A photoelastic and strain-gauge analysis of interface force transmission of internal-cone implants.

The objective of this study was to compare force transmissions in the peri-implant bone region of implants with various conical implant-abutment mating designs. Photoelastic models of solitary Bicon, Astra Tech, and synOcta and monoblock ITI implants were fabricated. Static vertical and 20-degree oblique forces of 75 N were applied on the implants in separate loading cases, and the generation of isochromatic fringes was observed and photographed in the field of a circular polariscope. Three-element strain gauges were bonded on the models in close proximity to the implants. Under the same loading protocol, the strain-gauge signals were digitized by a data-acquisition system and displayed on a computer using corresponding software at a sample rate of 10 kHz, and the principal strains were calculated. Isochromatic fringe orders around ITI and Astra Tech implants were similar at the collar region and slightly higher than around the Bicon implant under both loading conditions. Strains around the Bicon implant were lower than those around all implants tested under vertical loading (P < .05), whereas the strains around both ITI implants were similar and lower than those around the Astra Tech implant (P < .05). Under oblique loading, strains around both ITI implants were higher than those around other implants tested (P < .05). However, these differences do not seem to have any clinical relevance. Internal-cone implants have similar interface force transfer characteristics that resemble a one-part implant. To reduce stresses in the peri-implant region, implant diameter may be more effective than the type of implant.