Sequential bone healing of immediately loaded mini-implants: histomorphometric and fluorescence analysis

Introduction: Mini-implants are often immediately loaded for orthodontic treatment; however, changes in interfacial tissues caused by early loading and its effects might compromise the mini-implant's function. The purpose of this study was to compare the healing of interfacial tissues 1, 4, and 12 weeks after the placement of titanium-alloy mini-implants in New Zealand rabbits; some of the implants were loaded immediately and others were left unloaded. Methods: Eighteen animals were used in the experiment. Each received 4 titanium grade 5 mini-implants (2.0 x 6.0 mm), 2 of which were immediately loaded with 1 N of force. Tissue healing was verified at 1, 4, and 12 weeks after placement. Four different fluorescent molecules were injected into the rabbits to label calcium deposition. After the rabbits were killed, mineralized bone samples with the mini-implants were removed, fixed, cut, stained, and observed with bright-field, polarized, and fluorescence microscopy. Results: After 12 weeks of healing, higher bone contact and bone area were observed than after 1 or 4 weeks, regardless of loading. Differences between the loaded and unloaded groups were not observed (P < 0.05) at 1 and 4 weeks. The bone deposition rate was higher in the loaded group. Conclusions: The 1-N immediate force application did not compromise bone formation around mini-implants. (Am J Orthod Dentofacial Orthop 2010; 137:80-90)