ORTHODONTIC INDEXES. A LITERATURE REVIEW

Abstract

Besides Angle's classification, which was applied only for diagnosis purposes [10], other systems are used to establish malocclusion diagnosis, such as the British Standards Institute Classification of 1983 [11], known as based on the relations between the superior and inferior incisors. [...]Angle's classification system has limited applicability in determining the severity of malocclusion, the priority of treatment or its effectiveness. 3.EPIDEMIOLOGICAL INDEXES Numerous epidemiological indices have been developed for orthodontic examination and, although valuable for traditional planning and research, they remain limited for assessing the priority of access to treatment. [...]the complexity of this system restricts its general application [14].The index of tooth position (ITP) was developed as an epidemiological tool [15], based on teeth as individual units, rather than on arch segments, so that dental movement, infra-occlusion, overocclusion are described as the total number of dental malocclusions, obtaining a special malocclusion score. Subsequent changes have brought little benefits, due to the assessment of tooth movement on a scale of 0 to 2 [16]. [...]this index is not appropriate to assess the individual need for treatment.

Headnote

Abstract

Dento-facial anomalies and the morpho-functional disorders that occur in the development of the maxillaries have an increasing frequency, a study made by Proffit suggesting that the need for orthodontic treatment in children under the age of 18 in the US would be 60% [1,2]. Over time, many authors have tried to evaluate the malocclusions using different types of indices: diagnosis classification indices, epidemiological indices, success rate of the treatment indices, need for orthodontic treatment indices. By reviewing the literature on this topic, a few controversies aroused regarding the reliability, validity and utility of these indices.

Keywords: orthodontics, evaluation indexes.

1.INTRODUCTION

Occlusal indices are defined as "tools in epidemiological studies, used to determine the need for orthodontic treatment, or the sum of deviations from normal occlusion", which can be used to evaluate patients and population groups where occlusal anomalies are considered to be deviations from the normal occlusion [3]. Diagnostic classification consists in classifying the type of malocclusion as described by Angle, collecting epidemiological data, recording each characteristic of the indices to be applied among the population and thus including epidemiological records of malocclusion. IOTN is the most widely used index to identify the need for treatment and the cut-off point of patients, along with the PAR index, which evaluates the success of the orthodontic treatment.

2.DIAGNOSTIC CLASSIFICATION INDEXES

The classic, original diagnosis of malocclusions was based on the two-dimensional anteriorposterior relationship between the first permanent maxillary and the mandibular molars, a method first described by Angle in 1899. Although intensely criticized, this method remains even today one of the most largely used. Numerous studies analyze the reliability of this method, demonstrating the limits of this classification, starting from the incorrect assumption that the first molars erupt into a constant "key" position (thus ignoring the consequences of migrations or losses of the first molars) [4], continuing with the lack of a threedimensional analysis of malocclusion, which is seen only in the sagital plane [5]. We can also mention other inconveniences, such as: lack of ability to discern the degree of dental health, functional and aesthetic parameters [6]. It also has a poor reproducibility [7-9] and does not take into account the dental relationships related to the facial profile.

Besides Angle's classification, which was applied only for diagnosis purposes [10], other systems are used to establish malocclusion diagnosis, such as the British Standards Institute Classification of 1983 [11], known as based on the relations between the superior and inferior incisors. There have been further attempts to conceive a classification system that includes a three-dimensional evaluation of the dental, skeletal and arch parameters [12]. In conclusion, Angle's classification system has limited applicability in determining the severity of malocclusion, the priority of treatment or its effectiveness.

3.EPIDEMIOLOGICAL INDEXES

Numerous epidemiological indices have been developed for orthodontic examination and, although valuable for traditional planning and research, they remain limited for assessing the priority of access to treatment. For example, an epidemiological tool (facial orthometer) was designed to quantify three components of malocclusion, namely dentition, occlusion and space anomalies [13]. Unfortunately, the complexity of this DFI index restricts its potential clinical applications. Bjork et al. introduced a malocclusion recording system for epidemiological purposes, based on the objective recording of three main occlusal categories: abnormalities in dentition or occlusion and spatial deviations. Using an objective registration procedure, a total number of 567 characteristics was recorded relative to the three categories. Consequently, the complexity of this system restricts its general application [14].The index of tooth position (ITP) was developed as an epidemiological tool [15], based on teeth as individual units, rather than on arch segments, so that dental movement, infra-occlusion, overocclusion are described as the total number of dental malocclusions, obtaining a special malocclusion score. Unfortunately, this epidemiological index is too imprecise to assess the need for treatment for each malocclusion. The misalignment index (MI), based on the discreet evaluation of each arch, divided into two, anterior and posterior segments, tends to underestimate the severity of malocclusion. Subsequent changes have brought little benefits, due to the assessment of tooth movement on a scale of 0 to 2 [16]. Therefore, this index is not appropriate to assess the individual need for treatment. The occlusal feature index (OFI) is based on the main occlusal features important in any orthodontic evaluation [17]: anterior mandibular crowding; intercuspidation, overbite and over jet. The sum of specific deviations from normal determines a global index of malocclusion severity, with values from 0 to 9. OFI scores show reasonable reliability and correlate well with the need for treatment, but they are imprecise in determining the priority of access to orthodontic treatment. The FDI System was developed for COCSTOC in FDI [18]. This system was later evaluated by the World Health Organization (WHO), thus obtaining the Fundamental Method for Classification of WHO / FDI Malocclusions. Created for the clinical examination of patients with all permanent teeth present, this index focuses on three fundamental areas of occlusal assessment: dental, inter-arcade and intra-arcade relationships. Specific features were recorded using coding for various aspects of malocclusion, along with the FDI identification system, so that to locate individual dental malrelations. One of the major impediments of the use of any of the mentioned systems arises from how malocclusion is determined as a single morphological variable [19], which oversimplifies the complexity of malocclusion. Even with trials based on population distributions to identify components that cause malocclusion, the reliability and validity of these derived qualitative systems remain controversial [20].

