Subsequently, the implant surfaces were rinsed with sterile saline solution and then all the implants were inserted in the contralateral side of the mandible of the same dog. After a 3-month osseointegration period, the animals were sacrificed with a high dose of pentobarbital (i.v.).

In group 2, the same procedures were applied as in group 1. However, unlike the implants in group 1, the implants in group 2 were sterilized by autoclave treatment at 121 °C for 30 min. Afterwards, the sterilized implants were inserted in the contralateral side of the mandible of the same dog from which the implants were retrieved. After a 3-month osseointegration period, the animals were sacrificed with a high dose of pentobarbital (i.v.).

In group 3, failed implants due to peri-implantitis were obtained from human subjects. The surface of the implants were cleaned and sterilized with autoclave and then the implants were inserted into the mandibles of the dogs. After a 3-month osseointegration period, the animals were sacrificed with a large dose of pentobarbital (i.v.).

In group 4 (control group), no implant insertion was performed and after a 3-month osseointegration period, the animals were sacrificed with a large dose of pentobarbital (i.v.). The preparation times, surgeries, and observation time points of all four groups were summarized on the time arrow (Fig. 5).

Experimental design

Resonance frequency analysis (RFA) measurements

Implant stability was measured using resonance frequency analysis (RFA) with an Osstell® device (Osstell AB, Goteborg, Sweden). All implants were placed with non-submerged healing protocol and the Osstell® sensor was positioned perpendicular to the long axis of the implant in accordance with the guidelines provided by the manufacturer. The results were calculated in the form of objective ISQ values (ranging from 1 to 100). The RFA measurements were performed from four different directions (mesial, distal, lingual, and vestibule), and the mean ISQ was recorded as the final value.