With increasing demand of the implant-supported prosthesis, it is advantageous to use the fixtures of different diameters according to bone quantity and quality of the patients. The diameter of the abutment screw also can be used as the same diameter with that of the standard fixture or directly proportional to the fixture diameter. As the effects of the various diameters of fixture and abutment screw on stress distribution is not yet examined, this study is to focus on the different design of single implant restoration using three dimensional finite element analysis. The five kinds of finite element models were designed by 3 diameter fixtures (m 3.3, 3.75, 5.0 mm) with 3 different abutment screws (m 1.5, 1.7, 2.0 mm). The crown for mandibular first molar was made using UCLA abutment according to Wheeler´s anatomy.
244 N was applied at the central fossa with two different loading direction, vertically and obliquely (30 0) and at the buccal cusp vertically. Maximum von Mises stresses were recorded and compared in the supporting bone, crowns, fixtures, and abutment screws.
The results were as follows:
(1) The minimum stress occured at the central fossa under vertical force and the difference from fixture or abutment screw in all elements such as supporting bone fixture crown a little. The maximum stress occured at the central fossa under oblique forces regardless of the diameter of fixture and abutment screw.
(2) The stress amount about on the supporting bone was equally distributed at the cortical bone and cancellous bone regardless of the diameter of fixture when the vertical force is applied. The stress showed tendency to increase as the rate of five to ten times at the alveolar bone under oblique force, also it was increased when the diameter of fixture was small.
(3) The stress amount of the small diameter fixture was more than the wide diameter fixture in fixture and crown , and it was not much influenced by the diameter of the abutment screw. The maximum stress value
occured at the load point under vertical force, and it was occurred at crown-fixture interface under oblique force.
(4) The stress amount of abutment screw w is different by the diameter of the fixture. It was decreased when the diameter of fixture was wide and distibuted along the whole thread, also it decreased as the diameter
of thread is smaller in 3.3mm fixture.
It showed tendency to decreased the supporting bone and crown fixture when fixture diameter was increased. The wide diameter fixture were not much influenced by the abutment screw diameter. When the abutment screw was wide, the stress in the small diameter was increased. The wide diameter was more advantageous than the small diameter due to the little stress.
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