4.INDICES OF TREATMENT SUCCESS

The success of the orthodontic treatment is dependent on three factors: a correct therapeutical plan, parental consent and support, and patient's cooperation. Several indexes have been developed to evaluate the results of the orthodontic treatments. Eismann [21] devised a method based on the scores assigned to fifteen morphological criteria, which were then summed up to provide a result index of the service. Unfortunately, the attribution of scores was largely subjective, which resulted in the neglect of overall objectivity. Later on, Gottlieb [22] conceived an alternative system, based on ten accepted criteria for orthodontic correction; however this system was inherently influenced by the allocation of five points for a corrected feature, as opposed to allocating only one point for the weakest skill. The Peer review index (PAR), developed as a specific index designed to measure the severity of malocclusion and the success of treatment [23], proved to be a simple tool that does not sacrifice either validity or reliability [24]. In addition, to evaluate the severity of pre-treatment malocclusion, the PAR index was suggested as an index for improving the severity of malocclusion and also for evaluating treatment's success [25,26]. Although considered to be significantly improved, the PAR index appeared as questionable when assessing the North America population, in comparison to the UK one, so that further studies need to be made to establish a consensus in terms of geographical areas [27].

5.INDICES OF TREATMENT NEED IN ORTHODONTICS

In the attempt to classify patient's need for orthodontic treatment, some indices have been developed to provide a method of evaluating treatment priority. Such indices, important in the allocation of financial resources to priority groups [28], are: HLDI- Handicapping Labiolingual Deviation Index [29]; Treatment Priority Index-TPI [30]; Handicapping Malocclusal Record- HMAR [31]; Occlusal Index-OI [32]; Swedish National Board for Health and Welfare [33]; Index of Orthodontic Treatment NeedIOTN [34]; Dental Aesthetic Index - DAI [35].

As to the reliability of TPI, even if it has been confirmed by several studies [36-38], the validity of the index in comparing different degrees of malocclusion remains controversial [39]. HMAR proved the lowest reliability and validity when evaluating the malocclusion severity in comparison to the alternatives HLDI, or OI [39]. Comparatively with other occlusal indices (HMAR, TPI, HLDI), OI showed the highest validity and reproducibility rate [37,39,40], although the absolute validity in relation to the "gold standard" of the consensus of subjective orthodontics remains low [41]. Other deficiencies are: the complexity to use the index [42], the tendency to underestimate the need for treatment [43], the failure to take into account the premature eruption of incisors or loss of molars [6] and the inter-proximal space, except for maxillary diastema over 2 mm [43].

Studies have evidenced the development of a series of occlusal indices for evaluating the need for orthodontic treatment and for quantifying the obtained results, such as: IOTN, with its two components, AC and DHC; DAI - dental aesthetics index; ICON - index for complexity, result and orthodontic necessity, PAR and SCAN - continuously standardized aesthetic necessity index. For all these indices, a weighing system is applied for certain features of malocclusion, reflecting that some deviations of the occlusal components are more important than others in the severity of a malocclusion. In this way, an index can provide an element of flexibility to reflect clinical changes. As the sum of these components reflects the severity of malocclusion, they can be used to analyze treatment priority. Several occlusal indices have been discovered over time, divided by Dr. William Shaw and his colleagues into five different categories: diagnostic indices, epidemiological indices, orthodontic treatment need indices, treatment outcome indices, orthodontic treatment complexity indexes[44]. In order to better exemplify the evolution of occlusal indices, Table 1 presents the classification of occlusal indices, respectively the five categories, indices name, researchers and the year of the discovery of each index. Occlusal indexes are commonly used in countries of Northern Europe, where "the government subsidizes dental health services as well as any part of national health services or national health insurance", in the UK and in 15 US states, but "because of the opinion of the AAO (Orthodontic Association) on the orthodontic indices that not any occlusal index is a valid scientific instrument of the need for orthodontic treatment, the use of occlusal indices in the United States is not encouraged and limited" (Table 1). [45]

