american journal of . orthodontics -...

American Journal of ORTHODONTICS . Founded in 1915 Volume 88 Number 4 October, 1985

Copyright 0 1985 by The C. V. Mosby Company

ORIGINAL ARTICLES

Dentofacial orthopedics in relation to somatic maturation

An analysis of 70 consecutive cases treated with the Herbst appliance

Hans Pancherz, D.D.S., Odont. Dr., and Urban HBgg, D.D.S., Odont. Dr. Malmii, Sweden

Mandibular treatment changes were related to somatic maturation in 70 consecutive cases of Class II malocclusion (52 boys and 18 girls, aged 10 to 18 years) treated with the Herbst appliance for an average period of 7 months. Sagittal and vertical alterations in mandibular condylar growth and sagittal changes in molar and incisor tooth position were analyzed by means of mouth-open profile roentgenograms. The somatic maturity level of the patients was assessed by means of longitudinal growth records of standing height. The treatment period was related to the peak height velocity by dividing the patients into three growth-period groups: prepeak, peak, and postpeak. Herbst treatment ‘resulted in Class I dental arch relationships in all patients. Post-Herbst treatment changes were not evaluated in this study. Sagittal condylar growth was increased and the mandibular molars and incisors were moved anteriorly. When the mandibular skeletal and dental changes were related to the subjects’ somatic maturation, significant differences between the different growth periods existed in boys and tendencies were noted in girls as follows: (1) sagittal condylar growth was most pronounced in the peak period, (2) anterior molar movement was equally large in all growth periods, and (3) anterior incisor movement was most extensive in the postpeak period. To take advantage of the increase in condylar growth response and to reduce the time of posttreatment retention, it is suggested that Herbst therapy be instituted close to peak height velocity. (AM J ORTHOD 88: 273-287, 1985.)

Key words: Orthodontics, velocity growth curves, cephalometry, skeletal changes, dental changes

T he most suitable period for growth intervention in orthodontic treatment is the subject of debate. Some authors’-“3 claim that the patient’s level of somatic development strongly influences the outcome of various orthodontic measures and that there are suitable and

From the Department of Orthodontics, School of Dentistry, University of Lund.

reliable methods to assess the maturation level in clinical work. Other authors”-” assert that somatic maturation has comparatively little intiuence on the success of orthodontic treatment and that the methods devised to estimate individual maturity in clinical work are too uncertain. Neither of the two conflicting opinions, however, is predicated on analyses of sufficient numbers of patients treated under standardized conditions.

273

274 Pancherz and Hiigg

Fig. 1. Intraoral photographs of a Class II, Division 1 malocclusion treated with the Herbst appliance A, Before treatment. B, Start of treatment. C, After treatment.

Table 1. Mandibular morphology and mandibular-cranial base relationships in 93 Class II malocclusions (B = Boys, G = Girls)

Variable (mm or degrees)

Herbst group (n = 70) Control group (n = 23)

n Mean SD n Mean SD

Mandibular jaw base B 52 111.5 length (pgn-co) G 18 111.3

P-angle (MLipgn-co) B 52 24.9 G 18 24.0

Go-angle (MLIRL) B 52 124.X G 18 126.9

Sagittal mandibular jaw B 52 76.8 position (s-n-pg) G 18 16.9

Vertical mandibular jaw B 52 31.4 position (MLINSL) G 18 31.9

6.69 23 110.0 5.13 4.04 - 2.90 23 24.7 3.42 2.92 - 6.05 23 125.2 6.87 6.51 --

3.51 23 77.3 2.38 4.50 5.80 23 29.6 5.62 6.76 - -

Table II. Occurrence of various events in 70 Herbst subjects and 23 control subjects (B = Boys, G = Girls, D = Sex difference)

Herbst group

Vaiiable (years)

Prepeak Peak Postpeak

n Mean SD II Mean SD n Mean SD

Age at peak B height ve- G locity D

Age at start of B

29 2

29 examination G 2 period D

Age at end of B 29 examination G 2 period D

Length of ex- B 29 amination G 2 period D

14.3 (12.5) (1.8) 12.0

(11.1) (1.1) 12.6

(11.5) (1.1) 0.6

(0.5) (0.1)

0.76 17 9

0.81 17 9

0.84 17 9

0.15 17 9

13.4 12.2

I .2*** 12.8 12.0 0.8**

13.4 12.7 0.7** 0.6 0.6 0.0

0.76 6 0.65 7

0.48 6 0.54 7

0.50 6 0.49 7

0. IO 6 0. II 7

12.9 0.86 11.0 1.20

1.9** 14.4 1.16 12.5 1.22

I .9” 15.1 1.20 13.1 1.17

2.0* 0.7 0.18 0.6 0.09 0.1

Age at peak height velocity

Mean SD Mean SD Total Herbst sample B 13.8 0.94 Swedish reference samplez4 B 14.1 1.08

G 11.8 1.09 G 12.0 1.02

*Significance at 5% level. **Significance at 1% level. ***Significance at 0.1% level.

