The influence of static and dynamic loading on marginal bone reactions around osseointegrated implants: an animal experimental study

Although it is generally accepted that adverse forces can impair osseointeg ration, the mechanism of this complication is unknown. In this study, stati c and dynamic loads were applied on 10 mm long implants (Branemark System(( R)), Nobel Biocare, Sweden) installed bicortically in rabbit tibiae to inve stigate the bone response. Each of 10 adult New Zealand black rabbits had o ne statically loaded implant (with a transverse force of 29.4 N applied on a distance of 1.5 mm from the top of the implant, resulting in a bending mo ment of 4.4 Ncm), one dynamically loaded implant (with a transverse force o f 14.7 N applied on a distance of 50 mm from the top of the implant, result ing in a bending moment of 73.5 Ncm, 2.520 cycles in total, applied with a frequency of 1 Hz), and one unloaded control implant. The loading was perfo rmed during 14 days. A numerical model was used as a guideline for the appl ied dynamic load. Histomorphometrical quantifications of the bone to metal contact area and bone density lateral to the implant were performed on unde calcified and toluidine blue stained sections. The histological picture was similar for statically loaded and control implants. Dense cortical lamella r bone was present around the marginal and apical part of the latter implan ts with no signs of bone loss. Crater-shaped bone defects and Howship's lac unae were explicit signs of bone resorption in the marginal bone area aroun d the dynamically loaded implants. Despite those bone defects, bone islands were present in contact with the implant surface in this marginal area. Th is resulted in no significantly lower bone-to-implant contact around the dy namically loaded implants in comparison with the statically loaded and the control implants. However, when comparing the amount of bone in the immedia te surroundings of the marginal part of the implants, significantly (P <0.0 07) less bone volume (density) was present around the dynamically loaded in comparison with the statically loaded and the control implants. This study shows that excessive dynamic loads cause crater-like bone defects lateral to osseointegrated implants.