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Growth changes in head posture related to craniofacial development
Growth changes in head posture related to craniofacial development Beni Solow, Dr. Odont.,* and Susanne Siersb~ek-Nielsen, D.D.S.** Copenhagen and Farum, Denmark Cross-sectional studies have demonstrated an association between craniocervical angulation and craniofacial morphology. It was the aim of the present study to determine if the growth coordination suggested by this association could be detected in a longitudinal analysis of growth changes in posture and craniofacial morphology. The sample comprised 43 children, 20 girls and 23 boys. Cephalometric radiographs obtained in the natural head position (mirror position) were taken on two occasions. Mean age at the first observation was 9.5 years; mean period of observation was 2.7 years with a range from 1 to 4 years. Forty-one reference points and four fiducial points were digitized on each film. Individual growth changes were determined by computerized structural superimposition of the digitized sets of points. Correlation coefficients were calculated between growth changes in 11 postural and 35 morphologic variables. Correlations of r = 0.41-0.55 (P < 0.01) were found between the change in craniocervical angulation and the true growth rotation of the mandible as assessed by the method of structural superimposition. On the average, a reduction of the craniocervical angle was seen in connection with increased forward rotation of the mandible and an increased craniocervical angle was found in conjunction with a less-than-average forward rotation of the mandible. The true mandibular rotation was masked by remodeling of the lower mandibular border. The changes in the conventional measures of head posture--the craniovertical angles-during the observation period showed no associations with the growth changes in craniofacial morphology. (AM J ORTHOD 89: 132-140, 1986.)
Key words: Head posture, craniocervical angulafion, craniofacial growth
T h e presence of a relationship between (on one hand) the posture of the head and the cervical column and (on the other) the form of the facial skeleton has been well established through cross-sectional studies on children and adults. A natural head posture characterized by a large craniocervical angulation is seen, on the average, in connection with a vertical facial development--that is, large afiterior and posterior facial dimensions and small anteroposterior dimensions, a small facial prognathism and large inclination of the mandibular and palatalplanes, and a small sagittal extent of the nasopharyngeal space. J-6 In principle, the presence of a correlation between two dimensions in a cross-sectional sample suggests that a coordination of the growth of these dimensions has occurred. Such correlations therefore are valuable indicators_in the search for growth-coordinating mechanisms in the craniofacial complex. However, the presence of significant correlations in cross-sectional studies can only provide in-
Presented in part at the Sixtieth General Session of the International Association for Dental Research in New Orleans, March 1982. Supported by Grant no. 82-3033 from the Danish Medical Research Council. *Institute of Orthodontics, Royal Dental College. **Farum Community Orthodontic Clinic.
132
direct evidence for the presence of previous growthcoordinating mechanisms. Moreover, nonbiologic, spurious factors have to be considered in the interpretation of the correlation coefficients observed in such crosssectional materials. 7 Direct observation of growth-coordinating mechanisms requires longitudinal material. The aim of the present study was to examine in a longitudinal sample whether the growth coordinations suggested by cross-sectional studies could actually be detected in the form of associations between growth changes in head and cervical posture and growth changes in craniofacial morphology. MATERIAL AND METHODS The sample comprised 43 children, 20 girls and 23 boys, admitted for treatment of various malocclusions at a community orthodontic clinic. The malocclusions comprised twelve Class I, twenty-five Class II, Division l, and six Class II, Division 2 cases. Before initiation of orthodontic treatment, the growth of the children was followed for a period of 1 to 4 years. The mean duration of this observation period was 2.7 years; the standard deviation was 0.8 years. Mean age at the initial examination was 9.5 years with a standard deviation of 1.4 years and a range from 7.7 to 12.9 years.
Growth changes in posture and morphology
Volume 89 Number 2
133
A
NsL_/ R E Fc r
/,
~
B
REFml
p 2 ~
ML
v=r~
OPT
CVT
Fig. 1. Reference points and lines on the cephalometric radiographs. Some postural angles are indicated. For definitions see Solow and Tallgren1 and Serensen, Solow, and Greve? 9
The present study is part of a project to elucidate the relationship between head posture and craniofacial morphology. The material used in this study consisted of lateral cephalometric radiographs taken at the start and end of the period of observation. Thus, no treatment was carried out during this period. The cephalometric radiographs were taken in the natural head position (mirror position) with the subject standing in orthoposition. 8,9 The radiographs were used for the cephalometric analysis and for measurement of the postural relationships. The radiographs were taken with a Dana Cephalix cephalometer that is vertically adjustable to record standing subjects. For lateral cephalometric films, the equipment has a fixed film-to-focus distance of 190 cm" and a fixed film-to-median plane distance of 10 cm. This ensures a constant enlargement of 5.6% of the median plane and thus permits precise analysis of growth changes of linear and angular dimensions, as well as direct structure-based superimpositions of sequential films of the same subjects. An 0.5-mm weighted lead wire was suspended in
Fig. 2. Fiducial points and lines on second cephaiometric film. A, Points nt and st are fiducial points transferred from film 1 to film 2 after superimposition of films on stable structures in anterior cranial base. Points n and s are independently marked nasion and sella points on film 2. REForb is the reference line through the fiducial points in the cranial base. On film 1, REForb coincides with NSL. B, Points pl and p2 are fiducial points transferred from film 1 to film 2 after superimposition of film on stable structures in the mandible. REFm~is the reference line through the fiducial points in the mandible, True rotation of the mandible is determined as growth change in angle REFoJ REFIne. During growth this rotation is masked by remodeling of lower mandibular border. Apparent rotation of mandible, that is, change in mandibular plane inclination NSL/ML, is therefore usually much smaller than true rotation.
front of the cassette to register the true vertical on the film. A movable ratio 8 grid and intensifying screens were used. Exposures were made at 80-86 kV and 32 mAs. Measurements Forty-one reference points and four fiducial points were marked directly on each film (Fig. 1) with a soft sharp pencil (Schwan Stabilo 8008). The two profile radiographs of each subject were marked concurrently to achieve consistency in the determination of the reference points. The four fiducial points were used for the computerized, structure-based analysis of growth changes.I° One pair of fiducial points was located in the anterior cranial base. On the first film, points n and s served as fiducial points. The second film was then superimposed on the first and oriented according to stable anatomic structures in the anterior cranial basel1; the fiducial points were transferred to the second film and were designated nt and st (Fig. 2). Because of growth at sella turcica and in the nasion
134
Am. J, Orthod.
Solow and Siersbcek-Nielsen
February 1986
Table I. Mean growth changes Mean at stage I
Variable
Mean
SD of
change
change
Linear dimensions 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
n-s n-sp n-gn s-ba s-ar s-pm s-tgo sp-gn ar-tgo sp-pm
11. ss-pm 12. p g n - c d 13. pg-tgo
68.82 47.14 106.57 43.31 32.56 43.18 70.04 61.77 41.36 50.86 46.70 103.69 68.88
2.49*** 3.45"** 5.70*** 2.07*** 2.23*** 2.51"** 4.88*** 2.29*** 2.62*** 2.78*** 2.42*** 5.79*** 4.52***
1.19 1.40 2.50 1.77 1.29 1.40 2.74 1.77 2.12 1.92 1.35 3.07 1.93
132.96 124.54 62.75 85.41 80.19 75.29 76.38 4.90 3.81 7.20 32.41 ---25.21 125.71
-0.89** -0.31 -2.14"** 0.40 0.28 0.54*** 0.88*** - 0.27 -0.61"** 0.46* -0.82** - 1.07"** - 2.62*** - 2.87*** - 1.28"** - 1.69"**
1.71 1.97 1.61 1.81 t.17 0.94 0.98 0.94 0.99 1.43 1.76 1.91 2.17 2.19 1.92 2.24
108.82 96.26 1.82 71.83 6.64 2.99
2.00** 1.42" 0.48*** 0.06 0.09 0.74**
4.78 3.53 0.63 1.93 1.46 1.47
Angular dimensions 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.
n-s-ba n-s-ar pm-s-ba s-n-sp s-n-ss s-n-sm s-n-pg ss-n-sm ss-n-pg NSL/NL NSL/ML REFJML NSL/REFmj REF~rJREF~ NL/ML ML/RL
~
Dentoalveolar relations 30. 31. 32. 33. 34. 35.
IL]NL IL]ML pr-n-ss CL/ML oj ob
Posture 36. 37. 38. 39. 40. 41. 42, 43. 44. 45. 46.
