INTRODUCTION

Accepted as a state of deviation but not a disease, malocclusion has diverse impacts on different individuals. Although some children suffer from even minor dental irregularities, others may not mind greater occlusal problems.¹ A conventional explanation for the disparities between clinical findings and their impacts on the quality of life can be found in the “Wilson and Cleary model,” which theoretically links the biological and physiologic variables of the individual patient with the overall quality of life through the effects of environmental and individual characteristics.² According to this model, oral health-related quality of life (OHRQoL) of children with malocclusion is expected to take shape from the interactions of clinical, personal, and environmental factors.

The complex nature of OHRQoL research makes it necessary to understand the effects of these factors and to control them during clinical trials when patient-reported outcomes are to be assessed.^3–5 Indeed, there are several studies in the medical literature that were carried out to identify the effects of personality factors on the health-related quality of life for various disorders. More recently, orthodontic patients also became subject to this kind of research assessing the relationships between certain personality traits and OHRQoL. The results from those studies have shown that personality factors such as self-esteem, self-consciousness, or psychological well-being are associated with the OHRQoL in children with malocclusions.^3,5–9

A popular approach to investigate personality is the five-factor model. The five-factor model is based on the study of trait adjectives people use to describe themselves or others,¹⁰ the lexical hypothesis that indicates that every important individual difference has to be represented by an adjective in any given culture.¹¹ The method enables identification of the basic dimensions of personality, combining traits that are defined as consistently cognitive, emotional, and behavioral patterns.¹² Another personality factor shown to be related with general health-related quality of life is dispositional optimism. It is defined as the expectation that good things will happen. Optimism disposition produces different behavioral patterns and coping strategies against problems and is therefore regarded as an important personality factor.¹³ However, only one published study was found on the comprehensive evaluation of personality traits⁴ in adult orthodontic patients, whereas no published study was found investigating dispositional optimism in relation to OHRQoL in orthodontic patients.

The aim of this study was to investigate the possible moderation effects of the basic personality dimensions and dispositional optimism on the relationship between orthodontic treatment need and OHRQoL in adolescent orthodontic patients. The null hypothesis was that personality traits do not moderate the relationship between orthodontic treatment need and OHRQoL.

MATERIALS AND METHODS

All 11- to 14-year-old children who applied for orthodontic consultations at the department clinic of the Van Yüzüncü Yil University between April 17, 2014 and February 1, 2015 were asked to fill out the questionnaire. Children with mental problems, reading difficulties, or craniofacial conditions were excluded. Researchers checked the questionnaires and made sure all of the questions were answered before participants left the clinic. Age, gender, and sociodemographic data were recorded. A priori sample size estimation was not performed.

RESULTS

A total of 230 patients (125 girls and 105 boys) with a mean age of 12.48 ± 1.1 participated in the study. A post-hoc power analysis showed that 81% power was achievable in the models with an overall r² of 0.15 and an r² increase of 0.03 due to the moderator variable.

Descriptive statistics for orthodontic treatment need, OHRQoL and personality trait scores are summarized in Table 1. According to the independent t-test results, girls and boys had similar levels of orthodontic treatment need. However, girls had significantly higher levels of emotional well-being scores, indicating a worse emotional situation. When compared for personality traits, girls were found to be more agreeable, and boys were more open to experience and negative valence.

Table 1 Descriptive Statistics for the Main Variables (n = 230)

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According to the intercorrelations (Table 2), orthodontic treatment need was weakly associated with total OHRQoL and its emotional and social well-being subscales. In addition, there were weak negative associations between orthodontic treatment need and extraversion and dispositional optimism. Modest to weak associations were observed between OHRQoL and some of the personality traits. Although extraversion, openness to experience, and dispositional optimism were negatively associated with much of the quality of life scores, neuroticism was positively associated with all subdimensions except for social well-being. On the other hand, conscientiousness (negatively) and negative valence (positively) had only very weak associations with the oral symptoms subscale. Agreeableness had no significant association with the OHRQoL.

Table 2 Intercorrelations Between the Main Variables

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For each of the dependent variables (OHRQoL and subdomains) ICON scores were tested to determine if they were significant predictors. According to the results, ICON scores significantly predicted overall quality of life, emotional well-being, and social well-being but did not predict oral symptoms and functional limitations. Therefore, moderation hypotheses were tested for overall OHRQoL, emotional well-being, and social well-being using multiple regression models. Before the regression analyses, the independent variables (ICON scores and personality traits) were mean centered as suggested by Aiken and West.²¹ In the first step, gender, age, DMFT scores, and ICON scores were entered in the regression models along with each of the personality trait scores one at a time. In the second step, non-significant predictors (gender and age in all cases and DMFT score in one case) were eliminated and the interaction of the mean-centered ICON score and the mean-centered personality trait score was added into the models.

