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.