An in vitro evaluation of distractors used for osteogenesis

Objective. The objective of this investigation was to evaluate and compare the mechanical behaviors of distracters used for osteogenesis under various conditions by means of common engineering standards. Study design. Five groups of 5 synthetic mandibles were used in this study (N = 25). The first portion of the investigation compared mandibles without intervention (group A [controls]; n = 5), mandibles that had uniform osteo tomies stabilized with an external distracter (group B; n = 5), and mandibl es that had simulated sagittal osteotomies rigidly fixated with 3 positiona l screws (group C; n = 5). The second portion of the investigation compared uniform osteotomies (group B; n = 5) and uniform corticotomies (group D; n = 5) that were stabilized with the same external distracter. The last port ion of the investigation compared osteotomies stabilized with an external d istracter (group B; n = 5) and osteotomies stabilized with an internal dist racter (group E; n = 5). Each construct was subjected to vertical loads on a mechanical testing unit. Common engineering standards, including yield lo ad, yield displacement, maximum load, displacement at maximum load, and sti ffness, were measured, recorded, and compared by means of a 1-way analysis of variance and a Scheffe multiple comparison test or independent-samples t test. The means between groups were considered significant for P<.05. A po lynomial best-fit curve was calculated for the load/displacement data for e ach group. Results. During the first portion of the investigation, no significant diff erences were noted between the control, rigidly fixated sagittal osteotomy, and external distracter with osteotomy groups for displacement at maximum load (P = .19). Significant differences were noted between groups for yield displacement (P = .009), yield load (P < .001), maximum load (P < .001), a nd stiffness (P < .007). Failures occurred in the control and rigidly fixat ed groups with fractures of the synthetic mandibles. Failures occurred in t he external distracter group with permanent deformation or torsion of the p ins. During the second portion of the experiment, no statistically signific ant differences were noted between the corticotomy and osteotomy groups in stiffness (P = .363), maximum load (P = .207), or yield displacement (P = . 940). Statistically significant differences were noted between groups for y ield load (P = .036) and displacement at maximum load (P = .010). Failures occurred in both groups with permanent deformation or torsion of the pins. During the last portion of the investigation, statistically significant dif ferences were noted between the external distracter and internal distracter groups in yield load (P < .001), yield displacement (P < .001), maximum lo ad (P = .001), and displacement at maximum load (P = .01); no significant d ifferences were noted in stiffness (P = .71). Failures occurred in the exte rnal distracter group with permanent deformation or torsion of the pins. Fa ilures occurred in the internal distracter group with fracture of the model or displacement beyond 30.0 mm. Conclusions. Different patterns of mechanical behavior were found between t he control and rigidly fixated sagittal osteotomy groups and the external d istractor group, between the corticotomy and osteotomy groups, and between the internal and external distractor groups.