- Email: [email protected]
Longitudinal evaluation of the treatment priority index (TPI)
RI
RTICLES
evaluation of the Tre I) Joseph Ghafari,* Stephen A. Locke,* and J. Marvin Bentley** Philadelphia,
Pa.
The Treatment Priority Index (TPI) is an epidemiologic tool used to rank malocclusions and assess the need for orthodontic treatment. The purpose of this study was to (1) evaluate the pre~ictab~li the TPI as an indicator of malocclusion severity, (2) evaluate the effect of orthodontic treatment on TPI values, and (3) compare the results with a national survey of American children aged 6 to 11 years and 12 to 17 years conducted by the United States Public Health Service. The TPI was recorded annually in a young student population of Juniata County, Pa., from 1975 to 1979, and later in 1985. The mean values of the TPI did not reflect the range of severity in the p~pul~t~o~. For this reason the Malocclusion Severity Scale (Burlington Growth Center) was used to identify four groups in 1985. Each group was tracked back to 1975. Further evaluation investigated the role af individual factors contributing to malocclusion over time (tooth displacement and occlusal ?ect~r$). The conclusions are as follows: (1) the TPI is a valid epidemiologic indicator of malocclusion but does not predict the severity of individual malocclusions in the permanent dentition, (2) TPI values decrease with orthodontic treatment, and (3) the average TPI values for this population were h than the national average between 6 and 11 years of age and slightly lower in late adolescent Xiewithin a treatment-need range of slight to elective. A characterization of treatment need relative to malocclusion severity that is different from the available scale is suggested. (AM J ORTH~D RTHOP
1989;96:382-9.)
he Treatment Priority Index (TPI) was developed to determine whether orthodontic treatment reduced the severity of malocclusion below the level of public health significance.’ Thereafter the TPI’s usefulness was recognized for epidemiologic surveys of malocclusion and as a screening tool in public health programs. 2,3 The TPI was based on the evaluation of models or clinical examinations of 375 12-year-old children. ’ The items measured were restricted to those describing an occlusal anomaly, excluding factors related to cause (such as habits), or measurements related to malocclusion per se (such as intercanine width). Set patterns or combinations of the selected items defined syndromes. A total of seven syndromes evolved defining the incisor relationship horizontally (underjet, overjet) and vertically (overbite, open bite), the occlusion of the buccal segments (posterior crossbite), and tooth displacement (rotation and crowding) (Fig. 1). On the basis of multiple regression analysis, the syndromes were weighted Supported in part by the Robert Wood Johnson Foundation 10188. *Department of Orthodontics, School of Dental Medicine, University sylvania. **Division of Public Affairs, Penn State University. Lllll14Q6
ID
No.
of Penn-
Table f. Levels of severity of a malocclusion as established by the Malocclusion Severity Estimate (MSE), the Treatment Priority Index (TPI), and for the present study
Virtually classic “normal” occlusion Minor manifestations of malocclusion and treatment need is slight Definite malocclusion but treatment elective Severe handicap, treatment highly desirable Very severe handicap with treatment mandatory
0 1-3
c3.99
4-6
4-6.99
7-9
T-9,99
>lO
>I0
according to the permanent first molar ~elatio~isb.i~,mesio-, neutro-, and distoclusion. A constant, also corresponding to the molar occlusion, was added to the TPI score. The final TPI value could range from 0 to >lO. The precursor of the TPI was the Malocclusion Severity Estimate (MSE) developed by Grainger at the Burlington Orthodontic Research Genter.4 Unlike the TPI, the MSE score was that of tbe syndrome with the
Treatment PrioriQ
Volume 96 Number 5
(7) Mesiochtsion
6) Distoclusion -
FIRST RELATION
MOLAR Choose
appropriate
column
Index
-
-
0 = 2
” = 2
8 1 N -
B G N
Weights
-
mm 9t 9
(1) upper overjet
1
(2) Lower overjet
2 3 3+ (3)
ti 1
Overbite
In
C,DW” third5
Bite 3/3+ 213-313
a-213
(4)
Opsnbite mm.
Co”nt about placed
c2 2-4 4t
In
CONSTANT I_.
WI
6
?iez,
(0.
2
rotated d!s2 mm.
MAX.TO BUCCAL
NO.
s.4 1.5 1.8 1.1 .6 .3 -
-
2 .4 .6 1.0 1.4 !.O -
.3 .6 L.l 1.8 t.5 1.4 -
1.3 2.9 5. 8.0 lot 1Dt -
.3 .6 1.1 1.8 2.5 3.4 -
.2 .4 A 1.0 1.4 LO -
!.9 1.5 .5
3.8 LO .7
8.0 4.1 1.5
3.8 2.0 .-I
::: .5
-
-
-
-
-
1.5 2.s 4.:
2.0 3.8 6.3
4.1 8.0 1Dt
2.0 3.8 6.3
I.! 2.2 4.c
-2 .: .I 2
-II .3 .5 .8 1.1 1.5 1.9 2.5 3.0
-2 1.1 1.9
--Ii
7
G -
0.27 --r;
F-
3.5
0
MAXTO LINGUAL
.O .4 .cl
Retrognathism
:t .2
WElGHTS
IS TREATb Fig.
0
.3 .5
,94:03 5.9 7.7 9.7 101
2)
NO. Weight
S1JM OF
1Dt 10+ 8.0 5.1 2.9 1.3 -
1:; 1.: 1’ 2:; 5.' = 0
1 no
gigi 2ULQB
.4 .5 .a 1 ':6 .?I -
Prognathism
Openbite
-
teeth 45’or about
Cwnt teeth rotated >45’=or displaced more than 2mm Y 2 Total score)
:: .O .6 .4 .2 -
1.01
31 2.3
4) 4.2
IT PRIORITY
1. Treatment
51 6.5
1:: 1.5 1.9 2.5 3.0
4.9 6.2 7.7 2.7
.: .! .! PRESENT
it 1.: 1’ 2:;
/ &y.& Max. EXP%lSlOl? Syndroma
i L.9 haax. colla~x Syodror
s.s E=zzz ma
-T --ii2 6 more 9.4
10
(TPI)
data
-l-
INDEX
Priority
largest value, regardless of the scores of the other syndromes. In the MSE the absence of occlusal disorders was not scored as zero. The TPI also differed from the SE by deleting potential tooth displacement (mixeddentition space analysis) and by rating distoclusion and mesioclusion equally. Levels of severity established from the MSE are shown in Table I. Popovich and Thompson5 compared the TPI with the subjective appraisal of the orthodontist. They used models from the Burlington Orthodontic Research Center at 3, 6, 9, 12, 14, and 16 years of age. Because of various stages of eruption and growth (for example, the eruption of the incisors not allowing the accurate evaluation of overjet and overbite), some syndromes were
Index
collection
form.
