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Class III malocclusion in Chinese (Cantonese): Etiology and treatment
Class III malocclusion in Chinese (Cantonese): Etiology and treatment Gordon
Kam-hung
Chan,
B.D.S., M.D.Sc.*
Kowloon, Hong Kong
T
he incidence of Class III malocclusion has been observed previously to be high in Hong Kong children. Mak7 recorded the number of Class III cases to be 18.86 per cent in his patients. In an earlier survey by Allwright and associatesl on a random sample of 1,123 Chinese children aged 6 to 11 years, the incidence of Class III cases was found to be 14.51 per cent. Elsewhere, however, the percentages of Class III have been found to be low. In an article by Litton and colleagues,‘; the incidence of Class III malocclusion in Caucasian children in five investigations was reported to be 1.6, 2.7, 0.48, 1, and 1 per cent. Even in another oriental Asian race, the Japanese, the incidence was only 6 per cent. What are the underlying factors for this striking difference? Can there be some ethnic-morphologic factors which cause this apparent high incidence of Class III in the Chinese? The present investigation was undertaken to answer these questions. Materials
and
methods
Thirty-six lateral cephalometric head films were drawn from files of patients currently under treatment. The patients chosen had to satisfy the following criteria : 1. Cantonese children (southern Chinese of Kwangtung Province), aged 8 to 17 years. 2. At least three maxillary incisors occluding lingually to the corresponding lower incisors.8 3. No previous orthodontic treatment when the head films were taken. The films were traced and measurements were recorded in the standard manner. There were twenty-one girls and fifteen boys in the sample, and their mean age was 12 years 4 months. Photographs of nine of the patients are shown in Fig. 1. *Senior Dental Hong Kong.
152
Officer,
Government
Dental
Center,
Yaumati
Polyclinic,
Kowloon,
Volume Number
Class III
65 2
Fig.
1. Photographs
of
nine
typical
Class
Ill
malocclusion
malocclusions
in Chinese
in Cantonese
153
children
Samples of this study were not sex differentiated, since Gianelly3 found that facial proportions showed little age and sex variation in children of the orthodontic age groups. Findings
and
discussion
Angular and linear measurements (magnification corrected) were recorded as illustrated in Fig. 2 (BjGrkP facial diagram). Results were statistically analyzed and compared with Bjork’s standards for the 12-year-old Swedish boys in Table I. As can be seen in Fig. 3, the cranial configurations (sella, articulare, and gonial angles) are very similar in the Chinese and Swedish children. The chin angle is slightly greater in the Cantonese because of alveolar prognathism. The over-all linear measurements are smaller in the Chinese than in the Swedes. This is to be expected, as the Chinese are of smaller stature and build than the Caucasians. The short menton-nasion distance would indicate some overclosure in the Chinese Class III children. The mandible is of normal length when compared, and so is the gonial angle. The mean S-N to mandibular plane angle in this study is only 34.2 degrees, which is unlike the textbook skeletal Class III cases (mandibular overgrowth) in which the S-N to mandibular plane angle can be as high as 40 to 50 degrees. A pertinent question is where the discrepancy lies if the mandible is normal. The etiologic site apparently is the short anterior cranial base: sella-nasion. The Chinese sella-nasion length is significantly shorter than the Caucasian norm. In fact, this is the factor in the Cantonese which is most significantly different from the Caucasian. The maxillary complex, being attached to the anterior
Fig.
2.
gonion;
Fig. and
The
facial
Me,
diagram
I. t test
Bjiirk’s
of
for
used
TPO,
menton;
3. Comparison Bjtirk’s study
Table and
Am. J. Orthod. February 1974
Chan
154
of facial 12-year-old
N-S-Ar S-Ar-Go Ar-Go-mand. plane Id-TPo to mand. plane S-N-Pr N-S S-Ar Ar-Go Go-TPo Me-N
analysis.
Id,
(tangent);
of
difference
S,
infradentale; study (dotted
between
on
Sella;
Ar,
Pr,
prosthion;
Cantonese line].
means
of
articulare;
children
present
study
GO,
N,
nasion.
(solid
on
line]
Cantonese
Swedes
Cantonese in present study (n = 36) Yeamrement
cephalometric
diagrams of present Swedish children
significance
12-year-old
in
pogonion
Swedes in BjGrk study (n = 3H)
Standard deciation
Mean
Mean
Standard deviation
t value
Signif icance
Probability
120.8” 144.44”
f 4.99 T? 6.4
122.9” 142.96”
+ 4.85 f 6.2
2.42 1.35
0.02
< <
0.01 0.1
N.S. N.S.
