WO2022036384A1

WO2022036384A1 - Dental restorative material

Info

Publication number: WO2022036384A1
Application number: PCT/AU2020/050878
Authority: WO
Inventors: David Brenton DUNN; Luhua Li
Original assignee: 3D Dental Technology Limited
Priority date: 2020-08-21
Filing date: 2020-08-21
Publication date: 2022-02-24

Abstract

The present invention relates to a dental restorative material including Boron Nitride. Advantageously, Boron Nitride may be of improved strength and aesthetics when compared with other types of known dental restorative material. The Boron Nitride may be in the form of a nanomaterial, preferably Boron Nitride Nanotubes (BNNTs) and/or Boron Nitride Nanotubes Nanosheets (BNNSs).

Description

DENTAL RESTORATIVE MATERIAL

TECHNICAL FIELD

[0001] The present invention relates to dental restorative materials. These materials range from direct dental restorative materials (filling materials) such as composite resins, through to indirect restorative materials such as ceramic materials utilized in a variety of prosthetic applications including; “inlays,” “onlays,” “veneers,” “crowns,” and “bridges,” as well as implant applications; “implants,” “abutments” and a variety of “bridge constructions.”

BACKGROUND

[0002] The reference to any prior art in this specification is not, and should not be taken as an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge.

[0003] Ceramic materials were introduced to dental applications almost 250 years ago and have become the mainstay of aesthetic dentistry for the last 100 years. From the initial applications of Feldspathic ceramics as high fusing porcelain jacket crowns for anterior teeth, denture teeth and partial coverage restorations, there have been continuous improvements in strength, aesthetics and methods of fabrication. Today’s clinician faces a complex decision making process when choosing a ceramic material for a particular clinical application. Most often this decision is made on the basis of strength, translucency, ability to bond adhesively, dental technician preference and/or, via advertising claims.

[0004] There have been a multitude of various classification systems for ceramic materials suggested and based upon criteria such as; clinical application, composition, ability to etch, processing methods, firing temperatures, microstructure, translucency, fracture resistance and antagonist wear. However, the most recent proposed classification of dental ceramics is based upon three major families:

1. Glass Matrix Ceramics

Non-metallic inorganic ceramic materials that contain a glass phase 2. Polycrystalline Ceramics

Non-metallic inorganic ceramic materials that do not contain a glass phase

3. Resin Matrix Ceramics

Polymer-matrices containing predominantly inorganic refractory compounds that may include a variety of other compounds.

[0005] Compared to resins, such as “composite resins,” and metals, such as gold alloys or amalgam alloys, (the commonly used alternative materials in restorative dentistry) ceramics have numerous clinical and aesthetic advantages. Metals are considered unaesthetic, have potential corrosion problems and allergic reactions leading to biological complications including inflammatory responses with eventual restorative failure. They also cannot be utilized with a minimally invasive approach (MIA) to treatment and rely upon luting and mechanical retentive factors for functional success. Metallic dental restorations also cause interference with modern medical instruments, such as magnetic resonance imaging (MRI). Resin restorative materials generally have poor mechanical strength, low wear resistance, water sorption, only low- average longevity and cannot be used in extensive restorations.

[0006] Ceramics can exhibit natural enamel-/dentine-like appearance, biocompatibility, high chemical resistance, and good mechanical properties. These attractive features are more desirable for restoration of damaged dental tissues, especially in more extensive restorations and where aesthetics is critical, as well as other dental applications such as implant bridges.

[0007] As previously classified, “Dental Ceramics” contain a wide variety of different materials including glassy ceramics, glassy ceramics with fillers, resins with ceramic fillers, polycrystalline ceramics, and polycrystalline ceramics with fillers. Despite significant advances in material science, there is still a “trade-off” between translucency and mechanical strength. The presence of glass or resin components may offer increased translucency and hence, higher aesthetic capability, however, this comes at the price of reduced mechanical properties, including transverse flexural strength. The glassy ceramics have an improved aesthetic appearance, but their mechanical strengths are low. The addition of traditional fillers to glassy ceramics leads to slight strengthening of the materials.

