Shear bond strength of porcelain to a base-metal compared to zirconia core

Recent clinical results for Zirconia all-ceramic restorations have revealed that the fracture rate 6-15% of the Zirconia framework is so low and the core of Zirconia has high stability. However, chipping-off fractures of porcelain are the most common reason for failures of Zirconia in the fixed partial dentures

Objectives: The purpose of this study was to compare the shear bond strength [SBS] of porcelain in the porcelain fused to metal and all-ceramic crowns with Zirconia core

Materials and Methods: Two groups were selected: porcelain fused to metal [PFM] and porcelain fused to Zirconia [PFZ] [n = 30].In the PFM group, a wax model [10 × 10 × 10mm]was used to cast metal base [Ni_Cr alloy]. In the PFZ group, an acrylic cubic model [10 × 10 × 10mm] was made as Zirconia model for scanning.15 cubic Zirconia samples were milled by CAD-CAM. The procedure of porcelain veneering was conducted by the conventional layering technique up to 2 mm thickness [2.5 × 2.5 × 2 mm]. All specimens were stored in water for 48 hrs. Thermal cycling was conducted for 20000 cycles between 55[degree sign]C and 5[degree sign]C alternatively for 30s.All samples were mounted in acrylic resin and the SBS test was performed, using a universal testing machine. The analysis of data was performed at a significance level of 0.05 using Kolmogorov-Smirnov and Mann-Whitney U-test

Results: Mean of SBS in PFM and PFZ was 24.57 and 20.88, respectively. The results of Mann-Whitney test showed that there was no statistically significant difference between the two groups of porcelain fused to metal and Zirconia in item shear bond strength [p = 0.455]

Conclusions: There was no significant difference between the two groups of PFM and PFZ in the item SBS

[Evaluation of anti-Helicobacter pylori activity of methanol extracts of some species of Stachys and Melia]

The gram-negative bacterium Helicobacter pylori [H. pylori], identified in 1982, is now recognized as the primary etiological factor associated with the development of gastritis and peptic ulcer disease. The growing problem of antibiotic resistance by the organism demands the search for novel compounds from plant based sources. The present study is aimed at evaluating the anti-Helicobacter pylori activity of 10 Iranian plant extracts on clinical isolates of H. pylori. Gastric biopsy samples were obtained from patients presenting with gastroduodenal complications. H. pylori was isolated from the specimens following standard microbiology procedures. The disk diffusion method was used to determine the susceptibility of 12 isolates to methanol plant extracts [Fruit and leaves of Melia azedarach, Melia indica and aerial parts of Stachys setifera, Stachys turcomanica, Stachys trinervis, Stachys subaphylla, Stachys byzanthina, Stachys persica, Stachys inflata, Stachys laxa]. The plants tested at 8 mg/disc concentration demonstrated anti-Helicobacter pylori activity with zone diameters of inhibition ranging from 12-38 mm. Of these, Stachys setifera [aerial parts], Melia indica [Fruit] and Melia azedarach [leaves] showed the most potent anti -H. pylori activity on the isolates. Due to the rise in antibiotic resistance, new sources of anti-H. pylori drugs are needed. The use of medicinal plants may have potential benefit in eradicating such problems. According to the results of this study, further studies will be necessary to investigate the effects of other plants of Iran against H. pylori infectio

[Effect of silica-sol and distilled water ratio on dimensional changes of casting posts]

Dimensional changes in acrylic patterns during laboratory process to fabricate casting are an important issue which could lead to many clinical consequences. Microleakage, lack of retention and fitness are few of problems which could be predicted in the case of dimensional changes in acrylic patterns. So, investigating the factors which could minimize the dimensional change is necessary. This study compares how different proportions of silica-sol and distilled water affect the dimensional changes in castings. This study was an experimental study wherein 30 specimens of acrylic patterns [Duralay] with similar dimensions were prepared and equally divided in five different groups and studied. Using extensiometer digital machine, the acrylic patterns were measured at three portions [length, coronal diameter and apical diameter] with accuracy of 10 microns. 1- The mean average of casting post length compared to changed acrylic patterns was statistically significant in pure distilled water group only. 2- The mean average of changes in casting coronal diameter did not demonstrate any significant differences compared to acrylic patterns. 3- The mean average of changes in casting post apical diameter compared to acrylic patterns using pure distilled water was significant. Because the least value in dimensional change was seen in 2/1, 3/1 ratio of silica-sol and distilled water, these ratios are recommended in fabrication of casting posts in order to have maximum accuracy and minimum micro leakage while building crowns and bridges