Prevalence and characteristics of impacted maxillary canines in southern Chinese children and adolescents

ORIGINAL ARTICLE

Oral Biosciences

Prevalence and characteristics of impacted maxillarycanines in southern Chinese children and adolescentsAnand K. Sajnani & Nigel M. King

Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China

Keywords

ectopic tooth, impacted canine, maxillary

canine, prevalence.

Correspondence

Dr Anand K. Sajnani, Pedodontist, Bin Muftah

Medical Centre,

Al Markhiya Street, P.O. Box. 201357,

Doha, Qatar.

Tel: +974-30181952

Email: [email protected]

Present address: Winthrop Professor in

Dentistry, School of Dentistry, University of

Western Australia, Perth, Australia

Received 17 June 2012; accepted 31 October

2012.

doi: 10.1111/jicd.12027

AbstractAim: The incidence of impacted maxillary canines in Caucasians reportedly

ranges from 1% to 3%. The objectives of this study were to estimate the preva-

lence and determine the characteristics of impacted maxillary canines in south-

ern Chinese children and adolescents.

Methods: This retrospective audit involved 533 subjects with impacted maxil-

lary canines that had been treated between February 1982 and February 2009.

A customized data entry form was prepared to record and evaluate the status

of impacted canines.

Results: The 533 subjects (327 females and 206 males) with impacted maxillary

canines, who were identified from the population of 26 039 subjects, repre-

sented a prevalence of 2.1%. Four hundred and forty-two (82.9%) of these sub-

jects had unilaterally impacted canines, while 91 (17.1%) of them had bilateral

impactions. In 442 subjects with unilateral canine impactions, 220 (49.8%)

were buccally placed, 194 (43.9%) were palatally placed, and 28 (6.3%) of the

canines were found to lie within the arch.

Conclusions: The overall prevalence of impacted maxillary canines in this study

of 2.1% was similar to the figures quoted for Caucasian populations. In sub-

jects with unilateral impactions, buccally impacted canines demonstrated a

slightly higher incidence (49.8%) compared to palatally impacted canines

(43.9%).

Introduction

Impaction is a pathological condition defined by the lack

of eruption of a tooth into the oral cavity within the time

and physiological limits of the normal eruption process.1

The permanent maxillary canine is second only to the

mandibular third molar in the frequency of impaction2,3

and is considered to be the most frequently impacted

tooth in childhood.4 Over the years, numerous studies

have been conducted to investigate the incidence and

prevalence of impacted maxillary canines in different pop-

ulations, see Table 1.

Scrutiny of the literature on impacted canines revealed

that numerous studies have been conducted on Cauca-

sian populations to determine the prevalence, gender dif-

ferences, and the buccal to palatal impaction ratio.

Although the Chinese comprise almost 20% of the

world’s population, very few studies have been con-

ducted to determine the status of impacted canines in

this particular population.

Additionally, there have been vast differences in the fig-

ures reported for these variables in Caucasian popula-

tions. For example, the incidence of impacted maxillary

canines has been reported to range from 1% to 3%.20

However, in an individual orthodontic practice, the inci-

dence was quoted to be as high as 23.5%.21 Likewise,

there have been differing views on the side distribution of

impacted maxillary canines. Harzer22 found a higher inci-

dence on the left side while Grande and co-workers23

reported a predilection for the right side in their study.

A more balanced ratio has also been observed in other

clinical studies.10,24

38 ª 2013 Wiley Publishing Asia Pty Ltd

Journal of Investigative and Clinical Dentistry (2014), 5, 38–44

The studies conducted by Montelius8 on Chinese sub-

jects noted a relative infrequency of impacted canine teeth

when compared with Caucasian populations. There is also

said to be significant variation between Caucasian and

Oriental populations in the number of males and females

presenting with impacted canines. Chinese males seem to

be more frequently affected than females, whereas the

reverse holds true for Caucasians.14 Similarly, palatally

impacted canines have been estimated to be five times

more prevalent in Caucasian than Chinese populations.25

Given the paucity of data and the apparent discrepan-

cies in the literature, a retrospective audit was conducted

to evaluate the status of impacted maxillary canines in a

southern Chinese population. The objectives of this study

were to determine the prevalence and characteristics of

impacted maxillary canines.

