US2072127A - Artificial teeth and method of forming the same - Google Patents

Description

March 2, 1937. PlLKlNGTON ET AL 2,072,127

ARTIFICIAL TEETH AND METHOD OF FORMING THE SAME Filed Aug. 15, 1952 5 Sheets-Sheet 1 WW W WWW March 2, 1937. E. PlLKlNGTON ET AL 7 2,972,127

ARTIFICIAL TEETH AND METHOD OF FORMING THE SAME Filed Aug. 15, 1932 S sheets-sheet 2 2 y ,9 I art/0014101715 Wax/M 35 March 2, 1937. E. L. PILKI'NGTON ET AL 72,072,127

ARTIFICIAL TEETH AND METHOD OF FORMING THE SAME Filed Aug. 15, 1932 3 Sheets-Sheet 3 Patented Mar. 2, 1937 ATE-T .FFIC

ARTIFICIAL TEETH AND METHOD OF FORM- ING THE SAME Ernest L. Pilkington and Joseph F. Turner, Detroit, Mich.

Application August 15, 193 2, Serial No. 628,932

.14 Claims.

The invention relates to the art of manufacturing artificial teeth and has for its object first, the obtaining of a construction of mechanical teeth superior to teeth of anatomical form; see- 0nd, to obtain a method of generating the basic form of such teeth; third, to so modify this basic form as to have more of the appearance of anatomical teeth and to also improve-the functioning thereof.

With these general and other more specific ob jects in view the invention consists in'the construction and method as hereinafter set forth.

In the drawings: a Figure 1 is a geometrical design showing the occlusal construction of our primary forms on the lower jaw from the transverse aspect; Figure 2 is a diagram illustrating the method of adapting an articulator to the process of cutting the occlusal surfaces of the primary tooth 0 forms shown in Figure 1;

Figures 3 and 4 are respectively front and side. views of one of the cutting tools;

Figures 5 and 7 are plan views illustrating, the occlusal view respectively of the upper and lowerright bicuspids and molars;

Figure 6 shows the right side elevation of the upper and lower units in engagement, the upper being one half cusp posterior to the'lower;

Figure 8 shows a transverse sectional vertical view of the teeth after they have been placed in dentures;

Figure 9 shows a transverse vertical sectional view of one upper and one lower molar illustrating a system of cusp plane relief;

Figure 10 is a perspective view of the lower second molar tooth illustrating both positive and negative trihedral planes and the balancingplane;

Figure 11 shows one of the finished tooth models embodying hand carved features simulating natural teeth without destroying the primary masticating surfaces and from which corresponding porcelain teeth may be made.

In normal human jaws there are thirty-two teeth, of which, twenty are bicuspids and molars. In artificial teeth experience has shown that only sixteen bicuspids and molars are either desirable or necessary. These are divided into four operating units, one on each side of the upper, as well as the lower jaw; each unit consisting of a two bicuspids and two molars.

The human mandible makes, in addition to the opening and closing movements, right and left lateral movements, protrusive (forward),

retrusive (backward) and any combination of these movements. Anatomists have shown that the human mandible moves in certain definite paths. In protrusive movement, the head of the condyle moves 5 forward and downward, the path taken being determined by the anterior wall of its socket, or glenoid fossa. The angle between the slope of this wall (XX Fig. 2) and the horizontal plane of occlusion (HI-I Fig. 2) is the protrusive angle. 10 Protrusive angles vary in all individuals, even in the same individual, ranging from 0 degrees to degrees, however, our records show that eighty-five percent come between 25 and 35 degrees, and further that ninety-four percent come 15 between 20 and 4.0 degrees. This indicates that 30 degrees is the center or average of ninety-four percent of human jaw actions from the protrusive standpoint, therefore we have allowed this to be the deciding factor in determining the vertical 20 aspect of our tooth surfaces.

The lateral movement of the condyle head influences the design of the occlusal or biting surfaces of artificial teeth. In this movement,

known as the Bennett movement, the head of the 5 condyle moves bodily sidewise during side bites in. a'direction determined by the posterior wall of the glenoid fossa. The angle of the paths of this horizontal movement is taken from the sagittal plane, (88' Fig. 1) and variesfrom 5 degrees 30 to 25 degrees in human jaws.

