FACE BOW

HISTORY :

If we wish to know something about face bow, how this

instrument is used and the significance of its application a short historical

survey of the ideas connected with these problems, and the working

'methods and instruments that they have given rise to, will give us clear

picture of the features to be remembered in this aspect.

About mid 18th century it began to be realised that in fabrications

of complete dentures it was important to mount the casts inthe articulator in

a given positional relation to the condylar elements. According to

Bonwill, 1860 the distance from he center of each condyle to the median

incisal point of the lower teeth is 10 cm and he advocated this

measurement to be followed while mounting but he did not mention

however at what level (vertically) the occlusal plane be paced in

relation to condyal mechanism. It appears that he advised the casts to be

mounted midway between the upper and lower parts of the articulator.

In 1866 an English dentist by name Balkwill devised methods

that were improvement on those proposed by Bonwill.

Balkwill demonstrated on apparatus with which he could measure

the angle formed by occlusal plane and the line joining condylar

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centers to the incisal point of the lower teeth and the angle varied from,

22° to 30°.

An other method for localizing the casts in the articulator was

constructed by Hayes in 1880 and the apparatus was called caliper.

However again there was no proper orientation possible.

Then in 1890 walker invented Clinometer with which it was

possible to obtain a good position of the cast in articulator. He used

mainly this instrument as instrument for condylar inclination

measurement device. A little later Gysi about the turn of the century

developed an instrument similar to a facebow primarily to record position

of the condyles however, it could be used to mount casts. But the

credit goes to Snow for inventing a Actual Facebow on which most of the

present day facebows are based. Snow introduced the facebow in 1899

and patented it in 1907.

In 1914 Dalbey introduced the use of ear type of facebow but it

was not until late 60's the ear type did gain popularity.

We are justified in staling that snow's facebow inspite of its very

simple construction was Epoch making in prosthetic dentistry. Since the

introduction of Snow's apparatus, no fundamental changes have been

made in the face bow design. Because snow determined the position of

the casts in the articulator not only in regard to distance of the mid incisal

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point from the condyles but also the other points of the occlusal plane

were given the correct relationship in relation to condyles.

PRINCIPLE OF FACE BOW USE :

The movements of the teeth are results of the rotation and slidings

made by the condyles. The better the casts on the articulator duplicate

the distances to the rotational condylar centres, the less the potential

errors produced by difference in the arcs of closure of the mandible and

the articulator.

The use of facebow is an integral part in procedures in analyzing

and studying occlusion, developing the occlusion for complete dentures

and other restoration.

The occlusal plane is related by making it parallel to a horizontal

plane so that it easier to relate it the articulator.

Snow recommended that the occlusal plane be made parallel with a

plane extending from the bottom of the glenoid fossa and passing

through the anterior nasal spine. This plane cannot be determined

directly on a living persons but it approximately, corresponds With a line

drawn from the upper parts the Tragus to the lower edge of the Nostil or

Alatragal line. This plane in European literature is referred as camper's

plane, in Americal literature it is referred so as Bromell's plane. Gysi and

kohler used a plane called as prosthetic plane which extends fro, the

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lower part of the tragus to the Ala of the nose. Wads-worth employed a

different plane which from the condyle area and runs at right angles to

a line that connects the most prominent points of the chin and forehead.

Over recent years, there has been a growing tendency to employ a

plane (i.e.) the Frankfort horizontal plane which is usually parallel to the

floor when an individual is in a upright position. Cephaornetrically the

Frankfort's plane is described a horizontal plane that passes through the

right and left portion (the mid point on the upper margin of external

auditory meatas) and the orbitale (the lowest point on interorbital rim).

The Horizontal plane forms a plane which is called as the Axis-

ORBITAL plane. This plane formed by the two posterior points of

reference and the one anterior point of reference which is usually the

infraorbital notch indicated by the pointer fixed on the face 'bow and the

posterior points of reference are those where the condylar rods are placed

thus when utilizing the two posterior (points) and anterior points the

occlusal plane is related to the face bow and through the face bow franfered

on to the articulator.

In the articulator there is a condylar plane estab lished by the

condylar spheres and a indicator for the anterior point of reference the

condular rods approximating the condyles through it the hinge axis are

attached to the centre at the condylar spheres of the articulator.

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Principle face bow use :

The prosthesis or indirect restorations that are planned and

fabricated with help of articulators should have the same relationship as

they have with articulator’s axis of opening as well as the patients

mandibular arc of movement.