Models with significant moderation effects are shown in Table 3. These moderations are also illustrated (Figure 1) by testing the conditional effects of ICON scores on OHRQoL at three levels of personality trait scores: one standard deviation below the mean, at the mean, and one standard deviation above the mean. The results showed that ICON score was significantly related to CPQ 11–14 total, emotional well-being, and social well-being scores, and extraversion significantly moderated these relationships (ΔR² = 0.03, ΔR² = 0.02, and ΔR² = 0.04, respectively). When these interactions were probed, it was observed that the effects of malocclusion severity on the OHRQoL, emotional well-being and social well-being were reduced when extraversion was one standard deviation above the mean (Figure 1). In addition, openness to experience moderated the relationship between malocclusion severity and OHRQoL with its emotional well-being dimension (ΔR² = 0.03 and ΔR² = 0.04, respectively). The probing resulted in findings similar to those of extraversion in which a one standard deviation increase in openness to experience resulted in a weaker association between the malocclusion severity and OHRQoL domains (Figure 1).

Table 3 Regression Models for the Significant Moderation Effects of Personality Traits on the Relationship Between Orthodontic Treatment Need and Quality of Life

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DISCUSSION

The main question of this study was whether the relationship between orthodontic treatment need and OHRQoL was moderated by personality traits or not. The null hypothesis was rejected. The results showed that, in the presence of high levels of extraversion or openness to experience, adolescents were less affected by their malocclusions. Neuroticism and dispositional optimism were also associated with the OHRQoL. However, neither had an impact on its relationship with orthodontic treatment need.

This study had two main limitations. First, the study sample consisted of orthodontic consultation patients at a single center. Therefore, the results may not be generalizable. Replication of this study in non-clinical samples of adolescents in different cultures could be beneficial. Second, the directions of the associations could not be certainly established because of the cross-sectional design of the study. Although personality traits are considered as stable and consistent characteristics,²² controlled, longitudinal studies are necessary for definite conclusions.

Caspi et al.²³ summarized the possible sources of the associations between health and personality. According to the authors, personality traits may (1) directly affect health like bruxing; (2) affect health through behaviors like smoking, or (3) affect individual responses to clinical symptoms. According to the results of this study, the third statement by Caspi et al.²³ seems to apply to adolescent orthodontic patients as well. Wrosch and Scheier²² also suggested that personality traits may have effects on the quality of life through their effects on people's reactions to certain situations. The current results were in accordance with this perspective along with the conceptualization of the quality of life by Wilson and Cleary, which was mentioned earlier.²

The moderation effect of personality traits on the relationship between malocclusion severity and OHRQoL was previously demonstrated by Agou et al.³ The authors reported that self-esteem was a more salient determinant of the OHRQoL than objective measures of malocclusion in Canadian adolescents seeking orthodontic treatment. This finding is logically linked to the results of the current study considering the associations between self-esteem and the basic dimensions of personality, especially extraversion.⁴ Extraversion is characterized by frequent experiences of positive mood and rejoice in social attention.^24,25 Indeed, the results showed that patients with high levels of extraversion were less affected by their malocclusions in terms of overall OHRQoL, emotional well-being, and social well-being.

Another significant moderator was openness to experience. In cases of high levels of openness to experience, patients' OHRQoL and emotional well-being were less affected by their malocclusion severity. According to McCrae and Costa, openness to experience, which is characterized by a broader and deeper scope of awareness, is not directly related to well-being but may amplify positive or negative affect.²⁶ One possible explanation for the protective effect in the current results may be the success of open adolescents in adapting to their malocclusions. However, further research is necessary to confirm and explain the mechanisms of this finding.

No other study was found in the orthodontic literature that tested a similar hypothesis in an adolescent patient sample. Nevertheless, Clijmans et al.⁴ investigated the moderating effects of basic personality dimensions on the OHRQoL in an adult patient sample from Belgium. The authors reported significant associations between certain personality traits and OHRQoL. However, they concluded that there was no evidence supporting the moderation effects of personality traits on the association between orthodontic treatment need and OHRQoL. The disagreement between the current results and Clijmans et al.⁴ could be caused by differences between the samples' ages, cultures, or the use of different measures for orthodontic treatment need and OHRQoL.

Additionally, the results demonstrated once again that orthodontic treatment need is weakly associated with OHRQoL and its emotional and social well-being dimensions in adolescents. This finding is consistent with previous studies,^27–30 and can be explained by (1) the general motivation of orthodontic patients to improve their appearance and (2) the exceptional functional and symptomatic problems reported by patients who have common malocclusions. The weakness of these associations highlights the importance of orthodontic treatment decisions for individual patients. According to the results of the present study, subjective impact of malocclusion results from the interactions of clinical and personal factors. Therefore, use of self-reported quality of life measures during orthodontic consultations may facilitate OHRQoL improvements for future orthodontic patients.

CONCLUSIONS

• OHRQoL is associated with extraversion, openness to experience, neuroticism, and optimism disposition in adolescents.

• Extraversion and openness to experience seem to have protective effects on the OHRQoL, social well-being, and emotional well-being against malocclusion severity.