Another movement of importance in the design of the occlusal surfaces of teeth is the so-called Gothic arch movement. This movement is carried out in practice by the incisal guide pins on 35 adaptable articulators, and is determined in the human jaws by'placing a pencil-tracer at a point corresponding to ,(I Fig. 1), between the central incisors of one jaw, and, making right and left lateral movements, thus recording on a card 40 firmly attached to the other jaw an obtuse angle (Gothic arch angle) which varies in human jaws from to degrees, and which represents the combined right and left movements. If a line (58' Fig. 1) be dropped back from (I) to point 45 (00) parallel to the sagittal plane, the composite angle will be divided into its right and left component angles, which vary from 50 to 65 degrees each.

- If on both b ows of any good adaptable articu- 50 lator, blocks of plaster (with carborundum powder incorporated) are fastened, the condyle inclinations set at 30 degrees, the incisal guide pin removed, and all masticating movements made with the articulator, therebygrinding the blocks 5.5

so that they will be in perfect approximation throughout any and all movements of the articulator, the resultant surfaces become perfect arcs I of spheres, the upper being convex, and the lower concave, and each arc the segment of a 12% inch sphere.

If the incisal guide pin is replaced, theincisal guide plane set at 30 degrees, and the lower block protruded, the blocks will separate progressively as the lower is pushed forward, and the opening varies as mandibular movements are made, showing that masticating movements do not take place in a horizontal plane, but actually take place in a plane more or less parallel to the condyle incli-' nations.

For this reason, all posterior teeth have to be provided with ridges or cusps having plane angles harmonizing with condyle inclinations as shown by the inclined cusp angles in Figure 2, and further, must be designed so that the crests of the cusps follow the antero-posterior curve (compensating curve CC Fig. 2) of the blocks, to compensate for the opening component in protrusive movement.

Artificial teeth thus far invented have either been copies of natural teeth (anatomical teeth) or have been radical departures (mechanical teeth). The anatomical teeth do not function because the cusp planes do not harmonize with either the cusp planes of adjacent teeth or opposing teeth, thereby causing cusp interference or locking during jaw movements. In mechanical teeth cusp interference has largely been eliminated by eliminating cusps, thereby encountering difficulty in protrusive bites through lack of balancing cusp planes. Until now no attempt has been made to combine the two principles and produce anatomical-mechanical teeth in which the two characteristisc are combined to a common maximum.

The perfect set of artificial teeth requires:

1. Teeth designed having average protrusive jaw movements, thus requiring a minimum of cusp change to fit higher or lower angles;

2. Teeth in which all primary cusp planes run parallel to corresponding planes in the opposing teeth, thus preventing intercusp interference during jaw movements;

' 3. Teeth in which all primary cusp planes during their movements harmonize, not only with opposing planes, but also with the angles (Bennett and Gothic arch) at which the human jaw moves in a lateral relation;

4. Teeth in which the transverse angles of the primary cusp planes are practically equal to the composite maximum Bennett and Gothic arch angles, thereby creating function within greater limits than the limits found in a large majority of human jaw movements;

5. Teeth in which ample grooves or gateways are provided for all opposing cusps, thereby permitting full freedom for cusp movement during mastication; I

6. Teeth in which all intermediate masticating movements are free from restraint, sliding from one position to another without interference;

7. Teeth in which the tooth opening angles (angle 3I-I--2A-HA Fig. 9) are such that the dentures in which the teeth are set are held firmly against the ridges at all times by the forces exerted by mastication;

8. Teeth, the primary forms of which require a minimum of hand carving to create superior anatomical characteristics without altering the primary character of the. cusp planes;

9. Teeth in which the method of cutting the primary forms may be adapted to produce intercusp clearance which allows a range in angles in protrusive, lateral, and balancing movements, and which will create clearance in intercusp movement,freedom in centric relation and provide a working latitude to compensate for discrepancies in the finished dentures due to unskilled labor or changes incurred during the vulcanization process.

Any method of designing artificial sets of teeth must be capable of designing them not only as upper and lower units of. eight'teeth, functioning.

in harmony with jaw movements as the two halves of a cutting and grinding machine, but must further be flexible enough to permit any tooth to be designed independently for any specialized purpose, or to permit the change in size and position of any tooth, or the position or angle of any cusp or series of cusps without altering the remainder of the tooth or teeth in the set.

