Etiology

3. ETIOLOGY

DEVELOPMENT OF VERTICAL MALOCCLUSION :

Vertical malocclusion can be divided into those, that are, dentoalveolar in origin
and those that are, predominantly skeletal due to the growth patterns of the jaws.
Skeletal deep bite is characterized by concave facial profile with a reduction of anterior
face height while, skeletal open bite is a convex facial profile with a pronounced
retrognathic mandible. The malocclusions are primarily the result of the growth pattern
of face and functional factors, greatly contributing to the final malocclusion10.

Mandibular Growth and Vertical malocclusion :10

Studies of facial growth using the metallic implant technique by Bjork and
Skiller have demonstrated that the direction of growth of the lower jaw varies greatly
in the normal population. The most common direction of condylar growth is vertical,
with some anterior component, a more extreme upward, forward growth pattern of the
condyle is not uncommon10.

Patients with upward and forward growth of the mandibular condyle often have
reduced anterior face height, usually develop a malocclusion characterized by a deep
bite. The direction of mandibular growth, as expressed at the chin, is mostly vertical.
Growth in this direction results in more horizontal displacement of the mandible and
effectively improves the position of the chin. In more extreme cases of upward, forward
growth of the condyle, a Class II, division 2 malocclusion in combination with skeletal
deep bite is common10.

The erupting dentition in this type of mandibular growth characteristically

undergoes a considerable amount of mesial migration of both the maxillary and
mandibular teeth with some degree of proclination of the mandibular incisors. Where
the amount of mesial migration of the lower posterior teeth does not equal the
advancement of the incisors by proclination, secondary crowding of the front teeth
frequently develops.10

Patients with the so called “long face syndrome” and a pronounced increase in
lower face height, in contrast have a more posteriorly directed growth pattern of the
mandibular condyle. The direction of mandibular growth, as expressed at the chin, is

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mostly vertical. The malocclusion observed in this type of patient is an anterior open
bite often in combination with a Class I or II malocclusion. These patients have little
or no improvement in horizontal mandibular position over time.10

GROWTH ROTATIONS AND VERTICAL MALOCCLUSIONS :10

The changes related to facial growth in the two extreme growth patterns are due
to differences in condylar growth direction, but are also the result of differences in
anterior face height (AFH) and posterior face height (PFH) development. These
differences in height development lead to rotational growth or positional changes of the
mandible that greatly influence the position of the chin. The factors that determine the
increase in AFH are the eruption of the maxillary and mandibular posterior teeth and
the amount of sutural lowering of the maxilla. PFH, is determined by the lowering of
the temporomandibular fossae and condylar growth. When vertical condylar growth
exceeds dentoalveolar growth, i.e. eruption of the teeth in the jaws, forward rotation of
the mandible occurs. In contrast, if dentoalveolar growth is greater than vertical
condylar growth, the resulting change in mandibular position is backward or posterior
rotation of the mandible. Patients with an anterior condylar growth pattern usually have
a greater amount of vertical growth than patients with posteriorly directed growth.10

Bjork demonstrated that under ideal circumstances the fulcurming point for
anterior or forward mandibular growth rotation is located at the incisors. If, proper
incisal contact is lacking, either as a result of lip dysfunction or a finger sucking habit
or if a severe sagittal skeletal jaw discrepancy exists, the patient will develop a skeletal
deep bite as a result of growth pattern. The fulcruming point in these instances is
located further back along the occlusal plane.11-16

The mandibular translates during growth without rotation. This posterior

growth rotation may result in an anterior open bite, depending on the extent of vertical
dentoalveolar compensation. When treated orthodontically these patients are at
increased risk for further mechanically induced posterior rotation by acceleration of
their molar eruption and require careful control.16

