1 INTRODUCTION

Dental trauma (DT) is a common condition, affecting mainly the young population.1 Approximately 20% of Brazilian children or adolescents have suffered some kind of DT in the both primary and permanent dentitions.2 Dental trauma may occur for several reasons, such as falls, domestic or automobile accidents, sports practice, and situations of violence.3-5

The impacts of DT can be identified in different aspects of the life of the individuals affected. It is common to observe pulp necrosis with infection and root resorption in teeth that have suffered severe trauma.6 Usually, cases of DT require specialized treatment and it might cause discomfort, anxiety, and unplanned financial expenses for the patients or their parents/guardians.7 Aesthetic damage is common, especially when untreated, as it may directly interfere with the quality of life of the patients and their social interactions.8, 9

As it is a global public health problem,10 preventing new cases of DT requires immediate public policies. Considering that Brazil has continental dimensions, the awareness of factors associated with the prevalence of DT in Brazilian children and adolescents is important for implementing specific preventive measures for this population. The most common factors cited in the literature are clinical characteristics such as inadequate lip coverage and malocclusion.5, 9, 11 Even though some Brazilian studies have assessed the association of these characteristics with the prevalence and incidence of DT in children and adolescents,5, 9, 11 their results show great divergence.

A previous systematic review1 focused on this problem and investigated risk factors for DT in the Latin American and the Caribbean populations, confirming that inadequate lip coverage and overjet greater than 5 mm are predisposing factors for DT. However, this study included only 12-year-old children and all the Brazilian studies selected were conducted before 2010. Thus, considering that Brazil is one of the countries that has published many studies about the epidemiology of DT,10 these data are out of date and the factors related to DT in primary or mixed dentitions in children are missing.

The aim of this systematic review was to summarize the existing data and investigate the association between clinical factors (lip sealing, overjet, and anterior open bite) and the presence of DT in different types of dentitions in Brazilian children and adolescents.

2 MATERIALS AND METHODS

This systematic review was reported according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) recommendations12 and the protocol was registered a priori in the PROSPERO database (CRD42020156290). Initially, the protocol was developed to assess all risk factors related to dental trauma in Brazilian children and adolescents. However, due to the large number of variables, only the clinical factors most cited in the literature were used, namely overjet, lip coverage, and open bite. Thus, the protocol initially registered was adjusted for the new outcomes, the guiding question, and eligibility criteria. This adjustment was made during the initial bibliographic search and before the study selection and data extraction.

The guiding question was defined as: ‘Are Brazilian children and adolescents with inadequate lip coverage, increased overjet, or anterior open bite more likely to suffer dental trauma than those without such conditions?'

The inclusion criteria were based on the PECO mnemonic, where: Population: Brazilian children and adolescents aged 0–19 years, regardless of gender, ethnicity, or other sociodemographic factors. The 19-year-old threshold was established according to the classification of the World Health Organization for ‘adolescent’.13 Exposition: Increased overjet (any threshold), anterior open bite, or inadequate lip coverage. To be included, studies had to perform clinical examinations to assess the participants' occlusion and describe in detail how malocclusion and lip coverage were classified. Comparator: Non-exposed participants (normal overjet, adequate lip coverage, and the absence of anterior open bite). Outcome: Presence of any type of dental trauma diagnosed by any classification system, as long as the diagnostic criteria and methods were clearly described in the studies. Study design: Cohort, case-control, or cross-sectional. There were no restrictions on date or language.

Reviews, letters to the editor, personal opinions, books, congress abstracts, case reports or case series, studies with participants who had a cleft lip and/or palate, other craniofacial deformities, or any syndrome or special needs (ie cerebral palsy or autism), and studies with samples composed only of traumatized teeth were excluded. In the case of studies with overlapping results, the most recent study was considered.

The bibliographic search was performed until July 2020 in the following databases: Embase, Medline (via PubMed), SciELO, Scopus, Web of Science, LILACS/BBO, OpenThesis, and OpenGrey. Additionally, the references of eligible studies were manually verified. All steps aimed to minimize selection and publication biases.

The search strategy included the following MeSH descriptors: ‘Tooth Injuries’, ‘Tooth Avulsion’, ‘Maxillofacial injuries’, ‘Brazil’. Additionally, the following synonyms and free terms were used to enhance the research: ‘Traumatic dental injury’, ‘Dental Trauma’, ‘Crown Trauma’, ‘Tooth Luxation’, ‘Dental injuries’, ‘Oral Injuries’, ‘Brazilian’. The Boolean operators AND and OR were used to enhance the research strategy through several combinations (Table 1). The search strategies were adapted for each database according to their rules of syntax.

