Histomorphometrical and CBCT Evaluation of Tissue Loss Progression Induced by Consecutive, Alternate Ligatures in Experimental Peri-Implantitis in a Dog Model: A Pilot Study

Objectives: Soft and hard tissue breakdown was histologically and radiologically assessed around implants with alternate, consecutively placed ligatures on the same edentulous dog hemimandible. The influence of ligatured implants (LI) on adjacent non-ligatured implants (NLI, as a possible naturally induced peri-implantitis) was also evaluated. Material and Methods: Three months after tooth extraction, five dental implants were placed in the dog hemimandible. Two months after abutment placement, ligatures were placed subsequently two months apart on alternate implants, while both intermediate implants were left without ligatures. Ligatures were kept in place during the entire experiment, and no plaque control measures were taken. Eleven months post-implantation, the animal was sacrificed. Undecalcified ground sections were cut, stained with Masson Goldner and MOVAT Pentachrome and evaluated by light microscopy. Soft and hard tissue loss was assessed using histomorphometric and CBCT parameters. Results: All NLI presented deep false peri-implant pockets on the oral aspect and pronounced vertical bone resorption on the buccal aspect. After 2, 4 and 6 months, during the breakdown period, more than 30% of the bone was lost in LI in all directions, while, despite immediate vicinity, NLI displayed less destruction. Intense inflammation, typical for induced peri-implantitis, was present, with similar intensity in LI as NLI, but in different parts of the lesions. Morphometry confirmed intense soft tissue inflammation, more bone resorption and higher amounts of infiltrated connective tissue in LI when compared with NLI. Conclusion: Within the limits of the present pilot study, the adequacy of the experimental dog model based on ligature-induced peri-implantitis was able to be successfully challenged by non-ligature models of spontaneously occurring peri-implant inflammation, while meeting the requirements for experimental designs with a very small numbers of animals. The influence of implants with severe peri-implantitis on adjacent implants resulted in less than expected tissue loss in the latter accession numbers.