Time Sensitivity Associated with Application of HEMA-free Adhesive

The water-soluble HEMA has polar properties with small dimension to enhance the wetting properties of the adhesive solution and the penetration efficacy of the adhesive into demineralized dentin [3]. HEMA has been reported to be positively influence bond strength to dentin. Because of its hydrophilic character, it is also frequently added to improve miscibility of hydrophobic and hydrophilic components in an adhesive solution. Van Landuyt et al. [4] found that when the concentration of the HEMA is 10% performed best result regarding to bond strength than the other group with the different concentration of the HEMA (0,19,36 %) [5]. The major drawback of the use of HEMA is its high allergenic potential. Fast penetration of this monomer through gloves and through skin due to its low molecular weight can cause contact dermatitis (allergic reaction type IV) [6,7]. HEMA may also deteriorate the mechanical properties of the polymerized adhesive, which can result in inferior mechanical strength of the cured adhesive, enhanced water uptake, swelling and marginal staining. To overcome these shortcomings, HEMA-free adhesives were introduced. Excluding HEMA, these adhesives are similar to HEMA-containing adhesives and consist of a complex blend of hydrophilic/hydrophobic ingredients, water and an organic solvent (acetone or ethanol) that is added in the formulation to avoid the phase separation and to keep this blend stable [8,9].