The marginal fit of a restoration is an important factor for its long-term success. During the fabrication, restorative materials are exposed to stresses. As a consequence, a marginal gap occurs between tooth and the restoration.
Objectives: The purpose of this study was to evaluate the marginal distortion during the firing of porcelain with three different marginal designs.
Material and Methods: Three marginal designs (shoulder, champher, knife edge) were evaluated in this study. A total of 21 porcelain fused to metal crowns were fabricated. They were divided into 3 groups of 7 crowns each. Metal copings were cast with precious metal. Thickness of the metal was 0.3mm. Dimensional changes were measured around the crown in 9 points in horizontal and vertical plane before and after the porcelain firing cycle with a profile projector (SPS 200 U, SOMET). Results were analyzed with “One-way ANOVA" and "student t test". Results: The results are displayed in the following table.
|
Groups |
Shoulder |
Champher |
Knife edge |
|
Horizontal Def. (µ) |
63.7 |
36.7 |
113.3 |
|
Vertical Def. (µ) |
15.75 |
24.1667 |
24.0556 |
At the horizontal plane, marginal discrepancy of champher was significantly smaller than shoulder (p<0.05) and knife-edge (p<0.05). Significant differences (p<0.05) were found between shoulder and champher, and knife-edge at the vertical plane.
Conclusion: Within the limits of this study, among the marginal designs evaluated, shoulder showed an excellent dimensional stability compare to the champher and knife-edge.