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1. ANATOMY & PHYSIOLOGY OF TMJ
TEMPOROMANDIBULAR JOINT
The area where cranio-mandibular articulator occurs is called the temporo-
mandibular joint.
Ginglymo-arthroidal compounds synovial joints:
Ginglymoid joint  hinging movement in one plane.
Arthroidal joint  hinge + gliding movements.
Compound  Presence of three bones (articular disc is considered as
non-ossified bone).
EMBRYOLOGY
The temporomandibular joint develops relatively late in embryonic life
compared with the large joints of the extremities.
During the seventh prenatal week the jaw joint lacks the condylar growth
cartilage, joint cavities, synovial tissue and articular capsule.
The two skeletal elements, mandible and temporal bone are not yet in articular
contact with each other.
In contrast with this in the same prenatal specimen all the major components of
the elbow, hip and knee joints are present in a form and arrangements closely
resembling that seen in the adult.
In a week-old human embryo, Meckel’s cartilage, the cartilage bar of the first
branchial area extends all the way from the chin to the base of the skull.
It persists in this form, serving as a temporary strut or scaffolding against with
the mandible and the base of the skull develop until the temporomandibular joint takes
over this function in fetal life.
1

2. The articular disk is one of the first components of the joint to become
organizable from its earlier appearance, in the 6week old embryo. The disk is
associated with the mandibular component of the joint and seems to be a derivative of
the first branchial arch.
Number of investigators – Kjellberg (1904), Hapman and Woolard (1938),
Symmons (1952), Moffett (1957 believe the extension of the lateral pterygoid muscle
posteriorly between the temporal squama and the mandibular condyle to the malleus
contributes to the formation of the medial part of the articular disk. Other investigators
refer to this connection as the retrodiscal ligament.
Most synovial joints develop from blastemata. The temporomandibular joint,
like the joints of the clavicle is formed from discontinuous blastemata separated from
each other by a zone of undifferentiated mesenchyme in the embryo.
As the bastemata approach each other through growth of the condyle, the
intervening mesenchyme condenses in to layers of fibrous connective tissue, which
form the peculiar articular tissue seen in this joint.
During the twelth week the condylar growth cartilage makes its first
appearance and the condyle begins to develop a hemispherical articular surface.
By the thirteenth week the condyle and articular disk have moved up into
contact with the temporal bone. Only when such articular contact has been made to do
the joint cavities develop, the inferior space appearing first.
Before the disk actually becomes compressed between the condyle and the
temporal bone, the entire disk is vascularized.
Blood vessels from the terminal branches of the external carotid artery and the
associated veins enter the disk posteriorly and extend completely through it to
anastamose with branches coming in anteriorly from the pterygoid vascular plexus.
By the twenty-sixth week all the components of the temporomandibular joint
are present except for the articular eminence. Meckel’s cartilage still extends through
2

3. the Claserian fissure, but by the thirty-first week it has been transformed into the
sphenomandibular ligament.
The Claserian fissure is the opening between the squamous and tympanic parts
of the temporal bone through which Meckel’s cartilage passes into the middle ear in
the fetus. It becomes the squamo-tympanic fissure after birth.
I) Anatomy of the TMJ:
The TMJ consists of 4 main structures:
a) Condyle.
b) Squamous part of the temporal bone.
c) The articular disc.
d) Ligaments.
a) Condyle:
- The portion of the mandible which articulates with the cranium around
which movement occurs.
- From the anterior view, it has medial and lateral projections called
poles. Medial pole is more prominent than the lateral pole.
- Media – Lateral length  15-20mm.
Anterio-posterior width  8-10mm.
- The actual articulating surface of the condyle extends both anteriorly
and posteriorly to the most superior aspect of the condyle. The
posterior articulating surface is greater than the anterior articulating
surface.
3

4. - A given point on each condyle has a free but relatively limited
mobility along its cranial joint surface. this is called as “contact
movement surface” of the condylar point. It is about 10-12mm long
and 2-3mm broad.
- Contact movement surface of the incisal point is slightly over 11mm
deep (sagittal direction) and 20mm broad (frontal direction).
- The tooth bearing part of the mandible therefore has a complete
freedom of movement inside a relatively marrow but long space.
b) Squamus part of the temporal bone:
- Mandibular condyle articulates at the base of the cranium with the
squamous portion of the temporal bone. it is referred to as the
articular/glenoid fossa.
- Posterior to this fossa is the squamo-tympanic fissure which runs
medio-laterally.
- Immediately anterior to the fossa is a convex bony prominence called
the articular eminence. Steepness of this surface dictates the pathway
of the condyle when the mandible is positioned anteriorly.
- The posterior roof of the mandibular fossa is quite thin, indicating that
this area of temporal bone is not designed to sustain heavy loads. The
articular eminences however is composed of thick dense bone and is
more likely to tolerate such heavy forces.
c) The articular disc:
- Composed of dense fibrous connective tissue devoid of any blood
vessels or nerves.
- In the sagittal plane, it can be divided into 3 regions according to
thickness. The central area is the thinnest, called the intermediate
4

