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DENTAL INSTRUMENTATION The History of Articulators: A Critical History of Articulators Based on Geometric Theories of Mandibular Movement, Part III: The “Balancer” Designs Edgar N. Starcke, DDS T HIS SERIES of articles on the “geometric school” of mandibular movement has been primarily concerned with those inventors whose theories and articulator designs have had an impact on the profession’s perception of mandibular move- ment and occlusion. Accordingly, this article will review the contributions of Harry Hagman and John Needles, who were tireless investigators of geometric principles. However, there are also those inventors whose articulators have remained ob- scure but have historical interest because they were based on an even more obscure theory, or were designed to reflect modifications of a theory that was currently in vogue. Examples of these articula- tors are those produced by Heinrich Schweitzer of New York City, George M. Hollenback of Encino, California, and Maurice J. Babb of Ardmore, Penn- sylvania. Maurice Babb’s instrument also represents a generic type of articulator design that is commonly known as a “balancer.” The term “balancer” was coined by Harry Hagman in the 1920s for devices that include features for determining a specific cure of occlusion projected from a rotational center lo- cated above the occlusional plane. Apparently, Babb was the first to receive a patent for an artic- ulator with this type of design, but it is doubtful that if any were ever produced. On the other hand, the Hagman line of “balancer” articulators, offered with an interesting variety of accessories, was a decided commercial success and will be covered in detail. Schweitzer’s “Projected Articulator” On May 8, 1913, Ellison Hillyer of Brooklyn, NY, presented a paper at the annual meeting of the Dental Society of New York. This paper reported that his “valued associate” at the New York College of Dentistry, Heinrich Schweitzer, had been inves- tigating the subject of articulation and had devised an articulator that “differs radically from all others in that the rotation point of the mandible is placed at the position of the vertebral axis.” 1 Hillyer claimed that Schweitzer had endeavored to prove his theory geometrically by constructing a double “Bonwill triangle” and making calculations on 3 arch sizes: 7, 10, and 13 cm (Fig 1). The triangles were constructed with a common base. Using the vertex of the posterior (occipital) triangle as the rotation point, Schweitzer scribed an arc through the condyle points. Bisecting this arc (by a line bisecting the 2 triangles), the points of the inter- section established the centers of circles that, when projected, were found to pass through the center of the foramen magnum—the vertebral axis. 1 Based on his deductions, Schweitzer constructed an articulator with the center of mandibular lateral motion in the area of the vertebral axis (Fig 2). A facebow was used to adjust the anterior triangle (incisor point) to individual requirements. Jaw re- lations were registered with an “incisor path guide” and a “molar path guide.” Hillyer commented that the articulator was “still in the somewhat unfin- ished stage.” 1 Even though Hillyer’s account may be the only source available for a description of this articulator, it has historical interest because it is based on principles very similar to Rupert Hall’s theory and apparently predates Hall’s work. George Hollenback’s Articulator According to James House, 2 George M. Hollen- back (Fig 3) based the design and functions of his articulator on Von Spee’s concepts and Monson’s “spherical” theory, utilizing the 4-inch radius that Monson found most applica- Correspondence to: Edgar N. Starcke, DDS, Copyright © 2002 by The American College of Prosthodontists 1059-941X/02/1104-0000$35.00/0 doi:10.1053/jpro.2002.129835 305 Journal of Prosthodontics, Vol 11, No 4 (December), 2002: pp 305-320

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Page 1: The History of Articulators-A Critical History of Articulators Based on Geometric Theories of Mandibular Movement-Part3

DENTAL INSTRUMENTATION

The History of Articulators: A CriticalHistory of Articulators Based on GeometricTheories of Mandibular Movement, Part III:The “Balancer” DesignsEdgar N. Starcke, DDS

THIS SERIES of articles on the “geometricschool” of mandibular movement has been

primarily concerned with those inventors whosetheories and articulator designs have had an impacton the profession’s perception of mandibular move-ment and occlusion. Accordingly, this article willreview the contributions of Harry Hagman andJohn Needles, who were tireless investigators ofgeometric principles. However, there are also thoseinventors whose articulators have remained ob-scure but have historical interest because they werebased on an even more obscure theory, or weredesigned to reflect modifications of a theory thatwas currently in vogue. Examples of these articula-tors are those produced by Heinrich Schweitzer ofNew York City, George M. Hollenback of Encino,California, and Maurice J. Babb of Ardmore, Penn-sylvania.

