Functional malocclusion /certified fixed orthodontic courses by Indian dental academy

FUNCTIONAL MALOCCLUSION

INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

TERMS
Occlusion – The relationship of maxillary and
mandibular teeth as that are brought into
functional contact.
Centric occlusion – Mandibular position dictated
by maximum and habitual intercuspation of
maxillary and mandibular teeth.
It is dentally determined position independent of
condylar position. Also called as intercuspal
position.

Centric Relation Occlusion.
The simultaneous even contact between maxillary
and mandibular teeth into maximum
interdigitation with the mandible in its most
unstrained and retruded position.
Also called as Retruded contact position.
According to Dawson : Centric relation can be
defined as the most superior position the
condyles can assume in the glenoid fossa.


It is not unstrained because it is achieved
by firm contraction of the elevator
muscles.
It is not most retruded as it is possible to
force the condyles distal to centric relation,
but such a displacement occurs only with
a downward movement away from centric
relation.


Centric Relation Occlusion.
The simultaneous even contact between maxillary
and mandibular teeth into maximum
interdigitation with the mandible in its most
retruded position – when centric relation and
centric occlusion coincide.
Considered to be the ideal occlusal relationship.
However, it does not usually occur in individuals
unless they have had an occlusal equilibration or
a complete dental arch rehabilitation.


Centric cusps/Supporting cusps : Primarily
responsible for maintaining the distance
between maxilla and mandible.
They are buccal cusps of mandibular posterior
teeth and lingual cusps of maxillary posterior
teeth. Occlude with opposing central fossa
areas.
Non centric or Guiding cusps : Buccal cusps of
maxillary posterior teeth and lingual cusp of
mandibular posterior teeth.

Centric cusps are broad & rounded whereas non
centric cusps are sharp.
Non centric cusps also give the mandible
stability so that when the teeth are in full
occlusion, a tight definite occlusal relationship
results. This is called maximum intercuspal
position.
If mouth is opened, then closed, the non centric
cusps will help the mandible back to the
intercuspal position. Therefore , the non centric
cusps are appropriately referred to as guiding
cusps.

Freedom in Centric: Provides for freedom
for the mandible to close into maximum
intercuspation in centric relation anteriorly
to centric occlusion, and in between as
well as slightly lateral and anterior to this
area of occlusal contacts.
In this concept , “ there is a flat area in the
central fossae upon which opposing cusps
contact which permits a degree of
freedom in eccentric movements
uninfluenced by tooth inclines”.

Also known as ‘long centric’.
This allows the mandible to close into an intercuspal
position without the need for gross neuromuscular
responses to premature occlusal contacts.
Point Centric : In long centric , supporting cusps make
contact with flat areas prepared in the restored teeth, not
only when condyles are in centric relation but also when
slightly anterior to centric relation.
However in the concept of point centric supporting cusps
must make occlusal contact at a point when the condyles
are only, and precisely in centric relation.


Ideal occlusion : An ideal relationship of maxillary and
mandibular teeth combining a functional occlusion along
with the absence of malocclusion as described by the six
keys of occlusion
Ash and Ramfjord (1995) defined ‘ideal occlusion’ as:
1. The coincidence of centric occlusion in centric relation
(CO = CR), when there is freedom for the mandible to
move slightly forwards from that occlusion in the same
sagittal and horizontal plane (freedom in centric).
2. When the mandible moves, there is immediate and

lasting posterior disclusion (anterior guidance on front
teeth)


The concept of normal occlusion emphasizes
the functional aspect of occlusion and the
capability of the masticatory system to adapt to
or compensate for some deviations within the
range of tolerance of the system.
A description of normal occlusion involves
occlusal contacts, alignment of teeth, overbite
and overjet, arrangement and relationship of
teeth within and between the arches, and
relationship of teeth to osseous structures.


Functional Occlusion – A static and dynamic
relationship of the teeth combining minimum
stress on TMJ, optimal function of the orofacial
complex, stability and esthetics of the dentition
and protection and health of periodontium.
Also known as Physiological occlusion.
Dynamic or Functional occlusion refers to the
occlusal contacts that are made while the
mandible is moving relative to the maxilla i.e.
during speech, mastication and swallowing.


The mandible is moved by the muscles of
mastication, and the pathways along
which it moves are determined by these
muscles, as well as by two guidance
systems:
• Posterior guidance system
• Anterior guidance system.


The Posterior Guidance System is provided by
the temperomandibular joints.
As the head of the condyle moves downward
and forward the mandible is moving along a
guidance pathway that is determined by the
intra-articular disc and the articulatory surfaces
of the glenoid fossa, all of which is enclosed in
the joint capsule.


