Polymerization composite shrinkage evaluation with 3D deformation analysis from microCT images.

OBJECTIVES: The aim of this study was to develop a method to experimentally determine and visualize the direction and amount of polymerization shrinkage. METHODS: We modified a composite to include 1.5 wt% traceable glass beads. A cylindrical cavity (6mm diameter, 3mm height) was restored with this traceable composite, with and without dentin adhesive, and digitized with high-resolution micro-computed tomography (microCT). Image segmentation was performed to extract the glass beads from the acquired 3D microCT images (uncured and cured). Afterwards, each glass bead was subjected to local rigid registration. The resulting displacement vectors were used to examine and calculate the changes. RESULTS: In unbonded restorations, the displacement vectors were oriented inwards to the center of mass, although not perfectly. Bonded restorations exhibited two contraction patterns: either toward one side of the cavity or toward the top-surface of the restoration. The displacement vector length values (mean/SD) for the bonded group (46.8 microm/10.0 microm) was significantly higher (p<0.01) than unbonded group (31.3 microm/8.5 microm), and the histogram curve was flatter (skew/kurtosis: 0.10/-0.56) as compared to the unbonded group (skew/kurtosis: 0.03/-0.26). SIGNIFICANCE: The proposed method can visualize real 3D displacement vectors generated by polymerization shrinkage. The bonding quality and cavity geometry are critical for the direction of polymerization contraction. This method has the potential to validate current models concerning the amount and orientation of shrinkage vectors.

Whitening effect and morphological evaluation of hydroxyapatite materials.

PURPOSE: To measure the efficacy of the whitening effect of non-oxidizing and non-acidic nano- and micro-hydroxyapatite materials on the enamel surface and to evaluate the surface changes after treatment. METHODS: Three hydroxyapatite suspensions and two hydroxyapatite mixtures in dissolvable polymer films were applied to a total of 30 extracted caries-free human premolars. After the last material application, a hydrodynamic shear force was generated and applied for 2 minutes to all teeth to simulate mechanical loading of the surface. The tooth color was measured with a dental spectrophotometer. The mean changes of the L*a*b* values between different measurements in each group were expressed as delta E and were analyzed with ANOVA and the Tukey's post-hoc test. RESULTS: The groups of the nano-hydroxyapatite, the hydroxyapatite-nanocrystals and the tricalcium-phosphate exhibited significant delta E values between baseline and after hydrodynamic shear force application (P<0.05). In conclusion, the materials used in the study are very promising alternatives to oxidizing bleaching agents.

Three-body-wear resistance of the experimental composites containing filler treated with hydrophobic silane coupling agents.

This paper evaluated the wear resistance of resin composite materials with fillers which were modified with a novel hydrophobic silane coupling agent. The novel silane coupling agent containing hydrophobic phenyl group 3-(3-methoxy-4-methacryloyloxyphenyl)propyltrimethoxysilane (p-MBS) was synthesized. The experimental light-cure hybrid composites containing 85wt% of filler modified with this silane were formulated. Twelve specimens were prepared for the three-body-wear test with the ACTA machine and the collected data were analyzed statistically using a one-way ANOVA and Tukey's multiple comparison test as the post hoc test. The wear of the composites containing fillers treated with p-MBS was significantly lower compared with the composite materials containing fillers pretreated with 3-methacryloyloxypropyltrimethoxysilane or the commercially composites (AP-X and ELS extra low shrinkage) after a wear test for 200,000 cycles (p<0.05). It is suggested that the resin composites containing fillers modified with the novel hydrophobic silane has high wear resistant, because of the coupling layers treated with this silane had an excellent affinity with the base resin and formed a highly hydrophobic layer on the filler surface.

Micro-computed tomographic evaluation of a new enzyme solution for caries removal in deciduous teeth.

This study evaluated a new enzyme solution (SFC-V) for dentin caries removal, and obtained results were compared with Carisolv. Both solutions were used with a prototype plastic instrument - this being a modified technique for Carisolv. Five carious deciduous teeth were sectioned, and both treatments were applied alternately to each half. Micro-CT observations showed that both treatments resulted in removal of the outer demineralized dentin layer: 28.6% for SFC-V and 28.2% for Carisolv. As for the remaining demineralized dentin, thicknesses of 0.27 microm (SFC-V) and 0.31microm (Carisolv) were observed with no statistically significant differences. FE-SEM analysis revealed that the use of Carisolv resulted in a rougher surface; whereas after SFC-V enzymatic treatment, an organized dentin collagen network with open tubules and few signs of bacteria were observed. In summary, the experimental enzymatic solution and the modified Carisolv treatment removed comparable amounts of carious dentin but with differing resultant surface morphologies.