The purpose of this study was to evaluate the long-term effect of aging in water on the physical properties of experimental composites having systematically controlled differences in degree of conversion (DC), filler volume fraction (Vf), and percentage of silane-treated fillers. Composites were made with a 50% Bis-GMA:50% TEGDMA light-cured resin and a 1-2 microm (average size) strontium glass filler (+ 5 wt% SiO2 microfiller). For composites A-E, the DC was varied from 56-66% by changing the curing time; for D and F-I, the Vf was varied from 28-62 vol%; and for D and J-M, the percent of fillers with a silane coupling agent (gamma-MPS) was varied from 20-100%. Fracture toughness (KIc), flexure strength (FS), elastic modulus (E), and hardness (KHN) were tested after soaking in water at 37 degrees C for 1 day, 6 months, 1 year, and 2 years. The KIc was reduced 20-30% for all composites after 6 months, with minimal changes thereafter. The FS was reduced for several composites at 6 months, but only those with poor cure (A and B) were lower at 2 years than they were initially. The E was not reduced for most composites. Hardness was reduced for most composites after 6 months, but many returned to their original levels at 2 years. Long-term aging in water caused a reduction in the KIc, independent of composition, but had little effect on other properties, suggesting limited degradation of composites in water.

No abstract

For the clinical wear of composite filing materials to be reduced, compositional factors such as degree of cure, filler level, and silanation level should be optimized. An oral-wear-stimulating machine was used to explore the effects of these factors on abrasion and attrition wear as well as on opposing enamel wear. The composites were made from Sr glass (1-2 micron avg) and a 50/50 Bis-GMA/TEGDMA resin. Series I (A-D, E) were light-cured (Triad II) for 9, 12, 25, and 40 sec/side to produce degree of cure (DC) as measured by FTIR of 56, 60, 61, and 63%, respectively. E received an additional heat cure (120 degrees C for 10 min) to reach a DC of 66%. Series II (D, F-I) were filled to 62, 53, 48, 37, and 28 vol%, respectively. In series III (D, J-M), the portion of fillers treated with a silane coupler (MPS) was 100, 80, 60, 40, and 20%, respectively. Samples were cycled 50,000 times against an enamel antagonist in a poppy seed/PMMA slurry in the oral wear simulator to produce abrasion (load = 20 N) and attrition (load = 70 N) simultaneously. Wear depth (micron: n = 5) was measured by profilometry. Results for each series were analysed by ANOVA/Turkey's (p < or = 0.05). The wear depths did reflect cure values, though only the abrasion difference for E < A was significant. Greater wear was correlated with lower filler levels (r2 = 0.88; p < 0.05), significantly increasing below 48 vol% (G). Wear increased linearly as the percent of silane-treated fillers was reduced (r2 = 0.99; p < 0.05). Abrasion and attrition did not differ significantly for any composite. Wear of the opposing enamel was largely unchanged by these factors. Compositional factors including degree of cure, filler level, and silanation directly affected the wear resistance of dental composites evaluated in an oral wear simulator.

The following guidance is meant to aid the researcher in choosing the most appropriate test methods when planning studies designed to assess certain key properties and characteristics of dental resin composites, specifically technique sensitivity and handling during placement, polymerization, and dimensional stability.

Monowave and polywave LEDs emitted nonhomogeneous light beams, but this did not affect the DC homogeneity of bulk fill composites. For composites containing CQ associated with alternative photoinitiators, polywave LEDs had a higher DC, but only at the top part of the restoration; lower wavelength absorption photoinitiators were ineffective in deeper areas.