Occlusal traits and orthodontic treatment need in 7‐ to 10‐year‐olds in Estonia

Abstract The aim of this study was to evaluate the distribution of occlusal traits and orthodontic treatment need and complexity in Estonian 7‐ to 10‐year‐old children. This data provides solid information for planning of orthodontic care. Data of 392 Estonian children (198 girls and 194 boys, mean age 9.0 years, range 7.1–10.4 years) was analysed in this cross‐sectional study. Assessed traits included first molar and canine sagittal relationship, overjet, overbite, crowding, midline diastema, crossbite, and scissor bite. Orthodontic treatment need and complexity were assessed using the Index of Complexity, Outcome, and Need. Parents' opinion regarding their child's teeth was determined using a questionnaire. The most prevalent occlusal traits were canine class I sagittal relationship (73.7%), midline diastema (73.0%), molar class I sagittal relationship (57.4%), and overbite ≥3.5 mm (51.8%). According to the Index of Complexity, Outcome, and Need, 64.3% of Estonian elementary school children were in need of orthodontic treatment. Treatment complexity was simple in 12.5%, mild in 38.8%, moderate in 22.7%, difficult in 14.0%, and very difficult in 12.0% of the children. Approximately 66.4% of the parents felt that their child needed orthodontic treatment. This study confirms earlier findings indicating that the most frequent sagittal relationship is class I in the first molars and class I in the canines. However, the sagittal relationship was asymmetric in more than half of the children. Correlation between objectively defined treatment need and parents' desire for treatment was high in Estonia.

no data exist on the prevalence of occlusal traits and orthodontic treatment need in Estonia, this study is the first in a series of extensive investigations analysing the prevalence of occlusal traits in children and adolescents from 3 to 21 years of age. Parents' and adolescents' expectations and perceptions concerning orthodontic treatment are also evaluated. The aims of this study were • to evaluate the distribution of occlusal traits in 7-to 10-year-old children in Estonia and • to evaluate the objective and subjective need for orthodontic treatment in Estonia.

| Clinical examination
Five occlusal traits were registered clinically in centric occlusion, separately for the left and right sides: (a) sagittal relationships of the first molars and canines, (b) overjet, (c) overbite, (d) crossbite, and (e) scissor bite. All clinical examinations were performed by Examiner 1. The examination was carried out in the school's dental office using a dental mirror, probe, pencil (0.3 mm), and millimetre ruler (Dentaurum 042-751 Münchner Modell).
Alginate impressions for plaster casts were taken from each child.

| Plaster casts
Examiners 1 and 2 registered three features from the plaster casts in order to achieve consensus: (a) end-to-end relationship of the first molars and deciduous and permanent canines separately for the right and left side, (b) crowding, and (c) diastemas between central incisors.
Registration of the occlusal traits was based on international standards (Brunelle, Bhat, & Lipton, 1996;Horowitz & Hixon, 1966;Moorrees, 1959); a detailed description of definitions is given in Appendix A. Furthermore, using the plaster casts, Index of Complexity, Outcome, and Need (ICON) for orthodontic treatment was assessed according to written instructions (Daniels & Richmond, 2000) by Examiner 1.

| Reliability
Before the intended study after 1 week, Examiner 1 re-examined clinically 22 children. To assure the validity of ICON assessments, 39 randomly selected plaster casts (10%) were analysed by both Examiner 1 and by an ICON calibrated Examiner 3. The intraexaminer reliability was good (r > .97). The interexaminer reliability varied from moderate (r = .50) to good (r > .93).

| Questionnaire
The guardians' opinions regarding a child's general dental health, tooth alignment, dental appearance, and opinion regarding orthodontic treatment need were gathered through five questions (Appendix B).
The questionnaire was filled out at home by one of the parents. More than one answer per question was allowed. Questions were modified for this study from similar questions in a previous study (Pietilä & Pietilä, 1996).

| Statistical analysis
The test-retest (Pearson's and Spearman's correlations) and chi-square test were used to compare the frequencies of specific features (IBM SPSS v.20 software for Windows). p values of less than .05 were considered statistically significant.

| Occlusal traits among 7-to 10-year-old Estonian children
The most prevalent occlusal traits in Estonian 7-to 10-year-old children were class I canine relationship (73.7%), midline diastema (73.0%), class I molar relationship (57.4%), and increased (≥3.5 mm) overbite (51.8%). The sagittal relationship in canines and molars was asymmetric in a large number of children (33.2% and 35.7%, respectively). The detailed prevalence of occlusal traits is presented in Table 1. There were only 17 children (4.3%, 9 girls and 8 boys) with symmetrical class I canine and molar relationships, overjet and overbite of 1-3 mm, without crowding, scissor bite, crossbite, and negative overbite. The overjet ranged from −1 to 10 mm (mean 3.1 mm, SD 1.67). The overbite ranged from −2 to 8.5 mm (mean 3.2 mm, SD 1.75). Crowding ranged from 1 to 8 mm in the maxillary and from 0.5 to 8.0 mm in the mandibular arch. The most frequent crowding was 2 mm in the maxillary and 1 mm in the mandibular arch (6.9% and 11.5%, respectively). Compared to boys, girls had 1.6 times greater odds of having crowding, and smaller odds of having canine end-toend, overjet ≥3.5 mm, and class II molar relationship. The width of the midline diastema was most frequently 2 mm (20.2%) in the maxillary arch (range 0.5-4.5 mm) and 0.5 mm (range 0.5-4.5 mm) in the mandibular arch (6.1%).