NSL/VER FH/VER NLIVER NSL/OPT NSL/CVT FH/OPT FH/CVT NL/OPT NL/CVT OPT/HOR CVT/HOR
98.40 89.07 91.02 95.06 99.83 85.72 90.50 87.86 92.63 93.34 88.57
- 0.22 -0.15 - 0.68 0.64 0.96 0.71 1.04 0.18 0.50 -0.86 - 1.19
~
3.84 4.23 3.92 4.91 4.97 5.72 5.74 5.06 5.13 5.77 5.54
*P < 0 . 0 5 . **P < 0 . 0 1 . ***P < 0 . 0 0 1 . Sample size = 43.
Mean age at stage 1 = 9.5 years; mean period of change = 2.7 years.
region, the position of the transferred fiducial points usually did not coincide with the anatomically determined sella and nasion points on the second film. The second pair of fiducial points was located in the mandible. On the first film, one point was located arbitrarily in the middle of the symphysis and one in the region below the first molar. The second film was then oriented according to stable trabecular structures in the mandible12; the two mandibular fiducial points were then transferred to the second film. The accurate transfer of fiducial points to the second film was facilitated by the use of a viewing device that magnifies a small viewing area and shields against extraneous light. Even so, the transfer of point nasion was often difficult because of high film density in this area. Therefore, a cross printed on a transparent sheet of cellophane was taped onto the first film to indicate the position of this point and to facilitate its transfer. The reference line connecting the two fiducial points in the cranial base was termed REFcrb and that connecting the two fiducial points in the mandible was designated REFml. Growth changes in the inclination of REFml relative to RgFcrb correspond in principle to the growth change in inclination of the implant line used by Bj6rk and Skieller, 13 although the method error would be expected to be somewhat larger since implants were not used. Changes in the angle REFcrb/REFml indicate the rotation of the mandible. Normally this rotation is partly concealed by marked remodeling of the lower mandibular border. Therefore, during growth the mandibular plane ML rotates much less than an implant line or a structure-based reference line. To distinguish between the two measures of mandibular rotation, use of the term true or total rotation is suggested to indicate the rotation of an implant line or a structure-based reference line; the term apparent rotation is used for the rotation of the commonly used mandibular plane in relation to the cranial base. The reference points and fiducial points were digitized as described by Solow and Tallgren. ~ The accuracy of the digitization was checked by superimposition of each film on a full-size Calcomp plot of the points produced by the PLOTCHECK program. The variables were calculated by the COORD program and the mean facial diagrams were produced by the POLREC program. ~ The statistical analysis was carried out by the SAS statistical package 15 at the NEUCC computer center in Copenhagen. The variables studied are listed in Table I. A set of 35 linear and angular variables were used to screen the following aspects of craniofacial morphology: cranial base size and form (nos. 1, 4, 5, 14, and 15); size and
Volume89 Number 2 Table U.
Growth changes in posture and morphology
135
Correlations between changes in posture and morphology Growth changes in postural variables
Craniovertical Craniocervical Growth changes in morphologic NSL/VER FH/VER NL/VER NSL/OPT NSL/CVT [ FH/OPT FH/CVT variables (No. 36) (No. 37) (No. 38) (No. 39) (No. 40) I (No. 41) (No. 42)
Cervical inclination NL/OPT (No. 43)
NL/CVT OPT/HOR CVT/HOR (No. 44) (No. 45) (No. 46)
Linear dimensions 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
n-s n-sp n-gn s-ba s-at s-pm s-tgo sp-gn ar-tgo sp-pm ss-pm pgn-cd pg-tgo
0.01 0.07 -0.05 - 0.03 - 0.07 -0.14 -0.09 -0.04 - 0.12 0.14 0.04 - 0.07 0.02
0.01 -0.13 -0.23 - 0.01 -0.03 -0.08 -0.12 -0.14 0.21 0.02 0.02 -0.23 -0.02
0.04 -0.12 -0.13 -0.05 -0.07 0.06 -0.11 -0.04 -0.16 0.05 -0.06 -0.09 0.04
-0.10 0.04 0.03 0.20 0.10 -0.05 -0.09 0.05 -0.20 0.00 -0.14 -0.15 0.03
-0.01 0.12 0.13 0.26 0.13 0.03 0.01 0.11 -0.09 0.09 -0.04 -0.02 0.09
-0.10 -0.11 -0.11 0.18 0.11 -0.01 -0.11 -0.04 -0.25 - 0.08 -0.13 -0.26 0.01
-0.03 -0.03 -0.03 0.24 0.14 0.06 -0.03 0.01 -0.16 0.00 -0.05 -0.14 0.06
-0.07 -0.11 -0.04 0.18 0.09 0.10 -0.10 0.05 -0.22 - 0.07 -0.21 -0.17 0.05
0.10 - 0.02 0.06 0.24 0.12 0.18 -0.01 0.11 -0.12 0.01 -0.12 -0.04 0.11
0.09 0.01 -0.06 -0.19 -0.13 -0.05 -0.01 -0.07 0.09 0.09 0.14 0.08 - 0.02
0.02 -0.07 -0.15 -0.26 -0.16 -0.12 -0.07 -0.12 0.00 0.02 0.07 -0.03 -0.07
0.30* 0.05 0.24 0.03 -0.17 -0.21 - 0.23 0.00 0.03 0.13 0.09 -0.01
0.08 -0.15 0.18 0.06 0.06 - 0.05 -0.07 0.13 0.14 - 0.07 -0.08 -0.11
0.20 -0.08 0.19 0.04 -0.10 - 0.10 -0.13 - 0.02 0.01 -0.24 -0.02 -0.07
0.01 0.05 -0.17 -0.07 -0.26 -0.30 -0.23 -0.03 -0.09 0.04 0.14 0.14
0.05 0.06 -0.20 -0.05 -0.27 =0.32* -0.20 -0.02 -0.12 0.03 0.09 0.13
-0.14 - 0 . I1 -0.17 -0.04 -0.07 -0.15 -0.09 -0.07 0.01 - 0 . I0 0.00 0.03
-0.10 -0.10 -0.20 -0.02 -0.08 -0.17 -0.07 0.08 -0.02 -0.11 -0.04 0.03
-0.07 -0.06 -0.20 -0.06 -0.20 -0.21 -0.14 -0.04 -0.10 -0.24 0.05 0.09
- 0.03 -0.05 -0.23 -0.05 -0.21 - 0.23 -0.12 -0.03 -0.13 -0.25 0.00 0.09
0.20 -0.01 0.30 0.08 0.11 0.11 0.04 0.03 0.09 0.05 - 0.06 -0.13
0.17 -0.02 0.35* 0.07 0.12 0.14 0.02 0.02 0.13 0.07 -0.01 - 0.14
26. NSL/REFr~ 27. R E F J R E F ~
0.04 -0.05
0.01 -0.04
-0.04 -0.08
28. NL/ML 29. ML/RL
-0.01 -0.18
- 0.02-0.25
0.16 -0.21
0.09 -0.10
0.06 -0.14
0.07 -0.15
0.04 -0.18
0.23 -0.13
0.19 -0.16
-0.09 -0.03
-0.06 0.00
0.08 0.15 -0.01 0.13 0.08 0.04
-0.15 0.09 0.03 0.14 -0.02 0.14
0.21 0.04 0.06 -0.12 0.22 -0.15
0.20 0.07 0.21 -0.04 0.24 -0.06
0.33* 0.15 0.07 -0.06 0.27 -0.25
0.32* 0.18 0.21 -0.29 -0.17
0.19 0.11 0.12 -0.07 0.23 -0.21
0.18 0.15 0.27 0.01 0.24 -0.11
-0.26 -0.04 -0.08 0.16 -0.21 0.28
-0.27 -0.08 -0.22 0.09 -0.24 0.21
-
-
Angular dimensions i4. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.
n-s-ba n-s-ar pm-s-ba s-n-sp s-n-ss s-n-sm s-n-pg ss-n-sm ss-n-pg NSL/NL NSL/ML REFcrb/ML
0.54*** 0.55***
0.50*** 0.54***
0.45** 0.47**
0.41"* 0.51"**
0.47** 0.50***
0.42** - 0 . 4 4 " * -0.42** 0.50*** -0.50*** -0.52***
Dentoalveolar relations 30. 31. 32. 33. 34. 35.
ILs/NL IL]ML pr-n-ss CL/ML oj ob
-0.13 -0.01 -0.05 0.08 -0.04 0.22
*P < 0.05. **P < 0.01. ***P < 0.001. Sample size = 43.
position of the maxillary complex (nos. 2, 6,'10, 11,o 17, 18 and 23); mandibular size, position, and form (nos. 9, 12, 13, 19, 20, 24-27 and 29); sagittal and vertical jaw relationships (nos. 21, 22, and 28); anterior and posterior facial heights (nos. 3, 7, and 8); bony nasopharynx (no. 16); and dentoalveolar relations (nos. 30-35).
