- Email: [email protected]
A reevaluation of the axis-orbital plane and the use of orbitale in a facebow transfer record
ABUTMENT
MOVEMIENT
OF APDS
18. Brodksy JF. Capu:o A:%, Furstman LL. Root tipping: a photoelahtichistopathol >gic cow&~ ion. Am d Orthod 1975;67:1-10. 19. de Alba JA. Caputo AA. Chaconas S,J. Effects of orthodontic intermaxillary class .‘I1 met lank 3 on cranio,‘acial structures Part I--photo&s tic analysis Angle Orthod 1979;49:21-8. 20. de Alba JA, Caputo AA. Chaconas SJ. Effects of orthodontic intermax illary class III mechanic> on craniofacial structures Part II -computers ized cephal metrics. Arlgle Orthod 1979;49:29-36. 21. Caputo AA Standlee Ji’. Biomechsnics in clinical dentistry. Chicago: Quintessence Publishing Co, 1987::15. 22. McGivern RF. Eick JD Sorensen SE. Development and evaluation of a method of photogrammetry for neasuring topographical changes of restoration>. in the mount. Proceedings of American Society of’ Photogrammetry, liniversit, of Illinois Symposium on close-range phrltogrammetry, I’rbana. 111 1971 :XN 2:1. Eick JI), Mc(>iver~, RE’ Sorensen :jE. A photogrammetric system for measuring topogra3hic,li changes o ‘anterior restorations [Absrract]. .J Dent Res l!G’1:50::!:19. 24. Eick .JD. JeIldresen ,JD, iiyge C. Comparison ofthree clinical evaluation systems used with amaizam restorations [Abstract]. .J Dent Res 1976: x+190. 26. Eick .JD, McGarral~H, i ,amb R, Jcndresen MD, Ryge G. Comparison of three evaluation sysrfms in controlled clinical studies [Abstract]. .J Dent Res 1!)81;60:521. 2h. Ryge G, Toln EM, Eick dD, Jendrcsen MD. Evaluation of clinical behavior of six dental amalgams [Ab>,tract]. J Dent Res 1983:62:6X 2;. Arlderson RX. Eick ,JD McGarrah HE, Lamb RD. Root surface mea-
28.
29.
X1.
.il.
32.
:3X
surements of mandibular molar teeth usmg stereophotogrammetry. ,J Am Dent Assoc 1983;107:618-5. hlensor MC. Attachment and semirigid connectors. in: Rhoads JE, Rudd KD. Morrow RM, eds. Dental laboratory procedures: fixed partial denture. St Louis: 0’ Mosby Co, 1986:362-6. Preiskel HW. Precision attachments in prosthodontics: the application of intracoronal and extracoronal attachments. Chicago: Quintessence Publishing Co, 1984:192-7. Browning JD, Eick JD, McGarrah HE. .4butment tooth movement measured in viva by using stereophotl,grnmmetrv .I PRIXTHET DENT 1987;57:323-8. Lamb RD, Eick JD. Close-range photogrammetry wth computer interface in dental research. Photogrammetric Engineering Remote Sensing 1987~53:1685-9. ,c * Patterson M, Eick JD, Eberhart AB. Gross K. Killoy U’J. The effectiveness of two sonic and two ultrasomc scaler tips in furcations. J Periodontol 1989;60:325-9. Zmner ID, Miller RD, Parker HM, Pannu FV. Prefabricated metal intracoronal semiprecision attachments for rtv~~vnblr partial dentures. Int .J Prosthodont 1989;2:35;-64.
Keprlnt
rcqiLP61.\
to
DR. TSAU-MALI CHOL SCHOOL OF DENTISTRI~~~~~~~~~~~ OF MISSOURI/KANSAS CIYI 6X E. 25~~ S,r. tiANS.kS (‘ITY. I\10 tidlt~l-??%
A reevaluation of the axis-orbital plane and the use of orbitale in a facebow transfer record John H. Pitchford, Bad Canstatt,
DDS*
German?
A fundamental assumption in prosthetic dentistry is that the axis-orbital plane usually will be parallel to the reference horizontal. Most articulator systems have incorporated this concept into their designs and use orbitale as the anterior reference point for transferring the vertical position of the maxillae to the articulator. The position of the maxillary cast is expected to be in the same vertical position as the maxillae with the subject’s head oriented in the esthetic reference position. However, the use of orbitale in conjunction with an articulator whose design assumption places the axis and orbital indicator parallel to the horizontal reference will result in a substantial mounting error. This article examines the cause and correction of the mounting error that results from the use of orbitale as the anterior reference point of a facebow transfer record made to an axis-orbital designed articulator. (J PROSTHET DENT 1991;66:349-55.)
Use of a facebow in conjunction with orbitale as the anterior reference point frequently results in an overly
The views anti1 opinions expressed herein are those of the author and do not necessarily reflect the views of the United States Army or the Department of Def.:nse. Presented bedore the Texas Secticsn of the American College of Prosthodontists, Fort Sam Houston, Texas. BLieutenant Colonel, U.S. Army. ClC.
10/l/22691
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steep anterioposterior angulation of the occlusal plane. Casts mounted on the articulator display maxillary incisal edges placed too inferiorly. The condylar readings are too high, usually 40 to 50 degrees instead of the expected 30 to 40 degrees, and the axial inclination of the maxillary anterior teeth is almost perpendicular to the reference horizontal (any surface that forms a right angle to the force of gravity, for example, the top of the laboratory bench or floor) instead of the expected 110 degrees.lm3Many experienced dentists will select an anatomic reference point below orbitale or place the orbital pointer of the facebow
349
PITCHFORD
Fig. 1. Line level ensures subject’s Frankfort plane is parallel to horizontal reference.
when an individual is sitting or standing erect with the head level and eyes fixed on the horizon. Failure to transfer accurately the anterioposterior relationship can result in substantial errors in the final occlusion of a prosthesis,5 while failure to transfer the correct vertical relationship can result in esthetic errors. In complete dentures this can result in an occlusal plane in which the maxillary posterior teeth seem to hang below the anterior teeth. An improperly selected occlusal plane may also result in denture instability and decreased masticatory efficiency.6 In both complete dentures and in fixed partial dentures, failure to transfer the esthetic reference position can result in unnatural axial inclination of the maxillary anterior teeth. If the vertical position error is large enough, balancing side occlusal errors are produced in complete dentures, and with fixed partial dentures the same error would produce nonworking occlusal interferences.5 This study examines the cause and suggests methods to correct facebow transfer record errors that result when orbitale is used in conjunction with an articulator designed with the axis-orbital indicator plane parallel to the reference horizontal.
