Objectives: to assess the efficiency of three methods of enamel remineralization on initial approximal caries: 1. a nano-hydroxyapatite gel, 2. gaseous ozone therapy 3. combination of a nano-hydroxyapatite gel and ozone.

Materials and Methods: Patients (n=92, age 20-30y) with initial approximal enamel lesions on premolar and molar teeth (n=546) randomly allocated to three groups subjected to a 6-months treatment: Group I: domestic nano-hydroxyapatite remineralizing gel, group II: in-office ozone therapy, group III: both remineralizing gel and ozone therapy. Caries lesions assessed on bitewing radiographs at baseline, after 1 year and after 2 years.

Inclusion Criteria:

-initial approximal enamel lesions on premolar and molar teeth

Exclusion Criteria:

• distal surface of the last tooth in arch, overlapping teeth
• fillings on approximal surfaces of teeth of interest
• ongoing orthodontic therapy with braces or other appliances