Mandibular prognathism in the context of comparative pathology

American Journal

of

ORTHODONTICS

Volume

63, Number

ORIGINAL

4,

APRIL,

1973

ARTICLES

Mandibular prognathism in the context of comparative pathology William Sncwkmento

T

S. Parker, rind

LInkis,

D.M.D.,

Ph.D.,*

and

Logan

M. Julian,

D.V.M.,

Ph.D.**

Cnlif.

he traditional report of research leaves the reader with the impression that the work was conducted from “introduction” to “conclusions” with neatness and dispatch. To imply that the work reported here flowed so smoothly is false. This implication ignores thousands of measurements and observations and !-cars of study and thought by two persons in two entirely different fields who joinecl forces. One of us has been in active dental pract,ice for 30 years, doing rclsc>arvh as a side effort; the other has been teaching veterinary anatomy for 25 \.ears, with research as his secondary vocation. The field of comparative lmthology provided the common ground for our exchange of ideas. Two studies, I’. “’ as yet unpublished, provided the seed for the thought that perhaps the clog’s skull could be usecl as a model for human cranial studies. In all of the healing arts, tlifferential diagnosis is the keystone to success. The ~~;~rly and correct identification of basal mandibular prognathism in children would permit the dentist to plan proper treatment and eliminate wasteful procedures Simple anterior, cross-bites could be treated at onec. Growth problems could be de!'errecl atid stn(lictl until the magnitude of the problem was established, am1 thtrl ~~Y.~w!*c*or‘rc&x-(~ mwsuws VOIIICIhc inxtitntcd. Furthermore, it is possible that ii pc~rsolis with IWI mantlibular prognathism ~0~1~1lx isolated ant1 studit for long pcriocls, measures could be (ir\-clq~tl to charigc the growth pattern. Cay’: stated that the objective of comparative medicine is to contribute to 11t11nallht~alth rcscarch through the stud;v of similar naturally occurring diseases in animals. Selection of the correct espcrimental animal is highly critical to the

Fig.

1. The

cephalometer

with

dog

skull

in place.

cccssful approach to each problem. Although dogs have long been domestica !ted tl selectively bred for specific purposes, few investigators have apprecia .totl LTl~~nlcndons range of variation available in this one species. Charles 12. oclta~~I’s’!’ monumental work on clogs remains a classic in this field. Donnestic sated dogs have the widest range of diversity in size and shape of the sl

su il1

1111 St'

weight of dogs varied from less than I kilogram to nearly 100 kilograms, brain weight \-arid only from 50 grams to 110 grams. Preliminary study,lj based on the classic mustard seed technique for determining cranial \-olumes, verified that, the cranial cavity varied from 49 C.C. in the toy Manchester terrier to 12’7 CC in the St. Bernard, a modest change in the brain volume as compared to the tliffrrencc~ in body weight. Since there is little variation in the cranium, the faciirl bongs must exhibit the greatest deviations in size and form when the skull has cliffercnt shapes. Because the early itlentification of basal mandibular prognathism in man is a significaant I)roblem, ii stutly of the Facial variations and their relationship to tlcntal occlusion in dogs was designed. Those mcasuremcnts ant1 relationships clcvclopc~l n-hich best rt~caled the nature of the facial changes in dogs exhibiting nnantlibular prognathism were then applied to a siimple population of human patients seeking orthodontic treatment. This investigation was thcrcfore uiltlertaken with a specific two-fold objective: ( 1) to analyze facial variations and their relationship to dental occlusion in dogs, with particular reference to mandibular prognathism, and (2) to determine if the same kinds of change oc(*ur in man. If the changes arc similar, t,hrn perhaps the dog may be used as a moclel for further studies of the facial bones and their relationship to dental occlusion for future human application. Materials

