FACE BOW A REQUIRED ENTITY FOR LOCATION OF THE HINGE AXIS
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CONTENTS Introduction Definition of Face Bow and Hinge Axis Review of the literature about Hinge axis & Face Bow History of Hinge axis & Face Bow Importance of locating hinge axis Concepts regarding hinge axis Location of hinge axis__ Arbitrary __ Kinematic Face bow -Parts Types of face bow
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Anterior & posterior points of reference Face bow recording procedure Mounting on to the articulator Significance of using face bow Indications for using face bow Summary & Conclusion References.
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INTRODUCTION The missing teeth are restored by the CD,FPD,RPD to restore function & esthetics .It is essential to develop proper occlusion for maintaining health of supporting structures orofacial musculature,TMJ. So there is a need for accurately locating the hinge axis & recording & transferring the same on to the articulator,
to enable the accurate reproduction of occlusal
relationship on an articulator. This is achieved by Face bow which records the position of jaws in relation to the condylar mechanism & aids in transferring the same relation onto the articulator.
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Definition of the face bow
The face bow is a caliper like device that is used to record the relationship of jaws to the opening axis of jaws and to orient the cast in this same relationship to the opening axis of articulator.- GPT
Definition of hinge axis
The hinge axis is defind as an imaginary line passing through the two mandibular condyles & around which the mandible may rotate without translatory movement.- GPT Terminal hinge axis It is an imaginary line which passes horizontally through the rotation centers of the right & left condyles when the condyles are in their most distal / retruded , unstrained position in their respective articular / glenoid fossa. www.indiandentalacademy.com
REVIEW OF LITERATURE OF HINGE AXIS & FACE BOW ď ą
Study was conducted by L. E. Kurth & I. K. Feinstein in
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1951
With the aid of an articulator & working model , they demonstrated that more than one point may serve as hinge axis. So they concluded that infinite no.of points exist which may serve as hinge points. It is unlikely to locate the hinge axis accurately .
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Robert G Schollhorn in 1957 He recorded the arbitrary center & true hinge axis in 70 dental students. He concluded that arbitrary axis of rotation which is 13mm ant. to the posterior margin of the tragus on tragal canthus line lies close to an average determined axis. In 95% of subjects Kinematic center lies within 5mm radius , Arstad considered to be within normal limits. So determining kinematic center is not necessary. www.indiandentalacademy.com
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Study conducted by Borgh &Posselt in 1958. Hinge axis points were registered by using Kinematic face bow mounted on a modified Hanau adjustable articulator. They conducted the experiment with 10 &15 degree openings. They concluded that the range of variation in location of hinge axis point were 1.5 mm for 10 degree opening & 1mm for 15 degree opening.
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Study was conducted by Richard l . Christiansen in the year 1959. He mounted the maxillary casts arbitrarily & with face bow records & studied the errors in occlusion. He concluded that it is advantageous to simulate on the articulator the anatomic relationships of residual ridges to the condyles for more harmoniously occluding complete dentures.
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Study conducted by T. D Foster in 1959. He stated that permanent study casts would be of more value if they are mounted in correct relationship to the FH plane particularly in facial deformity involving the jaws.
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Study was conducted by Arne Lauritzen & George H. Bodner in 1961. They marked true hinge axis & arbitrary hinge axis by 3 methods .They concluded that in 67% of cases the true hinge axis was 5 to 13 mm away from the arbitrarily located hinge axis points.
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Study was conducted by Vincent R. Trappazzan , Jhon B.Lazzari in 1961. They conducted the study on 14 subjects . They concluded that in 57.2% of the subjects more than one hinge axis point was located on either one or both sides. 42.8% of the subjects showed single hinge axis point on left & right side of the face.
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Study was conducted by Lauritzen & Wolford in 1961.
An experimental instrument was designed to determine how accurately the centers of 15, 10, 5 degree arc of movement could be located consistently. The result indicated that 10 degree range of movement is sufficient for hinge axis location . The attainable accuracy by an experienced operator in locating the the center of10 degree arc is within 0.2mm.
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Study was conducted by Arthur F. Aull in 1963.
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He concluded that the horizontal axis is a hypothetical line. Terminal hinge position is most posterior position. Arbitrary location fails to satisfy the requirements. Do not support the split axis theory. No evidence found to believe that here is more than one hinge location.
