Orthodontic load on short maxillary implants with reduced sink depth: an experimental study

The aim of this study was to investigate experimentally the positional stability and histomorphometric findings of length-reduced temporary anchorage devices (Orthosystem, length: 4 mm) with reduced sink depth.

For this purpose, four maxillary pre-molars ((2)P(2), (3)P(3)) were extracted from each of four foxhounds. After a 16-week alveolar healing period, 16 implants (four per dog) were inserted into the edentulous areas. Four implants (one per dog) were placed simultaneously in the mid-palatal area. The implants were intentionally submerged to about three-quarters of their length. After a 10-week unloaded implant healing period, the implants in the P3 areas and the palate were loaded (test implants) by means of transpalatal bars fixed on the implants in the P3 areas and Sentalloy traction springs ( approximately 2 N continuous force) inserted mid-sagittally between palatal implants and bars (force application period: 24 weeks). The implants in the P2 areas served as controls.

Clinical measurements and histological evaluation revealed positional stability of the loaded fixtures. Alveolar control implants (ACI) were inserted to a mean depth of 3.2 mm, alveolar test implants (ATI) to 3.3 mm and palatal test implants (PTI) to 2.6 mm. The mean direct bone contact percentage values were 71.3% (ACI), 79.6% (ATI) and 72.2% (PTI).

These results suggest that, probably due to the relatively high percentage of bone contact with implant surface, only 3 mm of intrabony implant length is sufficient to retain positional stability during long-term orthodontic loading.