and

methods

Xumcrous inrestigators2, 3, 5, o, I22 ao, 21 have reported studies of the skulls of various animals using standard anthropologic methods and instruments. Our stu(lit>s on tlogs inclutletl many linear measurements performed with conventional instrunicnts. Tn addition, a cephalomc+r was atlaptetl to accept dog skulls (Fig. 1). The ccphalomcter,” a mocdification of the craniomctcr which LWJSradiographs, is \vicl~l~ cntplo~~~l to anal-xc various clctails of human head anatomy. Cephalotntkt ric illt’asII1’(11r1elits A\-erc also made on oi~tliodorrtic patients and comp:rrcd \vith the findings obtained from clog skulls to determine the uscfulncss of the clog as a motltll for further studies. 8tudies of the (70~ Yliull. The: collection of purebrctl dog skeletons of the DCpart~~ciit of Anatomy, School of Veterinary hIeclicine, University of California ;rt Davis, provitletl the canine material stndietl. The best specimen skull of each of thirty-scveil hwls \vas wlcc+cvI illlCt nttlasurccl to provide parametrrs for tllc spccitx 7’1~ l)rtlccls4 il~~luclt~(l wertt Airedale terrier, akita, hascnji, beagle, borzoi, ihmttril tr.l.i,ii-r. bc~se!*: hldl~iog. Pairn tcw+r. ( ‘hihu;ihua. (+how c*liow, cocker sI)allirl, eollitx, tl~~~~l~shul~d.(lalmati;~ll, l~ol~~~*rnn~lpinschcr, (Gcrrnan ~hel)llt~rtl, ( +t~nan short-h;rirtcl pointer. great I)anc, greyhound, Irish setter, Irish wolfhoun~l, I,al)oratlor ytitrievcr, I,akcluld tcrricr, miniatltre poodle, Kt~wfoundland, pointer, f’omeranian, pootllc, pug, Rhodesian ritlgcback, Samoyed, Saint Bernard. Shctlalltl nlrq~ttog, toy Manchcstcr terrier, \\‘eimarancr! and whippet. The following measurements and observations were recortiecl : 1. The relatiopship of the jaws to each other and to the total skull. In this study, anatomic points in the skull of the dog comparable to those

4712. J. Orthod. April i9i3

Fig.

2.

Close-up

plastic

shelf

to

Table

1. Reference

view

of

support

beagle

skull points

are and

skull in planes

in

adapted

cephalometer.

Elongated

ear

rods

and

position. used

in dog

studies

Ba-Basion, the most forward point on the anterior margin of the foramen magnum FP-Frankfort plane, established on lateral head films by connecting the lowest point on the shadow of the left bony orbit with the uppermost part of t,he ear rod I-Inion, the central surface point on the external occipital protuberance N-N&on, the junction on the median plane of the right and left frontonasal sutures 0-Orbitale, the lowest point of the orbit of the left side of the skull PNS-Posterior nasal spine, the posterior nnsn! spine of the palatine bone Po-Porion, the highest and most central point of the lead marker on the ear rod Pg-Pogonion, the most rostra1 part of the mandible at the symphysis located between the roots of the lower central incisor teeth Pr-Prosthion, the rostra1 end of the intermaxillary suture located betwen the roots of the upper central incisor tepth

widely accepted in human anatomy were utilized. Table I yummarizes and defines the anatomic landmarks and planes used in this study. The skull of each specimen was placed in a standard cephalometer especially adapted to compensate for the reduced interauricular width of canine skull (Fig. 2). Radiographs were made of each specimen on Eastman Kodak “no screen” film at a 60 inch target-film distance with l~$ second exposure. These films were developed in Eastman Kodak s-rap developer, using the standard time and temperature technique. Each radiograph was traced on drafting acetate. The plane of reference sclcct,etl was E’rankfort plane (Fig. 3). Lines

Volwme Nu?rLber

63 4

Mandibular

prognuthism

343

FP

Fig.

3. Landmarks

Frankfort of

projections

Fig. PNS,

and

plane;

4.

at

prosthion;

right

angles

Landmarks

posterior

reference

Pr,

and nasal

spine

of

measure of

points

Pg, points

points palatine

used

pogonion;

Pr and

used bone;

to

relate

Pr-Pg, Pg.

to

analyze

jaws. distance

variations

PO, (in

Porion; mm.)

in the

0, on

skull.

FP,

orbitale;

Frankfort

N,

plane

Nasion;

Pr, prosthion.

~wrpendicular to this plane were drawn to prosthion and pogonion. A linear measurement betwee these two points on the Frankfort plane i J’r-J’g) established the anteroposterior relationship between the upper ant 1 lower jaw structuws without refercnw to the teeth. 2. Wntal owlusion. i\ccording to our ohserrations, “normal” drntal \lltlhc ! lcscrihtd on the Poliowing hasis : All of tht: t~~vlh in the maxilla from the incisors back to and including the uppw l’owth premolar (upper carnassial ) should occlude labially or buccalllv to the lowr teeth. The buccal cusps of tile upper first and second molars shonl~l owlude buccally to the lower teeth. The cusps of the lower molars sl101~1~1 c.lose illto or 1~ dire&cd into the central fossae of the upper molars. Variation from this arrangement in a buccal or lingual dire&on constitutes ;I cross-bite and was considered a malocclusion. Anterior cross-bites were wcor(letl as an indication of mandibular prognathism in dogs.

