Tissue healing in implants immediately placed into postextraction sockets : a pilot study in a mini-pig model

Objective. A pilot in vivo study was conducted to evaluate (1) the rate of osseointegration at apical, middle, and coronal levels of oral implants immediately installed into fresh extraction sockets; (2) the maturation of the newly formed bone surrounding implants during 60 days of healing; and (3) the epithelium seal development. Study design. The premolars of 8 male adult mini-pigs were extracted at each mandibular site under general anesthesia. In the experimental side, Frialit-2 implants were immediately inserted. The gap between bone and implants ranged between 3 and 6 mm circumferencially. Bone specimens were obtained at 7, 15, 30, and 60 days after surgery for histologic and histomorphometric studies. Bone-to-implant contact (BIC), bone volume, trabecular thickness, number, and separation were recorded. Nonparametric exact tests were used to evaluate data. Results. BIC at the coronal level was observed close to 0% at day 7 and increased up to 60% at day 60 after surgery on an average. BIC increased from 11.7% to 47.38% at middle level and from 53.4% to 67.38% at apical level from day 7 to day 60. With respect to bone maturation, in the earlier stages of healing, many thin trabeculae were observed, which, particularly at coronal level, became significantly fewer and thicker in more advanced stages. At day 60, the features of the bone were similar to those of baseline. The epithelium never migrated more than 1.8 mm apically to the top of the alveolar bone level. Conclusion. When implants are placed immediately into fresh extraction sockets, in minipig models osseointegration also occurs without initial bone contact.