Photoelastic Evaluation of Load Transfer to an Implant Connected to a Natural Tooth under Varying Types of Periodontal Support

Purpose: The purpose of this study was to compare the stress transfer from a fixed restoration, supported by an implant restored with either a segmented or non-segmented implant abutment, connected to a simulated tooth with decreased foundational support by photoelastic evaluation.Methods: A photoelastic model of a human left mandible, edentulous posterior to the first premolar, was fabricated, with a 3.75×13 mm screw-type implant embedded within the edentulous area. The edentulous areas were restored with a three-unit fixed prosthetic restoration with the distal implant abutment connected to the simulated tooth abutment. The implant abutments consisted of either a segmented conical abutment or a non-segmented UCLA abutment. A hemiseptal periodontal defect was created by the removal of buccal and disto-buccal tissues to simulate decreased support caused by a 4 mm infrabony defect. Vertical occlusal loads were applied at fixed locations on the restorations for the simulated periodontal condition. The stresses which developed in the mandible were monitored photoelastically and recorded photographically.Results: Decrease of the foundational support of the tooth resulted in higher stresses transferred to the mesial and apical aspects of the implant as compared with those in the non-defect control condition. Similar results were obtained for both segmented and nonsegmented abutment restorations.Conclusion: Within the limitations of this study, application of load to the simulated abutment teeth with decreased periodontal support resulted in higher stresses around the supporting implant structure for both abutment designs. The distribution and intensity of the stresses were similar for segmented and nonsegmented abutments.