Materials and methods

The present investigation was conducted on a population

of southern Chinese children and adolescents with

impacted maxillary canines that had been treated in the

Paediatric Dentistry and Orthodontics Clinic at the Prince

Philip Dental Hospital, The University of Hong Kong,

Hong Kong SAR. Southern Chinese was defined as those

Chinese children whose ancestors originated from the

provinces south of the Yangtze River and spoke different

dialects to people from the north.

The sample was drawn from the 26 039 children and

adolescents who had attended the Paediatric Dentistry

and Orthodontics Clinics at the Prince Philip Dental

Hospital from February 1982 to February 2009. The

records of subjects with impacted maxillary canines were

traced from the list of patients attending the consulta-

tion clinics and the Joint Paediatric–Orthodontic clinics.

Every effort was made to trace all patients with at least

one impacted maxillary canine. The canine was diag-

nosed as being impacted if it failed to erupt into the

oral cavity within the expected time of eruption or if

the tooth demonstrated an ectopic location on a radio-

graph (taken beyond the expected age of eruption) and

would fail to erupt into the oral cavity at a later time

considering all known physiologic processes. The chro-

nologic age of the children and adolescents at their first

visit, or at the time of diagnosis of the impacted canine,

ranged from 7.9 to 25.8 years with a mean of 15.1 years

(�4.3 years). A few of these subjects were diagnosed at a

later time. Subjects with any form of oro-facial cleft or

medical complications including metabolic and endo-

crine disorders were excluded from the study. After

obtaining a list of subjects, the case notes and radio-

graphs were retrieved. A customized data entry form was

prepared to record and evaluate the status of impacted

canines (Figure 1). The data collection form sought all

relevant information of the patient and the status of the

impacted canines, and was used to record the general

descriptive data about the subjects, such as, hospital

number, gender, date of birth, ethnic group, chief com-

plaint, the teeth involved, date of diagnosis, date of first

visit, and the radiographic diagnosis.

Table 1. The prevalence of impacted maxillary canines in studies conducted and published between 1929 and 2008

Author and year Sample size Country Frequency (%) Remarks

Cramer 19295 1000 USA 1.4 –

R€ohrer 19296 3000 Germany 2.06 –

Mead 19307 1462 USA 1.57 –

Montelius 19328 5017 China Zh – 1.7,

Cu – 5.9

–

Dachi and Howell 19619 3043 USA 0.92 M:F 1:2.3

Bass 196710 9102 England 1.65 M:F 1:2.2

Thilander and Jakobsson 19682 384 Sweden 1.8 M:F 1:4

Takahama and Aiyama 198211 3367 Japan 0.27 Impaction – microform

of cleft lip and palate

Ericson and Kurol 198612 505 Sweden 1.7 –

Brin et al. 198613 2440 Israel 1.53 (palatal

impactions)

M:F 1:1

Oliver et al. 198914 50 Cu sample – UK Zh

sample – Hong Kong

– Cu:Zh 3.4:1 (palatal

impactions)

Chu et al. 200315 7486 Hong Kong 0.8 –

Leifert and Jonas 200316 8556 Germany 2.75 M:F – 1:3

Sacerdoti and Baccetti 200417 1000 Italy 2.4 M:F – 1:3

Zhong et al. 200618 10488 China 2.05 M:F – 1.8:1

Prskalo et al. 200819 170 Croatia 4.71 M:F – 1:1

M, male; F, female; Zh, Chinese; Cu, Caucasian.

