HK1105867B - Ultrasonic curing of dental filling materials - Google Patents

Description

Ultrasonic curing of dental filling materials

Technical Field

The present invention relates to composite materials, in particular in the form of dental filling materials, which exhibit a low or even negligible volume shrinkage, or even a small expansion rate (e.g. up to 0.5%) when cured. The invention also relates to a method of controlling the volumetric shrinkage of a composite material when cured, and a method of repairing a tooth. The present invention also relates to ultrasonically curing dental filling materials. The invention further relates to a population of zirconia particles and a method of making such zirconia particles.

Background

Generally, shrinkage occurs when a polymerizable resin base material (e.g., a monomer or a mixture of monomers) is polymerized. Most of the critical shrinkage occurs after the gel point in the crosslinked material, or when the monomer-polymer mixture reaches the glass transition point in the linear thermoplastic material, as indicated, for example, by William j.bailey et al in "Ring-opening polymerization with Expansion in Volume", ACS Symposium 59, No.4, p.38-59 (1977). This publication also states that in polymer technology, for many applications, it is desirable that the polymerization should be accompanied by near zero shrinkage or even expansion. Examples of areas where near zero shrinkage is desired are: unstrained composites, potting resins, high gloss coatings, binders for solid propellants, impression materials, and structural adhesives. Zero shrinkage materials have found particular application in r.i.m. (reaction during molding) technology.

However, expansion is even desirable in areas such as precision casting, high strength adhesives, pre-stretched plastics, rock-cracking materials, elastomeric sealants, and dental fillings.

Dental plastic fillings are based on the principle of polymerization of a resin base containing monomers or oligomers. This can lead to shrinkage when the plastic dental filling material polymerizes. This means that small micro-cracks open between the tooth and the filling. The cracks may cause secondary caries or discoloration of the plastic filling. Microcracking results in a reduction in the mechanical properties of the composite. In the field of bone cements, shrinkage creates a porous structure between the bone cement and the implant cement. This can also cause mechanical degradation and implant failure. In the field of imprint materials, shrinkage can cause problems that may lead to dimensional incompatibility.

It is therefore clearly useful to utilize a filler material which counteracts the shrinkage which normally occurs when curing a polymeric resin base material and which can normally be used in a polymerization process (i.e. not limited to thermal curing for practical purposes).

Zirconia is widely used as a filler component in composite materials, such as dental materials. Zirconia can exist in three basic crystalline phase forms: tetragonal phase, cubic phase and monoclinic phase. Specific volume (density) of these three phases^-1) Respectively 0.16, 0.16 and 0.17cm³/g。

Summary of The Invention

The present invention provides a perfect solution to the above mentioned shrinkage problem, especially the shrinkage problem known in dental composites.

The main aspect of the present invention relates to composite materials, in particular dental filling materials.

Another broad aspect of the invention relates to a method of controlling the volumetric shrinkage of a composite material upon curing, and a method of repairing a tooth.

Further aspects relate to the use of a composite material as defined herein in medicine, particularly in dentistry, and the use of a filler component for the preparation of a composite material for the restoration of a mammalian tooth.

Still further aspects relate to populations of zirconia particles and methods of making the same.

Brief Description of Drawings

Figure 1 shows a molar tooth repaired by the method of the present invention.

Detailed Description

As noted above, the present invention provides novel composite materials that can be used in applications where volume shrinkage upon curing is undesirable or even inhibited.

More particularly, the present invention provides a composite material comprising one or more fillers and a polymerizable resin base, wherein said one or more fillers comprise at least one filler component which is present in a metastable first phase and which is capable of undergoing a martensitic transformation to a stable second phase, wherein the volume ratio between said stable second phase and the metastable first phase of said filler component is at least 1.005.

A particular feature of the present invention is that the martensitic transformation of the filler component can be triggered by a triggering mechanism (see further below).

Many polymer resin bases (see also below) are known to exhibit volume shrinkage when cured. It is therefore a particular feature of the present invention that there is a filler component which reduces or eliminates the volume shrinkage caused by the polymerizable resin base, or even counteracts this volume shrinkage, to the extent that the composite exhibits net volume expansion when the polymer resin base is cured.

Thus, in a preferred embodiment of the composite, the resin base component, when polymerized and in the absence of any compensating effect from the filler component or components, causes a volume shrinkage (Δ V) of the composite of at least 0.50 percent_{Resin composition}) And wherein when said resin base is polymerized and when said filler component is phase-converted, said composite exhibits an uncompensated volumetric shrinkage (AV) relative to that due to the resin base_{Resin composition}) Total volumetric shrinkage (Δ V) of at least 0.25% less dots_{General assembly}). More particularly, the volume shrinkage (Δ V)_{Resin composition}) Is at least 1.00%, such as at least 1.50%, and the total volume shrinkage (Δ V)_{General assembly}) At least 0.50% less than the uncompensated volumetric shrinkage, for example 1.00% less.

Alternatively, the present invention provides a composite material comprising one or more fillers and a polymerizable resin base, wherein the one or more fillers comprise at least one filler component comprising metastable zirconia in either the tetragonal or cubic phase, wherein the resin base, when polymerized and in the absence of any compensatory action from the one or more filler components, causes a volume shrinkage (av) of the composite material of at least 0.50%_{Resin composition}) And wherein when said resin base is polymerized and when said filler component is phase-converted, said composite exhibits an uncompensated volumetric shrinkage (AV) relative to that due to the resin base_{Resin composition}) Total volumetric shrinkage (Δ V) of at least 0.25% less dots_{General assembly})。

The composite material typically comprises 5-95% or 10-90% by weight of one or more fillers and 5-95% or 10-90% by weight of a polymerisable resin base, especially 30-95% or 30-90% by weight of one or more fillers and 5-70% or 10-70% by weight of a polymerisable resin base.

The composite material typically comprises, by volume, 20 to 80% of one or more fillers, and 20 to 80% of a polymerisable resin base, for example 25 to 80% or 25 to 75% of one or more fillers and 25 to 75% of a polymerisable resin base.

Preferably, the composite material is substantially solvent-free and water-free. The term "substantially free of solvent and free of water" means that the composite material comprises less than 4.0%, such as less than 1.0%, or less than 0.5% by weight of solvent and/or water.

Filler/filler component

In view of the foregoing, it will be apparent that one or more fillers, and in particular one or more filler components, are important components in composite materials.

Fillers are commonly used in combination with polymeric materials to provide the mechanical properties required of such materials, such as abrasion resistance, opacity, color, radio-opacity, hardness, compressive strength, compressive modulus, flexural strength, flexural modulus, and the like.

The term "filler" should be understood in the general sense that fillers conventionally used in polymer-bound composites may also be used in the context of the present invention. The polymerizable resin base (see further below) can be said to constitute a "continuous" phase in which the filler is dispersed.

An illustrative example of a filler is barium sulfate (BaSO)₄) Calcium carbonate (CaCO)₃) Magnesium hydroxide (Mg (OH)₂) Quartz (SiO)₂) Titanium dioxide (TiO)₂) Zirconium oxide (ZrO)₂) Alumina (Al)₂O₃) Lanthanum oxide (La)₂O₃) Amorphous silica, silica-zirconia, silica-titania, barium oxide (BaO), barium magnesium aluminosilicate glass, Barium Aluminoborosilicate Glass (BAG), barium-, strontium-or zirconium-containing glass, ground glass, YtF₃Or YbF₅Particulates, glass fibers, metal alloys, and the like. Metal oxides, e.g. titanium dioxide (TiO)₂) And zirconium oxide (ZrO)₂) Alumina (Al)₂O₃) Lanthanum oxide (La)₂O₃) Constitute a particularly useful group of fillers for use in the composite material of the invention.

The content of the one or more filler materials in the composite material is typically 5-95%, alternatively 10-90%, such as 30-95%, for example 40-95%, such as 60-95% by weight. It will be appreciated that a combination of two or more fillers may be desirable, as may a fairly broad particle size distribution of the fillers, in order to allow for dense packing of the fillers, thus facilitating incorporation of high levels of fillers into the composite. Typically, the composite has a distribution of one or more fine particle sizes plus fine and/or nano-sized fillers (5-15%). This distribution allows for more efficient packing, so that smaller particles will fill the spaces between large particles. This provides filler contents of, for example, up to 77-87 wt.%. An example of a filler with a particle size distribution is a structured microfiller of 0.4 microns and the distribution is as follows: 10% by weight of the filler particles have an average particle size of less than 0.28 microns; 50% by weight of the filler particles have an average particle size of less than 0.44 microns; 90% by weight of the filler particles have an average particle size of less than 0.66. mu.m.

