Microfilled composites

Resins are also used for permanent tooth-colored veneers on fixed prostheses, ie, crown and bridges. Compositions for this application include acryflcs, vinyl—acryflcs, and dimethacrylates, as well as silica- or quartz-microfilled composites. The resins are placed on the metallic substrates of the prostheses and cured by heat or light. These resins are inexpensive, easy to fabricate, and can be matched to the color of tooth stmcture. Acrylic facings do not chemically adhere to the metals and are retained only by curing the resin into mechanical undercuts designed into the metal substrate. They have relatively low mechanical strength and color stability, and poor abrasion and strain resistance they also deform more under the stress of mastication than porcelain veneers or facings. 

The DTS has been used as a strength criterion for meeting American Dental Association specification 27. Reported DTS values for microfilled composites range from 30-50 MPa and for the conventional and hybrid composites, from 45-75 MPa [199-204], The wide variation in the ranges of properties reported may relate not only to differences in materials, but also to test methodologies such as state of hydration, surface roughness of the samples, and strain rates [205,206]. 

Thermal expansion differences exist between the tooth and the polymer as well as between the polymer and the filler. The tooth has a thermal expansion coefficient of 11 x 10-6/°C while conventional filled composites are 2-4 times greater [63, 252], Stresses arise as a result of these differences, and a breakdown between the junction of the restoration and the cavity margin may result. The breakdown leads to subsequent leakage of oral fluids down the resulting marginal gap and the potential for further decay. Ideal materials would have nearly identical thermal expansion of resin, filler, and tooth structure. Presently, the coefficients of thermal expansion in dental restorative resins are controlled and reduced by the amount and size of the ceramic filler particles in the resin. The microfilled composites with the lower filler loading have greater coefficient of thermal expansions that can be 5-7 times that of tooth structure. Acrylic resin systems without ceramic filler have coefficients of thermal expansion that are 9 times that of tooth structure [202-204, 253],... 

Resin composites can be classified according to filler particles as fine-particle, hybrid, microhybrid and microfilled other classifications such as flowable or packable are related to their manipulation [1-3]. Quartz and glass (several types) fillers in fine-particle composites have sizes of about 0.5 to 3 pm. Microfilled and hybrid composites contain colloidal silica particles of 0.01 to 0.02 pm diameter incorporated in the polymer matrix. The microfilled composites also contain these submicron particles in groimd 10 to 20 pm filler particles of the polymerized oligomers. The filler volume fraction for composite products varies widely from about 20% to 70%. Clinical selection of composites depends upon strength, wear resistance and esthetics needed for the particular tooth restoration. 

Use of colloidal silica in the so-called microfilled composites allows these resins to be polished, so that less wear occurs and less plaque accumulates. It is more difficult, however, to make these with a high fraction of filler. All the dental composites exhibit creep. The stiffness changes by a factor of 2.5 to 4 (depending on the particular material) over a time period from 10 sec to 3 h under steady load [Papadogianis et al, 1985]. This creep may result in indentation of the restoration, but wear seems to be a greater problem. 

Product 23 (light-cured microfiller composite resin)... 

Physical PropGrtiGS. Table 2 shows some physical properties of unfilled (neat) resins and filled composites. Microfilled composites generally have inferior properties compared to conventional or the more recent hybrid restoratives, with... 

Property Unfilled PMMA Microfilled composite Conventional and filled hybrid composite... 

Micro corrosion cells, 38-15 Microfilled composites, 41-6 Microfluidic gradient generator, in cell-biomaterial microscale interactions study, 46-7-46-9 Microindentation technique, in cell-biomaterial microscale interactions study, 46-9... 

Although nanocomposites have been marketed as materials presenting superior mechanical performance, in some cases the wear and fatigue properties of composites containing nanoparticles were similar or worse than microfilled composites [4], Additional studies, nevertheless, report that dental nanocomposites present high translucency, high polish and polish retention similar to those of microfilled composites, while maintaining physical properties and wear resistance equivalent to those of several hybrid composites [5]. 

Rice SL, Bailey WF, Wayne SF, Burns JA Comparative in vitro sliding-wear study of conventional, microfilled and light cured composite resin and glass ionomer cement. J Dent Res 1984 63 1173-1175. 

Aggregate composition mixture of natural components, mainly quartz-based, including microfillers... 

Mineral microfillers have been tested in a plasticized starch matrix [CAR 01]. For example, micrometric particles of kaolin have been incorporated by extrusion. Due to a significant compatibility between the matrix and the filler, we note an increase in the glass transition temperature, a reduction in water absorption and an increase in the rigidity of the material. However, with the corresponding filler contents, these composites no longer satisfy the standards of biodegradation (at least 90% of the material has to be degraded). 

Beun S, Bailly C, Dabin A, Vreven J, Devaux J, Leloup G (2009) Rheological properties of experimental Bis-GMA/TEGDMA flowahle resin composites with various macrofiller/microfiller ratio. Dent Mater, 25, 198-205. 

It has been shown that, by adding 6% in weight of multi-walled carbon nanotubes or 71.7% in weight of silicon carbide (SiC) microparticles to an epoxy resin, the thermal conductivity of the composites reached values that are 2.9 and 20.7 times that of the neat epoxy, respectively (Zhou et al., 2010). Moreover, to further improve the thermal conductivity of the composites, these authors partially replaced microfillers with nanofillers to obtain a... 

SF is sometimes erroneously called microsilica (crushed crystalline silica), which is also a microfiller of similar chemical composition but with larger particles ranging from 4 to 40 pm. 

The quantitative determination of the influence of the ITZ is essential for mechanical properties (strength and Young s modulus) and durability (porosity) of cement-based composites, but it is difficult to determine the values of bond between two adjacent materials in concrete. Moreover, all measures aimed at modification of the ITZ, like the application of some kinds of microfillers, have an impact on the properties of the composite material itself, and these effects make analysis of test results more complex. The measurements of the ITZ properties in artificial specimens do not allow all conditions to reproduce correctly and tests performed on specimens built from concrete and stone parts have not snpplied particularly useful findings. Tests performed by several researchers, for example, Roy and Jiang (1995) or Mindess and Rieder (1998) on specimens in which the ITZ was artificially created between concrete and stone parts did not supply results that may be directly used for analysis of the interface between matrix and aggregate grains in concrete. 

Goldman, A., Bentui A. (1993) Effects of pozzolanic and non-reactive microfillers on the transition zone in high strength concretes , in Proc. Int. Conf. RILEM Interfaces in Cementitious Composites, Toulouse, October 1992, E6cFN Spon, pp. 53-61. 

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