referring now to fig1 the dental articulator is illustrated as an instrument having a lower frame member 10 and upper frame member 11 . the instrument is of the arcon type , having posterior condylar spherical elements 12 which are distally carried by a lower lateral cross member 14 . the lower frame member has substantially vertical standards 16 at opposite sides thereof which extend into supporting engagement with the lateral cross member 14 . the base 18 of the lower frame member extends anteriorly to an incisal pin support member 20 that is removably secured thereto by thumb screw 22 . the base 18 of the lower frame member 10 also has a pair of posterior legs 24 and a pair of anterior legs 26 , elevating base 18 above a work table or support , to provide vertical clearance to accommodate thumb screws 22 and 28 , the latter extending through the base and having a threaded shank 30 for the removable attachment of dental cast support members , not illustrated . the base also bears one or more of pins 32 which , with shank 30 of thumb screw 28 , index dental casts to the instrument . the upper frame member 11 includes an upper lateral cross member 34 which , as the lower lateral cross member 14 , extends coextensively with the condylar axis of the articulator . the condylar axis of the articulator extends through the centers of the spaced - apart , distally carried condylar spherical elements 12 . the longitudinal member 36 of the upper frame member 11 extends anteriorly to support the incisal pin member , generally indicated at 38 . this incisal pin member is carried at the anterior of the upper frame member 11 by thumb screw 40 which extends through a slot , not shown , in the leading edge of member 36 and into threaded engagement with a fore end bracket 42 . bracket 42 bears a flange 44 for abutment against the leading edge of member 36 and an integral , vertical bracket 46 having an arcuate face 48 which is engaged by a mating arcuate face of the head 50 of the incisal pin member 52 . head 50 has a vertical slot which receives the shank of thumb wheel 54 , the latter extending through the slot and into threaded engagement with a bore in vertical bracket 46 , whereby the vertical position of the incisal assembly can be fixedly adjusted on the anterior of the instrument , thereby providing for fixed adjustability of the spaced - apart positions of the upper and lower frame members in their closed position . in the preferred embodiment , the incisal pin assembly can be provided with the fixedly adjustable shoe 56 having a key 57 that is slidably mounted in a groove of the mounting block 58 at the base of pin 52 . the shoe 56 rests on an abutment surface , button 60 , carried on the upper surface of the aforementioned incisal table 20 . the latch mechanism of the invention includes a pin member 62 centrally carried on the upper lateral cross member 34 . this pin member , which is shown in greater detail in fig7 comprises a bracket member 64 dependent from the undersurface of the upper lateral cross member and laterally , outwardly projecting pin shafts 66 . the other member of the hinge assembly of the invention comprises a latch hook arm generally indicated at 68 which is pivotally mounted on a pivot axle 70 which is secured to the lower lateral cross member 14 by bracket 72 . the latter bracket is slidably mounted to the lower lateral cross member 14 by screw fasteners 74 which project through vertically elongated apertures 76 of bracket 72 . bracket 72 bears a posteriorly projecting flange 78 that extends beneath the lower lateral cross member 14 . preferably , the lower lateral cross member 14 has a central bore 80 that receives compression spring 82 which is biased between the flange 78 and the cross member 14 whereby bracket 72 is resiliently biased downwardly , away from the hinge pins 66 . the hook arm latch member 68 has a posteriorly directed arm 84 and a pin detenting notch 86 for resiliently restraining pin 66 when the hook arm member is rotated in the direction of arrow 88 . hook arm member 68 also bears a posteriorly projecting lever arm 90 which projects subjacent of the undersurface of the upper lateral cross member 34 so that rotational opening of the articulator by moving of the upper member along the arc shown by arrow 92 causes the posterior lower edge of the lateral cross member 34 to engage lever arm 90 , deflecting this lever arm and pivoting the hook arm member 68 in the direction indicated by line 88 , engaging the latch mechanism and interlocking the upper and lower frame members . referring now to fig2 the articulator is illustrated in a rear elevational view . as there illustrated , upper frame member 34 bears distal fossa guide members 92 and 94 which have , on their undersurface , slots 96 which are elongated in the anterior - posterior direction , i . e ., longitudinal axis , of the instrument . slots 96 receive the condylar , spherical elements 12 which are distally mounted on the lower lateral cross member 14 . elements 12 project on shafts 98 which are received within bores in the lower lateral cross member 14 and interlocked thereto by set screws 100 . the lower frame member of the articulator has a base member 18 with posterior legs 24 and distal and upwardly projecting standards 16 that support opposite ends of the lower lateral cross member 14 . the view of fig2 also shows that the flange 78 of bracket member 72 which projects beneath the center of lateral cross member 13 and is resiliently biased downwardly by compression spring 82 . the upper end of bracket 72 is received between opposite side flanges 102 of the hook arm member 68 and bears the pivot axle 70 for the mounting of the hook arm member . the upper end of bracket 72 is grooved to receive a torsion spring 104 which has its opposite ends resiliently biased between the bracket 72 and the undersurface of the lever arm 90 whereby the hook arm member 68 is resiliently biased away from the pin member 62 , assuming the