ORIENTATION JAW RELATIONJAW RELATION: Three dimensional spatial relationship of the maxillae to the mandible. According to boucher, Jaw relations can be classified into : 1. Orientation 2. Vertical 3. Horizontal Orientation relations establish the reference in the cranium. Vertical relation establishes the amount of jaw separation allowable for the dentures. Horizontal relations establish the front-to-back and side-to-side relationships of one jaw to the other.ORIENTAION JAW RELATION: To record orientation jaw relation, mandible is kept in its most posterior position atwhich it can rotate in the sagittal plane around an imaginary transverse axis passing throughor near the condyles. This record gives the angulation of maxilla to the base of skull. The relation ofmaxillary cast to the axis of rotation of the articulator must be the same relation that existsbetween the maxillae and the terminal hinge axis in the skull. This is necessary in order todevelop on the articulator certain occlusal scheme that will need minimum adjustment in themouth. Casts are mounted on the articulator with the maxillary cast preferably related to theterminal hinge axis and the mandibular cast related to the maxillary cast by means of atentative centric relation record. Reproducing the horizontal axis is on the most importantsteps because accuracy of all the other relationships depends on a correct starting poing. So itis necessary to know first about terminal hinge axis or transverse horizontal axis. It is important to note that it the relationship between the jaws and the axis ofmovement, not an anatomical relationship between the jaws and the TMJ¶s.HINGE AXIS: An imaginary line around which the mandible may rotate within the sagittal planeTerminal hinge axis: An imaginary line around which the mandible may rotate within the sagittal plane inthe most retruded postion. As the patient¶s jaw opens and closes, the posterior border of its movement, at least inthe earliest phases, is the arc of a circle in the sagittal plane around an imaginary transverseaxis passing through or near condyles. The same is true for articulator also. Similarly other
movement also occurs in arcs. For an accurate reproduction of those movements, the axes ofthe those arcs should coinicide between patient and instrument, particulary when verticaldimensions are to be changed. Review of literature: - Gray¶s anatomy - first described hinge like action in the lower compartment of the temporomandibular joint. - The importance of locating the transverse horizontal axis (THA) was first expressed by Campion in 1905. - 1921 ± McCollum, Stuart and others reported discovery of the first positive method of locating the axis. He emphasized that the maxillary cast should be at the same orientation on the articulator as the patient¶s maxillae was to the temporomandibular joints. - Brotman, Weinberg and Zuckerman demonstrated the importance of this axis through mathematical models of occlusal errors that would result with deviations from the THA of the patient. - Wilkie also described the importance of the anterior reference point. - Lauritzen and Wolford demonstrated varying degrees of accuracy in locating the THA on patients in the range of 0.5 to 2 mm among skilled operators. - Kurth and Feinstein Borgh and Posselt, Winstanley, and Bowley and Piercell demonstrated the same magnitude of error on experimental model systems with a known arc of closure but without patient-related variables. These studies have emphasized that a certain amount of error would be expected because of operator- and equipment-related variables. - Snow ± recognized the importance of the hinge axis in mandibular movements and developed a face-bow to be used to transfer the postion of the axis of the articulator. Significance: - Learnable, repeatable and recordable position that co-incides with the position of centric relation - Condyles are in definitive postion in fossae during terminal hinge movements.FACE-BOW: Face bow is calliper like device used to record the relationship of the maxillae to thetemporomandibular joints. The primary use of facebow is to mount the maxillary cast accurately on thearticulator. It uses 3 distrinct reference points (two posteriors and one anterior) to locate thecast on the articulator. The posterior reference points are the hinge axis of each condyle andanterior point is the arbitrary point.