Since it is practically difficult to orient the mandible to the

articulator, the maxillary cast is related to the articulator with same

relationship with the existing relationship between maxillary and

condyles of TMJ which is center of mandibular movements, the

mandibular cast is related to maxillary cast which in turn is oriented in the

articulator. To accomplish this act of orientation the device face bow is

utilized.

Before we (study) know more about the facebow and its use a

brief description about the terminal hinge Axis will help us in better

understanding of the face bow.

The terminal hinge axis is an imaginary axis around which the

condyle can rotate without translation and this axis is assumed from

which all the mandibular movements of opening and closing take place.

The THA is the most retruded hinge position and is significant because

it learnable, repeatable and recordable that coincides with the centric

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relation. The limits of the hinge movement in this position is about 12°-

15° at condyles or 19-21 mm in the incisal region.

The condyles are in a definite position in the fossa during the

rotation. Snow recognised the importance of this axis and to transfer this

axis to the articulator led to development of facebow and in 1921

McCollum, Stuart and others reported the first method of transferring this

axis. Since then many have put forward views that are very diverse from

each other.

Sloane stated

"The mandibular axis is not a theoretical assumption but difinitely

demonstrable biomechanical fact. It is the axis which on the mandible

rotates in an opening and closing function when comfortably but not

forcibly retruded."

"The hinge position or terminal hinge position is that position of

mandible from which or in which hinge movements of a variable wide

range is possible.

But contrary to them Brekke, Trapozzano and Lazzari and Lucia

questioned existence of the single hinge like axis of rotation for mandible

since the ideal mechanical set up is never found in living tissues.

Controversy arises as to the presence of single relationship of TH

position to entire portion. There are differences in concepts and

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interpretations of the findings. These differences in findings are

understandable and these seems to be general agreement that when the

mandible is in centric relation the mandible is in its most posterior

unstrained position from which a trained individual can voluntarily open

and close the mandible in hinge movement. Since it is a repeatable and

recordable position it is a point of return.

Therefore we strive to capture this imaginary axis and transfer this

to the articulator and depending upon how accurately the face bow

capture and transfer this to articulator led to the coining of words like

Kinematic face bow and Arbitrary face bows.

The occlusal plane or the wax rim is related to the TMJ by using a

horizontal plane and this relationship is transferred to the articulator using

a facebow register the GLENO MAXILLARY.

Relationship in three plane of:

o Anterio-posterior sagital plane

o Transvers or frontal

o Vertically

The maxilla is related to a horizontal plane usually formed by 3

points of references.

Two posterior points of reference

One anterior point of reference

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If the inaxillary cast is positioned without the correct maxilla hinge

axis relationship arcs of movement in the articulator will occur which

are different from those of patient.

Occlusion that is restored to an incorrect arc of closure will have

interceptive and deflective tooth contacts.

Such contacts are undersirable and contribute to:

o Periodontal problem

o Muscle spasm

o TMJ pain

o Loss of supporting bone

Location of hinge axis was discussed by Campion first time told

that axis of opening should coincide with the articulator axis.

Theoretically unless the extra THA is located and transferred

the inter occlusal space used for recording in jaw relations will induce

errors in casts mounted on articulators. The error produced may not have

serious consequence in removable prosthesis with non-rigid attachments

in such conditions the intended tolerances and mobility of the supporting

tissues make the precise location of THA a exercise with no great

advantages. On the other hand fixed and removable prosthesis of rigid

attachments demand close tolerances in cusp path ways.

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Facebow Transfer:

Use of kinematic face bow : The technique for locating the axis

for dentulous and edentulous patients is same except for the mode of

attachment of the clutch to the mandible. The clutch directly cemented

on the teeth and in case of edentulous condition clutch is attached to

mandibular wax rim and the chin clamp is used to stabilize the

mandibular denture base because of the instability and soft tissue mobility,

inaccuracy creep in which defeat the purpose of axis location. The patient

is trained to make a limited opening and closing movements of about 19-

20mm in insial region within the rotational movement of the condyles.

These points are directly marked on the skin or flag or grid with graph

paper placed on it and this distance is measured from the tragus and is

used as the posterior reference point and the facebow transfer is done in

usual means.

