Comparative study between the conventional technique and cerec in lab technique in constructing three unit all ceramic bridges

The purpose of this study was to compare the flexural strength and marginal accuracy of a newly introduced Y/Zr Inceram bridges made from Yitrium Zirconia ready made ceramic blocks and constructed by computer controlled milling and sintering Cerec in Lab technique, against Al Zr/ Inceram bridges constructed by the conventional slip cast techniques as a control. Fourteen three-unit FPDs substructures were fabricated: Seven three-unit FPDs substructures were fabricated from Yitrium Zirconia ready made ceramic blocks using the Cerec In Lab technique and seven were constructed from Al Zr/Inceram using the conventional slip cast technique. An Instron testing machine was used to evaluate the flexural strength of the two types of bridges; where a load was applied perpendicular to the long axis of the substructure, in the middle of the occlusal surface of the pontic until failure. The marginal accuracy of the tested substructures was measured using a traveling microscope. Values were recorded and statistically analyzed. Results showed that the highest flexural strength values, exceeding 700 MPa, and the highest marginal accuracy were achieved with Y/Zr Inceram bridges that were constructed using computer controlled milling and sintering Cerec In Lab technique. The differences in mean values were statistically significant with a p-value <0.0001. So it was concluded that the high flexural strength and marginal accuracy record by Y/Zr Inceram bridges constructed using Cerec In Lab technique indicates that it could be useful for highly loaded all-ceramic restorations, especially in the molar region

Microstructural, chemical and mechanical assessment of two feldspathic porcelain materials

Objectives: To evaluate two different feldspathic porcelain materials, namely: Vita Dur Alpha and VitaVM7; firstly by examination of the surface morphology of unetched and etched specimens using scanning electron microscopy [SEM], secondly by studying their chemical compositional element concentration using energy dispersive X-ray [EDX] analysis, thirdly by studying their surface hardness property and finally by determining their shear bond strength to dentine after two hydrofluoric acid etching durations [5 and10 seconds]

Materials and Methods: Twenty specimen discs for each material were prepared and randomly assigned into four groups according to the following experimental protocol: Surface morphology and elemental analysis assessment, microhardness and shear bond strength testing

Results: The surface morphology showed that the two tested materials have a two-phase structure with a major amount of leucite crystals in a glassy vitrous phase. The two phases are more homogeneously distributed in VitaVM7. In Vita Dur Alpha, microcracks were observed in the glassy matrix within the leucite crystals. The surface morphology produced by different hydrofluoric acid [HF] duration [5 and 10 seconds], followed a distinct pattern for each tested material. The pattern was more evident in the VitaVM7 etched specimens. More intense surface disruption was seen in the 10 second-etched specimens. Results of the EDX analysis revealed the presence of considerable amount of alkali metal ions in both tested materials, which were slightly higher in Vita Dur Alpha. VitaVM7 was characterized by having higher silica content. No statistical significant difference was found between the mean VHN values of the two tested materials. There was statistical significant difference between the mean shear bond strength values of the two tested materials regardless of the etching duration. The 10-second etched VitaVM7 yielded the highest mean shear values, whereas, the 10-second-etched Vita Dur alpha yielded the least mean shear values

Conclusions: Differences in ceramic microstructure and ceramic composition are controlling factors in the development of micromechanical retention produced by etching and chemical adhesion mediated by silane. Structure homogeneity did not significantly decrease the hardness of the tested ceramic materials. Hydrofluoric acid etching for 10 seconds does not seem to be the method of choice for conditioning ceramics having inhomogeneous phase distribution and high alkali content. The data provided by the EDX analysis coupled with the information from the SEM elucidated the results obtained from the mechanical testing

Nerve glucose, fructose, sorbitol and myo-inositol in experimental diabetes

In a trial to investigate the biochemical changes associated with diabetic polyneuropathy, nerve contents of glucose, fructose, sorbitol and myoinositol were studied in 20 normal healthy rats versus 20 rats with alloxan-induced diabetes. There was significant increase in the nerve contents of glucose, fructose and sorbitol of diabetic animals as compared to controls. On the contrary, nerve myoinositol showed significant decline in diabetic rats. It appears that the accumulation of alcohol sugars leads to tissue swelling, thickening of basement membranes and reduction in the nerve conduction velocity of the affected diabetic nerves. Moreover, the decreased nerve myoinositol found in diabetic animals, could be an integral factor in the pathogenesis of diabetic neuropathy, since decreased nerve myoinositol inhibits series of biochemical events responsible for maintaining nerve excitability and conductivity