P o s t u r a l r e l a t i o n s w e r e a s s e s s e d b y 11 v a r i a b l e s . T h e c r a n i o v e r t i c a ! a n g u l a t i o n ( t h a t is, t h e p o s i t i o n o f t h e h e a d in r e l a t i o n to t h e t r u e v e r t i c a l ) w a s e x p r e s s e d by the angles b e t w e e n the craniofacial reference lines N S L , F H , a n d N L a n d t h e t r u e v e r t i c a l , V E R ( n o s . 3638). T h e c r a n i o c e r v i c a l a n g u l a t i o n ( t h e p o s i t i o n o f t h e h e a d in r e l a t i o n to t h e c e r v i c a l c o l u m n ) w a s e x p r e s s e d
136
S o l o w a n d Siersbcek-Nielsen
Am. J. Orthod. February 1986
CHANGE R E F c r b / R E F m l
be reproduced without systemic error and with a method error of 1.5°--that is, in the individual subject, the true growth rotation of the mandible could usually be assessed within + 3° by the structure-based method of superimposition.
3o
•
•o
• • •
e •
-3
•
•
RESULTS
• eo
•
•
~
• ®
6
oo
•
-6
N = 43
r = 0.55 p < 0.001
-9-
,
-12
I
i
-8
~ -4
o
;
°
CHANGE N S L / O P T
Fig.
3. Scattergram illustrating association between change in
craniocervical angulation and true rotation of mandible. In present longitudinal sample, average true rotation of mandible was - 2 . 8 ° (negative value indicates forward rotation); average change in craniocervical angutation was practically zero.
by the angles between the craniofacial reference lines NSL, FH, and NL and the cervical column reference lines OPT and CVT (nos. 39-44). Cervical inclination in relation to the true horizontal was expressed by variables 45 and 46. Some of these angles (NSL/VER, FH/ VER, NL/VER, NSL/OPT, NSL/CVT, OPT/HOR, and CVT/HOR) are indicated on Fig. 1. For detailed definitions of the reference points on the cervical column, see Solow and Tallgren.l Method error
Method errors for morphologic and postural variables and for growth changes calculated from digitized reference points have been reported previously. 74° The method errors for the postural variables~the standard deviations of the individual measurements--ranged from 2.3 ° to 3.4°. 9 The method error for the computerized, structurebased assessment of the true or total rotation of the mandible has not been described. To determine "this method error, the four fiducial points on each film were removed from 20 pairs of films in the present series. The entire orientation procedure was repeated, the fiducial points were marked and digitized again, and the growth changes of the angle REFc,b/REFml were recalCulated. The growth changes of the 20 subjects could
A survey of the mean changes for the postural and morphologic angular variables is presented in Table I. The tabular data are given only for the total sample as it was not the purpose of this study to provide sex- and age-specific descriptions of growth changes. No significant mean changes were found for the postural variables. Individual changes were large but not unusual and ranged from a decrease of 13° to an increase of 12° . On the average, the cranial base angle was reduced by 0.9°; mandibular prognathism increased by 0.9°; and the mandible rotated forward. The forward rotation of the reference line ML was - 0 . 8 °, but the true forward growth rotation of the mandible as assessed by the fiducial-point line REFmI was - 2 . 9 °. The associations between the age changes in postural relations and the growth changes in craniofacial morphology were studied by correlation analysis. The results are presented in Table II illustrating that a complete screening of skeletal changes was made. A clear pattern of associations was found. The eight variables expressing changes in craniocervical angulation and in cervical inclination showed correlations ranging from r = 0.41 (P < 0.01) to r = 0.55 (P < 0.001) with the two variables that expressed the true rotation of the mandible as determined by the method of structural superimposition. Of the remaining 200 associations in the correlation matrix of all variables, only 5 reached the 5% level of significance. Since no systematic tendency in the pattern of these associations was observed, they could be ascribed to the effect of chance. No relationship could thus be demonstrated between changes in craniovertical angulation and changes in craniofacial morphology. The association between the change in craniocervical angulation and the growth rotation of the mandible is further illustrated in the scattergram of the association between changes in angles NSL/OPT and REFcrb/REFml (Fig. 3). It is seen that a decrease in craniocervical angulation was associated with larger-than-average forward growth rotation of the mandible and that an increase in craniocervical angulation was associated with a backward or a less-than-average forward growth rotation of the mandible. The average craniofacial growth changes in the ten subjects with the largest reduction in craniocervical an-
Volume89
Growth changes in posture and morphology
Number 2
MAX
REDUCTION
MAX
NSL/OPT
AVERAGE GROWTH,
10 S U B J E C T S
INCREASE
AVERAGE GROWTH,
137
NSL/OPT 10 SUBJECTS
t k O
Q
.....
9.3 Y E A R S
- -
12.3 YEARS
Fig. 4. Mean facial diagrams illustrating average facial growth in the 10 subjects with the largest reduction in craniocervical angulation (mean = -5.7°). Notice large true rotation of mandible (mean = - 4 . 5 °) and forward downward displacement of hyoid bone. Diagrams are superimposed on fiducial points representing stable structures in anterior cranial base with REForb arbitrarily positioned horizontally.
gulation and in the ten subjects with the largest increase in craniocervicaI angulation are illustrated by mean facial diagrams in Figs. 4 and 5. These diagrams visualize the remarkable difference in average mandibular rotation in the two subsamples ( - 4 . 5 ° vs. - 1 . 2 ° ) , and also suggest that the changes in craniocervical angu!ation are related not only to mandibular rotation, but also to the general growth direction of the face. The subgroup with the largest reduction in craniocervical angulation and greater forward growth rotation of the mandible also displays a tendency to forward growth direction of the face and an average downward forward displacement of the hyoid point; the subgroup with the largest increase in craniocervical angulation and lessthan-average forward growth rotation of the mandible displays a more downward growth direction of the face and a downward backward displacement of the hyoid point relative to the anterior cranial base. This relation between changes in posture and morphology becomes even more conspicuous in selected subjects with the greatest observed changes in craniocervical posture (Figs. 6 and 7--cases from opposite ends of scattergram).
.....
9.6 Y E A R S
- -
12.3 Y E A R S
Fig. 5. Mean facial diagrams illustrating average facial growth in the 10 subjects with the largest increase in craniocervical angulation (mean = + 7.0°). Notice less than average true rotation of the mandible (mean = - 1 . 2 °) and downward backward displacement of hyoid bone. Superimposition of diagrams is the same as in Fig. 4.
DISCUSSION The longitudinal material analyzed in the present study was obtained by using observations recorded prior to the commencement of treatment performed at a suburban community orthodontic clinic outside Copenhagen, Denmark. Since the sample was selected on the basis of the presence of some type of malocclusion, it cannot be considered representative of the population. However, the aim of the study was to examine general growthcoordinating mechanisms and such mechanisms may be assumed to operate in all subjects whether or not malocclusion is present. For the same reason, the sample was not divided into age- or sex-specific groups. The correlation coefficients between the postural changes and the growth changes in craniofacial morphology revealed that the changes in craniocervical angulation and cervical inclination were associated with the degree and direction of the true mandibular growth rotation as assessed by the structure-based method of superimposition of the cephalometric films. Practically no associations were found with the growth changes of any of the remaining 33 morphologic variables or between the changes in the conventionally used craniovertical angles and the changes in morphology. The findings in the present study were made pos-
138
Solow and Siersbcek-Nielsen
Am. J. Orthod. February !986
II
f/
\\~
F 3309 . . . . . 8.5yrs --11.9yrs
F 5079 . . . . . 8.4yrs --11.3yrs
Fig. 6. Facial growth in Case F 330 observed from 8.5 to 11.9 years of age prior to orthodontic treatment. Shaded area indicates the true displacement of the mandible relative to the anterior cranial base. There is a marked reduction iri craniocervical angulation, the mandible rotates markedly forward, and the facial growth direction is predominantly horizontal. SuperimpoSition is made on cranial base structures.
