WO2021165795A1

WO2021165795A1 - Ascorbic acid component for use in a method of treating the surface of a prepared tooth

Info

Publication number: WO2021165795A1
Application number: PCT/IB2021/051124
Authority: WO
Inventors: Kai U. CLAUSSEN; Manfred Ludsteck; Reinhold Hecht; Ingo R. Haeberlein
Original assignee: 3M Innovative Properties Company
Priority date: 2020-02-19
Filing date: 2021-02-11
Publication date: 2021-08-26
Also published as: EP4106710A1

Abstract

The invention relates to an ascorbic acid component for use in a method of restoring and/or treating the surface of a prepared tooth in the mouth of a human being or animal, the method comprising the step of bringing the ascorbic acid component or a composition comprising the ascorbic acid component in contact with the surface of the prepared tooth, the surface of the prepared tooth comprising collagen fibers containing disulfide moieties, the ascorbic acid component being applied in an amount and for a time effective to reduce or cleave at least a part of the disulfide moieties contained in the collagen fibers.

Description

Ascorbic Acid Component for Use in a Method of Treating the Surface of a Prepared Tooth

Field of the Invention

The invention relates to ascorbic acid components for use in a method of restoring and/or treating the surface of a prepared tooth in the mouth of a human being or animal.

The ascorbic acid component or the composition comprising the ascorbic acid component is brought in contact with the surface of a prepared tooth comprising collagen fibers and is able to partially reduce disulfide moieties being present in collagen fibers.

Background

Dental composites are well known in dentistry and are widely used as restorative materials (filling composites) or as cements (resin cements) in the prosthodontic field. Generally, composites are hydrophobic in nature and contain (as main parts of the formulation) inorganic fillers, a (meth)acrylate-based resin matrix and initiators for the radical polymerization.

To get adhesion to enamel and dentin, composites typically require a pre-treatment of the tooth surface by using a bonding agent or a bonding system. This may result in a rather complex and time-consuming procedure. Therefore, attempts were made to develop self- adhesive composites which do not require the use of an additional bonding agent/system resulting in materials which are easier and faster to use for the dentist.

Self-adhesive resin cements (SARC) are meanwhile well-established materials in the prosthodontic area. A commercially available product is e.g. RelyX ™ Unicem 2 Automix (3M Oral Care). These materials are formulated as two-component systems and cure by a sophisticated curing mechanism.

SARCs have the ability to self-etch and bond to enamel and dentin without the need of a separate adhesive. This is typically accomplished by using adhesive monomers containing phosphoric acid moieties. It is assumed that the phosphoric acid moiety forms an ionic bond with hydroxyapatite crystals being present in both enamel and dentin. The self-etching capability requires SARCs to contain a redox initiator system that works in acidic environments (pH<7).

Many redox initiator systems fulfill these requirements (to some extent) and are currently represented in the SARC market by different products of several manufacturers.

Various dental compositions curing by different mechanisms are also described in the patent literature. Some of them contain an ascorbic acid component as part of a redox-initiator system or as stabilizer.

US 4,918,136 (Kawaguchi et al.) describes an adhesive composition comprising a certain monomer mixture, filler, a polymerization initiator and a certain amount of ascorbic acid or a derivative thereof. US 5,501,727 (Wang et al.) relates to a curable dental composition comprising an ethylenically unsaturated moiety, an oxidizing agent and a metal complexed ascorbic acid. The incorporation of metal complexed ascorbic acid provides a curable composition that exhibits improved color stability.

US 5,338,773 (Lu et al.) describes a dental cement composition useful as dental luting cement, liner, base and restorative. The cement is said to have superior adhesion to tooth without separately acid etching dentin or enamel. The cement can be provided as a powder/liquid composition, wherein the powder contains a strontium aluminofluorosilicate glass powder, benzoyl peroxide, ascorbyl palmitate and copper acetyl acetonate.

J. M. Antonucci et al. describes new initiator systems for dental resins. The initiator systems contain peresters and hydroperoxides as oxidants, natural reducing agents such as ascorbic acid as accelerators in combination with redox metal systems (Journal of Dental Research, Vol. 58, No. 9, Sept. 1979, pages 1887-1899).

US 2011/0245368 A1 (Yarimizu et al.) describes a paste type polymerizable composition comprising a peroxide, an ascorbic acid compound, (meth)acrylate having an acid group, (meth)acrylate not having an acid group, a filler not reacting to acid and water. The composition is said to be storage stable.

US 2008/0207841 A1 (Koers et al.) describes an accelerator solution suitable for forming a redox system with peroxides and having high storage stability. The solution consists essentially of a reducing agent selected from ascorbic acid and sodium formaldehyde sulphoxylate, a metal salt selected from transition metal salts, lithium salts and magnesium salts, and an organic oxygen-containing solvent.

US 2018/168938 A1 (Schmuecker et al.) relates to a multicomponent polymer-modified glass ionomer cement, the composition comprising one or more radically polymerizable organic monomers (M), a basic glass composition (G) as crosslinking agent for polymers containing carboxylic acid groups (P) chosen from the group consisting of homo- and copolymers of an a,b-unsaturated carboxylic acid (C) and also, as constituent of a polymerization initiator system for it one or more compounds (A) chosen from the group consisting of the isomers of ascorbic acid, the salts of the isomers of ascorbic acid, the esters of the isomers of ascorbic acid and the ethers of the isomers of ascorbic acid and one or more compounds (S) chosen from the group consisting of sulfinic acids, salts of suifinic acids and salts of organoboron compounds.

WO 2017/100231 A1 (3M) describes a kit of parts for dental use comprising a Part A and a Part B, Part A comprising component(s) comprising an ascorbic acid moiety, a stabilizer selected from sulfite(s), phosphite(s) or mixtures thereof, Part B comprising polymerizable component(s) without acidic moieties, polymerizable component(s) with acidic moieties, transition metal component(s) and organic peroxide(s). The component(s) comprising an ascorbic acid moiety, the stabilizer(s), the transition metal component(s) and the peroxide(s) forming an initiator system for curing an acidic composition.

JP 2003/012429 A (Soeno Mitsuhiro) describes a surface treating agent for attaching a dental restoration to dentin. To the dentin surface a phosphoric acid solution is applied first, washed with water and dried, followed by the application of a sodium-hypochlorite solution. Subsequently, an aqueous solution of ferric chloride and ascorbic acid is applied. The surface is washed and dried. After that the dental restoration is fixed with an adhesive composition.

US 4,918,136 (Kawaguchi et al.) relates to an adhesive composition comprising a monomer mixture of vinyl monomers having an acidic group and a vinyl monomer copolymerizable with said vinyl monomer, a filler, a polymerization initiator and an ascorbic acid or derivative thereof.

Pouran Samini et al. report that using sodium ascorbate as antioxidant surface treatment agent can help to increase the fracture toughness in dental applications. It is described that sodium ascorbate may suppress the denaturing effect of etching on dentin collagen, offering protection against the degradation of composite-dentin bonds and is an important component in the synthesis of hydroxyproline which stabilizes the collagen triple helix (J. Clin Exp. Dent. 2018; 10(6):e528-36).

M. C. G. Erhardt et al have analyzed the role of an anti-oxidant (ascorbic acid) on resin- dentin bonds resistance to degradation of two adhesives. Two mechanisms are proposed to explain the stability of the resin-dentin interface: a) the preservation of the collagen integrity promoted by ascorbic acid incorporation, and b) the inhibitory effect of ascorbic acid on dentin matrix metalloproteinase-2 acitivty (J. of Dent. 39(2011) 80-87).

Summary of the Invention

To ensure a stable fixation of a dental restoration to the surface of a prepared tooth, a self-adhesive resin cement composition is typically needed.

The self-adhesive resin composition should not only allow a firm adhesive bonding of the dental cement to the dental restoration but also to the surface of the prepared tooth.

In particular, there is a need for a method which allows a sufficiently strong adhesion of a self-adhesive resin composition to dentin in an aqueous environment, ideally, without the need for an additional etching step.

This objective is addressed by the present invention.

In one embodiment the invention features an ascorbic acid component for use in a method of restoring and/or treating the surface of a prepared tooth in the mouth of a human being or animal, the method comprising the step of bringing the ascorbic acid component or a composition comprising the ascorbic acid component in contact with the surface of the prepared tooth, the surface of the prepared tooth comprising collagen fibers containing disulfide moieties, the ascorbic acid component being applied in an amount and for a time effective to reduce or cleave at least a part of the disulfide moieties contained in the collagen fibers as described in the present text and claims.

The invention is also directed to an ascorbic acid component for use in a method of restoring and/or treating the surface of a prepared tooth, the method comprising the steps of applying the ascorbic acid component to the surface of the prepared tooth as part of or in combination with a composition comprising polymerizable monomers, an initiator and optionally fillers, for enabling the composition to come in contact with collagen fibers containing disulfide moieties which are present in the surface of the prepared tooth and reducing at least a part of the disulfide moieties, and allowing the polymerizable monomers to interact with or bond to the reduced disulfide moieties, optionally attaching a dental restoration as described in the present text and claims wherein the method does typically not comprise a step of etching the surface of the prepared tooth with an etchant such as a composition comprising phosphoric acid.

Unless defined differently, for this description the following terms shall have the given meaning:

One component composition” means that all of the components mentioned are present in the composition during storage and use. That is, the composition to be applied or used is not prepared by mixing different parts of the composition before use. In contrast to one-component compositions, those compositions are often referred to as two-component compositions (e.g. being formulated as powder/liquid, liquid/liquid or paste/paste compositions).

“Two component composition” means that the components are provided as a kit of parts or system in parts separated from each other before use. For use, the respective components or parts need to be mixed.

A “dental composition” or a “composition for dental use” or a “composition to be used in the dental field” is any composition which can be used in the dental field. In this respect the composition should be not detrimental to the patients^' health and thus be free of hazardous and toxic components being able to migrate out of the composition. Examples of dental compositions include permanent and temporary crown and bridge materials, artificial crowns, anterior or posterior filling materials, adhesives, mill blanks, lab materials, luting agents and orthodontic devices. Dental compositions are typically hardenable compositions, which can be hardened at ambient conditions, including a temperature range from 15 to 50°C or from 20 to 40°C within a time frame of 30 min or 20 min or 10 min. Higher temperatures are not recommended as they might cause pain to the patient and may be detrimental to the patient^'s health. Dental compositions are typically provided to the practitioner in comparable small volumes, that is volumes in the range from 0.1 to 100 ml or from 0.5 to 50 ml or from 1 to 30 ml. Thus, the storage volume of useful packaging devices is within these ranges.

