Field of The Invention

[ 0001 ] The inventions described below relate to the f ield of photocurable materials for additive manufacturing of dental prosthesis .

Background

[ 0002 ] Dental protheses such as denture bases , denture teeth, partial dentures , crowns , inlays and onlays and other dental restorations , and dental f iller materials for restoration of natural teeth are made with additive manufacturing techniques and the application of UV or visible light to photocurable material .

[ 0003 ] Additive manufacturing is a general description of the process where materials are added successively by layers to produce the f inal part . This is also known as three- dimensional printing . Photocurable materials may be used in several methods of additive manufacturing including stereolithography ( SLA) , digital light processing (DLP) , and ink j et printing with single or multiple j ets .

[ 0004 ] In one application using SLA, a resin mixture is poured into a vat and the UV/visible light applied to the resin mixture to cure the resin is controlled by a mirror to focus the light exactly where the resin is to be cured and solidif ied . The vat is lowered on an associated printing plate and is raised layer by layer with repeated curing to produce a f inal part . Alternatively, with DLP , UV/visible light applied to the resin mixture over an entire cross section of the part is cured at once and repeated layer by layer .

[0005] Another alternative involves a method called continuous liquid interface production (CLIP) in which a semi- permeable oxygen layer or window is created to allow continuous flow of resin into an area where the resin is cured continuously .

[0006] Ink jet printing uses an ink jet or multi jet printer, to print uncured resin onto a plate. The resin is cured as it exits the nozzle to produce a solid layer. This printing is done continuously until the final form of a part is achieved. Multiple jets may be loaded with different materials and operated in conjunction with each other to form a part out of different compositions of materials.

[0007] A number of resin formulations are currently available for use in these printing systems. However, improvements in materials for dental prosthesis are needed to facilitate increased clinical longevity and reliability and improved mechanical and physical properties.

Summary

[0008] The devices and methods described below provide for (1) a new photocurable material, useful in additive manufacturing techniques, to make dental protheses such as denture bases, denture teeth, partial dentures, crowns, inlays and onlays and other dental restorations, or to make dental filler materials for restoration of natural teeth, (2) dental prostheses and products such as denture bases, denture teeth, partial dentures, crowns, inlays and onlays and other dental restorations, or to make dental filler materials for restoration of natural teeth, and natural teeth restored with the photocurable material , and ( 3 ) a method of making dental prostheses with the photocurable material and additive manufacturing techniques , all with improved properties such as f lexural strength, fracture toughness , and/or wear rate .

[ 0009 ] The new photocurable material is a resin matrix including an ethoxylated difunctional bisphenol A dimethacrylate ; a methacrylate monomer , a difunctional urethane acrylate and a stabilizer . The new photocurable material may alternatively be formulated with a resin matrix comprising an ethoxylated difunctional bisphenol A dimethacrylate ; a methacrylate monomer , a difunctional urethane acrylate and a stabilizer . The resin of the photocurable material is composed of at least one kind of dimethacrylate ; and at least one kind of methacrylate monomer ; and at least one kind of difunctional urethane acrylate .

[ 0010 ] Dental prostheses such denture bases , denture teeth, crowns , overlays , onlays and other dental restorations may be fabricated with the photocurable material , using additive manufacturing methods , to create dental prostheses comprising a cured material resulting from photocuring the photocurable material .

[ 0011 ] The material may be used in a method of manufacturing of dental prostheses or restoring natural teeth with additive manufacturing techniques . The material and method of manufacture provides dental prostheses comprising the cured dental composite obtained by photocuring the new photocurable material . Detailed Description of the Inventions

[0012] The improved photocurable material may consists of no more than 35 wt . % of at least one kind of ethoxylated difunctional bisphenol A dimethacrylate; of no more than 10 wt . % of at least one kind of methacrylate monomer; of no more than 5 wt . % of at least one kind of difunctional urethane acrylate; of no more than 0.1 wt . % of at least one kind of optical brightener; of no more than 2 wt . % of at least one kind of silica particles having methacrylate functionalization layers and having an average particle size of less than about 200 nm; of no more than 50 wt. % of at least one kind of inert glass; of no more than 10 wt. % of at least one kind of heavy metal oxide; of no more than 1 wt . % of at least one kind of ultraviolet/visible (UV/Vis) light-photo polymerization initiator; at least one colorant; and at least one stabilizer, The photocurable material is in a liquid state and attains a solid state after curing. The viscosity of a liquid state of the photocurable material is less than 2000 centipoise (cps) (2 Pascal - second) at room temperature or 25° C.