The object of the present invention is to pro,- vide such' a method to produce primary forms of the sixteen posterior teeth which can be used as models in the manufacture of artificial denture teeth. The primary forms are made of plaster or artificial stone and represent the upper right and left first bicuspids, second bicuspids, first molars and second molars, and the lower right and left first bicuspids, second bicuspids, first molars, and second molars.

A further object is to provide these teeth with biting surfaces made up of cusps which '20 degrees from the sagittal plane). The points RC and RC are the rotation centers which are in the articulator behind and outside thecondyles and which are geometrically determined by dropping perpendiculars from the incisal point junction I of the right and left Gothic arch angles 1 GI and G'I and extending them to intersect lines from the condyle points'M and Q and perpendicular to the lines XX and X'X' which represent the lateral angles (Bennett movement). The points RC and RC represent the geometrical cen 7 forms of in principle, design and action include and em- I body the above mentioned requisites of a perfect ters from which concentric arcs AA and BB may be struck to represent the direction of side bite movements of the teeth. Thus RC and RC are the rotation points of a mandible havingthe Gothic arch angles of 60 degrees (each side), and lateral Bennett angles of 20 degrees (each side), out of which all horizontal movement comes. Lines MG and QG' locate the buccal surfaces of the upper teeth. v

If several points lingual to and more or less parallel to lines MG and QG' corresponding to the several elevations and depressions of the lower teeth be located, and, using points RC and RC as centers, concentric arcs of circles be drawn through these points corresponding to lines AA and BB, they will together with lines DD drawn through these several points andflparallel to the sagittal plane SI, outline in a definite way the I occlusal surfaces of the lower posteriorteeth geometrical figure with the cusps placed distally one half cusp with reference to the lower teeth and buccally according to the lines MG and QG', and are, in common with the lower teeth developed from concentric arcs from the same rotation centers, therefore the primary cusp planes of one jaw necessarily harmonize with the opposing cusp planes of the opposite teeth during jaw movements.

Figure 2 shows a schematic side elevation of the machine for cutting the primary forms, any good adaptable articulator will serve in this capacity. The point M represents the right condyle, also shown as M in Figure 1. Point I, also shown in Figure 1, represents the point where the upper central incisor meets the lower central incisor. The plane V is the incisal guide plane fixed to the lower portion of the machine at an angle of 30 degrees from the horizontal plane of occlusion, and by which, the incisal guide pin W- is guided in the right and left lateral movements. The dotted circle Y represents the condyle of the machine, which corresponds. to the glenoid fossa of the human skull and serves to guide the upper portion of the machine in any predetermined direction relative to the lower portion.

The line XX represents the condyle inclination which is 30 degrees from the horizontal plane of occlusion, shown as line HH'. The are CC represents the arc of a sphere whose radius-is 6 inches, the center of which is represented by R, and which, as before described, is obtained by grinding two blocks of plaster together on an articulator with the conciyle inclinations set at 30 degrees, thus establishing the lateral and anteroposterior tooth curve.

The method employed to cut our primary tooth forms for the lower right and left posterior teeth, is to'flx a block of plaster or artificial stone to the lower portion of the cutting machine, this block to have the equivalent of the concave arc of a 12% inch sphere. This block is fixed in position so that its antero-posterior arc corresponds to are CC shown in Figure 2, while its lateral arc corresponds to are CC shown in Figure 8.

The cutting tool, shown as m, Figure 4, is selected according to the angles necessary for any particular cut and attached to the upper portion of the machine in a position so that the point of the cutter, when the machine is in centric position, rests on the block at a point corresponding to a point shown in Figure 1, formed by the intersection of arcs AA and BB.