5. zone. The disc becomes thicker anteriorly and posteriorly with the
posterior zone, slightly thicker than the anterior zone.
- From an anterior view, the disc is more thicker medially that laterally,
which results in increased space between the condyle and the fossa
towards the medial aspect of the joint.
- The articular disc is attached posteriorly to a region of loose
connective tissue which is highly vascularised and innervated called
the retrodiscal tissue.
Superiorly  Superior retrodiscal lamina (elastic fibers) attaches the disc
to tympanic plate – Bilaminary zone.
Inferiorly  Inferiorly retrodiscal lamina (collagenous fibres) attaches
the inferior border of the disc to the posterior margin of the articulate
surface of the condyle.
- Anteriorly, the articular disc is attached to the capsular ligaments.
Superior attachment  anterior margin of the articular surface of the
temporal bone.
Inferior attachment  anterior margin of the articular surface of the
condyle.
- Articular disc divides the joint into 2 distinct cavities:
i. Superior cavity bordered by the mandibular fossa and
the superior surface of the disc.
ii. Inferior cavity bordered by the mandibular condyle and
the inferior surface of the disc.
5

6. d) Ligaments:
Classified as:
i. Functional ligaments: Collateral ligaments.
Capsular ligaments.
Temporomandibular ligament.
ii. Accessory ligament - Sphenomandibular ligaments.
Stylo-mandibular ligaments.
i. Collateral-ligament (discal ligaments):
- Attach the medial and lateral borders of the articular disc to the
poles of the condyle.
- They function to instruct the movements of the disc away from the
condyle.
- They are responsible for the hinging movement of the TMJ.
ii. Capsular ligament:
- The entire TMJ is surrounded and incompassed by the capsular
ligament.
- It is attached superiorly to the temporal bone along the borders of
the articular surfaces of the mandibular fossa and articular
eminence. Inferiorly it attaches to the neck of the condyle.
- It resists any medial, lateral or inferior forces that tend to separate
or dislocate the articular surfaces.
- A significant function is to encompass the joint and retain the
synovial fluid.
6

7. iii. Temporomandibular ligament (lateral ligament) 2 parts:
i) Outer oblique portion – it extends from the outer
surface of the articular tubercle and zygomatic process postero-
inferiorly to the outer surface of the condylar neck.
It resists the excessive dropping of the condyle, limiting the
extent of mouth opening. If the mouth was to open wider, the
condyle would need to move downward and forward across the
eminence. This change in opening movement is brought about by
the tightening of the TM ligament.
ii) Inner horizontal portion: extends from outer
surface of articular tubercle and zygomatic process and attaches to
the lateral pole of condyle and posterior part of articular disc. It
limits the posterior movement of the condyle and disc.
iii) Sphenomandibular ligaments: Arises from spine of
sphenoid and attaches to lingual. Does not have significant
limiting effects on the mandible.
iv) Stylomandibular ligament: Across the styloid
process and attaches to angle and posterior border of ramus of the
mandible limits excessive protrusive movement of mandible.
Neuromuscular aspect of the masticatory system:
The energy required to move the mandible and allow function of the
masticatory system is provided by the muscles. The most important of these
are the muscles of mastication each of which has a different function but all
act in a cooperative way to effect jaw movement.
However to produce adequate mandibular function, they must
collaborate with other muscle groups namely the suprahyoids, infrahyoids and
the post vertebral muscle groups.
7

8. I] Masticatory Muscles:
1. Masseter.
2. Temporalis.
3. Medial pterygoid.
4. Lateral pterygoid
II] Suprahyoid muscles:
1. Mylohyoid.
2. Geniohyoid.
3. Stylohyoid.
4. Digastric.
Their function is two fold:
- If the muscles of mastication, close the jaws and fix the mandible
in its position, the suprahyoid muscles will elevate the hyoid bone
and larynx which is attached to it by a membrane, which is
necessary for swallowing.
- If however the infrahyoids are contracted, the hyoid bone is made
stable and immovable. If the suprahyoids then contract, against
the secured hyoid bone the mandible will be retracted and
depressed. Its movement will be down and back.
III] Infrahyoid muscles:
1. Sternohyoid.
2. Omohyoid.
3. Thyrohyoid.
8