If teeth are touching during a protrusive or
lateral movement of the mandible, then
those teeth also provide a guidance to the
mandibular movement.
This is the Anterior Guidance and is
provided by whichever teeth touch during
eccentric movements of the mandible.


Thus, Anterior guidance or Anterior coupling can
be defined as the tightly overlapping relationship
of the opposing maxillary and mandibular
incisors and canines which produces disclusion
of the posterior teeth when the mandible
protrudes and moves to either side from 1-4mm.
Anterior guidance can be further classified into:
• Canine guidance
• Group function

Canine Guided Occlusion – during the
lateral excursion, contact occurs only
between the upper and lower canine, and
first premolar on the working side. There is
no contact between the teeth on the nonworking side.
The theory of canine protected
occlusion was put forward by Nagao
(1919), Shaw (1924) and D’Amico (1958).

It is based on the impression that the canine
is the most appropriate tooth to guide the
mandibular excursion, because:
1) The canine has a good crown: root ratio,
capable of tolerating high occlusal forces.
2) The canine root has a greater surface
area than adjacent teeth, providing greater
proprioception.
3) The shape of the palatal surface of the
upper canine is concave and is suitable
for guiding lateral movements.

Group function Occlusion (Shyler, 1929) –
during the entire lateral movement, the
buccal cusps of the posterior teeth on the
working side are in contact. There is no
contact on the non-working side.
This is also known as Unilateral
Balanced Occlusion.


Balanced Occlusion – during the entire lateral
movement, all of the posterior teeth on the
working side, and one or more teeth on the
non-working side contact simultaneously.
Present day thinking has completely
dismissed this concept for restoring the natural
dentition. However, it is desirable in a patient
wearing a set of complete dentures.


• Eccentric Relations.

Refers to any deviation of the mandible
from the centric occlusion position. This
includes lateral and protrusive movements
and any combination of these.
Protrusive relation.
It is that position with the mandible moved
anteriorly and downward, so that both
mandibular condyles and discs are
forward in their glenoid fossa.

As the mandible moves forward, the incisal edges
of the mandibular anterior teeth glide against the
lingual fossae of the maxillary anteriors. When
the mandible is fully protruded, the incisal edges
of the mandibular incisors are in front of the
maxillary anterior teeth.
The average maximum forward protrusion of the
mandible is 8.3mm (range 2.5 to 16mm)


Lateral Relation.
In lateral relation, the mandible is moved to the
right or left side and slightly downward (as in
mastication).
If the mandible moves to the right side, the right
condyle remains relatively stationary (while
rotating), and the left condyle and disc move
downward, forward and inward within the
articular fossa.


• Working Side.

The side towards which the mandible moves
during function. Usually, the posterior upper and
lower teeth are aligned with the upper buccal
cusps directly over the lower buccal cusps and
with the lower lingual cusps directly beneath the
upper lingual cusps during working side tooth
contacts (group function).
The condyle only rotates on its vertical axis and
moves laterally 1-2mm or less . Minimal
movement

Maxillary Dynamic Occlusion


• Balancing/Non-working Side.

It is the side away from which the mandible moves.
On the balancing side, the upper lingual cusps
are aligned over the lower buccal cusps, but
usually do not contact during the opposite side
working tooth relation.
Any balancing side tooth contacts are thought to
be destructive to both the involved teeth and
damaging to the TMJ on the opposite side.
The balancing side mandibular condyle moves
medially, downward and forward 5-12 mm.

The features of an ‘ideal’ functional occlusion
include:
a) Bilateral occlusal contacts in the retruded
contact position.
b) Coincidence in the retruded contact position and
the intercuspal position, or a short slide between
the two (<1mm).
c) Contact between opposing teeth on the working
side during lateral jaw movements – canine
protected or group function.
d) No contact between teeth on the non-working
side during lateral excursions.

Posselt’s Envelope of Motion
Posselt (1957) described the extreme or
border movements of the mandible as an
envelope of motion. The occlusion
achieved during the normal functional
movements, such as swallowing and
chewing, occurs within this relatively small
space.


Sagittal Movement
Frontal Movement


During lateral movement of the mandible,
the condyle of the working side rotates
and moves laterally, as well as upwards,
downwards or backward. The lateral
component is called the Bennett
Movement. On an average, it measures
0.5mm.
It is also called the Bennett shift,
Lateral shift, or Immediate side shift.