ª 2013 Wiley Publishing Asia Pty Ltd 39

A.K. Sajnani and N.M. King Impacted canines in young Chinese

Results

A total of 533 subjects with 624 impacted maxillary

canines were identified from the 26 039 subjects in the

study, which represented a prevalence of 2.1%. Four hun-

dred and forty-two (82.9%) of these subjects had unilat-

erally impacted canines, while 91 (17.1%) of them had

bilateral impactions.

In the 442 subjects with unilateral impactions, 220

(49.8%) of the impacted canines were buccally placed,

194 (43.9%) were palatally placed, and 28 (6.3%) were

found to lie within the arch. In the same group of sub-

jects, 216 (48.9%) had the canine impacted on the left

side and 226 (51.1%) impacted on the right side. Subjects

with the canine impacted on the right side showed a

predilection for the tooth to be buccally positioned

(n = 122, 54%) when compared to those that were pala-

tally positioned (n = 88, 38.9%). By contrast, subjects

with a canine impacted on the left side exhibited a predi-

lection for the tooth to be palatally located (n = 106,

49.1%), when compared to those that were buccally

located (n = 98, 45.4%; Figure 2). There was an apparent

steady decrease in the frequency of palatally impacted

canines from February 1982 to January 2009, while the

proportion of subjects with buccally impacted canines

during the same period rose (Figure 3).

Of the 91 children and adolescents with bilaterally

impacted canines, 75 (82.4%) demonstrated a uniform

pattern of distribution between the right and left sides,

that is if the left impacted canine was buccally located

then the right impacted canine was also observed to be

buccally located. Indeed in this group, 48 subjects had

bilaterally impacted canines that were buccally located

and formed 52.8% of all cases with bilateral impactions.

Likewise, 25 subjects had bilaterally impacted canines that

were palatally positioned and constituted 27.5% of the

total cases with bilateral impactions. The remaining 16

subjects with bilateral impactions (17.6%) showed the

opposite pattern, with one canine being impacted bucally

whereas the antimere was impacted palatally.

Of the 533 subjects with impacted maxillary canines,

327 (61.4%) were females and 206 (38.6%) were males.

The majority of the females, 270 (82.6%), had unilaterally

Data collec on form

Name: Record No:

Date of birth (age): Gender: M F

Dental age: Ethnic group: Ch Others

Chief complaint: Tooth involved: 13 23

Inspec on Y N Palpa on Y N

Posi on:

Date of diagnosis: Cause of impac on:

Date of 1st visit:

Radiographic diagnosis: 13 23

Posi on:

Figure 1. Data entry form that was used to

record the findings of patients with impacted

maxillary canines.

Figure 2. Location of 442 unilaterally impacted canines within the

right and left sides. , Buccal; , Palatal; , Arch.

Figure 3. Changes in location of unilaterally impacted canines in the

period from February 1982 to February 2009. , Buccal; Palatal.


Impacted canines in young Chinese A.K. Sajnani and N.M. King

impacted canine while 57 (17.4%) had bilateral impac-

tions. Males followed a similar trend, 172 (83.5%) had

unilateral impaction while only 34 (16.5%) had bilateral

impactions. Interestingly, a change in the proportion of

males and females affected by impacted maxillary canines

was observed over time. Between February 1982 and Jan-

uary 2000, females were almost twice as frequently

affected than males, with 65.3% of the affected being

females and the remaining 34.7% males. However, since

February 2000 this difference significantly decreased to

12.6%, with 43.7% of the affected being males and 56.3%

being females (Figure 4).

Although the majority of the subjects were diagnosed

to have an impacted canine during an initial screening, a

further 57 (10.7%) were diagnosed at a later time. In

these cases the mean time of delay in diagnosis was

5.4 years (�2.7 years) after the initial screening.