Am.

J. Orthod. April 1973

Beagle

52mm

A

Fig.

5.

Pr

PNS

BO Triangle

ABC

of

beagle

skull

illustrating

method

of

constructing

triangles

Pr

e Fig.

6. Ventral

PNS,

posterior

view nasal

Baof

dog spine

PNS v skull of

PNS - Pr ,-A

illustrating palatine

palatal

measurements.

B, Basion;

Pr,

prosthion;

bone.

3. The measurement from nasion to prosthion was recorded (Fig. 4). 1. The measurement from prosthion to posterior nasal spine was recorded (Fig. 4). 5. The measurement from posterior nasal spine to nasion was recorded ( Fig. 4). 6. The measurements previously described in 3, 4 and 5 were individually laid out on drafting paper by means of a compass and a protractor. The resulting triangles were drawn and the angles measured. A. Angle A identified that angle with its apex at prosthion (Figs. 4 and 5). B. Angle B identified that angle with its apex at nasion (Figs. 4 and 5). C. Angle C identified that angle with its apex at the posterior nasal spine (Figs. 4 and 5). ‘7. The measurement from basion to posterior nasal spine was made (Fig. 6). 8. The measurement from basion to prosthion was made (Fig. 6). 9. Measurements were made in order to establish the general configuration of the mandible. Comparisons were made between breeds with

Fig.

Table

7. Outline

of

II. Reference

beagle

points

mandible

and

illustrating

planes

used

method

in human

of

measuring

angle.

studies

A-Point ;\, the deepest point on the maxillary midline between the antclrior nas:\l sl)iw ant1 prosthion B-Point IS, the deepest midline point on the mandible between infradentale and pogoniou .\NS-Anterior nnsal spine, the spinous process of the maxilla forming the most antrriol~ projection of the floor of the nasal cavity VP--Frankfort plane, established on lateral head films by connecting the lowest lwint OJI the shadow of the left bony orbit with the uppermost part of thv cnr rod N-Nasion, the anterior limit of the frontonasal suture +--Orbit:rlr, the lowest point of the orbit of the left side of thcl skull PNS--Posterior nasal spine, the posterior nasal spine of the palatine Ilone Pot .Porioll, the highest, most central point of the Irad marker on the en? w
Fig. anterior spine;

8.

Reference nasal PO,

porion;

points spine;

and FP,

Pg,

planes Frankfort

pogonion;

used plane; S, sella

in

human N,

turcica;

studies.

nasion; SN,

0, line

A,

Point

orbitale;

A; PNS,

B,

point posterior

9;

ANS, nasal

S-N.

Sflldies of the humax skull. One hundred fifty-eight patients, including 137 t’ro~t~ private orthodontic practice and 21 from the School of Dentistry, linivcrsity of California Medical Center at San Fran&so, were studied. The patients from the university represented extreme examples of Class III malocclusion 01 mandibular prognathism, depending on the reader’s preferred definition. A cephalometric radiograph of each patient was obtained. Table II summarizes and defines the anatomic landmarks and planes used in this study. The following measurements and observation were recorded : 1. The relationship of the jaws to each other and to the skull. The human cephalometric radiographs mere traced on drafting acetate. Where prosthion was used as the ant,erior point on dog skulls, point A was used on man (Fig. 8). Point B was used as the anterior point of the mandible on man, where pogonion was used on the dog. The problem here is one of s&antics. The word pogodon is used to indicate different points in the anatomy of the dog and in the anatomy of man. Although prosthion describes the same point in dogs and man, point A is the accepted point to indicate the basal structure of the human maxilla and not just, alveolar bone. Point B is the accepted point to indicate the basal structure of the human mandible. 2. Frankfort plane was drawn and perpendicular lines dropped to point A and point B. Again a linear measurement was made between t,hcsc two points on the Frankfort plane, establishing the anteroposterioi relationship between the upper and lower jaws without reference to the teeth (F’ig. 9).

FP

Fig.

9. Reference points FP, Frankfort

orbitale; right

angles

of

points

used

to

A and

relate

A-B,

plane;

jaws distance

in man. (in

mm.)

A,

Point on

A;

Frankfort

B,

point plane

B; PO, of

porion;

projections

0,

at

B.