9. They mainly function to depress the hyoid bone and along with the
suprahyoid muscles stabilize the hyoid bone during function.
IV] The post vertebral muscles are also important in chewing and maintaining
functional balance. They form a continuous chain from the base of the skull to
the base of the spine. They are anti-gravity muscles which sustain functional
posture in relation to chewing.
Masseter Elevation
Protraction
Extreme lateral movements
Temporalis Principal positioner.
Elevator
Unilateral contraction leads to lateral movement on same
side
MP Elevation
Lateral positioning of mandible
Simple protraction
Sub activity dividing protraction and opening
LP Protrusion
Lateral movement (LP + MP + M + T)
9

10. BLOOD SUPPLY
Generally, all blood vessels in the vicinity of a joint contribute to its supply.
Thus joints are usually excellent sites for the development of a collateral circulation.
Its blood supply is derived from articular branches of the numerous arteries that make
up the terminal field of the external carotid artery.
LYMPHATIC DRAINAGE:
The lymphatic drainage of the joint has been described briefly by Tanasesco
(1912) who found lymph channels on each surface of the joint. These channels are
most prominent on the lateral and posterior surfaces. The lymphatic vessels on the
lateral surface drain into the preauricular and parotid nodes. On the posterior surface,
six or seven channels converge on the external carotid artery, fuse in to large trunks,
across the digastric muscle, and enter the submandibular nodes.
NERVE SUPPLY:
Auriculo temporal nerve.
Massetric nerve laterally.
Mechanics of mandibular movements:
Mandibular movements occur as a complex series of inter related 3-
dimensional rotational and translational activities. It is determined by
combined and simultaneous activities of both TMJ’s.
Two types of movements occur in the TMJ:
(i) Rotational.
(ii) Translational.
10

11. I) Rotational movements:
Rotation is the movement of a body about aits axis. Rotation occurs
when the mouth opens and closes around a fixed point or axis within the
condyles.
Rotation occurs in the inferior cavity of the joint between the superior
surface of the condyle and inferior surface of the articular disc.
Rotation of the mandible can occur in 3 reference planes around a point
called the axis. They are:
a) Horizontal axis of rotation:
- Mandibular movement around a horizontal axis of rotation is an
opening and closing motion. It is referred to as hinge movement
and the horizontal axis around which it occurs is referred to as
hinge axis.
- The hinge movement is the only example of mandibular activity in
which a pure rotational movement occurs.
- When the condyles are in the most superior position in the
articular fossa, and the mouth is purely rotated open, axis around
which movement occurs is the “terminal hinge axis” – to study in
detail.
b) Frontal (vertical axis of rotation):
Mandibular movement around the frontal axis occurs when one condyle
moves anteriorly out of the terminal hinge position with the vertical axis of the
opposite condyle remaining in the terminal hinge position.
11

12. c) Sagittal axis:
Mandibular movement around the sagittal axis occurs when one condyle
moves inferiorly while other remains in the terminal hinge position.
II) Translational movements:
It can be defined as a movement in which every point of the growing
defect has simultaneously the same velocity and direction.
Translation occurs within the superior joint cavity between the superior
surface of the articular disc and inferior surface of the articular fossa.
Border movements:
When the mandible moves through the outer range of motion,
reproducible desirable limits result, which are called as border movements.
Border movements can be described in 3 reference planes:
(i) Sagittal.
(ii) Horizontal.
(iii) Frontal.
(i) Sagittal plane border and functional movements:
In the sagittal plane, it has 4 distinct components:
a) Posterior opening border.
b) Anterior opening border.
c) Superior contact border. Occlusal and incisal surfaces
d) Functional  neuromuscular system
12
Determined by ligaments and
morphology of T.M.J.