A common scenario affecting the skeletal problem is mandibular growth and

growth rotation, which unfavorably impacts dentoalveolar development in both the

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 Etiology

maxilla and mandible. Bjork and Bjork and Skieller have performed numerous studies
that have shown that the most common direction of condylar growth is vertical, with
some anterior component. Patients with a pronounced short lower anterior facial height
generally exhibit upward and forward condylar growth. These individuals generally
have a deep vertical overbite with a deep mentolabial sulcus and a strong overclosed
appearance. In contrast, patients with long face syndrome have a more posteriorly
directed growth pattern of the mandibular condyle. These backward growth rotators
have increased anterior facial height, a more posterior position of the chin, and in
extreme cases, an anterior open bite may develop. Serial images of the patient taken to
monitor the direction of condylar growth would be very useful or the diagnosis of
vertical growth. At the present time, serial imaging poses certain concerns, most
significantly radiation exposure. Advances in imaging technology may, in the future,
permit the clinician to use these methods for diagnostic purposes with greater safety.16

An understanding of the maxillomandibular growth rotation of the patient

would be most helpful in the diagnosis of vertical variations. Bjork has contributed
information that offers some guidelines for the clinician to assist in the determination
of the growth rotation of the mandible so that the concomitant vertical changes are more
easily understood. Bjork’s method of prediction of condylar growth rotation from a
cephalogram offers the clinician some guidelines. Bjork identified seven specific
structural features that might develop as a result of remodelling during a particular type
of growth rotation. Bjork’s suggestions for predicting condylar rotation have, however,
not been widely used by the speciality because (1) some of the indicators cannot be
easily seen on the average cephalogram, (2) the use of the indicators is very time
consuming for the clinician, and (3) there has been no scientific validation of the
suggested indicators because of difficulties encountered in study design. Some in the
speciality also question whether several of the suggestions are valid indicators of a
particular type of growth rotation. However, when used for their intended purpose, as
guidelines only, the indicators have some useful clinical applications in the diagnosis
of the patient with vertical dysplasia.16

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 Etiology

The forward rotator, exhibits several of Bjork’s indicators including

observations that (1) the condylar head curves forward, (2) the mandibular canal is
curved, (3) the symphysis has a backward cant, (4) the interincisal angle is obtuse and
(5) lower anterior facial height is short.

The backward rotator exhibits (1) a straight inclination of the condyle, (2) a
relatively straight mandibular canal, (3) the symphysis slopes forward and, (4) lower
anterior facial height is long.

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Bjork’s Seven Structural Guidelines

Characteristics Forward Rotator Backward Rotator

Inclination of the condylar head Curves forward and Straight or slopes up

back

Curvature of the mandibular canal Curved Straight

Shape of the mandibular lower Curved downward Notched
border

Inclination of the symphysis Slopes backward Slopes forward

(Anterior aspect just below “B”
point)

Interincisal angle Vertical or obtuse Acute

Interpremolar or intermolar angles Vertical or obtuse Acute

Anterior lower face height Short Tall

Isaacson, Isaacson et al and Schudy following on Bjork’s reports, studied jaw

rotation caused by vertical condylar growth. A succinct summary of the findings of
these investigators is that a forward mandibular rotation occurs when vertical condylar
growth exceeds the sum of the vertical growth of the maxillary sutures and the
maxillary and mandibular alveolar processes. If growth of the maxillary sutures and
the maxillary/ mandibular alveolar processes exceeds vertical condylar growth, a
backward rotation occurs, and the face becomes longer. An understanding of the effect
of condylar growth on mandibular position is fundamental if the clinician is to
adequately and appropriately diagnose a vertical dimension abnormality11-16.

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Fig 3.1- Upward and Forward Mandibular Condylar Growth

Fig 3.2- Posterior – Directed Growth Pattern of the Mandibular Condyle

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 Etiology

3.4

3.3

3.6
3.5

Fig.3.3 and 3.4 : Characteristic Facial Growth Pattern and Mandibular Growth
in a subject with skeletal deep bite.

