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The effect of metal recasting on porcelain-metal bonding: a force-to-failure study
Ruohong Liu1, William M Johnston, Julie A Holloway
1College of Dentistry, The Ohio State University, Columbus, Ohio, USA.
Statement Of Problem:
Noble dental alloys are commonly remelted in the dental laboratory, but the effect of repeated casting on porcelain bond strength requires further documentation.
Purpose:
The purpose of this study was to determine if casting up to 3 times affected metal ceramic bond strength for 3 noble alloys using methodology in ANSI/ADA Specification No. 38.
Material And Methods:
Representative high-gold (Brite Gold XH), gold-palladium (W-5), and palladium-silver (IPS d.SIGN 53) alloys were cast into metal strips (25 x 3 x 0.5 mm), using torch melting. IPS InLine porcelain with overall dimensions of 8 x 3 x 1.1 mm was centrally applied on each strip. Metal ceramic specimens were also prepared after each alloy was melted a second and third time. There were 12 specimens in each of the 9 groups. Force to failure and porcelain bond compatibility index (tau(b)) were determined for each specimen, and statistical comparisons were made using the Ryan-Einot-Gabriel-Welsch multiple range test (experimental alpha=.05). Fractured specimens were examined with a scanning electron microscope.
Results:
Mean values of tau(b) for specimen groups ranged from 40.6 to 48.2 MPa, and there were no significant differences among the 3 alloys after the first casting. For the high-gold alloy, tau(b) was significantly different for the first and third castings. Increases in size and frequency of interfacial voids were observed with the SEM when all alloys were cast 2 additional times.
Conclusions:
All 3 alloys had adequate porcelain bond strength (>25 MPa). The bond strength for the high-gold alloy was significantly greater for the third casting than for the first casting.