3. Points N and Y were marked, and the plane SN was established. Additional lines from N to A and N to B establish the angles SNA and SNB (Fig. 10). These angles are commonly used to relate the jaws to the skull and to each 0ther.l’ 4. Dental occlusion was observed and classified. Anterior cross-bites were recorded as an indication of mandibular prognathism. 5. The points N, PNS, and ANS were identified and marked on the tracing of each cephalogram. T,ines were drawn between these points, forming triangles. The angles were measured and identified as angles A, 73, and C, as in items 6, A, B, and C for dog skulls (Fig. 11). A. Angle A was identified as that angle with its apex at anterior nasal spine (ANS). B. Angle B was identified as that angle with its apex at nasion (N). (1. Angle C was identified as that angle with its apes at posterior nasal spine (PNS) Results

and

discussion

‘l’ublcs 1 II z;lrrdic.s oj’ the al~glcs of constant, than

and IV summarize tllc analysis of the measurements made. iltt. tluy skiill. i,‘t:i cranial cavity (I’ig. 13). It has been saitl that when this shortening leas bc~me extreme, as in the prognathic breeds, a situation of regional achonttroplasia has occurred” (Fig. 14). As the measurement basion-posterior nasal spine correlates highly with the measurement basion-prosthion (R = 0.94))

Fig.

Fig.

10.

drawn

Fig. terior

Fig. 11

10

Reference from

11,

S to

Reference

nasal

spine;

points N;

A,

points N,

used point used

nasion;

to A; to

relate 6,

jaws

point

establish

A, angle

in man.

PNS,

triangles. A;

S, Sella

turcica;

N,

nasion;

SN,

line

ANS,

an-

6.

B, angle

6;

Posterior

C, angle

nasal

spine;

C; S, sella

turcica.

a constant relationship between these portions of the base of the skull is indicated. This infers that not only the bones of endochondral origin become shorter in dogs with a short cranial base, but also bones of intramembranous origin are affected. Therefore, the notion that achondroplasia correctly describes the shortening in the base of the skull must be questioned. At the same time that there is a shortening of the base of the skull, the mandible lms tended to maintain its length, resulting in prognathism. The shape of the mandible remained very constant, regardless of body size, as did the mandibular angle, with a mean of 14.38 degrees t 0.301 degree, However, in those brectls in which mandibular prognathism is a characteristic, this angle increased to a mean of 18.38 degrees + 0.581 degree. The entire lower border of’ the mandible was bowed, a condition previously noted in dwarf cattle.ll Regarding the interrelationship of the jaws, the mean difference between pr~ost.llion-pogonioll measured on the F’rankfort plane (equivalent to A-B in man) was 4.0 mm. + 1.48 mm., with a minimum of -28.0 mm. in the English bulldog a11d a maximum of 15.0 mm. in the Airedale. Thus, there was a wide variation in anteroposterior relationship in the dental arches of dogs. The number of teeth in cross-bite was found to be a mean of three and varied from no teeth in cross-bite to a maximum of twenty-one in the English bulldog. There is a high correlation (R = 0.84) between the measurement prosthion pogonion and the number of teeth in cross-bite. ~~izldie~ of the laun~tr~ ~1~~11.Examination of the data which dealt with the intc~rrclntiolislii~) of the jaws in man, which included measurements of many persons with malocclusions, revealed that the mean value of angle ANB was 2.5 degrees t 0.36 degree, with a range of 26 degrees. Exclusion of the severe (Jlass 111 University of California group from the sample produced a mean value for angle ANB of 3.8 degrees _+ 0.35 degree and range of 18 degrees.

Table

III.

Analysis

of

the

measurements

of dog

skulls I

Description or name of varinblc The

relationship

Jfinimu

/ m / xoxitr1

u ili !

Range

of the jaws 4.0-k 2.90 90.10

(Pr-%I Anterior cross-bites Nasion-prosthion i mm. ,I Prosthion-posterior nnwl spine (mm.) Posterior nasal spine-nasiou (mm.1 AIngle A (degrees) Angle B (degrees) Angle C (degrees) Hasion-posterior nasal (mm.) Hasion-prosthion (mm.) Mandibular angle Total length of mnndilk