eliminated or modified at certain ages. The authors concluded that the TPI was a useful epidemiologic index at ages 3 through 16. The TPI values were more consistent in indicating prevalence of malocclusion than the subjective appraisal of the orthodontist because of the latter’s relatively high weighting for rotated or displaced teeth. Between 1963 and 1965, the TPI was used by the United States Department of Mealth, Education, and Welfare for a national survey of 6 to 1 l-year-old American children2 A similar evaluation was later conducted ( 1966 to 1970) of American youths aged 12 to 17 years. 3 Both surveys underscore the importance of quantifying occlusal disorders for public health purposes and the
Glzafari, Locke, and Bentley
MALES,TAEATED
400
FEMALES, TREATED
300 FEMALES, NO TREATMENT 200
100 MALES, NO TREATMENT
75
76
77
70
79
85
YE.444
Fig. 2. Sample size, tracking population and girls, treated and untreated.
backward
usefulness of the TPI as a scoring system to rank malocclusions. Yet the long-term predictability of the TPI has not been established. The above-mentioned national surveys were cross-sectional studies that provided information about the rate of malocclusion and need for orthodontic treatment at different ages, but not the longitudinal development of malocclusion. The current study is a longitudinal evaluation of the TPI in a rural Pennsylvania population. The goals were to (1) evaluate the predictability of the TPI as an indicator of the severity of a malocclusion, (2) evaluate the effect of orthodontic treatment on TPI values, and (3) compare the results with the above-cited national surveys conducted by the United States Public Health Service.
Students in the public schools of Juniata County, Pa, were examined annually between 1975 and 1979 to evaluate the health effects of dental education. As part of this study that focused mainly on caries prevention, the orthodontic TPI (Fig. 1) was recorded to evaluate the prevalence of malocclusion. When first examined, the students were just entering the transitional stage of dental development. The average age was 6 years. TPI recording was postponed to the next year on the basis of the following criteria: (1) uneruption of the first permanent molars and/or ermanent central incisors, (2) extraction of the first molars, and (3) active orthodontic treatment. To establish reliability and consistency, the data, except for baseline data, were collected between the end of April and the beginning of June each year for the 4 years of the study. To ensure calibration, the four examiners (a dentist, two dental hygienists, and a registered nurse) attended educational seminars, in-house
from
1985
to 1975,
showing
distribution
of boys
clinical calibration exercises, and external evaluations. Pair-wise comparability studies were pe~o~ed during the annual examinations to monitor inter- and intraexaminer variability. They were designed in four different models: Model 1. Children involved in the comparability studies were evaluated in succession by each examiner. These observations were performed before the field examination period. Model 2. Each child was examined in the morning by one examiner and again in the afternoon by the same examiner to evaluate overall intraexaminer comparability. These evaluations were also performed before the held examination period. Model 3. Each child was examined first by one examiner and then by a second examiner in immediate succession. Model 4. Each child was evaluated by one examiner in the morning and again in the afternoon by the same examiner. In contrast to models 1 and 2, evaluations per models 3 and 4 were conducted t~ou~bout the entire length of the field examination series. In all of these four approaches, the comp~~bility between or within the examiners was never less than 9 1% . This figure represents a high level of agreement between examiners and implies that differences that might be observed as outcomes of the program, if they are greater than lo%, cannot be attributed to bias in the data resulting from examiner errors6 The data were recorded in the field on forms that were collected and checked for legibility at the end of each day and subsequently entered into a mainframe computer. Orthodontic TPI data were keypunched. A printout was then generated and compared with the initial data to verify the reliability of the input. When an input discrepancy was observed, correction was
Treatment
made. In case of incomplete information, the form was referred back to the field for resolution through reexamination if required. In November 1985, a follow-up study included those children of the original cohort still in the Juniata County school system. The goal of the follow-up study was to determine whether there were any long-term effects of the dental health education program. One examiner was checked against an orthodontist (S.L.) and an examiner from the original study, following the guidelines of the original study protocol. Examiner reliability was calculated from 25 (approximately 6%) repeated evaluations. Intraclass correlation on repeated measures produced an estimate of reliability for single measures of TPI equal to 0.87. The data were entered into an IBM-PC XT. Reliability of input was verified by the same methods used for the original data. However, if a problem or error was noted, it was not possible to return the form back to the field and the data for the individual were deleted. The initial data from the mainframe computer were transferred to the IBM-PC XT and the files were merged. The students still in the Juniata school system in 1985 who had participated in the original study numbered 442, of whom six were eliminated. The distribution of this group by sex and history of orthodontic treatment or no treatment is shown in Fig. 2. Not all the students examined in 1985 had an evaluation record every year between 1975 and 1979. The absence of these records was due to at least one of the exclusion criteria mentioned above. However, each of the students evaluated in 1985 had at least one record between 1975 and 1979. Differences in TPI scores over time were evaluated by paired t tests between matched samples of subjects.
The mean TPI values for orthodontically treated and untreated students and for both groups are shown in Fig. 3. The difference in TPI values between 1979 and 1985 were statistically significant (p < 0.01) for both treated and untreatd groups, but not for the total population. Since the 1985 TPI values for the treated group were less than 7, and the 1985 Treatment Priority Indices for the untreated group ranged between 0 and 20, the Malocclusion Severity Estimate (MSE) scale (Table I) was applied to the latter group. The severity groups thus established were ~3.99, 4.0 to 6.99, 7.0 to 9.99, and 210. Each group was then tracked backward through previous examination years to evaluate the TPI change over time. The distribution of students within these oups is illustrated in Fig. 4. There were more boys
Mean
Priority
Index
TPI ,treat~ent
6
Fig. 3. Mean TPI values for students who had received orthodontic treatment, those who had not, and the total of both i*p < 0.01). groups. Distribution of population is shown in Fi
than girls in all groups, and more students in the ~3.99 and 4.0 to 6.99 groups than in the more severe groups. Fig. 5. illustrates the mean TPI values over time as they developed into the 1985 severity groups. A statistically significant change was noted between 1979 and 1985 for all groups (p < 0.01) except the 4.0 to 6.99 group. The starting point for all groups fell within a range of 3 to 7 TPI values. At this point the separate contributions to the TPI by the occlusion and tooth displacement were analyzed. When all the individual occlusal factors (horizontal, vertical, cross-lingual, cross-buccal, and the constant) were grouped together as occlusal or interarcb factor, their mean value was highest in the 1985 210 group: 10.27 in girls and 8.0 in boys. A statistically significant increase in occlusal values (p < 0.01) was observed in the female 210 group between 1979 and 1985. Although statistically significant (p < O.Ol), a slight decrease of the occlusal values in the male ~3.99 group was observed for the same time period. The intraarch factor, represented by the displacement factor, showed opposite trends for boys and girls than did occlusal factors. The mean value in the 1985 > 10 female group was 3.18, lower than the corresponding value for the male group, 5.59. In both sexes mean values of the displacement factor increased between 1979 and 1985 in the most severe tracks (7.0 to 9.99 and 3 10). However, rate and amount of increase were greater for boys than girls. Statistically significant differences were noted only for the G3.99 and 210 male groups between 1979 and 1985. The mean TPI for the untreated group, the mean TPI for all (treated and untreated students), and the
3
Gkafari,
Locke,
and Bentley
75
76
77
78
79
85
YEAR Fig.
4. Distribution
of untreated
students
by year
and
1985
severity
track.