Fig. 7. Facial growth in Case F 507 observed from 8.4 to 1 i .3 years of age prior to orthodontic treatment. There is a large increase in craniocervical angulation, the mandible does not rotate forward, and the growth direction is predominantly vertical. Superimposition is made on cranial base structures.
sible by the adoption of two relatively new techniques. The first of these is the recording of the cephalometric radiographs in a posture that ensures not only a natural position of the head, but also a natural position of the cervical column. To make these recordings, it is essential (as described in detail by Siersba~k-Nielsen and Solowg) that the radiographic operator does not position the subject's head by manipulating it with the hands. Any sagittal manipulation of the head will influence the craniocervical angulation and cervical inclination, even when special precautions (projected lines, fluid level) are taken tO reproduce a previously determined position of the head in relation to the true vertical. The second of these techniques is the computerized application of Bj6rk's procedure of structural superimposition as described by Sam/is and Solow. ~° The position of structural superimposition is indicated on both films of the individual subject by one pair of 15ducial points of orientation for each area of superimposition. In principle, the points may be located in the area of superimposition as described by Bj6rk and Skieller ]3 or they may be located in theedges or corners of the cephaiometric films as described by B'aumrind and Miller 16 and McWilliam. 17 The fact that the changes in craniocervical inclination are associated with the true rotation of the mandible as determined by the structure-based superimposition--but not with the apparent rotation of the man-
dible as determined by the change in inclination of the mandibular plane--fits well with the normal dramatic remodeling pattern of the mandibular border ~4that generally occurs in a direction that masks the true rotation. Possibly, the stress and strain produced by the soft tissues surrounding the mandibular border during the displacement of the bone relative to the surrounding soft-tissue matrix results in appositional and resorptive periosteal activity that relocates the borders relative to the internal structures of the mandibular body and at the same time counteracts the displacement of the border relative to the surrounding soft tissues. In the present study, the mean true forward rotation of the mandible was - 2 . 6 ° and the angle NSL/ML changed only - 0 . 8 °. This indicates a 69% relocation of the mandibular border--an even higher figure than that found by Bj6rk and Skieller. ~3 Two aspects of the present longitudinal analysis are of particular interest as they relate to previous crosssectional studies of the association between posture and morphology. The first aspect concerns the type of postural relationship that was related to craniofacial growth. The study comprised three types of postural variables: the conventional craniovertical angles, the craniocervical angles, and the angles expressing cervical inclination. In the cross-sectional study of adult male students,~ the pattern of correlation coefficients suggested that the
Volume 89 Number 2
craniocervical angles were more strongly associated with craniofacial morphology than were the craniovertical angles; a similar pattern was found in a crosssectional study of children. 6 The present study confirmed this tendency--practically no associations were found between changes in morphology and changes in the craniovertical angles NSL/VER, FH/VER, and NL/ VER, whereas the marked associations with morphology were found for the angles expressing craniocervical angulation and cervical inclination. The natural position of the head in relation to the true vertical (as expressed by the craniovertical angles) has had an important place in orthodontic diagnosis and cephalometric analysis because of its role in the esthetic evaluation of the facial profile. It still serves this function. From a developmental point of view, on the other hand, the craniocervical angulation and the cervical inclination may have greater relevance since the developmental associations observed in the present study were almost entirely limited to these postural variables. In studies of head posture aimed at elucidating developmental associations, it is important, therefore, to employ recording methods that ensure not only a natural position of the head in relation to the true vertical, but also a natural position of the cervical column in relation to the true horizontal and a natural craniocervical angulation. The second interesting aspect of the present longitudinal analysis is the fact that the changes in craniocervical angulation and cervical inclination were associated with the growth rotation of the mandible (r = 0.410.55). Although numerically moderate, these correlations of 0.41-0.55 between mandibular rotation and posrural change indicate the presence of a relatively strong biologic coordinating mechanism, since the correlations are able to appear despite the relatively large method error of both variables. Correlations larger than this magnitude are rarely observed in craniofacial studies when spurious or topographic factors are not involved. In the previous cross-sectional study of head posture and craniofacial morphology in adult male dental students, 1 the average differences in craniofacial morphology between subjects with large and small craniocervical angulation showed graphically a striking similarity to the average morphologic differences between subjects with large and small mandibular plane inclination. This was interpreted as suggesting a specific relationship between the craniocervical angulation and the development of the mandible. However, the presence of such a specific relationship could not be detected statistically in that study, probably because of its crosssectional design. It is therefore of interest that in the
Growth changes in posture and morphology
139
present longitudinal study the same specific association between change in craniocervical angulation and the growth rotation of the' mandible emerges as a main finding, documented statistically, graphically, and in individual case analyses. Clinically, it is well known that the growth pattern of the mandible is one of the most characteristic features of facial development. This is reflected in most cephalometric analysis systems and also in the concern for mandibular development in orthodontic treatment planning. Statistically, the role of the mandible in total facial development is reflected in the fact that the variances of measurements relating the vertical development of the mandible to the upper face and the cranial base are much larger than variances of other craniofacial dimensions when technical factors, such as reference point distances, are taken into account. 7 As a consequence of the importance of the developmental pattern of the mandible, much effort has been devoted to explaining and predicting this pattern. The present study suggests that the analysis of functional factors, such as the craniocervical angulation, may be a useful supplement in this respect. From a research point of view, the finding of a relationship between changes in craniocervical angulation and the developmental pattern of the mandible raises some interesting questions: (1) Is it possible that the change in craniocervical angulation could be a causal factor in determining the mandibular developmental pattern and, if so, by what mechanism could such an influence be effectuated? (2) What factors could conceivably induce long-term changes in craniocervical angulation? Possible answers to these questions are provided by the hypothetical model for the relationship among posture, craniofacial morphology, and the adequacy of the nasopharyngeal airway suggested by Solow and Kreiborg. 18 Several studies on assessment of head posture, craniofacial development, and airway adequacy have yielded results consistent with the prediction of this model. In particular, much evidence documents the joint occurrence of obstructed nasopharyngeal airway, increased craniocervical angulation, and a vertical development of the mandible and the face as a whole. (For a review, see Solow, Siersbmk-Nielsen, and Greve. 6) In the interpretation of correlation studies of facial development, considerable caution should be exerted. In cross-sectional studies, only indirect inference can be made about the presence of growth-coordinating mechanisms. Growth-coordinating mechanisms can be studied directly in longitudinal studies of growth changes such as the present study, but even in such
140
Solow and Siersbcek-Nielsen
studies as these, o n l y indirect inference can be m a d e about the possibility o f predicting g r o w t h b e h a v i o r o f facial dimensions. Direct e x a m i n a t i o n o f the possibility o f predicting craniofacial d e v e l o p m e n t requires an e x p e r i m e n t a l design in which possible d e t e r m i n i n g parameters are measured and related to subsequent facial growth. O n the basis of the present study, an analysis o f the correlation b e t w e e n head posture in children and the subsequent p a t t e m o f craniofacial g r o w t h w o u l d s e e m to be o f particular interest. The authors wish to express their indebtedness to Dr. Hans E. Jonassen, D.D.S., Director, Municipal Child Dental Health Service, Farum, and dental auxiliaries Inge Christensen, Jeanne v. Btilow, Linda Jeppesen, Jytte Laursen, Annette Olsen and Bente Julsgaard. REFERENCES 1. Solow B, Tallgren A: Head posture and craniofacial morphology. Am J Phys Anthropol 44: 417-436, 1976. 2. Thompson BP: Cra~iocervical angulation and morphologic variables in children: A cephalometric study, MS Thesis, University of North Carolina, Chapel Hill, 1978. 3. Opdebeek H, Bell WH, Eisenfeld J, Mishelevich D: Comparative study between the SFS and LFS rotation as a possible morphogenetic mechanism. AM J ORTHOD74: 509-521, 1978. 4. Marcotte MR: Head posture and dcntofacial proportions. Angle Orthod 51: 208-213, 1981. 5. yon Treuenfels H: Die Relation der Atlasposition bei prognather und progener Kicferanomalie. Fortschr Kieferorthop 42: 482491, 1981. 6. Solow B, Siersba~k-Nielsen S, Greve E: Airway adequacy, head posture and craniofacial morphology. AMJ ORTHOD86: 214-223, 1984. 7. Solow B: The pattern of craniofacial associations. A morphological and methodological correlation and factor analysis study
Am. J. Orthod. February 1986
8. 9.
10. 11.
12. 13. 14.
15. 16.
17.
18.
