Abstract
Objective
Low cognitive ability may reduce the ability to understand the importance of oral health and to perform the necessary practices to maintain proper oral hygiene. Early loss of primary teeth following high caries risk may lead to malocclusion of permanent dentition. This study aimed to evaluate the relationship between the cognitive levels of adolescents and their orthodontic treatment needs.
Material and Methods
Between January 2018 and May 2018, 200 adolescents aged 10 – 15 who applied to the Pediatric Dentistry Clinic of Marmara University and sought orthodontic treatment were invited to participate in the study. The orthodontic treatment needs of 150 adolescents who agreed to participate were evaluated with the Index of Orthodontic Treatment Need - Aesthetic Component and their cognitive levels were evaluated with the Raven Standard Progressive Matrices (SPM) Test. P-value < 0.05 was considered statistically significant.
Results
The mean age (± standard deviation) of 126 adolescents (77 females and 49 males) who completed the SPM test was 11.8 (± 1.3). There was no consistency between the intellectual level and the need for orthodontic treatment (Kappa value = 0.071, p-value = 0.081). There was no correlation between malocclusion severity and intelligence quotient scores of adolescents (ρ [rho] = -0.089, p = 0.322). According to Multiple logistic regression results, there was no difference between ‘borderline need’ (p = 0.059) and ‘great need’ (p = 0.881) from ‘no need’ for orthodontic treatment in adolescents with different intelligence quotients.
Conclusions
The results showed no evidence for an association between malocclusion and intelligence quotient.
Keywords: MeSH Terms: Persons with Mental Disabilities, Index of Orthodontic Treatment Need, Malocclusion, Intelligence Test, Child, Adolescent
Author Keywords: Raven’s Progressive Matrices Test
Introduction
People have a combination of different personality traits, one of which is the individual intelligence known as the Intelligence Quotient (IQ). Deviations in the individual intelligence profile affect intellectual development, behavioral skills, and cognitive skills (1). Low cognitive ability may weaken the ability to understand the importance of oral health and the need to perform proper oral hygiene, such as nutrition and brushing habits, especially at young age (1, 2). In 2014, it has been shown that the prevalence of caries is higher in children with borderline cognitive intelligence (3). Caries and subsequent early loss of primary teeth may cause malocclusion in the permanent dentition. Studies have shown that mentally retarded individuals with low IQ (70 scores or less) have poor oral health, larger numbers of untreated malocclusions, and an increased need for treatment (2-5). Moreover, it has been suggested that deviations in dentofacial appearances, such as incisors crowding and median diastemas, have a profound negative impact on perceived intelligence by other individuals (6).
Spearman's two-factor theory of intelligence consists of two factors: factor g and factor s. The factor g represents general intelligence, while the factor s represents specific ability (7). Raven Standard Progressive Matrices Test (SPM) is a test that can be administered individually or on a group, assessing nonverbal reasoning ability and general intelligence (Spearman’s g factor) (8, 9).
SPM offers several advantages. It has a short application and is not affected by individual’s socio-economic status, language, or literacy status. It also minimizes cultural bias. Moreover, the test evaluates the ability to think clearly and make sense out of events (9, 10).
The Index of Orthodontic Treatment Need (IOTN) objectively evaluates patients with malocclusion who need treatment most in terms of dental health and perceived aesthetic impairment (11). The scores of the components are not combined, the two components (aesthetic component and dental health component) are evaluated separately, and it is determined whether the patient needs orthodontic treatment. It has been reported that the need for orthodontic treatment is between 7.9% and 10.9% in different countries according to the aesthetic component (AC) index (12).
This study aimed to investigate the relationship between the cognitive levels of adolescents and their orthodontic treatment needs. The null hypothesis of this study was that there is no difference in the need for orthodontic treatment in adolescents with different cognitive levels.
