seminar 3 face bows and articulation
TRANSCRIPT
FACE BOWS AND ARTICULATION
INTRODUCTION
Early articles on prosthetic dentistry in which the face -bow is mentioned
are, broadly of two kinds those its use is insisted on and those in which it is
dismissed as a useless if harmless toy. Whereas this subject which used to be
hotly debated by hostile schools of thought, has now lost its emotional content.
The crusading spirit and the intolerance have evaporated. This is not to say that
everywhere reason how prevails; on the contrary, the issue has never really been
decided.
Authors of modern textbooks and of articles in current periodical literature
who mention or describe the use of a face-bow do so as a matter of course; they
assume acceptance of the face-bow and no longer bother to insist on its use or
attempt describe what it achieves. With equal confidence, those in the other
camp omit all reference to it. This they do without embarrassment or apology, the
instrument is considered unworthy of mention.
DEFINITION
The Glossary of Prosthodontic Terms, 7th edition, the Academic of
Prosthodontics 1999:
Face-bow: A caliper-like instrument used to record the spatial relationship
of the maxillary arch to some anatomic reference point or points and then
transfer this relationship to an articulator; it orients the dental cast in the same
relationship to the opening axis of the articulator. Customarily the anatomic
references are the mandibular condyles transverse horizontal axis and one other
selected anterior point: called also hinge bow.
Ear bow: An instrument similar to a face-bow that indexes to the external
auditory meatus and then registers the relation of the maxillary dental arch to the
external auditory means and a horizontal reference plane. This instrument is
used to transfer the maxillary cast to the artilulator. The earbow provides an
average anatomic dimension between the external auditory meatus and the
horizontal axis of the mandible.
Kinematic face-bow: A face bow with adjustable caliper ends used to
locate the transverse horizontal axis of the mandible.
EVOLUTION
In the 1860's, it was realized in complete denture prosthesis that it was
important to mount the plaster casts in the articulator in a given positional relation
to the condylar mechanism. one of the proposers of this theory was Bonwill who
concluded, from the examination of 4000 dead and 6000 'living jaws' that the
distance from the center of each condyle to the median incisal point of the lower
teeth is 10.0 centimeters. He used this standard for mounting casts on his
articulator. Bonwill did not mention, however, at what level the occlusal plane
should be placed in relation to the condylar mechanism. It appears that he
mounted his casts midway between the upper and lower members of the
articulator, and deemed this quite satisfactory.
An English dentist by the name of Balkwill unknowingly improved upon
Bonwill's ideas. Unknowingly, because it is doubtful as to whether Balkwill was
acquainted with Bonwill or his theories. In 1866, Balkwill demonstrated an
apparatus with which he could measure the angle formed by the occlusal plane
of the teeth, and a plane passing through the lines extending from the condyles
to the incisal line of the lower teeth. According to his investigation, this angle
termed the "Balkwill angle" had an average measurement of 22.0 to 30.0
degrees. He could also determine the approximate distance from the each
condyle to “the front of the gums". These were the measurements that he
subsequently used for mounting plaster casts in an apparatus it is assumed
closely corresponding to an articulator.
It appears that the position that Balkwill achieved with his casts on the
articulator was much more accurate than what Bonwill's method had achieved. It
is unfortunate, however, that Balkwill's theories were quickly forgotten, and it took
until the turn of the century for these theories to be rediscovered.
Another mechanism for localizing the plaster casts in the articulator was
constructed by Richmond S.Hayes in 1886. This apparatus, know as the 'Hayes
Caliper," did not represent any particular progress in the solution of these
problems. Only the median incisal point was localized in relation to its distance
from the two condyles, no control of the proper orientation of the occlusal plane
was recognized.
Walker then invented the 'Clinometer' in the 1890's, which would have
been capable of obtaining a relatively good value for the position of the lower
cast in relation to the condylar mechanism, much better than with all the previous
instruments. Its main disadvantage, however, was that it was a very large and
complex device. Unfortunately, Walker only used his instrument for measuring
the inclination of the condyle path, and he appears not to have expanded on the
possibilities of using the instrument as a face bow. His technique for mounting
casts on an articulator was according to Bonwill's method.