[0013] Several different methacrylates may be used, alone or in combination with ethoxylated difunctional bisphenol A dimethacrylate and other methacrylates. Additional multifunctional methacrylates that may be used in the photocurable resin include ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 2,2 bis [4 - (methacry loxy ethoxy) phenyl] propane, tricylodecane dimethanol dimethacrylate, 1 , 10-decandiol dimethacrylate, 1 , 6 -hexane-diol dimethacyrlate , neopentyl glycol dimethacrylate, trimethyolpropane trimethacrylate, ethoxylated trimethyolpropane trimethacrylate, di trimethyolpropane tetramethacrylate, dipentaerythritol pentamethacrylate, ethyoxylated pentaerythritol tetramethacrylate, propoxylated glyceryl trimethacrylate, and propoxylated trimethylolpropane trimethacrylate .

[0014] A photocurable component comprising at least one kind of ultraviolet/visible (UV/Vis) light-photo- polymerization initiator is used for curing of the part. A preferred light-photo-polymerization initiator includes 1-2 wt . % of 2 -hydroxy-4- methoxybenzophenone, 1.0 - 2.5 wt . % diphenyl (2 , , 6-trimethylbenzoyl) phosphine oxide with less than 0.1 wt . % of stabilizer Butylated hydroxytoluene. Other photo- initiators that may be used include bis (2,4, 6- trimethylbenzoyl ) phenyl phosphine oxide, 2- hydroxy- 2 -methyl - 1 -phenyl 1 -propanone, and benzophenones (BP) .

[0015] Other stabilizers that may be used in the photocurable resin include 4 -methoxyphenol , phenothiazine, bis (tridecyl) thiodipropionate, and other compounds that prevent generation and propagation of amine complexes.

[0016] Optionally, an optical brightener and a colorant may be included in the resin material . Other colorants based on a variety of metal oxides may be used to impart a range of colors to the resin material . Examples include but are not limited to various types of iron oxides, copper oxides, chromium oxides, cobalt oxides, zinc oxides, nickel oxides, vanadium oxide, cerium oxide, and other metals and various oxidation states. For example, the composition may include < 0.1 wt . % of optical brightener and < 0.1 wt . % of iron oxides colorant .

[0017] The material also contains at least one kind of silica particle having methacrylate functionalization layers and having an average particle size of less than about 200 nm. In one composition, the filler material consists of no more than 5 wt . % of at least one kind of silica particles having methacrylate functionalization layers and having an average particle size of less than about 200 nm; of having more than 40 wt. % of at least one kind of inert glass; and of no more than 15 wt. % of at least one kind of heavy metal oxide. In one composition filler also includes 40 - 60 wt.% of barium aluminoborosilicate , 0-15 wt.% of ytterbium trifluoride, and 1- 5 wt.% of fumed silicon dioxide.

[0018] The photocurable material includes fillers which may comprise quartz, fused silica, chemically derived silica, pyrogenic silica, colloidal silica, aluminous silica, glass ceramics, soda lime glasses, borosilicate glasses, strontium glasses, zinc glass, fluoro-aluminate glass, and various mixtures of these components. Filler particles may be spherical, irregular, needle like, dense, partially porous, porous, or a mixture thereof .