Typically, the filler has a particle size of 0.01 to 50 microns, for example 0.02 to 25 microns, and may comprise nano-sized fillers having a maximum particle size of 100 nm.

In some embodiments, the filler has a particle size of 0.2 to 20 microns with some very fine particulates of about 0.04 microns. As an example, rather large filler particles may be used in combination with amorphous silica to provide dense packing of the filler.

The term "particle size" is intended to refer to the shortest dimension of the particulate material in question. In the case of spherical particles, the diameter is the "particle size", while for fibrous or needle-shaped particulate materials, the width is the "particle size". It will of course be appreciated that an important feature of such particles is the actual crystal size, since under the given conditions the crystal size (rather than the particle size) is decisive for the preferred crystalline phase (see also below).

In embodiments where the composite is used in dental applications, particularly useful fillers are zirconia, amorphous silica, ground barium-, strontium-, or zirconium-containing glasses, ground acid-etchable glasses, YtF₃Or YbF₅Microparticles, glass fibers, and the like.

The one or more fillers include at least one filler component. The term "filler component" is intended to mean a filler or a fraction of a filler having specific physical properties, i.e. the inherent ability to compensate (by expansion) for the volume shrinkage caused by polymerizing and curing the resin base. Thus, some fillers, such as zirconia, may be included in the composite material, and some fraction of these filler particles may have specific physical properties, i.e. be present in metastable crystalline phases (see below), thus constituting the filler component.

The particle size of the filler component is typically 0.01 to 50 microns.

The filler component typically comprises 20 to 100%, such as 30 to 100%, for example 40 to 100% or 50 to 100% by weight of the total weight of the filler or fillers.

The filler component typically comprises from 15 to 90%, such as from 25 to 90%, such as from 30 to 90%, more particularly from 60 to 85% of the total weight of the composite, when calculated on the total weight of the composite.

One or more filler elements are present as a metastable first phase and are capable of undergoing a martensitic transformation to a stable second phase, wherein the volume ratio between the stable second phase and the metastable first phase of the filler element is at least 1.005, such as at least 1.01, or even at least 1.02 or at least 1.03.

In the context of the present invention, the term "metastable first phase" means that the filler component present in this phase has a higher free energy than the free energy of the second phase and that the activation energy barrier (F) must be overcome before a transition from the first phase (high energy state) to the second phase (low energy state) can take place. Therefore, the phase transition does not spontaneously proceed.

The phase transformation is martensic (martensic), which is defined to mean that the crystal structure of the filler component does not require additional atoms to undergo transformation. Thus, the transition can be very fast, almost immediate.

The expression "free energy" refers to the sum of the free energies contributed by the bulk of the particle, the surface of the particle and the strain. For practical purposes, only the free energy of the bulk of the particles and the surface of the particles need to be considered.

Thus, when considering various materials as potential filler ingredients, there are associated three main requirements to consider:

1. the first requirement of the filler component is that the second crystal phase in the selected particle size range is "stable" under "standard" conditions, i.e. standard pressure (101.3kPa) and at least one temperature of 10-50 ℃, i.e. corresponding to the conditions when the product is used.

2. A second requirement of the filler component is that the metastable first crystalline phase of the filler component may be present under the same "standard" conditions.

3. A third requirement of the filler component is that the specific volume ratio between said stable second phase and said metastable first phase of said filler component is at least 1.005.

The expression "stable" refers to a phase that does not spontaneously transform under the conditions required for the filler composition to transform from the first metastable phase. Thus, a "stable" phase need not always have the "global" lowest free energy phase, but often does so.

Filler ingredients relevant in the context of the present invention include the specific crystalline forms of some of the above-mentioned fillers, especially metal oxide fillers. A very useful example is ZrO₂(see in particular further below in the section "population of zirconia particles"). Zirconia can exist in three main crystalline phase forms:tetragonal phase, cubic phase and monoclinic phase. Specific volume (density) of these three phases^-1) Respectively 0.16, 0.16 and 0.17cm³(ii) in terms of/g. Thus, the volume ratio of the monoclinic phase (second phase) to one of the first two phases (first phase) is higher than 1.005 (i.e. 1.045 and 1.046, respectively). Under standard conditions, the tetragonal and cubic phases have higher bulk energy than the monoclinic phase.

Illustrative examples of filler components are:

metastable tetragonal zirconia (0.16 cm ═ by volume)³/g) which can be converted into the monoclinic phase (specific volume of 0.17 cm)³(v/g), (volume ratio ═ 1.045);

metastable cubic phase zirconia (0.16 cm ═ by volume)³/g) which can be converted into the monoclinic phase (specific volume of 0.17 cm)³(v/g), (volume ratio 1.046);

lanthanum sesquioxide (Ln)₂O₃) Wherein Ln is Sm-Dy. At 600-2200 ℃, the monoclinic phase is transformed into the cubic phase, and the volume expansion is 10 percent.

Nickel sulfide (NiS), transformed from rhombohedral to hexagonal at 379 ℃ with a volume expansion of 4%. The density was 5.34 g/ml.

Dicalcium silicate (wollastonite) (Ca)₂SiO₄) At 490 c, the transition from the monoclinic phase to the rhombohedral phase was 12% by volume expansion and the density was 3.28 g/ml.

Boric acid lutetium (LuBO)₃). At 1310 ℃, the hexagonal phase is transformed into the rhombohedral phase, with a volume expansion of 8%.

At standard temperature and pressure, the surface energy of the tetragonal phase of zirconia is lower than that of the monoclinic phase, which results in tetragonal (pure) zirconia crystals that are stable at room temperature. For the difference in surface energy, the crystals must be small (<10nm) to compete for the difference in bulk energy of the tetragonal and monoclinic phases.

For metastable tetragonal or cubic zirconia the particle size is preferably in the range 5-80000nm, e.g. 20-2000nm, but it is believed that an average particle size in the range 50-1000nm, e.g. 50-500nm, provides the best balance between optical and structural properties.

In one embodiment, the filler component is capable of undergoing a martensitic transformation under the influence of ultrasound.

In view of the above, the filler component preferably comprises metastable tetragonal or cubic crystalline phase of zirconium oxide (ZrO)₂) (see further below for part "zirconia particle population").

In another embodiment, the filler component is capable of undergoing a martensitic transformation upon exposure to a chemical trigger.

In some cases, the activation energy barrier (F) is not large enough to prevent premature transition from the first phase to the second phase. This can lead to spontaneous transformation of the composite upon storage. Thus, in some embodiments, it is advantageous to stabilize the natural filler ingredient in order to obtain a metastable phase that does not undergo a more or less spontaneous, i.e. premature, transformation of the composite material on storage. The stabilisation of the metastable phase may be achieved, for example, by doping, by surface-modified filler particles, etc., as will be explained below.

Doping

Many crystalline phases can be stabilized using dopant materials. Generally, as the content of the dopant increases, the phase is more stable. In terms of energy, the higher the activation energy barrier (F), the more dopants are used. However, in order to trigger a phase transition, the activation energy barrier must be low enough for the triggering method to overcome the activation energy barrier, but high enough so that the transition does not occur spontaneously.

Typically up to 20 mol% of one or more dopants are used to stabilize the zirconia. Stabilizers such as calcium, cerium, barium, yttrium, magnesium, aluminum, lanthanum, cesium, gadolinium, and the like, as well as oxides and combinations thereof, may be used to stabilize the zirconia. More specifically, for some useful dopants, the recommended mol% content is: y is₂O₃(1-8％)、MgO(1-10％)、CaO(1-18％)、CeO₂(1-12%) and Sc₂O₂(1-10%). For example, 0-1% Y₂O₃Typically do not sufficiently stabilize the tetragonal and cubic phases of zirconia, and such doped zirconia would therefore still spontaneously undergo a phase transition to the monoclinic phase at room temperature. Addition of too high a content of Y₂O₃E.g., greater than or equal to 8%, will stabilize the tetragonal and cubic phases to such an extent that the activation energy barrier is too high to overcome with most triggering methods. At some point between the activation energy barriers, the transition may be triggered as described below. Adding more dopant makes triggering more difficult and therefore slower. Adding less dopant makes zirconia unstable and unusable as a filler component. It should be noted that commercial grade zirconia contains a small amount of hafnium. As mentioned above, this small amount of hafnium is negligible because hafnium is considered an integral part of the zirconia.]

In a preferred embodiment, by using a compound selected from Y₂O₃、MgO、CaO、CeO₂And Sc₂O₃Thereby stabilizing the metastable phase of zirconia.

ZrO₂Recommended content of dopant is Y₂O₃(1-5%), MgO (1-5%), CaO (1-10%) and CeO₂(1-6%), more particularly about 1-2%.

