In vivo bone tissue response to a canasite glass-ceramic.

The aim of this study was to determine the biocompatibility and osteoconductive potential of a high-strength canasite glass ceramic. Glass-ceramic rods were produced using the lost-wax casting technique and implanted in the mid-shafts rabbit femurs. Implants were harvested at 4, 13 and 22 weeks and prepared for light and electron microscopy. Hydroxyapatite was used as a control material. Hydroxyapatite implants were surrounded by new mineralised bone tissue after 4 weeks of implantation. The amount of bone surrounding the implant increased slightly at 13 weeks. In contrast, canasite glass and glass ceramic implants were almost entirely surrounded by soft tissue during all the time periods. Close contact between bone and canasite glass-ceramic implant without the intervening fibrous tissue was observed in only a few regions. The canasite formulation evaluated was not osteoconductive and appeared to degrade in the biological environment. It was therefore concluded that the canasite formulation used was unsuitable for use as implant. Further work is required to improve the biocompatibility of these materials with bone tissue. It is possible that this could be achieved by reducing the solubility of the glass and glass ceramic.

Osseointegration and osseoconductivity of hydroxyapatite of different microporosities.

The aim of this study was to determine the relationship between changes in microporosity and the osseointegration and the osseoconductivity of hydroxyapatite (HAp). HAp cylinders were manufactured by a combination of uniaxial powder pressing and different sintering conditions, with different percentages of microporosity: HAp-I with 3.96+/-0.75% microporosity, HAp-II with 15.66+/-1.60% microporosity, and HAp-III with 29.72+/-0.69% microporosity. These HAp cylinders were surgically implanted in rabbit femurs. After 8 and 12 weeks, the femurs were removed, fixed, sectioned, ground, and stained by Stevenel's blue/Van Gieson for light microscopy and histomorphometry. Some ground sections were routinely processed for SEM. The osseointegration and the osseoconductivity were determined by means of image analysis and the data were submitted to ANOVA. In all cases the cortical bone was repaired and the HAp facing the medullary canal was lined with endosteum, which in some areas exhibited thin bone tissue formation. SEM observations showed no differences in the morphology of tissue-HAp interfaces for the three different porosities of HAp. There were no statistical differences between the groups related to either osseointegration or osseoconductivity. These results suggest that neither osseointegration nor osseoconductivity of HAp are influenced by changes in HAp microporosity.

Ceramic surface preparations for resin bonding.

PURPOSE: To evaluate the effects of hydrofluoric acid (HF) and acidulated phosphate fluoride (APF) primers on differently prepared leucite-containing feldspar ceramic surfaces. MATERIALS AND METHODS: Discs of a leucite-containing feldspar ceramic were prepared following the manufacturer's instructions. Surfaces were either polished, grit blasted or prepared with a diamond bur and then subjected to a range of etching procedures using HF or APF. The surface topography was examined using scanning electron microscopy (SEM). Back-scattered imaging, EDS and X-ray diffraction (XRD) were used for microstructural and compositional analysis. RESULTS: The etching process with HF consisted of a preferential attack of the leucite phase relative to the glass but also removed all features of the previous surface preparation. In contrast, APF etching resulted in the formation of surface deposits, superimposed on the surface roughness created by the prior surface preparations. It was not possible to identify the deposits after APF etching using XRD.

Shear vs. tensile bond strenght of resin composite bonded to ceramic / Força elástica da união do cisalhamento de resina composta com cerâmica

Since the mode of failure of resin composites bonded to ceramics has frequently been reported to be cohesive fracture of either ceramic or resin composite rather than separation at the adhesive interface, this study was designed to question the validity of shear bond strength tests. The reasons for such a failure mode are identified and an alternative tensile bond strength test evaluated. Three configurations (A, conventional; B, reserved; and C, all composite) of the cylinder-on-disc designed were produced for shear bond strength testing. Two-dimensional finite element stress analysis (FEA) was carried out to determine qualitatively the stress distribution for the three configurations. A tensile bond strength test was designed and used to evaluated two ceramic repair systems, one using hydrofluoric acid (HF) and the other acidulated phosphate fluoride (APF). Results from the shear bond strenght tests and FEA showed that this particular test has as its inherent feature this measurement of the strength of the base material rather than the strength of the adhesive interface. In the tensile test, failure invaliably occured in the adhesive layer, with HF and APF showing a similar ability to improve the bond of resin composite to ceramic. It is concluded that the tensile bond strength test is more appropriate for evaluating the adhesive capabilities of resin composite to ceramics