Influence of different fillers on the properties of an experimental vinyl polysiloxane.
The aim of the study was to evaluate the effect of the incorporation of different fillers on an experimental vinyl polysiloxane (VPS) at two different concentrations, 20% and 40%. Different fillers were added to an experimental VPS. The study was developed in two stages: (i) incorporation of fillers in different concentrations: (a) 20 wt% fillers, and (b) 40 wt%. The fillers were added to experimental VPS and mixed with a speed mixer; (ii) characterization of experimental VPS; after the base paste and catalyst paste were mixed, the experimental VPS was used to make specimens specifically for each test, which were stored at 23°C for 24 hours. The tests were designed according to the specific standardization for the analysis of tensile strength, detail reproduction, Shore A hardness, and elastic recovery. For analysis of filler size pattern, scanning electron microscopy at 1500× magnification was used. The aerosil OX-50 40% (AE), and pure aluminum hydroxide 40% (PAH) groups presented the highest tensile strength and Shore A hardness values. However, those were the only groups that did not present continuous detail reproduction of an intersection of 20 μm line. The elastic recovery was not statistically significant. The undesirable characteristics of VPS (lowest Shore A hardness and tensile strength) were observed when it was added to the composition of acrylic polymer (AP) and fiberglass (FG) in both concentrations, 20% and 40%. In groups AE and PAH, agglomerates of nanofillers were shown in SEM micrography, while the other groups presented different shapes and fillers sizes.
Technical Surfactant Effect on Precipitation Method of Glutinous Rice Flour Filler Size Reduction
Most of the materials used in dentistry contain fillers as part of their composition to modify their chemical and mechanical properties. Filler size reduction needs economic and environmentally friendly materials to control the viscosity on a simple precipitation method using surfactant. Technical surfactants with more affordable prices also could develop filler size reduction. The study aims to analyse different technical surfactant effects on the glutinous rice flour precipitation method of filler size reduction used as an organic filler in dental applications. Precipitation technique is used by preparing the mixture by adding glutinous rice solution of bi-distilled water or sodium hydroxide with different 4% technical surfactant (Span 80 and Tween 80) dropwise to absolute ethanol. Samples were centrifuged at 3000 and 6000 rpm, then washed and characterized using Scanning Electron Microscope (SEM), Fourier Transform Infra-Red (FTIR), X-ray Diffraction (XRD), and Dynamic Light Scattering (DLS). As the result of this study, a size reduction of 714.8 nm with spherical and rod-like shapes could be generated from glutinous rice flour with the addition of Span 80 technical surfactant in 3000 rpm centrifugation speed for organic filler materials using sodium hydroxide solvent. This study suggested an opportunity for the country’s available source improvement in determining dental materials viscosity and its reinforcement.
Effect of occlusal contact size on interfacial stresses and failure of a bonded ceramic: FEA and monotonic loading analyses.
OBJECTIVE
This study investigated whether contact area (i.e. facet size) would influence the loads necessary for subsurface radial crack formation in porcelain specimens bonded to a dentin analog material.


METHODS
Dental porcelain discs (0.5 mm, 1 mm, and 1.5 mm thick) were bonded to compliant bases simulating dentin, and loaded with either a 1 mm, 2 mm, or 3 mm diameter aluminum piston until fracture. Pop-in of the subsurface radial crack from the bonded interface was detected using the acoustic emission (AE) method. Pre-test and post-test finite element analysis (FEA) was used to model the experiment and to calculate subsurface failure stresses.


RESULTS
There were significant differences in loads sustained before fracture according to both the ceramic thickness and the piston diameter (p<0.05; ANOVA and post-hoc Scheffe). Failure loads were found to be proportional to the square of the porcelain thickness. For all thicknesses, significantly higher loads were sustained beneath the 3mm piston than beneath the 1mm piston. FEA calculated failure strengths for the 1 mm thick porcelain (calculated from experimental mean loads) differed significantly for loading with the 1mm piston (168 MPa) or 3 mm piston (60 MPa).


CONCLUSIONS
It appears that both ceramic thickness and contact facet size may be clinically controlled to increase load-bearing ability of all-ceramic crowns. Single value strengths may not accurately model bonded dental ceramics; adjustments such as with Weibull scaling may improve accuracy. These results further suggest that small spherical indenters do not create clinically analogous contact conditions.