Surface modification

The surface energy can be changed by surface modification. By modifying the surface by adsorption chemistry, the surface energy of the first phase can be reduced so that the sum of the surface energy and the bulk energy is lower than the surface energy and the bulk energy of the second phase, thus "flipping" the order of stability of the first and second phases. In this way, "metastability" of the first phase occurs because the first phase is "stable" as long as the chemical component is adsorbed thereto. Thus, the first phase is stabilized until the surface modification is altered or removed by, for example, treatment with a chemical trigger.

Polymerizable resin base

Another important component of the composite is the polymerizable resin base.

The term "polymerizable resin base" is intended to mean a composition or mixture of ingredients, e.g., monomers, dimers, oligomers, prepolymers, etc., that can undergo polymerization to form a polymer or polymer network. The polymer is typically referred to as an organic polymer. The resin base is typically classified according to the main monomer component.

The polymerizable resin base is typically present in the composite in an amount of 5 to 95% by weight, alternatively 10 to 90%, for example 10 to 70%, for example 10 to 60%, for example 10 to 40%.

Essentially any polymerizable resin base may be used in the context of the present invention. The polymerizable resin base components of particular interest are of course such that, when used without compensating filler components, they will cause the composite to shrink in volume once cured.

The term "curing" is intended to mean the polymerization and hardening of the resin base.

Examples of resin bases are methyl acrylate, methyl methacrylate, ethylene glycol, ethylene succinate, caprolactam, acrylic acid, acrylonitrile, vinyl acetate, 2-vinylpyridine, ethylene oxide, ethylene glycol, acetaldehyde, lactones, glycols + acids, e.g. ethylene glycol + terephthalic acid, and the like.

One preferred group of hardenable resins includes materials having free radical reactive functional groups, and includes monomers, oligomers, and polymers having one or more ethylenically unsaturated groups. Alternatively, the hardenable resin may be a material selected from the group of resins including cationically active functional groups. Alternatively, the hardenable resin may be a material having reactive functional groups that can condense upon chemical reaction.

Particularly interesting resin bases for dental applications are those based on compounds selected from the group consisting of Methacrylic Acid (MA), Methyl Methacrylate (MMA), 2-hydroxyethyl methacrylate (HEMA), triethylene glycol dimethacrylate (TEGDMA), bisphenol a-glycidyl dimethacrylate (BisGMA), bisphenol a-propyl dimethacrylate (BisPMA), polyurethane-dimethacrylate (UEDMA) and HEMA condensed with butanetetracarboxylic acid (TCB), and combinations based on the above mentioned compounds. Such a resin base is disclosed and discussed, for example, in US 6572693. Particularly useful combinations of compounds are TEGDMA and BisGMA, see for example US 3066112.

Other Components of the composite Material

The composite may include other components that provide beneficial rheological, cosmetic, etc. properties. Examples of such other components are dyes, fragrances, polymerization initiators and co-initiators, stabilizers, fluoride release materials, sizing agents, biocides, flame retardants.

Thus, the resin base may include initiators and co-initiators, and illustrative examples of such compounds particularly for dental applications are Benzoyl Peroxide (BPO), Camphorquinone (CPQ), phenylpropanedione (PPD), and N, N-bis (2-hydroxyethyl) p-toluidine (DEPT), ethyl N, N-dimethyl-p-aminobenzoate (DAEM).

The weight content of the other components in the composite material is typically 0-10%, such as 0-5%, for example 0-4% or 1-5%.

Dental filling material

In view of the above, the present invention also provides a dental filling material in the form of a composite material as defined above. In particular, the filler component in the composite material comprises zirconium oxide (ZrO) in the form of a metastable tetragonal or cubic crystalline phase₂)。

In a particularly interesting embodiment, the dental filling material consists of:

40-90% by weight of one or more fillers, wherein said one or more fillers comprise at least one filler component comprising metastable zirconia in the form of tetragonal or cubic crystalline phases.

10-60% by weight of a polymerizable resin base based on one or more compounds selected from the group consisting of Methacrylic Acid (MA), methacrylate (MMA), 2-hydroxyethyl methacrylate (HEMA), triethylene glycol dimethacrylate (TEGDMA), bisphenol a-glycidyl dimethacrylate (BisGMA), bisphenol a-propyl dimethacrylate (BisPMA), polyurethane dimethacrylate (UEDMA) and HEMA condensed with butanetetracarboxylic acid (TCB);

0-5% by weight of additives; and

0-4% by weight of solvent and/or water.

In order to avoid premature curing of the polymerizable resin base, it is advantageous to prepare and store the composite as a two-component material to be mixed immediately before use.

Use of composite materials

The composite material can be used and cured essentially as a conventional composite material of the same type, except for the fact that: should allow for control of the martensitic transformation in conjunction with curing of the resin base.

It is believed that the martensitic transformation can be activated by physical means (e.g., application of mechanical pressure, tension, ultrasound, Roentgen radiation, microwaves, longitudinal waves, electromagnetic radiation such as light, near infrared radiation, heat, etc.), or by chemical means (e.g., modification of the surface free energy by contacting the surface of particles of the filler component with a chemical, such as a component or additive in the composite material, such as water).

It will be appreciated that the martensitic transformation of the filler component should preferably take place together with the curing (polymerization and hardening) of the resin base component. However, since the crystals are small, the expansion due to the phase transition does not cause deterioration of the mechanical properties of the cured compound. Thus, after curing, a transition will occur triggered by a slow mechanism, such as diffusion of water into the cured compound or internal tensile stress built up by curing shrinkage. Triggering the transition prior to curing is undesirable because there is little or no loss of volume compensation (depending on how much transition is made before curing is initiated). The ultrasonic triggering mechanism may be of particular interest because it uses a cavity-triggered transition. In order to have a cavity, the molecules should preferably be able to move, e.g. at least partially in an uncured state, so that ultrasonic triggering should preferably occur during curing of the composite material.

In one embodiment, the martensitic transformation of the filler component is initiated by the application of ultrasound. Ultrasound is defined herein as energy having a frequency of 10kHz to 10 MHz. More typically, the ultrasound used has a frequency of 10-1000kHz, such as 15-100kHz, and most conventional devices operate at a frequency of 15-50 kHz. An example of a conventional device is e.g. an ultrasonic scaler for removing dental tartar in dentistry.

Using (10-1000kHz and power higher than 1W/cm)²Of (d) a metastable phase of the sonication in the liquid/flowable state, creating a microcavity. The energy in these cavities is above the activation energy barrier and triggers a phase transition. The energy is introduced, for example, in the form of free radicals or by filler particle collision for surface modification.

Example (c): treatment of tetragonal zirconia crystals with ethanol in an ultrasonic bath (400kHz) produced a phase transition. The dispersion of zirconia particles in the resin base can be phase-converted by ultrasound using a descaler, i.e. a device used by the dentist to remove dental calculus.

In another embodiment, the martensitic transformation of the filler component is initiated by exposing the surface of the filler component to a chemical trigger.

In order to perform a phase transition of a system in which the first phase is metastable, but in which the activation energy barrier is high (because the surface energy of the first phase is low), the activation energy barrier may be lowered by surface modification. Activation of the phase transition can be initiated by surface modification. The activation energy barrier may be the energy barrier required to perform a surface modification that makes the surface energy of the phase higher (or makes it more similar to the surface of the second phase).

Example (c): it is known to treat tetragonal zirconia with a compound containing at least one lone pair of electrons to induce phase transformation. The mechanism of this process has not been demonstrated, but it involves some surface modification that triggers phase transition. Identification of Water (H)₂O), acid and base (e.g., 5M HC1O₄And 5M NaOH) and glycerol at 95 ℃ triggered the maximum conversion of the phase transition within 120 hours. Other non-aqueous solvents, e.g. acetonitrile (CH)₃CN), ethanol (C)₂H₅OH) and formamide (NH)₂CHO), smaller conversion rate that triggers phase transition under the same conditions. Non-aqueous solvents, e.g. toluene (C) having no lone pair of electrons₆H₅CH₃) And cyclohexane (C)₆H₁₂) The phase transition cannot be triggered under the same conditions.

Example (c): the zirconia particles are dispersed in a resin base. The zirconia particles must have a size and doping level such that the aqueous phase transforms the particles. The dispersion was then kept dry in a test tube. When applied as a filling material to teeth, water from the teeth and normal air humidity within the mouth will trigger a phase transition. In this application, the dispersion can be used only in the form of a thin layer to provide water to the zirconium oxide particles. Since the crystals are small, the expansion due to the phase transition does not deteriorate the mechanical properties of the cured compound. Thus, the triggered transition may occur after curing by a slow mechanism, such as diffusion of water into the cured compound.

