Perception of malocclusion and school performance in adolescents: a systematic review

Abstract This study aimed to assess the potential association between perception malocclusion and school performance in children and adolescents. An electronic search was performed in ten databases. Based on the PECO acronym (Population, Exposition, Comparator, and Outcome), the eligibility criteria included observational studies that compared the school performance of children and adolescents with and without the perception of malocclusion. There were no restrictions on the language or year of publication. Two reviewers selected the studies, extracted the data, and assessed the risk of bias by using the Joanna Briggs Institute tool for cross-sectional studies. School performance was measured by analyzing student grades; levels of absenteeism; and child or adolescent self-perception and/or the perception of parents, guardians, close friends, and teachers regarding the impact of malocclusion on school performance. The data were described narratively/descriptively. The search resulted in 3,581 registers, of which eight were included in the qualitative synthesis. These studies were published between 2007 and 2021. Two studies concluded that there was no significant association between school performance and perception of malocclusion, five studies found that only some of the children with malocclusion had their school performance affected, and one study concluded that there was a significant association between perception of malocclusion and low school performance. Considering all variables and the very low certainty of evidence, the perception of malocclusion seems to negatively impact school performance when associated with external and subjective factors. Further studies using additional measurement standards are required.


Introduction
Individuals undergo several physical and emotional changes from birth to adulthood. 1 Children and adolescents show a high worldwide prevalence of malocclusion. 2This is associated with multiple factors such as dental caries, pulpal and periapical lesions, dental trauma, abnormality of development, and oral habits. 3Moreover, on its own, facial growth from childhood to adolescence is unable to correct most of the malocclusions of primary dentition. 2alocclusions constitute oral changes with a global prevalence of 39% among adolescents. 4In some phases of their development, children and adolescents spend a considerable number of years in schools and other education and training institutions. 1The presence of oral disorders may affect the school life of these individuals. 5,6Some explicit and extreme malocclusions may also be related to bullying in childhood and adolescence. 7here is evidence that certain oral conditions, such as caries, periodontal disease, tooth loss, and orofacial pain, may negatively affect oral healthrelated quality of life 8,9 and school performance. 10owever, the primary evidence in the literature on the role of malocclusion in the school performance of children and adolescents has not yet been gathered into secondary studies.Thus, the present systematic review aimed to investigate and expose the existing scientific evidence about the impact of the perception of malocclusion on children and adolescents' school performance.

Methodology Protocol registration
The protocol of this systematic review was described according to the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols guidelines 11 and registered in the International Prospective Register of Systematic Reviews database under number CRD42020172295 (https://www.crd.york.ac.uk/prospero/).Moreover, this systematic review was reported according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines 12 and conducted according to the norms of the Joanna Briggs Institute manual for Evidence Synthesis 13 and according to the Conducting Systematic Reviews and Meta-Analyses of Observational Studies of Etiology guidelines. 14esearch question and eligibility criteria This systematic review aimed to answer the following guiding question based on the PECO acronym (Population, Exposition, Comparator, and Outcome): "Do children and adolescents with malocclusion present lower school performance than individuals without malocclusion?"

Inclusion criteria
Population: Children and adolescents up to 19 years old, according to the World Health Organization 15 Exposition: Malocclusion perceived by the individuals and/or their parents/guardians and assessed using reliable methods, such as selfperception or dental indices Comparator: Children and adolescents who did not report perceived malocclusion and without any diagnosed malocclusion Outcome: School performance (grade analyses, level of absenteeism, and child or adolescent selfperception or the perception of parents, guardians, and/or teachers regarding the impact of malocclusion on school performance) Type of study: observational studies (crosssectional, case-control, or cohort studies) There were no restrictions on language or year of publication.

Exclusion criteria
Studies with a sample of individuals with current or previous orthodontic treatment Studies with a sample of syndromic individuals Studies assessing school performance using the perception of malocclusion images by third parties Review articles, letters to the editor or editorials, personal opinions, book chapters or books, textbooks, case reports or case series, reports, and congress abstracts Studies with overlapping samples; when two or more studies were conducted in the same place, by the same authors, and in similar years, but published in different journals or years.In this case, the most recent study that best described the methodology and results was considered.