36

35 33 33

‘8.00 00.00 31.00

15.00 “1.00 12X.00

43.00 01.00 07.00 95.00

90.20

4220

39.00

134.00

46.90 3t’.lO

1.700 1.500 0.990

1.560

"7.00 xi.00 ti5.00 43.00

6i.00 66.00 94.00 88.00

3.450 7.730 0.301 6.200

31.00

103.00

72.00 11.50 61 .OO

335.00 20.00

75.00 73.20

40.00 4 1.00 29.00 45.00

spine 70.00

157.10 14.38 137.70

195.00

72.00 163.00

8.50 134.00

By definition, any patient with mandibular prognathism will have point B farther forward than other persons with either normal or maloccluded teeth. I;\-aluat,ion of jaw-to-jaw relationship using the A-B distance on Frankfort ~)lane (Fig. II) as Pr-Pg was applied to dogs (F’ig. 3) produced a mean value of X.19 mm. & 0.417 mm. and a range of -10.0 mm. to 19.0 mm. Of even greatel significance was the fact that persons who developed a real mandibular ~~rognathism were bettctr identified and the measurement A-B on P’rankfort l)lanct provided a more: relevant indication of the (measurement) developing c*llange in occlusion. (‘onvcrsely, the currently acccptctl measurement of the ;Lligltb XXI3 was v~‘1.y poor for preclicting this change in the jaw relationship. Table T- illustrates this kind of patient history. While the patient’s ANB angle showed little 01’ no change, the A-B measurement readily revealed the qualit ()f the growt,h. Review of other methods of assessing anteroposterior dysplasia” indicates that, m(~asurement of ,1-B on Frankfort plane has not been previously 2pl)lic:tl. In the routine praeticck of tlentislry, the evaluation of the kind and (luzrrllit~~ of eliaiige in tlic i~c~l;~tionsliil~of the ja\vs in those patients suspccteci oi t I(~veloping tnIc tllilll~lit~U13t~ ~)rogiiathism presents ;I very real problelll for tile .tinics:ri:. it :ti)lx’;lri: tllal l!rck lyb1?(>9 nf tht? t;ncr in t ilow I)(‘rsc~lls witil IIlilllllihllli*i~ 1 I~O~il;lt ll/sIli ;ll'tl)oSil hit'fl tllCll'c' ~mstc'ricJYl)1111([(‘1' th s!.i~lli, as iii tht? progiiatliie I)r.tJc>rlsof tlogs. 21tiglr C’ rcnrains rclat,ivfly constant, and the rariatiolis occur itr illIKlt% ,\ anti B. As tlrc, ltatient IJccomes prognathic, allglc 11 becomes 1arge1 m(1 xigl~ I3 I~omt’s smaller i E’ig. 1.5). ( )bviously. human beings do not exhibit 11~~\viclk. Ixligr of variation in F;1c4:11 t?-pcs sfwn i,t rlogs. lbut thv si~nic basic I’at~tolx ;Il’tt in IJkk)-. Statistical allal+ of the data in this study indicatetl that the meaii \alur c)F aligle -1 ilr l)iitielltS with niantlihul;~r ~~rognatllisnl ant1 :or (-‘lass 111 clcntal

350

Parlcer and Julian

Table IV.

Analysis

of the

measurements

of orthodontic

patients Sam-

Description All pntients All patients except UC group Class I pntients Class II patients Class TII patirwts UC group of patients only Males Females All patients All patients except UC group Class I patients Chss IL patients Class IIT paticuts UC group of patients 0nl.v Males lhnales All lxltients All patients except UC group Class I patients Clnss IT 1xLtients Class ITT patients cc group of l~nticntn only Males Females All patients All patients except, UC group Chss I patients

Relation

of upper

Pie size

Mean

(SNA)

158

80.3

of variable

or name jaw

to skull

Standnrd error of Xinimean mzlm 31.0

Illaximvm

1 IRange

70.00

93.00

23.00

I,

,,

,I

I,

,I

I,

,I

137

80.7

0.2x

73.00

X9.00

16.00

I!

I,

?,

,,

I,

II

I,

62

81.0

0.41

73.00

89.00

l(i.O(l

,I

,I

,I

I,

I,

,I

II

57

80.7

0.43

74.00

88.00

14.00

0

I,

I,

I,

I,

I,

I,

39

7x.7

0.80

70.00

93.00

"X.00

I,

,,

8,

,I

I,

,r

II

,I ,I 0 I, to skull

I, II (SNB)

i8.2 80.1 81.0 i7.9

1.40 0.45

70.00 73.00

23.00

I, ,I jam

21 58 79 158

93.00

,, 0 ,, ,I of lower

88.00

0.33 tr.37

73.00

89.00

13.00 16.00

67.00

96.00

-I "0.0(1

,I I, Relation

I,

,I

,I

I,

I,

,I

I,

137

72.0

0.33

67.00

96.00

L'9.00

t,

I,

I,

I,

I,

I,

I,

62

77.0

0.40

69.00

S-1.00

15.00

!I

I,

II

I,

,I

I,

,I

5i

75.3

0.38

67.00

X1.00

14.110

0

,I

II

I,,,,,

II

39

83.0

I).iS

i-1.00

96.00

Yli. 00 “‘)

II

,I

,,

I,

,I

,I

I,

21

si.0

I!