[0008] Lithia-silicate glass and related ceramics are another common class of Glass Matrix Ceramics in the market. The microstructure of lithia-silicate normally consists of reinforcing crystals embedded in a glass matrix. Such microstructures enable cracks to propagate in the glass matrix around the reinforcing crystals, decreasing the material strength and toughness. In general, lithia-silicate glassy ceramics have good/excellent aesthetic characteristics but relatively low mechanical properties. In terms of lithia- silicate and other glass-ceramics, their mechanical strength is over half those of polycrystalline ceramics, such as zirconia. To improve their mechanical properties, various fillers (e.g. zinc oxide, zirconia, and leucite) have been added to glass ceramics. One of the most frequently used glassy ceramics in dentistry is lithium disilicate, which consists of many components, such as quartz, lithium dioxide, phosphor oxide, alumina, potassium oxide, and others.

[0009] Polycrystalline ceramics are today more often utilized due to their improved strength and toughness. One example is zirconia (ZrO2) with yttria (Y2O3), which is one of the strongest dental ceramics. More recently, fillers and /or glasses have been added to polycrystalline ceramics for better aesthetics properties but at the “cost” of reduced mechanical properties. Zirconia (ZrO2) and related ceramics are one of the most robust and strongest ceramic materials in dentistry. The most widely used polycrystalline ceramic is yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) with excellent mechanical, biocompatibility, and corrosion characteristics. The main advantage of zirconia and related ceramics are their high fracture toughness, which is attributed to the phase transformation and the creation of barriers to prevent further propagations of cracks during loading. This unique effect has not been found in other ceramics. However, zirconia and related ceramics have aesthetic compromises limiting the range of clinical indications, mainly related to their lack of translucency with the opacity coming from grain boundaries and other defects in zirconia.

[00010] Ceramic feldspathic veneering is one solution to improve the aethetic issues, however, veneering ceramics have very low flexural strengths (90-100MPa,) and are easy to delaminate, chip and fracture. Other attempts to improve the translucency of zirconia and related ceramics are adding glass, yttria, and/or other oxide fillers, but these lead to reduced mechanical properties. However, the opacity of the glass ceramics with fillers increases. Glass and polycrystalline-ceramics also have a common issue in that they are inherently brittle.

[00011] Despite all the attractive features and benefits of current dental ceramics, there are still a few challenges. There is no “perfect” material and a compromise always exists between strength and aesthetics. Often in the clinical pursuit of improved aesthetics, there is a significant risk of restorative failure of the material, more often than not, resulting in both clinician and patient frustration along with a significant cost for retreatment.

[00012] The preferred embodiment provides improved strength and aesthetics when compared with other types of known dental restorative material.

SUMMARY OF THE INVENTION

[00013] According to one aspect of the present invention, there is provided a dental restorative material including Boron Nitride.

[00014] Advantageously, Boron Nitride may be of improved strength and aesthetics when compared with other types of known dental restorative material. The Boron Nitride may be in the form of a nanomaterial, preferably Boron Nitride Nanotubes (BNNTs) and/or Boron Nitride Nanotubes Nanosheets (BNNSs).

[00015] The dental restorative material may further include a reinforcing dental ceramic material. The ceramic material may include any one or more of a: glassy ceramic, resin ceramic, glassy ceramic with other filler, polycrystalline ceramic, and polycrystalline ceramic with other filler.

[00016] The dental restorative material may further include any one or more of: lithia- silicate, lithium disilicate, lithium silicate, zinc oxide-, leucite- and zirconia-reinforced lithium disilicate, zirconia, zirconia oxide, yttria-stabilized zirconia, and alumina.

[00017] The dental restorative material may further include a metal. The metal may include Titanium. [00018] The dental restorative material may further include Zirconia,

[00019] According to another aspect of the present invention, there is provided a method for manufacturing a dental restorative material, the method involving: mixing a material with Boron Nitride to form a mixture.

[00020] The material may include a ceramic. The ceramic may be a glassy ceramic. The material may be in powder form. The mixing may involve mechanical mixing, sonication, and/or ball milling. The method may involve mixing in a dry or wet environment.

[00021] The method may involve pressing the mixture to form one or more blocks. The mixture may be pressed at room temperature, or an elevated temperature, in a protective gaseous atmosphere.

[00022] The method may involve annealing the blocks. The method may involve shaping the blocks.

[00023] The method may involve applying the mixture by inkjet printing, 3D gelprinting (3DGP), thermoplastic 3D printing (T3DP), and digital light processing stereolithography (SLA) or other additive manufacturing (3D printing) methods.