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Dentofacial orthopedics in relation to somatic maturation 275

Fig. 2. The Herbst appliance. A, Working position of the appliance with the teeth in occlusion. B, Partial maxillary and mandibular anchorage. C, Total maxillary and mandibular anchorage.

Herbst group

PrepeaklPost- peak mean

difference

1.4***

PeakiPostpeak mean

difference

0.5 1.2*

Control group Prepeak

Prepeak Peak HerbstlControl mean

n Mean SD n Mean di’erence

21 13.8 0.76 2 (12.9) 0.5*

-o.s*** - 2.4*** - I .6*** 21 11.3 0.85 2 (12.5) 0.7** -0.5

- o.t3** - 2.5*** - 1.7*** 21 11.8 0.84 2 (13.0) 0.8** -0.4

0.0 -0.1 -0.1 21 0.5 0.03 2 (0.5) 0.1 0.0

276 Pancherz and Hiigg

OLP

Fig. 3. Measures of mandibular condylar, molar, and incisor changes. Mandibular tracings of mouth-open profile roentgenograms superimposed on the anterior and inferior mandibular bone contours. - - - - Before the examination period. -After the examination period. co,

COP

i

m

IL

ML

OL

OLP

(Condyle superior)-The most superior point of the condyle determined by a tangent parallel to OL (Condyle posterior)-The most posterior point of the condyle determined by a tangent parallel to OLP (Incision)-The incisal tip of the most prominent mandibular central incisor (Molar)-The mesiobuccal cusp tip of the mandibular permanent first molar (lncisal line)-The axis of the most prominent mandibular central incisor through i (Mandibular line)-The tangent to the lower border of the mandible (Occlusal tine)-A line through m and the buccal cusp tip of the mandibular first premolar. The line from the initial roentgenogram was used as a reference line for measurements on roentgenograms both before and after examination. (Occlusal line perpendiculare)-A line perpendicular to OL through the most anterior point of the bony chin symphysis. The line from the initial roentgenogram was used as a reference line for measurements on roentgenograms both before and after examination.

When commonly used orthodontic appliances are employed, it is obviously difficult to design a study that analyzes the effects of orthodontic measures in relation to somatic maturation. Removable appliances (for ex- ample, functional appliances, headgear) are generally worn part-time and require the patient’s cooperation. Furthermore, the treatment time with these appliances is prolonged over several years making it difficult to differentiate between treatment effects and normal growth changes, especially as suitable untreated control subjects are generally not available for an extended period of time.

On the other hand, with the Herbst appliance”.” it is possible to create an experimental situation similar to that in animal studies of growth interventive mea-

VELOCITY mm

AGE

Fig. 4. Distance and velocity curves of standing height.

sures related to somatic maturation.‘“-” The Herbst appliance is a fixed functional appliance worn 24 hours a day. It does not require the cooperation of the patient and the treatment time is short (6 to 8 months).

The aim of this study was to relate mandibular skeletal and dental changes to the level of somatic maturation in growing subjects with Class II malocclusions treated with the Herbst appliance.

SUBJECTS

The original sample of consecutive patients treated with the Herbst appliance at the Orthodontic Depart- ment, Faculty of Odontology, Malmii, Sweden, comprised 73 cases of Class II malocclusion. Three subjec& discontinued treatment after 2 to 3 weeks and were not included in this study. The remaining 70 subjects (52 boys and 18 girls, aged 10 to 16 years) were treated with the Herbst appliance (Fig. 1) for an average period of 7.1 months (SD = 1.7 months).

Twenty-three untreated Class II subjects, all boys aged 9 to 14 years, were used as a control group for an average period of 6.2 months (SD = 0.4 months).

