Morphometry of orthopantomographic mandibular bone changes during radiation therapy.

It is generally considered that mineral loss in the bone must amount to 30 per cent or more before any changes become visible to the naked eye in conventional radiography of the skeleton. Early changes in the mandibular bone during radiation therapy are therefore difficult to detect. Abnormalities of the bone caused by irradiation are vascular and cellular in nature. Morphometry detects the changes earlier than conventional radiography. Nineteen patients with a malignant process in the oral cavity or the naso- or hypopharynx but with no evidence of metastases in the mandibular periosteum or bone marrow were given radiation therapy. They were investigated using morphometry together with orthopantomography. The investigation demonstrated a decrease in the number of trabeculae and an increase in the amount of marrow space and compact bone during irradiation. Thus it is possible to detect early radiographic changes by morphometry, but this method is more laborious than scintigraphy. The abnormalities of the mandibular bone were reversible, which signifies the recovery of bone after irradiation with therapeutic doses.