Influence of Surface Area and Geometry of Specimens on Bond Strength in a Microtensile Test: An Analysis by the Three-Dimensional Finite Element Method Raquel C. Ferreira, DDS, MS, PhD, 1 Juliana Caldas, DDS, 1 Gustavo A. Paula, DDS, MS, 2 Rodrigo C. Albuquerque, DDS, MS, PhD, 2 Carla M. Almeida, DDS, 1 Walison Arthuso Vasconcellos, DDS, MS, PhD, 2 & Rodrigo Barreto Caldas, PhD 3 1 Department of Dentistry, UNIMONTES, Minas Gerais, Brazil 2 Department of Operative Dentistry, UFMG, Belo Horizonte, Brazil 3 Department of Engineering, UFMG, Belo Horizonte, Brazil Keywords Microtensile test; stress concentration; adhesion; bond strength; dental adhesive. Correspondence Raquel C. Ferreira, UNIMONTES—Dentistry, Campus Universit ´ ario Professor Darcy Ribeiro, S/N – Vila Mauric ´ eia, Montes Claros, Minas Gerais 39401-089, Brazil. E-mail: ferreira_rc@hotmail.com Raquel C. Ferreira is supported by the Fundac¸˜ ao de Amparo ` a Pesquisa do Estado de Minas Gerais (grant for Incentivo ` a Pesquisa e ao Desenvolvimento Tecnol ´ ogico; CDS-BIP-00164-09). This study was supported by the Fundac¸˜ ao de Amparo ` a Pesquisa do Estado de Minas Gerais (CDS APQ-1848-4.03/07). Accepted November 16, 2010 doi: 10.1111/j.1532-849X.2011.00743.x Abstract Purpose: This study employed three-dimensional (3D) finite element analysis to inves- tigate the stress distribution patterns in a microtensile test with the goal of evaluating the effects of the bond surface area and geometry on bond strength. Materials and Methods: Finite element models of six specimens were generated: three stick models and three hourglass models. All models simulated the bond strength between dentin and ceramic. The mechanical properties of the materials—the modulus of elasticity and Poisson’s coefficient—were defined according to a literature review. The base of each specimen was considered inserted (constrained area) and possessed nodes with displacements restricted in all directions. A traction load, which was calculated to generate a uniformly distributed stress of 20 N/mm 2 at the bond interface, was applied to the top of the specimen. The distribution pattern of the generated stress was qualitatively and quantitatively measured based on color scales ranging from blue to red, according to the von Mises equivalent stress. Results: Specimens with similar shapes demonstrated similar stress distributions. Ceramic specimens had a higher stress value (30.35 MPa) compared to specimens consisting of resinous cement (23.59 MPa) and dentin (19.77 MPa). At the bond interface, the specimens with square sections demonstrated stress values ranging from 22.00 to 24.20 MPa. For the circular section, the stress values ranged from 23.40 to 27.00 MPa. Conclusion: The maximum stress values determined for the circular and square sec- tions were similar among specimens with the same interface area. At the bond interface, the highest stress values were observed in hourglass-shaped specimens. Adhesive procedures have caused marked changes in dental practices and alterations in clinical restorative procedures. The rapid development of adhesives together with esthetic restora- tive materials has improved the quality of restorative dentistry. In addition, the development of adhesives has created a need to measure the adhesive bond strength of restorative materials to mineralized tissues. An understanding of the physical phe- nomena that occur in a tooth cavity during material placement, setting, and functional processes is crucial for determining the appropriate restorative techniques and selecting the best mate- rial. 1,2 In recent years, several methods have been developed to evaluate the adhesive bond strength of materials to dental substrates, including mechanical tensile tests, shear tests, and the microtensile test. 1-11 Sano et al 12 proposed the use of the microtensile test in den- tal studies. This test uses specimens of very small dimensions, typically hourglass or stick (parallelograms) shaped, which re- quire a great deal of care at the time of the specimen prepa- ration. 5,12 Some of the advantages of the microtensile test are the possibility of measuring the bond strength in a small area of the interface, the ability to map the bond strength in dif- ferent regions of the tooth, 4,12,13 the requirement for a smaller number of teeth (material savings), 2 and a smaller number of cohesive failures. 14 Although the microtensile bond strength testing method is considered a more reliable adhesion test, it is labor intensive, time consuming, and technically demand- ing. 5 Other limitations include the following: very low bond strengths (<5 MPa) are difficult to measure, specimens are 456 Journal of Prosthodontics 20 (2011) 456–463 c  2011 by the American College of Prosthodontists