Anterior Point of Reference

REMOVABLE PROSTHODONTICS

The anterior point of reference

Noel D. Wilkie, D.D.S.* Naval Regional Dental Center, Pearl Harbor, Hawaii

I- ositioning the maxillary cast in an articulator is an essential part of many techniques in dentistry.

Two major objectives are restoration of the occlusion

and control of the form and the position of the teeth. The degree of knowledge that the dentist and the

auxiliaries have, coupled with their ability to apply this knowledge, will determine how well these objec-

tives are satisfied. The dentist should thoroughly understand the

concept of the anterior point of reference and how it

should be chosen to accomplish the treatment objectives. The student of prosthodontics should give

concentrated thought to the anterior point of refer-

ence and be acquainted with several concepts as

alternatives to be used in treating the difficult patient. Both dentist and student should be thor-

oughly familiar with the difficulties that arise if the

choice and the use of the anterior reference point are

not well coordinated with all individuals taking part in fabricating the prosthesis.

To do less means that the maxillary cast will be

positioned in the articulator arbitrarily. Such uncon- scious or purposeful neglect by the dentist may result in additional and unnecessary record making, an

unnatural appearance in the final prosthesis, and

even damage to the supporting tissues. To delegate the positioning of the maxillary cast in the articula-

tor to someone who is not fully knowledgeable and who is unaware of the consequences of an arbitrary

mounting can result in extra expense and unnecessary trauma to the patient.

The maxillary cast in the articulator is the baseline from which all occlusal relationships start, and it should be positioned in space by identifying three

points which cannot be on the same line. The plane

is formed by two points located posterior to the maxillae and one point located anterior to them (Fig. 1).

POSTERIOR POINTS OF REFERENCE

Often the two posterior points are located by

measuring prescribed distances from skin surface

landmarks. Some of the commonly used posterior

points were shown by Beck to be clinically near

the hinge axis. He concluded that the Bergstrom

point* (Fig. 2, a) most frequently is closest to the

hinge axis. He identified the Beyron point? (Fig. 2, h) as the next most accurate posterior point of refer-

ence. Studies by Weinberg state that a deviation

from the hinge axis of 5 mm will result in an

anteroposterior displacement error of 0.2 mm at the second molar. An error of this size is usually of no

consequence in removable prostheses with nonrigid

attachments. With these prostheses: intended toler-

ances in the occlusion and the mobility of the supporting tissues may make a precise location of the

hinge axis an exercise with no advantage.

On the other hand, fixed and removable partial dentures with rigid attachments demand close toler-

ances in cusp pathways. These restorations may

require the use of a kinematic technique that will locate the hingeaxis exactly.

If the maxillary cast is positioned without the correct maxillae-hinge axis relationship, arcs of

movement in the articulator will occur which differ from those of the patient. Verification of the man-

dibular cast position by using interocclusal records made at increased vertical dimensions of occlusion

The opinions or assertions contained herein are those of the writer and are not to be construed as official or as reflecting the views of the Department of the Navy.

Presented before the Academy of Denture Prosthetics, San Anto- nio, Texas.

*Captain, DC, USS; Commanding Officer.

*Bergstrom point: A point 10 mm anterior to the center of a spherical insert for the auditory meatus and 7 mm below the Frankfort horizontal plane. (Adapted from Beck.)

fBeyron point: A point 13 mm anterior to the posterior margin of the tragus of the ear on a line from the center of the tragus to the corner of the eye. (Adapted from Beck.)

MAY 1979 VOLUME 41 NUMBER 5

ANTERIOR POINT OF REFERENCF.

Fig. 1. A spatial plane is formed by two posterior points and one anterior point.

will be difficult or impossible unless subsequent records are the same thickness. Also, an occlusion

that is restored to an incorrect arc of closure may have interceptive and deflective tooth contacts in the hinge-closing movement if there are subsequent

changes in the vertical dimension of occlusion.