The depth of cut is adjusted, and with the moving parts of the machine M, .Q and V, Figure 2, set at angles hereinbefore stated, we cause the upper portion of the machine to make the right lateral motion, corresponding to arcs AA Figure 1, thereby cutting a groove in the plaster, which represents the mesial inclined plane of one cusp and the distal inclined plane of the adjacent cusp. The machine is returned to centric position, another tool selected according to the angulation necessary for the left lateral cut, and left lateralmotions made, corresponding to arcs BB, Figure 1. One out only is made at a time and all cuts are made in lateral direction only. Continuing these cuts from each of the several points, as shown in Figure 1 and points IA, 2A, 3A, etc., Figure '7, give the primary forms of the occlusal or chewing surfaces of the eight lower teeth. In cutting the primary forms of the upper teeth it is only necessary to reverse the cutting tools to the lower portion of the machine and place a block of plaster having a convex surface on the upper portion, otherwise the process is substantially the same, except for minor details such as starting points for the cutters and direction of cuts, which, due tome way the cutting machine moves, necessarily are in the exact opposite direction as compared with the lower cuts.

Figure 5 represents the upper, and Figure 7 the lower right side occlusal views of our primary tooth forms after all cuts have been made followlng the essentials of the geometrical design of Figure 1. A study of the projecting lines will show that Figure 6 is a view of the right side buccal aspect of the upper and lower teeth when they are in occlusion, and further, that the upper teeth are setone half cusp distal to the lower teeth, thus showing how. the mesial and distal slopes of the lower cusps approximate the distal and mesial slopes of the upper cusps, and how if the lower teeth are pushed forward in protrusive relation, these planes willslide one upon the other. Then if the lower jaw is moved in lateral or side movement the lower cusp will slide through the grooves provided for them in the upper teeth or upon the inclined planes provided in our teeth for balancing'movements. Thus, the plane surface illustrated in Figure '7 extending from the mesial of the first bic'uspid distlally to the dlsto-marginal ridge of the first molar as represented by (BA- UA'); (0B0B'); (HA-4A): etc., to points (3BSA'); also the plane surface 4Y', 4A in the distal of the first molar running distally to points (SA-45A) at the distal of the second molar represent the guiding planes for the opposing teeth during mastication or the so-called balancing planes, also shown as line (2A|3A) in Figure 9. v

The contact of this; plane against the corresponding plane in the upper teeth supports this s de of the denture when active chewing is taking place on the other or working side, thus balancing the lower denture against the upper.

The lines AA and BB in Figure 7 represent arcs of concentric circles dropped from the rotation centers shown as RC and RC Figure 1, and which together with lines DD also shown in Figure 1 map out the occlusal surfaces of the teeth.

The points 0A, IA, 2A, 3A, etc., in Figure 7 represents the points where the cutting tools start their cuts for the lingual cusp cuts and the balancing plane cuts, and points such as M for the buccal cusp cuts in the lower jaw. Likewise points 013, I3, 213, etc., Figure 5, for the balancing plane cuts and buccal cusp cuts and points as NN for the lingual cusp cuts for the upper jaw. All points are further shown and designated by the same figures in the buccal view shown in Figure 6.

buccal and lingual cusp planes at different levels. The transverse planes in all teeth are cut on concentric arcs from the rotation centers, the buccal and their contiguous lingual cusp planes are cut on the same are from one rotation center, but are interrupted vertically by the balancing plane which has its origin in the other rota.- tion center.

In Figure 9 the lines 3H-2A and l3A-MM represent the lingual and buccal cusp planes which are cut on the same concentric arc (AA Figure 1) from the' occlusal aspect, but which, as shown by Figure 9 from the transverse vertical aspect, are cut at different levels to conform to the lateral curve of the arc of a 12% inch trihedral corner of posing upper in the positive Figure 10 with IE, 23, 3B, 4B and 4B and B, Figure ing at point 53, also shown 'as 53, Figure 7.

The counterpart of this positive corner in the opposing upper tooth,-is shown by planes I, 8 and 9, Figure 5, meeting together at point 513 to form a negative trihedral corner. The positive the lower tooth fits exactly into and is complementary to the negative trihedral angle comer in the upper tooth when the upper and lower teeth are articulated.

The junction of the balancing plane XY, XY, the mesial and distal lingual cusp planes. at point 5A forms a trihedral angle corner in negative relief, with the three. faces I, 2 and 3 meeting at point Figure '7. I v

The complementary'positive corner in the optooth is shown in Figure 5 the three faces of the trihedral angle.- meeting at point 5A. In this manner all positive and negative trihedral angle corners of the lower teeth fit into their complementary negative and positive trihedral angle corners of the upper teeth. ,Thepoints of the negative trihedral angle corners in the lower jaw are shown in Figure '7 as IA, 2A, 3A,'- 4A andSA, and

5B; for the upper jaw the negative trihedral angle corners are IB, 2B, 3B, 5,' and the positive corners are IA, 2A, 3A, 4A, 5A and 6A.