13. a) Posterior opening border movements:
Occurs as two stage hinging movements. In the first stage, the condyles
are stabilized in their most superior positions in the articular fossae.
The most superior condyle position from which hinge axis movement
occur is called anterior relation. (Retruded contact position, terminal hinge
axis or ligamentous position).
In anterior relation, mandible can be rotated around the horizontal axis
to a distance of only 20-25mm as measured between the incisal edges of the
maxillary and mandibular teeth.
At this point of opening, the TMJ ligament tightens, after which,
continued opening results in an anterior and inferior translation of the
condyles.
This is the 2ns stage of the posterior opening border movements.
As the condyles translate, axis of rotation of the mandible shifts into the
bodies of the rami, most likely in the area of attachment of the
sphenomandibular ligament.
Maximum opening is reached when the capsular ligament will prevent
further movement of the condyles. This opening is in the range of 40-60mm
measured between the incisal edges of the Mx and Md teeth.
b) Anterior opening border movement:
When the mandible is maximally opened, closure accompanied by
contraction of the inferior lateral pterygoids (which keep the condyles
positioned anteriorly) will generate the anterior opening border movement.
Since the maximum protrusive position is determined in part by the
stylomandibular ligaments, as closure occurs, tightening of the ligament
produces a posterior movement of the condyles.
13

14. Condylar position is most anterior in the maximally open but no the
maximally protruded position.
c) Superior contact border movements:
Throughout this entire movement, tooth contact is present. It depends
on:
- Amount of variation between centric relation and maximum
intercuspation positions.
- Steepness of cuspal inclines of posterior teeth.
- Amount of vertical and horizontal overlap of anterior teeth.
- Lingual morphology of maxillary anterior teeth.
- The general inter arch relationships of the teeth.
- The initial contact in terminal hinge closure (centric relation
occurs between the mesial inclines of a maxillary tooth and the
distal inclines of the mandibular tooth.
- When muscular force is applied to the mandible, a supero-anterior
movement or shift will occur until the intercuspal position is
reached. This slide is present in 10% of the population and is
approx 1.25mm ±1mm.
- When the mandible is protruded from maximum intercuspation
contact between the incisal edges of the mandibular anterior tooth
and lingual inclines of the maxillary anterior teeth results in an
antero-inferior movement of the mandible.
- This continues until the maxillary and the mandibular teeth are in
an edge to edge relationship, at which time a horizontal pathway
is followed.
14

15. - As the incisal edges of the mandibular teeth pass beyond the
incisal edges of the maxillary teeth, the mandible moves in a
superior direction, until the posterior teeth contact.
- The occlusal surfaces of the posterior teeth, then dictate the
remaining pathway of the maximum protrusive movement which
joins with the most superior position of the anterior opening
border movement.
d) Functional movements:
- They usually take place between the border movement and
therefore considered free movements.
- Most functional activities require maximum intercuspation and
therefore typically begin at and below the intercuspal position.
- When the mandible is at rest it is found to be located approx-2-
4mm below the intercuspal position. This position has been called
cervical rest position. This position is variable.
- The myostatic reflex is active at this position, and the teeth can be
quickly and effectively brought together for immediate function.
Postural effects on functional movements:
a) Head position is erect: Postural
position of the mandible is 2-4mm below the intercuspal position
(elevator muscles contact  mandible goes directly to ICP).
b) Head positioned 45° upward:
postural position of the mandible will be altered to a slightly retruded
position. This change is related to the stretching and elongation of
various tissues that are attached to and support the jaws (elevation
15

16. muscles contact – path of closure is slightly posterior to path of closure
in erect position).
c) Head positioned 30° downward
(alert feeding position). If the elevator muscles contact with the head in
this position, the path of closure will be slightly anterior to that in
upright position. (Elevator muscles contract – path of closure is slightly
anterior to path of closure in erect position).
Horizontal plane border movements:
- Gothic arch tracer is used to record mandibular movements in the
horizontal plane.
- Consists of recording plate attached to the maxillary teeth and a
recording stylus attached to the mandibular teeth. As the mandible
moves, stylus generates a line on the recording plate that
coincides with this movement.
- The mandibular movements when viewed in a horizontal plane are
rhomboid-shaped and has 4 distinct component movements plus a
functional movement.
a) Left lateral border.
b) Continued left lateral border with
protrusion.
c) Right lateral border.
d) Continued right lateral border with
protrusion.
a) Left lateral border:
16

17. With the condyles in CR position, contraction of the right inferior lateral
pterygoid, will cause the right condyle to move anteriorly and medially. If the left
inferior lateral pterygoid stays relaxed the left condyle will remain situated in CR
and the result will be a left lateral border movements.
b) Continued left lateral border movements with protrusion with the
mandible in the left lateral border position contraction of the left inferior
lateral pterygoid muscle along with continued contraction of the right
inferior lateral pterygoid muscle will cause the left condyle to move
anteriorly and to the right. This causes a shift in the mandibular midline
back to coincide with the midline of the face.
c) Right lateral border movement:
Once the left border movements have been recorded the mandible
is returned to CR and the right lateral border movements are recorded.
- Contraction of the left inferior lateral pterygoid muscle will cause
the left condyle to move anteriorly and medially.
- If the right inferior lateral pterygoid muscle stays relaxed, the
right condyle will remain situated in the CR position. The
resultant movement will be right lateral border movement.
d) Continued right lateral border movement with protrusion contraction of
the right inferior lateral pterygoid muscle along with the continued
contraction of the left inferior lateral pterygoid muscle will cause the
right condyle to move anteriorly and to the left.
- Since the left condyle is already in its maximum anterior position,
the movement of the right condyle to its maximum anterior
position will cause the shift in the mandibular midline back to co-
incide with the midline of the face.
e) Functional movements:
17