Maurice Babb’s instrument also represents ageneric type of articulator design that is commonlyknown as a “balancer.” The term “balancer” wascoined by Harry Hagman in the 1920s for devicesthat include features for determining a specific cureof occlusion projected from a rotational center lo-cated above the occlusional plane. Apparently,Babb was the first to receive a patent for an artic-ulator with this type of design, but it is doubtfulthat if any were ever produced. On the other hand,the Hagman line of “balancer” articulators, offeredwith an interesting variety of accessories, was adecided commercial success and will be covered indetail.

Schweitzer’s “Projected Articulator”On May 8, 1913, Ellison Hillyer of Brooklyn, NY,presented a paper at the annual meeting of the

Dental Society of New York. This paper reportedthat his “valued associate” at the New York Collegeof Dentistry, Heinrich Schweitzer, had been inves-tigating the subject of articulation and had devisedan articulator that “differs radically from all othersin that the rotation point of the mandible is placedat the position of the vertebral axis.”1 Hillyerclaimed that Schweitzer had endeavored to provehis theory geometrically by constructing a double“Bonwill triangle” and making calculations on 3arch sizes: 7, 10, and 13 cm (Fig 1). The triangleswere constructed with a common base. Using thevertex of the posterior (occipital) triangle as therotation point, Schweitzer scribed an arc throughthe condyle points. Bisecting this arc (by a linebisecting the 2 triangles), the points of the inter-section established the centers of circles that, whenprojected, were found to pass through the center ofthe foramen magnum—the vertebral axis.1

Based on his deductions, Schweitzer constructedan articulator with the center of mandibular lateralmotion in the area of the vertebral axis (Fig 2). Afacebow was used to adjust the anterior triangle(incisor point) to individual requirements. Jaw re-lations were registered with an “incisor path guide”and a “molar path guide.” Hillyer commented thatthe articulator was “still in the somewhat unfin-ished stage.”1

Even though Hillyer’s account may be the onlysource available for a description of this articulator,it has historical interest because it is based onprinciples very similar to Rupert Hall’s theory andapparently predates Hall’s work.

George Hollenback’s ArticulatorAccording to James House,2 George M. Hollen-back (Fig 3) based the design and functions ofhis articulator on Von Spee’s concepts andMonson’s “spherical” theory, utilizing the4-inch radius that Monson found most applica-

Correspondence to: Edgar N. Starcke, DDS,Copyright © 2002 by The American College of Prosthodontists1059-941X/02/1104-0000$35.00/0doi:10.1053/jpro.2002.129835

305Journal of Prosthodontics, Vol 11, No 4 (December), 2002: pp 305-320

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ble. Produced in 1928, this articulator has 2rotation points (Fig 4). The lower rotationpoint, A, represents the hinge axis; a facebowconnects with this lower point to mount thecasts. The upper rotation point, B, is the guidefor lateral movement. This articulator also pro-vides anterior guidance in the form of an in-cisal pin, C, and a custom guide cup, D. Mod-eling plastic or plaster was used to hand carve

gothic-arch paths, which were determined bycheck bites.2 As discussed later, the idea of auniversal joint for lateral mandibular move-ment combined with some type of controllingincisal guide mechanism was also expressed byHarry Hagman and John Needles.