Deflective contacts also may be present in functional and parafunctional lateral movements from the time

the restoration is initially inserted. Such contacts are undesirable in either natural or artificial occlusions

and can contribute to periodontal trauma, muscle

spasm, TMJ pain, and loss of supporting edentulous

tissues.

THE ANTERIOR POINT OF REFERENCE

The selection of the anterior point of the triangu- lar spatial plane determines which plane in the head

will become the plane of reference when the prosthe-

sis is being fabricated. The dentist can ignore but

cannot avoid the selection of an anterior point. The

act of affixing a maxillary cast to an articulator relates the cast to the articulators hinge axis, to the

vertical axes, to the condylar determinants, to the anterior guidance, and to the mean plane of the

articulator. The act achieves greater importance by the use of a constant third point of reference and repeatable posterior points of reference. When three

points are used the position can be repeated, so that different maxillary casts of the same patient can be positioned in the articulator in the same relative position to the end-controlling guidances. With complicated and time-consuming recording tech-

Fig. 2. Posterior points of reference. a, Bergstrom point. b, Beyron point.

Fig. 3. Orbitale (o), axis-orbital plane (a-o), and Frankfort horizontal plane (f-o).

niques such as a pantographic tracing, the dentist does not have the time, nor the patient the means, to repeat records each time the technique calls for a new maxillary cast. For this reason it is important to identify the mark permanently or be ahle to repeti- tively measure an anterior point of reference as well as the posterior points of reference.

THE JOURNAL OF PROSTHETIC DENTISTRY 489

WILKIE

Fig. 4. Face-bow supported at the level of the axis-orbital plane.

Fig. 5. Maxillary record base and vertical support arm are fixed by plaster in the transfer cup.

SELECTION OF AN ANTERIOR REFERENCE POINT

In selecting the reference plane, the dentist should have knowledge of the following anterior points and

the rationale for the selection of each. 1. Orbitale (FZg. 3). In the skull, orbitale is the

lowest point of the infraorbital rim. On a patient it can be palpated through the overlying tissue and the skin. One orbitale and the two posterior points that determine the horizontal axis of rotation will define the axis-orbital plane. Relating the maxillae to this plane will slightly lower the maxillary cast anteriorly from the position that would be established if the Frankfort horizontal plane were used. Practically,

Fig. 6. The transfer cup is attached to the articulator.

the axis-orbital plane is used because of the ease of

locating the marking orbitale and because the

concept is easy to teach and understand. Orbitale and the two posterior landmarks defining

the plane are transferred from the patient to the

articulator with the face-bow. The articulator must have an orbital indicator guide that is in the same

plane as the hinge of the articulator. Orbitale is

transferred from the patient to this guide by means of the orbital pointer on the anterior crossarm of the

face-bow. The axis-orbital plane can be transferred to the

articulator in another manner. The face-bow itself is

raised to the axis-orbital plane on the patient (Fig.

4). A metal arm attached to the maxillary record

base is rigidly fixed by plaster in a cup that also attaches to a vertical support arm on the face-bow

(Fig. 5)* and subsequently to a vertical support arm on the articulator (Fig. 6).t The relationship of these

two vertical support arms to the hinge line is

identical. Therefore the record base which is rigidly

fixed to the vertical arm attachment can be trans-

ferred from the patient to the articulator. This will

relate the maxillary cast to the axis-orbital plane or to any other plane with which the face-bow is paralleled on the patient.

2. Orbitale minus 7 mm (Fig. 7)~ The Frankfort horizontal plane passes through both poria and one orbital point. Because porion is a skull landmark,

Sicher recommends using the midpoint of the upper border of the external auditory meatus as the posterior cranial landmark on a patient. Most articulators do not have a reference point for this landmark. Gonzalez pointed out that this posterior tissue

*Hanau Earpiece Face-bows, Models 140-l and 140-2. Hanau

Engineering Co., Inc., Buffalo, N. Y. fHanau Transfer Index, lModels 140-10.5 and 140-106, Hanau

E:ngineering Co., Inc., Buffalo, N. Y.

