Sub-crestal positioning of implants results in higher bony crest resorption: an experimental study in dogs

Objective: To compare peri-implant soft- and hard-tissue integration at implants installed juxta- or sub-crestally. Furthermore, differences in the hard and soft peri-implant tissue dimensions at sites prepared with drills or sonic instruments were to be evaluated. Material: and methodsThree months after tooth extraction in six dogs, recipient sites were prepared in both sides of the mandible using conventional drills or a sonic device (Sonosurgery((R))). Two implants with a 1.7-mm high-polished neck were installed, one with the rough/smooth surface interface placed at the level of the buccal bony crest (control) and the second placed 1.3mm deeper (test). After 8weeks of non-submerged healing, biopsies were harvested and ground sections prepared for histological evaluation. Results: The buccal distances between the abutment/fixture junction (AF) and the most coronal level of osseointegration (B) were 1.60.6 and 2.4 +/- 0.4mm; between AF and the top of the bony crest (C), they were 1.4 +/- 0.4 and 2.2 +/- 0.2mm at the test and control sites, respectively. The top of the peri-implant mucosa (PM) was located more coronally at the test (1.2 +/- 0.6mm) compared to the control sites (0.6 +/- 0.5mm). However, when the original position of the bony crest was taken into account, a higher bone loss and a more apical position of the peri-implant mucosa resulted at the test sites. Conclusions: The placement of implants into a sub-crestal location resulted in a higher vertical buccal bone resorption and a more apical position of the peri-implant mucosa in relation to the level of the bony crest at implant installation. Moreover, peri-implant hard-tissue dimensions were similar at sites prepared with either drills or Sonosurgery((R)).