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Scientific Section |
Orthodontic Department, University Dental Hospital of Manchester, Higher Cambridge Street, Manchester M15 6FH, U.K.
Dr N. A. Mandall, Orthodontic Department, University Dental Hospital of Manchester, Higher Cambridge Street, Manchester M15 6FH, U.K.
Abstract
The aim of this investigation was to establish whether the Index of Orthodontic Treatment Need is reliable over time between the ages of 11 and 19 years. It consisted of a longitudinal sample of 314 11- and 15-year-old and 142 19-year-old subjects who had not received orthodontic treatment or extractions. The changes in the aesthetic component (AC) and the dental health component (DHC) of the Index of Orthodontic Treatment Need (IOTN) were measured between the ages of 11 and 19 years.
The results suggested that the dental health component of IOTN was reliable over time between the ages of 11–19 years despite temporal changes in the separate occlusal traits that comprise the index. The aesthetic component of IOTN tended to show an improvement over time.
The Index of Orthodontic Treatment Need is a reliable index over time when taking into account occlusal changes that are occurring during the 11–19-year age range. The study provides some reassurance to clinicians that an IOTN grading at age 11 years is unlikely to change by the time the patient is 19 years.
Refereed Scientific Paper
Key words: Index of Orthodontic Treatment Need, Occlusal Index, Reliability
Introduction
Epidemiological indices have been used to measure orthodontic treatment need from a normative or clinician's viewpoint. Such measurements are important for health services planning and monitoring of population trends. Previous indices (Angle, 1899
; Bjork et al., 1964) were not designed to quantify treatment need. Later, Summer's Occlusal Index (Summers, 1971) and Grainger's Treatment Priority Index (Grainger, 1967) were developed that included well defined measurements, but no assessment of function.
The Index of Orthodontic Treatment Need (IOTN; Brook and Shaw, 1989) defines specific, distinct categories of treatment need, whilst including a measure of function. It has been shown to be easy to use for epidemiological studies, acceptable to the profession and public and amenable to statistical analysis (Brook, 1987; Holmes, 1992).
The reliability of IOTN over time has not previously been investigated and this is important because there are minor changes in occlusion, during adolescence, that might influence IOTN recordings. Previous literature provides evidence for such minor changes in occlusion, for example, an increase in lower labial segment crowding during development of the dentition (Sakuda et al., 1976; Sinclair and Little, 1983). Other examples include a tendency for above average overjets to decrease between 12 and 20 years (Bjork, 1953; Savin and Savara, 1972) and overbite to reduce as well, despite increasing between 9 and 12 years of age (Moorrees, 1959; Adams, 1972, Sinclair and Little, 1983).
In the light of these occlusal changes, it is pertinent to ask whether any index, currently in use, records the same grading throughout adolescence. It could then be used to inform patients who are 11–12 years old, with more certainty, that their priority for treatment would be unlikely to change as they grow older. Therefore, the aim of this study was, first, to establish whether IOTN was reliable over time between the age of 11 and 19 years old for subjects who had not received orthodontic treatment. The second aim was to investigate the changes over time in the occlusal traits that comprise the dental health component of IOTN.
Sample
Study casts of a longitudinal sample of 11-year-old (n = 314), 15-year-old (n = 314) and 19-year-old (n = 142) subjects were examined. The study casts originated from an observational survey reported by Shaw and Addy (1986). Originally, a sample of 1018 11–12-year-old South Wales school children were selected by disproportionate stratified sampling so that occlusal features of low prevalence, but high orthodontic interest were represented. In this study, children were selected according to the following criteria:
shows the number of children followed up in Shaw's study and the number obtained after the selection criteria for this study were applied. The reduction in sample size at age 19 years was because the subjects had either failed to return, had commenced orthodontic treatment between 15 and 19 years of age, had teeth extracted or anterior crowns placed.
