the development of an index of orthodontic...

tjaoftai JcmmmlcfOnJudaula 11 (1989) 309-320 C 19*9 European Orthodontic Society

The development of an index of orthodontic treatmentpriority

Peter H. Brook* and William C. Shaw"* University College Hospital, London

** University Dental Hospital of Manchester, England

SUMMARY The aim of this study was to develop a valid and reproducible index of orthodontictreatment priority.

After reviewing the available literature, it was felt that this could be best achieved by using twoseparate components to record firstly the dental health and functional indications for treatment,and secondly the aesthetic impairment caused by the malocclusion.

A modification of the index used by the Swedish Dental Health Board was used to record theneed for orthodontic treatment on dental health and functional grounds. This index was modifiedby defining five grades, with precise dividing lines between each grade.

An illustrated 10-point scale was used to assess independently the aesthetic treatment need ofthe patients. This scale was constructed using dental photographs of 12-year-olds collectedduring a large multi-disciplinary survey. Six non-dental judges rated these photographs on avisual analogue scale, and at equal intervals along the judged range, representative photographswere chosen.

To test the index in use, two sample populations were defined; a group of patients referred fortreatment, and a random sample of 11 -12-year-old schoolchildren. Both samples were examinedusing the index and satisfactory levels of intra- and inter-examiner agreement were obtained.

Introduction

Whilst many indices exist to record malocclu-sion, it is important to distinguish those thatclassify malocclusions into types (Angle, 1899)and those that record prevalence in epidemi-ological studies (Bjork et al., 1964), from thoseindices that attempt to record treatment need orpriority. Furthermore, indices used to recordtreatment success and treatment difficulty willhave differing requirements.

Many indices have been developed with theintention of categorizing malocclusions into var-ious groups, according to the urgency and needfor treatment (Summers, 1971; Salzmann, 1968;Linder-Aronson, 1974; Lundstrdm, 1977; Gra-inger, 1967; Draker, 1960). Individuals withgreatest treatment need can then be assignedpriority when orthodontic resources are limited,and when the availability of treatment isunevenly spread. Similarly, individuals with littleneed for treatment can be safeguarded from thepotential risks of treatment (Shaw, 1988).

Recent research has called into question many

of the previously held views on the benefits oforthodontic treatment (Shaw et al., 1980). Theremay be small effects on the susceptibility totemporomandibular dysfunction (Roth, 1973;Mohlin and Thilander, 1984) and periodontaldisease (Horupe/ al., 1987;Sandali, 1973;Daviesetal, 1988; Addy etal, 1988). However, so manystudies have been undertaken on these subjects,with differing conclusions, and often only weakstatistical associations, that it is difficult tobelieve that the effect, with a small number ofspecific exceptions, can be anything but minor.There will be a reduced incidence of trauma toincisors where treatment reduces their promi-nence. However, treatment needs to be carriedout early (before the child is 10-years-old) if thepeak incidence of trauma is to be avoided(Jarvinen, 1979). The avoidance of tooth impac-tion is also desirable.

The main benefit to the patient of orthodontictreatment may be in improved aesthetics andsocial-psychological well-being, and additionallythe effect this may have on attitudes to dentalhealth. This has important implications in the

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310 PETER H. BROOK AND WILLIAM C. SHAW

construction of any treatment priority index.Such an index must involve an aesthetic assess-ment, and allow appropriate weighting for thiscomponent.

Subjects and materials

The following criteria were considered to beimportant in the development of a new index oforthodontic treatment need.1. Separate components to record:

(a) Functional and dental health indicationsfor treatment.(b) Aesthetic impairment.

2. For the functional and dental health compo-nent, each occlusal trait thought to contributeto the longevity and satisfactory functioningof the dentition, needs to be defined, andeasily measurable cut-off points between eachgrading need to be established.

In view of the uncertainty of the relative contri-bution that each occlusal trait makes to thelongevity and satisfactory functioning of thedentition and indeed the doubt surrounding theimportance of aesthetics in the provision oforthodontic care, the indices needed to be suffi-ciently flexible to allow for adjustment of cut-offpoints and relativities between the categories, asthe results from adequate longitudinal researchbecome available.

