curve of Spee to pass through the mandibular condyle,which has been demonstrated to allow posterior dis-clusion on mandibular protrusion.7 As the angle ofcondylar guidance is greater than the curve of Spee,posterior disclusion is achieved.8

The Broadrick flag9 (Broadrick Occlusal PlaneAnalyser; Teledyne Water Pik, Fort Collins, Colo.)permits reconstruction of the curve of Spee in harmo-ny with the anterior and condylar guidance, allowingtotal posterior tooth disclusion on mandibular protru-sion. Its use assumes proper functional and estheticpositioning of the mandibular incisors. Should theanterior guidance be inappropriate, it must beredesigned prior to use of the Broadrick flag.

The position of the designed restorations shouldnot interfere with lateral excursive mandibular move-ments. The tooth arrangement in the bucco-lingual

Prosthodontic management of the curve of Spee: Use of the Broadrick flag

Christopher D. Lynch, BDS,a and Robert J. McConnell, BDS, PhDb

National University of Ireland, Cork, Ireland

Proper management of the occlusal plane is an essential consideration when multiple long-spanposterior restorations are designed. When restorations are added to an existing tooth arrangementcharacterized by rotated, tipped, or extruded teeth, excursive interferences may be incorporated,resulting in detrimental sequelae. The curve of Spee, which exists in the ideal natural dentition,allows harmony to exist between the anterior tooth and condylar guidance. An instrument calledthe Broadrick flag has been used to assist in the reproduction of tooth morphology that is com-mensurate with the curve of Spee when posterior restorations are designed; its use prevents theintroduction of protrusive interferences. Consideration also must be given to lateral excursivemovements when the occlusal plane is designed. In this article, the importance of the curve of Speein prosthdontic and restorative dentistry is discussed, and a patient treatment demonstrating useof the Broadrick flag is described. (J Prosthet Dent 2002;87:593-7.)

In the normal natural dentition, there exists ananteroposterior curve that passes through the cusp tipof the mandibular canine and the buccal cusp tips ofthe mandibular premolars and molars, and thatextends in a posterior direction to pass through themost anterior point of the mandibular condyle.1Originally described by Ferdinand Graf Spee1 in 1890,this curve exists in the sagittal plane and is best viewedfrom a lateral aspect (Fig. 1); it permits total posteriordisclusion on mandibular protrusion, given properanterior tooth guidance.

Spee located the center of the curve along “a hori-zontal line through the middle of the orbits behind thecrista lachryma posterior,”2 a structure identified inthe textbooks of the era3 as a vertical ridge on thelacrimal bone giving partial origin to the orbicularisoculi muscle. Spee’s idea was advanced in 1920 byGeorge Monson.4 Based on anthropological observa-tions, Monson described a 3-dimensional sphere thatpassed through the incisal edges and occlusal surfacesof the mandibular teeth. It is not usually noted thatwhile Spee described a curve of approximately 2.5-inch radius (6.5-7.0 centimeters),1 Monson2 pro-posed the now widely accepted curve of 4-inch radius.Spee noted that it would be possible to locate the cen-ter of the curvature “by reconstruction andmeasurement with the compass.”

The curve of Spee may be pathologically altered insituations resulting from rotation, tipping, and extru-sion of teeth. Restoration of the dentition to such analtered occlusal plane can introduce posterior protru-sive interferences.5 Such interferences have beenshown to cause abnormal activity in mandibular eleva-tor muscles, especially the masseter and temporalismuscles.6 This can be avoided by reconstructing the

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aRegistrar, Department of Restorative Dentistry.bProfessor, Department of Restorative Dentistry.

Fig. 1. Curve of Spee. (Reproduced by Dr Mary McConnellfrom Spee FG. Die Verschiebungsbahn des Unterkiefers amSchädel. Arch Anat Physiol 1890;16:285-94)

plane is referred to as the curve of Wilson.10 The curveof Monson4,11 is, in effect, a combination of the curvesof Spee and Wilson in a 3-dimensional plane.

