Influence of finish line design on marginal adaptation of electroformed metal-ceramic crowns.
BACKGROUND
Gold electroformed metal-ceramic restorations have been promoted as alternatives to conventional metal-ceramic restorations. However, little is known about the relationship between tooth preparation design and marginal adaptation for this type of crown.


OBJECTIVE
This study evaluated the influence of 3 different finish line designs on the marginal adaptation of electroformed metal copings and metal-ceramic crowns.


METHODS
Three steel dies were prepared for maxillary central incisor crowns with 3 finish line designs: shoulder, rounded shoulder, and deep chamfer preparations. Eight standardized electroformed metal-ceramic crowns were fabricated for each group. Marginal discrepancies were measured at 60 points for each specimen along the circumferential margin at 4 sites (labial, mesial, lingual, and distal surfaces, with 15 points for each site) before and after firing procedures using a laser microscope. Data among the 3 different groups were statistically analyzed using the Kruskal-Wallis test and the Mann-Whitney U test with the Bonferroni correction. Marginal discrepancies between prefiring and postfiring procedures were evaluated using the Wilcoxon signed-ranks test (alpha = .05).


RESULTS
Significant differences in the marginal discrepancies of electroformed metal copings without porcelain and metal-ceramic crowns were found among all groups. The lowest range of median marginal discrepancy values (P < .05) at 4 sites, both before and after firing, occurred with the deep chamfer preparation (17.64-21.78 microm and 23.96-25.72 microm, respectively). The highest range values were observed in the shoulder preparation (38.13-49.89 microm and 73.87-89.44 microm, respectively). In all situations, the marginal discrepancies of the postfiring procedures were significantly greater (P = .02 or less) than those of the prefiring procedures.


CONCLUSIONS
Within the limitations of this study, the marginal adaptation of electroformed metal copings or metal-ceramic crowns is affected by finish line design and sequentially diminished by porcelain firing procedures.
Department of Crown and Bridge Prosthodontics, Nihon University School of Dentistry, Tokyo, Japan.
Hisaka
H
Shiratsuchi
Futoshi
F
Komine
Yoshiyuki
Y
Kakehashi
Hideo
H
Matsumura
D000538:Aluminum Silicates / Q000737:chemistry; D003442:Crowns; D000044:Dental Abutments; D003776:Dental Porcelain / Q000737:chemistry; D017267:Dental Prosthesis Design; D004563:Electrochemistry; D006047:Gold Alloys / Q000737:chemistry; D006358:Hot Temperature; D006801:Humans; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D018613:Microscopy, Confocal; D017680:Potassium Compounds / Q000737:chemistry; D013499:Surface Properties; D019231:Tooth Preparation, Prosthodontic
D000538:Aluminum Silicates; D006047:Gold Alloys; D016876:Metal Ceramic Alloys; D017680:Potassium Compounds; D003776:Dental Porcelain; C016447:feldspar