Synthesis and evaluation of HEMA-free glass–ionomer cements for dental applications

Objective. The objective of this study was to synthesize and characterize amino acid acrylate and methacrylate derivatives, use them to formulate light-cured glass–ionomer cements (LCGICs), and evaluate their mechanical strengths. Materials and methods. Acrylate and methacrylate derivatives of six amino acids were synthesized and characterized using FT-IR and 1HNMR spectroscopy. The LCGICs were formulated using a newly synthesized polymer having pendant methacrylate groups (in other words, a methacryloyl derived polymer or MDP), amino acid derivatives, water, and Fuji II LC glass. Compressive strength of the cements and viscosities of the resin liquids were used as screening tools in order to determine the optimal formulation. The specimens were conditioned in distilled water at 37 °C for 24 h prior to testing. Results. The measured compressive strengths (MPa) of the cements were found to depend on the amino acid derivative used: acryloyl aspartic acid (268.5)>methacryloyl beta-alanine (259.1)=methacryloyl glutamic acid (254.5)=acryloyl beta-alanine (251.9)>acryloyl glutamic acid (238.8)>methacryloyl aspartic acid (210.9). Methacryloyl beta-alanine (MBA) was selected for further formulations due to its relatively low solution viscosity and high compressive strength. Effects of MDP content and power/liquid (P/L) ratio were significant. The formulation with a liquid composition of 50/25/25 (MDP/MBA/water) and P/L ratio of 2.7/1 was found to give optimal properties and handling of all the formulations studied. Conclusions. A novel HEMA-free LCGIC system based on amino acid derivatives has been developed. This system may eliminate potential cytotoxicity in current LCGICs caused by leached 2-hydroxyethyl methacrylate (HEMA). The optimal MBA-modified cements were 20% higher in compressive strength, 70% higher in diametral tensile strength (DTS) and 93% higher in flexure strength (FS), as compared to Fuji II LC cement.