Development of the dental health componentWith these criteria in mind, the index of treat-ment priority used by the Swedish Dental Board(Linder-Aronson, 1974) was used as the basis forgrading the functional and dental health indica-tions for treatment. There are five grades, grade 1representing little or no need for treatment andgrade 5 representing great need of treatment(Table 1). An attempt was made to try toestablish from the literature meaningful valuesfor cut-off points between grades for each occlu-sal trait that represents a quantifiable threat tothe dentition.

Most of the traits are recorded using a milli-metre rule, modified to incorporate a device forangular measurements. Crowding was recordedby measuring the largest displacement betweenteeth in the arches, using a modified version ofthe index described by Lau et al. (1984).

In use, only the highest scoring trait need berecorded, as this determines the grading of thepatient.

The aesthetic componentThe second part of the overall assessment oftreatment priority, was to record the aestheticimpairment contributed by the malocclusion.For this component the SCAN Index (Standar-dized Continuum of Aesthetic Need) was utilized(Evans and Shaw, 1987).

This scale was constructed using dental photo-graphs of 1000 12-year-olds collected during alarge multi-disciplinary survey. Six non-dentaljudges rated these photographs on a visualanalogue scale, and at equal intervals along thejudged range, representative photographs werechosen giving a 10-point scale from 0.5 (attrac-tive dental appearance) to 5.0 (unattractive den-tal appearance) (Fig. 1).

Testing the indexTwo-hundred and twenty-two patients referredto a regional orthodontic centre for advice ortreatment were examined under ideal lightingconditions with radiographs available. Bothcomponents of the index were applied and thepatients were also asked to give their own ratingon the aesthetic scale.Intra-examiner error was estimated by the sameexaminer seeing 67 of these patients on twooccasions, at least one week apart, withoutreference to notes. A second examiner assessed72 of the patients independently of the firstexaminer to estimate inter-examiner error. Tosimulate the use of the indices in a screeningprogramme, 333, 11-12-year-old school childrenwere examined. A cross section of schoolsattended by children from a broad range of socialbackgrounds were visited, and all available chil-dren in the first year of secondary education wereexamined. Each child was examined in the schoolmedical room using an angle-poise lamp forlighting, a simple millimeter rule and a dentalmirror. Again, both components of the indexwere applied, and the self rating recorded on theSCAN scale. In addition a dental surgery assist-ant recorded her rating on the SCAN scale.Forty-six children were chosen at random for re-examination.

Amongst the school sample 58 (17.4 per cent)of the children were undergoing, or had com-pleted orthodontic treatment. The orthodontistinvolved in the treatment of each of thesechildren was contacted so that details of theoriginal malocclusion and information from the

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ORTHODONTIC TREATMENT PRIORITY 311

Table 1 Index of orthodontic treatment need dental health component: for use on patients.

Grade 5—Very greatDefects of deft lip and/or palate.Increased overjet greater than 9 mm.Reverse overjet greater than 3.5 mm with reported masticatory or speech difficulties.Impeded eruption of teeth (with the exception of third molars) due to crowding, displacement, the presence of supernumerary

teeth, retained deciduous teeth and any other pathological cause.Extensive hypodontia with restorative implications (more than one tooth missing in any quadrant) requiring pre-restorative

orthodontics.

Grade 4—GreatIncreased overjet greater than 6 mm but less than or equal to 9 mm.Reverse overjet greater than 3.5 mm with no reported masticatory or speech difficulties.Reverse overjet greater than 1 mm but less than or equal to 3.5 mm with reported masticatory or speech difficulties.Anterior or posterior CTOssbites with greater than 2 mm displacement between retruded contact position and intercuspal

position.Posterior lingual crossbites with no occlusal contact in one or both buccal segments.Servere displacement of teeth greater than 4 mm.Extreme lateral or anterior open bite greater than 4 mm.Increased and complete overbite causing notable indentations on the palate or labial gingivae.Patient referred by colleague for collaborative care e.g. periodontal, restorative or TMJ considerations.Less extensive hypodontia requiring pre-restorative orthodontics or orthodontic space closure to obviate the need for a

prosthesis (not more than 1 tooth missing in any quadrant).