Materials and methods
Ethical approval and study population
The participants in this cross-sectional study were adolescents (females or males) aged 10 to 15 who applied to the Pediatric Dentistry Clinic, Faculty of Dentistry, at XX University between January 2018 and May 2018. The exclusion criteria were as follows: children with orthodontic treatment, children with a history of dental and/or craniofacial trauma, children with cleft lip and palate and craniofacial anomalies and children with systemic disease. 200 adolescents seeking orthodontic treatment were invited to participate in the study taking account of attrition. The study was conducted in accordance with the principles of medical research involving human subjects stated in the Declaration of Helsinki. The study protocol was assessed and approved by the XX University School of Dentistry Clinical Research Ethics Committee with approval number XX.
Assessment of the need for orthodontic treatment
One well-trained pediatric dentist with four years of clinical experience and an orthodontist with thirteen years of clinical experience evaluated participants according to the IOTN-AC index. The AC index consists of a 10-image scale (Figure 1) to evaluate malocclusion, and grade 1 represents the best dental aesthetics, while grade 10 represents the worst dental aesthetics (12-14). Aesthetic component grading is divided into three main groups according to treatment needs: Grades 1 – 4: no need for orthodontic treatment; grades 5 – 7: the borderline need for orthodontic treatment; and grades 8 – 10: great need for orthodontic treatment (15).
Figure 1.
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Representative images of the Aesthetic Component (AC) index (12-14)
Assessment of the intelligence quotient
The cognitive abilities of adolescents were evaluated with the SPM Test. It contains 5 sets (A, B, C, D, E) of 12 items each, 60 items in total. These items are geometric analogy problems that contain a set of geometric shapes, each item missing an input. Participants choose the correct answer from eight alternatives. The first missing item in the first set is obvious. The following items get complicated. Sets and items must be given to all participants in the same order. The obtained raw SPM scores were converted to percentiles to measure performance compared to norms (7). Percentiles were divided into six groups according to the Current Wechsler classification: intellectually superior: 95% and above; definitely above the average in intellectual capacity: 95% – 75%; intellectually average: 75% – 25%; definitely below the average in intellectual capacity: 25% – 5%; intellectually impaired: 5% and below (9).
Sample size calculation
Since there has been no previous study evaluating the relationship between intellectual profile and malocclusion level, a pilot study evaluating 45 participants was conducted to calculate the sample size. The sample size calculation applied with the G*power Version 3.1.9.6 program was based on the pilot study, with 95 confidence (1-α), 85% test power (1-β), d=0.318 effect size, and 37 samples to be taken in each group of the need for orthodontic treatment (no need, the borderline need, great need). The total number of samples was determined as 111. After the research protocol had been explained to the children and their parents or caregivers, informed consent documents were read. Children and their parents who agreed to participate were included in the study. 150 adolescents (77 females, 49 males) agreed to participate in the study. Of these adolescents, 24 children were excluded from the study because they did not complete all the items.
Statistical analyses
Intra- and inter-examiner reliability was assessed with the Cohen’s Kappa test. The Kappa values were interpreted according to the categories suggested by Landis and Koch (16). Descriptive statistic parameters were presented as frequency, percentage (%), mean ± standard deviation (mean ± SD), and median (minimum – maximum). The Kolmogorov-Smirnov test was used to determine whether continuous variables were normally distributed; the Independent Sample t-test and Mann-Whitney U test were used to compare two independent groups according to their normality. The Kappa consistency test and multiple logistic regression analysis were used to assess the relationship between categorical variables. The relationship between the intelligence quotient scores and the severity of malocclusion was examined using Spearman’s correlation coefficient. Statistical analysis was performed using the SPSS Version 26.0 (IBM Corporation, Chicago, Illinois, United States of America) software, and a p-value < 0.05 was considered statistically significant.
Results
The mean age (± SD) of 126 adolescents, 77 females (11.9 ± 1.4) and 49 males (11.6 ± 1.2), who completed the SPM test was 11.8 (± 1.3). The intra-examiner Kappa values were 0.896 and 0.904 for two examiners (almost perfect), and the inter-examiner Kappa value was 0.896 (almost perfect). The participants' median AC index (min – max) was 5 (1 – 10). There was no significant difference between females and males in terms of the severity of the malocclusion (p = 0.910) and the need for orthodontic treatment (p = 0.609).