18. As in the sagittal plane, functional movements in the horizontal
plane most often near the intercuspal position. During chewing, range of
jaw movements begins same distance away from MICP but as food is
broken down into smaller particles, jaw action moves closer and closer to
ICP.
III) Frontal (vertical) border and functional
movements:
When mandibular motion is viewed in the frontal plane, a should like
pattern can be seen that has 4 distinct movement components:
a) Left lateral superior border.
b) Left lateral opening border.
c) Right lateral superior border.
d) Right lateral opening border.
The movement in the plane has not been traditionally traced, on
understanding of them is useful in revisualizing mandibular activity 3-
dimensionally.
a) Left lateral superior movement:
When the mandible in maximum intercuspation a lateral movement is
made to the left. A recording device will disclose an inferiorly concave path
being generated.
The precise mixture of this path is primarily determined by the
morphology and inter arch relationships of the maxillary and mandibular
teeth that are un contact during this movement.
Of secondary influences are the condyle-disc-fossa relationships and
morphology of the working or rotating side TMJ.
18

19. b) Left lateral opening border:
From the maximum left, lateral superior border position on opening
movement produces a laterally convex path. As maximum opening is
approached, the ligaments lighter and produce a medially directed
movement that causes a shift in the mandibular midline to coincide with the
midline of the face.
c) Right lateral superior border movements:
Once the left frontal border movements are recorded the mandible is
returned to maximum intercuspation from this position a lateral movement
is made to the right that is similar to left lateral superior border movements.
d) Right lateral opening border movements:
From the right lateral superior border position on opening movement
produces a laterally convex path similar to that of the left lateral opening
border movements.
e) Functional movements:
As in other planes, functional movements in the frontal plane begin and
end and the intercuspal position.
During chewing, the mandible drops directly inferiorly until the desired
opening, is achieved. It then shifts to the side the bolus is placed and rises
up. As it approaches maximum intercuspation, the bolus is broken down
between the opposing teeth. It the final mm of closure the mandible quickly
shifts back to the ICP.
Envelope of motion (given by Posselt):
By combining mandibular border movements in all 3 planes a 3-D
envelope of motion is produced. This represents maximum range of movement
of the mandible.
19

20. The superior surface of the envelope is determined by tooth contacts.
Other borders are primarily determined by ligaments and joint anatomy.
20

21. REFERENCE POINTS
POSTERIOR POINTS OF REFERENCE
The arbitrary method is an accepted technique for locating the mandibular
hinge axis. Although many studies have compared various arbitrary hinge axis points
with kinematic location, there is no consensus as to which arbitrary point most closely
and consistently lies on or near the kinematic axis.
Various arbitrary hinge axis points:
Name Location
Denar 12mm anterior to posterior border of tragus and 5mm inferior to
line extending from the superior border of tragus to OCE.
TSN 12mm anterior to center of TAM and 2mm Frankfort plane.
12mm anterior to center of EAM and 2mm inferior to portion-
canthus line.
Whip-Mix According to the design of their ear-bow in anteroposterior
direction at anterior wall of EAM and in superior-inferior
direction approximately at level of most prominent point of
21

22. posterior border of tragus.
Prothero On line from superior margin of EAM to OCE interecting with
line 13 edge of EAM according to Rachey condyle marker.
Barndrup-
Wognsen
12mm anterior to most prominent point of posterior border of
tragus on line from it to OCE.
Beryon 13mm anterior to posterior margin of tragus online from the
center of tragus to OCE.
Gvst 13mm anterior to anterior margin of EAM on line from superior
margin of EAM to OCE.
Bergstrom 10mm anterior to center of spherical insert of his face-bow and
7mm below Frankfort plane.
22

