Effects of hypodontia on craniofacial structures and mandibular growth pattern.

RESEARCH Open Access
Effects of hypodontia on craniofacial structures
and mandibular growth pattern
Amelia Kreczi, Peter Proff, Claudia Reicheneder and Andreas Faltermeier*
Abstract
Introduction: This study was performed to examine craniofacial structures in persons with hypodontia and to
reveal any differences, that may occur, when agenetic teeth are only found in the maxilla, the mandible or in both
jaws. The groups consistent of 50 children (33 girls, 17 boys) aged between 9 and 13.5 years were analyzed and
assigned to three subgroups. Group 1 = upper jaw hypodontia. Group 2 = lower jaw hypodontia. Group 3 =
hypodontia in both jaws.
Materials and methods: Eleven angular and three index measurements from lateral encephalographs and two
linear measurements from dental blaster casts were calculated. All data was statistically analyzed, parameters with p
< 5% were investigated for each subgroup respectively.
Results: In comparison with standards the study group showed bimaxillary retrognathism and a reduction of the
lower anterior facial height. Moreover both overbite and overjet significantly increased. Other values laid within the
normal ranges. Evaluating results of the subgroups, differences in the means of SNA, SNB and overjet between the
groups were observed.
Analysis of the mandibular growth pattern revealed, that neither vertical nor horizontal patterns are dominant in
hypodontia patients.
Conclusions: In certain dentofacial parameters differences between persons with hypodontia and such with full
dentition exist. According to our findings agenetic teeth may have a negative influence on the saggital
development of a jaw and the lower face and may be responsible for increased overbites. This should receive
attention in orthodontic treatment of hypodontia patients.
Keywords: hypodontia, mandibular growth, missing teeth
Introduction
Congenital missing teeth are a common anomaly in the
craniofacial skeleton. The prevalence of dental agenesis
varies dependent on continent, race and gender as a meta
analysis by Polder et al. [1] reveals. In white Europeans a
total prevalence of 5.5 percent was found in permanent
dentition, not including the third molar. The number of
missing teeth in the maxilla was comparable with that in
the mandible. Several studies confirm, that females are
concerned more frequently from this anomaly than males
[1-3]. Excluding the third molar the most common teeth
showing agenesis are the mandibular second premolar and
the lateral maxillary incisor [4,5]. Whereas in maxillary
lateral incisors bilateral agenesis occurs more often, unilat-
eral agenesis is more common in other teeth [1]. Depen-
dent on the number of agenetic teeth, hypodontia,
oligodontia and anodontia can be differentiated. The mai-
jority of persons with hypodontia suffers from only one or
two missing teeth [1,6].
Oligodontia is described as very heterogeneous [7] and
rather rare (0.6-0.7 percent) [8]. Moreover taurodontism,
reduced tooth length and delayed tooth formation were
observed in relationship with this anomaly [9]. It has
been emphasized, that especially persons with more
severe hypodontia should be closely surveyed for syndro-
mal illnesses such as ectodermal dysplasia, because with
the number of agenetic teeth also the probability, that
hypodontia is part of a sydrome increases [10].
* Correspondence: Andreas.Faltermeier@klinik.uni-regensburg.de
Department of Orthodontics, University Clinics, Franz-Josef-Strauss-Allee 11,
D-93042 Regensburg, Germany
Kreczi et al. Head & Face Medicine 2011, 7:23
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HEAD & FACE MEDICINE
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any medium, provided the original work is properly cited.

However hypodontia also exists as isolated condition.
