SHEAR BOND STRENGTHS OF CERAMIC BRACKETS BONDED WITH DIFFERENT LIGHT-CURED GLASS-IONOMER CEMENTS - AN IN-VITRO STUDY

The purpose of this study was to evaluate the shear bond strengths of four light-cured glass ionomer cements used for direct bonding of cera mic brackets, and to compare the results with a two-paste chemically-c ured composite resin. Two commercially available polycrystalline ceram ic brackets, with either chemically or mechanically retentive bracket bases, were evaluated. The brackets were bonded to 100 freshly extract ed bovine incisors, and, after storage in tap water at room temperatur e for 24 hours, they were subsequently tested in a shear mode using a universal testing machine. The maximum bond strength and the site of b ond failure were recorded. With the mechanically retentive base, Fuji Ortho LC produced the highest bond strength (18.50 MPa), which was not significantly different from the values achieved with Concise (14.88 MPa) (P > 0.1) and Photac Bond (13.86 Mpa) (P = 0.1). The lowest bond strength was provided by locomp A20 (5.23 MPa). With the chemically re tentive base, the highest bond strength was measured with Concise (29. 27 MPa), which was significantly (P < 0.01) higher than the values for Photac Bond (16.27 MPa) and Fuji Ortho LC (13.48 MPa). Again locomp A 20 produced the lowest bond strength (3.21 MPa). Three cements (Dyract Ortho, locomp A20 and Fuji Ortho LC) provided higher shear bond stren gths with the mechanical retention system, whereas Concise and Photac Bond gave higher strengths with the silane-treated bracket bases. Howe ver,the strengths were statistically significantly different only for locomp A20 (P = 0.001) and Concise (P = 0.001). With the mechanically retentive base, Dyract Ortho and locomp A20 failed at the enamel-adhes ive interface, whereas Photac Bond and Concise debonded at the bracket -adhesive interface. Fuji Ortho LC failed at both, the bracket-adhesiv e (40 per cent) and the adhesive-enamel (60 per cent) interface. With the chemically retentive base, all the adhesives failed at the enamel- adhesive interface. Only one bracket fracture occurred in this study, and no enamel damage was detected.