Maurice J. Babb’s “Balancer” DesignArticulator

In 1918, Maurice Babb received a patent for anarticulator with a design that closely resembled

Figure 1. A diagrammatic representation of H.Schweitzer’s rotation axis of the mandible. Schweitzer’stheory was that the center of mandibular lateral rotationwas in the area of the foramen magnum. (Reprinted bypermission.1)

Figure 2. Schweitzer’s “Projected Articula-tor” with mounted casts showing the molarand incisal path guides in place. (Reprintedby permission.1)

Figure 3. George M. Hollenback, DDS. (Reprinted bypermission.3)

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that of Harry Hagman’s “Balancer” patented morethan a decade later (Fig 5). Generally, this type ofarticulator (as well as condylar articulators withoptional features providing “geometric” solutions)was based primarily on Monson’s “spherical” the-ory. Although it was not specifically stated, RupertHall’s “conical” theory was likely the basis forBabb’s articulator. In the patent letter description,the rotational center for the “upper jaw model

Figure 4. George Hollenback’s articulator.Hollenback described it as having 2 rotationpoints, a lower one for hinge movement (A)and an upper one for lateral movement (B).Harry W. Hahn of Los Angeles, California,manufactured this instrument in about1928, although less than 20 were produced.It was not patented. (Reprinted fromHouse, 1970, p. 141.2)

Figure 5. The Maurice J. Babb Articulator, 1918.This articulator was highly adjustable to “accommo-date individual requirements.” The patent drawingsreveal that the rotational mechanism allowed “arcu-ate” movement of the upper cast holder in an ante-rior/posterior direction but not in a lateral direction.Any lateral movement would have had to come fromhorizontal rotation of rod 20 in sleeve 17. (Reprintedfrom the 1918 U.S. Patent.4)

Figure 6. Harry C. Hagman. (Reprinted by permis-sion.5)

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Figure 7. (A) Hagman Balancer. (Reprinted from the 1929 U.S. Patent.6) (B) Hagman Balancers shown in an earlyadvertisement. The Hagman Balancers were produced by the Cleveland Dental Manufacturing Company until the early1930s, after which they were produced by the Hagman Balancer Company. (Reprinted by permission from Dent Surv1930;6:144.)

Figure 8. (A) Frontal view of the Balancer applied to a human skull. This shows the concept of an occlusal arc guidein position conforming to an ideal occlusal plane. (Reprinted by permission.8) (B) Hagman Balancer. Lateral view of theBalancer applied to a human skull illustrating that the occlusal plane is “in line” with the condyles. (Reprinted bypermission from Dent Surv 1930;6:118.)

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holder” is located at a position above the incisalpoint on a line oblique to the occlusal plane: “Thepivotal point (41) is arranged to oscillate, describ-ing a geodesic line about the surface of a cone, as inthe natural grinding movements in the humanmouth.” The hinge axis (28) is on a level with theocclusal plane (31).4

There has been some speculation concerningthe fate of Babb’s articulator. The design wasquite adequate for this type of articulator, andit was well constructed by the S. S. WhiteDental Manufacturing Co., a leading producerof dental equipment. Why, then, has it becomemerely a footnote in the history of articulators?After all, other instruments of similar designwere very successful over many years. Produc-tion issues associated with World War I mayhave limited its adoption, but the more likelyreason for its failure was simply a lack ofpromotion. James House has suggested that it

is not enough to develop and produce a well-designed, well-made articulator to gain wideacceptance by the profession; history has shownthat aggressive salesmanship and promotion,usually by the inventor himself on the “speak-ing circuit,” has been the key to the successfulmarketing of new articulator designs.2 Babbassigned the patent to the S. S. White Co., withwhom he obviously had a business arrange-ment, possibly as an employee. In any case,Babb himself did not promote this articulator.

A Successful Venture: The Hagman“Balancer”

In 1929, Harry C. Hagman (Fig 6) of Minneap-olis, MN, received the first of 2 patents for the“Balancer” articulator, a design concept thathe had been developing since the early 1920s.5-7

Introduced in 1925 (Fig 7A), the Hagman Bal-

Figure 9. The 3 basic models of the Hagman Balancer: (A) the chrome-plated “Deluxe Balancer, (B) the “JuniorBalancer,” a cadmium-plated economy model, and (C) the “Special Deluxe Model R,” with an extended hinge axis andadjustable functioning head. (A and B, from the collection of the University of Texas Health Sciences Center, HoustonDental Branch; C, from the collection of the Houston Veterans Affairs Medical Center, Dental Service.)