Selected cephalometric recordings describing mandibular morphology and mandibular-cranial base relationships are shown in Table I. The measuring points and reference lines used have been defined in an earlier report. I4

The design of the appliance used in patient treatment is shown in Fig. 2. At the start of treatment, the mandible in each patient was advanced to an end-to-end incisal relationship. Partial maxillary and mandibular anchorage was employed in 20 subjects and total maxillary and mandibular anchorage in 50 subjects. No

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significant difference with respect to mandibular treatment changes (variables, see Methods) existed between these two anchorage systems.

METHODS Analysis of profile roentgenograms

Sagittal and vertical changes in mandibular condylar growth, and sagittal changes in mandibular molar and incisor tooth position occurring during the examination period were analyzed by means of mouth-open profile roentgenograms. In the Herbst group, roentgenograms were taken (1) at the start of treatment before the appliance was inserted and (2) after treatment on the day the appliance was removed. In the control group, roentgenograms were taken before and after the examination period.

The registrations from the roentgenograms were made on matt acetate tracing film on which the reference points were marked with a finely sharpened 5H pencil. Where double projection gave rise to two points, the midpoint was used. Linear measurements were made to the nearest 0.5 mm and angular measurements to the nearest 0.5”. No correction was made for linear mag- nification (approximately 7% in the median plane). The measuring points and reference lines used are shown in Fig. 3.

Measuring procedure

Mandibular tracings from before and after the examination period were superimposed with the anterior and inferior mandibular bone contours used for orien- tation (Fig. 3). The original occlusal line (OL) and occlusal line perpendiculare (OLP) were used as a reference grid for sagittal and vertical registrations (Fig. 3). The profile roentgenographic analysis comprised four linear measurements (variables l-4) and one angular measurement (variable 5). Changes of the variables that occurred during the examination period were registered as

after minus, before diflerences: 1. co,-OLP--Sagittal condylar growth 2. co,-OL--Vertical condylar growth 3. m-OLP--Sagittal molar position change 4. i-OLP-Sagittal incisor position change 5. IL/ML--Incisor inclination change

Sagittal here refers to a relation with the functional occlusal plane and not the head-carrying plane or the Frankfort horizontal.

Analysis of growth curves

Longitudinal growth records of standing body height over a 5- to lo-year period were available for all subjects. The growth records were obtained from the childrens’ school clinics and from the Orthodontic

\ Peak

-1 0 +l years

Fig. 5. Division of the velocity curve of standing height into three growth periods: peak (the period at peak height velocity 2 1 year), prepeak (the period before peak), and postpeak (the period after peak).

Department in Malmo. At the Orthodontic Department, body height measurements were made to the nearest 1 mm with registrations performed about every month. At the school clinics, body height measurements were made to the nearest 0.5 cm. Registrations were done every year or every second year from 7 years of age onward. Data from the school clinics were included in the analysis only when they covered a period before the subjects were registered at the Orthodontic De- partment .

By means of a computer program, individual distance and velocity curves of standing height were constructed (Fig. 4). The velocity curves were smoothed by spline function.23 By visual inspection the peak height velocity was identified on the velocity curves and three growth periods established (Fig. 5): prepeak, peak, and postpeak. The examination period in each subject was assigned to one of the three growth periods. If the examination period coincided with more than one growth period, the subject was assigned to the growth period that covered most of the examination period. The distribution of the Herbst and control subjects in relation to the peak height velocity is shown in Fig. 6. The occurrence of events is given in Table II.

Statistical methods

The arithmetic mean (Mean) and standard deviation (SD) were calculated for each variable. To assess the statistical significance of the changes that occurred dur-

278 Puncherz and H&g

CONTRO BOYS

‘L

HERBST 22- 21- BOYS ::Z

IS-- 17 - 1F.P

4 I

-b I I I

-3 -2 -I PHV

years

+2 +3 +4

Pre-Peak Post -Peak years

Fig. 6. Distribution of 70 Herb.9 subjects (cases 1 to 70) and 23 control subjects in relation to the peak height velocity (PHV). Division of the subjects into three growth-period groups: prepeak, peak, and postpeak. The length of the examination period (-) is shown.

