Viscoelastic Properties of Collagen-Adhesive Composites under Water Saturated and Dry Conditions

This is the peer reviewed version of the following article: Singh V, Misra A, Parthasarathy R, Ye Q, Spencer P. 2015. Viscoelastic properties of collagen–adhesive composites under water-saturated and dry conditions. J Biomed Mater Res Part A 2015:103A:646–657. , which has been published in final form at http://doi.org/10.1002/jbm.a.35204. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.To investigate the time and rate dependent mechanical properties of collagen-adhesive composites, creep and monotonic experiments are performed under dry and wet conditions. The composites are prepared by infiltration of dentin adhesive into a demineralized bovine dentin. Experimental results show that for small stress level under dry conditions, both the composite and neat adhesive have similar behavior. On the other hand, in wet conditions, the composites are significantly soft and weak compared to the neat adhesives. The behavior in the wet condition is found to be affected by the hydrophilicity of both the adhesive and collagen. Since the adhesive-collagen composites area part of the complex construct that forms the adhesive-dentin interface, their presence will affect the overall performance of the restoration. We find that Kelvin-Voigt model with at least 4-elements is required to fit the creep compliance data, indicating that the adhesive-collagen composites are complex polymers with several characteristics time-scales whose mechanical behavior will be significantly affected by loading rates and frequencies. Such mechanical properties have not been investigated widely for these types of materials. The derived model provides an additional advantage that it can be exploited to extract other viscoelastic properties which are, generally, time consuming to obtain experimentally. The calibrated model is utilized to obtain stress relaxation function, frequency-dependent storage and loss modulus, and rate dependent elastic modulus

Effect of Gingival Hemostatic Agents on the Surface Detail Reproduction and Dimension Stability of Three Elastomeric Impression Materials

This study aimed to evaluate the effects of aluminum chloride based hemostatic agents on the surface detail reproduction and dimension stability. Three impression materials were investigated after contaminated with three commercial astringents with different concentration of aluminum chloride. The specimens from three impression materials were fabricated with a stainless-steel mold that followed the American Dental Association specification no.19. The mold was preliminarily contaminated with three hemostatic agents racestyptine, Dryz, and Expasyl™—and 80 specimens from each impression material—polyvinylsiloxane (PVS), polyether, and polyvinylsiloxane ether (PVSE), were fabricated and subjected to each astringent. The surface detail reproduction was examined using a stereomicroscope at 4x magnification, and the dimensional stability was analyzed at 24 hr with a measuring microscope. The surface detail data were statistically analyzed with Fisher’s test at a significance level of 0.05. The dimensional stability data were analyzed using two-way ANOVA and Tukey’s test at a significance level of 0.05. Aluminum chloride hemostatic agents can affect the surface detail reproduction of impression materials differently (p<0.05). Thus, the first null hypothesis was rejected. PVS showed the highest percentage of satisfactory surface detail regardless of the hemostatic agent used in this study. PVSE showed a reduced percentage of satisfactory surface detail when the concentration of aluminum chloride was high. The three hemostatic agents affected the dimensional stability of each material differently (p<0.05). Therefore, the second null hypothesis was also rejected

Changes in resin-infiltrated dentin stiffness after water storage

Plasticization of polymers by water sorption lowers their mechanical properties in a manner that is predictable by the polarity of their component resins. This study tested the hypothesis that when adhesive resins were used to create resin-infiltrated dentin, the reductions in their flexural moduli after water storage would be lowered proportional to their hydrophilic characteristics. Three increasingly hydrophilic resin blends were used to fabricate polymer beams and macro-hybrid layer models of resin-infiltrated dentin for testing with a miniature three-point flexure device, before and after 1-4 weeks of water storage. Flexural modulus reductions in macro-hybrid layers were related to, and more extensive than, reductions in the corresponding polymer beams. Macro-hybrid layers that were more hydrophilic exhibited higher percent reductions in flexural modulus, with the rate of reduction proportional to the Hoy's solubility parameters for total intermolecular attraction forces (δt) and polar forces (δp) of the macrohybrid layers.link_to_subscribed_fulltex