A statistical evaluation of microtensile bond strength

d e n t a l m a t e r i a l s ( 0 ) 385–391 available at www.sciencedirect.com journal homepage: www.intl.elsevierhealth.com/journals/dema A statistical evaluation of microtensile bond strength methodology for dental adhesives George J Eckert a , Jeffrey A Platt b,∗ a Division of Biostatistics, Indiana University School of Medicine, Indiana University Purdue University Indianapolis, Indianapolis, IN, USA b Department of Restorative Dentistry, Indiana University School of Dentistry, Indiana University Purdue University Indianapolis, 1121 West Michigan Street, Indianapolis, IN 46202, USA a r t i c l e i n f o a b s t r a c t Article history: Objectives The purpose of this study was to determine the correlation between beams from Received 14 October 2005 the same tooth in a microtensile bond strength study and to examine their effect on the Received in revised form interpretation of results 18 January 2006 Methods A flat occlusal dentin surface was exposed using wet 180, 240, and 320-grit SiC Accepted February 2006 paper on caries-free human molar teeth Adhesive was applied followed by mm of composite (CoreRestore2) applied in mm increments Four adhesives were used: Optibond FL, light-cure, dual-cure, and self-cure Optibond Solo Plus Nine beams (1 mm2 ) were obtained Keywords: from fifteen teeth for each group, labeled to indicate the orientation of the beams to each Microtensile bond strength other and stored in artificial saliva at 37 ◦ C for week or months Microtensile dentin Adhesion bond strengths were determined using a non-trimming technique Statistical comparisons Adhesive incompatibility between adhesive-storage combinations were performed using ANOVA Analyses were per- Statistical methodology formed assuming statistical independence between all beams and then repeated using a random tooth effect to account for correlations between beams from the same tooth Results Significant correlations were found between beams No pattern was observed in the correlations related to the orientations of the beams to each other Conclusions regarding statistical significance of comparisons (at alpha = 0.05) were sometimes affected by the incorrect assumption of independent beams The degree of correlation was large enough to severely affect power and sample size calculations Significance Analyses of microtensile dentin bond strength studies need to account for correlations between beams to avoid over-stating statistical significance of study results © 2006 Academy of Dental Materials Published by Elsevier Ltd All rights reserved Introduction The evaluation of a dental adhesive/tooth interface often involves an attempt to determine interfacial bond strength Disagreement exists as to the most effective and beneficial way to determine that bond strength The last decade has seen a tremendous rise in the use of a methodology that has been termed microtensile bond strength testing [1] The popularity ∗ of the microtensile methodology is based on the idea that a better understanding of the strength of the adhesive interface can be obtained with smaller specimens The technique has been associated with fewer dentin cohesive failures and the ability to evaluate regional differences in bond strengths [2] This type of information may lead to more predictable restorative procedures and ultimately decrease the cost of dental care Corresponding author Tel.: +1 317 274 7229; fax: +1 317 278 7462 E-mail address: jplatt2@iupui.edu (J.A Platt) 0109-5641/$ – see front matter © 2006 Academy of Dental Materials Published by Elsevier Ltd All rights reserved doi:10.1016/j.dental.2006.02.007 386 d e n t a l m a t e r i a l s ( 0 ) 385–391 The methodology uses multiple specimens (∼1 mm2 in cross-sectional area) that are obtained from one tooth either as beams or dumbbell shaped specimens Comparisons between adhesives or conditions are often made after pooling the data from those specimens As many as 20 specimens per tooth may be obtained [3] and the number of teeth used for each group appear to have been as few as one [4] The data from these investigations is often evaluated using a statistical methodology known as analysis of variance (ANOVA) During 2004 and the first months of 2005, at least 30 articles were published using some form of parametric ANOVA [5–34] This type of analysis assumes an independence of all of the specimens included within each group being compared [35] It is conceivable that, because the dentin substrate is not uniform, pooling of multiple data points from a single tooth is acceptable methodology However, this assumption requires a significant deviation from the accepted statistical method and, as such, should be thoroughly validated Without that validation, the results of many microtensile evaluations are called into question Dental adhesives have become more confusing to the dental practitioner as more choices have become available An example of this is a current adhesive that provides four different choices; multi-component, light-cured single component, dual-cured single component, and self-etch Advertisements have stated that this provides the practitioner with “the flexibility to choose your technique” [36] Recent concerns about adhesive-core material compatibility [37] and adhesive permeability [38] may provide significant concerns when selecting the adhesive Significant portions of the data fueling the concerns have come from microtensile testing Furthermore, the durability of some adhesives is adversely affected with time [39] A discussion of the clinical implications of these issues is reported elsewhere [40] In this study, the intent was to provide the data necessary (1080 strength measurements) to an appropriate statistical analysis for evaluation of the microtensile technique The various adhesives were selected with the expectation that differences between mean values would be seen The hypothesis tested was that there is a correlation between beams taken from the same tooth for microtensile testing that will impact the statistical interpretation of the results Materials and methods Eight groups of 15 teeth were fabricated for this study (Table 1) Human molar teeth collected under an IUPUI/Clarion IRB approved protocol, were treated in 10% formalin for