Table II. Comparison of mean TPI values from U.S. Public Health Service (USPHS) studies of 6 to 1l-year-old children’ and 12 to 17-year old youths3 with this study’s mean TPI for untreated and both treated and untreated (all) students
AI1 Untreated USPHS *Not
computed
4.1 3.7 3.3 because
4.9 4.3 3.2 of small number
4.5 3.9 3.1
4.2 3.9 3.2
4.2 3.7 3.2
+ * 5.2
* * 5.1
4.3 4.7 5.0
3.6 3.6 5.1
4.6 5.0 4.8
4.4 4.5 4.9
of observations
total mean TPI of the U.S. Public Health Service (USPHS) study are shown in Table II. There is a difference of approximately 1 TPI unit from age 6 to 10 years between the mean TPI for all and the USPHS total mean. The difference decreases to 0.5 at age 11 because of an increase in the USPHS values from age 10 to 11. When differentiated by sex, male values were similar at age 11. The USPHS survey of 12 to 17-yearold youths showed higher TPI values (approximately 0.5 unit) than the present study in boys, girls, and the total population.
The first objective of this study was to evaluate the as a longitudinal indicator of malocclusion severity. The TPT trends were in an opposite direction for orthodontically treated and untreated students (Fig. 3). The mean TPl scores in the treated group up to 1979 were greater than 4---that is, in a range indicating a definite malocclusion calling for elective or highly desirable treatment (Table I). In this respect the TPI clearly gauged the original severity of malocclusions and their
TPI
4.2 3.7 3.1
improvement through treatment, altbough the range of TPI scores in 1985 reached up to 7. This range may reflect (1) an early treatment without successful interception of a developing malocclusion, (2) compromised results of orthodontic treatment, or (3) i~ad~¶~ate retention and relapse of treatment results. In contrast the mean TPI scores for the untreated group, although statistically significant between 1979 and 1985, showed an increase of only 0.5 in this time period and did not reflect the wider range of 1985 TPI values (0 to 20). Severity channels were thus defined according to the MSE scale and tracked back over time. This approach was more descriptive than mere averages in evaluating the untreated group. Indeed the 1975 and 1985 mean TPI values for this group (Fig. 3) would indicate a constant level of severity calling for elective orthodontic treatment (MSE, Table I). The accuracy of this statement was challenged when severity tracks were established. From 1975 to 1979, a period when most students had a transitional dentition, the four tracks, at times overlaping, describe an envelope within a range of 4
Volume 96 5
Treatment Priarity
Index
Number
Table III. Percentages of children according to malocclusion severity between the U.S. Public 4th Service surveys of 6 to 1 l-year-old
TPI85 >lO.W
TPI85 7.0-9.99
cl
24.4 39.0 22.4 8.7 5.5
1-3 4-6 7-9 210 *Data adapted Harvey.3
from
Kelly,
Sanches,
TPI 85 4.06.99
11.0 34.8 25.2 13.0 16.0 and Van Kirk’
and Kelly
TPl85 <3.99 0 74
76
78
80
82
84
86
YEAR
and
to 7 in the untreated group (Fig. 5). Predicting malocclusion severity from values within this envelope is questionable in view of the 198.5 outcome, except perhaps for two groups: (1) the ~3.99 1985 TPI group, which shows the least degree of severity between 1975 and 1979, and (2) the 210 1985 TPI group, which exhibits the highest degree of severity in the same time period. The previous observations suggest that the TPI is an acceptable indicator of malocclusion, a conclusion supported by Popovich and Thompson.5 However, malocclusion predictability may not depend on TPI values recorded in the transitional dentition. The inability of the TPI to depict crowding of the unerupted permanent canines and premolar-s could be a reason for missing an increase in malocclusion severity over time. Although the analyses of correlation coefficients, stepwise regression, scattergrams, and percentage contribution by each individual factor to TPI total score showed that a change of the latter over time could not be attributed to a single factor, the stepwise regression analysis ranked the displacement factor first in boys and second in girls in 1985. Popovich and Thompson’ recommended increasing the weighting for displaced teeth to improve the age-specific reliability of the TPI. A mixeddentition space analysis would clearly improve the predictability of the TPI,’ as would the inclusion of skeletal, functional, and neuromuscular disturbances. However, an original premise in developing the TPI was the possibility that technicians-not necessarily orthodontists-could collect the data. Additional records, not only adequate training, would be required to perform space analysis. The results also suggest that in the 210 1985 TPI group, crowding and rotation (displacement factor) were more severe in male than female subjects; the opposite seems true for the occlusal factors. This finding may indicate that growth contributed to the devel-
Fig. 5. Average TPI values tracks for untreated students
in the different I%5 only (*p < 0.01).
TPI
severity
opment of less severe occlusal conditions and greater tooth displacement in boys. This suggestion is based on the assumption that growth would have proceeded over a longer period of time and possibly in greater amounts in boys than in girls. Skeletal and dental ages would provide better references than chronologic age by relating maturational stages of growth to treatment need of developing malocclusions. An assessment of the TPI over a period of 18 months in 216 subjects aged 3 to 1%years showed a gradual, but not statistically significant, increase of the index when displayed by dental developmental stage--that is, primary, mixed, and permanent detentions .7 However, only average values of the TPI were considered by the authors of the study. In answer to the second objective of our investigation, orthodontic treatment indeed affected TPI values and was applied in patients who obviously had a severe malocclusion (Fig. 3). Treatment app~e~tly occurred between 1979 and 1985, an observation suggesting that orthodontic therapy was probably carried into the permanent dentition, at least for most students. Insofar as the TPI reflected the effect of treatment, its validity is enhanced. Its use to gauge the efficacy of orthodontic treatment, but not necessarily early (preventive/ interceptive) treatment, is evident from the results of this study. Comparison of the mean TPI values from the rural Pennsylvania population, particularly those of the untreated group, with those of the USPIIS surveys2.3 shows differences in magnitude, but generally similar trends (Table II). The TPI values in the USPHS data increase between ages 10 and 11, probably reflecting the dentitional transition from primary to permanent. IIowever, the mean value recorded at age 11 was less than 4, within the area of “minor manifestations of malocclusion with a slight treatment need” (MSE scale). Starting at age 12,
Ghafari,
Am. J. Orthod.