' Referring to the geometrical design of the transverse occlusal cusp angles of our teeth Fig-.

ure 1, the angles formed by the inter-sections of the arcs AA and BB with the lines DD, progressively become less from the mesial of the first bicuspid to the distal of the second molar, the progressive difference being greater inthe angles between arcs BB and lines DD than the angles. between the arcs -AA and lines DD. As before mentioned the arcs AA, BB and lines DD map out the occlusal surfaces of our teeth, the arcs BB outlining the balancing planes of the teeth, and the arcs AA, the buccal and lingual cusps. Since the primary cusps following these arcs develop the cusp planes and corners of the teeth and all cusps follow the arcs AA and BB, the angles of the faces of the trihedral angle corners made by the intersections of these cuts vary progressively from the first'bicuspid to the second molar, therefore no two trihedral angle corners, either positive or negative, upper lower, have the same combination of angles. All face angles (lower disto-lingual) such as 2, Figure 10, and 9 (upper mesio-buccal) Figure 5, in

' the negative trihedral angles, together with all such as 6 (lower mesio-buccal) Figll (upper 'disto-lingual) Figure 5, trihedral angles, become progressively less from the first bicuspid tov the second molar. The other two face angles of each triface angles ure l0, and

u hedral angle, such-as faces I and 3, Figure 10. land 1 and 8, Figure and the faces 4 and 5, Figure 5in the negative corners, 10, and I0 and -l2, Figure 5, in the positive trihedral corners, become progressively greater from first bicuspid to sec- W the lowerdenture.

curve corresponding to CC, Figure 2, and HH' 5A, also shown as point 5A,

the positive corners as 0B,.

- 35 degrees with the average of 30 degrees.

prosthetic operators use some method to transfer 0nd molar. Therefore no two faces of any. single trihedral angle either positive or negative, upper or lower, have the same angle.

Referring to Figure 9, the angle 3H, 2A, I3A formed by the lingual cusp plane 3H-,2A, and the balancing plane 2A, l3A, form what is known as the tooth openings for the lower tooth, and the angle 2A, I3BMM the tooth opening angles for the upperteeth. The importance tooth opening angles play in securing the best balance between cutting and grinding ability and denture stability is illustrated in Figure 8, which shows a sectional view at the first molar region after these teeth have been made into upper and lower dentures. U represents the upper denture and CC shows the lateral the horizontal plane ofocclusion corresponding to HH, Figure 2; R the center from which C0 the arc of a 12% inch sphere was struck, also shown as R, Figure 2. CD and AB are sectional views of upper and lower right first molars,

.through point 3A, Figure 6, with the vertical lingual cusp angle shown at 16 degrees, and the vertical balancing plane angle at 32 degrees from the horizontal plane of occlusion.

The vertical forces of mastication when applied as in chewing food between the balancing planes, represented by line ee', the lateral force developed is in the direction of the arrow I, thereby becoming a retention force. When food is caught between planes marked 9' and n, the direction of the lateral force is indicated by the arrows g and h, both of which fall within the' border of the denture and are retention forces. When equal pressure is brought to bear on planes cc and a and n, the resultin force is in a vertical direction or parallel to the long axis of the tooth, thereby becoming a retention force.

Acute cusp angles, while being efficient in cutting food, develop less friction, permit slippage, and develop strong displacement forces. Obtuse cusp angles develop a large increase in friction, a lesser ability to out food, and require greater force to masticate, thereby creating a tendency to dislodge the dentures and an eventual injury to the soft tissues under the denture from overuse. Thus it is apparent that there is a balance in angulation of posterior teeth which gives the proper-stability of the denture with a maximum of cutting and grinding ability. Our invention embodies all of these qualities to a common maximum, and since the composite angles from the horizontal aspect at which our teeth are out are beyond the large majority of human mandibular movements, and our cusp planes are all cut on concentric arcs from the rotation centers, we therefore have all ,lower cusp planes parallel in -all relations to the opposing upper cusp planes during masticating movements, it-

, of the necessary mechanical requirements of the perfect denture.

