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Journal of Dental Herald
Journal of Dental Herald
www.dherald.in
(October 2014) Issue:4, Vol.:1
E ISSN No. : 2348 – 1331
P ISSN No. : 2348 – 134X
Case Report
Class II Division 1 Malocclusion: Genetics Or Environment? A Case Report Of Monozygotic
Twins
Dr Gaurav Thakur1, Dr Anil Singla2, Dr Vivek Mahajan3, Dr H.S Jaj4, Dr Vinit Singh5
1
Senior Lecturer, Dept Of Orthodontics, Himachal Institute of Dental Sciencies, Poanta Sahib
Prof and Head, Dept Of Orthodontics, Himachal Dental College Sundernagar
Senior Lecturer, Dept Of Orthodontics, Himachal Dental College Sundernagar
4
Reader, Dept Of Orthodontics, Himachal Dental College Sundernagar
5
PG Student, Dept Of Orthodontics, Himachal Dental College Sundernagar
2
3
Abstract
Twin study is one of the most effective methods available for investigating genetically determined variables of malocclusion. A pair of monozygotic
twins with different malocclusion phenotypes (Class II Division I and Class II Division I subdivision) is presented. The case report supports the
hypothesis that heredity is not the sole controlling factor in the etiology of Class II Division I malocclusion. So the purpose of this evaluation of
monozygotic twins is to assess the genetic and environmental components of variation within the craniofacial complex.
Key Words
Class II Division I, monozygotic twins, Genetics
Introduction
The focus of the orthodontist must be on the relationship of the
craniofacial variation to the ultimate occlusal relationship.
Orthodontists are charged with the task of altering the dental
and skeletal morphology in growing and non growing
individuals[1] . So a better understanding of the relative effects
of genes and environment on the dentofacial and occlusal
parameters should improve our knowledge on the etiology of
orthodontic disorders and therefore also on the possibilities
and limitations of orthodontic treatment and treatment
planning[2].
A wide range of genetic and environmental factors have been
suggested as contributing to the development of Class II and
Class III[3] malocclusion. Class III malocclusion as described
by Angle represents small proportion of total population. Its
etiology is generally believed to be genetic, and familial
occurrence has been demonstrated in different studies. The
Class II Div 2 malocclusion as described by Angle[4] has
incidence rate of 1.5% to 7%[5-7]. Its etiology is generally
believed to be genetic, and familial occurrence has been
documented in several studies of twins and triplets[8-10].
The etiology of Class II Div 1 is wide ranging and complex.
The Class II Div 1 malocclusion exhibiting skeletal anomalies
such as prognathic maxilla or retrognathic mandible can be due
to hereditary cause but the size, position and relationship of the
jaws are to a large extent affected by genes. Natal factors like
trauma to condylar region due to forceps delivery can lead to
underdevelopment of mandible. Post natal factors like
traumatic injury to mandible and temporomandibular joint,
infectious conditions like rheumatoid arthritis, abnormal
function such as mouth breathing, thumb sucking has low
Quick Response Code
Address For Correspondence:
Dr Gaurav Thakur
Senior Lecturer, Dept Of Orthodontics, Himachal
Institute of Dental Sciencies, Poanta Sahib
tongue position leading to unrestrained activity of buccinator
muscle[11]. For investigation of genetically determined
variables in orthodontics, twin study method is most effective.
The purpose of this study is to assess the variation of craniodentofacial complex of monozygotic twins in Class II Div I
malocclusion.
Case Report
A pair of monozygotic female twins is presented. The girls
exhibited marked similarity in facial appearance (Figure I).
Zygosity was determined using dermatoglyphics and
confirmed from hospital records where twins were conceived.
In twin 1 Class II Div 1 subdivision malocclusion is seen with
overjet of 5mm and overbite of 4mm and in twin 2 Class II Div
1 malocclusion is seen with overjet of 5mm and overbite of
7mm respectively (Fig 2, 3). Both had similar dentition,
however there occlusion were dissimilar to some extent (Fig 2,
3). Cephalometric parameters of both twins are shown in table
1 and table 2. Few cephalometric parameters showed
differences in skeletal morphology (Table 1). Degree of
differences in cranio-facial dental morphology of twins is
shown in cephalometric superimpositions (fig- 4).
Cephalometric analysis showed class II skeletal base in both
the malocclusion but it was more pronounced in twin 2.
Position of maxilla was more forward in twin 2 as compared to
twin 1. Mandibular body length was small in twin 1. Effective
maxillary length was more in twin 2 and effective mandibular
length was quite similar. Position of condyles was more
posterior in twin 2 (Table 1). Position of upper and lower lip
was significantly different in both the twins (Table 2). The
position of underlying skeletal bases and there dentition
contributed to such difference. There was difference in
proclination of upper and lower incisors. Thus marked
differences in cranio- dentofacial was noted between
monozygotic twins.
Discussion
The lack of available genetic data on human skeletal
characteristics has effect on the progress toward the solution of
some fundamental problems in orthodontics. Various attempts
to establish morphological criteria for orthodontic diagnosis
©Journal of Dental Herald (October 2014 Issue:4, Vol.:1).
036
Front View
Lateral View
Fig 2 – Intraoral Photographs Of Twin 1
Fig 3- Intraoral Photographs Of Twin 2
Twin 1
Twin 2
Fig 1- Extra Oral Photographs Of Twin 1 And Twin 2
purposes have been hampered by a need for more information
related to genetic variation in the face and skull[12]. So
variability observed in craniofacial skeleton must undoubtedly
have some effect on occlusal articulation of the teeth as the
denture bearing area are contained in the various skeletal
elements making up the craniofacial complex[1]. Many traits
in cranio- dentofacial structures relate to additive genetic and
environment factors[13-14]. The region affected by
environmental factors can be improved by orthodontic
treatment[3],[14],. The separation of these two factors in the
contribution of severity of malocclusion is significant for
clinical orthodontics.