The term "compound" or “component” is a chemical substance which has a particular molecular identity or is made of a mixture of such substances, e.g., polymeric substances. A “monomer” is any chemical substance which can be characterized by a chemical formula, bearing polymerizable groups (including (meth)acrylate groups) which can be polymerized to oligomers or polymers thereby increasing the molecular weight. The molecular weight of monomers can usually simply be calculated based on the chemical formula given.

As used herein, "(meth)acryl" is a shorthand term referring to "acryl" and/or "methacryl”. For example, a "(meth) acryloxy" group is a shorthand term referring to either an acryloxy group (i. e., CH₂=CH-C(0)-0-) and/or a methacryloxy group (i. e., CH₂=C(CH₃)-C(0)-0-). Similarly, (meth)acrylate is a shorthand term referring to “acrylate” and/or “methacrylate.”

A “hardenable component or material” or “polymerizable component” is any component which can be cured or solidified e.g. by heating to cause polymerization, chemical crosslinking, radiation-induced polymerization or crosslinking by using a redox initiator. A hardenable component may contain only one, two, three or more polymerizable groups. Typical examples of polymerizable groups include unsaturated carbon groups, such as a vinyl group being present i.a. in a (meth)acrylate group.

An “ethylenically unsaturated acidic compound” is meant to include monomers, oligomers, and polymers having ethylenic unsaturation and acid and/or acid-precursor functionality. Acidic precursor functionalities include, e.g. anhydrides, acid halides and pyrophosphates. The acidic group preferably comprises one or more carboxylic acid residues, such as -COOH or -C0-0-C0-, phosphoric acid residues, such as -0-P(0)(0H)0H, phosphonic acid residues such as C-P(0)(0H)0H, sulfonic acid residues, such as -SO₃H or sulfinic acid residues such as -SO₂H.

A “filler” contains all fillers being present in the hardenable composition. Only one type of filler or a mixture of different fillers can be used.

By "paste" is meant a soft, viscous mass of solids (i.e. particles) dispersed in a liquid.

A “particle” means a substance being a solid having a shape which can be geometrically determined. The shape can be regular or irregular. Particles can typically be analysed with respect to e.g. grain size and grain size distribution.

A “powder” is characterized by containing only solid components in particle form.

An "adhesive" or "dental adhesive" refers to a composition used as a pre-treatment on a dental structure (e. g., a tooth) to adhere a "dental material" (e. g., "restorative" an orthodontic appliance (e. g., bracket), or an "orthodontic adhesive") to a dental surface. An "orthodontic adhesive" refers to a composition used to adhere an orthodontic appliance to a dental (e. g., tooth) surface. Generally, the dental surface is pre-treated, e. g., by etching, priming, and/or applying an adhesive to enhance the adhesion of the "orthodontic adhesive" to the dental surface.

A "dental surface" or “tooth surface” refers to the surface of tooth structures (e. g., enamel, dentin, and cementum) and bone. A "self-etching" composition refers to a composition which bonds to a dental surface without pre-treating the dental surface with an etchant. Preferably, a self-etching composition can also function as a self-primer wherein no separate etchant or primer is used.

A "self-adhesive" composition refers to a composition that is capable of bonding to a dental surface without pre-treating the dental surface with a primer or bonding agent. Preferably, a self-adhesive composition is also a self-etching composition wherein no separate etchant is used.

A “self-curing composition” means a composition which cures by a redox-reaction without application of radiation.

An "untreated" dental surface refers to a tooth or bone surface that has not been treated with an etchant, primer, or bonding agent prior to application of a self-etching adhesive or a self- adhesive composition.

An "unetched" dental surface refers to a tooth or bone surface that has not been treated with an etchant prior to application of a self-etching adhesive or a self-adhesive composition of the present invention.

An "etchant" refers to an acidic composition that is capable of fully or partially solubilizing (i. e., etching) a dental surface. The etching effect can be visible to the naked human eye and/or instrumentally detectable (e. g., by light microscopy). Typically, an etchant is applied to the dental structure surface for a period of 10 to 30 seconds.

“Radiation curable” shall mean that the component (or composition, as the case may be) can be cured by applying radiation, preferably electromagnetic radiation with a wavelength in the visible light spectrum under ambient conditions and within a reasonable time frame (e.g. within about 60, 30 or 10 seconds).

A “derivative” or “structural analogue” is a chemical compound showing a chemical structure closely related to the corresponding reference compound and containing all featured structural elements of the corresponding reference compound but having small modifications like bearing additional chemical groups like e.g. alkyl moieties, Br, Cl, or F or not bearing chemical groups like e.g. alkyl moieties in comparison to the corresponding reference compound. That is, a derivative is a structural analogue of the reference compound. A derivative of a chemical compound is a compound comprising the chemical structure of said chemical compound. Another example of a derivative is a salt formed by a chemical compound e.g. in an acid-base reaction.

The following examples might illustrate this: tetramethyl bis-phenol A bearing four additional methyl groups with respect to the reference compound bis-phenol A, and bis-phenol F not bearing two additional methyl groups with respect to the reference compound bis-phenol A are derivatives of bis-phenol A within the meaning of this definition. Component(s) comprising a certain chemical moiety can often be classified as derivatives or structural analogues of that chemical moiety.

A component comprising an “ascorbic acid moiety” is a component comprising the following structural element:

wherein the symbol “ * “ indicates a connection to another chemical moiety or atom.

The term “visible light” is used to refer to light having a wavelength of 400 to 800 nano meters (nm).

“Ambient conditions” mean the conditions which the composition described in the present text is usually subjected to during storage and handling. Ambient conditions may, for example, be a pressure of 900 to 1,100 mbar, a temperature of 10 to 40 °C and a relative humidity of 10 to 100 %. In the laboratory ambient conditions are typically adjusted to 20 to 25 °C and 1,000 to 1,025 mbar (at maritime level).

A composition is “essentially or substantially free of” a certain component, if the composition does not contain said component as an essential feature. Thus, said component is not wilfully added to the composition either as such or in combination with other components or ingredient of other components. A composition being essentially free of a certain component usually does not contain that component at all. However, sometimes the presence of a small amount of the said component is not avoidable e.g. due to impurities contained in the raw materials used.

As used herein, “a”, “an”, “the”, “at least one” and “one or more” are used interchangeably. Also herein, the recitations of numerical ranges by endpoints include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

Adding an “(s)” to a term means that the term should include the singular and plural form. E.g. the term “additive(s)” means one additive and more additives (e.g. 2, 3, 4, etc.).

Unless otherwise indicated, all numbers expressing quantities of ingredients, measurement of physical properties such as described below and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. The terms “comprise” or “contain” and variations thereof do not have a limiting meaning where these terms appear in the description and claims. “Consisting essentially of” means that specific further components can be present, namely those which do not materially affect the essential characteristic of the article or composition. “Consisting of” means that no further components should be present. The term “comprise” shall include also the terms “consist essentially of” and “consists of”.

Detailed Description of the Invention

The use of an ascorbic acid component in a method as described in the present text has a couple of advantageous properties.

Hard dental tissue, in particular dentin, is a calcified tissue of the human body and forms together with enamel, cementum and pulp the essential components of a tooth.

Upon preparation of a tooth, the hard enamel is often partially removed so that the softer dentin becomes visible.

Dentin typically contains major portions of hydroxyl apatite and organic materials. A certain portion of the organic material is formed by collagen (about 20 wt.%), the parts are mainly water (about 10 wt.%) and hydroxyapatite (about 70 wt.%). In contrast to dentin, enamel is mainly composed of hydroxyapatite only.

Collagen consists mainly of amino acids strains which are arranged in the shape of a triple helix. This triple helix is stabilized inter alia by disulfide bridges (e.g. formed by cysteine, or cystine).

It has been found that by applying an ascorbic acid component or a composition containing an ascorbic acid component, the bond strength of a polymerizable composition applied to the tooth surface can be improved.

A possible explanation for this observation is that the ascorbic acid component is able to react or interact with the collagen material. This reaction or interaction typically includes the reduction or cleavage of disulfide bonds being present in the collagen fibres (e.g. resulting from cystine).

Without wishing to be bound to a particular theory, it is assumed that if disulfide bridges in the collagen fibres being present in the surface of a prepared tooth are opened or cleaved, the collagen material becomes more accessible for other components applied to the surface of the prepared tooth. Thus, the material containing the collagen fibres can possibly be infiltrated by a dental cement composition more easily.

Further, it is assumed that by applying the ascorbic acid component described in the present text to a prepared tooth surface containing disulphide moieties, the disulphide moieties are cleaved by reduction and temporarily thiyl radicals (-S ) are formed. These thiyl radicals may be able to start a polymerization reaction. By hydrogen abstraction, thiol groups can be formed that may function as a chain transfer agent. Chain transfer agents can be used to control the molecular weight in radical polymerization proceedings as growing polymer chains are typically terminated by hydrogen abstraction from the thiol group.

It was found that a composition comprising an ascorbic acid component in combination with polymerizable components (with acidic groups and/or without acidic groups) and an initiator system showed a high degree of conversion (DOC) of the polymerizable component in the dentin cement interface. This is a hint that the polymerizable moieties of the polymerizable components interact directly with or bond to the dentin structure.

A high DOC value is typically correlated with a high shear bond strength as the smear layer being present on the surface of the prepared tooth is effectively incorporated into the cement.

If desired, this reaction can be further analysed by applying the tests described in the example section.

Further, it has been found that by using the method described in the present text a high bonding strength of a dental cement can be realized, in particular on wet (i.e. not dry) dentin tooth surfaces (i.e. dentin surfaces which have been rinsed with water and slightly dried with air), which have not been etched and rinsed before.

The presence of a so-called smear layer, which typically remains after the preparation of the tooth surface by the dentist, is considered beneficial.

If a smear-layer is present, it can be infiltrated by a dental cement composition containing the ascorbic acid component and thus become part of the final dental restoration.

Thus, by using the ascorbic acid component as described in the present text, the bonding of a polymerizable composition (which may also contain the ascorbic acid component) to the surface of a prepared tooth (in particular dentin) can be improved.

This finding and the new use of the ascorbic acid component is in contrast to the use of ascorbic acid components described in the literature so far.

In the literature, ascorbic acid components are typically used as part of a redox initiator system comprising in addition organic peroxides and transition metal components. The use of ascorbic acid components for reducing disulfide bridges in collagen fibres being present in dentin is not suggested.

Further, not etching the surface of the prepared tooth with an etchant such as a composition comprising phosphoric acid might help to reduce the risk of a possible post operative sensitivity.

The possible use of ascorbic acid components in combination with dental adhesives may have already been described in the literature, however, the specific effect and use described in the present text has not been suggested before. The invention is directed to an ascorbic acid component for use in a method of restoring and/or treating the surface of a prepared tooth in the mouth of a human being or animal.

