A Morphological Study on the Relationship between Arch Form and Craniofacial Structures in Skeletal Class I and Class III Japanese Patient

(Original) zar"7Is tw:}]'i: 25 : 124--134, 1999

key vvords : skeletal Class I - skeletal ClassM -Arch form, Basal arch

A Morphological Study on the +Relationship between

Arch Form and Craniofacial Structures in

Skeletal Class I and Class III Japanese Patient

ROBERTA MIYOE NARUZAWA, YASUHIRO MINOSHIMA, TORU KAGEYAMA,

TOSHIO DEGUCHI, and SABURO KURIHARA

Department ofOrthodontics, Matsumoto Dental University School ofDentisti yi

(Chief: Prof S. Kurihara)

Department ofOrthodontics, Eastman Dental Institute, University College

London, Visiting Professor2 (Chief: Prof N. Hunt)

Summary

Available studies about differences among races, related to prevalence ofmalocclusion or

morphology ofhead and dental arches, suggest a hypothesis that the high prevalence of

skeletal ClassMmalocclusion in Asian ancestry populations could be correlated with a ten-dency toward a brachycephalic head form and larger arches widths.

The purpose of the present study was to evaluate anteroposterior relationship of upper and lowerjaws associated to form of dental arches, maxilla, mandible, face and head.

Materials in this research consisted of pretreatment lateral and posteroanterior

cephalo-metric radiographs and orthodontic models ofJapanese females with skeletal Class I and

ClassM.

Strong correlations between head form and jaws anteroposterior relationship could not be found. However, results indicated that skeletal ClassMhave statistically significant

smaller length ofmaxi11a and greater length ofmandible, than the skeletal Class I group.

Moreover, basal arch length and width of mandible were significantly bigger in skeletal

ClassMgroup.

'Ihese results suggest that skeletal ClassM, at least in this sample, might be associated to local malformation factors.

Introduction

It is important to consider the high prevalence ofmandibular prognathism in patients ofAsian an-cestry, in contrast to its low prevalence in Caucasians.

if}Jlitw:i!]},t` 25(2)•Åq3) 1999 125

According to Lew et alr'., among Chinese students, the prevalence of ClassMmalocclusion is ap-proximately 129o. Endo2' and Susami et al.3', in studies of frequencies of anterior crossbite and edge-to-edge incisal relationships in Japaneses reported ranges from 2.39o to 139o and 2.79o to 7.4% re-spectively. However, among patients submitted to orthodontic treatment, the prevalence of

mandi-bular prognathism becomes 389o in males and 359o in females, being the most frequent

malocclu-sion, according to Kawahara`).

On the other hand, in Americans, Graber5' reported that mandibular protrusion is rare, represent-ing only 2-39o of the patients that undergo treatment, while the incidence of mandibular retrusion is high, representing about 2/3 of the patients.

Head form and occlusion could have some correlation. According to Enlow6', in individuals with dolichocephalic head form, the forward basicranial rotation, and also, the horizontally Ionger ante-rior and middle segments of cranial floor, would result in a forward placement of the maxi11a and backward placement of the mandibular corpus, positioning the molars in a tendency toward a Class

ll position.

On the other hand, in individuals with brachycephalic head form, the horizontal length of the na-somaxi11ary complex is also relatively short and because the brachycephalized basicranium is wider but less elongated in the anteroposterior dimension, the middle and anterior cranial fossae are

cor-respondingly foreshortened, resulting in a relative placement of the entire mandible, causing a

greater tendency toward a prognathic profile and a Class M relationship.

As observed by Graber5', some correlation among the form of head, face and arches could exist. Dolichocephalic individuals trend to have long narrow faces and relatively narrow dental arches,

while brachycephalic individuals trend to have very broad and relatively short faces and broad,

round dental arches. Mesocephalic individuals would fit somewhere in between these two.

Those data suggest the hypothesis that the high prevalence of skeletal CIass M malocclusion in

Asian ancestry populations could be correlated with a tendency toward a brachycephalic head form and larger arches widths.

Despite the several investigations in either head form'-iO' and arches dimensionsi"i6', few data is

found in Japanese individuals. Furthermore, most of them were undertaken on normal occlusion samples.

