Orthodontic status and treatment need of 13 to 15 year-old children in Kwa-Zulu Natal South Africa : An epidemiology study using the Dental Aesthetic Index ( DAI )

Data was collected through an intraoral examination of occlusal status and the malocclusion and orthodontic treatment need was assessed through use of the Dental Aesthetic Index (DAI). Questionnaires were developed to collect information on the learners’ health status and socio demographic profile. The results indicated that 144 (53.3%) of the 270 learners had DAI scores <25 (no abnormality or minor malocclusion not requiring orthodontic treatment); 26 learners (9.6%) had DAI scores of between 26-30 (definite malocclusion requiring elective orthodontic treatment); 59 learners (21.9%) had DAI scores of between 31-35 (severe malocclusion requiring orthodontic treatment); and 41 learners (15.2%) had DAI scores >36 (very severe or handicapping malocclusion requiring mandatory orthodontic treatment). There was an increase in the proportion of malocclusion in older children. The age group of 15 years old had a mean and standard deviation of 30.02+8.9 when compared to the age group 13 years old (27.76+12.17). The association between gender distribution and severity of malocclusion was found to be statistically significant (p=0.01).

The prevalence of malocclusion among school going children in KwaZulu-Natal remains poorly defined despite the known physiological and psychological impact of this dental occurrence.
The aim and objectives of this study was to determine the prevalence of malocclusion and possible treatment need in [13][14][15] year-old school going children in Durban, Kwa-Zulu Natal.
This was a descriptive, cross-sectional epidemiological study conducted on 270 school-going children aged 13 to 15 years, in the Umlazi and Pinetown school districts. A two-staged clustered and systematic random sampling technique was used to draw the study sample.
Data was collected through an intraoral examination of occlusal status and the malocclusion and orthodontic treatment need was assessed through use of the Dental Aesthetic Index (DAI). Questionnaires were developed to collect information on the learners' health status and socio demographic profile.
The results indicated that 144 (53.3%) of the 270 learners had DAI scores <25 (no abnormality or minor malocclusion not requiring orthodontic treatment); 26 learners (9.6%) had DAI scores of between 26-30 (definite malocclusion requiring elective orthodontic treatment); 59 learners (21.9%) had DAI scores of between 31-35 (severe malocclusion requiring orthodontic treatment); and 41 learners (15.2%) had DAI scores > 36 (very severe or handicapping malocclusion requiring mandatory orthodontic treatment). There was an increase in the proportion of malocclusion in older children. The age group of 15 years old had a mean and standard deviation of 30.02+8.9 when compared to the age group 13 years old (27.76 +12.17). The association between gender distribution and severity of malocclusion was found to be statistically significant (p=0.01).
The present study primarily indicated a significant prevalence of malocclusion in the identified children. Although 53.3% of children did not require treatment, 37.1% presented with severe and handicapping malocclusion. This suggests a definite and mandatory treatment need for this group of children. The study could provide useful baseline epidemiological data that could inform oral health planning on the prevalence of malocclusion and orthodontic treatment need for [13][14][15] year-old school going children in the identified geographical area.

