Recording and measuring malocclusion: A review of the literature

Recording and measuring malocclusion: A review of the literature Endarra L. K. Tang, BDS, MDS, ~ and Stephen H. Y. Wei, BDS(Hon.), MDS, DDS, MS b

Sai Ying Pun, Hong Kong The methods of recording and measuring malocclusion can be broadly divided into two types: qualitative and quantitative. Among the qualitative methods of recording malocclusion, Angle's method of classifying malocclusion with or without modifications is probably the most widely used. The "WHO/FDI Basic Method for Recording of Malocclusion" was published in 1979 to establish an assessment format to determine the prevalence of malocclusion and to estimate treatment needs of a population. Among the many occlusion indices developed by various research workers, the occlusal index developed by Summers appeared to have the least amount of bias, is best correlated with clinical standards and has the highest validity during time. More recently, methods have also been developed to enable assessment of treatment need according to grade index scales. However, experience in using these methods is still very limited. (AMJ ORTHODDENTOFACORTHOP 1993;103:344-51 .)

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review of the literature related tothe re, cording and measuring of malocclusion severity found that most of the investigations were published between the 1940s and the 1970s. In the past decade, there have been few publications that discussed this topic. A good method of recording or measuring malocclusion is important for documentation of the prevalence and severity of malocclusion in population groups. This kind of data is not only important for the epidemiologist, but also for those who plan for the provision of orthodontic treatment in a community or for the training of orthodontic specialists. If the method is universally accepted and applied, data collected from different population groups can be compared. A method that measures malocclusion quantitatively can also be used to assess treatment effects of orthodontic appliances. The objective of this article is to review the literature related to the methods of recording and measuring malocclusion that can be broadly divided into two types: qualitative and quantitative methods. QUALITATIVE METHODS OF RECORDING MALOCCLUSION

Many research workers have attempted to devise qualitative methods of recording malocclusion, mainly

From the Faculty of Dentistry, University of Hong Kong, Prince Philip Dental Hospital 9 Lecturer, Department of Children's Dentistry and Orthodontics . . . . b Professor and Head, Department of Children's Dentistry and Orthodontics; Dean, Faculty of Dentistry. Copyright 9 1993 by the American Association of Orthodontists. 0889-5406/93/Sl.00 + 0.10 811135189

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for epidemiologic studies. The earliest methods of recording malocclusion were qualitative ones. A sum9 mary of the more important methods is presented in Table I. 1.9 Angle's method of classifying malocclusion has been widely accepted and used since it was first published in 1899. There have been many critiques of Angle's classification of malocclusion. Case j~ pointed out that Angle's method disregarded the relationship of the teeth to the face; and although malocclusion was a threedimensional problem, Angle's system had only taken into account anteroposterior deviations in the sagittal plane. When reliability was tested by Gravely and Johnson, tt they found that the between-examiner errors, as well as the within-examiner errors in categorizing Angle Class II, Division 2 malocclusions, were both relatively high. They suggeted some reasons why Angle's system was unreliable, including difficulty associated with asymmetry between left and right sides, or where tooth movements had occurred because of factors such as crowding and premature loss ofdeciduous teeth. In such cases clinical judgements must be made to determine the nature of the underlying malocclusion, and therefore inconsistencies between and within examiners might occur. It was concluded that comparisons of the distribution of malocclusion in different Communities, classified according to Angle's system, should only be made if observations were made in each community by the same examiner because the within-examiner errors were randomly distributed and tended to cancel each other out. Nonetheless, it must be remembered that Angle devised his classification method as a prescription for treatment, not as an index of malocclusion or an

Tang and Wei 3 4 5

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Table I, S u m m a r y o f q u a l i t a t i v e m e t h o d s o f r e c o r d i n g m a l o c c l u s i o n Angle (1899) ~

Classification of molar relationship devised as a prescription for treatment.

Stallard (1932)2

The general dental status, including some malocclusion symptoms, was recorded. No definition of the various symptoms was specified.

McCall (1944) 3

Malocclusion symptoms recorded include: molar relationship, posterior crossbite, anterior crowding, rotated incisors, excessive overbite, openbite, labial or lingual version, tooth displacement, constriction of arches. No definition of these symptoms was specified. Symptoms were recorded in an 'all-or-none' manner.

