Orthodontic risk factors for temporomandibular disorders (TMD). I: Premolar extractions Charles R. Kremenak, DDS, MS," D. David Kinser, DDS, MS, b Heidi A. Harman, DDS, MS, = Curtis C. Menard, DDS, MS, d and Jane R. Jakobsen, BS, MA ° Iowa City and Des Moines, Iowa, Olathe, Kan., and Fairbanks, Alaska
Concern about claims that premolar extractions may put patients at risk for temporomandibular disorders (TMD) led to this study. We report first findings from a longitudinal study of orthodontic patients begun in 1983. By using the methods of Helkimo, we collected TMD data before initiation of orthodontic treatment, between 0 and 12 months after debanding, and 12 to 24 months after debanding. Analyses related Helkimo scores with premolar extractions in 65 patients for whom orthodontic treatment had been completed. Twenty-six patients were treated without premolar extractions, 25 had four premolars extracted, and 14 had two upper premolars extracted. Tests for significance of differences between mean Helkimo scores were conducted for the nonextraction group compared with the extraction groups, and between pretreatment and posttreatment Helkimo scores for each group. Results included: (1) no significant intergroup differences between mean pretreatment or posttreatment scores, and (2) small but statistically significant (p < 0.05) differences (in the direction of improvement) between mean pretreatment and posttreatment scores for both the nonextraction group and for the four premolar extraction group. (AMJ ORTHODDENTOFACORTHOP 1992;101:13-20.)
P r e m o l a r s are frequently extracted for orthodontic purposes? Edward Angle had opposed the use of extractions, and the early years of the twentieth century saw much controversy on the topic. 2 By the mid-1940s, however, pathbreaking clinical research by Rudolf Hotz3 and Birger Kjellgren4 in Europe and B. F. DeweP in the United States had begun to restore premolar extractions to a place of respectability in the orthodontist's armamentarium. In recent years there has been a resurgence of controversy about extractions for orthodontic purposes, fueled mainly by concerns about risk factors for temporomandibular disorders (TMD). The issues have received wide attention, and the topic has been reviewed in recent papers by Sadowsky, Theisen, and S a k o l s 6 and Dibbets and van der Weele, 7 while the broader topic of all orthodontic treatment as a risk factor for TMD was reviewed in 1990 by Reynders. 8 From the University of Iowa. Support for the study was provided by the research fund of the University of Iowa Department of Orthodontics, the Minnesota Occlusion Study Group, and grant #89006 from the American Association of Orthodontists. =Professor, Department of Orthodontics. bAdjunct Associate Professor, Department of Orthodontics, and in private practice, Des Moines, Iowa. Cln private practice, Olathe, Kan. aln private practice, Fairbanks, Alaska. CResearch Assistant, Department of Preventive and Community Dentistry. 811132283
New findings from the prospective longitudinal study by Sadowsky and colleagues 6 supported the assumption that extractions should not be viewed as risk factors for increased joint sounds. Results from the 15year follow-up of orthodontic patients in Groningen by Dibbets and van der Weele7 were both reassuring and cautionary. Assessments of patients with TMD signs and symptoms from their prospective longitudinal study showed the frequency of "serious" problems such as pain, limitation of mouth opening, and crepitation was not significantly different in extraction patients than in those treated without extractions. However, subjectively assessed clicking was much more frequent in the extraction patients, and the difference was statistically significant. The present study is, to our knowledge, the only other prospective longitudinal study to focus on the problem of whether premolar extractions are risk factors for TMD. We present preliminary findings, through January 1991, from ongoing work that is part of a broader longitudinal investigation of possible relationships between orthodontics and TMD begun in 1983. SUBJECTS AND METHODS
Subjects were 65 unselected orthodontic patients from the graduate orthodontic clinlc at the University of Iowa. Criteria for enrollment in the longitudinal study were informed con13
14
Am. J. Orthod.Dentofac.Orlhop. January 1992
Kremenak et al.
