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Since restored teeth are subject to more damages than intact teeth, investigating their fracture behavior is important. However, so far, improvement of the debonding behavior of the restoration and fracture of restored teeth considering the geometry of the restoration and different restorative materials has remained understudied. The aim of this paper is to numerically and experimentally investigate the debonding behavior of the restoration in premolar teeth in order to reduce the stress of restoration thereby reducing the mechanical failure. the fracture test for intact and Standard Class-II Mesial–Occlusal–Distal (MOD) restoration premolar teeth restored with several types of composite and conventional adhesive was performed in order to investigate their fracture behavior. The mechanical properties and fracture of composites as well as the adhesives used in experimental tests were obtained through separate standard mechanical tests. In addition, a number of composites and other adhesives were also chosen from other references, and by numerically simulating the fracture process of intact teeth and those restored with the materials of interest, the fracture behavior and yield load limit were investigated and predicted for them. Next, in order to reduce the stresses of bonding region and improve the damage behavior, using the stress-induced material transformation (SMT) optimization algorithm applied as code in finite element (FE) software, the shape of the restoration has been optimized based on different restorative materials. In order to confirm the numerical results, the fracture tests of teeth samples were performed with conventional and optimized restoration forms. Furthermore, using scanning electron microscopy (SEM) method, the fracture surface of the tested samples was examined. since the fracture behavior of teeth restored with different materials is different, the optimized MOD restoration would be also different for each of these restorative materials. By selecting TU-shape for the restoration in each of the samples, the debonding resistance and final fracture of teeth compared to the MOD restoration increased 51% in P d and 11% in P f for numerical results and 40% in P d and 4% in P f for experimental results. The obtained results suggest that choosing a proper shape for the restoration based on the properties of restorative materials leads to diminished normal and shear stresses and enhanced debonding resistance. Also, the yield load limit of the defective teeth would also improve considerably. The clinical importance of this study is to predict strength of restored teeth and cavity shape optimization under variable conditions. Also, this paper introduces effective parameters on strength reduction/enhancement to dentists. [ABSTRACT FROM AUTHOR]

• This study helps to predict the strength of premolar teeth. • Taguchi Method was used to design the experiments and reduce the number of tests. • The interaction effect results of Taguchi analysis recommended spherical indenter. • The results of SEM indicated that the presence of micro-cracks leads to fracture. • The quality, gender and indenter factors are more effective than other parameters. The purpose of this study is to investigate dental strength and mechanical behavior of Premolar teeth with fissure sealants. Due to the large number of studied parameters, Taguchi algorithm was used to design the experiments and reduce the number of tests. 36 Premolar teeth were selected from three different age groups (child/young/Adult), gender (Male/Female), indenter (Flat/Wedge/Sphere) two types of quality (Intact/Restored) and jaw (Maxilla/Mandible). In this study, two kinds of adhesive (Margin/Single Bond) and fissure sealant material (Seal.it/Wetbond) with various strength and modulus of elasticity were chosen. Also, tooth was stored under different relative humidity amounts (52% and 95%), and was curried by light cure device with intensities of 1000 and 1200 W/cm2. The etching process was performed in acid concentrations of 32% and 37%. The compressive loading was carried out using a universal test machine under displacement-control. The results of interaction effects of gender on age demonstrated that in young age group, male teeth are stronger than female teeth while in child and adult age groups, male and female teeth show relatively same values. The interaction effect results of Taguchi analysis between different indenter surfaces and age groups recommended the spherical indenter, due to the distinction of strength results among different age groups and consequently, ability to investigate the interaction effects between indenter and other parameters. As expected, the results show that the quality factor is the most effective factor. In terms of dental materials and jaw type, the amount of changes is also quite noticeable. Also, the effect of other parameters (humidity, etching, light cure intensity, and adhesive) is negligible in comparison with others. [ABSTRACT FROM AUTHOR]