ORIENTATION JAW RELATION AND FACEBOW

PRECEPTOR

Dr Vishwas Bhatia

PRESENTER

Dr Manjima Khandelwal

CONTENTS

• Introduction
• Orientation Jaw Relation
• Hinge Axis
• Terminal Hinge Axis
• Facebow
• History of facebow
• Types of facebow
• Parts of facebow
• Reference Points
• Significance of facebow
• Advantages and Disadvantages
• Procedure
• Mounting on Articulator
• Recent Advances
• Conclusion
• References

• Jaw Relation is defined as any spatial relationship of maxilla to mandible.

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• Jaw Relation Record is defined as a relationship of any positional relationship of maxilla relative to mandible.

Glossary of Prosthodontic Terminologies-9

Establishes reference to cranium

Establishes amount of jaw separation allowable

Establishes front to back and side to side relation of one jaw to another

An accurate determination, recording and transfer of jaw relation record from edentulous patient to the articulator is essential for restoration of function, facial appearance and maintenance of patient health.

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ORIENTATION JAW RELATION

Orients mandible to cranium in such a way that when mandible is kept in the posterior position, mandible can rotate in a sagittal plane around an imaginary transverse axis passing through or near condyles.

It can be recorded using a facebow.

HINGE AXIS

• Hinge Axis is defined as the imaginary line around which the mandible may rotate within the sagittal plane without translation.

-GPT-9

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• Condyles are not restricted to any one position in the fossae when movement occurs.

Heartwell

TERMINAL HINGE AXIS

• Terminal Hinge Axis is defined as the most retruded hinge position of the mandible.

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• It is learnable, repeatable and recordable that coincides with Centric Relation.

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• It is 12⁰-15⁰ during mouth opening or 19-20mm at incisal edges.

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• Condyles are in definite position in the fossa during terminal hinge axis.

SCHOOLS OF THOUGHT REGARDING THE HORIZONTAL AXIS

Aull A; A Study of the Transverse Axis; J Prosthet Dent; 1963; May; 13(3); 469-479

FACEBOW

Calliper like devices that is used to record the relationship of the jaws to TMJ or opening axis of the jaws and to orient the cast in this same relationship to opening axis of the articulator.

GPT-9

HISTORY OF FACEBOW

A study was conducted by Kurth and Feinstein in 1951:

They concluded that with the aid of an articulator and a working model, we have demonstrated that more than one point may serve as a hinge axis. Thus we conclude that an infinite number of points exist which may serve as hinge points.

It is unlikely that the hinge axis can be located with any degree of accuracy.

Kurth L.E.; I. K. Feinstein I.K.; Journal of Prosthetic Dentistry; The Hinge Axis of the Mandible; May; 1951; 1; 3; 327-332

Lazzari in 1955 enlisted advantages of face-bow which are as follows:

1. It permits a more accurate use of lateral rotation points for the arrange- ment of teeth.
2. It aids in securing the anteroposterior cast position with relation to the condyles of the mandible.
3. It registers the horizontal relationship of the casts quite accurately, thus assists in correctly locating the incisal plane.
4. It is an aid in the vertical positioning of the casts on the articulator.

Lazzari J; Journal of Prosthetic Dentistry; Application Of The Hanau Model “C” Face-bow; 1955; 5; 5; 626-628

A study was conducted by Schallhorn in 1957:

He recorded the arbitrary centre and true hinge axis in 70 dental students.

The arbitrary axis of rotation as set forth by Snow, Gilmer, Hanau, Gysi, and others, of 13 mm anterior to the tragus on the trageal-canthus line comes very close to an average determined axis on individuals with normal jaw relationships.

In over 95 % of the subjects, the kinematic center lies within a radius of 5 mm from the ar- bitrary center, which is considered by Arstad” and others to be within the limits of negligible error.

determining of the kinematic center of rotation is not nearly as important

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In 1860, according to Bonwill, the distance from the centre of each condyle to the median incisal point of the lower teeth is 10 cm.

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He used this standard for mounting his casts in the articulator.

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In 1866, Balkwill designed an apparatus called “bite- frame”.

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He made apparatus to measure the angle between the occlusal plane and the plane passing through the lines extending from the condyles to the incisal line of the lower teeth .

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Angle =22⁰-30⁰

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The position of Balkwill’s casts in the articulator was much more correct than by Bonwill’s method

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In 1880 Hayes used tong like device which he called it “articulating caliper”.

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This instrument was not used as a facebow. Its only purpose was to record the distance from the patient’s condyles to a point along the midline of the maxillary occlusion rim.

