Transcript Fundamentals Of Occlusion

Fundamentals Of
Occlusion
Fahim Vohra
SDS 333
Fundamentals Of Fixed Prosthodontics
Chap 2, Pg 11-23.
Outline
• Definitions
• Mandibular movement
• Normal vs Pathological Occlusion
• Occlusal Interferences
• Schemes of Occlusion
• Determinants of Occlusion
The Temporo-Mandibular Joints
Why Is Occlusion Important ?
• Assist in diagnosis
• Planning in restorative care
To minimize failure
Ensure predictable outcome by minimising loads on teeth
Managing the environment so that we get the minimal amount
of surprises (Similar to wearing a car seatbelt), the less the
patient has to adapt the better.
Definitions
OCCLUSION
A relationship between the masticatory surfaces of the
maxillary and mandibular teeth
The relationship between tooth contacts and mandibular
movements
Centric Occlusion
Relationship of the mandible to the maxilla when the
teeth are in maximum occlusal contact, irrespective of
the position or alignment of the condyle-disk
assemblies.
The relationship between the maxilla and mandible
when the teeth are maximally meshed with the
mandible in its most cranial position
Centric Relation
A relationship of the mandible to the skull where the
condyle is in an anteriorly, superiorly braced position
along the articular eminence of the glenoid fossa, with
the articular disc interposed between the Condyle and
eminence.
Mandibular Movements
• Mandibular movements occur around three axes
a) Horizontal axis
b) Vertical axis
c) Sagittal axis
Horizontal Axis (Rotation)
Horizontal Axis of Rotation
This movement occurs in the sagittal plane when the
• Opening
and closing
mandible
in centric
relation makes a purely rotational
openingmotion
and closing border movement around the
• Hinge
axis
transverse
horizontal
axis, which extends through both
condyles.
• Pure rotational
movement
• Terminal hinge axis
when the condyles
are in their most
superior position
VerticalAxis
axis (Rotation)
Horizontal
of Rotation
• This
Opening
and occurs
closing
movement
in the horizontal plane when the
motion moves into a lateral excursion. The center for
mandible
rotation
• this
Hinge
axis is a vertical axis extending through the
rotating or working-side condyle.
• Pure rotational
movement
• Terminal hinge axis
when the condyles
are in their most
superior position
Working side
• The side towards which the mandible moves during excursion
OR Mandible moving toward the cheek
• Working side condyle pivots within the socket and is better
supported.
Balancing side (Non working side)
• The side opposite to the direction in which the mandible
moves OR Mandible moving toward the tongue
• Balancing side condyle has a downward orbiting path and is
more prone to injury or damage.
Balancing
Side
Balancing
side.
Workingside.
Side
Working
Condyle
hashas
downward
path
Condyle
downward
path.
Condyle
pivots
Condyle
pivots.
Movement direction
Mandible and TMJ
Sagittal Axis
Horizontal Axis of Rotation
This movement occurs when mandible moves to working side,
the condyle on the opposite side (Non working side) travels
forward and downwards simultaneously. When viewed in the
• Opening and closing
frontal plane, this produces a downward arc on the non working
motion
side, rotating about an anteroposterior (sagittal) axis passing
Hinge
through• the
otheraxis
condyle
• Pure rotational
movement
• Terminal hinge axis
when the condyles
are in their most
superior position
Pure Hinge Movement
It occurs as the result of the condyles rotating in the
lower compartments of the temporomandibular joints
within a 10- to 13-degree arc, which creates a 20- to
25-mm separation of the anterior teeth
Translation Movement
• Occurs when the mandible moves forward (protrusion)
• Teeth, condyles, and rami, all move in the same direction and
to the same degree.
• Occurs within the superior cavity of the joint
when the
le moves
(protrusion)
condyles, and
l move in the
irection and to
me degree
within the
r cavity of the
anslational Movement
Maximum Opening
(Translation & Rotation)
Occurs in the upper compartment of the joint as the mandible
drops down farther . Then the horizontal axis of rotation shifts to
the area of the mandibular foramen, as the condyles translate
forward and downward while continuing to rotate.
Protrusive Position
When the mandible slides forward so that the
maxillary and mandibular anterior teeth are in
an end-to-end relationship, it is in a protrusive
position.
Bennett Movement
It is defined as “the bodily lateral movement/
lateral shift of mandible resulting from
movements of condyles along lateral inclines of
mandibular fossa during lateral jaw movement”
Dr Norman Bennett
Bennett Angle
The angle formed between the sagittal plane and the
average path of advancing condyle as viewed in the
horizontal plane during lateral mandibular movements.
