Necessity of latency period in craniofacial distraction: Investigations with in vitro microdistractor and clinical outcomes.

BACKGROUND: To determine the need for latency period in membranous bone distraction, we performed 1) in vitro comparison of preosteoblasts suspended in a 3D microdistraction model and 2) a clinical study comparing mandibular distraction cases with/without latency. METHODS: In the In Vitro study, Preosteoblasts polymerized in 3D-collagen gel were placed in a microdistractor and separated into three groups: 1) distraction with latency, 2) distraction without latency, and 3) static. After 2, 4, 6, and 8 days, cell proliferation, total protein levels, alkaline phosphatase activity, and osteogenic gene expression were assessed through RT-PCR. In the clinical study, patients underwent mandibular distraction in two groups: 1) latency and 2) no latency (n = 45). The rest of the distraction protocol was identical. Outcome was based on clinical examination, radiographs at six months, and 3D CT scans. RESULTS: In the In Vitro study, The distraction without latency group compared to the latency group had delays in: proliferation, total protein count, alkaline phosphatase activity, osteogenic gene expression in CBFA-1 (fourfold vs. eighteenfold), and in osteocalcin (twofold vs. sixfold). The distraction without latency group had higher apoptotic levels during the first four days compared to the latency group (68% vs. 14%). For the clinical study, similar perioperative complications (5% vs. 6%), X-ray mineralization (93% vs. 94%), bone volume, (8.6 vs. 9.1 cc) and bone density of central distraction zone (78% vs. 81%) were observed with or without latency. CONCLUSIONS: In vitro studies showed poorer results in cell survival, proliferation and osteogenic activity compared to distraction with latency; yet, clinically, there were no differences in distraction with latency versus without.