Fig. 3.5 and 3.6 : Characteristic Vertical Facial Growth Pattern and Mandibular
Growth and Dentoalveolar Development

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 Etiology

Anterior and Posterior Facial Height : 17

Vertical dimension skeletal abnormalities are not solely caused by condylar
growth direction. They are also caused by differences in anterior facial height and
posterior facial height development. These differences in height development can lead
to rotational growth or to changes in mandibular position that greatly influence the
position of the chin. Etiologies influencing unfavorable differences in development of
anterior and posterior facial height are multifactorial. These factors can, for simplicity,
be subdivided into those caused by (1) dentoalveolar development and (2)
environmental factors.17

Dentoalveolar Development : 18
Issacson et al studied dentoalveolar development in three groups of subjects –
those with short anterior facial height, those with average anterior facial height, and
those with excessive anterior facial height. The amount of maxillary posterior alveolar
development was found to decrease as the MP-SN angle decreased. In patients with
long anterior facial height (high MP-SN angles), the mean distance from the occlusal
plane to the inferior edge of the palate was 22.50 mm. this distance decreased to 19.6
mm for the average group and 17.1 mm for the group with short anterior facial height
(low MP-SN angles). This difference of 5.1 mm of dentoalveolar development between
the high angle and low angle groups is of significance.18

Mandibular posterior alveolar development similarly decreased with decreases

in the MP-SN angle but much less dramatically than those found in the maxilla.
Mandibular height showed a mean of 31.2 mm for the long anterior face height group,
28.2 for the average group, and 28.3 for the short anterior face height group.

The findings of the Issacson et al study were confirmed in a study performed by

Janson et al. These investigators found that all dentoalveolar heights were significantly
greater in long anterior facial height patients than in patients with normal facial height.
Also, in the short lower anterior facial height, all dentoalveolar heights were
significantly shorter than in the normal lower anterior facial height group.

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 Etiology

The differences in dentoalveolar development, most particularly in the maxilla,

have a significant impact on the anterior facial height of the orthodontic patient. Moller
and Ingervall and Thilander have postulated that excessive maxillary posterior
dentoalveolar development is associated with weaker masticatory musculature in high
angle patients compared with the strong musculature commonly associated with short
anterior facial height patients.18

Environmental Role – Swallowing and Tongue Posture :17

The role of tongue posture, swallowing and breathing are still subjects of debate,
argument, and studying orthodontics. Their respective impact on the vertical dimension
are in need of continued study and research.17

Mouth Breathing :19

The relationship between mouth breathing, altered posture, and the
development of malocclusion is not as clear cut as the theoretical outcome of shifting
to oral respiration might appear at first glance. Recent experimental studies have only
partially clarified the situation. Current experimental data for the relationship between
malocclusion and mouth breathing are derived from studies of the nasal oral ratio in
normal versus long face children. The data from the study show that both normal and
long face children are likely to be predominantly nasal breathers under laboratory
conditions. A minority of the long face children had less than 40% nasal breathing,
whereas none of the normal children had such low nasal percentages. When adult long
face patients are examined, the findings are similar; the number with evidence of nasal
obstruction is increased in comparison to a normal population, but the majority are not
mouth breathers in the sense of predominantly oral respiration.

Airway problems, such as large adenoids, tonsils, or blocked airways caused by

septum deviations, large conchae, or allergies are frequently observed in high angle
patients and may affect mandibular posture, allowing more freedom for posterior
eruption. This hypothesis is supported by Linder-Aronson who showed closing of the

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mandibular plane angle and reduction in the anterior face height after removal of
adenoids and tonsillectomy.18,19

It appears that research on respiration, upto the present time, has resulted in two
opposing views; (1) total nasal obstruction is highly likely to alter the pattern of growth
and lead to malocclusion experimental animals and humans and individuals with a high
percentage of oral respiration are overrepresented in the long face population, but (2)
the majority of individuals with the long face pattern of deformity have no evidence of
nasal obstruction and must therefore have some other etiologic factor as the principal
cause.19

