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The anchorage quality of mini-implants towards translatory and extrusive forces
Ulrike Fritz1, Peter Diedrich, Gero Kinzinger
1Department of Orthodontics, University of Aachen, Germany. ufritz@ukaachen.de
Aim:
The objective of the present experimental animal study was to investigate the stability of mini-implants (submersion depth 4 mm, Ø 3.3 mm) for orthodontic anchorage. Additionally the histomorphologic effects of orthodontic loading were to be analyzed, especially with regard to the activity and location of periimplant osteodynamic reactions.
Material And Method:
16 titanium implants (Orthosystem, Straumann, Waldenburg, Switzerland) were inserted in edentulous areas of the upper and lower jaw of four foxhounds. After a 6-month healing period the fixtures were loaded with extrusive forces (50 cN) in group 1, and with translatory forces (200 cN) in group 2. The osteodynamic changes during the 6-month force application period were documented using stains with calcium affinity (polychrome sequential labeling). The histologic analysis comprised: microsection method, fluorescence microscopy, toluidine blue staining, histomorphometry.
Results:
All osseointegrated implants were stable throughout the test period. With respect to the apposition lines, the histomorphometric analysis showed more distinct osteodynamic activity in extrusively loaded than in translatorily loaded implants. The activity was more pronounced in the marginal area than in intermediate and apical implant areas. The extent of peri-implant remodeling activity was up to 980 micro m after extrusive loading and 300-700 microm after translatory loading.
Conclusions:
The results suggest that even mini-implants are suited to orthodontic anchorage tasks. The question of the required minimum size of orthodontic anchorage implants remains unanswered.