HERBST 162 GIRLS - 53

Table Ill. Size of method error (ME) in the cephalometric analysis of landmark changes

Variable ME

the different cephalometric landmarks that occurred during the examination period was calculated with the formula

-

Sagittal condylar growth (co,-OLP) Vertical condylar growth (co,-OL) Sagittal molar position (m-OLP) Sagittal incisor position (i-OLP) Incisor inclination (IL/ML)

0.40 mm 0.52 mm 0.47 mm 0.31 mm

I .60”

ing the examination period, t tests for paired samples were performed; to compare the Herbst and control subjects and the different growth periods, t tests for independent samples were performed. The levels of significance used were P < 0.001 (***), P < 0.01

(**), and P < 0.05 (*). P 3 0.05 was considered not significant (NS).

The size of the combined method error (ME) in locating, superimposing, and measuring the changes of

ME = J

Z;dZ

x

where d represents the difference between two registrations of a pair and n is the number of duplicate registrations. Cephalograms before and after treatment from ten randomly chosen Herbst subjects were traced and superimposed with measurements recorded on two occasions. The results of the ME calculations are given in Table III.

RESULTS

Herbst treatment resulted in Class I dental arch relationships in ail 70 patients investigated (Figs. 9-l 1). The changes in the cephalometric variables measured are given in Table IV.

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Pre - Peak

Peak

Post - Peak

4 b

mm 65432 I 0 I 2 3 4 5 6 7 8 mm

Flg. 7. Mandibular condylar and incisor changes contributing to overjet correction in 52 boys (-) and 18 girls ( - - - -) treated with the Herbst appliance. The subjects were arranged in relation to the peak height velocity in the order given in Fig. 6.

In the evaluation of the effects of the Herbst appliance, comparison with the control group could be made only for boys in the prepeak period. Herbst treatment resulted in the following changes: sagittal condylar growth was increased (1.5 mm, P < 0.001); vertical condylar growth seemed unaffected; the mandibular molars were moved anteriorly (1.5 mm, P < 0.001); the incisors were moved anteriorly (2.4 mm, P < 0.001) and proclined 8.4” (P < 0.001).

In the evaluation of changes occurring during Herbst treatment in relation to somatic maturation, a comparison between all three growth periods could be made

in boys. Because of an insufficient sample size in girls, a comparison in this sex could only be made between the peak and postpeak periods. The comparison demonstrated that sag&al condylar growth in boys was significantly greater in the peak period than in the prepeak (1 .O mm, P < 0.05) and postpeak (1.5 mm, P < 0.05) periods. Vertical condylar growth was significantly larger in the peak and postpeak periods when compared to the prepeak period (1.1 mm, 0.001 < P < 0.05). The amount of anterior molar movement was similar in all three growth periods. The mandibular incisors were moved anteriorly significantly more in the post-

280 Pancherz and H&g

Table IV. Mandibular skeletal and dental changes in 70 Herbst subjects and 23 control subjects (B = Boys, G = Girls, D = Sex difference)

Herhst group

Prepeak Variable

(mm or degrees) n Mean

I. Sagittal condylar B 29 2.3 growth (co,-OLP) G 2 (1.5)

D (0.8) 2. Vertical condylar B 29 1.2

growth (co,-OL) G 2 (1.5) D (-0.3)

3. Sagittal molar pc- B 29 cl.7’ sition (m-OLP) G 2 (~2.3)’

D (-0.6) 4. Sagittal incisor B 29 ~2.4’

position (I-OLP) G 2 (t2.3)’ D (0.1)

5. Incisor inclination B 29 8.3 (IL/ML) G 2 (6.8)

D (1.5)

‘t, +, Changes in sagittal tooth position (Fig. 2) *Significance at 5% level. **Significance at 1% level. ***Significance at 0. I% level.

SD

0.85

0.91

0.79

0.98

4.42

n

17 9

17 9

17 9

17 9

I7 9

Peak

Mean

3.3 2.6 0.7 2.3 I.2 l.I”*

+I .x1 -1.9’ -0.1

c2.l’ +?.?I -0. I

X.0 8.2

-0.2

SD n

1.53 6 0.84 7

0.94 6 0.53 7

1.18 6 0.64 7

0.92 6 0.97 7

4.02 6 3.38 7

Postpeak

Mean SD

1.8 I .23 2. I 0.82

-0.3 2.3 1.21 1.4 I.25

0.9 +I .8’ I .07 ~1.6’ 0.49

0.2 +3.5’ 1.26 c2.1’ 1.05

I .4* 11.5 6.51

9.4 3.36 2.1

peak period than in the prepeak period (1.1 mm, P < 0.05) and peak period (1.4 mm, P < 0.01). The proclination of the mandibular incisors tended to be more pronounced in the postpeak period than in the prepeak (3.2”, NS) and peak (3.5”, NS) periods. In girls no significant differences in condylar growth and tooth position changes existed when the peak and postpeak periods were compared.