The surface of the prepared tooth comprises collagen fibers which contain disulfide moieties, which can be reduced or cleaved by the ascorbic acid component.

The ascorbic acid component described in the present text comprises component(s) comprising an ascorbic acid moiety such as salts and esters of ascorbic acid, ethers, ketals, or acetals.

Suitable salts include the alkali metal and earth alkali metal salts like Na, K, Ca and mixtures thereof.

Esters of ascorbic acid include those which are formed by reacting one or more of the hydroxyl functions of ascorbic acid with a carboxylic acid, in particular the C2 to C30 carboxylic acid.

Suitable examples of C2 to C30 carboxylic acids include the fatty acids, like caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic acid, a-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid and docosahexaenoic acid.

Preferred are sometimes ascorbic components, which can be easily dissolved in or mixed with other components, which may be applied in combination with the ascorbic acid component, such as polymerizable components without acidic moieties.

That is, using an ascorbic acid component having in addition a hydrophobic moiety can be preferred.

Suitable hydrophobic moieties include saturated and unsaturated aliphatic residues (e.g. C2 to C30 or C12 to C30). Those ascorbic acid derivatives may also function as surface-active substances (substances having a so-called “head / tail structure”).

Particularly preferred are ascorbyl palmitate, ascorbyl stearate, mixtures and salts thereof.

The ascorbic acid component is used in an amount effective to reduce at least a part of the disulfide moieties being present in the collagen of the prepared tooth.

The amount of disulfide moieties which can be reduced typically depends on the amount of ascorbic acid components which is used.

A suitable amount for the ascorbic acid component is typically at least 0.0001 pm or at least 0.0005 pm or at least 0.001 pmol per mm² of the treated surface of the prepared tooth.

There is no particular upper limit unless the desired effect or restoration of the tooth cannot be achieved. A higher amount may help to accelerate the cleavage of the disulphide moieties and/or may help to access deeper regions of the dentin. If the ascorbic acid component is applied with or as part of a polymerizable composition which may be used for fixing a dental restoration to the tooth surface, a suitable amount is typically in a range of 0.0001 pmol to 1 pmol or 0.001 pmol to 0.1 pmol or 0.001 pmol to 0.01 pmol calculated for the composition containing the ascorbic acid component to be applied per mm² of the surface of the prepared tooth to be treated.

If the ascorbic acid component is part of a composition, the ascorbic acid component is typically used in the following amounts with respect to the weight of the whole composition:

Lower limit: at least 0.01 wt.% or at least 0.05 wt.% or at least 0.1 wt.%;

Upper limit: utmost 5 wt.% or utmost 3 wt.% or utmost 1 wt.%;

Range: 0.01 wt.% to 5 wt.% or 0.05 wt.% to 3 wt.% or 0.1 wt.% to 1 wt.%.

If the amount of the ascorbic acid component comprising the ascorbic acid moiety is too high, the effectiveness of a redox initiator system used for curing a dental composition, if present, might be affected.

If the amount of the ascorbic acid is too low, the desired cleavage of the disulfide bridges in the collagen fibres of the prepared tooth may not take place in the desired amount.

If the ascorbic acid component is used in combination or as part of a redox-initiator system, the amount should be adjusted (in particular increased) so that the ascorbic acid component can fulfil two functions: reducing the disulfide bridges in the collagen fibres and acting as reduction component in the redox-initiator system. E.g., if the ascorbic acid component is used in combination with an oxidizing component, the amount of the ascorbic acid component should be adjusted appropriately.

The ascorbic acid component is applied to the surface of a prepared tooth.

The surface of the prepared tooth to be treated comprises collagen fibres. The collagen fibres contain disulfide moieties. The disulfide moieties help to form or stabilize the 3- dimensional structure of the collagen fibres. In contrast to enamel which does not comprise collagen fibres, dentin comprises about 20 wt.% collagen fibres.

The ascorbic acid component is applied in an amount and for a time period effective to reduce at least a part of these disulfide moieties.

The amount and the time period typically depend on the size of the surface of the prepared tooth to be treated.

The size of the dentin surface area to be treated is typically in the range of 1 mm² to 100 mm² or 1 mm² to 50 mm² for one tooth.

A time period for the treatment of at least 10 s or at least 20 s or at least 30 s or at least 1 min can already be sufficient.

If the ascorbic acid component is used as part of a separate treatment composition which is removed from the treated surface of the tooth, a suitable treatment time is typically in the range of 10 s to 15 min or 10 s to 10 min. If the ascorbic acid component is used in combination with or as part of a polymerizable composition for fixing a dental restoration, the ascorbic acid component will remain as part of that composition on the surface of the prepared tooth.

The time period for the treatment is typically related to the amount of the ascorbic acid component used. For a small amount of ascorbic acid component, a longer treatment period may by appropriated and vice versa.

The ascorbic acid component can be applied in various forms and in combination with other components, if desired.

According to one embodiment, the ascorbic acid component is applied to the prepared tooth surface separately.

According to another embodiment, the ascorbic acid component is applied together with or as part of a composition. Such a composition typically contains different components.

If desired, the composition can be characterized by the following properties alone or in combination: a) pH value: 0 to 7 or 1 to 5, if brought in contact with a wet (aqueous) pH sensitive paper; b) viscosity: 0.01 to 1,000 or 1 to 500 Pa*s at 28°C and a shear rate of 10 s ¹.

Depending on the intended use, the viscosity of the composition can be adjusted.

If the composition is used as dental fissure sealant or dental flowable composite, suitable viscosities include e.g. from 1 to 150 Pa*s or from 10 to 120 Pa*s (23°C; shear rate: 100 1/s).

If desired, the viscosity can be determined as described in the Example section.

The composition can be a self-etching composition, a self-adhesive composition, a self curing composition or a self-etching, self-adhesive and self-curing composition.

According to one embodiment, the ascorbic acid component is applied together with a solvent.

The ascorbic acid component is typically dissolved in the solvent.

Examples of solvents which can be used include, but are not limited to linear, branched or cyclic, saturated or unsaturated alcohols, ketones, esters, cyclic ethers (e.g. tetrahydrofuran (THF)) or mixtures of two or more of said type of solvents with 2 to 10 C atoms. Preferred alcoholic solvents include methanol, ethanol, iso-propanol and n-propanol.

Other suitable organic solvents are THF, acetone, methylethyl ketone, cyclohexanol, toluene, alkanes and acetic acid alkyl esters, in particular acetic acid ethyl ester.

According to one embodiment, the ascorbic acid component is applied together with a stabilizer.

Generally, all kinds of stabilizer(s) can be used which are suitable to stabilize the ascorbic acid component for the intended use.

If the stabilizer is to be used in a dental or orthodontic formulation, the stabilizer should be acceptable from a toxicological point of view. In particular, stabilizer(s) selected from sulfite(s), phosphite(s), benzotriazole(s) and mixtures thereof were found to be useful.

Benzotriazole component(s) are known for their ultraviolet radiation absorbing properties, a property which, however, is not considered relevant for the stabilization of ascorbic acid components. Nevertheless, it has been found that benzotriazole component(s) can help to stabilize the ascorbic acid components during preparation and storage. Thus, using the ascorbic acid component in combination with a benzotriazole component can sometimes be preferred.

Preferred are sometimes organic stabilizer(s), that is, stabilizer(s) which are not salts. Without wishing to be bound to a particular theory it is believed that the solubility of the stabilizer in the composition and/or the pKs value of the stabilizer needs to be considered. Using a stabilizer having a high solubility is sometimes preferred. Using less acidic stabilizers is sometimes preferred, as well.

It was found that the stabilizing effect of organic sulfite or organic phosphite stabilizers is sometimes better than those of inorganic sulfite or inorganic phosphite stabilizers.

According to one embodiment, the stabilizer(s) can be characterized by at least one or more of the following features: molecular weight: 80 to 600 or 120 to 350 g/mol; being a liquid at 23°C.

If the ascorbic acid component and the stabilizer(s) are part of a composition, the stabilizer(s) is/are typically present in the following amount:

Lower amount: at least 0.01 or at least 0.05 or at least 0.1 wt.%;

Upper amount: up to 5 or up to 3 or up to 1 wt.%;

Range: 0.01 to 5 wt.% or 0.05 to 3 wt.% or 0.1 to 1 wt.%; wt.% with respect to the weight of the whole composition.

According to one embodiment, the ratio of ascorbic acid component to stabilizer(s) is typically in a range of 1 : 5 to 5 : 1 or 1 : 2 to 2 : 1 with respect to mol.

According to one embodiment, the stabilizer(s) is used in excess over the component(s) comprising the ascorbic acid moiety with respect to mol.

Using an excess of stabilizer can sometimes be beneficial to stabilize the system against oxygen which may migrate through the packaging system during storage of the kit of pats.

Examples of inorganic sulfite(s) include lithium sulfite, sodium sulfite, potassium sulfite, calcium sulfite, sodium bisulfite and mixtures thereof.

Examples of organic sulfite(s) include di-alkyl or aryl (e.g. Ci to C12) sulfites (e.g. diethyl sulfite, di-n-propyl sulfite, di-isopropyl sulfite, glycol sulfite, 1,3-propylen sulfite), diallylsulfite and mixtures thereof.

Mixtures of organic and inorganic sulfites can also be used, if desired. Examples of inorganic phosphite(s) include calcium hypophosphite, sodium phosphite and mixtures thereof.

Examples of organic phosphite(s) include di-alkyl or aryl (e.g. Ci to C40) phosphites, (e.g. di-ethylphosphite, di-butylphosphite, di-iso-propylphosphite, di-n-propylphosphite, tri-phenyl- phosphite, tri-allylphosphite) and mixtures thereof.

Examples of benzotriazole components which can be used include Methyl-1 H- benzotriazole, 1-Chlorobenzotriazole, 5-Chlorobenzotriazole, 1 H-Benzotriazole, 3H- Benzotriazole-5-carboxylic acid, 2-[3-(2H-E3enzotriazol-2-yl)-4-hydroxyphenyl]ethyl methacrylate and mixtures thereof.

Mixtures of organic and inorganic phosphites can also be used, if desired.

Mixtures of organic and inorganic phosphites and/or sulfites can also be used, if desired.

According to one embodiment, using stabilizers selected from organic sulfites, organic phosphites and mixtures thereof is preferred.

Using a mixture of a phosphite stabilizer and a benzotriazole stabilizer can sometimes be preferred.

According to one embodiment, the ascorbic acid component is applied as part of or together with a composition comprising polymerizable components comprising acidic moieties.

The acidic components can be polymerizable component(s) with acidic moiety(s). One or more polymerizable component(s) with acidic moiety(s) may be present, if desired.

