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No practical methods are presently available for measurement of alveolar bone activity at one instant of time. However, roentgenological methods making measurements at 2 different times can be used to assess alveolar bone activity. The most sensitive, specific and accurate method for this purpose presently in use is 125I absorptiometry. This method has the further advantage of giving the patient minimal radiation exposure. New methodology is under development which obviates the need for fixed geometry and could provide a 3-dimensional image of alveolar bone.

THE BJORN TECHNIQUE is widely used in periodontal studies as a standardized measure of alveolar bone. Recent studies have demonstrated the feasibility of using 125I absorptiometry to measure bone mass. The purpose of this study was to compare 125I absorptiometry with the Bjorn technique in detecting small sequential losses of alveolary bone. Four periodontal-like defects of incrementally increasing size were produced in alveolar bone in the posterior segment of the maxilla of a human skull. An attempt was made to sequentially reduce the amount of bone in 10% increments until no bone remained, a through and through defect. The bone remaining at each step was measured using 125I absorptiometry. At each site the 125I absorptiometry measurements were made at the same location by fixing the photon source to a prefabricated precision-made occlusal splint. This site was just beneath the crest and midway between the borders of two adjacent teeth. Bone loss was also determined by the Bjorn technique. Standardized intraoral films were taken using a custom-fitted acrylic clutch, and bone measurements were made from the root apex to coronal height of the lamina dura. A comparison of the data indicates that: (1) in early bone loss, less than 30%, the Bjorn technique underestimates the amount of loss, and (2) in advanced bone loss, more than 60% the Bjorn technique overestimates it.

PREVIOUS STUDIES have shown that 125I absorptiometry gives an accurate and sensitive measure of alveolar bone mass. The purpose of this study was to determine the relationship between alveolar bone mass determined by 125I absorptiometry and bone density obtained by analysis of standardized intraoral radiographs by the Magiscan System. A defect of increasing size was made at one site of the alveolar bone in a human skull. The amount of bone remaining at each step was calculated using 125I absorptiometry. Standardized radiographs were also taken at each step and the relative density in the area of the defect was determined by the Magiscan System. The Magiscan's System Computer Memory permits analysis of identical areas on a longitudinal series of films of the same alveolar bone location. The results indicate that in estimating amounts of alveolar bone the Magiscan analysis of standardized intraoral radiography is similar in sensitivity and accuracy to 125I absorptiometry.