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The Index of Orthodontic treatment Need (IOTN)
IOTN consists of two components, the dental health component (DHC) and the aesthetic component (AC). The dental health component is a grading of 1–5, where 1 = no need for treatment and 5 = great need for treatment. The grade allocated depends on the measurement of the most severe occlusal trait and is summarized in Figure 1. The aesthetic component of the index is designed to complement the dental health component by recording the severity of anterior aesthetic tooth arrangement with grade 1 being no aesthetic need through to grade 10, great aesthetic need for treatment (Figure 2).
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Examiner Reliability
One examiner (SC), who was calibrated in the use of IOTN, assessed the study models. Intra-examiner reliability was measured by re-scoring a random sample of 100 models 6 weeks apart.
Statistics
IOTN scores for the index and each dental health component were compared across ages 11–15, 15–19, and 11–19 years. However, for some dental health components, the recorded frequencies were too small to allow analysis therefore, they were excluded. The data were dichotomised to allow McNemar test to be carried out. This looks specifically for statistically significant changes in IOTN score in one direction or another, and ignores any IOTN scores that stay the same over time. Weighted kappa statistic was used to confirm the examiner calibration and to assess intra-examiner reliability.
Results
Reproducibility
The results of the examiner calibration were 0•80 for the dental health component and 0•77 for the aesthetic component of IOTN. Over the 6-week time interval, intra-examiner reliability was 0•88 for the dental health component of IOTN and 0•70 for the aesthetic component. Kappa values ranged from 0•61 to 1•00 for the separate occlusal traits recorded as part of IOTN DHC.
Descriptive Statistics
The final sample therefore consisted of study models of 314, 11, 314, 15, and 142, 19-year-olds. The data in Table 2 describes the percentage of subjects in different aesthetic and dental health component categories over time. Tables 3–8 summarize the percentage of subjects with specific malocclusion traits at 11, 15, and 19 years. However, it is not possible to infer trends from these initial summary statistics because some subjects may have moved IOTN grading in an upward or downwards direction, and some may have stayed in the same category.
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. Potential important trends that these results highlighted were that 11-year-old children's IOTN AC seemed to stay fairly constant or improve over time. Similarly, an appreciable percentage of subjects tended to see a reduction in overjet and overbite between 11 and 19 years of age. It was further noted that 36 per cent of the children with IOTN displacement of contact points grades 1–2 at 11 years worsened during their teenage years.
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shows any statistically significant changes with age for the dental health component and aesthetic component of IOTN. In addition to overall IOTN grade, temporal changes in occlusal traits comprising the dental health component are also summarised in Table 10.
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).
There was no statistically significant change in overall IOTN DHC grade or anterior crossbite between the ages of 11 and 19 years. In contrast, overjet measurement reduced significantly between 11 and 19 years, meaning that there was a statistically significant change in this IOTN trait over time. Of the children who changed IOTN category over time, more of the children went into a lower category than went into a higher category for the following additional variables:
Worsening of IOTN grading over time (Table 10).
For posterior crossbites and displacement of contact points (crowding), more of the children, who changed IOTN category, went in a higher rather than a lower direction. Therefore, the trend was for these variables to worsen between 11 and 19 years of age.
For further analysis, the time periods 11–15 and 15–19 years were examined separately (Table 11). A statistically significant change was not seen in IOTN DHC grade, but was seen in the aesthetic component of IOTN grade between 11 and 15 years. As indicated before this tended to be an improvement in anterior aesthetic tooth appearance. Considering the separate components of IOTN DHC, most of the statistically significant changes were occurring in the 11–15-year age range, rather than 15–19 years. The notable exceptions to this were crowding and overbite changes that were also occurring at a statistically significant level between 15 and 19 years of age.
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The study has suggested that the IOTN dental health component grade is reliable between 11 and 19 years of age. This is despite being comprised of occlusal traits that change over time. In contrast, the IOTN aesthetic component grade was not as reliable between the ages studied but showed that anterior aesthetic appearance tended to improve during adolescence.
