Dental adhesive composition
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a dental adhesive (or cement), composition usable for adhering and firmly fixing dental restorative materials comprising ceramics such as calcium metaphosphate crystallized glass, and further, for example, alloys, porcelain materials, and/or composite resins, to the teeth. 
     2. Description of the Related Art 
     Various dental adhesives have been utilized for the therapy of teeth suffering from caries, such as zinc phosphate cement, carboxylate cement, glass ionomer cement, etc. Further, in recent years, as a newer type of dental adhesive, composite resin cements containing a vinyl monomer having phosphoric acid group or carboxylic acid anhydride group in the molecule, such as 4-methacryloxyethyltrimellitic acid anhydride and methacryloxyethlyphenyl hydrogen phosphate, are now commercially available. This composite resin cement can be used for the adhesion of a crown, or inlay to the teeth, and further, can be itself utilized as a dental restoring material by reinforcing the adhesion to the teeth by using another dental adhesive composition in combination therewith. 
     On the other hand, aesthetic considerations in dentistry have become important recently, and various new material ceramics have been developed in response to this need. Particularly, because castable ceramics such as calcium metaphosphate crystallized glass have characteristics similar to natural teeth in mechanical strength and the aesthetic sense, they are suitable for use as a dental restorative material. However, when utilizing such a material, a dental adhesive composition must be used for adhering and firmly fixing the dental restorative material comprising castable ceramics. 
     However, the dental adhesive composition of the prior art, although having a good adhesive force between teeth and a dental restorative material comprising, for example, an alloy, a porcelain material, or a composite resin, is not able to firmly adhere the dental restoring material comprising castable ceramics to the teeth, and a dental adhesive composition for such castable ceramics has not been proposed in the prior art. 
     Accordingly, a dental adhesive composition effective for adhering and fixing a dental restorative material comprising castable ceramics such as calcium metaphosphate crystallized glass to the teeth is desired. 
     SUMMARY OF THE INVENTION 
     Accordingly, the object of the present invention is to obviate the above-mentioned problems and to provide a dental adhesive composition having an excellent adhesive force between a dental restorative material comprising, for example, an alloy, a porcelain material, or a composite resin and teeth, and capable of adhering and stably and firmly fixing a dental restoring material comprising castable ceramics such as calcium metaphosphate crystallized glass to teeth. 
     Other objects and advantages of the present invention will be apparent from the following description. 
     In accordance with the present invention, there is provided a dental adhesive composition comprising a compound having the formula (I): ##STR2## 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present inventors have found that a product obtained by polymerization and curing of a compound represented by the above-mentioned formula (I) can be firmly adhered and fixed to a dental restorative material comprising castable ceramics such as calcium metaphosphate crystallized glass, even in saliva, that a polymer of such a compound of the formula (I) or a copolymer thereof with another polymerizable monomer is excellent as the adhesive for the dental restorative material comprising castable ceramics such as calcium metaphosphate crystallized glass, and further, that it is suitable as an adhesive for the dental restorative material comprising, for example, an alloy, a porcelain material, or a composite resin, and therefore, that a dental adhesive composition containing the compound of the formula (I) is free from the formation of gaps between the teeth and the dental restorative material or drop-off of the dental restorative material due to poor adhesion and can remarkably improve marginal leakage, thereby effectively inhibiting secondary caries, to accomplish the present invention. 
     The dental adhesive composition according to the present invention contains the compound of the formula (I) as mentioned above, and is adhered to the teeth by curing in use, and is used for the purpose of adhesion to the teeth, such as for adhesive or adhesion enhancement for adhering the dental restoring material prepared with ceramics, and further, for example, dental alloys and porcelains, to the teeth. 
     According to the present invention, the (N,N-dicarboxymethyl)aminomethyl group in the compound (I) may be at any position of ortho-, meta- and para-positions of the benzene ring of styrene, but particularly preferably is positioned at the meta-position or the para-position. The compound having the formula (I) is contained as a monomer in the present dental adhesive composition. 
     The dental adhesive composition according to the present invention may contain any other components, depending on, for example, the kind of the adhesive composition and the purpose of use. For example, when the present composition is used as the adhesive for adhesion between the teeth and the dental restorative material, only the compound having the formula (I) can be used as the adhesive monomer and, when used, the composition is polymerized and cured in the presence of a curing agent. However, generally speaking, the compound having the formula (I) is mixed with another polymerizable monomer, and the monomers are polymerized and cured in the presence of a curing agent when used. 
