In practice dental treatments, teeth extracted from human bodies and animals have conventionally been used so as to experience the grinding sensation of a natural tooth. However, there are hygienic problems associated with extracted teeth and infection may occur if hygiene control is not sufficiently conducted. Thus it was impossible to conduct training freely. Furthermore since extracted teeth comprise a natural living material, there arises a problem of corruption and it is necessary to pay a careful attention to storage.
Therefore, there has been a need for a method which enables the experience of the grinding sensation of a tooth without using a natural tooth.
Now a tooth for a dental arch model, which is used for practice treatments in the oral cavity, is often produced using an epoxy resin or a melamine resin, and are well known in the art.
However, a tooth for a dental arch model formed of an epoxy resin or a melamine resin is in the form of a natural tooth, but exhibits a grinding sensation different from that of a natural tooth. Therefore, even when performing formation trainings such as abutment tooth formation and cavity preparation, grinding sensation and handling properties are different from those of actual dental works in the oral cavity, and thus the training effect could not be obtained.
Specifically, an epoxy resin and a melamine resin are soft. Thus there is a tendency to over grind and even when performing training using such a model tooth, the grinding may not be similar to that of a hard natural tooth.
Furthermore, a natural tooth is formed of an enamel texture and the dentin texture and an enamel texture and the dentin texture are harder than a resin, and thus the enamel texture, with which a crown portion of the dentin texture is coated, and the dentin texture have different hardnesses. As a result, in case of a transition during grinding from the enamel texture to the dentin texture, the dentin texture may be excessively ground and thus a tooth may not be satisfactorily produced.
That is, it is required that a grinding sensation varies similarly to a natural tooth in the transition part from the enamel portion to the dentin portion of a tooth for a dental arch model. Therefore as a matter of course, it is important that the enamel portion reproduces the grinding sensation of the enamel texture, while the dentin portion reproduces the grinding sensation of the dentin texture.
As a result of the need for a harder material, a composite type tooth is commercially available. However even in case of a composite type tooth, since the dentin portion and the enamel portion exhibit the same grinding sensation, the grinding sensation of the composite type tooth is different from that of a natural tooth. Therefore, even when performing formation trainings such as abutment tooth formation and cavity preparation, the grinding sensation and handling properties are different from those in case of dental works in the oral cavity in practice, and thus the training effect could not be obtained. To state the matter clearly, the grinding sensation includes slipperiness and is substantially different from a natural tooth.
Japanese Unexamined Utility Model Publication (Kokai) 1-90068 discloses that a the enamel texture layer is formed of glass/ceramics having a Vickers hardness controlled within a range from 350 to 450, comprising a phlogopite crystal [NaMg3(Si3AlO10)F2] and a lithia-alumina-silica-based crystal (Li2O.Al2O3.2SiO2, Li2O.Al2O3.4SiO2) precipitated simultaneously; a tooth root layer is prepared in advance by adding white, red and yellow colorants to a polyol (base resin), mixing with an isocyanate prepolymer (curing agent), injecting the mixture into a silicone rubber mother mold under vacuum conditions and curing the mixture at a normal temperature; and a dentin texture recognition layer, which exists between the enamel texture layer and the tooth root layer thereby bonding both layers, and is formed of an adhesive resin having an opaque color.
However, the tooth comprising an enamel texture layer formed of a phlogopite crystal or a lithia-alumina-silica-based crystal is not well adapted for use because it feels too hard when grinding as compared with a natural tooth, and also it is not well adapted for use because the dentin texture recognition layer is formed of an adhesive resin which feels too soft when grinding.
Furthermore, the dentin layer is formed of an adhesive layer is disclosed. It is described that an enamel layer portion and a tooth root layer portion are formed and bonded. It is recognized as the dentin layer formed of a thick adhesive layer.
Japanese Unexamined Patent Publication (Kokai) No. (hereinafter referred to briefly as “JP-A-”) 5-224591 discloses a tooth model which has a grinding sensation extremely similar to that of a natural tooth, and is suited for the training of practical dental grinding.
The tooth model comprises a crown portion whose surface has a Knoop hardness of at least 70 or more and a tooth root portion whose surface has a Knoop hardness of at least 10 to 40. The tooth model contains, as main components, an inorganic matter powder and a crosslinking resin in a weight ratio of 20%:80% to 70%:30%.
The above prior art discloses that “a tooth model may be formed of a raw material having any hardness, for example, metal, ceramics or a resin, or may be a cavity in view of the method for producing a tooth model and economic considerations”. However, this is not a tooth model which can exhibit a difference in the grinding sensation between the enamel portion and the dentin portion.
JP-A-5-216395 discloses a tooth model which has a grinding sensation extremely similar to that of a natural tooth and is suited for the training of practical dental grinding, and a method for producing the same. The tooth model contains, as main components, a hydroxyapatitte powder having a porosity of 40 to 80% and a (meth)acrylate ester-based resin in a weight ratio of 20%:80% to 50%:50%. However, this is not a tooth model which can exhibit a difference in the grinding sensation between the enamel portion and the dentin portion.