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Study was conducted by Walter R. Teteruck in 1966 He recorded the hinge axis by ear piece face bow, hinge axis technique, conventional transfer procedures. He concluded that 33% of the conventional axis locations were within 6mm of the true hinge axis as compared to 56.4% located by ear piece face bow.
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Study was conducted by Vincent R. Trapazzano &John B. Lazzari in 1967.
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They concluded that the patient should be relaxed & two operators are required for location. Because of the presence of multiple hinge axis points increasing or decreasing of the vertical dimension on the articulator needs new interocclusal record.
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Study was conducted by Edwin R. Thorp , Dale E. Smith, & Jack I. Nicholls in 1978. They compared 3 arbitrarily located axis to the true hinge axis locations. they concluded 57% of the arbitrary locations were within 6mm of the true hinge axis. The results revealed very small difference in accuracy between hinge axis face bow,Hanau –132 SM face bow& Whip mix face bow.
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Study was conducted by Keki R. Kotwal in 1979. He made the casts of the dental arches of the skull & made interocclusal records, mounted the casts with & without face bow on to the Whip Mix articulator . He concluded that face bow transfer allows more accurate arc of closure on the articulator when the inter occlusal records are removed .
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Study was conducted by F.M. WALKER in 1980. He concluded that arbitrary hinge axis location dose not exist. Arbitrary axis locations recommended in the literature will create 6mm or more error .The true axis located inferior to tragus canthus line.
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Study was conducted by Mahmoud Khanics Abdel razek in1981 He located the arbitrary hinge axis by 5 methods in 120 dentulous patients & compared with true hinge axis location . He concluded that none of the methods was ideal, Dawson`s palpatory method is acceptable .
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Study was conducted by C.C. Beard, J.A. Clayton in 1981. They concluded that Trapazzano & Lazzari `s study was reproduced & the results were different when a different means of determining the arcing of the styli were used. So the study substantiates other studies that reported the presence of only one terminal hinge axis & also for accurate location high degree interpretation & operator`s perception are required.
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Study was conducted by Jhon H. Pitchford in 1991. He concluded that a compromised esthetic result can be produced by an ant. Reference point not in harmony with design of articulator. Minor variation of the face bow , position of orbitale pointer & indicator will allow an average value transfer of the esthetic reference position to an articulator
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Study was conducted by William W. Nagy, Thomas J. Smithly & Carl G. Wirth in 2002.
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More than 96% of the predetermined points were within 2mm of the kinematic axis, 67% were within 1mm no significant difference between right & left side. They concluded that predetermined axis point was well within 5mm clinical norms for estimated location of transverse horizontal mandibular axis for the population studied.
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Study was conducted by Virgillo Ferrario, Chairello Sforza, Graziano Serrao & Johannes H. Schmitz in 2002 They assessed reliability of the postural face bow by comparing the values with those obtained by computerized non invasive instrument. They concluded that postural face bow reliably reproduced the spatial orientation of the occlusal plane relative to the true horizontal plane.
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HISTORY OF THE HINGE AXIS Gray recognized that mandible moves by rotations, forward & lateral movements of the condyle in the glenoid fossa. Balkwell of England in 1824 called attention to the sliding action Bonwill assumed that forward motion of joint was on a straight line in forward direction. After 40 yrs Walker proved that the motion was forward & downward.
Bennett of England unaware of Balkwell`s proposals showed that condyles in all individuals make a side shift motion to a greater or lesser extent in the lateral movements called as Bennett movement. www.indiandentalacademy.com
Snow in 1899 recognized the importance of hinge axis & he constructed the face bow. Camplon in 1905 concluded that the dental casts should be mounted onto the articulator in such away that the rotational axis of articulator coincides with opening axis of mandible. In 1921 Dr. B.B. McCollum,along with Dr. Robert Harlan located the first actual kinematic axis.
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HISTORY OF THE FACE BOW In 1860 Bonwill concluded that the distance from the center of the condyle to the median incisal point of the lower teeth is 10 cm. In 1866 Balkwill demonstrated an apparatus to measure the angle formed by the occlusal plane of lower teeth & the plane passing through the condyles & incisal plane of lower teeth.
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In 1880 Hayes constructed an apparatus called Caliper with median incisal point localized in relation to the two condyles.
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In 1890 Walker invented Clinometer used to obtain the relative position of the lower cast in relation to the condylar mechanism
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At about a turn of a century Gysi constructed an instrument for registering the condylar path & used as face bow also.
Snow 1899 constructed simple instrument which has become prototype for all the face bows constructed in present days.
