Statement of problem Whether splinting or not splinting adjacent implants together can optimize the stress/strain transfer to the supporting structures remains controversial. Purpose The purpose of this study was to compare the photoelasticity and digital image correlation (DIC) in analyzing the stresses/strains transferred by an implant-supported prosthesis. Material and methods A polymethylmethacrylate model was made with a combination of acrylic resin replicas of a mandibular first premolar and second molar and threaded implants replacing the second premolar and first molar. Splinted (G1/G3) and nonsplinted (G2/G4) metal-ceramic screw-retained crowns were loaded with (G1/G2) and without (G3/G4) the presence of the second molar. Vertical static loads were applied to the first molar implant-supported crown (50 N-photoelasticity; 250 N-DIC). The resulting isochromatic fringes in the photoelastic models were photographed, and a single-camera 2-dimensional DIC system recorded the deformation at the surface of the resin models. Results Residual stresses were present in the photoelastic model after screw fixation of the crowns. The following average photoelastic stress results (MPa) were found around the loaded implant: G1 (20.06), G2 (23.49), G3 (30.86), G4 (37.64). Horizontal strains (εxx, %) between the molars averaged over the length of the loaded implant were found by DIC: G1 (0.08 ±0.09), G2 (0.13 ±0.10), G3 (0.13 ±0.11), G4 (0.16 ±0.11). Splinted crowns transferred lower stresses to the supporting bone when the second molar was absent. The second molar optimized the stress distribution between the supporting structures even for nonsplinted restorations. Conclusions Both methods presented similar results and seemed capable of indicating where issues associated with stress/strain concentrations might arise. However, DIC, while apparently less sensitive than photoelasticity, is not restricted to the use of light-polarizing materials.
Bibliographical noteFunding Information:
Supported by research grant 2007/06995-3 from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and by research grant 2450/09-7 from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Capes) . The authors thank Neodent for supplying the implants and implant components, and the Minnesota Dental Research Center for Biomaterials and Biomechanics (MDRCBB) for hosting Rodrigo Tiossi's visit and for providing the DIC equipment to support this study.