Objective: This study evaluated the progression of experimental peri-implantitis in dogs using implants with different surface coatings. Methods: Thirty-six implants with four different surfaces (machined; titanium plasma-sprayed-TPS; hydroxyapatite-HA; and acid-etched) were placed in 6 mongrel dogs. Five months after implantation, peri-implantitis was induced by ligatures placement to facilitate plaque accumulation. The ligatures were changed at 20 day-intervals for 60 days. After sixty-days the ligatures were removed and supragingival plaque control was initiated for 12-months. Clinical attachment level (CAL), bone height and microbiological samples were obtained at baseline, at 60 days and at 425 days. The microbiological samples were studied by polymearase chain reaction by amplifying the 16S rDNA and by use of strain specific probe. Results: CAL changed around all implant surfaces after ligature placement (p<0.0001). However, the means of CAL were not statistically significant among the different surfaces (p>0.05). The range of CAL variation, calculated between baseline and 60 days and between 60 and 425 days decreased. The HA showed the greatest bone loss measurement (4.78±0.38mm) and the TPS showed the smallest bone loss (4.27±0.62mm). However, statistical significance was not assessed for different coatings (p>0.05). Bone loss increased during the entire experiment (p<0.0001). Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia, Bacteroides forsythus, Campylobacter rectus, Fusobacterium nucleatum, Fusobacterium nucleatum ss vicentii, Eikenella corrodens, Neisseria spp., Treponema spp. and spirochetes were detected around all surfaces both after 60 and 425 days, although no statistically differences were observed around different implant surfaces. Conclusions: The clinical data observed at initial phase showed rapid and severe peri-implant tissue breakdown associated with bacterial shift toward gram-negative flora. After ligature removal, the progression of peri-implantitis was observed. While there was no significant difference observed between different implant surfaces, HA surfaces appeared to be more susceptible to peri-implantitis in this experimental dog model.(Grants FAPESP 00/02433-1 and 98/10100-0, CAPES)

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