Stereophotogrammetric analysis of abutment tooth movement in distal-extension removable partial dentures with intracoronal attachments and clasps

SECTION

EDITORS

Louis BlatterPeln

S. Howam

Payne

!Stereophotogrammetric analysis of abutment tooth Imovement in distal-extension removable partial dentures with intracoronal attachments and clasps Tsau-Man Chou, Dorsey J. Moore, L’nivemity

DMD, MScD, DSCD,~ J. David Eick, DI)S,c and Daniel E. Tira, PhDd

of MissouriLKarsas

City, School of Dentistry,

PhD,b

Kansas City. MO.

This study applied the three-dimensional measurement technique of stereophotogramlmetry to measure abutment tooth movement under occlusal loading as a function of intracoronal attachment and clasp design. Six distal-extension removable partial denture designs were studied: (1) RPI-mesial occlusal rest, proximal plate, bucc:al l-bar; (2) cast circumferential clasp; (3) P.D. locking semiprecision attachment; (4 i Thompson dowel nonlocking semiprecision attachment: (5) McCollum precision attachment; and (6) Stern G/L precision attachment. The movement in microns was determined by computer analysis. The Thompson dowel semiprecision attachment generated the most abutment movement in a gingival direction. The clasp-retained designs generally had less total movement than the attachment designs. Clasps and attachments for the abutment teeth adjacent to the distalextension hlases generally moved more than the abutment teeth. (J PROSTHET DENT

1991;66:343-9.

C

linical research in the field of bilateral distal-extaension removable partial dentures has been performed mainly on clasp-retained prostheses.‘-lo The I-bar clasp with its mesial rest system has been used successfully to reduce stress on a but ment teeth”, iz and has been used as a control or in .a cclmparisol group for other studies. Although some research has been reported,‘:j-‘” much of what is known about the effect of precision- and semiprrcision-attachment retained removable prostheses on their supporting .cStruct.ure.L: is based on empirical findings. A decision to use either ~ntracoronal or extracoronal attachment is usually based on the size and shape of the abutment. LVhen spaze is adequate, int,racoronal attachments may be the design of choice, since they have been shown to direct the functional forces along the long axes of the abutment teeth.‘. This study eva; uat::s intracoronal attachments as supports for distal-extension removable partial dentures. Photoelastic analysis and conparison of force transmis-

-This work was suppcmrteti by Weldon Spring Foundation grant No. K-3-40306. BP,ssociate Professor, Department of Removable Prosthodontics. %urator’s Professor and Acting Chairman, Department of Oral Biology. W.G.B. Robinson Profe-sor and Chairman, Department of Removable Prosthodonti~s. dA.ssociate Professor. Askistant De In for Student Programs. 10/l/27152

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sion by intracoronal attachments with clasp-retained distal-extension removable partial dentures have been previously conducted.” Despite the ability of the two-dimensional or quasi three-dimensional technique of photoelasticity to predict the effects of stress in biological systems,“-“” photoelasticity techniques may imperfectly reproduce the true three-dimensional strain pattern.21 This study applies a three-dimensional measuring techs. “” 2’ interfaced with a nique, stereophotogrammetry,s, computer, to measure abutment tooth movement of removable partial denture frameworks under occlusal loading. The null hypothesis tested in this study was “there is no significant difference in the degree of movement of the abutment tooth around the axis of rotation as a function of int,racoronal attachment and clasp design.”

MATERIAL

AND

METHODS

The mandibular removable partial denture was selected for study because the mandibular ridge generally provides less support for a removable partial denture. Three photoelastic models of a mandible with anterior teeth and first premolars were made using different resin simulators for the teeth, bone. and periodontal ligaments.is The models differed slightly with respect to the abutment teeth to accommodate modifications necessary for the removable partial denture designs select,ed for study. The teeth with their roots were formed from a high-modulus plastic (PLM-1, Photolastic, Inc.. Raleigh, N.C. 1. A low-modulus plastic

thlolloplast

H. RutIalo

I>ental

Mfg.