LITERATURE
2. Distance from incisal edges to orbitale is measured. Three millimeters is subtracted for the thickness of the acrylic resin bar. Fig.
above the orbital indicator of the articulator.4 Others have elected to dispense with the use of an anterior point completely and instead adjust the facebow inferiorly-superiorly on the articulator until the occlusal plane is parallel to the top of the laboratory bench.4 The goal of the facebow transfer record is to record the anterioposterior and vertical relationship of the maxillae to the transverse horizontal axis and to transfer this relationship to the articulator. The facebow is fairly accurate in recording the anterioposterior relationship, but the vertical relationship transferred to the articulator is frequently not the esthetic reference position-the position of the head
350
REVIEW
In the design of many articulator systems there is an assumption of parallelism between the Frankfort horizontal plane, the axis-orbitale plane, the upper member of the articulator, and the horizontal reference plane. In a cephalometric study of 21 edentulous subjects, Gonzales and Kingery’ found that the axis-orbital planes and Frankfort planes were not parallel to one another, but were instead separated by an average distance of 7 mm between porion and the axis. To correct for this error, they suggested raising the orbital pointer by 7 mm above the orbital indicator on the articulator, or lowering the anterior reference point 7 mm on the patient. Either correction would result in an occlusal plane 7 mm higher in the articulator. In another cephalometric study of 10 subjects, Bailey and Nowlin2 found a difference of 7 degrees or 16 mm between the radiographic position of the maxillary teeth and the position determined by the orbital pointer. Bailey and Nowlin explained this discrepancy as being the difference between porion and the axis. Stade et a1.,3in a study of 10 subjects using a bubble level, found the suggested 7 mm correction to be inadequate and indicated that 16.4 mm is needed to duplicate the esthetic reference position. Stade et al., also suggested that the use of orbitale and the axis orbitale plane may result in improper cants to the maxillary cast when it is mounted on an articulator. Little has been published on the exact nature of the vertical relationship that is transferred to the articulator by the facebow, and conflicts exist in the information that is found in the literature.
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REFEREB
CE POINT
Fig. 4. Distance from orbital indicator to incisal edges of maxillary anterior teeth is measured with stainless steel orthodontic wire.
Fig. 3. Bubble gauge attached to facebow indexes and transfers vertical posit ion of maxillae to articulator.
MATERIAL
AND
METHODS
This study was divided intc three parts. Part one was designed to test the ability of the facebow to record and transfer the vertical position of the maxillary occlusal plane when the subject’s Frankfort plane was parallel to the reference horizontal. The position of orbitale (using Salzmann’s tech:nique”) was located and marked with an indelible marker. A builder’s line level (Johnson line level no. 5ij5, Johnson Level and Tool Mfg. Co., Inc., Milwaukee, Wis.) on a steel rod was used ‘;o ensure that the subject’s Frankfort plane was parallel ~0 the reference horizontal (Fig. 1). While the subject was in this position, a Boley gauge was used to me:rsure the perpendicular distance between orbitale and the edge of an acrylic resin bar placed on the subject’s central incisor!; (Fig. 2). Three millimeters were subtracted far the thickness of the acrylic resin bar. A Hanau 159-4 earpiece facebow (Teledyne Hanau, Buffalo: N.Y.) was placed in the conventional manner. A bubble gauge (Stanle:y utility leve no. 42-182, Stanley Tools/ Division of ‘The Etaniey Works, New Britain, Conn.) was then added to the facebow and the head position was clhecked to ensure that the suoject’s Frankfort plane was parallel to the reference horizontal. The gauge was leveled and tightened. thereby indexng the subject’s Frankfort plane position to the reference horizontal (Fig. 3). The facebow was transferred to a Hanau 158-H2 (Teledyne Hanau) articulator that was secured to a level platform. On the articulator, two me,ssurements were made using a stainless steel orthodontic wire, one with the orbital pointer of the facebow at i he level 6if the orbital indicator of the articu-
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lator, and the second made with the bubble gauge indexed to the Frankfort position (Fig. 4). Both measurements were made from the orbital indicator to an indentation in the wax record that represented the edge of the maxillary central incisor. Part two of the study was designed to test the ability of the facebow to transfer the esthetic reference position to the articulator. To the three measurements made in part one, a fourth was added. A second bubble gauge was added to the facebow and the subject was placed in the esthetic reference position, sitting erect, head level, and eyes gazing at the horizon (Fig. 5). This position was indexed by the second bubble gauge. On the articulator the distance from the orbital indicator to the incisal edge of the wax record for the esthetic reference position indexed by the bubble gauge was measured. Part three of the study was designed to determine the vertical relationship of the porion to orbitale and to indirectly determine the relationship of orbitale to the axis of the condyle. A steel rod was secured to an earpiece taken from a Hanau facebow so that the steel rod would be at the level of the porion when the earpiece was in a subject’s ear (Fig. 6). A builder’s line level was added to the steel rod and the subject was instructed to stand erect with head level and eyes staring into a wall mirror. This was a patient-selected esthetic reference position. The steel rod was made parallel to the horizontal reference by use of the line level. The vertical distance from t.he rod (porion) to the subject’s orbitale was measured.
RESULTS Part one of the study demonstrated that the use of orbitale could accurately transfer the vertical relation of the maxillae to the articulator when the subject’s Frankfort plane was determined to be parallel to the reference horizontal. \‘alr~r A represents the incisal edge (IE) to orbit-
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PITCHFORD
Table I. Relationship of incisal edges to orbitale in Frankfort horizontal position Subject No. & initials 1 KBt 2 JFt 3 PL 4 PC 5D0 6GL IEM 8JH 9JK
Fig.
5. Second bubble gauge is added to facebow in part
two of the study and is used to index esthetic reference position.
Totals Average SD
A 0 to IE* Boley
B 01 to IE pointer
C 01 to IE Frankfort
58.25 58.50 49.00 56.75 44.25 52.00 52.25 55.00 52.00 478.00 53.11 4.62
55.50 59.50 49.50 55.00 45.50 50.50 52.00 56.75 52.25 476.50 52.94 4.23
65.00 59.50 49.50 57.00 49.25 52.00 59.75 61.25 53.25 506.50 56.28 5.55
*Orbit& (0) to incisal edge (IE). tSubject was used in parts 1 and 2.