Table !. N o n e x t r a c t i o n and extraction subgroups and their sizes at the three times considered
I
Posnreatment
Pretreatment 0 to 12 mo[ 12 to 24 mo Nonextraction group* Extractions Four premolar extraction group** Two premolar extraction group*** Combined extraction group
n = 26
n = 22
n = 16
n = 25
n = 21
n = 17
n = 14
n = 14
n = 9
n = 39
n = 35
n = 26
*The presence or absence of third molars was disregarded for this analysis. **One premolar per quadrant; any combination was allowed, but 21 of the 25 patients had four first premolars extracted, as did 18 of the 21, at 0-12 mo., and 15 of the 17 at 12-24 mo. ***All had extraction of one upper premolar per quadrant; these were first premolars in 12 of the 14 patients seen before treatment and at 0-12 too., and 8 of the 9 at 12-24 too. Five patients also had extractions of an additional tooth in the lower arch; a central incisor in one case, a premolar in two cases, and a molar in two cases. sent, willingness to participate, and age between 16 and 25 years at the beginning of treatment. As shown in Table I, 39 of the patients had premolars extracted as part of their orthodontic treatment. Of these, 25 had four premolars extracted and 14 had two upper premolars extracted. About a third of each group were males and two thirds females (Table II). Most patients in the nonextraction and four premolar extraction groups had Class I malocclusions at the outset of treatment, whereas all 14 patients in the two premolar extraction group had Class II malocclusions. Age at the beginning of treatment averaged 19 to 20 years for all groups (Table III). Length of treatment was significantly shorter (p < 0.001) for the nonextraction group, averaging 16 months compared with about 24 months for the extraction groups (Table III). Information in the middle section of Table III pertains to the average amount of time that elapsed, after debanding, before each of the series of Helkimo examinations was performed. Scores from examinations performed in the first 12 months after debanding were averaged for the first period (0 to 12 months); scores from examinations performed between 12 and 24 months after debanding were averaged for the second. The first posttreatment examinations were, on average, 6 to 7 months after debanding, with the second about 10 months later. The lower section of Table III summarizes the chronologic events for each of the groups and shows that, for the nonextraction group, on average, 2.8 years elapsed between the initial (pretreatment) TMD examination and the second posttreatment examination, whereas the analogous interval for the four premolar and combined extraction groups was 3.4 years. The table also shows that, at the end of the study, extraction patients were 1.2 years older on average than the nonextraction patients.
As subsequent tables will show, comparisons were made between the nonextraction group and the four premolar extraction group, and between the nonextraction group and the larger combined extraction group. The TMD assessments were made on each patient before orthodontic treatment was begun and at intervals thereafter. The technique for the clinical examination and collection of the TMD records was as reported by Helkimo. 9 Patients' responses to queries about symptoms, as well as examiner-determined clinical signs, are numerically weighted for severity and summed to classify the level of TMD for each patient. The Helkimo technique, when properly used, is of value for the collection of epidemiologic data such as that obtained here. When used with proper attention to reliability, it permits comparisons of scores obtained by different examiners within the same longitudinal study, as well as with the results of similar studies reported by others. Careful attention was given to interexaminer re/lability during collection of the data reported here. All the present data were collected by graduate students in the Iowa Department of Orthodontics. Each annual change of clinical examiner was preceded by a period of training, "calibration," and reliability testing of the new examiner. If, during the testing, mean interexaminer differences were significantly greater (p < 0.05) than zero, additional training and calibration was required. Data reported here are in the form Helkimo has called "dysfunction scores." Each patient's Helkimo score summarizes the findings from the prescribed set of muscle and joint palpations, observations of sounds and smoothness of jaw movement, and measurements of mandibular mobility. Resulting scores may range from a low of zero, if the patient is normal and has no symptoms, to as high as 25 if the patient has severely impaired mobility, locking or luxation of a joint, tenderness to palpation in 4 or more of the 12 muscle palpation sites, tenderness to palpation of the posterior aspect of a joint, and pain on two or more of four mandibular movements.