Grade 3—ModerateIncreased overjet greater than 3.5 mm but less than or equal to 6 mm with incompetent lips at rest.Reverse overjet greater than 1 mm but less than or equal to 3.5 mm.Increased and complete overbite with gingival contact but without indentations or signs of trauma.Anterior or posterior crossbite with less than or equal to 2 mm but greater than 1 mm displacement between retruded contact

position and intercuspal position.Moderate lateral or anterior open bite greater than 2 mm but less than or equal to 4 mm.Moderate displacement of teeth greater than 2 mm but less than or equal to 4 mm.

Grade 2—LittleIncreased overjet greater than 3.5 mm but less than or equal to 6 mm with lips competent at rest.Reverse overjet greater than 0 mm but less than or equal to 1 mm.Increased overbite greater than 3.5 mm with no gingival contact.Anterior or posterior crossbite with less than or equal to 1 mm displacement between retruded contact position and intercuspal

position.Small lateral or anterior open bites greater than 1 mm but less than or equal to 2 mm.Pre-normal or post-normal occlusions with no other anomalies.Mild displacement of teeth greater than 1 mm but less than or equal to 2 mm.

Grade 1—NoneOther variations in occlusion including displacement less than or equal to 1 mm.

study models could be used in place of therecordings taken at the school visits. In practice,as many of the children were only just commenc-ing treatment, the gradings were little changed.

Results

Reproducibility of the index

Dental health component

Intra-examiner agreement ranged from a Kappavalue of 0.837 for the referred population seenunder ideal conditions, to 0.754 for the non-referred population. In total there were 14 errors

out of 118 re-tests and in all cases the disagree-ment was only by one grade. Guidelines for theinterpretation of the Kappa statistic (Landis andKoch, 1977) are shown in Table 2.

Inter-examiner agreement ranged from 0.731-0.797. In total there were 21 out of 154 measure-ments that were not agreed. There were only 2cases where the error was by more than onegrade.

SCAN componentFor the referred sample there were three raters;the patient and the two examiners. This gave twopatient ratings (PI and P2), two ratings by

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81:4 PETER H. BROOK AND WILLIAM C. SHAW

05

1-5

25

35

45

Figure 1 The SCAN Scale. Originally presented in colour in a horizontal arrangement. 0.5 extreme left. 5 extreme right.

Table 2 Guidelines for the interpretation of Kappa.

Kappa statistic Strength of agreement

<0.000.00-0.200.21-0.400.41-0.600.61-0.800.81-1.00

PoorSlightFairModerateSubstantialAlmost perfect

examiner 1 (PB1 and PB2), and one rating byexaminer 2 (WCS). The examiner reproducibi-lity, and the comparability of patient and exa-miner ratings, were investigated using Pearson'scorrelation coefficient. The results are listed inTable 3 with the number of repeat examinationsin parenthesis.

Whilst the correlations between the orthodon-

Table 3 Examiner variability. Pearson's correlationcoefficients for SCAN.

Referred Population

PB1

PB2

PI

P2

PB2

0.87(72)

PI

0.50(82)

0.45(72)

P2

0.36(72)

0.40(72)

0.67(72)

WCS

0.71(82)

0.73(72)

0.37(82)

0.29(72)

tists were quite high, they were poorer than thoseobtained by Evans and Shaw (1987), where self-retaining lip retractors were used during theorthodontists' and the patients' assessments. For

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this reason, self-retaining cheek retractors wereused routinely for the examination of the non-referred sample.

In the school survey, 46 subjects were ratedtwice by the orthodontist (PB) on the SCANscale. Additionally, there was a rating by thedental surgery assistant on two occasions (DSA1and DSA2), and two subject ratings (SI and S2).Again, these relationships were examined usingPearson's correlation coefficient (Table 4).

On this occasion intra-examiner agreement forthe orthodontist (PB) was better. The DSA'sreproducibility was less good. There was how-ever, superior inter-examiner agreement on thisoccasion. There was also better correlationbetween the subjects' and the professionals'ratings.

General features of the referred and non-referredpopulationsThe numbers of patients falling into each DentalHealth Index grade for each group are illustrated

Table 4 Examiner variability. Pearson's correlationcoefficients for SCAN.