Co..

Inc.,

343

CHOU

Fig.

Fig.

1. RPI distal-extension

prosthesis.

2. Circumferential clasp distal-extension prosthesis.

Brooklyn, N.Y.) surrounded the teeth with a thickness of approximately 1 mm to simulate the periodontal ligament. The alveolar bone was formed from a plastic of intermediate modulus (PL-2, Photolastic, Inc.). The teeth, roots, and bone contours of the model were of average size and shape. The removable partial denture designs investigated were: Design 1. RPI concept (Fig. 1). This system contains a mesial occlusal rest and buccal I-bar engaging an O.Ol-inch undercut and a distal guiding plate. Design II. Cast circumferential clasp (Fig. 2). This design has a cast circumferential clasp arm engaging an O.Olinch undercut and a distal occlusal rest. Design III. P.D. (Austenal Co., Chicago, Ill.) locking semiprecision attachment (Fig. 3). This attachment was used in combination with a lingual milled retentive arm.28 Design IV. Thompson dowel nonlocking semiprecision attachment (Fig. 4). A retentive dimple was placed on the lingual surface at the level of the gingival shelf and in

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Fig.

ET AL

3. P.D. locking semiprecision attachment prosthesis.

Fig. 4. Thompson dowel nonlocking semiprecision attachment prosthesis.

a line continuous with its occlusal surface. The dimple was one half the depth of a No. 5 round bur.2g Design V. McCollum (APM-Sterngold, Huntington Beach, Calif.) precision attachment (Fig. 5). The retention of the McCollum attachment is entirely frictional. A bracing arm was made on the lingual surface of the abutment. Design VI. Stern G/L (APM-Sterngold) precision attachment (Fig. 6). The retention of the Stern G/L attachment is increased by a mechanical lock. The attachment was made with a lingual bracing arm according to the manufacturer’s recommendation. Eighteen removable partial denture frameworks (three castings for each of the six designs) were made of cobaltchromium alloy (Vitallium, Howmedica, Inc., Chicago, Ill.). All frameworks were produced by one laboratory using standardized conditions and methods. The rationale for splinting two abutment teeth for designs III through IV is based on a study by Kratochvil et a1.15It showed that splinted abutments produced the best

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Fig.

5. :McCollum precisic,n attachment

prosthesis,

Fig.

6. Stern G/I, precision

prosthesis.

attachment

force transmission to the supporting structures for these designs. Designs I and II used the conventional single abutment. Porcelain-fused-to-metal (P.FM) crowns were made for the abutment teeth fc?r design:, I, II, III, V, and VI. Complete gold crowns were made for the abutments of design IV, which had the Thompson dowels. The crowns were cemented to the abutment teeth with a mixture of equal parts of zinc phosphate cement and petroleum jelly. This cementing medium allowed for sase of placement and removal of crowns. Each of the 18 frameworks was carefully fitted to its model and was checked for proper seating of the re,sts and proper position and contact of the retainers. Plastic denture basseswere attached to the frameworks with a uniform 1 mm space between the denture bases and the ridges of the models. The 1 mm space was lined with silicone impression material (MoLoplast B) to simulate muco:ja resiliency. A loading pyramid with a flat upper surface

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Fig.

7. Setup of load platform.

Fig. 8. Stereocameras are photographing movement of clasp and abutment tooth with aid of single surface planar mirror.

was attached to each denture base with autopolymerizing acrylic resin in the region of the left first molar and left second premolar. A positioning platform was made for the models to assure stability during loading and to standardize the position of t.he model relative to the light source and camera (Fig. 7). An Instron (Instron Corp., Canton. Mass.) testing machine was used to apply uniform loads through the platform. The test model was aligned on the compression table and the loading stylus was lowered to contact the surface of the platform. The machine was then engaged and loads were applied at the crosshead rate of 0.5 mm/min. Each prosthesis was initially seat.ed with a 30 kg load. This load was released and stereophotographs were made at 0 load. A 30 + 0.2 kg load was then applied and a second set of stereophotographs was made (Fig. 8). This process was repeated three times for each framework. A second framework was placed on the saml-’ test modei. seated,

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CHOU

Table

I.