Several years later, around the turn of the century, Gysi constructed an
instrument for registering the condylar path and did employ his device as a face
bow. At about the same time that Gysi produced his instrument, Snow
constructed an instrument that eventually became the prototype for all present
day face bow designs .In 1953, Brabdrup - Wognsen stated that, “we are justified
in stating that Snow's face bow inspite of its very simple construction was epoch
making in prosthetic dentistry". Since the introduction of Snow's face bow in
1907, no fundamental changes have been made in the face bow. Snow
determined the location of the plaster casts in the articulator, not only with regard
to the distance of the median incisal point from the condyles, but also all were the
other points on the occlusal plane given their correct position in relation to the
condyles.
Although this instrument solved many of the problems that previous
models did not address, all factors still were not address; all factors still were not
taken into account. It was also necessary to ascertain at what level in the
articulator the occlusal plane should be placed. An average level was placed on
many articulators to deal with this problem. hanau placed a groove on the incisial
guide pin. in complete denture prosthesis, the inferior border of the maxillary
occlusion rim is placed on a level with this groove thus placing the occlusal plane
about 3.5 cm below a horizontal plane passing through the intercondylar shaft.
interestingly, his was Balkwill's previously introduced average value position.
Still, this does not allow for individual deviations which may naturally
occur. snow attempted to individualize the location of the occlusal plane in this
third dimension by affixing his bite fork in the upper occlusion rim in such a way
that with the rim in the patient’s mouth, the handle was parallel with a plane
extending from the button of the glenoid fossa and passing through the anterior
nasal spine. since this plane is not visible clinically, it was noted that it
approximates the line from the superior border of the tragus of the ear to the
inferior border of the ala of the nose. This plane is commonly referred to as
Camper's line (in Europe) or the Broomwell plane (American literature). Snow
then placed his bite fork horizontally when the casts were mounted on the
articulator.
Another such plane was described by Gysi which he termed " protetische
Ebene" (the prosthetis plane), which travels from the inferior border of the tragus
of the ear to the inferior border of the ala of the nose. This line is only slightly
different from Camper's line and allows for a shallower occlusal plane.
Wadsworth employed yet another plane, which he described as extended from
the condyle area and running at right angles to a line that connects the most
prominent points of the chin and forehead.
The next plane which is important to note, is one that corresponds to the
Frankfort horizontal plane. Utilizing the Snow face bow a pointer is attached that
has its end touching the lowest border of the infraorital rim. When mounted on
the articulator, the end pointer is placed on a level with the intercondylar shaft.
this pointer is now termed the infraorbital pointer, and the location to which it is
pointed (infraorbital rim, infraorbital foramen or nasion utilized with the whip mix
facebow) has been termed the anterior reference point or third point of reference.
This method can be made even more complete by employing other
measures. After the position of the patient’s condyles is determined, the following
method is used to find the condylar axis. On a line extending from the tragus of
the ear to the canthus of the eye, a point is marked 13.0 mm anterior of the
posterior margin of the most prominent point of the tragus. The presumed
transverse horizontal axis is assumed to pass through these points which
termed, the approximately determined condyle points, or later called Beyron's
point. Smaller opening movements of the mandible, in the form of pure rotation,
are assumed to take place around the transverse horizontal axis. however, it was
later determined from investigations by Beyron that the center of the condyle is
not always situated inside this approximately determined point, and other
investigations have shown that the position of the axis of rotation does nor pass
through the centers of the condyles. Beyron's investigations showed that the
relationship of this axis and the condylar points rarely coincide, but that they are
nevertheless very close to each other, and offer little clinical consequence.
Beyron's point has come to be the main reference point to indicate the
arbitrary and is the theory behind the use of arbitrary facebows, specifically
earbow facebows.
The format of Beyron's experiment to test this concept was as follows:
A modification was made to a Snow facebow, in which the bite fork was
removed from the stem that attached to the horizontal bow of the facebow. a
custom splint like device, much like a removable partial denture frame work, was
fabricated for the mandibular arch of the subject. After fitting the frame work, it
was then soldered to the bite fork stem.
Cardboard disks were then attached to the patients face in the location of
each condyle. The modified bite fork was inserted into the patient’s mouth, and
the facebow attached. Styli were placed on the facebow in the condyle region,
and the patient was gently guided to perform only hinge movement. the markings
that were made on the cardboard disks were at first small arcs, but after
adjustment of the location of the styli, evolved into specific points, which
indicated the precise location of the rotational axis of the mandible, or transverse
horizontal axis. His investigation determined that the location of these axis points
were, most commonly, on a line drawn from the center of the tragus of the ear to
the canthus of the eye, and the axis is located 13.0mm anterior to the posterior
margin of the tragus.