| Orthodontic treatment need and complexity of treatment
According to ICON, 64.3% of Estonian 7-to 10-year-olds were in need of orthodontic treatment (ICON score > 43). The scores ranged from 7 to 105 (median score 50), the most frequent score being 44 (11.2%).
There were no gender differences in treatment need (χ 2 (1) = 1.7, p = .21). Distribution of treatment complexity is presented in Table 2.

| Parents' views and orthodontic treatment need
Approximately 65.6% of the parents were satisfied or very satisfied with their child's dental health. The association between parents' satisfaction and objective treatment need was statistically significant (χ 2 (3) = 12.83, p = .005). More than half of the parents (53.1%) were satisfied or very satisfied with the alignment and appearance of their child's teeth. Satisfaction with the alignment of a child's teeth and parents' assessment of orthodontic treatment need were statistically significantly associated (χ 2 (4) = 19.78, p < .001). Approximately 66.4% of parents felt that their child needed orthodontic treatment, mainly for improvement of dental appearance (37.1%), reduction in the amount of caries (23.1%), and ease of cleaning (19.6%).
Approximately 56.5% of children whose parents did not want orthodontic treatment were in need of orthodontic treatment according to ICON (Table 3). Parents' opinion regarding treatment need did not differ for girls and boys. A statistically significant association was found between parents' desire to get a child's teeth straightened and treatment need as assessed using ICON (χ 2 (1) = 5.59, p = .022).

| DISCUSSION
This study is the first population-based study registering occlusal traits and orthodontic treatment need among 7-to 10-year-olds in Estonia.
The largest ethnic groups in Estonia are Estonians (68% of the population) and Russians (28%); the remaining 4.0% consist of 142 other ethnicities. For practical reasons, sampling was done in cities.
Children were randomly selected and can be considered representative of those cities' child population. We have no reason to believe that the situation in the countryside or in other cities is different, because Estonia has neither big cities and slums nor long distances between population centres. Any possible regional differences in Estonia and their possible correlation to the socioeconomic status of families need to be assessed in future studies.
This study confirmed earlier findings, namely, that the most frequent sagittal relationship is class I in the first molars and class I in canines. Worth noting is that at the age of 7-to 10 years, asymmetric sagittal molar and canine relationships were frequent in Estonian children. Asymmetry or laterality (directional asymmetry) is a common finding in many craniofacial structures (Pirttiniemi & Kantomaa, 1992).
Decay, early loss of the deciduous teeth, discrepancy in tooth size and quantity, derangements in the temporomandibular joint, or asymmetric habits may create asymmetric occlusal development (Moorrees, 1959;Thilander & Rönning, 1985). Prevalence of class II molar relationship was 21.9%, which is in line with the prevalence reported from other countries, 9.2-28.0% in mixed dentition (Dimberg, Lennartsson, Söderfeldt, & Bondemark, 2013;Lux, Dücker, Pritsch, Komposch, & Niekusch, 2009;Myllärniemi, 1970). In part, the variability may be related to differences in applied criteria and in the interpretation of findings. Most studies have not differentiated between sagittal symmetry and asymmetry. The range of overjet in 7-to 10-year-old Estonian children was similar to that of 9-year-old children in Germany (Lux et al., 2009), but unlike in Germany, there was no difference between boys and girls in Estonia. Compared with Finnish children, Estonian children had a higher prevalence of an increased overjet in mixed dentition (Myllärniemi, 1970). It is possible that Estonian children with an overjet of ≥6 mm would benefit from early orthodontic treatment (Artun & Al-Azemi, 2009;Järvinen, 1978). The recent Cochrane Review also concludes that early orthodontic treatment is effective, for example, in reducing the incidence of incisal trauma year-olds, where those with erupting incisors had already been excluded from analyses (Dimberg et al., 2013).
In the age group of 7-to 10-year-olds, the youngest children were just entering to early mixed dentition, whereas some 10-year-olds already had permanent dentition. Hence, considerations for interseptive procedures range from assisting proper eruption of incisors and first molars to spacing or crowding and skeletal relationships.
All dentists face these occlusal traits in yearly dental examinations.
In addition, the frequent asymmetric sagittal relationships observed in this study bring additional challenge for orthodontic planning.
In this age group, there exists no generally accepted treatment need index, quick to apply, and use in assessment of plaster casts.
Despite the fact that ICON is designed for late-mixed dentitions (Daniels & Richmond, 2000), we used it for assessment of orthodontic treatment need. Its assessments are clearly determined and it also provides data on treatment complexity. The 10 included photographs Aesthetic Component of the Index of Orthodontic Treatment Need (AC/IOTN) represent slightly older children. However, they can easily be used as a reference to the level of dental aesthetics; there is no intention to point out a similar dentition to the one that the child has but to select the photograph with as pleasing an occlusion.
As a matter of fact, there is no photograph representing, for example, negative overbite or class III relationship. In the future, the ICON scores will be comparable with those of the older age group of Estonian adolescents. Although ICON is useful in assessing treatment need, it does not assist in planning the timing of treatment, which is an important aspect of paediatric orthodontic care.
Girls seem to pay more attention to their appearance and are more interested in orthodontic treatment than boys (Birkeland, Bøe, & Wisth, 2000;Jung, 2010). In Estonia, parents' opinions were not influenced by the child's gender. Future studies should assess the age at which Estonian children themselves begin to pay attention to occlusal traits and dental appearance.
As determined with ICON, orthodontic treatment need in Estonia is higher than reported in epidemiological studies from Latvia and Finland (Heikinheimo, 1978;Liepa, Urtane, Richmond, & Dunstan, 2003).
The expectations and wishes of parents are in line with ICON, partly because the index is sensitive to visible deviations. This study confirms earlier findings (Birkeland et al., 2000;Kiekens, Maltha, van't Hof, & Kuijpers-Jagtman, 2006) that patients' main expectations regarding orthodontic treatment are related to improvement in dentofacial aesthetics. This study fills a significant knowledge gap in oral health in Estonia by providing an overview of dental traits among 7-to 10- year-old children.

