Abstract:
An extender device connects between the halves of an articulator thereby increasing the width of the articulator while still allowing the articulator to be handled as one piece during its application to the models. In an embodiment, the extender device is of a snap-fit design.

Description:
RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/669,728, filed Apr. 8, 2005. The entire teachings of the above application are incorporated herein by reference. 
     
    
     BACKGROUND  
       [0002]     In the fabrication of dental prosthetics, such as false teeth or caps, a negative impression is made of the teeth of a dental patient using a thermoplastic material. The negative impression is then filled with a hardenable material to form a die. The die is affixed to a base formed of similar hardenable material to form a dental model. A dental model articulator is used to correlate upper and lower dental models in the forming and adjustment of the dental prosthesis.  
         [0003]     The appeal of using a one-use or dispensable articulator is one primarily of time. A reusable articulator needs to be mounted to the models of the teeth with dental plaster, which requires considerable time in the processes of mixing, placing, curing, clean-up and then the subsequent removal of the hardened plaster from the models and articulator after completion of the prosthesis so as to allow re-use of the articulator. Dispensable articulators can save the time involved with these steps and have the added advantages of allowing the completed work to be returned to the dentist still articulated to allow verification of the mounting and to increase the presentation value of the case. Typically, a one-use articulator is secured to the dental models using an adhesive, thereby eliminating the use of plaster. To allow this, the articulator must provide a mechanism to adapt glueable members to angular differences of surfaces on the models. Such a mechanism is not needed as part of a reusable articulator because its members are allowed a large range of angular and positional differences within the masses of plaster that are used to affix the articulator to the models.  
         [0004]     U.S. Pat. Nos. 5,957,688; 6,499,999 and 6,705,864 disclose a single-use dental articulator which employs a hinge joint that uses an integrated locking mechanism. This locking mechanism allows for the articulator to provide sliding-type translatory motions in the released mode as well as accurate centric-type positioning of the dental models when the locking mechanism is engaged.  
       SUMMARY  
       [0005]     Articulators of the type disclosed in U.S. Pat. Nos. 5,957,688; 6,499,999 and 6,705,864 are typically made of a plastic resin. For such devices there may exist a certain amount of “play” even in the locked mode due to the deflection of the “cymbal” elements of the hinge joint when a lateral motion is applied between the jaw segments of the dental models. This deflection allows a corresponding lateral motion within the hinge joint which is evidenced by motions out of the centric position between the two models. Although this is not typically a severe problem, there can be certain cases when more centric stability is desired.  
         [0006]     When lateral force is applied between the opposing models, the motion appears as a rotation about an axis that is perpendicular to the occlusal plane and between the two hinge joints of the articulator. U.S. Pat. No. 6,402,512 describes a device which can be applied to the articulator hinge joint which physically constrains the non-axial motion in the joint to effect more stability. This requires separate devices be applied and removed from the articulator to lock and release the joints.  
         [0007]     The present approach reduces this undesired motion by widening the distance between the two hinge joints thereby increasing the radius to the aforementioned perpendicular axis of effective rotation. Lengthening this radius then amplifies the required amount of motion between the halves of each hinge joint to allow a similar amount of lateral displacement of the models from the centric position.  
         [0008]     In accordance with the present approach, an extender device connects between the halves of the articulator thereby increasing the width of the same articulator while still allowing the articulator to be handled as one piece during its application to the models. In an embodiment, the extender device is of a snap-fit design.  
         [0009]     Accordingly, a dental model articulator comprises a pair of arms, each arm having a first arm segment and a second arm segment, the first arm segment terminating at its distal end in a first arm connection element that is pivotably engageable with one of first and second dental models and terminating at its proximal end in a node element, the second arm segment terminating at its distal end in a second arm connection element that is pivotably engageable with the other of the first and second dental models and terminating at its proximal end in a retaining element, the retaining element receiving the node element to define a hinge joint; the articulator further comprises a pair of extender elements, each extender element connecting a pair of arm connection elements.  
         [0010]     The present approach provides a more elegant solution to increase the stability of the articulator on the particular cases that may require more accuracy. This widening approach affords the technician more stability of the case during its manufacture while not hindering the convenience of the operation of the articulator. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.  