There was no statistically significant difference in the number of correct answers to the intelligence test between females (37.2 ± 8.6) and males (36.8 ± 7.7) (p = 0.841). Raw SPM scores were transformed to percentiles for comparison with norms (Table 1), and there was also no significant difference in intelligence profiles in females and males (p = 0.778).
Table 1. The intelligence quotient scores by gender and need for orthodontic treatment.
|
Intelligence quotient scores
Mean ± SD |
|
|---|---|
| Total | 61.7 ± 13.7 |
| Sex | |
| Female | 62.0 ± 14.4 |
| Male | 61.3 ±12.9 |
| Aesthetic Component Index | |
| No need | 63.1 ± 14.4 |
| Borderline need | 57.5 ± 14.2 |
| Great need | 64.5 ± 10.9 |
| SD: standard deviation | |
According to the Current Wechsler classification, 81.7% (n = 103) of participants were intellectually average and 18.3% (n = 23) above the average in intellectual capacity. There was no statistical difference between these groups in terms of the severity of the malocclusion (p = 0.590). When the Kappa test was applied between the intellectual level and the need for orthodontic treatment, no consistency was detected (Table 2).
Table 2. The relationship between the intellectual level and the need for orthodontic treatment.
| Intellectually average | Above the average in intellectual capacity | Total | ||
|---|---|---|---|---|
| No need n (%) |
47 (45.63%) | 13 (56.52%) | 60 (47.62%) | Kappa value = 0.071 p-value = 0.081 |
| Borderline need n (%) |
29 (28.16%) | 4 (17.39%) | 33 (26.19%) | |
| Great need n (%) |
27 (26.21%) | 6 (26.09%) | 33 (26.19%) | |
| Total n (%) |
103 (100) | 23 (100) | 126 (100) | |
| n: number | ||||
No correlation was observed between the severity of malocclusion and the intelligence quotient scores of the adolescents (ρ [rho] = - 0.089, p = 0.322). The relationship between the need for orthodontic treatment and the intelligence quotient scores was analyzed by multiple logistic regression, the results are presented in Table 3.
Table 3. Multiple logistic regression based on the need for orthodontic treatment and intelligence quotient scores.
| Odds ratio | 95% confidence interval | p-value | |
|---|---|---|---|
| No need | Reference | ||
| Borderline need | 0.970 | 0.940 – 1.001 | 0.059 |
| Great need | 1.002 | 0.971 – 1.035 | 0.881 |
Discussion
For patients who need orthodontic treatment, it is crucial that a pediatric dentist detects malocclusions early. After that, he/she applies preventive treatments and refers them to the orthodontist. There is a high prevalence of malocclusion in patients with mental retardation at different IQ levels, with accompanying motor disorders, diet habits, oral hygiene status, high caries level, dental anomalies, and the contribution of these factors (1). Healthy individuals with a low intelligence quotient may also be weaker in understanding the importance of oral hygiene and performing the necessary practices. It has been reported that healthy individuals with lower intelligence quotients have larger numbers of dental caries (2). Moreover, Vellappally et al. (17) reported that caries and malocclusion were prevalent in mentally retarded patients aged 12-18 years, but there was no correlation between caries and malocclusion. Based on this idea, this study aimed to evaluate the orthodontic treatment needs of adolescents with different cognitive levels. To our best knowledge, there is no study in the literature evaluating the relationship between cognitive level and the need for orthodontic treatment.
The IOTN index has two components scored separately as the aesthetic component (AC) and the dental health component (DHC), which determine the need for orthodontic treatment. The DHC index evaluates malocclusion site-specific and considers the most prominent and worst impairment. The DHC index can thereby classify mild local irregularities as a high need for treatment (18). For that reason, the AC index was used in the current study, which provides a generalized and fast evaluation from the photographs of the anterior region. However, it should be noted that some malocclusions that can be diagnosed from the lateral may be missed in the AC index (12). Therefore, the fact that the need for orthodontic treatment was evaluated with a single index is a limitation of this study.