Study selection
The search results were exported to the EndNote Web™ software (Thomson Reuters, Toronto, Canada) for cataloging and removing duplicates.The results obtained in the partial search of the "gray literature" were exported to Microsoft Word (Microsoft, Washington, USA) to manually remove duplicates.Before the selection of studies, a calibration exercise was performed when the examiners discussed the eligibility criteria and applied them to a sample of 20% of the eligible studies to determine the interexaminer agreement.
After reaching an adequate level of agreement (kappa ≥ 0.81), the reviewers (ACC and DMP) performed a detailed analysis of the titles and abstracts of the studies, applying the inclusion and exclusion criteria mentioned above.Studies that did not meet these criteria were excluded.Next, the full texts of the eligible preliminary studies were obtained and evaluated.In this phase, the excluded studies were listed separately, specifying the reasons for their exclusion.Two eligible reviewers independently performed the entire selection process.Disagreements were resolved by consulting with a third reviewer (LRP).

Data extraction
Two reviewers (ACC and DMP) independently extracted data from eligible studies.A calibration exercise was performed to ensure consistency between the two reviewers, in which information was jointly extracted from one eligible study.A third reviewer (LRP) performed calibration.The following data were extracted: identification and characteristics of the study (author, year, country, research location, and application of ethical criteria), sample characteristics (number of participants, age group, sex distribution, and method of malocclusion analysis), and main outcome characteristics (school grades, absenteeism, relationship with bullying, and assessment of school performance by parents or teachers).In case of incomplete or insufficient data, the corresponding author was contacted via e-mail up to three times at weekly intervals.

Risk of bias assessment Evaluation of methodological quality
The studies were assessed for the risk of individual bias using the JBI Critical Appraisal Tools for use in the JBI Critical Appraisal Checklist for Analytical Cross-Sectional Studies. 16Two authors (ACC and DMP) independently assessed each domain for the risk of bias as recommended by the PRISMA statement. 12ach question could be answered as follows: "Yes," if the study did not present biases for the domain assessed in the question; "No," if the study presented biases for the domain assessed in the question; "Uncertain," if the study did not provide sufficient information to assess the question bias; and "Not Applicable," if the question did not fit in the study.

Evaluation of control statements for possible confounders and bias consideration
The control statements for possible confounders and risk of bias were evaluated based on the methodology described by Hemkens et al. 17 First, eligible studies that mentioned only bivariate analysis or did not report multivariate analysis were excluded from this evaluation.Second, two independent reviewers (ACC and DMP) critically appraised the remaining studies.The reviewers were blinded, and a third reviewer (LRP) was consulted in case of disagreements.Each article had the Abstract and Discussion sections analyzed in consideration of confounders using six questions which were previously established.Only the sixth question considered the Conclusion section.If the conclusion section was absent, the last paragraph of the Discussion section was considered.

Assessment of confounding factors
The confounding factors were assessed based on the methodology described by Wallach et al. 18 It was conducted by two reviewers (ACC and DMP), independent and blinded.A third reviewer (LRP) was consulted during disagreements.All studies included in the evaluation of control statements for possible confounders and bias consideration had their Methods and Result sections analyzed.The aim was to list the variables included in each study and identify which variables were used to perform adjustment, stratification, or matching between groups.
Adjustment variables were analyzed using multivariate logistic regression analysis or Poisson's regression.Stratification variables were those used in the sample selection to make strata.Matching variables ensured compatibility of characteristics between groups.In addition, variables considered possible confounding factors were set together in their respective confounding domains.

Summary of measurements and synthesis of results
T he dat a col le cted were orga n i zed a nd described descriptively or narratively (qualitative synthesis) according to the findings presented in each study.School performance was measured by analyzing student grades; levels of absenteeism; and child or adolescent self-perception and/or the perception of parents, guardians, close friends, and teachers regarding the impact of malocclusion on school performance.

