Pooled prevalence estimates of malocclusion among Indian children and adolescents: a systematic review and meta-analysis

Objectives: To estimate the pooled prevalence estimates of the malocclusion among child and adolescent population of India.


Introduction
Malocclusion is defined as an irregularity of the teeth or a malrelationship between the dental arches beyond the range of what is accepted as normal. It is a multifactorial oral condition caused by general factors such as heredity, congenital defects, nutritional deficiencies and abnormal pressure habits. Malocclusion can also occur due to factors located in the dental arch such as anomalies of tooth size, shape, supernumerary teeth, dental caries and premature loss of primary teeth [1,2]. Measurement of extent and severity of malocclusion in an individual or population is done by indices such as Dental Aesthetic Index (DAI) [3], Index of Orthodontic Treatment Needs (IOTN) [4] or through Angles classification [5]. In primary dentition, terminal plane relationship of second molars is recorded to predict possible malocclusion in future [6]. Epidemiology of malocclusion is predominantly assessed based upon individual studies or national health oral survey although systematic reviews were being conducted in recent past among Iranian [7] and Chinese children [8]. There are no data available regarding the prevalence of malocclusion in global oral data bank of World Health Organization (WHO) because it considers malocclusion as a condition rather than a disease [9].
In India, only one national oral health survey has been conducted in the year 2002-03. This survey had reported a huge burden of untreated oral diseases including malocclusion across the country [10]. India is a young country with children of up to 0-14 years of age constituting 29% of its population [11]. This can be considered as an opportunity for public health dentists and other oral health policy makers to plan and implement various primary preventive dentistry programs which can have long term benefits for our future generations. However, for planning such programme we need recent data on burden of oral diseases in India.
Currently, India has no mechanism for continuous surveillance of oral diseases nor there is no separate budget for oral health [12]. Therefore, to fill up the time gap before another nationwide survey is instituted, integrated studies such as a systematic review and meta-analysis can act as an invaluable tool to update oral health policy makers regarding the current burden of oral diseases in Indian population. Hence, we conducted this systematic review and meta-analysis with the aim to provide a comprehensive data to relevant stakeholders on prevalence of malocclusion among children and adolescent population of India. The patient, intervention, comparison, outcomes (PICO) method as applicable in relation to the topic of the review: Patient: Indian children and adolescents less than or equal to 19 years of age Intervention = clinical examination for assessing malocclusion Comparison: Not applicable Outcomes: prevalence of malocclusion Focused question: What is the pooled prevalence of malocclusion among children and adolescent population in India?

Methods
The review protocol is registered with PROPSERO (registration number -CRD42018094345). PRISMA guidelines for conducting a systematic review were followed throughout the study period [13].

Information sources and literature search
Relevant articles were retrieved electronically by searching PubMed/MEDLINE, PubMed Central, Scopus, Complimentary index, Ebscohost, SciELO, Open DOAR, TRIP databases, Science Citation Index, Web of Science and finally Google Scholar. The search period was restricted from 1st January 2000 in order to obtain data from recent studies only. Other filters used were restrictions on language i.e. English and study participant's age should be under 20 years.
The search strategy was built with medical subject headings (MeSH) terms and relevant text words. The MeSH terms employed were "Malocclusion" [All Fields] AND "child" [All Fields] AND Adolescent [All fields] AND "India" [All Fields] as search strategy if the search engine permits. In addition, key words such as prevalence, Dental Aesthetic Index (DAI), Index of Orthodontic Treatment Needs (IOTN), Angle classification of malocclusion and primary dentition were used in order to broaden the search.
Relevant studies were searched independently by two authors (AM and AV). Initially titles were searched followed by abstracts and finally full texts were read. The first round of search was upto 30th April 2018; a second round was performed to include the entire list of relevant articles published upto 31st December 2019.
The calibration of the reviewers was done by conducting discussion sessions prior to the commencement of the study. A list of inclusion and exclusion criteria was prepared and both the reviewers were subjected to analyse 10 abstracts. Afterwards, an assessment was done and this procedure was repeated until a high inter-examiner agreement (k=0.92) was achieved. The results were then compared after the complete selection of the eligible articles by both the reviewers and in case of disagreement, a third reviewer (AN) was asked to review the article independently for inclusion. After the identification of articles in the databases, the articles were imported into Mendeley reference manager for the removal of duplicate articles. In addition, reference list of retrieved studies were searched to look out for more studies. In case of any clarification or additional data were required the concerned study author/s were contacted via e-mail.

