Abstract:
A dental model, in particular for practice purposes, is provided, and has a support plate with recesses for artificial teeth, each of which has a tooth stump that fits into the associated recess. A gum mass overlaps both the teeth of a row of teeth and the recesses. The teeth are each disengageably held on the plate and in their associated recess with friction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims foreign priority benefits under 35 U.S.C. §119(a)-(d) from German patent application Ser. No. P 100 23 842.4 filed May 16, 2000. In addition, this application claims the benefit under 35 U.S.C. §119(e) of U.S. provisional patent application ser. no. 60/215,922 filed Jul. 3, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a dental model that includes a support plate having recesses for receiving the stumps of artificial teeth, and that is suitable in particular for practicing and for demonstration purposes, preferably for preparing carious locations and providing the cavity with filling materials. Furthermore, all work that a dentist performs on a patient can be performed on the dental model. 
     Such a practice dental model is known, e.g. from U.S. Pat. No. 3,886,661. In this solution, a practice set of teeth can be inserted into a plate. The design of a natural jaw is constructed using various elements. One advantage of this solution compared to other known solutions in which the teeth can only be exchanged all at one time is that, depending on the practical exercise, the tooth to be worked on can be exchanged so that running costs are lower. On the other hand, however, special teeth must be produced and maintained as replacements for this model, so that it is necessary to maintain a special inventory. 
     Furthermore, it has already been suggested that a dental model be realized that combines a hard guide material with an elastic material for the bearing or support material. This is meant to simulate the bearing stiffness of the natural jawbone, whereby the employment of silicone rubber is meant to ensure that individual teeth can be removed but will not fall out inadvertently. However, in these solutions the guide and mounting of the tooth itself is elastic. The tooth thus moves laterally when pressure is exerted so that such a tooth is suitable, e.g., for model work. However, fairly strong lateral pressure must be exerted, e.g. during drilling, so that such elastically-borne models of the jaw are not suitable. 
     Another problem with this type of dental model is the disengageable bearing of the teeth. When the tooth is borne elastically gripping in the associated root recess, drilling dust that falls into the recess gradually exercises a negative effect on the gripping properties so that the recess must either be cleaned regularly, which is a time-consuming process, or the model has to be exchanged after short periods of time. 
     In dental models which bear the teeth fixed, a special coupling must be realized in order to provide a fixed support to the tooth, but one that can be disengaged. Even in the combined bearings already suggested that are made partially from fixed recess regions and partially from elastic recess regions, drill dust can penetrate into the gap in the region of the fixed bearing. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     The object of the invention is to create a dental model of the aforementioned general type that is improved with regard to the simple and reliable exchangeability of individual teeth, secureness of bearing, and stability of the teeth under load. The dental model should be able to be employed numerous times and should be consistent with a patient case in shape and material. 
     This object is realized by the dental model of the present invention, which is characterized primarily by a tooth gum mass that overlaps both the teeth as well as the recesses, wherein the teeth are releasably held, with friction, on the support plate and in the respective recesses. 
     In accordance with a particularly advantageous aspect of the present invention, using the mounting in accordance with the invention the tooth can be secured and supported in the plate. In addition, the bearing of the tooth in the recess in question is also sealed automatically in the plate so that no drilling dust can penetrate into this critical region. The crown tooth can thus be fixed permanently and in a stable manner in the plate comprising stiff material, even against lateral forces that are introduced, e.g. by a dental drill. In addition, the gum mass partially surrounds the tooth so that the jaw of a patient is simulated. When one tooth is exchanged for another, the support of the tooth by the tooth stump and by friction elements causes the tooth to assume exactly the same position. 
