Bone-to-implant contact of orthodontic implants in humans--a histomorphometric investigation

The purpose of the present study was to evaluate the percentage of direct bone-to-implant contact (BIC) of orthodontic anchorage implants (Orthosystem) after active orthodontic treatment. Twenty orthodontic implants (diameter, 3.3 mm; length, 4 or 6 mm) were inserted for orthodontic anchorage in different anatomical regions of 18 adult patients (nine males, nine females) aged 18-63 years. Fifteen implants (one per patient) were placed in the mid-palatal area, one implant (one patient) in the retromolar area of the mandible, one in the retromolar area and the mid-palatal area (one patient), and two (bilaterally, one patient) in the zygomatic area. The duration of the unloaded healing period was 3 months while that of the loading period ranged from 9 to 22 months. Subsequently, the implants were removed with a bone drill and prepared for histological and histomorphometric evaluation. Histological analysis was performed using the ground thin-section technology. Outcome variables were clinical implant survival and BIC rates. Statistical evaluation included analysis of the measured values, minimum, maximum, means, and standard deviations of the means. The mean percentage of direct BIC at the endosseous implant body was 68.22 per cent for the palatal implants [n = 16, standard deviation (SD): 14.35], 64.85 per cent (SD: 2.89) for the retromolar implants (n = 2), and 60.45 per cent (SD: 0.49) for the zygomatic implants (n = 2). A relatively high BIC was registered at the surfaces of the loaded implants. This finding might favour the maintenance of osseointegration during orthodontic loading of length-reduced implants.