Clinical probing and radiographic assessment in relation to the histologic bone level at oral implants in monkeys

Clinical probing level and radiographic bone level were compared to histologic bone level around screw type oral implants in 4 monkeys (Macaca Fascicularis). Two implants in each monkey retained a fixed partial prosthesis in supra-occlusal contact with an antagonizing splint. These implants were brushed 1 x a week and subgingival cleaning was performed 1 x a month. Unloaded implants in the same monkeys were never cleaned and, additionally, a cotton cord was placed around these to promote plaque accumulation. After 18 months, intraoral radiographs of the implants were obtained and probing levels were recorded with a metal probe using a standardized force of 0.2 N (Vivacare TPS Probe) and again using a moderate, unstandardized pressure. Immediately afterwards the animals were sacrificed. Sections, approximately 50 microns thick, of the implants and surrounding tissue were cut. The average probing levels with unstandardized pressure were 1.1 mm and 3.9 mm coronal to the histologic bone levels for implants with plaque accumulation or excessive occlusal load, respectively. With standardized probing force, the difference between the probing levels and histologic bone levels were even larger. The radiographic bone levels were on average only 0.5 mm and 0.1 mm short of the histologic bone levels for the two groups of implants. Only the radiographic bone level revealed a statistically significant correlation with the histologic assessment.