This clinical report describes the effective applica-tion of the Broadrick flag in prosthodontic andrestorative dentistry and reviews the principles of itsuse from anatomical science.

CLINICAL REPORT

A 26-year-old man seeking restoration of missingteeth in the maxillary left and mandibular right poste-rior quadrants was referred to the RestorativeDepartment of the Cork University Dental School andHospital (Wilton, Cork, Ireland). On clinical examina-tion, it was found that the maxillary left secondpremolar, maxillary left first molar, and mandibularright first molar were absent. The endodontically treat-ed maxillary left first premolar was fractured close tothe gingival margin.

Diagnostic casts were mounted in a semi-adjustablearticulator (Denar Anamark Fossae; Teledyne Water

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Pik). Visual examination confirmed that the occlusalplane on the right side was normal (Fig. 2, A). Aftertrial preparations and a diagnostic wax-up, a decisionwas made to restore this space with a combinationfixed partial denture.12 However, a marked discrepan-

Fig. 2. A, Mounted diagnostic casts of patient’s right side.Mandibular right first molar was absent. Occlusal plane onthis side was considered normal. B, Mounted diagnosticcasts of patient’s left side. Marked discrepancy was evidentin level of occlusal plane: mandibular left first molar wasextruded, resulting in narrow occluso-gingival space forpotential pontic to replace maxillary left first molar.

Fig. 3. A, Anterior survey point (ASP) was selected on mid-point of disto-incisal edge of mandibular left canine, fromwhich long arc of 4-inch radius was drawn on flag with useof compass. B, Posterior survey point (PSP) was located ondisto-buccal cusp of distal left mandibular molar. If positionof this tooth were deemed unacceptable, anterior border ofcondylar element on articulator could be selected as PSP.

A

B

A

B

cy was noted in the level of the occlusal plane on thepatient’s left side. The mandibular left first molar wasextruded, resulting in a narrow occluso-gingival spacefor a pontic that would replace the maxillary left firstmolar (Fig. 2, B).

The Broadrick flag was chosen to assess and, if nec-essary, redesign the level and orientation of theocclusal plane on the patient’s left side. The anteriorguidance and esthetic appearance of the mandibularanterior teeth were assessed clinically and found to besatisfactory. The maxillary cast was removed from thearticulator, and the flag was attached to the uppermember of the articulator. The anterior survey point(ASP) was chosen on the midpoint of the disto-incisaledge of the mandibular left canine, from which a longarc of 4-inch radius was drawn on the flag with a com-pass (Fig. 3, A). Because the position of the distalmandibular molar was judged to be acceptable, theposterior survey point (PSP) was located on the disto-buccal cusp of this tooth (Fig. 3, B), and a short arcwas drawn on the flag to intersect the long arc at thecenter of the curve of Spee (Fig. 4, A). The point of

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the compass was placed at the center of the flag, and a4-inch radius was drawn through the buccal surfaces ofthe mandibular teeth. The mandibular left first molarwas markedly extruded, while the heavily restoredmesial cusps of the mandibular left second molar werebelow the level of the curve (Fig. 4, B).

On the stone cast, the occlusal surface of themandibular first molar was reduced to the level of theredefined occlusal plane (Fig. 5, A). This tooth wasplanned for restoration with a gold onlay; themandibular left second premolar with a metal-ceramiccrown; the mandibular left second molar with a complete-coverage gold crown; and the maxillary leftedentulous area with a 3-unit fixed partial denture,with the maxillary left first premolar and second molaras abutments. Trial preparations were performed onarticulated duplicate casts, and the diagnostic wax-upwas fabricated (Fig. 5, B). Care was taken to ensureeven occlusal contacts in maximum intercuspation andavoid posterior interferences in protrusive or lateralexcursions. The occlusion was restored to a canine-protected occlusion.

Fig. 4. A, Short arc of 4-inch radius was drawn from PSP on flag to intersect long arc at cen-ter of curve of Spee. B, Point of compass was placed at center of flag, and 4-inch radius wasdrawn through buccal surfaces of mandibular teeth. Note extrusion of mandibular left firstmolar; mesial cusps of mandibular left second molar were below level of curve.

