Purpose: The aim of the present study was to histomorphometrically investigate crestal bone changes at nonsubmerged implants (Camlog) with different machined collar lengths in a dog model. Materials and Methods: One-stage insertion of sandblasted acid-etched screw-type implants with machined neck sizes of 1.6 mm (CAM) and 0.4 mm (CAM+) was performed in the mandibles of 4 beagle dogs. Both types of implants were inserted so that the implant shoulder (IC) exceeded the alveolar crest for 0.4 mm. Placement was followed by the connection of standard abutments. The animals were sacrificed after 2 and 12 weeks. Dissected blocks were processed for histomorphometric analysis (eg, distance between IC and the coronal extension of bone-implant contact [CBI], the distance between IC and the apical extension of the inflammatory cell infiltrate, and the percentage of bone-implant contact). Results: Histomorphometric analysis revealed significantly increased mean IC-CBI (CAM: 2.4 ± 0.3 mm; CAM+: 1.6 ± 0.1 mm) and BIC (CAM: 77%; CAM+: 80%) values in both groups at 12 weeks. However, mean IC-CBI values were significantly higher in the CAM group (P .01). An inflammatory cell infiltrate was localized to the implant-abutment interface of both CAM and CAM+ implants, and BC was clearly separated from aICT by a subepithelial connective tissue zone. Conclusions: Within the limits of the present study, it was concluded that (1) rough-surfaced implant necks reduced crestal bone level changes after 12 weeks of healing, and (2) microbial leakage apparently did not contribute to the marginal bone resorption in either group. Keywords: animal study, histomorphometry, machined neck, marginal bone level, microbial leakage, rough neck