Study selection (inclusion and exclusion criteria)
This systematic review concentrated on short listing the population or school based cross sectional studies conducted on Indian children and adolescents (<20 years) assessing prevalence of malocclusion according to different indices and classifications. Studies that did not report the prevalence of dental malocclusion, sample size, abstracts submitted to conferences, case report studies, seminars, case-control studies and clinical trials not providing an accurate estimation of the prevalence were excluded from this review. Studies that did not obtain a minimum score of quality assessment and studies with a participant population of over 19 years of age were also excluded.
Studies recording malocclusion as a part of a study on the associations with specific parameters such as nutrition status, socioeconomic status, quality of life, caries and periodontal diseases, studies conducted on special children, those suffering from any systemic condition or syndrome were not included in this review.

Data extraction
Relevant data were extracted by two independent reviewers (AM and AV) from eligible studies under the following domains: study characteristics (study ID, first author's name, year of publication, sampling technique, total sample size, sample size in terms of gender and age, age range of the studied population); Description and assessment of exposure (overall and gender wise prevalence and severity of malocclusion according to different indices or classification).

Quality assessment
For assessing quality of the eligible studies for metaanalysis a checklist used in previous studies was utilized [7,14]. This checklist contains twelve (12) questions which are designed to assess the methodological quality of the observational studies. The main domains covered using these questions were: appropriateness and/or description of the (1) sample size, sample characteristics and sampling method (2) research question and study design (3) role of researcher (4) data collection methods (5) data analysis methods. For each question a score of 0 or 1 is assigned based on whether the answer is negative or positive, respectively. Two reviewers (AM and AV) carried out the quality assessment independently. Points of diversion were discussed with third reviewer (AN) and consensus was obtained for final score of the study in question.

Statistical analysis
Statistical analyses were performed in MedCalc software. Heterogeneity between the eligible studies was calculated using Cochrane Q and I 2 Based on level of heterogeneity, random or fixed effects model were utilized to estimate the overall prevalence of malocclusion. Confidence interval was kept at 95% and relevant forest plots were prepared for each scoring criteria category of indices and classification used in the review as well as for the overall prevalence. Gender wise pooled estimate of prevalence was calculated from the data available from the included studies. Statistical difference between the two gender was calculated using chi-square test at significance level of p<0.05.

Results
Literature search and quality assessment Figure 1 describes the whole sequence of literature search and shortlisting of studies. Initial search with pre-selected key words and identified MeSH terms from various databases produced 1,090 titles. After removal of duplicates, 850 records were left. All these remaining records were screened for their titles and abstracts; and 81 articles were found eligible for full text reading. Further, 21 studies were excluded for not meeting the inclusion criteria. Finally, sixty (60) articles were found eligible for final qualitative and quantitative analysis.

Characteristics of included studies and pooled prevalence
Basic characteristics of individual studies conducted using different malocclusion indices and classification are summarized in Tables 1, 2. Statistically significant heterogeneity was observed among primary studies therefore we used random effects model for estimation of pooled prevalence. Pooled estimates of malocclusion according to different measurement tools are described as follows: Dental Aesthetic Index (DAI) We found 34 studies  and one nationwide survey [10] Table 3).

Terminal plane relationship of second primary molars
Flush terminal plane and mesial step relationship together accounted for more than 80% cases. Less than ten percent children had distal step relationship and asymmetric molar relationship. Out of the seven studies [67][68][69][70][71][72][73] included in this category, only one study had provided gender wise data. The authors of this study reported that males had significant to highly significant higher prevalence for all the three molar relationships compared to females [70].

