Comparison of the correlation of photoelasticity and digital imaging to characterize the load transfer of implant-supported restorations.
BACKGROUND
Whether splinting or not splinting adjacent implants together can optimize the stress/strain transfer to the supporting structures remains controversial.


OBJECTIVE
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.


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.
Postdoctoral Research Associate, Department of Dental Materials and Prosthodontics, University of São Paulo-Ribeirão Preto School of Dentistry, Ribeirão Preto, SP, Brazil.
Rodrigo
R
Tiossi
Assistant Professor, Department of Prevention and Oral Rehabilitation, Federal University of Goiás-School of Dentistry, Goiania, Brazil.
Erica M
EM
de Torres
Assistant Professor, Department of Dental Materials and Prosthodontics, University of São Paulo-Ribeirão Preto School of Dentistry, Ribeirão Preto, SP, Brazil.
Renata C S
RC
Rodrigues
Associate Professor, Department of Restorative Sciences, University of Minnesota-School of Dentistry, Minneapolis, Minn.
Heather J
HJ
Conrad
Professor, Department of Dental Materials and Prosthodontics, University of São Paulo-Ribeirão Preto School of Dentistry, Ribeirão Preto, SP, Brazil.
Maria da Gloria C
Mda G
de Mattos
Professor and Director, Minnesota Dental Research Center for Biomaterials and Biomechanics, University of Minnesota-School of Dentistry, Minneapolis, Minn.
Alex S L
AS
Fok
Professor, Department of Dental Materials and Prosthodontics, University of São Paulo-Ribeirão Preto School of Dentistry, Ribeirão Preto, São Paulo, Brazil. Electronic address: rribeiro@forp.usp.br.
Ricardo F
RF
Ribeiro
D001031:Apatites / Q000737:chemistry; D001696:Biomechanical Phenomena; D002858:Chromium Alloys / Q000737:chemistry; D003442:Crowns; D015921:Dental Implants; D017267:Dental Prosthesis Design; D019094:Dental Prosthesis, Implant-Supported; D003799:Dental Stress Analysis; D004853:Epoxy Resins / Q000737:chemistry; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008334:Mandible / Q000033:anatomy & histology; D016876:Metal Ceramic Alloys / Q000737:chemistry; D008953:Models, Anatomic; D009532:Nickel / Q000737:chemistry; D010781:Photography / Q000379:methods; D019904:Polymethyl Methacrylate / Q000737:chemistry; D013314:Stress, Mechanical; D014025:Titanium / Q000737:chemistry
D001031:Apatites; D002858:Chromium Alloys; D015921:Dental Implants; D004853:Epoxy Resins; D016876:Metal Ceramic Alloys; C506670:d.SIGN ceramic; C040654:titanium nickelide; D009532:Nickel; D019904:Polymethyl Methacrylate; D014025:Titanium