Crestal bone loss related to immediate implants in crestal and subcrestal position: A pilot study in dogs

Objectives: The aim of the present study was to compare crestal bone loss with different implant designs inserted immediately in crestal or subcrestal position in post-extraction sockets in a dog model. Materials and Methods: The mandibular second, third, fourth premolars, and the first molars of six adult fox hound dogs were extracted bilaterally, and 48 implants were placed immediately in both hemi-arches of each dog. Randomly, eight implants (sky classic ® and blue sky ®) were inserted, four crestally (control group) and four 2 mm subcrestally (test group). Both groups were treated with a minimal mucoperiosteal flap elevation approach. After a 12-week healing period, the animals were sacrificed, and samples were obtained. Biopsies were processed for ground sectioning. Histomorphometric analysis was carried out to compare buccal and lingual bone height loss. Results: All implants were clinically and histologically osseointegrated. Healing patterns examined microscopically at eight and 12 weeks for both groups (crestal and subcrestal) yielded similar qualitative bone findings. At 12 weeks, the distance from the top of the implant collar to the first BIC (ISBc) showed significant difference between implant positions (crestal or subcrestal) in the buccal aspect (P = 0.1253), values for the crestal group being higher (1.79 ± 0.3 mm) in comparison with the subcrestal group (0.89 ± 0.5 mm). Better results were achieved by both implant designs when implants were placed in the deeper position. No significant differences were found in BIC values (P > 0.05). The total BIC at 8 weeks was (46.22 ± 4.29%) for the crestal group and (49.72 ± 2.21%) for the subcrestal group; at 12 weeks, it was (41.54 ± 3.87%) for the crestal group and (56.87 ± 3.46%) for the subcrestal group. Conclusions: Within the limitations of this study, the findings suggest that apical positioning of the top of the implant does not jeopardize bone crest and peri-implant tissue remodeling. However, less resorption of the lingual and buccal crest may be expected when implants are placed 2 mm subcrestally, but this is not related to implant design. Moreover, implants placed subcrestally produced better bone-to-implant contact measurements.