In case of Arbitrary type facebow the posterior points are selected

on a anatomical average of l3mm anterior to the tragus on a line from

tragus to the outer cantus of the eye and the fork is attached to the

maxillary teeth or wax rim. The fork is either inserted in the rim or a

index is used. The condylars (elements) rods are adjusted till the fork is

centered and the pointer for third point of reference of orbital pointer or

the nasion relator is adjusted and once all the locknuts or secured the

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facebow should support by itself without any movement than the

condylar lock nuts are released and the face bow transferred to the

articulator with the condylar rods approximating the condylar spheres of

the articulator and the pointer pointing to the built in orbital indicator and

the cast is placed in the record base and mounted.

Thus the plane of occlusion when viewed on the articulator will be

similar to that of the patient in an upright position and the occlusion

plane is placed in a similar, relation in the articulator as that exists in the

patient's mouth.

Description of Facebow :

The facebow consists of 'U' shaped frame or assembly i.e. large enough

to extend from the region of the TMJ to a position 2-3 inches in front of

the face and wide enough to avoid contact with sides of the face. In the

condular region there are condylar rods with graduation extending from

the main assembly which are placed over the posterior reference points,

the reading the condylar rods help us to center the facebow. Once the

facebow is adjusted there are locknuts that are tightened. The part of the

assembly that is attached to wax rim is called bite plane or fork through

the stem or yolk. The fork is attached to the main frame and there are

pointer for the third point of reference like orbital pointer or nasion

relator.

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The facebow or hinge bow for kinematic is also similar in

construction except that instead of the fork attached to maxilla it is

attached to the mandible and there are attachments where the flages or

grids with graph paper are attached to frame which either attached to the

maxi, teeth or held by head straps or worn as spectacles. The clutch or the

fork on the mandible in case of edentulous patiet is stabilized using a chin

clamp.

The arbitrary axis of rotation as set forth by Snow, Gilmer, Hanau,

Gysi and others of 13mm anterior to the tragus on the tragus-canthus line

very close to an average determined axis.

The procedures locating hinge axis calls for rather lengthy and

difficult procedure, which require use of a large and bulky apparatus,

which pose problems of attaching the apparatus to the mobile mandible

securely and this problem is more compounded in edentulous jaws where

the soft tissues and mandibular denture bases are unstable.

This lead Craddok and Symmons in 1952 to state that "search for

the axis in addition to being trounlesome is of no more that academic

interest for it will never be found to lie more than few milimeters distant

from the assumed center of the condule itself. This can be done

palpation 10-13mm anterior to tragus.

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The T.H.A. is not only difficult to locate but also difficult to

relocate the same point of axis. Kenneth and Fein-Stein attempted to

locate the axis and were successful only in relocating it within a radius of

2mm.

Borjh and Posselt could relocate it within 1.5mm.

USE OF F.B. AND RELATION TO THE ARTICULATORS

REFERENCE POINTS

One recommended method of positioning, the maxillary cast vertically in

Hanan articulator is to relate the maxillary cast with the F.B. still attached

to the articulator till the maxillary central incisors .edges or the maxwax

rim are aligned to the level of Incisal Reference Notch. 30mm below the

Horizontal condylar plane described by the centers of the condyles and the

infra-orbital indicator, unfortunately there is no Anatomic relationship

between the anterior reference point of orbital and I. R. Notch in other

words the 30mm is not the correct distance between orbitals and maxi

incisal edges. There are other incisal reference notches placed 37, 54

and 47mm below the condylae place. But according to Gonzalers and

kingery the centre of the condyle is 7mm below the porion which forms the

frankforth horizontal plane and therefore the axis-orbital plane should be

placed 7mm below to set a proper parallelism and therefore the

infraorbital foramina should be used as anterior points of reference.

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POSTERIOR POINTS OF REFERENCE

Often the posterior points are located by measuring prescribed

distances from skin surface landmarks. Some of the commonly used

posterior points were shown by beck to be clinically near the hinge axis.

He concluded that pergstorm point followed by beyron point were most

frequently close to hinge axis. It is known that balanced occlusion is

necessary for the stability of the dentures and for the health of the oral

tissues. An accurate place of orientation does appear to be essential step in

C.D. fabrication.

An error of this size may not have serious consequence in

removable prosthesis with non rigid (connectory) attachments, in

such conditions the intended tolerances and mobility of the supporting

tissues make the precise location of the Hinge axis a en... with no great

advantage on the other hand fixed and removable prosthesis with rigid

attachment demand close tolerances in cusp path ways.