Karaagac et al. (12) stated that according to the IOTN-AC index, approximately 11% of the patients need treatment, and 80% do not need treatment. On the contrary, the results of this study showed that 26% of the participants needed orthodontic treatments. Since the adolescents evaluated in this study were selected from patients seeking orthodontic treatment, the need for orthodontic treatment was high, while 48% of the participants did not need any orthodontic treatments. In support of this idea, approximately 5% of children in the school population aged 11–14 years, and 37% of children seeking orthodontic treatment at the same age had a great treatment need according to the AC index (11). As inferred from this study, the need for orthodontic treatment in the general population of adolescents is low. In order to determine the relationship between the IQ and malocclusion level, it was necessary to reach a certain number of participants at each malocclusion level. Therefore, patients who applied to the Pediatric Dentistry Clinic and sought orthodontic treatment were included in this study. Since individuals with low IQ may be less likely to pay attention to malocclusion aesthetically, including just individuals seeking orthodontic treatment may be considered a limitation of the study. However, given that the study participants were adolescents and that the primary decision-making authorities for healthcare services were their legal guardians, predominantly parents, it can be inferred that the impact of this factor was minimal. In addition, since Balija et al. (19) reported that the prevalence of dental anomalies in orthodontic patients aged 12–16 was similar to that of the general population, the adolescents with dental anomalies were not excluded from the study.
In the present study, the SPM Test was used to assess the cognitive level of adolescents. Since the SPM is a relatively long test consisting of 60 items (20), it was applied to larger numbers of adolescents than the required sample size, considering that there would be adolescents who did not complete the test.
Although there is no study in the literature comparing the IQ with the need for orthodontic treatment, some studies have evaluated its relationship with several malocclusions (21, 22). They reported that IQ is not associated with skeletal malocclusion types (Class I, II, or III), facial growth patterns (vertical or horizontal), (21) or occlusion patterns such as crossbite and open bite (22). Similar to these findings, in the current study, no relationship was found between the severity of malocclusion and the need for orthodontic treatment in patients with different IQ levels. Since no significant difference was observed, the null hypothesis of this study was accepted. Additionally, Perillo et al. (23) reported in a study that crowding was a 5-fold higher risk factor and crossbite was a 6-fold higher risk factor for score abnormalities in global self-concept.
Durhan et al. (24) investigated the relationship between intelligence profiles and gingivitis in children aged 10-15 years. They observed that there was no relationship between cognitive status and periodontal status. However, in contrast to this study, Navit et al. (3) stated that the IQ was associated with moderate gingivitis, while the IQ was not associated with dental caries. Dhanu et al. (2) on the other hand, reported that as the IQ level increased, dental caries decreased, but there was no direct relationship between them. Individuals with low intellectual levels may have a poor ability to comprehend and learn the importance of oral health and necessary practices (25-27), thus leading to a higher prevalence of gingivitis. However, this relationship may not be sufficiently strong to cause dental caries, and thus malocclusion.
In this study, healthy adolescents without systemic disease seeking orthodontic treatment who came to the Pediatric Dentistry Clinic for examination were included. Thus, mentally retarded adolescents were not included, and the IQ levels of the adolescents were not in a very wide range. Therefore, another limitation of the study was that patients in every IQ group could not be included in the study. Whether patients are below or above the threshold might make a difference in understanding the importance of oral and dental health and fulfilling their obligations.
Conclusions
It was observed that there was no relationship between the intelligence quotient level of the patients and the need for orthodontic treatment. However, since there are studies advocating different opinions about the effect of cognitive level on other factors such as caries risk and gingival health, we think that the evidence value of these data should be increased by further studies on the need for orthodontic treatment. There was no significant difference between the genders in terms of the severity of malocclusion and the need for orthodontic treatment.
Acknowledgements
The study protocol was assessed and approved by the Marmara University School of Dentistry Clinical Research Ethical Committee with approval number 2017-159.
Footnotes
Conflict of interest statement
The authors declare no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
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