In the present audit, the patients displayed a variety of teeth with periodontal disease including localization, number of diseased teeth and variability of surfaces involved. It was decided that only the six deepest pockets from every patient will be included in the audit. These pockets were only measured before and after the application of gaseous ozone. This approach although practical might have affected the BPE score. In some patients, although all the teeth with pockets including the six deepest improved by few millimetres, their BPE score did not. This may be due to the fact that for various reasons not all the treated pockets improved. It might be that these were the patients who did not keep systematically daily diaries and consequently did not comply with the given oral hygiene instructions.