The polymerizable components with acid moiety can typically be represented by the following formula

AnBCm with A being an ethylenically unsaturated group, such as a (meth)acryl moiety,

B being a spacer group, such as (i) linear or branched Ci to C12 alkyl, optionally substituted with other functional groups (e.g. halogenides (including Cl, Br, I), OH or mixtures thereof) (ii) Ob to C12 aryl, optionally substituted with other functional groups (e.g. halogenides, OH or mixtures thereof), (iii) organic group having 4 to 20 carbon atoms bonded to one another by one or more ether, thioether, ester, thioester, thiocarbonyl, amide, urethane, carbonyl and/or sulfonyl linkages, and

C being an acidic group, or precursor of an acidic group such as acid anhydride, m, n being independently selected from 1, 2, 3, 4, 5 or 6, wherein the acidic group comprises one or more carboxylic acid residues, such as - COOH or -CO-O-CO-, phosphoric acid residues, such as -0-P(0)(0H)0H, phosphonic acid residues, such as C-P(0)(OH)(OH), sulfonic acid residues, such as -SO3H or sulfinic acid residues such as -SO2H.

Examples of polymerizable components with acid moiety include, but are not limited to glycerol phosphate mono(meth)acrylate, glycerol phosphate di(meth)acrylate, hydroxyethyl (meth)acrylate (e.g., HEMA) phosphate, bis((meth)acryloxyethyl) phosphate, (meth)acryloxy- propyl phosphate, bis((meth)acryloxypropyl) phosphate, bis((meth)acryloxy)propyloxy phosphate, (meth)acryloxyhexyl phosphate, bis((meth)acryloxyhexyl) phosphate, (meth)- acryloxyoctyl phosphate, bis((meth)acryloxyoctyl) phosphate, (meth)acryloxydecyl phosphate, bis((meth)acryloxydecyl) phosphate, caprolactone methacrylate phosphate, citric acid di- or tri methacrylate, poly(meth)acrylated oligomaleic acid, poly(meth)acrylated polymaleic acid, poly(meth)acrylated poly(meth)acrylic acid, poly(meth)acrylated polycarboxyl-polyphosphonic acid, poly(meth)acrylated polychlorophosphoric acid, poly(meth)acrylated polysulfonate, poly(meth)acrylated polyboric acid, and the like. Derivatives of these hardenable components bearing an acid moiety that can readily react e.g. with water to form the specific examples mentioned above, like acid halides or anhydrides are also contemplated.

Also monomers, oligomers, and polymers of unsaturated carboxylic acids such as (meth)acrylic acids, aromatic (meth)acrylated acids (e.g., methacrylated trimellitic acids), and anhydrides thereof can be used.

Some of these compounds can be obtained, e.g., as reaction products between isocyanatoalkyl (meth)acrylates and carboxylic acids. Additional compounds of this type having both acid-functional and ethylenically unsaturated components are described in US 4,872,936 (Engelbrecht) and US 5,130,347 (Mitra). A wide variety of such compounds containing both the ethylenically unsaturated and acid moieties can be used. If desired, mixtures of such compounds can be used.

Using (meth)acrylate functionalized polyalkenoic acids is often preferred as those components were found to be useful to improve properties like adhesion to hard dental tissue, formation of a homogeneous layer, viscosity, or moisture tolerance.

According to one embodiment, the composition contains (meth)acrylate functionalized polyalkenoic acids, for example, AA:ITA:IEM (copolymer of acrylic acid:itaconic acid with pendent methacrylates).

These components can be made by reacting e.g. an AA:ITA copolymer with 2- isocyanatoethyl methacrylate to convert a portion of the acid groups of the copolymer to pendent methacrylate groups. Processes for the production of these components are described, e.g., in Example 11 of US 5,130,347 (Mitra)); and those recited in US 4,259,075 (Yamauchi et al.), US 4,499,251 (Omura et al.), US 4,537,940 (Omura et al.), US 4,539,382 (Omura et al.), US 5,530,038 (Yamamoto et al.), US 6,458,868 (Okada et al.), and EP 0 712 622 A1 (Tokuyama Corp.) and EP 1 051 961 A1 (Kuraray Co., Ltd.).

If present, the polymerizable component(s) with acidic moiety(s) should be present in an amount so that the pH value of Part B is below 6, or below 4 or below 2, if brought in contact with water. If present, the polymerizable component(s) with acidic oiety(s) is typically present in the following amounts:

Lower limit: at least 2 wt.% or at least 3 wt.% or at least 4 wt.%;

Upper limit: utmost 50 wt.% or utmost 40 wt.% or utmost 30 wt.%;

Range: 2 wt.% to 50 wt.% or 3 wt.% to 40 wt.% or 4 wt.% to 30 wt.%; wt.% with respect to the weight of the whole composition.

Alternatively or in addition, the ascorbic acid component described in the present text is applied with or as part of a composition comprising polymerizable component(s) without acidic moiety(s).

One or more polymerizable component(s) without acidic moiety(s) may be present, if desired.

The polymerizable component(s) without acidic moiety(s) is typically a free-radically polymerizable material, including ethylenically unsaturated monomer, monomers or oligomers or polymers.

Suitable polymerizable component(s) without acidic moiety(s) can be characterized by the following formula:

AnBAm with A being an ethylenically unsaturated group, such as a (meth)acryl moiety,

B being selected from (i) linear or branched Ci to C12 alkyl, optionally substituted with other functional groups (e.g. halogenides (including Cl, Br, I), OH or mixtures thereof) (ii) O_d to C12 aryl, optionally substituted with other functional groups (e.g. halogenides, OH or mixtures thereof), or (iii) organic group having 4 to 20 carbon atoms bonded to one another by one or more ether, thioether, ester, thioester, thiocarbonyl, amide, urethane, carbonyl and/or sulfonyl linkages, m, n being independently selected from 0, 1, 2, 3, 4, 5 or 6 with the proviso that n+m is greater 0, that is that at least one A group is present.

Such polymerizable materials include mono-, di- or poly-acrylates and methacrylates such as methyl acrylate, methyl methacrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n- hexyl (meth)acrylate, stearyl (meth)acrylate, allyl (meth)acrylate, glycerol di(meth)acrylate, the diurethane dimethacrylate called UDMA (mixture of isomers, e.g. Rohm Plex 6661-0) being the reaction product of 2-hydroxyethyl methacrylate (HEMA) and 2,2,4-trimethylhexamethylene diisocyanate (TMDI), glycerol tri(meth)acrylate, ethyleneglycol di(meth)acrylate, diethyleneglycol di(meth)acrylate, triethyleneglycol di(meth)acrylate, 1,3-propanediol diacrylate, 1,3-propanediol dimethacrylate, trimethylolpropane tri(meth)acrylate, 1,2,4-butanetriol tri(meth)acrylate, 1,4- cyclohexanediol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, sorbitol hexa(meth)acrylate, bis[1-(2-(meth)acryloxy)]-p- ethoxyphenyldimethylmethane, bis[1-(3-methacryloxy-2-hydroxy)]-p-propoxyphenyldimethyl- methane (BisGMA), bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethyl ethane and trishydroxyethyl-isocyanurate trimethacrylate; the bis-acrylates and bis-methacrylates of polyethylene glycols of molecular weight 200-500, copolymerizable mixtures of acrylated monomers (see e.g. US 4,652,274), and acrylated oligomers (see e.g. US 4,642,126); and vinyl compounds such as styrene, diallyl phthalate, divinyl succinate, divinyl adipate and divinylphthalate; polyfunctional (meth)acrylates comprising urethane, urea or amide groups. Mixtures of two or more of these free radically polymerizable materials can be used if desired.

Further polymerizable components which may be present include di(meth)acrylates of ethoxylated bis-phenol A, for example 2,2'-bis(4-(meth)acryloxytetraethoxyphenyl)propanes, urethane (meth)acrylates and (meth)acrylamides. The monomers used can furthermore be esters of [alpha]-cyanoacrylic acid, crotonic acid, cinnamic acid and sorbic acid.

It is also possible to use the methacrylic esters mentioned in EP 0 235 826, such as bis[3[4]-methacryl-oxymethyl-8(9)-tricyclo[5.2.1.0²'⁶]decylmethyl triglycolate. Suitable are also 2,2-bis-4(3-methacryloxy-2-hydroxypropoxy)phenylpropane (Bis-GMA), 2,2-bis-4(3-methacryl- oxypropoxy)phenylpropane, 7,7,9-trimethyl-4, 13-dioxo-3, 14-dioxa-5, 12-diazahexadecane-1 ,16- dioxy dimethacrylate (UDMA), urethane (meth)acrylates and di(meth)acrylates of bishydroxy- methyltricyclo-(5.2.1.0²'⁶)decane.

These ethylenically unsaturated monomers can be employed in the dental composition(s) either alone or in combination with the other ethylenically unsaturated monomers. In addition or besides those components, other hardenable components which can be added include oligomeric or polymeric compounds, such as polyester (meth)acrylates, polyether (meth)acrylates, polycarbonate (meth)acrylates and polyurethane (meth)acrylates. The molecular weight of these compounds is typically less than 20,000 g/mol, particularly less than 15,000 g/mol and in particular less than 10,000 g/mol.

Polymerizable monomers comprising a hydroxyl moiety and/or a 1,3-diketo moiety can also be added. Suitable compounds include 2-hydroxyethyl (meth)acrylate (HEMA), 2- or 3- hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6- hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, dialkylene glycol mono(meth)acrylate, for example, diethylene glycol mono(meth)acrylate, triethylene glycol mono(meth)acrylate, tetraethylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, dipropylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, and further 1,2- or 1,3- and 2,3-dihydroxypropyl (meth)acrylate, 2- hydroxypropyl-1 ,3-di(meth)acrylate, 3-hydroxypropyl-1 ,2-di(meth)acrylate, N-(meth)acryloyl-1 ,2- dihydroxypropylamine, N-(meth)acryloyl-1,3-dihydroxypropylamine, adducts of phenol and glycidyl (meth)acrylate, for example, 1-phenoxy-2-hydroxypropyl (meth)acrylate, 1-naphthoxy-2- hydroxypropyl (meth)acrylate, bisphenol A diglycidyl (meth)acrylate and the like, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate and 2,3-dihydroxypropyl (meth)acrylate are particularly preferable.

An example of a polymerizable component with 1,3-diketo group is acetoacetoxy ethylmethacrylate (AAEMA). If desired, mixtures of one or more of these components can be used. Adding these components may be used to adjust the rheological properties or to influence mechanical properties.