Average range is 7.5-12.8 degree
BSC
Bennett angle
Sagittal plane
WSC
Posterior Determinant of Occlusion
TMJ – Temporomandibular Joint
Bony surfaces
The dentist has no control on the
posterior determinants i.e. TMJ
Anterior Determinant of Occlusion
Teeth
• Incisors
• Canines
• Premolars
• Molars
Anterior Determinants Of Occlusion
Posterior teeth
Provide vertical stops
Guide mandible to CO
Anterior teeth
Guide mandible in protrusive, retrusive and lateral
excursions
The closer the tooth located to a determinant , more it
will be influenced by it.
Occlusal Interferences
• Interferences are undesirable occlusal contacts that may
produce mandibular deviation during closure to maximum
intercuspation or may hinder smooth passage to and from the
intercuspal position .
• These can be of following types
a)
b)
c)
d)
Centric
Working
Non working
Protrusive
Centric Interferences
It is a premature contact that occurs when the mandible
closes with the condyles in their optimum position in
the glenoid fossae (CR) . It will cause deflection of the
mandible in a posterior, anterior, and/or lateral direction
Working Side Interference
It occurs when there is contact between the maxillary
and mandibular posterior teeth on the same side of the
arches as the direction in which the mandible has
moved. If that contact is heavy enough to dis-occlude
anterior teeth, it is an interference .
Non-Working Side Interference
• It is an occlusal contact between maxillary and mandibular
teeth on the side of the arches opposite the direction in which
the mandible has moved in a lateral excursion .
• It has the potential for damaging the teeth, PDL, MOM and
TMJ due to changes in the mandibular leverage, the
placement of forces outside the long axes of teeth and
disruption of normal muscle function.
Protrusive Interference
• It is a premature contact occurring between the mesial
aspects of mandibular posterior teeth and the distal aspects
of maxillary posterior teeth .
• The proximity of the teeth to the muscles and the oblique
forces make them potentially destructive.
• They also interfere with the patient's ability to incise properly
Ideal Occlusion
An ideal occlusion should provide comfort and function in
a predictable way.
1) Ideal occlusion at tooth level
Cusp tip to fossa or cusp to marginal ridge contact – i.e no incline
contacts
2) Ideal occlusion at articulatory system level
Posterior stability, Anterior guidance, Lack of posterior
interferences.
3) Ideal occlusion at patient level
Within the adaptability of the rest of the articulatory system.
Features Of Ideal Occlusion
A) Anterior Guidance:
• In lateral excursions of the mandible, workingside contacts (preferably on the canines)
disocclude or separate the nonworking teeth
instantly.
• In protrusive excursions, anterior tooth contacts
will disocclude the posterior teeth.
Protrusive Guidance
Excursive Guidance
Features Of Ideal Occlusion
B) Posterior stability:
Enough posterior teeth in each arch with solid and stable
contacts in appropriate positions to evenly distribute loads and
to allow the mandible to close in a reproducible CO. Posterior
teeth contact more heavily than anterior teeth
It is enhanced by tall cusp – deep fossa
Maintains teeth position
CO or ICP is easily reproduced
Increased masticatory function
Signs of lack of PS, drifting, fremitus, fractured rest, mobility & wear
Lack Of Posterior Stability
Features Of Ideal Occlusion
C) Absence of posterior interferences
The non-working
side
Features Of Ideal Occlusion
D) Centric Occlusion is achieved at centric
relation position
E) Occlusal loads are axially transmitted through
the teeth
Organization Of Occlusion
• There are three recognized concepts that
describe how teeth should contact in various
mandibular positions
1. Bilateral balanced occlusion
2. Unilateral Balanced occlusion
(Group function)
3. Mutually protected occlusion
(Canine protected)
Bilateral Balanced Occlusion
• It dictates that a maximum number of teeth
should contact in all excursive positions of the
mandible.
• Use for complete denture occlusal scheme as
contacts on non-working side prevent tipping
of the denture
• Not used for fixed prosthodontics, as very
difficult to achieve
Unilateral Balanced Occlusion
• Also called group function
• It requires teeth on the working side to be in
contact in lateral excursion and teeth on the
non-working side are free of any contact.
• Avoids destructive , oblique forces on the nonworking side.
• Prevents wear of maxillary palatal and
mandibular buccal cusps
Mutually Protected Occlusion
• Also called canine protected occlusion
• Anterior teeth overlap prevents the posterior teeth
from making any contact on either the working or
the nonworking sides during mandibular excursions.
• Anterior teeth bear all the load and the posterior
teeth are dis-occluded during excursions. Protecting
the posterior teeth
• In CO, posterior teeth direct forces through their long
axis and anterior teeth are slightly in or out of
contact. Protecting the anterior teeth.
