Ultrasonic and power-driven instrumentation is gaining in significance as an acceptable alternative to manual periodontal root treatment. Some question whether they do not remove too much tooth substance. Various ultrasonic scalers, hand instruments and two power-driven systems were compared by assessing the loss of tooth substance due to root instrumentation. Quantitative analysis of this effect of the instruments used was performed on 20 freshly extracted, non-periodontally involved, large human molars. In the first study, 40 specimens were randomly assigned to four groups of treatment: combined use of ultrasonic scaler and Periopolisher diamond-coated inserts (US-POL), hand instruments (MANUAL), Perioplaner-Periopolisher system (PPL-POL) and Periokit ultrasonic-designed scalers (PERIOKIT). The second study involved two treatment groups, ultrasonic scaler alone and hand instruments, each allocated with 20 teeth (small root fragments). An unpaired two-tailed t test was carried out for both studies to compare the average weight loss of root substance with the modes of instrumentation. The level of significance was set at p<or=0.05. The overall results of the first and second experimental trials did not reveal obvious differences in weight loss between the manual, ultrasonic or power-driven root treatments. Based on the results of these two comparative studies, the power-driven inserts or the various ultrasonic scalers tested did not remove more tooth substance than conventional hand instruments. They may thus be a useful alternative for the debridement of root surfaces.