UNTREATEDPERIODONTAL DISEASE leads in time to decreased height of the supporting alveolar bone. Longitudinal studies of periodontal disease require that accurate determinations be made at specified intervals of the amount of bone loss around teeth. In clinical practice, general practitioners and periodontists depend on both radiographs and pocket measurements for information about the extent of bone loss in their patients.There is disagreement about the relative accuracy with which radiographs and pocket measurements reveal actual bone loss. Some investigators have found radiographs useful for the study of bone destruction or the progression of bone resorption around various teeth. 1-4 However, one investigator has reported that radiographs underestimated actual bone loss, 5 and one group of investigators discontinued attempts to evaluate alveolar bone loss from radiographs because of many difficulties encountered in making accurate assessments. 6 Although it is generally accepted that there is a reciprocal relation between the bottom of the gingival sulcus and the crest of the underlying bone, 7 there is also disagreement as to the accuracy with which pocket measurements reveal bone loss. The average distance from the base of the pocket to the alveolar crest was found by one investigator 8 to be 1.83 mm and 1.50 mm by another. 9 The prevailing view today, however, is that radiographs without periodontal probe measurements are of dubious value. 10 This study was designed to determine the relative accuracy of pocket and radiographic measurements in assessing periodontal destruction. METHOD Eighteen patients at the United States Public HealthService Hospital in San Francisco who required and were willing to undergo surgical treatment for periodontal disease were selected for this study.Radiographic measurements and pocket measurements by periodontal probe were made before surgery, and these were compared with readings of actual measurements of bone loss made during periodontal surgery. These measurements served as a standard inasmuch as bone was exposed to view and permitted accurate direct measurement of bone loss.Before any measurement or surgical procedures were performed, each patient received a thorough prophylaxis. Then, radiographs were taken using a parallel (long-cone) technique 10-12 and XCP film holders. A grid 13 was attached to each film at the time of exposure. The grid consisted of a plexiglas device approximately the size of the film in which fine wires spaced 1 mm apart were embedded. Wires in the grid ran both lengthwise and crosswise and every fifth wire was slightly thicker. Radiographic measurements, both mesially and distally to each tooth in the areas in which surgery was to be done, were made to assess bone loss by measuring the distance from the cementoenamel junction to the alveolar crest. Where either the cementoenamel junction or alveolar crest was obscured by decay, fillings, crowns or by overlapping images, measurements were not made.Measurements with a periodontal probe* were also mad...