Another example is: the zirconia particles are dispersed within a monomer-containing resin base that releases water during the curing process. These monomers may contain both amino and carboxyl groups, such as omega-aminocarboxylic acids, which eliminate water in a condensation process or via an esterification reaction between monomers containing acid and alcohol groups. When the curing process is started, the water released from the condensation process will initiate a phase transformation of the zirconia particles, thus compensating for the shrinkage caused by the polymerization.

In one variant, the chemical trigger is a component of the polymerizable resin base.

In another variant, the chemical trigger is the product produced when polymerizing the resin base.

In yet another embodiment, the martensitic transformation of the filler component is initiated by exposing the filler component to a tensile stress. For ceramic sintered zirconia, a tensile stress of 200MPa was demonstrated to trigger the phase transition. When curing dental fillings, tensile stresses of up to 20MPa are observed. The preparation of less stable, metastable zirconia particles will reduce the force required to initiate phase transformation within the zirconia.

Example (c): the zirconia dispersion within the resin base may be cured slightly. Curing causes shrinkage that results in tensile stress, which reduces the stress by phase-shifting the zirconia particles.

Method of the invention

In view of the above, the present invention also provides a method of controlling volumetric shrinkage of a composite material upon curing, the method comprising the steps of:

(a) providing a composite material comprising one or more fillers and a polymerizable resin base, wherein the one or more fillers comprise at least one filler component present in a metastable first phase and capable of undergoing a martensitic transformation to a stable second phase, wherein the volume ratio between the stable second phase and the metastable first phase of the filler component is at least 1.005;

(b) polymerizing and curing the resin base component and causing the filler component to undergo a martensitic transformation from said first metastable phase to said second stable phase.

Preferably, the filler component should be triggered to undergo a martensitic transformation either simultaneously with or after curing in order to fully benefit from the volume expansion of the filler component.

In one embodiment, the martensitic transformation of the filler component is initiated by the application of ultrasound (10-1000 kHz). In this case, the martensitic transformation is preferably triggered at the same time as or after initiation of the curing, but before completion of the curing.

In another embodiment, the martensitic transformation of the filler component is initiated by exposing the surface of the filler component to a chemical trigger. In this case, the martensitic transformation is preferably triggered at the same time as or after initiation of the curing, but before completion of the curing.

More specifically, the present invention further provides a method of repairing a tooth, the method comprising the steps of:

(a) preparing a cavity in a tooth;

(b) filling the cavity with a dental filling material as defined above; and

(c) the resin base in the dental filler material is polymerized and cured and the filler component in the dental filler material undergoes a martensitic transformation from a first metastable phase to a second stable phase.

The method of restoring a tooth as defined above may generally include some or all of the steps listed in example 9.

In one embodiment, the martensitic transformation of the filler component is initiated by the application of ultrasound (10-1000 kHz). In another embodiment, the martensitic transformation of the filler component is initiated by exposing the surface of the filler component to a chemical trigger.

More generally, the invention also relates to the composite material as defined herein for use in medicine, especially dentistry.

The invention also relates to the use of a filler component in the preparation of a composite material for the restoration of a mammalian tooth, wherein the filler component has a metastable first phase and is capable of undergoing a martensitic transformation into a stable second phase, wherein the volume ratio between the stable second phase and the metastable first phase of the filler component is at least 1.005. The filler component and the composite material are preferably as defined herein.

Martin transformation and curing of resin base Components by ultrasonic bonding

The inventors have also found that inducing martensitic transformation of the filler component by means of the application of ultrasound can be advantageously combined with curing the resin base component by means of ultrasound.

It is believed that applying ultrasound will provide the following advantages: the curing process, which results in a reduction in the net volume of the body, will be offset by the volume expansion caused by the martensitic transformation of the filler component.

Thus, in a further embodiment of the above method, the polymerization of the resin base is initiated by applying ultrasound.

The ultrasound used (as above) is typically 10kHz to 10MHz, preferably 15 to 50kHz, for example 20 to 50 kHz. Lower frequency sound devices may also be used because the cavity is created by sound wave propagation, however, frequencies below 15 or 20kHz may be heard by normal human ears and may therefore be inconvenient to use.

As regards the power of the ultrasound employed, it is typically from 0.1 to 500W/cm²E.g. 30-100W/cm². On the one hand, the ultrasonic power should be high enough to create a cavity and, on the other hand, low enough not to damage the teeth. Ultrasound is typically applied through a descaler. The ultrasound may be applied directly to the bulk of the resin base or indirectly by conduction of sound waves through a medium to the resin. For dental applications, suitable media are the teeth in which the dental filling material is placed or the metal matrix typically used to prepare cavities in molars.

The application of ultrasound with the aid of the initiated polymerization is typically carried out for a period of 10 to 300 seconds, for example 20 to 120 seconds.

Although it is considered that the polymerization initiator is not strictly necessary, it is considered that the polymerizable resin base favorably includes a polymerization initiator such as one selected from a peroxy group-containing compound and an azo group-containing compound (e.g., AIBN).

On the other hand, it is believed that the polymerization accelerator/co-initiator (e.g., EDMAB 4-ethyl dimethylaminobenzoate) may be omitted. A co-initiator is often added to initiate at room temperature. Conventional non-photopolymerizable dental materials are based on two-component resin systems. The initiator, e.g. benzoyl peroxide, and the co-initiator, e.g. EDMAB 4-ethyl dimethylaminobenzoate, are kept separate until use, and in use, the two resins are mixed together. The addition of a co-initiator to the initiator allows the monomer to be cured at room temperature. Thus, in contrast to conventional non-photopolymerizable dental filling materials, the dental filling materials in some embodiments of the present invention can be prepared, stored and shipped as a one-component system.

A general advantage of this aspect of the invention is that ultrasound has a large penetration depth, packing of filler particles can be improved, and curing of the resin base can be carried out while martensitic transformation of the filler component takes place, compared to normal photo-curing (UV-curing) used in dentistry. The application of ultrasound to the filler-based resin causes the filler particles to move, thus allowing the particles to find optimal packing within the cavity. This means that even small cracks in the cavity will be filled with filler particles (and monomer resin).

Most organic polymers are prepared from monomers containing reactive double bonds that undergo chain extension or addition reactions. The most straightforward method of preparation is by free radical initiation. At high power (at least 1W/cm)²) The lower ultrasound creates a cavity. As ultrasound passes through the liquid, the expansion cycle exerts a negative pressure on the liquid, thereby pushing the molecules apart from each other. Once prepared, the cavity absorbs energy and grows. At high or low sound intensities, once the cavity overgrows, it can no longer absorb energy efficiently. Without energy input, the cavity itself can no longer be maintained. The surrounding liquid gushes in and bursts inside the cavity. It is the internal bursting of the cavity that creates an unusual environment for chemical reactions. The bursting of the cavity bubble generates high temperatures and pressures, which are described in the literature, because of the generation of free radicals using ultrasound. Freedom of movementThe radicals then initiate a polymerization reaction, resulting in a fully cured dental material.

Curing of resin base in dental filling materials by means of ultrasound

The inventors have also found that curing the dental filling material itself by means of ultrasound provides some advantages compared to using conventional curing methods, in particular UV-curing, especially in view of the fact that: ultrasound has a large penetration depth compared to normal light (e.g., ultraviolet light).

Accordingly, in a further aspect, the present invention provides a method of repairing a tooth, the method comprising the steps of:

(a) preparing a cavity in a tooth;

(b) filling the cavity with a dental filling material comprising a polymerizable resin base; and

(c) applying ultrasound to the dental filling material in order to initiate curing of the resin base component in the dental filling material.

About frequency (10kHz-10MHz) and power (0.1-500W/cm)²) And application time (10-300 seconds), further as defined above.

The filling material is in particular as defined above, and thus, in one embodiment, the dental filling material comprises:

30-90% by weight of one or more fillers; and

10-70% by weight of a polymerizable resin base.

More particularly, the one or more fillers include at least one filler component that exists as a metastable first phase and is capable of undergoing a martensitic transformation to a stable second phase, wherein the volume ratio between the stable second phase and the metastable first phase in the filler component is at least 1.005.

Preferably, the filler component should be triggered to undergo a martensitic transformation, either simultaneously with or after curing, in order to fully benefit from the volume expansion of the filler component. More preferably, the martensitic transformation is triggered simultaneously with or after initiation of cure, but before completion of cure.