In their recent study De Coster et al. reported [11], that
hypodontia shows a genetically and phenotypically het-
erogeneity and most frequently results from various gen
mutations. Further it was observed, that the incidence of
agenetic permanent teeth has increased in the Caucasian
population over the last century [3]. Hobkirk and Brook
[10] surveyed their patients in a multidisciplinary clinic
for the management of hypodontia in Newcastle and
revealed, that the most common complaints were poor
appearance and lack of function. Apart from that, alter-
nations in the craniofacial morphology may be relevant
for orthodontic treatment of hypodontia patients. Possi-
ble reasons for a relationship between hypodontia and
skeletal structures are, among others, the fact that teeth
serve as functional units, whereby local bone growth is
stimulated [12]. It can therefore be hypothesized, that
congenital missing teeth cause underdevelopement of the
jaw basis. This theory is stregthend by findings of bimax-
illary retrognathism [13], reduced maxillary and mandib-
ular length [14] and more backward chins [15]. In
contrast to this, several studies reveal more prognathic
mandibles [16,17]. It was suggested, that severe hypodon-
tia causes a lack of occlusal support, which results in an
underdevelopment of the lower face and anterior rotation
of the mandible, leading to prognathism of the lower jaw
[16]. Øgaard and Krogstad [15] confirmed this, finding a
decrease of mandibular plane angle and a reduced ante-
rior facial height in persons with more than 10 congenital
missing teeth. The reduction of the anterior facial height
is a common report in studies on hypodontia, but wheter
it results from a reduction in the upper facial height [5],
the lower facial height [18] or both [14] is dicussed con-
troversially. Despite these relevant observations, both
Yüksel and Ücem [19], who examined the effects of
hypodontia dependent on the location of the missing
teeth and Øgaard and Krogstad [15] come to the conclu-
sion, that tooth agenesis has little effect on the cranifacial
growth pattern. In accordance with this, the recent study
of Bauer et al. [18], who investigated the general growth
pattern according to Segner [20] and Hasund [21], failed
to reveal statistically relevant correlation between cranio-
facial growth pattern and the congenital absence of cer-
tain permanent teeth. Alternatively to an unique growth
pattern, typical dentofacial structures in persons with
hypodontia may be due to a dental and functional com-
pensation [15]. Especially various malpositions of incisors
were attributed to functional alternations, such as imbal-
ance of lip-tongue pressure [19].
Little consent about the influence of hypodontia on
the facial skeleton is found in literature. More research
is required on this subject and hence our aim was to
investigate craniofacial morphology of individuals with
non-syndromic hypodontia in a german population.
While it has been examined, whether the tooth type
(anterior and posterior hypodontia) and the number of
agenetic teeth (mild, moderate and severe hypodontia)
play a role in considering morphological characteristics,
none of the recent studies seems to investigate the
effects of hypodontia for each jaw respectively. There-
fore we specified significant results obtained from a
sample with randomly distributed agenetic teeth in
forming three subgroups and investigate the effects of
upper jaw hypodontia, lower jaw hypodontia and both
jaw hypodontia respectively. Modified standard values
for Regensburg following norms published by Segner
[20] and Hasund [21] severd as controls. The general
mandibular growth pattern analyzed according to Björk
[22] was also objective of this study.
Materials and methods
The material for this retrospective statistic comprised
orthopantomograms, lateral cephalometric radiographs
and dental plaster casts of 50 children with at least two
congenitally missing teeth in one jaw. The data was col-
lected from 17 boys and 33 girls aged between 9 and
13.5 years (mean 11,5 years) and prior to any orthodon-
tic treatment. Children with ectodermal dysplasia, cleft
lip and palate, or other craniofacial anomalies were not
included in the study group. Figure 1 and 2 show an
orthopantomogram (1) and a lateral encephalometric
radiograph (2) of a person with 13 congenital missing
teeth.
The number of missing teeth in each subject was
recorded from orthopantomograms and verified by ana-
mnesis and clinical examination, both documented in each
patient’s file. It ranged from 2 to 18 teeth with a mean
value of 5 missing teeth per person (Figure 3). The lateral
cephalometric radiographs were taken in a multigraph
(Siemens, Germany, focus-film-distance 4.0 m).
All reference points were manually scanned and digi-
tized by a single investigator using a numonics lightbox.
Landmarks are shown in Figure 4. Eleven angular and
Figure 1 Radiographs of a person with 13 congenital missing
teeth: Orthopantomogram.
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five linear measurements were calculated automatically
by the computer program Ratisbona (Dentofacial planer
Version 7.02).
Overjet (saggital) and Overbite (vertikal) were mea-
sured with a caliper in blaster casts, manufactured at
the same time as the x-rays were taken.
Angular mesurements in degrees (°):
saggital: ∠SNA: inclination of maxilla to skullbase
∠SNB: inclination of mandibule to skullbase
∠ANB difference: saggital jaw relationship (0.4 ×
SNA+0.2 × ML-NSL- 35.16 = individual ANB; indiv.
ANB-ANB = ANB difference)
Figure 2 Radiographs of a person with 13 congenital missing
teeth: lateral encephalometric radiograph.
Figure 3 Survey of number of agenetic teeth in the sample (N = 50).
Figure 4 Landmarks for analysis of lateral encephalographs. S,
sella turcica; N, nasion; Ba, basion; Go, gonion; Me, menton; Pog,
pogonion; B, B-Point; A, A-Point; LI’, lower incisor rout edge; LI,
lower incisor crown edge; UI, upper incisor crown edge; UI’, upper
incisor rout edge; Sp, anterior nasal spine; SP’, posterior nasal spine;
Pt, pterygomaxillary fissure; Ar, articulare.