TABLE 1. Strategies for database search Database Search strategy (July, 2020) MEDLINE (via PubMed)

#1 ("traumatic dental injury"[Title/Abstract] OR "traumatic dental injuries"[Title/Abstract] OR "Tooth Injuries"[MeSH Terms] OR "dental trauma"[Title/Abstract] OR "crown trauma"[Title/Abstract] OR "Tooth Avulsion"[MeSH Terms] OR "Tooth Avulsion"[Title/Abstract] OR "tooth luxation"[Title/Abstract] OR "dental injury"[Title/Abstract] OR "dental injuries"[Title/Abstract] OR "dentoalveolar trauma"[Title/Abstract] OR "crown fracture"[Title/Abstract] OR "Oral Injuries"[Title/Abstract] OR "Tooth Fractures"[MeSH Terms] OR "Tooth Fractures"[Title/Abstract] OR "traumatic injuries" [Title/Abstract] OR "traumatic injury" [Title/Abstract])

#2 ("Brazil"[MeSH Terms] OR "Brazil"[Title/Abstract] OR "brazil*"[Title/Abstract] OR "Brazilian"[Title/Abstract])

#1 AND #2 Web of science

#1 ts = (“Traumatic dental injur*”) OR ts = ("Tooth Injuries") OR ts = ("Dental Trauma") OR ts = ("Crown Trauma") OR ts = ("Tooth Avulsion") OR ts = ("Tooth Luxation") OR ts = ("Dental injur*") OR ts = ("dentoalveolar trauma") OR ts = ("crown fracture") OR ts = ("Oral Injuries") OR ts = ("Tooth Fractures") OR ts = ("traumatic injuries")

#2 ts = ("Brazil") OR ts = ("Brazilian")

#1 AND #2 Scopus

#1 (TITLE-ABS-KEY ["Traumatic dental injur*"]) OR (TITLE-ABS-KEY ["Tooth Injuries"]) OR (TITLE-ABS-KEY ["Dental Trauma"]) OR (TITLE-ABS-KEY ["Crown Trauma"]) OR (TITLE-ABS-KEY ["Tooth Avulsion"]) OR (TITLE-ABS-KEY ["Tooth Luxation"]) OR (TITLE-ABS-KEY ["Dental injur*"]) OR (TITLE-ABS-KEY ["dentoalveolar trauma"]) OR (TITLE-ABS-KEY ["crown fracture"]) OR (TITLE-ABS-KEY ["Oral Injuries"]) OR (TITLE-ABS-KEY ["Tooth Fractures"]) OR (TITLE-ABS-KEY ["traumatic injuries"])

#2 TITLE-ABS-KEY ("Brazil" OR “Brazilian”)

#1 AND #2 Embase

#1 (‘traumatic dental injuries’:ti,ab,kw OR ‘tooth injuries’:ti,ab,kw OR ‘dental trauma’:ti,ab,kw OR ‘crown trauma’:ti,ab,kw OR ‘tooth avulsion’:ti,ab,kw OR ‘tooth luxation’:ti,ab,kw OR ‘dental injuries’:ti,ab,kw OR ‘dentoalveolar trauma’:ti,ab,kw OR ‘crown fracture’:ti,ab,kw OR ‘tooth fractures’:ti,ab,kw OR ‘traumatic injuries’:ti,ab,kw)

#2 (brazil:ti,ab,kw OR brazilian:ti,ab,kw)

#1 AND #2 LILACS and BBO

#1 ab:("Traumatic dental injury" OR "Trauma Dental" OR "Tooth Injuries" OR "Dental trauma" OR "'tooth fractures" OR “dental injuries” OR “Traumatismos dentários” OR “Traumatismo dental” OR “Fraturas dentais” OR “Fraturas dentárias” OR “fratura dos dentes”)

#2 ab:("Brazil" OR "Brasil" OR "Brazilian")

#3 (db:["BBO" OR "LILACS"])

#1 AND #2 AND #3 OpenGrey ("Traumatic dental injuries" OR "Tooth Injuries" OR "Dental Trauma") OpenThesis ("Traumatic dental injuries" OR "Tooth Injuries" OR "Dental Trauma") AND ("Brazil" OR “Brazilian”)

Then, the records were exported to the EndNote Web™ software (Thomson Reuters) and two calibrated reviewers (WAV and PHG) independently performed a methodical analysis of all the titles and abstracts of the studies. Duplicate results were considered only once and studies outside the objectives of this systematic review were excluded in this phase. Subsequently, preliminary eligible studies had their full texts evaluated to verify whether they fulfilled the eligibility criteria. When both reviewers disagreed, a third reviewer (AJS) was consulted to make a final decision.