128.89”
+ 6.14
131.090
?r 6.11
2.05
0.05
<
0.02
N.S.
73.61” 83.07’ 60.88 31.36 40.49 70.01 104.32
? k + ? + f +
68.58” 83.68” 68.75 34.35 42.13 72.84 113.12
t + t f k i -t
mm. mm. mm. mm. mm.
5.61 3.54 2.4 3.06 3.28 5.44 6.47
N.S. = Not significant. *Significant beyond the 0.001 level. **“Highly significant, much beyond
the
mm. mm. mm. mm. mm.
0.001
5.4 3.67 2.97 2.85 3.6 4.12 5.42
5.28 0.95 15.35 5.7 2.61 3.77 9.05
< 0.01
<
0.001 0.3 0.001 0.001 0.001 0.001 0.001
< < < < <
* N.S. *** * N.S. * *
level.
cranial base, is thus positioned posteriorly in relation to the normal mandible, giving rise to anterior cross-bite. This phenomenon, short sella-nasion length, is found not only in children of this study but also in normal adult Chinese of previous studies. Measurements for Chinese given by Ghan,* Hong,4 and WeP give varying S-N measurements of
Fig. 4. Removable acrylic in Cantonese children.
Fig.
5.
lower
Canine and arch following
Pig. 6. retention
Plaster are
casts illustrated
appliances
molar Class
of
bands and III treatment.
typical in Fig.
Class 7.
for
correcting arch
III
wire
malocclusion
anterior serve
as
in
cross-bites posttreatment
the
Cantonese.
in
Class retainer
Treatment
III
cases in
the
and
66.1 mm. and 64.9 mm., with standard deviations of 3.1 in each instance. Wei’s” measurements for Australian aborigines is 70.5 mm., also with a 3.1 standard deviation. By contrast, Krogman and Sassouni5 report an S-N reading of 73.22 mm. for Swedes, with a standard deviation of 3.26. Suggestions
for
treatment
Orthodontists generally agree that anterior cross-bites should be corrected early. If the patients are referred early enough, they are treated with simple removable appliances in the early mixed-dentition stages when the upper and lower incisors are erupting. These appliances may consist of an upper acrylic
156
Fig. Fig. arch
Am. J. Orthod. February 1974
Chan
7. A and 6. C and wire.
B, Fixed D, Lower
appliance retainer
used consisting
in treatment of molar
of Class and canine
III malocclusion bands and an
shown in 0.020 inch
plate or a combination of upper and lower plates (Fig. 4). Anterior cross-bites usually are corrected in 4 to 5 months. If sufficient overbite is present, no retention is necessary. Occasionally the patient may experience difficulty in wearing the lower plate. Early loss of the deciduous molars and first permanent molars makes retaining a lower removable appliance a problem. In such cases, light to moderate forces on a head cap-chin cup, with the edge extending to near the vermilion border of the lower lip, will correct the anterior cross-bite. When patients are seen lat,c in the permanent dentition, a skeletal discrepancy is present. The maxillary complex is hindered from developing its maximum forward growth potential and the face will have a “sunken-in” appearance, even after the anterior cross-bite is corrected. Crowding is usually a problem in the maxillary arch, but, whereas the arch length is short anteroposteriorly, the maxillary width is usually sufficient. Models of the thirty-six cases studied were analyzed, and only five (14 per cent) were found to have posterior cross-bite. Rapid maxillary expansion does not seem to be indicated, and is not necessary, in the treatment of Chinese Class III cases. In retention, the emphasis is on the mandibular arch. The corrected lower incisors sometimes have a relapsing tendency in treated late permanent-dentition
Class III
malocclusion
in Chinese
157
cases, Fig. 5 illustrates a retention appliance consisting of molar and canine bands and an 0.022 inch labial arch wire. Fig. 6 illustrates a typical Class III malocclusion as it occurs in Cantonese children. A fixed appliance was used in treatment, as illustrated in Fig. 7. It also illustrates the fixed lower banded appliance most frequently used in the retention of these cases. Summary
and
conclusion
1. Lateral cephalometric head films of thirty-six Chinese (Cantonese) children were analyzed. 2. The criteria for selection were: Cantonese children between 8 and 17 years of age, with at least three maxillary incisors occluding lingually to the lower incisors. Patients had no previous orthodontic treatment. 3. The results were compared with BjGrkW norm for 12-year-old Swedish children. Statistical tests for significance of difference between means of the two samples compared were carried out. 4. The sella-nasion length is significantly shorter in Cantonese than in Swedes. This accounts for the high incidence of Class III malocclusion in the Cantonese. 5. Suggestions for treatment are presented. 6. Although the maxillary arch is short anteroposteriorly, the maxillary width is sufficiently wide when measured from molar to molar. Rapid maxillary expansion is not indicated and is found to be not necessary in the treatment of Chinese Class III malocclusion. Grateful College for Services for
appreciation is extended his assistance in statistical permission to publish this
to Mr. analysis paper.