ET AL

Buccolingual movements of clasps and attachments Design

Mean Std. dev.

I

II

IV

V

VI

0.058 0.077

0.057 0.044

-0.040 0.017

-0.125 0.036

0.230 0.035

Buccal = positive values; lingual = negative values: all measurements are in millimeters.

Table

II.

Buccolingual movements of abutment teeth Design

Mean Std. dev.

I

II

III

IV

V

VI

-0.036 0.070

0.042 0.115

-0.132 0.211

0.007 0.098

-0.049 0.092

0.119 0.151

Buccal = positive values; lingual = negative value; all measurements are in millimeters.

Table

III.

Mesiodistal movement of clasps and attachments Design

Mean Std. dev.

I

II

IV

V

VI

-0.082 0.092

0.015 0.063

0.276 0.041

0.031 0.033

0.274 0.169

Mesial = positive values; distal = negative values; all measurements are in millimeters.

and the testing process was repeated three times. The procedure was repeated for the third framework. Thus each framework design was tested nine times. The stereophotographs of each load level were analyzed using standard stereophotogrammetric techniques* (Balplex 760 research stereophotogrammetric plotter, Bausch and Lomb Inc. Rochester, N.Y.) and the results of each plot were programmed into the computer for analysis. The movement in the buccolingual (X) , mesiodistal (Y) , and occlusogingival (Z) directions was measured to an accuracy of 10km and to a clinical precision of 25pm.10qllp 30-32The total movement in each direction between 0 and 30 kg by load application for the clasp or attachment and for the abutment tooth adjacent to the clasp or attachment was calculated. Several points (a minimum of seven) on the clasp and on the abutment tooth, and at least two points on the attachment were used. The number of points that were measured was limited by the size of the clasp or attachment and by the quality of the photography. Due to technical problems of simultaneous load application by the Instron machine and positioning of the stereophotogrammetry cameras and the small size of the attachment, data for design III could not be obtained for the attachment. Determination of the effect of the design on movement

*References

346

8 to 10, 22 to 27, and 30-32.

of both attachment or clasp and abutment tooth in each of the three directions was done using a single-factor analysis of variance (ANOVA, p < 0.05). Where warranted, pairwise design group mean comparisons were performed using a Newman-Keuls Student range test. This procedure was also used to determine if differences existed between the movement of the abutment tooth and clasp/attachment movement within each of the framework designs in each of the three directions. The appropriate error terms for these latter comparisons were generated from a two-factor (location-tooth or clasp-and direction) repeated measures analysis of variance in each design.

RESULTS The mean and standard deviation of buccolingual movements of clasps and attachments are listed in Table I. The results of the ANOVA applied to these movements indicated a statistically significant design effect (F = 15.71, p < 0.0001). With respect to specific comparisons, statistically significant differences (p < 0.05) in movement existed between design VI and each of designs V, IV, II, and I; between designs I and V; and between designs II and V. The greatest change in a huccal direction was experienced with design VI, while the largest lingual movement was seen with design V. Table II shows the same buccolingual movements of the abutment tooth adjacent to the clasp or attachment. Anal-

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‘Table

V.

(kclusogingival

movement

of clasps and attachments Design II

I

‘Table

VI.

Occlusogingival

movement

of abutment

I\

\

VI

teeth Design

I

II

III

Mear

0.016

0.085

Std. tit-v.