Table II. Relationship of incisal edges to orbitale in Frankfort and esthetic reference positions Subject No. % initials 1 KBt 2 JFt 3 SB 4GB 5CT 6 PJ 7 CA
Fig.
6. Steel rod is added to earpiece from Hanau face-
bow. Steel rod is leveled and distance from rod to orbitale is measured.
ale (0) distance as measured with a Boley gauge, and the average value for the nine subjects in part one was 53.11 mm (Table I). Value B represents the distance as measured on the articulator from the orbital indicator (01) of the articulator to the incisal edges (IE) of the wax record with the orbital pointer placed at the level of the articulator’s orbital indicator. The average distance for value B was 52.94 mm. In this case, the Hanau facebow acts as a caliper and values A and B should closely agree. Value C was the distance from the orbital indicator to the incisal edges with the subject’s Frankfort plane parallel to the reference horizontal as indexed by the bubble gauge. The Frankfort plane position indexed by the bubble gauge placed the incisal edges 56.28 mm below the orbital indicator. The difference of 3.34 mm between the position recorded by the orbital pointer and the bubble gauge indicates that the facebow is reasonably accurate in recording and transferring the vertical position of the maxillae to the articulator when the subject’s 352
8RT 9ME Total Average SD
A 0 to IE* Boley
B 01 to IE pointer
c 01 to IE Frankfort
D 01 to IE ERP
60.75 57.00 57.00 53.00 52.00 57.50 47.00 49.25 57.25 490.75 54.53 4.48
61.00 59.00 58.00 58.50 55.00 57.00 49.75 49.50 62.25 510.00 56.67 4.51
69.00 57.75 62.25 65.50 60.00 54.25 49.50 57.00 62.00 537.25 59.69 5.88
51.75 49.50 41.25 39.00 44.75 37.50 41.00 44.50 39.37 389.00 43.22 4.84
ERP, Esthetic reference position. *Orbitale (0) to incisal edge (IE). TSubject was used in parts 1 and 2.
Frankfort plane is parallel to the reference horizontal. The observed mounting error when using orbitale as the anterior reference point is not due to a design flaw in the facebow nor in the use of orbitale as the reference point. Part two of the study was designed to evaluate the relationship of the esthetic reference position to the Frankfort horizontal plane. It was determined that the facebow used with orbitale is unable to transfer the esthetic reference position to the articulator, but instead places the incisal edges of the maxillary teeth significantly lower. Again measurements were made on nine subjects; the three measurements made in part one were repeated and a fourth measurement was made (Table II). A bubble gauge indexed the vertical position of the facebow to a patient-selected
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Table
-
AND
III. Subject
ANTEHIOIt
\;ertical
REFERE;“?CE
relation
No.
of porion to orbitale B
A 0 to
& initials
POINT
lE*
55.92$ 1 PR 59.50 2 KB 48x3 3 RT 46..iO 4 CA 50.00 5 PL 50.:%3 6 JK ;,2. 1.5 7EM 52. I,? 8GC 34.00 9WM 64.15 10 cc 35. I :i 11 SH .A. 25 12 GB 56.2,5 13 ,JH 5c5.5?I 14 PC us. 10 15 DT iil.!:i 16 PM il. 10 17 MC 14. JO 18 JG 18. JO 19 LI, ei.5.30 20 DM 10<51.32 Total 52.59 Average 4.33 SD _-_-. ~ *Orbit& (0) tcsIIK& edpv (IIS). Kkbitale (0) teahorizontal reference iliK). $fome value are avrrages ,.f several rreasurements.
0 to HRP
12.00 3.00 11.00 8.50 8.25 13.00 3.00 12.00 12.00 21.00 22.00 8.00 16,OO 15.00 11 .oo 4.00 1.5.00 7.50 9.60 16.00 227.75 11.39 5.24
esthetic reference position. When this position was transferred to the articulator, the distance from the orbital indicator to the in&al edges wa:j 43.22 mm (u&e 0). This was 13.45 mm higher than the position indexed by the orbital pointer, (u&e Z3) and 16.47 mm higher than the bubble gauge..indexed Frankfort plane position (value C). This error is the direct result aIf the assumption of parallelism between the axis-orbital plane and the horizontal reference when a subiect is in the esthetic reference position. The manufacturers have incorporated this error into their articul.ator design by placing the axes of the articulator and the orbital indicators on a plane parallel to the horizontal reference. The source of the error is the difference in vertical ,position of o.-bitale and the axis of t,he condyle. In the esthetic refere ?ce position, orbitale is significantly higher l;han the por on or the axis. In part three of the study, measurements on 20 subjects were made elf the .vertical relat onship of porion to orbitale (Table III). In the esthetic reference position, orbitale averaged 11.4 mm above porion, with a standard deviation of 5.24 mm. Gonzales and Kingery,’ and studies by Bergstrom determined that the axis of the condyle is 7.1 mm below the porion. Therefore in the esthetic reference position, orbitale wou.ld be approximately 18.5 mm higher than the axis. When a jfacebow transfer record using orbitale as the anterior reference point is ransferred to an articulator
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t?
54 1
18 I 36 1-28 -44
Fig. 7. In esthetic reference position, orbitale (0) ages 18 mm higher than horizontal reference plane passing through axis. Incisal edges (IE) of maxillary rior teeth average 36 mm below condylar plane; the of values is from 28 to 44 mm.
L
averfHR) anterange
-46 -62
Fig. 8. With axis-orbital plane parallel to horizontal reference (HR), incisal edges (U?) of maxillary anterior teeth are an average of 54 mm below axis-orbital plane; range of values is from 46 t.o 62 mm.
whose design assumption places the axes and the orbital indicator of the articulator on a plane parallel to the reference horizontal, the incisal edges of the maxillary anterior teeth will be placed an average of 18.5 mm too low in the articulator when compared with the esthetic reference position. This average error is consistent with the values found by Bailey and Nowlin.2 and bv St,ade et al.”
DISCUSSION Gonzales and Kingery’ correctly observed the lack of parallelism between the Frankfort horizontal plane and the axis-orbit,al plane. The 7 mm correction they suggested
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PITCHFORD
Fig. 9. In articulators designed with axis-orbital indicator plane parallel to horizontal reference, addition of 18 mm allows average value transfer of esthetic reference position.
