A Comparison of the Shear Bond Strength and Failure Mode to Metals of Unsupported and Supported Luting Cement Specimens Joshua J. Cheethama / Joseph E. A. Palamarab / Martin J. Tyasc / Michael F. Burrowd Purpose: To compare the mean shear bond strength (SBS) and failure mode of a resin-modified glass-ionomer luting cement (RM-GIC) to five different metals using unsupported and supported cement specimens with different placement of the shear load. Materials and Methods: A RM-GIC was bonded to five metals using “unsupported” and “supported” techniques at a SBS-specimen diameter of 2.36 mm. The bond was stressed to failure using shear knife and wire loop debonding protocols. For the shear knife method, the distance of the shear force from the interface was 0 mm or 0.3 mm. Failure analysis was assessed by stereomicroscope and SEM. Results: Two-way ANOVA and post-hoc Tukey’s test revealed a significant difference between the unsupported and supported mean SBS. The SBS of supported specimens, where the shear force was applied to the mold that enclosed the specimens, were in most cases statistically significantly higher (p < 0.05) than specimens that were not supported. The mean bond strengths of RM-GIC ranged from 4.5 ± 2.3 MPa to 27.4 ± 3.7 MPa. Analysis of the failure mode showed significant differences (p < 0.001) for the test methods except for adhesion to gold-based metal. The adhesive failure mode was between 91% and 97% for supported specimens and between 47% and 63% for unsupported specimens. Conclusion: Within the limits of this study, supported specimens exhibited higher mean SBS than unsupported specimens. The method of debonding had a significant effect on the mean SBS for RM-GIC bonded to metal. Mold-supported specimens had a higher incidence of adhesive failure than unsupported cement specimens. Keywords: shear bond strength, adhesive, resin-modified glass ionomer, metal. J Adhes Dent 2014; 16: 251–260. doi: 10.3290/j.jad.a31345
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acro- and microshear bond strength (SBS) is the second most studied adhesion test for dental materials that exhibit adhesive properties, only overtaken in popularity by the microtensile bond strength test.30 Due to the large number of varying factors between a
PhD Student, Melbourne Dental School, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Australia. Designed the study, performed the experiments, analyzed the data, wrote the manuscript, discussed the results and commented on the manuscript at all stages in partial fulfilment of the requirements for a degree.
b
Associate Professor, Melbourne Dental School, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Australia. Designed the study, analyzed the data, wrote the manuscript, discussed the results and commented on the manuscript at all stages.
c
Honorary Professorial Fellow, Melbourne Dental School, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Australia. Designed the study, analyzed the data, wrote the manuscript, discussed the results and commented on the manuscript at all stages.
d
Clinical Associate Professor, Faculty of Dentistry, The University of Hong Kong. Designed the study, analyzed the data, wrote the manuscript, discussed the results and commented on the manuscript at all stages.
Correspondence: Joseph E. A. Palamara, Melbourne Dental School, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, 720 Swanston Street, Victoria, 3010 Australia. Tel: +61-3-9341-1532, Fax: +61-3-9341-1599. e-mail:
[email protected] Vol 16, No 3, 2014
Submitted for publication: 01.06.13; accepted for publication: 31.10.13
and within these SBS tests, it is not considered possible to correlate studies, particularly if the substrate is dentin or enamel.9,19,21,34 Although simple, it has been reported that SBS tests can be affected by many variables, including bonding area, type of loading, and crosshead speed.10,18,29,32 The stress concentration at the loading point can cause uneven stress distributions, resulting in tensile and torquing forces at the adhesive interface and ultimately, premature failure of the bond.4,36 In studies on adhesion to teeth, the occurrence of cohesive failure in dentin is common during bond strength testing. In SBS testing, this has been described by a “tensile monolithic fracture hypothesis”, where cracks initiating in the dental material diverge into dentin.39 Interpretation of these mixed failure modes therefore becomes complex. Various methods and equipment have been used to overcome variables such as uneven stress distributions.2,6 The most frequently reported method for determining SBS is to apply a load onto the surface of a cylindrical specimen bonded to a substrate. A shear knife, notched shear knife or wire loop is then used to apply stress to the specimen, either as close as possible to 251
Cheetham et al
Table 1
Metal substrate compositions
Substrate type
Name
Manufacturer
Batch no.
Material composition
Nickel-based metal
Rexillium III
Pentron Alloys; San Diego, CA, USA
2627903
76% Ni, 14% Cr, 6% Mo, 2% Al, 2% Be, Ti, Co
Cobalt-based metal
Wironit
Bego; Bremen, Germany
12419
64% Co, 28.6% Cr, 5% Mo, 1% Si, 1% Mn, 0.35% C
Titanium
Titanium grade 1
Titanium International; Coolaroo, Victoria, Australia
4273378
99.5% Ti
Gold-based metal
Argenco 68
Argen; San Diego, CA, USA
3943835
68.7% Au, 12.4% Cu, 3.3% Ag, 2.9% Pd, 2.9% Pt,