EXPERIMENTAL PERI-IMPLANT TISSUE BREAKDOWN AROUND HYDROXYAPATITE-COATED IMPLANTS

THIS STUDY MONITORED EXPERIMENTAL peri-implant tissue breakdown around hydroxyapatite (HA)-coated titanium dental implants. Thirty-two HA-co ated cylindrical implants, in groups of two, were bilaterally inserted in the posterior maxilla and mandible in 4 Macaca mulatta monkeys. Tw o months after healing-abutment connection, a 2-month plaque control p rogram was initiated. Clinical and radiographic recordings and peri-im plant submucosal microbial samples were then obtained (baseline). Cott on ligatures were next placed around the healing-abutments and plaque control measures were abandoned. Clinical and radiographic recordings were repeated at 5 and 10 months post-baseline. Microbial samples were repeated at 10 months post-baseline, and ligatures were removed. Clin ical, radiographic, and microbial examinations were again repeated at 11 months post-baseline. Mean modified plaque index (mPI; P < 0.01), g ingival index (GI; P < 0.01), and bleeding on probing (BOP; P < 0.05) scores increased over the plaque accumulation period, The mPI, and GI scores decreased after ligature removal (P < 0.001). Mean probing dept h (PD) and clinical attachment level (AL) increased between baseline a nd the 5- and 10-month examinations (Delta PD 3.0 mm; Delta AL 2.7 mm; P < 0.05). PD values were reduced following ligature removal (P < 0.0 5), AL values and BP scores remained unchanged. A significant negative correlation was found between induced defect depth and width of kerat inized mucosa at baseline (P = 0.03). At baseline, the submucosal micr obiota was dominated by coccoid cells. Following ligature placement, t he microbiota included a large proportion of Gram-negative anaerobic r ods, predominantly Porphyromonas gingivalis, Bacteroides forsythus, an d Fusobacterium species as well as beta-hemolytic streptococci. Ligatu re removal had a limited effect on the composition of the submucosal m icrobiota. This non-human primate study indicates that ligature-enhanc ed plaque accumulation is a precursor of progressive peri-implant tiss ue breakdown around HA-coated implants. The associated microbiota rese mbles that of peri-implantitis and destructive periodontal disease in humans, This preclinical model may be useful to study modalities aimed at arresting peri-implant tissue breakdown and at regeneration of bon e in peri-implantitis defects.