Mechanical and Thermal Stress Behavior of a Conservative Proposed Veneer Preparation Design for Restoring Misaligned Anterior Teeth: A 3D Finite Element Analysis  
[PERSON]  
1 Conservative Department, College of Denistry, University of Sulaimani, Sulaimani 46001, Iraq; [EMAIL_ADDRESS] Conservative Department, College of Denistry, University of Sulaimani, Sulaimani 46001, Iraq; abdulsalam.kudid@univsul. commonly-used treatment modality [6]. This approach is currently considered as one of the most desirable, biocompatible, and conservative methods for satisfying a patient's esthetic requirements with minimum damage to tooth structures, by bonding a thin layer of veneer to the tooth surface using adhesive and luting cement [7; 8]. The life expectancy of laminate veneers is influenced by multiple factors, such as tooth morphology, porcelain thickness, the type of luting cement and adhesive system, periodontal response, marginal adaptation, functional and parafunctional activities, and the geometry of the preparation [9]. Preparation design is one of the critical factors affecting the ultimate success and maintenance of veneer restorations. The choice of minimal or no tooth preparation is a key factor in prognosis [10]. Although initial reports described a non-preparation technique, such a design may have negative effects on gingival tissue health resulting from over-contouring and a bulky margin, which restricts cleaning to create an unnatural gingival profile. In addition, gingival recession is also a common problem that has led experts to believe that this approach is compromised [5; 11]. Moreover, the four basic conventional types of non-overlapped (window and feathered-edge) and overlapped (butt-joint and palatal chamfer) preparations optimize the bulky profile and overall contour and provide a definite finishing line, but the thickness of the preparation requires the unnecessary removal of sound tooth structure, exposing the dentin, and thereby reducing the bonding values and causing flexion in the tooth structure [12; 13]. Minimally invasive veneer preparation designs, which have recently become popular, have also been described as an ultraconservative approach that involves less tooth reduction with thicknesses of 0.3-0.5 mm [11]. The suggested design aims to fulfill the three main criteria of strength, fit, and esthetics by overcoming the over-contouring and gingival problems of the non-preparation design as well as preserving as much of the tooth structure as possible, unlike the conventional design. Although veneers are widely used as a conservative method, they have several drawbacks such as microleakage, marginal discrepancies, postoperative sensitivity, fractures, periodontal or pulpal disease, and debonding [14]. The most common failures associated with veneers are fracture and marginal defects, which are observed in 67% of cases after 15 years of clinical performance [15]. The high rates of failure are related to the amount and angle of stresses during mastication, cement polymerization shrinkage, and exposure to different thermal loads [16; 17]. Dental preparation has also been considered as a factor influencing the failure of veneers [18]. Since certain variables in biomedical devices cannot be developed, tested, and monitored in living subjects using in vivo models because of ethical considerations and cannot be assessed in in vitro tests because of serious experimental difficulties [19], a multidisciplinary approach using finite element analysis (FEA) is being increasingly used since it offers an alternative approach to overcoming these problems. As a result, FEA has become an effective tool for visualizing and modeling the biomechanical characteristics of various dental and biological structures, thereby limiting the costs and risks involved in real-life experience [17; 20]. Besides, this approach allows an estimation of the failure risk of unsuccessful dental treatment instead of experiencing this in clinical practice [21].