The present study was undertaken for evaluate the correlation between the anteroposterior

posi-tion ofupper and lowerjaws, and the morphology of coronal and basal arches, maxi11a, mandible,

face and head, in Japanese females with skeletal Class I and skeletal ClassM.

Materials and Methods

Materials

Sets ofpretreatment recordings of30 patients were selected from the clinics at Department of Or-thodontics, Matsumoto Dental University. Each set consisted oflateral and anteroposterior cephalo-metric projections and orthodontic models.

Samples consisted of female individuals between ages of 12yOm and 16yllm (average age of 15y8 m), which comprises the period after peak and before completion of growth. 15 individuals were skeletal Class I (12yO-16y2m) patients and 15, skeletal ClassM (14y6-16yllm).

Classification ofskeletal I and M was based on cephalometric analysis, considering ANB angle

126 NARUZAWA et al. : Relationship to Arch Form and Craniofacial Structures

Casts exhibiting severe crowding, missing or not fu11y erupted permanent teeth (second and third molars not included), evidence of tongue thrusting, teeth with obvious abnormality ofsize or shape, or ectopically erupted teeth were excluded from the sample.

Methods

Cephalometric linear measurements were taken from lateral and posteroanterior cephalogram

tracings ofthe subjects as showed in Fig.1 and 2, respectively.

1. Cephalometricanalysis 1) Lateral cephalogram

Length ofmaxilla {A-Ptm (FH)År : distance from A to Ptm, parallel to Frankfurt Horizontal plane (FH).

Length ofmandible ÅqPog-Ar (FH), : distance from Pog to Ar, parallel to FH. Facial length {S-Or (FH)År : distance from S to Or, parallel to FH.

Head length {G-BaÅr : the linear distance from G to Ba. Usually, in cephalic index evaluation, linear distance from Ba to Op craniofacial surface landmarks is taken, but the limited size of available lateral cephalometric projection films did not permit visualization ofOp point.

Anteroposterior displacement ofjaws {A-B (FH), : distance between A and B points,

dicular to the Frankfort Plane.

2 ) Posteroanterior cephalogram (P-A)

Width ofmaxiIla {Mxl-Mxr) : linear distance between Mx points ofleft and right sides. Width ofthe mandible ÅqGol-Gor} : linear distance between Go points ofleft and right sides. Facial width {Lol-Lor} : linear distance between intersection points of major wing of

sphe-Eur Mxt s Eul Mx1

0

Gor 9 Gol Fig.1 1.Headlength:G-Ba 2.Eaeiallength:S-OreH) 3.Lengthofmaxilla:A-Ptm{F}D

4. Length ofmandible : Pog-Ar (FID 5. Anteroposterior displacement ofjaws : A-B (FH)

Measurement variables for Iateral

cephalogram

Fig.2

6.Hesdwidth:Eul-Eur 7. Faedal vidth : Lol-Lor 8.Widthofmaxil1a:Mxl-Mxr 9.Widthefthemsndible:Gol-Gor

Measurement variables teriorcephalogram

posteroan-lt';L,4-Åql:i'I'"tt': 2to2'3 1999 127

2

noid bone and orbita contour, ofleft and right sides, named Lo point in Sassounii" analysis.

Head width `Eul-Eur) : linear distanee between the outermost points in cranium skeleton

contour, regarding midsag.qital plane. Usually, to evaluate the cephalie index, it is used Eu-Eu craniofacial surface landmarks. Midsagittal plane was determined at crista galli.

. Model analysis

Sagittal and transverse measurements in horizont•al plane of coronal and basal arches were

taken directly on casts as shoxKrn in Fig.3 and 4, respectively, using calipers readings at the near-est O.5mm and Otsubo's sliding calipers]'L

1

} Coronal arch measurements

Tooth material (TM) : suin of mesio-distal diameters of 12 teeth comprised between

nent first molars (ineisors, cuspids, bicuspids and first molars}.

Coronal arch length (CL) : distanee between the midincisal edge Cbuccal side ) of central sors and the line tangent to the distal face ofpermanent first molars, measured parallel to tal suture ; in case of a minimum central incisors erowding, it• was used the middle point tween their midineisal edges.

Coronal arch width (.CW) : distance between summits ofbuccal cusps of first bicuspids,

2 ) Basal arch measurements

Basal arch len.qth (BL) : distance from the innermost point at central incisors alveolus (point A in maxiIla and point B in mandible) to the line tangent• to the distal face of permanent first

molars.

