Continuous and intermittent bone distraction using a microhydraulic cylinder: an experimental study in minipigs.

Distraction osteogenesis of the mandible is an option in the treatment of mandibular hypoplasia. Today, only intermittent distraction devices are available for clinical application. The aim of this study in minipigs was to evaluate continuous bone distraction using a microhydraulic cylinder. After a seven-day interval, continuous or intermittent distraction of 1.5 mm/day was established for 10 days. Immediately after active distraction, two animals and 20 days later the other four animals were killed and radiographs taken. The mandible was then removed en bloc and the distracted bone examined histologically. Intermittent distraction forces of up to 2500 kPa were necessary to move the cylinders' piston. The pressure needed for continuous distraction was considerably lower (1200-1300 kPa). While the specific histological structure of the varying zones in the distraction gap was similar after continuous and intermittent distraction, bone healing was accelerated after continuous distraction as shown by ultrasonography and scanning electron microscopy.