Certainty of evidence
Two reviewers (WAV and MTCV) independently ranked the overall strength of evidence using the Grading of Recommendations, Assessment, Development and Evaluation tool. 19To assess the criteria in systematic reviews without meta-analyses, the authors followed the adaptations proposed by Murad et al. 20

Study selection
The electronic search identified 3,581 results distributed into nine electronic databases, including the "gray literature".After removing duplicates, 3,098 results remained for the analysis.Careful reading of the titles and abstracts excluded 3,071 results.Twentyseven registers were sought for retrieval and three were not retrieved.Twenty-four studies remained for full-text reading.At this stage, 16 studies were excluded because they did not meet the inclusion criteria.2][23][24][25][26][27]

Characteristics of the eligible studies
The studies were published between 2007 and 2021 and performed in five different countries: Brazil, 10,22,24,25 Chile, 26 India, 23 Mongolia, 27 and Peru. 21All studies reported the following ethical criteria with the approval of an ethics committee and/or application of a consent form to the research participants.The sample included 9,369 children and adolescents allocated to public and private schools.The reported ages varied between 3 and 19 years.
Malocclusion was assessed using the Dental Aesthetic Index (DAI), 10,22,23,26 self-perceived malocclusion, 21 malocclusion exam for the presence of dentofacial features, 24 the use of a Community Periodontal Index (CPI) probe, 25 and the Index of Orthodontic Treatment Need (IOTN). 27The tools used to measure the school performance of participants varied among grades, 10,22,23,26,27 self-reports by adolescents, 21,25 and absenteeism. 24able 2 details the information of each eligible study.
The study by Paula et al. 22 did not show a significant association between the need for orthodontic treatment (assessed using the DAI) and school performance, with an odds ratio (OR) of 1.33 (0.87-2.03).Similarly, Julca-Ching and Carruitero 26 did not find a significant difference in school performance scores between young individuals with normal occlusion and those with malocclusion, regardless of severity.Furthermore, both studies highlighted the potential association between the influence of external and subjective factors, especially related to family members and socioeconomic conditions, and the impact of malocclusion on school performance.
Ortiz et al. 10 reported that some adverse oral conditions, such as malocclusion, as well as subjective and socioeconomic factors, might have impacted adolescents' academic performance.Bernabé et al. 21bserved that only 0.6% of the children analyzed reported some impact of malocclusion on their education, with the impact intensity ranging from mild to moderate.
In turn, Basha et al. 23 found that 42% of students with malocclusion presented impact on school performance, with grades below average over the last three years.Regarding the self-perceived impact, 20% of the students reported that school performance was affected by their dental appearance.As for the perception of parents, 77% felt that the school performance of their children was affected by dental appearance, 79% of teachers reported such perception, and 32.7% of the close friends of the students analyzed mentioned such a relationship.Badrakhkhuu et al. 27 also observed that schoolchildren in Mongolia with dental crowding, a type of malocclusion, might be prone to poor academic performance, particularly in arts and physical education.
Neves et al. 24 showed a prevalence of 8.5% in school absences due to oral problems.Lastly, Cunha et al. 25 observed a significant association between malocclusion (such as accentuated overjet and  open bite) and school performance, directing the measurement to school failure (OR, 1.40 (1.31-1.50))after adjusting for confounding factors.Table 3 shows the main outcomes and quantitative results regarding the presence of malocclusion and its impact on school performance in each eligible study.

Risk of individual bias of the studies Methodological quality of the eligible studies
Only two studies 24,26 met all criteria from the checklist.Three studies 21,23,26 did not meet the fifth, sixth, and eighth question criteria because they lacked proper confounding acknowledgement and did not perform multivariate analysis to adjust for their variables, showing high potential biases in their methodology.Table 4 shows more details about the methodological evaluation of the eligible studies.