CLASSIFICATION OF FACE BOWS
1. Arbitrary facebow
fascia facebow
earpiece facebow - with orbital indicator
with nasal relator
2.Kinematic facebow
USE
Orient the maxillary cast to the articulator in the same relationship to the
opening and closing axis of the articulator as exists between the maxilla and the
opening and closing axis in the temporomandibular joints.
When the casts is oriented to the articulator, the facebow retains the cast
in its correct relation until it is attached to the upper member with plaster.
WHEN TO USE? THE FACEBOW SHOULD BE USED WHEN
Cusp form teeth are used
Balanced occlusion in eccentric position is desired
A definite cusp fossa or cusp tip to cusp inclination is desired
Interocclusal check records are used for verifications for jaw positions.
The occlusal vertical dimension is subject to change, and the relations of
the tooth occlusal surfaces are necessary to accommodate the change.
When there is significant error in antroposterior, lateral, vertical relations.
To determine the position of the real condyle axis of motion.
Accurate mounting of casts in the articulator, both in relation to the
position of the condyles and to certain points on the head.
ADVANTAGES FOR USING A FACE BOW
It permits a more accurate use of lateral rotation points for the
arrangement of teeth.
It aids in securing the natroposterior cast position with relation to the
condyles of the mandible.
It registers the horizontal relationship of the casts quite accurately, and
this assists in correctly locating the incisal plane.
It is an aid in the vertical position of the cast on the articulator.
This face bow transfer will be exact in the positional relation of the casts
and, in addition, will permit interposing wax for check bites without
producing the usual inaccuracy. this fact is of great advantage in complete
dentures and of special advantage in bite opening cases.
The face bow transfer allows a more accurate arc of closure on the
articulator when the interocclusal records are removed and the articulator
is closed.
FACE BOW NOT NECESSARY
When monoplane teeth are arranged on plane in occlusal balance and the
mandible is in the most retruded relation to the maxillae at an acceptable
vertical dimension of jaw separation.
No alterations of the occluding surfaces of the teeth that would necessitate
changes in the vertical dimension of the occlusion originally recorded.
No inter occlusal check records that would be at a different vertical
dimension from that in the original interocclusal record.
When articulators that are not designed to accept a face bow transfer are
used in denture procedures.
When theses conditions are analyzed, several factors must be considered-
It is questionable if one occlusal form of posterior tooth is indicated for all
patients.
Electromyographic, laminographic, cinefluroscopic and mechanical
methods of studying the contacts of the occluding surfaces of the teeth
and muscle function indicate that teeth do make contact when the jaws
are eccentrically related.
Changes do occur in the vertical dimension of occlusion as a result of
waxing, flasking, processing, and mounting procedures. resorption of the
bone and changes in the soft tissues that form the basal seat for the
dentures alter the vertical dimension of occlusion.
Use of interocclusal check records to verify articulator mountings.
The occluding surfaces of the teeth are altered to correct for changes in
the vertical dimension of occlusion.
There is no scientific proof that the errors when the face bow is not used
are within the acceptable physiologic range in all individuals.
When an articulator with rotational center that can be adjusted to confirm
to the rotational centers to the mandibular movements is used, the face
bow in an accurate method of relating the casts to these centers.
A universal jig is more convenient for mere cast mounting. But to eliminate
errors and to be reproducible in the same subject face-bow is used.
A face-bow does not capture and transfer with any accuracy the important
head asymmetries. Anatomic asymmetric axis positions can lead to the
inaccurate use of conventional face-bows. This can result in improperly canted
incisal and occlusal planes.
KINEMATIC FACE-BOW VS ARBITRARY FACE-BOW
There are essentially two kinds of face-bows in use today. These are the
empirical or arbitrary or anatomical face-bow and the kinematic or physiological
or hinge face-bow. The kinematic facebow will locate the opening axis
physiologically with gnathologic procedures accurately.The arbitrary face - bow
locates the opening axis with the help of anatomical landmarks. The arbitrary
face-bow centers of rotation are located 13mm anterior to the auditory meatus on
the line toward the outer canthus of the eye. 75% of the arbitrary axis locations
with the (arbitrary face-bow) will be within 6mm of the kinematic centre of
rotation.