19.
on young male adults. Acta Odont Scand 24(Suppl 46): 57-88, 1966. Solow B, Tallgren A: Natural head position in standing subjects. Acta Odont Scand 29: 591-607, 1971. Siersb~ek-Nielsen S, Solow B: Intra- and interexaminer variability in head posture recorded by dental auxiliaries. AM J ORTHOD82: 50-57, 1982. Sarn~is K-V, Solow B: Early adult changes in the skeletal and soft-tissue profile. Eur J Orthod 2: 1-12, 1980. Bj6rk A, Skieller V: Normal and abnormal growth of the mandible. Appendix: Superimposition of profile radiographs by the structural method. Eur J Orthod 5: 40-44, 1983. Bj6rk A: Prediction of mandibular growth rotation. AMJ ORa'HOD 55: 585-599, 1969. Bj6rk A, Skieller V: Facial development and tooth eruption. AM J ORTHOD62: 339-383, 1972. Bj6rk A: Variations in the growth pattern of the human mandible: Longitudinal radiographic study by the implant method. J Dent Res 42: 400-411, 1963. Helwig JT, Council-KA (editors): SAS User's Guide, 1979 edition. SAS Institute Inc., Raleigh, North Carolina, 1979. Baumrind S, Miller DM: Computer-aided head film analysis: The University of California San Francisco method. AM J ORTHOD78: 41-65, 1980. McWilliam JS: Orientation of orthogonal coordinate systems used for registration of cephalometfic landmarks. Scand J Dent Res 90: 145-150, 1982. Solow B, Kreiborg S: Soft-tissue stretching: A possible control factor in craniofacial morphogenesis. Scand J Dent Res 85: 505507, 1977. SCrensen H, Solow B, Greve E: Assessment of the nasopharyngeal airway. Acta Otolaryngol 89: 227-232, 1980.
Reprint requests to:
Dr. Beni Solow Institute of Orthodontics Royal Dental College 160, Jagtvej DK-2100 Copenhagen O, Denmark
Key words: Head posture, craniocervical angulafion, craniofacial growth
T h e presence of a relationship between (on one hand) the posture of the head and the cervical column and (on the other) the form of the facial skeleton has been well established through cross-sectional studies on children and adults. A natural head posture characterized by a large craniocervical angulation is seen, on the average, in connection with a vertical facial development--that is, large afiterior and posterior facial dimensions and small anteroposterior dimensions, a small facial prognathism and large inclination of the mandibular and palatalplanes, and a small sagittal extent of the nasopharyngeal space. J-6 In principle, the presence of a correlation between two dimensions in a cross-sectional sample suggests that a coordination of the growth of these dimensions has occurred. Such correlations therefore are valuable indicators_in the search for growth-coordinating mechanisms in the craniofacial complex. However, the presence of significant correlations in cross-sectional studies can only provide in-
Presented in part at the Sixtieth General Session of the International Association for Dental Research in New Orleans, March 1982. Supported by Grant no. 82-3033 from the Danish Medical Research Council. *Institute of Orthodontics, Royal Dental College. **Farum Community Orthodontic Clinic.
132
direct evidence for the presence of previous growthcoordinating mechanisms. Moreover, nonbiologic, spurious factors have to be considered in the interpretation of the correlation coefficients observed in such crosssectional materials. 7 Direct observation of growth-coordinating mechanisms requires longitudinal material. The aim of the present study was to examine in a longitudinal sample whether the growth coordinations suggested by cross-sectional studies could actually be detected in the form of associations between growth changes in head and cervical posture and growth changes in craniofacial morphology. MATERIAL AND METHODS The sample comprised 43 children, 20 girls and 23 boys, admitted for treatment of various malocclusions at a community orthodontic clinic. The malocclusions comprised twelve Class I, twenty-five Class II, Division l, and six Class II, Division 2 cases. Before initiation of orthodontic treatment, the growth of the children was followed for a period of 1 to 4 years. The mean duration of this observation period was 2.7 years; the standard deviation was 0.8 years. Mean age at the initial examination was 9.5 years with a standard deviation of 1.4 years and a range from 7.7 to 12.9 years.
Growth changes in posture and morphology
Volume 89 Number 2
133
A
NsL_/ R E Fc r
/,
~
B
REFml
p 2 ~
ML
v=r~
OPT
CVT
Fig. 1. Reference points and lines on the cephalometric radiographs. Some postural angles are indicated. For definitions see Solow and Tallgren1 and Serensen, Solow, and Greve? 9
The present study is part of a project to elucidate the relationship between head posture and craniofacial morphology. The material used in this study consisted of lateral cephalometric radiographs taken at the start and end of the period of observation. Thus, no treatment was carried out during this period. The cephalometric radiographs were taken in the natural head position (mirror position) with the subject standing in orthoposition. 8,9 The radiographs were used for the cephalometric analysis and for measurement of the postural relationships. The radiographs were taken with a Dana Cephalix cephalometer that is vertically adjustable to record standing subjects. For lateral cephalometric films, the equipment has a fixed film-to-focus distance of 190 cm" and a fixed film-to-median plane distance of 10 cm. This ensures a constant enlargement of 5.6% of the median plane and thus permits precise analysis of growth changes of linear and angular dimensions, as well as direct structure-based superimpositions of sequential films of the same subjects. An 0.5-mm weighted lead wire was suspended in
Fig. 2. Fiducial points and lines on second cephaiometric film. A, Points nt and st are fiducial points transferred from film 1 to film 2 after superimposition of films on stable structures in anterior cranial base. Points n and s are independently marked nasion and sella points on film 2. REForb is the reference line through the fiducial points in the cranial base. On film 1, REForb coincides with NSL. B, Points pl and p2 are fiducial points transferred from film 1 to film 2 after superimposition of film on stable structures in the mandible. REFm~is the reference line through the fiducial points in the mandible, True rotation of the mandible is determined as growth change in angle REFoJ REFIne. During growth this rotation is masked by remodeling of lower mandibular border. Apparent rotation of mandible, that is, change in mandibular plane inclination NSL/ML, is therefore usually much smaller than true rotation.
front of the cassette to register the true vertical on the film. A movable ratio 8 grid and intensifying screens were used. Exposures were made at 80-86 kV and 32 mAs. Measurements Forty-one reference points and four fiducial points were marked directly on each film (Fig. 1) with a soft sharp pencil (Schwan Stabilo 8008). The two profile radiographs of each subject were marked concurrently to achieve consistency in the determination of the reference points. The four fiducial points were used for the computerized, structure-based analysis of growth changes.I° One pair of fiducial points was located in the anterior cranial base. On the first film, points n and s served as fiducial points. The second film was then superimposed on the first and oriented according to stable anatomic structures in the anterior cranial basel1; the fiducial points were transferred to the second film and were designated nt and st (Fig. 2). Because of growth at sella turcica and in the nasion
134
Am. J, Orthod.
Solow and Siersbcek-Nielsen
February 1986
Table I. Mean growth changes Mean at stage I
Variable
Mean
SD of
change
change
Linear dimensions 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
n-s n-sp n-gn s-ba s-ar s-pm s-tgo sp-gn ar-tgo sp-pm
11. ss-pm 12. p g n - c d 13. pg-tgo
68.82 47.14 106.57 43.31 32.56 43.18 70.04 61.77 41.36 50.86 46.70 103.69 68.88
2.49*** 3.45"** 5.70*** 2.07*** 2.23*** 2.51"** 4.88*** 2.29*** 2.62*** 2.78*** 2.42*** 5.79*** 4.52***
1.19 1.40 2.50 1.77 1.29 1.40 2.74 1.77 2.12 1.92 1.35 3.07 1.93
132.96 124.54 62.75 85.41 80.19 75.29 76.38 4.90 3.81 7.20 32.41 ---25.21 125.71
-0.89** -0.31 -2.14"** 0.40 0.28 0.54*** 0.88*** - 0.27 -0.61"** 0.46* -0.82** - 1.07"** - 2.62*** - 2.87*** - 1.28"** - 1.69"**
1.71 1.97 1.61 1.81 t.17 0.94 0.98 0.94 0.99 1.43 1.76 1.91 2.17 2.19 1.92 2.24
108.82 96.26 1.82 71.83 6.64 2.99
2.00** 1.42" 0.48*** 0.06 0.09 0.74**
4.78 3.53 0.63 1.93 1.46 1.47
Angular dimensions 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.
n-s-ba n-s-ar pm-s-ba s-n-sp s-n-ss s-n-sm s-n-pg ss-n-sm ss-n-pg NSL/NL NSL/ML REFJML NSL/REFmj REF~rJREF~ NL/ML ML/RL
~
Dentoalveolar relations 30. 31. 32. 33. 34. 35.
IL]NL IL]ML pr-n-ss CL/ML oj ob
Posture 36. 37. 38. 39. 40. 41. 42, 43. 44. 45. 46.
NSL/VER FH/VER NLIVER NSL/OPT NSL/CVT FH/OPT FH/CVT NL/OPT NL/CVT OPT/HOR CVT/HOR
98.40 89.07 91.02 95.06 99.83 85.72 90.50 87.86 92.63 93.34 88.57
- 0.22 -0.15 - 0.68 0.64 0.96 0.71 1.04 0.18 0.50 -0.86 - 1.19
~
3.84 4.23 3.92 4.91 4.97 5.72 5.74 5.06 5.13 5.77 5.54
*P < 0 . 0 5 . **P < 0 . 0 1 . ***P < 0 . 0 0 1 . Sample size = 43.