23. ANTERIOR POINTS OF REFERENCE
Three points in space determine the position of the maxillary cast in an
articulator the dentist is most frequently concerned with selecting the posterior two of
the three reference points. The selections of the anterior point of the triangular spatial
plane determine which plane of the head will become the plane of reference when the
prosthesis is being fabricated. The dentist can ignore but cannot avoid the selection of
an anterior point. The act of affixing a maxillary cast to an articulator relates the cast
to the articulators hinge axis, to the anterior guidance, and to the mean plane of the
articulator. The act achieves greater importance by the use of a constant third point of
reference. When three points are used the position can be repeated, so that different
maxillary casts of the same patient can be positioned in the articulator in the same
relative position to the end controlling guidances.
SELECTION OF AN ANTERIOR REFERENCE POINT.
In selecting the reference plane, the dentist should have knowledge of the
following anterior points and the rationale for selection of each.
1. Orbitale. In the skull, orbitale is the lowest point of the infraorbital rim. On a
patient it can be palpated through the overlying tissues and the skin One
orbitale and two posterior points that determine the horizontal axis of rotation
will define the axis-orbital plane. Relating the maxillae to this plane will
slightly lower the maxillary cast anteriorly from the position that would be
established if the Frankfort horizontal plane were used. Practically, the axis-
orbital plane is used because of the ease of locating the marking and because
the concept is easy to teach and understand.
23

24. 2. Orbitale minus 7mm. The Frankfort horizontal plane passes through both poria
and one orbital point. Because potion is a skull landmark-, Sicher recommends
using the midpoint of the upper border of the external auditory meatus as the
posterior cranial Iandmark on a patient. Bergstrom's arcon articulator
automatically compensates for this error by placing the orbital index 7mm
higher than the condylar horizontal axis.
3. Nasion minus 23mm. According to Sicher, another skull landmark, the Nasion
can be approximately located in the head as the deepest part of the midline
depression just below the level of eyebrows. The Nasion guide, or positioner,
of the Quick-mount face-bow, which is designed to be used with. the Whip-
Mix articulator, fits 'into this depression.
24

25. 4. Incisal edge plus articulator midpoint to articulator axis-horizontal plane
distance. Guichet has emphasized that a logical position for the casts in the
articulator would be one which would position the plane of the articulator. A
deviation from this objective may position casts high or low relative to the
instrument's upper and lower arms. The effects of these high or low positions
may be inaccurate occlusal relationships due to dimensional changes in the
artificial stone or plaster used for cast-mounting purpose
In accordance with this concept, the distance from the articulator's mid-
horizontal plane to the articulator's axis-horizontal plane is measured. This same
distance is measured above the existing or planned incisal edges on the patient, and its
uppermost point is marked as the anterior point of reference on the face. The inner
canthus is used because it is an accessible, unchanging landmark on the head.
With this technique the face-bow transfer will carry the predetermined posterior
points of reference and this anterior point of reference to the articulator's axis-
horizontal plane.
5. Alae of the nose. A part of many complete denture techniques is to make the
tentative or the actual occlusal plane parallel with the horizontal plane. A line
from the ala of the nose to the center of the auditory meatus describes the
Camper's line. Augsburger concluded, in a review that the occlusal plane
parallels this line with minor variations in different facial forms.
25

26. Other intraoral landmarks, esthetics, consideration for the residual ridges, and
tongue and cheek guidance factors may alter the final occlusal plane.
Also when relating the maxillary case in space to a horizontal reference plane,
the relating planes are usually thought of and being viewed from the lateral aspect.
When viewed from the frontal aspect, there are reference lines as well. The hinge
line,-- the interpupillary line, and a transverse line across the occlusal surfaces are
three common frontal-view reference lines. The later two are observed in the
articulator. Generally these three lines are not parallel.
This is caused by posterior hinge reference points that are not equidistant from
the eye pupas. An occlusal plane that is parallel to the interpupillaly line will be
pleasing to the eye of the viewer. It cannot be guaranteed that an occlusal plane
parallel to the hinge will have the same pleasing appearance.
26

