iDentistry The Journal September-December 2017 | Page 34

The Journal
The objectives of this review were (1) to col¬lect
the comprehensive data about the interaction
between orthodontics and genetics, (2) to
discuss the evidence based impact of heredity
on the development of malocclusions in all the
three planes (3) to introduce the cause and the
consequence re¬lationships between genetics
and malocclusions.
A S S O C I AT I O N
MALOCCLUSION
OF
GENETICS
IN
A literature review carried out by Lauweryns in
1993 concluded that 40% of the dental and
skeletal variations that lead to malocclusion
6
could be attributed to genetic factors.
Hughes and Townsend in 2001 quantified the
extent of variation in different occlusal features
such as interdental spacing, overbite, overjet
and arch dimensions of Australian twins and
indicated a moderate to relatively high genetic
7
contribution to the observed variation. Some
other studies have come to opposite
conclusion. A series of studies by Corruccini et
8,9,10
al
also showed variable and frequently
insignificant genetic variance for dental
characteristics such as, sagittal molar
relationship, overbite, overjet, posterior
crossbite and rotations of anterior teeth.. Harris
and Johnson also noted almost all of the
occlusal variability within their sample of
untreated subjects was acquired rather than
11
inherited.
There are two general ways in which
predisposing or causative factors for
malocclusion could be due to heritable
characteristics. One would be inheritance of a
disproportion between the size of the teeth and
the jaws resulting in crowding or spacing,
whereas the other would be inheritance of a
disproportion in the position, size, or shape of
the mandible and maxilla.
33
However genetic influences on each of these
traits are rarely due to a single gene, which
would be necessary for malocclusion to be due
to the simple inheritance of discrete skeletal
and dental characteristics. Instead they are
often polygenic with the potential for
environmental influence. 12
Twin studies by Lundstrom showed that
heredity played a significant role in determining
the following characteristics: tooth size, width
and length of the dental arch, height of the
palate, crowding and spacing of teeth, and
13
degree of overbite.
MALOCCLUSION ASSOCIATED WITH
ANTERO-POSTERIOR PLANE
Class II Malocclusion
In 1975, Harris14 sug¬gested the concept of
polygenic inheritance for Class II division 1
malocclusions.
Environmental factors can also contribute to the
etiology of class II division 1 malocclusion so to
aid in the prevention of malocclusion it is crucial
to begin identifying and correcting the
environmental factors that contribute to a
disharmony in the face and jaws. 15
The other mal¬occlusion type in the “Class II”
category is Class II division 2 malocclusion and
is characterized by a well-developed
mandibular basal bone, prominent chin,
decreased lower facial height with anterior
rotation of the mandible and smaller
mesiodis¬tal tooth size. 16 Class II division 1
malocclusion and class II division 2
malocclusion both have polygenic inheritance
in common. Class II division 2 is relatively rare
type of malocclusion, representing between
17
2.3% and 5% of all malocclusions. The results
of the twin studies showed that the identical
twins demonstrated 100% con¬cordance for
Class II division 2 malocclusion, indicating a
strong genetic influence in the de¬velopment of
Class II division 2 deep-bite maloc-clusions. 18
Vol. 13 No. 3
Sep-Dec 2017