Mean age at stage 1 = 9.5 years; mean period of change = 2.7 years.
region, the position of the transferred fiducial points usually did not coincide with the anatomically determined sella and nasion points on the second film. The second pair of fiducial points was located in the mandible. On the first film, one point was located arbitrarily in the middle of the symphysis and one in the region below the first molar. The second film was then oriented according to stable trabecular structures in the mandible12; the two mandibular fiducial points were then transferred to the second film. The accurate transfer of fiducial points to the second film was facilitated by the use of a viewing device that magnifies a small viewing area and shields against extraneous light. Even so, the transfer of point nasion was often difficult because of high film density in this area. Therefore, a cross printed on a transparent sheet of cellophane was taped onto the first film to indicate the position of this point and to facilitate its transfer. The reference line connecting the two fiducial points in the cranial base was termed REFcrb and that connecting the two fiducial points in the mandible was designated REFml. Growth changes in the inclination of REFml relative to RgFcrb correspond in principle to the growth change in inclination of the implant line used by Bj6rk and Skieller, 13 although the method error would be expected to be somewhat larger since implants were not used. Changes in the angle REFcrb/REFml indicate the rotation of the mandible. Normally this rotation is partly concealed by marked remodeling of the lower mandibular border. Therefore, during growth the mandibular plane ML rotates much less than an implant line or a structure-based reference line. To distinguish between the two measures of mandibular rotation, use of the term true or total rotation is suggested to indicate the rotation of an implant line or a structure-based reference line; the term apparent rotation is used for the rotation of the commonly used mandibular plane in relation to the cranial base. The reference points and fiducial points were digitized as described by Solow and Tallgren. ~ The accuracy of the digitization was checked by superimposition of each film on a full-size Calcomp plot of the points produced by the PLOTCHECK program. The variables were calculated by the COORD program and the mean facial diagrams were produced by the POLREC program. ~ The statistical analysis was carried out by the SAS statistical package 15 at the NEUCC computer center in Copenhagen. The variables studied are listed in Table I. A set of 35 linear and angular variables were used to screen the following aspects of craniofacial morphology: cranial base size and form (nos. 1, 4, 5, 14, and 15); size and
Volume89 Number 2 Table U.
Growth changes in posture and morphology
135
Correlations between changes in posture and morphology Growth changes in postural variables
Craniovertical Craniocervical Growth changes in morphologic NSL/VER FH/VER NL/VER NSL/OPT NSL/CVT [ FH/OPT FH/CVT variables (No. 36) (No. 37) (No. 38) (No. 39) (No. 40) I (No. 41) (No. 42)
Cervical inclination NL/OPT (No. 43)
NL/CVT OPT/HOR CVT/HOR (No. 44) (No. 45) (No. 46)
Linear dimensions 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
n-s n-sp n-gn s-ba s-at s-pm s-tgo sp-gn ar-tgo sp-pm ss-pm pgn-cd pg-tgo
0.01 0.07 -0.05 - 0.03 - 0.07 -0.14 -0.09 -0.04 - 0.12 0.14 0.04 - 0.07 0.02
0.01 -0.13 -0.23 - 0.01 -0.03 -0.08 -0.12 -0.14 0.21 0.02 0.02 -0.23 -0.02
0.04 -0.12 -0.13 -0.05 -0.07 0.06 -0.11 -0.04 -0.16 0.05 -0.06 -0.09 0.04
-0.10 0.04 0.03 0.20 0.10 -0.05 -0.09 0.05 -0.20 0.00 -0.14 -0.15 0.03
-0.01 0.12 0.13 0.26 0.13 0.03 0.01 0.11 -0.09 0.09 -0.04 -0.02 0.09
-0.10 -0.11 -0.11 0.18 0.11 -0.01 -0.11 -0.04 -0.25 - 0.08 -0.13 -0.26 0.01
-0.03 -0.03 -0.03 0.24 0.14 0.06 -0.03 0.01 -0.16 0.00 -0.05 -0.14 0.06
-0.07 -0.11 -0.04 0.18 0.09 0.10 -0.10 0.05 -0.22 - 0.07 -0.21 -0.17 0.05
0.10 - 0.02 0.06 0.24 0.12 0.18 -0.01 0.11 -0.12 0.01 -0.12 -0.04 0.11
0.09 0.01 -0.06 -0.19 -0.13 -0.05 -0.01 -0.07 0.09 0.09 0.14 0.08 - 0.02
0.02 -0.07 -0.15 -0.26 -0.16 -0.12 -0.07 -0.12 0.00 0.02 0.07 -0.03 -0.07
0.30* 0.05 0.24 0.03 -0.17 -0.21 - 0.23 0.00 0.03 0.13 0.09 -0.01
0.08 -0.15 0.18 0.06 0.06 - 0.05 -0.07 0.13 0.14 - 0.07 -0.08 -0.11
0.20 -0.08 0.19 0.04 -0.10 - 0.10 -0.13 - 0.02 0.01 -0.24 -0.02 -0.07
0.01 0.05 -0.17 -0.07 -0.26 -0.30 -0.23 -0.03 -0.09 0.04 0.14 0.14
0.05 0.06 -0.20 -0.05 -0.27 =0.32* -0.20 -0.02 -0.12 0.03 0.09 0.13
-0.14 - 0 . I1 -0.17 -0.04 -0.07 -0.15 -0.09 -0.07 0.01 - 0 . I0 0.00 0.03
-0.10 -0.10 -0.20 -0.02 -0.08 -0.17 -0.07 0.08 -0.02 -0.11 -0.04 0.03
-0.07 -0.06 -0.20 -0.06 -0.20 -0.21 -0.14 -0.04 -0.10 -0.24 0.05 0.09
- 0.03 -0.05 -0.23 -0.05 -0.21 - 0.23 -0.12 -0.03 -0.13 -0.25 0.00 0.09
0.20 -0.01 0.30 0.08 0.11 0.11 0.04 0.03 0.09 0.05 - 0.06 -0.13
0.17 -0.02 0.35* 0.07 0.12 0.14 0.02 0.02 0.13 0.07 -0.01 - 0.14
26. NSL/REFr~ 27. R E F J R E F ~
0.04 -0.05
0.01 -0.04
-0.04 -0.08
28. NL/ML 29. ML/RL
-0.01 -0.18
- 0.02-0.25
0.16 -0.21
0.09 -0.10
0.06 -0.14
0.07 -0.15
0.04 -0.18
0.23 -0.13
0.19 -0.16
-0.09 -0.03
-0.06 0.00
0.08 0.15 -0.01 0.13 0.08 0.04
-0.15 0.09 0.03 0.14 -0.02 0.14
0.21 0.04 0.06 -0.12 0.22 -0.15
0.20 0.07 0.21 -0.04 0.24 -0.06
0.33* 0.15 0.07 -0.06 0.27 -0.25
0.32* 0.18 0.21 -0.29 -0.17
0.19 0.11 0.12 -0.07 0.23 -0.21
0.18 0.15 0.27 0.01 0.24 -0.11
-0.26 -0.04 -0.08 0.16 -0.21 0.28
-0.27 -0.08 -0.22 0.09 -0.24 0.21
-
-
Angular dimensions i4. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.
n-s-ba n-s-ar pm-s-ba s-n-sp s-n-ss s-n-sm s-n-pg ss-n-sm ss-n-pg NSL/NL NSL/ML REFcrb/ML
0.54*** 0.55***
0.50*** 0.54***
0.45** 0.47**
0.41"* 0.51"**
0.47** 0.50***
0.42** - 0 . 4 4 " * -0.42** 0.50*** -0.50*** -0.52***
Dentoalveolar relations 30. 31. 32. 33. 34. 35.
ILs/NL IL]ML pr-n-ss CL/ML oj ob
-0.13 -0.01 -0.05 0.08 -0.04 0.22
*P < 0.05. **P < 0.01. ***P < 0.001. Sample size = 43.
position of the maxillary complex (nos. 2, 6,'10, 11,o 17, 18 and 23); mandibular size, position, and form (nos. 9, 12, 13, 19, 20, 24-27 and 29); sagittal and vertical jaw relationships (nos. 21, 22, and 28); anterior and posterior facial heights (nos. 3, 7, and 8); bony nasopharynx (no. 16); and dentoalveolar relations (nos. 30-35).