As hereinbefore mentioned 85 per cent of protrusive condyle inclinations are between 25 and All . 2,072,127 p the trial blterlms from the mouth to the articufull number of primary planes of the full set of lator. Operators register condyle movements in posterlors have been out. The clearance angles is at the expense of the original form and (5111- to be understood that this clearance or relief 10 balancing cusp planes of the primary tooth form Figure 7 shows the occlusal view of the lower so as to create all) degree range in condyle inright posterior teeth which may be used as an 15 trusive jaw "angle combinations could be'fitted cut in the lingual cusps. The han e in the di- 20 -from the average degree setup without alterrection of the cute is illustrated by the arrows ing the teeth by grinding. From the transverse 3A, QQand A, Q and the direction of the standpoint such a method should change all cuts are in lingual direction. The cuts for the at This method should further provide relief bei0n,'- tart lng at points as MM, and uttin in 2 slight freedom in centric or rest position; It and MM2D', to and over the crest of the upper should slightly widen all necessary sulci and redge of th al n in an n the in er-P ifilieve all necessary tooth planes and marginal mal space between the second bicuspids and first $0 ridges to allow free movement of opposing cuspsmolars. 30

535 reliefs and clearances are all machine cut with addition to the change in lateral direction of 4o porate these new and novel features in our tooth f h fir molar, f rm an angle of- 30 degrees contacts to point contacts with the opposing teeth, c m s necessary 6 p n t cu te s at t e 45 go cusp plane, the angle 3X 3A, 3X hows th cusp of the lower firstlmolar, and the line 3A, 3X

from 30 degrees to a greater or less degree. Ihe Uppe and w r sp p ane l Ot e c ea ances 55 g condyle inclinations are lessened, and again, the hang in lateral d cti of t ut e s W e 35 that this clearance is taken equally from the upand lower teeth would be the angles as repre- 05 per cusp planes as well as the lower cusp planes sented by 3H, 2A, 3H, for the lingual cusps, and as illustrated in Figure 6. The amount of clearl3A MM, 2A, f r'the u al sp and ith r ance as specifically shown is approximately five the upper or lower clearance alone would be one degrees. This schematic view also shows, how a of t s a 7 m the plane contacts are altered to become point The internal clearance of the teeth is reprecontacts, the points of contact being IA, 2A, 3A, sented by the change in the angles of the baltA, 5A. I ancing planes, shown as XY, XY, Figure 10, also The method employed to produce these lateral, shown as lines 24, ISA, in Figure 9, and also repprotrusive, retrusive and internal clearances, is resented by the vertical clearance in the puccal to start with the completed model in which the and lingual cusp planes made by the lateral Figure 11 illustrates one clearance cutters. The method to secure the balancing plane clearance is to incorporate the proper angles in the cutting tools, and, as illustrated on the lower jaw Figure '7, starting at the interproximal space between the two bicuspids point 2A, the direction of the cut is changed from 2A, 2B, and 2A, 23, to the directions of the arrows 2A, ST, and 2A, 9T, thus changing the angle of the balancing plane of the mesial cusp of the first molar. 7

planes on both upper and lower posteriors, thus producing a clearance as shown in Figure 9.

The angle 23', 2A, 23 represents the angle of clearance that is cut off the lower balancing plane. The angle 24', angle cut off the upper balancing plane. Thus the clearance between these two balancing planes becomes rectangular in appearance.

Our clearance system is therefore a series of lateral cuts for the buccal cusps of all teeth, a similar series for the lingual cusps, and another series for the balancing planes. The buccal and lingual cuts produce lateral clearance,-protrusive and retrusive clearance, and also part of the internal clearance. These lateral cuts together with the cuts for the balancing planes produce complete relief and change posterior teeth from plane contacts to point contacts. The relief angles of teeth treated by this method are necessarily small and do not change the'character of the form sufficiently to alter the compensating or lateral curves which, as hereinbefore stated, are the arcs of a 12%' inch sphere. The relief sufficiently great to relieve or alter all necessary surfaces so that they. will have the necessary clearance to balance, without change of curve or setup in the denture, in protrusive and retrusive relation as much as 5 degrees above and 5 degrees below the angle at which they were cut, or any bilateral combination of angles within this range. The relief angles also provide a sufficient lateral clearance to effectively eliminate cusp interference in lateral produce freedom from cusp locking in centric relation. The system further produces sufficient clearance to compensate to -a large extent for movement of teeth during vulcanization and discrepancies in the setup.

