Effects of Regional Tooth Structure and Sectioning Orientation on Micro-Shear Bond Strength

Published

October 16, 2008

Author(s)

Joseph M. Antonucci, Walter G. McDonough, Gary E. Schumacher, Y Shimada

Abstract

Enamel and dentin are anisotropic materials because of their highly oriented microstructures that arises from the prismatic apatite structure of enamel and the tubular structure of dentin, respectively. The purpose of this study was to examine the regional effects of tooth structure and the direction of tooth sectioning on the bonding ability of a self-etching primer system (Clearfil Liner Bond 2V), compared to a non-priming system that requires phosphoric acid (H₃PO₄) as an etchant (K-etchant gel and Clearfil photobond). To assess bond strength, a newly developed micro-shear bond test was employed. Compared to conventional shear tests, the micro-shear procedure allows for the testing of extremely small bonded surface areas, e.g., approximately} 0.4 mm², and thus, lends itself to the regional and orientational mapping of tooth structure. Two regions of enamel, cuspal and middle coronal enamel, and three regions of dentin, cuspal, cervical (near the dentin-enamel junction) and root dentin, were chosen and then sectioned in three different directions, horizontally, axially and tangentially. Slices of the sectioned tooth structure were bonded with each adhesive system and studied by the micro-shear bond test. In addition, observations of the conditioned surfaces and the sheared sites after debonding were performed with scanning electron microscopy (SEM).In the case of enamel bonding, the bond strengths of the non-priming system were significantly influenced by the anisotropic structure of enamel; high at the surface perpendicular the enamel prisms (26 MPa to 31 MPa) and low at the surface parallel to the enamel prisms (13 MPa to 14 MPa; one way ANOVA, P < 0.05, Student's t-test, P < 0.05). The lower bond strengths obtained with the H₃PO₄ based adhesive, when the bonding was parallel to the enamel prisms, probably were due to creation of a weakened apatitic surface created by over etching. By contrast, the effect of the self-etching primer was less influenced by the orientation of the prismatic structure of enamel; 20 MPa to 22 MPa was obtained from all surfaces (one way ANOVA, P > 0.05; Student's t-test, P > 0.05). With both bonding systems no significant differences in enamel bonding between cuspal and middle coronal enamel were observed (Student's t-test, P > 0.05). However, significant differences were observed in the case of the horizontal sections with the non-priming system (Student's t-test, P < 0.05).In the case of dentin bonding, the self-etching primer system gave significantly higher bond strengths (22 MPa to 26 MPa) than the non-priming system (12 MPa to 16 MPa; Student's t-test, P < 0.05). With regard to sectioning orientation and region, no significant differences were observed with either of the systems (one-way ANOVA, P > 0.05), but the mean shear bond strengths tended to be slightly higher toward the cusp, and lower close to the root dentin. SEM microphotography showed that the self-etching primer effectively modified the smear layer without being excessively destructive of either enamel or dentin surfaces. The moderate surface treatment of dentin by the self-etching primer may account for the high bond strengths obtained with this adhesive system. By contrast, the H₃PO₄ based adhesive gave lower bond strengths to dentin because the hybrid layer formed does not provide good mechanical interlocking with the infused, polymerized resin due to acid-induced collapse of demineralized collagen.

Citation

International Symposium on Advanced Materials With Biomedical Applications

Pub Type

Journals

Keywords

adhesion, anistropy, dentin, enamel, micro-shear bond test, self-etching primer

Citation

Antonucci, J. , McDonough, W. , Schumacher, G. and Shimada, Y. (2008), Effects of Regional Tooth Structure and Sectioning Orientation on Micro-Shear Bond Strength, International Symposium on Advanced Materials With Biomedical Applications (Accessed December 15, 2024)