Effect of ozone treatment on the molecular composition of dentin

Objective: To test the hypothesis that ozone treatment induces changes on the molecular composition of sound, acid-demineralised and carious dentin. Methods: Disk-shaped specimens of intact, acid-demineralized (10s etching with 37% phosphoric acid liquid) and carious dentin (early, moderate and advanced lesions) were prepared from extracted molars kept in water with 0.5% sodium azide at 8 oC. The disks were studied by reflection FTIR microscopy at the same region before and after treatment with HealOzone (Kavo, Germany) employing 8 sequencial cycles of 40 s each, plus water rinsing and air drying. Any changes in the mineral to matrix ratio (Ca-PO ~1070 cm-1/amide II ~1550 cm-1) on the dentin surfaces after ozone treatment were normalized versus the values of native dentin and express in percentage. Four specimens were tested per group. Kruskal-Wallis ANOVA on Ranks was used to compare the percentage changes in the mineral to matrix ratio among the substrates (á:0.05). Results: No peak shifting was observed on dentin specimens to support formation of additional compounds. The changes in the mineral to matrix ratio as calculated were [%, mean(SD)]: +4,07(0,46) intact dentin; +13,95(3,70) acid-demineralized dentin; +5,60(0,61) early lesions; +9,09(1,22) moderate lesions and 0 advanced lesions. ANOVA showed significantly higher changes in the groups of acid-demineralized and medium lesions versus the intact. The changes in the intact group reflect the contribution of the loosely bound smear layer removed from the vacuum and ozone flow. The changes in the acid-demineralized and moderate lesion groups imply additional degradation of exposed collagen. On advanced lesions, no mineral could be identified before and after ozone treatment, suggesting the presence of a thick demineralized zone. Conclusions: Prolonged ozone treatment on acid-demineralized and moderately carious dentin specimens slightly increases the mineral to matrix ratio probably due to selective attack of ozone on exposed collagen.