Basal arch width {,BW) : distance between the mucogingival junctions below• buccal cusp tips offirstbicuspids,

Fig.3 Measurement xvidth and length in nal archs

Fig.4 Measurement width and length in

l28 NARUZAWA et al. : Relationship to Arch Form and Craniofacial Structures

3) Upper and lower coronal arches

ship

Mesial Step (MS) : the distance between the mesial faces of upper first molar and lower fist molars (Fig.5);it was used the

mean of right and left sides measurements. It represents a form of evaluation of Angle maloeclusion classification.

In cases with first molars mesio-distal

asymmetric position, basal arch length and coronal arch length were determined as the

mean ofright and left sides measurements,

paraliel to palatal suture.

Ratios between Iengthlwidth

ments were calculated as percentage.

Fig.5 Measurement in upper and lower coronal

archs relationship

Measurements analysis were carried out into two parts :

A sequential analysis of anteroposterior displacement ofjaws, using A-B CFH ) measurement as parameter l

A comparison between mean values ofClass I and CIass III groups.

Decrease of the A-B CFH) reading means a increasing tendency toward a skeletal Class M malocclusion, while increased readings represents a increasing tendency toward a skeletal Class ll malocclusion. A-B {FH} measurement was selected as a parameter due to its larger range ofvariation, compared with ANB angle, for example. Furthermore, ANB angle can be

verely affected by position variation ofpoint NL""2i'.

3. Statisticalanalysis

Statistic analysis was conducted as follows :

A two-sided test of sigtiificance (t tesO was used to compare means of cephalometric and model

measurements in skeletal Class I and ClassM groups,

Using a Pearson's correlation coeffieient• at a significance level of 959E , data were evaluated in a

sequential anteroposterior positional change ofmaxilla and mandible, using A-B {FH) ment as parameter.

Results

Results ofdescriptive statistics for the measurements obtained from cephalograms and models are shown in Table 1 and 2, respectively.

1 . Class I Å~ ClassM gr'oups(ttesO

Relevant findings oftwo-sided t test are summarized below. 1 ) Cephalometricanalysis

A, Lateral cephalogram measurements

Skeletal ClassM individuals had smaller length ofmaxilla (A-Ptm measuremenO, with

nificance at the 1"/( level,

B. Posteroanterior cephalogram (P. A.) measurements

kE}Zgtw-pF 25(2)•(3) ₁₉₉₉ 129

Table1

Cephalometric measurements of skeletal Class I and ClassM groups

ClassIgroup(n=15) ClassMgroup(n=15)

Measurement

mean

S.D.

_mean

S.D. tvalue rvalue

Lateral Cephalogram

A-Ptm (FH)

Pog-Ar (FH) S-Or (FH)

G-Ba

A.B (FH) P. A. Cephalogram

Eu-Eu

Lo-Lo

Mx-Mx

Go-Go

Lateral/P. A.

A-Ptm (FH)/Mx-Mx

Pog-Ar (FH)/Go-Go S-Or (FH)ILo-Lo G-Ba (FH)/Eu-Eu 48.1 77.0 56.3 121.2

5.3

162.7 93.1 69.7 100.4 69.2 76.8 60.6 74.6 2.1 5.4 5.1 5.5 3.0 6.7 4.6 3.5 5.9 4.1 5.8 5.9 5.1 45.4 79.9 54.7 121.4 -2.0 161.9 92.8 69.1 102.5 66.0 78.3 58.9 75.1 1.9 5.8 2.8 4.8 4.4 6.3 1.8 3.3 6.6 5.4 8.5 3.4 4.9 ** O.398 -O.491 -O.O09 O.044 O.211 -O.123 O.125 -O.259 O.178 -O.233 O.062 -O.104

unit : mm ttest:**pÅqO.Ol; *pÅqO.05

Table 2 Model measurements of skeletal Class I and ClassM groups

ClassIgroup(n=15) ClassMgroup(n=15)

Measurement

_mean

S.D.

