AbstractsEngineering

Fiber reinforced composites (FRCs) are increasingly used in dentistry with their tooth-matching mechanical, physical and aesthetic properties. The most commonly used FRC products consist of E- or S-glass fibers and methacrylate-based resin matrices. The commonly used methacrylate monomer bis-phenol A glycidyl methacrylate (bis-GMA) has a very high viscosity and possibly leads to a low degree of conversion (DC). In this PhD study, the much less viscous urethane dimethacrylate (UEDMA) was chosen as a replacement for bis-GMA, diluted by hydroxypropyl methacrylate (HPMA) to build up the resin system. This thesis comprises four studies. In study 1, three study groups of 70.6wt%, 49.0wt% and 27.4wt% UEDMA mixed with HPMA in the resin, all reinforced with unidirectional E-glass fibers (42.0vol%), were light-cured for 40 s. The control group had a resin blend of 70.6wt% bis-GMA and 27.4wt% methyl methacrylate (MMA). The prepared specimens were stored dry for 24 h or in deionized water at 37 ℃ for 1, 3, 6 and 12 months. Water sorption up to 40 d and Vickers hardness together with flexural properties after each storage period were investigated. The results suggested that water storage at 37 ℃ induced certain degradation to the mechanical properties of FRC. The group with the highest UEDMA content (70.6wt%) exhibited the lowest 40 d water sorption, the highest hardness and the highest flexural strength and modulus after most storage periods among the UEDMA-containing experimental groups, while the control group had an even better performance in most aspects tested. From study 2 to study 4, the UEDMA content was raised to 70.6wt%, 80.6wt% and 90.6wt%. The three resins, without fiber reinforcement, were tested for the DC after 40 s light-curing and monomer leaching in a 75% ethanol:water solution. Specimens prepared of these three resins reinforced with unidirectional E-glass fibers were tested for 40 d water sorption and mechanical properties (Vickers hardness, flexural properties) after 24 h dry storage, 1 and 3 month deionized-water storage at 37 ℃ and thermal cycling between 5 ℃ and 55 ℃ for 6,000 times. The control group was the same as in study 1. The experimental resins showed higher DC compared to the control resin, while higher UEDMA content was accompanied with lower DC. The resin with highest UEDMA content (90.6wt% UEDMA + 7.4wt% HPMA) exhibited the lowest monomer leaching. The UEDMA-based experimental groups exhibited higher 40 d water sorption than the bis-GMA-based control group. While the group with lowest UEDMA content (70.6wt% UEDMA + 27.4wt% HPMA) showed lowest water sorption among the experimental groups. The bis-GMA-MMA-based FRC specimens showed a superior performance in most tested mechanical properties than the UEDMA-HPMA-based FRCs, and with a higher UEDMA content the mechanical properties were more promising for dental use. Water storage at 37 ℃ might induce some decrease in the mechanical properties, while thermal cycling influenced the mechanical properties in a more complicated way. There…