The patients included in the audit did not experienced respiratory or other medical problems and there were no adverse effects observed after the use of ozone. However, they were not screened for smoking although the deleterious effects of smoking on periodontal health have been well-documented [23-25]. This might be responsible for some patients not responding to the treatment. However, the patient population represented subjects who did not respond to conventional periodontal treatment. It is possible that patients who are diagnosed and treated for the first time might have responded more favourably to ozone treatment. Nevertheless, the authors wished to audit the usefulness of ozone in more resistant cases.