Fig. 10. Whip Mix quick mount facebow requires addition of 18 mm to nasion relator to allow average value transfer of esthetic reference position.
would be adequate if the Frankfort plane were parallel to the horizontal reference plane. In the 16 subjects of parts one and two, it was necessary to have each subject lower his head to place the Frankfort plane parallel to the reference horizontal. The term “Frankfort horizontal plane” is a misnomer and as defined the plane will usually not be parallel to the horizontal reference when a subject is in the esthetic reference position. The values measured in part three of this study indicate that the Frankfort plane would form an angle of 8 degrees with respect to the horizontal reference. If the Frankfort plane is not parallel to the reference horizontal, then the axis-orbital plane, whose posterior point is 7 mm lower, could not possibly be parallel to the reference horizontal. This study indicates that the axis-orbital plane would form an angle of 13 degrees to the reference horizontal. Contrary to its definition in the Glossary of Prosthodontic Terms,s the axis-orbital plane may not be used as a horizontal reference plane and the assumption of parallelism between these planes results in a vertical position of the maxillary cast in the articulator that is significantly different from the position of the maxillae in the esthetic reference position. The values found in this study and those of Bailey and Nowlin2 and Stade et a1.3indicate that in the esthetic reference position the incisal edge of the maxillary central incisors will be approximately 36 mm below the condylar plane-a horizontal plane passing through the axes of the articulator or the transverse horizontal axis of the subject (Fig. 7). For 90% of the population the esthetic reference position places the incisal edge of the maxillary central incisors from 28 to 44 mm below the condylar plane (Fig. 7). In the standard axis-orbital articulator, a facebow transfer record using orbitale as the anterior reference point would place the incisal edges of the maxillary teeth about 54 mm below the condylar plane of the articulator (Fig. 8). The range of values would be from 46 to 62 mm (Fig. 8). So large
is the error in the vertical position of the maxillary cast that the range of values fail to overlap. While orbitale is not the cause of the error, modification of the facebow relationship of orbitale to the incisal edges or occlusal plane can correct the error. In the design of Whip Mix (Whip Mix Corp., Louisville, KY.), TMJ (TMJ Instrument Co., Santa Ana, Calif.), Panadent (Panadent Corp. Colton, Calif.), Stewart (C. E. Stewart, Gnathological Instruments, Ventura, Calif.), and older model Hanau (Teledyne Hanau) articulators, the orbital indicator and axes of the articulator form a plane parallel to the reference horizontal. Raising either the orbital indicator or the orbital pointer 18 mm will correct the mounting error of standard articulator systems (Fig. 9). In the Hanau 158 H2 and other articulator systems in which the orbital indicator is 7 mm higher than the axes of the articulator, the correction is 11 mm. Correction for the Whip Mix articulator requires modifying the facebow by adding 18 mm to the nasion relator (Fig. 10). Some articulators have a reference notch located 30 mm below the condylar plane.7 Positioning the edges of the maxillary central incisors 6 mm below the reference notch would allow an average value transfer of the esthetic reference position to the articulator and would eliminate the use of the orbital pointer.
354
CONCLUSION The idea that porion and orbitale would form a plane parallel to the reference horizontal was originally adopted at an anthropologic congress in Frankfort, Germany, in 1882.gSince the porion is not a point easily referenced by the articulator or the facebow, it was easy for the early designers of articulators and facebows to substitute the axis for the porion. In this fashion the axis-orbital plane became a reference horizontal. In 1955 the Research Report by McCollum and StuartlO solidified this concept by stating the axis-orbital plane is horizontal or nearly so when the
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REFERENCE
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body is erect. The Glossary of Prosthodontic Termss made this concept a fact. This concept has been incorporated into the design of many articulators and, when coupled with the use of orbitale as the anterior reference point, will place the maxillary cernral incisors an al,erage distance of 54 mm below the condylar plane of the articulator. It might be interesting to note that, in 1866 Balkwill found the incisal edges of mandibular incisors to be 35 mm below the condylar plant.” while 124 years later the results of this study indicate the incsal edges of the maxillary incisors average 36 mm below The condylar plane. The findings of this study indicate: 1. Neither the Frankfort plane nor the axis-orbital plane is parallel to the reference horizontal in the esthetic reference position. The use of either, plane as a reference horizontal in a facebow transfer record will place the maxillary cast too low in the articulator. 2. In the esthetic reference position, orbitale averages 18.5 mm higher than rhe axis, and the axis-orbital plane will form an angle of 13 degrees to the reference horizontal. Orbitale averages i 1.45 mm higher than the porion in the esthetic reference position, and the Frankfort plane will form an angle of 8 degrees to the horizontal reference. 3. In the csthet.:.c reference position the incisal edge of the maxil1ar.v central incisors will be 36 mm below the condylar plane. A compromised esthetic result can be produced by the use of an anterior reference point not in harmony with the design .)f the articulator. Minor alterations
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of the facebow, orbital indicator, or in the position of the orbital pointer will allow an average value transfer of the esthetic reference position to the articulator
REFERENCES 1
Bailey JO. Nowlin ‘IT’. Evaluation of the rhlrd point of reierence for mounting maxillary casts on the Hanau articrdat(~r. I PR~STHET DEW 1981;51:199-201. ,> ,I. Stade EH. Hanson JG, Baker CL. Esthetic conslderatmns in the use ol ,I PROSTHET DENT 1982;48:254-6 fawbows. 4. Il’ilkie ND. The anterior point of referente. .1 PROSTHET I)ENT 1979: 2.
41:4X8-96 i.
Weinberg DENT
6.
LA. An evaluation
of the face-lwv
mountmg.
.J PROSTHE?
1961;11::%4’.
Okane H. Yamrhina ‘I’, h’agasawa ‘T, Tsuru H. l‘hr rtiect of anteropoxterior inclination of the occlu~al plane m bit in: txxce .I PR~STHET DENI 1979;42:491-.X)1.
Lauciello FH, Appelbaum M. .4natomic comparison to arbitrary reference notch on Hanau articulators. J PROSTHET DENT 19X3:40:676-81. 8. (;lossary of prosthodontic terms. .I I%osTHFX’ DENT 19X7;5R:713-62. 9. Krueger GE. Schneider RI,. A plane of wientation with an extracranial 7.
anterior Ii). 11
point
uf reference.
d I’ROSTHET
DENT
198656:56-(ii),
RlrCollu~n IiH. Stuart PI?. A wsearch report i’nir, .Utc,. (‘ahi’: Scientific Press. 1955:5,i. Hrandrull-\Voynsen ‘I‘. The face bow. its srgnlficawt ,Irtd application. .I PHOXTHET
I)EK?-
195:1;:i:HlH-.:O.