Sclare (1945)4

Specific malocculsion symptoms were recorded, which include Angle's classification of molar relationships, arch constriction with incisor crowding, arch constriction without incisor crowding, superior protrusion with incisor crowding, superior protrusion with incisor crowding, superior constriction without incisor crowding, labial prominence of canines, lingually placed incisors, rotated incisors, crossbite, open bite, and close bite. No definition of these symptoms was specified. Symptoms were recorded in an 'all-or-none' manner.

Fisk (1960) n

Dental age was used for grouping patients. Three planes of space were considered: I. Anteroposterior relationship: Angle's classification, anterior crossbite, overjet (mm), negative overjet (mm). 2. Transverse relationship: Posterior crossbite (maxillary teeth biting buccally or lingually). 3. Vertical relationship: open bite (mm), overbite (mm). Additional measurements include labiolingual spread (Draker, 1960), spacing, therapeutic extractions, postnatal defects, congenital defects, mutilation, congenital absence, supernumerary teeth.

Bjrrk, Krebs, and Solow (i964) 6

Objective registration of malocclusion symptoms'based t,n detailed definitions. Data obtained could be analyzed by computers. Three parts: I. Anomalies in the dentition: Tooth anomalies, abnormal eruption, malalignment of individual teeth. 2. Occlusal anomalies: Deviations in the positional relationship between the upper and lower dental arches in the sagittal, vertical, and transverse planes. 3. Deviation in space conditions: Spacing or crowding.

Proffit and Ackerman (1973)7

5-step procedure of assessing malocclusion (no definite criteria for assessment was given): 1. Alignment: Ideal, crowding, spacing, mutilated. 2. Profile: Mandibular prominence, mandibular recession, lip profile relative to nose and chin (convex, straight, concave). 3. Crossbite: Relationship of the dental arches in the transverse plane, as indicated by buccolingual relationship of posterior teeth. 4. Angle classification: relationship of the dental arches in the sagittal plane. 5. Bite depth: Relationship of the dental arches in the vertical plane, as indicated by the presence or absence of anterior open bite, anterior deep bite, posterior open bite, and posterior collapse bite. Five major groups of items were recorded (with well-defined recording criteria): !. Gross anomalies. 2. Dentition: Absent teeth, supernumerary, malformed incisor, ectopic eruption. 3. Space conditions: Diastema, crowding, spacing. 4. Occlusion: a. lncisal segment: Maxillary overjet, mandibular overjct, crossbite, overbite, open bite, midline shift. b. Lateral segment: Anteroposterior relations, open bite, posterior crossbite. 5. Orthodontic treatment need judged subjectively: Not necessary, doubtful, necessary, urgent. Five features of occlusion measured: 1. Overjet (ram) 2. Overbite (mm) 3. Posterior crossbite (number of teeth in crossbite, unilateral, or bilateral). 4. Buccal segment crowding or spacing (mm) 5. Incisal segment alignrficnt (classified as acceptable, crowded, spaced, displaced, or 'rotated', following defined criteria).

WHO/FDI (1979) s

Kinaan and Bruke (1981)9

e p i d e m i o l o g i c tool as it w a s u s e d l a t e r b y o t h e r re-

e t a12, 6 a s i m p l i f i e d m e t h o d w a s d e v e l o p e d d u r i n g the

searchers. O n t h e b a s i s o f the p r i n c i p l e s d e v e l o p e d for d e f i n i n g a n d r e c o r d i n g i n d i v i d u a l traits o f m a l o c c l u s i o n b y B j & k

years 1 9 6 9 - 1 9 7 2 b y the W o r k i n g G r o u p 2 ( W G 2 ) o f the F D I C o m m i s s i o n o n C l a s s i f i c a t i o n a n d Statistics for Oral C o n d i t i o n s . D u r i n g t h e p e r i o d 1973 to 1976 the

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Table II. The requirements for an index

