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.