The primary purpose of the study was to determine if, with an open flap approach, ultrasonic or hand instrumentation could remove all calculus from previously untreated teeth with moderate to severe loss of attachment. To be included in the study, teeth had to have at least 5 mm of attachment loss, be scheduled for extraction and be graded 2 or 3 on the Calculus Index of the Periodontal Disease Index system. Under local anesthesia, full-thickness, envelope-type flaps were elevated apical to the crest of bone to allow access to the root surfaces which were then treated with hand or ultrasonic instrumentation until the roots felt hard and smooth to a Hartzell explorer. The teeth were then removed, rinsed, and lightly scrubbed to remove debris and a No. 14 wheel bur was used to place a groove along the coronal extent of the connective tissue attachment. A stereomicroscope at magnification X 4.6 was used to quantitate the percentage of residual calculus on 25 teeth treated by each method. Overall, hand-scaled root surfaces demonstrated less residual calculus (5.78%) than ultrasonically treated surfaces (6.17%). Twenty teeth treated by each method were then prepared for histologic evaluation and evaluated under the light microscope at magnification X 100 for residual calculus and relative smoothness. Residual calculus was found on four ultrasonically and 12 hand-treated teeth and was almost evenly distributed between anterior and posterior teeth for both methods. The finding of considerably less calculus on histologic than on stereomicroscopic examination may have been due to the loosening of deposits by instrumentation, especially ultrasonic vibration, and their subsequent release during histologic preparation.(ABSTRACT TRUNCATED AT 250 WORDS)