Stereophotogrammetric analysis of casts of normal and abnormal palates

American JoumaEof ORTHODONTICS Volume 60, Number

ORIGINAL

1, July,

1971

ARTICLES

Stereophotogrammetricanalysis of casts of normal and abnormal palates Samuel Berkowitz, South Wami, Fla.

D.D.S.,

M.S.

T

he three-dimensional analysis of the changing form of the palate as a result of growth and orthodontic treatment has been studied by various anthropometric instruments. In practically all instances the measurements were limited to height, length, and depth. In a few instances, attempts were made to investigate changes in the shape of the vault by the use of more complex surveying apparatus. Unfortunately, those measuring techniques, whether they involve the use of rulers, tapes, calipers, 1p4o stereocomparators,z or pantographs,3-s have not thoroughly yielded all the meaningful knowledge from casts of the palate. Much important information has been lost, has been misread, or has gone unappreciated because of the inability of the investigator to realize the geometric changes in form and changes in mass that occur as a reflection of growth and treatment. A thorough search of the literature has shown that there is no science for the measurement of surfaces comparable to that of stereophotogrammetry, whether the subject be of microscopic dimension or the macroscopic sweep of the earth’s surface or the ocean’s bottom. The basic principle of stereophotogrammetry is that of binocular vision. When two photographs of the same object are taken from slightly separated points, they can be viewed in a manner that will give a three-dimensional model surface. This same principle has been used with a stereopticon of years past. With the aid of suitable optical contouring devices, the stereophotograph allows the object to be composed as a relief map. Photogrammetric methods permit a This thesis won Essay Contest.

one

of

the

Special

Merit

Awards

This investigation was supported by the Children’s National Institutes of Health, Health, Education, for Craniofacial Anomalies, University of Illinois.

in the

1970

Bureau and and Welfare,

Milo

Hellman

by Grant through

DE the

Prize 02872, Center

1

2

Berkowitz

Amer.

J. Orthodoat. JuZg 1971

mathematic and graphic analysis of solid objects, such as casts. It is the only system which permits a numerical determination of geometric data and, therefore, it can supply more analytical information than graphic tracing methods. The development of a stereophotogrammetric technique for the geometric analysis of cleft palate casts was described in a previous article,Q which detailed both a method for taking close-order stereoscopic pictures of palatal casts and the spatial orientation of casts necessary for the graphic representation of serial changes. The general principles of photogrammetry were reviewed, and the literature dealing with its application to biologic problems was thoroughly documented. Since the initial stereophotogrammetric study of cleft palate casts was limited to linear and cartographic analyses in which geometric changes were pictorially represented, it was decided that the investigation should be expanded to include the study of orthodontically treated cases, cases of Apert’s syndrome (acrocephalosyndactylism) , and additional cleft palate cases. The basic objective was to quantify specific areas and to measure the changing form and mass of objects and the volume within a delineated anatomic space. It is expected that, through this study, meaningful knowledge might be uncovered which would help explain the changes to the palatal vault which occur as a consequence of treatment and growth. To meet these additional objectives, a further sophistication of the stereophotographic method was essential. Unfortunately, the conversion of the existing Speed Graphic camera9 was not entirely satisfactory, It was neither economical nor efficient for the study of a large number of casts, and since the geometric quality of image coordinates was poor because of flatness defects of the image, a greater degree of measuring accuracy was needed. Therefore, a more advanced stereometric camera had to be designed and constructed in order to meet these increased demands. Not only were there to be graphic analyses, but the data to be extracted from the contoured maps were to be studied and analyzed with the aid of electronic computers with large memories. The use of computers necessitated the formulation of specific programs which are unique for the geometric analyses of relatively small three-dimensional objects. The

stereophotographic

camera

(Figs.

