Patent GB-490852-A (GB)
Title: Improvements in or relating to artificial teeth and methods of forming them
IPC: A61C13/097
Filed: 1937-02-23
Abstract: 490,852. Artificial teeth. PILKINGTON, E. L., and TURNER, J. F. Feb. 23, 1937, No. 5483. [Class 81 (ii)] Model forms for artificial teeth are made with buccal and lingual trihedral cusps having aligned transverse ridges with grooves between, the buccal and lingual portions of each transverse groove in alignment in each of the teeth. The forms are generated by transverse movement (of a suitable tool) such that two of the faces of each trihedral group are generated from a common centre on the same side of the jaw and the third from a centre common to all the teeth on the other side of the jaw. The apices of all the cusps are positioned to lie in the surface of a sphere and all of the cusps remain in contact in transverse movement. The positive trihedral angles are made slightly less to the extent of 5‹ than the negative trihedral angles with which they engage, so as to allow sufficient freedom of movement. The bicuspid teeth have only positive trihedral angles. The points of generation RC are determined as described with reference to Figs. 1 and 2, in which points M, Q indicate the position of the mandibular joint, point I is the incisal point and the angle G, G represents the combined " Gothic Arch angles. X<1>X<1>, XX represent the lateral paths of the condyles during side movements. The lower point RC is determined by drawing a line from the point I perpendicular to the line G<1>I to intersect a perpendicular from the line XX representing the condyle or " Bennet " movement. The upper point RC is similarly determined. Arcs AA, BB drawn through points selected on lines parallel to MG, QG<1>, with the points RC as centres, together with lines DD parallel to the sagittal plane S<1>I serve to define the occlusal surfaces of the lower teeth, the upper teeth being developed from the same figure with the cusps displaced by one half cusp distance. A machine for cutting the teeth is shown schematically in Fig. 2, and may be an articulator in which M indicates the jaw condyle, Y the condyle of the machine, I the central point of meeting of the incisors, V a guide plane inclined at 30‹ to the plane of occlusion and guiding the pin W in right and left movements, X<1>X<1> indicates the 30‹ inclination of the condyle, and the arc C, C<1> which is of 6 3/16 inch radius about the point R, denotes the curve to which the distal points of the teeth conform. A cutting tool 50 of suitably chosen form is mounted in the machine and caused to move along arcs corresponding to the arcs AA, BB so as to cut grooves in a plaster block, the tool being changed according to the inclination of the facet desired. In cutting the model for the upper teeth the tools are placed in the lower part of the machine and operate on a convex block. The theoretical considerations determining the method of cutting the teeth facets, and the method of modifying the angles of the facets to produce. sufficient clearances to prevent locking effects between the teeth in use, are described in detail in the Specification in a manner unsuitable for abridgment. An example of a lower second molar made according to the invention is shown in Fig. 10 and a finished model is shown in Fig. 11 embodying features carved on the mechanically produced facets corresponding to those of a natural tooth.