Response of the expanded inter-premaxillary suture to intermittent compression. Early bone changes.

OBJECTIVE

To determine the response of the expanded premaxillary suture in the rat to an externally applied force. Specifically, to investigate early bone changes in the expanded suture to intermittent loading and unloading.

METHODS

Twenty-four 50 to 60 day-old Wistar rats were assigned to three groups. The inter-premaxillary sutures in all animals were expanded with a 50 g force applied to the upper incisors. Group I served as the control, whereas in Groups II and III the incisors were subjected to intermittent loading and unloading after five days of expansion. The intermittent forces were produced by a cam (0.416 mm, 100 cycles per minute) applied to the disto-gingival margins of the upper incisors. The mechanical stimuli were applied daily over nine days for six seconds in Group II (30 grams force, 10 cycles/day) and 10 minutes in Group III (30 grams force, 1000 cycles/day). Bone regeneration in the suture was evaluated histomorphometrically. The area of new bone (microm2), the perimeter around the new bone (microm), Feret's diameter (microm) and the percentage of new bone to non-ossified tissue (%) were measured and compared.

RESULTS

Statistically significant differences were found between the groups for all histomorphometric parameters. New bone area (p < 0.001), bone perimeter (p < 0.001), Feret's diameter (p < 0.001) and percentage of new bone (p < 0.001) were significantly larger in the experimental groups as compared with the Control group. The histomorphometric measurements confirmed that more new bone was deposited in the sutures subjected to intermittent loading and unloading.

CONCLUSION

The application of cyclic loading and unloading to the orthopaedically expanded inter-premaxillary suture during the early retention phase stimulated the formation of new bone.