Discussion
The results of our review showed that the pooled overall prevalence of malocclusion in Indian children and adolescents ranged from 28.4% in studies conducted using DAI to more than 60% for IOTN and Angles classification. The National Oral Health Survey of India conducted in the year 2002-03 had reported the prevalence of malocclusion (using DAI) to be 23.6, and 23.9 % in 12 and 15 years age group, respectively [10]. As compared to this nationwide survey our review reports a five percent increase in prevalence of malocclusion in Indian children. We included the data from this national survey except for five year old children since DAI is not recommended for this age group [75]. We did not find any other nationwide survey or Full-text ar cles assessed for eligibility (n = 81) Full-text ar cles excluded as they didn't meet inclusion criteria (n = 21) Studies included in quan ta ve synthesis (meta-analysis) (n = 60) systematic review conducted on Indian children for comparison with our data. Systematic reviews conducted in Iran [7] and China [8] have reported prevalence of 83.1 and 45.5% for any type of malocclusion in their native children. These reviews included studies conducted using Angles classification only. It has been well-established that different types of malocclusions are associated with impaired oral health and function [76]. Possible consequences of untreated malocclusion are pain in temperomandibular joint/s region, increased risk of trauma, speech problem and difficulty in mastication leading to food restriction [77,78]. In the current review, the overall pooled prevalence as per Angles classification was 66.7%. Angles class 1 was the most prevalent type of malocclusion observed in Indian children. This finding is in consensus with studies and systematic reviews conducted in other countries [7,8]. Angles class I malocclusion can cause visible irregularities such as crowded anterior teeth or large midline diastema between incisors in the dental arches [7,79]. A systematic review conducted to assess global prevalence of class 3 malocclusion has reported a prevalence range of 0-26.7 %, whereas, our review shows a pooled prevalence of 2.2% only. Studies have reported a low prevalence of class III malocclusion in Indian children when compared with other racial groups [8,80]. The evaluation of terminal plane relationship of primary second molars can act as predictor for assessing future malocclusions in children. Pooled estimates of our review shows that half of Indian children have flush terminal plane or commonly known as end-on relationship. The future forward growth of mandible can lead to development of class III malocclusion in children with flush terminal relationship [81]. We observed a higher prevalence of malocclusion among Indian boys as compared to girls. These results are contradictory to the trends seen in Iran [7] where girls had a higher prevalence of malocclusion. No gender difference was observed among the Chinese children [8].

Strengths and limitations
One of the limitations of the present review is that we didn't search data from grey literature which might be relevant to this review. Other major limitation is the occurrence of statistically significant heterogeneity among primary studies. We were unable to identify the source/s of this heterogeneity although we have used random effect model for estimation of results. The variation in quality of studies could be another possible limitation. In spite of these limitations, our review has many positive aspects. It is the first systematic review where all the studies conducted using most common indices and classification used for recording malocclusion were included for pooled analysis. We have followed international guidelines for data search and extraction and each study was scrutinized for its quality based on criteria

Conclusions
Apart from these functional problems, malocclusion has a significant impact on the social esteem and emotional well-being of a person. All the visible malocclusions have often been associated with bullying and a lower selfesteem among teenagers [76,82]. A recent systematic review reported that malocclusion has a negative impact on oral health related quality of life of individuals [83]. Therefore, the knowledge of burden of malocclusion in a population is important for instituting preventive measures especially in children and adolescents to avoid its physical and psychosocial impact later in their life. To conclude, the pooled data analysis of this review showed that the prevalence of malocclusion is increasing in Indian children. The reason for higher prevalence of malocclusion among Indian boys in comparison to girls needs to be investigated further. These results can help policy makers to work on feasible preventive and interceptive orthodontic measures for controlling malocclusion among Indian children and adolescents.
Research funding: None declared. Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission. Competing interests: Authors state no conflict of interest.