Photoelastic Stress Analysis of Load Transfer by Implant Supported Restorations

Objectives: Controversy exists regarding splinting adjacent implant-supported restorations when a distal proximal tooth contact is present or absent. The aim of this study was to compare two designs of implant-supported prostheses using photoelastic stress analysis. Methods: A photoelastic model (Araldite) was made with acrylic resin replicas of a first premolar and a second molar and with threaded implants (Titamax GT - Neodent) replacing the second premolar and first molar. A second model was made without the second molar acrylic resin replica. Metal-ceramic screw-retained crown designs were splinted (G1 and G3) and non-splinted (G2 and G4). The splinted metal frameworks presented levels of misfit with the abutments under 20 μm and strains transferred to the bone simulant were analyzed after tightening the abutment screws. Vertical static loads applied to the crowns included a balanced occlusal (100N) and simultaneous punctiform load on the second premolar and first molar implants (100N). Resulting stresses were monitored and photographed. Results: Quantification (MPa) of the isochromatic fringes determined the following results according to each load condition: balanced occlusal G1 (14.06), G2 (18.81), G3 (10.79), G4 (12.44), and simultaneous punctiform G1 (16.31), G2 (12.19), G3 (10.88), G4 (13.74). Stresses were generated in the models after screw fixation of the crowns despite the low levels of misfit. Splinting the crowns resulted in better stress distribution in the supporting bone and body of the implant when the second molar replica was absent. The presence of a second molar and of an effective proximal contact contributed to a better stress distribution between supporting structures even when non-splinted restorations were analyzed. Conclusions: Within the limitations of this study it is recommended to splint adjacent restorations when an effective distal contact is absent. Grant sponsor: FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo); Grant number: 2007/06995-3.