Mandibular ramus height restoration by distraction osteogenesis (DO) is a key procedure in mandibular hypoplasia reconstruction. The objective of this study was to evaluate short-term skeletal changes in the regenerated bone after vertical mandibular ramus DO. Eight Beagle dogs underwent bilateral vertical mandibular ramus DO. Horizontal masseter dissection was performed on both sides and 15% vertical masseter reduction was done on one side to resemble the clinical condition of hypoplastic muscle mass as seen in HFM. After a 7-day latency period, DO was performed 0.5 mm twice a day for 12 days. Four dogs were sacrificed at one-month after the end of distraction and four dogs two-month after. One dog was an unoperated, intact control. After sacrifice, micro computed tomography and mechanical testing of distracted sites were used to assess bone formation and the three point bending strength of the DO site, respectively. Repeated-measures analysis of variance was used to test for differences among times and presence/absence of masseter reduction. One-month and two-month specimens demonstrated bone volume values and mechanical strength below the control values.