Compensating for poor primary implant stability in different bone densities by varying implant geometry: a laboratory study.

The aim of this study was to determine the influence of implant diameter and length on primary stability in artificial bone blocks. In total, 240 implants of various diameters (Ø 3.3, 4.1, and 4.8mm) and lengths (8 and 12 mm) were inserted in four artificial bone blocks of different densities (D1-D4). The primary stability for each bone block density was measured and compared with the primary stability of a narrow and short implant (Ø 3.3mm, length 8mm) in the next higher density block. Analysis was done by three-way ANOVA, and mean differences were determined with the 95% confidence interval. Levels of primary stability achieved by choosing the next higher diameter or length were not comparable to those of the next level of block density. However, equivalent values could be achieved by selecting the largest diameter for short and long implants in the lowest block density D4, as well as for long implants in bone type D2. The diameter of an implant has greater influence on primary stability than length. In particular, in the case of poor bone quality, a variation of implant geometry can lead to significant improvement in primary stability.