Exploring the impact of malocclusion and dentofacial anomalies on the occurrence of traumatic dental injuries in adolescents

Recent evidence has demonstrated that traumatic dental injuries (TDI) exert a negative impact on oral health–related quality of life (OHRQoL).^1,2  The high prevalence and treatment costs underscore the need for educational and prevention programs based on a comprehensive understanding of the condition. However, TDI has a complex multifactorial etiology, and few significant risk factors have been consistently confirmed.^3,4 

A recent meta-analysis⁵  of observational studies reported that increased overjet may double or even triple the risk of TDI to the anterior permanent teeth. Likewise, a meta-analysis⁶  of intervention studies concluded that the early orthodontic treatment of prominent maxillary anterior teeth reduced the incidence of TDI in comparison to results achieved with late treatment. However, few studies have assessed the effect of other dentofacial anomalies, such as the molar relationship, open bite, misalignment, and diastema. Moreover, no study has investigated the association between the occurrence of TDI and malocclusion or the need for orthodontic treatment based on internationally accepted criteria.

The Dental Aesthetic Index (DAI) is endorsed by the World Health Organization and is a valid, reliable tool for the assessment of malocclusion.^7,8  This index is used to evaluate dentofacial anomalies, classify malocclusions, and determine orthodontic treatment need.⁹  Recent studies^10–12  have demonstrated that the occurrence of malocclusion (assessed using the DAI) can increase the risk of dental caries and exert a negative impact on OHRQoL. Clarifying the role of malocclusion in the occurrence of TDI could contribute to the recognition of this condition as a common risk factor for health outcomes and broaden the understanding of the benefits of orthodontic treatment.¹³  Moreover, the identification of occlusal characteristics that constitute risk factors for TDI could contribute to the establishment of preventive measures and indicate treatment priorities.

The objectives of this study were to (1) investigate the association between malocclusion and TDI in a population of adolescents in southern Brazil, (2) identify components of the DAI that might contribute to TDI, and (3) quantify the strengths of the associations.

This cross-sectional study was part of a broad-scoped project designed to estimate the impact of oral health outcomes on the quality of life of adolescents aged 11 to 14 years in the city of Osório, southern Brazil.¹⁰  This study received approval from the Human Research Ethics Committee of the Universidade Luterana do Brasill (process No. 200913OH). The guardians of the participants signed a statement of informed consent, and the adolescents agreed to participate in the study.

The City of Osório has an estimated population of 40,000 inhabitants, and the public water supply is fluoridated (0.7 mg/L). The source population consisted of 1996 adolescents aged 11 to 14 years enrolled in public schools in the city (inclusion criteria), representing 85% of the population in this age group residing in the city. The exclusion criteria were current or past history of the use of an orthodontic appliance and adolescents who were not intellectually capable of answering the questionnaire.

One-stage cluster sampling was conducted considering adolescents enrolled in public schools. Three sample size calculations were performed to estimate the effect of malocclusion, dental caries, and TDI on OHRQoL, opting for the condition that required the largest sample size based on the following parameters: 80% power, 95% confidence level, mean (standard deviation) CPQ11-14 score of 15.5 (12.2) among adolescents without orthodontic treatment need (nonexposed) and 20.5 (16.9) among those with orthodontic treatment need (exposed),¹⁴  and 1:3 proportion of exposed to nonexposed. A correction factor of 1.4 (design effect) was applied to increase the precision of the study due to the cluster sampling method, determining a minimum sample of 498 adolescents. Considering a nonresponse rate of 20% and a prediction of 10% of the adolescents wearing an orthodontic appliance, it was determined that 700 subjects should be evaluated with regard to eligibility. All 12 public schools in Osório constituted the cluster units, five of which were randomly selected following stratification based on the size of the school: large (n = 1/3), medium size (n = 2/5), and small (n = 2/4). The final sample (n = 509) had a 90% power to capture the association between overjet and TDI, according to the following parameters: prevalence rates of 28.6% and 13.1% for TDI among exposed (with overjet) and nonexposed (without overjet) adolescents and a 95% confidence level.¹⁵ 

All data were collected by a single examiner who had undergone training and calibration exercises.

Parents/caregivers answered a structured questionnaire addressing the adolescent's sex and age, ethnicity, family structure, household income, and mother's schooling. Ethnic group was defined based on skin color (white, brown, or black) and subsequently dichotomized as white or non-white based on previously established criteria (Brazilian Institute of Geography and Statistics). Family structure was classified as either nuclear (adolescent lived with both parents) or nonnuclear (adolescent lived with only one parent or neither parent). Mother's schooling was recorded in number of complete years of study and was categorized as ≤8 years and >8 years. Household income was defined as the sum of the monthly wages of all economically active members of the family (in Brazilian currency), divided by the Brazilian monthly minimum wage (BMMW) and stratified in tertiles.

The physical examination involved recording clinical signs of malocclusion, TDI, and dental caries. Total collection time for the clinical data was 5 months. Prior to the study, the examiner underwent a training and calibration process involving 36 hours of theoretical and practical exercises with an experienced epidemiologist. Intraexaminer Kappa reproducibility coefficients were 0.82, 0.92, and 1.00 for malocclusion, dental caries, and TDI, respectively.

