Journal of Dental Research, Vol 67, 1430-1433, Copyright © 1988 by International & American Associations for Dental Research Online Journals
Bisphosphonate effects on alveolar bone during rat molar drifting
A. B. Hardt
Department of Oral Biology, University of Nebraska Medical Center, College of Dentistry, Lincoln 68583-0740.
The remodeling of bone during molar drifting and cortical growth in the rat
maxilla and the effects of dichloromethylene bisphosphonate (Cl2MBP) on
these processes were investigated in 30 age-matched rats. A control group
of six rats was killed at 10 weeks of age. Beginning at 10 weeks of age, 12
rats were treated with daily subcutaneous injections of Cl2MBP (10 mg/kg),
and 12 control rats were injected daily with normal saline. Six rats of
each group were killed at 12 and at 20 weeks of age. All rats were injected
with fluorescent bone labels eight and one days before termination.
Calcified and decalcified vertical sections through the lingual roots of
maxillary molars were prepared for histomorphometry. Bone apposition rates,
remodeling activity, and bone cell populations were quantified by image
analysis on depository and resorptive surfaces of alveolar bone and on
cortical bone surfaces. The drift rates of the first and second molars were
calculated. Results showed that in control animals the drift rate of the
first molar exceeded that of the second molar (p less than 0.05),
supporting a previously proposed mechanism for age-dependent narrowing of
interdental bone. Cl2MBP treatment decreased remodeling activity on
resorptive surfaces of alveolar bone, despite a transient increase in
osteoclasts. Cl2MBP also decreased the osteoblast number and bone
apposition rate on depository surfaces of alveolar bone, and reduced the
rate of molar drifting (p less than 0.05). However, Cl2MBP treatment had no
detectable effect on osteoblast number or bone apposition on cortical bone
surfaces. These results support the concept that bisphosphonates influence
bone formation indirectly through a coupling mechanism which links
formation with resorption.