     It is also particularly advantageous that the appearance of the dental model approximates nature, whereby the gum mass can be colored to approximate natural gums. The holding force of the gum mass can be widely adapted to requirements. For instance, an undercut can be provided that works against an undercut in the tooth and forms a disengageable lock. The gum mass can also have undercuts that work against undercuts in the plate. Preferably both the plate and the teeth each have a projecting lug or peg and the gum mass has corresponding recesses. It is particularly advantageous in this regard if the plastic alveolar crest that forms the recesses for the teeth also has rough surfaces on its lateral sides. This ensures that there is a certain positive fit between plate and gum mass that promotes the gum gripping the plate. 
     It is understood that the pre-stress of the gum mass when held on the alveolar crest or with regard to the teeth in broad areas can be adapted to the requirements. The gum mass can comprise, e.g., pink silicone that is somewhat transparent so that the course of the tooth is visible to the attending dentist using the dental model for practice, at least in the region of the anterior teeth. 
     In accordance with the invention it is particularly advantageous that teeth mass-produced can be used for the dental model in accordance with the invention. The teeth in accordance with the invention can be constructed in a plurality of layers in a manner known per se and provided with a tooth stump made of inexpensive plastic. Preferably, however, the teeth are made of one material. The tooth stump fits into the associated recess in the alveolar crest of the plate, whereby the tooth is already securely borne due to the conical embodiment of both the recess and the tooth stump. 
     Preferably immediately adjacent to the area of the tooth stump surrounded by the recess the tooth has a peg or projection that extends laterally and forms an undercut. The peg or projection engages in a recess in the model, fitting rather precisely, so that the tooth is also held in to place by this frictional element. The gum mass has at a plurality of locations undercuts that work against the plate so that they grip the teeth and model securely. 
     The model in accordance with the invention can be used for a model of the upper jaw or lower jaw. In addition, it is easy to disengage the tooth in the guide from the friction and in the recess so that after a practical session the tooth can be exchanged with no further action required. In accordance with the invention it is also particularly advantageous that the base plate can be mass-produced from an inexpensive plastic. In addition, the plate can also be used in an articulator so that it is possible to simulate chewing and, e.g., it is possible to check the occlusion when bridges are being prepared. One or two teeth can simply be removed from the model so that the result is a working model for preparing a bridge. 
     In accordance with one advantageous aspect of the invention, identical shapes are provided for the recess and the associated tooth stump for identical or corresponding teeth. Thus it is possible to reduce the different tooth shapes to be maintained for a dental model, whereby there is still nonetheless distinct or noninterchangeable insertability. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional details, advantages, and features result from the following description of an exemplary embodiment with respect to the drawings. 
     FIG. 1 is a schematic sectional view along the line I—I in FIG. 3, illustrating a detail of a dental plate in accordance with the invention; 
     FIG. 2 is a schematic sectional view along the line II—II in FIG. 3, illustrating a detail of a dental plate in accordance with the invention; and 
     FIG. 3 is a top-view of a dental plate of one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     The dental model  10  shown in a top-view in FIG. 3 is illustrated in substantial detail in a sectional view in FIG.  1 . The dental model has a plate  12  that is integrally constructed and that carries an alveolar crest  14  that has a plurality of recesses that are embodied suitably for receiving teeth  16 . 
     FIG. 1 illustrates a tooth. A recess  17  has inclined, upwardly diverging sides. Fitting therewith, the tooth  16  has a tooth stump  18  that is embodied conically. The tooth stump  18  and the recess  17  are not circular; rather, they are preferably oval, and the fit is selected such that a certain free space remains between the tooth stump  18  and the bottom of the recess  17 . 
     Due to the slight cone angle, the tooth  16  is already fixed fairly well in the recess  17 . 
     Extending laterally away immediately adjacent to the tooth stump  18  is a lug or peg  20  that precisely supports the tooth  16  as described below. The peg  20  rests against on the alveolar crest  14 , whereby the clamping effect between tooth stump  18  and recess  17  is not negatively affected. The cone angle of the tooth stump  18  is preferably between 2° and 20°, preferably between 5° and 12°, and especially about 8°. Such an embodiment ensures disengageable clamping. 