The condyle of the
non-working side
moves downwards,
forwards and inwards,
creating the Benett
Angle.
It is also called the
Progressive side shift

Mandibular Deviation – refers to the direction
and movement of the mandible from the first
tooth contact with the jaw in centric relation to
the centric occlusion position. The direction of
deviation is usually upward and forward
(1.25mm), with or without a lateral component.
Mandibular Deflection – refers to any contact
of opposing teeth which guides or directs the
mandible away from centric relation, either
forward or to one side or both, as the teeth slide
into centric occlusion

Disclusion – refers to the separation of all
the posterior teeth on one side as the
mandible moves to that side. It is caused
by the opening component produced by a
deep vertical overlap of the canines


Functional Cross bite
Usually associated with unilateral posterior crossbite with
mandibular shift.
Clinical presentation is a unilateral crossbite with a
functional shift of the mandible toward the crossbite side.
A centric occlusion (CO) to centric relation (CR)
discrepancy is evident in an Functional cross bite,
whereas CO and CR are usually coincident in a true
unilateral crossbite.
A bilateral crossbite due to skeletal imbalance between
maxillary and mandibular transverse dimensions differs
from an Functional cross bite only in degree of severity;
the maxillary to mandibular width discrepancy is less
with functional cross bite.

Lateral shift of the mandible in an functional
cross bite results in a mandibular skeletal (and
often dental) midline deflection to the crossbite
side. The maxillary arch is usually symmetrical
with coincident maxillary dental and skeletal
midlines.
The maxilla is transversely constricted in an
Functional cross bite with marginal ridges in line
and absence of simple dental crossbite.
Because of this transverse maxillary deficiency,
frequently more crowding is seen in the maxilla
than in the mandible.

The crossbite side in an Functional cross bite
often shows a partial or full Class II molar
relationship; the non-crossbite side shows a
Class I relationship due to rotational closure of
the mandible.
Pretreatment tomograms reveal an asymmetric
condyle position; the non-crossbite side is down
and forward in the fossa and the crossbite side
is centred in the fossa.
Early correction of posterior crossbites may help
prevent signs and symptoms of
temporomandibular disorder (TMD).

Children with unilateral posterior cross
bites have been reported to have lower
maximum bite forces and lower numbers
of occlusal contacts than children without
malocclusions.
However , the bite force does not seem to
vary between Angle malocclusion types.
Orthodontic treatment may be needed to
improve function.

Treatment
Posterior crossbites in the deciduous dentition
showed self-correction of between 0% and 9%
Removal of functional interferences has been
shown to be useful only in patients under the
age of 5, with success rates ranging from 27% to
64%
In a study of 76, 4-year-old children with
posterior crossbite, Lindner (1989) reported 50%
correction after functional grinding

Success rates for treatment with expansion
appliances in the early mixed dentition stage
range from 84% to 100%.
Advantage of early treatment (deciduous or very
early mixed dentition) is improvement of
maxillary arch length deficiency secondary to
maxillary constriction, because the permanent
incisors are afforded more space before or
during eruption than if the crossbite is treated at
a later age.

When expansion is carried out during the late
deciduous dentition, the first permanent molars
usually erupt into satisfactory transverse
positions

Overexpansion is desired to the point where the
lingual cusps of upper molars contact the buccal
cusps of lower molars.
Other treatment involves removal of occlusal
interferences & elimination of functional shift.

There is a growing body of evidence that
untreated crossbites will lead to
permanent growth alteration, making early
treatment crucial.
Evidence from tomographic studies has
shown that the condyles in child crossbite
patients are related asymmetrically within
the fossa, but that symmetry is restored
after early treatment.

It has been inferred that the glenoid fossa and
condyle will undergo remodelling during growth
to compensate for condylar asymmetry if left
untreated, although no longitudinal research has
provided conclusive evidence of glenoid fossa
and condylar skeletal adaptation.
Symmetry of the mandible and its rotational
position relative to the cranial base is altered in
adult patients with untreated posterior
crossbites.


Correction of functional cross bite with maxillary
expansion in growing patients has been shown
to establish condyle and dental symmetry and to
realign the mandibular rotation.
Once these adaptations are firmly established in
adulthood, treatment may combined orthodontic
and surgical approach.
To achieve the potential benefits of correcting
functional cross bite, maxillary expansion must
be performed early, before fusion of the palatal
halves.

Occlusal Interference
Defined as: A cuspal contact forcing the mandible
to deviate from a normal pattern of movement –
Posselt (1968).
Undesirable occlusal contact that may produce
mandibular deviation during closure to maximum
intercuspation, or may hinder smooth passage
to and from the intercuspal position – Glossary
of orthodontic terms (2000).


Features of occlusion that are likely to interfere
with function or parafunction:
1. Occlusal contacts on the non-working side.
2.

Unilateral contacts in the retruded contact
position.

3.

Long slides (>1mm) between the retruded
contact position and the intercuspal position.

4. Asymmetry in the slide between the retruded
contact position and the intercuspal position.


Working side interferences
Occlusal interference on the working side
may be detected during lateral excursion
with the teeth in contact, but such an
interference may not cause overt clinical
symptoms if the patient does not use the
working side during function or
parafunction.