DSA1

DSA2

SI

S2

PB1

School

DSA2

0.78(46)

Population

SI

0.66(46)

0.61(46)

S2

0.70(46)

0.69(46)

0.78(46)

PB1

0.80(46)

0.85(46)

0.64(46)

0.68(46)

PB2

0.81(46)

0.88(46)

0.61(46)

0.69(46)

0.95(46)

Table 5 Distribution of Dental Health grades.

Dentalhealthgrade

Grade 1Grade2Grade 3Grade 4Grade 5

Total

Referred population

Numbers Percentage

11140

11239

203

0.55.4

19.755.219.2

100.0

School population

Numbers Percentage

2493

1079217

333

7.227.932.127.6

5.1

100.0

in Table 5, and Figs. 2 and 3. The SCAN Indexscores are illustrated in Table 6, and Figs. 4 and5.

Discussion

Reproducibility

Dental health component

In general, the reproducibility of this index wasvery good. The same grade was re-chosen 86.4per cent of the time with different examiners, andin 93 per cent of cases for the same examinerunder the more ideal clinic setting (the referredpopulation).

The common traits causing disagreement, indescending order of frequency were; crowding,increased overjet, crossbites and overbites.Crowding represents a problem in recordingwhen the patient is in the mixed dentition.Further refinement of the index in terms of themixed dentition analysis of crowding, may leadto an improvement in reproducibility.

Evidently, the less than ideal conditions of theschool examination resulted in poorer reproduci-bility. Should reproducibility levels similar tothat of the referred population be required, thenbetter lighting, better patient seating facilitiesand a more relaxed work rate would be required.

SCAN component

Whilst the correlation coefficients for the SCANratings were reasonably high for the schoolsurvey, they were less satisfactory for the referredpopulation. It was felt that this may have beendue to the omission of the self-retaining lipretractors for this sample.

During the original development of the index,both front and side views of the dentition wereavailable. This enabled conditions such as largeoverjets to be more readily assessed. During thesurveys, it was noted that the areas around 1.5and 4.0 on several raters graphs, showed slightinconsistencies. An inspection of the indexdemonstrates the difficulties that may be leadingto these effects. Both the representations of 2.0and 4.5 show increased overjets, that a lay personin the absence of a side view, may not find toodispleasing.

So, in summary, incorporation of side viewsmay assist in identifying large overjets. Someguidelines for assessing the relative attractivenessof features not depicted on the scale, may also be

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REFERRED POPULATION DHI

1 2 3 4 5

DENTAL HEALTH INDEX SCOREFigure 2 Distribution of ratings for the Dental Health Index obtained from examination of 222 patients referred to a regionalorthodontic centre.

desirable. Self-retaining cheek retractors are auseful aid to recording dental aesthetics.

The referred sampleAs expected, the referred sample showed a largeproportion of patients scoring in the highergrades of the Dental Health Index, with all but 6per cent in the highest three grades. The ortho-dontists' SCAN ratings showed a similar shift tothe unattractive side. The patient ratings showedthis effect to a much smaller extent.

The school populationThere was a much more even spread of patientsamongst the grades of the Dental Health Indexfor this population, with approximately onethird of the subjects in grade 3, and one thirdeither side of this. The professional ratings using

the SCAN Index, showded a distribution skewedtowards the attractive end of the scale. Thepatient ratings are skewed even further towardsthe attractive end of the scale, i.e. there was atendency for subjects to overrate their dentalattractiveness.

Comparison of the two samplesFrom an overview of the data recorded from thesamples, it appears quite obvious that there aresignificant differences between them. Indeed themedian test and the /-test demonstrate thisreadily for the Dental Health component and theSCAN component respectively (p< 0.0001).

However, the findings from the two surveysare not directly comparable. Firstly, the referredsample had a wide age spread, and secondly,when applying the Dental Health component to

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SCHOOL POPULATION DHI

1 2 3 4 5

DENTAL HEALTH INDEX SCOREFigure 3 Distribution of ratings for the Dental Health Index obtained from examination of 333 unselected schoolchildren.

the referred population, the examiners hadaccess to radiographs. For the school sample, itwas necessary to set criteria for such parametersas unerupted or missing teeth, i.e. except forincisors and first molars, all teeth were assumedto be present, at age 11-12 years, premolars andcanines were assumed to be unerupted but notimpacted, missing upper lateral incisors andlower incisors were assumed to be developmen-tally absent whereas missing upper central inci-sors and first molars were assumed to have beenextracted.