Occlusal Traits Comprising the Dental Health Component of IOTN that Improved over Time
Temporal occlusal changes recorded in this study were in broad agreement with previous literature. For example, a reduction in overjet during the teenage years was also found by Bjork (1953), and Savin and Savara (1972). However, we have shown that most of this overjet reduction is likely to occur between 11 and 15 years, and probably reflects facial changes during the pubertal growth spurt. Similarly, lip competency improved much more markedly during the latter age group although a general improvement in lip competency has previously been reported cross-sectionally (Stephenson, 1962; Luffingham, 1978). Despite the comparisons with previous literature that have been made, it is difficult to compare the results of this study with other work because of the drop-out between 15 and 19 years of age. This may have affected the distribution of occlusal traits for the 19-year age group data. Not all reductions in severity of occlusal traits were confined to the 11–15-year-old group. In the case of overbite, changes were occurring from 11 to 19 years and this is likely to reflect continued vertical growth that occurs during the teenage years. Previous studies also confirm a reduction in overbite depth between 11 and 19 years of age (Moorrees, 1959; Adams, 1972; Sinclair and Little, 1983).
Perhaps these improvements in overjet and overbite are instrumental in influencing changes in aesthetic component grades as the orthodontically untreated individual gets older. This could be a possible explanation for the improvement in IOTN AC scores over time. Alternatively, more subjects with higher aesthetic component grades at age 11 years, may have sought orthodontic treatment and therefore would not have been included in the 19 years old sample.
Occlusal Traits Comprising the Dental Health Component of IOTN that Worsened over Time
Contact displacements or crowding increased between 11 and 19 years and this appears to be universally supported for the lower labial segment (Barrow and White, 1952; Cryer, 1966; Lundstrom, 1969; Humerfelt and Slagsfold, 1972; Sakuda et al., 1976; Sinclair and Little, 1983).
In contrast, there is a diversity of opinion about molar arch widths during the growth phase of the dentition. Some studies have shown a reduction in arch width (Brown and Daugaard-Jenson, 1951; Barrow and White, 1952; Sinclair and Little, 1983’ Bishara et al., 1989), whilst others suggest small increases of approximately 1 mm (Moorrees, 1959; Sillman, 1964; Lundstrom, 1969; Humerfeld and Slagsvold, 1972). From this literature, a reduction in maxillary arch width over time, or perhaps growth changes between the arches, may explain why posterior crossbites were worse at 19 years than 11 years in this study. Alternatively, possibly the eruption of the second permanent molars may have been a factor in worsening the posterior crossbite grading. However, it is important that severity of IOTN grade for posterior crossbite relies on the amount of mandibular displacement and there does not seem to be any evidence of the extent of the displacement being correlated with the size of the crossbite. This is an area that would need further investigation.
The Reliability of the Dental Health Component of the Index of Orthodontic Treatment Need
It is interesting to see that the dental health component of IOTN overall is reliable between 15–19 years despite being sensitive enough to detect changes in separate occlusal traits. However, it is important to see if these results might be applicable to the general population. When the 11-year-old data was compared with other population studies (Tables 12 and 13), the distribution of DHC grades compared favourably with Brook and Shaw (1989), and Holmes (1992) whose subjects could be divided into almost equal thirds of definite, borderline, and no treatment need. The subjects in this study followed a similar pattern with the exception of less subjects in grade 1 and slightly more subjects in grade 5. This may have been as a result of the disproportionate stratified sampling that was designed to increase the frequency of dental abnormalities.
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References
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This article has been cited by other articles:
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  M. Souames, F. Bassigny, N. Zenati, P. J. Riordan, and M. L. Boy-Lefevre Orthodontic treatment need in French schoolchildren: an epidemiological study using the Index of Orthodontic Treatment Need Eur J Orthod, December 1, 2006; 28(6): 605 - 609. [Abstract] [Full Text] [PDF]
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