     Provided surrounding the alveolar crest and intensively covering it and also a part of the teeth  16  is an elastic mass for the gum mass  22 ; it ensures a connection between the plate  12  and the teeth  16 . The gum mass  22  is made of gum-colored dyed silicone and surrounds the teeth in a manner that is like the manner in which natural gums surround teeth. The alveolar crest  14  has a recess  24  into which the peg  20  fits precisely. The peg  20  thus forms an undercut against a lateral surface in the recess  24 , the elastic resistance of which is overcome when the tooth  16  is pulled therefrom. 
     In accordance with the invention it is particularly advantageous that the recess  24  in the upper region of the alveolar crest  14  is held by the cam-shaped peg  20 . At that point the alveolar crest is still relatively elastic so that it is possible to pull the tooth out. The bearing between recess  24  and peg  20  supports the frictional bearing of the tooth stump  18  in the recess  17 . 
     Preferably the gum mass  22  rests against the teeth  16  with a slight pre-stress. This means that drilling material that falls cannot penetrate into the bearing gap. 
     Furthermore, the gum mass has structured surfaces  28  and  30  that face the alveolar crest  14 . These surfaces are a negative image of the associated surfaces of the alveolar crest  14 , thus stabilizing and improving the bearing between plate  12  and gum mass  22 . 
     In the exemplary embodiment illustrated in FIG. 1 a bore or through-hole  31  is provided such that it passes through the plate  12 . It extends approximately in the center between the underside of the plate  12  and the recess  17 . If necessary, the tooth  16  can be pressed out via this bore  31  using a suitable article, e.g. a thick nail. Despite the very secure and drill-stable bearing or support of the tooth on the plate  12 , this solution permits the tooth to be exchanged as needed. 
     Furthermore it is provided that the gum mass  22  ends somewhat below the upper side  32  of the plate. The plate  12  has fitting edge connection depressions and the gum mass  22  extends correspondingly, as can be seen in FIG.  1 . This embodiment improves support while reducing the tendency to become soiled. 
     FIG. 2 shows that the plate  12  is also connected to the gum mass by additional back tapers or undercuts. In this regard, provided on the rearward end of the alveolar crest  14  is a lug or peg  34  that penetrates into an associated recess  36  in the gum mass  22 . A plurality of corresponding connections are also provided distributed across the alveolar crest so that overall the gum mass  22  is well secured to the plate  12  but is also borne so that it can disengage due to its elasticity. 
     As can be seen from FIG. 3, the gum mass  22  is essentially U-shaped and extends across the plate  12  following the alveolar crest. The teeth  16  are arranged in a row that coincides with the arrangement of real teeth. The material for the profiled holder  12  is a fairly stiff yet inexpensive plastic material, e.g. an epoxy resin. Based on the slender embodiment of the alveolar crest  14 , however, there is a certain elasticity so that the attending dentist will find the same mechanical conditions that he will encounter later in the mouth of a patient. 
     The teeth  16  are produced from two or more layers. Preferably they have a cutting and dentine layer, whereby the tooth stump  18  is an additional layer. The hardness of the cutting and dentine layer and of the neck of the tooth is essentially comparable to that of a natural tooth so that the practicing student will find the same qualities in the dental model that he would find in the natural teeth of a patient. 
     The teeth  16  are made of a composite material and are industrially pre-fabricated. Such materials are described, e.g. in U.S. Pat. No. 4,267,097 (equivalent to DE 24 03 211 C2) or in CA 2,051,333 (equivalent to DE 40 29 230 C2), the disclosures of which are hereby incorporated into this application by this reference thereto. 
     While a preferred form of this invention has been described above and shown in the accompanying drawings, it should be understood that applicant does not intend to be limited to the particular details described above and illustrated in the accompanying drawings, but intends to be limited only to the scope of the invention as defined by the following claims.