Of occlusion ~3a4 1. Status of the group is expressed by a single number which corresponds to a relative position on a finite scale with definite upper and lower limits; running by progressive gradation from zero, i.e., absence of disease, to the ultimate point, i.e., disease in its terminal stage. 2. The index should be equally sensitive throughout the scale. 3. Index value should correspond closely with the clinical importance of the disease stage it represents. 4. Index value should be amendable to statistical analysis. 5. Reproducible. 6. Requisite equipment and instruments should be practicable in actual field situation. 7. Examination procedure should require a minimum of judgement. 8. The index should be facile enough to permit the study of a large population without undue cost in time or energy. 9. The index would permit the prompt detection of a shift in group conditions, for better or for worst. 910. The index should be valid during time.

m e t h o d w a s field tested and modified. Final modifications were carried out by the WG2 in collaboration With the World Health Organization. The final version of the "WHO/FDI Basic Method For Recording of Malocclusion" was published in the Bulletin of the World Health Organization in 1979. 8 The primary objective of the assessment method was to determine the prevalence of malocclusion and dental irregularities and to estimate the treatment needs of a population, as a basis for the planning of orthodontic services. Trends can be identified when reviewing the development of the qualitative methods of recording malocclusion. Researchers in the earlier days did not define the malocclusion symptoms to be recorded, 24 thus malocclusion symptoms were recorded in an all-or-none manner. However, in 1964 Bj6rk, Krebs, and Solow 6 developed a detailed method to record malocclusion with clearly defined items. The methods developed by the WHO/FDI s also followed the trend of recording malocclusion symptoms with very carefully defined criteria. In the earlier methods, only a few malocclusion symptoms were selected arbitrarily as the items to be recorded. 24 In the later methods, there was an increasingly obvious tendency to record items that were logically grouped, ss IDEAL INDEX OF OCCLUSION

The requirements for an index of occlusion are similar to the requirements of any dental index, and.were summarized in a World Health Organization Report, ~2 Table II, points 1 to 9. Summers added point (10) to the list ~ and explained what he meant by "validity

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during time. ''~3ts According to Summers, developmental changes in occlusal disorders may consist of either a "basic orthodontic defect" or a "symptom" of a developmental change. A basic orthodontic defect may be defined as a constant occlusal dysfunction, whereas a symptom of a developmental defect may be defined as an adaptation to development that may be an accommodation either to normal growth or to a basic orthodontic defect. A symptom may either be constant (present at all ages) or variable (fluctuating with age). An index must concentrate on, and be sensitive to the basic orthodontic defect, and must not be unduly sensitive to the symptom. By definition, then, for an index to be valid during time, the index score for the occlusal disorder should either remain constant or increase during time, indicating that the occlusal disorder is the same or getting worse. The index score should not decrease during time, indicating that the occlusal disorder is getting better. This is because, although there is frequent mention in the literature of the self-correction of malocclusion, there actually are few instances of self-corrected malocclusions. 16 QUANTITATIVE METHODS OF MEASURING MALOCCLUSION AND ITS SEVERITY

Attempts to develop quantitative methods of measuring malocclusion were made somewhat later than those for qualitative methods. Most of the indices for measuring malocclusion severity were developed in the 1950s and 1960s, and a summary of the more important indices is presented in Table III. t3J7-23 In 1951 Massler and FrankeP 7 made the initial attempt to develop a quantitative method of assessing malocclusion. The total number of displaced or rotated teeth was the basis for the evaluation of prevalence and incidence of malocclusion in population groups. In 1959, VanKirk and PennelP s proposed the malignment index, which involved the grading of tooth displacement and rotation. They defined quantitatively tooth displacement and rotation, which was a step forward. The handicapping labiolingual deviation index (HLDI) was developed by Draker ~9 in 1960. Carlos and Ast 24 tested the ability of the HLDI in distinguishing "handicapping" and "nonhandicapping" malocclusions. Clinical judgement made by orthodontists was used as the standard. The distribution of HLDI scores in the two groups were found to be largely overlapping, which indicated that the HLDI was unable to distinguish the so called handicapping malocclusion. The occlusal feature index was proposed by Poulton and Aaronson in 1961. 20 This index was considered incomplete since only four features of occlusion were measured and scored (refer to Table III).

