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

The present experiment in the Labrador dog was performed to study tiss ue alterations that occurred in a peri-implantitis lesion following li gature removal. The study was carried out in 5, 1-year old Labrador do gs. The mandibular right and left 1st molars and 4th and 3rd premolars were extracted to establish recipient sites for implants. After 3 mon ths of healing, 4 titanium fixtures, 2 in each jaw quadrant, were inst alled and abutment connection carried out in a 2nd stage procedure aft er another 3 months. After a-month period of healing, cotton floss lig atures were placed in a submarginal position around the neck of the fi xture 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 or iginal bone height at each individual implant, the ligatures were remo ved. 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 h istometric and morphometric analyses. The results from the clinical ex aminations and the microscopic analyses of the peri-implant tissues re vealed that: (i) 1 month after ligature removal, an active, destructiv e 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 uns table 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 osteocl astic activity on the surface of the bone crest.