355
MOVEMIENT
OF APDS
18. Brodksy JF. Capu:o A:%, Furstman LL. Root tipping: a photoelahtichistopathol >gic cow&~ ion. Am d Orthod 1975;67:1-10. 19. de Alba JA. Caputo AA. Chaconas S,J. Effects of orthodontic intermaxillary class .‘I1 met lank 3 on cranio,‘acial structures Part I--photo&s tic analysis Angle Orthod 1979;49:21-8. 20. de Alba JA, Caputo AA. Chaconas SJ. Effects of orthodontic intermax illary class III mechanic> on craniofacial structures Part II -computers ized cephal metrics. Arlgle Orthod 1979;49:29-36. 21. Caputo AA Standlee Ji’. Biomechsnics in clinical dentistry. Chicago: Quintessence Publishing Co, 1987::15. 22. McGivern RF. Eick JD Sorensen SE. Development and evaluation of a method of photogrammetry for neasuring topographical changes of restoration>. in the mount. Proceedings of American Society of’ Photogrammetry, liniversit, of Illinois Symposium on close-range phrltogrammetry, I’rbana. 111 1971 :XN 2:1. Eick JI), Mc(>iver~, RE’ Sorensen :jE. A photogrammetric system for measuring topogra3hic,li changes o ‘anterior restorations [Absrract]. .J Dent Res l!G’1:50::!:19. 24. Eick .JD. JeIldresen ,JD, iiyge C. Comparison ofthree clinical evaluation systems used with amaizam restorations [Abstract]. .J Dent Res 1976: x+190. 26. Eick .JD, McGarral~H, i ,amb R, Jcndresen MD, Ryge G. Comparison of three evaluation sysrfms in controlled clinical studies [Abstract]. .J Dent Res 1!)81;60:521. 2h. Ryge G, Toln EM, Eick dD, Jendrcsen MD. Evaluation of clinical behavior of six dental amalgams [Ab>,tract]. J Dent Res 1983:62:6X 2;. Arlderson RX. Eick ,JD McGarrah HE, Lamb RD. Root surface mea-
28.
29.
X1.
.il.
32.
:3X
surements of mandibular molar teeth usmg stereophotogrammetry. ,J Am Dent Assoc 1983;107:618-5. hlensor MC. Attachment and semirigid connectors. in: Rhoads JE, Rudd KD. Morrow RM, eds. Dental laboratory procedures: fixed partial denture. St Louis: 0’ Mosby Co, 1986:362-6. Preiskel HW. Precision attachments in prosthodontics: the application of intracoronal and extracoronal attachments. Chicago: Quintessence Publishing Co, 1984:192-7. Browning JD, Eick JD, McGarrah HE. .4butment tooth movement measured in viva by using stereophotl,grnmmetrv .I PRIXTHET DENT 1987;57:323-8. Lamb RD, Eick JD. Close-range photogrammetry wth computer interface in dental research. Photogrammetric Engineering Remote Sensing 1987~53:1685-9. ,c * Patterson M, Eick JD, Eberhart AB. Gross K. Killoy U’J. The effectiveness of two sonic and two ultrasomc scaler tips in furcations. J Periodontol 1989;60:325-9. Zmner ID, Miller RD, Parker HM, Pannu FV. Prefabricated metal intracoronal semiprecision attachments for rtv~~vnblr partial dentures. Int .J Prosthodont 1989;2:35;-64.
Keprlnt
rcqiLP61.\
to
DR. TSAU-MALI CHOL SCHOOL OF DENTISTRI~~~~~~~~~~~ OF MISSOURI/KANSAS CIYI 6X E. 25~~ S,r. tiANS.kS (‘ITY. I\10 tidlt~l-??%
A reevaluation of the axis-orbital plane and the use of orbitale in a facebow transfer record John H. Pitchford, Bad Canstatt,
DDS*
German?
A fundamental assumption in prosthetic dentistry is that the axis-orbital plane usually will be parallel to the reference horizontal. Most articulator systems have incorporated this concept into their designs and use orbitale as the anterior reference point for transferring the vertical position of the maxillae to the articulator. The position of the maxillary cast is expected to be in the same vertical position as the maxillae with the subject’s head oriented in the esthetic reference position. However, the use of orbitale in conjunction with an articulator whose design assumption places the axis and orbital indicator parallel to the horizontal reference will result in a substantial mounting error. This article examines the cause and correction of the mounting error that results from the use of orbitale as the anterior reference point of a facebow transfer record made to an axis-orbital designed articulator. (J PROSTHET DENT 1991;66:349-55.)
Use of a facebow in conjunction with orbitale as the anterior reference point frequently results in an overly
The views anti1 opinions expressed herein are those of the author and do not necessarily reflect the views of the United States Army or the Department of Def.:nse. Presented bedore the Texas Secticsn of the American College of Prosthodontists, Fort Sam Houston, Texas. BLieutenant Colonel, U.S. Army. ClC.
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steep anterioposterior angulation of the occlusal plane. Casts mounted on the articulator display maxillary incisal edges placed too inferiorly. The condylar readings are too high, usually 40 to 50 degrees instead of the expected 30 to 40 degrees, and the axial inclination of the maxillary anterior teeth is almost perpendicular to the reference horizontal (any surface that forms a right angle to the force of gravity, for example, the top of the laboratory bench or floor) instead of the expected 110 degrees.lm3Many experienced dentists will select an anatomic reference point below orbitale or place the orbital pointer of the facebow
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PITCHFORD
Fig. 1. Line level ensures subject’s Frankfort plane is parallel to horizontal reference.
when an individual is sitting or standing erect with the head level and eyes fixed on the horizon. Failure to transfer accurately the anterioposterior relationship can result in substantial errors in the final occlusion of a prosthesis,5 while failure to transfer the correct vertical relationship can result in esthetic errors. In complete dentures this can result in an occlusal plane in which the maxillary posterior teeth seem to hang below the anterior teeth. An improperly selected occlusal plane may also result in denture instability and decreased masticatory efficiency.6 In both complete dentures and in fixed partial dentures, failure to transfer the esthetic reference position can result in unnatural axial inclination of the maxillary anterior teeth. If the vertical position error is large enough, balancing side occlusal errors are produced in complete dentures, and with fixed partial dentures the same error would produce nonworking occlusal interferences.5 This study examines the cause and suggests methods to correct facebow transfer record errors that result when orbitale is used in conjunction with an articulator designed with the axis-orbital indicator plane parallel to the reference horizontal.