490 MAY 1979 VOLUME 41 NUMBER 5

ANTERIOR POINT OF REFERENCE

Fig. 7. 11-0, Axis-orbital plane. f-0, Frankfort horizontal plane. Facial landmark (o minus 7 mm) used to relate maxillary cast to Frankfort horizontal plane.

landmark on the average lies 7 mm superior to the

horizontal axis. The recommended compensation for this discrepancy is to mark the anterior point of

reference 7 mm below orbitale on the patient or to

position the orbital pointer 7 mm above the orbital indicator of the articulator. Bergstroms arcon artic-

ulator automatically compensates for this error by placing the orbital index 7 mm higher than the

condylar horizontal axis. In either technique, the Frankfort horizontal plane of the patient becomes the

horizontal plane of reference in the articulator. 3. Nasion minus 23 mm. According to Sicher,

another skull landmark, the nasion (Fig. 8), can be

approximately located in the head as the deepest

part of the midline depression just below the level of the eyebrows. The nasion guide, or positioner, of the

Quick Mount face-bow* (Fig. 9), which is designed to be used with the Whip-Mix Articulator,* fits into

this depression. This guide can be moved in and out, but not up and down, from its attachment to the face-bow crossbar. The crossbar is located 23 mm below the midpoint of the nasion positioner. When

the face-bow is positioned anteriorly by the nasion guide, the crossbar will be in the approximate region of orbitale. The face-bow crossbar and not the nasion guide is the actual anterior reference point locator. During the face-bow transfer, the crossbar of the

*The Whip-Mix Corp., Louisville, Ky.

THE JOURNAL OF PROSTHETIC DENTISTRY

Fig. 8. The nasion.

Fig. 9. Nasion guide (ng) and face-bow crossbar (cb).

face-bow supports the upper frame of the Whip-Mix articulator. The inferior surface of the frame is in the

same plane as the articulators hinge points. From

this it can be concluded that the Quick Mount

face-bow used with the Whip-Mix articulator employs an approximate axis-orbital plane.

Locating the orbital point with this technique is

dependent upon the large nasion guide, the morpho- logic characteristics of the nasion notch, and the

variance of the nasion-orbitale measurement from 23 mm in the patient.

4. Incisal edge plus articulator midpoint to articulator

axis-horizontalplane distance. Guichet has emphasized that a logical position for the casts in the articulator

would be one which would position the plane of occlusion near the mid-horizontal plane of the articulator. A deviation from this ob.jective may position casts high or low relative to the instruments upper and lower arms. The effect of these high or low positions may be inaccurate occlusal relationships

491

\tlLKIE

Fig. 10. Campers line (cl) and occlusal plane (op).

due to dimensional changes in the artificial stone or

plaster used for cast-mounting purposes. In accordance with this concept, the distance from

the articulators mid-horizontal plane to the articulators axis-horizontal plane is measured. This same

distance is measured above the existing or planned

incisal edges on the patient, and its uppermost point is marked as the anterior point of reference on the face. This point can be recorded for future use by

measuring vertically downward to it from the inner

canthus of the eye and recording this measurement.

The inner canthus is used because it is an accessible, unchanging landmark on the head.

With this technique the face-bow transfer will carry the two predetermined posterior points of

reference and this anterior point of reference to the anticulators axis-horizontal plane. The dentist can then proceed, knowing that the incisal edges will fall on the articulators mid-horizontal plane unless a

subsequent decision raises or lowers them. It must be recognized that this technique does not

relate the Frankfort plane or the axis-orbital plane parallel to the horizontal plane. Additionally, only the incisal edges or the most anterior portion of the occlusal plane will be midway between the upper and lower articulator arms. A tentative or an actual occlusal plane will not be parallel to the horizontal plane unless by coincidence.