[0019] The filler particles may be functionally coated to improve adherence to and suspension in the resin matrix. Different types of silane coatings that may be used to functionally coat the filler particles include dimethyl di chi orosi lane , vinyl trichloro- silane , methyltrimethoxy- silane , dimethyldimethoxy- silane , trimethylchloro- silane , phenyl trimethoxy- silane , diphenyldimethoxy- silane , methyltriethoxy- silane , dimee thy Idiethoxy- silane , vinyl -trimethoxy- silane , methyldicrholorsilane , diethylsilane, and other types of silane. Filler may consist of particles in a size range of up to 20 microns but typically consists of particles in a size range of less than 10 microns and preferably consist of particles in a size range of less than 5 microns. They may be a mixture of sizes or of a uniform size. The filler material may comprise a first plurality of particles with sizes in the range of 10 to 20 microns, a second plurality of particles with sizes in the range of 5 to 10 microns, and a third plurality of particles with sizes smaller that 5 microns, preferably without a significant number of larger particles. In another embodiment, the filler material may consist of particles in the range of 5 microns and smaller, preferably with a median size of 3 microns, without a significant number of larger particles. In another embodiment, filler material may consist of a first plurality of particles with sizes in the range of 10 to 20 microns, a second plurality of particles with sizes in the range of 5 to 10 microns, and a third plurality of particles with sizes smaller that 5 microns, where the third plurality of particles has a median size of 3 microns, where, again, the filler material does not include a significant number of larger particles.

[0020] Heavy metal oxides may include those metals having an atomic number that is greater than 20 and/or a density greater than 5 g/cm ³ such as zinc, cerium, yttrium, strontium, barium, zirconium, hafnium, niobium, tantalum, tungsten, bismuth, molybdenum, tin or combinations thereof .

[0021] The viscosity of the composition is measured using a Brookfield DV-III Ultra Programmable Rheometer equipped with a CPA 51Z spindle at a speed to achieve 10% torque. One preferred viscosity is achieved by design of the mixture is based on the inclusion of at least one kind of ethoxylated difunctional bisphenol A dimethacrylate, at least one kind of methacrylate monomer, at least one kind of difunctional urethane acrylate, at least one kind of silica particles, at least one kind of optical brightener, at least one kind of inert glass, at least one kind of heavy metal oxide, at least one kind of UV/Vis light-photo-polymerization initiator, at least one colorant, and at least one stabilizer, and is less than 1000 centipoise (cps) at room temperature or 25°C.

[0022] The viscosity of the photocurable material may range up to 2000 centipoise (cps) at room temperature or 25°C but will vary depending upon the exact ratio of various monomer components and filler components. Lower viscosity resins such as triethylene glycol dimethacrylate when used in higher ratios will decrease the viscosity as will lower concentrations of filler.

[0023] Various properties of the new photocurable material were tested and compared to existing materials used for denture prosthesis. The tested embodiment included the components described in paragraph [0012] above.

[0024] Biaxial flexural strength of tested embodiment of new photocurable material and other denture materials determined according to ISO Standard 6872-2015 and are presented in Table 1. Biaxial flexural strength of the tested embodiment of the new photocurable material for teeth are presented in Table 2.

[0025] Table 1. Biaxial Flexural Strength of Printed

Materials for Denture Bases

[0026] Table 2. Biaxial Flexural Strength of Printed Tooth

Restorations and Denture Teeth

[0027] The fracture toughness of the tested embodiment of the new photocurable material for tooth materials was determined according to ISO Standard 2079 and is presented in Table 3. [0028] Table 3. Fracture Toughness of Tooth Materials

[0029] Wear of the new photocurable material for tooth materials was determined using a pin on plate method where a cylinder of the invention material was run against a tooth substitute plate material under a 400-gram load with continuous water flow. The wear rates were determined for the new photocurable material and compared to existing materials currently in clinical use. Wear rates are shown in Table 4.

[0030] Table 4. Mean Wear Rate of Tooth Materials

[0031] The photocurable material described above is intended for use in creating dental prosthesis comprising a cured component created by additive manufacturing from the photocurable material . These prostheses may be made with a method of printing a dental prosthesis using the photocurable material in any additive manufacturing technique including photocuring the photocurable material .

[ 0032 ] While the preferred embodiments of the devices and methods have been described in reference to the environment in which they were developed, they are merely illustrative of the principles of the inventions . The elements of the various embodiments may be incorporated into each of the other species to obtain the benef its of those elements in combination with such other species , and the various benef icial features may be employed in embodiments alone or in combination with each other . Other embodiments and conf igurations may be devised without departing from the spirit of the inventions and the scope of the appended claims .