LITERATURE
2. Distance from incisal edges to orbitale is measured. Three millimeters is subtracted for the thickness of the acrylic resin bar. Fig.
above the orbital indicator of the articulator.4 Others have elected to dispense with the use of an anterior point completely and instead adjust the facebow inferiorly-superiorly on the articulator until the occlusal plane is parallel to the top of the laboratory bench.4 The goal of the facebow transfer record is to record the anterioposterior and vertical relationship of the maxillae to the transverse horizontal axis and to transfer this relationship to the articulator. The facebow is fairly accurate in recording the anterioposterior relationship, but the vertical relationship transferred to the articulator is frequently not the esthetic reference position-the position of the head
350
REVIEW
In the design of many articulator systems there is an assumption of parallelism between the Frankfort horizontal plane, the axis-orbitale plane, the upper member of the articulator, and the horizontal reference plane. In a cephalometric study of 21 edentulous subjects, Gonzales and Kingery’ found that the axis-orbital planes and Frankfort planes were not parallel to one another, but were instead separated by an average distance of 7 mm between porion and the axis. To correct for this error, they suggested raising the orbital pointer by 7 mm above the orbital indicator on the articulator, or lowering the anterior reference point 7 mm on the patient. Either correction would result in an occlusal plane 7 mm higher in the articulator. In another cephalometric study of 10 subjects, Bailey and Nowlin2 found a difference of 7 degrees or 16 mm between the radiographic position of the maxillary teeth and the position determined by the orbital pointer. Bailey and Nowlin explained this discrepancy as being the difference between porion and the axis. Stade et a1.,3in a study of 10 subjects using a bubble level, found the suggested 7 mm correction to be inadequate and indicated that 16.4 mm is needed to duplicate the esthetic reference position. Stade et al., also suggested that the use of orbitale and the axis orbitale plane may result in improper cants to the maxillary cast when it is mounted on an articulator. Little has been published on the exact nature of the vertical relationship that is transferred to the articulator by the facebow, and conflicts exist in the information that is found in the literature.
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.‘.~TF;R107!
REFEREB
CE POINT
Fig. 4. Distance from orbital indicator to incisal edges of maxillary anterior teeth is measured with stainless steel orthodontic wire.
Fig. 3. Bubble gauge attached to facebow indexes and transfers vertical posit ion of maxillae to articulator.
MATERIAL
AND
METHODS
This study was divided intc three parts. Part one was designed to test the ability of the facebow to record and transfer the vertical position of the maxillary occlusal plane when the subject’s Frankfort plane was parallel to the reference horizontal. The position of orbitale (using Salzmann’s tech:nique”) was located and marked with an indelible marker. A builder’s line level (Johnson line level no. 5ij5, Johnson Level and Tool Mfg. Co., Inc., Milwaukee, Wis.) on a steel rod was used ‘;o ensure that the subject’s Frankfort plane was parallel ~0 the reference horizontal (Fig. 1). While the subject was in this position, a Boley gauge was used to me:rsure the perpendicular distance between orbitale and the edge of an acrylic resin bar placed on the subject’s central incisor!; (Fig. 2). Three millimeters were subtracted far the thickness of the acrylic resin bar. A Hanau 159-4 earpiece facebow (Teledyne Hanau, Buffalo: N.Y.) was placed in the conventional manner. A bubble gauge (Stanle:y utility leve no. 42-182, Stanley Tools/ Division of ‘The Etaniey Works, New Britain, Conn.) was then added to the facebow and the head position was clhecked to ensure that the suoject’s Frankfort plane was parallel to the reference horizontal. The gauge was leveled and tightened. thereby indexng the subject’s Frankfort plane position to the reference horizontal (Fig. 3). The facebow was transferred to a Hanau 158-H2 (Teledyne Hanau) articulator that was secured to a level platform. On the articulator, two me,ssurements were made using a stainless steel orthodontic wire, one with the orbital pointer of the facebow at i he level 6if the orbital indicator of the articu-
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lator, and the second made with the bubble gauge indexed to the Frankfort position (Fig. 4). Both measurements were made from the orbital indicator to an indentation in the wax record that represented the edge of the maxillary central incisor. Part two of the study was designed to test the ability of the facebow to transfer the esthetic reference position to the articulator. To the three measurements made in part one, a fourth was added. A second bubble gauge was added to the facebow and the subject was placed in the esthetic reference position, sitting erect, head level, and eyes gazing at the horizon (Fig. 5). This position was indexed by the second bubble gauge. On the articulator the distance from the orbital indicator to the incisal edge of the wax record for the esthetic reference position indexed by the bubble gauge was measured. Part three of the study was designed to determine the vertical relationship of the porion to orbitale and to indirectly determine the relationship of orbitale to the axis of the condyle. A steel rod was secured to an earpiece taken from a Hanau facebow so that the steel rod would be at the level of the porion when the earpiece was in a subject’s ear (Fig. 6). A builder’s line level was added to the steel rod and the subject was instructed to stand erect with head level and eyes staring into a wall mirror. This was a patient-selected esthetic reference position. The steel rod was made parallel to the horizontal reference by use of the line level. The vertical distance from t.he rod (porion) to the subject’s orbitale was measured.
RESULTS Part one of the study demonstrated that the use of orbitale could accurately transfer the vertical relation of the maxillae to the articulator when the subject’s Frankfort plane was determined to be parallel to the reference horizontal. \‘alr~r A represents the incisal edge (IE) to orbit-
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PITCHFORD
Table I. Relationship of incisal edges to orbitale in Frankfort horizontal position Subject No. & initials 1 KBt 2 JFt 3 PL 4 PC 5D0 6GL IEM 8JH 9JK
Fig.
5. Second bubble gauge is added to facebow in part
two of the study and is used to index esthetic reference position.
Totals Average SD
A 0 to IE* Boley
B 01 to IE pointer
C 01 to IE Frankfort
58.25 58.50 49.00 56.75 44.25 52.00 52.25 55.00 52.00 478.00 53.11 4.62
55.50 59.50 49.50 55.00 45.50 50.50 52.00 56.75 52.25 476.50 52.94 4.23
65.00 59.50 49.50 57.00 49.25 52.00 59.75 61.25 53.25 506.50 56.28 5.55
*Orbit& (0) to incisal edge (IE). tSubject was used in parts 1 and 2.
Table II. Relationship of incisal edges to orbitale in Frankfort and esthetic reference positions Subject No. % initials 1 KBt 2 JFt 3 SB 4GB 5CT 6 PJ 7 CA
Fig.
