Keywords
hypodontia - mild - root - dimension - control
Introduction
Hypodontia, also known as “selective tooth agenesis” or “congenital tooth absence,”
is the condition in which one to six teeth excluding the third molars are congenitally
missing.[1]
[2] It is the most common developmental anomaly in humans with a reported range of 4.4%
to 13.4%,[2]
[3] occurring more commonly among females.[2]
[3]
The exact etiology of hypodontia is unknown, but it is multifactorial in nature[4]
[5]
[6] and can be affected by genetic and environmental factors.[1]
[2]
[6]
[7] It may arise as part of a recognized genetic syndrome or more commonly as a solitary
non-syndromic anomaly.[7] Nonsyndromic hypodontia most commonly affects the permanent dentition, with the
mandibular second premolars having the highest incidence, followed by the maxillary
lateral incisors.[7]
Hypodontia may be classified as either complete and partial; or according to the number
of congenitally missing teeth, as mild (2 teeth or less congenitally missing), moderate
(3 to 5 teeth congenitally missing), and severe (6 or more teeth congenitally missing).[3]
[6]
[8] The latter is also known as oligodontia. The most severe form of tooth agenesis
occurs in the absence of the entire primary or permanent dentition and is termed anodontia.
However, anodontia rarely occurs without an accompanying genetic disorder such as
ectodermal dysplasia[9]
[10]
Patients with hypodontia may present with disturbances in facial growth patterns,
several features of malocclusion including midline deviations and deep overbites which
may result in a loss of function, decreased aesthetics, and oral health-related quality
of life issues.[4]
[11]
[12]
[13]
[14]
[15] Management of patients with hypodontia is challenging and requires an interdisciplinary
approach, careful treatment planning, long-term maintenance, and family counselling.[5] Treatment may include strategic extraction of primary teeth, up-righting and aligning
teeth orthodontically, and placement of intra-bony implants.[16] Other treatment options may include autotransplantation and protraction of third
molars.[16]
An association between hypodontia and reduced tooth crown dimensions of the remaining
dentition has been reported by some studies,[8] and a positive correlation between the severity of hypodontia and the extent of
reduction in tooth crown dimensions has further been detected.[8] However, to date, there have been no studies in the literature that have comprehensively
investigated the effects of hypodontia on tooth root dimensions of the remaining dentition.
Therefore, the aim of this study was to compare root dimension measurements between
subjects with mild hypodontia and an age- and sex-matched control group. The information
obtained from this study may aid in the understanding of the etiology of hypodontia
and facilitate the diagnosis, treatment planning, and management of these complex
cases.
Materials and Methods
Participants
Ethical approved was sought and granted from Research Ethics Committee at University
of Sharjah to use patient records from the University Dental Hospital Sharjah (Reference
number: REC-18–02–12–04-S).
A sample size calculation was performed for this case-control study and it was determined
that 20 subjects would be required in each group to detect a clinically significant
difference of 0.9 mm with 0.05 α and 0.2 β. The study sample ([Fig. 1]) consisted of 50 individuals: 25 hypodontia patients and 25 age- and sex-matched
controls, with full complement of the permanent dentition. Each subgroup consisted
of 14 males and 11females. All hypodontia subjects were selected from the University
Dental Hospital Sharjah database, Sharjah, UAE, and the controls were selected from
the same database, ensuring each hypodontia subject was matched with a control in
terms of age and gender. Subjects clinical notes and orthopantomograms (OPTs) were
examined to ensure the details were correct and the inclusion criteria were met. The
inclusion criteria for hypodontia subjects were as follows:
-
No general medical conditions or syndromes
-
Had no supernumerary teeth
-
Had completely formed roots of the permanent dentition excluding third molars
-
No previous orthodontic treatment
-
Had 1-2 teeth congenitally absent excluding the third molars.
Fig. 1 Study sample selection and measurements recorded.
The inclusion criteria for control subjects were the same as for hypodontia subjects,
except control subjects should have had no congenital absence of the permanent teeth.
The age range for the whole sample was 12 to 20 years, and the mean age range for
both groups was 14.92 years with a standard deviation (SD) of 2.91 years.