The kinematic method requires more elaborate equipment and the
technique involved is more time consuming. The advantage of the kinematic
face-bow appears to be theoretical than real, this can be used in fixed partial
prosthesis where the actual opening axis is required. When used correctly, if of
proved value, but that is practical application the arbitrary technique of transfer
as advocated by Hanau with the model C face-bow is acceptable.The simplest
form of orienting the cast to the articulator is the arbitrary method. The arbitrary
method of locating the centre of condylar rotation is acceptable if the technique
includes palpation of the condyles to check the accuracy of the arbitrary method.
EAR FACE-BOW VS FASCIA FACE-BOW
The ear face-bow has ear plugs at the condyle ends of the face-bow.
these ear pieces are placed in the external auditory meatus (posterior reference
points) inward, upward and anteriorly to hit the bony point and this stabilizes and
nasion as the anterior reference point. The ear face-bow technique has clear
advantages over the most widely used method of arbitrary location. The
accuracy, speed of handling, and simplicity of orienting maxillary casts with the
ear face – bow are recommendations for its use in many routine restorative
procedures.
These fascia or snow type face-bow come into contact with the skin on the face,
some problems are:
The condylar locator rods at their point of contact with the skin are so wide
that they cover all about very large facial markings and make the accurate
location.
The rods must be centered on the patient if an articulator without condyle
extension pins is used. This procedure usually requires assistance and is
often frustrating and time consuming.
The wrench assembly for both the face-bow fork and the orbital pointer
locks require some measure of force in tightening to assure security which
in turn nearly always results in some relocation of the condylar rods.
The orbital pointer itself may result in some discomfort or actual soft tissue
damage when used carefully or by inexperienced dentist.
There is an average inconsistency of 7.1mm at the level of condyles
between the Frankfort horizontal plane established cephalometrically and
the orbital plane established by Hanau technique. This error when
transferred to the articulator may result in maxillary cast, which are
mounted too low in the articulator, possible leaving insufficient space for
mandibular cast mounting.
HINGE AXIS
Synonymous terms: Terminal hinge axis, Transverse hinge axis, Transverse
horizontal axis.
Hinge axis is a horizontal axis around which the condyles rotate during
opening and closing movement upto a range of 20-25mm. It is the horizontal or
transverse axis where a pure rotation of condyles takes place prior to translation
of the condyle. The left and right centers where condyle exhibits pure rotation is
known as hinge axis point. An imaginary line that passes horizontally /
transversely through the rotation centers of the left and right condyle is known as
Transverse horizontal axis or transverse hinge axis. Since the rotation of
condyles occur when the mandible is in its terminal retruded centric relation
position, it was known as terminal hinge axis. Today with the changing concept of
centric relation, viz, anterior-superior bracing, the term transverse horizontal axis
is preferred to terminal hinge axis. The discrepancy of hinge axis between RUM
position and anterior – superior opposition is 0.2mm (Hobo).
Pure rotation of condyles take place in the first 10-13 degree arc of
mandibular opening and closing or during the initial mouth opening of 15-20 mm.
later the condyles and disc translates along the slopes of articular fossa. This
movement is a combination of rotation and translation.
Like centric relation, hinge axis is stable, reproducible and repeatable.
Therefore, it is used as an important reference in mounting casts in articulator, so
that the opening axis of articulator coincides with the terminal hinge axis.
Mc Collum was the first to define the theory of hinge axis. He together with
Robert Harlan introduced a method to record hinge axis and developed the first
hinge axis facebow in 1927.
Kohno (1972) termed the horizontal axis connecting the left and right
rotational center as “Kinematics Axis”.
Keyword: When the condyles exhibit pure rotation movement, the mandible is in
centric relation. In other words in centric jaw relation a pure condylar rotation
occurs along transverse hinge axis.
If the opening axis of this hinge movement was matched to the articular
axis, then vertical dimension of prothesis of stude casts can be altered in the
articulator – Hobo.
ARBITRARY LOCATION OF HINGE AXIS POINTS
1. 11-5 axis – 11mm forward on aline joining upper notch of tragus to outer
canthus of eye. From this point 5mm down is the arbitrary hinge axis.
2. 11-13 mm forward on ear – eye plane. Use Denar axis orbital plane
indicator.
3. Ear piece / plug face bow utilizes external auditory meatus as posterior
reterence point. On an average the external auditory meatus is 6 to 6.5
mm posterior and 2.5mm superior to the actual hinge axis point. This
relationship of external auditory meatus to hinge axis is relatively constant.