Wai-kee Kam of the and to the Director
Hong Kong Technical of Medical and Health
REFERENCES
1. Allwright, W. C., and Burndred, W. H.: A survey of handicapping dentofacial anomalies among Chinese in Hong Kong, Int. Dent. J. 14: 505-519, 1964. 2. Ghan, G. K. H.: Chinese (Cantonese)-A roentgenographic cephalometric appraisal, AM. J. ORTHOD. 61: 279-285, 1972. 3. Gianelly, A. A.: Age and sex cephalometric norms? AM. J. ORTHOD. 57: 497-501, 1970. 4. Hong, Y. C.: The roentgenographic cephalometric analysis of the basic dentofacial pattern of Chinese, J. Formosan Med. Assoc. 59: 918-935, 1960. 5. Krogman, W. M., and Sassouni, V.: A syllabus of roentgenographic cephalometry, Philadelphia, 1957, Philadelphia Center for Research in Child Growth, pp. 260-261. 6. Litton, S. F., Ackermann, L. V., Isaacson, R. J., and Shapiro, B. L.: A genetic study of Class III malocclusion, Ahi. J. ORTHOD. 58: 565-577, 1970. 7. Mak, K. L.: An analysis of treated orthodontic patients in Hong Kong, Dent. Mag. 86: 258-259, 1969. 8. Mills, J. R. E.: An assessment of Class III malocclusion, Dent. Pratt. Dent. Rec. 16: 452467, 1966. 9. Wei, S. H. Y.: Craniofacial variation in a group of Chinese students-A roentgenographic cephalometric study in three dimensions, unpublished M.D.S. thesis, University of Adelaide, 1965.
Kam-hung
Chan,
B.D.S., M.D.Sc.*
Kowloon, Hong Kong
T
he incidence of Class III malocclusion has been observed previously to be high in Hong Kong children. Mak7 recorded the number of Class III cases to be 18.86 per cent in his patients. In an earlier survey by Allwright and associatesl on a random sample of 1,123 Chinese children aged 6 to 11 years, the incidence of Class III cases was found to be 14.51 per cent. Elsewhere, however, the percentages of Class III have been found to be low. In an article by Litton and colleagues,‘; the incidence of Class III malocclusion in Caucasian children in five investigations was reported to be 1.6, 2.7, 0.48, 1, and 1 per cent. Even in another oriental Asian race, the Japanese, the incidence was only 6 per cent. What are the underlying factors for this striking difference? Can there be some ethnic-morphologic factors which cause this apparent high incidence of Class III in the Chinese? The present investigation was undertaken to answer these questions. Materials
and
methods
Thirty-six lateral cephalometric head films were drawn from files of patients currently under treatment. The patients chosen had to satisfy the following criteria : 1. Cantonese children (southern Chinese of Kwangtung Province), aged 8 to 17 years. 2. At least three maxillary incisors occluding lingually to the corresponding lower incisors.8 3. No previous orthodontic treatment when the head films were taken. The films were traced and measurements were recorded in the standard manner. There were twenty-one girls and fifteen boys in the sample, and their mean age was 12 years 4 months. Photographs of nine of the patients are shown in Fig. 1. *Senior Dental Hong Kong.
152
Officer,
Government
Dental
Center,
Yaumati
Polyclinic,
Kowloon,
Volume Number
Class III
65 2
Fig.