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vertikal: ∠NL-ML: vertical jaw relationship
∠NL-NSL: maxillary plain inclination
∠ML-NSL: mandibular plane inclination
∠Gn-Pt/Ba-N: facial axes
∠ArGoMe: gonionangle
dental: ∠UI/NA: inclination of upper incisor
∠LI/NB: inclination of lower incisor
∠UI/LI: interincisal angle
Linear measurements in mm:
Saggital: Wits value: saggital distance A-B projected on
the occlusal plane
Dental: Overjet (saggital)
Overbite (vertical)
Indexes: Hasund index: upper to lower anterior facial
height (N-SP’x100/SP’-Me)
Jarabak index: posterior to anterior facial height (S-
tgo × 100/N-Me)
Statistical methods:
All statistical analysis were done using SPSS (Statisti-
cal Package for Social Sciences, Chicago, IL, USA) ver-
sion 15.0 for windows.
The results were calculated with the student’s t-test
for paired samples. In case the p-value was < 0.05 the
difference between our distribution and the distribution
of the equivalent standart value was considered to be
statistically significant.
After analysing the parameters stated abouve for the
total examination group, persons were asigned to three
subgroups:
Group 1: Two or more congenitally missing teeth in
the maxilla (11 subjects).
Group 2: Two or more congenitally missing teeth in
the mandible (12 subjects).
Group 3: Two or morge congenitally missing teeth in
both jaws (27 subjects).
In case a singel tooth was missing in one of the jaws,
it was not taken into consideration in this management.
The data of each group was analyzed seperately with
the statistical methods stated abouve. However only
parameters that showed a significance level of at least
5% in the first analysis were considered (SNA, SNB,
Hasund index, overjet, overbite).
To investigate on the general mandibular growth pat-
tern, lateral encephalographs were examined by a single
investigator according to Björk [22]. This method is
established on the basis of six mandibular structure
signs, three of them objective measurments, the others
subjective parametres. The gonionangle, the norderva-
langle and the hasund index were calculated for each
person by methods explained earlier in the text. The
shape of the condylus, the mandibular canal and the
mandibular symphysis were assessed using a lightbox
and a table with reference shapes as shown in Figure 4.
Each parameter was appraised with a score ranging
from three minus to three plus. Minus indicating verti-
cal growth and plus indicating horizontal growth. The
mandibular growth patterns is characterized by two
components: the translation and the rotation. In accor-
dance with Björk, the shape of the condylus and the
gonionangle determined the translation, and the scores
for all six parameters together determined the rotation
of the mandible (Figure 5).
Results
In our study the most frequent tooth missing was the
lower second premolar (27%), followed by the upper lat-
eral incsisor (17%) and the upper second premolar
(15%). In the upper jaw hypodontia group (1) 38% inci-
sor agenesis and in the lower jaw hypodontia group (2)
80,7% premolar agenesis was found. Table 1 shows pre-
valences of dental agenesis for all tooth types.
Our sample comprised 33 females and 17 males.
Hence approximately twice as many females were
effected than males. In angular and linear measurements
significant associations between mean values of the
examination group compared to standart values were
observed. In the saggital plain both the maxilla and the
mandible showed a retrognathic inclination to the skull-
base (reduced ∠SNA and ∠SNB). Further the Hasund
index between upper and lower anterior facial height
increased. Analysis of the dental parametres revealed
significantly increased vertical overbite and saggital
overjet (Table 2).
The statistical analysis showed no significant differ-
ence in the values: individual ANB, Wits appraisal,
∠ArGoMe, ∠Gn-Pt/Ba-N, Jarabak index, ∠ML-NSL,
∠NL-NSL, ∠ ML-NL, ∠UI/NA, ∠LI/NB and ∠UI/LI. All
results are shown in Table 2.
In the evaluation of the subgroups only parameters,
that revealed significant associations in the first analyses
were taken into consideration. The results show, that in
each group the Hasund index and the overbite signifi-
cantly increased.
In Group 3 bimaxillary retrognathism could be
revealed, while in group 2 only the mandible showed a
retrognathic inclination. Group 1 had neutrally inclined
mandibles and retrognathic maxillas, altough the differ-
ence in values was not statistically significant. An
increased overjet was only found in group 2. Results are
listed in Table 3. Analysis on the general mandibular
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Figure 5 Mandibular growth pattern analyses according to Björk (1968).
Table 1 Distribution of agenetic teeth according to thooth type in the study group (50 people)
Upper jaw Tooth type 17 16 15 14 13 12 11 21 22 23 24 25 26 27
Number of missing tooth 4 2 20 4 3 22 1 1 22 5 6 19 2 6
Lower jaw Tooth type 47 46 45 44 43 42 41 31 32 33 34 35 36 37
Number of missing tooth 8 1 35 5 3 6 12 12 6 3 6 35 1 6
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