Ultrasonic Curing of Dental Filling Materials

Abstract

The present invention relates to a composite material exhibiting a low or even negligible volumetric shrinkage upon curing, or even a small expansion (e.g. up to 0.5%), in particular composite materials in the form of dental filling materials. The present invention also relates to a method of controlling volumetric shrinkage of a composite material upon curing, and to a method of reconstructing a tooth. The present invention also relates to ultrasonic curing of dental filling materials. The present invention further relates to a population of zirconia particles and methods for preparing such zirconia particles (e.g. zirconia in the tetragonal phase or zirconia in the cubic phase). The martensitic transformation of the filler ingredients is, e.g., triggered by application of ultrasound or by a chemical trigger.

1 . A composite material comprising one or more fillers and a polymerizable resin base, wherein said one or more fillers comprise at least one filler ingredient, said filler ingredient(s) being present in a metastable first phase and being able to undergo a martensitic transformation to a stable second phase, the volume ratio between said stable second phase and said metastable first phase of said filler ingredient(s) being at least 1.005. 
     
     
         2 . The composite material according to  claim 1 , wherein said resin base, upon polymerization and in the absence of any compensating effect from the one or more filler ingredients, causes a volumetric shrinkage (ΔV resin ) of the composite material of at least 0.50%, and wherein said composite material, upon polymerization of said resin base and upon phase transformation of said filler ingredient(s), exhibits a total volumetric shrinkage (ΔV total ) of at least 0.25%-point less than the uncompensated volumetric shrinkage (ΔV resin ) caused by the resin base. 
     
     
         3 . The composite material according to any one of the preceding claims, comprising:
 30-95% by weight of the one or more fillers; and   5-70% by weight of the polymerizable resin base.   
     
     
         4 . The composite material according to any one of the preceding claims, which comprises less than 4% (w/w) of solvents and/or water. 
     
     
         5 . A composite material comprising one or more fillers and a polymerizable resin base, wherein said one or more fillers comprise at least one filler ingredient, said filler ingredient(s) including metastable zirconia in the tetragonal or cubic crystalline phase, wherein said resin base, upon polymerization and in the absence of any compensating effect from the one or more filler ingredients, causes a volumetric shrinkage (ΔV resin ) of the composite material of at least 0.50%, and wherein said composite material, upon polymerization of said resin base and upon phase transformation of said filler ingredient(s), exhibits a total volumetric shrinkage (ΔV total ) of at least 0.25%-point less than the uncompensated volumetric shrinkage (ΔV resin ) caused by the resin base. 
     
     
         6 . The composite material according to  claims 5 , comprising:
 30-95% by weight of the one or more fillers; and   5-70% by weight of the polymerizable resin base.   
     
     
         7 . The composite material according to any one of the  claims 5 - 6 , which comprises less than 4% (w/w) of solvents and water. 
     
     
         8 . The composite material according to any one of the preceding claims, which is a dental filling material. 
     
     
         9 . The dental filling material according to  claim 9 , wherein the filler ingredient(s) of the composite material include(s) zirconia (ZrO 2 ) in metastable tetragonal or cubic crystalline phase. 
     
     
         10 . The dental filling material according to  claim 9 , consisting of:
 40-85% by weight of the one or more fillers, wherein said one or more fillers comprise at least one filler ingredient, said filler ingredient(s) include(s) metastable zirconia in the tetragonal or cubic crystalline phase;   15-60% by weight of the a polymerizable resin base, said resin base being based on one or more compound selected from the group consisting of methacrylic acid (MA), methylmethacrylate (MMA), 2-hydroxyethyl-methacrylate (HEMA), triethyleneglycol dimethacrylate (TEGDMA), bisphenol-A-glycidyl dimethacrylate (BisGMA), bisphenol-A-propyl dimethacrylate (BisPMA), urethane-dimethacrylate (UEDMA), and HEMA condensed with butanetetracarboxylic acid (TCB);   0-5% by weight of additives; and   0-4% by weight of solvents and/or water.   
     
     
         11 . A method of controlling the volumetric shrinkage of a composite material upon curing, comprising the step of:
 (a) providing a composite material comprising one or more fillers and a polymerizable resin base, wherein said one or more fillers comprise at least one filler ingredient, said filler ingredient(s) being present in a metastable first phase and being able to undergo a martensitic transformation to a stable second phase, the volume ratio between said stable second phase and said metastable first phase of said filler ingredient(s) being at least 1.005;   (b) allowing the resin base to polymerize and cure, and allowing the filler ingredient(s) to undergo a martensitic transformation from said first metastable phase to said second stable phase.   
     
     
         12 . The method according to  claim 11 , wherein the martensitic transformation of the filler ingredient(s) is initiated by application of ultrasound. 
     
     
         13 . The method according to any one of  claims 11 - 12 , wherein the polymerization of the resin base is initiated by application of ultrasound. 
     
     
         14 . The method according to any one of the  claims 11 - 13 , wherein the composite material is as defined in any one of  claims 1 - 10 . 
     
     
         15 . A composite material as defined in any one of the  claims 1 - 10  for use in medicine, in particular in dentistry. 
     
     
         16 . A population of zirconia particles having an average particle size in the range of 50-2000 nm and a BET surface area of in the range of 10-250 m 2 /g, said particles being present in a metastable first phase and being able to undergo a martensitic transformation to a stable second phase. 
     
     
         17 . The population according to any one of the preceding claims, wherein the particles have crystal domain sizes in the range of 8-100 nm, such as in the range of 10-50 nm, such as 8-20 nm. 
     
     
         18 . A method for the preparation of a population of zirconia particles as defined in any one of the  claims 16 - 17 , said method comprising the step of heating a sample of amorphous zirconia to a temperature within ±3 K of the crystal formation temperature as determined by DSC. 
     
     
         19 . The method according to  claim 18 , wherein the amorphous zirconia particles have a BET surface area of in the range of 250-550 m 2 /g, such as in the range of 350-550 m 2 /g. 
     
     
         20 . A method for the preparation of a population of zirconia particles as defined in any one of the  claims 16 - 17 , said method comprising the step forming a suspension of a powder of small tetragonal crystals of zirconia in a strong aqueous base, and heating the suspension to a temperature in the range of 150-200° C. 
     
     
         21 . The method according to  claim 20 , wherein the suspension is heated for a period of not less than 2 hours.