INTRODUCTION

In recent years, there has been increased interest in the development of an index of orthodontic treatment difficulty. An orthodontic index is a numerical scale that is derived by scoring specific features of a malocclusion to objectively assess some parameter, such as how far a malocclusion varies from an ideal occlusion. The reasons for this increased interest are 3-fold. First, the index could be used to allocate resources. This is, in theory, based on the belief that patients could be treated utilizing the most effective appliances, by practitioners competent to carry out treatment to a high or optimal standard. Second, an index could be used to obtain appropriate remuneration. If a case is considered difficult, it is likely to take more time and effort, thus, time and effort should be awarded accordingly. Third, an index of orthodontic treatment difficulty could be used to increase professional esteem among individuals or groups of practitioners who treat difficult cases to a high standard. Although all these objectives seem plausible, it is questionable whether they have validity, as treatment difficulty may mean different things to different clinicians for different cases.

Despite the common belief that one case may be more difficult to treat than another, exactly what defines a case as easy or difficult is still not clear. The terms complexity, difficulty, and severity are often used in the same context. Both difficulty and severity are defined by the Oxford English Dictionary as “needing much effort or skill.” Complexity is defined as “intricate or complicated,” which is not dissimilar to difficulty. However, in terms of orthodontics, the authors suggest that difficulty and complexity are synonymous and should be defined as a measure of effort and skill, while severity is a measure of how far a malocclusion deviates from normal.

However, these definitions are not mutually exclusive. Rowe1 studied the assessment of 30 orthodontists in examining the pretreatment records and giving their opinion regarding difficulty of treatment. The study casts were analyzed with an objective measure of malocclusion. They found that treatment difficulty and malocclusion severity were distinct but related entities, even though some factors of malocclusion were not reliable predictors of perceived treatment difficulty.

DeGuzman et al2 attempted to validate the Peer Assessment Rating (PAR) Index3 for malocclusion severity and treatment difficulty by using the opinions of a panel of 11 American orthodontists. They found a close association between the orthodontists' perception of severity of malocclusion and perceived difficulty of treatment.

Richmond et al4 studied the professional perception of orthodontic treatment complexity by sampling specialist and nonspecialist practitioners in General Dental Services (GDS) in the United Kingdom (UK). Data for 280 cases were collected, including the use of the IOTN and PAR indices. They concluded that cost (in the GDS cost is directly related to the appliance type), number of appointments, length of appointments, age of patient at the start of treatment, and initial PAR score (equivalent to initial malocclusion severity) were all significant associations with the judgment of difficulty. In effect, in the UK treatment difficulty was already being rewarded with higher fees. In addition, this study found no predictive factors prior to treatment to assess orthodontic treatment. Only post-treatment factors were important in assessing treatment difficulty. Cassinelli5 found that difficulty in patient care was associated with high initial PAR score, treatment plan changes, extractions, total number of appointments, and treatment duration.

The Index of Complexity, Outcome & Need (ICON) was derived from the expert opinion of 97 practicing specialist orthodontists from Germany, Greece, Hungary, Italy, Netherlands, Norway, Spain, United Kingdom, and the United States.6 It is a single assessment method to record complexity, outcome, and need designed for use on patients or study models. The ICON measures 5 components and taking about 1 minute to complete.

The pretreatment ICON score exhibited a strong linear relationship with the mean case score of the 97 orthodontist's perceptions of difficulty (R² = 0.756). The authors devised different levels of difficulty based on the mean subjective opinions of the 98 orthodontists: Easy <29; Mild 29–50; Moderate 51–63; Difficult 64–77; and Very Difficult >77.

The aim of this study was to determine those factors that are related to difficult and easy treatments and to assess the use of the ICON as an indicator of treatment difficulty.

MATERIALS AND METHODS

The study was carried out in 2 centers—one in Dresden, Germany and the other in Cardiff, UK. Eight specialist orthodontists in each center were invited to participate in the study. An explanatory letter and 10 questionnaires (5 for easy cases and 5 for difficult cases) were sent in advance to each participant. Each orthodontist was asked to supply 5 completed cases they regarded as being easy to treat and 5 they regarded as being difficult to treat. The selection of cases was deliberately polarized into easy and difficult to increase the chance of detecting possible factors related to difficulty.

Patient-related factors selected for collection in the questionnaires and reasons for the case being regarded as easy or difficult are as shown in Table 1. The orthodontists were invited to write up to 5 factors that they considered as making the case difficult or easy beyond the fixed questions on the questionnaire.