Wylie[15](1944) was the first to compare the craniofacial
pattern of related individuals by means of cephalograms,
reporting on twin pairs. Curtner[16] (1953) reported on five
families, three of which included twins. Sabine Ruf and Hans
Pancherz[17] (1999) studied a pair of monozygotic twins with
different malocclusion phenotypes (Class II Div 2 and Class II
Div 1) . Jena and Duggal[3] (2005) studied monozygotic twins
having Class III malocclusion.
Twin study is one of the most effective methods available for
investigating genetically determined variables in
orthodontics[3]. Discordances in the malocclusion in
dizygotic twins is a frequent finding. However malocclusion
discordance in monozygotic twins is rare[17] . However ,
Leech[18] (1955) reported a malocclusion discordance in
monozygotic twins, one of Leech’s twin exhibited a Class II
Div 1 malocclusion and other Class II Div 2 malocclusion.
Pancherz et al[19] (1997) and Ruf and Pancherz[17] (1999)
showed that , except for the position of maxillary incisors,no
difference exists in dentoskeletal morphology when
comparing Class II Div 1 and Class II Div2 malocclusion.
©Journal of Dental Herald (October 2014 Issue:4, Vol.:1).
Fig- 4: Cephalometric Superimposition Of Twin 1 And 2
Whether Class II Div 1 malocclusion is genetically determined
or not, studies are lacking in this field. So in the present
investigation, analysis of a pair of twins was done to explore
genetic influences on variations in craniofacial complex on
monozygotic twins.
In the present evaluation of the pair of twins, convexity of
face(Angle of convexity) in twin 2 was more as compared to
twin 1 (Table 1). Relatively more forward position of maxilla
(SNA and Nasion perpendicular to Point A) in twin 2 and
backward position of mandible( ANB , Nasion perpendicular
to pogonion and mandibular body length) in twin 1 is seen
(Table 1). However according to Townsend and Richards[20]
antero-posterior position of the mandible is genetically
determined. But in the present study discordance in position of
mandible is seen. Anterior facial height of both the twins is
apparently equal. The shape of the cranial base (Saddle angle)
is different among twins. This characteristic played a major
role in discordance of Class II Div I malocclusion. So this is in
favor of the study conducted by Lobb[1] who stated that the
form of the cranial base is least genetically controlled and
037
Table 1-skeletal Parametres
Table 2 - Dental Parametres
PARAMETERS
Twin 1
Twin 2
Upper Incisor
7mm
7mm
Angle SNA
790
810
To A- Pog Line
Angle SNB
730
730
Upper Incisor
200
140
Angle ANB
60
80
To Na
Ramus angle
600
560
Upper Incisor
10mm
13mm
Ant Facial Height
131mm 129.5mm
N- Pog Line
Posterior facial Height
79mm
80mm
Lower Incisor
Jarabak ratio
60.3%
61.77%
To Nb
8mm
8mm
Mandibular Angle
320
330
Lower Incisor
Y axis
650
640
To N- Pog Line
6mm
6mm
SN- GOGN
400
380
Over Jet
5mm
5mm
4mm
7mm
-4mm
-2mm
-4mm
-1mm
Anterior Cranial Base Length
71mm
75mm
Overbite
Ramus Height(Ar- go)
47mm
45mm
Upper Lip To
Mandibular Body Length(Go- Me)
74mm
69mm
Esthetic Line
Effective Mandibular Length
122mm 121mm
(E Line)
Effective Maxillary Length
94mm
97mm
Lower Lip To
Maxillo- Mandibular
28mm
24mm
Esthetic Line
Facial angle
820
840
(E Line)
Basal plane angle
200
200
Saddle angle
1280
1210
Articular angle
1480
1480
Angle of Convexity
100
160
N perpendicular to point A
-3mm
-1mm
N Perpendicular to Pog
-13mm - 15mm
strongly influenced by environment factors. The relative
position of maxilla (Angle SNA), effective length of mandible
and maxilla were different in both twins (table 1). These
characteristics played significant role in severity of Class II
malocclusion in twin 2. Position of upper incisors was more
variable than lower incisors. Proclination of upper incisor was
more in twin 1(table 2).Such dentoalveolar compensation can
be attributed to environmental variations. There was
difference in position of upper lip in twin 1 and twin 2(table 2).
However according to Ruf and Panchrez[17],, it is not
primarily lip position that is responsible for the difference in
incisor inclination , but rather incisor position itself[21,22].
Conclusion
It is concluded that genetics is not the sole contributing factor
for etiology of Class II Div 1 malocclusion. The variability
observed in the various components of craniofacial complex in
monozygous twins, resulting in precise relationship of the
dentition, supports the argument that the craniofacial skeleton
is not under strong genetic control as entity (Lundstrom[23]
1954, Nakata et al[24] 1973, Saunders et al[25] 1980). Rather,
it represents a complex integrated balance between those
morphologic units under strong genetic control and those units
which may accommodate for the variance within the system
and provide structural integrity necessary for functional
occlusion. Since studies are lacking in this field and there are
many open questions to be answered , therefore further studies
need to be carried out to elucidate the true etiology of Class II
Div I malocclusion.
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Source of Support : Nill, Conflict of Interest : None declared
©Journal of Dental Herald (October 2014 Issue:4, Vol.:1).
038