Verifications of the mandibular cast portioning by use of inter

occlusal records made at increased vertical dimensions of occlusion will

be difficult if not impossible when the interocclusal records are made at

same thickness. Changes in vertical dimensions of occlusion.

Bergstorm point : 10mm anterior to the centre of spherical insert

for the auditory meantus and 7mm below the Frankforth H. plane.

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Beyron point 13mm anterior to the posterior margin of the tragus of the

ear on a line from the centre of the margins to the corner of the eye.

The selection of the (anterior) points of reference is useful so that

different maxillary casts of the same patient can be positioned in the

articulator in the same relative position. The points give the procedure

the value of constant determination and also reduce time with

complicated time consuming recording techniques such as pantographic

tracings to repeat the records each time the technique calls for a new casts.

For this reason it is important to identify the mark permanently or be able

to repeatively measure a anterior reference, point as well as the posterior

points of reference.

Selection of Anterior Point of Reference

1. Obritale : In the skull orbitate is the lowest point on the

infraorbital rim. On a patient it can be palpated through overlying

skin and orbitate and the the posterior points that determine the

horizontal axis is defined as the axis - orbital plane. Practically the

axis orbitory plane is used because of the ease of locating and points

easy to understand.

This plane can be transferred to articulator with the help of the

orbital pointer and indicator on the articulator.

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2. Orbitale minus 7Tnm : The frankfort ' s horizontal plane passes

through the poria and one orbitale because these points are (skull)

bony landmarks. Sicher recommends using the mid point of the

external auditory meatus as the posterior cranial landmark. Most

articulators do not have reference point for these posterior land marks

lies 7mm superior to the axis and recommends composition by making

anterior point of reference 7mm below the orbitale or positioning the

orbitale pointer 7mm above in the articulator to the orbitale indicator.

3. Nasion minus 23mm : Again according to Sicher another skull

landmark the Nasion can be used as the anterior reference point. The

nasian guide or positioner which relates to the deepest part of the

midline depression just below the level of eyebrows, as used in whip-

mix and SAM quick mount face bow is designed so that it moves in

and out but not up and down from its attachments to the cross bar.

The cross bar is located approximately 23mm below the nasion. When

the face bow is positioned the cross bar will at the level of the orbitale.

The disadvantages of using this kind of face is that this technique

depends upon the large nasion guide the morphologic characteristics

of the Nasion notch and the variance of the Nasion orbitale

measurements from 23mm in the patient.

4. Incisal edge plus anterior midpoint to articulator axis

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Horizontal plane distance.

Guichet - Emphasized that a logical position of casts in the articulator

would be one which would position the plane of occlusion near the mid

horizontal plane or articulator. The the mid horizontal distance to the

axis condyler plane is measured, this measured distance measured onto

the patients from the existing incisal edges or planned occlusal plane and

then transfer is done.

5. Alae of the Nose : The occlusal plane actually parallels the

horizontal plane which was concluded by Angsbreber in review of

literature that the occlusal plane parallels the campu's line with minor

variations knowing this we can transfer camper plane from the patient

to the articulator by using either right or Ala as the anterior reference

point.

Importance of selection of anterior reference point

1. A planned choice of anterior reference point will allow the

dentist and auxiliaries to visualize and anterior teeth and

occlusion in the articulator in the same frame of reference that

would in patient i.e. as if patient standing in normal postural

position with eyes looking straight ahead.

2. The act of affixing a maxillary cast with its determined hinge

axis to an articulator with its axis in the condyler

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determinants achieves greater importance by the use of the

three points of easy reference where are constant and

repeatable.

To use or not use :

The value of the face bow has been the topic of considerable

discussion and contraversy in prosthesis dentistry for many years. Logan

considered indispensable Craddock and Symmons considered it as futile

exercise. While Stansberry described a technique of positioned records

and told that use of face bow was useless. Lazzari set forth the advantages

of using a facebow.

1. It permits a more accurate use of lateral rotational points for

arrangement of teeth.

2. It aids in securing anterioposterior positioning of the cast in

relation to the condyles.

3. A correct horizontal plane is established. Therefore the

incisor plane is also properly established.

4. It helps in vertical positioning of the cast in articulators.

Face bow transfer is not required in following conditions.

The articulators developed not to receive face bow transfer.

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Some theories of occlusion specially the Monson's

spherical theory of occlusion.

When monoplane teeth are arranged in a occlusal

balance.

No alteration of occluding surfaces of the teeth that

necessitates the changes in verticle dimension.