5. Alae of the nose. A part of many complete denture techniques is to make the tentative or the

actual occlusal plane parallel with the horizontal

plane. lhis can be achieved in two ways: i 1: a lint

from the ala* of the nose to the center of the auditor)

meatus describes Campers line (Fig. IO). Au,gsbtuger

concluded, in a review of the literature, that the occlusal plane parallels this line with miuor maria-

tions in different facial types. Knowing this, the dentist can transfer C.Iampers lint from the patient

to the articulator by marking the right or left ala on

the patient, setting the anterior reference pointer of the face-bow to it, and with the face-bow, transfer-

ring the ala anteriorly. and the hinge points posteriorly, from the patient to the articulators hinge-of,- bital indicator plane. 4 second method of estab-

lishing this relationship is to make a wax occlusion

rim parallel to C:ampers line on the face (Fig-. 1 I j. The desired location for the maxillary incisal edges

should be marked on the wax occlusion rim as an initial step in determination of the occlusal plane.

This ensures that the tentative occlusal plane will

not be too high or low. The wax occlusion rim made parallel with Campers line is transferred to the

articulator with a face-bow (Fig. 12). Its occlusal

plane is rnade parallel with the upper and 1owe1 articulator arms (Fig. 13). In this way, the ala-cl~lc

plane (a plane that coincides with Campers line) anti

the tentative occlusal plane arc horizontal and

become the planes of reference in this technique. Other intraoral landmarks, esthetics. considera-

tion for the residual ridges, and tongue and cheek guidance factors may alter the ,/inal o~clu.sni plnnr.

Laboratory auxiliaries do not have the benefit or

knowledge of these patient-related factors. lhere-

fore, if the laboratorysjudgment alone is relied upon to establish the final occlusal level, an unsightly

plane or one which transmits the wrong forces to the weaker ridge may result.

Practically, the dentist may omit the construction of an occlusion rim or elect not to identify a tentative occlusal plane. However, when performing the try-in and record verification procedures with the patient.

the occlusal plane should be adjusted to the opti- mum position that will favor esthetics, transmit the desired forces to the ridges, and permit comfortable control of food morsels by the tongue and the cheeks.

*The a/a nm is defined as the rounded eminence of the inferior

lateral surface of the nose. (Adapted from Henry Gray: Anato-

my of the Human Body, W. H. Lewis ied). Philadelphia, 1942,

Lea & Febiger. p 1010.)

492 MAY 1979 VOLUME 41 NJMBER 5


Fig. 11. Making the occlusion rim parallel to Campers line

Fig. 12. Transfer of the occlusion rim to the articulator with a face-bow

DISCUSSION

Other reasons for selecting an anterior point of

reference must be considered.

1. A planned choice of an anterior reference point

will allow the dentist and the auxiliaries to visualize the anterior teeth and the occlusion in the articulator in the same frame of reference that would be used when looking at the patient. The objective is usually

to achieve a natural appearance in the form and the position of the anterior teeth. Mounting the maxillary cast relative to the Frankfort horizontal plane will accomplish this objective. When this reference plane is used, the teeth will be viewed as though the patient were standing in a normal postural position with the eyes looking straight ahead.

2. An occlusal piane not paraliel to rhe horizontal

in the beginning steps of denture fabrication may be

unknowingly located incorrectly because of a

tendency for the eye to subconsciously make planes and lines parallel. Therefore the dentist may wish to

initially establish the restored occlusal plane parallel to the horizontal in order IO better control the

occlusal plane in its final position. The objective is to achieve a natural appearance in the occlusal plane. Mounting the cast relative to LumpPrs ~.VZB best meets

this objective. 3. The dentist may wish to establish a baseline for

comparison between patients, ar for thch same patient at different periods of time. Only through the use of a three-point mounting that is const,ml: from one


WILKIE

Fig. 13. A maxillary cast in the articulator is related to Campers line.