When the changes that occurred during Herbst treatment were evaluated in relation to sex, a comparison between the boys and girls could be made only for the peak and postpeak periods. In the peak period, sagittal and vertical condylar growth were more pronounced in the boys than in the girls. However, the sex difference was statistically significant for vertical condylar growth only (1.1 mm, P < 0.01). The amount of anterior movement of the mandibular molars and incisors was about the same in both sexes. In the postpeak period. there were no significant sex differences in sagittal and vertical condylar growth or in the amount of anterior molar movement. The mandibular incisors, however, were moved anteriorly to a greater extent in boys than in girls (1.4 mm, P < 0.05). In both sexes the lower incisors tended to be advanced more than the molars. This was especially apparent in the postpeak period.

Overjet correction

In the Herbst subjects, the mandibular contribution to overjet correction consisted of the sum of sagittal changes in condylar growth and in incisor tooth position (Fig. 7). In the total patient material, the average sum of these changes amounted to 5.0 mm. On average, the values tended to be largest in the peak boys.

The interrelationship between the condylar and incisor changes that contributed to overjet correction varied considerably among the subjects, irrespective of sex and somatic maturation (Fig. 7). The following tendencies were, however, noted: in the boys condylar changes dominated in the peak period and incisor changes in the postpeak period. In the girls condylar and incisor changes were, on average, equally large in the different growth periods.

Class II molar correction

In the Herbst subjects, the mandibular contribution to Class II molar correction consisted of the sum of sagittal changes in condylar growth and in molar tooth position (Fig. 8). In the total patient material, the average sum of these changes amounted to 4.3 mm. On average, the values tended to be largest in the peak boys.

The interrelationsip between the condylar and molar

Volume 88 Number 4


Herbst group

PrepeaklPostpeak mean difference

0.5

PeaklPosTpeak mean difSerence

1.5* 0.5

Conrrol group Prepeak

Prepeak Peak HerbstiControl

n Mean SD n Mean mean difference

21 0.8 0.58 2 (2.0) I .5***

- 1.1*** -1.1* 0.0 21 0.9 0.80 2 (1.3) 0.3 -0.2

0.1 0.1 0.0 21 co.2’ 0.33 2 (ta.5) I .5*** -0.3

0.3 1.1* 1.4** 21 0.0 0.45 2 (-0.5)’ 2.4*** -0.1

0.3 -3.2 -3.5 21 -0.1 1.64 2 (-1.8) 8.4*** -1.2

changes that contributed to Class II molar correction varied considerably among the subjects, irrespective of sex and somatic maturation (Fig. 8). There was a ten- dency, however, for the condylar changes to dominate in both sexes. This was especially apparent in the peak boys.

CASE PRESENTATION

Three boys .whose Class II, Division 1 malocclusions were treated with the Herbst appliance at different levek of somatic maturation are presented.

CASE 11

The patient (Fig. 9) was 11 years of age and had been treated with the Herbst appliance for 6 months. Treatment was performed during the prepeak period. The Herbst appliance was constructed- with partial maxillary and mandibular anchorage (Fig. Z!). The mandibular contribution to overjet reduction was 5.5 mm; sagittal condylar growth was 3.0 mm and ‘the incisors were moved anteriorly 2.5 mm (proclined 4.5”). The mandibular contribution to Class II molar correction (o&correction) was 4.0 mm; sagittal condylar growth was 3.0 mm and ihe molars were moved anteriorly 1 .O mm. No retention was used after Herbst treatment.

C&E 42

The patient (Fig. 10) was 13 years of age and had been treated with the Herbst appliance for 7 months. Treatment was performed du.ring the peak period. The Herbst appliance was constructed with total maxillary and mandibular anchorage ( Fig. 2). The mandibular contribution to overjet reduction

was 6.5 mm; sagittal condylar growth was 5.0 mm and the incisors were moved anteriorly 1.5 mm (proclined 7.0”). The mandibular contribution to Class II molar correction (overcorrection) was 7.0 mm; sagittal condylar growth was 5.0 mm and the molars were moved anteriorly 2.0 mm. An activator for interocclusal adjustments was used for 1 year after Herbst treatment.