| CONCLUSION
The present results indicate that • the most prevalent occlusal traits were class I canine sagittal relationship, midline diastema, class I molar sagittal relationship, and increased overbite; • more than half of Estonian children had an asymmetrical canine and molar relationship; • according to ICON, 64.3% of Estonian 7-to 10-year-olds were in need of orthodontic treatment; • a statistically significant association was found between parents' desire to straighten their child's teeth and treatment need assessed using ICON. Parents' opinion regarding orthodontic treatment need did not differ in a statistically significant way on the basis of the child's gender; and • the parents' main expectation from orthodontic treatment was improvement in dentofacial aesthetics.

ACKNOWLEDGMENTS
We thank the participants of the study for their important contributions. Sunnak, R., Johal, A., & Fleming, P. S. (2015). Is orthodontics prior to 11 years of age evidence-based? A systematic review and meta-analysis. Journal of Dentistry, 43, 477-486. Thilander, B., & Rönning, O. (1985). Introduction to orthodontics (5th ed.  Molar classes II and III were registered in the accuracy of ≥1/2 cusp width. In cases of obvious tooth migration, no attempt was made to endeavour the original intercuspation. Registration was not done when the first molar was missing.
The sagittal relationship of the canines was measured between perpendicular projections, on the occlusal plane, from the tip of the maxillary canine and the contact point of the mandibular canine and the first deciduous molar or the first premolar.
Canine class I: the tip of the maxillary canine occluded to the distal surface of the mandibular canine.
Canine end to end: the tip of the maxillary canine articulated to the tip of mandibular canines. A deviation of 1 mm or more to the mesial or distal was classified as canine class II or I, respectively.
Canine class III: the tip of the maxillary deciduous canine occluded more than 1 mm posterior to the distal surface of the mandibular canine In the case of missing canine, the registration was not recorded.
No attempt was made to compensate for drift of teeth due to premature extraction or any other reasons.

A.2. | Horizontal plane
The overjet (positive) was measured in 0.5-mm intervals as the hori-

A.4. | Transversal plane
The posterior crossbite was registered in the canine, premolar, and molar area when the buccal cusp of the maxillary tooth occluded lingual to the buccal cusp of the mandibular antagonists (at least one pair of teeth). Teeth in an end-to-end position were registered as crossbite.
A scissor bite was recorded in the premolar and molar area when lingual cusps of maxillary teeth occluded buccally of the buccal surfaces of corresponding mandibular teeth.

A.5. | Crowding
Crowding of the teeth was estimated as total space deficiency (in millimeters) of the anterior teeth (incisors only). The amount of crowding was recorded in the maxillary and mandibular arch as the difference between the total mesio-distal tooth diameter and the arch circumference. The possible influence of growth in arch width was not estimated.

A.6. | Midline diastema
Midline diastema between the central incisors in the upper and lower arch was measured in 0.5-mm intervals between the mesial margin of the right and left incisors on the middle height of the tooth crown.