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Bond strength of resin composite to differently conditioned amalgam.

Ozcan M, Vallittu PK, Huysmans MC, Kalk W, Vahlberg T

Department of Dentistry and Dental Hygiene, University of Groningen, Faculty of Medical Sciences, Antonius Deusinglaan 1, 9713 AV, Groningen, The Netherlands, mutluozcan@hotmail.com.

Bulk fracture of teeth, where a part of the amalgam restoration and/or the cusp is fractured, is a common clinical problem. The aim of this study was to evaluate the effect of different surface conditioning methods on the shear bond strength of a hybrid resin composite to fresh amalgam. Amalgams (N = 84) were condensed into acrylic and randomly assigned to one of the following treatments (N = 6): (1) Alloy primer + opaquer, (2) Air-particle abrasion (50 mu m Al(2)O(3)) + alloy primer + opaquer, (3) Silica coating (30 mu m SiO(x)) + silanization + opaquer, (4) Opaquer + pre-impregnated continuous bidirectional E-glass fibre sheets, (5) Silica coating + silanization + fibre sheets, (6) Silica coating + silanization + opaquer + fibre sheet application. Non-conditioned amalgam surfaces were considered as control group (7). The mean surface roughness depth (R(Z)) was measured from the control group and air-abraded amalgam surfaces. The resin composite was bonded to the conditioned amalgam specimens using polyethylene molds. All specimens were tested under dry and thermocycled (6.000, 5-55 ( composite function)C, 30 s) conditions. The shear bond strength of resin composite to amalgam substrates was measured in a universal testing machine (1 mm/min). Surface roughness values for the non-conditioned control group (R(Z) approximately 0.14 mu m) and for air-particle abraded surfaces with either Al(2)O(3) or SiO(x) (R(Z) approximately 0.19 mu m and R(Z) approximately 0.16 mu m, respectively) did not show significant differences (p = 0.23) (One-way ANOVA). In dry conditions, silica coating and silanization followed by fibre sheet application exhibited significantly higher results (14.8 +/- 5.6 MPa) than those of the groups conditioned with alloy primer (2.2 +/- 0.7 MPa) (p < 0.001), air-particle abrasion+alloy primer (4.4 +/- 2.0 MPa, p < 0.001), silica coating + silanization alone (6.2 +/- 0.8 MPa, p = 0.009) or non-conditioned group (1.4 +/- 0.6, p < 0.001). Silica coating and silanization followed by additional fibre sheets with opaquer application (23.6 +/- 6.9 MPa) increased the bond strength significantly compared to those of other groups (group 5 vs group 6, p = 0.007; other groups vs group 6, p < 0.001). Thermocycling decreased the bond strengths significantly for all of the conditioning methods tested (for group 1, p < 0.001; for group 2, p = 0.013; for group 3, p = 0.002; for group 4, p = 0.026; for group 5, p = 0.002; for group 6, p < 0.001 and for group 7, p < 0.001).

Published 3 January 2006 in J Mater Sci Mater Med, 17(1): 7-13.
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