I,

I,

,I

I,

I,

,I

1.09

58

76.i

0.52

21.00 22.00

I,

,,

,I

I,

79

7i.l

95.00 89.00 96.00 11.00

“ti.00

0

Relation

I,

other

158

2.5

0.36

i4.00 67.00 69.00 --19.00

137

3.8

0.35

7.00

11.nn

15.011

62

4.0

0.26

0.00

11.00

11.00

I,

37

5.4

o.“n

1.00

9.00

8.00

II

39

-4.2

0.59

-15.00

5.00

39.00

-5.9

".Oll

I ;.w

9.00 11.00

15.00 18.00

19.00

44.00

19.00

29.00

19.00

19.00

I,

of jams

to each

( ANB)

rt

II

0

I,

I,

I,

I,

!I

I,

I,

I,

I,

,I

I,

II

I,

T,

,I

I,

,I

I,

,I

r,

I,

I,

I,

0.44

I!

,I

I,

I,

,I

I,

II

21

0.79

-15.00

II

I,

,,

I,

I,

I,

,I

58

3.4

0.59

-

,I

,I

II

,,

I,

of

jaws

0

I,

I,

I,

I!

I!

I,

,I

,I

,I

Relation

to each

I,

6.00

I,

79

(A-R)

158

4.0 6.00

0.31 0.594

- 7.00 -25.00

I,

,I

137

8.19

0.417

-10.00

I,

I,

6’

8.65

0.302

other

0.00

24.00

StanSam-

Description (hss

of

unviable

&Id error

Mean

of

mean

Mini-

Nazi-

mum

mum

Rnng~

1I

\zlticlrts Chss

or name

pie size

/

patimts UC group of patit9lts only X!hlW I~‘cnl:1lcs All patients hll p:ttients except UC group Class I patients Cl:rss II patients CIlllRS III l>:ttivnts UC group of’ p:~tionts onl? Maks l~‘enl:llcs All patients All patients escqt UC grOL1,'

(‘l:m I patients Class I1 pntieuts Clnss 111 patients UC group of patients only M:?lc9 Females .Lll patients All patients except UC group mss I patients Chss II patients c1:1ss 111 patients UC group of patients only Males Females

Angle

5;

10.26

0.34(1

5.00

16.00

ll.Nl

I,

3!)

~-4.43

1.075

25.00

14.Oll

an.on

I, I, ,I

21 58 79 158

-8.29 8.32 8.10 86.C

1. 199

0.74i O.-li(i 02)

-25.00 - 8.00 -10.00 78.00

0.00 19.00 18.00 98.00

5.00 “7.00 i’R.00 20.00

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78.00

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0.39

78.00

93.00

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86.2

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79.00

94.00

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39

4Y.7

O.li8

81.00 OS.(IO !7.0(1

21 58 7’) 158

89.1 86.8 83.X 46.0

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0.54

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l‘l.1lO

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“I 58 ‘79 158

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0.73 0.40 0.33 0.23

37.00 38.00 39.00 37.00

l”.oO

I,

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47.3

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37.00 55.00 lS.lM

62

47.5

0.3 I

42.00 55.00

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N

Angle

,,

C

I,

8,

I,

I,

r,

n

,I

I,

41.00

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54.00

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.4m.

J. Orthod. April 1973

N Cairn

0

Terrier

$..

t

12.

ing

similarity

Table

Half-scale

V.

reproduction of

Record

shape of

years years years years years years years

9 4 6 8 6 7 0

and a patient

of

skull

diagrams

of

months

months months months months months months

cairn

terrier

and

great

Dane

illustrat-

proportion. who

developed

a true

SNA (degrees)

Age 10 11 12 13 1-C 15 17

Pr

PNS

Ba Fig.