In one embodiment, such filler component preferably comprises metastable tetragonal or cubic phase zirconia (ZrO)₂) For example, wherein by using a compound selected from Y₂O₃、MgO、CaO、CeO₂And Sc₂O₃To stabilize the metastable phase of zirconia. Thus, the particle size, content, etc. of the filler component are further as described herein.

However, in one embodiment, the polymerizable resin base includes a polymerization initiator, for example, a polymerization initiator selected from a peroxy group-containing compound and an azo group-containing compound (e.g., AIBN).

Zirconia particle group

Metastable zirconia has been found to be particularly suitable as a filler in composite materials. In particular, zirconia which allows martin to convert to a stable second phase has been found to be particularly useful in order to counteract the shrinkage which normally occurs in composites.

Thus, a further aspect of the invention relates to a population of zirconia particles having an average particle size in the range 50 to 2000nm, said particles being present in a metastable first phase and being capable of undergoing a martensitic transformation to a stable second phase, said transformation progressing to an extent of at least 80% within 300 seconds when tested according to the "zirconia particles transformation test" defined herein.

Furthermore, the present invention relates to a method for producing such a zirconia particle group.

The population of zirconia particles defined above exists in a metastable first phase and is capable of undergoing a martensitic transformation to a stable second phase. Preferably, the volume ratio between the stable second phase and the metastable first phase of the zirconia particles is at least 1.005, such as at least 1.01, or even at least 1.02 or at least 1.03.

As mentioned above, the population of particles of the first aspect of the invention is present as a metastable first phase and is capable of undergoing a martensitic transformation to a stable second phase, the transformation progressing to an extent of at least 80% in 300 seconds when tested according to the "zirconia particles transformation test" defined herein. Preferably, the transition is carried out to an extent of at least 80% within 10-100 seconds, for example within 20-60 seconds.

Therefore, when considering various crystal forms and particle sizes of zirconia particles, two main requirements are considered in relation:

1. a first requirement of the zirconia particles is that the second crystalline phase within the selected particle size range is "stable" under "standard" conditions, i.e. standard pressure (101.3kPa) and at least one temperature of 10-50 ℃, i.e. corresponding to the conditions when using the product (typically a composite).

2. A second requirement of zirconia particles is that the metastable first crystalline phase of the zirconia particles may be present under the same "standard" conditions.

For metastable tetragonal or cubic phase zirconia, the particle size is preferably in the range of 50-2000nm, but an average particle size in the range of 50-1000nm is believed to provide the best balance between optical and structural properties.

The zirconia particles can undergo martensitic transformation under the influence of ultrasound. The zirconia particles may also undergo a martensitic transformation when exposed to a chemical trigger.

In view of the above, the filler component preferably comprises metastable tetragonal or cubic phase zirconia (ZrO)₂)。

Stabilization of the metastable phase may be achieved, for example, by doping, by surface-modified zirconia, or the like, such as described herein above.

Detailed description of the preferred embodiments

In order to obtain a phase which can undergo rapid phase transitionConverted zirconia particles, large surface area, e.g. 10-250m²G, even better 50-200m²The particles of/g are preferred and may also be obtained in the manner described herein.

Thus, a further aspect of the invention relates to a mean particle size of from 50 to 2000nm and a BET surface area of from 10 to 250m²A population of zirconia particles, the particles being present in a metastable first phase and capable of undergoing a martensitic transformation to a stable second phase.

Preferably, this population of zirconia particles can undergo martensitic transformation to a degree of at least 80% in 300 seconds when tested according to the "zirconia particles transformation test" defined herein.

As mentioned above, the average particle size is typically in the range of 50-2000nm, for example 50-1000nm, especially 100-600 nm.

Although the zirconia particles typically have a particle size of 50-2000nm, the particles are believed to include smaller crystalline regions having a uniform crystal lattice. Thus, it is preferred that the particles have a crystalline domain size of 8-100nm, for example 8-50nm, for example 8-20 nm.

Furthermore, it is believed that the zirconia particles advantageously may have some porosity so as to allow for rapid transformation (as described herein). Therefore, the average pore size of the particles is preferably 10 to 50 nm.

With respect to porosity, zirconia particles having a porosity of 0.1-20%, such as 0.2-10%, are considered to be of particular interest.

A particular group of particles of interest are those in which the zirconia particles have the following characteristics:

a. an average particle size of 50-2000nm and a BET surface area of 10-250m²Per g, or

b. An average particle size of 50-1000nm and a BET surface area of 10-250m²Per g, or

c. An average particle size of 100-600nm and a BET surface area of 10-250m²Per g, or

d. An average particle size of 50-2000nm and a BET surface area of 50-200m²Per g, or

e. An average particle size of 50-1000nm and a BET surface area of 50-200m²Per g, or

f. An average particle size of 100-600nm and a BET surface area of 50-200m²Per g, or

g. An average particle size of 50-2000nm and a BET surface area of 50-80m²Per g, or

h. An average particle size of 50-1000nm and a BET surface area of 50-80m²Per g, or

i. An average particle size of 100-600nm and a BET surface area of 50-80m²Per g, or

j. An average particle size of 50-2000nm and a BET surface area of 75-150m²Per g, or

k. An average particle size of 50-1000nm and a BET surface area of 75-150m²Per g, or

An average particle size of 100-600nm and a BET surface area of 75-150m²Per g, or

m. average particle size of 50-2000nm and BET surface area of 125-200m²Per g, or

n. average particle size of 50-1000nm and BET surface area of 125-200m²Per g, or

o.average particle size of 100-600nm and BET surface area of 125-200m²Per g, or

p. average particle size of 100-350nm and BET surface area of 50-80m²Per g, or

q. an average particle size of 250-500nm and a BET surface area of 50-80m²Per g, or

r. average particle size of 400-600nm and BET surface area of 50-80m²Per g, or

s, an average particle size of 100-350nm and a BET surface area of 75-150m²Per g, or

t. average particle size of 250-500nm and BET surface area of 75-150m²Per g, or

u.average particle size of 400-600nm and BET surface area of 75-150m²Per g, or

v. average particle size of 100-350nm and BET surface area of 125-200m²Per g, or

w. average particle size of 250-500nm and BET surface area of 125-200m²Per g, or

x, average particle size of 400-600nm and BET surface area of 125-200m²/g。

Preparation of zirconia particle group

The population of particles defined above may be prepared by one of the methods described below.

Method A

One method of preparing the population of zirconia particles defined above involves heating amorphous zirconia over a narrow temperature range. Accordingly, the present invention provides a process for preparing a population of zirconia particles as defined above, said process comprising the steps of: a sample of amorphous zirconia is heated to a temperature within the crystal formation temperature and not above the transition temperature of the zirconia from the tetragonal to the monoclinic phase (both of which can be measured by DSC or XRD). Heating the sample to a temperature below the crystal formation temperature will result in a sample with little or no crystals and no potential for phase transformation. Heating the sample to a temperature much higher than the crystal formation temperature (e.g., 200K higher) will gradually transition the sample from the tetragonal phase to the monoclinic phase. However, it may be preferred to heat it to a temperature slightly above (say 20 ℃) the crystal formation. This will ensure that the zirconia is transformed from the amorphous state to the tetragonal phase.

The heating process may be carried out at normal air standard pressure, but is preferably carried out in dry air, because the moisture (water) promotes the formation of monoclinic phase of zirconia. A dry air stream is therefore preferred, but other dry inert atmospheres, such as nitrogen, argon or helium, can also be used. An incremental heating (ramp) of 5 ℃ is useful depending on the oven, since controlled heating is required so as not to overshoot. Once the set point temperature is reached, the sample should be kept at that temperature long enough for the crystallization process to occur (say 30-120 minutes), but not too long (say 8 hours) because the sintering of the crystals can produce too much monoclinic phase.

Preferably, the amorphous zirconia particles have a BET surface area of 250-550m²(g), or 250-²G, e.g. 350-550m²(g), or 550m of 350-²/g。

By using basic solutions, e.g. NH₃Precipitation from solution of zirconates, e.g. ZrOCl₂·8H₂O synthesis of this amorphous zirconia. After precipitation, the zirconia is digested, preferably in the mother liquor, at a typical pH range of 6-10, for example in the range of 8.0-10.0, for a suitable period of time, for example 120-. Alternatively, at pH 10, by using an alkaline solution, e.g. concentrated NH₃Precipitation from solution of zirconates, e.g. ZrOCl₂·8H₂And O synthesizing amorphous zirconia. After precipitation, the zirconia is digested in the mother liquor, preferably at reflux (at 100 ℃), for a suitable period of time, for example 6 to 24 hours, for example 8 to 20 hours.

