Influence of substrate, shape, and thickness on microtensile specimens' structural integrity and their measured bond strengths.
OBJECTIVE
To verify whether substrate, shape, or thickness of microtensile specimens have a significant influence on their measured bond strength.


METHODS
Sixty-four extracted molars provided microtensile specimens, which were prepared on enamel and dentin, in different shapes and thicknesses. The teeth were randomly divided into 16 groups (n = 4). Groups 1-8 included hourglass-shaped specimens. In Groups 1-4 specimens were prepared from enamel and in a thickness at the bonding interface of 0.5 mm x 0.5 mm, 1 mm x 1 mm, 1.5 mm x 1.5 mm, and 2 mm x 2 mm, respectively. In these same thicknesses, hourglasses were trimmed in Groups 5-8, but the specimens were prepared from dentin. Groups 9-16 included specimens obtained following the non-trimming technique. Groups 9-12 provided enamel sticks in the four evaluated thicknesses. In these same thicknesses and shape but from dentin were cut the specimens of Groups 13-16. Two specimens from each group were viewed using a scanning electron microscope. On the other ones, microtensile bond strength was measured and the values were statistically analyzed.


RESULTS
Substrate, shape, and thickness of the specimens had a significant effect on their recorded bond strength (p < 0.05). Higher bond strength values were recorded by dentin versus enamel specimens and by sticks versus hourglasses. Also, bond strength decreased as specimen thickness increased. SEM analysis revealed that the trimmed specimens, especially if from enamel, often exhibited lines of fracture in the area of action of the bur.


CONCLUSIONS
It seems advisable to avoid the trimming action particularly on enamel specimens. If the hourglass shape is preferred, the cross-sectional area should not exceed 1 mm x 1 mm.
Goracci
Cecilia
C
Department of Dental Materials, School of Dentistry, University of Siena, Viale Bracci, Siena, Italy. cecilia.goracci@tin.it
Sadek
Fernanda T
FT
Monticelli
Francesca
F
Cardoso
Paulo E C
PE
Ferrari
Marco
M
D000704:Analysis of Variance; D001840:Dental Bonding; D003743:Dental Enamel / Q000033:anatomy & histology* / Q000648:ultrastructure; D003799:Dental Stress Analysis; D003804:Dentin / Q000033:anatomy & histology* / Q000648:ultrastructure; D006801:Humans; D008855:Microscopy, Electron, Scanning; D018709:Statistics, Nonparametric; D013718:Tensile Strength; D019228:Tooth Crown / Q000033:anatomy & histology*; D014082:Tooth Fractures / Q000209:etiology; D019246:Tooth Preparation / Q000009:adverse effects