Bonding orthodontic brackets to porcelain : an in vitro assessment of the shear bond strength to feldspathic porcelain subjected to etching and/or to pretreatment with two silane coupling systems

Abstract

Six groups of nine feldspathic porcelain buttons embedded in acrylic were randomly subjected to different surface regimens: no surface treatment, chemical treatment with two different silane systems, mechanical retention with hydrofluoric acid etching, combined mechanical retention and chemical treatment (with two silane systems). Five premolar teeth, also embedded in acrylic, were used as a control group. Orthodontic lower incisor brackets of known surface area were bonded to porcelain and enamel surfaces by means of a microfilled orthodontic composite. The samples were stored in water for seven days, and thermocycled (100 cycles, between 4 and 60[degrees]C). The groups were then subjected to shear forces directed parallel to porcelain and enamel surfaces in an Instron testing machine. The debonded porcelain surfaces were observed microscopically. Mean bond strengths and s.d. for each group were calculated and compared. The mean bond strengths (in kg/cm2) were: Group A (no surface treatment): bonding failed during water storage or thermocycling; Group B (one component silane system, Porcelain jacket conditioner, by Reliance): 121.13 [plus or minus] 41.6; Group C (two components silane, Silane porcelain primer, Caulk/Dentsply): 118.33 [plus or minus] 587; Group D (8% hydrofluoric acid etching for 4 min.): 34.07 [plus or minus] 23.07; Group E (8% hydrofluoric acid for 4 min., plus one component silane system, by Reliance): 219.87 [plus or minus] 37.39; Group F (8% hydrofluoric acid for 4 min., and two component silane system, by Caulk/Dentsply): 124.89 [plus or minus] 76.85. The results suggest that: - combined mechanical and chemical phenomena produce the highest strength, but porcelain fractures result; - etching porcelain with 8% hydrofluoric acid produced less bond strength than silane treatment; - silane primed porcelain surfaces and natural teeth may produce comparable results; the two silanes tested behaved differently.