Evaluation of control statements for possible confounders and bias consideration
All eight eligible studies were analyzed, and three studies were excluded for mentioning only bivariate analysis or not reporting multivariate analysis.After this, five studies 10,22,24,25,27 were included in the evaluation of control statements for possible confounders and bias consideration.Only one study 27 did not mention the term "confounding" and only two studies 27,28 mentioned the term "bias".Only two studies 10,25,28 mentioned non-adjusted variables that were not measured.6.30.6 Self-perceived malocclusion primarily affected psychological and social everyday activities.These findings provide further evidence to support the importance of psychological and social components of oral health on children's lives.
de Paula et al. 22 24. 3  38.4The results of this study showed that socioenvironmental factors, subjective perceptions, and oral health status of children -particularly carious lesions, have an important impact on school performance, demonstrating the need for planning public health dentistry based on intersectoral public policies.
Basha et al. 23 100 20.2 Untreated gross dental malocclusion significantly affects the psychosocial wellbeing of adolescents, who may avoid participating in social activities and tend to underperform in school.
Neves et al. 24 34.8 8.5 The prevalence of preschool absenteeism due to oral problems was 8.5 % and associated with the occurrence of cavitated dental caries.Further studies, especially investigations with a longitudinal design, are needed to garner a better understanding of this problem.
da Cunha et al. 25

nr
Oral disorders and social factors were associated with school failure in adolescents.A successful school trajectory was a strong determinant of health; therefore, actions between the educational and health sectors must be developed for adolescents, especially those who fit this profile.
Julca-Ching and Carruitero 26 52.8 26.8 The need for orthodontic treatment in school-going children did not show an impact on academic performance, self-esteem, and bullying scores.The need for orthodontic treatment, as measured by the Dental Aesthetic Index, did not prove to be a determining factor in the presence of such variables in school-going children.
Badrakhkhuu et al . 272.6 nr School-going children in Mongolia with dental crowding may be prone to poor academic performance, particularly in arts and physical education.Further randomized controlled trials are needed to determine whether the treatment of crowding boosts academic performance.
Ortiz et al. 28 42.5 nr Adverse oral conditions as well as subjective and socioeconomic factors impacted adolescents' academic performance.
nr, not related to the study.
Four studies 22,24,25,27 reported the need for caution when interpreting their results.Only one study 27 included limitations in the Conclusion section.The results of the evaluation of the control statements for confounders and bias consideration are presented in Table 5.

Assessment of confounding factors
Eighty-six variables were identified in the studies included in this analysis.They were classified into five domains: dentofacial features, school environment, sociodemographic and socioeconomic factors, residential environment, and dental services.The domain with the most variables was the dentofacial feature domain with 20 different variables.The most frequent variables were age, sex, and family income, which were present in all studies.There was high heterogeneity among all studies, as well as their variables within the school environment, residential environment, and dental services domains.Some variables had similar meanings; thus, they were set together in standardized terms for better analysis.The confounding domains identified in the eligible studies are presented in Table 6.
In addition, 59 continuous and categorical variables were used as adjustment variables.Age and sex were used for adjustment in three studies and were the most commonly used variables within the adjusted variables.Only one study 24 used stratification variables: school district and school type.Only age was used to match groups; this matching variable was present in two studies. 10,22

Certainty of evidence
The certainty of evidence was classified as "very low" and downgraded due to the risk of bias, inconsistency, and indirectness (Table 7).