Purpose : y To orient the maxillary cast to the articulator in the same relationship to the opening and closing axis of the articulator as exists between the maxillae and the opening and closing axis in the temporomandibular joints. y It also retains the cast in its correct relation until it is attached to the upper member with plaster.Review: y 1880 ± Hayes used a tongue like device which is called ³calliper´. This instrument was not used as the facebow is used today, but it did relate the edian incisal point to its distance from the condyles. y Gysi ± developed an instrument similar to a facebow primarily to record the paths of the condyles. However, it was also used to transfer the maxillary cast to the articulator. y 1905 ± Campion was the first who felt that the axis of the articulator should coincide with that of the patient. y Snow ± introduced Snow face-bow. The majority of facebows used today are modification of this. The snow type of facebow utilizes arbitrarily located marks on the skin at the condyle points as the hinge axis position. So this is called arbitrary face- bow. The condylar rods are adjusted to these points. There are no adjustments to compensate for asymmetric hinge points either vertically or horizontally. Therefore, if the terminal hinge rotational centers are to be located, a facebow capable of being adjusted to any asymmetric location must be used. y Preston presented various limitations and errors of the facebow transfer technique due to both equipment and anatomic asymmetry. The occlusal errors that result from deviations from the THA of the patient were shown to be due to the differences in the arc of closure between the patient and the articulator. Parts of facebow: y U-shaped frame: It is large enough to extend from the region of one TMJ around the front of the face (5 to 7.5 cm in front) to the other TMJ and wide enough to avoid contacts with the sides of the face. y Condylar rods: It is that part that contact the skin near the TMJ. y Fork: it is that part that attaches to the occlusal rims. The fork attaches to the face bow by means of a locking device, which also serves to support the facebow, the maxillary occlusal rim and the maxillary cast while the cast are being attached to the articulator. The fork of the arbitrary facebow is attached to the maxillary occlusal rim, so the record is a simple relationship between the upper jaw and the approximate axis of the jaw opening. Indication: y When cusped teeth are used which allows minor changes in the occlusal vertical dimensions without having to make new maxillomandibular records
y Balanced occlusion in eccentric position is desired y Definite cusp fossa or cusp tip to cusp incline relation is desired. y Interocculsal check records are used for verification of jaw position. y The occlusal vertical dimension is subject to change, and the alteration of tooth occlusal surfaces are necessary to accommodate the change.Different school of thoughts regarding use of facebow: - When monoplane teeth are arranged on a plane in occlusal balance and the mandible is in the most retruded relation to the maxillae at an acceptable vertical dimension of jaw separation. o It is questionable if one occlusal form of posterior tooth is indicated for all edentulous patients. o Electromyographic, laminographic, cinefluoroscopic ad 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. - No alteration of the occluding surfaces of the teeth that would necessitate changes in the vertical dimension of the occlusion originally recorded. o 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. o The occluding surfaces of the teeth are alteredto correct for changes in the vertical dimension of occlusion. - No inter-occlusal check records that would be at a different vertical dimension from that in the original interocclusal record. o Dentists use inter-occlusal records check record to verify articulator mounting. - When articulators that are not designed to accept a face-bow transfer are used in the denture procedures. o When an articulator with rotational centers that can be adjusted to conform to the rotational centers of mandibular movements is used, the face-bow is an accurate method of relating the casts to these centers. o There is no scientific proof that the errors when the face-bow is not used are within the acceptable physiologic range in all individuals.Encountered errors when facebows are not used for orientation: y Disharmony in centri occlusion. y Anterior or posterior and/or superior or inferior to the axis when the vertical dimensios recorded is not maintained.
y Below or posterior to the rotational centers so that the distal cusp inclines of the mandibular teeth make premature contact with the mesial cusp inclines of the maxillary teeth. y Above and anterior to the rotational centers so that the mesial cusp inclines of the mandibular teeth make premature contact with distal cusp inclines of the maxillary teeth.Types :Facebow is of 2 types: 1. Kinematic 2. ArbitraryKinematic / hinge facebow : The kinematic type of facebow is used to locate the terminal hinge axis andtransfer this record to the articulator when mounting the maxillary cast. This type of facebowcan be used on the articulator with a slight mechanical modification of the articulators.Arbitrary face bow: It is the one which is generally used in the construction of complete denturesand is based on average computations of an axis opening of the jaw. It is simple to use andrelatively accurate. Kinematic Arbitrary Less accurate AccurateRecords true hinge axis Records hinge axis arbitrary using anatomic average values.Time consuming Less time consumingRequires assembly to customized accordingly Self centeringError of 1mm is expected Error of 5mm is expectedDoesn¶t use anterior reference point Uses anterior reference point for future adjustments to the articulator.Indication: Indications: - Particularly when change in the - For all the complete denture vertical dimesion of occlusion is procedures where change in vertical made. dimensions at occlusion is not significant.