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ancer was designed according to Monson’sspherical theory. Hagman believed that themandible functioned in an arc (arcuate move-ments) from centric relation, as determined bythe curve of occlusion of the mandibular teeth,and that all movements of the human jaw canbe produced in an articulator functioning froma single point of rotation. Therefore, the Bal-ancer articulator was designed to reproduce allranges of movement so as to determine andrestore the mandibular path of occlusion.8 Theoperating mechanism of the Balancer (Fig 7B)was a single ball and socket (universal) jointcalled the “functioning head” (C), from whichwas suspended a pendulum (H) holding themaxillary cast mounting plate (62) by verticalsleeve (63). Hagman explained that when the castsare mounted in the Balancer, the “functioninghead”* (representing the spherical center of rota-tion) is located about 4 inches directly above theocclusal plane (Fig 8A). In this way, the occlusalplane forms the base of an isosceles triangle withthe functioning head as the apex. The hinge islocated to be “in line with” or concentric to theocclusal path (Fig 8B).9

The Hagman Balancer was well received andwas popular with dental practitioners for manyyears. It is true that Hagman aggressively pro-moted his products, but he was also very per-ceptive and eventually incorporated the versa-tility demanded by the marketplace into theBalancer line of articulators. This versatility isdemonstrable in the number of techniques(and, naturally, the various accessories pro-vided) for assessing the arcs of occlusion andfor mounting casts in the instrument.

Several “improvements” in design were madeover the years; and eventually, Hagman produced 3distinct models (Fig 9), each designed to performthe same basic functions but obviously intended tomeet a particular demand of the marketplace. Theoriginal Balancer would ultimately become knownas the “Deluxe Balancer.” It is likely that the ear-liest models (as patented) were produced with the

“plasterless” feature; that is, the casts weremounted with clamps and thumbscrews (see Fig7B). However, this feature was soon replaced withremovable cast mounting plates. The “BalancerJunior,” which appeared in 1934, was a smaller,simpler, less expensive version of the “Deluxe”model (Figs 9B and 10). Casts were mounted di-rectly to the “Junior Balancer,” which had no re-movable cast mounting plates. For those clinicianswho insisted on using a facebow, the “Special De-luxe Balancer Model R” had an extended hinge axisand adjustable functional head (Fig 9C). Thismodel could be purchased only through specialorder.†*Hagman confused the issue somewhat by comparing the

universal movement of the “functioning head” with Broomell’sdescription of the ginglimus-diarthodial function of the temporo-mandibular joint. Even though Hagman was trying to establishsome validity for the notion that the functioning head providedfor all except the hinge movements of the mandible, there isreally no correlation between the 2.

†Perhaps some of those who purchased the Model R reallybelieved that they knew what a single extended hinge axis was. Theymay have even believed that they knew: “What is the sound of 1hand clapping?”

Figure 10. Hagman Junior Balancer. (Reprinted fromthe 1938 U.S. Patent.7)

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Harry Hagman believed that “the ‘Balancer’articulator functioned similarly to the natural jawand should not be limited to any one mountingtechnique.”9 Therefore, each of the “Balancer”models was supplied with special accessories toaccommodate most dentists’ preferences formounting casts. These were the “plane-line,” flat-plane guide, and mounting jig (occlusal level) tech-niques; the use of the curved occlusal plane arcguides and dividers; and, of course, the facebow

attachment (Model R only). The curved occlusal arcguide plates and the dividers were also used forassessing the occlusal curvature of the mandibularteeth or occlusion rim.