Method B

Another method of preparing the population of zirconia particles defined above involves the steps of: a suspension of small tetragonal crystalline phase powder of zirconia is formed in a strong aqueous base, such as an alkali metal base, e.g. KOH or NaOH, under reflux over 24 hours. The crystals are then grown in a strong base suspension (1-5M) to a size where the bulk energy of the crystals becomes comparable to the surface energy of the stable tetragonal phase, thereby lowering the activation energy barrier. Under hydrothermal conditions, for example at high temperatures of 150 ℃ -. Under these conditions, resolubilization and reprecipitation occur. In order to obtain sufficiently large crystals, the zirconia particles must be kept in the pressure reactor for 24 hours.

Preferably, the suspension is heated for a period of not less than 2 hours.

Composite material

In general, it is believed that the above-defined particle populations are particularly useful as filler components in composites. In particular, the zirconia particles of the present invention are useful in applications where the composite volume shrinkage upon curing is undesirable or even prohibitive.

More particularly, the present invention provides a composite material comprising one or more fillers including zirconia particles as defined herein and a polymerisable resin base.

It is a particular feature of the present invention that the martensitic transformation of the zirconia particles can be promoted by a triggering mechanism.

Thus, in a preferred embodiment of the composite, the resin base, when polymerized and in the absence of any compensation from the zirconia particles, will cause a volumetric shrinkage (Δ V) of the composite of at least 0.50 percent_{Resin composition}) And wherein when said resin base is polymerized and when said zirconia particles are phase-transformed, said composite exhibits an uncompensated volumetric shrinkage (av) greater than that due to the resin base_{Resin composition}) Total volumetric shrinkage (Δ V) of at least 0.25% less dots_{General assembly}). More particularly, the volume shrinkage (Δ V)_{Resin composition}) Is at least 1.00%, such as at least 1.50%, and the total volume shrinkage (Δ V)_{General assembly}) At least 0.50% less, for example 1.00% less, than uncompensated volumetric shrinkage.

The composite material typically comprises 5-95% or 10-90% by weight of one or more fillers including zirconia particles, and 5-95% or 10-90% by weight of a polymerizable resin base, especially 30-95% or 30-90% by weight of one or more fillers, and 5-70% or 10-70% by weight of a polymerizable resin base.

The composite material typically comprises, by volume, 20 to 80% of one or more fillers (including zirconia particles) and 20 to 80% of a polymerisable resin base, for example 25 to 80% or 25 to 75% of one or more fillers and 25 to 75% of a polymerisable resin base.

Preferably, the composite material is substantially solvent-free and water-free. The term "substantially free of solvent and free of water" means that the composite material comprises less than 4.0%, such as less than 1.0%, or less than 0.5% by weight of solvent and/or water.

Alternatively, the present invention provides a composite material comprising one or more fillers (including zirconia particles) and a polymerisable resin base, wherein the one or more fillers comprise metastable zirconia in the tetragonal or cubic phase, wherein when the resin base is polymerised and in the absence of any compensatory action from the zirconia particles, it causes a volume shrinkage (av) of the composite material of at least 0.50%_{Resin composition}) And wherein when said resin base is polymerized and when said filler component is phase-converted, said composite exhibits an uncompensated volumetric shrinkage (AV) relative to that due to the resin base_{Resin composition}) Total volumetric shrinkage (Δ V) of at least 0.25% less dots_{General assembly})。

It is apparent that the filler or fillers, and in particular the zirconia particles, are an important component in the composite. Fillers are generally described above in the section "fillers/filler ingredients".

The one or more fillers comprise at least one filler component which, for the purposes of this section, comprises at least zirconia particles. The term "filler component" is intended to mean a filler or filler fraction having specific physical properties, i.e. inherently capable of compensating (by expansion) for the volume shrinkage caused by the polymerization and curing of the resin base.

The zirconia particles typically comprise 20 to 100%, such as 30 to 100%, for example 40 to 100% or 50 to 100% by weight of the total weight of the filler or fillers.

The zirconia particles typically comprise from 15 to 90%, such as from 25 to 90%, for example from 30 to 90%, more particularly from 60 to 85% of the total weight of the composite, when calculated on the total weight of the composite.

Another important component of the composite is the polymerizable resin base described in detail in the section "polymerizable resin base".

The composite material may include other components as described in the section "other ingredients in the composite material".

The population of zirconia particles is particularly useful in conjunction with dental filling materials, see, for example, the "dental filling materials" section. The general use of the population of zirconia particles in the composite material is as described above in the "use of composite material" section.

The resin base can be advantageously cured by means of ultrasound by initiating the martensitic transformation of the population of zirconia particles using ultrasound, see for example the section "initiation of martensitic transformation and curing of the resin base by means of ultrasound bonding".

Examples

Transformation test of zirconia particles

Test composites were prepared by mixing 65% by volume of the zirconia particles to be tested with 35% by volume of a polymeric resin system (36% (w/w) BisGMA, 43.35% (w/w) UDMA, 20% (w/w) TEGDMA, 0.3% (w/w) Camphorquinone (CQ), 0.3% (w/w) ethyl N, N-dimethyl-p-aminobenzoate (DABE), and 0.05% (w/w)2, 6-di-tert-butyl-4-methylphenol (BHT)).

The test composite was placed in a cylindrical cavity of 4mm diameter and 20mm depth at 37 ℃. Using an ultrasonic descaler EMS PIEZON Master 400TM (28.5 kHz; 100W/cm)²) Ultrasound was applied for 300 seconds. Super-superThe top of the acoustic cleaner was placed directly into the mixture.

The phase transformation was measured using powder XRD. The volume fraction V of monoclinic zirconia can be determined according to the following relation_m：

X_m＝(I_m(111)+I_m(11-1))/(I_m(111)+I_m(11-1)+I_t(111))

V_m＝1.311X_m/(1+0.311X_m)

Wherein I_m(111) And I_m(11-1) the linear intensities of the (111) and (11-1) peaks of monoclinic zirconia, and I_t(111) Is the intensity of the (111) peak of tetragonal zirconia.

Preparation of the Filler component

Example 1 tetragonal nanometer sized zirconia

The preparation of tetragonal nano-sized zirconia (ZrO) is described below₂) The method of (1). From ZrOCl₂·8H₂Preparation of 0.5M ZrOCl from O and pure Water₂And (3) solution. At constant pH 10, with 1.5M NH₃Precipitated amorphous zirconia ZrO_x(OH)_4-2x. The mixture was kept under magnetic stirring for 10 days. The precipitate was then washed with pure water and the filter cake was then heated to 120 ℃ overnight. The filter cake was then pulverized to a fine white powder and placed in an oven with a dry atmosphere at 450 ℃.

Example 2 tetragonal nanometer sized zirconia

The preparation of tetragonal nano-sized zirconia (ZrO) is described below₂) The method of (1). From ZrOCl₂·8H₂Preparation of 0.5M ZrOCl from O and pure Water₂And (3) solution. At constant pH 8.5 with 1.5M NH₃Precipitated amorphous zirconia ZrO_x(OH)_4-2x. The mixture was kept under mechanical stirring for 10 days. The precipitate was then washed with pure water until no chloride ions were detected, and finally with 96% ethanol. Then drying in an oven at 60 deg.CThe filter cake was left overnight. The filter cake was then pulverized to a fine white powder. To obtain particles that can undergo rapid phase transitions, large surface areas are preferred, e.g., 250-550m²G, more preferably 350-²Powder per gram. The powder was then heated in an oven with a dry atmosphere for 2 hours at a temperature increasing to the crystal formation temperature for 4 hours (460 ℃ for this billet). The crystal formation temperature was determined by DSC of amorphous zirconia powder.

Example 3 preparation of yttria stabilized tetragonal micron sized zirconia

The preparation of yttria-stabilized tetragonal micron-sized zirconia (ZrO)₂) The method of (1). By dissolving 1.5% (mol) of Y in hot (90 ℃ C.) pure water₂O₃And 98.5 mol% of ZrOCl₂·8H₂And O, preparing a solution. The solution was then allowed to cool to room temperature. The solution was then diluted with ethanol and added dropwise to 1.5M NH₃In solution. This results in the precipitation of zirconium and yttrium ions as their hydroxides. The precipitate was filtered from the solution using a buchner funnel. The filtrate was resuspended in ethanol by manual stirring and subsequently filtered, whereby the filtrate was rinsed several times. The precipitate was then dried by constant crushing in a mortar using a pestle. Both the mortar and pestle were preheated to 130 ℃ prior to comminution. The dried powder was then calcined at 600 ℃ for 2 hours. The calcined powder was then suspended in pure water, and a beaker containing the suspension was sonicated for 12 hours to break up aggregates within the powder. To separate out the larger particles, the suspension was allowed to stand for 15 hours. The supernatant was removed and flocculated by changing the pH of the solution to 10. The resulting floc was dried on a hot plate using a continuously heated alumina mortar to give the final dry powder. The powder was then heated in an oven to 1200 ℃ in order to grow the crystals to a size of 100nm, where the 100nm size is 1.5% Y₂O₃Critical dimensions of stabilized zirconia. The resulting micropowder was allowed to cool to room temperature.