After the selection, a calibration exercise was performed with both reviewers (WAV and PHG), in which some information was extracted jointly from an eligible study. Any disagreement between the reviewers was solved through discussions and when two reviewers disagreed, a third reviewer (AJS) was consulted to make a final decision. The two reviewers (WAV and PHG) extracted the following data: identification (author, year, city, state, and region of the research), sample characteristics (number of patients and distribution by gender, age range, and dentition type), characteristics of data collection (sample collection location, trauma diagnosis criteria, and clinical characteristics), main results, and funding sources. In the case of missing data, the corresponding authors were contacted by e-mail.

The checklist proposed by Fowkes and Fulton14 was used to assess the risk of bias in the eligible studies. The tool is based on five domains: (1) Whether the study design was appropriate for the objectives; (2) Whether the sample was representative; (3) Whether the control group was acceptable; (4) Whether the quality of measurements and outcomes were adequate; and (5) How confounding factors and distorting influences were addressed. Two calibrated reviewers (WAV and PHG) independently assessed the risk of bias for each eligible study. Each item was classified as a ‘major problem’, ‘minor problem’, ‘no problem’, or ‘not applicable’. In case of divergence between the reviewers, a third reviewer was consulted (AJS).

To determine the risk of bias in each study, three questions were formulated at the end of the evaluation: (1) Are the results erroneously biased in a certain direction?; (2) Are there any serious confounding or other distorting influences?; and (3) Is it likely that the results occurred by chance? If the answer for all three questions was ‘no’, then the study was considered to have a low risk of bias.14

Meta-analyses were performed to verify the relationship between DT and clinical factors. This study used odds ratio (OR) as the effect measure and a 95% confidence interval (CI). All analyses were considered as they included the number of events (traumatic dental injuries) and the total population of each group (exposed group - subjects with inadequate lip coverage, and non-exposed control group - subjects with adequate lip coverage). For the overjet analysis, the thresholds of >2, >3, ≥3, and >5 mm were considered. Initially, meta-analyses were performed according to the dentition type, based on the age range of the population: primary dentition (0–6 years), mixed dentition (7–11 years), and permanent dentition (12–19 years).15 Due to the large number of studies overlapping dentition types in the same sample (children in mixed or permanent dentition, aged 8–13 years), meta-analyses were also performed based on the age range that best represented these studies (7–14 years).

The heterogeneity across studies was evaluated with I² statistics and classified as low (I² < 50%), moderate (I² = 50% to 75%), and high (I² > 75%).16 Initially, the random effects model was used in all analyses to minimize the heterogeneity effect among the studies. When the I² was low (<50%), the analysis was supplemented with the fixed model.15 All analyses were performed with R software with meta and metafor packages.17

When possible, three sensitivity tests were performed for each meta-analysis, as follows: (1) Only studies with a low risk of bias were included; (2) Outliers were removed; and (3) Including only studies with a low risk of bias and removing outliers. To be considered an outlier, the confidence interval of the study did not overlap the confidence interval of the pooled effect.17

The funnel plot was used to analyse the publication bias when more than 10 studies were included.18 The publication bias was evaluated by visually inspecting asymmetry in the funnel plot and using the Egger test.