RESULTS Results are s h o w n in Tables IV, V, VI, and V I I , and in Figs. I and 2. Table IV contains m e a n H e l k i m o scores f r o m all 65 patients for w h o m w e h a v e pretreatment scores and at least one posttreatment score. Table V pertains to a subset o f the 42 patients studied for the longest time. T h e results m a y be s u m m a r i z e d as follows: (1) T h e r e w e r e no important o r clinically significant differences b e t w e e n m e a n H e l k i m o scores in any o f the four groups either b e f o r e or after orthodontic treatment, and (2) there w e r e no important or clinically significant differences b e t w e e n pretreatment and posttreatment H e l k i m o scores in any o f the f o u r groups. T h e direction o f the before and after treatment changes in Table IV suggests an overall trend toward i m p r o v e m e n t in T M D . It should be noted, however, that s a m p l e sizes in this table d e c r e a s e with time. This is because s o m e patients did not return for f o l l o w - u p e x a m i n a t i o n s , or because it is not yet t i m e for t h e m to
Volume 101 Number I
Risk factors for TMD: Premolar extractions
15
Table II. N u m b e r o f m a l e a n d f e m a l e p a t i e n t s a n d p a t i e n t s w i t h t h e v a r i o u s t y p e s o f m a l o c c l u s i o n in e a c h o f the s a m p l e s
Nonextraction group
[ [
Four premolar extractiongroup
Two premolar extraction group
Combined extraction group
Sex Female M ale
17 9
17 8
I0 4
27 12
Angle class Class I Class II, Division 1 Class II, Division 2
23 2 1
20 3 2
0 13 1
20 16 3
Table III. D e s c r i p t i v e s t a t i s t i c s f o r a g e , l e n g t h o f t r e a t m e n t , a n d t i m e a f t e r d e b a n d i n g f o r t h e H e l k i m o examinations (means and standard deviations)
Nonextraction group Age at start of treatment (yr) ~ ± sd) Months in treatment before deband for 0-12 mo. postdeband scores Months after deband for 0-12 mo. examination Months in treatment before deband for 12-24 mo. postdeband scores Months after deband for 12-24 mo. examination
I
Four premolar extraction group
Two premolar extractiongroup
Combined extractiongroup
19.2 ± 3.4 n = 26 16.0 ± 4.6* n = 22 7.1 ± 3.7 n = 22 16.1 --+ 3.7 n = 16 17.2 ± 5.6 n = 16
19.9 ± 3.2 n = 25 23.3 ± 6.2 n = 21 6.1 - 3.3 n = 21 23.8 ± 6.3 n=17 17.0 ± 3.4 n = 17
19.3 -'- 3.5 n = 14 24.9 ± 9.0 n = 14 6.3 ± 2.9 n = 14 22.8 --- 5.6 n=9 18.7 ± 3.9 n=9
19.7 --- 3.2 n = 39 24.0 ± 7.4 n = 35 6.2 -_- 3.1 n = 35 23.4 ± 6.0 n=26 17.6 ± 3.6 n=26
20.5 21.1 22.0 2.8
21.8 22.8 23.3 3.4
21.4 21.9 22.8 3.5
21.7 22.5 23.2 3.5
Mean years of age Deband First postdeband examination Second postdeband examination Total years pretreatment to second examination
*Mean months in treatment was significantly lower for the nonextraction group than for the extraction groups (p < 0.001).
T a b l e IV. H e l k i m o s c o r e s ( s c a l e = 0 - 2 5 ) f o r t h e f o u r s a m p l e s b e f o r e t r e a t m e n t , 0 - 1 2 m o n t h s a f t e r d e b a n d i n g , a n d 1 2 - 2 4 m o n t h s a f t e r d e b a n d i n g . ( S c o r e s a r e r e p o r t e d as m e a n s a n d s t a n d a r d d e v i a t i o n s . )
I Nonextraction I Fourpremolar I Two premolar group extraction group extractiongroup glean pretreatment Helkimo scores
Mean Helkimo scores 0-12 too. after debanding
Mean Halkimo scores 12-24 mo. after debanding
1.8 range n 1.0 range n 1.2 range n
--= = ± = = ± = =
d o s o . S i n c e it is p r e f e r a b l e , in s t a t i s t i c a l t e s t i n g f o r
2.4 0-7 26 2.6 0-12 22 2.1 0-8 16
2~2 range n 1.1 range n 1.2 range n
- 2.8 = 0-12 = 25 ___ 1.3 = 0-6 = 21 _ 2.0 = 0-8 = 17
1.4 range n 1.0 range n 1.4 range n
± = = = = -4= =
2.0 0-6 14 2.0 0-6 14 2.5 0-8 9
Combbzed extractiongroup 1.9 range n 1.1 range n 1.3 range n
± = = ± = = -4= =
2.5 0-12 39 1.6 0-6 35 2.1 0-8 26
only those patients who had contributed data both be-
to c o m p a r e p r e t r e a t m e n t a n d p o s t t r e a t -
f o r e t r e a t m e n t a n d 12 to 2 4 m o n t h s a f t e r d e b a n d i n g .
merit s c o r e s f o r t h e s a m e p a t i e n t s , t h e s u b s e t o f 4 2
P a i r e d t t e s t s w e r e u s e d in c o m p a r i s o n s o f t h e p r e t r e a t -
p a t i e n t s in T a b l e V w a s s e l e c t e d ; it w a s c o m p r i s e d o f
m e n t a n d 12 to 24 m o n t h p o s t t r e a t m e n t m e a n s c o r e s . '°
improvement,
16
Kremenak et al.
