## 4 Discussion
Encouraging results were also obtained from salivary tests that assessed the presence of _Streptococcus Mutans_, the primary bacterium involved in the onset of the carious process [32; 33]. At T0, 82% of the tested patients were positive, i.e., their _Streptococcus Mutans_ salivary count was higher than 500.000 CFU/mL, and these results were compatible with their clinical condition of multiple caries in an active phase. At T1, results were almostthe opposite of those at T0 and only 9% of the patients were positive for _Streptococcus Mutans_; thus, the third null hypothesis was rejected. This significant result can be explained thanks to both the antimicrobial activity of ozone [13; 15; 16; 17] and the improvement of the patients' oral hygiene and food habits, which, however, might also represent a bias in the evaluation of ozone antibacterial effects. Moreover, an important result was also gained in patients' and their family's quality of life and so the null hypothesis that ozone therapy on ECC-affected teeth would not alter the quality of the affected dentin was also rejected. The results of ECOHIS questionnaires showed that dental caries had a negative impact on the quality of life for both patients and their families; from this point of view, ECC is, in fact, not only an oral problem but it might also have systemic consequences and psychological and economic repercussions [2; 6; 7]. For each of the five main domains of the questionnaire, a reduction in the scores was registered between T0 and T1. The total scores of the pain symptoms (domain 1) decreased by six points (15 to 9), showing the efficacy of ozone analgesic activity [19; 20; 21; 22]. Comparing the answers given by parents to the first question of the questionnaire (domain 1) and those given by patients about their perceived dentin hypersensitivity evaluated at the dental chair according to the WBFPRS, an inconsistency is evident. This might be explained considering preschool children's difficulty in expressing their symptoms appropriately due to their young age. The decrease in the scores for the answers to the questions on oral functions such as nutrition and language (domain 2; mean score 11.75-10.75), as well as of those on social life and relations (domain 3; mean score 5.75-4.5), showed an essential improvement in these conditions and a positive impact of ozone therapy also on the psychological and social spheres of patients and their families. ECC had, in fact, a substantial impact not only on affected children but also on their families, and this was highly appreciable in the answers to questions on the patient's caregivers' emotional state and economic and financial aspects (domains 4 and 5). Most parents stated that they felt upset and guilty for their children's oral status and declared that they had to take days off from work to take them to the dentist. Even if the scores of these domains decreased from T0 to T1 (mean scores 27-22 and 14-13, respectively), they remained higher compared to the other domains. This is probably because parents had to take their children to the dental appointments scheduled for this study. Furthermore, at T1, parents were more aware of ECC and its consequences, being also more conscious of the importance of oral health for systemic wellness [2; 6; 7]. Salivary tests and ECOHIS questionnaires were performed at T0 and T1 to evaluate the direct effect of ozone therapy on patients' salivary bacterial load and their quality of life immediately after treatment. Ozone therapy has several advantages: being a simple and non-invasive technique, it can be easily used in young and/or anxious or fearful pediatric patients to improve their cooperation and help them to become used to traditional restorative treatments [14]. In addition, being a non-aerosol-producing therapy, it is especially recommended during this unique COVID-19 pandemic time because it helps reduce the risk of cross-infections in the dental practice [34].