Measurements Recorded
Root dimension measurements ([Fig. 2]) of all permanent teeth excluding third molars were made on standardly taken OPTs
of all subjects on MiPACS Dental Enterprise Solution™. Measurements made were as follows:
Fig. 2 Root dimension measurements for a (i) single rooted tooth, (ii) upper multi-rooted
tooth and (iii) lower multi rooted tooth. CEJ, cemento-enamel junction.
-
The mesiodistal width (A) at the cemento-enamel junction (CEJ): This was measured
digitally with the aid of the “ruler” tool up to the second decimal digit.
-
The length (B) was defined as the maximum length between the root apex and the midpoint
of measurement A.
-
The second mesiodistal width (C) was measured by drawing a line at halfway and perpendicular
to the length of the root (B).
All measurements were performed by one trained operator twice and the mean value of
the two measurements was recorded. The measurements error was assessed by carrying
out the above measurements twice 8 weeks apart on six tooth types (3 from the maxillary
arch and 3 from the mandibular arch) on 20 randomly selected OPTs, of which 10 were
hypodontia patients and 10 were control subjects. No statistically significant difference
was detected between the two measurements using a paired sample t-test (p > 0.05). The method error was assessed using Dahlberg formula. The range of the measurements
error between the double measurements was found to be 0.09 to 0.25 mm, which was considered
very small when compared with the average values of the measurements in the study.
Statistical Analysis
Statistical analyses were performed using SPSS Ver. 24.0 for Mac OS X. The data were
found to be normally distributed (p < 0.05; Kolmogorov–Smirnov test); therefore, parametric testing was applied. Two-sample
t-tests were applied to compare hypodontia and control groups. Differences were considered
statistically significant at p < 0.05.
Results
[Table 1]
[Fig. 3] show comparison of root dimension measurements A, B, and C of the permanent maxillary
teeth between the hypodontia and control groups. [Table 2]
[Fig. 4] show comparison of root dimension measurements A, B and C of the permanent mandibular
teeth between the hypodontia and control groups. Hypodontia patients had significantly
smaller mesiodistal root dimension A of the maxillary first and second premolars,
maxillary first molars, and mandibular second premolars (p < 0.05). Hypodontia subjects also demonstrated significantly shorter root dimensions
B of the maxillary central incisors, maxillary canines, maxillary first premolars,
and mandibular first molars (p < 0.05). Additionally, they had reduced mesiodistal root dimension C of the maxillary
central incisors, maxillary second premolars, maxillary first molars, and mandibular
first and second premolars (p < 0.05).
Table 1
Comparison of root dimension measurements of the permanent maxillary teeth in hypodontia
patients and controls
|
Tooth
|
Measurement
|
Hypodontia (mean ± SD)
|
Controls (mean ± SD)
|
p-Value
|
|
U1
|
A
|
6.94 ± 1.22
|
7.51 ± 0.79
|
0.055
|
|
B
|
17.05 ± 1.98
|
18.65 ± 1.73
|
0.005
|
|
C
|
5.53 ± 0.98
|
6.26 ± 0.71
|