Locke, and Bentley
the mean ‘SPI values increase to a higher level of severity in the area of “definite malocclusion but treatment elective.“3 This increase of severity with age also was demonstrable when we compared percentages of children according to malocclusion severity between both national surveys-that is, 6 to 11 -year-old children’ versus 12 to 17-year-old youths3 (Table III). The most significant differences seem to occur between the ends of the scale-that is, normal occlusion (24.4% vs. 11%) and very severe handicap (5.5% vs. 16%). The present longitudinal study indicates trends similar to those of the USPHS study for the >10 and 7 to 9.99 severity groups and possibly the 4 to 6.99 group if one considers the small difference between the younger (22.4%) and older (25.2%) children in the national surveys (Table III). However, although the combined percentages of children with no or minor manifestations of malocclusion (MSE = 0 and 1 to 3) are higher in the 6 to 1 l-year-old children than in the 12 to 17-yearold youths, the present study shows that the average TPI values of c3.99 remain in the low severity track over time. No definite conclusion may be formulated about this difference, particularly since both USPHS surveys included children who had orthodontic treatment (2.5% and 10.7% in the 6 to 11 and 12 to 17year-old groups, respectively) and whose TPI values were not presented separately. Population differences and the nature of the experiments are probable contributing factors. Although Juniata County is a rural region and the students formed a somewhat homogeneous group mainly of European background, the USPHS study randomly selected children of presumably more varied backgrounds and regions. The government’s investigation was a cross-sectional study based on age; the Juniata County survey was set as a longitudinal study. Quantifying malocclusion is needed for epidemiologic and public health programs. It is nonetheless a complex problem since many variables define a malocclusion. Indeed the existence of various methods1.3.8-2’that attempted to quantify the characteristics of malocclusion stems from disagreement over the definition and importance of those characteristics. Analyses considering tooth displacement, occlusal relationships, and facial, skeletal, and functional parameters should be expected to accurately reflect the complexity of malocclusion. A mere clinical examination performed to quantify malocclusion in a reproducible and consistent manner without the assistance of other records , particularly radiographs, primarily reflects dental relationships. Therefore unless such records are available, an ‘“index” or gauge of malocclusion is useful but somewhat limited in scope. Summers** differentiated between basic orthodontic
Dmtofac. Ortiq. November 1989
defects and symptoms. Orthodontic defects include neuromuscular problems, skeletal discrepancies, tooth structure discrepancies, or any combination thereof. An index monitoring a basic defect over time would increase or remain the same at best, in cessity of treatment for improvement index monitoring orthodontic symptoms over time can improve, remain unchanged, or deteriorate. According to this characterization, the c3.99 1985 TPI group would have symptoms only (Fig. 5), while the 7.0 to 9.99 and 210 1985 TPI groups “would reflect defects. The 4.0 to 6.99 1985 TPI group may have disclosed symptoms, or possibly defects considering the starting range (Fig. 5); however, the occlusion seemed stable or at least included variables that added up to similar TPI values over time. These observations suggest that the TPI could help differentiate between defects and symptoms. In their longitudinal comparison of the T an orthodontist’s subjective appraisal of serial models at intervals between ages 3 and 16, Popovich and Thompson’ showed that an age-specific crossclassification demonstrating the least number of misclassified individuals was obtained when a cutoff point of 4.5 was established. They considered the ranges of 0 to 2.5, 2.5 to 4.5, and B4.5 the best limits for categorizing TPI scores as low, middle, and high in priority, respectively. Persons with TPI scores between 4 and 6 (MSE, Table I), or between 4 and 6.99 as adapted for this study from the MSE would consequently qualify for highly desirable or mandatory rather than elective treatment. Perhaps the qualification of treatment as elective in the presence of a definite malocclusion (4 to 6 as per MSE and TPI, Table I), and as highly desirable in the presence of a severely handicapping malocclusion (7 to 9 as per MSE and TPI, Table I) should be revised. For example, elective treatment might be associated with minor ~~ifestati~~s of malocclusion (I to 3); dejinite malocclusion (4 to 6) would be indicative of highly desirable treatment; and severe (7 to 9) and very severe (>lO) handicap might be combined for mandatory treatment. The differentiation is not academic since the present TPI scale is used by several funding agencies to determine eligibility for orthodontic treatment. An investigation similar to that conducted by Popovich and Thompson’ and involving more than just one orthodontist is needed to determine a more adequate scale, or perhaps different weighting of the factors making up the TPI. SUMMARY
AND CONCLUSIO
A longitudinal evaluation of the Treatment Index, performed annually between 1975 and I979, and
Treatment Priority
in 1985, was conducted in a young rural student population and demonstrated the following results: 1. The mean values of the TPI did not reflect the range of severity in the population. 2. Four severity groups were thus recognized for untreated students on the basis of 1985 TPI values: <3.99, 4.0 to 6.99, 7.0 to 9.99, and >lO. A statistically significant increase in the average TPI scores was noted between 1979 and 1985 for the most severe groups. 3. A change of the TPI score over time could not be attributed to a single factor (crowding/rotation or any occlusal factor). However, the stepwise regression analysis ranked the displacement factor first in boys and second in girls in 1985. 4. The TPI values decreased with orthodontic treatment. 5. The average TPI scores for this population were found to be higher than the national average between 6 and 11 years and slightly lower in late ndoleslcence. The following conclusions are suggested by this study: 1. The TPI is a valid epidemiologic indicator of malocclusion but does not predict the future severity of malocclusions in the permanent dentition. Because malocclusion is a multifactorial problem, minor malocclusions may be associated with functional disturbances or may increase in severity with age. Thus determination of the need of orthodontic treatment must remain an individual assessment. 2. Although helpful in describing the general need for treatment in a given population, epidemiologic indexing of malocclusion should not become a means to determine the need of orthodontic treatment in the individual patient. A modified characterization of a severity scale was suggested to apply in epidemiologic studies using the TPI. 3. When determining the need for orthodontic therapy, government funding agencies or insurance carriers must account for the individual variations characterizing a malocclusion. We wish to acknowledge Carol A. Ram, BSN, and Nina Markovic, BDH, members of the evaluating team.
1. Grainger RM. The orthodontic treatment priority index. Washington, DC: National Center for Health Statistics, 1967. Public Health Service publication no. 1000 (Vital and health statistics; series 2, no. 25). 2. Kelly JE, Sanches M, Van Kirk LE. An assessment of the occlusion of the teeth of children 6-11 years. Washington, DC:
3.
4.
5.
6. 7.
8. 9.
10. 11.
12. 13. 14. 15. 16. 17. 18. 19.
20.
21.
22.
index
National Center for Health Statistics, 1973. DHEW publication no. (HRA) 74-1612 (Vital and health statistics; series 11, no. 130). Kelly JE, Harvey CR. An assessment of the occlusion of the teeth in youths 12-17 years. Washington, DC: National Center for Health Statistics, 1977. DHEW publication no. (HRA) 771644 (Vital and health statistics, series 11, no. 162). Grainger RM. Burlington Orthodontic Research Center progress report. Series 6, University of Toronto, Division of Dental Research, 1961:9-11. Popovicb 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. Rural Dental Health Program. Progress Report No. 2. 1976; 5:172-3, 186-94. Holmes DE, Machen JB, Fields HW, McIver FT. An assessment of the treatment priority index over time [Abstract]. J Dent Res 1987;66:(Abst 1100):244. Massler M, FrZnkel JM. Prevalence of malocclusion in children aged 14 to 18 years. AM J ORTHOD 1951;37:751-68. Elasser WA. Studies of dentofacial morphology. I. A simple instrument for appraising variations. Angle Orthod 195 1;21:16371. VanKirk LE Jr, Pennell EH. Assessment of malocclusion in population groups. AM J ORTHOD 1959;45:752-8. Draker HL. Handicapping labio-lingual deviations: a proposed index for public health purposes. AM J ORTHOD 1960;46:295305. Poulton DR, Aaronson SA. Relationship between occlusion and periodontal status. AM J ORTHOD 1961;47:690-9. Bjiirk A, Krebs AA, Solow B. Method for epidemiological registration of malocclusion. Acta Odontol Stand 1964;22:27-41. Summers CJ. The occlusal index: a system for identifying and scoring occlusal disorders. AM J ORTHOD 1971;59:552-67. Gupta OP. Methdology and epidemiology of malocclusion in children [Abstract]. Int Assoc Dent Res 1967;45:113. Salzmann JA. Handicapping malocclusion assessment lo establish treatment priority. AM J ORTHOD 1968;54:749-65. Freer IJ, Adkin BL. New approach to malocclusions and indices. J Dent Res 1968;47:1111-7. Ingervall B, Ronnennan A. Index for need of orthodontic treatment. Odontol Revy 1975;26:59-82. Heikinheimo K. Need of orthodontic treatment in 7-year-old Finnish children. Community Dent Oral Epidemiol 1978;6:12934. Foster TD, Menezes DM. The assessment of occlusal featilres for public health planning purposes. AM J ORTHOD 1976;69:8390. Helm S. Orthodontic treatment priorities in the Danish Child Dental Health Services. Community Dent Oral Epidemiol 1982;10:260-3. Summers CJ. Some effects of the developmental changes on the indices of malocclusion. J Public Health Dent 1966;26:212-20.