Occlusal Arc Guides

These metal guides represent spherical seg-ments with radii of 2, 3, or 4 inches attached to

Figure 11. (A) A Hagman “Deluxe Balancer” with a 4-inch occlusal arc guide attached to the functioning head andrelated to mandibular occlusion rims. (B) A Hagman “Junior Balancer” with a 4-inch arc guide applied to mandibularocclusion rim for mounting the mandibular cast. (C) An early model of the Hagman “Deluxe Balancer” with a mountedmandibular cast and the denture teeth set to conform to a 4-inch arc guide. (D) An early model of the Hagman “DeluxeBalancer” with the maxillary teeth arranged to articulate with the mandibular teeth set by the 4-inch arc guide.

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the functioning head extending from the pen-dulum. The lower cast was compared to succes-sive arcs, and the one closest to the naturalocclusal curve was selected (Fig 11A). Mount-ing the casts involved setting the mandibularcast against the mounting plate so that thecenter of the pendulum bisected the center ofthe curvature of the occlusal plane. With themandibular cast supported in position by clayor wax, the maxillary cast was related to themandibular cast and secured with plaster to themaxillary cast holder. The clay or wax supportwas removed and replaced with plaster to

mount the mandibular cast. For mountingedentulous casts and fabricating complete den-tures, either the plane-line method (for mono-plane occlusion) or an arc guide could be ap-plied to mount the mandibular cast (Fig 11B).The maxillary cast was mounted in centricrelation to the mandibular cast, and the man-

Figure 12. Deluxe Balancer with dividers applied to adentulous mandibular cast. (From the collection of Uni-versity of Texas Health Sciences Center at HoustonDental Branch.)

Figure 13. These drawings of a Junior Balancer illus-trate the simple plane line mounting technique. TheJunior Balancer was used for one patient at a timebecause the casts were mounted directly to the lowerstage and upper cast support.

Figure 14. The BalancerFlat Plane Guide (A). Thisdevice is for mounting themandibular cast when amonoplane occlusion isplanned (B). Standardizedmeasurements are used torelate the height of the ret-romolar pad (11B) and thedepth of the normal anteriorsulcus (10B) to the heightof the occlusal plane. (Re-printed with permission.9)

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dibular teeth were arranged to conform to thearc guide (Fig 11C). The maxillary teeth werethen set to the mandibular teeth (Fig 11D).

The Dividers

A mandibular cast was placed on the lower stage ofthe balancer, supported with clay or wax, and cen-tered as previously described. A pair of special6-inch dividers was set to an approximate radius of5-1/4 inches, and the curved end of the dividers wasinserted into the depression of the top screw of theBalancer. The opposite (straight) end served as aguide to determine the curve or height of theocclusal plane and to assess what modifications arenecessary (Fig 12).

It is interesting to note that Hagman, perhaps inan attempt to boost the credibility of this proce-dure, expressed the notion that the use of dividersfor mounting casts “injects a scientific element inestablishing the level of the occlusal plane and indetermining the amount of extrusion and intrusionof the individual teeth from personal diagnosis, toarrive at an ideal occlusal plane.”9

The Plane-Line Mounting Technique

This procedure was suggested for diagnostic castsand for complete denture construction wheremonoplane occlusion was planned. Using the stan-dard cast supports, occlusally related casts weresimply mounted with the occlusal plane orientedparallel to and midway between the cast holders(Fig 13).

The Flat Plane Guide

This accessory was another mounting device in-tended primarily to establish the position of theocclusal plane for complete denture monoplanesetups (Fig 14A). The Flat Plane Guide consists ofa flat horizontal plate (F.1) attached to the func-tioning head by a central vertical standard (F.2).The plate was adjustable both vertically (F.7) andhorizontally in the slot (F.8). The heels of the platewere angulated to rest on the retromolar pads (11),and an incisal depth pin (F.4) determined theheight of the incisal rim (Fig 14B). General averagemeasurements were used from the crest of theridge or normal peripheral border to establish theincisal height.9