Am. J. Orthod. Dentofac. Orthop. January 1992
N=25l LU rr 0 L)
I1.........,.
4,/=R
2
03 0 . . . .
_J
uJ -r-
1
0 19
20
21
22
23
24
AGE IN Y E A R S Fig. 1. Changes with age in mean Helkimo scores for nonextraction and four premolar extraction groups. Means plotted are shown in Table IV; error bars are standard errors of means. Vertical lines between first and second means show the average age at debanding. The first means, at 19.2 and 19.9 years (see Table II1), were from examinations immediately before starting orthodontic treatment. The second means on each trend line were from reexaminations during the first year after debanding; the third were from follow-up examinations in the second posttreatment year. All data were from reexaminations of the same groups of patients. Declining sample sizes were the result of incomplete data sets at one of the later ages; each patient contributed at least a pretreatment and one posttreatment score. Four patients in each of the two groups shown here contributed a posttreatment score only in the second year after debanding.
Table V. Helkimo scores from subsets from the larger samples. Each subset contains data from an uninterrupted series of examinations from pretreatment through the 12 tO 24-month after debanding examination. The results of paired t tests of differences between means are indicated None.rtraction group Pretreatrnent H e l k i m o s c o r e
2 . 5 --- 2 . 8
2.5 ±
range = 0-7
range =
n= H e l k i m o s c o r e 12-24 m o . a f t e r d e b a n d i n g
Mean difference T e s t statistic P value
Four premolar extraction group
16
3.0 0-12
n=
17
1.2 ±
2.1
!.2 ±
2.0
range =
0-8
range =
0-8
n=
16
n=
17
1.3 ±
2.2
1.2 ±
1.9
Two premolar extraction group 0 . 3 +-- 0 . 5
1.7 -
range = 0-I
range =
n=
9
2.6 0-12
n=
26
2.5
1.3 _
2.1
range = 0-8
range =
0-8
1.4 ± n= -l.l
9 --+ 2 . 7
t =
2.34
t =
2.70
t =
p
Concern about claims that premolar extractions may put patients at risk for temporomandibular disorders (TMD) led to this study. We report first findings from a longitudinal study of orthodontic patients begun in 1983. By using the methods of Helkimo, we collected TMD data before initiation of orthodontic treatment, between 0 and 12 months after debanding, and 12 to 24 months after debanding. Analyses related Helkimo scores with premolar extractions in 65 patients for whom orthodontic treatment had been completed. Twenty-six patients were treated without premolar extractions, 25 had four premolars extracted, and 14 had two upper premolars extracted. Tests for significance of differences between mean Helkimo scores were conducted for the nonextraction group compared with the extraction groups, and between pretreatment and posttreatment Helkimo scores for each group. Results included: (1) no significant intergroup differences between mean pretreatment or posttreatment scores, and (2) small but statistically significant (p < 0.05) differences (in the direction of improvement) between mean pretreatment and posttreatment scores for both the nonextraction group and for the four premolar extraction group. (AMJ ORTHODDENTOFACORTHOP 1992;101:13-20.)