Examinations were conducted at the schools with the adolescent seated in a chair. The teeth were brushed, dried with gauze, and examined with the aid of a mouth mirror and millimeter probe. The DAI was used to classify malocclusion with regard to severity and treatment need as well as to identify separate dentofacial anomalies.¹⁶  Four malocclusion categories were established on the basis of severity and treatment need, as follows: normal or minor malocclusion/no treatment need (DAI ≤ 25); definite malocclusion/treatment elective (DAI 26–30); severe malocclusion/treatment highly desirable (DAI 31–35); and handicapping malocclusion/treatment mandatory (DAI ≥36).

The outcome of the present study (TDI) was based on the classification proposed by Andreasen and Andreasen¹⁷  and categorized according to occurrence (yes/no). Dental caries experience was evaluated using the Decayed, Missing, and Filled Teeth index recommended by the World Health Organisation⁷  and dichotomized as “yes” or “no.”

Statistical analysis was conducted using the Statistical Package for Social Sciences, version 13.0 (SPSS Inc, Chicago, Ill). Poisson regression with robust variance was performed to investigate the association between malocclusion and TDI. Crude prevalence ratios (PR) were calculated for the malocclusion categories and control variables. The multivariate model involved a hierarchical determination on three levels representing distal, medial, and proximal determinants of TDI: (1) demographic characteristics (sex, age, and ethnicity); (2) socioeconomic characteristics (household income, family structure, and mother's schooling); and (3) clinical characteristics (dental caries and malocclusion). The stepwise backward procedure was used for the selection of variables on each level, with the elimination of variables with higher P-values from the level until only those with P < .20 remained. The variable sex was maintained in the final model independently of its level of significance. The final model determined PR estimates for the variables selected after adjusting for variables on the same and higher levels that remained in the multivariate model. With the hierarchical approach, it is recommended that variables on the distal level not be adjusted for variables on the proximal level to avoid a reduction in, or the improper loss of, an effect due to overadjusting.¹⁸  To quantify the association between orthodontic treatment need and TDI, an additional analysis was performed combining the severe and handicapping malocclusion categories, which identified treatment as being desirable or mandatory. For the identification of dentofacial anomalies associated with TDI, multivariate analysis was performed in which all DAI components were included, maintaining those with P < .20 and the confounding variables identified in the previous model. The level of significance was set to P < .05.

The sample was composed of 509 adolescents aged 11 to 14 years. Table 1 shows that approximately 70% of the families had a household income of up to two times the BMMW, and 62.3% of the adolescents belonged to nuclear families. Mother's schooling ranged from 0 to 15 years (mean, 6.9 ± 3.2 years). A total of 44.8% (228/509) of the adolescents had dental caries, 32.4% (165/509) had normal occlusion or minor malocclusion, 24% (122/509) had defined malocclusion, 21.6% (110/509) had severe malocclusion, and 22% (112/509) had handicapping malocclusion (Table 1).

The prevalence of TDI was 11.6% (59/509) and varied considerably among the different malocclusion categories: 7.9% of adolescents with normal occlusion or minor malocclusion; 8.2% of those with defined malocclusion; 17.3% of those with severe malocclusion; and 15.2% of those with handicapping malocclusion (P = .014). No significant differences were found with regard to demographic or socioeconomic variables (Table 1).

After adjustments for potential confounding variables (Table 2), the multivariate analysis revealed that the probability of TDI was 2.2-fold higher among adolescents with severe malocclusion (PR 2.22; 95% confidence interval [CI] 1.14–4.31) and nearly twofold higher among those with handicapping malocclusion (PR 1.95; 95% CI 1.01–3.85). When the two categories were combined to characterize adolescents with highly desirable or mandatory treatment need, the probability of TDI was more than twofold higher (PR 2.05; 95% CI 1.12–3.74) in comparison to that of adolescents without treatment need (data not shown in a table). The category “elective treatment need” was not associated with the outcome (PR 1.07; 95% CI 0.48–2.35).

The crude analysis of the DAI components (Table 3) demonstrated that maxillary misalignment, maxillary overjet, and the molar relationship were associated with TDI. The other orthodontic characteristics were not associated with the outcome. Table 4 shows the multivariate model, which demonstrated that the probability of TDI was nearly twofold higher among adolescents with overjet greater than 3 mm (PR 1.96; 95% CI 1.14–3.37) and 2.2-fold higher among those with an abnormal molar relationship (PR 2.24; 95% CI 1.17–4.32). A post hoc analysis was performed to isolate the effect of the distal step molar relationship and mesial step molar relationship on the outcome after the adjustment for potential confounding variables. Adolescents with a distal step molar relationship had a more than twofold greater probability of having TDI (PR 2.15; 95% CI 1.12–4.12) compared to those with a normal molar relationship, independent of sex, family structure, and overjet. The mesial step molar relationship was not associated with the outcome (PR 3.75; 95% CI 0.86–16.2) (data not shown in a table).