position shown in fig1 and 2 . as previously mentioned , the hook arm member of the hinge assembly can be moved into a pin detenting position whereby the pin 66 is resiliently received within notch 86 of the hook arm member . fig3 illustrates this view with the articulator in a closed position . the posteriorly projecting arms 84 of the hook arm member have been rotated past the point of engagement with pins 66 and for a sufficient distance that pins 66 are received within detenting notches 86 of the hook arm member . the hook arm member is restrained in this position , against the bias of torsion spring 104 by the downward force exerted by compression spring 82 which restrains the hook arm member and prevents its rotation to the unlocked position of fig1 and 2 . the hook arm member can be released from its locking position by the application of a slight upward pressure on the undersurface of bracket 72 , sufficient to overcome the resilient bias of compression spring 82 and permit upward translation of bracket 72 and hook arm member 68 , whereby the posteriorly projecting arms 84 will clear pins 66 , and permit rotation of the hook arm member to the open position shown in fig1 and 2 . the articulator as thus described can be supplied with alternate constructional features such as the alternate incisal pin member generally indicated at 110 . this incisal pin member is similar in construction to the pin member 38 previously described in that it also has longitudinal rib 112 that is received in a slot in the leading edge of upper frame member 36 , a flange 44 which serves as an abutment and forward stop for the frame member 36 and bracket 42 which has a threaded bore to receive the end of thumb wheel 40 . the vertical bracket 46 dependent from bracket 42 is shaped similarly to that previously described , with an arcuate forward face 48 that is in contact with a mating arcuate face of the head 50 of the incisal pin . the incisal pin 114 projects downwardly from the head 50 and bears a rounded lower end which is received in a concavity 116 of incisal table 118 which is carried on the lower frame member . fig5 illustrates the mounting means for the spherical condylar elements 12 . as previously mentioned , these elements are carried at the upper end of shafts 98 which are received within bores 120 located at opposite ends of the lower lateral cross member 14 . the shafts 98 are fixedly secured to lateral cross member 14 by set screws 100 which are engaged in threaded transverse bores 122 of the lower lateral cross member 13 . each shaft 98 bears a flat 124 for engagement by the set screw 100 . shaft 98 also has a rounded lower end 126 which projects into bore 120 to the position shown by broken line 128 . in this position , the lower end of this shaft is engaged by the pointed , inboard end of set screw 130 whereby the advance of set screw 130 can provide a vertically adjustable abutment or stop for the shaft 98 , and the spherical elements 12 can thereby be fixedly adjusted in a vertical direction by advance or retraction of set screw 130 . once the correct elevation is reached and the instrument thereby calibrated to an exact centric relationship of the upper and lower frame members , the shafts 98 are fixedly secured to the upper cross member 14 by set screws 100 . fig6 is a perspective view of the lower lateral cross member 14 and associated structure as viewed from the rear of the instrument . as there illustrated , the lateral cross member 14 bears end portions 132 which are attached to the upper ends of standards 16 and locked thereto by screws 134 which engage threaded bores in standards 16 . screws 134 extend through bores 133 which are counterbored at 135 to receive the heads of the screws . bores 133 are slightly oversized to permit horizontal alignment adjustment of the lateral cross member 14 . the distally mounted spherically mounted condylar elements 12 are shown as supported by shafts 98 . the flange 78 of bracket 72 projects beneath the undersurface of the lateral cross member 14 . the hook arm member 68 of the hinge assembly is illustrated with its opposite side flanges 102 which receive , therebetween , the upper end of bracket 72 . the bracket 72 is mounted in an upright , transverse groove 136 in the forward face of the lateral cross member 14 . the upper end of hook arm member 68 bears a pair of rearwardly projecting arms 84 with a central slot 138 to thereby define a clevis structure for receiving the pin bracket 64 of the pin member 62 of the latch assembly . each of the opposite arms 68 bears a pin detenting notch 86 , previously described . referring now to fig7 the undersurface of the upper lateral cross member 34 is shown . as there illustrated , the forward edge of lateral cross member 34 is fixedly secured to the forwardly projecting frame member 36 by a groove ( not shown ) along the upper surface of the lateral cross frame member and by screws 140 . the undersurface of lateral cross member 34 bears a central recess 142 in which is mounted the pin bracket 64 of the pin member 62 . this bracket has a flat flange portion 144 which is bored to receive mounting screws 146 that secure the pin member 62 to the undersurface of lateral cross member 34 . the bracket 64 bears laterally , outwardly projecting pins 66 which are engaged by the previously described hook arm member 68 . the lateral cross member 34 also distally carries opposite fossa guide blocks 150 which have the previously described , elongated slots 96 for receiving the spherical condylar elements 12 . as previously mentioned , the articulator also includes semi - adjustment capability whereby the instrument can be set to duplicate the most clinically significant mendibular movements . fig8 - 10 illustrate an embodiment of the invention having such capability . as there illustrated , the upper lateral cross member 35 bears distal clamp blocks 151 which have an arcuate surface and which have a central aperture 152 that is intersected