The Occlusal Level and Mounting Jig

This device was suggested by Dr. E. T. Tinker8 formounting related casts on the Balancer in the samerelative position or level as in the mouth and as aguide to determine the level of the occlusal planefor the occlusion rims or for natural teeth (Fig15A). The occlusal level consists of a vertical rod(V) to which is attached an adjustable bitefork (C)and an attachment (AT) for securing the verticalrod to the Balancer. Using the adjustable bitefork,the occlusal level was applied using standard meth-ods, that is, with either an occlusal index or occlu-sion rims (Fig 15B, C, and D). The vertical rod wasset so that it lined up with the center of the face andwas oriented vertically in both facial and profileperspectives (Fig 16 A and B). The vertical rod wasthen placed into the attachment, and the bitefork(with the related occlusal records) was centeredbetween the upper and lower cast holders andsecured in the Balancer. This device could be usedto mount casts arbitrarily without the patient.

The Facebow Attachment

The Special Deluxe Balancer Model R featured aposterior crossbar, also known as an extended hingeaxis, for attachment of a facebow or hinge axisrecorder (Fig 17A). The functioning head of theModel R was adjustable in an anterior-posteriordirection to ensure that the pendulum was alwayscentered directly over the occlusal plane. Figure17B is an illustration from a 1950 price list demon-strating the use of a mounting board to relate theHagman Hinge Axis Recorder to a Deluxe BalancerModel R.

The Balancer Natural Path Recorder andGothic-Arch Tracing Device

These intraoral and extraoral tracing deviceswere provided for “those who desire to recordthe influences or characteristics of condylarmovements, muscles or inherent habits of func-tion.”9 The technique for recording the naturalpath included both devices and was a novelapproach for producing a custom incisal guidetable. After the casts were mounted in theBalancer with any of the preferred methods,new record bases were constructed, and theBalancer Gothic Arch Tracing Device was

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mounted on the casts (Fig 18). Soft wax wasplaced in the maxillary tracing cup (T1) for thepatient to generate protrusive and lateral oc-clusal pathways with mandibular tracer point(T2). The wax was removed from the cup, castin a silver or other suitable metal, and returnedto the tracing cup to provide a stable andwell-defined record of the patient’s naturalfunction (Fig 18C). These metal intraoral

record paths were followed to hand-generatewax pathways in the Balancer Natural PathRecorder (Fig 19). The Recorder consists of anincisal pin (PR1) with a cone-shaped end (PR5)that can move within the incisal wax receptacle(PR2). As with the intraoral wax record, theextra-oral wax record was cast in metal. Fordentulous patients, this mechanism providedthe operator with a custom incisal guide table.

Figure 15. The Balancer Occlusal Level and Mounting Jig (A). This device consists of a vertical rod with attachedadjustable bite mark and is used for either dentulous or edentulous patients (B, C, D). As a mounting jig intended forleveling and centering the casts in the Balancer, it was probably used more often without the patient. (Reprinted bypermission.9)

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The “Inclinator” Attachment

This mechanical incisal guide table could be inter-changed with the Natural Path Receptacle. It wasdesigned to be a controlling “gothic arch” incisalguide with adjustments for protrusive and lateralexcursions (Fig 20).

The Balancer Clasp Surveyor

All models of the Balancer provided for attachmentof the Clasp Surveyor (Fig 21) by simply removingthe upper cast holder, locking the pendulum withsetscrew A, and securing it to the Balancer withscrew E. This device was a “broken arm” type witha spring-loaded marker for automatic return of thestylus to the original position when released.