CASE 52

The patient (Fig. 11) was 16 years of age and had been treated with the Herbst appliance for 8 months. Treatment was performed during the postpeak period. The Herbst appliance was constructed with total maxillary and mandibular anchorage (Fig. 2). The mandibular contribution to overjet reduction was 6.5 mm; sagittal condylar growth was 1 .O mm and the incisors were moved anteriorly 5.5 mm (proclined 23.5”). The mandibular contribution to Class II molar correction (overcorrection) was 4.0 mm; sagittal condylar growth was 1 .O mm and the molars were moved anteriorly 3 .O mm. An activator for interocclusal adjustments was used after Herbst treatment.

DISCUSSION

The results of this investigation represented by the Herbst appliance indicate that the level of somatic development influences the outcome of dentofacial or- thopedic treatment. Although’the control subjects were followed for a shorter period than the treated subjects, the differences could not affect the results because changes in the controls over the observation period ‘were already very small.


Pre - Peak

Post-Peak

4 b mm 65432101 2 3 4 5 6 7 8 mm

Fig. 8. Mandibular condylar and molar changes contributing to Class II molar correction in 52 boys (-) and 18 girls ( - - - - ) treated with the Herbst appliance. The subjects were arranged in relation to the peak height velocity in the order given in Fig. 6.

Although there were wide interindividual variations in the skeletal and dental response to Herbst treatment, sagittal condylar growth changes dominated on average in the peak treatment period and tooth movements in the postpeak treatment period (Table IV, Figs. 7 and 8). These findings are in agreement with those from studies in monkeys fitted with mandibular protrusive appliances. In younger animals the extent of condylar growth was increased and the growth direction sagittally

oriented. *O,** In mature animals, on the other hand, the adaptive potential of the condyle was reduced while compensatory tooth movements were more pronounced~*0.22.*b.21

Maturity assessment in the present subjects was done by means of individual velocity curves of standing height, a method found suitable in clinical orthodontics.4 The peak period comprised a 2-year interval around the peak height velocity (Fig. 5). This interval

Volume 88 Number 4


Fig. 9. CASE 11. A, Plaster casts from before treatment (leffj, after treatment (middle), and 5 years posttreatment (right). B, Superimposed cephalometric tracings from before treatment ( - - - - ) and after treatment (-). Facial tracings superimposed on the nasion-sella line at sella. Mandibular tracings superimposed on the anterior and inferior mandibular bone contours. The OL/OLP reference grid is shown. C, Velocity curve of standing height. The treatment period ( . ) is shown.

was considered adequate for analysis of growth interventive measures because there seems to be a definite alteration in growth rate before and after that period.5

It has been demonstrated in several human growth studies that the timing of the pubertal growth of the mandible is closely related to that of standing height. 5x2*-34 Furthermore, the peak of the pubertal growth spurt of standing height and that of the mandible is considerably less in girls than in boys.3’.32,35 The differences in the amount of condylar growth between the sexes and the various maturity groups in the Herhst subjects may therefore be explained by a corresponding difference in the amount of basic condylar growth.5 In the peak and postpeak girls. the difference in sagittal condylar growth was relatively small (NS). This may be explained by the fact that they differed significantly (P < 0.05) in their maturity pattern, represented by the age at peak height velocity (Table II). It is well known

&at the peak is larger and the intensity of the growth spurt is more pronounced in early maturers for both the mandible36 and standing height.37*38 It seems likely that, at least in boys in the earlier growth periods, the increase in sagittal condylar growth accomplished with the Herbst appliance resulted from an equal addition to basic condylar growth, irrespective of maturation.

The method of using velocity curves of standing height for the evaluation of maturity-related growth changes in the mandible seemed to be more accurate in boys than in girls. This may be caused by the ex- istence of a relatively larger gap between the occurrence of the pubertal growth spurt of standing height and that of the mandible in girls .5.33 Furthermore, girls may show a larger gain in mandibular growth than boys in the postpubertal growth period, as is the case for standing height.23

The dental changes with Herbst treatment were ba-

284 Pancho-z and Htigg Am. .I. Orthod. Omhrr 19x5

Fig. 10. CASE 42. A, Plaster casts from before treatment (lerr), after treatment (middle), and 2 years posttreatment (right). 6, Superimposed cephafometric tracings from before treatment (- - - -) and after treatment (- ). Facial tracings superimposed on the nasion-sella line at sella. Mandibular tracings superimposed on the anterior and inferior mandibular bone contours. The OL/OLP reference grid is shown. C, Velocity curve of standing height. The treatment period ( ) is shown.