Reprint requests to: Dr. Joseph Ghafari Department of Orthodontics School of Dental Medicine University of Pennsylvania 4001 Sprue St. Philadelphia, PA 19104
RTICLES
evaluation of the Tre I) Joseph Ghafari,* Stephen A. Locke,* and J. Marvin Bentley** Philadelphia,
Pa.
The Treatment Priority Index (TPI) is an epidemiologic tool used to rank malocclusions and assess the need for orthodontic treatment. The purpose of this study was to (1) evaluate the pre~ictab~li the TPI as an indicator of malocclusion severity, (2) evaluate the effect of orthodontic treatment on TPI values, and (3) compare the results with a national survey of American children aged 6 to 11 years and 12 to 17 years conducted by the United States Public Health Service. The TPI was recorded annually in a young student population of Juniata County, Pa., from 1975 to 1979, and later in 1985. The mean values of the TPI did not reflect the range of severity in the p~pul~t~o~. For this reason the Malocclusion Severity Scale (Burlington Growth Center) was used to identify four groups in 1985. Each group was tracked back to 1975. Further evaluation investigated the role af individual factors contributing to malocclusion over time (tooth displacement and occlusal ?ect~r$). The conclusions are as follows: (1) the TPI is a valid epidemiologic indicator of malocclusion but does not predict the severity of individual malocclusions in the permanent dentition, (2) TPI values decrease with orthodontic treatment, and (3) the average TPI values for this population were h than the national average between 6 and 11 years of age and slightly lower in late adolescent Xiewithin a treatment-need range of slight to elective. A characterization of treatment need relative to malocclusion severity that is different from the available scale is suggested. (AM J ORTH~D RTHOP
1989;96:382-9.)
he Treatment Priority Index (TPI) was developed to determine whether orthodontic treatment reduced the severity of malocclusion below the level of public health significance.’ Thereafter the TPI’s usefulness was recognized for epidemiologic surveys of malocclusion and as a screening tool in public health programs. 2,3 The TPI was based on the evaluation of models or clinical examinations of 375 12-year-old children. ’ The items measured were restricted to those describing an occlusal anomaly, excluding factors related to cause (such as habits), or measurements related to malocclusion per se (such as intercanine width). Set patterns or combinations of the selected items defined syndromes. A total of seven syndromes evolved defining the incisor relationship horizontally (underjet, overjet) and vertically (overbite, open bite), the occlusion of the buccal segments (posterior crossbite), and tooth displacement (rotation and crowding) (Fig. 1). On the basis of multiple regression analysis, the syndromes were weighted Supported in part by the Robert Wood Johnson Foundation 10188. *Department of Orthodontics, School of Dental Medicine, University sylvania. **Division of Public Affairs, Penn State University. Lllll14Q6
ID
No.
of Penn-
Table f. Levels of severity of a malocclusion as established by the Malocclusion Severity Estimate (MSE), the Treatment Priority Index (TPI), and for the present study
Virtually classic “normal” occlusion Minor manifestations of malocclusion and treatment need is slight Definite malocclusion but treatment elective Severe handicap, treatment highly desirable Very severe handicap with treatment mandatory
0 1-3
c3.99
4-6
4-6.99
7-9
T-9,99
>lO
>I0
according to the permanent first molar ~elatio~isb.i~,mesio-, neutro-, and distoclusion. A constant, also corresponding to the molar occlusion, was added to the TPI score. The final TPI value could range from 0 to >lO. The precursor of the TPI was the Malocclusion Severity Estimate (MSE) developed by Grainger at the Burlington Orthodontic Research Genter.4 Unlike the TPI, the MSE score was that of tbe syndrome with the
Treatment PrioriQ
Volume 96 Number 5
(7) Mesiochtsion
6) Distoclusion -
FIRST RELATION
MOLAR Choose
appropriate
column
Index
-
-
0 = 2
” = 2
8 1 N -
B G N
Weights
-
mm 9t 9
(1) upper overjet
1
(2) Lower overjet
2 3 3+ (3)
ti 1
Overbite
In
C,DW” third5
Bite 3/3+ 213-313
a-213
(4)
Opsnbite mm.
Co”nt about placed
c2 2-4 4t
In
CONSTANT I_.
WI
6
?iez,
(0.
2
rotated d!s2 mm.
MAX.TO BUCCAL
NO.
s.4 1.5 1.8 1.1 .6 .3 -
-
2 .4 .6 1.0 1.4 !.O -
.3 .6 L.l 1.8 t.5 1.4 -
1.3 2.9 5. 8.0 lot 1Dt -
.3 .6 1.1 1.8 2.5 3.4 -
.2 .4 A 1.0 1.4 LO -
!.9 1.5 .5
3.8 LO .7
8.0 4.1 1.5
3.8 2.0 .-I
::: .5
-
-
-
-
-
1.5 2.s 4.:
2.0 3.8 6.3
4.1 8.0 1Dt
2.0 3.8 6.3
I.! 2.2 4.c
-2 .: .I 2
-II .3 .5 .8 1.1 1.5 1.9 2.5 3.0
-2 1.1 1.9
--Ii
7
G -
0.27 --r;
F-
3.5
0
MAXTO LINGUAL
.O .4 .cl
Retrognathism
:t .2
WElGHTS
IS TREATb Fig.