Protrusive interferences : Usually are on the
distal facing inclines of maxillary teeth and
mesial facing inclines of maxillary teeth.
Interferences between the maxillary and
mandibular anterior teeth in lateral or in
protrusive excursions should be corrected by
grinding on the lingual aspect of maxillary
incisors & cuspids along the path of interference.


Balancing side interferences : are those
that occur between maxillary & mandibular
supporting cusps & their occlusal inclines.
Since these cusps maintain centric stops
and thus are essential to the stability of
the tooth position, removal of interferences
has to be done with great care.
Main rule is to do the whole grinding on
only one of the 2 interfering cusps or
inclines if they both serve as centric stops
for the teeth.

Common interference sites in Orthodontic
cases
In orthodontic cases, there are some factors that
usually tend to present interferences during the
finishing stages.
The most common are : a) lingual crown torque
of the upper second molars;
b) accentuated lingual crown torque of the lower
second molars;
c) incorrect anteroposterior relation between the
maxilla and the mandible; and
d) incoordination of the upper and lower arch
widths.

These factors can induce interferences in
the balancing side.
During treatment, these potential
interference factors should be corrected
by orthodontic mechanotherapy.


Lower Incisor extraction and.
Functional Occlusion
Cases in which there is a severe Bolton discrepancy,
with disproportionately larger lower anterior teeth than
upper anterior teeth, usually present a good relation of
these teeth at the end of treatment, when one lower
incisor is extracted.
On the other hand, if the discrepancy is not severe
enough, the anterior guidance will be compromised
because the upper anterior teeth curvature radius will be
disproportionately larger than the lower anterior teeth
curvature radius as long as there is a normal buccal
intercuspation..

The anteroposterior distance of the lower to the
upper anterior teeth will be increased, and
consequently the anterior teeth will not be able
to disclude the posterior teeth on the beginning
of protrusion.
As a result, many interferences on posterior
teeth may develop.
Cuspid guidance will also be compromised,
because the ideal relation of 0.0005 inch
between these teeth will not be established.
Moreover, there will be a tendency for relapse of
the overbite and overjet

Occlusal interference & bruxism
Lindqvist (1973) examined 78 , 14 yr old
children, 34 children had bruxofacets & reported
tooth grinding. Types of functional malocclusion
recorded in the study were lateral shift of the
mandible & nonfunctional side interferences.
Results showed significantly higher frequency of
occlusal interferences in subjects with bruxism
than in those without it.


Nilner’s (1983) examination of 440 children aged
7-14 years investigated the relationship between
functional malocclusion & bruxism.
Types of functional malocclusion recorded in the
study were interferences in terminal hinge
movement, mediotrusion interferences , and
cuspid rise.
It was found that dental wear in lateral sections
was more pronounced in bites with mediotrusion
interferences than in bites without them.


However Vanderas et al (1995) from
review of studies regarding relationship
between malocclusion & bruxism
concluded that statistically significant
correlations reported by the reviewed
studies are inconsistent & without
biological significance.


TMD & Functional malocclusion
Liu , Tsai (1998) investigated the role of
functional malocclusion in temporomandibular
disorders (TMD) in untreated orthodontic
patients.
A total of 508 orthodontic patients were
enrolled. All patients were evaluated for the
presence of various types of functional
malocclusion and clinical signs of TMD before
treatment.
The frequencies of TMD were 44.2% in patients
with retruded position (RP) interference and
38.1% in those without such interference .

The frequency of TMD in patients with protrusive
interference was greater than those without
(32.2% vs. 18.4%).
Patients with balancing interference had a
significantly higher frequency of TMD than those
without (49.2% vs. 23.9%).
Authors concluded that patients with functional
malocclusion of balancing or protrusive
interference type have an increased risk for
developing TMD.


Seligman & Pullinger (1991) assessed the
published research literature concerning the
relationship of functional movements of the
mandible to the TMD.
They reported that most controlled surveys fail to
demonstrate any association between working
and non working contacts and TMD signs or
symptoms.
These types of eccentric occlusal contacts are
so common & variable that they lack the
sensitivity & specificity for defining a present or
potential TMD population.


The following is a list of signs or symptoms from
occlusal interferences:
1. Occlusal wear.
2. Excessive tooth mobility.
3. Temporomandibular joint sounds.
4. Limitation of opening or movement.
5. Myofascial pain.
6. Contracture of mandibular musculature,
making manipulation difficult or impossible.
7. Some types of tongue-thrust swallow.


If a patient has any of these signs or symptoms
and the mandible is difficult to manipulate, it
would be wise to pursue a cautious course of
action and use a splint to see if the symptoms
can be eliminated or alleviated and what
changes occur in mandibular position, before
placing orthodontic appliances.
According to Roth : ‘It is important to realize that
a "little bit of clicking" of the TMJ's is abnormal.
That occlusal wear is abnormal, unless the
patient is chewing whale hides for a living. We
must be aware that when occlusal harmony is
present, most of these signs are not present’.

