18 Measuring Other Conditions in Oral Epidemiology
Other conditions have been studied in oral epidemiology with varying amounts of success. Some, like temporomandibular disorders, present so many inherent difficulties that they will probably always be extremely difficult to measure. Others such as soft tissue lesions other than oral cancer and precancers (e.g., oral pemphigus, lichen planus) have simply not attracted much attention.
Malocclusion is a difficult entity to define because individuals and cultures vary widely in perceptions of what constitutes a malocclusion problem. Quite a number of malocclusion indexes have been devised, but probably because of this perceptual problem, none has ever emerged as a standard. These issues have not changed over the years, and there are thoughtful, still valid commentaries from the 1970s on the problems of classifying and scoring malocclusions.13,15
Angle’s classification, which dates from the nineteenth century,1 may still be useful in treatment planning but is of no use in epidemiology because it is a nominal categorization. Most other indexes suffer from the limitation that they record specific conditions (e.g., overbite, posterior crossbite) rather than the status of the whole occlusion. The Malalignment Index31 assesses rotation and tooth displacement, whereas the Occlusal Feature Index24 records crowding, cuspal interdigitation, and vertical and horizontal overbite. The Handicapping Labio-Lingual Deviations (HLD, which, interestingly enough, is also the developer’s initials) Index11 received considerable public health use when it was applied to assess treatment needs for a public orthodontic program in New York State. Grainger developed the Treatment Priority Index (TPI) for assessing treatment needs, an index that was used once, but only once, in a national study of orthodontic needs of children.30 None of these indexes has seen much use in the years beyond its introduction. One modestly successful measure is the Occlusal Index, or OI,29 which measures nine characteristics: dental age, molar relation, overbite, overjet, posterior crossbite, posterior open bite, tooth displacement, midline relations, and missing permanent maxillary incisors. Its use demands a fair degree of examiner skill and training, but it is probably closer to a complete malocclusion index than those listed earlier.
In Europe the Index of Orthodontic Treatment Need (IOTN) has received some use since it was first introduced in 1989.4 It was modified from an existing Swedish scale and combines both a functional and an esthetic measure. Functional occlusion is categorized into five different grades, whereas the esthetic measure uses a 10-point ordinal scale that allows the individual to determine his own esthetic perception of the dentition. The IOTN has shown some promise for use in public health19 but has not been widely adopted. The Peer Assessment Rating (PAR) index is designed to capture all the occlusal anomalies that might be found in malocclusion in a single score.25 This sounds ambitious, but the PAR index has been found to equal the OI in reliability.5 The search still continues for an omnibus measure, and the Index of Complexity, Outcome, and Need (ICON) arrived with the new millennium.10 It has been shown to correlate well with patients’ perceptions of esthetics, speech, function, and need for treatment.17
The very proliferation of these indexes underlines the difficulties in measuring this complex issue. The Fédération Dentaire Internationale jumped on the bandwagon with its attempt to develop an internationally accepted index and simplified method of determining malocclusion.12 It was not successful; the result was a carefully qualified method of measuring occlusal traits. The index has been used9 but seems to offer no more value than the other indexes described.
The complexities of malocclusion, and the frustrations that have grown up with the inadequacies of these indexes, have led many researchers to believe that functional malocclusion is virtually unmeasurable for epidemiologic purposes. In terms of trying to interpret group data on overbites, crowding, and other clinical conditions, that may well be true. Orthodontic indexes developed in the late 1980s, however, take a different philosophical approach in that they assess esthetic rather than clinical aspects of function. One is the Dental Aesthetic Index (DAI), published in 1986 after years of testing.8 The DAI starts from the premise that the impact of malocclusion on other oral pathology is doubtful and that the main benefit of orthodontic treatment is its effect on the individual’s social and psychological well-being. The DAI makes objective measurements of aesthetic acceptability according to social norms, and it has been validated for this use in a number of different countries. As noted earlier, the IOTN also includes an esthetic component measured on a 10-point ordinal scale.