_mean

S.D. tvalue rvalue

Coronal Arch

Maxilla

CL

CW

cucw

TM

CIrrM

CWII]M

Mandible

CL

CW

cucw

TM

CIA]M

CWII]M

Basal Arch

Maxi11a

BL

BW

BLXBW

BIA]M

BWA]M

Mandible

BL

BW

BIVBW

BurM

BWII]M

Mesial Step

IM-IM

37.8 42.3 89.7 89.9 42.1 47.1 33.6 34.4 97.9 82.2 41.0 41.9 33.0 44.5 74.3 36.7 49.6 31.5 39.8 79.2 38.4 48.5

278

1.9 2.5 5.5 4.e 1.6 2.6 1.5 1.6 4.6 2.8 2.1 2.2 1.1 3.2 5.4 2.0 3.9 1.6 1.6 3.0 2.0 2.2 O.96 36.9 42.9 86.0 89.7 41.2 47.9 32.5 34.8 93.7 82.3 39.5 42.3 31.7 44.9 70.6 35.4 50.1 33.3 42.0 79.4 40.5 51.1 5.59 2.0 2.3 4.0 3.7 2.9 3.1 1.3 2.0 6.5 3.5 1.8 2.7 1.9 2.1 4.2 2.6 3.4 1.2 1.4 2.4 1.4 2.5 2.11 * * * * * * ** ** ** * ** O.285 -O.085 O.352 -O.O02 O.262 -O.086 O.254 O.O12 O.166 -O.028 O.253 O.029 O.564 -O.076 O.513 O.329 -O.063 -O.495 -O.526 -O.044 -O.470 -O.430 -O.792

130 NARUZAWA et al. : Relationship to Arch Form and Craniofacial Structures

C. Lateral1P. A. measurements ratio

Significant differences could not be found.

2) Modelanalysis

A. Coronal arch measurements

a) Maxi11a

Coronal length/coronal width ratio was greater for skeletal ClassM group, with

cance at the 59o level.

b) Mandible

Coronal length and coronal length/tooth material ratio measurements were smaller in

skeletal Class- , at the 59o level.

Coronal length/Coronal width ratio was bigger in skeletal Class M , significant at the 59o

level.

B. Basal arch measurements

a) Maxi11a

In skeletal ClassM individuals, basal length measurement was smaller, while basal

lengthlbasal width ratio was bigger, with significance at the 59o level.

b) Mandible

Basal length measurement (pÅqO.Ol), basal lengthltooth material ratio (pÅqO.Ol), basal

width measurement (pÅqO.Ol) and basal width/tooth material ratio (pÅqO.05) showed cantly bigger values in skeletal ClassM individuals.

C. Mesial step measurement

The distance between mesial surfaces ofupper and lower first molars was greater in skeletal ClassM individuals, with significance at the 19o level.

2 . Evaluation according to A-B (FH)-(Pearson's correlation coefficient)

Following, relevant findings ofPearson's correlation analysis are summarized (Figs. 6-10).

1) Cephalometricstudy

A. Lateral cephalogram measurements a) Maxi11a

Length of maxilla (A-Ptm (FH) measurement) and A-B (FH) showed correlation (r=

O.398). This means some tendency to become smaller with increasing ofClassM severity.

b) Mandible

Length of mandible (Pog-Ar (FH) measurement) and A-B (FH) showed correlation (r=

O.491). This means tended to become bigger as severity ofClassM.

B. Posteroanterior cephalogram (P-A) measurements Significant correlation coefficients could not be found. C. Lateral /P. A. measurements ratio

Significant correlation coefficients could not be found.

2) Model study

A. Coronal arch measurements

a) Maxi11a

Coronal length/coronal width ratio and A-B (FH) showed correlation (r=O.352). This means tendency to become smaller with increasing ofClassM severity.

b) Mandible

kE5J4scts\ 25(2)•(3) 1999 131 (mm) 54

52

50

48

A-Ptm

46

44

42

40

Fig. 6 (m m) 36

35

34

33

32

_BL 31

30

29

28

%

o

oo

oo

o

-10 -8 -6 -4 -2 O 2 4 6 8 10 12

A-B(FM (mm)

Length ofMaxi11a : correlation analysis

between A-Ptm and A-B (FH)

-10 -8 -6 -4

-2 O 2 4 6 8 10 12

A-B (FH) (mm)

Fig. 8 Length ofMandibular basal arch length :

relation analysis between BL and A-B (FH)