The polymerizable component(s) without acidic moiety(s) is typically present in the following amounts:

Lower limit: at least 5 wt.% or at least 10 wt.% or at least 20 wt.%;

Upper limit: utmost 65 wt.% or utmost 55 wt.% or utmost 45 wt.%;

Range: 5 wt.% to 65 wt.% or 10 wt.% to 55 wt.% or 20 wt.% to 45 wt.%; wt.% with respect to the weight of the whole composition.

The ascorbic acid component for use in a method as described in the present text may also be applied together with or as part of a composition comprising one or more organic peroxides.

Generally, all organic peroxide(s) can be used, if suitable to achieve the desired result.

In contrast to inorganic peroxides, organic peroxide(s) do not comprise metals or metal ions. Thus, organic peroxides typically only comprise C, O, H and optionally halogens (e.g. F, Cl, Br). Organic peroxides which can be used include di-peroxide(s) and hydroperoxides.

According to one embodiment, the organic peroxide is used in excess with respect to the weight of the component comprising the ascorbic acid moiety.

According to one embodiment, the organic peroxide is a di-peroxide, preferably a di peroxide comprising the moiety R₁-O-O-R₂-O-O-R₃, with Ri and R₃ being independently selected from H, alkyl (e.g. Ci to Ce), branched alkyl (e.g. Ci to Ce), cycloalkyl (e.g. C₅ to C₁₀), alkylaryl (e.g. C₇ to C₁₂) or aryl (e.g. C₆ to C₁₀) and R₂ being selected from alkyl (e.g. (Ci to Ce) or branched alkyl (e.g. Ci to Ce).

Examples of suitable organic diperoxides include 2,2-Di-(tert.-butylperoxy)-butane and 2,5-Dimethyl-2,5-di-(tert-butylperoxy)-hexane and mixtures thereof.

According to another embodiment, the organic peroxide is a hydroperoxide, in particular a hydroperoxide comprising the structural moiety

R-O-O-H with R being (e.g. Ci to C₂₀) alkyl, (e.g. C₃ to C₂₀) branched alkyl, (e.g. C₆ to C₁₂) cycloalkyl, (e.g. C₇ to C₂₀) alkylaryl or (e.g. C₆ to C₁₂) aryl.

Examples of suitable organic hydroperoxides include t-butyl hydroperoxide, t-amyl hydroperoxide, p-diisopropylbenzene hydroperoxide, cumene hydroperoxide, pinane hydroperoxide, p-methane hydroperoxide and 1,1,3,3-tetramethylbutyl hydroperoxide and mixtures thereof. Other peroxides which are often described in the literature are ketone peroxide(s), diacyl peroxide(s), dialkyl peroxide(s), peroxyketal(s), peroxyester(s) and peroxydicarbonate(s).

Examples of ketone peroxides include methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, methyl cyclohexanone peroxide, and cyclohexanone peroxide.

Examples of peroxyesters include alpha-cumylperoxyneodecanoate, t-butyl peroxypivarate, t-butyl peroxyneodecanoate, 2,2,4-trimethylpentylperoxy-2-ethyl hexanoate, t- amylperoxy-2-ethyl hexanoate, t-butyl peroxy-2-ethyl hexanoate, di-t-butylperoxy isophthalate, di-t-butylperoxy hexahydroterephthalate, t-butylperoxy-3,3,5-trimethylhexanoate, t-butylperoxy acetate, t-butylperoxy benzoate and t-butylperoxymaleic acid.

Examples of peroxidicarbonates include di-3-methoxy peroxidicarbonate, di-2-ethyl hexyl peroxydicarbonate, bis(4-t-butylcyclohexyl)peroxidicarbonate, diisopropyl- 1-peroxydicarbonate, di-n-propyl peroxidicarbonate, di-2-ethoxyethyl-peroxidicarbonate, and diallyl peroxidicarbonate.

Examples of diacyl peroxides include acetyl peroxide, benzoyl peroxide, decanoyl peroxide, 3,3,5-trimethylhexanoyl peroxide, 2,4-dichlorobenzoyl peroxide and lauroylperoxide.

Examples of dialkyl peroxiodes include di-t-butyl peroxide, dicumylperoxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperpoxy)hexane, 1 ,3-bis(t-butylperoxyisopropyl)benzene and 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexane.

Examples of peroxyketals include 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1- bis(t-butylperoxy)cyclohexane, 2,2-bis(t-butylperoxy)butane, 2,2-bis(t-butylperoxy)octane and 4,4-bis(t-butylperoxy)valeric acid-n-butylester.

The organic peroxide(s) is typically present in the following amounts:

Lower limit: at least 0.01 wt.% or at least 0.05 wt.% or at least 0.1 wt.%;

Upper limit: utmost 5 wt.% or utmost 4 wt.% or utmost 3 wt.%;

Range: 0.01 wt.% to 5 wt.% or 0.05 wt.% to 4 wt.% or 0.1 wt.% to 3 wt.%; wt.% with respect to the weight of the whole composition.

If the amount of the organic peroxide(s) is too high, the setting time of the composition may be too fast.

If the amount of the organic peroxide(s) is too low, the setting time of the composition may be too slow.

The ascorbic acid component for use in a method as described in the present text may also be applied together with or as part of a composition comprising one or more transition metal components.

Suitable transition metal component(s) include organic and/or inorganic salt(s) selected from titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper and/or zinc, with copper and iron being sometimes preferred.

Useful salts include acetate(s), chloride(s), sulphate(s), benzoate(s), acetylacetonate(s), naphthenate(s), carboxylate(s), bis(1-phenylpentan-1,3-dione) complexes, salicylate(s), complexes with ethylenediaminetetraacetic acid of either of the transition metals and mixtures thereof.

According to one embodiment, the transition metal component is in an oxidation stage, which allows the component to be reduced. Useful oxidation stages include +2, +3, +4, +5, +6 and +7, as applicable.

Copper component(s) are sometimes preferred. The oxidation stage of copper in the copper component(s) is preferably +1 or +2.

Typical examples of copper component(s) which can be used include salts and complexes of copper including copper acetate, copper chloride, copper benzoate, copper acetylacetonate, copper naphthenate, copper carboxylates, copper bis(1-phenylpentan-1,3- dione) complex (copper procetonate), copper salicylate, complexes of copper with thiourea, ethylenediaminetetraacetic acid and/or mixtures thereof. The copper compounds can be used in hydrated form or free of water. Especially preferred is copper acetate.

The amount of transition metal component which can be used is not particularly limited. The transition metal salt should be used in an amount sufficient to achieve the intended purpose.

The transition metal component(s) is typically present in the following amounts:

Lower limit: at least 0.00001 wt.% or at least 0.0001wt.% or at least 0.001 wt.%;

Upper limit: utmost 3 wt.% or utmost 2 wt.% or utmost 1.5 wt.%;

Range: 0.00001 wt.% to 3 wt.% or 0.0001 wt.% to 2 wt.% or 0.001 wt.% to 1.5 wt.% wt.% with respect to the weight of the whole composition.

If the amount of transition metal component used is too high, the setting time of the composition may be too fast.

If the amount of transition metal component used is too low, the setting time of the composition may be too slow and adhesion may be reduced.

The ascorbic acid component for use in a method as described in the present text may also be applied together with or as part of a composition comprising one or more photo initiators.

The nature of the optional photo-initiator is not particularly limited unless the intended purpose is not negatively affected.

By incorporating a photo-initiator a composition is obtained which can be characterized as “dual curing”, that is, it contains a redox-initiator system which is suitable to harden the composition without radiation (“dark-curing or self-curing”) and a photo-initiator system which is suitable to harden the composition upon the application of radiation (“light-curing”).

Suitable photo-initiators for free radical polymerization are generally known to the person skilled in the art dealing with dental materials. Typical photo-initiators comprise a combination of a sensitizing agent and a reducing agent, which is often referred to as photo-initiator system. As the sensitizing agent, those which can polymerize the polymerizable monomer(s) by the action of a visible light having a wavelength of 390 nm to 830 nm are preferred.

Suitable sensitizing agents often contain an alpha di-keto moiety.

Examples thereof include camphorquinone, benzil, diacetyl, benzyl dimethyl ketal, benzyl diethyl ketal, benzyl di(2-methoxyethyl) ketal, 4,4,'-dimethylbenzyl dimethyl ketal, anthraquinone, 1-chloroanthraquinone, 2-chloroanthraquinone, 1,2-benzanthraquinone, 1- hydroxyanthraquinone, 1-methylanthraquinone, 2-ethylanthraquinone, 1-bromoanthraquinone, thioxanthone, 2-isopropyl thioxanthone, 2-nitrothioxanthone, 2-methyl thioxanthone, 2,4- dimethyl thioxanthone, 2,4-diethyl thioxanthone, 2,4-diisopropyl thioxanthone, 2- chloro-7- trifluoromethyl thioxanthone, thioxanthone- 10, 10-dioxide, thioxanthone-10-oxide, benzoin methyl ether, benzoin ethyl ether, isopropyl ether, benzoin isobutyl ether, benzophenone, bis(4- dimethylaminophenyl)ketone, 4,4,'-bisdiethylaminobenzophenone.

As the reducing agent, tertiary amines and the like are generally used. Suitable examples of the tertiary amines include N,N-dimethyl-p-toluidine, N,N-dimethylaminoethyl methacrylate, triethanolamine, methyl 4-dimethylaminobenzoate, ethyl 4- dimethylaminobenzoate, methyldiphenylamine and isoamyl 4-dimethylaminobenzoate. As other reducing agents, sodium sulfinate derivatives and organometallic compounds can also be used. These compounds may be used singly or in admixture.

Moreover, ternary photopolymerization initiating systems consisting of a sensitizer, an electron donor and an onium salt as described in US 6,187,833, US 6,025,406, US 6,043,295, US 5,998,495, US 6,084,004, US 5,545,676 and WO 2009/151957 and US 6,765,036 can be used. These references are herewith included by reference.

In the ternary photo-initiator system, the first component is an iodonium salt, i.e. , a diaryliodonium salt.

The iodonium salt is preferably soluble in the monomer and storage stable (i. e., does not spontaneously promote polymerization) when dissolved therein in the presence of the sensitizer and donor. Accordingly, selection of a particular iodonium salt may depend to some extent upon the particular monomer, polymer or oligomer, sensitizer and donor chosen. Suitable iodonium salts are described in US 3,729,313, US 3,741,769, US 3,808,006, US 4,250,053 and US 4,394,403, the iodonium salt disclosures of which are incorporated herein by reference. The iodonium salt can be a simple salt (e.g., containing an anion such as Cl , Br, I or C4H5 SO3) or a metal complex salt (e.g., containing SbFsOH or AsF₆). Mixtures of iodonium salts can be used if desired. Preferred iodonium salts include diphenyliodonium salts such as diphenyliodonium chloride, diphenyliodonium hexafluorophosphate and diphenyliodonium tetrafluoroborate.