Out of the 533 subjects in the study, only 70 (13.1%)

were aware that they had an unerupted permanent

canine, and an even smaller number, 24 (4.5%), com-

plained of retention of the primary canine. In spite of

being unaware of the status of their unerupted canines,

104 (19.5%) subjects had requested a consultation and

treatment for other orthodontic problems. A major pro-

portion of subjects, 155 (29.1%), was referred by general

dental practitioners. The School Dental Care Service,

which is a dental health care program for almost all

primary school children, referred 63 subjects (11.8%).

Discussion

Prevalence

This retrospective study was carried out in the only dental

hospital in Hong Kong SAR where multidisciplinary spe-

cialist services are available. Most subjects attend by self-

referral, and if deemed suitable for teaching purposes are

accepted for treatment. Subjects with impacted canines

are usually placed in the Paediatric Orthodontic Consul-

tation Clinic for multidisciplinary treatment planning. In

addition, a significant number of subjects were referred

by general dental practitioners in the private sector

(29.1%) and by the School Dental Care Service (11.8%).

Thus, the prevalence figure of 2.1% for impacted maxil-

lary canines can be expected to be representative of the

population as a whole or at least of those who sought

treatment.

Adolescence is considered to be the period between

ages 13 and 19 years and can be defined as a time

between the beginning of sexual maturation (puberty)

and adulthood.26 It is a time of physiological maturation

in which a person becomes “adult-like” in behaviour.

However, the physical, psychological, and cultural expres-

sions associated with adolescence can begin earlier and

end later,26,27 For instance, although puberty has been

historically associated with the onset of adolescent devel-

opment, it now typically begins prior to the teenage years

and there has been a normative shift of it occurring in

preadolescence, particularly in females.28 Likewise, physi-

cal growth, as distinct from puberty (particularly in

males) and cognitive development generally seen in ado-

lescence, can also extend into the early twenties. Thus,

chronological age provides only a rough marker of ado-

lescence and scholars have found it difficult to agree upon

a precise definition of adolescence.27,28 However, in our

study almost all of the subjects were within the age group

of 10–20 years, and was defined as a sample of children

and adolescents.

It has been suggested that Europeans have palatally dis-

placed canines five times more frequently than Asians.25

This mathematical estimate was based on the findings of

Montelius8 and Oliver and his co-workers.14 Montelius8

reported that impacted maxillary canines were twice as

prevalent in Caucasians as in Chinese. The data were

derived from the radiographs, available in a medical col-

lege hospital, that had been gathered over a 10 year per-

iod; however, no attempt was made to include all of the

cases during the period. Also, the ages of the subjects

were not specified, which is unfortunate because Rayne29

emphasized that the bias towards females having

impacted maxillary canines occurs only in teenagers,

while there appears to be a preponderance of males dur-

ing adulthood. Moreover, for more than half of their

sample in the Chinese group, only partial radiographs

were available whereas 90% of the Caucasian group had

full-mouth radiographs; this could have contributed to

the apparently higher frequency of impacted canines in

the Caucasian group.

Oliver and co-workers,14 who studied a sample of only

29 Chinese subjects in Hong Kong, found palatally dis-

placed canines in 28% of the subjects. However, the study

Figure 4. The frequencies with which impacted maxillary canines

affected females and males in the period from February 1982 to

February 2009. , Male; Female.



was performed to examine the morphology of the lateral

incisors in subjects with a unilaterally impacted canine

and not to specifically determine the prevalence of

impacted maxillary canines in the sample and the popula-

tion at large. Moreover, the sample was not randomly

selected and was further biased by the inclusion of only

those subjects who had good quality radiographic and

clinical records.

The prevalence of impacted maxillary canines in the

general Caucasian population can be estimated to be

2%10,29,30 with palatally displaced canines occurring in

approximately 70% of the cases.6,25,31,32 If these data,

obtained from studies on Caucasian populations are inte-

grated into the present study, a numerical estimate may

be calculated of the relative prevalence of palatally dis-

placed canines between the Caucasians and Chinese.