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No control of proper orientation of the occlusal plane.

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In 1894 George k Bagby devised an apparatus called “bagby jaw gage”.

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Walker in 1896 devised an apparatus, to measure the path of each condyle individually, and he called it as “facial clinometer’, with which it would have been possible to obtain a relatively good value for the position of the lower cast in relation to the condylar mechanism.

The facial clinometer, designed to measure the downward and forward condylar paths, did not allow for active transfer of the casts to the articulator.

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G B Snow in 1899 determined the position of plaster cast in the articulator, not only with regard to the distance of median incisal point from the condyles, but all the other points on the occlusion plane were given their correct position in relation to the condyles.

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Wadsworth in 1921 devised an face bow with the anterior reference point based on Wadsworth’s “naso-optic-condylar” triangle.

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Alfred Gysi in 1928 developed first facebow to record sagittal condylar path and apparatus is supported by bite fork attached to lower occlusal rim.

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PARTS OF FACEBOW

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U SHAPED FRAME

• Large enough to extend from thee region of TMJ to a position 2-3 inches in front of the face and wide enough to avoid contact with the sides of the face.
• All other components of the face bow are attached to the frame with the clamps.
• It records the plane of the cranium.

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• Consists of
• Two lateral arms
• Central screw
• External ear piece
• Orbital pointer
• Nasion pointer

CONDYLAR RODS

• Part of facebow that contacts the skin over TMJ.
• These are two small metallic rods on either side of the free end of the U shaped frame
• It helps to locate the hinge axis or the opening axis of the TMJ.
• Some facebow have a earpiece attached to these metallic rods that are inserted into the external auditory meatus of the patient.

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BITE FORK

• Part that is attached to the occlusal rims.
• It is attached to the main U shaped frame with the help of bite fork assembly also called as stem.

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ORBITAL POINTER

• It marks the anterior reference point (orbitale).
• It can be locked in positioned with a clamp.

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NASAL RELATOR

• Some facebow have nasal relator as the anterior

point of reference for nasion.

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LOCKING NUTS:

• Part of the face bow that attaches the bite fork to the U shaped frame.
• Also supports the face bow, occlusal rims and the casts during articulation.

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• The art of affixing a maxillary cast to an articulator relates the cast to the articulator’s hinge axis, to the vertical axes, to the condylar determinants, to the anterior guidance, and to the mean plane of the articulator.

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• The act achieves greater importance by the use of a constant third point of reference and repeatable posterior points of reference.

Wilkie N; The Anterior Point of Reference; JPD; May 1979; 41; 5; 488-496

craddock

ANTERIOR POINT OF REFERENCE

• Orbitale (B)
• Orbitale minus 7mm (C)
• Nasion (A) minus 23mm
• Incisal edge plus articulator midpoint to articulator axis-horizontal plane distance.
• Alae of the nose (D)
• 43mm superior from the lower border of upper lip or lateral incisor.

Wilkie and kumar mix

ORBITALE

• Orbitale is the lowest point of the infraorbital rim which can be palpated on the patient through the overlying tissues and the skin.
• One orbitale and two posterior points that determine the horizontal axis of rotation will define the axis-orbital plane.
• Relating the maxillae to this plane will slightly lower the maxillary cast anteriorly from the position that would be established if the Frankfort horizontal plane were used.

wilkie

The articulator must have an orbital indicator guide that is in the same plane as the hinge of the articulator.

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A

B

Orbitale is transferred from the patient to this guide by means of the orbital pointer on the anterior crossarm of the face-bow.

wilkie

• The axis-orbital plane can be transferred to the articulator in another manner.
• The face-bow itself is raised to the axis-orbital plane on the patient.
• A metal arm attached to the maxillary record base is rigidly fixed by plaster in a transfer cup that also attaches to a vertical support arm on the face-bow and subsequently to a vertical support arm on the articulator.

wilkie

Practically, the axis‑orbital plane is used because of the ease of locating the marking orbitale and because the concept is easy to teach and understand.

kumar

ORBITALE MINUS 7mm

• The Frankfort horizontal plane passes through both poria and one orbital point.
• Because porion is a skull landmark, Sicher recommends using the midpoint of the upper border of the external auditory meatus as the posterior cranial landmark on a patient.
• Most articulators do not have a reference point for this landmark.

wilkie

• Gonzalez pointed out that this posterior tissue landmark on the average lies 7 mm superior to the horizontal axis. The recommended compensation for this discrepancy is to mark the anterior point of reference 7 mm below orbitale on the patient or to position the orbital pointer 7 mm above the orbital indicator of the articulator.

