in vitro study on the effect of degree of convergence angles and different surface treatments on retention of resin bonded full coverage prostheses

This study was directed to evaluate the effect of different degrees of convergence angle [10°, 15°, 20° or 25°] and different types of surface treatments of alloy [Sandblasting with 250 microns] [A1203], tin-electroplating and 9.6% hydrofluoric acid etching] on retention of resin bonded full coverage restorations. A total of sixty sound molar teeth were retained in self-cure acrylic resin blocks and divided into four main groups of 15 each. Each group was subjected to preparation with convergence angle [10°, 15°, 20° or 25°]. The four main groups were sub-divided into three sub groups of 5 each. The restorations of each one of these subgroups was subjected to sandblasting with 250 microns [A1[2]O[3]], tin electroplating or 9.6% hydrofluoric acid etching. All samples after treatment were cemented to its prepared tooth using adhesive resin cement and subjected to tensile test using Lloyd testing machine. The failure load was recorded in kilograms. From the results it was found that, elevation of convergence angle of the prepared tooth surfaces reduced the retentive strength of resin bonded full coverage restorations. Sandblasting using 250 microns [A1[2]O[3] produced a superior bond strength compared with tin electroplating and 9.6% hydrofluoric acid etching

Effect of marginal metal thickness and depth of finish line on the marginal distortion during porcelainization of two types of non-precious alloys

These in vitro studies evaluated the marginal distortion of ceramo-metal restoration under the effect of marginal metal thickness and type of ceramo metal alloy. Two types of ceramo metal alloys; nickel chromium alloy [Wiron 77], and cobalt chromium alloy [Remanium CSE], and one type of dental porcelain [Ceramco II] were used in this study. A master model consisted of three stainless steal master dies fixed on a master base were fabricated. The dies were prepared with shoulder finish line with three different depths [0.5mm, 0.8mm and 1.0mm]. Thirty wax patterns were divided into three groups [10 each] according to finish line depth, and each group subdivided into two subgroup [5 each] according two type of alloy. Porcelain was built up and fired according to the manufacture's instructions. Marginal discrepancy between the cast and the die was measured under stereomicroscope with 16X magnification at four points following each firing stage of porcelain [degassing, opaque, body porcelain and glaze] firing cycle. The results revealed that, both types of alloys revealed no significant differences although the nickel chromium alloy had been shown lower marginal distortion than cobalt chromium alloy. Thinning of metal margin is preferred where there was no significant difference between different finish line depths tested. Porcelain firing had significant effect on marginal distortion, specially in degassing stage