Dr. John Needles’s First ArticulatorJohn Walter Needles of Pueblo, CO, is probablybest known for his functionally generated pathtechnique known as the “Needles-House chew-in.”2 He also developed a split-cast method fortesting the adaptability of articulators12 anddesigned an incisal control system as the pri-mary guidance for lateral mandibular move-ment. He is also remembered for his collabo-ration with Milus M. House on various aspectsof articulator design, including a rotary grind-er.2 Needles also produced 2 articulators.13 The

first, and the only 1 that was patented (in1921),14 was the “adaptable spherical articula-tor” (balancer-type design), which also fea-tured a “guiding mechanism that restricted itsmotion to a definite incisal path.”15

Why did Needles choose this hybrid design? Hehad been convinced that Gysi’s theories on condylarmovement and the relationship of the “gothic-arch”incisal path to his concept of mandibular rotationcenters were conclusive.16 However, by about 1920,Needles had also become persuaded by what he re-ferred to as “the fundamental truth” of George Mon-son’s “spherical” theory. Its appeal to him was that “itfitted in with the observed conditions almost per-fectly.”15 Needles faced a paradox: 2 seemingly con-flicting theories on the nature of mandibular move-ment, each believed to be fundamentally sound.Could Dr. Monson’s Spherical Theory and the con-cepts of Dr. Gysi be combined in a practical artic-ulator?

Needles’s initial idea was to design an artic-ulator based on the spherical theory but tomodify it so as to leave the size of the spherevariable, to conform to different patients(Fig 22). It was accepted that the averageradius of the sphere was 4 inches, but that itfrequently varied in both directions. Therefore,if the rotation center or “universal joint” (axle30) could be brought forward by adjusting theassembly (26) along the rotational axis (threaded

Figure 16. Applying the Occlusal Level. The prongs of the bite fork were adjustable so that the standard could be setvertically in both the facial (A) and profile (B) positions. (Reprinted by permission.9)

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Figure 17. (A) The Special Deluxe Model R Balancer. This model, with both the extended hinge axis and adjustablefunctioning head features, illustrates how the facebow is applied and the head adjusted to assure that the cast iscentered directly below the pendulum. (Balancer, from the collection of the Veterans Affairs Medical Center DentalService; Snow Facebow, from the collection of the author.) (B) Special Deluxe Model R with extended hinge axis. TheHagman Hinge Axis Recorder is in place using a mounting board. (Reprinted by permission.10)

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shaft A), then the center of the universal jointcould be adjusted to be opposite the incisal point.If the articulator was then adjusted by means ofthe incisal pin (37) and guide mechanism (8), sothat the universal joint was in a plane verticallyabove the deepest position of the curve of occlu-sion, it would be in approximately the correctposition. Needles’s gothic arch incisal guidemechanism8 was designed as a primary guidingsystem with the idea that “Gysi’s rotation centerrepresents one point on a rotational axis passingthrough the center of the sphere. This rotation

center could be considered as a pole located onthe surface of the sphere and that rotation aboutone of these axes corresponds to the working biteon that side.”15

Another idea to emerge from Needles’s conceptof mandibular movement and approach to articula-tor design was his “functionally generated path”method for recording jaw relations. This techniqueinvolved shaping modeling plastic occlusion rims toconform to the surface of a sphere. The rims weretested in the mouth and altered so that they re-mained in contact while the patient executed all

Figure 18. (A) Balancer Gothic-Arch (Intraoral) Tracer. The parts include the maxillary tracing cup (T1) for retainingan aluminum disk (T4) for Gothic arch tracings or wax for generating a natural path. Also pictured are the tracer point(T2) and tripod table (T3). (B) The Balancer Gothic-Arch Tracer mounted on the casts with record bases. (C) Fornatural path tracings, the wax is removed from the cups, cast in a silver alloy, and returned to the cup, creating a durablepatient-generated (intraoral) record that is traced when producing the hand-generated natural path (extraoral) tracing.(Reprinted by permission.10)

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Figure 19. The Balancer Natural Path (extra-oral) Tracer. (Reprinted by permission.11)

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lateral and protrusive excursions. Needles reportedthat “tracings of the actual masticatory movementsare recorded on the lower rim by embedding threepins‡ in the upper rim. The [resulting 3-dimen-sional tracings] furnish a means of knowing whenwe have secured a correct central occlusion . . . andalso afford the data necessary for adjusting anarticulator.”15