6. Steel rod is added to earpiece from Hanau face-
bow. Steel rod is leveled and distance from rod to orbitale is measured.
ale (0) distance as measured with a Boley gauge, and the average value for the nine subjects in part one was 53.11 mm (Table I). Value B represents the distance as measured on the articulator from the orbital indicator (01) of the articulator to the incisal edges (IE) of the wax record with the orbital pointer placed at the level of the articulator’s orbital indicator. The average distance for value B was 52.94 mm. In this case, the Hanau facebow acts as a caliper and values A and B should closely agree. Value C was the distance from the orbital indicator to the incisal edges with the subject’s Frankfort plane parallel to the reference horizontal as indexed by the bubble gauge. The Frankfort plane position indexed by the bubble gauge placed the incisal edges 56.28 mm below the orbital indicator. The difference of 3.34 mm between the position recorded by the orbital pointer and the bubble gauge indicates that the facebow is reasonably accurate in recording and transferring the vertical position of the maxillae to the articulator when the subject’s 352
8RT 9ME Total Average SD
A 0 to IE* Boley
B 01 to IE pointer
c 01 to IE Frankfort
D 01 to IE ERP
60.75 57.00 57.00 53.00 52.00 57.50 47.00 49.25 57.25 490.75 54.53 4.48
61.00 59.00 58.00 58.50 55.00 57.00 49.75 49.50 62.25 510.00 56.67 4.51
69.00 57.75 62.25 65.50 60.00 54.25 49.50 57.00 62.00 537.25 59.69 5.88
51.75 49.50 41.25 39.00 44.75 37.50 41.00 44.50 39.37 389.00 43.22 4.84
ERP, Esthetic reference position. *Orbitale (0) to incisal edge (IE). TSubject was used in parts 1 and 2.
Frankfort plane is parallel to the reference horizontal. The observed mounting error when using orbitale as the anterior reference point is not due to a design flaw in the facebow nor in the use of orbitale as the reference point. Part two of the study was designed to evaluate the relationship of the esthetic reference position to the Frankfort horizontal plane. It was determined that the facebow used with orbitale is unable to transfer the esthetic reference position to the articulator, but instead places the incisal edges of the maxillary teeth significantly lower. Again measurements were made on nine subjects; the three measurements made in part one were repeated and a fourth measurement was made (Table II). A bubble gauge indexed the vertical position of the facebow to a patient-selected
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Table
-
AND
III. Subject
ANTEHIOIt
\;ertical
REFERE;“?CE
relation
No.
of porion to orbitale B
A 0 to
& initials
POINT
lE*
55.92$ 1 PR 59.50 2 KB 48x3 3 RT 46..iO 4 CA 50.00 5 PL 50.:%3 6 JK ;,2. 1.5 7EM 52. I,? 8GC 34.00 9WM 64.15 10 cc 35. I :i 11 SH .A. 25 12 GB 56.2,5 13 ,JH 5c5.5?I 14 PC us. 10 15 DT iil.!:i 16 PM il. 10 17 MC 14. JO 18 JG 18. JO 19 LI, ei.5.30 20 DM 10<51.32 Total 52.59 Average 4.33 SD _-_-. ~ *Orbit& (0) tcsIIK& edpv (IIS). Kkbitale (0) teahorizontal reference iliK). $fome value are avrrages ,.f several rreasurements.
0 to HRP
12.00 3.00 11.00 8.50 8.25 13.00 3.00 12.00 12.00 21.00 22.00 8.00 16,OO 15.00 11 .oo 4.00 1.5.00 7.50 9.60 16.00 227.75 11.39 5.24
esthetic reference position. When this position was transferred to the articulator, the distance from the orbital indicator to the in&al edges wa:j 43.22 mm (u&e 0). This was 13.45 mm higher than the position indexed by the orbital pointer, (u&e Z3) and 16.47 mm higher than the bubble gauge..indexed Frankfort plane position (value C). This error is the direct result aIf the assumption of parallelism between the axis-orbital plane and the horizontal reference when a subiect is in the esthetic reference position. The manufacturers have incorporated this error into their articul.ator design by placing the axes of the articulator and the orbital indicators on a plane parallel to the horizontal reference. The source of the error is the difference in vertical ,position of o.-bitale and the axis of t,he condyle. In the esthetic refere ?ce position, orbitale is significantly higher l;han the por on or the axis. In part three of the study, measurements on 20 subjects were made elf the .vertical relat onship of porion to orbitale (Table III). In the esthetic reference position, orbitale averaged 11.4 mm above porion, with a standard deviation of 5.24 mm. Gonzales and Kingery,’ and studies by Bergstrom determined that the axis of the condyle is 7.1 mm below the porion. Therefore in the esthetic reference position, orbitale wou.ld be approximately 18.5 mm higher than the axis. When a jfacebow transfer record using orbitale as the anterior reference point is ransferred to an articulator
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t?
54 1
18 I 36 1-28 -44
Fig. 7. In esthetic reference position, orbitale (0) ages 18 mm higher than horizontal reference plane passing through axis. Incisal edges (IE) of maxillary rior teeth average 36 mm below condylar plane; the of values is from 28 to 44 mm.
L
averfHR) anterange
-46 -62
Fig. 8. With axis-orbital plane parallel to horizontal reference (HR), incisal edges (U?) of maxillary anterior teeth are an average of 54 mm below axis-orbital plane; range of values is from 46 t.o 62 mm.
whose design assumption places the axes and the orbital indicator of the articulator on a plane parallel to the reference horizontal, the incisal edges of the maxillary anterior teeth will be placed an average of 18.5 mm too low in the articulator when compared with the esthetic reference position. This average error is consistent with the values found by Bailey and Nowlin.2 and bv St,ade et al.”
DISCUSSION Gonzales and Kingery’ correctly observed the lack of parallelism between the Frankfort horizontal plane and the axis-orbit,al plane. The 7 mm correction they suggested
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PITCHFORD
Fig. 9. In articulators designed with axis-orbital indicator plane parallel to horizontal reference, addition of 18 mm allows average value transfer of esthetic reference position.