by radial slot 154 . screw 155 ( see fig1 ) extends through slot 154 into a threaded bore whereby the block 151 can be compressed about shaft 156 to fixedly secure the latter . aperture 152 receives trunion 156 that carries a semi - adjustable fossa guide assembly generally indicated at 158 . the guide assembly 158 has an arcuate flange 160 which butts against the outer lateral face of block 151 and which bears indicia such as scale 162 ( shown in fig1 ) which cooperates with an index mark 163 on the posterior edge of block 151 whereby the angular orientation to the superior plate 164 of the guide assembly 158 can be observed . the superior plate 164 has a posterior wall 166 which has a surface 168 with a curvilinear contour corresponding to average anatomical border movement of the mandibular for the rotating condular path . this rotating path is preset to an average anatomical inclination , out and back of approximately 25 degrees , which is the angle of inclination of the surface area indicated at 170 . the undersurface of superior plate 164 preferably is grooved longitudinally at 183 to provide a guideway for an opposed condylar spherical element 12 , useful in duplicating a protrusive mandibular movement . groove 183 can be from 2 to about 5 millimeters in depth . in the preferred embodiment , the medial wall bracket 180 is laterally adjustable on the fossa guide assembly 158 . to this end , the forward face of the superior guide plate 164 bears groove 184 which receives rib 186 of the forward plate 188 of the medial wall bracket 180 . the lateral position of the medial wall bracket 180 on the fossa guide assembly 158 is fixedly secured by a set screw 190 ( see fig9 ) which projects through a threaded bore in the top surface of superior guide plate 164 into groove 184 , bearing against rib 186 and restraining the medial guide bracket 180 . indicia in the form of a scale 185 are provided on the top edge of medial guide bracket 180 to cooperate with an indicia in the form of scale 187 carried on superior plate 164 whereby the degree of lateral transaction of the medial wall bracket can be observed in a vernier manner and recorded . the semi - adjustable fossa assembly 158 can also bear an adjustable , medial wall guide member . this guide member can be a small plate 172 pivotally carried on the undersurface of the lower edge 178 of medial wall bracket 180 by screw 174 which extends through arcuate slot 176 of plate 172 . the lower edge 178 of bracket 180 can bear an arcuate groove 182 to provide for recessed mounting of the medial wall guide member . the articulator as thus described has a number of significant features . the latch mechanism whereby the upper and lower frame members of the articulator can be interlocked in both the open and closed articulator positions constitutes a substantial advance in arcon type articulators . this latch mechanism can be employed with substantially all arcon type articulators since these commonly employ upper and lower lateral cross members that are coextensive with the condylar axis of the instrument . because the upper and lower frame members of the articulators can be interlocked , the articulator can be inverted in an upside - down position for mounting of casts without use of a plastering stand . the latch mechanism serves as an accurate locator of centric position of the frame members . the latch hook arm centers on the pin member , receiving the pin bracket member between its opposite arms . the downward force exerted on the upper frame member by the latch hook arm seats the condyles in their respective centric detents , thereby providing a centering action on the outboard fossa members that cooperates with the centering action of the latch hook arm and pin member . the articulator having the limited or semi - adjustment capability is a useful tool for diagnosis and fabrication of restorations which can be made without the complexity of a pantograph and fully adjustable articulator . the semi - adjustment capability of the condylar fossa guide elements illustrated and described with regard to fig7 - 9 achieves duplication of the clinically significant movements of the mandible without encumbering the construction with less used , adjustment capabilities which characterize more recent advances in arcon type articulators . the invention has been described with reference to the illustrated and presently preferred embodiments thereof . it is not intended that the invention be unduly limited by this illustration and description of the presently preferred embodiment . instead , it is intended that the invention be defined by the means , and their obvious equivalents , set forth in the following claims .
there is disclosed a dental articulator of the arcon type having a centric lock mechanism including a pin carried on the upper frame member and a cooperative hook arm which is pivotally mounted on the lower frame member and movable between pin engaging and detenting and pin releasing positions . the latch mechanism is spring biased to restrain the hook arm in the pin detenting position from which it can be released by pressure application to overcome the resilient bias of a compression spring loading on the mechanism . the latch mechanism is operative to lock the upper and lower frame members together when the frame members are in their closed or centric position and when the frame members are open , freely permitting rotational movement of the members between the open and closed positions while , nevertheless , retaining the frames interlocked . the articulator is also disclosed with a simple fossa guide structure allowing for a limited degree of freedom of movement without any adjustment capability and , in an alternative embodiment , with fossa guides permitting the independent adjustability of the angle of the eninentia , immediate and progressive side shifts and , optionally with an entirely adjustable fossa including adjustable top and / or rear fossa guides .