## 4 Discussion
### Probiotics as a Treatment Option for Halitosis
The authors state though that the clinical significance of the VSC reduction observed in this study (from 201 \(\pm\) 71 ppb to 180 \(\pm\) 47 ppb) remains uncertain, as the established threshold for the clinical diagnosis of halitosis is typically considered between 150 and 160 ppb [30]. [PERSON] et al. were able to show that tongue scraping in combination with oral probiotics allows for lasting effects in terms of VSC levels even after cessation of probiotic intake. Post-treatment measurements, after the discontinuation of the intervention, exhibited statistical differences favoring the probiotic group [23]. Concerning the organoleptic test (OLT), not all the included studies investigated it, as it lacks objectivity. The included clinical trials that did examine it, all observed a decrease in organoleptic scores after probiotic therapy [21; 22; 24; 26; 28; 29]. Nonetheless, [PERSON] et al. and [PERSON] et al. were the only ones who found improvements that differed significantly among the study groups [24; 26]. This could be due to a small sample size [29], no prior removal of tongue coating [21], but also due to the subjectivity of this evaluation method, which decreases its statistical power in the identification of differences [29]. Tongue coating was analyzed in four of the included clinical trials [21; 23; 28; 29]. The dorsum of the tongue is coated with papillae, and within the crevices of these papillae, a build-up of bacteria, dead epithelial cells, and food particles occurs. This accumulation of plaque on the tongue can lead to halitosis. A plaque with a thickness of 0.1-0.2 mm can reduce oxygen levels, thus creating an anaerobic environment conducive to bacterial colonization [23]. [PERSON] et al. investigated the effect of probiotic administration together with the prebiotic inulin on halitosis and tongue coating. Prebiotics, with inulin being one of the most used ones, are indigestible fibers present in foods like onions, cereals, and bananas and can be consumed along with probiotics, forming a combination known as symbiotics. This combination stimulates the growth and function of microbial flora by suppressing the proliferation of harmful pathogens and supporting the immune defense. [PERSON] et al. found that within each treatment group, all three groups exhibited a significant decrease in the coating index after the treatment. While there was no significant difference in the reduction among the treatments, patients treated with the probiotic _L. salivarius_ and inulin showed a trend towards a lower coating index compared to those treated with _L. salivarius_ alone. But this difference was not statistically significant compared to the placebo group [29]. [PERSON] et al. observed that the application of _S. salivarius_ did not produce a noteworthy impact on halitosis accompanied by tongue coating when the tongue coating was not pre-treated either physically or chemically. This suggests that the removal of tongue coating is necessary before employing _S. salivarius_ for effective results [21]. This is coherent with the results of the study carried out by [PERSON] et al., in which they concluded that the \"effect of tongue scraping with a probiotic continued even after the cessation of the treatment\" [23]. Conversely, [PERSON] et al. were able to show significant improvements in tongue coating scores in the probiotic group compared to the placebo group, even though the authors did not perform any removal of tongue coating before probiotic administration. This may be because the study carried out by [PERSON] et al. was a crossover randomized controlled trial, which gave rise to the period effect. The investigators performed a washout period of 2 weeks but stated that extended washout periods might be necessary to assess alterations in the tongue coating scores [28]. Bad breath improvement (BBI) scores were measured in the studies carried out by [PERSON] et al. and [PERSON] et al.