Objective

The objective of this work is to find potential alternative monomers to 2-hydroxyethyl methacrylate (HEMA) for dental materials (self-etch adhesives and luting composites).

Methods

Monomers 1–9 were tested as potential HEMA substitutes. Methacrylates 4, 5 and 6 and (N-methyl)acrylamides 7–9 were synthesized and characterized by ¹H NMR spectroscopy. The reactivity of each monomer was studied using photo-DSC. Mixtures of monomers 1–9 with the urethane dimethacrylate UDMA (1/1: wt/wt) were formulated and cured. The water sorption and solubility of these materials were determined according to ISO 4049. Luting composites based on monomers 1–9 or on HEMA were formulated. The flexural strength and modulus of elasticity were measured using a three-point bending setup, according to ISO 4049. Self-etch adhesives containing monomers 1–9 or HEMA were prepared and used to mediate a bond between the dental composite Tetric EvoCeram^® and both dentin and enamel. The shear bond strength (SBS) was measured using a Zwick universal testing machine.

Results

Polymerizable diols 3 and 4 as well as (N-methyl)acrylamides 7–9 were found to be significantly more reactive than HEMA. Resins based on the hydrophilic monomers 3, 7 and 8 exhibited a significantly higher water sorption than the corresponding HEMA-containing material. Luting composites containing monomers 2, 3, 6 and 7 showed similar or even improved mechanical properties compared to the reference material containing HEMA. Self-etch adhesives containing monomers 4 and 9 provided significantly higher dentin SBS than the reference material.

Significance

Some of the evaluated monomers are promising candidates for the development of HEMA-free dental materials.