In an attempt to overcome this, a sub-group of25 from the referred sample, with a similar agerange to the school sample was selected. Anyconditions that would have required radiographsto confirm the diagnosis, were regraded using the

Table 6score).

SCANrating

0.51.01.52.02.53.03.54.04.55.0

Total

Distribution of SCAN

Referred

Numbers

02

191728333948

88

202

Population

Percentage

0.01.09.48.4

13.816.319.223.6

3.93.9

100.0

ratings (Orthodontist

School 1Population

Numbers Percentage

165465596233261251

333

4.816.219.517.718.69.97.83.61.50.3

100.0

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REFERRED POPULATION SCAN

4 5 6 7

SCAN RATING8

Figure 4 Distribution ot raungs for the SCAN index obtained from examination of 222 patients referred to a regionalorthodontic centre.

criteria set for the population seen withoutradiographs.

It was still evident that the samples were drawnfrom different populations (Mest p< 0.001 forthe SCAN ratings; median test p< 0.001 for theDental Health ratings). These tests seeminglyvalidate the index, at least in terms of thepriorities of patients or dentists in bringing aboutreferral to an orthodontist.

Comparison with previous methods of recordingtreatment priorityAngle's classification (Angle, 1899) has beenshown to have poor reproducibility (Gravely andJohnson, 1974) and has no usefulness in record-ing treatment priority. For epidemiological use,the registration techniques described by Bjork etal. (1964) and Baume et al. (1973) may be quite

acceptable as it has been shown that most of thetraits can be recorded with a high degree ofprecision (Helm et al., 1975; Helm, 1977) with upto 80 per cent agreement. However in their pureform they do not record treatment priority.

The allocation of weighting factors to traitscan give an overall figure that is intended torepresent a score of severity, and thus treatmentpriority. Several indices of this type have beendeveloped (Summers, 1971; Draker, 1960; Gra-inger, 1967). Correlation coefficients for exa-miner agreement for such indices have rangedfrom a Spearman correlation coefficient of 0.903(Summers, 1971) to as low as 0.34 (Albino et al.,1978) in a community screening setting. Thevalidity of such indices relies on acceptance of theauthors' weightings.

Indices based upon the classification of mor-

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SCHOOL POPULATION SCAN

30

PERCENTAGE

2 5 -

20 -

15 -

1 0 -

5 -

19.517.7

18.6

9.97.8

3.6

1.50.3

1 82 3 4 5 6 7

SCAN RATINGFigure 5 Distribution of ratings for the SCAN index obtained from examination of 333 unselected schoolchildren.

10

phological traits rely on the subjective opinion ofan experienced judge to define the dividing linesbetween each trait (Linder-Aronson, 1974;Lundstrom, 1977; Malmgren, 1980). Used assuch, the percentage concordance ranges from55.9 to 74.6 per cent (Malmgren, 1980).

Subjective clinical opinion alone has agree-ment of about 80 per cent in most studies(Bowden and Davies, 1975; Helm et ai, 1975)but the validity of such judgements dependsupon the examiners' knowledge of the harmfuleffects of malocclusion. In addition, inexper-ienced examiners will find it difficult to applysuch techniques.

The orthodontic index of treatment need"described in this report has examiner agreementlevels that compare well with any of thosepreviously described (80.5-93 per cent). As its

development was based upon a full analysis ofthe available literature (Brook, 1987) and theexperience gained from a longitudinal survey(Shaw et ai, 1986), it is not felt that its validitycan be inferior to that of other indices. Theinclusion of a separate index to record aestheticimpairment removes the most subjective elementfrom indices of this kind. Good levels of agree-ment for this component have been demon-strated (Pearson's correlation coefficient valuesfrom 0.71-0.95).

Some support for the validity of the indexcomes from the observation that fewer subjectsin the lower grades were referred for orthodonticadvice. The extent to which it represents com-mon professional opinion is presently beingevaluated. However, true validity (i.e. that theindex measures what it purports to measure)

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Table 7 Interrelationship between the SCAN and Dental Health Index scores.