This was the first study to investigate associations among TDI and malocclusion, orthodontic treatment need, and dentofacial anomalies in adolescents using the DAI. The most important finding was a significantly higher occurrence of TDI in adolescents with severe and handicapping malocclusion and those with orthodontic treatment need. The orthodontic characteristics associated with the outcome were accentuated overjet and an abnormal molar relationship.

The fact that no previous studies have investigated the association between TDI and malocclusion as a whole or orthodontic treatment need impedes comparisons of the present findings. These associations are largely due to the fact that the two exposures (overjet and molar relationship) have considerable weight in the calculation of the DAI and contribute decisively to a higher score and greater need for orthodontic treatment. The prevalence of TDI was higher among adolescents with a maxillary misalignment equal to or larger than 3 mm. Although this variable has less weight in the calculation of the DAI and did not achieve statistical significance in the final model, it is possible that it at least partially contributed to the association between malocclusion and TDI.

The association between overjet and TDI is well documented in earlier studies^5,19  involving different populations. The results of a systematic review of intervention studies even suggest a reduction in the incidence of TDI with the treatment of prominent maxillary anterior teeth. However, the studies that contributed to the meta-analysis had only low to moderate methodological quality, indicating that this association needs to be investigated further.⁶ 

The molar relationship is a condition that represents an important aspect of normative orthodontic diagnoses, and few studies have assessed its influence on TDI, especially while controlling for possible confounding factors. Studies^20,21  involving schoolchildren and adolescents in India reported a greater occurrence of TDI in the presence of Angle Class II, but no multivariate analysis was mentioned. In agreement with these findings, the present results demonstrated a more than twofold greater probability of TDI among adolescents with an abnormal molar relationship, and the additional analysis demonstrated that the association stemmed from a distal step molar relationship. It is interesting to note that the effect remained even after controlling for overjet, demonstrating an independent effect of this malocclusion in the anteroposterior direction.

The plausibility of the molar relationship and overjet associations resides in the increase in the level of exposure to TDI in adolescents with maxillary protrusion or protruded maxillary anterior teeth. Moreover, it is possible that such clinical conditions cause, at least in part, insufficient lip coverage. According to the authors of previous studies,^5,22,23  lip incompetence leaves the incisors more vulnerable to TDI. Crowding, spacing, diastema, and misalignment were not associated with TDI in the present study. These findings may be explained by the fact that such dentofacial anomalies are more likely related to changes in the arch perimeter and therefore do not predispose adolescents to a greater risk of TDI in the same way as do changes in the anterioposterior direction.

Among the clinical implications of the present study, the prevention of malocclusion, especially an abnormal molar relationship and overjet, can potentially contribute to a reduction in the occurrence of TDI among adolescents. This is particularly important considering the high frequency of such exposures in the sample (more than 60% and nearly 50%, respectively). Malocclusion affects individuals both physically and psychologically, as it exerts an influence on growth, appearance, speech, and chewing function; increases the risk of dental caries; and alters an individual's perception with regard to quality of life.^10,11  The association found with TDI in the present study points to malocclusion as a common risk factor for oral problems and underscores the importance of developing actions to promote oral health. The implementation of policies and actions that address common health risks and conditions is an effective form of intervention.¹³ 

Methodological aspects of the present study should be addressed. The cross-sectional design is a limitation, as it does not allow the drawing of conclusions regarding a cause-and-effect relationship. However, since malocclusions, including an abnormal molar relationship and overjet, are established soon after the teeth enter occlusion,²⁴  it is plausible that the exposures evaluated in this study preceded the occurrence of TDI. Thus, the possibility of reverse causality bias is low in this type of investigation. Measurement bias is a possibility in studies that investigate different clinical conditions. The DAI may underestimate the occurrence of malocclusion, since its composition prioritizes esthetic issues in the classification of malocclusion and the indication for treatment need. However, this index has been incorporated into the International Collaboration Study of Oral Health Outcomes of the World Health Organisation.²⁵  It is a validated tool and has been widely used in epidemiological studies. The possibility of measurement bias of the outcome is low as a result of the extensive previous training of the examiner and the high intraexaminer reproducibility.

The results of the present study were obtained from a representative population of adolescents in a municipality in southern Brazil and cannot be extrapolated directly to all populations. The external validity of the findings depends on the setting of the study, characteristics of the participants, exposures examined, and outcomes assessed.²⁶  Thus, the results of the present study can be generalized to predominantly white adolescents with a low socioeconomic status. It is also possible that the strength of the association detected varies in other communities, depending on the prevalence of the exposures and outcomes evaluated.

• • 

  Severe and handicapping malocclusions, which characterize orthodontic treatment need, are associated with the occurrence of TDI in adolescents.

• • 

  The dental anomalies associated with the outcome are accentuated overjet and an abnormal molar relationship.

• • 

  Future studies should investigate whether the treatment of malocclusion, especially accentuated overjet and an abnormal molar relationship, can help reduce the occurrence of TDI in adolescents.