1. Photographs
of
nine
typical
Class
Ill
malocclusion
malocclusions
in Chinese
in Cantonese
153
children
Samples of this study were not sex differentiated, since Gianelly3 found that facial proportions showed little age and sex variation in children of the orthodontic age groups. Findings
and
discussion
Angular and linear measurements (magnification corrected) were recorded as illustrated in Fig. 2 (BjGrkP facial diagram). Results were statistically analyzed and compared with Bjork’s standards for the 12-year-old Swedish boys in Table I. As can be seen in Fig. 3, the cranial configurations (sella, articulare, and gonial angles) are very similar in the Chinese and Swedish children. The chin angle is slightly greater in the Cantonese because of alveolar prognathism. The over-all linear measurements are smaller in the Chinese than in the Swedes. This is to be expected, as the Chinese are of smaller stature and build than the Caucasians. The short menton-nasion distance would indicate some overclosure in the Chinese Class III children. The mandible is of normal length when compared, and so is the gonial angle. The mean S-N to mandibular plane angle in this study is only 34.2 degrees, which is unlike the textbook skeletal Class III cases (mandibular overgrowth) in which the S-N to mandibular plane angle can be as high as 40 to 50 degrees. A pertinent question is where the discrepancy lies if the mandible is normal. The etiologic site apparently is the short anterior cranial base: sella-nasion. The Chinese sella-nasion length is significantly shorter than the Caucasian norm. In fact, this is the factor in the Cantonese which is most significantly different from the Caucasian. The maxillary complex, being attached to the anterior
Fig.
2.
gonion;
Fig. and
The
facial
Me,
diagram
I. t test
Bjiirk’s
of
for
used
TPO,
menton;
3. Comparison Bjtirk’s study
Table and
Am. J. Orthod. February 1974
Chan
154
of facial 12-year-old
N-S-Ar S-Ar-Go Ar-Go-mand. plane Id-TPo to mand. plane S-N-Pr N-S S-Ar Ar-Go Go-TPo Me-N
analysis.
Id,
(tangent);
of
difference
S,
infradentale; study (dotted
between
on
Sella;
Ar,
Pr,
prosthion;
Cantonese line].
means
of
articulare;
children
present
study
GO,
N,
nasion.
(solid
on
line]
Cantonese
Swedes
Cantonese in present study (n = 36) Yeamrement
cephalometric
diagrams of present Swedish children
significance
12-year-old
in
pogonion
Swedes in BjGrk study (n = 3H)
Standard deciation
Mean
Mean
Standard deviation
t value
Signif icance
Probability
120.8” 144.44”
f 4.99 T? 6.4
122.9” 142.96”
+ 4.85 f 6.2
2.42 1.35
0.02
< <
0.01 0.1
N.S. N.S.
128.89”
+ 6.14
131.090
?r 6.11
2.05
0.05
<
0.02
N.S.
73.61” 83.07’ 60.88 31.36 40.49 70.01 104.32
? k + ? + f +
68.58” 83.68” 68.75 34.35 42.13 72.84 113.12
t + t f k i -t
mm. mm. mm. mm. mm.
5.61 3.54 2.4 3.06 3.28 5.44 6.47
N.S. = Not significant. *Significant beyond the 0.001 level. **“Highly significant, much beyond
the
mm. mm. mm. mm. mm.
0.001
5.4 3.67 2.97 2.85 3.6 4.12 5.42
5.28 0.95 15.35 5.7 2.61 3.77 9.05
< 0.01
<
0.001 0.3 0.001 0.001 0.001 0.001 0.001
< < < < <
* N.S. *** * N.S. * *
level.
cranial base, is thus positioned posteriorly in relation to the normal mandible, giving rise to anterior cross-bite. This phenomenon, short sella-nasion length, is found not only in children of this study but also in normal adult Chinese of previous studies. Measurements for Chinese given by Ghan,* Hong,4 and WeP give varying S-N measurements of
Fig. 4. Removable acrylic in Cantonese children.
Fig.
5.
lower
Canine and arch following
Pig. 6. retention
Plaster are
casts illustrated
appliances
molar Class
of
bands and III treatment.
typical in Fig.
Class 7.
for
correcting arch
III
wire
malocclusion
anterior serve
as
in
cross-bites posttreatment
the
Cantonese.
