Association between Dentofacial Features and Bullying from Childhood to Adulthood: A Systematic Review

Bullying occurs when an individual is repeatedly victimised by negative actions performed by peers. As oral features, like malocclusion and dental structural defects, can promote psychological distress, which is also found in those who are bullied, we aimed to study the association between orofacial conditions and bullying. A systematic review (PROSPERO CRD42022331693), including articles dealing with bullying and dentofacial traits, was performed following the PRISMA chart. The iterative search of eligible publications was carried out on 27 March 2023 on four databases (PubMed, PubPsych, Web of Science and Cochrane Reviews) and in the grey literature. Among the 25 articles included, 4 referred to qualitative studies, which analysed 632 interviews with children, 8 interviews with parents, 292 letters, and 321 Twitter posts. The other 21 were cross-sectional studies, which included 10,026 patients from 7 to 61 years old. Two of the qualitative studies and seven of the cross-sectional studies rated a low risk of bias, according to Joanna Briggs Institute’s Critical Appraisal Tools. The majority of studies (88%) reported a relationship between malocclusion or structural defects and exposure to bullying among young adolescents. Structural dental abnormalities and severe malocclusion should be managed, among others, for psychological questions because they crystallise the loss of self-confidence and increase the risk of bullying.


Introduction
Bullying occurs when a child or adolescent is victimised repeatedly over time by negative actions performed by one or more peers [1]. This aggressive behaviour can manifest itself in different forms, sometimes in combination (verbal, physical, via social media . . . ). Victims tend to be anxious and insecure with low self-esteem. They also have depressive tendencies that persist into adolescence and early adulthood, even after victimisation has stopped [2].
Facial aesthetics serve a great purpose in social interactions [3], and a positive relationship exists between facial attractiveness and interpersonal popularity, as well as others' favourable evaluation of one's personality and social behaviour [4].
Dental features such as occlusion, colour or shape of teeth have a significant impact on facial appearance and, more globally, on the general perception of body image. As the eyes are focused on the face in normal social interactions, it is invariably impossible to hide or disguise them [5]. Therefore, if these features deviate from the norm, the general aesthetics of the person concerned may be altered.
Among these deviations, malocclusion is one of the most common oral disorders and can be defined as a significant discrepancy from the ideal occlusion involving a condition of imbalance in the position of the teeth, facial bones and soft tissues [6]. Even if it is not considered a disease, orthodontic treatments are proven to be necessary to treat both functional and aesthetic alterations and prevent traumatic risks [7][8][9].
From a purely dental perspective, structural defects can be defined as disturbances in dental hard tissue matrices and their mineralisation during the period of odontogenesis [10]. It could include, among others, developmental defects of enamel, dental enamel hypoplasia, amelogenesis or dentinogenesis imperfecta. These last two are rare, hereditary, developmental disorders [11], whereas the others can have an environmental origin. They can affect the structure, clinical appearance and sensitivity of the teeth of both dentitions. Because of aesthetic and masticatory function alterations, guidelines for restorative treatment recommend covering the surface with direct composite resin or composite resin veneers in young children and adolescents until adulthood [12].
Abnormal dental features like malocclusion and dental structural defects are increasingly visible in early adolescence, with the eruption of permanent teeth and maxillomandibular growth. These orofacial features can lead to significant anxiety and other emotional or behavioural problems [1,10]. Their treatment usually occurs at a crucial stage of psychosocial development, which is also a period of high exposure to bullying.
Given that malocclusion and dental defects can promote psychological distress and decrease self-esteem [13,14], which are also personality traits found in bullied [15], we aimed to study the association between these orofacial conditions and bullying. We hypothesised that patients with malocclusions or teeth anomalies were prone to bullying.

Study Design
This study has been conducted as a systematic review of the literature. The protocol has been established in accordance with the recently updated PRISMA grid [16] and registered on the International Prospective Register of Systematic Reviews (PROSPERO) database under the number CRD42022331693. The Joanna Briggs Institute (JBI) Manual has been used to evaluate bias [17].

