The study was
conducted at a large community dental clinic in the Minneapolis/Saint Paul
metropolitan area, where the first author is employed. Sixty-eight percent of
the patient population in this clinic is Southeast Asian.
After approval from
the Institutional Review Board at the University of Minnesota,
a random sample of 700 subjects
was selected from 14,328 active patients. The clinic computer was used to
determine subject ethnicity based on surname. Subjects with a known systemic
disease or craniofacial syndrome were
excluded. Raw data including ethnicity, radiographic findings, age, and gender
were obtained from the chart. Dental radiographs, including bitewings,
periapical, occlusal, and/or panoramic films, were evaluated by one reader (SS)
for the different dental anomalies. Not all patients had full radiographic
coverage of their oral cavities, and some radiographs showed missing teeth.
Therefore, the entire oral cavity could not be evaluated in every patient for
all dental anomalies. All statistical tests used Fisher’s exact test.
The observed dental
anomalies are recorded in Table 1. Due to variations in radiographic coverage,
cases of fusion and gemination were combined in the category of fusion.
Prevalence was compared between two main groups: Asian versus non-Asian.
Sixty-two percent (435/700) of patients were Southeast Asian, with 401 Hmong,
17 Cambodian, 12 Vietnamese, four Chinese, and one Laotian.
tests checked whether the racial difference in
incidence of these anomalies depended upon other patient characteristics
(e.g., gender) using logistic regression and the likelihood ratio test.
None of these tests approached statistical significance (P > 0.05).
involving the number of teeth include hypodontia (one or more missing teeth), oligodontia (six or
more missing teeth), anodontia (complete absence of teeth), and hyperdontia (one or more extra
teeth, also known as supernumeraries). In the population as a whole, the
prevalence of hypodontia in the
permanent teeth ranges from 1.6% to 9.6.% (excluding third molars); the incidence
for third molar hypodontia is around 20%.1
premolars and maxillary lateral incisors are the next most commonly missing
teeth. Among Asians, mandibular incisors are reported as the most commonly
missing teeth.2,3 In our study, Asians were not more likely than non-Asians to
have one or more missing teeth. However, they were more likely to have missing
permanent mandibular incisors (p = 0.025), while non-Asians were more likely to
have missing premolars (p = 0.008). Asians and non-Asians did not differ
significantly in missing canines, maxillary lateral incisors, or primary
mandibular lateral incisors. In the population as a whole, hypodontia of
primary teeth has incidence under one percent and usually affects the
mandibular incisors.4 Prevalence of supernumerary teeth has been reported
between one percent and three percent in
Caucasians versus 2.7–3.4% in Asians,5 though in our study, no significant
difference for supernumeraries was observed.
Alterations in the
size of teeth include microdontia (teeth smaller than normal) and macrodontia
(teeth larger than normal). Both of these conditions may be either generalized
to all the teeth or isolated to one or several teeth. Generalized and relative
macrodontia have a combined prevalence of 3.6% in southern Chinese.6 Neither
isolated nor relative macrodontia were observed in our study. The permanent
maxillary lateral incisor and the primary canine are the most commonly affected
teeth in isolated microdontia of the permanent and primary dentitions. In the
population as a whole, the prevalence of peg-shaped microdont laterals
reportedly varies from 0.8% to 8.4%.4 A Japanese study found the prevalence of
microdontia of the permanent and primary dentitions to be 1.9% and 2.3%,
respectively.7 In our study, Asians were more likely than non-Asians to have
peg laterals (p = 0.004).
Variations in the
shape of teeth include double teeth (fusion and gemination), talon cusp, dens evaginatus, and dens
invaginatus (dens in dente). Gemination and fusion are differentiated from
isolated macrodontia by their clinical or radiographic appearance, and by
counting the number of teeth present (Figures 1 & 2). The prevalence of
fusion in the primary and permanent dentitions is about 0.1% to 1%.8 Bilateral
cases of fusion have a prevalence of 0.02%.4
Fusion of the primary
dentition is usually seen in the mandibular canine and lateral incisor
regions.9 In 30%-50% of Caucasian
and 75% of Japanese cases, fusion in the primary dentition is followed by
anomalies in the permanent dentition, usually hypodontia.10,11 Among Asians
generally, the prevalence of fusion in the primary dentition ranges from 1.2%
to 5.2%, but in populations of European ancestry the prevalence is less than
one percent.9 In our study, fusion was rarely identified in either non-Asians
Talon cusps, also
known as dens evaginatus of the anterior incisors, occur predominantly in the
permanent dentition, and most occur as an additional lingual cusp on the
maxillary lateral or central incisors (Figure 3).12,13 The prevalence for talon
cusps is estimated at less than one percent to eight percent, but extensive
prevalence studies have not been conducted.4 Talon cusp was not found in our
The term dens
evaginatus is usually reserved for a cusp-like elevation which most often
occurs in the center of the occlusal surface of premolars and molars (Figure
4)14,15 Among Caucasians, the occurrence
of dens evaginatus is rare, but the prevalence among Asians is up to 15%,4 and
in Native Americans and Alaskans the prevalence soars to close to 100%.4
Dens evaginatus can be
difficult to identify based on radiographs alone. However, several cases of
dens evaginatus and fusion were observed in Asians.
The term dens
invaginatus is reserved for a deep surface invagination, or infolding, of the
crown on the lingual surface of predominantly maxillary teeth (Figure 5).4 This
condition presents with varying degrees of
severity with an invagination or infolding of enamel and dentin that may extend
into the pulp chamber, the root, or sometimes reach the root apex.4 The
permanent maxillary lateral incisor is the most commonly affected tooth, and
dens invaginatus occurs bilaterally in 43% of cases.16,17 In our
study, Asians were significantly more likely than non-Asians to have dens
invaginatus (p = 0.0002).
Our study points out
differences in the prevalence of various dental anomalies between non-Asian and Asian dental
populations in a major metropolitan dental practice. Asians, in this study,
were more likely to present with a dental anomaly than non-Asians. Dental
practitioners who are aware of ethnic differences in the occurrence of dental
anomalies will be more alert to finding them in patients during routine
examinations. This information can be helpful in evaluating siblings or family
members for similar dental anomalies and may be predictive of normal patterns
of tooth development and/or eruption. This will
allow for prompt clinical interventions to avoid complicating pathology, such
as a non-carious pulpal exposure in dens invaginatus and traumatic exposure due
to cusp fracture in both dens evaginatus and
talon cusp. The presence of hypodontia, hyperdontia, and microdontia such as
conical teeth, may be important in the diagnosis of craniofacial syndromes such
as ectodermal dysplasia or cleidocranial dyplasia.18,19
untreated, many of these dental anomalies may ultimately present complex
treatment challenges in the areas of endodontics, orthodontics, prosthodontics,
and restorative dentistry. ■
The authors thank Bla
Xiong for her patience and help in management of patient records, and Dr.
Shanti Kaimal for critical review of this manuscript.
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*Dr. Stecker is
in private practice at Community Dental Care in Saint Paul, Minnesota.
**Dr. Beiraghi is
Professor, Department of Developmental and Surgical Science, and Head, Division
of Pediatric Dentistry, University of Minnesota
School of Dentistry, Minneapolis,
***Dr. Hodges is
in the Division of Biostatistics at the University of Minnesota
Dr. Peterson is in private practice
and is the CEO of Community Dental Care in Saint Paul, Minnesota.
‡Dr. Myers is
Associate Professor and Director of NIDCR’s TIRR Laboratory, Department of
Diagnostic & Biological Sciences, University of Minnesota School of
Dentistry Minneapolis, Minnesota.