in
Class retainer
Treatment
III
cases in
the
and
66.1 mm. and 64.9 mm., with standard deviations of 3.1 in each instance. Wei’s” measurements for Australian aborigines is 70.5 mm., also with a 3.1 standard deviation. By contrast, Krogman and Sassouni5 report an S-N reading of 73.22 mm. for Swedes, with a standard deviation of 3.26. Suggestions
for
treatment
Orthodontists generally agree that anterior cross-bites should be corrected early. If the patients are referred early enough, they are treated with simple removable appliances in the early mixed-dentition stages when the upper and lower incisors are erupting. These appliances may consist of an upper acrylic
156
Fig. Fig. arch
Am. J. Orthod. February 1974
Chan
7. A and 6. C and wire.
B, Fixed D, Lower
appliance retainer
used consisting
in treatment of molar
of Class and canine
III malocclusion bands and an
shown in 0.020 inch
plate or a combination of upper and lower plates (Fig. 4). Anterior cross-bites usually are corrected in 4 to 5 months. If sufficient overbite is present, no retention is necessary. Occasionally the patient may experience difficulty in wearing the lower plate. Early loss of the deciduous molars and first permanent molars makes retaining a lower removable appliance a problem. In such cases, light to moderate forces on a head cap-chin cup, with the edge extending to near the vermilion border of the lower lip, will correct the anterior cross-bite. When patients are seen lat,c in the permanent dentition, a skeletal discrepancy is present. The maxillary complex is hindered from developing its maximum forward growth potential and the face will have a “sunken-in” appearance, even after the anterior cross-bite is corrected. Crowding is usually a problem in the maxillary arch, but, whereas the arch length is short anteroposteriorly, the maxillary width is usually sufficient. Models of the thirty-six cases studied were analyzed, and only five (14 per cent) were found to have posterior cross-bite. Rapid maxillary expansion does not seem to be indicated, and is not necessary, in the treatment of Chinese Class III cases. In retention, the emphasis is on the mandibular arch. The corrected lower incisors sometimes have a relapsing tendency in treated late permanent-dentition
Class III
malocclusion
in Chinese
157
cases, Fig. 5 illustrates a retention appliance consisting of molar and canine bands and an 0.022 inch labial arch wire. Fig. 6 illustrates a typical Class III malocclusion as it occurs in Cantonese children. A fixed appliance was used in treatment, as illustrated in Fig. 7. It also illustrates the fixed lower banded appliance most frequently used in the retention of these cases. Summary
and
conclusion
1. Lateral cephalometric head films of thirty-six Chinese (Cantonese) children were analyzed. 2. The criteria for selection were: Cantonese children between 8 and 17 years of age, with at least three maxillary incisors occluding lingually to the lower incisors. Patients had no previous orthodontic treatment. 3. The results were compared with BjGrkW norm for 12-year-old Swedish children. Statistical tests for significance of difference between means of the two samples compared were carried out. 4. The sella-nasion length is significantly shorter in Cantonese than in Swedes. This accounts for the high incidence of Class III malocclusion in the Cantonese. 5. Suggestions for treatment are presented. 6. Although the maxillary arch is short anteroposteriorly, the maxillary width is sufficiently wide when measured from molar to molar. Rapid maxillary expansion is not indicated and is found to be not necessary in the treatment of Chinese Class III malocclusion. Grateful College for Services for
appreciation is extended his assistance in statistical permission to publish this
to Mr. analysis paper.
Wai-kee Kam of the and to the Director
Hong Kong Technical of Medical and Health
REFERENCES
1. Allwright, W. C., and Burndred, W. H.: A survey of handicapping dentofacial anomalies among Chinese in Hong Kong, Int. Dent. J. 14: 505-519, 1964. 2. Ghan, G. K. H.: Chinese (Cantonese)-A roentgenographic cephalometric appraisal, AM. J. ORTHOD. 61: 279-285, 1972. 3. Gianelly, A. A.: Age and sex cephalometric norms? AM. J. ORTHOD. 57: 497-501, 1970. 4. Hong, Y. C.: The roentgenographic cephalometric analysis of the basic dentofacial pattern of Chinese, J. Formosan Med. Assoc. 59: 918-935, 1960. 5. Krogman, W. M., and Sassouni, V.: A syllabus of roentgenographic cephalometry, Philadelphia, 1957, Philadelphia Center for Research in Child Growth, pp. 260-261. 6. Litton, S. F., Ackermann, L. V., Isaacson, R. J., and Shapiro, B. L.: A genetic study of Class III malocclusion, Ahi. J. ORTHOD. 58: 565-577, 1970. 7. Mak, K. L.: An analysis of treated orthodontic patients in Hong Kong, Dent. Mag. 86: 258-259, 1969. 8. Mills, J. R. E.: An assessment of Class III malocclusion, Dent. Pratt. Dent. Rec. 16: 452467, 1966. 9. Wei, S. H. Y.: Craniofacial variation in a group of Chinese students-A roentgenographic cephalometric study in three dimensions, unpublished M.D.S. thesis, University of Adelaide, 1965.