0
.3 .5
,94:03 5.9 7.7 9.7 101
2)
NO. Weight
S1JM OF
1Dt 10+ 8.0 5.1 2.9 1.3 -
1:; 1.: 1’ 2:; 5.' = 0
1 no
gigi 2ULQB
.4 .5 .a 1 ':6 .?I -
Prognathism
Openbite
-
teeth 45’or about
Cwnt teeth rotated >45’=or displaced more than 2mm Y 2 Total score)
:: .O .6 .4 .2 -
1.01
31 2.3
4) 4.2
IT PRIORITY
1. Treatment
51 6.5
1:: 1.5 1.9 2.5 3.0
4.9 6.2 7.7 2.7
.: .! .! PRESENT
it 1.: 1’ 2:;
/ &y.& Max. EXP%lSlOl? Syndroma
i L.9 haax. colla~x Syodror
s.s E=zzz ma
-T --ii2 6 more 9.4
10
(TPI)
data
-l-
INDEX
Priority
largest value, regardless of the scores of the other syndromes. In the MSE the absence of occlusal disorders was not scored as zero. The TPI also differed from the SE by deleting potential tooth displacement (mixeddentition space analysis) and by rating distoclusion and mesioclusion equally. Levels of severity established from the MSE are shown in Table I. Popovich and Thompson5 compared the TPI with the subjective appraisal of the orthodontist. They used models from the Burlington Orthodontic Research Center at 3, 6, 9, 12, 14, and 16 years of age. Because of various stages of eruption and growth (for example, the eruption of the incisors not allowing the accurate evaluation of overjet and overbite), some syndromes were
Index
collection
form.
eliminated or modified at certain ages. The authors concluded that the TPI was a useful epidemiologic index at ages 3 through 16. The TPI values were more consistent in indicating prevalence of malocclusion than the subjective appraisal of the orthodontist because of the latter’s relatively high weighting for rotated or displaced teeth. Between 1963 and 1965, the TPI was used by the United States Department of Mealth, Education, and Welfare for a national survey of 6 to 1 l-year-old American children2 A similar evaluation was later conducted ( 1966 to 1970) of American youths aged 12 to 17 years. 3 Both surveys underscore the importance of quantifying occlusal disorders for public health purposes and the
Glzafari, Locke, and Bentley
MALES,TAEATED
400
FEMALES, TREATED
300 FEMALES, NO TREATMENT 200
100 MALES, NO TREATMENT
75
76
77
70
79
85
YE.444
Fig. 2. Sample size, tracking population and girls, treated and untreated.
backward
usefulness of the TPI as a scoring system to rank malocclusions. Yet the long-term predictability of the TPI has not been established. The above-mentioned national surveys were cross-sectional studies that provided information about the rate of malocclusion and need for orthodontic treatment at different ages, but not the longitudinal development of malocclusion. The current study is a longitudinal evaluation of the TPI in a rural Pennsylvania population. The goals were to (1) evaluate the predictability of the TPI as an indicator of the severity of a malocclusion, (2) evaluate the effect of orthodontic treatment on TPI values, and (3) compare the results with the above-cited national surveys conducted by the United States Public Health Service.
Students in the public schools of Juniata County, Pa, were examined annually between 1975 and 1979 to evaluate the health effects of dental education. As part of this study that focused mainly on caries prevention, the orthodontic TPI (Fig. 1) was recorded to evaluate the prevalence of malocclusion. When first examined, the students were just entering the transitional stage of dental development. The average age was 6 years. TPI recording was postponed to the next year on the basis of the following criteria: (1) uneruption of the first permanent molars and/or ermanent central incisors, (2) extraction of the first molars, and (3) active orthodontic treatment. To establish reliability and consistency, the data, except for baseline data, were collected between the end of April and the beginning of June each year for the 4 years of the study. To ensure calibration, the four examiners (a dentist, two dental hygienists, and a registered nurse) attended educational seminars, in-house
from
1985
to 1975,
showing
distribution
of boys
clinical calibration exercises, and external evaluations. Pair-wise comparability studies were pe~o~ed during the annual examinations to monitor inter- and intraexaminer variability. They were designed in four different models: Model 1. Children involved in the comparability studies were evaluated in succession by each examiner. These observations were performed before the field examination period. Model 2. Each child was examined in the morning by one examiner and again in the afternoon by the same examiner to evaluate overall intraexaminer comparability. These evaluations were also performed before the held examination period. Model 3. Each child was examined first by one examiner and then by a second examiner in immediate succession. Model 4. Each child was evaluated by one examiner in the morning and again in the afternoon by the same examiner. In contrast to models 1 and 2, evaluations per models 3 and 4 were conducted t~ou~bout the entire length of the field examination series. In all of these four approaches, the comp~~bility between or within the examiners was never less than 9 1% . This figure represents a high level of agreement between examiners and implies that differences that might be observed as outcomes of the program, if they are greater than lo%, cannot be attributed to bias in the data resulting from examiner errors6 The data were recorded in the field on forms that were collected and checked for legibility at the end of each day and subsequently entered into a mainframe computer. Orthodontic TPI data were keypunched. A printout was then generated and compared with the initial data to verify the reliability of the input. When an input discrepancy was observed, correction was
Treatment
made. In case of incomplete information, the form was referred back to the field for resolution through reexamination if required. In November 1985, a follow-up study included those children of the original cohort still in the Juniata County school system. The goal of the follow-up study was to determine whether there were any long-term effects of the dental health education program. One examiner was checked against an orthodontist (S.L.) and an examiner from the original study, following the guidelines of the original study protocol. Examiner reliability was calculated from 25 (approximately 6%) repeated evaluations. Intraclass correlation on repeated measures produced an estimate of reliability for single measures of TPI equal to 0.87. The data were entered into an IBM-PC XT. Reliability of input was verified by the same methods used for the original data. However, if a problem or error was noted, it was not possible to return the form back to the field and the data for the individual were deleted. The initial data from the mainframe computer were transferred to the IBM-PC XT and the files were merged. The students still in the Juniata school system in 1985 who had participated in the original study numbered 442, of whom six were eliminated. The distribution of this group by sex and history of orthodontic treatment or no treatment is shown in Fig. 2. Not all the students examined in 1985 had an evaluation record every year between 1975 and 1979. The absence of these records was due to at least one of the exclusion criteria mentioned above. However, each of the students evaluated in 1985 had at least one record between 1975 and 1979. Differences in TPI scores over time were evaluated by paired t tests between matched samples of subjects.