SATB (degrees)

83 82 82 84 85 86 84

It should be noted that the A-B measurement of the jaws long before the ANB measurement

mandibular

prognathism

ANB (degrees)

81 80 80 82 83 85 85 showed

2 2 2 2 2 1 1 a change

in

A-B (mm.1 5.0 5.5 4.0 3.0 1.0 -1.0 -2.0

anteroposterior

relation

did.

oc.(dlusion varied significantly (p = 0.05) from the mean of the total sample pol)ulntion (Table IV). Tested against the population, including the group from tbc I:niversity of California clinic, the results remained significant (p = 0.05). A\s angle C’ remained constant, it is obvious that angles A and B must vary de~~entlcntly on each other. ‘I’be disco\-ery that the skulls of human beings with mandibular prognathisni \-ariccl in the same manner as the skulls of dogs with mandibular prognathism is an excellent example of applied comparative pathology. Further confirmation of this discovery sl~o~dcl bc pursued, using a Tery large sample. The A-B measuremcnt on l~‘rankfort, plane and the angles A, B, and C described in this article offer diagnostic clues which should be studied further to Terify their validity anal ~meCnlt~ss. L1lso, it may well bc argued that in the future a large group of l)c13or1s lvitli normal dental occlusions slioulcl be included in the sample popl&I iolr. This 1~1s not done in the present study, as the priniary purpose was to inr-cstigatc the way in which patients with one type of malocclusion varic>tl from otllc~ I)aticnts I\-ith various kinds of malocclusion, that is, the Class IJ I group, \vhicah often has mandibular prognathism presenting serious treatment problems. J\t l)rcscnt superimposition of successive head films and gross evaluation of the available tlnta offer perhaps the best method. Observation of changes in angle

Beagle

English

Bulldog

pug Fig.

13.

Change

in

configuration

of

triangle

ABC

in

dogs

with

shortened

skulls.

.\W is not helpful hecausc these c*hanges do not reveal the true situation. As i IIV 111(1ils111’eIllt-‘llt, ,1-B 011 the Frankfort, plane appears to reveal a tendency I o\~artl mandihnlar ~)~*og~~;~thisn~. this measurement is of significant, value to the ~!~z:atiei~lg dentist. very will the cdriticism leveled by some at the use of nl~~aSUr~ri~cnts to iJrrtlict growth.‘. ‘, I” However, the clinician is faced daily with the pwbl(~nl of being able to predict growth for his patients. Meaningful measureInelrts from I’CSWI’~~Iwhic*h give clues to growth changes are most certainly applicahlc in cslinical practice. lli Obviously, the use of such measurements must be \vith the knowlt~tlgc of individual variations. In patient,s exhibiting mandibular prognathism, studies of the triangle ABC ~lrawl on their c*ephalometrit tracings show a change similar to that observed in tlrc 1)rognathiC: breeds of dogs in shape and location of the triangle. \\-cl

\ltl~I~~l~Stitl tl

tt~nlprcvl

354

Fig.

Parker ami Julian

14.

Lateral

shortening that

on

of the

view the

right

skull (beagle)

Am

dog

of

and has

skulls

illustrating

prognathism. brain

typical

Skull

case

of

on

82 c.c.,

changes

left

(pug]

a similar

Fig. tions

15.

Triangles for

with

sample mandibular

ABC

for

a

brain

with case

extreme of

77

cc.;

volume.

Mon

Dog angles

associated has

J. Orthod. Afwill973

dog

populations.

and Broken

man. lines

Solid indicate

lines

indicate configuration

configuration of

triangles

of

mean for

tri-

popula-

prognathism.

Vor those who wish to use these data as a possible clue to facial development, it should be not,ed that the mean value of angle A is 86.6 degrees, as determined by this study. However, it should also be noted that this sample included a large group of patients from the University of California with mandibulal I)rognathisrn of a degree needing surgical correction. When these cases are climinatctl from the sample, the mean drops to 86.2 degrees. As the mean value I1 of angle A for our Class I sample is 85.7 degrees and that for the Class saml~lc is 86.2 degrees, for clinical purposes, the size of angle A will be around ii6 degrees in persons who arc not likely to develop major Class III problems. L iow\.~‘1~, when there are other symptoms indicating a possible Class 111 situntioll, if angle A is greater than 86 degrees and approaches 88 degrees 01’ larger, it woulcl be well to consider that the patient may be developil% a serious mandibular prognathism. In the patient records examined by US, tllc angles of the triangle ABC remain reasonably constant through the growth of

8y lm .----JPy Fig.

