Halitosis is defined as an unpleasant odour that emanates from the oral cavity and can originate intraorally and/or extraorally [37]. Its aetiology is multifactorial, affecting both men and women. Despite its high prevalence, information on the incidence of malodour oral in children remains undefined.
The results of the present systematic review revealed an estimated prevalence of halitosis of 36,6%, a finding similar to that of Villa et al., who reported a prevalence of 37,4% [13]. However, the prevalence rates observed in the different studies included in the review were heterogeneous, ranging from 7,6% [19] to 87% [21]. This variability between the different studies could be due to variations in the methods of measuring halitosis, the diverse criteria for including or excluding children in the studies, different sample sizes, and distinct criteria used to consider the presence of halitosis. This is especially true when comparing the subjective organoleptic method and self-reported halitosis by parents, which is often unreliable. In fact, it has been suggested that self-reported halitosis tends to underestimate the prevalence of this condition primarily because subjects cannot detect their own odour or are embarrassed to report it in interviews [38]. However, Silva et al., concluded in their meta-analysis on the prevalence of halitosis in adults that the method used for the evaluation of halitosis did not seem to influence the heterogeneity between the studies and that self-evaluation can be a useful instrument to estimate the prevalence of halitosis, mainly in large epidemiological studies when it is not possible to use organoleptic measurements [11].
To date, we can only highlight two systematic reviews published by Bawazir et al., 2021 and Silva et al., 2022, whose common objective was to determine the etiological factors of halitosis in children [39–40]. Therefore, this publication highlights a significant lack of longitudinal studies in this area.
The present meta-analysis analysed the following etiological factors for the developing of halitosis in children and adolescents: sex, presence of caries, presence of oral respiration, tongue coating, gingival inflammation, low frequency of brushing, poor oral hygiene index, and presence of dental plaque. Other factors, such as age or type of occlusion, could not be analysed, as the studies did not provide the required information.
Boys showed a higher risk of halitosis than girls, but the result was not significant (p = 0.71). This result was consistent with previous studies, such as Patil et al., Nalçaci et al. and Kim et al., since men showed a significantly higher prevalence of halitosis than women in their studies (p < 0.001) [20, 28, 33]. In contrast, Villa et al. and Zhang et al. suggested that pubertal age in girls was a predictive factor for halitosis, associating this finding with sexual hormones at this age [13, 31]. On the other hand, the rest of the studies that analysed sex did not find an association between the presence of volatile sulphur compounds and sex [10, 16, 21, 22, 27].
Mouth breathing was one of the factors that most contributed to the presence of halitosis in the paediatric population, since breathing through the mouth leads to a loss of moisture in the tongue and palate because the oral cavity remains open the greater part of the time, causing halitosis. These findings were in accordance with authors such as Alquitami et al., Patil et al., Kanehira et al., and Motta et al. [19–22]. However, Nalçaci et al. did not find any relationship between oral respiration and the presence of halitosis [33].
It should be noted that the main cause of halitosis was the coating of the tongue located on the posterior back of the tongue since in all the investigations that analysed the relationship between these variables [7, 10, 16, 17, 20, 25, 26, 27, 28, 30, 33, 34], a highly significant association between tongue coating and halitosis was found, considering it to be the greatest risk factor for the appearance of halitosis. Likewise, authors such as Kara et al., Keceli et al., Patil et al., Çiçek et al., and Nalçaci et al. concluded that brushing the tongue significantly reduces VSC concentrations more than just brushing the teeth [2, 16, 20, 25, 33]
Regarding the presence of caries as a risk factor in the appearance of halitosis, discrepancies were found, since authors such as Amir et al., Guedes et al., Almadhi et al., and Nalçaci et al. found a significant association between oral malodour and the presence of dental caries [7, 10, 23, 33]. However, Almadhi et al. attributed this association to the fact that the sample selected in their study included children with a high caries index [23]. On the other hand, Nalçaci et al. related oral malodour with the severity of dental caries [33] In contrast, authors such as Alqutami et al., Kanehira et al., Patil et al. and Ueno et al. did not show a correlation between these variables, associating it with the fact that glucose and sucrose can create an acidic environment that would suppress VSC production [19, 20, 21, 27]. It is important to highlight the studies by Tanaka et al., 2008 and Ren et al., 2016 whose objective was to evaluate the supragingival plaque of children to determine the presence of periodontopathic bacteria [41, 42]. An interesting result was that the group had worse oral hygiene had a greater presence of periodontal pathogenic bacteria that could be one of the main causes of oral malodour. However, there is a lack of conclusive studies about.
On the other hand, when the presence of gingival inflammation and poor oral hygiene were analysed in 10 studies [2, 7, 10, 16, 18, 19, 20, 26, 27, 36], bad odour was significantly associated with gingival pathology and plaque accumulation. The explanation given by the authors for this fact is that the presence of plaque increases the growth of anaerobic bacteria, which cause the production of VSCs that lead to halitosis.
Regarding brushing frequency, the studies by Keceli et al., Kanehira et al., Almadhi et al., Yokoyama et al. and Nalçaci et al. did not find a correlation between these variables, associating these results with poor brushing technique on the part of children who participated in their studies [16, 21, 23, 26, 33]. In contrast, in the study by Patil et al., children who brushed twice a day showed a greater reduction in oral malodour than children who brushed only once a day [20].
One of the main limitations of this review is the heterogeneity of the investigated samples; the different halitosis measurement methods; and the different clinical indices used to assess the presence of oral respiration, tongue coating, and caries.
In conclusion, more research is required to analyse the presence of halitosis in the paediatric and adolescent populations with standardized criteria to determine the causes and risk factors and to design studies of high methodological quality. Studies should focus on boys and girls with a clearly defined age range, and the samples should be evenly distributed between the sexes with the same instrument for the objective measurement of halitosis. The results of our systematic review and meta-analysis provide an estimate of the prevalence of halitosis in children and adolescents and the associated risk factors. Given the high rate of halitosis in children population, the social impact on people and multifactorial aetiology, more longitudinal studies are necessary to help understand its appearance in this population.