Discussion
The present systematic review aimed to assess whether adolescents with malocclusion tend to have lower school performance than those without malocclusion.The evidence from the studies included in the qualitative synthesis suggests that this dental condition affects student performance when associated with external factors, especially those related to family members and socioeconomic conditions.
School performance can be assessed by using several indicators.The quantitative indicators relate to the grades obtained by students in evaluations, tests, and homework, the approval rate, 22 and levels of absenteeism. 25Indicators obtained from self-perception or the perception of parents, guardians, teachers, or close friends are considered qualitative indicators because they depend on a subjective interpretation and the individual judgment of a situation. 28Therefore, the analysis of school performance is associated with objective factors and organic, cognitive, psychological, socioeconomic, and educational factors. 29The eligible Table 4. Risk of bias assessed with the Joanna Briggs Institute Critical Appraisal Tools for use in the JBI Critical Appraisal Checklist for Analytic Cross-Sectional Studies studies of this review showed high heterogeneity for the tools for measuring school performance among the young people assessed.
In this context, the presence of abnormal dentofacial characteristics, such as malocclusion, may negatively interfere with the school performance of individuals, as suggested by some of the eligible studies. 10,21,24,25,27In general, poor health conditions of students might harm their cognitive development and participation in school activities, increasing the levels of absenteeism, 30 which corroborates the negative impact of malocclusion on school performance. 10,21,24,25,27In studies that used qualitative indicators, 21,23 there was a focus on the self-perception of students with malocclusion and the perception of parents, teachers, and close friends.Divergent results from the perceptions of parents and teachers to that of students and close friends showed that, in most cases, adults did not understand the situations and difficulties that children and adolescents faced in school. 23owever, the neutral results of those impacts on school performance from other eligible studies 22,26 highlighted the strong influence of external and subjective factors when dealing with different adverse situations on behavioral changes and decreased school performance, such as poor family socioeconomic conditions, 31 low level of education of parents or guardians, 31 household overcrowding, 32,33 and the type of school attended by the child or adolescent. 22ligible studies were conducted in different countries, with major socioeconomic and cultural factors that might have influenced the results.For

Abstract and Discussion
Is the term "confounding" mentioned in the Abstract or Discussion?
Specific: if the authors used the exact term "confounding" 2 (40%) Alluded: if the authors used a similar term or phrase 2 (40%) No: if the authors used neither the exact nor similar term 1 (20%) Is the term "bias" used in the Abstract or Discussion?
Yes: if the authors used the term "bias" 2 (40%) No: if the authors did not use this term 3 (60%) Is there any specific mention of non-adjusted variables in the Abstract or Discussion?
Yes: if there was a specific mention of non-adjusted variables with no reasons presented 0 Not measured: if there was a specific mention of non-adjusted variable not being measured 2 (40%) Other reasons: if there was a specific mention about non-adjust variables, with plausible reasons for not adjusting them 0 No reasons: if there was a specific mention about non-adjusted variables, with implausible reasons for not adjusting them 0 No: if there was no mention about any non-adjusted variable 3 (60%) Is there any mention about confounders affecting results in the Abstract or Discussion?
Likely: if the authors used terms such as "likely" or convincing statements implying that the confounders were not controlled 1 (20%) Possibly: if the authors used terms such as "possibly" or unsure statements suggesting that the confounders were or were not controlled 4 (80%) Unlikely: if the authors used terms such as "unlikely" or convincing statements suggesting that the confounders were controlled 0 No mention: if there was no mention of this possibility 0 Is there any statement on the need for caution in interpretating the results?Yes: if there was explicit mention about the need for caution in interpretating the results obtained in the study 4 (80%) No mention: if there was no mention about this need for caution 1 (20%)

