[ evaluation of the marginal integrity of porcelain fused to base metal crowns after extension of porcelain to the border of the margin]

In PFM restorations, marginal coverage of the metal framework with porcelain, without producing an overcontoured margin is necessary to enhance esthetics. The aim of this study was to evaluate the marginal integrity of a porcelain fused to base metal crown after extension of porcelain to the border of the margin. Thirty brass standard dies were prepared and divided into 3 groups of 10, based on different finishing lines: 90° shoulder, 1.2-mm-wide; 135° slopping shoulder, 1.2-mm-wide; and shoulder, 0.7-mm-wide with a 45° bevel, 0.5 mm-long. For each die a brass cap was fabricated according to the specific finishing line to accommodate a 0.5 mm thickness. Two metal copings were made on each die which were used as test and control samples. The marginal gap of each coping was measured at 4 points under a reflective microscope after casting and oxidation. Porcelain was applied and extended to the border of the margins in the test group and 0.5 mm short of the borders in the control group. Marginal gaps were measured once more at the same points after porcelain firing. Statistical analysis was performed using t-test. The marginal gaps of all copings increased after porcelain firing. Extension of porcelain to the border of the margins did not significantly increase the marginal gaps. These results indicated that porcelain can be extended to the border of the crown's margin without producing a significant increase in the marginal gap

[ survey of the principles of partial denture construction by dental laboratories in Shiraz]

Background: As conventional prosthesises are still the most common prosthetic treatment for public, this study has been conducted to assess the communication between the dentist and dental laboratories and find the supervision of the dentists on lab works

Materials and Methods: In this descriptive, cross- sectional study, by referring to ten dental laboratories, seven basic steps of the construction of PDRs have been considered and all the necessary information was recorded in a questionnaire

Results: In %83 of the cases, RPDs were constructed on the study diagnostic casts and for %100 of the cases no border molding had been done. %83.7 of the retentive clasps were not actually retentive, but again in %83.7 of them there was some form of reciprocal component. In %96.7 of the cases, the clasp arms were fabricated on unprepared tooth surfaces. All major connectors were rigid and in %42.9 of the cases they had enough distances to gingival margins. In most cases, indirect retainers were absent or were made in wrong places. Only in 10 out of 35 distal extension cases, RPD design was considered and for the rest, no special design was observed. In only %5, guiding planes were made on prepared tooth surfaces and finally it appeared that the majority of RPDs were designed by dental technicians rather than by dentists

Conclusion: The results indicate that dentists frequently use techniques that require a minimum of appointment time. Therefore, a greater emphasis is required to be put on continuation of education for dentist, along with better and more detailed communication between the dentists and dental laboratories