Thus, the ratio of prevalence of all types of maxillary

canine impactions in Caucasians and Chinese would be

2.0:2.05, while for palatally displaced canines it would

occur in 70% and 45% of Caucasians and Chinese respec-

tively. Therefore, the prevalence of palatally displaced

canines in Caucasians and Chinese can be calculated to

be 70% 9 2:45% 9 2.05, which gives a ratio of 1.4:0.9 or

approximately 1.5:1. Thus, the mathematical estimate

based on the currently available data indicates that Cauca-

sians may be expected to have palatally impacted canines

approximately 1.5 times more frequently than Asians.

Unilateral impactions

A wide variation in the distribution of unilaterally

impacted canines has been reported, with Takahama and

Aiyama11 and Harzer22 reporting a higher incidence on

the left side while others have reported a higher incidence

on the right side.23,33 However, the present study found a

more balanced distribution between the two sides, which

is in agreement with the findings of Bass10 and Stahl and

Grabowski.24 Moreover, a predilection for the tooth to be

located buccally when impacted on the right side and to

be positioned palatally when impacted on the left side

was noted in the current study. Two possibilities exist

that may explain these findings. The differences reported

in the various studies could be due to the fact that the

studies were conducted in different populations, and con-

cordant with the racial groupings, a genetic influence in

the occurrence of impacted maxillary canines has been

observed. Conversely, this could be a chance finding due

to differences in the sample size and creation, grouping

methods, clinical examination methods, and the radio-

graphic techniques used to make the diagnosis in the dif-

ferent studies.

A change in the trend with respect to the position of

the impaction of the canine was apparent over time in

the present study. A possible explanation could lie in the

ethnic composition of the sample. Hong Kong has wit-

nessed a steady increase in the immigrant population

from The People’s Republic of China.34,35 Although this

study was performed at only one location, the 27 year

period over which the samples were drawn may have

brought about a significant change in the relative propor-

tions of the various ethnic groups in Hong Kong. Alter-

natively, this finding could have occurred as a result of

the number of subjects with palatally impacted canines,

who sought treatment, remaining stable, while there has

been an increase in the number of subjects with buccally

impacted canines who have subsequently sought specialist

orthodontic treatment during the later periods rather

than, as happened in the past, just requesting a general

practitioner to extract the buccally displaced canine as an

economic and quick, compromise treatment option.

Bilateral impactions

Most of the studies published on impacted maxillary

canines have dealt with the characteristics of unilateral

impactions.2,9,12,14 Also, data regarding the bilateral

occurrence of impacted maxillary canines has been com-

promised because of the failure of many investigators to

distinguish unilateral palatal impactions from the other

types. However, bilateral occurrences have been reported

to range from 8% to 45%.30,31,33,36 The current study is

in agreement with the higher occurrence figure. Peck

and co-workers25 suggested that this high rate of bilater-

alism is elevated beyond chance occurrence and points

to an intrinsic etiological factor as a genetic mechanism.

However, it is highly likely that the existence of this

genetically determined condition brings about an envi-

ronmentally generated alteration to the eruption pattern

and pathway of canines consistent with a lack of guid-

ance from the lateral incisor that may lead to bilateral

occurrence of palatally displaced canines.37 Also, it has

been suggested that buccal displacement of maxillary

canines that occurs bilaterally is not directly related to

genetics and results usually because of generalized

crowding, or space deficiency within the dental arch.

However, the present study found that 17.6% of the

cases with bilateral impactions demonstrated an opposite

pattern of impaction between the two sides, with one

canine being impacted buccally, while the antimere was

impacted palatally. This leads to one of the following

hypotheses: (a) both buccally and palatally displaced

canines have genetic factors contributing to their dis-

placement and that the subsequent impaction, or guid-

ance from the lateral incisor, contributes to the

impaction; and (b) the position to which they are dis-

placed can be attributed to purely random factors.