A B

The diagnostic wax-up was duplicated, and vacuum-formed acrylic templates were fabricated.With use of the mandibular acrylic template, themandibular left first molar was reduced intraorally tothe occluso-gingival height predetermined on thediagnostic cast. Further occlusal reduction for a castgold restoration then was performed and the onlaypreparation completed. Cast dowel-and-core restora-tions were fabricated for the maxillary first premolarand mandibular second premolar and cemented in thenormal manner. With the respective template as aguide, controlled conservative reduction was per-formed on the mandibular and maxillary left secondmolars. Provisional restorations were fabricated.

After a 4-week trial period, the patient reported thatthe provisional restorations were comfortable. Noabnormal wear facets were evident, occlusal contactswere present in MIP, no interferences in protrusiveand lateral excursions were detected, and the gingivalhealth remained optimal. Final restorations were fabri-cated in the traditional manner (Fig. 6). At subsequentrecall appointments, the occlusion remainedunchanged. The patient reported total comfort andsatisfaction with the masticatory performance andesthetics of the definitive restorations.

DISCUSSION

The Broadrick flag is a useful tool in prosthodonticand restorative dentistry, as it identifies the most likelyposition of the center of the curve of Spee. However,this position should not be regarded as fixed orimmutable. Esthetics and function place a considerabledemand on the design of the occlusal plane.Compromise can be achieved by altering the length ofthe radius of the curve. In patients with a retrognathicmandible, a standard 4-inch curve would result in a flatposterior curve, causing posterior protrusive interfer-ences. Such “low” mandibular posteriors would alsolead to extrusion of the opposing maxillary teeth. If themaxillary posterior teeth were to be restored to this lowocclusal plane, the crown-to-root ratio would be lessthan ideal. Hence, a 33⁄4-inch curve is more appropriatewhen a class II skeletal relationship exists. Conversely, a4-inch curve would create a steep posterior curve inpatients with a class III skeletal relationship, leading tofurther posterior interferences. A 5-inch radius wouldbe more suitable in this situation.

The center of the curve also may be varied to achievethe same effect. The center should always lie along thelong arc drawn from the anterior survey point, but itmay be moved in an anterior or posterior directionfrom the intersection of this arc with that drawn fromthe posterior survey point. This alteration will notaffect the position of the anterior survey point, animportant fact when the position of the mandibularanterior teeth is esthetically and clinically suitable.

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Fig. 5. A, Occlusal surface of mandibular first molar reducedto level of redefined occlusal plane on stone cast. B, Diagnostic wax-up of restorations on patient’s left side.

Fig. 6. Definitive restorations cemented on left side.

A

B

When the center of the curve or its radius is alteredfor esthetic reasons, care must be taken not to createnew interferences. Needles7 noted that to ensure pos-terior disclusion on mandibular protrusion, the curveshould extend through the condyle. When the PSP islocated, the level and orientation of the distal molartooth may not always be suitable. Should this be thescenario, it follows that the PSP may be taken as theanterior border of the condyle, represented by themost anterior point on the condylar element on thearticulator. Care should be taken to ensure that theangle of the condylar guidance is not less than thecurve of Spee, as this would introduce posterior pro-trusive interferences.8

It should be further considered that the arrange-ment of the maxillary and mandibular teeth influenceslateral excursive movements. When viewed from afrontal aspect, the mandibular molars have a slight lin-gual inclination and the buccal cusps of these teeth arehigher than the lingual. This arrangement is referredto as the curve of Wilson,10 and it facilitates lateralexcursions free from posterior interferences. Attentionshould be paid to this principle when the diagnosticwax-up is designed. Monson4,11 proposed that themandibular teeth should be arranged to close arounda sphere of 4-inch radius, with the mandibular incisaledges and cusp tips touching the sphere, thus permit-ting protrusive and lateral excursions free fromposterior interferences. It bears repeating that the nowwidely accepted 4-inch radius was proposed byMonson rather than Spee.4

Hyperactivity in the temporalis and masseter mus-cles has been demonstrated during mandibularprotrusive movements when inappropriate posteriortooth contacts are present.6 Careful restoration designto ensure proper anterior guidance will prevent theintroduction of such interferences and the establish-ment of such abnormal activity. Excursive interferencesmay result in wear, fracture of restorations, and tem-poromandibular joint dysfunction.

