Purpose: The aim of the present study was to evaluate the validity of a new experimental microthreaded scalloped (MTS) implant design in comparison to a conventional flat-top (FT) implant by measuring the proximal bone loss at different interimplant distances in a canine model. Materials and Methods: MTS implants were placed in one side of the posterior mandible and conventional flat-top (FT) implants were placed in the other side of the mandible in 10 beagle dogs. In five dogs, four each of the MTS and FT implants were placed with an interimplant distance of 2 mm. In another five dogs, three each of the MTS and FT implants were placed at an interimplant distance of 5 mm. All 70 implants (35 MTS and 35 FT implants) were placed in a nonsubmerged (one-stage) manner. The animals were sacrificed 4 months after implant placement, and the crestal bone levels around the MTS and FT implants were measured and compared on radiographs and histologic sections. Results: The experimental MTS im­plants showed significantly less crestal bone loss (0.81 ± 0.34 mm) than the FT implants (1.60 ± 0.42 mm) on radiographs (P < .001). Histologic measurement also demonstrated that there was significantly less (P < .001) marginal bone loss around the MTS implants (0.74 ± 0.41 mm) than around the FT implants (1.53 ± 0.52 mm). There was no statistically significant difference in bone loss between the 2-mm and 5-mm interimplant distances for either MTS or FT implants (P > .05). Conclusion: The experimental MTS implant was more effective in preserving the proximal bone than the conventional FT external-hex implant with the same surface. In this canine model, placement of the implants at either a 2-mm and or a 5-mm interimplant distance did not result in significant differences in marginal bone loss for both MTS and FT implants. This experiment demonstrated a potential benefit of the microthread design on a scalloped implant. Int J Oral Maxillofac Implants 2010;25:681–689

Key words: interimplant distance, microthreaded scalloped implant, proximal bone healing