While transferring the face bow to articulator, ear pieces are seated in the
auditory pins of the articulator which are related to the articulator’s
intercondylar axis in the same way as the external auditory meatus relates
to the hinge axis on the subject. Ear piece, face bow and articulator are
mechanically designed to accept this relationship. When this type of face
bow is used, infra orbitale is used as the third reference point. Some ear
piece face bows use the nasal relator as the third reference.
LOCATION OF ACTUAL HINGE AXIS POINTS
Hinge axis points can be located with a kinematic facebow / hinge axis
face bow. The face bow is securely attached to the mandibular teeth with a
clutch. The styli at the posterior end of the horizontal arms of the face bow are
adjusted to obtain the point of rotation during opening and closing movements
with mandiable in retrusive closure. This represents the center of rotation. A mark
is made on the face of the subject by the stylus which is located in the hinge axis
position. This mark represents the hinge axis point. However, the actual center of
condylar rotation is about 17mm medial to the hinge axis point on the skin.
Subsequently, the relation between hinge axis points and maxillary arch / teeth is
recorded and transferred to the articulator.
WHAT IS TERMINAL HINGE AXIS
(Synon, transverse hinge axis, transverse horizontal axis)
It is an imaginary line / axis which passes horizontally through the rotation
center of the right and left condyles when they are in their most distal / retruded
unstrained positions in their respective articular / glenoid fossa.
This transverse horizontal axis connecting both the condyles which
exhibits a pure rotation during opening and closing movements of the mandible
(circa 12.5 mm mouth openings) is stationery. Translation of this axis occurs
when further mouth opening is made. Note that only in the centric position this
axis is stationary without any translation. Therefore this axis is also known as
terminal hinge axis (hinge axis during terminal jaw closure). The condyles usually
function from this terminal hinge position during the various masticatory
movements and deglutition. The GPT prefers the term transverse horizontal axis
in lieu of terminal hinge axis. This is because GPT recognizes the anterior
superior position of the condyle and no the terminal hinge closure of the
mandible in RUM position. The definition of the centric has now been changed
from RUM to anterior superior position.
However, since it is believed that rotation takes place in anterior superior
position of the condyle, (otherwise transverse horizontal axis to GPT would not
exist) the use of the classical term “ terminal hinge axis” is not objectionable.
Keyword: “Transverse hinge axis does not translate”
VALUE OF TRUE HINGE AXIS-WHY RECORD & TRANSFER HINGE AXIS?
1. Allows centric relation record in dentulous situations to be
accurately mounted on articulator with the use of inter occlusal
centric record. After the upper and lower dentulous casts are
mounted with the centric interocclusal record, the centric record is
removed and the articulator is closed in centric relation. If the axis
of the articulator and the hinge axis of the patient are not matched,
then there will be changes in centric relation. Further it is
impossible to check the accuracy of centric interoccusal record
without a hinge axis transfer. Hinge recording is required to check
the accuracy of two centric records.
2. It is starting point of lateral movements.
3. Permits vertical dimension to be changed in the articulator. Without
hinge axis the accuracy of centric interocclusal record is
questionable as inter occlusal records are taken with an increase in
vertical dimension. Occlusal discrepancies occur when the
interocclusal centric record is removed from the articulator and the
casts are closed in occlusion.
4. Allows the transfer of the opening axis to the articulator so that
occlusion would be on the same arc of closure as the lower jaw.
5. Opening and closing movements of the mandible are reproduced in
the articulator because the opening axis of the articulator is
coincident with the hinge axis of patient. Therefore teeth contact
each other in the articulator exactly as they do in the mouth.
Benefit : It is helpful in diagnosis / treatment planning of mounted study casts.
To sum up:
a. “Mounting on adjustable articulators using hinge axis location enables the
articulators to duplicate the opening and closing movement of the
mandible in the terminal hinge relation”
b. “Accurate transfer of centric relation”
Keyword: A true centric interocclusal record is obtained while freezing the lower
jaw in terminal hinge closure at a convenient vertical height.
Instrumentation for hinge axis techniques
1. Hinge axis locator
2. Hinge axis transfer bow
3. Semi adjustable articulator viz. Dentatus – ARL
4. Orbital indicator
5. Mounting table
6. Axis jig
7. Rim lock clutch tray / sectional screw lock clutch
8. Bite fork
9. Tatoo needle and tattoo dye
10.Wooden parallel bar
11.Articulator support bar
12.1X 1cm self adhesive 1mm graph paper.