sically a result of anchorage loss. The telescope mechanism produces an anteriorly directed force on the lower teeth which thereby results in their mesial movement and proclination (Figs. 9-l 1). In several cases the incisors were advanced more than the molars. This could be explained by the fact that the telescope mechanism, via the lingual arch wire, also exerts a downward force on the lower front teeth which will thus be moved further forward due to proclination and a leveling of the Curve of Spee. Since it is thought that neuromuscular adaptation will occur less easily in older than in younger subjects and because general muscle strength increases with maturation,39 the forces upon the den- tition exerted by the appliance will be enhanced in the older subjects. This could explain the differences in tooth movement found in the various maturity groups. The possibility cannot be excluded, however, that there are differences in the amount of force exerted by the

musculature that depend upon the facial morphologic pattern of the individual patient.40,4’ In the analysis of mandibular morphology (p-angle and Go-angle) and mandibular-cranial base relationships (the angles s-n- pg and ML/NSL) in the present study, no significant differences were found in the three growth-period groups.

The question of when Herbst treatment should be instituted to be most effective in relation to the patient’s level of somatic maturation cannot be answered easily. A possible advantage of early (prepeak) treatment is that, by normalizing the skeletal and soft-tissue morphology at a young age, it would provide a basis for normal continuing development of these structures.42 On the other hand, early treatment in the mixed den- tition seems to necessitate retaining the result until all permanent teeth have erupted into a stable occlusion. In subjects with unstable occlusal conditions, there is

Volume 88 Number 4


Fig. 11. CASE 52. A, Plaster casts from before treatment pefij, after treatment (middle), and 1 year posttreatment (rig/tt). B, Superimposed cephalometric tracings from before treatment (- - - -) and after treatment (- ). Facial tracings superimposed on the nasion-sella line at sella. Mandibular tracings superimposed on the anterior and inferior mandibular bone contours. The OL/OLP reference grid is shown. C, Velocity curve of standing height. The treatment period ( . . ) is shown.

a risk of occlusal relapse43 because approximately 50% of the total maxillary and mandibular changes that con- tribute to Class II correction are caused by tooth move- mentsw Furthermore, early treatment may be fruitless in the long run as severe, skeletal Class II discrepancies seem to strive constantly to reassert themselves, re- gardless of how early they are treated.

In comparison with the prepeak period, the peak period seems suitable for Herbst treatment. The ortho- dontist can take advantage of the increase in condylar growth and the time of retention could be shortened, provided all permanent teeth have erupted and a stable cuspal interdigitation is established. Furthermore, the problems of relapse caused by unfavorable posttreatment growth will be reduced when treatment is performed at this later stage.

When remo’vable functional appliances (such as the activator, Frankel, or bionator) are employed, waiting

for peak growth can easily result in insufficient time for growth-related intervention. Since treatment with these appliances often takes 2 to 4 years (that is, requires periods exceeding the duration of the peak growth period), the final stages of treatment may occur in a nongrowing phase. Treatment with the Herbst appliance, on the other hand, is of short duration and can usually be completed within 6 to 8 months. This means that the Herbst treatment method can be used successfully even in postpubertal patients, provided condylar growth is not completed.

Finally, a word of caution-the Herbst appliance should not be used in nongrowing patients since skeletal alterations will be minimal** and the treatment effects are confined to the dentoalveolar area. Furthermore, there will be an increasing risk of development of a dual bite4’ with dysfunction symptoms of the temporomandibular joints as a possible consequence.46


This study has been supported by the Faculty of Odon- tology, Malmii, and the Swedish Dental Society.

REFERENCES I. Lager H: The individual growth pattern and stage of maturation

as a basis for treatment of distal occlusion with overjet. Tram Eur Orthod Sot, pp 137-145. 1967.

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Dentqfacial orthopedics in relation to somatic maturation 287

appliance treatment: A cephalometric investigation. AM J ORTHOD 82: 104113, 1982.

45. Held AJ, Spirgi M, Cimasoni G: An orthopedically treated adult case of Class II malocclusion. AM J 0~~~0~49: 761-765, 1963.

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Reprint requests to: Dr. Hans Pancherz Department of Orthodontics University of Giessen Schlangenzahl 14 D-6300 Giessen, F.R. Germany

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