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[Stress analysis at the metal-enamel junction of the anterior adhesive bridge on non-prepared teeth with three dimensional photoelastic experiment].

To study the dynamic action at the metal-enamel junction of an adhesive bridge, the author calculated the values of principal stress and maximum shearing stress, and determine the stress distribution at the junction of the adhesive bridge, for which an unprepared central incisor and a canine were used as abutments for a defect of the maxillary lateral incisor, using a three-dimensional photoelastic experiment. Two models were produced for the experiment on the basis of assumed intercuspal position: Model 1 with a loading point set around the incisal edge and model 2 with a loading point at the lingual cingulum. The results were as follows. (1) In both Models, tensile stress was distributed as the principal stress at the metal-enamel junction, except for the loading point, in the adhesive bridge of the non-prepared type. (2) The maximum principal stress was observed in compressive stress at the loading point in the central incisor of Model 2, being 720 kgf/cm2. Model 2 tended to show a higher concentration of stress at the loading point than Model 1. (3) Values of compressive stress at the loading point of the central incisor and canine were compared in Models 1 and 2. The central incisor showed higher stress values than the canine in both models; the canine had 50-60% of the stress values in the central incisor. (4) Investigation of distribution of the maximum shearing stress revealed a value of 360 kgf/cm2 on the surface directly under the loading point of the central incisor and 240 kgf/cm2 at the loading point of the canine in Model 2, and 215 kgf/cm2 at the loading point of the central incisor and 120 kgf/cm2 at the loading point of the canine in model 1. These values were all above the shearing stress of adhesive resin cement.