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• Bergstrom’s Arcon Articulator automatically compensates for this error.

wilkie

Bergstrom articulator and face-bow: The articulator axis is located 10 mm anterior to the spherical insert for the external auditory meatus and 7 mm below the Frankfort horizontal plane.

beck

In either technique, the Frankfort horizontal plane of the patient becomes the horizontal plane of reference in the articulator.

wilkie

NASION MINUS 23 mm

• According to Sicher, another skull landmark, the nasion (Fig. 8), can be approximately located in the head as the deepest part of the midline depression just below the level of the eyebrows.

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• The Nasion guide or positioner of the Quick Mount facebow which is designed to be used with the Whip-mix Articulator fits into this depression.

WILKIE

• The nasion guide, or positioner, of the Quick Mount face-bow fits into this depression. This guide can be moved in and out, but not up and down, from its attachment to the face-bow crossbar.
• The crossbar is located 23 mm below the midpoint of the nasion positioner.
• When the face-bow is positioned anteriorly by the nasion guide, the crossbar will be in the approximate region of orbitale.
• During the face-bow transfer, the crossbar of the face-bow supports the upper frame of the Whip-Mix articulator.

WILKIE

Whipmix Quick Mount Facebow

INCISAL EDGE PLUS ARTICULATOR MIDPOINT TO ARTICULATOR AXIS-HORIZONTAL PLANE DISTANCE.

• Guichet has emphasized that a logical position for the casts in the articulator would be one which would position the plane of occlusion near the mid-horizontal plane of the articulator.
• A deviation from this objective may position casts high or low relative to the instrument’s upper and lower arms and may lead to improper occlusal relationship.

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• In accordance with this concept, the distance from the articulator’s mid-horizontal plane to the articulator’s axis-horizontal plane is measured. This same distance is measured above the existing or planned incisal edges on the patient, and its uppermost point is marked as the anterior point of reference on the face.
• The dentist can then proceed, knowing that the incisal edges will fall on the articulator’s mid-horizontal plane unless a subsequent decision raises or lowers them.

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Only the incisal edges or the most anterior portion of the occlusal plane will be midway between the upper and lower articulator arms. A tentative or an actual occlusal plane will not be parallel to the horizontal plane unless by coincidence.

ALAE OF THE NOSE

• A line from the alae of the nose to the center of the auditor meatus is described as Camper’s line.
• Augsburger concluded, in a review of the literature, that the occlusal plane parallels this line with minor variations in different facial types.
• Knowing this, the dentist can transfer Camper’s line from the patient to the articulator by marking the right or left ala on the patient and the hinge points posteriorly.

Maxillary wax occlusion rim should be parallel to Camper’s line on the face.

SELECTION OF ANTERIOR REFERENCE POINT

• Selection of the right anterior point of reference is highly subjective which necessitate special attention during its selection.
• A well designed and precise selection of the anterior reference point will allow the dentist to clearly visualize the anterior teeth and the occlusion in the articulator in the same frame of reference that would be used when looking at the patient.
• The objective is usually to achieve a natural appearance in the form and the position of the anterior teeth. Articulating the maxillary cast relative to the Frankfort horizontal plane will attain this goal.

POSTERIOR POINT OF REFERENCE

• Beyorn’s Point
• Gysi’s Point
• Bergstorm’s Point
• Teteruck and Lundeen Point
• Beck’s Point
• Brandup Wogensen Point
• Schlosser’s Point
• Prothero’s Point
• Weingberg Point
• Lauritzen and Bodner’s Point
• Swenson’s Point
• Craddock and Simmon’s Point

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• Beyron’s point: A point 13mm anterior to the posterior margin of tragus of ear on a line drawn from the center of the tragus of tragus to the corner of the eye (Tragus-Canthus line)

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• Gysi's point: A point 11-13mm anterior to upper tragus of the ear on a line drawn from the center of the tragus of tragus to the corner of the eye (Tragus-Canthus line).

• Bergstorm's point: A point 10mm anterior to the center of the spherical insert for the external acoustic meatus and 7mm below the Frankfort horizontal plane.

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• Teteruck and Lundeen's point: 13mm from the base of the tragus to the canthus.

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Beck’s Point: 10mm anterior to the center of the external auditory meatus and 7mm below the Frankfort plane.

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• Brandrup - Wognsen point: On line extending from the tragus to the lateral angle of eye, a point is marked at about 12mm in front of posterior margin of the most prominent tragus.

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• Schlosser's point: A line drawn from the upper margin of the external auditory meatus to the outer canthus of eye. A point about 13mm in front of the tensed anterior margin of the meatus, on this line is used as the arbitrary hinge axis point.