1 and

2)

To fulfill most photogrammetric demands, two basic photographic systems can be used to obtain stereoscopism. Q,lo The object can be photographed in two positions,llp I4 or two identical cameras can photograph a fixed object. The method to be selected will be determined by the nature and size of the object. Convergent stereocameras were developed and used when the object to be studied was fixed and its movement relative to the camera could not be controlled.12-15 The photographic technique. A Galileo-Santoni stereoplotter was employed for contouring and, since it is normally used with a principle distance setting of _+ 153 mm., a Schneider Super Angulon lens with an equivalent focal length of 95 mm, and a principle distance of approximately 152.73 mm., was selected for

Volume Number

60 1

Stereophotogrammetric

a,nalysis of pa,late ca,sts 3

2

Fig. 1. The stereophotographic system placement of casts on the stage plane. magazine accepts a 9 by 9 inch glass stage plane. Note the precision track relative to the lens. Fig. mm.

2. The optics of and an equivalent

showing two model stages and windows for the The stage plane moves laterally 5 inches. The film plate. A precision grid is placed on the face of the which controls the movements of the stage plane

a Schneider Super Angulon focal length of 95 mm.

lens

with

a principle

distance

of

152.73

the stereocamera. Since this lens has an angular field of view of 100 degrees, maximum stereoscopism can be achieved. The stereophotographic camera and system were modeled after a Speed Graphic camera and model carrier framework previously described.g However, important structural changes were devised to improve handling and increase measuring accuracy, such as (a) the use of glass plates as negatives and (b) the

4 Berkowitz

Fig. 3. contour

Contour map of Kennedy half-dollar to lines can be drawn at 0.01 mm. intervals.

Amer.

show

the

high

level

of

accuracy,

J. Orthodoat.

Jukv1971

in that

proper alignment of film plate to the lens and the placement of collimating marks on the cassette. In ordinary cameras the flatness of the film is uncontrolled. Air pockets can exist between the film and the film support. When glass plates are used as a negative material, flatness of the image plane is reliable and deformation to the film by tensions from the transport mechanism is eliminated. Since the negative is a 23 by 23 cm. glass plate, it can be used as a diapositive as well. This eliminates the need for other optical systems, such as enlargers, which would produce additional errors because of lens aberrations. The image plane (glass plate) is perpendicular to the camera axis at the principle point when passing through the projection center of the lens. This minimizes tangential distortion arising from eccentric lens elements. The plotting image. The lens was calibrated to have a principle distance of 152.73 mm. and an equivalent focal length of 95 mm. Since the lens was found to have a 5 mm. larger focal length than was ordered, and because of the physical limitations of the apparatus which failed to compensate for this larger focal length, we were unable to maintain a 1:2 ratio of the image to the object size. The resulting image was therefore calibrated as being 70 per cent of the object (east) size. It was determined that the negative plates with the casts, appearing black, would be more satisfactory for plotting since the white casts, printed as positives, were difficult to use in the stereoplotter. This also made possible a greater saving in time and money, since it was not necessary to make additional plates. Four collimating marks whose intersection indicated the optical center of the lens were positioned on the film cassette and reproduced on the glass film plate. This was done in order to achieve proper positioning or “centering” of plates in the stereoplotter. Stereoscopism. In order to achieve maximum stereoscopic effect, the model

Stereophotogrammetric

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60 1

Table

I. Three-dimensional

accuracy

values

deviation

Maximum (mm.)

(mm.)

X Y Z

Table

casts

5

tests (Fig. 3) Standard

Coordinate

analysis of paI&

!: 0.055 f 0.069 +_ 0.358

error

+ 0.075 - 0.150 + 0.655

II Types 1.

2.

3.

of

cast

I

Orthodontic A. Standard treatment B. Opening midpalatine suture Cleft lip and palate A. Unoperated unilateral left cleft lip and palate B. Complete bilateral cleft lip and palate* C. Dizygotic twins* D. Pierre Robin syndrome* Apert’s syndrome (acrocephalosyndactylism) Total

*Casts were grammetry

graphically of serial

No.

of

children

No.

of casts

15 7

35 24

9

9

1 2 1

5 2 6

5

11

a0

analyzed and described in Berkowitz casts of cleft palate, Angle Orthodontist

-

sz and Pruzansky: 38: 136-149,

Stereophoto1968.