Eligibility Criteria
We included all types of studies, quantitative and qualitative, assessing both bullying and dental traits such as malocclusion and tooth abnormality or dental defects. The samples had to include children, adolescents or their parents. Studies published in English, French, and/or Spanish were eligible to be included. We excluded case reports, literature reviews, and studies looking at orofacial clefts, oligodontia or patients with dental caries.

Sources of Information and Search Strategy
The iterative search of eligible publications was carried out on 27 March 2023 on four databases (PubMed, PubPsych, Web of Science and Cochrane Reviews) and in the grey literature. The search procedure submitted was: (tooth abnormality OR malocclusion OR amelogenesis imperfecta OR dentinogenesis imperfecta OR dental enamel hypoplasia OR developmental defects of enamel) AND (bullying OR relational aggression OR cyberbullying OR emotional abuse OR harassment OR school violence OR teasing OR victimization) NOT (carie) NOT (decay).
The reference list of each study selected has been analysed to identify additional studies that had not been found in the first search.

Study Selection
Results obtained from the database research were exported to Rayyan ® software [18]. Duplicates have been detected and removed. Two evaluators (AB and EN) independently reviewed the titles and abstracts of the publications in order to determine whether or not they met the eligibility criteria mentioned above. When in doubt, the full text was analysed to determine if the article was suitable for inclusion. If the reviewers were not blinded by authorship or the name of the journals, they were blinded to each others' decisions.
Disagreements between individual judgements were planned to be resolved by asking a third reviewer (TC) for their opinion.

Data Collection
The full-text review of selected articles enables systematic extraction of the following data: authorship, year and country in which the study was performed, type of study, main objective, information on the study sample features (number, age, inclusion and exclusion criteria), how dental characteristics and bullying exposure were assessed, the tools used for data collection, the tests used for statistical analyses and the main outcomes.

Bias Assessment
In order to assess the trustworthiness, relevance and results of the selected articles, Checklists for Analytical Cross-Sectional Studies and for Qualitative Research from Joanna Briggs Institute's (JBI) Critical Appraisal Tools were used [17].
For the qualitative research assessment, each question in the checklists could be answered as "yes", "no", "unclear" or "not applicable". A "yes" response was quantified by 1 point, a "no" response by 0 points and an "unclear" response by 0.5 points. The total score was then reported out of 100. Two evaluators (AB and EN) independently assessed each domain of the checklists.
Concerning the cross-sectional studies evaluation, question 3 received a "no" response when dentofacial condition (dental features, malocclusion and/or dental structure abnormalities) was assessed using a self-reported questionnaire but not a validated tool. In the same way, question 7 received a "no" response when bullying was assessed in a nonvalidated way. Questions 5 and 6 were answered as "no" when no confounding factors had been identified, and no strategy to deal with them had been developed. Question 8 was answered as "no" when adequate statistical tests have not been used considering variables.
The risk of bias would be rated as high when the study reached a score of less than 49%, moderate when it reached a score between 50% and 69%, and low when it reached a score of more than 70% [19].

Study Selection
A total of 171 references were obtained after research was conducted on four databases (PubMed, PubPsych, Web of Science, Cochrane Reviews) and grey literature. After the removal of duplicates, 147 articles were screened by a careful reading of their titles and abstracts. A further 120 of them were then excluded because they did not correspond with the aim of this review leaving 27 articles selected for full-text reading and assessment of the eligibility criteria. After full-text reading, two more articles were excluded: one did not focus on the subject of this research, and the other was a case report. In the end, 25 articles were included fulfilling the eligibility criteria ( Figure 1).