Fig. 10. Whip Mix quick mount facebow requires addition of 18 mm to nasion relator to allow average value transfer of esthetic reference position.
would be adequate if the Frankfort plane were parallel to the horizontal reference plane. In the 16 subjects of parts one and two, it was necessary to have each subject lower his head to place the Frankfort plane parallel to the reference horizontal. The term “Frankfort horizontal plane” is a misnomer and as defined the plane will usually not be parallel to the horizontal reference when a subject is in the esthetic reference position. The values measured in part three of this study indicate that the Frankfort plane would form an angle of 8 degrees with respect to the horizontal reference. If the Frankfort plane is not parallel to the reference horizontal, then the axis-orbital plane, whose posterior point is 7 mm lower, could not possibly be parallel to the reference horizontal. This study indicates that the axis-orbital plane would form an angle of 13 degrees to the reference horizontal. Contrary to its definition in the Glossary of Prosthodontic Terms,s the axis-orbital plane may not be used as a horizontal reference plane and the assumption of parallelism between these planes results in a vertical position of the maxillary cast in the articulator that is significantly different from the position of the maxillae in the esthetic reference position. The values found in this study and those of Bailey and Nowlin2 and Stade et a1.3indicate that in the esthetic reference position the incisal edge of the maxillary central incisors will be approximately 36 mm below the condylar plane-a horizontal plane passing through the axes of the articulator or the transverse horizontal axis of the subject (Fig. 7). For 90% of the population the esthetic reference position places the incisal edge of the maxillary central incisors from 28 to 44 mm below the condylar plane (Fig. 7). In the standard axis-orbital articulator, a facebow transfer record using orbitale as the anterior reference point would place the incisal edges of the maxillary teeth about 54 mm below the condylar plane of the articulator (Fig. 8). The range of values would be from 46 to 62 mm (Fig. 8). So large
is the error in the vertical position of the maxillary cast that the range of values fail to overlap. While orbitale is not the cause of the error, modification of the facebow relationship of orbitale to the incisal edges or occlusal plane can correct the error. In the design of Whip Mix (Whip Mix Corp., Louisville, KY.), TMJ (TMJ Instrument Co., Santa Ana, Calif.), Panadent (Panadent Corp. Colton, Calif.), Stewart (C. E. Stewart, Gnathological Instruments, Ventura, Calif.), and older model Hanau (Teledyne Hanau) articulators, the orbital indicator and axes of the articulator form a plane parallel to the reference horizontal. Raising either the orbital indicator or the orbital pointer 18 mm will correct the mounting error of standard articulator systems (Fig. 9). In the Hanau 158 H2 and other articulator systems in which the orbital indicator is 7 mm higher than the axes of the articulator, the correction is 11 mm. Correction for the Whip Mix articulator requires modifying the facebow by adding 18 mm to the nasion relator (Fig. 10). Some articulators have a reference notch located 30 mm below the condylar plane.7 Positioning the edges of the maxillary central incisors 6 mm below the reference notch would allow an average value transfer of the esthetic reference position to the articulator and would eliminate the use of the orbital pointer.
354
CONCLUSION The idea that porion and orbitale would form a plane parallel to the reference horizontal was originally adopted at an anthropologic congress in Frankfort, Germany, in 1882.gSince the porion is not a point easily referenced by the articulator or the facebow, it was easy for the early designers of articulators and facebows to substitute the axis for the porion. In this fashion the axis-orbital plane became a reference horizontal. In 1955 the Research Report by McCollum and StuartlO solidified this concept by stating the axis-orbital plane is horizontal or nearly so when the
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NUMBER
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ORBITALE
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ANTERIOR
REFERENCE
POINT
body is erect. The Glossary of Prosthodontic Termss made this concept a fact. This concept has been incorporated into the design of many articulators and, when coupled with the use of orbitale as the anterior reference point, will place the maxillary cernral incisors an al,erage distance of 54 mm below the condylar plane of the articulator. It might be interesting to note that, in 1866 Balkwill found the incisal edges of mandibular incisors to be 35 mm below the condylar plant.” while 124 years later the results of this study indicate the incsal edges of the maxillary incisors average 36 mm below The condylar plane. The findings of this study indicate: 1. Neither the Frankfort plane nor the axis-orbital plane is parallel to the reference horizontal in the esthetic reference position. The use of either, plane as a reference horizontal in a facebow transfer record will place the maxillary cast too low in the articulator. 2. In the esthetic reference position, orbitale averages 18.5 mm higher than rhe axis, and the axis-orbital plane will form an angle of 13 degrees to the reference horizontal. Orbitale averages i 1.45 mm higher than the porion in the esthetic reference position, and the Frankfort plane will form an angle of 8 degrees to the horizontal reference. 3. In the csthet.:.c reference position the incisal edge of the maxil1ar.v central incisors will be 36 mm below the condylar plane. A compromised esthetic result can be produced by the use of an anterior reference point not in harmony with the design .)f the articulator. Minor alterations
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of the facebow, orbital indicator, or in the position of the orbital pointer will allow an average value transfer of the esthetic reference position to the articulator
REFERENCES 1
Bailey JO. Nowlin ‘IT’. Evaluation of the rhlrd point of reierence for mounting maxillary casts on the Hanau articrdat(~r. I PR~STHET DEW 1981;51:199-201. ,> ,I. Stade EH. Hanson JG, Baker CL. Esthetic conslderatmns in the use ol ,I PROSTHET DENT 1982;48:254-6 fawbows. 4. Il’ilkie ND. The anterior point of referente. .1 PROSTHET I)ENT 1979: 2.
41:4X8-96 i.
Weinberg DENT
6.
LA. An evaluation
of the face-lwv
mountmg.
.J PROSTHE?
1961;11::%4’.
Okane H. Yamrhina ‘I’, h’agasawa ‘T, Tsuru H. l‘hr rtiect of anteropoxterior inclination of the occlu~al plane m bit in: txxce .I PR~STHET DENI 1979;42:491-.X)1.
Lauciello FH, Appelbaum M. .4natomic comparison to arbitrary reference notch on Hanau articulators. J PROSTHET DENT 19X3:40:676-81. 8. (;lossary of prosthodontic terms. .I I%osTHFX’ DENT 19X7;5R:713-62. 9. Krueger GE. Schneider RI,. A plane of wientation with an extracranial 7.
anterior Ii). 11
point
uf reference.
d I’ROSTHET
DENT
198656:56-(ii),
RlrCollu~n IiH. Stuart PI?. A wsearch report i’nir, .Utc,. (‘ahi’: Scientific Press. 1955:5,i. Hrandrull-\Voynsen ‘I‘. The face bow. its srgnlficawt ,Irtd application. .I PHOXTHET
I)EK?-
195:1;:i:HlH-.:O.
355