     In the above-mentioned case, examples of another polymerization monomer are one or more monomers selected from the group consisting of (a) styrene, (b) acrylic acid and derivatives thereof, and (c) methacrylic acid and derivatives thereof. Specific examples of acrylic acid derivative, methacrylic acid derivatives are methyl acrylate and methacrylate, hydroxyethyl acrylate and methacrylate, ethylene glycol diacrylate and methacrylate, di- or tri- or tetraethylene glycol di-acrylate and methacrylate, glycidyl acrylate and methacrylate, 2,2&#39;-bis(acryloxy and methacryloxyphenyl)propane, 2,2&#39;-bis [4-(3-acryloxy and methacryloxy)-2-hydroxypropoxyphenyl]propane, 1,3-butanediol diacrylate and methacrylate, triacrylic acid and methacrylic acid trimethylolpropane, bisoxyethylenated bisphenol A diacrylate and methacrylate. 
     Also, if necessary, for adjusting viscosity, curing speed, polymerization shrinkage or the like of monomers or copolymers, oligomers of the compound having the formula (I) or other vinyl monomers may be formulated, and further, inorganic fillers, preferably having particle sizes of 50 μm or less, such as silica, glass beads, aerosil, alumina, silicon nitride, or quartz powder, these inorganic fillers subjected to silane coupling agent, such as γ-methacryloxypropyltrimethoxysilane or vinyltrimethoxysilane, for improving bonding to the resin, or organic composite fillers coated on the filler surface with the above vinyl monomer and other fillers, and curing agents, polymerization inhibitors, colorants, antioxidants, UV-ray absorbers or the like, may be used. 
     The polymerization and curing of the compound having the formula (I) and a mixture of the compound (I) with another polymerizable monomer copolymerizable therewith, may be carried out by methods such as the chemical polymerization system and photopolymerization system, and in this case, as the curing agent, amines and peroxides may be suitably used for the chemical polymerization, and camphorquinone, benzoin alkyl ether for the photopolymerization. 
     Although, the amount of the compound having the formula (I) is not particularly limited, when another polymerizable monomer as mentioned above is utilized, it is preferably made 1 to 30% by weight, more preferably 2 to 15% by weight, based on the another polymerizable monomer. If less than 1% by weight, the adhesive effect becomes poor, and the hardness of the cured product may be sometimes lowered if more than 30% by weight is added. The amount of the above another polymerizable monomer formulated should be preferably made 10% to 60% by weight, based on the whole composition, and the amount of the filler formulated should be 40% to 90% by weight, based on the whole composition. 
     When the dental adhesive composition according to the present invention is used as the adhesive enhancer such as an adhesive liner or bonding agent, preferably the composition is prepared by containing the compound of the formula (I) in 1% to 15% by weight, based on the whole composition, in an organic solvent such as ethanol, ethyl ether, or chloroform, 
     The dental composition can be also prepared by containing the compound of the formula (I) in 1% to 15% by weight, based on the whole composition, in the above another polymerizable monomer or a mixture of the above organic solvent and the above another polymerizable monomer. In these cases, the composition containing the compound having the formula (I) will effect polymerization and curing of the compound having the formula (I) in the presence of a curing agent in the use thereof. 
     The dental adhesive composition according to the present invention has an excellent adhesiveness to a dental restorative material comprising castable ceramics such as calcium metaphosphate crystallized glass, and further, exhibits a good adhesiveness to teeth and the dental restorative material comprising, for example, an alloy, a porcelain material, a composite resin, and maintains a high adhesiveness even in water and saliva, and therefore, can adhere and firmly and stably fix the dental restorative material to the teeth, whereby the formation of gaps between the teeth and the dental restorative material due to poor adhesion can be prevented and the marginal leakage can be improved to prevent secondary caries. 
    
    
     EXAMPLES 
     The present invention will now be further illustrated by, but is by no means limited to the following Examples, wherein all parts indicate parts by weight. 
     EXAMPLE 1 
     A compound having the above-mentioned formula (I) was dissolved at a concentration of 5% in ethanol a dental adhesive composition (I) was prepared. 
     Then, each of the enamel surface of bovine teeth embedded in a holder with gypsum, the dental gold-silver-palladium alloy, the nickel-chromium alloy, and a plate with one side of 10 mm and a thickness of 1.5 mm of calcium metaphosphate crystallized glass prepared by casting was finished by a polishing machine to a uniform smooth surface, and these were used as the materials to be adhered. Further, an acrylic resin rod and a stainless steel rod 6 mm in diameter×40 mm in length were finished by a polishing machine to a uniform smooth surface. 
     Subsequently, the above smooth surface to be attached was treated with 3M phosphoric acid for 30 seconds, washed with water for 30 minutes, and dried by compressed air. The above adhesive composition was applied on the dry teeth surface and, after drying, by using the adhesive (II) with the recipe shown below, the above acrylic resin rod was adhered to a material to be attached, which is the bovine enamel or the calcium metaphosphate crystallized glass, and the above stainless steel rod was also adhered to a material to be attached, which is the gold-silver-palladium alloy or the nickel-chromium alloy. The adhesive strength was measured by a Strograph (manufactured by Toyo Seiki K.K.) (cross head speed=5 mm/min.), for those stored at room temperature and for those stored in artificial saliva at 37° C. for 7 days. 