Fig. 14. A maxillary cast in the articulator related to Campers line as horizontal. Making the dotted line parallel with the horizontal relates the maxillary cast to the Frankfort horizontal plane.

patient to another or for the same patient can valid comparisons be made. Orthodontists, investigators using cephalometrics, anthropologists, and other dental specialists have used the Frankfort horizontal plane more frequently than any other plane of reference to accomplish this objective. Although other planes can be used, the dentist should make sure that all auxiliary personnel know Z&C/I plane is

being used and understand the rationale for its

use.

Confusion occurs in practical application of the

objectives when the dentist and the laboratory tech-

nicians apply different objectives to the same

patient. The dentist may very well have positioned the maxilllary cast in relation to the Frankfort

horizontal plane or used one of the other more superior anterior points of reference. Laboratory

personnel may then proceed to establish the occlusal plane parallel to the horizontal; or, said another

way. parallel to the upper and lower articulator

arms. The result will be an occlusal plane that drops from anterior to posterior when placed in the

patients mouth and lines of force that will not be at

right angles to the mean plane of the ridge. This fault is commonly observed; it results when the

dentist ignores the selection of an anterior point of reference and the laboratory arbitrarily establishes every occlusal plane parallel to the articulator arms.

The consequences of the reverse situation will also be detrimental to the patient. The dentist may use

Campers line as the reference for the maxillary cast mounting. The laboratory may then position the anterior teeth and the occlusal plane as though the Frankfort horizontal plane were being used. The result will be an occlusal plane that rises severely from anterior to posterior in the patients mouth and maxillary anterior teeth that may be excessively linguoverted. Again, force transmission to the residual ridges may not bc as desired.

The advantages and disadvantages of using either

494 MAY 1979 VOLUME 41 NUMBER 5


Fig. 15. A maxillary cast related to Campers line (dotted line) as the horizontal plane of reference. The occlusal plane (solid line) is parallel to Campers line and the horizontal. RULE: to achieve the effect of the Frankfort plane (double line) as the horizontal reference plane, raise the back of the articulator.

the Frankfort horizontal plane or Campers line as

the plane of reference have been pointed out. Both philosophies can be applied advantageously when the dentist uses the following technique.

First, decide on the principal plane of reference to

be used. Next, position the face-bow on the marked posterior points of reference and align the anterior reference pointer to the alternate anterior reference

point on the face. Then carry the face-bow to the articulator. Relate it posteriorly to the hinge and

anteriorly to the articulators anterior point of refer-

ence guide. With the maxillary cast in place, mark a

line on the cast parallel to the horizontal. Return the

face-bow to the patient and repeat the steps; but this time use the principal anterior point of reference and

affix the maxillary cast to the articulator once the face-bow transfer is made. In this manner the cast

will be mounted parallel to one plane of reference, and a line parallel to the other will be visible on the

maxillary cast (Fig. 14). As a more practical and less time-consuming

alternative, the following technique can be used: (1) If the Campers line-horizontal reference plane is used,

raise the back of the articulator to achieve the effect of the Frankfort horizontal plane mounting (Fig. 1.5); (2) if the Frankfort horizontal plane reference is used, raise the anterior of the articulator to achieve the effect of paralleling the occlusal plane and Campers line (Fig. 16) with the horizontal.

There is one last precaution to observe when relating the maxillary case in space to a horizontal

Fig. 16. A maxillary cast is related to the Frankfort plane (double line) as the horizontal plane of reference. RULE: to achieve the effect of Campers line (dotted iine) and the occlusal plane (solid line) as the horizontal refcrrnce plane, raise the front of the articulator.