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CONCEPTS REGARDING HINGE AXIS ď ą
Sloane stated that The hinge axis is not a theoretical assumption , but definitely demonstrable biomechanical factor.
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Sicher stated that The terminal hinge position is the most retruded position of the mandible, the centric position .
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FOUR MAIN SCHOOLS OF THOUGHTS
Group 1 ---Absolute location of hinge axis. There is a definite transverse axis & should be located accurately. Group 2 ---Arbitrary location of hinge axis Believe that arbitrary location of hinge axis is reliable, even though accurate location is valuable. Craddock & Symmons stated that – The search for the axis is troublesome , more of academic interest as it will never be found more than few mms distant from the true center of the condylar rotations . .
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Group 3 --Non believers in transverse hinge axis location. It is impossible to locate hinge axis with accuracy. More theoretical than practical.
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Group 4 --Split axis rotation Believe that the condyles rotate independent of each other. The proponents of Transographic theory. Page first suggested & Frank supported this.
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The proponents of Gnathology State that there is one transverse hinge axis & it can be accurately located.
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The proponents of transographics claim that Transograph is the only instrument that can duplicate it.
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Others claim that Better to use articulator like Hanau, that utilizes a Face-bow mounting &an average of several readings for excursive movements.
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IMPORTANCE OF HINGE AXIS LOCATION RECORD & TRANSFERRING ON TO ARTICULATOR
Determination of terminal hinge position.
The hinge axis recording is required to check the accuracy of two centric records.
It is the starting point of lateral movements.
Allows the transfer of the opening axis of jaws to the articulator so that occlusion would be on the same arc of closure as in the patients mouth
It permits vertical dimension to be changed in the articulator. www.indiandentalacademy.com
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Opening & closing movements of the mandible reproduced in the articulator.
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Helps in proper positioning of the casts in relation to intercondylar shaft.
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LOCATION OF HINGE AXIS
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ARBITRARY METHOD OF LOCATING HINGE AXIS 1) Beyron`s point 2)Bergstrom`s point 3)Dawson`s palpatory method 4)Gysi`s point
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5) Lejoyeux point- 10 to 11mm infront of the ear on aline to the canthus & 5mm below it. 6) Abdal-Hadi point-It is based on the high co relation between the width profile of the face &X co-ordinate of kinematic point. Y = 9.5+0.95(X) A constant distance equal to 0.5 m was used above the line passing from center of the external auditory meatus to canthus to locate the supero inferior position. 7) Lauritzen-Bodner axis-10 to 12mm anterior & 5mm below the porion on Frankfort horizontal plane www.indiandentalacademy.com
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Study was conducted by Heinz O. Beck in 1959 He concluded that 83% of Bergstrom,53% of Beyron, 17% of Gysi points were within 5mm of the Kinematic axis. Study conducted by Craddock& Symmon. Study was conducted by Walker in 1980 He concluded that arbitrary location of hinge axis dose not exist& wide dispersion from true hinge axis point will create large errors & poor accuracy.
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KINEMATIC METHOD OF LOCATING HINGE AXIS Posselt stated that maximum separation of incisal edges in hinge motion to vary from 15 to 20mm or 10 to 13 degree opening & closing arc available for hinge axis location In terminal hinge position the mouth opening is 12.5mm. Kurth & Feinstein located the hinge axis within 2mm of area for 10 degree arc of opening. Borgh & posselt located within 1mm of area for 15 degree & 1.5mm for 10 degree of opening arc.
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Fabrication of the clutch– Attach clutch tray to lower teeth. Assemble the hinge axis locator. Attach the side arms to the cross bar in mounting column. Attach the assembled hinge axis locator to the Stem of the clutch tray. Mark approximate center of condyle on the subject`s face. Adjust the hinge axis locator
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Place the graph paper . Location of the hinge axis points.
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OTHER METHODS OF RECORDING HINGE AXIS •
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Pantograph– two face bows, one holds six recording tables attached to the mandible & other with 6 styluses attached to the maxillae. Transograph. Stereograph Computerized Axiograph
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FACE BOW ď ą
PARTS OF THE FACE BOW -U shaped frame -Condylar rods -Ear pieces -Bite fork -Locking device -Orbital pointer
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TYPES OF THE FACE BOW Arbitrary type –Facia type --Ear piece type. Kinematic type of face bow. ARBITRARY TYPE OF FACE BOW In this type the axis is located by using anatomical land marks. Condyle rods of the face bow are placed over the arbitrarily marked centers of hinge axis. Facia type --The approximate points on the skin over the TMJ region are used as posterior points of reference &the condyle rods of the face bow are placed over it. www.indiandentalacademy.com
Ear piece type of face bow –the ear pieces of the face bow are placed into external auditory meatus . An average distance from the external auditory meatus to an arbitrary hinge axis is built into the face bow design. This distance is compensated for in the articulator by offsetting the mounting point by an equivalent amount.
