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Abstract
This study was designed to evaluate the effect of dynamic fatigue forces on the retentivity of different resin bonded bridge designs. The investigated designs were (1) conventional (fixed-fixed) design, (2) functionally-split design, (3) fixed-supported design, and (4) cantilever design. In the laboratory part of the study 60 freshly extracted human maxillary central incisors, and 80 maxillary canines with matching dimensions were selected. Identical preparations for all the central incisors and for all the canines were made using the Celay copy milling machine. Proximal grooves were added for 30 central incisors and 40 canines. The proximal grooves were identically prepared using the Celay machine. The prepared teeth were mounted in a specially constructed device that provided the teeth with artificial periodontal membrane with controllable elasticity. This device allowed control of teeth mobility to simulate the average normal teeth nobilities. This mounting device was used to construct 80 laboratory models, representing identical cases of missing maxillary lateral incisors. The laboratory models were divided into 2 divisions : Division I: 40 models with abutments prepared without grooves. Division II: 40 models with abutments prepared with grooves. Each division consisted of 30 models with 2 abutments (central incisor and canine) and 10 models with one abutment (canine only) Each division was divided into 4 groups according to bridge design applied;
Group A: 10 models, received conventional fixed-fixed resin-bonded bridges, Group B: 10 models, received functionally-split resin-bonded bridges, Group C: 10 models, recieved fixed-supported resin-bonded bridges, and Group D: 10 models, received cantilever resin-bonded bridges.