INTRODUCTION
personal relationships, 4,5 and is also associated as an aetiological factor in sleep-related breathing disorders. 6,7,8 The World Health Organisation (WHO) has included malocclusion under the heading of Handicapping Dentofacial Anomaly 9 which is defined as an anomaly which causes disfigurement or impedes function, and that treatment is required should the functional disability impact on the individual's well-being. 10,11 Malocclusion is listed as the third priority of oral health problems, after dental caries and periodontal disease, in children and young adults. 12,13,14 The orthodontic status (prevalence of malocclusion) and treatment need of the population varies among different countries, as well as among the different age and gender groups within the respective populations. 15,16,17 Various orthodontic epidemiological studies have been conducted internationally 8,18 but there is a lack of published or recent data on the prevalence and severity of malocclusion and the orthodontic treatment need for children aged 13 to 15 years in KwaZulu-Natal. 19,20 Furthermore, very little has been done to quantify the proportion of the population that could benefit from orthodontic treatment 21,22 or identify measurement tools that could increase consistency and accuracy in the reporting methods. 23 Occlusal indices are useful for research, audit, patient management and quality assurance in the treatment of malocclusion. 24,25 The epidemiological data on orthodontic treatment need is essential for the effective planning of dental education, dental public health programmes, training and deployment of dental manpower, screening for treatment priority and clinical treatment, resource planning and funding. 12,26,27,28 The increasing importance of appearance and dental aesthetics as well as functional concerns have increased the demands for orthodontic treatment at early ages 4,29,8,18 and as public interest in oral health care increases, so will the demand for orthodontic treatment. 30,31,13 Different indices have been developed for various aspects of orthodontic care but these indices have not been uniformly adopted. 32,33 The Dental Aesthetic Index (DAI) was adopted as a cross-cultural index by the World Health Organisation (WHO) for assessment of orthodontic treatment needs. 34 This index has been used by researchers for diverse communities and populations without the need to modify the index, and its clinical and aesthetic components (ACs) allows for a single score that can depict the physical and aesthetic aspects of the occlusion. 35,36,19,37,38 The DAI index could therefore be used to identify orthodontic treatment need within different ethnic groups 24 or determine malocclusion rates and orthodontic treatment need in different countries. 26,39,40,41 However the DAI does have some disadvantages. The reporting and scoring does not include important features such as cross-bite, midline deviation, or over-bite and may under-diagnose the need for orthodontic treatment. 42,43 The DAI may under estimate the need for orthodontic treatment in cases where the canine is displaced and/or when the incisors are rotated or crowded. In cases of increased over-bite, the DAI may overestimate the treatment need when there is an increase in overjet, even in normally aligned teeth. 37,44 Despite these clinically specific limitations, the DAI has been used in international collaborative studies 45 and has been used worldwide in epidemiologic studies of orthodontic treatment need in several industrialized and developing countries. 46,39 The index has been established as an essential armamentarium for the oral health care worker and epidemiologist. 47,3 This was a descriptive cross-sectional epidemiological study conducted in the Umlazi and Pinetown high school districts. The sample comprised of 270 school going children aged 13 to 15 year (n=270). A two-staged clustered and systematic random sampling technique was used to draw the study sample. A list of the schools was obtained from the KwaZulu-Natal Department of Education.
A traditional cluster design was used to create a group of 33 clusters with between four to eleven schools per geographical area. Eight learners per school were independently selected by a staff member in each of the identified school to reduce potential bias in participant selection. This provided a 95% confidence interval (CI). The inclusion criteria included male and female children attending the selected schools between the ages of 13 and 15.
The Dental Aesthetic Index (DAI)

3
Largest anterior irregularity on the maxilla in mm.

1
Largest anterior irregularity on the mandible in mm.

4
Vertical anterior open bite in mm antero = posterior molar relation.

4
Largest deviation form normal either left or right: 0=normal. 1= half cusp either mesial or distal, 2=one full cusp or more. Either mesial or distal.

