THE ROLE OF LATENCY IN MANDIBULAR OSTEODISTRACTION

Even though osteodistraction has been well established in the extremit ies, the parameters used in craniofacial distraction have been essenti ally borrowed from orthopaedic experience. Latency is widely practised but its relevance has not been fully investigated. The purpose of thi s study was to establish the role of latency in mandibular distraction osteogenesis. Twenty-two growing Wethers sheep were allocated to four experimental groups. Sir; animals were allocated to each of Groups A, B and C and underwent bilateral mandibular corticotomies and attachme nt of an external lengthening de,ice, Latent periods of 0, 4 and 7 day s respectively were observed prior to beginning distraction, The distr action protocol consisted of a rate of 0.5 mm tn ice daily for 20 days , followed by a consolidation phase of 20 days after which the sheep w ere killed, Histology, bone densitometry and 3-point mechanical testin g were performed on the harvested mandibles. Group D formed the contro l group (n=4). Histologically, the distracted bone exhibited bone form ation primarily via intramembranous ossification with scattered island s of cartilage. The regenerated bone had mechanical properties signifi cantly weaker than the undistracted control group (P<0.05), but betwee n the experimental groups no statistically significant differences wer e demonstrable either in mechanical strength or DEXA density. These da ta indicate that a change in latency does not alter the properties of the regenerated bone in mandibular distraction osteogenesis and indeed no latent interval may be necessary at all in craniofacial distractio n. This has implications for the duration of del ice fixation in distr action procedures.