Does the Conclusion include any limitation about confounders?
Yes: if there was a mention of this limitation 1 (20%) No: if there was no mention of this limitation 4 (80%)  Not serious none Two studies concluded that there was no significant association between school performance and perception of malocclusion, five studies found that only part of the children with malocclusion had their school performances affected, and one study concluded that there was a significant association between perception of malocclusion and low school performance.
⨁ Very Low a -The majority of the studies presented import bias due to confounding factors.b -The studies presented divergent results.c -The main outcome was assessed using different tools that indirectly evaluated school performance.GRADE Working Group grades of evidence High certainty: Very confident that the true effect is close to the estimated effect.Moderate certainty: Moderately confident in the estimated effect; the true effect is likely close to the estimated effect, but it may be substantially different.Low certainty: Limited confidence in the estimated effect; the true effect may be substantially different from the estimated effect.Very low certainty: Very little confidence in the estimated effect; the true effect may be substantially different from the estimated effect.
example, low-and middle-income countries, such as Brazil and India, still present concerns about child labor, which can affect the physical and mental health of this population. 34In poor families, it may be common to observe children and adolescents working to help their parents or relatives with monthly bills.These less privileged conditions may also be related to typical public health and social questions, which are already associated with impaired school performance: dental caries and worse oral health, 35 altered sleep time, 36 and less access to proper schooling resources and equipment, 37 especially in the recent online study methods. 36ll eligible studies were cross-sectional.This type of study can lead to limitations when analyzing outcomes, as they analyze exposure and outcome at the same time, which impairs the inference of causality. 38Furthermore, observational studies do not present permutability between their study groups, because of the lack of randomized variables. 39On the other hand, as the focus is on malocclusions, it may favor a cause-and-effect interpretation, as they can be considered as inborn characteristics of the individuals. 38However, it is still not a longitudinal design to better estimate the exact correlation of the variables studied.This could also underestimate the role of confounding factors.Some potential biases in the eligible studies should be acknowledged.First, the performance of only bivariate analysis or the lack of multivariate analysis in observational studies are common and dangerous pitfalls.Observational studies have a high risk of presenting several uncontrolled confounders, which limits their results. 14Multivariate analysis is a reliable statistical test to provide proper adjustment of variables, reducing the potential confounding influence. 38Secondly, this reduction is unfortunately not absolute, and the interpretation of results should be performed with caution.Although there was acceptable prudence in selected studies regarding this caution, they lacked proper acknowledgement of non-adjusted variables and inclusion of limitations in the Conclusion section.
The confounding domains identified in the selected studies brought up some confounders to be considered in the association between malocclusion and school performance.It is important to highlight them because of their potential roles as causes, effects, or coincidences without any relationship.However, inferences about the roles of each variable are limited to be made based on observational studies. 14Therefore, further studies with longitudinal and controlled designs are necessary to better understand this association.
This review had a few limitations.First, different observational designs might have affected the presence of divergences among the individual results of the studies, especially regarding the absence of standardization of the tools for assessing malocclusions.Most studies 10,[22][23][24][25][26][27] were based on dental professionals' perception measurements to assess malocclusions, such as the DAI, malocclusion exam, IOTN, and the use of a CPI probe.Only one study 21 subjectively measured malocclusion using Child Oral Impacts on Daily Performances, with the self-perception of individuals.Subjective measurements may be subject to the influence of individual experiences, considering that the same condition may be understood differently by each individual.Moreover, the assessment of several school performance indicators was verified among the studies and some of them 21,23,26 did not perform analyses to deal with confounding factors associated with the outcomes.Thus, owing to the lack of measurement standards, the results may not reflect the true impact of malocclusion on school performance.Further studies with the application of more standardized and better-designed methodologies are encouraged to address such limitations.Another significant limitation worth noting is that malocclusion may relate to other factors that can also affect school performance, such as bullying. 40The lack of analysis of confounding factors was a bias identified in part of the eligible studies and deserves attention when interpreting the results.Some strengths of this systematic review must be highlighted, such as its preparation according to specific instructions 12 and caution to minimize biases.Moreover, this is the first systematic review to specifically assess the impact of malocclusion on the school performance of children and adolescents.The evidence summarized may be useful for the decisionmaking of governments and school administrators, especially regarding the need to establish a partnership between schools and dental professionals in an attempt to provide better oral health and higher access to dental treatments, such as orthodontic treatment to correct malocclusions.

Conclusion
The very low certainty evidence suggests that the perception of malocclusion negatively affects the school performance of students when associated with external factors, especially those related to family members and socioeconomic conditions.Considering the limitations of this systematic review, the results may not accurately reflect the impact of malocclusion on school performance.Nevertheless, the findings provide important data to encourage health actions toward the development of oral health care programs for students, aiming to improve their quality of life physically and psychologically, and consequently, their school performance.
Figure shows the details of the study selection process.

Figure .
Figure.Flowchart depicting the study selection process (Preferred Reporting Items for Systematic Reviews and Meta-Analyses flow diagram).

Table 1 .
Strategies for database search

Table 2 .
Main characteristics of the eligible studies nr: not related to the study; SD, standard deviation; * CPI probe was used to perform measurements.

Table 3 .
Main outcomes of the eligible studies

Table 5 .
Evaluation of control statements for possible confounders and bias consideration

Table 6 .
Confounding domains identified in selected studies

Table 7 .
Summary of findings by the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) for the outcomes of the systematic review