TABLE 1. Patient Related Factors Which are Significant in Influencing the Difficulty of an Orthodontic Treatment

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The ICON index assesses 5 factors. The scores are then weighted and totaled to give the total ICON score. Two examiners were trained and calibrated in the use of the ICON. The ICON scores were recorded for both pre- and post-treatment study models.

RESULTS

The Root Mean Square of the calibration exercise was less than 7 points and the mean difference compared to the gold standard was below 2 points, which indicated excellent reliability. Sixteen specialist orthodontists, 8 in Dresden and 8 in Cardiff, submitted a total of 160 completed cases, 80 designated as easy cases and 80 designated as difficult.

A logistic regression demonstrated patient-related factors that were statistically significant in influencing the complexity of an orthodontic treatment in both countries (Table 1).

A chi-squared analysis of reasons, as supplied by the specialist orthodontists, was carried out to discover which reasons, if any, had a statistically significant influence in the perceptions of difficulty of a case in both countries. The results for this are shown in Tables 2, 3, and 4.

TABLE 2. Results of Analysis of Reasons to Show Influence on the Difficulty of a Case in Germany

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DISCUSSION

The greater the number of appointments, the older the patient, and the greater the ICON score, the more likely the case will be considered as difficult. However, the odds ratio for these factors are not greatly predictive of treatment difficulty (Exp (B) = 1.1). It is interesting that factors such as skeletal pattern (anteroposterior and vertical) were not considered important in the statistical model. Also, a change in treatment plan, extraction patterns, and length of treatment were not found to have an effect on difficulty. This is contrary to that reported by Cassenelli although the total number of appointments was found to have an influence.5

A detailed look at the reasons cited by the orthodontists revealed some differences between easy and difficult cases in Germany and the UK, and there may be a difference between Europe and the United States. More influence was placed on dysfunction in Germany than in the UK. This probably reflects the ethos of orthodontic training in Germany. In the UK, crowding was cited as an important factor by practitioners in difficult and easy cases. This can be explained by the fact that when crowding matches extractions, the alignment is more straightforward than where extraction residual spaces need to be closed or extra space needs to be created. Compliance seems to be an important factor in cases considered to be easy. The optimal age for treatment was cited for 20 of the easy cases in Germany but not in the UK. This optimal age is the subjective age designated by German orthodontists as the right age to undertake orthodontic treatment. Including 2 centers in 2 different countries has highlighted similarities and differences in decision-making by orthodontists regarding treatment difficulty.

When the data from Germany and the UK is combined, more factors come into play. When considering difficulty, skeletal relationships, crowding and molar relationships showed statistically significant differences. There were also statistically significant differences between factors common to Germany and the UK: cooperation, overbite, and compliance (Table 5). Lack of cooperation and compliance seem to be more important in Germany than in the UK, while overbite is more important in the UK than in Germany. None of the orthodontists cited soft tissues as a factor in determining difficulty. Although orthodontist's reliability in assessing soft tissues is very poor, it is often cited as an indication for treatment difficulty.8

TABLE 5. Comparison of Factors Common to Both Easy and Difficult Cases in Germany and the UK

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This study emphasizes that if treatment goes according to plan the case is regarded as easy. However, if treatment is disrupted for any reason, resulting in a change of treatment plan that increases the number of appointments, the case would be regarded as difficult.

The ICON was developed to assess orthodontic treatment difficulty, need, and outcome. The initial correlation of ICON scores with orthodontists subjective opinions of difficulty was high (R² = .756).6 The relatively low odds ratio for the ICON score may reflect the polarization of easy and difficult cases rather than comparing ICON scores with a continuous scale of difficulty.

Orthodontists' reliability in assessing treatment difficulty has been reported as poor and this will have an effect on determining which factors are important in its assessment. It appears that treatment difficulty means different things to different practitioners for different cases.

CONCLUSIONS

This study indicates that the main distinguishing factors between easy and difficult cases appear to be pretreatment age, number of appointments, and pretreatment ICON score. Although these factors are statistically significant, they are not particularly good predictors of treatment difficulty.

The factors stated by the orthodontists indicate the multifactorial aspect of orthodontic treatment difficulty. However, there were 3 factors commonly cited in Germany and the UK: cooperation, overbite, and compliance. Lack of cooperation and compliance seem to be more important in Germany than in the UK, while overbite is more important in the UK than in Germany.