Sequential bone healing of immediately loaded mini-implants

Introduction: The relatively small size and the ability to load mini-implants without delay are important changes in the simplification of bone rigid anchorage. The purpose of this study was to analyze interfacial healing 1, 4, and 12 weeks after the placment of titanium mini-implants in New Zealand rabbits by removal torque test (RTT) and scanning electron microscopy (SEM). Methods: Eighteen animals were used in the experiment, in which 72 titanium grade 5 mini-implants 2.0 mm in diameter and 6.0 mm long, were placed. Each animal received 4 mini-implants; 2 were immediately loaded with 1 N. Results: The RTT means for the unloaded mini-implants at 1, 4, and 12 weeks were 15.2 +/- 4.2 N mm (n = 5), 13.1 +/- 5.7 N mm (n = 5), and 54.4 +/- 12.8 N mm (n = 4), respectively. The loaded groups had means of 12.7 +/- 5.1 N mm (n = 4), 11.1 +/- 5.4 N mm (n = 4), and 32.9 +/- 12.8 N mm (n = 5) for the same healing periods, respectively. The statistical evaluation indicated significance in the comparison between loaded and unloaded 12-week groups (P < 0.05). SEM analysis in the loaded group showed the formation of less fibrous interfacial tissue after 4 weeks and more lamellar appearance after 12 weeks. Conclusions: The immediate 1-N load did not cause significant changes in the fixation of the mini-implants after 1 and 4 weeks of bone healing. Nevertheless, after 12 weeks, the loaded group had significantly lower RTT values than the unloaded group without compromising the stability of the mini-implants (P < 0.05).