P r e m o l a r s are frequently extracted for orthodontic purposes? Edward Angle had opposed the use of extractions, and the early years of the twentieth century saw much controversy on the topic. 2 By the mid-1940s, however, pathbreaking clinical research by Rudolf Hotz3 and Birger Kjellgren4 in Europe and B. F. DeweP in the United States had begun to restore premolar extractions to a place of respectability in the orthodontist's armamentarium. In recent years there has been a resurgence of controversy about extractions for orthodontic purposes, fueled mainly by concerns about risk factors for temporomandibular disorders (TMD). The issues have received wide attention, and the topic has been reviewed in recent papers by Sadowsky, Theisen, and S a k o l s 6 and Dibbets and van der Weele, 7 while the broader topic of all orthodontic treatment as a risk factor for TMD was reviewed in 1990 by Reynders. 8 From the University of Iowa. Support for the study was provided by the research fund of the University of Iowa Department of Orthodontics, the Minnesota Occlusion Study Group, and grant #89006 from the American Association of Orthodontists. =Professor, Department of Orthodontics. bAdjunct Associate Professor, Department of Orthodontics, and in private practice, Des Moines, Iowa. Cln private practice, Olathe, Kan. aln private practice, Fairbanks, Alaska. CResearch Assistant, Department of Preventive and Community Dentistry. 811132283
New findings from the prospective longitudinal study by Sadowsky and colleagues 6 supported the assumption that extractions should not be viewed as risk factors for increased joint sounds. Results from the 15year follow-up of orthodontic patients in Groningen by Dibbets and van der Weele7 were both reassuring and cautionary. Assessments of patients with TMD signs and symptoms from their prospective longitudinal study showed the frequency of "serious" problems such as pain, limitation of mouth opening, and crepitation was not significantly different in extraction patients than in those treated without extractions. However, subjectively assessed clicking was much more frequent in the extraction patients, and the difference was statistically significant. The present study is, to our knowledge, the only other prospective longitudinal study to focus on the problem of whether premolar extractions are risk factors for TMD. We present preliminary findings, through January 1991, from ongoing work that is part of a broader longitudinal investigation of possible relationships between orthodontics and TMD begun in 1983. SUBJECTS AND METHODS
Subjects were 65 unselected orthodontic patients from the graduate orthodontic clinlc at the University of Iowa. Criteria for enrollment in the longitudinal study were informed con13
14
Am. J. Orthod.Dentofac.Orlhop. January 1992
Kremenak et al.
Table !. N o n e x t r a c t i o n and extraction subgroups and their sizes at the three times considered
I
Posnreatment
Pretreatment 0 to 12 mo[ 12 to 24 mo Nonextraction group* Extractions Four premolar extraction group** Two premolar extraction group*** Combined extraction group
n = 26
n = 22
n = 16
n = 25
n = 21
n = 17
n = 14
n = 14
n = 9
n = 39
n = 35
n = 26
*The presence or absence of third molars was disregarded for this analysis. **One premolar per quadrant; any combination was allowed, but 21 of the 25 patients had four first premolars extracted, as did 18 of the 21, at 0-12 mo., and 15 of the 17 at 12-24 mo. ***All had extraction of one upper premolar per quadrant; these were first premolars in 12 of the 14 patients seen before treatment and at 0-12 too., and 8 of the 9 at 12-24 too. Five patients also had extractions of an additional tooth in the lower arch; a central incisor in one case, a premolar in two cases, and a molar in two cases. sent, willingness to participate, and age between 16 and 25 years at the beginning of treatment. As shown in Table I, 39 of the patients had premolars extracted as part of their orthodontic treatment. Of these, 25 had four premolars extracted and 14 had two upper premolars extracted. About a third of each group were males and two thirds females (Table II). Most patients in the nonextraction and four premolar extraction groups had Class I malocclusions at the outset of treatment, whereas all 14 patients in the two premolar extraction group had Class II malocclusions. Age at the beginning of treatment averaged 19 to 20 years for all groups (Table III). Length of treatment was significantly shorter (p < 0.001) for the nonextraction group, averaging 16 months compared with about 24 months for the extraction groups (Table III). Information in the middle section of Table III pertains to the average amount of time that elapsed, after debanding, before each of the series of Helkimo examinations was performed. Scores from examinations performed in the first 12 months after debanding were averaged for the first period (0 to 12 months); scores from examinations performed between 12 and 24 months after debanding were averaged for the second. The first posttreatment examinations were, on average, 6 to 7 months after debanding, with the second about 10 months later. The lower section of Table III summarizes the chronologic events for each of the groups and shows that, for the nonextraction group, on average, 2.8 years elapsed between the initial (pretreatment) TMD examination and the second posttreatment examination, whereas the analogous interval for the four premolar and combined extraction groups was 3.4 years. The table also shows that, at the end of the study, extraction patients were 1.2 years older on average than the nonextraction patients.