0.0x

0.068

ysis of data resulted m a statktically significant difference among design groups (F = 2.54, p < 0.05). Pairwise comparisons found that there was a significant difference in movement only between design VI and design III. Design ‘VI changed in the buccal direction and design III changed in the lingual direction. Table III presents the mesiodistal movements of clasps and attachments. Results of the ANOVA showed a statis tically significant design effec~t (F = 9.83, p < 0.05). Analysis of specific comparisons found statistically significant differences in movement between design IV and each of the designs I, Il., and V, and between design VI and each of the designs I, II: and V. Greatest movements were associated with designs IV ;and VI. The mesiodistal movement of the abutment teeth was not found to be significantly different among all the designs (Table IV). This outcome was also found with respect to the occlusogingival movement of clasps and attachments (Table V). The data given in Table \‘I summarize the abutment tooth movement for all six prostheses in the occlusogingival direction. Analysis of data resulted in a statistically s#ignificant difference among design groups (F = 3.75, 1-1< 0.01). Only significant differences in movement between design group IV and design group I, and between design group IV and design group II were found. The

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IV

\

vi

0.119

0.231

0.1 46

0,121

0.032

0.139

0.06s

!?.K6

greatest movement of the abutment tooth in an occlusogingival direction was observed for design group IV. Tooth-clasp or tooth-attachment comparisons in each of the three directions were performed for designs 1, II, IV, V, and VI. As previously noted, data for at,tachment movement for design III were not obtained. Results of these comparisons showed statistically significant differences (p < 0.05) between tooth movement and clasp/attachment movement in each of the three directions only for the design IV system. The abutment tooth always moved less than the attachment. This was generally true for the other four designs, but the data were not statistically significant.

DISCUSSION This investigation is an extension of’ that conducted by Chou et al.,” in which a photoelastic analysis was used to compare force transmission by intracoronal attachments with that of clasps for retainers of distal-extension removable partial dentures. The chief limitation of the quasi three-dimensional technique of photoelastic stress analysis is its inability to provide true three-dimensional stress distribution data within the model.“’ In this study, the threedimensional technique of stereophotogrammetry to measure tooth movement under occlusal loading of intracoronal attachment and clasp designs was used. Design I (RPI system, class II lever) generally caused less

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movement of the abutment teeth than design II (circumferential clasp with distal rest, class I lever) (Tables II and VI), but this movement was not statistically significant. Hence the theoretical concepts of mesial and distal rest placement become less clear. As previously suggested,s l7 perhaps the direction in which functional force is applied and the contour of the supporting ridges have greater influence on abutment tooth movement than rest placement. There was considerable variance associated with each reported movement. At least two factors contributed to this variability. These are the variability among framework castings because three frameworks were evaluated for each design, and the repeatability requirement of testing the same framework three times. In addition, the error associated with the stereophotogrammetry equipment i.e., its accuracy (10 pm, precision 25 pm),8,g,30-32contributed to the variance. Even though the variance was large and real differences between designs may not have been shown, it was felt that reseating the same framework three times on the model would simulate the variability within a single patient. Likewise, the testing of three castings for each design would simulate the differences between frameworks of the same design or the variability between patients. It is recognized that these test conditions do not totally reproduce the clinical situation; however, it was felt that they do simulate actual clinical variability reasonably well, even though the resulting variance was rather large. Generally, the designs with semiprecision intracoronal attachments caused more movement than those with clasps. Specifically, the framework with the Thompson dowel semiprecision attachments generated more abutment tooth movement in a gingival direction than designs I and II (Table VI). This could be because of the difficulty of establishing the dowel rest seats in the Thompson dowel system. Zinner et al.33 stated that the inaccuracies of the casting and fitting procedures associated with semiprecision intracoronal attachment systems may compromise the fit of the completed prosthesis. Compared with a previous photoelastic stress analysis,17 this study determined buccolingual and occlusogingival movements. The results for the mesial-distal movements were similar to those of the previous study.