         [0012]     FIGS.  1  to  3  show perspective posterior, side and rear views, respectively, of a first embodiment of an articulator of the having two articulator arms mounted to full arch dental models.  
         [0013]      FIG. 4  is a rear view of one arm of the articulator of  FIG. 1 .  
         [0014]      FIG. 5  is a rear view of either the upper or lower half of both arms of the articulator of  FIG. 1  interconnected.  
         [0015]      FIG. 6  is a partial cross-sectional view of one hinge joint of the articulator.  
         [0016]      FIG. 7A  is a front perspective view of an embodiment of an extender device.  
         [0017]      FIG. 7B  is a rear perspective view of an embodiment of an extender device.  
         [0018]      FIG. 8  is an exploded view of the extender device of  FIGS. 7A and 7B  in combination with a pair of articulator arms.  
         [0019]      FIG. 9  is a perspective view of the assembled articulator of  FIG. 8 .  
         [0020]      FIG. 10  is a perspective posterior view of the assembled articulator having two arms and respective extender devices mounted to full arch dental models. 
     
    
     DETAILED DESCRIPTION  
       [0021]     Referring to  FIGS. 1-4 , an embodiment of an articulator  100  redintigrating a pair of full arch dental models  10  and  11  is there shown. The articulator  100  comprises a pair of arms  33 ,  34  that are identical in structure. It should be noted that the following description generally employs a pair of reference characters to refer to a particular element or feature of the respective arms. The arms  33 ,  34  each include an arm segment  33   b,    34   b  and a pair of parallel, bifurcated arm segments  33   a ,  34   a . The parallel arm segments  33   a ,  34   a  terminate at a distal end in cylindrical rod-like elements  35 ,  38  and at a proximal end in a pair of coaxial cymbals  60 ,  61 . The arm segment  33   b ,  34   b  terminates at a distal end in cylindrical rod-like element  36 ,  37  and at a proximal end in node  40 ,  41 . The node is retained between the pair of cymbals  60 ,  61  supported by the bifurcated arm segments  33   a ,  34   a  to form a hinge joint  20 ,  21 .  
         [0022]      FIG. 4  illustrates arm  33  which is identical to arm  34 . A preferred assembly of articulator  100  is formed by connecting the arms  33 ,  34  to each other in a complementary fashion to provide a single assembly for ease of handling. Specifically, the complementary connection is formed by snap-fitting cylindrical stem  35   a  into cylindrical rod-like element  36  and stem  38   a  into element  37  to form the articulator shown in  FIGS. 1-3 . Referring to  FIG. 5 , the portion of arm  33  that includes parallel arm segments  33   a  is shown connected to the portion of arm  34  that includes arm segment  34   b.    
         [0023]     A model connector defining a single axis pivot mechanism is incorporated into the base of each model  10 ,  11  in the form of transverse half-cylinders or channels  12  and  13  which traverse the posterior of the models ( FIGS. 1 and 3 ). The channels can be either cut into the existing models or formed when the models are cast to provide connection at a range of angles about the radial axis of the transverse channels for mating the cylindrical rod-like elements  35 ,  36 ,  37 ,  38  which form the complement to these pivot mechanisms. While the channels  12 ,  13  are shown located on the posterior of the models, it is also possible to locate the channels at the top or bottom of the respective models. In alternate embodiments, the channels can instead be formed at the distal ends of the arm segments and the cylindrical elements can be incorporated in the models to provide the single axis connexus.  
         [0024]     The cylindrical elements  35 ,  36 ,  37 ,  38  have sufficient transverse axial width such that any adjustment motion of the cylindrical elements within the channels is limited to radial motion about the channel axis and transverse motion along this axis. With the dental models placed at a closed and centric occlusal (i.e., closed bite) relationship as shown in  FIG. 2 , the arm segments of the respective arms intersect at an angle of between approximately 40 to 170 degrees, the angle being dependent upon the vertical distance between the models  10  and  11 .  