platform is moved 5 inches lateral to each position and the casts are photographed off the lens’s centric axis. Plotting accuracy. Accuracy tests were performed by Professor H. M. Karara of the Department of Photogrammetry at the University of Illinois (Table I). X and Y are in the plane of the base of the model and Z is perpendicular to the base. Materials

The cases selected for investigation were chosen because of extraordinary architectural changes in the configuration of the palatal vault resulting either from abnormal developmental processes or from treatment. The cases of clefts and Apert’s syndrome were obtained from the Center for Craniofacial Anomalies of the University of Illinois Medical Center. Dr. Andrew Haas generously provided cases depicting opening of the midpalatal suture through orthodontic expansion. For comparison with Dr. Haas’s cases, I selected cases treated by conventional full-band appliances from my practice. Ninety-two dental casts of forty children were analyzed by photogrammetric means (Table II). The standard orthodontic treatment cases were of white male and female children of various ages who underwent various mechanistic treatment programs. In each instance at least two dental casts were obtained-one before and one

6

Berkowitz

Fig.

4. Contoured

Amer.

map

of nine

unoperated

complete

unilateral

cleft

after treatment. In some cases a third or fourth demonstrate the stability of the results achieved.

dental

Specific

II

problems

selected

for

study

in

Part

I and

Part

lip and

J. Orthodont. July 7 971

palate

casts,

cast was available

to

1. Within a single type of cleft, such as a complete unilateral cleft lip and palate, what is the variance in the amount of tissue in each palatal segment B Is there a constant relationship between the size and shape of the smaller segment and that of the larger? (Fig. 4.) 2. Description and measurement of the changes in the peculiar dysmorphosis of the palate pathognomonic to the premature synostoses of the craniofacial sutures in Apert’s syndrome (Figs. 5, 6, and 7). 3. Changes in form and size of normal palates as a result of growth and mechanotherapy. Since various orthodontic procedures were performed at different ages, the results had to be related to the age at which treatment was instituted. 4. In the treatment of maxillary deficiency by the rapid opening of the midpalatal suture, what changes occur in the shape and volumes of the vault space as a consequence of this treatment? Findings

Unilateral complete cleft lip and palate (Pig. 8). Although all nine cases are of a homologous sample, this analysis reveals that there are many differences as well as similarities in their size and form. Some of these characteristics are best exposed by profile (cross-section) analysis. 1. The noncleft palatal segment was always larger and longer than the cleft segment (Table III). 2. When profile studies were made of the palatal segments, geometric comparisons revealed that the nasal surface of the segments joining the cleft was

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60 1

Fig. 5. Contoured

Stereophotogrammetric

maps

of

casts

of

five

cases

of

Apert’s

asa1ys-b of palate casts

syndrome

at

various

ages.

7

8 Berkowitz

Fig. 6. Lateral and frontal syndrome (acrocephalosyndactylism) lary casts (2-l).

Amer.

cephaloroentgenograms and contoured

of a 12-year-old maps of mandibular

J. Orthodont.

July1971

patient with Apert’s (2-4), and maxil-

positioned at the same superior-inferior level or the cleft segment was more superior and positioned above the level of the inferior surface of the nasal septum. 3. The chart comparing profiles of the vault (Fig. 9) demonstrated that the widths of the vault space varied greatly between cases. Despite this variance in vault width, the slopes in all cases appear similar. This might signify that the distances between alveolar crests were not a function of vault angulation. The case with a narrow vault space does not necessarily present steeper slopes to the palatal shelves ; nor does the wide vault have more obtuse slopes, which would be the case if angulation were a factor. 4. The percentage differences between the cleft (smaller) and noncleft (larger) palatal segments were based on the ratio of the efective lengths. This percentage difference can vary according to the geometric relationship of the palatal segments to one another. The actuaZ Zen&h percentage differences (Table III) more accurately reflect anatomic size and are not influenced by the geometry of the palate. Comparison of the widths of the cleft space between the palatal

Stereophotograrnrnetric CONNECTING

Fig.

7.