“We must realize that the patients we are
treating, for the most part, are children with
exceptionally high tolerance levels and adaptive
capacities. We must also realize that tolerance
levels decrease with age. Therefore, what the
child patient can tolerate in terms of occlusal
interferences at the age of 14 or 15, he may not
be able to tolerate at age 20 or 25, without
symptoms”.
Patients do not adapt to occlusal interferences,
they tolerate them; but they tolerate them less
well as they get older.

OCCLUSAL INTERFERENCES TEND TO
MAKE TEETH AND JAWS A FOCUS
FOR VENTING PSYCHOLOGICAL
STRESS.
When the teeth and jaws are stressed by
gnashing, clenching, and grinding, the
weakest link or links of the chain will break
down.
If the patient is prone to periodontal
disease, the working over of occlusal
interferences in the presence of plaque
will start periodontal breakdown.

If the periodontium and hygiene are good,
the patient may experience occlusal wear.
If the joints are the weakest link in the
chain, then the patient may develop
temporomandibular joint dysfunction or
disease.
Patients may develop symptomatology in
any or all of these areas simultaneously.


The patient with "minor" or subclinical
symptomatology could be just waiting for
someone to subject him to orthodontic
tooth movement, before the symptoms
become overt.
Once this has happened, there is usually
no turning back. The orthodontist has now
got the ball and he'd better know which
way to run.

In terms of their reactions to occlusal
interferences, patients could be classified
into three categories:
1. Those with symptomatology.
2. Those that are either psychologically
and/or physically predisposed to
developing a problem.
3. Those that are neither symptomatic nor
predisposed to developing symptoms


Examination
On initial examination, the orthodontist should
attempt to manipulate the mandible into clinical
centric relation .
Recording of centric relation jaw position.
- Bilateral manipulation of mandible into
centric relation.
- Use of leaf gauge (anterior
deprogrammer).
- Use of sliding guiding inclined gauge (or
sliding guide) for anterior deprogramming and
recording CR.

Manual guidance of the mandible into centric relation


If the discrepancy is a large one, a mounting on
a simple anatomical articulator (such as a WhipMix or Hanau) is indicated, so that the
discrepancy can be studied and steps for its
correction can be integrated into the treatment
plan.
If the mandible is difficult to manipulate and
upon attempting to hinge the mandible closed a
fair amount of resistance is encountered; and
then, once the teeth are contacted, there is no
centric prematurity, do not believe what you are
looking at in the mouth.

The patient has closed into his habitual centric
occlusion and the musculature is in a state of
contracture, to posture or accommodate the
mandible to the existing occlusion.
It will require splint therapy to free the
musculature, so that the true discrepancy can be
revealed.
The temporomandibular joints should be
palpated for popping or grating sounds. The
musculature should be examined for
tenderness.

If these signs are present, then splint therapy
and cephalometric TMJ tomograms are
indicated, prior to attempting to begin
orthodontic treatment.
The occlusion should be inspected for wear
facets and checked to see if the patient can
contact these areas of wear or faceting.
The patient should be checked for his ability to
execute left and right lateral excursions and
protrusive movements.

If the patient cannot execute gliding movement
on the anterior teeth in all excursions : there are
posterior interferences or incorrect anterior
coupling, even though this may not look like the
case intraorally.
For instance, if the patient cannot keep the
anterior teeth together in a protrusive movement
either from centric forward or protrusive back,
there is a severe enough posterior interference
present to prevent him from making this
movement without separating his teeth.

The amount of maximum opening should
be noted as it is an indicator of the state
of contracture of the mandibular
musculature.
Normal maximum opening from the incisal
edge of the lower incisors to the incisal
edge of the upper incisors averages
approximately 45 to 50mm.


Diagnosis & Treatment planning
Whenever any of the symptomatology
mentioned is found on examination, it is wise to
utilize splint therapy to unearth the true
maxillomandibular relationship prior to placing
orthodontic appliances.
Once the discrepancies are apparent, the
orthodontist will make a treatment plan to deal
with all of the discrepancies present in the case;
not just one to cover only those discrepancies
he can see intraorally.

Standard orthodontic models and cephalometric
headfilms have been traditionally taken in
habitual centric occlusion. We must have
records taken in centric relation as well, if any
significant centric discrepancy exists in a
particular case.
This is necessary for us to evaluate how much of
the discrepancy lies in which planes of space, so
that we can elect to use the appropriate
mechanics that will deal with each of the
discrepancies.

