Effect of dehiscences to the bone response of implants with an Acid-etched surface: an experimental study in miniature pigs.

Spontaneous early exposure of submerged implants during the healing phase as a factor for early crestal bone loss around the implants is still being controversially discussed. The aim of this study was to examine the potential impact of dehiscences on the osseointegration process of acid-etched dental implants with a shortened healing period in the maxilla. Five animals received a total of 15 titanium implants 8 weeks postextraction. Eight of these implants were placed in the maxilla to osseointegrate within a shortened healing period of 3 months, whereas the remaining implants were inserted in the lower jaw and served as controls with a regular healing time. Polyfluorochrome sequential labeling with xylenol orange, calcein green, and alizarin complexone was performed 2, 5, and 8 weeks after implant placement. After 12 weeks of unloaded and submerged healing, the animals were killed and the implants removed en bloc. After the processing of the undecalcified PMMA-embedded samples, thin ground sections (40-60 µm) were made. The histomorphometric determination of the bone-to-implant contact (BIC) was calculated using light microscopy. The peri-implant bone apposition rate and the direction of bone growth were determined with the fluorescence microscope. For statistical evaluation, the Mann-Whitney U test, Wilcoxon signed ranks test, and Friedman test were chosen. During the healing period, nonartificial dehiscences were observed at 9 implants. The average BIC was 54.19% (14.51%-68.97%). There were significantly lower BIC rates detected for the cervical part of the implants compared with the middle part. An influence of dehiscences on the osseointegration could not be proven. There were no significant differences between the BIC values of the upper and lower jaw. During the observation period from the third to the eighth week after implantation, the average new bone formation rate was 2.32 µm/d (1.76-2.82 µm/d). During this period, the amount of new bone growth decreased insignificantly. Based on the sequence of the polyfluorochrome labeling, an implantopetal (53.03%) as well as an implantofugal bone growth (46.97%) have been observed. It could be assumed that the acid-etched implants offered a prerequisite to osseointegrate under a shortened healing period. The observed dehiscences seemed not to have compromised the rate of osseointegration.