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Table III. S u m m a r y o f v a r i o u s i n d i c e s o f o c c l u s i o n Massler and Frankel (1951) t7 Malalignment index by Vankirk and Pennell (1959) ~8 Handicapping labiolingual deviation index by Draker (1960) ~9 Occlusal feature index by Poulton and Aaronson (1961) -o Malocclusion severity estimate by Grainger (1960-61)~

Occlusal index by Summers (1966) t~

Treatment priority index by Grainger (1967) 2

Handicapping malocclusion assessment record by Salzmann (1968) '-3

Count the number of teeth displaced or rotated. Assessment of tooth displacement and rotation is qualitative--all or none. Tooth displacement and rotation were measured. Tooth displacement defined quantitatively: <1.5 mm or >1.5 mm. Tooth rotation defined quantitatively: <45* or >45 ~. Measurements include cleft palate (all or none), traumatic deviations (all or none), overjet (mm), overbite (mm), mandibular protrusion (mm), anterior open bite (mm), and labiolingual spread (a measurement of tooth displacement in ram). Measurements include lower anterior crowding, cuspal interdigitation, vertical overbite, and horizontal overjet. Occlusion features measured and scored according to defined criteria. Seven weighted and defined measurements: (1) Overjet, (2) overbite, (3) anterior open bite, (4) congenitally missing maxillary incisors, (5) first permanent molar relationship, (6) posterior crossbite, (7) tooth displacement (actual and potential). Six malocclusion syndromes were defined: 1. Positive overjet and anterior open bite. 2. Positive overjet, positive overbite, distal molar relationship, and posterior crossbite with maxillary teeth buccal to mandibular teeth. 3. Negative overjet, mesial molar relationship, and posterior crossbite with maxillary teeth lingual to mandibular teeth. 4. Congenitally missing maxillary incisors. 5. Tooth displacement. 6. Potential tooth displacement. Nine weighted and defined measurements: (1) Molar relation, (2) overbite, (3) overjet, (4) posterior crossbite, (5) posterior open bite, (6) tooth displacement, (7) midline relation, (8) maxillary median diastema, (9) congenitally missing maxillary incisors. Seven malocclusion syndromes defined: h Overjet and open bite. 2. Distal molar relation, overjet, overbite, posterior crossbite, midline diastema, and midline deviation. 3. Congenitally missing maxillary incisors. 4. Tooth displacement (actual and potential). 5. Posterior open bite. 6. Mesial molar relation, overjet, overbite, posterior crossbite, midline diastema, and midline deviation. 7. Mesial molar relation, mixed dentition analysis (potential tooth displacement), and tooth displacement. Different scoring schemes and forms for different stages of dental development: deciduous dentition, mixed dentition, and permanent dentition. 11 weighted and defined measurements: (1) Upper anterior segment overjet, (2) lower anterior segment overjet, (3) overbite of upper anterior over lower anterior, (4) anterior open bite, (5) congenitally absence of incisors, (6) distal molar relation, (7) mesial molar relation, (8) posterior crossbite (maxillary teeth buccal to normal), (9) posterior crossbite (maxillary teeth lingual to normal), (10) tooth displacement, (11) gross anomalies. Seven malocclusion syndromes were defined: (1) Maxillary expansion syndrome, (2) overbite, (3) retrognathism, (4) open bite, (5) prognathism, (6) maxillary collapse syndrome, (7) congenitally mlssmg mc~sor. Weighted measurements consist of three parts: I. Intraarch deviation--missing teeth, crowding, rotation, spacing. 2. Interarch deviation--overjet, overbite, crossbite, open bite, mesiodistal deviation. 3. Six handicapping dentofacial deformities: (i) Facial and oral clefts, (2) lower lip palatal to maxillary incisors, (3) occlusal interference, (4) functional jaw limitation, (5) facial asymmetry (6) speech impairment. This part can only be assessed on life patients.

