Influence of Crown-to-Implant Ratio on Stress Around Single Short-Wide Implants: A Photoelastic Stress Analysis

Purpose: The aim of this study was to evaluate the photoelastic fringe patterns around two short-wide implants supporting single crowns with different crown-to-implant (C/I) ratios. Materials and Methods: External hexagon (EH) cylindrical implants (5 x 7 mm) or Morse Taper (MT) conical implants (5 x 6 mm) were embedded individually into photoelastic resin blocks. Each implant received a single metal-ceramic crown, with a C/I ratio of 1: 1 or 2: 1 (n = 10). Each set was positioned in a polariscope and submitted to a 0.5 kgf compressive load, applied axially or obliquely (30 degrees). The polariscope images were digitally recorded, and based on isoclinal and isochromatic fringes, the shear stress was calculated at 5 predetermined points around each implant. Data were analyzed by two-way ANOVA (alpha = 0.05). Results: Under axial loading, the stress was concentrated at the crestal region, and there were no differences between C/I ratio or implant types. In contrast, under oblique loading, EH implants showed lower stress values than the MT group and the 2: 1 C/I ratio showed higher stress concentration for both implant types (p < 0.05). Moreover, MT implants showed stress distribution through a higher area than the EH implant did, with a tendency to direct the stress toward the implant's apex under oblique loading. Conclusion: MT conical short-wide implants showed higher stress values that were distributed through a higher area directed to the implant apex. The C/I ratio influences the stress distribution only under oblique loading.