Profiles

of

Apert’s

PNUPI~ES,

syndrome

5ECllON

compared

analysis

of

palate

casts

9

C-C’

to

normal

palates,

Cases

2-12

and

2-13.

segments revealed that the anterior cleft width was always smaller than the greatest cleft width and the posterior cleft width. The posterior cleft width was never the greatest cleft width. Apert’s syndrome (Figs. 5,6, and 8). Since this study was limited to the hard palate, a thorough analysis of the roentgenocephalograms could not be included. However, it is important to establish that, depending upon the degree of malformation of the craniofacial structures, there is a concomitant effect on the sha.pe and form of the maxillary arch which, in turn, influences the occlusion. Fig. 6 depicts the typical craniofacial deformation with its associated palatal form. Examination of cephalometric films taken at the same time as the casts demonstrated the great range of variation in deformity of the skull and its parts that can exist between cases, even though they are similarly classified. Apert’s

10

Berkowitz

Table

Ame)‘.

J. Orthodont. J&t/ 1971

111 Actual cleft

Case No.

A-P and

length

nonclcft

Right

of the segment Left

Ratio

of

smnller

to larger segment Per

cent

1 2

37.3 38.1)

24.6

67

29.6

3 4

42.0

24.6

78 59

38.6

5

39.3

28.3 25.0

64

6 7 8

38.6 38.3 36.3

21.0 24.0 22.6

54 63 61

9

40.1

27.3

67

68

syndrome with minimal craniofacial deformity can produce a facial profile that is actually convex, with a maxillary dental protrusion and a slight anterior openbite. Nevertheless, the palate demonstrated the typical bulbous alveolar ridge, and the vault height was significantly less than in normal children of comparable age. The major difference between the various degrees of cranial deformation lies in the configuration of the alveolar ridges. Superimposed profiles of serial changes in the form of the hard palate revealed that the identifiable characteristics appear within the first year, The vault space was narrow and V shaped and had a double slope to the alveolar borders. Bulbous alveolar ridges with a narrow but high vault are the most conspicuous intraoral features and are pathognomonic of Apert’s syndrome. Standard

treated

orthodontic

cases

1. Maxillary growth during orthodontic treatment influences the shape and size of the vault. The most noticeable changes seen clinically are the increase in intramolar width and alveolar height. The present study revealed a concomitant marked increase in volume of the vault space as a consequence of increased maxillary growth. 2. In some cases there were no changes in the width of the vault space, although there might be increases in intertooth width as well as alveolar height. Satisfactory orthodontic treatment was achieved in this case. 3. Where there were negligible changes in either vault space or maxillary size, there was poor response to orthodontic treatment. Expansion and advancement procedures were not satisfactory ; thus, it was necessary to remove two maxillary premolars. One case showed no increase in vault space ; however, there was marked expansion in tooth position as seen by the change in intermolar width. In this case expansion was successful because the teeth were originally in a cross-bite relationship. 4. In a case in which teeth were removed during the mixed dentition, leading to four premolar extractions, there was no effect on transverse vault space changes. One case showed good orthodontic results with very little change in vault space, while another with equally good orthodontic results showed a marked increase in vault space size.

Stereophotogrammetric

analysis

of

palate casts

11

contour map of a complete unilateral cleft lip and palate cast. Profiles were Fig. 8. Typical drawn through various sections and along the alveolar crests a, Section A-A’, premaxillary area of large segment. b, Section B-B’, greatest height of each palatal segment. C, Section C-C’, area of posterior palate near pterygomaxillary fissure. d, Section E, actual length along alveolar crest of large segment. e, Section F, actual length along alveolar crest of small segment.

5. In one case, when teeth were removed in the permanent dentition, there was no change in vault width or shape. 6. A tooth-borne expander was used to correct a bilteral cross-bite in the early deciduous dentition. In this case, after 6 months, there was a slight change in vault space but after two years there was a marked increase in vault space. In another, however, there was relatively no change immediately after treatment or after one year. 7. In almost all cases the most significant profile change in the anteroposterior dimension was in the position of the vault apex relative to the intramolar line. The anterior palate appears to move posteriorly to the intramolar line, while remodeling of the palate occurs in the area posterior to the line, thus increasing the vault surface area and relocating the apex more posteriorly. Rapid separation of midpalatine suture 1. The apex of the vault often showed smaller increments of increase than did the intramolar width. In many instances the effect on tooth movement over bone separation was twice as great. The tracing of the retention cast demonstrated tooth relapse without relapse in vault width. In only one insta.nce did the vault space decrease after expansion; however, the degree of relapse was only one half the original separation.