SUMMARY

AND CONCLUSIONS

Most studies on bilateral distal-extension removable partial dentures did not include movement of teeth serving as abutments for precision and semiprecision attachment removable partial dentures. This study applied the threedimensional technique of stereophotogrammetry to measure movement under occlusal loading of abutment teeth for intracoronal attachment and clasp removable partial dentures. The six distal-extension RPD designs studied were the (1) RPI, (2) cast circumferential clasp, (3) P.D. locking semiprecision attachment, (4) Thompson dowel nonlocking semiprecision attachment, (5) McCollum pre-

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cision attachment, and (6) Stern G/L precision attachment. Conclusions from the results of this study are: 1. The design of the clasps and attachments affected the degree of movement of the abutment teeth of a distal-extension removable partial denture but generally did not affect the direction of movement. 2. Clasps and attachments for the abutment teeth adjacent to the distal-extension base generally moved more than the abutment teeth. 3. The semiprecision and precision attachment framework designs generally created more movement than the clasp design frameworks. 4. The Thompson dowel semiprecision attachment produced more abutment tooth movement in a gingival direction. We thank Dr. Robert P. Chappell for his assistance in the preparation of the manuscript.

REFERENCES 1. Tebrock OC, Rohen RM, Fen&r RK, Pelleu CB Jr. The effect of various clasping systems on the mobility of abutment teeth for distal-extension removable partial dentures. J PROSTHET DENT 1979;41:511-6. 2. Nally NN. Methods of handling abutment teeth in class I partial dentures. J PROSTHET DENT 1973;30:561-6. 3. Kratochvil FJ, Caputo AA. Photoelastic analysis of pressure on teeth and bone supporting removable partial dentures. J PROSTHET DENT 1974;32:52-61. 4. Clayton JA, Jaslow C. A measuring of clasp forces on teeth. J PROSTHET DENT 1971;25:21-43. 5. Thompson WD, Kratochvil FJ, Caputo AA. Evaluation of photoelastic

stress patterns produced by various designs of bilateral distal-extension removable partial dentures. J PROSTHET DENT 1977;38:261-73. 6. Frank RP, Brudvik JS, Nicholls JI. A comparison of the flexibility of wrought wire and cast circumferential clasps. J PROSTHET DENT 1983;49:471-6. I. Firtell DN, Grisius RJ, Muncheryan AM. Reaction of the anterior

abutment of a Kennedy class II removable partial denture to various clasp designs: an in vitro study. J PROSTHET DENT 1985;53:77-82. 8. Browning JD, Meadors LW, Eick JD. Movement of three removable partial denture clasp assemblies under occlusal loading. J PROSTHET DENT 1986;55:69-74. 9. Browning JD, Jameson WE, Stewart CD, McGarrah HE, Eick JD. Ef-

fect of positional loading of three removable partial denture clasp assemblies on movement of abutment teeth. J PROSTHET DENT 1986; 55:347-51. 10. Eick JD, Browning JD, Stewart CD, McGarrah HE. Abutment tooth movement related to fit of a removable partial denture. J PROSTHET DENT 1987;57:66-72. 11. Krol AJ. Removal partial denture design: an outline syllabus. 3rd ed.

San Francisco: University of the Pacific, 1981:83. 12. Henderson D, McGivney GP, Castleberry DJ. McCracken’s removable

partial prosthodontics. 7th ed. St Louis: CV Mosby Co, 1989103. 13. Mensor MC. The rationale of resilient hinge-action stress-breakers. J PROSTHET DENT 1968;20:204-15. 14. White JT. Visualization of stress and strain related to removable partial denture abutment. J PROSTHET DENT 1978;40:143-51. 15. Kratochvil JF, Thompson WD, Caputo AA. Photoelastic analysis of

stress patterns on teeth and bone with attachment retainers for removable partial dentures. J PROSTHET DENT 1981;46:21-8. 16. Baker JL, Goodkind RJ. Theory and practice of precision attachment removable partial dentures. St Louis: CV Mosby Co, 1981:72. 17. Chou TM, Caputo AA, Moore DJ, Xiao B, Sakumura JS. Photoelastic analysis and comparison of force transmission characteristics of intracoronal attachments with clasp distal-extension removable partial dentures. J PROSTHET DENT 1989;62:313-9.

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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.

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: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

349