{m m} 95 92.5

90

87.5

85

82.5 Pog-Ar sO 77.5

75

72.5

70

67.5 Fig. 7 (mm) 9

8

7

6

5

MS 4

3

2

1

o

Fig. 9 `f'

%

-tO -8 -6 -4 -2 O 2 4 6 8

A-B (FH)

Length of Mandible : correlation between Pog-Ar and A-B (FH)

10 12 (mm) analysis

o

o

oo

o

-tO -8 -6 -4 -2 O 2 A-B (FH}

4 6 8 10 l2

(mm)

Mandibular basal arch width : correlation analysis between MS and A-B (FH)

(mm)45

44

43

42

41 BW 40

39

3B

37

36

Fig. 10

s

0

0

-10 -8 -6 -4 -2 O 2 4 6 8 IO 12

A-B(FH) (mrn)

Mesial step : correlation analysis between

BW and A-B (FH) B. Basal arch measurements

a) Maxilla

Basal length measurement (r=O.564), basal length/basal width ratio (r=O.513) and A-B

(FH) showed strong correlation. This means a tendency to become smaller with increasing of

ClassM severity.

b) Mandible

Basal length measurement (r=O.495), basal length/tooth material ratio (r=O.470), basal width (r=O.526), basal width/tooth material ratio (r=O.430), and A-B (FH) showed

correla-132 NARUZAWA et al. : Relationship to Arch Form and Craniofacial Structures

tion. In this measurement, basal width showed strong correlation. This means tendency to

become bigger with increasing ofClassM severity. '

C. Mesial step measurement

The distance between mesial surfaces ofupper and lower first molars and A-B (FH) showed

strong correlation (r=O.792). This rneans tended to become bigger as severity of ClassM

creased.

Discussion

Difference among races seems to be relevant also in head and arches form. As studied by Farkas22'

in a cephalic index analysis, Caucasians have a trend toward mesocephalism, Chineses toward brachycephalism, while Africans have a dolichocephalism tendency. In a mode! measurements study

on normal occlusion samples, Aoki et al.23' reported that arch width is larger in Japaneses than in

Americans.

[Phe purpose ofthe present study was to evaluate anteroposterior relationship ofupper and lower jaws associated to the morphology of dental arches and craniofacial structures. Measurements were

taken on pretreatment cephalograms and plaster models from Japanese females with skeletal Class

I andClassM.

This study was canied out into two parts :

A sequential analysis of anteroposterior displacement ofjaws, using A-B (FH) measurement as parameter ;

A comparison between means ofClass I and ClassM groups.

Differences between the two ways of analyze might be explained by Jarvinen2`'s study, that ported that ANB angle and A-B (FH) are not always directly comparable. However, in statistical re-sults ofthis study, great differences were not found.

In this study, no significant difference on tooth material measurements between Class I and

ClassM groups was found, but values for both groups were greater than those found by Otsuboi6' on normal occlusion samples. These results confirm that tooth size is related to malocclusion.

Results ofthe present study are in according to findings ofBraun et al.25', which reports that Class

M individuals have smaller arch length and greater arch width of mandibular coronal arches than

Class I subjects. Maxillary coronal arch widths were similar in both groups.

Significant differences were found for basal arch measurements but not for coronal arch. It might be correlated to dental compensations, such as accentuated Spee Curve, dental crowding or tipping. Results ofthis study agree with findings ofRichardson et al.26', which observed lack ofcorrelation be-tween the size ofthe apical base, the alveolar arch and the dental arch.

Although strong correlation between head form and anteroposterior relationship of upper and

lower jaws was not found, results indicated that there were significant correlations in lengths of

maxillary and mandibular bones, and in basal arches measurements.

Skeletal Class M group, compared to Class I , have significantly smaller length of maxiIla and greater length ofmandible, and those tendencies increase with severity ofClassM malocclusion.

Moreover, basal arch length and width ofmandible were bigger in skeletal ClassM group, and

these measurements trend to become greater with increase ofClassM severity.

[rliese results suggest that skeletal ClassM, at least in this sample, might be associated to local malformation, considering two factors : the expression ofsize discrepancy between maxi11a and

man-ta71Åqdi:2i!-L 25(2)•(3) 1999 133

dible, apart ofgrowth of other craniofacial structures ; the anteroposterior alignment and rotation of maxi11a and mandible, contributing to create a Class M malocclusion.

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