[00024] The method may involve applying the mixture by extrusion. The method may involve forming a slurry or solution by adding the mixture with any one or more of a: solvent, water, plastic, (photo)polymer, co-polymer, and catalyst.

[00025] The method may involve extruding the slurry or solution onto a platform. The slurry or solution may be extruded mechanically and/or thermally through a nozzle. The slurry or solution may be extruded as a layer, and solidified before the application of another layer. Each layer may be naturally self-solidified, or cured by heat, ultraviolet (UV) radiation and/or laser.

[00026] The method may involve sintering a 3D printing including the mixture. The method may involve annealing the sintered 3D printing. [00027] The method may involve further mixing a photopolymer resin to form the mixture. The method may involve subjecting the mixture to laser or LED light irradiation for solidification.

[00028] The material may include a glass-forming component.

[00029] According to another aspect of the present invention, there is provided a dental restorative material formed in accordance with the foregoing method.

[00030] Any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[00031] Nanomaterials can be used in reinforcing dental ceramic materials to solve the current challenges. Boron nitride nanotubes (BNNTs) have a huge surface area, outstanding mechanical strength, excellent thermal stability, very high thermal conductivity, and negative thermal expansion coefficient. BNNTs are electrically insulating with a wide bandgap (5-6 eV). Their Young’s modulus is in the range of ~0.9- 1 .2TPa and strength of ~30GPa. BNNTs are stable up to 900°C in air. Boron nitride nanosheets (BNNSs) are another form of BN nanomaterial with a similar structure to graphene. BNNSs also have many attractive properites. BNNSs have a high thermal conductivity of ~750 W/mK at room temperature, large Young’s modulus of 0.87 TPa, and breaking strength of 71 GPa. BNNSs have a high chemical and thermal stability (up to 850°C in air). BNNTs and BNNSs are also highly flexible, i.e. bending to 180° for thousands of times without failure. The outstanding thermal stability of BNNTs and BNNSs makes them more suitable than their carbon counterparts, namely carbon nanotubes (CNTs) and graphene which start to oxide at around 400°C to reinforce ceramics. Furthermore, BNNTs and BNNSs are transparent to visible light; in contrast, CNTs and graphene absorb visible light and hence black in appearance. That is, BNNTs and BNNSs are excellent fillers in dental ceramics for purposes of aesthetics and mechanical strength improvement.

[00032] BNNTs and/or BNNSs can be added to all dental ceramics, including glassy ceramics, resin ceramics, glassy ceramics with other fillers, polycrystalline ceramics, and polycrystalline ceramics with other fillers. Fillers such as lithia-silicate, lithium disilicate, lithium silicate, zinc oxide-, leucite- and zirconia-reinforced lithium disilicate, zirconia, zirconia oxide, yttria-stabilized zirconia, alumina and other ceramics can be used for enhanced strength, toughness, durability, and abrasive resistance. The fillers can also be used to improve the physical properties of metals such as titanium/titanium alloys and other ceramic materials currently used in implants.

[00033] The BNNT and/or BNNS reinforced dental ceramics show noticeably improved mechanical strength. The toughness of the reinforced dental ceramics is also enhanced because these BN nanomaterials block the crack propagation routes and dissipate the stress energy. The negative thermal expansion coefficients of BN NTs and BNNSs can partly compensate the shrinkage of ceramics after sintering. Furthermore, BNNTs and BNNSs pose no negative impact on the translucency of dental ceramics. This allows glassy ceramics with and without other fillers to maintain their translucency but increase their mechanical properties. BNNTs and/or BNNSs also allow polycrystalline ceramics to add oxide, glass, and/or other fillers to increase their translucency but maintain their mechanical properties.

[00034] BNNT and/or BNNS can also be applied to other dental materials in applications such as Titanium and ceramic dental implants in both oral and maxillofacial and orthopedic applications, bonded dental bridges and dental intraradicular posts in restoration of endodontically treated teeth.

[00035] Manufacture methods

[00036] Two main methods can be used to produce BNNTs and/or BNNSs reinforced dental ceramics: subtractive manufacturing (SM) and additive manufacturing (AM).

