Stress distribution of multiple implant-supported prostheses: Photoelastic and strain gauge analyses of external hexagon and morse taper connections

Abstract

Background: To evaluate the stress distribution of three-element prostheses on two different implant systems (External Hexagon (EH) or Morse Taper (MT)) and with two different retention mechanisms (screw-retained or cemented), by photoelastic analysis and strain gauge analyses. Material and Methods: Four photoelastic and 24 strain gauge models of a partially edentulous maxilla were made and were divided in four groups according to connection and retention system: Group I (EH-C) – external hexagon+ cement-retained prosthesis; Group II (EH-S) external hexagon+screw-retained prosthesis; Group III (MT-C) – morse taper+cement-retained prosthesis; Group IV (MT-S) – morse taper+screw-retained prosthesis. The implants were installed in the axial position, the first in the region of element 15 and the distal implant in the region of element 17. Loads of 100 N were applied on the occlusal surface of the prosthesis for 10 seconds. For the photoelasticity analysis, photographic images were taken and were evaluated according to the number of high-intensity fringes. For the strain gauge analysis, the strain gauges were positioned on the marginal crest of the implants and on the apical region, being numbered for analysis of the stress distribution in each region. The electrical signals were captured and processed by specific software. Results: Higher concentration of tension was observed in the apical region of the implants and mainly in the distal implant, where the formation of fringes was higher. The microstrain values obtained for each group were similar: EH-C (454±18,3 μɛ); EH-S (469±94 μɛ); MT-C (466±49,8 μɛ); MT-S (460±36,6 μɛ). It was observed that apical position had higher stress concentrations for all analyzed groups. Conclusion: The different connections and fixation mode did not interfere in the amount of tension generated in the tissue adjacent to the implant, also the region that generated the greatest amount of tension was in the apical region of the anterior implant.