An in vivo analysis of an elliptical dental implant design

The interface attachment strength and histology of an elliptical hydroxylapatite-coated (HA) endosseous dental implant were compared with those of an otherwise identical cylindrical dental implant. The implant designs were tested in two canine in vivo models: healed mandibular extraction sites and the femoral unicortical plug. The implants were evaluated 15 weeks post-implantation. The elliptical geometry of the dental implant was not found significantly to enhance axial pull-out strength or torsional implant-bone interface attachment in either in vivo model. The cylindrical implant absorbed more energy to failure in both the mandible and the femur; however, the difference was not statistically significant. Differences in the interface shear attachment strength between the two models (mandible and femur) were statistically significant when the maximum load to failure was normalized by the actual bone contact surface area. In all cases, femoral values were significantly greater. Examination of HA-coating thickness revealed uniform coatings on both implant types which were well maintained in vivo. Mechanical failure occurred primarily at the metal substrate-HA interface in each type of implant in both models. The amounts of bone apposition to both implants in both models were identical. Coating break-up and inflammatory response to the particulate debris were minimal.