MALOCCLUSION SEVERITY ESTIMATE (MSE) G r a m g e r - d e v e l o p e d the m a l o c c l u s i o n severity est i m a t e ( M S E ) , in the B u r l i n g t o n R e s e a r c h Center. It c a n b e u s e d e i t h e r o n m o d e l s o r o n patients. Validity

w a s tested b y c o m p a r i n g t h e i n d e x scores o f a s t u d y s a m p l ~ w i t h clinical s t a n d a r d s o b t a i n e d b y h a v i n g five o r t h o d o n t i s t s a n d o n e p u b l i c h e a l t h d e n t i s t array t h e s e o c c l u s i o n s a c c o r d i n g to e s t h e t i c s , f u n c t i o n , a n d treat-

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ment difficulty. The correlation between the ranks of the standard and those of the MSE was high, the correlation coefficient r, = 0.845. The MSE was also found to be highly reproducible (rs = 0.959). However, there were at least three possible shortcomings of the MSE, namely: (1) the index was derived from data of 12-year-old patients and therefore might not be valid for earlier stages of dental development in the deciduous and mixed dentitions; (2) the MSE score didn't reflect all measurements that were accumulated; and (3) the absence of any occlusal disorder was not scored as zero. The MSE was later revised, and the revised version was called the treatment priority index, 2~ and will be discussed later.

OCCLUSAL INDEX (OI) The occlusal index (O1) was developed by Summers 'in 1966, ~3 and was based on the malocclusion severity estimate, with attempts to remedy its shortcomings. The first shortcoming of the MSE could be remedied in part by defining normality over time, in particular equating the mixed dentition analysis with actual tooth displacement; and in part by giving different weights to certain items in different dental age groups if these items would have their "norms" changing as dental development proceeded. A scoring scheme for each stage of dental development (i.e., deciduous, mixed, and permanent dentition stages) was therefore developed, and different scoring forms were used for subjects in each stage. The second shortcoming of the MSE was remedied in the OI by considering the scores of all syndromes in arriving at the final OI score. The MSE considered only the score of the syndrome with the highest score, but in the OI, the other scores were also considered by adding half of the sum of the remaining scores to the highest score among the seven syndromes. The third shortcoming of the MSE was remedied by adjusting for norreality, so that the absence of any ocelusal disorder would be scored as zero. The validity, validity during time, and intraexaminer reliability of the occlusal index were tested by Summers." Validity was again tested by comparing index scores against clinical judgement, which was used as the standard. Serial data derived from the University of Michigan's growth study was used in testing for validity during time. Annual study casts taken from age 9 to 16 years of 47 subjects who had received no orthodontic treatment were used. Validity during time was tested by averaging the OI scores of the casts from this sample and noting any change in the index score during time. The average OI scores obtained from the series of casts in this sample did increase during time, thus demonstrating the ability of the occlusal index to be

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recording the basic malocclusion defect as it becomes evident.

TREATMENT PRIORITY INDEX (TPI) Grainger, 2' in 1967, modified the MSE to develop the treatment priority index (TPI). Grainger described the index as a method of assessing the severity of the most common types of malocclusion, and hence, provided a means of ranking patients according to the severity of malocclusion, the degree of handicap, or their priority of treatment. The prerequisites for determining a handicap were defined by Grainger:'- as follows: (1) unacceptable esthetics, (2) significant reduction in masticatory function, (3) traumatic condition predisposing to tissue destruction, (4) speech impairment, (5) unstable occlusion and (6) gross or traumatic defects. On the basis of these six prerequisites for determining a handicap, items to be observed in the TPI were selected. A few manifestations of malocclusion, such as midline diastema and slight asymmetry, were rejected as being of little public health significance. Measurements could be made either clinically or indirectly from dental study casts. In an attempt to revise the MSE, the TPI had corrected for scoring normalities as zero. ttowever, it had deleted the "mixed dentition analysis," which measures potential tooth displacement. It is also inadequate for assessing the occlusion of the deciduous or mixed dentition. Inspection of the TPI form reveals that distal and mesial molar relations are considered equal. Nonetheless, the OI and the TPI were similar in many aspects as might be expected because both were based on the MSE. Most of the measurements in the two indices were common, so were their definitions and methods of assessment. Popovich and Thompson z5 compared the TPI and the subjective appraisal of orthodontists longitudinally, because the index had not been evaluated at different age levels when it was first developed. From their results, Popovich and Thompson concluded that the ratings of 0 to 2.5, 2.5 to 4.5 and greater than 4.5 were the best limits for categorizing TPI scores as low, middle, and high in treatment priority, respectively. Ghafari et al. 26 did a longitudinal evaluation of the TPI. They found that TPI was a valid epidemiologic indicator of malocclusion, but TPI values recorded in the transitional dentition do not predict the future severity of malocclusion in the permanent dentition.