12

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Berkowitz

CONNECTING REGISTERED

Pmm.cs ON YWIS

or RIGHT AT x-30

J. Orthodont. July 1971

AND LEFT SEGMENT

THROUW

SECTIDN C-C’

-

Fig. 9. segment. alveolar

Profiles of both palatal segments Variations in slopes and widths crests of right and left segments

along line through the midpoint of of vault space can be studied. Distances are compared.

the lesser between

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60 1

Stereophotogrammetric

analysis of palate casts

13

2. There was no noticeable influence on vault height as a consequence of rapid expansion in 50 per cent of the cases. In the other cases, the increase in vault height was less than the increase in palate expansion. 3. The slopes of the alveolar processes, before and after expansion, were parallel. No change in angulation of the palate was noted as a consequence of rapid separation of the midpalatal suture. Discussion

In many of the photogrammetric studiesX7-Is performed to date, the one great advantage constantly alluded to is the measuring accuracy of this highly objective method. To date, most of the studies on the effect of orthodontic treatment on the mandibular and maxillary arches have been limited to changes in arch width and length29 20-22but few of these studies23-25 were directed toward a longitudinal investigation of changes in contour, surface area, and vault space. Unilateral complete cleft lip and palate (Fig. 9). The qualitative and quantitative analysis of nine newborn infants was the initial step in a continuing serial investigation. This first phase was designed to make geometric comparisons within a homologous sample to determine the degree of in-group variation. The literature reveals varying opinions concerning the pathogensis and development of the cleft palate. *O One point of contention is whether there is not only a failure of several parts to unite but whether each part is inherently deficient in mass as a result of arrested growth, faulty development, or atrophy. Since most of these opinions are based in part or entirely on observation rather than measurement, it is hoped that this longitudinal study will help to clarify the natural history of the developing cleft palate and answer the fundamental question concerning tissue adequacy. A more complete analysis will be forthcoming. As far as this study has gone, no constant relationship has been found between the size and shape of the smaller and larger segments. What the geometric analysis has shown is that, although the palatal segments may be close to or far from one another, the internal vault slopes appear to be similar. This might signify that, as a result of clefting, there has occurred a bodily displacement of the maxillary palate rather than a torquing off of a point of rotation. Apert’s syndrome (acrocephalosyndactylism). This is a relatively rare malformation, recognizable at birth, and has not been produced in laboratory animals. In addition to the craniofacial malformations, there is syndactylism of the hands and feet. Hypertelorism and exophthalmos present complicating features in the later years.z6-30 The palates of patients with this syndrome are highly arched, the teeth are crowded, the maxilla is hypoplastic, and the antra appear to be small or nonexistent. The characteristic features of mesiocclusion, open-bite, and posterior crossbite are also found in the malocclusion of Downs’ syndrome, which demonstrates many similar craniofacial anomalies, 31 but the shape of the vault and alveolar ridges appears to be pathognomonic of Apert’s syndrome.

14

Berkowitz

Amer.J.

Orthochmt.

