Biomedical subjects

I L Denry

Publications and source records attributed to I L Denry.

22 records · Page 2Linked to original sources

PubMed1993

Fluoroalkylethyl silane coating as a moisture barrier for dental ceramics.

The performance of dental ceramics is reduced in wet environments due to stress-corrosion limiting restoration lifetime. As analysis suggests that fracture is typically initiated from the internal surface, placement of a thin coating before a restoration is cemented to place may prevent fracture if it acts as a moisture barrier. Of coatings we tested, a fluoroalkylethyl silane (du Pont MPD-7680) showed promise. This study aimed to test a range of concentrations on glass and to determine any strength improvement on dental ceramics. Glass slides (n = 8-9) were indented (29-N load) stored 24 h, etched, coated with 100, 50, and 25% fluorosilane in isopropyl alcohol, and air-cured for 24 h. The slides were fractured on a biaxial fixture in water at 0.5 mm/min and maximum stresses calculated. Uncoated controls were tested in water and liquid N2 to determine the inert strength without stress-corrosion. Results showed increasing mean strength from uncoated (53.6 MPa) to 100% (68.0 MPa) which compared to the 80.4 MPa inert strength. ANOVA showed P < .05. Subsequently the experiment was repeated on discs of three dental ceramics (n = 7-10): feldspathic (Ceramco), glass-ceramic (Dicor MGC), high-leucite (Optec) with the 100% solution only. Mean strength was significantly (P < .01) enhanced in the feldspathic (56.2 MPa, untreated, 70.7 MPa, treated) but not the high-leucite (83.1, 83.0) or the glass-ceramic (283.9, 271.4). Fluoroalkylethyl silane coating reduced stress-corrosion in glass and feldspathic porcelain. It may be a practical approach to reducing fracture of ceramic restorations.

Ceramics↗

PubMed1993

Flexural strength and fracture toughness of Dicor glass-ceramic after embedment modification.

Previous studies on the surface properties of Dicor castable glass-ceramic have shown the formation of a specific crystalline phase at the glass-ceramic/embedment interface. If this phase is not removed by grinding, it leads to an undesirable strength decrease. The aims of this study were: (1) to determine the nature of this surface layer, (2) to promote the formation of a different crystalline phase at the surface with the intention of improving the properties of the glass-ceramic, by modification of the composition of the Dicor ceramming embedment, and (3) to evaluate the fracture toughness and flexural strength of Dicor glass-ceramic after embedment modification. Modifications were made to the embedment by incorporation of 2.5 wt% of lithium fluoride and ceramming at various temperatures. X-ray diffraction was used to determine the crystalline nature of the surface layer. Fracture toughness was investigated by the indentation technique. The maximum bi-axial stresses were calculated after the samples were fractured in water on a ball-on-ring fixture at 0.5 mm/min. With the recommended embedment and ceramming cycle, the crystalline phase constituting the ceram layer was a calcium magnesium silicate CaMg(SiO3)2 (diopside). The crystalline composition of the ceram layer was successfully modified by addition of 2.5 wt% lithium fluoride to the embedment. This promoted the crystallization of mica in the ceram layer and increased the fracture toughness of the glass-ceramic when the ceramming temperature was 950 or 975 degrees C. The flexural strength was significantly increased when the ceramming temperature was 1000 degrees C.

Aluminum↗

PubMed1993

Enhanced chemical strengthening of feldspathic dental porcelain.

Previous studies on ion exchange of dental ceramics have shown that the biaxial flexural strength can be improved by exchanging potassium for sodium ions at temperatures below the strain point. The rubidium ion is bigger than the potassium ion and can also be considered as a candidate for replacing smaller ions, i.e., sodium or potassium, although it has not been used for dental ceramics. The double-step method uses the exchange of a small ion for a large ion (Li for Na) above the strain point, and the further exchange of a large ion for a small ion (K for Li) below the strain point. The purpose of this study was to compare the effect of rubidium-for-potassium ion exchange with that of potassium-for-sodium exchange (Tuf-Coat, G-C International Corp., Japan) on the flexural strength of a feldspathic dental porcelain and to test the hypothesis that a double-step ion exchange can lead to greater strengthening than potassium ion exchange alone. Weight measurements were performed before and after treatment. Qualitative chemical analyses allowed the rubidium, potassium, and sodium concentration profiles to be determined along cross-sections of the specimens. The maximum biaxial stresses were calculated after specimens were fractured in water on a ball-on-ring fixture at 0.5 mm/min. Relative to the untreated control group, the flexural strength of the potassium-exchanged groups was significantly increased, except for those treated at 400 or 500 degrees C. All the groups treated with RbNO3 exhibited a significant increase in flexural strength, with a maximum for the group treated at 450 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum Silicates↗

PubMedDate not supplied

Surface layer characterization after dual ion exchange of a leucite-reinforced dental porcelain.

The dual ion-exchange technique has been shown to improve the strength of feldspathic dental porcelains by first replacing constituent alkali ions with smaller ions above the strain point, and then exchanging the smaller ions for larger ions at temperatures below the strain point. The strength increase is directly related to the thickness of the surface-exchanged layer. This study evaluated the thickness of the exchanged layer after dual ion exchange of a leucite-reinforced dental porcelain. Optec HSP porcelain disks were fabricated, submitted to a dual ion-exchange treatment, and indented at various loads before determining the biaxial flexure strength. The mean flexural strength for the ion-exchanged groups was significantly higher than for control groups, except when the depth of the median crack exceeded 138 microns. Wavelength Dispersive Spectrometry analyses on cross sections showed that the mean potassium amount in the glassy matrix was significantly lower (P < .001) for the treated specimens than for the controls. The mean thickness of the exchanged layer after dual ion exchange was estimated at 140 microns.

Aluminum Silicates↗