Interphase structure-property relationships in dental nanocomposites
Introduction: The material properties of composites are influenced in large part by the chemical and physical properties of the interphase since this phase provides a crucial link between the organic matrix and the inorganic filler. This effect is especially important in nanocomposites because of the increased amount of interfacial area compared to conventional composites. Composites used for dental restorative applications are typically comprised of a thermoset dimethacrylate matrix phase, a silica filler phase, and a silane interphase (usually derived from 3-methacryloxypropyltrimethoxysilane, “MPTMS”) that covalently bonds the filler and the matrix. Objective: The aim of this research was to better understand the relationships between interphase composition and the resultant mechanical properties of thermoset methacrylate nanocomposites, ultimately for the purpose of improving the properties of dental materials through manipulation of the interphase. Materials and Methods: Silica nanoparticles were silanized with several types of silanes and blends of silanes to generate a variety of interphases. Composites prepared using these fillers were analyzed for uncured paste workability, vinyl conversion during photo-polymerization, flexure strength, and modulus.
1. Uncured pastes with improved workabilities and visible light-cured composites with mechanical properties that were similar to composites with interphases containing only MPTMS were obtained by blending the traditional MPTMS silane and a non-reactive aliphatic silane (octyltrimethoxysilane, “OTMS”).
2. Cured composites with higher moduli than composites with aliphatic MPTMS interphases resulted from the use of an aromatic silane (styrylethyltrimethoxysilane, “SETMS”).
3. The workability of the uncured composite paste was improved compared to the composite containing the SETMS interphase and the high modulus of the cured composite was maintained when the SETMS was blended at a 50:50 ratio by mass with MPTMS or OTMS.
4. A compression testing method was developed for measuring the modulus of uncured pastes for the purpose of quantitatively assessing paste workability.
Discussion: This research has contributed to our understanding of the relationships between interphase chemistry and the mechanical properties of dental nanocomposite materials. We have also shown that blended silane systems can improve the properties of uncured pastes and cured composites compared to traditional systems with MPTMS interphases. It is expected that these property improvements via blended silane surface treatments will also apply to other types of composites, e.g. those with macro-sized fillers. This work was supported by an interagency agreement of NIST with the National Institute of Dental and Craniofacial Research (Y1-DE-1021-04) and the NRC.
*NIST, 100 Bureau Drive MS 8545, Gaithersburg , MD 20899. Polymers Division, Biomaterials Group, bldg 224, rm B120, ph: 301-975-8091, fax: 301-975-4977, firstname.lastname@example.org. Not a Sigma Xi member. Category: Materials.