The mean TPI values for orthodontically treated and untreated students and for both groups are shown in Fig. 3. The difference in TPI values between 1979 and 1985 were statistically significant (p < 0.01) for both treated and untreatd groups, but not for the total population. Since the 1985 TPI values for the treated group were less than 7, and the 1985 Treatment Priority Indices for the untreated group ranged between 0 and 20, the Malocclusion Severity Estimate (MSE) scale (Table I) was applied to the latter group. The severity groups thus established were ~3.99, 4.0 to 6.99, 7.0 to 9.99, and 210. Each group was then tracked backward through previous examination years to evaluate the TPI change over time. The distribution of students within these oups is illustrated in Fig. 4. There were more boys
Mean
Priority
Index
TPI ,treat~ent
6
Fig. 3. Mean TPI values for students who had received orthodontic treatment, those who had not, and the total of both i*p < 0.01). groups. Distribution of population is shown in Fi
than girls in all groups, and more students in the ~3.99 and 4.0 to 6.99 groups than in the more severe groups. Fig. 5. illustrates the mean TPI values over time as they developed into the 1985 severity groups. A statistically significant change was noted between 1979 and 1985 for all groups (p < 0.01) except the 4.0 to 6.99 group. The starting point for all groups fell within a range of 3 to 7 TPI values. At this point the separate contributions to the TPI by the occlusion and tooth displacement were analyzed. When all the individual occlusal factors (horizontal, vertical, cross-lingual, cross-buccal, and the constant) were grouped together as occlusal or interarcb factor, their mean value was highest in the 1985 210 group: 10.27 in girls and 8.0 in boys. A statistically significant increase in occlusal values (p < 0.01) was observed in the female 210 group between 1979 and 1985. Although statistically significant (p < O.Ol), a slight decrease of the occlusal values in the male ~3.99 group was observed for the same time period. The intraarch factor, represented by the displacement factor, showed opposite trends for boys and girls than did occlusal factors. The mean value in the 1985 > 10 female group was 3.18, lower than the corresponding value for the male group, 5.59. In both sexes mean values of the displacement factor increased between 1979 and 1985 in the most severe tracks (7.0 to 9.99 and 3 10). However, rate and amount of increase were greater for boys than girls. Statistically significant differences were noted only for the G3.99 and 210 male groups between 1979 and 1985. The mean TPI for the untreated group, the mean TPI for all (treated and untreated students), and the
3
Gkafari,
Locke,
and Bentley
75
76
77
78
79
85
YEAR Fig.
4. Distribution
of untreated
students
by year
and
1985
severity
track.
Table II. Comparison of mean TPI values from U.S. Public Health Service (USPHS) studies of 6 to 1l-year-old children’ and 12 to 17-year old youths3 with this study’s mean TPI for untreated and both treated and untreated (all) students
AI1 Untreated USPHS *Not
computed
4.1 3.7 3.3 because
4.9 4.3 3.2 of small number
4.5 3.9 3.1
4.2 3.9 3.2
4.2 3.7 3.2
+ * 5.2
* * 5.1
4.3 4.7 5.0
3.6 3.6 5.1
4.6 5.0 4.8
4.4 4.5 4.9
of observations
total mean TPI of the U.S. Public Health Service (USPHS) study are shown in Table II. There is a difference of approximately 1 TPI unit from age 6 to 10 years between the mean TPI for all and the USPHS total mean. The difference decreases to 0.5 at age 11 because of an increase in the USPHS values from age 10 to 11. When differentiated by sex, male values were similar at age 11. The USPHS survey of 12 to 17-yearold youths showed higher TPI values (approximately 0.5 unit) than the present study in boys, girls, and the total population.
The first objective of this study was to evaluate the as a longitudinal indicator of malocclusion severity. The TPT trends were in an opposite direction for orthodontically treated and untreated students (Fig. 3). The mean TPl scores in the treated group up to 1979 were greater than 4---that is, in a range indicating a definite malocclusion calling for elective or highly desirable treatment (Table I). In this respect the TPI clearly gauged the original severity of malocclusions and their
TPI
4.2 3.7 3.1
improvement through treatment, altbough the range of TPI scores in 1985 reached up to 7. This range may reflect (1) an early treatment without successful interception of a developing malocclusion, (2) compromised results of orthodontic treatment, or (3) i~ad~¶~ate retention and relapse of treatment results. In contrast the mean TPI scores for the untreated group, although statistically significant between 1979 and 1985, showed an increase of only 0.5 in this time period and did not reflect the wider range of 1985 TPI values (0 to 20). Severity channels were thus defined according to the MSE scale and tracked back over time. This approach was more descriptive than mere averages in evaluating the untreated group. Indeed the 1975 and 1985 mean TPI values for this group (Fig. 3) would indicate a constant level of severity calling for elective orthodontic treatment (MSE, Table I). The accuracy of this statement was challenged when severity tracks were established. From 1975 to 1979, a period when most students had a transitional dentition, the four tracks, at times overlaping, describe an envelope within a range of 4
Volume 96 5
Treatment Priarity
Index
Number
Table III. Percentages of children according to malocclusion severity between the U.S. Public 4th Service surveys of 6 to 1 l-year-old
TPI85 >lO.W
TPI85 7.0-9.99
cl
24.4 39.0 22.4 8.7 5.5
1-3 4-6 7-9 210 *Data adapted Harvey.3
from
Kelly,
Sanches,
TPI 85 4.06.99
11.0 34.8 25.2 13.0 16.0 and Van Kirk’
and Kelly
TPl85 <3.99 0 74
76
78
80
82
84
86
YEAR
and
to 7 in the untreated group (Fig. 5). Predicting malocclusion severity from values within this envelope is questionable in view of the 198.5 outcome, except perhaps for two groups: (1) the ~3.99 1985 TPI group, which shows the least degree of severity between 1975 and 1979, and (2) the 210 1985 TPI group, which exhibits the highest degree of severity in the same time period. The previous observations suggest that the TPI is an acceptable indicator of malocclusion, a conclusion supported by Popovich and Thompson.5 However, malocclusion predictability may not depend on TPI values recorded in the transitional dentition. The inability of the TPI to depict crowding of the unerupted permanent canines and premolar-s could be a reason for missing an increase in malocclusion severity over time. Although the analyses of correlation coefficients, stepwise regression, scattergrams, and percentage contribution by each individual factor to TPI total score showed that a change of the latter over time could not be attributed to a single factor, the stepwise regression analysis ranked the displacement factor first in boys and second in girls in 1985. Popovich and Thompson’ recommended increasing the weighting for displaced teeth to improve the age-specific reliability of the TPI. A mixeddentition space analysis would clearly improve the predictability of the TPI,’ as would the inclusion of skeletal, functional, and neuromuscular disturbances. However, an original premise in developing the TPI was the possibility that technicians-not necessarily orthodontists-could collect the data. Additional records, not only adequate training, would be required to perform space analysis. The results also suggest that in the 210 1985 TPI group, crowding and rotation (displacement factor) were more severe in male than female subjects; the opposite seems true for the occlusal factors. This finding may indicate that growth contributed to the devel-
Fig. 5. Average TPI values tracks for untreated students
in the different I%5 only (*p < 0.01).
TPI
severity
opment of less severe occlusal conditions and greater tooth displacement in boys. This suggestion is based on the assumption that growth would have proceeded over a longer period of time and possibly in greater amounts in boys than in girls. Skeletal and dental ages would provide better references than chronologic age by relating maturational stages of growth to treatment need of developing malocclusions. An assessment of the TPI over a period of 18 months in 216 subjects aged 3 to 1%years showed a gradual, but not statistically significant, increase of the index when displayed by dental developmental stage--that is, primary, mixed, and permanent detentions .7 However, only average values of the TPI were considered by the authors of the study. In answer to the second objective of our investigation, orthodontic treatment indeed affected TPI values and was applied in patients who obviously had a severe malocclusion (Fig. 3). Treatment app~e~tly occurred between 1979 and 1985, an observation suggesting that orthodontic therapy was probably carried into the permanent dentition, at least for most students. Insofar as the TPI reflected the effect of treatment, its validity is enhanced. Its use to gauge the efficacy of orthodontic treatment, but not necessarily early (preventive/ interceptive) treatment, is evident from the results of this study. Comparison of the mean TPI values from the rural Pennsylvania population, particularly those of the untreated group, with those of the USPIIS surveys2.3 shows differences in magnitude, but generally similar trends (Table II). The TPI values in the USPHS data increase between ages 10 and 11, probably reflecting the dentitional transition from primary to permanent. IIowever, the mean value recorded at age 11 was less than 4, within the area of “minor manifestations of malocclusion with a slight treatment need” (MSE scale). Starting at age 12,
Ghafari,
Am. J. Orthod.