The spherical shape of the occlusion rimscould be formed using a template. Indeed, thiswas the most commonly used method for manyyears. Needles, however, was initially con-cerned with determining the position of thecenter of the sphere by accurately locating theposition of the surface of the occlusion rims (i.e.,surface of the sphere) in the articulator. Toaccomplish this, Needles designed an arcuate knifethat “swings on its . . . axis passing through thecenter of the sphere. If the distance from its rota-tional center is taken as its radius and the knifeblade is ‘warped’ to [conform to a segment of an arc

‡The original functionally generated path technique in-volved the use of 3 tracing pins, 1 in the midline and 2 in theareas of the second molars. Triangular-shaped tracing studswere created for the “Needles-House Chew-in” procedure. Fourof these studs were used, 2 in the second molar areas, and 2 inthe canine areas, replacing the 1 in the midline.

Figure 20. The Balancer Inclinator Attachment. This isessentially a mechanical incisal guide mechanism thatwas interchangeable with the Natural Path Recorder.(Reprinted by permission.9)

Figure 21. The BalancerClasp Surveyor Attachment(B). This is a broken arm de-vice with a spring-loadedmarker. (Reprinted by per-mission.9)

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Page 16: The History of Articulators-A Critical History of Articulators Based on Geometric Theories of Mandibular Movement-Part3

of] its radius . . . and if the knife is adjusted to passthrough the incisor point [of the lower occlusionrim], the articulator is approximately adjusted.”17

This brief look at how “geometric” theories ofmandibular movement influenced articulator designwill be concluded in the next issue of the Journal ofProsthodontics.

References1. Hillyer E: The development of the anatomic articulator.

Dent Cosmos 1913;55:989-10052. House JE: The design and use of dental articulators in the

United States from 1840-1970. Master’s thesis, University ofIndiana, 1970, pp 114-142; 180-183

3. George M. Hollenback, DDS (portrait for essayist advertise-ment). Dent Surv 1929;5:64

4. Babb MJ: Articulator. US Patent No. 1,285,896, November26, 1918

5. Promotional campaign for pledged laboratories. Dent LabRev 1956;31:36

6. Hagman HC: Dental Articulator. US Patent No. 1,736,006,November 19, 1929

7. Hagman HC, Lagaard AST: Dental Articulator. US PatentNo. 2,119,579, June 7, 1938

8. Hagman HC (ed): Dental Origins. Minneapolis, MN, HarryC. Hagman, 1973, pp 1-179

9. Hagman HC: A Manual on Articulation. Minneapolis, MN,Hagman Balancer Co., 1953, pp 1-72

10. Nichols IG (ed): Prosthetic Dentistry. St. Louis, MO, Mosby,1978, p 190

11. Hagman HC: Hagman Balancer Company price list. Min-neapolis, MN, 1950

12. Hall RE: An analysis of the development of the articulator.J Am Dent Assoc 1930;17:3-50

13. House MM: Studies in prosthesis. J Am Dent Assoc 1931;18:827-852

14. Needles JW: Articulator. US Patent No. 1,368,408, February15, 1921

15. Needles JW: The problem of articulation. J Am Dent Assoc1924;11:1220-1224

16. Starcke EN: The history of articulators: Pursuing the evolu-tion of the incisal-pin and guide, Part II. J Prosthodont2001;10:113-121

17. Needles JW: The mechanics of spherical articulation. J AmDent Assoc 1922;9:866-881

Figure 22. John Needles’ Adjustable Spherical Articula-tor. (Reprinted from the 1921 U.S. patent.13)

Figure 23. (A) John Nee-dles’ Adjustable SphericalArticulator with the arcuateblade in position to carve thesurface of the mandibular oc-clusion rim into a sphericalshape. (B) A view of the ar-cuate blade and a chart foradjusting the curvature ofthe blade. The cutting bladeis a metal band blade thatcan be “warped” by movingthe center jackscrew in andout. (Reprinted by permis-sion.16)

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