For instance, we may have a case in which there
appears to be unilateral Class II molar
relationship, but in centric relation of the
mandible there is really a bilateral Class II molar
relationship end-on.
If we base our mechanics upon a unilateral
Class II relationship and treat accordingly, we
will wind up with a case treated out of centric
that is bilateral Class I in habitual centric closure
and unilateral end-on Class II on the side
opposite the original habitual centric Class II in
centric relation.

If it is bilateral end-on Class II then our
mechanics must deal with a bilateral Class
II situation, in order to be able to finish the
case in bilateral Class I and in centric
relation occlusion.
TMJ tomograms : Cephalometric
tomography of the joints is of great
diagnostic benefit

In the large majority of cases, gnathologic
centric relation will yield a normal looking
position on a cephalometric tomogram.
But it is important to realize that a normal
looking position on a cephalometric tomogram
does not necessarily mean that the patient has a
centrically related occlusion.
This is because the 3-d relationship of the
condyles in the fossae is reduced to two
dimensions on the tomogram.

Therefore, slight movement of the
condyles, particularly lateral or vertical
axis rotary movements will be difficult, if
not impossible, to discern when this type
of movement occurs in small amounts
between centric relation and centric
occlusion.


Repositioning Splint
The purpose of the repositioning splint is to enable the
operator to find "true" centric (which is stable and
comfortable); to test the patient's response to change in
the occlusion, prior to embarking upon a complex course
of occlusal therapy; and, finally, to see if the mandibular
centric relation position can be stabilized.
Eugene Dyer popularized the use of the repositioning
splint, which he now calls a craniomandibular orthopedic
appliance. Dyer also pointed out a number of years ago
that, in centric relation, the condyles are usually in the
superior-anterior portion of the fossae.

The splint is used whenever a patient is
symptomatic and/or when the mandible is
difficult to manipulate or, better yet, when the
mandible is not easy to manipulate.
Initially, splint treatment is directed toward
alleviation of pain-dysfunction symptoms and the
diagnosis of the true maxillomandibular
relationship.
The splint is a means of relaxing the mandibular
musculature and resolving the inflammatory
changes within the joint capsules.

Allows remodeling of the joints to occur, if there
have been some previous degenerative
changes.
It tests the patient's response to occlusal
change without actually changing the occlusion;
and allows the operator to know if the
mandibular position can be stabilized, and what
the exact extent of the discrepancy is that must
be corrected.

It puts the patient to the test in terms of his
or her desire to undergo complex occlusal
therapy.
It also allows the patient to know what he
might expect, in terms of comfort, if the
complete correction of the occlusion is
undertaken.
Usually done prior to any type of
irreversible occlusal treatment.


The objective in making the repositioning
splint is to seat the condyles in the most
superior position possible on every visit,
and to adjust the occlusal surface of the
splint to achieve maximum intercuspation
at this position of the mandible at the most
closed vertical dimension obtainable.


The mandibular postural changes during
splint therapy are of three different types:
1. Changes due to relaxation of the
musculature that postures the mandible
incorrectly due to muscle contracture or
spasms.
2. Changes due to elimination of
intracapsular inflammatory fluid.
3. Changes due to remodeling or
recontouring of the bony parts of the joints
(e.g. condyles or fossae).

Splint therapy must be continued until
there has been no change in mandibular
positioning in centric relation for at least
three months.
In some of the more difficult cases, where
there is some radiological evidence of
recontouring of bony parts of the joints, six
months stabilization on the splint is a good
indicator that it is all right to proceed with
more definitive treatment.

Gnathological Objectives
Historically, gnathology has been
associated with restorative dentistry and
prosthetics and, although there have been
some orthodontists involved in the early
gnathological research, no one until recent
years has attempted to describe the
occlusion of the natural dentition in terms
of tooth positions necessary to achieve an
occlusion that meets gnathological goals.

The gnathological objectives are aimed at
harmonizing the occlusal morphology or
natural tooth positions with closure of the
mandible in centric relation, and with
border excursions of the mandible.


First objective : Obtain a stable centric
relation of the mandible and have the
teeth intercusp maximally at this
mandibular position.
All centric stops should hit equally and
simultaneously and the stress of closure
should be directed, as nearly as possible,
down the long axes of the posterior teeth.
There should be no actual contact of the
anterior teeth in centric closure (.0005"
clearance).

Second Objective : to have a harmonious glide
path of anterior teeth working against each other
to separate or disclude the posterior teeth
immediately, but gently, as soon as the
mandible moves out of centric closure.
The glide path provided by the anterior teeth
must be in harmony with the way in which the
mandible moves through border excursions.
There should be sufficient overbite and overjet
at the maxillary incisor tips to allow for a gentle
glide path.


