facebow

Dr. Monia M.N. Kandil

-I- Face bows

Definition

A dental device which is used to determine the relationship between the maxilla and the axis of rotation (hinge axis) of the TMJ and transfer this relation to the articulator, to ensure the best mounting of the upper cast in relation to the articulators.
Face-bow

Is an imaginary transverse line around which the mandible can rotate without translatory movement of the condyles, about the hinge axis.

Hinge Movement

Free way space


MP
MO
ICP
RCP
HA
MP = Maximal protrusion ICP = Intercuspal position RCP= Retruded Contact position HA = Hinge axis MO = Maximum opening EE=edge to edge
Posselt’s Figure EE



1. Exact hinge axis: Accurate method using “kinematic” hinge axis locator (mandibular face bow).

2. Arbitrary hinge axis: based on anatomic averages:

Beyron’s point 11-13 mm from tragus Palpate condylar pole.Ear-bow. 13mm
The condylar axis lies nearly 11 mm anterior to the tragus of the ear on an imaginary line between the outer canthus of the eye and the upper surface of the tragus of the ear or lies 13 mm in front of the anterior margin of the external auditory meatus.

So.. The face-bows types

Maxillary (Arbitrary) face-bows are less accurate than the Kinematic type. Mandibular (Kinematic face-bows) can reproduce the exact opening & closing movement of the patient on the articulator. When the relationship between the maxilla & the axis of rotation has been reproduced, the mandibular cast can be accurately positioned & mounted through the use of an interocclusal record.

MAXILLARY FACE BOW

 ( Mandibular Face Bow )

To locate the exact terminal hinge axis (rotational axis of the TMJ )

2. To record the centric relation.
A device, with adjustable side arms, which is attached to the mandible and used:

Mandibular Face Bow

Limited opening and closing allows the condylar rods to draw arcs. The rods are moved towards the center of the arcs, until they move in a point . The latter is called the still point and represents the condylar axis. The condyle in this position lies in the most retruded unstrained position in the glenoid fossa, so mandible and maxilla are in centric.

So the Face-bow Records

1) Duplication of the same opening & closing arc as natural teeth and 2) Aids in reproducing lateral movements.


Occlusal discrepancies in the mouth. If discrepancies are left uncorrected, occlusal & associated neuromuscular disorders may result.

Components:

Graduated Condylar Rods
Tightening clamp
U Shaped Bow
Bite Fork
Universal Joint / Jack Clamp
Infraorbital Pointer
Graduations on the rod

1- Facebow with infra-orbital pointer.

2- The ear-bow uses the external auditory meatus reference point.

Face-bow Record(maxillary)

Casts are prepared for mounting by cutting in thickest part of the base: three V-shaped grooves, two in the posterior section and one in the anterior.
Before Face Bow Record

11- 13 mm

1- The condylar axis is determined either: arbitrary or by using mandibular face bow record.

1- Mark the relative position of the condylar axis.

The condylar axis lies nearly 13 mm. In front of the anterior margin of the external auditory meatus or 11 mm. anterior to the tragus of the ear.


2- A third point of reference placed on the lowest point on the infra orbital margin, is determined for establishing the axio-orbital plane.


3- Bite fork is heated and inserted into the rim midway its height and parallel to its plane.

X
4- Insert occlusion block in patient’s mouth and keep it in place. The lower occlusion block may be used for this purpose to support the upper block.


5- Slip the clamp of face-bow on the stem of bite fork. Let the clamp be loose.
6- Adjust the condylar rods of face-bow to the width of the face, in such a way that:
A- Both condylar rods lie on cheek marks. B- Condylar rods show equal calibration with slight tension.

The equal calibration can be done by:

A- Lock one condylar rod to show calibration of 6, for example, place it over the mark of the condylar axis. b- Bring the other cond. rod over the opposite mark of cond. axis, apply slight tension and read calibration on that side. Say it reads for example 8. Add both calibrations together and divide them equally 6+8=14/2=7. c- Lock condylar rods firmly.


d- Recheck and be sure that no displacement occur during locking of clamp. E- Lock the clamp firmly on the stem of bite fork then release condylar rods after adjustment of infra orbital pointer. this establishes the elevation of the face bow in relation to the axis-orbital plane.

7- Adjust the infra-orbital pointer to be placed on the lowest point on the infra orbital margin.

8- Generally the intercondylar axis will parallel the interpupillary plane. Check the alignment of the face-bow with that plane.
9- The universal joints are then tightened with then the entire assembly is inspected to make certain that :


A- The maxillary record base is properly seated. B- The fork parallels the occlusal plane. C- The frame of the face-bow parallels the interpupillary plane. D- The condylar rods are just lightly contacting the face over the arbitrarily located axis. E- The condylar rods show equal readings. F- All lock screws are firmly set.

Maxillary Face Bow Transfer

The slide bar clamp is unscrewed and The entire assemble is now removed and transferred to the articulator.


Assembly is now centralized on the articulator. Again notice position of - condylar rods - infraorbital pointer - bitefork bypass incisal pin
Maxillary Face Bow Transfer

The entire assemble is transferred to the articulator.

Re-equalizing the calibrations to bilaterally equivalent readings of the condylar rods, before tightening. The face bow is adjusted by the elevating screw to align the occlusal plane with the groove marked around the halfway point of the incisal pin.

The third point reference, must be positioned in its place.

The entire face bow with maxillary cast in place must be raised until the tip of the pointer contacts the infraorbital plane indicator (infraorbital plate).