In conclusion, it appears that mouth breathing may contribute to the development of

orthodontic problems but is difficult to indict as a frequent etiologic agent. Clinically,
most orthodontists refer mouth breathers to an otolaryngologist for an evaluation. This
problem should be carefully evaluated during the diagnosis of patient with excess
vertical dimension. 17-20

Swallowing and Tongue Posture :

One viewpoint holds that tongue thrust swallowing is seen in (1) younger
children with reasonably normal occlusion in whom it represents only a transitional stage
in normal physiologic maturation and (2) in individuals who have displaced incisors. In
the latter, it is an adaptation to the space between the teeth. Others argue that tongue
thrust swallowing simply has too short a duration to have an impact on tooth position.
Pressure by the tongue against the teeth during a typical swallow lasts for approximately
1 second. A typical individual swallows about 800 times per day while awake but has only
a few swallows per hour while asleep. The total per day, therefore, is usually under 1,000.
One thousand seconds of pressure, of course, totals only a few minutes, not nearly
enough time, it is argued, to affect the equilibrium.17,18,20,21

It is believed that if a patient has a forward resting posture of the tongue, the duration
of this pressure, even if very light, could affect tooth position, vertically or horizontally.

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Tongue-tip protrusion during swallowing is sometimes associated with a forward tongue

posture.17

During the diagnosis of the patient with a vertical dimension problem, the
clinician must understand that condylar growth, sutural lowering of the maxillary complex,
dentoalveolar development, dental eruption, and the patient's oral environment/habits are
interrelated. There is not generally a single causative factor that predisposes the patient
to too much or too little vertical development of lower facial height. To simplify, one might
conclude as a general rule, that when vertical condylar growth exceeds tooth eruption
(alveolar development), forward mandibular rotation occurs. The result is increased
posterior facial height and an increase in the ratio of posterior facial height to anterior
facial height. Conversely, if dentoalveolar growth and tooth eruption are greater than
vertical condylar growth, the resultant mandibular change is backward rotation. The anterior
facial height/posterior facial height ratio decreases. Environmental factors can play a role,
but the role is, at times, difficult to assess and varies from patient to patient.17,18,20,21

STEEP EXCESS VERTICAL PATTERN

The Backward Rotator :
For the patient with long anterior facial height, the mandibular anterior teeth are
most often positioned in a more retracted posture over basal bone. Lip procumbency can
be best resolved if the mandibular anterior teeth are upright. The amount of uprighting
that must be achieved is a matter of (1) clinical preference and must be determined
during the treatment planning phase of the treatment protocol or (2) the dictates of the
malocclusion. If indeed the facial profile of the patient with excess vertical dimension
is long, a vertical reduction genioplasty can be effective for facial esthetics. It is
fundamental for the clinician to be able to visualize the post-treatment positions of the
mandibular anterior teeth during treatment plan preparation. For many patients with
excessive lower anterior facial height, extractions may be necessary. The question of
which teeth should be extracted can be answered only after a thorough and accurate
differential diagnosis.9,10,11,22

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The Overclosed Forward Rotator :

Patients with short anterior vertical facial height have a unique set of problems
that require different diagnostic considerations. The following diagnostic guidelines
should be considered when a patient with this skeletal pattern is treated without surgical
intervention.

Mandibular incisors, if well aligned before treatment, can be allowed to remain

in their pretreatment position. Uprighting of mandibular incisors has an adverse impact
on facial esthetics of the low-angle patient. However, the mandibular incisors, if
malaligned, should not be proclined beyond their bony support for the purpose of
alignment.

Some overdosed forward rotator malocclusions are characterized by a deep

vertical over-bite, maxillary incisor protrusion, and/or crowding. Correction of the
overbite for these patients is best accomplished by intrusion and retraction of the maxillary
incisors.9,10,11,22

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