RESEARCH < 415
The exclusion criteria included the following: a child on orthodontic treatment or had a previous history of orthodontic treatment; a child with a known medical condition (a health questionnaire was administered to rule out any medical condition that could be exacerbated by the clinical examination); and where no parental consent or child assent was obtained.
Ethical clearance was obtained from the Biomedical Research Ethics Committee (BREC), University of Kwa-Zulu Natal. Gatekeeper permission was granted by the Kwa-Zulu Natal Department of Education. Permission was also obtained from the relevant school authorities and informed consent was obtained from parents or guardians of the participants. In addition, participant assent (child consent) were obtained prior to the study.
Data collection included a health questionnaire. A second questionnaire was used to collect socio-demographic information such as gender, age, school district (urban, peri-urban and rural), number of people in household, source of income, income level of parent, education level and access to dental treatment. All questions were closed-ended.
For calibration and pre-examination training, the researcher selected twenty study models of patients that underwent a full orthodontic examination and were representative of the age groups and types of malocclusion that were anticipated in the sample population. Three dental experts, who were familiar with the criteria for the different variables of the DAI evaluated each study model.
The independent scores obtained from this process were used as the gold standard for comparison with scores obtained in this study. The primary investigator in this study examined the twenty orthodontic study models within a five day interval and an adequate reproducibility index was obtained (k=0.91).
The research instruments was pre-tested in a pilot study among ten children attending a high school that was not on the selected school list. The questionnaires, clinical examination process and data capturing sheet were pretested to identify any challenges and corrective changes were made. All participants were examined by a single examiner. A full mouth clinical examination was conducted under natural light and disposable gloves, tongue blades, mouth mirror and Community Periodontal Index Probe were used.
The clinical examination was done according to the Dental Aesthetic Index (DAI), which is rank-ordered on a continuous scale to assess severity levels in order to prioritize treatment need. Each participant was examined and scored for the ten components of the DAI and this score was multiplied by its corresponding regression coefficient using the rounded weights ( Table 1).
Data consisting of DAI components were recorded according to the WHO Oral Health Survey form. 34 Intra-examiner consistency was obtained by repeating the clinical examination for every 5 th learner and the two scores for the same learner was compared. High levels of infection control was maintained.
Two-way frequency tables for DAI groups by gender, age, location type were compiled. A log linear analysis was performed to investigate the interactions in these two-way tables. A p-value <0.05 indicated that the variables in that particular interaction term differ significantly.
If an interaction term was found to be significant, the nature of the interaction was further investigated by considering the parameter estimates and associated p-values for each interaction. The Chi-square test [X2] was used for comparison of severity of malocclusion. One way Analysis of Variance [ANOVA] test was used for comparison of mean DAI scores between the age groups and in DAI scores.
The 'Z' test was used to compare the mean DAI scores between gender groups. The DAI was dichotomized into ≤25 (no malocclusion) and, >25 (prevalence of malocclusion) to determine whether an association existed between the malocclusion and socio demographic variables. Post-hoc analysis was conducted between intragroup variables to determine significance values. The data was analysed using the Statistical Package for Social Sciences software [SPSS version 24].
The demographic characteristics of the study population (n=270) by age and gender is summarised in (  Table 3).
The distribution of the DAI components by gender is presented in Similarly statistically significant differences were observed in the occurrence of midline diastema. A total of 172 learners (63.7%) had no diastema and 98 learners (36.3%) had a diastema greater than 2mm (p=0.04). The anterior maxillary irregularity was significant when the prevalence was compared between males and females (p=0.03), however there was no statistically difference in the anterior mandibular irregularity (p=0.06).
When the prevalence of an anterior maxillary overjet (p= 0.00) and anterior mandibular overjet (p=0.04) was compared between the males and females, statistically significant differences were observed.  The comparison of various international studies using the DAI is summarised in Table 7. The results of the current study reflect a mean DAI score of 27.67 at a 95% confidence interval (CI).

RESULTS
The gender distribution of the prevalence of malocclusion and orthodontic treatment need by categories of the DAI are depicted in Table 8. The mean and standard deviation were 28.93+11.6 for males and 25.85+10.744 in female learners respectively. This variation in the results were statistically significant (p = 0.01).
The results of the association between and socio demographic variables and malocclusion as classified by the dichotomised DAI are depicted in Table 9. No significant differences were observed in the prevalence of malocclusion in the different school districts (urban, periurban, rural) (p=0.62), or in source of income (p=0.08). The prevalence of malocclusion and the learners' access to dental treatment (public or private health care) was statistically significant (p=0.02) The Dental Aesthetics Index (DAI) establishes a list of occlusal traits in categories that are arranged in grades to allow observation of the severity of malocclusion and the orthodontic treatment need in an identified population. 37,38,48 Establishing the index's cross-cultural validation and duplicity is necessary because cultural standards regarding the position of teeth may differ from country to country, and the degree of attractiveness and treatment need also vary [26]. Rwakatema DS noted that although diastema mediale may be regarded as unaesthetic in western societies, it is considered as a sign of beauty by Tanzanians. 49 The mean DAI score of the present study was 27.67, and 53.3% of the children examined, had a dental appearance that required no orthodontic treatment (DAI score of <25). A definite malocclusion occurred in the remaining 46.7% of which a small number proportion of the study sample (n=26, 9.6%) fell in the category of elective treatment. This finding suggest that that 37% of learners examined, required definitive orthodontic treatment. The literature further suggest that children may not be aware of their orthodontic need for treatment due to poor dental knowledge, or inadequate access to treatment due to socio economic constraints or non-availability of treatment services. 44,9 The components that primarily contributed to the variation in DAI scores in this study population were spacing in the incisal segments, diastema, largest anterior irregularities in the maxilla and mandible, maxillary overjet and anteroposterior molar relationship. These findings are similar to those reported in studies from Australia, 50 Malaysia, 39 New Zealand 51 and Nigeria. 21 The number of children not requiring orthodontic treatment (53.3%) was consistent with a previous study conducted by van Wyk and Drummond (53%) 19 but these findings were lower when compared to 12-13 year old Malaysian children (62.5%) 39 and 12-18 year old Nigerian children (77.4%). 21 However the mean DAI score (27.67) of this study is much higher than the previously reported South African study, (16.8) 20 as well as that of the Nigerian study (22.3) 21 and Tanzanian study (24.6). 49 This difference could possibly be explained in that the previous South African survey was a national survey compared to the current study and that younger learners were included in the previous sample. It could also be suggested that there is an increasing prevalence and severity of malocclusion in the 13 to 15 year old learners. The distribution of DAI scores and orthodontic treatment need according to age indicated an increase in the proportion of malocclusion in the 15 year old children, (although there was no statistical significance between the age groups).