Example 4 yttria stabilized tetragonal micron-sized zirconia

The preparation of yttria-stabilized tetragonal micron-sized zirconia (ZrO)₂) The method of (1). By dissolving 1.5% (mol) of Y in hot (90 ℃ C.) pure water₂O₃And 98.5 mol% of ZrOCl₂·8H₂And O, preparing a solution. The solution was then allowed to cool to room temperature. The solution was then diluted with ethanol and added dropwise to 1.5M NH₃In solution. This results in the precipitation of zirconium and yttrium ions as their hydroxides. The precipitate was filtered from the solution using a buchner funnel. The filtrate was resuspended in ethanol by manual stirring and subsequently filtered, whereby the filtrate was rinsed several times. The precipitate was then dried by constant crushing in a mortar using a pestle. Both the mortar and pestle were preheated to 130 ℃ prior to comminution. Then, the amorphous powder was suspended in pure water, and a beaker containing the suspension was sonicated for 12 hours to pulverize aggregates in the powder. To separate out the larger particles, the suspension was allowed to stand for 15 hours. The supernatant was removed and flocculated by changing the pH of the solution to 10. The resulting floc was dried on a hot plate using a continuously heated alumina mortar to give the final dry powder. The amorphous powder was then heated in an oven to 450 ℃ (identified crystal formation temperature) for crystal growth to 100nm size, where 100nm size is 1.5% Y₂O₃Critical dimension of phase transition of stabilized zirconia. The resulting micropowder was allowed to cool to room temperature.

Example 5 hydrothermal Synthesis of tetragonal Nano-sized zirconia

From ZrOCl₂·8H₂Preparation of 0.1M ZrOCl from O and pure Water₂And (3) solution. Amorphous zirconium oxide ZrO was precipitated by adding 10M KOH until a pH of 13.5 was reached_x(OH)_4-2x. The suspension was then refluxed for 24 hours, resulting in the formation of small tetragonal crystals. The zirconia particles were filtered over Nytran 0.2 microns and washed with pure water until chloride ions were undetectable. The particles were then washed with 96% ethanol and dried in an oven at 60 ℃ overnight. Grinding the cake to a fine white with a mortar and pestleA colored powder. The small tetragonal fine white powder was transferred to a teflon beaker and suspended in 5M KOH. The beaker was placed in a sealed autoclave and heated to 170 ℃ over 24 hours. The suspension was filtered over Nytran 0.2 μm and washed with pure water and ethanol. The powder was dried in an oven at 60 ℃.

Example 6-tetragonal nanosized zirconia.

The preparation of tetragonal nano-sized zirconia (ZrO) is described below₂) The method of (1). From ZrOCl₂·8H₂Preparation of 0.5M ZrOCl from O and pure Water₂And (3) solution. At constant pH 10.0, with concentrated NH₃Solution precipitation of amorphous zirconia ZrO_x(OH)_4-2x. The mixture was left under mechanical stirring at reflux for 12 hours. The precipitate was then washed with pure water until no chloride ions were detected, and finally with 96% ethanol. The filter cake was then dried in an oven at 60 ℃ overnight. The filter cake was then pulverized to a fine white powder. To obtain particles that can undergo rapid phase transitions, large surface areas are preferred, e.g., 250-550m²G, more preferably 350-²Powder per gram. The powder was then heated in an oven with a dry atmosphere for 2 hours at a temperature increasing to the crystal formation temperature (443 ℃ for this billet). The crystal formation temperature was determined by DSC of amorphous zirconia powder.

Example 7 preparation of composite Material

Examples of preparing the resin base are described below. The resin used in this example (all in weight) consisted of 49% Bis-GMA (bisphenol A-glycidyl dimethacrylate), 49% TEGDMA (triethylene glycol dimethacrylate), 0.2% CPQ (camphorquinone), 1% EDMAB (ethyl 4-dimethylaminobenzoate), 0.8% Norbloc 7966(2- (2 '-hydroxy-5' -methacryloyloxyethylphenyl) -H-benzotriazole).

Shrinkage of this resin base with about 80% (wt%) or 55% (vol%) of non-phase shifting filler particles can be measured to 2% using a Watts apparatus, resulting in a monomer shrinkage of 5% (% vol). This was compensated by phase transition expanded zirconia particles (having an expansion ratio of 4.4%), resulting in a low expansion ratio of 0.17%. In this example, the two types of filler particles used had a composition of 85% by weight of particles having an average particle size of 0.1 μm and 15% by weight of particles having an average particle size of 15 nm.

Examples of surface treated composite dental materials are described below. The filler material is treated with a combination of a resin-compatibilized surfactant and an agent that enhances the strength of the material of the invention by copolymerizing surface treatment groups. The resin compatibilizer used for the zirconia particles given in this example was mono (polyethylene glycol) maleate. The reagent is used by dispersing zirconia particles in an aqueous solution of the reagent. A preferred enhancer is gamma-methacryloxypropyltrimethoxysilane, which is used in the form of a pentane solution of the reagent.

The filler and resin are mixed and then ready for use.

Example 8 Martin conversion by ultrasound

In forming a restoration (restoration) using the composite material given in example 1, a tooth surface is created by removing any portion of the enamel, and dentin which has decayed or damaged as necessary. A retaining groove (groovee) is then formed in the dentin to hold the restoration on the tooth, if desired. The practitioner then adds opacifiers and pigments to match the color of the composite to the color of the teeth. The composite material is then deposited on the tooth surface to replace any lost material. Once the practitioner is satisfied with the appearance of the restoration, the composite is exposed to a visible light source to cure the resin and activate the adhesive by crosslinking the polymer matrix. While applying curing light, an ultrasonic scaler at a frequency of 42kHz was continuously applied to the treated teeth. A descaler is used over the entire tooth to achieve a uniform phase transition of the zirconia particles. After curing the composite, the surface is polished.

Example 9 general procedure

The general procedure used by the dentist is set forth below.

Step # of	Procedure (ii)	Remarks for note
			1	Diagnosis of dental caries	Visual inspection: enamel surface fissures and discoloration. Mineral loss observable by X-ray
2	Drilling away the infected enamel	Rule: the enamel was removed until uninfected dentin was observed all along the perimeter of the cavity
			3	Excavating infected dentin	Rule: the probe does not adhere anywhere within the dentinal tissue
4	Determination of infection of pulp and root canal	If penetration occurs during excavation in step 3, the pulp is infected
			5	Digging out dental pulp and root canal	All soft tissue in the pulp and all root canals is removed mechanically (→ tip opening minus 1-2mm)
6	Root canal disinfection and sterilization
			7	Application of root canal cement	Adhering the filler to the root canal side
8	Root canal filling	Usually gutta-percha
			9	Preparation of Retention bars	Drilling out conical root canal matched with titanium rod
10	Cement for applying retention bar
			11	Insertion-adapted retention bar	It is necessary to leave a space for the composite material layer
12	Determining the kind of cavity
			13	Cavity preparation	Rule: as small as possible, but with a shape which avoids weakening the inherent properties of the tooth
14	Selecting the color of the composite	Ivory teeth as much as possible in terms of color and opacity
			15	Selecting and conditioning tooth substrates	To restore the normal shape
16	Etched enamel and dentin	Mechanically bonding the enamel posts and dentinal tubules. May not be required without composite shrinkage
			17	Applying composite materials	May be greater than one layer-meaning that steps 17-19 must be repeated until sufficient filler volume is reached
18	Initiating UV curing to polymerize composite materials	Simultaneously start step 19
			19	Inducing an ultrasonic phase transition	The main shrinkage occurs within the first 3-4 minutes of the filler material setting. Over the next 1 hour, the filling shrunk by about 1%. Ultrasound should typically be used for about 60 seconds. The power of the ultrasound should be high enough,so as to trigger a transition, and low enough so as not to damage living tissue. Giving a trigger frequency of 28.5kHz
20	Removing excess composite material
			21	Filler for polishing composite materials	If the composite shrinks, it can be delayed so that hygroscopic expansion occurs prior to polishing.

