J Oral Maxillofac Surg
61:918-927, 2003
Alterations of Morphology and
Microdensity in the Condyle After
Mandibular Osteodistraction in the Rat
Zi Jun Liu, DDS, PhD,* Gregory J. King, DMD, DMSc,†
and Susan W. Herring, PhD‡
Purpose: In this study, we examined the effects of mandibular distraction osteogenesis on the
morphology and the microdensity of the rat condyle.
Materials and Methods: One hundred twenty-nine rats were allocated to 4 experimental groups (n =
32 or 33). Each received unilateral mandibular ramus osteotomy and distraction device placement. After
a 3-day latency, these were distracted once a day for 5 days. The slow distraction group was distracted
a total of 1 mm (0.2 mm/d); the moderate group, 2 mm (0.4 mm/d); the rapid group, 3 mm (0.6 mm/d);
and the sham group, no distraction (0.0 mm/d). Eight to 9 rats in each group were sacrificed at each of
4 time points after device placement (6, 10, 24, and 38 days). Baseline data were obtained 3 days after
osteotomy and device placement without distraction from an additional 10 rats. Radiographs of the
hemimandibles were scanned and measured to evaluate changes in condylar size (height, width, and
area), angulation, and bone microdensity converted to equivalent bone thickness using a stepwedge. The
wet weights of masseter muscle were measured at the time of harvest.
Results: 1) Muscle weight gains over time were significantly lower in the treated than the untreated
sides throughout the consolidation period (P .001). 2) Condylar size and angulation on the untreated
side increased postoperatively, whereas there was a significant reduction of these parameters (P .01
to .001) on the treated side at 24 and/or 38 days. 3) Condylar microdensity significantly increased on the
untreated side at 24 and 38 days (P .05 to .01) but not on the treated side. 4) Faster or larger distraction
caused more severe size reduction and more upright condylar angulation, prevented an increase in bone
microdensity on the treated side, especially during the consolidation periods (P .05 to .01), and
retarded increase in muscle weight, whereas a slower distraction rate showed few negative, and even
some positive effects. 5) Correlations in size, angulation, and microdensity between right and left
condyles became less significant over time. 6) There were positive correlations between muscle weight
and condylar size, angulation, and microdensity.
Conclusion: An increased rate of mandibular distraction has significant negative effects on condylar
morphology and microdensity.
© 2003 American Association of Oral and Maxillofacial Surgeons
J Oral Maxillofac Surg 61:918-927, 2003
As a dynamic method for generating new bone, dis-
traction osteogenesis has been widely accepted as the
treatment of choice for the surgical correction of
hypoplasias of the craniofacial skeleton. However, the
procedure can be difficult to control and its side
effects are not well understood.
1
In osteodistraction, a
tensile force is applied across an osteotomy to
lengthen a bone. The forces produced by the distrac-
tion maneuvers are superimposed on the normal me-
chanics of the bone, and thus put unusual loads on
the entire craniofacial skeleton, which could alter the
process of normal growth and/or adaptive remodel-
ing in the region.
Some have raised concerns about undue loading of
joints during lengthening of long bones by distrac-
tion.
2,3
Early surgery for distraction may also retard
the growth potential of the mandible and its associ-
ated soft-tissue structures.
4
When the mandible is
Received from the Department of Orthodontics, University of
Washington, Seattle, WA.
*Assistant Professor.
†Professor and Chair.
‡Professor.
This work was supported by National Institute of Dental and
Craniofacial Research Grant DE13061.
Address correspondence and reprint requests to Dr Liu: Depart-
ment of Orthodontics, Box 357446, University of Washington,
Seattle, WA; e-mail: zjliu@u.washington.edu
© 2003 American Association of Oral and Maxillofacial Surgeons
0278-2391/03/6108-0092$30.00/0
doi:10.1016/S0278-2391(03)00294-5
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