Fig. 17. Frontal view reference line. IP. Interpupillary line. hi, Hinge line. op, Transverse line across occlusal surfaces.

reference plane. The relating planes are usually thought of as being viewed from the lateral aspect. When viewed from the frontal aspecr, there are reference lines as well. The hinge line, rhe interpupillary line, and a transverse line across the occlusal surfaces are three common frontal-view reference lines (Fig. 17). The latter two are observed in the patient, with the hinge line being better seen in the articulator. Generally these three lines art not paral-


WILKIL

lel. This is caused by posterior hinge reference points that are not equidistant from the eye pupils. An occlusal plane that is parallel to the interpupillary line will be pleasing to the eye of the viewer. It

cannot be guaranteed that an occlusal plane parallel

to the hinge will have the same pleasing appearance.

This further justifies the dentist making these deter-

minations in the patient and further contraindicates

giving auxiliary personnel the opportunity to decide on occlusal plane location relative to articulator landmarks.

SUMMARY

Three points in space determine the position of the maxillary cast in an articulator. The dentist is most frequently concerned with selecting the posterior two

of the three reference points. In addition, the dentist

will, either consciously or unknowingly, select the anterior of these points of reference. This decision

will affect the development of occlusion and esthet-

ics. The dentist and the auxiliaries must share a common objective in using an anterior point of

reference. Five commonly used anterior points of

reference and the reasons for the use of each har,c, been discussed.

REFERENCES

I.

2.

3.

4.

5.

6.

7.

Beck, II. 0.: A clinical evaluation of the Arcon concept ,>I articulation .J PKOSTHET DENT 9:409, 1959. Weinberg. 1,. A.: An evajuation of the face-bow mountiny. ,J PRosTHEtT I-hmT 11:X?, 1961. &her, H.: Oral Anatomy, ed 2. St. Louis, 195. Ihc C 1. .Mosby Cu.. p 91. Gonzakx. J H., and Ii mgery, K. II.: Evaluation oi plants ~)t rrfwcnw for orienting maxillary casts on articulaturc. .J :1m I)rnt Assoc 76:329, 1968. Beck. Ii. 0.: and Morrison, W. E.: Investigation of an .4rcorl articulator. J PROSTFIEI. DENT 6:359, 1956. Guichct, N. F.: Occlusion, A Teaching Manual. Anaheim. 1970, The LIenar Corp., p 56. f\ugsburger. K. Ii.: Occlusal plane relation to facial type. .j P~cxrm~. Ihvr 3:75.5. 1953.

Reprint requests to. CAPTAIN NOEL D. WILKIE, IX, CJSN

COMMANDING OPFICER

NAVAL REGIONAI. I)EvrAL &vr~~ Box 111

PEARL HARBOR, I~AWAII 96860

ARTICLES TO APPEAR IN FUTURE ISSUES

Fabrication of a maxillary occlusal treatment splint Harmon F. Adams, D.D.S.

Posterior maxillary osteotomies: An aid for a difficult prosthodontic problem John M. Alexander, D.D.S., and ,Joseph E. Van Sickels, D.D.S.

Technique for making a customized shade guide Samuel W. Askinas, D.D.S.. and Daniel A. Kaiser. D.D.S., M.S.D.

The effect of relining on the accuracy and stability of maxillary complete dentures-An in vitro and in vivo study M. T. Bar-co, Jr., D.D.S., M.S.D., B. K. Moore, Ph.D., M. L. Swartz, M.S., M. E. Boone,

D.D.S.. M.S.D., R. W. Dykema, D.D.S., M.S.D.. and R. W. Phillips, M.S., D.Sc.

Temperature change caused by reducing pins in dentin Wayne W. Barkmeier, D.D.S., M.S., and Robert I,. Cooley, D.M.D., M.S

Simplified Class V matrix or resin restorations .Janet G. Bauer, D.D.S.

Current concepts in cranioplasty John Beumer, III, D.D.S., M.S., Dave N. Firtell, D.D.S., and Thomas A. Curtis, D.D.S.

MAY 1979 VOLUME 41 NUMBER 5

Anterior Point of Reference

Documents

anterior reference point

maxillary cast

posterior points of

accurate posterior point

bergstrom point

beyron point

removable prosthodontics

removable prostheses