     Adhesive (II) recipe: 
     
         ______________________________________                                    
Part A                                                                    
Methyl methacrylate                                                       
                   2 parts                                                
Polymethyl methacrylate                                                   
                   0.4 parts                                              
N,N-dimethyl-p-toluidine                                                  
                   0.04 parts                                             
Part B                                                                    
Methyl methacrylate                                                       
                   2 parts                                                
Polymethyl methacrylate                                                   
                   0.4 parts                                              
Benzoyl peroxide   0.04 parts                                             
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     Before use, the parts (A) and (B) were mixed at a weight ratio of 1:1. 
     EXAMPLE 2 
     Using 5 parts of the compound having the formula (I), 10 parts of methyl methacrylate, 20 parts of diethylene glycol dimethacrylate, 50 parts of bisphenol A-diglycidyl methacrylate, 2 parts of N,N-dimethyl-p-toluidine as the liquid components, these liquid components were mixed with 100 parts of quartz powder with particle sizes of 50μ or less, which had been given a silane coupling treatment, and 1 part of benzoyl peroxide to prepare an adhesive (III). This adhesive was applied on the smooth surfaces of four kinds of materials to be adhered in the same manner as in Example 1, and the adhesive strength of each was measured. 
     COMPARATIVE EXAMPLES 1-3 
     Commercially available dental adhesive Chemiace (produced by Sunmedical Co.), Superbond C &amp; B (produced by Sunmedical Co.), and Panavia EX (produced by Kuraray Co.) were applied on the smooth surfaces of four kinds of materials to be adhered in the same manner as in Example 1, and the adhesive strength of each was measured. 
     The above commercially available dental adhesives have the following compositions. 
     
         ______________________________________                                    
Chemiace                                                                  
Powder portion:                                                           
              Trimethylolpropane trimethacrylated                         
filler                                                                    
              Benzoyl peroxide (i.e., catalyst)                           
Liquid portion:                                                           
              Epoxy acrylate resin                                        
              Methyl methacrylate                                         
              Diethyl para-toluidine (i.e.,                               
              catalyst)                                                   
Adhesive monomer:                                                         
              4-META                                                      
 ##STR3##                                                                 
Superbond C &amp; B                                                           
Powder portion:                                                           
              Polymethyl methacrylate powder                              
Liquid portion:                                                           
              Epoxy acrylate resin                                        
              Methyl methacrylate                                         
              Tributylborane oxide (i.e.,                                 
              catalyst)                                                   
Adhesive monomer:                                                         
 ##STR4##                                                                 
Panavia EX                                                                
Powder portion:                                                           
              quartz powder                                               
Liquid portion:                                                           
              Methyl methacrylate type monomer                            
Adhesive monomer:                                                         
              phenyl P                                                    
 ##STR5##                                                                 
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     The results of the adhesive measurements as mentioned above are summarized in Table 1. 
     
                                           TABLE 1                                 
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                                        Unit: kg/cm.sup.2                 
                        Example         Comparative example               
                         1                    2     3                     
                        Adhesive (I) +                                    
                                2       1     Superbond                   
                                                    Panavia               
Adhesive                Adhesive (II)                                     
                                Adhesive (III)                            
                                        Chemiace                          
                                              C &amp; B EX                    
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Material                                                                  
     Bovine enamel                                                        
               After 1 day at                                             
                        143     138     130   155   145                   
to be          room temperature                                           
attached                                                                  
               After 7 days in                                            
                        100      92      85   121   115                   
               artificial saliva                                          
     Gold-silver-                                                         
               After 1 day at                                             
                        198     183     205   220   240                   
     palladium alloy                                                      
               room temperature                                           
               After 7 days in                                            
                        155     143     185   204   196                   
               artificial saliva                                          
     Nickel-chromium                                                      
               After 1 day at                                             
                        263     250     272   265   300                   
     alloy     room temperature                                           
               After 7 days in                                            
                        190     202     265   232   255                   
               artificial saliva                                          
     Calcium phosphate                                                    
               After 1 day at                                             
                        115     121      75    80    50                   
     crystallized glass                                                   
               room temperature                                           
               After 7 days in                                            
                         99     102      31    46    6                    
               artificial saliva                                          
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     From the results in Table 1, it is clear that the present product has a better adhesiveness to the bovine teeth enamel, the gold-silver-palladium alloy, the nickel-chromium alloy than the adhesive of the prior art, and further, has an excellent adhesiveness to the calcium metaphosphate crystallized glass.