Methods: A total of 89 patients with 2 leathery lesions each (178 PRCL’s in total) in the middle severity lesion group 2 (J Dent Res 1993,73: 623-629) were recruited. The lesions were randomly assigned into two groups; treated with ozone, or no ozone and received a professionally applied remineralising solution1. The Ozone treatment was applied by a different operator than the one recording the clinical criteria used to define the severity of the lesions. When no Ozone was applied the cup and suction system were placed on the control lesion for the same time interval as on the test lesions. Remineralising pastes, mouthrinses and sprays were also dispensed to each patient with instructions. At baseline, 3, 6, 12, 18 and 21 months, the lesions were clinically assessed as soft, leathery or hard, scored with the validated root caries severity index and received treatment as at baseline.

Results: After 21 months, 81 patients completed the study. There were no observed adverse events. At 21 months, 100% of ozone treated PRCL’s had reversed, whilst only 8% of the control lesions reversed (p < 0.001). At 21 months, in the control group,12% of the PRCL’s had progressed from severity index 2 to 3 (p < 0.001); i.e. they had become more severe.

Conclusions: Leathery non cavitated primary root caries can be treated non-operatively with ozone. This novel treatment regime using ozone is an effective alternative to conventional "drilling and filling".