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

ABSTRACT

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