TERMINAL HINGE AXIS TECHNIQUE
Consists of the following stages:
a. Recording hinge axis point
b. Hinge axis transfer to articulator ( matching articulator axis to patients
hinge axis)
c. Mounting upper cast to hinge axis.
d. Mounting lower cast with centric inter occlusal centric record.
TYPES OF HINGE AXIS FACE BOWS
There are hinge axis bows which record both the hinge axis and transfer
of hinge axis to articulator in one instrument. “T.M.J instrument” face bow is one
such example. There is also a technique of recording hinge axis with a hinge axis
locator and after obtaining the hinge axis point, transfer of hinge axis is done with
a hinge axis transfer bow. Both the techniques are acceptable. The later
technique is more rational and precise, in spite of its cumbersome procedure.
The procedure is challenging and should be done methodically avoiding even the
slightest possible error to obtain correct results.
There is no dispute over the pressure of hinge axis as some may have
earlier believed. The technique of recording hinge axis, its transfer and mounting
casts with inter occlusal centric records itself is a proof for the presence of a
reproducible hinge axis. Do not doubt the value of terminal hinge axis and its
importance in mounting casts to this relation in the articulator. When casts are
mounted arbitrarily on an articulator, without terminal hinge axis record and
transfer, centric relationship and the eccentric relationship of casts in the
articulator will not be the same as it is present in the mouth.
Hence for precise dental procedures such as mounting of study casts,
selective grinding, diagnostic wax up, extensive restorative procedures and in
diagnosis of occlusion in T.M.J dysfunction recording of hinge axis and its
transfer if beneficial. Arbitrary face bows such as ear face bow and facia bow
have its own accuracy limitations. However it should be kept in mind that a
correct arbitrary face bow transfer is better than an inaccurate time consuming
hinge axis record.
“In the absence of true hinge axis mounting, arbitrary face bow serves the
purpose, but to a lesser accuracy”.
METHOD TO LOCATE HINGE AXIS
The hinge axis locator is assembled on the side of the patients face to
record hinge axis points. The locator consists of stylii and adjustable side arms,
which are attached to an anterior cross bar that is firmly attached to the
mandibular clutch. Since this assembly is attached to the mandible, the stylus
moves when the mandible is opened and closed. The stylus moves in an arc
form when the condyles execute pure rotation. The stylus bodily forward when
there is hinge movements. The condyles should remain in centric relation during
hinge closure without any translation.
By a trial and error method observe the movement of stylus and the side
arms are adjusted till the tip of the stylus remains stationary without arcing
movement during the hinge closure of mandible. The hinge axis point is now
identified by allowing this stylus to make an indelible mark on the side of the face.
PROCEDURE OF HINGE LOCATION AND TRANSFER WITH TMJ
INSTRUMENT
A. Axis location
1. Attach the clutch to lower teeth with plaster
2. Attach cross bar to the clutch rod / stem
3. Attach side arms with stylus to the cross bar
4. Adjust the stylus to the arbitrary center of condyle
5. Guide the mandible to terminal hinge closure and observe the movement
of stylus.
6. There will be arcing of stylus tip if the tip does not coincide with the
condylar center of rotation.
7. Adjust the side arms so that the stylus tip is moved toward the center of
arc until the stylus tip rotates without arcing movements. This indicates
the hinge axis point.
8. Register the hinge axis point on the other side of the face by a similar
procedure.
9. Apply indelible ink on the tip of stylus. Gently guide the mandible to the
optimum centric position. Slide the stylus tips to contact skin to leave a
mark.
10.These two marks indicate the posterior reference points which are used
later for face bow transfer.
11.Mark the anterior third reference point on the nose 43mm above the
incisal edge of right lateral incisor. This represents midway between
upper and lower casts. This can also be established on the right side of
the face by palpation of infra orbital foramen area.
B. Axis transfer
1. Add softened low fusing compound to the face bow bite on its upper side.
2. Place it in the mouth against the maxillary teeth and let the patient to
lightly occlude on the bite fork to record the cusp tips and incisal edges.
The teeth should not penetrate the compound.
3. Attach cross bar and side arms to the stem of bite fork. Position the stylii
on either sides on the posterior reference points (hinge axis points). Lock
stylus in this position.
