Journal of Dental Medicine

This investigation was performed according to the widespread application of base metal alloys and few articles published about the marginal integrity of restorations fabricated by these metals.Three standard dies of a maxillary first premolar were prepared with a flat shoulder finish line in buccal aspect and chamfer in palatal. One of them left with no change. On the buccal aspect of the second and third dies 135?and 1607 bevel were added respectively Using dual wax technique, nine wax patterns were formed on each die and casting procedure of selected non precious alloy was performed by centrifugal method. Marginal gaps of each copping seated on dies were measured by scanning electron microscope (SEM) with X500 magnification. Measurements were done on three areas of marked dies on buccal aspect. Measurement son palatal aspect was done on marked midpalatal point as control.Results and statistical analysis showed no significant difference among marginal gaps in lingual aspect.But on the buccal aspect there were statistically significant differences among the groups (P<0.001). Flat shoulder had the best marginal integrity (mean 4 micron). Shoulder with 160' bevel had the most marginal gap (mean 26.5 micron) and shoulder with 1357 bevel was between two other groups (mean 15.7 micron).

Statement of Problem: In order to eliminate the esthetic problem of metal collar in porcelain fused to metal crowns various techniques, such as shoulder porcelain, have been suggested.

Purpose: The aim of this study was to investigate the effects of repeated porcelain firing cycles on the marginal integrity of shoulder in porcelain fused to metal crowns, made of two kinds of alloys: noble and base-metal.

Materials and Methods: In this experimental study, four groups of ten brazen models (Die) were used. Metal crowns of groups A&B were made of a noble alloy and those of C&D of a base-metal alloy. Groups A&C had the shoulder width of 1mm and groups B&D had the shoulder width of 1.5mm. After degassing and opaqing, shoulder porcelain was completed in the area of shoulder. At this stage, the average vertical gap of margin was measured by a reflective microscope (400). Data were analyzed using ANOVA and Duncan tests.

Results: No simoltaneouse interaction between the type of alloy and the shoulder width was found (P=0.709). The type of alloy had a significant effect on marginal integrity (P=0.021) attributing the best marginal integrity of shoulder porcelain to base-metal alloys. Shoulder width played also a significant role on marginal integrity (P=0.00) indicating that the reduction of shoulder width would increase the marginal integrity.

Conclusion: According to these findings, the best marginal integrity of shoulder porcelain is achieved through shoulder width of 1mm along with base-metal alloys.