P o s t u r a l r e l a t i o n s w e r e a s s e s s e d b y 11 v a r i a b l e s . T h e c r a n i o v e r t i c a ! a n g u l a t i o n ( t h a t is, t h e p o s i t i o n o f t h e h e a d in r e l a t i o n to t h e t r u e v e r t i c a l ) w a s e x p r e s s e d by the angles b e t w e e n the craniofacial reference lines N S L , F H , a n d N L a n d t h e t r u e v e r t i c a l , V E R ( n o s . 3638). T h e c r a n i o c e r v i c a l a n g u l a t i o n ( t h e p o s i t i o n o f t h e h e a d in r e l a t i o n to t h e c e r v i c a l c o l u m n ) w a s e x p r e s s e d
136
S o l o w a n d Siersbcek-Nielsen
Am. J. Orthod. February 1986
CHANGE R E F c r b / R E F m l
be reproduced without systemic error and with a method error of 1.5°--that is, in the individual subject, the true growth rotation of the mandible could usually be assessed within + 3° by the structure-based method of superimposition.
3o
•
•o
• • •
e •
-3
•
•
RESULTS
• eo
•
•
~
• ®
6
oo
•
-6
N = 43
r = 0.55 p < 0.001
-9-
,
-12
I
i
-8
~ -4
o
;
°
CHANGE N S L / O P T
Fig.
3. Scattergram illustrating association between change in
craniocervical angulation and true rotation of mandible. In present longitudinal sample, average true rotation of mandible was - 2 . 8 ° (negative value indicates forward rotation); average change in craniocervical angutation was practically zero.
by the angles between the craniofacial reference lines NSL, FH, and NL and the cervical column reference lines OPT and CVT (nos. 39-44). Cervical inclination in relation to the true horizontal was expressed by variables 45 and 46. Some of these angles (NSL/VER, FH/ VER, NL/VER, NSL/OPT, NSL/CVT, OPT/HOR, and CVT/HOR) are indicated on Fig. 1. For detailed definitions of the reference points on the cervical column, see Solow and Tallgren.l Method error
Method errors for morphologic and postural variables and for growth changes calculated from digitized reference points have been reported previously. 74° The method errors for the postural variables~the standard deviations of the individual measurements--ranged from 2.3 ° to 3.4°. 9 The method error for the computerized, structurebased assessment of the true or total rotation of the mandible has not been described. To determine "this method error, the four fiducial points on each film were removed from 20 pairs of films in the present series. The entire orientation procedure was repeated, the fiducial points were marked and digitized again, and the growth changes of the angle REFc,b/REFml were recalCulated. The growth changes of the 20 subjects could
A survey of the mean changes for the postural and morphologic angular variables is presented in Table I. The tabular data are given only for the total sample as it was not the purpose of this study to provide sex- and age-specific descriptions of growth changes. No significant mean changes were found for the postural variables. Individual changes were large but not unusual and ranged from a decrease of 13° to an increase of 12° . On the average, the cranial base angle was reduced by 0.9°; mandibular prognathism increased by 0.9°; and the mandible rotated forward. The forward rotation of the reference line ML was - 0 . 8 °, but the true forward growth rotation of the mandible as assessed by the fiducial-point line REFmI was - 2 . 9 °. The associations between the age changes in postural relations and the growth changes in craniofacial morphology were studied by correlation analysis. The results are presented in Table II illustrating that a complete screening of skeletal changes was made. A clear pattern of associations was found. The eight variables expressing changes in craniocervical angulation and in cervical inclination showed correlations ranging from r = 0.41 (P < 0.01) to r = 0.55 (P < 0.001) with the two variables that expressed the true rotation of the mandible as determined by the method of structural superimposition. Of the remaining 200 associations in the correlation matrix of all variables, only 5 reached the 5% level of significance. Since no systematic tendency in the pattern of these associations was observed, they could be ascribed to the effect of chance. No relationship could thus be demonstrated between changes in craniovertical angulation and changes in craniofacial morphology. The association between the change in craniocervical angulation and the growth rotation of the mandible is further illustrated in the scattergram of the association between changes in angles NSL/OPT and REFcrb/REFml (Fig. 3). It is seen that a decrease in craniocervical angulation was associated with larger-than-average forward growth rotation of the mandible and that an increase in craniocervical angulation was associated with a backward or a less-than-average forward growth rotation of the mandible. The average craniofacial growth changes in the ten subjects with the largest reduction in craniocervical an-
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Fig. 4. Mean facial diagrams illustrating average facial growth in the 10 subjects with the largest reduction in craniocervical angulation (mean = -5.7°). Notice large true rotation of mandible (mean = - 4 . 5 °) and forward downward displacement of hyoid bone. Diagrams are superimposed on fiducial points representing stable structures in anterior cranial base with REForb arbitrarily positioned horizontally.
gulation and in the ten subjects with the largest increase in craniocervicaI angulation are illustrated by mean facial diagrams in Figs. 4 and 5. These diagrams visualize the remarkable difference in average mandibular rotation in the two subsamples ( - 4 . 5 ° vs. - 1 . 2 ° ) , and also suggest that the changes in craniocervical angu!ation are related not only to mandibular rotation, but also to the general growth direction of the face. The subgroup with the largest reduction in craniocervical angulation and greater forward growth rotation of the mandible also displays a tendency to forward growth direction of the face and an average downward forward displacement of the hyoid point; the subgroup with the largest increase in craniocervical angulation and lessthan-average forward growth rotation of the mandible displays a more downward growth direction of the face and a downward backward displacement of the hyoid point relative to the anterior cranial base. This relation between changes in posture and morphology becomes even more conspicuous in selected subjects with the greatest observed changes in craniocervical posture (Figs. 6 and 7--cases from opposite ends of scattergram).
.....
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Fig. 5. Mean facial diagrams illustrating average facial growth in the 10 subjects with the largest increase in craniocervical angulation (mean = + 7.0°). Notice less than average true rotation of the mandible (mean = - 1 . 2 °) and downward backward displacement of hyoid bone. Superimposition of diagrams is the same as in Fig. 4.
DISCUSSION The longitudinal material analyzed in the present study was obtained by using observations recorded prior to the commencement of treatment performed at a suburban community orthodontic clinic outside Copenhagen, Denmark. Since the sample was selected on the basis of the presence of some type of malocclusion, it cannot be considered representative of the population. However, the aim of the study was to examine general growthcoordinating mechanisms and such mechanisms may be assumed to operate in all subjects whether or not malocclusion is present. For the same reason, the sample was not divided into age- or sex-specific groups. The correlation coefficients between the postural changes and the growth changes in craniofacial morphology revealed that the changes in craniocervical angulation and cervical inclination were associated with the degree and direction of the true mandibular growth rotation as assessed by the structure-based method of superimposition of the cephalometric films. Practically no associations were found with the growth changes of any of the remaining 33 morphologic variables or between the changes in the conventionally used craniovertical angles and the changes in morphology. The findings in the present study were made pos-
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II
f/
\\~
F 3309 . . . . . 8.5yrs --11.9yrs
F 5079 . . . . . 8.4yrs --11.3yrs
Fig. 6. Facial growth in Case F 330 observed from 8.5 to 11.9 years of age prior to orthodontic treatment. Shaded area indicates the true displacement of the mandible relative to the anterior cranial base. There is a marked reduction iri craniocervical angulation, the mandible rotates markedly forward, and the facial growth direction is predominantly horizontal. SuperimpoSition is made on cranial base structures.
Fig. 7. Facial growth in Case F 507 observed from 8.4 to 1 i .3 years of age prior to orthodontic treatment. There is a large increase in craniocervical angulation, the mandible does not rotate forward, and the growth direction is predominantly vertical. Superimposition is made on cranial base structures.