16.

requiring

Cephalometric surgical

lm tracings

intervention.

of Note

person constancy

who

developed of

triangle

the individual. Fig. 16 shows the triangles for many pears before mandibular resection Summary

and

severe

mandibular

prognathism

ABC.

from a patient was performecl.

who was followctl

conclusions

The purpose of this work was to study the comparative morphology of the skulls of tlifferent breeds of dogs and to assess the relationship of these variations to dental ocdusion. Xomc of thfxc measurements \vere applied to man to tlctcrmillc il’ the same wlationships occurrecl in man and if the dog could be ;I useful motlel for furtlwr studies with potential human apl)lication. The nlt~as\ll’(‘ill(‘lits wcrv inatlc lising standart anthropologic mcthotls antI instruments, as \wll as rw( liographs of thrx skull made in a cephwlometer. A specimen ol’ each of thirt\--seven clifft>rcnt brawls of’ clogs ant1 158 tl~lltill records of c~c~lltnll)alit~rits wcrc utilized. F’~nit these studies, the following wnclusions may be drawn : 1. The measurement A-K reveals changes occurring in the relation of mnntlihle to maxilla which angle ANB does not. Measurement A-B should 1x1stu(lied further to wrify its prognostic valur~ in clinical I”‘ac+ic*c. 2. ‘1’11~triangle AM tlcscrihing the rclatioldiip of the l~ones ot’ thth lllt:lol’ t’il(‘P in ~log;s \\‘a9 i’cb!lnt-i to clc~sc*rilwthr sarilc~ \ari;\ticons in liiiill. i~‘ilrt h(q* stlrcl>. 01’ this trialiplt~ shonl~l lw contluc*tctl \\ith il ytlry larg(b Si~llll>lf’ and in clinical praeticc to serif>- its cliagnostiv value. 3. The skull of the dog may ver:- definitely be used for further studies of human facial variation. 1. \Yith regartl to the base of the skull in (logs, the contributions of c~ntlochondral ant1 intramemh~allous bones were constant. This indicates that achondroplasia is not fully tlescriptivc of any shortening of the base of the skull.

REFERENCES

I. l::wrington, 2.

::. -1. 3. 6. 7. 8. 9. 10.

S.: Anthropometry and anatomy, London, 1953, E~ncvc:lolwdir Press. face in profile, Lund, 1947, Berlingska Hoktryckeriet. to orthodontia, -$nglc Broatlbn~t, B. H.: A new s-ray technique and its application ortlloll. 1: 45-66, 1931. The ;\mc~ric:tn Kennel Club: The complete dog book, Garden City, 196S, Doul~lctlay 6 Com pany. Ev:111s, E’. G.: Methods of studying the biomecl~anical significance of borw form, zlm. J. Phys. Anthropol. 11: 413-435, 1953. Gay, XVilliam I.: Comparative medicine, Science 158: 1220-1237, 1967. Hirschfeld, W. J., and Movers, R. E.: Prediction of craniofacial growth: The state of art, rlz~r. J. ORTHOD. 60: 435-441, 1971. Hixon, E. H.: Cephalometrics: A perspective, Angle Orthod. 42: 200, 1972. Hrdlicka, A.: 14nthropometry, Philadelphia, 1930. J~ohnson, L. E.: A statistical evaluation of cephalometric prediction, Angle Orthod. 38: Bjiirk,

284.304,

The

1968.

11. Julian, 14. Frogman, 47:

.l~oltn

Arnt‘:

Logan W.

325-342,

M. : Personal communication. M.: Growth changes in the

skull

and

face

of

the

chimpanzee,

hm.

J. Anat.

1930.

13. Miller, Malcolm E.: Anatomy of the dog, Philadelphia, 1965, W. B. Saunders Company. 1-J. Parker, William S., and Julian, Logan M.: A preliminary investigation of the functional morphological basis for the loss of alveolar bone from periodontal disease in the dog, unpuldished report, 1969. 15. Parker, William S., and Julian, Logan &I.: A study of the comparative morphology and pathology of the skulls of dogs by quantitative analysis, unpublished report, 1969. 16. Ricketts, R. M.: Cephnlometric analysis and synthesis, Angle Orthod. 31: 111-156, 1961. 17. Salzmnnn, J. A.: Orthodontics: Practice and technics, Philadelphia, 195i, .J. B. Lippincott Company. 18. Salzmnnn, J. A.: Roentgenographic cephalometrics, Philadelphia, 1961, J. B. Lippincott Company. 19. Stockard, Charles R.: The genetic and endocrinic basis for differences in form and behavior, Philadelphia, 1941, The Wistar Institute. 20. Tappcn, TV. C.: A comparative function analysis of primate skulls by the split line technique, Hum. Biol. 26: 220-238, 1954. 21. Weidenreich, Franz: Apes, giants and man, Chicago, 1946, ITniversity of Chicago Press. 22. Wylie, W. L.: The assessment of anteroposterior dysplasia, Angle Orthotl. 17: 97-109, 1947. 2430

L

St.