4. Now position the orbital reference pin to the anterior third reference point.
5. Lock the face bow and remove the face bow record and clamp it on the
transfer board.
6. Place axis jig on the transfer board and adjust the orbital reference
indicator on the orbital indicator pin.
7. Adjust the axis jig o match the tip of the stylus. This alignment of axis jig
tip with the stylus tip completes the hinge axis transfer.
8. Place the maxillary cast into the cusp indentations on the bite fork of the
face bow. Secure the cast in this position on to the mounting ring of the
axis jig. Axis jig is used only for mounting the maxillary cast. Later remove
mounting plate with the maxillary cast from axis jig and transfer it to the
articulator.
Note: The axis jig is made to the identical specification of the articulator. The
maxillary cast position to intercondylar axis and orbital reference plane is the
same between these instruments.
STEP BY STEP PROCEDURE OF HINGE AXIS REGISTRATION AND
TRANSFER USING AN AXIS LOCATOR AND TRANSFER BOW.
A. Hinge axis location
1. Attach clutch tray to lower teeth
2. Assemble hinge axis locator
a. Adjust side arms – 10mm forward
b. Adjust outer square tubing parallel to cradle
c. Place needle equidistantly into sleeves bushes
3. Attach side arm to cross bar in mounting column
4. Attach assembled hinge axis locator to stem of clutch tray
5. Mark approx center of condyle on the subjects face
6. Adjust the hinge axis locator so that the condylar needle coincides with
condylar mark on subjects face.
7. Place graph paper on the skin of condylar area.
8. Location of hinge axis points.
a. Train the patient and guide mandible to THR
b. Adjust the needle till no more arcing
c. Mark the hinge axis point on the skin.
B. Hinge axis transfer
1. Assembly of transfer bow
a. Adjust side arms
b. Hang down 3 locking clamps with the handles facing operator
c. Fix anterior cross bar to mounting column with its handle facing
operator
d. Attach one adjusted side arm to the right end of the cross bar
e. Attach the other side arm to the left end of the cross bar ( male and
female adjustments)
f. Collect stops inserted over needles at the needle end.
g. Collect stops RH, LH inserted into the plastic sleeves of side arm,
to project equidistantly tighten screw.
h. Transfer the assembly transfer bow over face and check for 5mm
clearance between needle and skin.
i. Assembled face bow is removed from mounting column, place it
upside down on flat surface, loosen locking screw (on patients right
side) to cross bar. Make both side arms parallel, then tighten screw.
j. Insert orbital pointer on patients left side. Handle is tightened with
the locking clamp upside down (handle up, clamp down).
2. Preparation of bit fork and recording upper and lower teeth identifications.
3. Attach transfer bow to bite fork and orient it to hinge axis. Tighten locking
clamp to cross bar.
4. Adjustment of orbital indicator.
5. Fine adjustment of condylar needles to hinge axis points.
6. Lock side arm adjustment screws.
7. Remove transfer bow, attach it to mounting column
8. Preparation of articulator.
C. Mounting upper casts
1. Place opened articulator on mounting table.
2. Loosen clamp on mounting column and adjust transfer bow to position it
closer to condylar axis pins.
3. Orbital pointer and needle should be in same horizontal level or slant
slightly anterior.
4. Adjust articulator leveler to bring the condylar axis pins to coincide with
condylar needles of transfer bow. Move articulator if required.
5. Tighten locking clamp on mounting column. (Keep I mind 4mm rise during
tightening).
6. Raise leveler for final adjustment.
7. Adjust orbital pointer pin to the orbital indicator plate.
8. Secure under surface of bite fork to wood parallel bar with soft plaster.
9. Place upper cast on bite fork.
10.Close articulator to lock incisal pin where pointer pin contacts under
surface or orbital indicator plate.
11.Remove orbital indicator plate and mount upper cast, finish mounting.
12.Control of correct mounting
a. On articulator
b. On patient
D. Orientation of lower cast to upper cast with centric interocclusal record
1. Obtaining inter-occlusal centric wax record
a. Lauritzen technique
b. Wax wafer technique
2. Mounting mower cast to centric record.
3. Verification of mounting and registration of THR with split cast technique.
4. Ascertain whether centric record was in THR by taking another wax record and
verify with split cast.
5. Proof for the presence of true hinge axis. Take several inter-occlusal wax
records in various vertical heights within the hinge movement range. Place
each record in the articulator with split cast to prove that all the records are
similar.