Malocclusions and oral dysfunctions: A comprehensive epidemiological study on 359 schoolchildren in France

Abstract Objectives The purpose was to conduct a comprehensive study of malocclusions and oral dysfunctions on 11‐year‐old children and to study the risk factors associated with malocclusions. Material and Methods A cross‐sectional descriptive epidemiological survey was conducted among 359 children in France. A clinical examination was conducted, and orthodontic and oral functional data were collected. In addition, the need for orthodontic treatment was evaluated using the criteria defined by of the French National Authority for Health (HAS). Finally, a univariate and multivariate analysis was performed to assess the risks associated with malocclusions. Results Most children (88%) exhibited a malocclusion, regardless of gender (p = .912). The examination of oral functions identified a large number of swallowing (87%) and respiration (42.7%) disorders. The presence of malocclusion was statistically linked to the low position of the tongue at rest (p < .001), abnormal swallowing (p = .03), and improper mouth breathing (p = .001). After a multivariate analysis, the type of respiration (odds ratio [OR] = 3.2 [1.4–7.3]) and the position of tongue at rest (OR = 3.43 [1.7–7.1]) were the two most prominent factors in the prediction of emerging malocclusion. Conclusion This epidemiological survey reveals a high prevalence of dental malocclusions and functional disorders. Oral respiration and the low position of the tongue at rest are the most important factors in the prediction of a malocclusion.

muscular types (Schwartz, 1956) and Sassouni classifications, for skeletal types, (Sassouni, 1969) based on muscle physiology, can really be considered as applications of Moss's theory.
Current data allow us to say that most cranial facial functions are instrumental in developing the face and in establishing occlusion: a balance between the different muscle groups will allow a more harmonious development (Talmant & Deniaud, 2000). Any imbalance and dysfunction will have an impact of morphogenesis and could lead to osseous deformations and anomalies of tooth position, form, and function being closely linked (Ovsenik et al., 2007). Though, the prevalence of oral respiration varies according to the different authors from 15% to 55% (Abreu et al., 2008;De Menezes et al., 2006;Huber & Reynolds, 1946;Leal et al., 2016). The prevalence of primary deglutition also varies from one author to another, reaching 36% for Garliner (1981). However, a very small number of national or international studies have been carried out on this subject. Indeed, the literature review reveals a significant number of "authors' views" (Delaire, 1997;Grabowski et al., 2007;Phillippe, 2007;Talmant & Deniaud, 2000) without any scientific evidence backed up by a strictly carried out study coming to light; indeed, only one study was identified, carried out in 2006 by the Epidemiology department of the Faculty of Dentistry in Paris (Souames et al., 2006), whose objective was to study orthodontic treatment need in French schools in the Val d'Oise department. It would therefore be interesting to study oral dysfunctions, especially primary swallowing and oral respiration and their consequences on dysmorphy.
Thus, the objective of this epidemiological survey, based on 11 year old patients, was to evaluate, in a screening situation, the relationship between malocclusion (simple extra-and intraoral examination) and oral dysfunctions through the low resting position of the tongue, swallowing and respiration and to highlight the potential impact of these risk factors on the development of malocclusions, as well as the need for orthodontic treatment according to the criteria defined by the French National Authority for Health (HAS) (HAS/ANAES et al., 2012). The second objective was to relate all these variables by uni-and multivariate analysis to deduce the risk factors associated with malocclusions.

| Ethical consideration and registration
This study was conducted in accordance with the Declaration of Helsinki. An ethical approval was sought before the study from the internal ethics committee of the Nice University, and an opinion on the project was also sought from the Institutional Review Board of the Nice University following its creation in 2021. It has also issued a favorable opinion on the project (01/2022, number 2022-008).
An authorization to conduct this study was obtained from school authorities, both the senator mayor of the city and the rector of the Academy of Nice approved the protocol, and an agreement was signed between the city of Cagnes-sur-mer and the University.
The children's parents were requested to sign an informed consent form, after being informed of the purpose and benefits of the study, before the beginning of the study.
This study is registered in the database for registration of clinical studies (ClinicalTrial.gov, identification number NCT04869839).

| Study design
This manuscript was written following the CONSORT (Consolidated Standards of Reporting Trials) guidelines.
The study was designed as an exhaustive cross-sectional study in the sixth-grade classes of all the elementary schools of the city of Cagnes-sur-mer (town of about 50,000 habitants located in the department of Alpes-Maritimes, France).

| Participants, eligibility and setting
A total of 359 children were therefore enrolled in the study among the 416 children registered in six-grade classes in Cagnes-sur-mer, that is, 86% of children, between April and May 2017; Very few parents refused to give their agreement (2%), and the remaining 12% consisted in the children who were absent on the day of the examination.

| Inclusion/exclusion criteria
All children whose parents gave their informed consent were included. No exclusion criteria were to be applied.

| Dental examinations
Children were welcomed in small groups to learn about oral health care, traumas and nutrition. Children were invited to sit, each in turn, on a chair in a separate room of their classroom to respect the children's privacy and the confidentiality of the collected data.
Clinical examinations were carried out using disposable dental kits (probe and mirror) under natural light or artificial light when natural light alone was deemed insufficient, by using a headlamp. Even though the screening was not performed under the same conditions as a dental chairside examination, a ruler was used, and so was a headlamp and a portable go-kart with an associated compressor and air/water syringe.
All orthodontic examinations were carried out by an orthodontist (ED) and who is an author of the article. The self-calibration was done beforehand by training with photographs. The other oral examinations were carried out by a general practicionner (LB), who is also an author of the article. Eight students in their final year of study were also present to assist and perform preventive actions with the children.
Each parent received a letter notifying them of their child's oral health status and whether or not an appointment with a dentist or an orthodontist was necessary.