JUQ/1971

Stmdavd orthodontic treatment cases. When looking at a highly constricted vault, one is prone to say that the arch requires expansion. The method chosen to achieve this result depends on the occlusal problems that exist as well as the shape of the vault. According to the character of force applied to spread the arch, there may be an increase in tooth arch size with very little change in the palatal portion.32 Lundstrom, Nance,*l and Brodie and associates34 wrote on the fallacy of assuming that the apical base could be broadened by widening the dental arches. Brodie and his co-authors stated that “actual bone changes accompanying orthodontic management seem to be restricted to the alveolar process.” Proponents of expansion as a general approach to treatment have claimed that removable appliances with expansion screws exert an influence on the entire palate and apical base as opposed to the limited effect of fixed appliances.** Lebret3 assessed the mode of action of labiolingual and removable appliances on the palate and alveolar processes by comparing the pre- and posttreatment palatal contours, using a symmetrograph and a pantograph for obtaining tracings of palatal contours. He demonstrated that the influence of labiolingual tooth-borne appliances was largely confined to changes in the alveolar process while the expansion plate with screw resulted in more pronounced changes involving the entire palatal contour. This latter change suggested involvement of the midpalatal suture. Lebret3 also studied a series of dental casts during the transition from the deciduous to the permanent dentition. His results showed that the alveolar process increased continuously in height and breadth. The shape of the top of the palatal vault remained essentially constant, except for an increase in breadth at the apex of the palatal vault in three fourths of the sample. He concluded that it was not possible to determine whether this increment was due to growth at the midpalatal suture, to bone remodeling, or to both. In the correction of bilateral cross-bite in the early mixed dentition, the expansion force is directed to the teeth alone. The effect of the Arnold expander is usually expended equally to both right and left buccal segments. It thus appears that the result is the spreading of the arch and widening of the vault through tooth movement associated with alveolar arch remodeling. Since the changes in tooth position occur in a relatively short period of time (approximately 3 months), the contribution of palatal growth to increasing vault width cannot be significant. In follow-up casts of the same series, however, it could easily be demonstrated that palatal suture growth was a contributory factor in widening of the palatal vault. There was no way to determine whether the original cast demonstrated arrested development. Whether early expansion stimulated or made possible a freer expression of vault growth is not known. Rapid separation of midpalatine suture (Fig. 10). Where there is compression of the maxilla with constriction of the buccal segments, excessive archlength disparity, and good axial position of the teeth, the treatment of choice may involve opening the maxillary suture and increasing arch width. Haas35, 36 clearly described the importance of selecting cases amenable to this therapy and did not claim that it was the only way to correct crowded dental arches.

Volume Number

60 1

Stereophotogrammetric

a,?zalysis of palate casts

15

12

13

14

15

16

17

Fig. 10. Contours of the palate at the level of the first molars. Each case has beforeand after-treatment lines which depict changes in palate form as a consequence either of treatment and/or growth, Cases 16 to 22 represent those palates which had palate splitting. , Before treatment. ----------, After treatment. -a--e--s -. -, After retention. All palates were superimposed and registered on the t mark, which is the bisection point on the line between molars.

Isaacson and colleagues37 measured the forces necessary to open the suture ; their study was part of a major undertaking to evaluate rapid-expansion procedures. The rapid increase in the width of the maxillary base occurred only after palate-opening procedures. This study confirmed that the gain in dental arch width. in many cases following this procedure was not stable but decreasetl slightly after treatment.38y 3g There was a further increase in width of the palate after active treatment in all expansion cases, and this could be attributed to the results of natural growth in the median palatine suture. There is no doubt that the effect of rapid expansion of palatal shelves is one

16

Berkowitz

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J. Orthodont. July 1971

of bodily movement. This is substantiated by the slopes of the alveolar processes remaining parallel as the expansion occurs. Summary

