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

Abstract

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. 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. 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. 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.