was observed. Discussion and conclusions: The adhesive AE2 containing G-IEMA presented comparable DBC, PS, WS and SL when compared to Bis-GMA containing adhesive AE1. For ER protocol, AE2 also showed better adhesive results; however, mechanical and physicochemical properties need to be improved for Self-etch procedures, nevertheless, this research is a significant contribution to help to create a new universal adhesive BPA-free with improved dentin bonding adhesion, using a versatile application mode (ER and SE).