Characteristics of the Selected Studies
Selected articles were published from 1980 to 2022. We included studies dealing with adults. One study [20] included adults between 28 and 34 years old and asked them about their exposure to bullying during their schooling. Their malocclusions had been previously assessed during their adolescence (between 13 and 19 years old). Two studies [8,21] included patients with no age limit (both children and adults). We chose to keep these studies because of the presence of children. Three studies [22][23][24] included parents and questioning them about their children's dental features and exposure to bullying. In total, 22 of the 25 included studies referred only to young people (7-18 years old) and their parents testifying about their child's experience.   Four of the articles referred to qualitative studies. The other 21 were cross-sectional studies. Three of the qualitative studies analysed interviews with a total of 632 children [25,26] and 8 interviews with parents [23]. Patients included were children and parents of children aged from 9 to 18 years. Two studies analysed written texts: 292 letters (143 from caregivers and 149 from children between 11 and 18 years old) [25] and 321 Twitter posts [27].
Altogether, the 21 cross-sectional studies included 10,026 patients. Two of the studies [28,29] dealt with the same cohort, and one of them [30] included some patients from a previous study [31]. Patients included were aged from 7 to 61 years. Three studies included adults [8,20,21], and two included parents of children under 18 years old [22,24]. Fourteen of these studies included children at school. Six of them included patients or parents from dental, maxillo-facial or orthodontic follow-up, and one of them included parents from social networks.
Eight of the selected articles mentioned a practitioner's assessment of the malocclusion, using the Dental Aesthetic Index (DAI) for five of them [7,9,33,34,39], the Aesthetic Component (AC) of the Orthodontic Treatment Need Index (IOTN) for four of them [8,9,30,31], associated with the Dental Health Component (DHC) of the IOTN for two of them [30,31] or with a patient's self-perceived need for orthodontic treatment assessment using a modified IOTN-AC scale [8].
Two articles referred to dental structure abnormalities using the modified Developmental Defects of Enamel (DDE) index to assess DDE [34,42] and the modified Dean index to assess dental fluorosis [34].

Results of Individual Studies
Of the 25 articles included, 5 focused only on malocclusion, 3 only on dental structural defects, and 20 more globally on dentofacial features. A total of 22 concluded that there was an association between bullying and oral condition. The percentage of people who were bullied varied greatly from study to study. The results of the four qualitative studies are detailed in Table 3. Those of the 21 cross-sectional studies are detailed in Table 4. Table 1. Qualitative studies' risks of bias assessed by checklist for Qualitative Research from Joanna Briggs Institute's (JBI) Critical Appraisal Tools [17]. The color are related to the bias assessment (green means low risk of biais). (1 = yes-0.5 = unclear-0 = no-NA = not applicable). (1 = yes-0.5 = unclear-0 = no-NA = not applicable). The more deviant the dental arrangement, the more salient will it be. With regard to targeted physical features, teeth were the number one target. Tooth shape and colour were the most common dentofacial targets, followed by an anterior open bite and protruded anterior teeth.      The prevalence of bullying was 29.6%. Those who indicated that they were criticised due to the condition of their teeth had a 4.37 times greater chance of victimisation. Those who felt that oral health had little effect on their relationship with other people had a 2.2 times greater chance of suffering from bullying than those who did not. It was possible to observe an association between bullying and dissatisfaction with oral health and body image.