The second component in a ternary photo-initiator system is a sensitizer. The sensitizer desirably is soluble in the monomer and is capable of light absorption somewhere within the range of wavelengths of greater than 400 to 1200 nm, more preferably greater than 400 to 700 nm and most preferably greater than 400 to 600 nm. The sensitizer may also be capable of sensitizing 2-methyl-4,6-bis(trichloromethyl)-s-triazine, using the test procedure described in US 3,729,313, which is incorporated herein by reference. Preferably, in addition to passing this test, a sensitizer is also selected based in part upon shelf life stability considerations. Accordingly, selection of a particular sensitizer may depend to some extent upon the particular monomer, oligomer or polymer, iodonium salt and donor chosen.

Suitable sensitizers can include compounds in the following categories: ketones, coumarin dyes (e.g., ketocoumarins), xanthene dyes, acridine dyes, thiazole dyes, thiazine dyes, oxazine dyes, azine dyes, aminoketone dyes, porphyrins, aromatic polycyclic hydrocarbons, p-substituted aminostyryl ketone compounds, aminotriaryl methanes, merocyanines, squarylium dyes and pyridinium dyes. Ketones (e.g., monoketones or alpha- diketones), ketocoumarins, aminoarylketones and p-substituted aminostyryl ketone compounds are preferred sensitizers. For applications requiring deep cure (e.g., cure of highly filled composites), it is preferred to employ sensitizers having an extinction coefficient below about 1000, more preferably below about 100, at the desired wavelength of irradiation for photopolymerization. Alternatively, dyes that exhibit reduction in light absorption at the excitation wavelength upon irradiation can be used.

For example, a preferred class of ketone sensitizers has the formula: ACO(X)_b B, where X is CO or CR⁵ R⁶, where R⁵ and R⁶ can be the same or different, and can be hydrogen, alkyl, alkaryl or aralkyl, b is zero or one, and A and B different and can be substituted (having one or more non-interfering substituents) can be the same or unsubstituted aryl, alkyl, alkaryl, or aralkyl groups, or together A and B can form a cyclic structure which can be a substituted or unsubstituted cycloaliphatic, aromatic, heteroaromatic or fused aromatic ring.

Suitable ketones of the above formula include monoketones (b=0) such as 2,2-, 4,4- or 2,4-dihydroxybenzophenone, di-2-pyridyl ketone, di-2-furanyl ketone, di-2-thiophenyl ketone, benzoin, fluorenone, chalcone, Michler's ketone, 2-fluoro-9-fluorenone, 2-chlorothioxanthone, acetophenone, benzophenone, 1- or 2-acetonaphthone, 9-acetylanthracene, 2-, 3- or 9- acetylphenanthrene, 4-acetylbiphenyl, propiophenone, n-butyrophenone, valerophenone, 2-, 3- or 4-acetylpyridine, 3-acetylcoumarin and the like. Suitable diketones include aralkyldiketones such as anthraquinone, phenanthrenequinone, o-, m- and p-diacetylbenzene, 1,3-, 1,4-, 1,5-, 1,6-, 1,7- and 1,8-diacetylnaphthalene, 1,5-, 1,8- and 9,10-diacetylanthracene, and the like. Suitable alpha-diketones (b=1 and X=CO) include 2,3-butanedione, 2,3-pentanedione, 2,3- hexanedione, 3,4-hexanedione, 2,3-heptanedione, 3,4-heptanedione, 2,3-octanedione, 4,5- octanedione, benzil, 2,2'- 3 3'- and 4,4'-dihydroxylbenzil, furil, di-3,3'-indolylethanedione, 2,3- bornanedione (camphorquinone), biacetyl, 1,2-cyclohexanedione, 1,2-naphthaquinone and the like. The third component of a ternary initiator system is a donor. Preferred donors include, for example, amines (including aminoaldehydes and aminosilanes), amides (including phosphoramides), ethers (including thioethers), ureas (including thioureas), ferrocene, sulfinic acids and their salts, salts of ferrocyanide, ascorbic acid and its salts, dithiocarbamic acid and its salts, salts of xanthates, salts of ethylene diamine tetraacetic acid and salts of tetraphenylboronic acid. The donor can be unsubstituted or substituted with one or more non interfering substituents. Particularly preferred donors contain an electron donor atom such as a nitrogen, oxygen, phosphorus, or sulfur atom, and an abstractable hydrogen atom bonded to a carbon or silicon atom alpha to the electron donor atom. A wide variety of donors is disclosed in US 5,545,676, which is incorporated herein by reference.

Alternatively, free-radical initiators useful in the invention include the class of acylphosphine oxides and bisacylphosphine oxides.

Suitable acylphosphine oxides can be described by the general formula

(R⁹)2 — P(=0) — C(=0) — R¹⁰ wherein each R⁹ individually can be a hydrocarbyl group such as alkyl, cycloalkyl, aryl, and aralkyl, any of which can be substituted with a halo-, alkyl- or alkoxy-group, or the two R⁹ groups can be joined to form a ring along with the phosphorous atom, and wherein R¹⁰ is a hydrocarbyl group, an S-, 0-, or N-containing five- or six-membered heterocyclic group, or a -Z-C(=0)-P(=0)- (R⁹)2 group, wherein Z represents a divalent hydrocarbyl group such as alkylene or phenylene having from 2 to 6 carbon atoms.

Preferred acylphosphine oxides are those in which the R⁹ and R¹⁰ groups are phenyl or lower alkyl- or lower alkoxy-substituted phenyl. By “lower alkyl” and “lower alkoxy” is meant such groups having from 1 to 4 carbon atoms. Examples can also be found e.g. in US

4,737,593.

Suitable bisacylphosphine oxides can be described by the general formula

wherein n is 1 or 2, and R⁴, R⁵, R⁶ and R⁷ are H, C1-4 alkyl, C1-4 alkoxyl, F, Cl or Br; R² and R³, which are the same or different, stand for a cyclohexyl, cyclopentyl, phenyl, naphthyl, or biphenylyl radical, a cyclopentyl, cyclohexyl, phenyl, naphthyl, or biphenylyl radical substituted by F, Cl, Br, I, C1-4 alkyl and/or C1-4 alkoxyl, or an S or N-containing 5-membered or 6- membered heterocyclic ring; or R² and R³ are joined to form a ring containing from 4 to 10 carbon atoms and being optionally substituted by 1 to 6 C1-4 alkyl radicals.

Further examples include: bis-(2,6-dichlorobenzoyl)phenylphosphine oxide, bis-(2,6- dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-4-ethoxyphenyl- phosphine oxide, bis-(2,6-dichlorobenzoyl)-4-biphenylylphosphine oxide, bis-(2,6-dichloro- benzoyl)-4-propylphenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-2-naphthylphosphine oxide, bis-(2,6-dichlorobenzoyl)-1-napthylphosphine oxide, bis-(2,6-dichlorobenzoyl)-4-chlorophenyl- phosphine oxide, bis-(2,6-dichlorobenzoyl)-2,4-dimethoxyphenylphosphine oxide, bis-(2,6- dichlorobenzoyl)decylphosphine oxide, bis-(2,6-dichlorobenzoyl)-4-octylphenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide, bis-(2,6-dimethoxy- benzoyl)phenylphosphine oxide, bis-(2,4,6-trimethylbenzoyl)-2,5-dimethylphenylphosphine oxide, bis-(2,6-dichloro-3,4,5-trimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide, bis-(2,6- dichloro-3,4,5-trimethoxybenzoyl)-4-ethoxyphenylphosphine oxide, bis-(2-methyl-1-naphthoyl)- 2,5-dimethylphenylphosphine oxide, bis-(2-methyl-1-naphthoyl)phenylphosphine oxide, bis-(2- methyl-1-naphthoyl)-4-biphenylylphosphine oxide, bis-(2-methyl-1-naphthoyl)-4- ethoxyphenylphosphine oxide, bis-(2-methyl-1-naphthoyl)-2-naphthylphosphine oxide, bis-(2- methyl-1-naphthoyl)-4-propylphenylphosphine oxide, bis-(2-methyl-1-naphthoyl)-2,5- dimethylphosphine oxide, bis-(2-methoxy-1-naphthoyl)-4-ethoxyphenylphosphine oxide, bis-(2- methoxy-1-naphthoyl)-4-biphenylylphosphine oxide, bis-(2-methoxy-1-naphthoyl)-2- naphthylphosphine oxide and bis-(2-chloro-1-naphthoyl)-2,5-dimethylphenylphosphine oxide.

The acylphosphine oxide bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide (formerly known as IRGACURE™ 819, Ciba Specialty Chemicals) is sometimes preferred.

Tertiary amine reducing agents may be used in combination with an acylphosphine oxide. Illustrative tertiary amines useful in the invention include ethyl 4-(N,N-dimethyl- amino)benzoate and N,N-dimethylaminoethyl methacrylate.

Commercially-available phosphine oxide photonnitiators capable of free-radical initiation when irradiated at wavelengths of greater than 400 nm to 1200 nm include a 25:75 mixture, by weight, of bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide and 2-hydroxy-2- methyl-1-phenylpropan-1-one (formerly known as IRGACURE™ 1700 (Ciba), 2-benzyl-2-(N,N- dimethylamino)-1-(4-morpholinophenyl)-1-butanone (formerly known as IRGACURE™ 369 (Ciba), bis^5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1 H-pyrrol-1-yl)phenyl) titanium (formerly known as IRGACURE™ 784 DC, Ciba), a 1:1 mixture, by weight, of bis(2,4,6- trimethylbenzoyl)phenyl phosphine oxide and 2-hydroxy-2-methyl-1-phenylpropane-1-one (formerly known as DAROCUR™ 4265, Ciba), ethyl-2, 4, 6-trimethylbenzylphenyl phosphine oxide (formerly known as LUCIRIN™ LR8893X, BASF), and Bis(2,4,6-trimethylbenzoyl)- phenylphosphine oxide. The sensitizing agent and reducing agent are typically present together in one part of the kit of parts described in the present text. Alternatively the components of a photo-initiator system can be spread between Part A and Part B.

For stability reasons, it can be preferred, if the photo-initiator or photo-initiator system is contained in Part A, i.e. the part containing the ascorbic acid or derivative(s) thereof.

The ascorbic acid component for use in a method as described in the present text may also be applied together with or as part of a composition comprising one or more fillers.

The nature and structure of the filler(s) is not particularly limited unless the intended purpose cannot be achieved.

Adding a filler can be beneficial e.g. for adjusting the rheological properties like the viscosity. The content of the filler may also influence the physical properties of the composition after hardening, like hardness or flexural strength.