         [0025]     The multiaxial motion provided by the articulator will now be described. Referring again to  FIG. 5 , node  40 ,  41  includes two opposed outwardly facing convex portions  40   a ,  41   a . Referring to  FIG. 6 , a partial cross-section of one joint  20  of the articulator is shown. The cymbals  60 ,  61  are concave and toroidal in shape. When the node  40 ,  41  is engaged with the cymbals  60 ,  61 , the convex portions  40   a ,  41   a  of each node  40 ,  41  are held in depressions or detents  60   a ,  61   a  at the center of each cymbal by resilience of the material in the bifurcated arm segment  33   a ,  34   a.    
         [0026]     The primary rotational motion of the node between the parallel arm segments is radial to an axis B that is shared coaxially by the cymbals. Because node  40 ,  41  and its connected arm segment  33   b ,  34   b  has no fixed axis when captured between the cymbals  60 ,  61 , hinging motion between the arm segment  33   b ,  34   b  and parallel arm segments  33   a ,  34   a  is allowed an amount of orthogonal deviation from the axis B, that is, motion is provided about a set of orthogonal axes. This multiaxial motion of the hinge joint  20 ,  21  allows the cylindrical connection elements  35 ,  36 ,  37 ,  38  at the extremities of the arms  33 ,  34  to align with the nonparallelism that is likely to exist between the channels  12 ,  13  of models  10 ,  11 .  
         [0027]     Multiaxial motion is only required and exhibited during alignment of the articulator  100  to the models. Once the two arms of the articulator  100  are affixed to the models, the only axial motion allowed by the articulator between the models is about a single axis A defined together by the two hinge joints  20 ,  21  ( FIG. 1 ). This common transverse hinge axis A lies interjacent and posterior to the dental models  10 ,  11  and is approximately perpendicular to a sagittal plane of the models.  
         [0028]     Each bifurcated arm segment  33   a ,  34   a  includes a resilient pawl or latch  50 ,  51  that is used to increase or decrease pressure (i.e., compression) on the node  40 ,  41  between the cymbals  60 ,  61 . The pawl includes a hooked portion  50   a ,  51   a  for engagement through opening  33   c ,  34   c  in the bifurcated arm segment  33   a ,  34   a . When the pawl is engaged, it increases the resilient pressure on the node between the cymbals to an amount that effectively limits or restrains any motion between the arm segments  33   a ,  33   b  and  34   a ,  34   b  to rotational motion about the common axis A. Releasing the pawl lessens the resilience to an amount such that protrusive and retrusive motions are permitted between the articulated models  10 ,  11  by allowing the cymbals to move apart, thereby permitting the convexities of the node to slide across the surfaces  60   b ,  61   b  of the cymbals. This free sliding motion is then limited in excursion by ridges  70 ,  71  at the periphery of the cymbals. Note that while the multiaxial motion about the hinge joints  20 ,  21  is used for alignment of the articulator, the free sliding motion is used for simulation of lateral and protrusive translatory motions once the articulator has been aligned and mounted to the models.  
         [0029]     Reference is now made to  FIGS. 7A and 7B , which show front and rear perspective views, respectively, of extender device  700 . The extender device is a cylindrical rod-like element that includes cylindrical base  702  and snap-fitting cylindrical stem  704 . The stem  704 , having a slot  714  for resilience, snap-fits into cylindrical rod-like element  36  or  37  of respective arms  34 ,  33  ( FIGS. 1-4 ). The base  702  has an opening  706  for receiving a snap-fitting cylindrical stem  35   a  or  38   a  of respective arms  33 ,  34  ( FIGS. 1-4 ). As shown in the embodiment, the device also has optional mold insert openings  708 ,  710  and  712  for ease of manufacture. Exploded and assembled views are shown in  FIGS. 8 and 9 , respectively.  
         [0030]      FIG. 10  illustrates the assembled articulator with the extender devices  700  connecting the pair of arms  33 ,  34 , with the assembly mounted to full arch dental models. With this arrangement, undesired motion is reduced by widening the distance between the hinge joint mechanism comprising the two hinge joints thereby increasing the radius to the perpendicular axis of effective rotation. Lengthening this radius then amplifies the required amount of motion between the halves of each hinge joint to allow a similar amount of lateral displacement of the models from the centric position.  
         [0031]     It should be understood that in certain applications, the distance between the hinge joint mechanism may be further widened by connecting two or more extender devices together.  
         [0032]     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.