Occlusal indices should be able to specifically identify the populations which do not need treatment, and those who need orthodontic treatment (sensitivity). An index must be fast and easy to use, accepted by the population and finally adapted to the existing resources [45]. IOTN is currently used in epidemiological studies due to its reliability, validity and ease of use in both young and adult populations [46]. It has 2 parts: the dental health component and the aesthetic component. The dental health component, based on the Swedish index, looks at the occlusal traits thought to be related to the morbidity of dentition and of the surrounding structures [33]. In the DHC component, for two or more anomalies recorded, only the highest one is recorded [44], as for the AC component only the frontal malocclusion is emphasized [46]. Cons et al. [35] have developed dAi to evaluate the clinical and aesthetic features of dental occlusion, by summing them up, thus obtaining 4 values of malocclusion severity, from minor to very severe. Keay et al. stated that DAI was used in both young and adult dentition, obtaining a higher performance of DAI in permanent dentition, compared to the mixed one [47].

6.CORRELATION BETWEEN THE RELIABILITY AND VALIDITY OF INDEXES

The reliability of DAI and DHC-IOTN was evaluated in a study of Firestone et al. who recorded a good sensitivity for both indexes, poor specificity (IOTN=19%, and DAI=14%), high and similar values for reproducibility, which makes them useful in epidemiological studies. Evaluation time for DAI was higher than for DHC-IOTN, which makes DHC-IOTN a fast implementation index. Firestone observed that ICON is a safe and valid index for treatment need, and also for the complexity and result of orthodontic cases. Sensitivity and specificity were relatively high for ICON. BorzabadiFarahani et al. analyzed ICON and concluded that it is a reliable substitute for DHC-IOTN, indicating a high correlation with it. A similar percentage was observed between these indices - of 89.5%, but also a difference of 10.5% regarding the need for orthodontic treatment. ICON offers several advantages over IOTN, including the ability to assess the complexity of malocclusion and to evaluate treatment outcome [48]. Cons et al. [35] shown that, compared to DAI, ICON is not affected, although it has similar deficiencies due to the lack of evaluation of occlusal anomalies, such as posterior inverse occlusion, tooth damage and deep overbite. Daniels and Richmond concluded that, compared to DAI, ICON registration is significantly easier, taking less time, being therefore suggested as a good substitute for DAI [49]. As other indices, ICON has some limitations: a base on subjective patient opinion, reducing objectivity and affecting the agreements between examiners to evaluate occlusal features of the index [49]. Richmond et al. [23] have specified that the IOTN and PAR indices are valid, against the UK opinion, as they cannot be representative of professional opinions from other countries. Other authors, such as Kerr and Buchanan, in 1993, considered it to be an unjustifiable harsh index in limited-purpose treatment. [50]. Otuyemi and Jones, in 1995, showed that PAR does not take into account periodontal destruction, decalcification, root resorption, dynamic occlusion and facial aesthetics. Although these points are true, there are difficulties in evaluating such reliable parameters, and their importance is questionable when evaluating complex disease cases [51].

7.CONCLUSIONS

There are five important factors to consider when choosing an instrument for assessing the effects of oral health: practical utility, fidelity, validity, objectivity/subjectivity; global/specific measures. When it comes to assessing the treatment needs in a population, three major issues must be pursued: the index must be concise and easy to use in the population within a reasonable time, the assessment scale must be relevant to the decision criteria, and the index must evaluate the variables specified by a model, to provide cause-effect information [52]. Considering the treatment plan and the choice of treatment solutions, the orthodontist also needs to evaluate pain prevention, restoration of the oral functions, maintenance of patient's physiognomy, hygiene and responsibility [53-55]. The conclusion is that there are differences in the validity of the indexes, even though it is not possible to evaluate the degree of validity with the knowledge we have today. IOTN is essentially an epidemiologic tool that has deficiencies in assessing individual cases. The occlusal measurements and the scoring and weighting systems of indexes are conventional. However, our understanding about the consequences of malocclusions has changed since the 1960s. Nowadays, we do not consider as a mandatory orthodontic treatment a patient with caries risk, periodontal disease, and temporomandibular dysfunction. The importance of facial aesthetics and the psychosocial consequences of malocclusions have been and still are widely discussed. In many cases, these may be the most important indicators for orthodontic treatment. However, the American Association of Orthodontists stated in 1990 that it does not recognize any index as a scientifically valid measurement of the need for orthodontic treatment [56]. This statement is still valid, because no new information about the consequences and disadvantages of malocclusions was found in the 1990s.

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