DISCUSSION
These results are in contrast to van Wyk and Drummond 19 who reported a high prevalence of malocclusion in the 12 year old group and a decline in the 15 year old group. A possible explanation could be the developmental differences due to the late mixed dentition stage that could aggravate the prevalence and severity of dentofacial anomalies. The current study focused on learners from age 13 and as such the malocclusions could have been possibly more established as defined by the components of the DAI.
There was a higher prevalence of females (40%) with missing anterior teeth as compared to males (23.8%). A greater number of males had spacing in the incisal segments (41.3%) and diastema (50.6%) as compared to females with 13.6% with spacing, and 15.5% with d iastema respectively. The presence of a diastema in the developing dentition at age 12 is regarded as a normal phenomenon. 52 In the absence of a deep overbite, these spaces normally close spontaneously. 52 If the space between the maxillary central incisors is greater than 2mm, spontaneous closure is unlikely. 52 A diastema of 2mm and greater, occurred more in males (28.8%) than in females (9.1%). The presence of anterior irregularity in the maxilla (68.1%) and mandible (70.7%) occurred more in males than in females. The presence of increased maxillary overjet (28.9%) was higher in males than females. These results are higher than the Tanzanian study (12%) 49 and Nigerian study (14.1%) 21 but closely comparable to the South African study (29.65%). 19 The mean DAI score of the present study (27.67) was higher than that of Caucasian Americans, 36 Australians, 50 Malaysians, 39 New Zealand, 51 Poles, 53 Iranians, 37 Tanzania 49 and Indian populations. 38 The scores were lower than that of Native Americans 36 and Caucasians Australians. 50 These differences could be due to different sample sizes and/or inclusion of younger and older age ranges. The differences could also be attributed to genetic predisposition, variation in growth and facial skeleton development, and occlusion due to population type.
The mean DAI score for males was (28.93) and females (25.85). The analysis of gender distribution of DAI scores and orthodontic treatment need revealed that males were found to have greater treatment need than females. This corresponds with other South African and Nigerian studies that found girls tend to have lower mean DAI scores than boys. 19,21,49 These gender differences in the DAI score should be interpreted with caution. The differences in dental development stage could contribute to the differences in the DAI representation for boys and girls.
No significant differences where observed in the distribution of malocclusion by school district (p=0.62). The results of the current study suggest that planning and provision of orthodontic services for urban, peri-urban and rural areas should not be prioritised differently. The prevalence of malocclusion by employment status (p=0.08) and income of parent (p=0.49) showed no statistical differences but the results suggested an association between the prevalence of malocclusion and access to dental treatment (p=0.02). These results possibly suggest that learners who had previous access to private health care to minimise caries and tooth loss had lower malocclusion scores. 54 Another possible explanation is that dental practitioners could have undertaken systematic serial extractions to alleviate crowding and thus contributed to lower incidence of malocclusion. 55 These findings could provide reliable base-line data regarding the prevalence and severity of malocclusion as well as useful epidemiological data on the orthodontic treatment need of 13 to 15 year-old children in the identified geographical areas in Durban. As both the general dental health and socio-economic status of the population of South Africa improve together with the "globalization" and awareness of dental aesthetic needs, it is foreseeable that the number of children seeking orthodontic treatment will also increase. 56 It should be noted that 'interceptive orthodontic' programmes can reduce the severity of the problems but rarely is so successful that later treatment becomes unnecessary. 52 Orthodontic services should therefore be comprehensive and appropriate to the specific needs of the individual. 52 This study provided useful base-line epidemiological data on the orthodontic treatment need of 13-15 year-old South African children in the selected geographical areas in Kwa-Zulu Natal and could make a contribution to oral health planning and policy decisions in the province. None.
Prof PJ van Wyk -Department of Community Dentistry University of Pretoria. Dr Perry Brown -College of Pharmacy and Pharmaceutical Sciences -Florida A&M University. Visiting statistician at University of KwaZulu-Natal.