Bone mineral content by photon absorptiometry of the mandible compared with that of the forearm and the lumbar spine.

A new method for measuring the bone mineral content (BMC) of the mandible by dual-photon absorptiometry (DPA) has recently been introduced. The purpose of the present investigation therefore was to examine the long-term precision for 32 months in vitro and in vivo for assessment of BMC in the mandible and to examine the relationship in vivo among BMC of the mandible, the forearms, and the lumbar spine as measured by DPA and/or single-photon absorptiometry (SPA). For comparison, the relationship between forearm BMC as measured by DPA and SPA was studied. The long-term precision of the mandibular BMC was 0.8% in vitro, independent of age and change of radioactive source, and 2.1% by assessment in vivo. A significant relationship (P less than 0.01) was found between BMC of the lumbar spine and the forearms and between the two sets of forearm BMC measured by DPA and SPA. Thus, relative BMC changes of the forearms can be compared without respect to type of forearm bone scanner used. The BMC changes of the mandible can only be evaluated by scanning of the mandible itself. The present DPA bone scanner is suitable for follow-up analyses of the BMC changes of the mandible and the forearms.