HANDICAPPING MALOCCLUSION ASSESSMENT RECORD (HMAR) In 1968, S.alzmann 23 developed the handicapping malocclusion assessment record (HMAR). The assess-

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ment record forms and the definition of handicapping malocclusion presented were officially approved by the Council on Dental Health of the American Dental Association, and the Board of Directors of the American Association of Orthodontists. Salzmann's purpose of developing the HMAR was to provide a means for establishing priority for treatment of handicapping malocclusion. Handicapping malocclusion and handicapping dentofacial deformity were defined as conditions that constitute a hazard to the maintenance of oral health and interfere with the well-being of the patient by adversely affecting dentofacial esthetics, mandibular function, or speech. A cut-off point was set at a score so that those patients whose scores were above the cut-off point would be treated by the professional personnel available in the community, at the same time keeping with the funds budgeted for~orthodontlcs. t The meas'urements were made according to the criteria, and point values were assigned to them. The relative point values, which were based on clinical orthodontic experience, had been tested by orthodontists from various parts of the United States. One important aspeci of the tlMAR is that it records and weighs functional problems, which no other index does. SUMMARY OF VARIOUS OCCLUSAL INDICES

Trends observed in the development of qualitative methods can also be seen when reviewing the development of the indices for measuring malocclusion. Earlier researchers who developed quantitative methods of measuring malocclusion only assessed malocclusion under a few arbitrarily chosen items. ~7-~_oMore carefully defined and systemically chosen items were measured and recorded in the later methods.'3":'-~ A turning point in the development of malocclusion indices can be observed when Grainger introduced the MSE in 1960-61.2~ Weights were first introduced to put different emphasis on various measurements. Later, weighting systems were also included in the OI, the TPI, and the ttMAR. Only the OI had developed different scoring schemes and scoring forms for patients in different stages of dental development, i.e, deciduous dentition, mixed dentition, and permanent dentition. EVALUATION OF MALOCCLUSION INDICES

The precision (reliability or reproducibility) of an index is the ability to produce the same score or measurement when one or more examiners measure the same case at the same or at a different time. The validity of an index can be defined as its ability to accurately measure what it purports to measure. Bias, or systemic

Tang and Wei 349 error, of an index or measurement is the magnitude and direction of its tendency to measure something other tfian what was intended. The score of an unbiased index should accurately reflect the intended characteristics. For malocclusion indices, severity of malocclusion and the priority for treatment based on need will be the intended characteristics. An index could be precise but biased. In such a case, the score will be reproducible but not an accurate portraya! of the occlusion. ttermanson and Grewe 27 tested the precision and bias of five malocclusion indices including the ttMAR, the O1, the TPI, and two other indices. Their results showed that only the OI and the TPI demonstrated nonsignificant interexaminer variability at the 1% level, and that the most precise and unbiased index would be the OI or the TPI. Grewe and Hagan :8 compared the HMAR, the OI, and the TPI for precision and bias when used in the same population. The results showed that all three indices were. highly reproducible. When bias, or systematic error, was evaluated, the results indicated that the OI described the clinical standard most accurately. Therefore, of the three inqlices tested in the study, no one index can be selected over the others with regard to precision, but the O1 would be the index of choice, with regard to having the least amount of bias. Summers 15 tested the validity of three indices: The CHAMPUS index used by the Office for the Civilian Health and Medical Program of the Uniformed Service, United States Army; the ItMAR, and the OI. The OI was found to be the most valid among the three indices. When validity during time was teste d , decreased scores were noted in the CHAMPUS index and the HMAR but not in the OI. Gray and Demirjian 29 compared the reproducibility and accuracY of four indices: the HLDI, the TPI, the OI, and the tlMAR. The results showed that all methods were highly reproducible, but the OI had the best correlation with the clinical standard, which was determined by subjectNe assessment of orthodontists. The ttLDI was found by Gray and Demirjian ~' to identify only the very worst cases and tended to lump all the others into a common pool. Therefore it was unacceptable for overall field use. The TPI and the OI were very highly correlated and had some common characteristics. Both needed very close and careful examination as subjective decisions were required in deCiding whether the molar relationship is distal or mesial by half a cusp or more than half a cusp on each side. A certain degree of subjective judgement was also involved in determining whether some teeth were rotated by 35 ~ to 45 ~ or more than 45 ~, and in determining displacement by 1.5 to 2 mm or more than 2 mm. The

