Peri-implant tissue healing at implants with different designs and placement protocols: An experimental study in dogs.

Abstract

To compare the peri-implant tissue response to subcrestal or crestal placement of implants with or without "platform-switched" implant/abutment connections. On each side of the mandible in six Labrador dogs, two "platform-switched" (PS) implants and two implants with matching implant/abutment diameters (PM) were placed in a crestal or a 1.5mm subcrestal position. Sulcus formers/abutments were connected, baseline radiographs obtained and the distance between the abutment-fixture junction (A/F) and the marginal bone level (B) was determined. Five months later, radiographic and clinical examinations were repeated and biopsies were obtained and processed for histological analysis. The radiographic analysis showed that marginal bone level changes occurred during the first observation period (13weeks). PS-implants showed minor marginal bone level alterations during the full observation period (20weeks), regardless of placement depth. For PM-implants, placement had a significant impact on bone level changes; crestal placement resulted in a mean bone loss of 0.4mm and subcrestal placement in a 1.5mm bone loss. The histometric measurements resulted in a distance A/F-B of 0.6 and 0.0mm for PS implants, placed in a crestal or subcrestal position, respectively. The corresponding distance at PM-implants was 1.5mm irrespective of placement protocol. The peri-implant mucosa was thicker at subcrestally placed implants as compared to a crestal placement. Bone remodeling occurred within the early healing phase. During the full 20weeks of observation, PS-implants demonstrated significantly less crestal bone loss compared to PM-implants.