A stereophotogrammetric camera was developed for nontopographic photogrammetry. The purpose was to derive three-dimensional information from serial casts in either a graphic or a mathematical manner and to permit the use of computers for analytic procedures. Suitable computer programs were designed for the comparative analysis of geometric data, such as vault space, tissue mass, surface area, and internal vault slopes, as well as many linear dimensions. Three problems particularly suitable for this type of analysis were selected for study: 1. Casts of patients with unoperated complete unilateral cleft lip and palate. 2. Serial casts of patients with Apert’s syndrome. 3. Comparison of cases treated by rapid orthodontic expansion and those treated by conventional full-banded appliance techniques. The results of the study yielded further evidence on the lack of homogeneity within a single type of cleft and indicated that mesodermal deficiency is not a universal finding. The topographic changes in the palatal vault of Apert’s syndrome shed further light on the nature of the abnormal maxillary growth. A direct relationship was established between the severity of the craniofacial defect, as revealed in the cephalometric x-ray and the configuration of the palate. The slopes of the palatal shelves before and after rapid maxillary expansion were similar, indicating horizontal deflection, without tilting, of the segments. This is in contrast to what has been observed clinically in expansion of cleft palate. The author gratefully recognizes the support of Samuel Pruzansky, whose encouragement enabled this project to be undertaken, Elmore Kerkela, who provided the technical design assistance and supervision in taking the stereophotographs and having the contours performed to specification, Harry Loh and Harold Berkey of Berkey Technical Corporation, New York, N. Y. for building the stereocamera, H. M. Karara for performing the accuracy tests, Sheldon Axler for designing the eamputer programs, and A. Haas and 5. Pruzansky for supplying many of the necessary casts for study. REFERENCES

1. Sillman, J. H.: Dimensional changes of the dental arch: Longitudinal study from birth to 25 years, AMER. J. ORTHODONT.59: 824-842, 1964. 2. Korkhaus, Ct.: A new orthodontic symmetrograph, INT. J. ORTHODONT.16: 665-668, 1930. 3. Lebret, L.: Growth changes of the palate, J. Dent. Res. 41: 1391-1404, 1964. 4. Cohen, J. T.: Growth and development of dental arches in children, J. Amer. Dent. Ass. 27: 1250-1260, 1940. 5. Goldstein, M., and Stanton, F. L.: Changes in dimensions and form of the dental arches with age, INT. J. ORTHODONT.21: 357-379, 1935. 6. Stanton, F. L., Fish, Q. D., and Ashley-Montague, M. F.: Description of three instruments for use in orthodontic and cephalometric investigations, with some remarks on map construction, J. Dent. Res. 11: 885, 1931.

i2~~“,“,“,” 7. Sedwick, 1958. 8. Chapman, J. 63:

Stereophotogrammetric

H. H.: 201-225,

J.,

and

The

Brawley, normal

R. dental

E.: arch

Palatometer, and

its

analysis AMER.

changes

from

J.

of pa&de ORTHODONT. birth

to

adult,

casts 24: Brit.

17

673-674, Dent.

1935.

