Effect of short glass fibers on the polymerization shrinkage stress of dental composite

Abstract

This study examines contraction stresses of seven short fiber reinforced composites (sFRC) exhibiting different volume loads and aspect ratios (AR)* of fibres. The shift towards a greater utilization of posterior resin composites in dentistry has seen increased interest in the use of randomly oriented short glass fibers in these restorative materials. While the effect of these fibers on modulus, strength, and toughness has been studied, very little information exists on their effect on polymerization shrinkage and even less on shrinkage stress. S2-glass fibers with an average AR of 68 were used to form three experimental groups with 5%, 10%, and 20% volume loads. Commercial sFRC with ARs of 20 and 100 were also tested. A tensilometer set up was used with moderate compliance, 5.4 J/cm irradiance, and a C-factor of 2.75. Data was statistically analyzed using ANOVA followed by post hoc Tukey's test. The addition of 5% of the experimental fiber did not significantly increase stress while the 10% and 20% groups resulted in 36.3% and 39.1% higher stress values, respectively, compared to the non-fiber control group (p < 0.05). Of all the sFRC groups, the very low AR material exhibited the lowest stress [0.682 MPa (p = 0.001)] while another commercial material with higher AR fibers exhibited the highest overall value [1.822 MPa (p < 0.001)] when compared to the control group. The results indicate that both short fiber volume and AR are important variables to consider with regards to setting stresses of sFRC. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1930-1937, 2017.

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“…This is interesting and could be attributed to the potential light transmitting capacity of the short glass fibers inside the canal as well as the greater transparency observed in SFRC material. This finding is in line with the result of curing depth performed in the study by Shouha and Ellakwa, which showed that SFRC exhibited the deepest cure (6.7 mm) in comparison with different conventional PFC composites 49) . Previous studies have also shown that FRCs conduct and scatter the light better than conventional PFC composites 47,50) .…”

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“…Interestingly, Shouha and Ellakwa reported that SFRC exhibited the deepest cure (6.7 mm) in comparison with different composite resins . This was explained by the effect of relatively well‐aligned millimeter‐scale fibers down the narrow mold enhancing light penetration, as well as the greater transiency observed in SFRC materials .…”

“…Interestingly, Shouha and Ellakwa reported that the addition of 5 wt% of short fiber fillers to resin matrix did not effect polymerization shrinkage stress values, whereas 10 and 20 wt% loading resulted in higher stress values . According to Shouha and Ellakwa, an increase in shrinkage stress from the fiber load of >5 wt% could arise predominantly from increases in modulus and stiffness of the material.…”

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“…46 Other studies showed that EverX Posterior developed either similar or higher polymerization stress and gap formation in vitro compared to other bulk-fill materials. 3,50 Strategy 2B: Self-healing composites…”