Three-Dimensional Image Correlation Analyses for Strains Generated by Cement and Screw-Retained Implant Prostheses

Purpose: This study aimed to measure and compare strains generated by splinted implant crowns retained by cement or screws for two implants with applied load. Materials and Methods: A stereolithic resin model was printed using computed tomography data from a patient missing all mandibular molar teeth. Two 4 × 6 mm implants were consecutively placed in the left side. One set of splinted cement and screw-retained crowns were made to fit the two implants. Image correlation technique was used for full-field measurement of strains using an image correlation software and two synchronized high-resolution digital cameras. A random dot pattern was applied to the model surface. Cameras recorded changes in random dot patterns as prostheses were loaded up to 400 N in vertical and oblique directions using a universal testing machine. Testing was repeated three times for cement and screw-retained prostheses. An image correlation algorithm used the dot pattern to define correlation areas or virtual strain gauge boxes. Three-dimensional coordinates of gauge box centers were determined for each recorded photograph and used to calculate strains. Strain distribution data were compared for major, minor, and von Mises strains for each loading condition, as well as peak and average strains for the field of view using an analysis of variance (α = 0.05). Results: Patterns and magnitudes of strain for cement- and screw-retained splinted crowns were similar under vertical loading. Neither peak nor mean strains were significantly different for the two retention methods. For oblique loading, peak strains were lower for the screw-retained crowns; however, there were no statistically significant differences between the two groups when strains were averaged throughout the entire field of view. Conclusions: Cement retention did not improve the magnitude of transferred strains for splinted implant crowns using either loading condition.