The influence of porcelain firing cycle on marginal fitness of electroformed metal-ceramic crowns

Metal ceramic restorations are widely used in crowns. The marginal fitness of these artificial crowns is prone to alteration during the firing cycle of porcelain. Gold electroformed metal-ceramic restorations have been introduced as alternatives to conventional metal-ceramic restorations. However little is known about the relationship between procelain firing procedures and marginal adaptation of this type of crown. The aim of the present study was to evaluate the influence of firing procedures on the marginal adaptation of electroformed metal-ceramic crown restoration. One steel die was prepared for maxillary molar crowns with deep chamfer finishing line design. Ten standardized gold electroformed copings were fabricated. Marginal discrepancy was measured at four sites along the circumferential margin of each coping (Midbuccal - Midpalatal – Midmesial - Middistal) using SEM (Mag: X400) prior to and after porcelain firing procedure. Data among the 2 different groups (before porcelain firing) were statistically analyzed using the paired t-test (α=0.05) analysis. The marginal discrepancy of the postfiring procedures (21.45±2.27μm) were significantly greater than those of the prefiring procedures (18.23±1.96 μm) (p<0.002). The porcelain-firing procedures influenced the marginal distortion of electroformed metal-ceramic crown restorations, but the marginal discrepancies for all copings and examined design are clinically acceptable (less than 100 μm).