Marginal Adaptation of Metal Ceramic Crowns Cast from Four Different Base Metal Alloys before and after Porcelain Application

Abstract

Introduction: Marginal adaptation of a crown is an important factor affecting its clinical acceptability and durability; also, poorly fitting cast restoration enables bacterial plaque accumulation and leads to teeth caries and periodontal deterioration.

Purpose: The purpose of this study was to evaluate marginal adaptation of 4all, Verabband2, T3 and Supremcast V base metal alloys before and after porcelain firing.

Material and Method: In this experimental study, a sound maxillary first premolar was prepared with chamfer and shoulder-bevel finish lines in palatal and buccal surfaces, respectively. Then the metal die was fabricated. Six points were marked 1 mm apical to the margin in the buccal and palatal surfaces. Forty impressions were taken from metal die by polyether impression material. Then, 10 frameworks were fabricated with each alloy type on stone dies. The vertical margin discrepancy between the frameworks and the marked points on metal dies were measured before and after porcelain firing. Paired sample t-test and One-way ANOVA, followed by multiple comparison tests (Tukey test) were used to evaluate data. In this study, statistical significance was defined at p<0.05.

Results: Before porcelain firing, T3 alloy showed the lowest marginal discrepancy on chamfer finish line (13.13 ± (1.26)); but, the highest values were for Supermcast V copings and shoulder-bevel finish after porcelain application (30.83 ± (2.01)). The mean marginal discrepancies of buccal and palatal surfaces before porcelain application were significantly lower for all alloy types (p<0.001).

Conclusion:  The marginal adaptation of all four metal alloys was clinically acceptable and the thermal cycles of porcelain firing affected marginal adaptation.

Keywords: Crown; Marginal adaptation; Metal ceramic alloys