[00037] Subtractive manufacturing

[00038] Ceramic powders are mixed with BNNTs and/or BNNSs at the desired percentage by mechanical mixing, sonication, and/or ball milling in dry or wet environment. The mixture is pressed at room temperature or elevated temperatures in a protective gaseous atmosphere. The obtained blocks are then annealed for one or multiple rounds at different temperatures depending on the ceramic material. Conventional and unconventional machining and/or milling for required geometry and shape could be achieved before annealing or after the initial round of annealing at relatively low temperatures. The high temperature annealing sinters the BNNTs and/or BNNSs reinforced dental ceramics.

[00039] Additive manufacturing

[00040] Compared to subtractive manufacturing, additive manufacturing or 3D printing has less material waste, capability to produce more complex geometry, and minimum processing of machining and milling. BNNTs and/or BNNSs reinforced dental ceramics and Titanium can be produced by various additive manufacturing techniques, such as but not limited to direct inkjet printing, 3D gel-printing (3DGP), thermoplastic 3D printing (T3DP), and digital light processing stereolithography (SLA).

[00041] In extrusion-based additive manufacturing techniques, including direct inkjet printing, 3D gel-printing (3DGP), thermoplastic 3D printing (T3DP), BNNTs and/or BNNSs are mixed with dental ceramic powders and necessary solvents, and/or water and/or plastics, (photo)polymers, co-polymer, catalysts etc. to form a slurry or solution. The slurry or solution is then extruded mechanically and/or thermally through a nozzle onto a base platform. Each deposited layer can be self-solidified or require heat and/or ultraviolet (UV) radiation and/or laser to solidify. Layer by layer deposition forms the product with designed geometry and shape. After the 3D printing, the material is sintered for one or multiple rounds of annealing at different temperatures depending on the ceramic material. If thermoplastic, photopolymer and/or other polymers are added to the slurry or solution, a first round of annealing at relatively lower temperatures is normally required to remove the polymers, and subsequent annealing at higher temperature is followed for sintering purpose.

[00042] In digital light processing stereolithography (SLA) and related additive manufacturing techniques, BNNTs and/or BNNSs and dental ceramic powders are mixed with photopolymer resin. The resin mixture is subjective to laser or LED light irradiation for solidification. After the 3D printing, the products normally need multiple rounds of annealing at different temperatures. The first annealing at relatively lower temperatures is to remove the polymer or resin in the product. The second round of annealing at higher temperature is to sinter the product. [00043] Example 1 : BNNTs and/or BNNSs reinforced zirconia based dental ceramics

[00044] Zirconia powder containing different amounts of yttria (Y2O3) and/or glass and/or other ceramic particles are mixed with BNNTs and/or BNNSs at desired percentage using mechanical mixing, sonication and/or ball milling methods. The powder mixture is then pressed at room temperature or elevated temperatures. Conventional and unconventional machining and/or milling can be conducted at this stage if required. The subsequent annealing is conducted at 1200-1900°C in inert atmosphere. High-density and high-toughness of zirconia based dental ceramics with good translucency can be achieved. 1wt.% BNNTs reinforced zirconia showed an increased flexural strength up to 30% and fracture toughness up to 75%. The adding of BNNTs and/or BNNSs has no adverse effect on the translucency of the zirconia and related dental ceramics.

[00045] Example 2: BNNTs and/or BNNSs reinforced lithium disilicate based dental ceramics

[00046] Glass-forming components (such as quartz, lithium dioxide, phosphor oxide, alumina, potassium oxide, and others) and BNNTs and/or BNNSs are mixed using mechanical mixing, sonication and/or ball milling methods. The powder mixture is then melted at 1200-1900°C and poured into a mold and cooled to room temperature. Conventional and unconventional machining and/or milling can be conducted at this stage if required. The obtained material is heated again to 300-1000°C depending on the chemical composition, and kept at the temperature for sufficient time, allowing nucleation and precipitation of nanocrystals from the glass matrix. The cooling-down process in this round of heating needs to be slow.

[00047] Alternatively, glass-forming components (such as quartz, lithium dioxide, phosphor oxide, alumina, potassium oxide, and others) can be melted at 1200-1900°C without BNNTs or BNNSs and then poured into a mold and cooled to room temperature. Then the material is processed into powder form. The powder is mixed with BNNTs and/or BNNSs at desired percentage by mechanical mixing, sonication and/or ball milling methods. The mixture is pressed at room temperature or elevated temperatures. Conventional and unconventional machining and/or milling can be conducted at this stage if required. The obtained material is heated again to 300-1000°C depending on the chemical composition, and kept at the temperature for sufficient time, allowing nucleation and precipitation of nanocrystals from the glass matrix. The cooling process in this round of heating needs to be slow.

