tresses induced by different loadings around weak abutments A. Kevser Aydin, DDS,a and A. Erman Tekkaya, MSc, Dr-Ingb University of Ankara, Faculty of Dentistry, and Middle East Technical University, Ankara, Turkey Stresses and deflections of abutments induced by various loadings were analyzed with a two-dimensional finite element model. The biomechanic system consisted of the mandibular posterior three-unit fixed partial denture (FPD). Four different loading types were analyzed: (1) a distributed force of 600 N; (2) concentrated nonaxial and (3) axial 300 N forces at the marginal ridge of the molar; and (4) a concentrated vertical 300 N force at the center of the pontic. All computations were conducted for three different alveolar bone levels. The premolar exerted a greater pressure during occlusal loadings (except axially) on the alveolar bone than the molar. According to the stresses induced in the alveolar bone, the most critical loading was the distributed force. With diminishing periodontal support, stresses elevated in the biomechanic system and critical increases were noted for the concentrated nonaxial load on the molar. (J PROSTHET DENT 1992;68:879-84.) T he primary purpose of the dentition is mastica- tion of food. This mechanism involves the muscles of mastication that provide the motion and force, the teeth exerting the force on the food, and the periodontium sup- porting the teeth. Forces applied to the masticatory system are manifested by the developm.ent of various stresses that are distributed according to the direction and magnitude of the forces, the periodontal support, and the shape of the roots. Under normal conditions, the dentition can tolerate the effects of functional forces, but this system can be al- tered by the loss of tooth and/or supporting bone causing an alteration in the stress levels. Hence, masticatory forces that are normally harmless may be traumatic in a compro- mised system. The effect of these changes on the masticatory system were analyzed by various authors. Hood et a1.l investigated stresses induced in the supporting bone surrounding a tilted molar by using both the photoelastic and the finite element methods. A similar finite element analysis was performed by Takahaski et a1.2 for a fixed partial denture (FPD) with a blade-vent implant abutment. The effect of various types of pontic designs was examined by Hood et ah3 using simple analytic models and photoelasticity. All of these studies were based on normal levels of alveolar sup- port. Conversely, Wright and Yettram analyzed with the finit.e element method the effect of the supporting alveolar bone for teeth individually loaded or designated as canti- lever FPD abutments under the action of various applied forces. Sulik and White5 studied the stresses surrounding aProfessor, Department of Prosthodontics, University of Ankara, Faculty of Dentistry. bAssociate Professor, Department of Mechanical Engineering, Middle East Technical University. 10/l/40359 THE JOURNAL OF PROSTHETIC DENTISTRY Fig. 1. Finite element model of FPD for normal perio- dontal support: dentin (orange), pulp (blue), periodontal ligament (between orange and green, 0.25 mm thick), thin lamina of compact bone (between green and violet-blue, 0.25 mm thick), cancellous bone (violet-blue), gold FPD (yellow). Total number of elements were 1240, nodes 1144, and width of cancellous bone was 54.4 mm. abutment teeth by using a photoelastic model at various levels of periodontal support. Finally, a quantitative two- dimensional finite element analysis was conducted for a similar problem by Tekkaya and Aydin,6 and in their study, the effect of an FPD on the induced stress was recorded. This study quantitatively analyzed, by the finite element method, the stress and deflections induced by different loads surrounding FPD abutments with various levels of periodontal support. 879