The cast is then supported in position (using Hanau mounting support prop) to support the weight of the maxillary cast and plaster during the mounting process.
Then accurately mount the maxillary cast to the articulator

Second type of Max. face bows

Procedures



MAXILLARY EAR BOW With Nose indicator

Mounting the upper cast

By face bow record.
2.By Bonwill triangle.

Mounting the upper cast

By Bonwill triangle
Plasticine

Vertical relations

Vertical relations
Rest vertical dimension The distance between two selected points one on the fixed part (maxillae) and one on the movable part (mandible) when the maxillofacial musculature is in a state of tonic equilibrium.
Occlusal vertical dimension The distance between two selected points one on the fixed part (maxillae) and one on the movable part (mandible) when occluding members (teeth) are in contact.

At Occlusion

At rest
Free-way space



There are many of factors that affect the measurement of vertical dimension which is: Patient must sit in upright position with head unsupported. Any tension should be avoided. Special attention and enough time should be given to those patients having neuromuscular disorder. No valid method for all patients, so it is advisable to use several methods and compare the result

Recording the rest vertical dimension (physiological methods):

Facial measurements (reference points)Tactile sense (opening ------- closing)Phonetics (em ….. 33…..55) Facial expression (skin tone and the lips contour) Anatomic land marks (Willis guide)

Recording the occlusal vertical dimension (mechanical methods):

Pre-extraction records Profile photographs Radiography (cephalometric profile and the condyles in the fossae) Articulated cast Facial measurements Swallowing followed by relaxing (cones of a soft wax ) Patients tactile sense Former dentures Edentulous patients (wax occlusion rims)

CENTRIC RELATION

METHODS TO GUIDE THE MANDIBLE IN CENTRIC RELATION
1 . Tongue retrusion 2 . Swallowing 3 . Fatigue 4 . Relaxation 5 . The Operator’s Fingers

Method Of Jaw Relation Records

WAX REGISTRATION METHOD  Physiological method. GRAPHIC TRACING METHODS  Intra & extra oral tracer. TERMINAL HINGE AXIS METHOD  mentioned before. CHEW-IN OR FUNCTIONAL RECORD METHODS  - Needle house, Patterson & Pantographic method-

Wax Registration Method

Graphic Tracing Method


CHEW-IN OR FUNCTIONAL RECORD METHOD - Needle house-
Bit rim from imp. comp. against 4 metal styli in the premolar & molars region: when the patient move his jaws the styli graved the occl. pattern within compound.

CHEW-IN OR FUNCTIONAL RECORD METHODS - Patterson -

The wax-bit has a groove that filled with a mixure of carbo-rundum & dental plaster, to indicate mand. movement

Pantograph

ECCENTRIC JAW RELATIONS
Methods of Registration
Wax registration method.Graphic tracing method.Chew – in or Functional method. Recording Protrusive and Lateral Relations to Adjust the Controls of Articulator.

Christensen Phenomena

When the mandible moves to edge to edge position , separation occurs distally between the natural dentition or occlusion rims .
Protrusive Record


The occlusion rims are reestablished and checked for 3mm. Clearance in a protrusive excursion

The protrusive relationship determines the angle of the horizontal condylar path

N.B. Physiologically 2mm. protrusion is the limit of functional range, But from the mechanical point of view, practically it is found that less than 4mm. protrusion increase the error of setting the condylar guidance of the articulator.

Horizontal condylar guidance

Lateral condylar guidance

Terminology

(Eccentric) Excursion The movement occurring when the mandible moves away from maximum intercuspation

Directions of Excursive Movements 1. Protrusive 2. Laterotrusive (working movement) 3. Mediotrusive (non-working movement) 4. Lateroprotrusive

Protrusive A movement of the mandible towards the anterior, pushing it forwards

Excursive Movements

Excursive Movements

Protrusive

Protrusive Record

Used to set condylar inclinationRecord is taken with the mandible in a protrusive jaw relationship  usually with “Wax sheet”

Excursive Movements

LaterotrusiveAlso called a working movementA movement of the mandibular condyle in a lateral direction, away from the midline  e.g. Left or right.

Mediotrusive Also called non-working or balancing movement. A movement of the mandibular condyle in a medial direction, towards the midline.
Excursive Movements

Lateral & Medial Excursions

Lateral & Medial Excursions

Excursive Movements

Laterotrusive and Mediotrusive
Balancing Side
Working Side



Lateroprotrusive A movement of the mandibular condyle with a protrusive and a lateral component. A combination of a protrusive and laterotrusive movement.
Excursive Movements

Protrusive Records

Balanced occlusion Used to set the condylar guidance Protrude a minimum of 5-6 mm Registration material placed bilaterally, posterior to canines Patient closes with mandible positioned anteriorly

Material must interdigitate with the opposing “V-shaped” notches Make at height greater than the established occlusal vertical dimensionWax is removed, chilledCondylar elements are released from hinge positionInstrument protruded, and the records approximated Protrusive Records

Factors that affect the centric relation record :

Resiliency of the tissues supporting the denture bases. Stability and retention of record bases. The tempro-mandibular joint and its neuro muscular mechanism. Technique employed in making the records. Amount of pressure applied in making the records. The skill of the dentist

Eccentric relation record :

The purpose of these records is to adjust the articulator to simulate the eccentric movements (lateral and protrusive) of the mandible to the maxillae. This adjustment permit arrangement of the teeth in balanced occlusion. The records are made in the same manner as for centric records, for lateral movement record, Hanu recommend the following formula : L=(H/8)+12 L :lateral condylar inclination degree. H :horizontal condylar inclination degree.

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