Discussion
The present literature review showed that the vast majority of studies found a relationship between dental malocclusion or structural defects and exposure to bullying, which occurred in 5.7 to 100% of the samples. Only three studies [9,33,39] did not report an impact of malocclusion on bullying.
Most of the studies included young adolescents. Indeed, the prevalence of bullying seems to be higher in children of 12-13 years and younger [28,29,31], and bullying tends to decrease with increasing age [44]. In order to standardise the source of information across all ages and to enable comparisons between the youngest schoolchildren and the older ones, some authors chose to use parents' questionnaires [22].
In this literature review, there is great variability in the clinical assessment tools for dental defects. In order to evaluate dentofacial condition, eight studies used clinical examination [23,24] or professional assessment [7,30,31,33,34,42], twelve used patients' self-evaluation [20,22,[25][26][27][28][29]32,35,37,40,43], and three used both [8,9,39]. The originality of our review, and maybe one of its limits, was to take an interest in both malocclusion and structural defects and to regroup all of them under one term: dentofacial features. Considering this, patients' self-evaluation could be considered a global smile evaluation and not only an evaluation of one precise element of the mouth.
There is no standard instrument to identify and assess bullying [45]. Twenty of the included studies chose to use questionnaires. Whatever the Likert scale, results were divided into "bullied" or "non bullied". Some authors mentioned that because of the sensitivity of the topics, anonymous questionnaires should enable avoiding the embarrassment of direct interview confrontation [22,28,29] and then enable more sincere responses. As this is the most current approach seen in the literature, we could suppose that previously published questionnaires have been chosen because of their validity and to be able to compare results with those of different other studies [22]. However, 13 of the cross-sectional studies used 8 different validated questionnaires, and the other 7 used author-created questionnaires. This drastically limits the possibility of comparing results.
Even if most of the included articles chose the same type of tool to assess bullying, comparison of results remains difficult also because time intervals of the exposure and cutoffs could be very different between all the studies. Effectively, the time intervals assessed extended from two days [8] to throughout schooling [20,37]. Most of the studies assessed exposure to bullying during one [22,28,29,33,34] or two months [30,31,40], probably to limit the risk of bias related to long-term memory. However, this adds the risk of underestimating the exposure to bullying of certain subjects. With regard to the cut-off, for example, during a period of one month, subjects were considered as victims of bullying from one [34] to two episodes of teasing [31,40], or if episodes were qualified as "always or almost always" for Ramos [9]. This emphasises the absence of consensus regarding the frequency of abuse.
This review highlights the fact that all authors are not interested in the same events: some of them assess the frequency of 'nicknames' or 'name-calling' [28,29,34], while others evaluate exposure to bullying in different forms: physical [7,22,35], verbal [7,22,34,35], cyberbullying [22,35], emotional, racist or sexual [7]. Moreover, bullying in multiple forms seems to be an emerging issue that has never been addressed, and that warrants attention [22]. Terminology could be crucial: according to Ross [46], teasing should not always be identified as bullying, but as a form of acceptance and dialogue among friends, with no significant harm intended to the recipient. However, peer aggression experiences that do not meet the bullying criteria can also be rated as harmful by victims [47]. Nevertheless, as soon as it results in harm and psychological distress, this aggressive behaviour should be considered bullying [31]. Bullying frequently comes from peers in the school setting, but unfortunately can also occur within the family [48].
According to JBI Critical Appraisal Tools, less than half of all the included studies rated a low risk of bias [7,8,23,26,[29][30][31]34,40], and four of the cross-sectional ones rated a high risk of bias [21,24,37,43]. Standardisation and refinement of assessment methodologies for these topics would be beneficial to improve research in the area of bullying and dentofacial characteristics.
Comparing results between studies performed in different countries with different socio-cultural contexts could be irrelevant because of differences in anti-bullying policies, the prevalence of dental structural defects or malocclusions and inaccessibility to aesthetic or orthodontic treatments. Twenty-five articles were included. Of the total, eight studies were performed in European countries [8,20,23,26,30,31,40,41], seven in South and Central America Countries [7,9,21,[33][34][35]43], three in African countries [32,37,39], three in Middle East countries [22,28,29], one in Asia [42], one in Oceania [25] and one in North America [24]. Moreover, studies were performed during different periods: two between 1985 and 1993 [20,24], four between 2004 and 2008 [37,39,41,42], and the others after 2010. As bullying policies and aesthetic or orthodontic treatments have evolved during these years, it is possible that the results may be different.
Considering exposure in terms of gender, some authors showed a significant difference, with more boys being victims than girls [22,28,35], while others underlined no significant differences [31,32,35]. However, differences could be more subtle: when males are more likely to endure direct forms of aggression, such as physical attacks, in contrast, females are exposed to more indirect types, which could be underestimated [49].