[00048] For example, 4wt.% BNNTs reinforced lithium disilicate showed an improved flexural strength up to 50% and fracture toughness by more than 100%. The addition of BNNTs and/or BNNSs has no adverse effect on the translucency of glassy ceramics with or without other fillers.

[00049] A person skilled in the art will appreciate that many embodiments and variations can be made without departing from the ambit of the present invention.

[00050] The dental restorative material can be applied directly to the tooth, or used in dental and orthopedic implants and associated components. The dental restorative material can be used in Ceramic/resin hybrid materials; Polymers such as denture resins; Dental and Orthopaedic implants both Titanium alloys and Ceramics such as zirconia oxide; Dental post systems for endodontically treated teeth; tooth supported adhesive bridges frameworks; composite resins and adhesive resin systems; tooth and implant supported bridge frameworks in titanium or ceramics; implant abutments in titanium and ceramic; printable ceramics and implants, especially titanium and ceramic.

[00051] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted by those skilled in the art.

[00052] Reference throughout this specification to ‘one embodiment’ or ‘an embodiment’ means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases ‘in one embodiment’ or ‘in an embodiment’ in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

Claims

The claims defining the invention are as follows:

1 . A dental restorative material including Boron Nitride.

2. A dental restorative material as claimed in claim 1 , wherein the Boron Nitride is in the form of a nanomaterial, preferably Boron Nitride Nanotubes (BNNTs) and/or Boron Nitride Nanotubes Nanosheets (BNNSs).

3. A dental restorative material as claimed in claim 1 , further including a reinforcing dental ceramic material.

4. A dental restorative material as claimed in claim 3, wherein the ceramic material includes any one or more of a: glassy ceramic, resin ceramic, glassy ceramic with other filler, polycrystalline ceramic, and polycrystalline ceramic with other filler.

5. A dental restorative material as claimed in claim 1 , further including any one or more of: lithia-silicate, lithium disilicate, lithium silicate, zinc oxide-, leucite- and zirconia- reinforced lithium disilicate, zirconia, zirconia oxide, yttria-stabilized zirconia, and alumina.

6. A dental restorative material as claimed in claim 1 , further including a metal, the metal preferably including Titanium.

7. A dental restorative material as claimed in claim 1 , further including Zirconia.

8. A method for manufacturing a dental restorative material, the method involving: mixing a material with Boron Nitride to form a mixture.

9. A method as claimed in claim 8, wherein the material includes a ceramic such as a glassy ceramic, or a glass-forming component.

10. A method as claimed in claim 8, wherein the material is in powder form and the mixing involve mechanical mixing, sonication, and/or ball milling.

11. A method as claimed in claim 8, wherein the mixing is performed in a dry or wet environment.

12. A method as claimed in claim 8, further involving pressing the mixture to form one or more blocks.

13. A method as claimed in claim 12, wherein the mixture is pressed at room temperature, or an elevated temperature, in a protective gaseous atmosphere.

14. A method as claimed in claim 12, further involving annealing and/or shaping the blocks.

15. A method as claimed in claim 8, further involving applying the mixture by inkjet printing, 3D gel-printing (3DGP), thermoplastic 3D printing (T3DP), or digital light processing stereolithography (SLA) or other additive manufacturing (3D printing) methods.

16. A method as claimed in claim 8, further involving applying the mixture by extrusion.

17. A method as claimed in claim 16, further involving: forming a slurry or solution by adding the mixture with any one or more of a: solvent, water, plastic, (photo)polymer, co-polymer, and catalyst; and extruding the slurry or solution onto a platform.

18. A method as claimed in claim 17, wherein the slurry or solution is extruded as a layer, and solidified before the application of another layer on the solidified layer, and so on, each layer being naturally self-solidified, or cured by heat, ultraviolet (UV) radiation and/or laser.

19. A method as claimed in claim 8, further involving: sintering a 3D printing including the mixture and annealing the sintered 3D printing; or mixing a photopolymer resin to form the mixture and subjecting the mixture to laser or LED light irradiation for solidification.

20. A dental restorative material formed in accordance with the method of claim 8.