The cuspids should be the main gliding
inclines on lateral excursion and the six
maxillary anterior teeth should articulate
with the six mandibular anterior teeth and
the mandibular bicuspids (first bicuspid in
nonextraction cases), so that the
protrusive load is spread over 14 teeth.


The gentle lateral and protrusive lift is not only
necessary from the standpoint of mandibular
movement, but necessary from the orthodontist's
point of view in terms of posttreatment stability
of the tooth positions.
Excessive lateral stress on the cuspids may
cause lingual movement of the lower cuspids
and resultant lower anterior crowding, and/or
labial movement of the maxillary cuspids .


Since the maxillary anterior teeth are retracted in
most cases, an improper anterior guidance in
protrusive will tend to enhance the chances of
relapse of the maxillary anterior teeth labially.
This is very commonly seen in posttreatment
orthodontic cases, because of bracket
placement that tends to elongate the maxillary
central incisors.
Thus, the central incisors become the only teeth
in contact in an incisive relationship.


In addition to this, most treated cases
exhibit insufficient torque of the maxillary
central incisors, thus creating too steep an
anterior lift and an insufficient glide path in
protrusive .


Inadequate labioaxial inclination of the
maxillary central incisors can also cause
them to be overstressed upon lateral and
lateroprotrusive movements, as well as
pure protrusive.
In posttreatment orthodontic cases, the
anterior teeth will tend to move to
accommodate mandibular movement, if
the anterior tooth positions interfere with
these movements.

A "mutually protective" occlusal scheme needs
to be established , where the anterior teeth
protect the posterior teeth from lateral stress
during movement and the posterior teeth protect
the anterior teeth from lateral stress during
closure into centric relation occlusion.
The anterior teeth are subjected to a minimum
of stress during movements, only if a gentle
glide path is provided that is in harmony with the
manner in which the mandible moves.

A centrically related occlusion and a mutually
protective excursive occlusal scheme are
dependent upon:
1. Proper individual tooth positioning.
2. Knowing when the mandible is in centric and
when it is not.
3. Coordination of arch form and arch width.
4. Control of the vertical dimension.
5. Anteroposterior correction between maxilla
and mandible.
6. Clinical awareness of excursive interferences

In addition, Roth advocated the concept of
overcorrection : so that settling into centric
relation and ideal intercuspation is most likely to
occur. This is necessary because - 1. Teeth will
move after appliance removal, no matter where
they are placed.
2. The curve of Spee will return or deepen after
appliance removal.
3. Teeth that are slightly tipped distally in the
buccal segments will tend to settle better than
teeth that are already mesially inclined.
4. As teeth in the buccal segments settle they
will tip mesially and rotate mesially.

5. As band spaces close, there is a
corresponding loss of torque of the
anterior teeth.
6. Teeth adjacent to an extraction site will
tend to rotate towards the extraction site.
7. Teeth adjacent to the extraction sites
tend to tip into the extraction sites.


8. Maxillary lingual cusps will tend to migrate
downward until they find an occlusal stop
against the opposing teeth (since the maxillary
lingual cusps are the centric supporting cusps of
the upper teeth).
Because these factors seem to occur most of
the time, it seems only logical to plan for these
things to happen during treatment and set up a
detailing or finishing goal that will overcome
these factors, thus allowing every conceivable
opportunity for the teeth to settle into the most
ideal occlusion after appliance removal.

Overcorrection is built in for all areas except for
buccolingual torque of the lower buccal
segment.
This is one area that is absolutely critical in
terms of exact positioning, because torque
errors in the lower buccal segments will not
settle out of the occlusion.
The lower buccal segment torque must be
correct, to act as a template for the maxillary
teeth to occlude with and to settle to.

AFTER CENTRIC IS OBTAINED
Check tooth detailing (by having patient to go
through test excursions — right lateral, left
lateral, protrusive) for:
1. Torque of upper incisors.
2. Artistic tip of upper incisors and cuspids.
3. Overbite and overjet.
4. Flatness of curve of Spee.
5. Second molar positions.
6. Look for anterior group function, posterior
clearance (minimal), cuspid guidance, and
balancing interferences.

At the end of appliance therapy, the occlusion
should almost resemble a "bilaterally balanced"
occlusal scheme during the excursions. In other
words, the anterior guidance should almost not
be quite adequate.
This is because the curve of Spee is leveled and
the overbite has been overcorrected.
After appliance removal, the curve of Spee will
return and the overbite will deepen to provide a
more ideal anterior guidance.


Selective Grinding
- In the centric relation, all premature contacts
are identified. Grinding is performed on the
inclines to alter or reshape all inclines into
cusp tips or flat surfaces. Contacts of cusp
tips to flat surfaces direct the occlusal forces
through the long axes of the teeth.


During lateral excursions, on the balancing
side, if there is an interference between a
cusp tip and a cusp incline, the incline
should be ground.
If the contact occurs between two centric
stop cusp tips, the least stable in centric
should be ground.