The size of the filler particles should be such that a homogeneous mixture with the hardenable component forming the resin matrix can be obtained-

The mean particle size of the filler may be in the range from 5 nm to 100 pm.

If desired, the measurement of the particle size of the filler particles can be done with a TEM (transmission electron microscopy) method, whereby a population is analyzed to obtain an average particle diameter.

The filler(s) typically comprise non-acid reactive fillers. A non-acid reactive filler is a filler which does not undergo an acid/base reaction with an acid.

Useful non-acid reactive fillers include fumed silica, fillers based on non-acid reactive fluoroaluminosilicate glasses, quartz, ground glasses, non water soluble fluorides such as CaF2, silica gels such as silicic acid, in particular pyrogenic silicic acid and granulates thereof, cristobalite, calcium silicate, zirconium silicate, zeolites, including the molecular sieves.

Suitable fumed silicas include for example, products sold under the tradename Aerosil™ series OX-50, -130, -150, and -200, Aerosil R8200, -R805 available from Degussa AG (Hanau, Germany), CAB-O-SIL™ M5 available from Cabot Corp (Tuscola, III), and HDK™ types e.g. HDK H2000, HDK H15, HDK H18, HDK H20 and HDK H30 available from Wacker.

Filler(s) which can also be used include nano-sized fillers such as nano-sized silica.

Suitable nano-sized particles typically have a mean particle size in the range of about 5 to about 80 nm.

Preferred nano-sized silicas are commercially available from Nalco Chemical Co. (Naperville, III.) under the product designation NALCO™ COLLOIDAL SILICAS (for example, preferred silica particles can be obtained from using NALCO products 1040, 1042, 1050, 1060, 2327 and 2329), Nissan Chemical America Company, Houston, Texas (for example, SNOWTEX-ZL, -OL, -O, -N, -C, -20L, -40, and -50); Admatechs Co., Ltd., Japan (for example, SX009-MIE, SX009-MIF, SC1050-MJM, and SC1050-MLV); Grace GmbH & Co. KG, Worms, Germany (for example, those available under the product designation LUDOX™, e.g., P-W50, P-W30, P-X30, P-T40 and P-T40AS); Akzo Nobel Chemicals GmbH, Leverkusen, Germany (for example, those available under the product designation LEVASIL™, e.g., 50/50%, 100/45%, 200/30%, 200A/30%, 200/40%, 200A/40%, 300/30% and 500/15%), and Bayer MaterialScience AG, Leverkusen, Germany (for example, those available under the product designation DISPERCOLL™ S, e.g., 5005, 4510, 4020 and 3030).

Surface- treating the nano-sized silica particles before loading into the dental material can provide a more stable dispersion in the resin. Preferably, the surface-treatment stabilizes the nano-sized particles so that the particles will be well dispersed in the hardenable resin and results in a substantially homogeneous composition. Furthermore, it is preferred that the silica be modified over at least a portion of its surface with a surface treatment agent so that the stabilized particle can copolymerize or otherwise react with the hardenable resin during curing.

Thus, the silica particles as well as other suitable non acid-reactive fillers can be treated with a resin-compatibilizing surface treatment agent.

Particularly preferred surface treatment or surface modifying agents include silane treatment agents capable of polymerizing with a resin. Preferred silane treatment agent include gamma-methacryloxylpropyltrimethoxysilane, available commercially under the trade designation A-174, available commercially from Witco OSi Specialties (Danbury, Conn.) and gamma-glycidoxypropyltrimethoxy silane, a product available under the trade designation G6720, available from United Chemical Technologies (Bristol, Pa.).

Alternatively, a combination of surface modifying agents can be useful, wherein at least one of the agents has a functional group co-polymerizable with a hardenable resin. For example, the polymerizing group can be ethylenically unsaturated or a cyclic function subject to ring opening polymerization. An ethylenically unsaturated polymerizing group can be, for example, an acrylate or methacrylate, or vinyl group. A cyclic functional group subject to ring opening polymerization generally contains a heteroatom such as oxygen, sulfur or nitrogen, and preferably is a 3-membered ring containing oxygen such as an epoxide. Other surface modifying agents which do not generally react with hardenable resins can be included to enhance dispersibility or rheological properties. Examples of silane of this type include, for example, alkyl or aryl polyethers, alkyl, hydroxy alkyl, hydroxy aryl, or amino alkyl functional silanes.

Besides an inorganic material the filler(s) can also be based on an organic material. Examples of suitable organic filler particles include filled or unfilled pulverized polycarbonates, poly(meth)acrylates, polyepoxides, and the like.

Examples of acid-reactive fillers which may be present include acid-reactive fluoroaluminosilicate glasses (sometimes also referred to as GIC glasses), basic fillers like the oxides, hydroxides and carbonates of calcium, magnesium, lanthanum, strontium, zinc or mixtures thereof. These fillers can be also surface treated. Suitable acid-reactive fillers are also described in e.g. in GB 1,316,129 and WO 95/22956 (Wang et al.).

The amount of filler to be used in the filler matrix usually depends on the purpose for which the composition should be used.

If present, the filler is typically present in the following amounts. The amount is given with respect to the weight of the whole composition.

Lower limit: at least 1 wt.% or at least 5 wt.% or at least 10 wt.%.

Upper limit: utmost 90 wt.% or utmost 80 wt.% or utmost 70 wt.%.

Range: 1 wt.% to 90 wt.% or 5 wt.% to 80 wt.% or 10 wt.% to 70 wt.%.

If the amount of filler is too low, mechanical strength of the cured composition might be too low for the intended application.

If the amount of filler is too high, undesirable handling properties like too high viscosity, or poor wetting and penetration of a dental hard tissue might occur.

The ascorbic acid component for use in a method as described in the present text may also be applied together with or as part of a composition comprising one or more additives.

Additives of adjuvants which can be used include accelerators, inhibitors or retarders, absorbers, stabilizers, pigments, dyes, wetting aids, and other ingredients well known to those skilled in the art. The amounts and types of each ingredient in the composition should be adjusted to provide the desired physical and handling properties before and after polymerization.

Examples of dyes or pigments, which can be used include titanium dioxide or zinc sulphide (lithopones), red iron oxide 3395, Bayferrox™ 920 Z Yellow, Neazopon™ Blue 807 (copper phthalocyanine-based dye) or Helio™ Fast Yellow ER. These additives may be used for individual colouring of the dental compositions.

Examples of photo-bleachable colorants which can be present include Rose Bengal, Methylene Violet, Methylene Blue, Fluorescein, Eosin Yellow, Eosin Y, Ethyl Eosin, Eosin bluish, Eosin B, Erythrosin B, Erythrosin Yellowish Blend, Toluidine Blue, 4', 5'- Dibromofluorescein and blends thereof. Further examples of photobleachable colorants can be found in US 6,444,725. The colour of the compositions of the invention may be additionally imparted by a sensitizing compound.

Examples of fluoride release agents which can be present include naturally occurring or synthetic fluoride minerals. These fluoride sources can optionally be treated with surface treatment agents.

Further additives, which can be added, include retarders, (such as 1,2- diphenylethylene), plasticizers (including polyethylene glycol derivatives, polypropylene glycols, low-molecular-weight polyesters, dibutyl, dioctyl, dinonyl and diphenyl phthalate, di(isononyl adipate), tricresyl phosphate, paraffin oils, glycerol triacetate, bisphenol A diacetate, ethoxylated bisphenol A diacetate, and silicone oils), flavorants, anti-microbials, fragrance, agents that impart fluorescence and/or opalescence.

There is no absolute need for these adjuvants or additives to be present, so adjuvants or additives might not be present at all. However, if present they are typically present in an amount which is not detrimental to the intended purpose.

If present, the additive(s) is (are) typically present in the following amounts. The amount is given with respect to the weight of the whole composition.

Lower limit: at least 0.01 wt.% or at least 0.05 wt.% or at least 0.1 wt.%;

Upper limit: utmost 15 wt.% or utmost 10 wt.% or utmost 5 wt.%;

Range: 0.01 wt.% to 15 wt.% or 0.05 wt.% to 10 wt.% or 0.1 wt.% to 5 wt.%.

The method of restoring and/or treating the surface of a prepared tooth may further comprise the step of attaching a dental restoration to the surface of the prepared tooth.

The dental restoration can have the shape of an onlay, inlay, veneer, dental crown, dental bridge, root pin, or implant.

The dental restoration may comprise a material selected from a ceramic material (e.g. zirconia, alumina), a glass ceramic material (e.g. lithium disilicate), a metal alloy or a dental composite material.

Metals which may be present in the metal alloy include Ti, Au, Pt, Pd, Ag, Zn, Co, Cr, Mo, W, Ni and combinations and alloys thereof.

Ceramic materials for dental applications are commercially available e.g. from 3M Oral Care (Lava™ Plus, Lava™ Esthetic).

Metal alloys for dental applications are also commercially available from Argen (Argedent™ 90, Argendent™ Euro), Wieland (Porta™ PK, Porta™ SMK), Bego (PontoStar™ H, BegoCer™ G, Wirobond™ 280), Dentaurum (Triloy™, Rematitan™ M, Remanium™ CS) and DeguDent (Degudent™ G, Degudor™).

Dental composite materials typically comprise polymerized (meth)acrylate components and fillers.

A typical application process for the ascorbic acid component or the composition comprising the ascorbic acid component described in the present text typically includes the following steps in the desired order: providing a composition comprising the ascorbic acid component for use as described in the present text, applying the composition comprising the ascorbic acid component to a surface of a dental restoration (e.g. the inner surface of a dental restoration having the shape of a dental crown), seating the dental restoration with the surface to which the composition has been applied onto the surface of prepared hard dental tissue (in particular dentin), optionally applying radiation (e.g. visible light) to the composition for a period of time sufficient to initiate the polymerisation process (e.g. 5 to 20 s), if the composition contains a photo-initiator, optionally self-curing of the composition for a period of time sufficient to initiate the polymerisation process, if the composition contains a redox initiator system.

Another application process for the ascorbic acid component or the composition comprising the ascorbic acid component described in the present text typically includes the following steps in the desired order: providing a composition comprising the ascorbic acid component for use as described in the present text, bringing the composition in contact with the surface of hard dental tissue (in particular dentin), optionally applying radiation (e.g. visible light) to the composition for a period of time sufficient to initiate the polymerisation process (e.g. 5 to 20 s), if the composition contains polymerizable components (e.g. polymerizable components without acid groups and/or polymerizable components with acid groups) and a photo-initiator, optionally self-curing of the composition for a period of time sufficient to initiate the polymerisation process, if the composition contains a redox initiator system, attaching a dental restoration to the surface of the prepared hard dental tissue.

If the composition is self-etching, no prior etching step or use of a bonding/primer is needed.

Thus, if desired, the composition described in the present text can be used as a self- adhesive, self-etching cement.