JP-A-5-241498, JP-A-5-241499 and JP-A-5-241500 describe an inorganic filler and hydroxyapatitte filler. However, in all tooth models disclosed in these publications, a resin is used as a base material and thus the problem of the grinding sensation is not solved. They are not tooth models which can exhibit a difference in grinding sensation between the enamel portion and the dentin portion.
JP-A-2004-94049 describes an invention which provides a model tooth for dental training, which enables an accurate shape measurement with laser beam.
The specification discloses that “known materials can be used as a material constituting a surface of a crown portion of the model tooth of the present invention and there can be used porcelain materials such as ceramics; thermoplastic resin materials such as acryl, polystyrene, polycarbonate, an acrylonitrile-styrene-butadiene copolymer (ABS), polypropylene, polyethylene, and polyester; thermosetting resin materials such as melamine, urea, unsaturated polyester, phenol, and epoxy; and materials obtained by adding various organic and inorganic reinforcing fibers (for example, glass fiber, carbon fiber, pulp, synthetic resin fiber, etc.), various fillers (for example, talc, silica, mica, calcium carbonate, barium sulfate, alumina, etc.), colorants (for example, pigment, dye, etc.) and various additives (for example, weathering agents, antistatic agents, etc.) to these main raw materials”. However, there is no description about preferable materials, and thus the problem of grinding sensation is not solved.
As a result of a study, the present inventors have found that it is necessary to use a sintered body of an inorganic material so as to exhibit the grinding sensation of a natural tooth. Because of the difficulty in controlling a hardness of an inorganic material, it is difficult to form an enamel portion and a dentin portion while controlling the hardness.
It is necessary to control a density and a particle shape of the sintered body and a sintering temperature so as to adjust the grinding sensation of the sintered body. The difference in a shrinkage rate and a thermal expansion coefficient between the enamel portion and the dentin portion upon sintering results in breaking, peeling and cracking. In addition, a gap may be formed between the dentin portion and the enamel portion. Thus, chipping may occur upon grinding and the gap gives a sensation different from the grinding sensation of a natural tooth. Thus the resultant tooth was not well adapted for use.
When a natural tooth is ground, a unique tough grinding sensation upon grinding of a living body is obtained. In particular, the dentin portion remarkably exhibits sensation of adhesion of an organic component contained in the dentinal tubule of the tooth to a bar, and sensation of inhibition of grinding.
Although various methods have been studied so as to obtain a tough grinding sensation peculiar to a natural tooth, a sufficient grinding sensation cannot be obtained using resin, composite or the like and such a sensation can not be obtained while pouring water on a conventional tooth for a dental arch model. A grinding sensation is required in which users feel a tough grinding sensation than that of an inorganic material even in case of the enamel texture because of a similar phenomenon.
However, neither a specific composition of a tooth model capable of realizing a grinding sensation of the enamel texture and the dentin texture of a natural tooth, nor a method for producing the same has been studied or reported.
A method of reproducing tooth pulp peculiar to a natural tooth has not been developed heretofore, and thus dental students could not experience exposure to tooth pulp. Dental pulp exposure (grinding down the tooth pulp portion) is the most important technique in a dental treatment. In case where tooth pulp exposure was carried out by mistake, the subsequent treatment method must be learned at the same time.
As a dental caries progresses in a natural tooth, the treatment position expands into the enamel layer, the dentin layer and the tooth pulp, and training for a root canal treatment such as a pulpectomy is most important. When a pulpectomy is carried out, since the tooth pulp is removed by a reamer and sensations of rubbing of the dentin wall surface with the reamer completely varies, training of root canal filling could not be carried out.
In a treatment of tooth pulp, a tooth designed for training of a root canal treatment is used, and also training of a root canal treatment (root canal cleaning, root canal extension, etc.) is carried out using a tooth with a small hole formed of a box-shaped acryl. However, sufficient training cannot be carried out since it is impossible to mount the tooth on a jaw and the hardness of the dentin texture varies.
It is required to develop a tooth for a dental arch model, which enables these experiences. In particular, dental students learn by hand the sensation of whether or not tooth pulp is completely removed upto the apical foramen during root canal cleaning, and thus it is difficult for beginners. Therefore, it is required to perform training using a tooth for a dental arch model in which tooth pulp in a natural tooth is reproduced.
Although removal of dental caries is an important procedure in a dental treatment, a carious dental portion is softer than a usual dentin portion and thus it is difficult to grind the carious dental portion. Therefore, it is necessary to perform training using a tooth for a dental arch model in which dental caries in a natural tooth are reproduced. It is also required to develop a method of confirming that a carious dental portion has been accurately removed.