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care needed to make such decisions required someone who was well acquainted with occlusion. If mistakes were made, they would be serious because large differences in weighting factors would result from the decisions made. The OI, when compared with the TPI, was slightly more complicated to use and would require even more calculations and clerical time. The HMAR correlates fairly well with the standard, but not as closely as the TPI or the OI. However, it had advantages as well. Subjective decisions were not as critical as the TPI or the OI, because only full-cusp discrepancies were noted. If errors were made, they were not usually serious because the weighting system applied was only to the anterior segment and mostly for esthetics. Recording and calculation of the index was also simpler and required less time. In conclusion, it appears that the OI has the least amount of bias; 2s is best correlated with clinical s t a n d a r d s 15"29 and has the highest validity during time. i~ GRADE INDEX SCALE FOR ASSESSMENT OF TREATMENT NEED

The orthodontic section of the Swedish Dental Society and the Swedish Medical Board developed a four grade index scale, 3~ which classify patients into grades ranging from very urgent need for orthodontic treatment to little need. However, the criteria for allocating patients into the various grades were not well defined, and the cut off points between points were somewhat vague. 3' INDEX OF ORTHODONTIC TREATMENT NEED (IOTN)

More recently Shaw et al. 3133 developed the index of orthodontic treatment need (IOTN), which consisted of the dental health component and the esthetic component. In the dental health component, occlusal traits thought to contribute to the longevity and satisfactory functioning of the dentition were defined and placed in five grades, with clear cut-off points. The esthetic component consisted of a 10-point scale illustrated by a series of numbered photographs that were rated for attractiveness. The index was found to be satisfactorily valid and reproducible. However, experiences in using this indice are still very limited, 31 and the index has not been applied extensively to other.population groups. CONCLUSION

There seems to be no universally accepted index for measuring malocclusion, yet. Although the OI had been shown to have the least amount of bias, is. best correlated with the clinical standards, and most valid during time among the various indices, it still has short-

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comings. Elderton and Clark 34 pointed out that there is a need to refine the OI to allow it to be used for cases where first permanent molars had been lost or had drifted, because difficulty and mistakes in measuring the malocclusion would arise in these situations. Tang and Wet, 35 in a study using the OI to assess treatment effectiveness of orthodontic appliances, thought that the OI is not ideal for measuring treatment effects of orthodontic appliances. It was because the OI does not take into account residual or extraction spaces, nor does it measure mesiodistal or buccolingual tooth inclinations. Further research would therefore be needed to develop better indices or to refine the present indices so that they can be more universally accepted. REFERENCES I. Angle Eli. Classificaiton of malocclusion. Dent Cosmos 1988;41:248-64. 2. Stallard H. The general prevalence of gross symptoms of malocclusion. Dent Cosmos 1932;74:29-37. 3. McCall JO. A study of malocclusion in pre-school and school children. Dent Items Interest 1944;131-3. 4. Sclare R. Orthodontics and the school children: a survey of 680 children. Br Dent J 1945;79:278-80. 5. Fisk RO. WlJen malocclusion concerns the public. Can Dent Assoc J 1960;26(7):397-412. 6. Bjrrk A, Krebs AA, Solow B. A method for epidemiological registration of malocclusion. Acta Odontol Scand 1964;22:2741. 7. Proffit WR, Ackcrman JL. Rating the characteristics of malocclusion: a systematic approach for planning treatment. AM J OR'mOP 1973;64(3):258-69. 8. Brzroukov V, Freer TJ, Helm S, Kalamkarov H, Sardoinfirri J, Solow B. Basic methods for recording malocclusion traits. Bull World ttealth Organ 1979;57(6):955-61. 9. Kinaan BK, Burke PII. Quantitative assessment of the occlusal features. Br J Orthod 1981;8:149-56. 10. Case CS. Techniques and principles of dental orthopedia (reprint of 1921 edition). New York: Leo Bruder, 1963:16-8. I I. Gravely JF, Johnson DB. Angle's classificate of malocclusion: an assessment of reliability. Br J Orthod 1973;I(3):79-86. 12. World tlealth Organization. An international methodology for epidemiological studies of oral disease. Manual No. 5: Epidemiological studies of periodontal disease. First draft. Geneva: World Health Organization, 1966. 13. Summers CJ. A system for identifying and scoring occlusal disorders. The occlusal index. [Doctoral dissertation]. Ann Arbor: University of Michigan, 1966. 14. Summers CJ. A system for identifying and scoring occlusal disorders. AM J OR'ntOD 1971;59(6):552-67. 15. Summers CJ. Test for validity for indices of occlusion. AM J On'mOP 1972;62(4):428-9. 16. Salzmann JA. Orthodontics in practice and perspective. AM J Oa'ntOD 1969;55(6):556-65. 17. Massler M, Frankel JM. Prevalence of malocclusion in children aged 14 to 18 years. AM J Oa'ntOD 1951;37:751-68. 18. VanKirk LK, Pennell EH. Assessment of malocclusion in population groups. AM J ORTtlOD 1959;4500):752-8. 19. Draker HL. Handicapping labiolingual deviations: a proposed index for public health purposes. AM J ORTttOD 1960;46(4):295305.