KINEMATIC TYPE OF THE FACE BOW Locates the opening axis physiologically with exceptional accuracy.
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ANTERIOR &POSTERIOR POINTS OF REFERENCE The selection of anterior point of reference determines which plane in the prosthesis becomes the plane of reference. The objective of the natural appearance in the form &the position of the teeth is achieved by mounting the maxillary cast relative to the FH plane. The objective of the natural appearance in the occlusal plane is achieved by mounting the cast relative to the Camper`s plane. To establish a standard line for comparison between the patients & for the same patient FH plane is frequently used for this purpose. www.indiandentalacademy.com
POSTERIOR POINTS OF REFERENCE 1) Bergstrom point—A point 10 mm anterior to the center of the spherical insert for the external auditory meatus & 7 mm below the FH plane.Beck stated that it lies close to hinge axis.
2)Beyron –A point 13 mm anterior to the posterior margin of the tragus of ear on a line from the center of the tragus to the outer canthus of the eye
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ANTERIOR POINT OF REFERNCE 1)
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Orbitale—It is the lowest point on the infraorbital rim along with the two posterior points forms Axis –Orbitale plane. Orbitale minus 7 mm—FH plane Porion to orbital point. the anterior point of reference marked 7mm below orbitale on the patient or position 7mm above orbital indicator . Nasion minus 23mm—. Incisal edge plus articulator midpoint to articulator axis –horizontal plane distance.- in this technique the occlusal plane will not be parallel to horizontal plane. Alae of the nose—In complete dentures the tentative occlusal plane is made parallel with the horizontal plane. www.indiandentalacademy.com
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FACE BOW TRANSFER PROCEDURE Seating the patient. Mark the Arbitrary axis or true hinge axis point. Mark the anterior point of reference. Contour the maxillary occlusal rim. Reduce the mandibular occlusal rim to allow adequate interocclusal distance for the bite fork & attached wax.
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Softened wax is rolled into horse shoe shape & attached to the bite fork. Attach the occlusion rim to the bite fork. In dentulous patients the maxillary teeth indentations are recorded . Place the bite fork along with the occlusion rim into the mouth & ask the patient to close which will help to stabilize maxillary record base. Secure the stem of the bite fork into the clamp of the face bow. Adjust the condyle rods onto the arbitrary axis points. Earpiece type of face bow. Adjust the width of the condyle rods equidistant bilaterally. Place the orbitale pointer over the mark.
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EAR PIECE TYPE OF FACE BOW Preparation of the bite fork . The facial reference point is marked The bite fork is inserted into the mouth. The stem of the bite fork secured into the clamp of the face bow. Ear pieces are inserted into external auditory meatus , tighten the screws.
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MOUNTING ON TO THE ARTICULATOR The condylar rods of the face bow are inserted over the condylar shaft & centered . While using the kinematic face bow the condylar shaft is extended to meet the styli. Raise or lower the face bow to adjust low lip line of the occlusion rim in level with groove marked on incisal pin. Adjust the orbital pointer pin to the orbital indicator. Support with cast support. Place the maxillary cast. Close the articulator to lock the incisal pin. Mount the upper cast.
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Mounting guide is utilized to mount the transfer rod & attached bite fork. In Slidematic face bow incisal guide block of articulator is replaced by articulator mounting index.
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SIGNIFICANCE OF FACE BOW 1) 2)
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Transverse hinge axis can be located with the aid of face bow. Records the position of maxilla in three planes with reference to two points glenoid fossa. To relate the maxillary casts to the transverse axis of the articulator. Mandibular hinge axis coincided & related to the maxillary by centric relation record. The path of closure will be similar. It aids in securing the anteroposterior cast position in relation to the condyles of the mandible. It registers the horizontal relationship of the casts accurately so assists in incisal plane location. Helps in restoring vertical height in the articulator. www.indiandentalacademy.com
Failure to use face bow can lead to error in occlusion of denture. Face bow transfer allows more accurate arc of closure on the articulator when the intetocclusal records are used. Arbitrary mounting of the cast -Lateral deviation of mounting causes occlusal interferences on rt. or lt. lateral working occlusion. -Vertical deviation affects the labial inclination . Anteroposterior position affects the cuspal angulation required for balance in protrusive occlusion varies. www.indiandentalacademy.com
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DISADVANTAGES
Time consuming .