DHIGrade

12345

Total

(Cumulative

SCAN Score0.5

2.14.24.54.84.8

4.8

1.0

5.415.619.520.421.0

21.0

Percentages)

1.5

6.325.837.239.640.5

40.5

2.0

6.631.851.357.358.5

58.5

2.5

7.234.860.975.376.8

76.8

3.0

7.235.164.584.986.7

86.7

3.5

7.235.165.791.594.5

94.5

4.0

7.235.167.293.998.2

98.2

4.5

7.235.167.294.899.7

99.7

5.0

7.235.167.294.8

100.0

100.0

Total

7.235.167.294.8

100.0

100.0

must await the compilation of a greater body ofknowledge than that which is currently available.It may accurately reflect contemporary profes-sional opinion, but this may be erroneous.

Epidemiological uses for the indexDuring testing of the index on the school sample,it was felt that it represented a simple, quick andreasonably reproducible method of recordingorthodontic treatment need. As all the traits aresimple to record, it may be possible for less highlytrained personnel to apply the index, followingsuitable training and calibration.

Further development of the index

As developed so far, the index records the dentalhealth need for treatment, and the aestheticimpairment, and by implication the social-pschological need for treatment. As yet, noattempt has been made to combine these into anoverall assessment of treatment need, or to definescores below which treatment should be with-held.

To assist discussion in this area, a tableshowing the cumulative percentages of patientshaving varying combinations of the DentalHealth grades, and the SCAN ratings has beenconstructed from the non-referred sample (Table7).

Many authors quote figures of around 50 percent for the percentage of children who wouldbenefit from orthodontic treatment (Gardiner,1956; Haynes, 1982; Foster and Walpole Day,1973). From Table 7, it can be seen that thisnumber would be obtained if patients scoringgrade 3 or less on the Dental Health Index and2.0 or less on the SCAN scale were excluded (51.3per cent), leaving 48.7 per cent. Other combina-

tions could produce a similar percentage. Analternative method would be to combine thescores from the two components to give anoverall score, then define limits based on thisfigure.

Eventual definitions of cut-offs must reflect thesetting in which treatment would be providedand include a consideration of the success rate ofthe treatment which would be available, theiatrogenic risks, and the cost (Shaw, 1987).

Conclusions

An index with two components has been devel-oped to record orthodontic treatment priority.The first of these components records need fortreatment on dental health and functionalgrounds. The second component records theaesthetic impairment, and by implication, thejustification for treatment on social-psychologi-cal grounds.

The indices were tested on a sample of patientsreferred for orthodontic treatment and advice,and on a random selection of 11-12-year-oldschool children. It was easy and quick to use andhad acceptable reproducibility. True validationof such an index must await the emergence offurther research data on the effects of malocclu-sion, but the present index can be adaptable tonew information. Work is currently in progressto gauge the extent to which the index reflectscommon professional opinion.

Defining specific ranges within which patientsshould, or should not be offered treatment has

'not been attempted but a mathematical modelhas been suggested that can define combinationsof the gradings that will encompass varyingproportions of a target population.

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Acknowledgements

The authors would like to thank Mr G. O. Taylorand his staff for providing access and assistancefor the school visits, Mrs H. Worthington andMrs C. Mitropoulos for advice with the studydesign and statistics, Mr J. Sinclair for computa-tional assistance and Mrs C. Corkill for acting asa scribe. The study was supported in part by agrant from the DHSS and BLG.

Address for correspondence

Professor W C ShawDepartment of OrthodonticsUniversity Dental Hospital of Manchesterand Turner Dental SchoolHigher Cambridge StreetManchester M15 6FHEngland

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international conference on the occasion of the 25thAnniversary of the Orthodontic Department of theUniversity of Nymegen, The Netherlands. October 22-24,1987. Editors: C F A Moorrees and F P G M van derLinden. Pp 63-81

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Summers C J 1971 The occlusal index: a system for identify-ing and scoring occlusal disorders. American Journal ofOrthodontics 57: 552-567

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the development of an index of orthodontic...

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