STEPS IN FACEBOW TRANSFER PROCEDURE IN COMPLETE DENTURE: 1. PRELIMINARY STEP: - Seat patient in comfortable position in the dental chair with backrest extending to slightly below the scapula. The patient¶s head should be in upright position with the headrest supporting the occiput. 2. LOCATION OF HINGE AXIS: Can be done by two methods: - Arbitrarily (with ear piece) - By kinematic facebow 3. FACEBOW RECORDING 4. FACEBOW TRANSFER 5. MOUNTING OF THE FACE-BOW 6. ATTACHING OF THE CASTARBITRARY FACE-BOW:In complete denture: - Adjust the rims and retention and stability of the denture base is checked. - Attach fork to the modelling compound rims . - Temper in water and seat the fork with rims into to the mouth - Remove the fork from the mouth - Chill it and check by keeping it on the cast - Reseat the rims in the mouth. - Ask the patient to grasp both arms of the facebow and guide the plastic earpiece in the external auditory meatus. - At the same time, the operator should slide the toggle onto the shaft of the bite fork, making certain that toggle is postioned above the shaft. - Tighten the 3 thumbscrew on the top of the face-bow. - Adjust the anterior reference point and tighten the thumb screw. - Transfer complete.In Fixed Prosthodontics:Anteriror reference point: Anterior reference point such as inner canthus of the eye or a freckle or mole on theskin is selected.Facebow record: - Add modelling compound/ hard base-plate wax to the facebow fork.
- Temper in water and seat the fork, making indetnations of the maxillary cusp tips deep enough to be able to located on cast - Remove the fork from the mouth - Chill it and check by keeping it on the cast - Reseat fork in mouth without distortion and ask patient to secure it between arches. - Ask the patient to grasp both arms of the facebow and guide the plastic earpiece in the external auditory meatus. - At the same time, the operator should slide the toggle onto the shaft of the bite fork, making certain that toggle is postioned above the shaft. - Tighten the 3 thumbscrew on the top of the face-bow. - Adjust the anterior reference point and tighten the thumb screw. - Transfer complete.KINEMATIC FACE-BOW: Hinge axis can be determined to be within 1mm. Kinematic facebow consists of 3components: - Transverse component - Two adjustable side armsIn complete denture:Hinge axis location: - Make an accurate impression of the mandibular basal seat and pour an accurate stone cast. - On the cast make an accurate record base of self-curing or processed acrylic resin. - Attach cpmpound occlusal rims firmly to the record base and secure a specifically designed bite fork to the rims, with the stem extending forward parallel to the sagittal plane. - Attach this assembly to the mandible with chin clamps or chin straps. Note: movement between teeth and the clutch may produce inaccurate styli rotaions.Facebow transfer: - Attach a hinge-bow to the stem and adjust the styli to the locations of the condyles. - The condyles are located by placing marks 13mm from the external auditory meatus on a line from the outer canthus of the eye to the superior border of the tragus of ear.
- Place the patient is semi supine position with headrest tilted slightly backward. - Assist or guide the patient in making hing openings and closings. - When the rotational centers have been located and verified, secure the styli. - Place the patient in upright postion with the head unsupported. - Move the styli to the side of the face and record with the dye. These points should be tattooed.In fixed prosthodontics:Hinge axis recording: 1. A clutch , which is essentially a segmented impression traylike device, is attached onto the mandibular teeth with a suitable rigid material such as impression plaster. 2. The transverse rod is attached to the transverse member that protrudes from the patient¶s mouth. 3. The side arms are then attached to transverse member and adjusted so that the stule are as close to the joint as possible. 4. Mandible is then manibpulated to produce terminal hinge movement. And the stylus location are adjusted with thumbscrews until they make pure rotational movement. 5. When pure rotational movement is verified, the position of hinge axis is marked on the patietnt¶s skin.Facebow transfer: 1. An impression of the maxillary cusp tips is obtained in a suitable recording medium on facebow fork. 2. The facebow is attached to the fork and arms are adjusted until the styli are aligned with the hinge axis marks. 3. The facebow is then transferred to the articulatorPROCEDURE FOR DIFFERENT TYPES OF FACEBOW: I. FOR HANAU FACE-BOW:Arbitrary axis for hanau face-bow: - Richey condylar marker is used to scrine an arc about 13mm anterior to the external auditory meatus. Using a ruler, held so that it runs from the corners of the eye to the top of the tragus of the ear, place a mark where this line intersects the arc made by the condyle marker. This locates the arbitrary axis for the hanau face-
