RESOLUTION OF LIGATURE-INDUCED PERI-IMPLANTITIS LESIONS IN THE DOG

The present experiment in the Labrador dog was performed to study tissue alterations that occurred in a peri-implantitis lesion following ligature removal. The study was carried out in 5, 1-year old Labrador dogs. The mandibular right and left 1st molars and 4th and 3rd premolars were extracted to establish recipient sites for implants. After 3 months of healing, 4 titanium fixtures, 2 in each jaw quadrant, were installed and abutment connection carried out in a 2nd stage procedure after another 3 months. After a-month period of healing, cotton floss ligatures were placed in a submarginal position around the neck of the fixture abutments. The ligatures were forced into a position ''apical'' of the margin of the peri-implant mucosa and secured. When the tissue destruction after 4-6 weeks was found to amount to about 25% of the original bone height at each individual implant, the ligatures were removed. 2 dogs were sacrified 1 month and 3 dogs 3 months after ligature removal. The animals were perfused with a fixative and block biopsies were obtained from the implant sites. The biopsies were prepared for histometric and morphometric analyses. The results from the clinical examinations and the microscopic analyses of the peri-implant tissues revealed that: (i) 1 month after ligature removal, an active, destructive inflammatory lesion was present in the soft and mineralized tissues adjacent the implants; while (ii) 2 months later, this lesion at most implant sites had become resting and encapsulated, was confined to the connective tissue adjacent to a pocket epithelium, and was separated from the bone surface by a dense collar of fibrous connective tissue. In 1 of the 3 dogs that were monitored for 3 months, however, 3 out of the 4 implants installed exhibited continued loss of bone, became unstable and were lost between the 10- and 12-week examination interval. The remaining peri-implant tissue at the 4th and remaining implant in this animal was found to harbor an active lesion that involved osteoclastic activity on the surface of the bone crest.