Abstract Dental calculus itself is not thought to affect gingival health, but its rough and porous surface retains plaque better than a calculus-free surface. In a population with a high degree of supragingival calculus, the effect of toothbrushing after a careful professional prophylaxis (group A) has been compared with the effect of tooth-brushing as the sole oral hygiene aid (group B). The subjects in this comparison were Indonesian soldiers, 20–25 years of age, none of whom had pathological pockets (CPITN≤2), but all had large amounts of calculus. They had no experience of modern oral hygiene practice but were given individual instruction in toothbrushing at the start of the study and were provided with toothpaste and toothbrush. Removal of calculus in group A took an average of 1 h per subject by an experienced clinician. Gingival health in both groups improved after 2 months: group A from 63% to 34% bleeding points and group B from 61% to 36%. There was thus no obvius benefit from the professional prophylaxis received by group A. The results are particularly relevant for populations in which professional prophylaxis is not normally available. However, they were obtained in a group of young, healthy individuals and may not be extrapolated to older and less healthy populations or to individuals with deep periodontal pockets. The improvement of gingival health through toothbrushing, in spite of the presence of calculus, supports the contention that plaque, rather than calculus as a non-inflammatory scale, provides the pathogenic potential.