Specialized equipments required.
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INDICATIONS FOR USING FACE BOW • • • • •
Cusp form teeth used. Balanced occlusion in eccentric positions desired. Definite cusp fossa to marginal ridge relation is desired. Interocclusal check records are used for verification. The occlusal vertical dimension is subjected to change & the alteration of tooth occlusal surfaces are necessary to accommodate the change.
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SUMMARY The FACEBOW records the position of maxilla in three planes in relation to two points that is glenoid fossae & also aids in mounting maxillary casts in same relation on to articulator..
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CONCLUSION The use of face bow is indispensable for diagnosis, treatment planning & treatment procedures. By using 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 the prosthesis.
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REFERENCES
Boucher’S Prosthodontic Rx for edentulous patient 9th edition. Syllabus of complete dentures by Charles M. Heartwell 4 th edition 5th edition. Essentials of complete Denture Prosthodontics by Sheldon Winkler-2 nd edition. Fundamentals of fixed Prosthodontics by Schillingburg 3 rd edition. Management of Temporomandibular Disorders & Occlusion 5 th edition. Jeffrey .P.Okeson. Evaluation, diagnosis, and treatment of occlusal Problems, Peter E Dawson Prosthodontic Rx for edentulous patients by Zarb Bolender 12 th edition. Hobo|Eiji Ichida |Lily .T .Garcia-Osseointegration & occlusal rehabilitation. www.indiandentalacademy.com
The hinge axis of the mandible Kurth & Feinstein J.P.D: 1951:327 Recording & Transferring the mandibular axis by Robert B. Sloane J.P.D. 1952:173. Evaluation of face bow by Craddock & Symmons J.P.D:1952:633. The face bow,it’s Significance & Application by Thure BrandrupWognsen J.P.D.:1953:618. A study of the arbitrary center &the kinematic center of rotation for face bow mounting by R.G. Schallhorn J.P.D:1957. Hinge axis registration on articulators Borgh & Posselt J.P.D 1958 Rationale of face bow is maxillary east mounting by Richard L. Christiansen J.P.D:1959:388. A clinical evaluation of the Arcon concept of articulator Heinz O.Beck J.P.D 1959 The use of face bow is making permanent study casts by T.D.Foster J.D.P : 1959 :717 Hinge axis location on an experimental basis Lauritzen & Wolford J.P.D 1961:1059 A study of Hinge axis determination Vincent R. Trapazzano & John B. Lazzari.J.P.D:1961:858 The accuracy of an ear face – bow by Walter .R.Teteruck, Harry.C.Lundeen J.D.P : 1966:16:1039 The anterior point of reference by Noel.D.Wilkie J.D.P 1979:41:5:488 www.indiandentalacademy.com
A study of transverse axis Arthur F. Aull J.P.D;1963:469 The physiology of the terminal rotational position of the condyles in the TMJ J.P.D: 1967:122 The need to use an arbitrary face bow when remounting complete dentures with Intercellular records by Keki.R.Kotwal in J.D.P. 1979:224 Discrepancies between arbitrary & true hinge axis by F.M. Walker a J.D.P:1980:43:279. Studies on validity of terminal hinge axis C.C.Beard, J.A.Clayton J.P.D: 1981:185 Clinical evaluation of methods used in locating the mandibular hinge axis by Mahmoud Khamics Abdel Razek J.P.D: 1981:369 The hinge axis evaluation of current arbitrary determination methods & proposal for new recording method J.P.D :1989 Re-evaluation of axis-orbital plane & the use of orbitale in a face bow transfer record by Jhon H.Pitchford J.P.D.:1991:66:347. Three dimensional assessment of the reliability of a postural face bow transfer by Virgillo Ferrario,Chairello Sforza,Graziano Serrao,& Johannes H. schmitz J.P.D.2002:87:210. Accuracy of predetermined transverse horizontal mandibular axis point. William W.Nagy, Thomas J.Smithy,Carl G.Wirth J.P.d :2002:387 www.indiandentalacademy.com
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