The use of an acrylic template can facilitate con-trolled conservative reduction. In the clinical reportpresented, the template was a vital tool for transferringthe designed blueprint from the diagnostic wax-up onthe articulator to the mouth. The template allowedaccurate reduction of the extruded mandibular firstmolar to the level of the redesigned occlusal plane, fol-lowed by appropriate reduction for the cast restoration.This ensured that the fabricated onlay was in harmonywith the occlusal plane and that minimal tooth struc-ture was removed. Acrylic templates also were used forconservative preparation of the other teeth.

SUMMARY

The Broadrick flag is a valuable tool in prosthodon-tic and restorative dentistry, in that it locates the center

of the curve of Spee. Extensive restorations designedwith this tool permit mandibular excursions free fromposterior interferences. Proper planning is required,but the predictability of a successful result can beenhanced by the use of a diagnostic wax-up, the trans-fer of information with an acrylic template, and theduplication of provisional restorations from the wax-up. With use of the Broadrick flag, the prosthodontistcan predictably produce high-quality restorations inharmony with the anterior and condylar guidance andavoid the introduction of possibly harmful sequelae tothe patient.

We thank Ms Catherine MacGillycuddy, BA, HDE, MA, for hertranslation of Ferdinand Graf Spee’s article from German to English,and Dr Mary McConnell, B Dent Sc, for her reproduction of thecurve of Spee in Figure 1. We acknowledge the assistance of DrMichael Shanahan, BDS, in the preparation of the clinical treatmentdescribed.

REFERENCES

1. Spee FG. Die Verschiebungsbahn des Unterkiefers am Schädel. ArchAnat Physiol 1890;16:285-94.

2. Spee FG, Biedenbach MA, Hotz M, Hitchcock HP. The gliding path ofthe mandible along the skull. J Am Dent Assoc 1980;100:670-5.

3. Schäfer EA, Symington J, Bryce TH. Quain’s elements of anatomy.London: Longmans, Green & Co; 1915. Vol. IV. Part I. p. 89.

4. Monson GS. Occlusion as applied to crown and bridgework. J Nat DentAssoc 1920:7;399-413.

5. Shillinburg HT, Hobo S, Whitsett LD. Fundamentals of fixed prostho-dontics. 3rd ed. Chicago: Quintessence; 1997. p. 85-6.

6. Williamson EH, Lundquist DO. Anterior guidance: its effect on elec-tromyographic activity of the temporal and masseter muscles. J ProsthetDent 1983;49:816-23.

7. Needles JW. Practical uses of the Curve of Spee. J Am Dent Assoc1923;10:918-27.

8. Needles JW. Mandibular movements and articulator design. J Am DentAssoc 1923;10:927-35.

9. Bowley JF, Stockstill JW, Attanasio R. A preliminary diagnostic and treat-ment protocol. Dent Clin North Am 1992;36:551-68.

10. Wilson GH. A manual of dental prosthetics. Philadelphia: Lea & Febiger;1911. p. 22-37.

11. Monson GS. Applied mechanics to the theory of mandibular movements.Dent Cosmos 1932;74:1039-53.

12. Chaffee NR, Cooper LF. Fixed partial dentures combining both resin-bonded and conventional retainers: a clinical report. J Prosthet Dent2000;83:272-5.

Reprint requests to:DR CHRISTOPHER D. LYNCH

DEPARTMENT OF RESTORATIVE DENTISTRY

UNIVERSITY DENTAL SCHOOL AND HOSPITAL

WILTON, CORK

IRELAND

FAX: (353)21-434-5737E-MAIL: clynch85@hotmail.com

Copyright © 2002 by The Editorial Council of The Journal of ProstheticDentistry.

0022-3913/2002/$35.00 + 0. 10/1/125178

doi:10.1067/mpr.2002.125178

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