On the working side, the sites to be ground are the
tips or inclines of the upper buccal and lower
lingual cusps, irrespective of the interference
spot (BULL law).
- During protrusive movement, interferences
usually occur between the mesial inclines of
lower cusps and the distal inclines of upper
cusps. Here, the inclines of the guide cusps
should be ground.


Criteria for judging outcome of equilibration –
1) There is no aymmetric shift from CR to CO. If
present, it is smooth, symmetric ,less than 1mm
in magnitude.
2) The completed adjustments have light or no
contact between the incisor teeth & firm contact
between as many posterior teeth as possible.
3) Patient perceives bilateral contact when
closing the teeth to centric relation occlusion.
4) Sharp occlusal sounds are produced when the
patient taps slowly or firmly into occlusion.


5) Tooth guidance under lateral &
protrusive contact is smooth & without
effort.
6) The displacement of mobile teeth is
minimized under closure & guiding
movements.


Conclusion
In recent years , orthodontists have voiced more
interest in occlusion and functional occlusion.
Treating a case to functional occlusion requires
thorough understanding of the concepts and
clinical mastery of the techniques
To treat to centric , the case must be diagnosed
in centric, monitored thoroughly & a clear end of
treatment goal must be established.

In today's consumer oriented practice it is better
to give our patients a functionally sound
treatment plan where the goal of every case
should be a centric relation occlusion.
Proffit summed up the goal of modern
orthodontics as “the creation of the best possible
occlusal relationships within the framework of
acceptable facial esthetics and stability of
results”.

References
1) Valiathan A, Srivastava AK. Oclusal equilibration
following orthodontic therapy. J Ind Orthod Soc 2000;
33: 17-22.
2) Prashanth VK & Ashima Valiathan: Ideal treatment
results - Is it an orthodontists dream or reality? Kerala
Dental Journal, 1995; 18(1): 1059-1061.
3) Liu JK, Tsai MY: Association of functional
malocclusion with temporomandibular disorders in
orthodontic patients prior to treatment. Funct
Orthod. 1998 ;15(3):17-20.


4) Roth RH : Functional occlusion for the
orthodontist part I .- part III. JCO 1981, 15 (1-3) ;
32-50, 100-123, 175-198.
5) Milosevic A. Occlusion: I. Terms, mandibular
movement and the factors of occlusion. Dent
Update 2003; 30:359-361.
6) Ash M. Philosophy of occlusion: past and
present. Dent Clin North Am 1995; 39(2): 233255.


7) Vlachos CC. Occlusal principles in
orthodontics. Dent Clin North Am 1995;
39(2): 363-378.
8) Okeson JP : Occlusion and functional
disorders of the masticatory system. Dent
Clin North Am 1995; 39(2): 285-300.
9) Clark JR, Evans RD : Functional
occlusion: I A Review. Journal of
Orthodontics 2001,28(1); 76-81.

10) Nilner M: Relationships between oral
parafunctions and functional disturbances and
diseases of stomatognathic system among
children 7-14 years. Acta Odontol Scand
1983(41) : 167-172.
11) Lindqvist B : Occlusal interferences in
children with bruxism. Odontol Revy
1973(24);141-148.
12) Vanderas AP, Manetas KJ : Relationship
between malocclusion and bruxism in children
and adolescents : a review. Pediatric Dentistry
1995, 17 (1) ; 7-11.

13) Parker WS. Centric relation and centric
occlusal – an orthodontic responsibility. Am J
Orthod 1978; 74(5): 481-499.
14) Viazis AD. Atlas of orthodontics. 1998
15) Daskalogiannakis J. Glossary of orthodontic
terms. 2000, Quintessence Publishing Co.
16) Christensen GJ. The major part of dentistry
you may be neglecting. J Am Dent Assoc 2005;
136: 497-499.


17) Ramfjord S, Ash M. Occlusion. 4th Ed., 1996,
W.B.Saunders Co. Pg- 141-158.
18) Okeson JP. Management of
temperomandibular disorders and occlusion. 5 th
Ed., 2003, Mosby.pg- 464-472, 567-581.
19) Moyers RE. Handbook of orthodontics. 4th
Ed., 1988, Year Book Medical Publishers. Pg –
108-117.


20) Seligman DA, Pullinger AG : The role of
functional occlusal relationships in
temperomandibular disorders: A review. J.
Craniomandibular disorders Facial Oral Pain
1991,5:265.
21) Kennedy DB, Osepchook: Unilateral
posterior crossbite with mandibular shift: A
review. JCDA 2005, 71(8): 569-573.
22) Bakke M: Bite force and occlusion. Semin
Orthod 2006,12 (2) : 120-126.

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