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Int J Oral Maxillofac Implants. 2014 Jul-Aug;29(4):819-25. doi: 10.11607/jomi.3191.

Microcomputed tomographic and biomechanical analysis of orthodontic microscrew stability under continuous or intermittent force.



To evaluate and compare the influence of continuous and intermittent forces on stability of titanium microscrews.


One hundred forty-four microscrews were inserted bilaterally in the intraradicular zones of the maxillary first molar and second premolar in 36 beagles. Loads were delivered consecutively in the continuous group (n = 12), in cycles of 12 hours on/paused for 12 hours in intermittent group A (n = 12), and in cycles of 24 hours on/paused for 24 hours in intermittent group B (n = 12). The on/off cycles were repeated for 1, 3, 5, or 7 weeks, after which the animals were sacrificed, and microcomputed tomography (micro-CT) and pull-out testing were performed.


The micro-CT parameters of the microscrews in all three groups increased gradually with loading time. The value of peak load at extraction (Fmax) increased and reached a peak at week 5 but dropped slightly at week 7. In the continuous group, all measurements were lower than those in the intermittent groups at all times examined. All values in intermittent group A were higher than those in intermittent group B.


An intermittent loading regimen appears to be more favorable for obtaining stability than continuous loading, and a 12-hour/12-hour on/off loading cycle is superior to a 24-hour/24-hour on/off protocol in promoting bone-implant contact.

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