As subsequent tables will show, comparisons were made between the nonextraction group and the four premolar extraction group, and between the nonextraction group and the larger combined extraction group. The TMD assessments were made on each patient before orthodontic treatment was begun and at intervals thereafter. The technique for the clinical examination and collection of the TMD records was as reported by Helkimo. 9 Patients' responses to queries about symptoms, as well as examiner-determined clinical signs, are numerically weighted for severity and summed to classify the level of TMD for each patient. The Helkimo technique, when properly used, is of value for the collection of epidemiologic data such as that obtained here. When used with proper attention to reliability, it permits comparisons of scores obtained by different examiners within the same longitudinal study, as well as with the results of similar studies reported by others. Careful attention was given to interexaminer re/lability during collection of the data reported here. All the present data were collected by graduate students in the Iowa Department of Orthodontics. Each annual change of clinical examiner was preceded by a period of training, "calibration," and reliability testing of the new examiner. If, during the testing, mean interexaminer differences were significantly greater (p < 0.05) than zero, additional training and calibration was required. Data reported here are in the form Helkimo has called "dysfunction scores." Each patient's Helkimo score summarizes the findings from the prescribed set of muscle and joint palpations, observations of sounds and smoothness of jaw movement, and measurements of mandibular mobility. Resulting scores may range from a low of zero, if the patient is normal and has no symptoms, to as high as 25 if the patient has severely impaired mobility, locking or luxation of a joint, tenderness to palpation in 4 or more of the 12 muscle palpation sites, tenderness to palpation of the posterior aspect of a joint, and pain on two or more of four mandibular movements.
RESULTS Results are s h o w n in Tables IV, V, VI, and V I I , and in Figs. I and 2. Table IV contains m e a n H e l k i m o scores f r o m all 65 patients for w h o m w e h a v e pretreatment scores and at least one posttreatment score. Table V pertains to a subset o f the 42 patients studied for the longest time. T h e results m a y be s u m m a r i z e d as follows: (1) T h e r e w e r e no important o r clinically significant differences b e t w e e n m e a n H e l k i m o scores in any o f the four groups either b e f o r e or after orthodontic treatment, and (2) there w e r e no important or clinically significant differences b e t w e e n pretreatment and posttreatment H e l k i m o scores in any o f the f o u r groups. T h e direction o f the before and after treatment changes in Table IV suggests an overall trend toward i m p r o v e m e n t in T M D . It should be noted, however, that s a m p l e sizes in this table d e c r e a s e with time. This is because s o m e patients did not return for f o l l o w - u p e x a m i n a t i o n s , or because it is not yet t i m e for t h e m to
Volume 101 Number I
Risk factors for TMD: Premolar extractions
15
Table II. N u m b e r o f m a l e a n d f e m a l e p a t i e n t s a n d p a t i e n t s w i t h t h e v a r i o u s t y p e s o f m a l o c c l u s i o n in e a c h o f the s a m p l e s
Nonextraction group
[ [
Four premolar extractiongroup
Two premolar extraction group
Combined extraction group
Sex Female M ale
17 9
17 8
I0 4
27 12
Angle class Class I Class II, Division 1 Class II, Division 2
23 2 1
20 3 2
0 13 1
20 16 3
Table III. D e s c r i p t i v e s t a t i s t i c s f o r a g e , l e n g t h o f t r e a t m e n t , a n d t i m e a f t e r d e b a n d i n g f o r t h e H e l k i m o examinations (means and standard deviations)
Nonextraction group Age at start of treatment (yr) ~ ± sd) Months in treatment before deband for 0-12 mo. postdeband scores Months after deband for 0-12 mo. examination Months in treatment before deband for 12-24 mo. postdeband scores Months after deband for 12-24 mo. examination
I
Four premolar extraction group
Two premolar extractiongroup
Combined extractiongroup
19.2 ± 3.4 n = 26 16.0 ± 4.6* n = 22 7.1 ± 3.7 n = 22 16.1 --+ 3.7 n = 16 17.2 ± 5.6 n = 16
19.9 ± 3.2 n = 25 23.3 ± 6.2 n = 21 6.1 - 3.3 n = 21 23.8 ± 6.3 n=17 17.0 ± 3.4 n = 17
19.3 -'- 3.5 n = 14 24.9 ± 9.0 n = 14 6.3 ± 2.9 n = 14 22.8 --- 5.6 n=9 18.7 ± 3.9 n=9
19.7 --- 3.2 n = 39 24.0 ± 7.4 n = 35 6.2 -_- 3.1 n = 35 23.4 ± 6.0 n=26 17.6 ± 3.6 n=26
20.5 21.1 22.0 2.8
21.8 22.8 23.3 3.4
21.4 21.9 22.8 3.5
21.7 22.5 23.2 3.5
Mean years of age Deband First postdeband examination Second postdeband examination Total years pretreatment to second examination
*Mean months in treatment was significantly lower for the nonextraction group than for the extraction groups (p < 0.001).