Guidance
Describes the influenced path the mandible
takes as a result of the contacting surfaces
of the teeth. Depending on the contact and
shape of the teeth they should be in
harmony
Protrusive Guidance
Influenced path the mandible takes as a
result of a forward thrust
Lateral Guidance
• Canine
• Describes the way in
which lateral
excursions are
affected by tooth to
tooth contacts
involving the canine
teeth only resulting in
disclusion of the
posterior teeth
Lateral Guidance
• Group function
• When lateral
excursions are guided
by more than one
tooth other than the
canines
Hanau’s Quint
By modifying the following five factors, a scheme of occlusion can
be developed that will suit a particular patient best.
1. Condylar guidance
2. Incisal guidance
3. Occlusal plane orientation
4. Compensating curves
5. Height of the Cusp
Except for the condylar guidance, all other factors can be modified during the
fabrication of a prosthesis and the anterior guidance plays a predominant role.
Anterior Guidance
• Guidance produced by the teeth themselves and not the
temporomandibular joint (can be on any tooth)
• The influence of contacting surfaces of anterior teeth on
mandibular movements.
• The influence of contacting surfaces of the guide pin and
anterior guide table on articulator movements.
• The fabrication of a relationship of the anterior teeth
preventing the posterior tooth contact in all eccentric
mandibular movements.
Effects Of Anatomic
Determinants Of Occlusion
Protrusive Incisal Path
The track of the incisal edges of
the mandibular teeth from
maximum intercuspation to
edge-to-edge occlusion.
Protrusive Incisal Path Angle
The angle formed by the protrusive incisal path and the horizontal
reference plane is the protrusive incisal path inclination. It
ranges from 50 – 70 degrees and is often 5-10º steeper than
the sagittal condylar guidance.
Incisal Guide Angle
The angle formed with the horizontal
plane of occlusion and a line in the
sagittal plane between the incisal
edges of maxillary & mandibular
central incisors when the teeth are in
maximum intercuspation.
The angle formed in the sagittal plane
between the horizontal plane and the
slope of the incisal guide table.
Importance of Anterior Guidance
Opening and closing of the mandible is simply a rotation of the
condyles in the articular fossae.
Importance of Anterior Guidance
As anterior guidance is normally steeper than the condylar guidance, the
anterior teeth guide the mandible downwards during protrusive or lateral
movement
and ..
Importance of Anterior Guidance
(during protrusive movement)
.. produces dis-occlusion or separation of the posterior teeth.
Importance of Anterior Guidance
(during lateral movement)
Importance of Anterior Guidance
Anterior guidance is linked to the combination of
horizontal & vertical overlap of the anterior teeth
and
can affect the occlusal surface morphology of
the posterior teeth.
Inter-relationship with Vertical & Horizontal Overlap of the
Anterior teeth
Anterior guidance can be made steeper by either increasing the vertical
overlap (overbite) ‘A-B’, or by reducing the horizontal overlap (over
jet) ‘C-A’ of the anterior teeth.
Anterior guidance can be made shallow by either decreasing the overbite
‘B-A’ or increasing the over jet ‘A-C’ of the ant. teeth.
Condylar Guidance & Posterior tooth Morphology
(without considering the role of A.G.)
Shallow condylar guidance normally requires shallow cusp
angle or short cusp height and steeper condylar guidance
requires steep cusp angle or longer cusp height.
Condylar side-shift & Posterior tooth Morphology
(without considering the role of A.G.)
‘side shift +’
‘No side shift’
Similarly, in the presence of an immediate lateral side shift during lateral
movement (Bennett’s movement) the cusp height and cusp angle
should be shallow.
Influence of Anterior Guidance on
Posterior tooth Morphology
Influence A.G. on Posterior tooth Morphology
(Effect of Overbite)
Greater overbite produces more
disocclusion hence permits longer
cusp height
Less overbite – less disocclusion –
shorter Cusp height.
Influence of A.G. on Posterior tooth Morphology
(Effect of Over jet)
Greater over jet necessitates shorter
cusp height.
Less over jet allows for long
cusp height.
Influence of A.G. on Posterior tooth Morphology
Summarizing,
greater anterior guidance allows posterior teeth to have
longer cusp height
&
smaller anterior guidance requires posterior teeth to have
shorter cusp height.
Influence of A.G. on Posterior tooth Morphology
By increasing the anterior guidance angle to compensate for
inadequate or shallow condylar guidance, it is possible to
increase the cusp height of the posterior teeth.
Influence of A.G. on Posterior tooth Morphology
Similarly, increasing the anterior guidance will permit
lengthening of the cusp that otherwise have to be shorter in
the presence of pronounced immediate lateral translation of
the condyles.
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