bow condyle rods, which is within 2mm of the true center of the opening axis of the jaws. - Plane of orientation can also be determined by the infraorbital notch as a third point of reference with the infra-orbital pointer of the hanau face ±bow.Face-bow transfer (hanau face-bow): - The bite fork is heated and inserted in the maxillary rim parallel to the occlusal plane. - The recoding base is inserted into the mouth, and the extension rod of the bite fork is passed through the locking device of the face-bow. - The condylar rods are oriented over the arbitrary centers of rotation and moved from side to side until the readings on the condyle rod scales are the same on both sides while the crossbar os parallel to a line between the pupils of the eyes. - The locknuts at the condylar rods are then tightened to suspend the face-bow, and the bite fork is securely attached to the assembly. - The condylar locknuts are then released, and the facebow and attached occlusal rim are transferred to the articulator. - The instrument should be locked in centric with the incisal pin flush with the upper member. - The condylar rods of the face-bow are inserted over the condylar ball extensions and centered before being locked in position by tightening the locknuts. - 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. A Hanau mounting support or prop may be necessary to support the weight of the maxillary cast and plaster during the mounting process. II. FOR WHIP-MIX FACE-BOW:Arbitrary axis for whip-mix face-bow: - Locating an arbitrary axis is not necessary when using whip-mix articulator, since it was designed and constructed after much research with a built-in-locator. The insertion of plastic ear piece into the external auditory meatus automatically locates the face-bow in the proper position.Face-bow transfer (whip-mix face-bow): - Attach the maxillary stabilized base to the bite fork. - Insert in the mouth and have the patient hold it in place with both thumbs using light pressure, or place the lower base in the mouth and close against the bite fork. - The face-bow is carried to the patient¶s face, and the face-bow fork toggle assembly is slipped onto the stem of the bow fork; the plastic earpieces are inserted into the external auditory meatus and brought slightly forward. - The nasion relator assembly is attached to the face-bow, the plastic nose piece should rest on the nasion, and the face-bow is tightened. - The face-bow is locked to the bite fork.
- The positioning of the face-bow and locking of the bite fork to the facebow must be done carefully or the purpose of the face-bow transfer is defeated. The entire assembly is then carried to the articulator. - The upper cast is attached to the articulator. - The proper use of the face-bow prevents errors of occlusion in the finished dentures during eccentric movement of the lower jaw within the functional range. III. FOR DENAR SLIDEMATIC FACEBOW:Arbitrary axis for Denar Slidematic Facebow: - It uses the external auditory meatus for determining the arbitrary hinge axis location. A built-in reference pointer aligns the face-bow with the horizontal reference plane. The anterior reference point is marked on the patient¶s right side using the Denar Reference Plane Locator. The point is 43mm above the incisal edge of the right central or lateral incisor for a dentulous patient. For an edentulous patient this distance is measured up from the lower border of the upper lip when the lips are relaxed.Face-bow transfer (denar slidematic face-bow): - The bite fork is heated and inserted into the maxillary occlusal rim parallel to the occlusal plane with the patient¶s midline aligned with the index ring of the bite fork. - The facebow is assembled on the patient by inserting the stem of the bite fork into the transfer jig as the ear piece is inserted into the external auditory meatus. - The right and left arms of the face-bow are geared for equidistance movement from its center. - Lock screw on the face-bow is tightened and lock screw on the anterior reference point is loosened. - The face-bow is raised or lowered until the pointer is aligned precisely with the anterior reference point. - Clamps on the transfer jig are then tightened. - The scale on the face-bow represents half the patient¶s intercondylar distance, which is of value in setting articulators having an intercondylar distance adjustment. The inter-condylar distance is recorded at this time. - The lock-screw on the face-bow is loosened, and the bow is opened and removed from the patient. - The face-bow is detached from the bite fork assembly. - The incisal table is removed from the articulator and the articulator index inserted in its place. - The transfer jig with the bite fork and maxillary occlusion rim attached is secured in the articulator index prior to mounting the maxillary cast.ATTACHING THE MAXILLARY CAST TO THE ARTICULATOR: Several ways are available for attaching the maxillary cast to the articulator:
- Artic-U-Loc : consists of a striker plate embedded in the base of the cast when it is poured, and a magnet that holds the cast to the articulator. This makes a secure mounting without the use of a pin. - Hanau split remounting plate: not as handy to use. The two parts are held together by a pin. The Whip-mix remounting plate, suggested by Dr. Samuel E. Guyer, provides a precise mounting and is easy to use. A pin provides a means of retention. - Notch method: Does not require any additional equipment. This has disadvantage of requiring plaster or compound to reattach it to the articulator should the cast come loose during any stage of the procedure.REFERENCES: 1. Sheldon winkler 2nd edition OF ESSENTIALSOF COMPLETE DENTURE PROSTHESIS 2. Charles m. heartwell, Jr, urthur O. Rahn . Syllabus of complete denture 4th edition. 3. Zarb and Bolender 12th edition . Prosthodontic treatment of edentulous patient/. 4. Rosenstiel, land, Fujimoto. Contemporary fixed prosthodontics 3rd edition. 5. Shillinburg et al. Fundamentals of fixed prosthodontics 3rd edition.