0.005
|
|
U2
|
A
|
6.04 ± 1.04
|
6.08 ± 0.57
|
0.902
|
|
B
|
17.07 ± 1.90
|
18.03 ± 1.80
|
0.094
|
|
C
|
4.82 ± 0.84
|
5.05 ± 0.44
|
0.296
|
|
U3
|
A
|
7.50 ± 0.90
|
8.01 ± 1.65
|
0.343
|
|
B
|
18.43 ± 3.31
|
21.73 ± 2.78
|
0.007
|
|
C
|
5.88 ± 1.32
|
6.44 ± 1.06
|
0.211
|
|
U4
|
A
|
7.10 ± 1.04
|
8.49 ± 0.68
|
0.038
|
|
B
|
15.49 ± 1.55
|
17.47 ± 2.49
|
0.015
|
|
C
|
5.75 ± 1.02
|
7.12 ± 0.81
|
0.039
|
|
U5
|
A
|
7.29 ± 0.61
|
8.12 ± 0.78
|
0.006
|
|
B
|
15.57 ± 2.00
|
17.02 ± 2.73
|
0.137
|
|
C
|
5.64 ± 0.81
|
6.35 ± 0.93
|
0.048
|
|
U6
|
A
|
10.19 ± 1.60
|
11.03 ± 0.82
|
0.026
|
|
B
|
15.98 ± 2.34
|
17.21 ± 2.22
|
0.076
|
|
C
|
8.15 ± 1.52
|
9.50 ± 1.21
|
0.002
|
|
U7
|
A
|
9.98 ± 0.84
|
10.41 ± 0.78
|
0.262
|
|
B
|
15.16 ± 1.99
|
15.07 ± 3.74
|
0.944
|
|
C
|
8.00 ± 0.84
|
8.32 ± 0.70
|
0.383
|
Table 2
Comparison of root dimension measurements of the permanent mandibular teeth in hypodontia
patients and controls
|
Tooth
|
Measurement
|
Hypodontia (mean ± SD)
|
Controls (mean ± SD)
|
p-Value
|
|
L1
|
A
|
4.62 ± 0.69
|
4.66 ± 0.41
|
0.81
|
|
B
|
14.51 ± 1.77
|
15.29 ± 2.04
|
0.162
|
|
C
|
3.99 ± 1.23
|
4.00 ± 1.21
|
0.98
|
|
L2
|
A
|
4.79 ± 0.72
|
5.10 ± 0.60
|
0.116
|
|
B
|
15.05 ± 1.54
|
15.78 ± 1.87
|
0.156
|
|
C
|
3.94 ± 0.64
|
4.26 ± 0.54
|
0.062
|
|
L3
|
A
|
7.00 ± 1.12
|
7.13 ± 0.71
|
0.691
|
|
B
|
18.39 ± 1.83
|
19.64 ± 3.37
|
0.223
|
|
C
|
6.26 ± 1.14
|
6.68 ± 0.91
|
0.263
|
|
L4
|
A
|
6.63 ± 0.90
|
7.02 ± 0.58
|
0.148
|
|
B
|
16.89 ± 1.31
|
17.53 ± 1.92
|
0.274
|
|
C
|
5.12 ± 0.70
|
5.63 ± 0.47
|
0.021
|
|
L5
|
A
|
6.97 ± 1.02
|
8.03 ± 0.87
|
0.012
|
|
B
|
17.00 ± 3.04
|
18.45 ± 3.33
|
0.272
|
|
C
|
5.48 ± 0.80
|
6.34 ± 0.88
|
0.023
|
|
L6
|
A
|
11.31 ± 1.64
|
11.75 ± 0.89
|
0.252
|
|
B
|
16.54 ± 2.34
|
17.97 ± 1.98
|
0.027
|
|
C
|
11.07 ± 1.58
|
11.68 ± 0.88
|
0.105
|
|
L7
|
A
|
11.76 ± 0.57
|
12.38 ± 0.61
|
0.031
|
|
B
|
14.64 ± 3.07
|
15.79 ± 3.35
|
0.438
|
|
C
|
10.80 ± 1.14
|
11.03 ± 3.07
|
0.726
|
Fig. 3 Root dimension measurements of the maxillary teeth in hypodontia patients and controls.
Fig. 4 Root dimension measurements of the mandibular teeth in hypodontia patients and controls.
Discussion
To date, our study is the first to report root dimension measurements in mild hypodontia
patients, and therefore it is not possible to compare our findings regarding root
dimension measurements in hypodontia patients with others. The most commonly congenitally
missing teeth found in our study sample were the mandibular second premolars and the
maxillary lateral incisors, followed by the mandibular lower incisors and the maxillary
second premolars ([Fig. 5]), which agrees with most previous investigations of the distribution of the congenitally
missing teeth of the permanent dentition.[3]
[4]
[5] As can be seen from [Tables 1 ]
[2 ]
[Figs. 3 ]
[4], the teeth which were most affected with a reduction in root length in the hypodontia
group, as compared with the control group, were mainly in the maxillary arch. More
specifically, they were located more mesial of each morphological class in the maxillary
arch, that is, the upper central incisors, upper canines, and upper first premolars.
