Stress analysis of traumatized incisor 81 Braz Dent J 12(2) 2001 Braz Dent J (2001) 12(2): 81-84 Two-dimensional Photoelastic Str essAnalysis of Tr aumatized I ncisor Bulent TOPBASI 1 Mahir GUNDAY 2 Mustafa BAS 1 Cafer TURKMEN 1 1 Department of Restorative Dentistry and 2 Department of Endodontics Marmara University, Faculty of Dentistry, Istanbul, Turkey In this study, stress of traumatized incisor and the effect of stress on tooth and alveolar bone was studied with two-dimensional photoelasticity. Two homogeneous two-dimensional maxillary central incisor models were prepared. Loads were applied to the labial side of incisal edge and middle third of the crown at angles of 45° and 90°. It was observed that stress was increased on teeth and alveoler bone when load was applied 90° on labial side of inci sal edge. Key Words: trauma, incisor teeth, photoelastic stress analysis. Correspondence: Dr. Bulent Topbasi, Department of Restorative Dentistry, Marmara University, Faculty of Dentistry, Buyuk Ciftlik Sok. No: 6 80200 Nisantasi, Istanbul, Turkey. Tel: +90-212-2319120-205, Fax: +90-212-2465247. E-mail: btopbasi@hotmail.com INTRODUCTION Although traumatic injuries of teeth are not fre- quent, fractures that affect the pulp can cause complex healing and treatment planning. The most vulnerable tooth is the maxillary central incisor, which sustains approximately 80% of dental injuries, followed by the maxillary lateral and the mandibular central and lateral incisors. Root fractures occur rarely on the middle third of the root, and crown fractures are more frequent (1,2). Dental injuries affect predominantly enamel only or enamel and dentin fractures of the maxillary incisors (1). The crown and the root of teeth are fractured according to the direction of the force. Frequently the contour of the fractures are very close to incisal on the labial surface. But on the palatal surface they are verti- cal to the cemento-enamel junction. Two types of methods can be used for studying the mechanical be- havior of teeth: the experimental methods of which the photoelastic method (3-6) and strain gauges (7,8) are well known and often applied for analysis of internal stresses; the numerical methods of which the finite element method is frequently applied (9-14). Noonan (3) was the first to apply photoelasticity to restorative dentistry. Photoelastic stress analysis is based on the property of some transparent materials to exhibit colorful patterns when viewed with polarized light. The patterns that develop are consequently re- lated to the distribution of the internal stresses. This study examined the effect of traumatic forces on the tooth and the surrounding alveoler bone by using two- dimensional photoelastic stress analysis. MATERIAL AND METHODS Two homogeneous two-dimensional central in- cisor modelswereprepared from AralditeB (Ciba-Geigy S.A., Bale, Switzerland), a birefringent plastic material with a modulus of elasticity within the range of human dentin. The geometry of the mid-labiolingual section of the human maxillary central incisor was adapted from Wheeler (15). The models were identical enlargements (X5) of an actual maxillary central incisor whose di- mensions compared with average sizes. Each specimen was 5 mm thick. Alveolar bone was also prepared from Araldite B. The models were loaded with a constant ISSN 0103-6440