T a b l e IV. H e l k i m o s c o r e s ( s c a l e = 0 - 2 5 ) f o r t h e f o u r s a m p l e s b e f o r e t r e a t m e n t , 0 - 1 2 m o n t h s a f t e r d e b a n d i n g , a n d 1 2 - 2 4 m o n t h s a f t e r d e b a n d i n g . ( S c o r e s a r e r e p o r t e d as m e a n s a n d s t a n d a r d d e v i a t i o n s . )
I Nonextraction I Fourpremolar I Two premolar group extraction group extractiongroup glean pretreatment Helkimo scores
Mean Helkimo scores 0-12 too. after debanding
Mean Halkimo scores 12-24 mo. after debanding
1.8 range n 1.0 range n 1.2 range n
--= = ± = = ± = =
d o s o . S i n c e it is p r e f e r a b l e , in s t a t i s t i c a l t e s t i n g f o r
2.4 0-7 26 2.6 0-12 22 2.1 0-8 16
2~2 range n 1.1 range n 1.2 range n
- 2.8 = 0-12 = 25 ___ 1.3 = 0-6 = 21 _ 2.0 = 0-8 = 17
1.4 range n 1.0 range n 1.4 range n
± = = = = -4= =
2.0 0-6 14 2.0 0-6 14 2.5 0-8 9
Combbzed extractiongroup 1.9 range n 1.1 range n 1.3 range n
± = = ± = = -4= =
2.5 0-12 39 1.6 0-6 35 2.1 0-8 26
only those patients who had contributed data both be-
to c o m p a r e p r e t r e a t m e n t a n d p o s t t r e a t -
f o r e t r e a t m e n t a n d 12 to 2 4 m o n t h s a f t e r d e b a n d i n g .
merit s c o r e s f o r t h e s a m e p a t i e n t s , t h e s u b s e t o f 4 2
P a i r e d t t e s t s w e r e u s e d in c o m p a r i s o n s o f t h e p r e t r e a t -
p a t i e n t s in T a b l e V w a s s e l e c t e d ; it w a s c o m p r i s e d o f
m e n t a n d 12 to 24 m o n t h p o s t t r e a t m e n t m e a n s c o r e s . '°
improvement,
16
Kremenak et al.
Am. J. Orthod. Dentofac. Orthop. January 1992
N=25l LU rr 0 L)
I1.........,.
4,/=R
2
03 0 . . . .
_J
uJ -r-
1
0 19
20
21
22
23
24
AGE IN Y E A R S Fig. 1. Changes with age in mean Helkimo scores for nonextraction and four premolar extraction groups. Means plotted are shown in Table IV; error bars are standard errors of means. Vertical lines between first and second means show the average age at debanding. The first means, at 19.2 and 19.9 years (see Table II1), were from examinations immediately before starting orthodontic treatment. The second means on each trend line were from reexaminations during the first year after debanding; the third were from follow-up examinations in the second posttreatment year. All data were from reexaminations of the same groups of patients. Declining sample sizes were the result of incomplete data sets at one of the later ages; each patient contributed at least a pretreatment and one posttreatment score. Four patients in each of the two groups shown here contributed a posttreatment score only in the second year after debanding.
Table V. Helkimo scores from subsets from the larger samples. Each subset contains data from an uninterrupted series of examinations from pretreatment through the 12 tO 24-month after debanding examination. The results of paired t tests of differences between means are indicated None.rtraction group Pretreatrnent H e l k i m o s c o r e
2 . 5 --- 2 . 8
2.5 ±
range = 0-7
range =
n= H e l k i m o s c o r e 12-24 m o . a f t e r d e b a n d i n g
Mean difference T e s t statistic P value
Four premolar extraction group
16
3.0 0-12
n=
17
1.2 ±
2.1
!.2 ±
2.0
range =
0-8
range =
0-8
n=
16
n=
17
1.3 ±
2.2
1.2 ±
1.9
Two premolar extraction group 0 . 3 +-- 0 . 5
1.7 -
range = 0-I
range =
n=
9
2.6 0-12
n=
26
2.5
1.3 _
2.1
range = 0-8
range =
0-8
1.4 ± n= -l.l
9 --+ 2 . 7
t =
2.34
t =
2.70
t =
p
