RESUMO
Background: Since it is difficult to precisely control the magnitude of force in orthodontic practice, controlling the duration of force is expected to prevent tissue damage. The use of an actuator as an appliance for intermittent force application is a possible solution for controlling the duration. However, effectiveness of an actuator for controlling the duration is still not clear. Aim: To determine whether a short loading duration of intermittent force has the potential to maintain a sound condition of the capillaries and induce dilation of capillaries, which is a requisite phenomenon for orthodontic tooth movement. Materials and methods: Six-week-old male hamsters with a dorsal skinfold chamber attached to an intermittent loading device were used. In three experimental groups, application of intermittent pressure that involved repetition of loading and unloading was performed. The durations of loading/unloading were 1 second/9 seconds (group T10), 1 second/19 seconds (group T20), and 1 second/29 seconds (group T30). Vessels were examined using a fluorescence microscope and a stereomicroscope for 5 days. Results: Widths of capillaries in groups T10 and T20 increased significantly (P < 0.01). In contrast, widths of capillaries in group T30 showed no significant difference from those in the control group. Only group T10 showed bleeding, obvious destruction of vessels, and a significant increase in the rate of disappearance of vessels. Conclusion: In the epidermis, although conditions are limited, a short loading duration of intermittent force maintains a sound condition of the capillaries at the tissue level and induces dilation of capillaries.