No inter occlusion check reports that would be of different

thickness.

But when we analyse the above said facts it is very clear that by

simply stating that the articulator is not designed to accept the face bow,

we cannot forget the step of facebow transfer and incorporate the errors

due to blind orientation of the casts on the articulator and we cannot

have single predetermined scheme of occlusal for all patients and we

cannot use mono plane teeth for all cases in fact when we are cusped form

of teeth facebow transfer becomes a must to achieve balance in entire

positions. Changes do occur in vertical dimensions in complete dentures

due to processing and dimension if to be retorations requires a facebow

transfer and in case any remound is desired any change is there in occlusal

records needs a facebow transfer.

Vertical dimension desired and planned on articulator require

facebow transfer. When use the following figures it becomes very clear

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that now varied the cuspal inclination when the casts are placed at

different levels in articulators of course the changes may not be so great in

positions but changes do occur.

Average mountings do not serve the diagnostic imposes in

distrubances that occur to positions teeth face transfer in not only useful

from prosthesis recontractive view that also diagnostic (tool in) procedure

in gnathological studies. The overall opinion to which majority of the

prosthodontics agree in put forward by the academy of denture

prosthodontics favouring the use facebow and concluded that "A

FACEBOW SHOULD BE USED FOR MOUNTING THE UPPER CAST

ON ANY ARTICULATOR THAT HAS A FIXED AXIS OF OPENING".

The correct orientation of the occlusal plane is a important step

and the inclination of the plane that we develop had effect on the

masticatory performance.

Kapoor and Soman showed that the masticatory performance was

influenced by the plane of orientation and Hideaki, Okene and others who

further carried out the research found that maximum clenching force was

greatest when the occlusal plane parallel to the camper's plane and the

force decreased when there was 5° tilt either anterior and posterior.

Modification of face bows and different types of face bows :

1. Accuracy - Kinematic

- Arbitrary - Eartype

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- Fascia

Eartype - Manual lenthing eg. HANAO

- Self centering or quick mount

eg. whip-mix, Bregstorm, SAM

Even though the Snow type FBS are mechanically simple they are

in convient to assembly on patient

- to locate

- to adjust the FB.

On the posterior points of reference directly on the skin. Therefore

in 1914 Dalbeg introduced the use of ear type of facebow where the

posterior ends were modified and may fit in the car but it was not until late

60's the ear type gained populatiry.

Now there are so many articulatory available that each articulator

had to use with special type of FB. Then Kelseg came out with adapter

which permits one type of face bow to be used 'with different articulatory.

Then there came the self centering type or quick mount type of the F.B.

With a built in gear mechanism where only one mechanism help to center

the fork.

- Slidematic facebow

- Quick mount or whipmix

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Bregstorm

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Springbow :

Further simplication of the arbitory lead to development of spring

bow which eliminate the wrencnes and screws and moving parts. It is one

piece low maintenance and lower cost.

Modifications :

Disadvantages of conventional face bow fork :

1. Heatedfork when inserted into the wax rims

distorts the carefully developed contours.

2. The width is fixed and sometimes difficult to

be used with larger or smaller arches.

3. When the face bow transfer is to done after the

centric occlusion interocclusion record, the possibility of the rim

distortion is introduced.

4. In treating the patients (for) immediate

maxillary denture the face bow transfer may be complicate by

remaining natural teeth.

Advantages of modified facebow fork :

1. Does not distort facial contours the wax rim.

2. Provides adjustability and can be used with any size ofarch.

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3. Minimum or no distortion when facebow transfer is made

after inter occlusal registration.

4. Can be used for immediate denture treatment with the

natural teeth.

It is attached to the palatal portions of the (denture) record base. A

new face bow design was introduced that further simplifies the arbitory

face bow technique.

Advantages include

1. Ease and efficiency of use

2. Steriligable parts

3. One piece low maintenance design

4. Adaptability to many articulators

5. Lower cost than other car piece types

Made up of spring steel and simply springs open and closes to

various head width.

CONCLUSION

Failure to use the facebow leads to error in occlusion.

Hinge axis is a component of every masticatory movement of the

mandible and therefore cannot be disregarded and this hinge axis should

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be accurately captured and transferred to the articulator. So it becomes a

fine representative of the patient and biologically acceptable restoration is

possible.

Whatever may be controversy reasoned by in the use of facebow

but it should form a integral part of one prosthodontic treatment.

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