Locke, and Bentley
the mean ‘SPI values increase to a higher level of severity in the area of “definite malocclusion but treatment elective.“3 This increase of severity with age also was demonstrable when we compared percentages of children according to malocclusion severity between both national surveys-that is, 6 to 11 -year-old children’ versus 12 to 17-year-old youths3 (Table III). The most significant differences seem to occur between the ends of the scale-that is, normal occlusion (24.4% vs. 11%) and very severe handicap (5.5% vs. 16%). The present longitudinal study indicates trends similar to those of the USPHS study for the >10 and 7 to 9.99 severity groups and possibly the 4 to 6.99 group if one considers the small difference between the younger (22.4%) and older (25.2%) children in the national surveys (Table III). However, although the combined percentages of children with no or minor manifestations of malocclusion (MSE = 0 and 1 to 3) are higher in the 6 to 1 l-year-old children than in the 12 to 17-yearold youths, the present study shows that the average TPI values of c3.99 remain in the low severity track over time. No definite conclusion may be formulated about this difference, particularly since both USPHS surveys included children who had orthodontic treatment (2.5% and 10.7% in the 6 to 11 and 12 to 17year-old groups, respectively) and whose TPI values were not presented separately. Population differences and the nature of the experiments are probable contributing factors. Although Juniata County is a rural region and the students formed a somewhat homogeneous group mainly of European background, the USPHS study randomly selected children of presumably more varied backgrounds and regions. The government’s investigation was a cross-sectional study based on age; the Juniata County survey was set as a longitudinal study. Quantifying malocclusion is needed for epidemiologic and public health programs. It is nonetheless a complex problem since many variables define a malocclusion. Indeed the existence of various methods1.3.8-2’that attempted to quantify the characteristics of malocclusion stems from disagreement over the definition and importance of those characteristics. Analyses considering tooth displacement, occlusal relationships, and facial, skeletal, and functional parameters should be expected to accurately reflect the complexity of malocclusion. A mere clinical examination performed to quantify malocclusion in a reproducible and consistent manner without the assistance of other records , particularly radiographs, primarily reflects dental relationships. Therefore unless such records are available, an ‘“index” or gauge of malocclusion is useful but somewhat limited in scope. Summers** differentiated between basic orthodontic
Dmtofac. Ortiq. November 1989
defects and symptoms. Orthodontic defects include neuromuscular problems, skeletal discrepancies, tooth structure discrepancies, or any combination thereof. An index monitoring a basic defect over time would increase or remain the same at best, in cessity of treatment for improvement index monitoring orthodontic symptoms over time can improve, remain unchanged, or deteriorate. According to this characterization, the c3.99 1985 TPI group would have symptoms only (Fig. 5), while the 7.0 to 9.99 and 210 1985 TPI groups “would reflect defects. The 4.0 to 6.99 1985 TPI group may have disclosed symptoms, or possibly defects considering the starting range (Fig. 5); however, the occlusion seemed stable or at least included variables that added up to similar TPI values over time. These observations suggest that the TPI could help differentiate between defects and symptoms. In their longitudinal comparison of the T an orthodontist’s subjective appraisal of serial models at intervals between ages 3 and 16, Popovich and Thompson’ showed that an age-specific crossclassification demonstrating the least number of misclassified individuals was obtained when a cutoff point of 4.5 was established. They considered the ranges of 0 to 2.5, 2.5 to 4.5, and B4.5 the best limits for categorizing TPI scores as low, middle, and high in priority, respectively. Persons with TPI scores between 4 and 6 (MSE, Table I), or between 4 and 6.99 as adapted for this study from the MSE would consequently qualify for highly desirable or mandatory rather than elective treatment. Perhaps the qualification of treatment as elective in the presence of a definite malocclusion (4 to 6 as per MSE and TPI, Table I), and as highly desirable in the presence of a severely handicapping malocclusion (7 to 9 as per MSE and TPI, Table I) should be revised. For example, elective treatment might be associated with minor ~~ifestati~~s of malocclusion (I to 3); dejinite malocclusion (4 to 6) would be indicative of highly desirable treatment; and severe (7 to 9) and very severe (>lO) handicap might be combined for mandatory treatment. The differentiation is not academic since the present TPI scale is used by several funding agencies to determine eligibility for orthodontic treatment. An investigation similar to that conducted by Popovich and Thompson’ and involving more than just one orthodontist is needed to determine a more adequate scale, or perhaps different weighting of the factors making up the TPI. SUMMARY
AND CONCLUSIO
A longitudinal evaluation of the Treatment Index, performed annually between 1975 and I979, and
Treatment Priority
in 1985, was conducted in a young rural student population and demonstrated the following results: 1. The mean values of the TPI did not reflect the range of severity in the population. 2. Four severity groups were thus recognized for untreated students on the basis of 1985 TPI values: <3.99, 4.0 to 6.99, 7.0 to 9.99, and >lO. A statistically significant increase in the average TPI scores was noted between 1979 and 1985 for the most severe groups. 3. A change of the TPI score over time could not be attributed to a single factor (crowding/rotation or any occlusal factor). However, the stepwise regression analysis ranked the displacement factor first in boys and second in girls in 1985. 4. The TPI values decreased with orthodontic treatment. 5. The average TPI scores for this population were found to be higher than the national average between 6 and 11 years and slightly lower in late ndoleslcence. The following conclusions are suggested by this study: 1. The TPI is a valid epidemiologic indicator of malocclusion but does not predict the future severity of malocclusions in the permanent dentition. Because malocclusion is a multifactorial problem, minor malocclusions may be associated with functional disturbances or may increase in severity with age. Thus determination of the need of orthodontic treatment must remain an individual assessment. 2. Although helpful in describing the general need for treatment in a given population, epidemiologic indexing of malocclusion should not become a means to determine the need of orthodontic treatment in the individual patient. A modified characterization of a severity scale was suggested to apply in epidemiologic studies using the TPI. 3. When determining the need for orthodontic therapy, government funding agencies or insurance carriers must account for the individual variations characterizing a malocclusion. We wish to acknowledge Carol A. Ram, BSN, and Nina Markovic, BDH, members of the evaluating team.
1. Grainger RM. The orthodontic treatment priority index. Washington, DC: National Center for Health Statistics, 1967. Public Health Service publication no. 1000 (Vital and health statistics; series 2, no. 25). 2. Kelly JE, Sanches M, Van Kirk LE. An assessment of the occlusion of the teeth of children 6-11 years. Washington, DC:
3.
4.
5.
6. 7.
8. 9.
10. 11.
12. 13. 14. 15. 16. 17. 18. 19.
20.
21.
22.
index
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