Mineralization and mechanical properties of the canine mandible distraction wound following acute molding

To investigate the influence of an acute single step callus manipulation immediately after distraction on mechanical properties and mineralization of the regenerate, custom made distraction devices were bilaterally placed in the mandibular angle of 15 beagle dogs, allowing to simultaneously compress and stretch the regenerate after completed linear distraction. The animals were divided in three groups (n=5): Group 1 and 2 underwent manipulation of the regenerate, group 3 remained in a linear position. After 42 (group1) and 90 (group 2 and 3) days of consolidation the animals were sacrificed. The mechanical properties were assessed in an Instron testframe and bone density quantified by quantitative computed tomography and three- dimensionally assessed (Scion Image processing and analysis software). After 6 weeks of consolidation 25% of the specimens reached a stiffness which was >/=90% of the mean values of the unoperated reference hemi-mandibles. After a 13 week consolidation period, 62.5% were as stiff as the referenced specimens. Manipulated regenerates, allowed to heal under stable conditions for 13 weeks, had the same mechanical properties as specimens that underwent pure linear distraction. A temporary but not significant delay of osseous healing had to be postulated for the stretched zone after 6 weeks, indicating this area to be more critical than the compressed area.