Investigation of UDMA and UDA/TEGDMA Monomer Mixtures for resin composite applications

Abstract

The monomer system in resin composites has evolved from conventional monomers, such and Bis-GMA and UDMA, to alternative monomer systems. The UDMA monomer has shown favourable properties compared to Bis-GMA, such as lower viscosity and improved mechanical properties. This has favoured the investigation of alternative UDMA monomers, as a monomer system for resin composite applications. The aims of this current research was to characterize two modified UDMAs and one UDA monomer, when diluted with TEGDMA, compared to conventional UDMA/TEGMA mixtures. The 8 resin mixtures were characterized to identify pre-cure properties such as viscosity and refractive index. Post-cure properties such as light transmission, polymerization shrinkage strain, and refractive index were also measured. The chemical structure of the monomer dominated over the properties. The UDMA-IPDI monomer, with a central cycloaliphatic core resulted in mixtures with high viscosities, and low polymerization shrinkage strain, compared to the conventional UDMA mixtures. Monomer elution from the 8 cured mixtures was determined using High Performance Liquid Chromatography over 90 days when stored in two different media. The degree of conversion was assessed using Fourier Transform infrared Spectroscopy. Mixtures formulated with PGDMA monomer, with a pendant aromatic group, resulted in the lowest degree of conversion and highest monomer elution. UDA mixtures showed the highest DC. A 40 s light curing duration is crucial to reducing high monomer elution. The mixtures were added with 60 wt. % fillers, and the resin composite formulations were assessed for pre-cure and post-cure properties. Similar to the mixtures, 70 UDMA-IPDI resin composites showed the highest viscosity, and low polymerization shrinkage strain. The flexural properties of the resin composite formulations was also examined. Resin composites formulated with UDMA-IPDI monomer showed the greatest reduction in flexural strength after 30 day water storage. By contrast, 70 UDA showed an increase in flexural strength. The effect of Bis-GMA on post-cure surface microhardness, chemical softening and DC of resin composite groups was explored. The PGDMA resin composites (with and without Bis-GMA) were least vulnerable to chemical softening, yet 70 UDMA-IPDI was most vulnerable. The extent of chemical softening was due to a combined effect of TEGDMA concentration, degree of conversion, and monomer crosslink density. The sorption, solubility and hygroscopic expansion of resin composite formulations was assessed after 120 days storage in water. The extent of water sorption was dependant on the chemical structure of the monomer, the diisocyanate core, and TEGDMA concentration. The water sorption positively corelated with hygroscopic expansion, and negatively corelated with water solubility.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	David Watts (Supervisor), Raymond Richmond (Supervisor) & Xiaohui Chen (Supervisor)