Example 10 ultrasonic curing of dental filling Material at Room temperature

A dental filling material consisting of 9.980g bis-GMA and 9.975g TEGDMA was prepared. The material (solution) was allowed to stand overnight under vacuum to evaporate the air absorbed in the monomer solution. A small portion (3g) of the solution was removed and placed in a glass vial with 63mg of benzoyl peroxide. The power of use is 100W/cm²For 60 seconds to cure the mixture.

EXAMPLE 11 ultrasonic curing of dental filling materials in a Cavity

A dental filling material consisting of 4.101g bis-GMA and 0.661g TEGDMA was prepared and 71mg benzoyl peroxide and 8.060g silicon oxide (surface coated with 3-methacryloxypropyltrimethoxysilane) were added. The material (solution) was allowed to stand overnight under vacuum to evaporate the air absorbed in the monomer solution. A portion of this material is placed into a small cylindrical void drilled into the excavated tooth. The pores were 2.5mm in diameter and 5mm deep and were intended to simulate a cavity. The power of use is 100W/cm²For 60 seconds to cure the mixture. Curing with the scaler is performed by moving the tip of the ultrasonic scaler over the undamaged tooth surface.

EXAMPLE 12 Simultaneous ultrasonic curing of phase-converted zirconia particles in dental Material in cavities

Preparation of a mixture of 4.101g bis-GMA and0.661g of TEGDMA dental filling material, and 71mg of benzoyl peroxide and 18.010g of zirconia particles (surface coated with mono (polyethylene glycol) maleate) were added. The zirconia particles (as described in example 1) were subjected to transformation by applying energy from an ultrasonic descaler. The material (solution) was allowed to stand overnight under vacuum to evaporate the air absorbed in the monomer solution. As in example 11, a portion of the material was placed in a small cylindrical void drilled in the excavated tooth. The power of use is 100W/cm²For 60 seconds to cure the mixture. Curing with the scaler is performed by moving the tip of the ultrasonic scaler over the undamaged tooth surface. At the same time, phase transformation of the zirconia particles is induced by ultrasound, thus preparing a volume-stable dental filling.

Claims (19)

1. A dental filling material comprising 30-95% by weight of one or more fillers and 5-70% by weight of a polymerizable resin base, wherein the one or more fillers comprise at least one filler component which is present in a metastable first phase and which is capable of undergoing a martin transition to a stable second phase, wherein the volume ratio between the stable second phase and the metastable first phase of the filler component is at least 1.005, and wherein the filler component is selected from the group consisting of metastable tetragonal zirconia, metastable cubic zirconia, monoclinic lanthanum sesquioxide, rhombohedral nickel sulphide, monoclinic dicalcium silicate and hexagonal lutetium borate.

2. The dental filling material of claim 1, wherein the resin base component, when polymerized and in the absence of any compensatory effect from the one or more filler components, causes a volumetric shrinkage of the dental filling material of at least 0.50%, and wherein the dental filling material exhibits a total volumetric shrinkage of at least 0.25% point less than the uncompensated volumetric shrinkage caused by the resin base component when the resin base component is polymerized and when the filler components phase-transform.

3. The dental filling material of claim 1 comprising less than 4% by weight of solvent.

4. A dental filling material according to any of claims 1 to 3, wherein the filler component is selected from the group consisting of metastable tetragonal and cubic zirconia phases.

5. The dental filling material of claim 4, consisting of:

40-85% by weight of one or more fillers, wherein the one or more fillers comprise at least one filler component that is a tetragonal or cubic phase of metastable zirconia;

15-60% by weight of a polymerizable resin base, said resin base being based on one or more compounds selected from the group consisting of: methacrylic acid, methyl methacrylate, 2-hydroxyethyl methacrylate, triethylene glycol dimethacrylate, bisphenol A-glycidyl dimethacrylate, bisphenol A-propyl dimethacrylate, polyurethane dimethacrylate and 2-hydroxyethyl methacrylate condensed with butanetetracarboxylic acid;

0-5% by weight of additives; and

0-4% by weight of a solvent.

6. A method of controlling volumetric shrinkage of a dental filling material as it cures, the method comprising the steps of:

(a) providing a dental filling material comprising 30-95% by weight of one or more fillers and 5-70% by weight of a polymerizable resin base, wherein the one or more fillers comprise at least one filler component which is present in a metastable first phase and which is capable of undergoing a martensitic transformation into a stable second phase, wherein the volume ratio between the stable second phase and the metastable first phase of the filler component is at least 1.005, and wherein the filler component is selected from the group consisting of metastable tetragonal zirconia, metastable cubic zirconia, monoclinic lanthanum sesquioxide, rhombohedral nickel sulphide, monoclinic dicalcium silicate and hexagonal lutetium borate;

(b) polymerizing and curing the resin base component and allowing the filler component to undergo a martensitic transformation from said first metastable phase to said second stable phase.

7. The method of claim 6, wherein the martensitic transformation of the filler component is initiated by the application of ultrasound.

8. The method of claim 6, wherein the polymerization of the resin base is initiated by the application of ultrasound.

9. The method of any of claims 6-8, wherein in the dental filling material, the resin base component, when polymerized and in the absence of any compensating effect from the one or more filler components, causes a volumetric shrinkage of the dental filling material of at least 0.50%, and wherein the dental filling material exhibits a total volumetric shrinkage of at least 0.25% point less than the uncompensated volumetric shrinkage due to the resin base component when the resin base component is polymerized and when the filler component is phase transformed.

10. The method according to any one of claims 6 to 8, wherein the dental filling material comprises less than 4% by weight of solvent.

11. The process according to any one of claims 6 to 8, wherein the filler component is selected from the group consisting of metastable tetragonal and cubic zirconia phases.

12. The method of claim 11, wherein the dental filling material consists of:

40-85% by weight of one or more fillers, wherein the one or more fillers comprise at least one filler component that is a tetragonal or cubic phase of metastable zirconia;

15-60% by weight of a polymerizable resin base, said resin base being based on one or more compounds selected from the group consisting of: methacrylic acid, methyl methacrylate, 2-hydroxyethyl methacrylate, triethylene glycol dimethacrylate, bisphenol A-glycidyl dimethacrylate, bisphenol A-propyl dimethacrylate, polyurethane dimethacrylate and 2-hydroxyethyl methacrylate condensed with butanetetracarboxylic acid;

0-5% by weight of additives; and

0-4% by weight of a solvent.

13. Use of a dental filling material comprising 30-95% by weight of one or more fillers and 5-70% by weight of a polymerizable resin base for the restoration of a mammalian tooth, wherein the one or more fillers comprise at least one filler component which is present in a metastable first phase and which is capable of undergoing a martensitic transformation into a stable second phase, wherein the volume ratio between the stable second phase and the metastable first phase of the filler component is at least 1.005, and wherein the filler component is selected from the group consisting of metastable tetragonal zirconia, metastable cubic zirconia, monoclinic lanthanum sesquioxide, rhombohedral nickel sulphide, monoclinic dicalcium silicate and hexagonal lutetium borate.

14. The use according to claim 13, wherein in a dental filling material the resin base component, when polymerized and in the absence of any compensating effect from the one or more filler components, causes a volumetric shrinkage of the dental filling material of at least 0.50%, and wherein the dental filling material exhibits a total volumetric shrinkage of at least 0.25% point less than the uncompensated volumetric shrinkage caused by the resin base component when the resin base component is polymerized and when the filler component phase is transformed.

15. The use of claim 13, wherein the dental filling material comprises less than 4% by weight of solvent.

16. Use according to any one of claims 13 to 15, wherein the filler component is selected from the group consisting of metastable tetragonal and cubic zirconia.

17. The use according to claim 16, wherein the dental filling material consists of:

40-85% by weight of one or more fillers, wherein the one or more fillers comprise at least one filler component that is a tetragonal or cubic phase of metastable zirconia;

15-60% by weight of a polymerizable resin base, said resin base being based on one or more compounds selected from the group consisting of: methacrylic acid, methyl methacrylate, 2-hydroxyethyl methacrylate, triethylene glycol dimethacrylate, bisphenol A-glycidyl dimethacrylate, bisphenol A-propyl dimethacrylate, polyurethane dimethacrylate and 2-hydroxyethyl methacrylate condensed with butanetetracarboxylic acid;

0-5% by weight of additives; and

0-4% by weight of a solvent.

18. Preparing a mean particle size of 50-2000nm and a BET surface area of 10-250m²A method of preparing a population of zirconia particles, said particles being present in a metastable first phase and being capable of undergoing a martensitic transformation to a stable second phase, the method comprising the steps of: a suspension of small tetragonal crystal powder of zirconia was formed in an alkali metal base and heated to a temperature of 150 ℃. about.200 ℃.

19. The method of claim 18, wherein the suspension is heated for a period of time of not less than 2 hours.