This finding does not agree with Butler’s morphological field theory,[17] as applied to the human dentition,[18] which suggests that the tooth which is positioned more mesially of each morphological
class is more under genetic control and less variable than the remaining teeth of
the same class. However, more recent studies investigating the etiology of anomalies
of tooth number and size have suggested a more comprehensive and clinically relevant
explanation of the association of anomalies of tooth number and size, where genetic,
epigenetic, and environmental factors were all thought to be involved with varying
degrees of influences depending on the individuals.[6]
[19]
[20] In our study, the teeth which were found to be affected in the hypodontia group
have longer roots than the teeth which were not affected. Therefore, it may well be
that there were more chances for the epigenetic and environmental factors to play
their roles and hinder their development in the hypodontia group as compared with
the unaffected teeth of shorter roots.
Fig. 5 Pattern of missing teeth in hypodontia cases.
With regard to widths measurements, a similar pattern to the differences in root measurements
mentioned above was also observed here, but with some degrees of variation; thus,
providing more support to the multifactorial etiology of anomalies of tooth number
and size.[6]
[19]
[20] Furthermore, it was found that the number of teeth which had a reduction in root
width at half way of the root was more than those which had a reduction in root width
at the cervical region. This is expected as the cervical region forms and calcifies
well before the middle area of the root and therefore it was more likely to have less
influential epigenetic and environmental variables during dental development.
It is of note that the maxillary lateral incisors, mandibular lower incisors, and
mandibular canines were neither affected in root length dimensions nor in root widths
measurements. This may be attributed to the simpler morphology and relatively smaller
sizes of their roots than those of the remaining teeth.
Patients with hypodontia often present with various features of malocclusion, and
require multidisciplinary management involving orthodontic treatment to close, redistribute,
and/or open spaces, followed by prosthetic replacement of the congenitally missing
teeth and/or restorative reshaping of the peg-shaped/microdontic teeth in the anterior
regions.[16]
[21]
[22]
[23]
[24]
[25] As hypodontia patients may have shorter and narrower roots than the average population,
it is important to carefully plan the anchorage in hypodontia patients and reinforce
it with several means, so that the desired tooth movements can be achieved with no
untoward effects.[22] Furthermore, it has been reported that short and narrow roots were at greater risk
of root resorption during orthodontic treatment, especially the maxillary incisors.[26]
[27]
[28]
[29] Therefore, in hypodontia patients, an optimal force system should be applied during
orthodontic treatment, with close monitoring to avoid significant root resorption,
especially, of the maxillary central incisors.
Moreover, it should be borne in mind that shorter and narrower size implants may suffice
in hypodontia patients during the planning phase to prosthetically replace the congenitally
missing teeth following the orthodontic treatment.[30]
[31] This is especially so, as patients with hypodontia were also reported to have smaller
clinical crowns of the remaining dentition when compared with controls,[8] and inadequate bone to house the standard-sized implants.[23]
[32]
The findings of our study should be interpreted with some caution due to some limitations
as is often the case with the majority of studies. In our study, we assessed root
dimension measurements on orthopantomograms, which are 2D projections of the teeth
with a reported average magnification error of 15 to 25%.[33]
[34]
[35] However, as our study was a comparison case-control study with all OPTs taken by one trained operator using a standard method, the comparison should
still remain valid. Furthermore, hypodontia patients in our study were all of mild
severity, having only one or two teeth congenitally missing; thus, the findings can
only apply for mild hypodontia patients. Further research should investigate the impact
of the severity of hypodontia on root dimension measurements using three-dimensional
imaging, as it may well be that the more severe the hypodontia the more reduction
in root dimension measurements. A similar finding has already been reported with regard
to size of the clinical crowns of the permanent dentition.[8]
Conclusions
Patients with mild hypodontia may have shorter and narrower roots of the whole permanent
dentition, except the upper lateral incisors, lower incisors, lower canines, and all
second molars, when compared with controls. In effect, this may affect the orthodontic
treatment planning and implant placement.