Gender differences

Gender differences have been reported in a number of pre-

vious studies with the majority favoring a predilection for

females.9,17,36 This higher frequency in females is suggested

to be due to the smaller cranium of the female leading to

diminution of the facial skeleton and the jaws; thus,

increasing the chance of impaction of a maxillary canine.6

Alternatively, it may be related to the higher frequency of

missing, small, and peg-shaped lateral incisors observed

together with impaction of palatally displaced canines that

are more commonly found in females.36 Nevertheless, the

higher occurrence in females may reflect a trend for more

females to seek orthodontic treatment.14 However, confu-

sion exists over the figures for a gender difference because

some studies have shown an approximately equal occur-

rence of the anomaly amongst males and females.13,16 Oli-

ver and his co-workers14 reported a higher prevalence of

impacted canine in males in their study, which was also

conducted on Hong Kong Chinese subjects. They sug-

gested that this may reflect a true difference, or may indi-

cate a demographic tendency in which the gender ratio for

subjects seeking treatment is reversed. The present study,

however, found the converse to be true, females being 1.5

times more frequently affected than males, in what is a

similar, but much larger study population.

Concise reporting on patterns of gender differences in

the occurrence of anomalies is useful to aid identification

of biological markers with genetic links involving sex

chromosomes. Peck and his co-workers25 demonstrated a

genetic origin of impaction of maxillary canines by high-

lighting this fact. However, small, peg-shaped or missing

lateral incisors are also more common among females

and they are often found in relation to impacted maxil-

lary canines thus offering support for the guidance the-

ory.37 Moreover, the current study found a change in the

gender ratio over time. Over the 27 year period from

which the samples were drawn, the ratio of female:male

dropped from approximately 2:1 during the 1980s and

early 1990s to 1.3:1 during 2003–2009. This finding could

be as a result of the males in the population now being

more aware of their facial appearance and hence more are

seeking orthodontic treatment. Thus, the difference in

gender predilection may not actually exist in the general

population. Irrespective of these findings and the figures

reported in the literature, it cannot be definitely con-

cluded that there is a higher predilection for females to

demonstrate genetic influences as the sole contributing

factor for impaction of maxillary canines. However, the

influence of hypodontia and microdontia of the maxillary

lateral incisors, which occur more frequently in females,

cannot be ignored.

In spite of attempting to include all cases with

impacted maxillary canines in the study, there may have

been some that were inadvertently omitted. Surprisingly,

most of the subjects were unaware of the impaction of a

canine at the time of diagnosis. However, these factors

may not be adequate to avoid bias that may have been

introduced into the sample since the majority of the sub-

jects needed other forms of dental treatment. Other

aspects which affect the occurrence and presentation of

an impacted maxillary canine, such as craniofacial mor-

phology, occlusion, and the space available in the maxil-

lary arch could not be considered as the study was

performed retrospectively.

Nevertheless, prevalence and characteristics of impacted

maxillary canine in Asian populations, particularly the

Chinese population, have been scarcely studied. This

study provides new knowledge on the features of

impacted maxillary canines in a large sample of southern

Chinese children and adolescents. Awareness of the preva-

lence and presenting characteristics allows for better treat-

ment plans and prediction of the prognosis of impacted

maxillary canines.

Conclusions

The prevalence of impacted maxillary canines in southern

Chinese children and adolescents is 2.05%, which is simi-

lar to the figures quoted in several studies conducted on

Caucasian populations. While there was a predilection for

females to be affected by both unilaterally and bilaterally

impacted maxillary canines, there was an almost equal

distribution of unilaterally impacted maxillary canines

between the left and right sides. In subjects with unilateral

impactions, buccally impacted canines demonstrated a

slightly higher incidence (49.8%) compared to palatally

impacted canines (43.9%).

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Prevalence and characteristics of impacted maxillary canines in southern Chinese children and adolescents