The certainty of evidence was assessed via the Grading of Recommendation, Assessment, Development, and Evaluation (GRADE) approach.19 The GRADE pro GDT software (http://gdt.guidelinedevelopment.org) was used to summarize the results. According to the system, observational studies start at a low level of certainty and can be downgraded based on the risk of bias, inconsistency, indirect evidence, imprecision, and publication bias. However, they can be upgraded if a dose-effect is shown, if the magnitude of the effect is large or very large, or if there is evidence that the influence of all plausible confounding factors would reduce a verified effect or suggest a spurious effect when the results show no effect. The level of certainty among the evidence identified was characterized as high, moderate, low, or very low.19

3 RESULTS

During the first phase of selection, 2493 results were found distributed in nine electronic databases. After removing duplicates, 1142 results remained for the analysis of titles and abstracts, from which 92 were considered eligible for the full-text analysis. After reading the full text, 37 studies were excluded (Supplementary Table S1). Thus, 55 studies5, 9, 11, 20-71 were selected for the qualitative analysis and 52 studies5, 9, 11, 20-68 for the quantitative analysis. Figure 1 reproduces the process of search, identification, inclusion, and exclusion of articles.

Flowchart of the search and selection process for eligible studies

The studies included were performed in 10 Brazilian states and the Federal District, between 2000 and 2019. Three studies included samples from a national survey.9, 20, 21 The total sample consisted of 66,576 children and adolescents aged 0–19 years. Most of the sample consisted of females (n = 27,499) and permanent dentition (n = 32,330). Only 20 studies5, 21, 26, 29, 35, 38, 40, 42, 45, 48, 52, 54, 57, 59, 61, 66, 67, 69-71 declared their funding sources, which were all government agencies.

The most used diagnostic criteria among the studies were by Andreasen,5, 11, 22-42, 67, 69 followed by the one established by O'Brien.20, 43-58, 68-71 Clinical examinations were performed mostly in public or private schools and health centres during national child vaccination days.

Overjet was evaluated in 48 studies5, 9, 11, 20-24, 26, 28-41, 43-50, 58, 60, 61, 63-67 at different thresholds (Table 2). Most studies (35 out of 48)5, 9, 11, 20, 23, 24, 26, 28, 29, 31-33, 35-42, 45-48, 50, 52, 53, 55, 56, 58, 60, 61, 63, 66, 67, 71 showed a positive association between increased overjet and DT, even in adjusted models after multivariate analyses (22 out of 27 studies).5, 9, 11, 20, 26, 28, 33, 35, 36, 38-42, 45-47, 53, 58, 61, 63, 71 In two studies,52, 67 increased overjet lost its significance after multivariate analyses.

TABLE 2. Summary of main characteristics of the eligible articles (n = 55) Characteristic N (%) Study design Cross-sectional 53 (96) Case control 1 (2) Cohort 1 (2) Publication year 2000–2009 14 (24) 2010–2019 41 (76) Publication language English 51 (93) Portuguese 4 (7) Sample origin – Brazilian region Northeast 8 (15) Central-West 4 (7) Southeast 24 (44) Southern 16 (29) All regions 3 (5) Setting of the study Private schools 1 (2) Public schools 13 (24) Private and public schools 29 (53) National child vaccination day 9 (16) Home 3 (5) DT diagnostic classification system Andreasen's 25 (46) O'Brien's 20 (36) Othersa 10 (18) Type of dentition Deciduous 18 (33) Mixed 2 (4) Permanent 25 (45) Mixed/Permanentb 10 (18) Oral characteristics investigatedc Lip coverage 35 (64) Increased overjet (>2 mm) 4 (7) Increased overjet (>3 mm) 25 (45) Increased overjet (≥3 mm) 4 (7) Increased overjet (>5 mm) 15 (27) Increased overjet (≥5 mm) 1 (2) Anterior open bite 13 (24) Abbreviation: DT, Dental trauma. a Ellis's, Hinds and Gregory, Glendor, SBBrasil and OMS. b Studies that included children from both dentitions. c The sum of the percentages reaches more than 100% because a study may have evaluated more than one characteristic.

The presence of an anterior open bite was evaluated in 13 studies,9, 28-32, 35, 39, 59, 60, 62, 67, 69 from which eight30, 31, 39, 59, 60, 62, 67, 69 showed a statistically significant association with DT. Finally, inadequate lip coverage was evaluated in 35 studies,5, 22-25, 27, 29, 31, 33, 35, 37, 38, 43-57, 61, 68-71 from which 215, 22-24,31, 35, 37, 38, 45, 47, 48, 50, 52, 53, 55-57, 61, 69, 70 showed a statistically significant association with DT. Only in two studies47, 53 did inadequate lip coverage lose its significance after multivariate analyses. Supplementary Table S2 shows the details of each eligible study.

Thirty-seven studies5, 9, 11, 20, 21, 25-28, 33-36, 38-