Photoelastic stress analysis of load transfer to implants and natural teeth comparing rigid and semirigid connectors

Statement of problem. Controversy exists regarding the connection of implan ts to natural teeth. Purpose. This simulation study measured photoelastical ly the biologic behavior of implants. Stress transfer patterns with variabl e implant support and simulated natural teeth through rigid and nonrigid co nnection were examined under simulated functional loads. Material and methods. A photoelastic model of a human left mandible edentul ous distal to first premolar was fabricated having 2 screw type implants (3 .75 x 13 mm) embedded within the edentulous area. Two fixed prosthetic rest orations were fabricated with either a nonsplinted proximal contact or a so ldered proximal contact, and cast precision dowel attachment between implan t areas and simulated tooth. Simulated vertical occlusal loads were applied at fixed locations on the restorations. Stresses, which developed in the s upporting structure, were monitored photoelastically and recorded photograp hically. Results. The rigid connector in the 1 implant situation caused only slightl y higher stresses in the supporting structure than the nonrigid connector. The distally loaded 1 and 2 implant-supported restoration produced the high est apical stresses, which occurred at the distal implant. The rigid connec tor demonstrated the greatest stress transfer in the 2 implant-supported re storation. Conclusions. Lower stresses apical to the tooth or implant occurred with fo rces applied further from the supporting abutment. Although the least stres s was observed when using a nonrigid connector, the rigid connector in part icular situations caused only slightly higher stresses in the supporting st ructure. The rigid connector demonstrated more widespread stress transfer i n the 2 implant-supported restoration. Recommendations for selection of con nector design should be based on sound clinical periodontal health of a too th and the support provided by implants.