Four of the included articles [22,26,28,40] found that teeth were one of the most frequent physical features targeted in people who were victims of bullying. Only one of them included patients from an orthodontic population, whereas the three others used school and social networks, so these results could be considered representative. The most frequently identified dental features targeted were prominent maxillary anterior teeth [20,22,24,27,28,32,40,49], spaced or missing teeth [22,27,28,32,40] and shape and colour of teeth [22,27,28,32], which can be qualified as conspicuous dentofacial characteristics. In Helm et al., study, 50% of the subjects with the most extreme maxillary overjets had experienced teasing [20].
This review shows that the more the dental condition (malocclusion, enamel defects, dental fluorosis, amelogenesis imperfecta) could be visible because of its severity or because of its anterior situation, the greater the risk of experiencing teasing or bullying [23,34,39,49]. However, in their literature review on the impact of malocclusion, Zhang et al. [4] found that, ironically, milder deviations in tooth position tend to evoke ridicule and teasing, whereas severe deformities will elicit strong emotional reactions such as pity or revulsion.
In their material and methods, most of the studies [9,20,22,28,29,[32][33][34][35]39,40] reported that they had excluded individuals with orthodontic appliances to avoid a confounding variable. Due to the conclusions of the study performed by Shaw et al. in 1980 [26], they hypothesised that wearing an orthodontic appliance should increase bullying exposure, whereas the more recent study of Seehra et al. [30] suggested that participants undergoing orthodontic treatment had a significant reduction in bullying. Scheffel et al. [48] underlined the same phenomenon in the short term in patients with dental structural defects after cosmetic treatments. These elements would benefit from being studied in depth in future studies.
A positive consequence of bullying could be the encouragement to initiate orthodontic consultation [27,40] and the motivation to follow the treatments. Therefore, it also influences the expectations regarding orthodontics [40] or cosmetic treatment [12], and communication between the practitioner and the patient is crucial. Effectively, improvement of dental occlusion or aesthetics may not be sufficient to enhance the psychological condition, self-esteem and the patient's exposure to bullying. In their literature review, Zhang et al. [4] pointed out that after orthodontic treatment, there was little evidence of a marked improvement in the social well-being of the patients. Social network posts examined by Chan et al. [27] confirm the positive psychological impacts of treatments for some victims. Even if it is difficult to determine the longevity and permanency of these positive effects, we know that the negative psychological effects of peer victimisation in school-aged children can continue during the transition to senior school and into adulthood [49]. Then, even if bullying decreases or stops, psychological consequences could persist, which may be devastating to a child, with long-term effects [2,50] leading to an increased rate of suicidal risk and self-injurious behaviour [49,51].
The authors did not limit themselves to the evaluation of the exposure to bullying but also looked at its consequences. Bullying because of dentofacial features increases absenteeism from school [22,28,32], with significantly more bullied students who dislike not only classes but also school outside of classes [32]. Effectively, episodes of bullying frequently take place during break times. Bullying also has negative consequences for academic performance [22]. In Al Bitar et al. study [28], 40% of students believed that bullying harmed their grades.
In three of the studies [7,29,31], bullying was associated with more negative effects of oral condition on Oral Health-Related Quality of Life (OHRQoL). However, it remained unclear whether this negative impact was due to the presence of malocclusion or peer victimisation [31]. We could suppose that the association of these two elements could increase consequences on quality of life.
Studies included in this review reported that individuals not satisfied with their body image [43], with self-hate or low self-esteem [27], or described as introverted [26] had more chances of being victims of bullying. It has already been described by Olweus et al. [2] with tendencies of being anxious and insecure. Some authors have put forward the hypothesis of a 'victim personality' [49], which may result from, or be exacerbated by, victimisation [50] and which remains with the individual despite changes in the social situation [49]. It plays a role in the initial instigation of bullying and may be influenced by social background and parenting [50]. This could explain the tendency for children who are victims to remain victims, even when the social situation changes [10], or the occasionally reported phenomenon of being bullied because of having a perfect normocclusion [26,27].

Conclusions
With regard to targeted physical features, orofacial features are number one. Thus, severe oral conditions like structural dental abnormalities and severe malocclusion should be managed for functional and aesthetic questions, but also psychological ones because they crystallise the loss of self-confidence and increase the risk of harassment. Practitioners who see their young patients during crucial stages of psychological development must be aware of identifying children at potential risk of experiencing bullying, counsel families, and propose early treatments if possible. Explanation about the aetiology of their condition through therapeutic education may also improve their knowledge and help them to cope with negative comments.

Data Availability Statement:
No new data were created or analyzed in this study. Data sharing is not applicable to this article.