sible by the adoption of two relatively new techniques. The first of these is the recording of the cephalometric radiographs in a posture that ensures not only a natural position of the head, but also a natural position of the cervical column. To make these recordings, it is essential (as described in detail by Siersba~k-Nielsen and Solowg) that the radiographic operator does not position the subject's head by manipulating it with the hands. Any sagittal manipulation of the head will influence the craniocervical angulation and cervical inclination, even when special precautions (projected lines, fluid level) are taken tO reproduce a previously determined position of the head in relation to the true vertical. The second of these techniques is the computerized application of Bj6rk's procedure of structural superimposition as described by Sam/is and Solow. ~° The position of structural superimposition is indicated on both films of the individual subject by one pair of 15ducial points of orientation for each area of superimposition. In principle, the points may be located in the area of superimposition as described by Bj6rk and Skieller ]3 or they may be located in theedges or corners of the cephaiometric films as described by B'aumrind and Miller 16 and McWilliam. 17 The fact that the changes in craniocervical inclination are associated with the true rotation of the mandible as determined by the structure-based superimposition--but not with the apparent rotation of the man-
dible as determined by the change in inclination of the mandibular plane--fits well with the normal dramatic remodeling pattern of the mandibular border ~4that generally occurs in a direction that masks the true rotation. Possibly, the stress and strain produced by the soft tissues surrounding the mandibular border during the displacement of the bone relative to the surrounding soft-tissue matrix results in appositional and resorptive periosteal activity that relocates the borders relative to the internal structures of the mandibular body and at the same time counteracts the displacement of the border relative to the surrounding soft tissues. In the present study, the mean true forward rotation of the mandible was - 2 . 6 ° and the angle NSL/ML changed only - 0 . 8 °. This indicates a 69% relocation of the mandibular border--an even higher figure than that found by Bj6rk and Skieller. ~3 Two aspects of the present longitudinal analysis are of particular interest as they relate to previous crosssectional studies of the association between posture and morphology. The first aspect concerns the type of postural relationship that was related to craniofacial growth. The study comprised three types of postural variables: the conventional craniovertical angles, the craniocervical angles, and the angles expressing cervical inclination. In the cross-sectional study of adult male students,~ the pattern of correlation coefficients suggested that the
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craniocervical angles were more strongly associated with craniofacial morphology than were the craniovertical angles; a similar pattern was found in a crosssectional study of children. 6 The present study confirmed this tendency--practically no associations were found between changes in morphology and changes in the craniovertical angles NSL/VER, FH/VER, and NL/ VER, whereas the marked associations with morphology were found for the angles expressing craniocervical angulation and cervical inclination. The natural position of the head in relation to the true vertical (as expressed by the craniovertical angles) has had an important place in orthodontic diagnosis and cephalometric analysis because of its role in the esthetic evaluation of the facial profile. It still serves this function. From a developmental point of view, on the other hand, the craniocervical angulation and the cervical inclination may have greater relevance since the developmental associations observed in the present study were almost entirely limited to these postural variables. In studies of head posture aimed at elucidating developmental associations, it is important, therefore, to employ recording methods that ensure not only a natural position of the head in relation to the true vertical, but also a natural position of the cervical column in relation to the true horizontal and a natural craniocervical angulation. The second interesting aspect of the present longitudinal analysis is the fact that the changes in craniocervical angulation and cervical inclination were associated with the growth rotation of the mandible (r = 0.410.55). Although numerically moderate, these correlations of 0.41-0.55 between mandibular rotation and posrural change indicate the presence of a relatively strong biologic coordinating mechanism, since the correlations are able to appear despite the relatively large method error of both variables. Correlations larger than this magnitude are rarely observed in craniofacial studies when spurious or topographic factors are not involved. In the previous cross-sectional study of head posture and craniofacial morphology in adult male dental students, 1 the average differences in craniofacial morphology between subjects with large and small craniocervical angulation showed graphically a striking similarity to the average morphologic differences between subjects with large and small mandibular plane inclination. This was interpreted as suggesting a specific relationship between the craniocervical angulation and the development of the mandible. However, the presence of such a specific relationship could not be detected statistically in that study, probably because of its crosssectional design. It is therefore of interest that in the
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present longitudinal study the same specific association between change in craniocervical angulation and the growth rotation of the' mandible emerges as a main finding, documented statistically, graphically, and in individual case analyses. Clinically, it is well known that the growth pattern of the mandible is one of the most characteristic features of facial development. This is reflected in most cephalometric analysis systems and also in the concern for mandibular development in orthodontic treatment planning. Statistically, the role of the mandible in total facial development is reflected in the fact that the variances of measurements relating the vertical development of the mandible to the upper face and the cranial base are much larger than variances of other craniofacial dimensions when technical factors, such as reference point distances, are taken into account. 7 As a consequence of the importance of the developmental pattern of the mandible, much effort has been devoted to explaining and predicting this pattern. The present study suggests that the analysis of functional factors, such as the craniocervical angulation, may be a useful supplement in this respect. From a research point of view, the finding of a relationship between changes in craniocervical angulation and the developmental pattern of the mandible raises some interesting questions: (1) Is it possible that the change in craniocervical angulation could be a causal factor in determining the mandibular developmental pattern and, if so, by what mechanism could such an influence be effectuated? (2) What factors could conceivably induce long-term changes in craniocervical angulation? Possible answers to these questions are provided by the hypothetical model for the relationship among posture, craniofacial morphology, and the adequacy of the nasopharyngeal airway suggested by Solow and Kreiborg. 18 Several studies on assessment of head posture, craniofacial development, and airway adequacy have yielded results consistent with the prediction of this model. In particular, much evidence documents the joint occurrence of obstructed nasopharyngeal airway, increased craniocervical angulation, and a vertical development of the mandible and the face as a whole. (For a review, see Solow, Siersbmk-Nielsen, and Greve. 6) In the interpretation of correlation studies of facial development, considerable caution should be exerted. In cross-sectional studies, only indirect inference can be made about the presence of growth-coordinating mechanisms. Growth-coordinating mechanisms can be studied directly in longitudinal studies of growth changes such as the present study, but even in such
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studies as these, o n l y indirect inference can be m a d e about the possibility o f predicting g r o w t h b e h a v i o r o f facial dimensions. Direct e x a m i n a t i o n o f the possibility o f predicting craniofacial d e v e l o p m e n t requires an e x p e r i m e n t a l design in which possible d e t e r m i n i n g parameters are measured and related to subsequent facial growth. O n the basis of the present study, an analysis o f the correlation b e t w e e n head posture in children and the subsequent p a t t e m o f craniofacial g r o w t h w o u l d s e e m to be o f particular interest. The authors wish to express their indebtedness to Dr. Hans E. Jonassen, D.D.S., Director, Municipal Child Dental Health Service, Farum, and dental auxiliaries Inge Christensen, Jeanne v. Btilow, Linda Jeppesen, Jytte Laursen, Annette Olsen and Bente Julsgaard. REFERENCES 1. Solow B, Tallgren A: Head posture and craniofacial morphology. Am J Phys Anthropol 44: 417-436, 1976. 2. Thompson BP: Cra~iocervical angulation and morphologic variables in children: A cephalometric study, MS Thesis, University of North Carolina, Chapel Hill, 1978. 3. Opdebeek H, Bell WH, Eisenfeld J, Mishelevich D: Comparative study between the SFS and LFS rotation as a possible morphogenetic mechanism. AM J ORTHOD74: 509-521, 1978. 4. Marcotte MR: Head posture and dcntofacial proportions. Angle Orthod 51: 208-213, 1981. 5. yon Treuenfels H: Die Relation der Atlasposition bei prognather und progener Kicferanomalie. Fortschr Kieferorthop 42: 482491, 1981. 6. Solow B, Siersba~k-Nielsen S, Greve E: Airway adequacy, head posture and craniofacial morphology. AMJ ORTHOD86: 214-223, 1984. 7. Solow B: The pattern of craniofacial associations. A morphological and methodological correlation and factor analysis study
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8. 9.
10. 11.
12. 13. 14.
15. 16.
17.
18.
19.
on young male adults. Acta Odont Scand 24(Suppl 46): 57-88, 1966. Solow B, Tallgren A: Natural head position in standing subjects. Acta Odont Scand 29: 591-607, 1971. Siersb~ek-Nielsen S, Solow B: Intra- and interexaminer variability in head posture recorded by dental auxiliaries. AM J ORTHOD82: 50-57, 1982. Sarn~is K-V, Solow B: Early adult changes in the skeletal and soft-tissue profile. Eur J Orthod 2: 1-12, 1980. Bj6rk A, Skieller V: Normal and abnormal growth of the mandible. Appendix: Superimposition of profile radiographs by the structural method. Eur J Orthod 5: 40-44, 1983. Bj6rk A: Prediction of mandibular growth rotation. AMJ ORa'HOD 55: 585-599, 1969. Bj6rk A, Skieller V: Facial development and tooth eruption. AM J ORTHOD62: 339-383, 1972. Bj6rk A: Variations in the growth pattern of the human mandible: Longitudinal radiographic study by the implant method. J Dent Res 42: 400-411, 1963. Helwig JT, Council-KA (editors): SAS User's Guide, 1979 edition. SAS Institute Inc., Raleigh, North Carolina, 1979. Baumrind S, Miller DM: Computer-aided head film analysis: The University of California San Francisco method. AM J ORTHOD78: 41-65, 1980. McWilliam JS: Orientation of orthogonal coordinate systems used for registration of cephalometfic landmarks. Scand J Dent Res 90: 145-150, 1982. Solow B, Kreiborg S: Soft-tissue stretching: A possible control factor in craniofacial morphogenesis. Scand J Dent Res 85: 505507, 1977. SCrensen H, Solow B, Greve E: Assessment of the nasopharyngeal airway. Acta Otolaryngol 89: 227-232, 1980.
Reprint requests to:
Dr. Beni Solow Institute of Orthodontics Royal Dental College 160, Jagtvej DK-2100 Copenhagen O, Denmark