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• Prothero’s Point: A line drawn from top of Richey condylar marker (placed in the external auditory meatus) to the outer canthus of eye. A point 13mm anterior to Richey condylar marker to this line is used as the arbitrary reference point.

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• Weinberg’s Point: This is a point 11-13mm anterior to the reference line drawn from the middle and the posterior border of the tragus of ear to the corner of eye.

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• Swenson’s Point: Described arbitrary location of the condyles as 11mm anterior to the meatus of ear on reference line from top of the meatus to the corner of eye.

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• Lauritzen and Bodner's point: A point 13mm anterior to the tragus on the tragus-canthus line.

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• Craddock and Symmon's point: A point 1cm anterior along a line drawn from the upper free margin of the tragus of ear to corner of eye.

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Arbitary Facebow

Kinematic Facebow

SIGNIFICANCE OF A FACEBOW USAGE

• The theoretical advantage of using a facebow includes the anatomical similarity of the resulting relationship between the teeth and the Condyles.
• The facebow transfer record is an integral part in analyzing and studying the occlusion of the natural teeth.
• The better the cast on an articulator duplicate the distances to the condylar rotation centers, the less the potential for articulator produced errors of motion. A facebow record is used to transfer these relationships.
• It records the intercondylar distance.
• The true hinge axis is recorded when kinematic facebow is used.

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ADVANTAGES

-ease and efficiency of use

-sterilizable parts

-one piece low maintenance design

-adaptability to other articulators

-direct and indirect mounting capability

-lower cost

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DISADVANTAGE

-inability to measure inter-condylar distance

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PROCEDURE

1. BITE FORK PREPARATION

Dentulous

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Edentulous patient

2. Bow preparation

3. PATIENT APPLICATION

MOUNTING ON TO THE ARTICULATOR

RECENT ADVANCES

Today there are more advanced techniques that make use of ultrasonic arcs, connected to computers with graphical representations and parameter calculations for programming the articulator, which record and analyse all the movements of patient’s mandible.

VIRTUAL FACEBOW TECHNIQUE

• This article describes a virtual technique for transferring the location of a digitized cast from the patient to a virtual articulator (virtual facebow transfer)

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• Using a virtual procedure, the maxillary digital cast is transferred to a virtual articulator by means of reverse engineering devices.

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• The following devices necessary to carry out this protocol are available in many contemporary practices: an intraoral scanner, a digital camera, and a specific software.

Solaberrieta E, Garmendia A, Minguez R, Brizuela A, Pradies G. Virtual facebow technique. Journal of Prosthetic Dentistry. 2015 Dec 1;114(6):751-5.

Technique

• Scan the maxillary and mandibular dental arches of the patient with an intraoral dental scanner.
• Place three adhesive targets on patient’s head.

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• Locate the irreversible hydrocolloid or scannable elastomeric impression material on a plastic colored facebow fork and introduce the facebow fork into patient’s mouth, pushing it against the maxillary arch.
• Make 8-10 photographs by using a digital camera and reverse engineering software to obtain the 3D spatial relationship of the shape of the head with target points related to the facebow.

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• Scan the impression and front side of the facebow fork with the intraoral dental scanner.
• Using reverse engineering software, load the facebow fork 3D geometry and align it to the maxillary digital cast by using the best fit command.

• Alignment of 3D face- facebow fork and impression facebow fork
• Blend the different surfaces of scanned maxillary digital cast into a single virtual cast.
• Eliminate surface abnormalities, remesh the organization of the triangulated mesh of points, and fill in the surface gaps that remain after data elaboration.
• Create the cranial coordinate system by using two TMJ points and the infraorbital point, locating the maxillary digital cast on this reference system.

• Transfer the maxillary digital cast to the virtual articulator software, bringinging the cranial coordinate system to coincide with the virtual articulator’s coordinate system.
• Locate the mandibular digital cast, scanning the virtual interocclusal record with an intraoral scanner in centric occlusion from three directions ( left, right and front)
• Match these scans with the maxillary and mandibular digital cast, positioning the mandibular digital cast towards the maxillary digital cast in virtual articulator in maximum intercuspation.

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CONCLUSION

• Failure to use the face bow 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 be accurately captured and transferred to the articulator. So it becomes a fine representative of the patient and biologically acceptable rotation is possible.
• By using the face bow the risk of occlusal errors are minimized thereby enhancing the accuracy of occlusion of new restoration or oral appliances upon insertion which facilitates patient comfort and acceptance of prosthesis.

REFERENCES