27. VARIOUS SCHOOLS OF THOUGHT
From early experiments there have evolved four main schools of thought
regarding the horizontal axis. They are as follows.
Group I. Absolute location of the axis.
There are those who believe that there is a definite transverse axis and it should
be located as accurately as possible. McCollum, Stuart &Lucia believe that the hinge
axis is a component of every masticatory movement and cannot be disregarded. The
investigators who endorsed this concept have established a repeatable point of
reorientation from which the above information and relationships may be obtained.
Group II: Arbitrary location of the axis.
The second group includes those who believe that the arbitrary location is not
worth the added effect. Craddock for one stated that the search for the axis, in addition
to being troublesome, is- of no more than academic interest. Though, this group
believed in location of the axis.
Group III Nonbelievers in the transverse axis locations.
Then, there is a third group who believes it is impossible to locate the terminal
hinge position with accuracy. Lauritzen and Watford confirm this, and Kurth and
Feinstein, using an articulator and a range of 2mm. That could be considered a point
of rotation or non-movement. The opening and closing movement was limited to
approximately 10 to 11 degrees. Borgh and Posselt could not record the axis on a
modified Hanau H articulator without errors. The errors amounted -to 1 to 5mm. At a
10 to 15 degree opening.
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28. Beck has proposed another reason for doubting the validity of the hinge axis location.
He claims that there can be many compensating movements of the condyle other than
pure rotation, and that these compensating movements are movements of translation
and side shift that are integrated with the movement of rotation. He concludes that the
opening and closing hinge movement of the mandible, together with its fragmentary
movements, cannot be repeated by the opening and closing movements of an
articulator, which is about one axis only. Therefore, an arbitrary terminal hinge
position would or could be just as accurate as one located with a kinematic face-bow.
Group IV Split axis rotation
These are believers of the Transographic theory. They believe in the "split axis" with
which each condyle rotates independently of the other.
Slavens states "by definition, an axis is always a line, never a point. Again, by
definition, an axis is invariably perpendicular to the path or plane of rotation It
controls. That means that the transverse axis of each joint is a line and both of these
are perpendicular to the same plane of opening and closing rotation. The significance
of the fact that these two transverse axes are never symmetrically positioned in the
same head becomes 'inescapable. Being perpendicular to the same plane of rotation,
they are parallel to each other even though asymmetrically positioned and, by
definition parallel lines never meet".
SINGLE AXIS OR MULTIPLE
About 1950, Dr. William Bransted, Dr. Raymond Gravy and D r. Robert Okey
conducted an experiment, which should the presence of a single axis.
Dr. Arne Lauritzen., working with a study group in 1957, repeated the same
experiment and arrived at the same conclusion.
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29. In 1959 the committee of the greater New York academy of prosthodontics repeated
this experiment and concluded that there was only one transverse axis through both
condyles. Later Lucia also conducted extensive experiments and concluded the
presence of a single axis.
McCollum And Stuart stated that only when a single THA exits, can the CR
registrations be made at an increased VD of occlusion..
The Transographic concepts postulated the existence of 2 materially
independent, non-collinear axes. Trapozanno & Lazzari support this theory. Later
Wienberg 7' conducted experiments to support this Transographic theory.
They concluded that multiple axes exist and their presence opens the Field for
interesting conjecture. Aull discussed the impossibility of the presence of a split HA,
or of a different HA for each condyle acting simultaneously. Harry page in his
experimentation in 1979 also supported the above views.
They don't defy the basic concept but view the rotational movement as occurring in a
manner different from that which is commonly thought of as occurring in the type of
movement. It is a tangential type of hinge movement occurring between a movable
extension and a fixed surface (condyle and glenoid fossa).
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30. THE HINGE AXIS AND CENTRIC RELATION
To secure a centric inter-occlusal record,, we attempt to "freeze" the terminal hinge
closure at a convenient vertical opening. Without the hinge axis, we would be unable
to secure an accurate centric inter-occlusal record because to obtain such a record the
recording medium must not be penetrated by the teeth or the occlusion rims. In order
to -avoid penetration (atleast in dentulous cases), we must obtain our centric
interocclusal record in an open relationship, and if we were not in the same arcs of
closure, our efforts would be useless. It is impossible to check a centric inter-occlusal
record without an axis mounting.
LOCATION OF THE HINGE AXIS
Different methods have been used to locate and transfer the hinge axis to the
articulator.
The first actual kinematic location was evolved through the California Gnathologic
society under the leadership of McCollum and credit for the idea of the mechanical
location of an axis was given to Harlan. The first location employed a modified Snow
face-bow and consumed as much as 8 hours.
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31. In 1957 Posselt analyze the transverse hinge movement by geometric construction
from profile roentgenograms, axis points recorded by means of kinematic face-bow
and checked by profile roentgenograms and also by Gnathothesiometric
measurements. The Gnathothesiometer a device which was proved useful for the