| Data collection
The following data were collected: ̶ Untreated dental caries. In such "screening" conditions in the schools, casts and X rays were not available. We were forced to limit ourselves to clinical examinations.

| Sample size calculation and statistical analysis
The previous study carried out in Paris revealed that 20% of the examined children needed and orthodontic treatment (De Menezes et al., 2006). Therefore, the minimum size of the sample to be obtained can be calculated thanks to the following formula: With t = standard normal variate (at 5% type I error (p < .05) it is 1.96).
p = expected proportion in population based on the prior study. e = absolute error or precision, set at 5%.
Therefore, the number of children to be included must be of at least 244.
Descriptive statistics were used to summarize data, then frequency tables and univariate analyses (cross-tabulated) were carried out using the "presence of a malocclusion" as the explained ̶ The examination of oral functions revealed that atypical swallowing was found in most children (87%), nasal respiration was present in only half of the children, and the resting tongue position was low in most cases (85%) ( Table 3).
Additionally, 88% of children needed an orthodontic treatment, according to the HAS classification.

| Univariate analyses exploring the relationships between the need of orthodontic treatment and other variables
Overall, most children (88%) exhibited a malocclusion, regardless of gender (p = .912) or age (p = .18). At a functional level, malocclusions were statistically linked to a low position of the tongue (p < .001), a primary swallowing (p = .03) and a mixed or oral respiration (p = .001; Table 4).

| Multivariate analysis
Finally, to prioritize the effects of univariate significant variables on our variable of interest, a logistic regression was carried out. After completing the multivariate analysis, only two variables remained significant, the others disappearing to their benefit: an abnormal respiration (mixed or oral) and a low position of tongue at rest, have a threefold increase in risk for malocclusion (Table 4).

| DISCUSSION
According to the present epidemiological survey of 359 children, the prevalence of dental malocclusions and functional disorders is significant, associated with a high need for orthodontic treatment according to HAS criteria. Furthermore, oral respiration and low T A B L E 1 General characteristics of study population.  Brook and Shaw (1989) in Manchester showed that 32.7% of 11-12-year-old schoolchildren needed orthodontic treatment whereas the study conducted by Burden in Ireland in 1995 showed that 36% were in need of orthodontic treatment (Burden, 1995). However, Ingervall and Hedegard noted 53% of care needs in 1975 in Lapland (Ingervall & Hedegård, 1974). Therefore, results vary both according to the country where the study is conducted and the index chosen.

| Caries status
The dental health status of the examined children was rather satisfactory since 71.5% of them had never experienced dental

| Part played by oral functions
Nearly half of the examined children had abnormal respiration. Under normal circumstances, and particularly at rest, in healthy subjects, the only physiological respiratory route is the nasal passage. Oral respiration is a complement used when highly needed (physical activity, stress…) or when there is an obvious nasal obstruction. The existence of labial open bite is considered as the translation of oral or mixed respiration (Harari et al., 2010). This is the reason why, in conducting the functional examination, the respiration was defined as  (Rossi et al., 2015).
Patients present an "adenoid" facial appearance: elongated face, opened mouth, pinched nose, under-eye shadows, and dry lips (Raffat & Ul Hamid, 2009). Overall, sleep disorders with non-restorative sleep and snores is frequently related with these malocclusions (Katyal et al., 2013). In this study, the high percentage of oral respiration could also be explained by the season in which the study was carried out. Indeed, at the end of spring and at the beginning of summer in Provence, many allergies occur due to an important exposure to pollens, particularly those of olive trees and cypresses.
Regarding swallowing, more than 87% of children experienced abnormal swallowing in this study. Regarding swallowing, more than 87% of children showed abnormal swallowing in this study. This figure seems high, although in the literature, not all authors are unanimous about the frequency of dysfunctional swallowing. Indeed, the prevalence of primary swallowing varies from 39% for Hanson and Cohen (1973) to 75% for Launey et al. (2014). For Fletcher et al. (1961), atypical swallowing decreases with age. Moreover, the Hanson report on the prevalence of lingual propulsion depending on age also shows a decrease in lingual propulsion in mixed dentition: it would be present in 40%-50% of children in early mixed dentition at 6/7 years of age, then it would decrease to nothing in 30%-40% in late mixed dentition at 11/12 years of age (Hanson & Cohen, 1973).
A good position of the tongue is important because it is maintained about 22 h a day. However, in the case of oral respiration, the tongue is in low position to disengage the upper airway (Garliner, 1981).

| Interactions between variables and the need for orthodontic treatment
Furthermore, this study not only aimed to estimate the oral health status and orthodontic need of children in a city in France: the objective was also to see to what extent the need for orthodontic treatment was correlated with oral dysfunction.
In the multivariate analysis conducted in this study, there were two significant variables: abnormal respiration and low position of tongue. Indeed, the analysis shows that when there is abnormal respiration, the probability of needing orthodontic treatment is

| LIMITATIONS
The need for orthodontic treatment was evaluated according to the criteria defined by the HAS. It would be advisable to evaluate this need using the IOTN index, which is the world reference index in this area, to be able to compare our results more easily with those of other research teams. This study was conducted in a screening context, and it was therefore not possible to take radiographs or dental impressions. The examinations were carried out with portable equipment, although artificial light was used when natural light alone was deemed insufficient. Indeed, in a screening context, the authorizations given by the official authorities (Hospital and Dental School of Nice) can only concern non-interventional procedures.
Thus not all of the IOTN criteria could be evaluated.

ACKNOWLEDGMENTS
We thank all teachers, parents and their children, the Senator mayor of Cagnes-sur-mer and the rector of the Academy of Nice.