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20. Poulton DR, Aaronson SA. The relationship between occlusion and periodontal status. AM J OR'nXOD1961;47(9):690-9. 21. Grainger RM. Malocclusion severity estimate. Pr~ress Report, Series VI. Burlington Orthodontic Research Centre, 1960-61: 911. 22. Grainger RM. Orthodontic treatment priority index. National Center for Health Service. Series II. No. 25. Washington: United States Department of Health, Education, and Welfare, 1967. 23. Salzmann JA. Handicapping malocclusion assessment to establish treatment priority. AM J ORTHOD 1968;54(10):749-69. 24. Carlos JP, Ast DS. An evaluation of the HLD Index as a decisionmaking tool. Public ttealth Rep 1966;81(7):621-6. 25. Popvich F, Thompson GW. A longitudinal comparison of the orthodontic treatment priority index and the subjective appraisal of the orthodontist. J Public Health Dent 1971;31:2-8. 26. Ghafari J, Locke SA, Bentley JM. Longitudinal evaluation of the Treatment Priority Index (TPI). A,',t J OR'I'tlOD DEN'rOFAC OR'mOP 1989;96:382-9. 27. Hermanso n PC, Grewe JM. Examiner variability of several malocclusion indices. Angle Orthod 1970;40:219-35. 28. Grewe JM' Hagan DV. Malocclusion indices: a comparative evaluation~ A,,,tJ OR'mOP 1972;61(3):286-94. 29. Gray AS, Demirjian A. Indexing occlusion for dental public health programs. AM J ORTHOD 1977;72(2):191-7.

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30. Linder-Aronson S. Orthodonties in the Swedish public dental health system. Trans Eur Orthod Soo 1974;233-40. 31. Shaw WC, Richmond S, O'Brien KD, Brook P, Stephens CD. Quality control in orthodontics: indices of treatment need and treatment standards. Br Dent J 1991;170(3):107-12. 32. Evans R, Shaw W. Preliminary evaluation of an illustrated scale for raring dental attractiveness. Eur J Orthod 1987;9:314-8. 33. Brook PH, Shaw WC. The development of an index of orthodontic treatment priority. Eur J Orthod 1989;I 1:309-20. 34. Elderton RI, Clark JD. Orthodontic treatment in the general dental service assessed by the occlusal index. Br J Orthod 1983;10:178-86. 35. Tang ELK, Wei SHY. Assessing treatment effectiveness of removable and fixed orthodontic appliances with the occlusal index. A.',iJ ORTHODD~,rrOFACORTHOP 1990;98:(6):550-6. Reprint requests to: Dr. Endan-a L.K. Tang Dept. of Children's Dentistry and Orthodontics 2IF., Prince Philip Dental Hospital 34 Hospital Rd. Hong Kong