measurement of the position of the mandible. This apparatus allows measurements (at
three points) in the three main planes on freely movable casts of the lower law.
In 1970 Knapp developed a measuring device using 6 potentiometers as sensors.
Long in 1970 used a intraoral device to locate the transverse hinge axis and he used a
Buhnergraph to verify the records. He encountered errors in either location or its
transfer to the articulator, which he corrected by moving the recording shaft to the
Buhnergraph and until the records made by it coincides.
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32. The computer graphics simulation was developed in 1978 to display the effects of
mandibular movement parameters of both the maxillary and mandibular teeth in the
occlusal plane, which can be graphically observed in the horizontal plane.
In 1979 Pantographic tracing using Denar Pantograph was used by Jackson to record
the mandibular movement.
Beard and Clayton in 1981 devised a modified hinge axis locator which was very
similar to that used by Trapozzano and Lazzari but has multiple styli. The results
obtained by this were supporting the single axis theory.
Hobo et al in 1983 developed a new electronic measuring device capable of measuring
6 degrees of freedom with an accuracy ±0.06mm.
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33. In the year 1988 Getz" et al used a double recording styli (at a distance of 2-4 inches
from estimated axis area) to identify the true axis of rotation.
In 1992 the terminal hinge axis was located on the individuals using the Axiotron, a
computerized Axiograph by Kinderknecht et al. In the later years there have been very
few experiments, which used any newer techniques.
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34. TECHNIQUE FOR LOCATING THE HINGE AXIS
The location and transference of the hinge axis are not very difficult procedures, but
they must be carefully carried out with great care because they form the foundation for
many other procedures.
A reference plane or clutch is cemented to the lower teeth with Truplastic. Graph-
lined flags are placed on the side of the face over the condyle areas to eliminate any
skin movement distraction. These flags may be attached to the maxillae by means of a
crossbar and a maxillary clutch, or they may be held in place by a head frame or other
contrivance. A crossbar is attached to the lower reference plate or clutch.
Adjustable side arms are placed on the lower. cross bar with the styli in the vicinity of
the condyles. The patient must now be instructed *in the hinge type of movement. The
pivoting part of the compass is on the center of rotation in the patient's condyle. The
stylus point is the tracing part of the compass. If we get the tracing point exactly on
the pivoting point, there will be no arcing on the tracing point. As we-approach the
center, the arcs will become smaller and little more arcing is required to magnify the
arc.
If there is any arcing we continue adjusting until it disappears completely. The axis
center must -be located on each. side. What we are locating is the hinge action on the
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35. side of the face. It is a point on the hinge axis and not the actual center of rotation. The
actual center is approximately 10 or 11 mm medial to this location.
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36. POSSIBLE NEED FOR BITE PLANE THERAPY
The patient naturally opens downward and forward combination of rotation and
translation. We must separate the rotation from the -translation so that we can locate
the center of vertical opening. In addition,, this opening and closing must be
accomplished in the terminal hinge position, for here we can get repeated concentric
arcs that will permit us to locate their center.
If a patient has difficulty in executing a pure hinge movement, it may be. necessary to
train him in this abnormal 'opening and closing movement. Training can be
accomplished by using the jig.
MARKING THE AXIS LOCATION ON THE PATIENT
When we are satisfied that we have located these points on the axis the marking
medium, Suchn as an indelible pencil, is rubbed on the end of the stylus. We make
sure the patient is in the terminal hinge position and then have him move his head out
of the headrest, making sure that he does not also move out of the terminal hinge
position. The stylus is gently pushed against his face to transfer the point to the skin.
These marks are made permanent by using a special needle and a little pink marking
dye -sulfide of mercury.
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37. Gordon has presented an alternate technique for recording the located axis point by
non-tattoing method.
SELECTION OF A FACE-BOW
From a purely theoretical point of view an ordinary face-bow such as a Snow or
Hanau can be used to locate the hinge axis. To attempt to use either one of them in
actual practice, however is impossibility.
It is far easier and more accurate to use a fully adjustable face-bow (i.e. one with arms
that can be independently adjusted by means of micrometer screws) for both the axis
locations and the transfers. By means of a face-bow transfer and the mounting frame
the upper cast can be properly mounted to the axis of the patient.
There are two types of face bow, the kinematic and arbitrary. The kinematic is used to
locate the true terminal hinge axis. The arbitrary facebow is the one generally used in
the construction of complete dentures and is based on average computations of an axis
opening of the jaw. It is simple to use and relatively accurate.
Arbitrary axis for Hanau face bow
When using a Hanau face bow, a Richey condylar marker is used to scribed an arc
about 13 mm anterior to the external auditory meatus.
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38. Arbitrary axis for Whip - Mix face bow
Locating the arbitrary axis is not necessary when using the Whip-Mix articulator. The
insertion of plastic ear pieces into the external auditory meatus automatically locates
the face bow in the proper position.
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