of our teeth after it has been separated from its adjacent teeth in the block, the excess plaster carved away,- and the anatomical features of a natural tooth incorporated, without destroying the primary cusp planes,

thereby bringing the primary forms with their precision cut planes and cusps up to the final perfected stage when they may be used as models from which artificial teeth may be manufactured. The grooves marked 20 have been carved into the mesial and distal marginal ridges in all teeth so as to form a series of landmarks, which,

if placed in alignment in adjacent teeth, will automatically place the teeth in dentures in their correct position both with relation to their opposing aswellas their adjacent teeth.

We have now described our new and improved forms together with our method of creating lateral, protrusive, retrusive and internal cusp plane relief in these forms. Our method is not restricted or'confined to the thirty degree teeth using as a basis the segment of a 12% inch sphere, this, in our opin-' ion, produces themost efficient and best. anatomical teeth, but the method can be used with equal facility to produce teeth using, as a basis, segment: from any sized sphere. Our system This method is used on all balancing I33, 24 represents the' jaw movements and teeth is one in which'all of lingual portions in alignment and the apices of allcusps lying in the surface of a sphere. Av further feature of the construction is that two of the faces of each cusp of teeth on one side of the jaw are generated by a transverse. movement from a center on the same side of the jaw while the third face of the cusp is ment of the jaw. opposed cusps in the upper and lower teeth remain in contact with each other. during either transverse or protrusive movements of the lower jaw, and without interference to such movements.

A further feature of our model is that the opposed faces of the'cusps in the upperand lower aw are vide freedom for jaw movement.

What we claim as our invention is:

v l. A model form for a series of artificial posterior teeth comprising buccal and lingual triour improved model form trihedral form with transverse atslightly divergent angles so as to prohedral cusps having aligned transverse ridges and grooves therebetween with the buccal and lingual portions of each transverse groove in alignment in each of the teeth.

2. A model formfor a series of artificial posterior teeth comprising buccal and lingual triterior teeth comprising buccal and lingual trihedral cusps having aligned transverse ridges and transverse grooves therebetween with the buccal and lingual portion of each groove in alignment,

two of the faces of each trihedral cusp being g'en-' erated by a transverse movement from a common center on the same side of the jaw and the third face being generated by a transversemovement from a common center on the opposite side of the jaw, the center for generating the two faces on one side of the jaw being generating the third face on the opposite side of the jaw.

4. A'model form for a series of artificial posterior teeth comprising buccal and lingual trihedral cusps having aligned transverse ridges and transverse grooves therebetween with the buccal and lingual portion of each groove in alignment, two of thefaces of each cusp being generated by a transverse movement from a common center on the same side of the jaw, of lines at an obtuse angle to each other in a plane passing through said center and the third sideof each cusp being generated by a transverse movement of-a line moving from a common center on the opposite side of the jaw, third side of the trihedral angles'on one side of the jaw being the same as thecenter of movement the same as that forthe center of movement of the aw. i 3. A model form for a series of artificial posfor. two sides of the trihedral angles on the opposite side of the jaw.

5. A model form for a series of artificial posterior teeth comprising upper and lower teeth on opposite sides of .the jaw all provided with buccal and lingual trihedral cusps having aligned transverse ridges and transverse grooves therebetween with the buccal and lingual portions of each groove in alignment, the apices of all of said cusps being relatively positioned to lie in the surface of a sphere and the faces of the cusps being in such angular relation that two of said faces of each cusp on one side of the jaw are generated by a transverse movement from a common center on the same side of the jaw, and a third side of each cusp being generated by a transverse movement from a common center on the opposite side of the jaw and all of said cusps of the teeth on the upper and lower jaws remaining in contact in all positions of transverse movement.