9. Berkowitz, S., and Pruzansky, S.: Stereophotogrammetry of serial casts of cleft palate, Angle Orthodont. 38: 136-149, 1968. 10. Hallert, K. B. P.: Photogrammetry in medicine, Photogrammetric Engineering 20: 81-88, 1965. 11. Nyquist, G., and Tham, P.: Method of measuring volume movements of impression, model and prosthetic base materials in a photogrammetric way, Acta Odont. Stand. 9: 1951. 12. Miskin, E. A.: The application of photogrammetric techniques to medical problems, Photogrammetric Record 3: 92-110, 1956. 13. Holm, O., and Krakau, C. E. T.: A photogrammetric method for estimation of the volume of superficial tumors and similar objects, Acta Univ. Lund. Sect. II 31: 1965. 14. Savara, B. 8.: Application of photogrammetry for quantitative study of tooth and face morphology, Amer. J. Phys. Anthrop. 23: 427-434, 1965. 15. Gruner, H., Zulguar-Naim, J., and Zander, H. A.: A short-range system for dental surgcrg, Photogrammetric Eng. 33: 1240-1245, 1967. 16. Burke, P. H., and Beard, F. H.: Stereophotogrammetry of the face, AMER. J. ORTHODONT. 53: 781-796, 1967. 17. Hallert, B.: Determination of the interior orientation of cameras for nontopographic photogrammetry, microscopes, x-ray instruments and television images, Photogrammetric Eng. 26: 748, 1960. 18. Zeller, N.: Microphotogrammetrical examination of the surfaces of tooth-fillings, Photogrammetric Eng. 23: 660-662, 1956. 19. Fagerholm, P. 0.: Close-up photogrammetry with single cameras, Photogrammetric Eng. 23: 665-668, 1956. 20. Cohen, J. T.: Growth and development of the dental arches in children, J. Amer. Dent. Ass. 27: 1250-1259, 1940. 21. Nance, H. N.: The limitations of orthodontic treatment, AMER. J. ORTHODONT. & ORAL SURG. 33: 177-223, 1947. 22. Howes, A. E.: Case analysis and treatment planning based upon the relationship of the tooth material to its supporting bone, AMER. J. ORTHOWNT. 33: 499-533,1947. 23. Shapiro, B. L.: Measurement of normal and reportedly malformed palatal vaults. 1. Normal adult measurements, J. Dent. Res. 42: 1039, 1963. 24. Walter, D. C.: Changes in the form and dimensions of dental arches resulting from orthodontic treatment, Angle Orthodont. 23: 3-18, 1953. 25. Redman, R. S., Shapiro, B. L., and Gorlin, R. J.: Measurement of normal and reportedly malformed palatal vaults. 3. Down’s Syndrome, J. Pediat. 67: 162-165, 1965. 2. Normal juvenile measurements, J. Dent. Res. 45: 266-269, 1966. 26. Park, E. A., and Powers, F. F.: Acrocephaly and scaphocephaly with symmetrically distributed malformations of the extremities, Amer. J. Dis. Child. 20: 235-315, 1920. 27. Lewin, M.: Facial and hand deformity in acrocephalosyndactyly, Plast. Reconstruct.. Surg. 12: 138-147, 1953. 28. Blank, C. E.: Apert’s syndrome (a type of acrocephalosyndactyly) ; observations on a British series of thirty-nine cases, Ann. Hum. Genet. 24: 151-164, 1960. 29. Woolf, R. M., Georgiacle, N. G., and Pickrell, K. L.: Acrocephalosyndactyly ; Apert’s syndrome-acrocephaly with syndactylism, Plast. Reconstruct. Burg. 24: 201-208, 1959. 30. Ogilvie, A. G., and Posel, M. M.: Scaphocephaly, oxycephaly, and hypertelorism, Arch. Dip. Child. 2: 146-154, 1927. 31. Kisling, E.: Cranial morphology in Down’s syndrome, Ph.D. thesis, Royal Danish Dental College, Copenhagen, Denmark, 1965. 32. Monson, G. S.: Constricted vaults, Dent. Cosmos 40: 914-920, 1959. 33. Lundstrom, A. F.: Malocclusion of the teeth regarded as a problem in connection with the apical base, INT. J. ORTHOWNT. 11: 591-602, 1925.

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34. Brodie, A. G., and others: Cephalometric appraisal of orthodont,ic results, Angle Ort,hodont. 8: 261-351, 1938. 35. Haas, A. J.: Rapid expansion of the maxillary dental arch and nasal cavity by opening the mid-palatal suture, Angle Orthodont. 31: 73-90, 1961. 36. Hsas, A. J.: The treatment of maxillary deficiency by opening the mid-palatal suture, Angle Orthodont. 35: 200-217, 1965. 37. Isaacson, R. J., Wood, J. L., and Ingram, A. H.: Forces produced by rapid maxillary expansion, Angle Orthodont. 34: 256-259, 1964. 38. Krebs, A.: Mid-palatal suture expansion studied by the implant method over a seven year period, Trans. Europ. Orthodont. Sot., pp. 131-142, 1964. 39. Skieler, V.: Expansion of the mid-palatal suture by removable plates analysed by the implant method, Trans. Europ. Orthodont. Sot., pp. 143-157, 1964. 40. Peyton, W. T.: The dimensions and growth of the palate in the normal infant and in the infant with gross maldevelopment of the upper lip and palate, Arch. Surg. 22: 704-737, 1931. 6601

S.W.

80th

St.

To extract an irregular tooth would answer but little purpose, if no alteration could be made in the situation of the rest; but we find that the very principle upon which teeth are made to grow irregular@ is capable, if properly directed, of bringing them even again. This principle is the power which many parts (especially bones) have of moving out of the way of mechanical (Hunter, John: Natural History of the Teeth, 1771.) IJ ressure.