Orthodontic anchorage capacity of short titanium screw implants in the maxilla. An experimental study in the dog

The aim of this study was to investigate experimentally the effect of long term orthodontic loading on the stability as well as on the peri-implant bone findings of short titanium screw implants (Bonefit, submersion depth 6 mm, phi 4 mm) inserted in regions with reduced vertical bone height. For this purpose, 6 maxillary premolars (1P1, 2P2, 3P3) were extracted from each of 2 foxhounds and reduction of alveolar bone height was performed by osteotomy. After a 16-week healing period, 8 implants (4 per dog) were inserted in the edentulous areas. Simultaneously, 2 implants (1 per dog) were positioned in the palatal suture (one-stage surgery). After an 8-week implant healing period, the fixtures in the P1/P2 areas (n = 4) and the palate (n = 2) were loaded (test implants) by means of transpalatal bars running anteriorly, fixed on the implants in the P1/P2 areas, and Sentalloy traction springs (approximately 2 N continuous force) inserted midsagittally between palatal implants and bars (force application period: 26 weeks). The fixtures in the P2/P3 areas served as controls (n = 4). Clinical measurements and histological evaluation revealed no implant dislocation of the loaded fixtures. These results suggest that short titanium screw implants inserted in the alveolar bone and palatal suture region retain their stability during long-term orthodontic loading, even following a relatively short unloaded implant healing period. Furthermore, it seems that long-term orthodontic loading may induce marginal bone apposition adjacent to the implants.