.6. A model form for a series of artificial posterior teeth in which all bicuspids have only positive trihedral angles formed by the abutting of three inclined planes, two of which run buccolingually and being generated from a common center on the same side of the jaw and the third running mesio-distally and being generated from a common center on the opposite side of the jaw.

'7. The method of generating model forms for artificial posterior teeth which consists inmoving in engagement with a cuttable blank cusp cutters for teeth on one side of the jaw transversely from a common center on the, same side of the jaw to form two faces of each trihedral cusp and for moving the cutter for the third face of the cusps transversely from a 'common center on the opposite side of the jaw whereby allfaoes of all of the cusps are generated by transverse movements from only two centers.

8. A model form for a series 'of artificial posterior teeth comprising upper and lower teeth on opposite sides of the jaw, all provided with trihedral cusps and transverse grooves therebetween with the buccal and lingual portions of each groove in alignment, the apices of all of 7 said cusps being relatively positioned to lie in the surface of a sphere and the faces of the cusps being in such angular relation that two of said faces of each cusp on one side of the jaw are generated by a transverse movement from a common center on the same side of the jaw and-a third face of each cusp being generated by a transverse movement from a common center on the opposite side of the jaw, all of said cusps of the teeth on the upper and lower jaws remaining in contact in all positions of transverse movement and the angles of the opposed cusps on the upper and lower jaws being slightly divergentto providefreedom for jaw movement.

9. A model form for a series of artificial posterior teeth comprising opposed upper and lower teeth on both sides of the jaw, all provided with positive trihedral cusps and negative trihedral recesses therebetween, all the positivetrihedral angles of the cusps simultaneously engaging the corresponding negative trihedral recesses on the opposed teeth and the positive trihedral angle being slightly less than the negative trihedral angle not to exceed a maximum of approximately five degrees to provide freedom of jaw movement in directions forward and rear and laterally.

10. Model forms for opposed upper and lower artificial teeth' including 'bicuspid teeth and molars,- each of said bicuspid teeth comprising only two positive trihedral cusps, with transverse grooves between adjacent teeth having the buccal and lingual portion of each groove in alignment, said positive trihedral cusps being separated by a balancing plane to form one positive trihedral buccal cusp, and one positive trihedral lingual cusp so positioned relatively to the molars, that the apices of each lingual cusp wholly occupy the interproximal space between the two opposing teeth.

11. Model forms for artificial molar teeth comprising trihedral cusps with transverse grooves therebetween and with buccal and lingual portions of each groove in alignment, having facets on their masticatory area formed of a plurality of surfaces arranged in inclined planes, said planes coming together at angles constituting trihedral cusps, said cusps being arranged in pairs bucco-lingually and having substantially the same alignment as the transverse grooves, and further, all facet surfaces extending in a transverse'direction being interrupted by a balancing plane and divided thereby into buccal and lingual portions.

12. Model forms for artificial posterior teeth, having blended into the occlusal anatomical surfaces, small grooves carved in the center of the mesial and distal marginal ridges of all teeth, so positioned that when the teeth are assembled they serve as land-marks, which are in alignment in adjacent teeth, when set correctly.

13. Model forms for upper and lower posterior teeth comprising buccal and lingual trihedral cusps having aligned transverse ridges and aligned transverse grooves therebetween with the buccal and lingual portions of each groove in alignment, no two trihedral angles in said models e'ither upper or lower positive or negative having the same angulation or combination of angles.

14. The method of generating model forms for artificial posterior teeth which consists in moving in engagement with a cuttable cusp cutter's for teeth on one side of the jaw transversely from a common center on the same side of the jaw to form two faces of each trihedral cusp and moving the cutters for the third face of the cusp transversely from a common center on the opposite side of-the jaw whereby all faces of all the cusps are generated by transverse movements from only two centers, forming opposed teeth which match with said generated teeth without clearance therebetween, and in refashioning said teeth by moving a new set of cusp cutters in engagement with the cuspal surfaces of said teeth from the aforesaid two centers only and in a transverse direction only, said new set of cuspcuttershaving the angles incorporated in them that would be required of cusp cutters to cut teeth at an angle of five degrees greater and five degrees less than the primary model forms thereby increasing the functional range.

' ERNEST L. PILKINGTON.

JOSEPH F. TURNER.

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