It has been found that etching the dental surface with a separate etching agent does typically not improve the adhesion the dental restoration to be dental surface.

Instead, it has been observed that by conducting a separate etching and/or rinsing step, the smear layer being present on the surface of the prepared tooth is more or less completely removed. Such a removal step may be contra productive, as the amount of disulfide bridges being present in the collagen fibres is largely reduced and thus only a minor amount of disulfide bridges is available.

Thus, according to one embodiment, the method does not comprise a step of etching the surface of the prepared tooth with an etchant such as a composition comprising phosphoric acid.

The composition containing the ascorbic acid component may be useful as anterior or posterior filling material, adhesive, cavity liner, flowable, cement, coating composition, root canal filler, root canal sealant or core build-up material. Suitable tools for applying radiation include dental curing lights. Suitable dental curing lights are described e.g. in US 2005/0236586 A1. The content of this document is herewith incorporated by reference. Suitable dental curing lights are also commercially available e.g. under the trade names Elipar™ S10 (3M Oral Care).

According to one embodiment, a composition comprising an ascorbic acid component for use in a process as described in the present text comprises or consists essentially of or consists of the ascorbic acid component, preferably in an amount of 0.01 wt.% to 5 wt.%, or 0.05 to 3 wt.%, or 0.1 to 2 wt.% or 0.1 to 1 wt.%, stabilizer(s) selected from sulfite(s), phosphite(s), benzotriazole(s) and mixtures thereof, preferably in an amount of 0.01 wt.% to 5 wt.%, or 0.05 to 3 wt.%, or 0.1 to 1 wt.%, transition metal component(s), preferably in an amount of 0.00001 wt.% to 3 wt.%, or 0.0001 to 2 wt.%, or 0.001 to 0.5 wt.%, organic peroxide(s), preferably in an amount of 0.01 wt.% to 5 wt.%, or 0.05 to 4 wt.%, or 0.05 to 3 wt.%, or 0.1 to 3 wt.%, polymerizable component(s) without acidic moieties, preferably in an amount of 5 wt.% to 65 wt.%, or 10 to 55 wt.%, or 20 to 45 wt.%, polymerizable component(s) with acidic moieties, preferably in an amount of 2 wt.% to 50 wt.%, or 3 to 40 wt.%, or 4 to 30 wt.%, or 3 to 20 wt.%, filler(s), preferably in an amount of 1 wt.% to 90 wt.%, or 5 to 80 wt.%, or 10 to 70 wt.%, or 40 to 85 wt.%, additives(s), preferably in an amount of 0.01 wt.% to 15 wt.%, or 0.05 to 10 wt.%, or 0.1 to 5 wt.%, wt.% with respect to the amount of the whole composition.

According to one embodiment, the composition comprising the ascorbic acid component for use in a method as described in the present text comprises, consists essentially of or consists of: the ascorbic acid component in an amount of 0.1 to 2 wt.%, stabilizer(s) selected form sulfite(s), phosphite(s), benzotriazole(s) and mixtures thereof in an amount of 0.1 to 1 wt.%, photo-initiator in an amount of 0.01 to 0.2 wt.%, filler(s) in an amount of 40 to 85 wt.%, polymerizable component(s) without acidic moieties in an amount of 10 to 55 wt.%, transition metal component(s) comprising a copper or iron ions containing salts in an amount of 0.005 to 0.5 wt.%, organic peroxide(s) having the structure R-O-O-H as described in the text above with

R being (e.g. Ci to C20) alkyl, (e.g. C3 to C20) branched alkyl, (e.g. C₆ to C12) cycloalkyl,

(e.g. C7 to C20) alkylaryl or (e.g. C₆ to C12) aryl in an amount of 0.5 to 3 wt.%, polymerizable component(s) with acidic moieties in an amount of 3 to 20 wt.%, additives(s) in an amount of 0.05 to 10 wt.%, wt.% with respect to the weight of the composition.

The compositions described in the present text are typically provided as a two-part composition. For reasons of storage stability, the two parts are typically separated from each other before use.

If the composition is provided as a two-component or two-part composition, the respective parts may look as follows:

Part A comprising component(s) comprising an ascorbic acid moiety, stabilizer selected from sulfite(s), phosphite(s) or mixtures thereof, polymerizable component(s) without acidic moieties, filler(s), optionally polymerizable component(s) with acidic moieties, optionally additive(s),

Part B comprising polymerizable component(s) without acidic moieties, polymerizable component(s) with acidic moieties, transition metal component(s), organic peroxide(s) selected from hydroperoxide(s) and di-peroxide(s), filler(s), optionally additive(s), wherein the kit of parts is provided as a paste/paste system.

Part A and Part B are typically provided in a ratio of 1:5 to 5:1 or 1:2 to 2:1 or 1:1 with respect to volume.

The composition described in the present text does typically not contain components comprising a sulfinate moiety (especially sulfinate salts such as sodium toluene sulfinate), barbituric acid moiety, thiobarbituric acid moiety, an aryl borate moiety, a thiourea moiety, or mixtures thereof.

Thus, the composition described in the present text may not comprise either of the following components or combinations thereof: component comprising a barbituric or thiobarbituric acid moiety, component comprising an aryl borate moiety, component comprising a sulfinate moiety, a thiourea moiety, component comprising a thiol- or di-thiol moiety. According to one embodiment the composition described in the present text does not comprise Bis-GMA in an amount of more than 1 or 3 or 5 wt.% with respect to the weight of the whole composition. According to one embodiment the composition described in the present text is essentially free of Bis-GMA.

According to a further embodiment, the composition described in the present text does not comprise HEMA in an amount of more than 1 or 3 or 5 wt.% with respect to the weight of the whole composition. According to one embodiment the composition described in the present text is essentially free of HEMA.

According to a further embodiment, the composition described in the present text does not comprise water in an amount of more than 0.5 or 1 or 2 wt.% with respect to the weight of the whole composition. According to one embodiment the composition described in the present text is essentially free of water. Keeping the amount of water low may help to reduce the risk of undesired swelling of the composition and may help to achieve the desired physical properties like sufficient flexural strength.

According to a further embodiment, the composition described in the present text does not comprise a polyacid in an amount of more than 0.5 or 0.2 or 0.1 wt.% with respect to the weight of the whole composition. Polyacids are typically used in so-called glass-ionomer cement compositions curing by the reaction of a polyacid with an acid-reactive filler in the presence of water. Thus, the composition described in the present text does not cure by a reaction of a polyacid with an acid-reactive filler in the presence of water.

Unavoidable traces of these components might be present (e.g. due to impurities in the raw materials used). However, those components are typically not willfully added in an amount to participate in the curing reaction.

A composition comprising the ascorbic acid component described in the present text can be prepared by mixing the respective components of the composition. If desired, a speed mixer can be used. For high viscous compositions a kneader is recommended.

If the composition contains a photo-initiator, the mixing is typically done under safe light conditions.

The ascorbic acid component or the composition comprising the ascorbic acid component is typically stored in a packaging device before use.

Suitable packaging devices include cartridges, syringes and tubes.

The volume of the packaging device used for storing is typically in the range of 0.1 to 100 ml or 0.5 to 50 ml or 1 to 30 ml.

A packaging device may also comprise two compartments, wherein each compartment is equipped with a nozzle for delivering the composition or parts stored therein. Once delivered in adequate portions, the parts can then be mixed by hand on a mixing plate. The packaging device may have an interface for receiving a static mixing tip. The mixing tip is used for mixing the respective compositions.

The packaging device typically comprises two housings or compartments having a front end with a nozzle and a rear end and at least one piston movable in the housing or compartment.

Cartridges which can be used are also described e.g. in US 2007/0090079 A1 or US 5,918,772, the disclosure of which is incorporated by reference. Some of the cartridges which can be used are commercially available e.g. from Sulzer Mixpac company (Switzerland).

Static mixing tips which can be used are described e.g. in US 2006/0187752 A1 or in US 5,944,419, the disclosure of which is incorporated by reference. Mixing tips which can be used are commercially available from Sulzer Mixpac (Switzerland), as well.

Other suitable storing devices are described e.g. in WO 2010/123800 (3M), WO 2005/016783 (3M), WO 2007/104037 (3M), WO 2009/061884 (3M), in particular the device shown in Fig. 14 of WO 2009/061884 (3M) or WO 2015/073246 (3M), in particular the device shown in Fig. 1 of WO 2015/07346. Those storing devices have the shape of a syringe. The content of these references is herewith incorporated by reference, as well.

The complete disclosures of the patents, patent documents, and publications cited herein are incorporated by reference in their entirety as if each were individually incorporated. Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. The above specification, examples and data provide a description of the manufacture and use of the compositions and methods of the invention. The invention is not limited to the embodiments disclosed herein. One skilled in the art will appreciate that many alternative embodiments of the invention can be made without departing from the spirit and scope of thereof.

The following examples are given to illustrate the invention.

Examples

Unless otherwise indicated, all parts and percentages are on a weight basis, all water is de-ionized water, and all molecular weights are weight average molecular weight. Moreover, unless otherwise indicated all experiments were conducted at ambient conditions (23°C; 1013 mbar).

Methods

Viscosity

If desired, the viscosity of the mixed pastes can be determined by using a Physica MCR 301 Rheometer (Anton Paar, Graz, Austria) with a plate/plate geometry (PP08) at a constant shear rate of 10s ¹ in rotation at 28 °C. The diameter of the plates is 8 mm and the gap between the plates is set to 0.75 mm. After mixing, about 200 mg of the mixture is placed on the cylindrical platform and the viscosity (in Pas) is determined. Each measurement should be performed twice. pH Value

If desired, the pH value of a composition can be determined as follows: A pH sensitive paper (Carl Roth™ company) is provided. A stripe of the pH sensitive paper is wetted. A small portion of the composition to be tested is placed on the wetted pH sensitive paper. After 5 s the colour change of the pH sensitive paper is determined.

Adhesion (Shear bond strength)

Bovine teeth are ground flat to expose dentin, polished (grit 320 sandpaper), water- rinsed, and gently air-dried. Stainless steel rods (diameter=4mm) are sandpapered, sandblasted, silanized (ESPE™ Sil, 3M Oral Care) and subsequently cemented (n=6) under standardized pressure (20g/mm²). Then, glycerine gel (Airblock™, Dentsply™) is applied around the margin. The specimens are stored for 10 min under pressure (36°C) followed by additional 24h (36°C; 100% relative humidity) without pressure. The specimens are subjected to shear bond strength (SBS) testing (Zwick Z010; n=6; speed=0.75mm/min). Data analysis is performed using One-Way ANOVA (Tukey; p<0.05).

Degree of Conversion (DOC)

If desired, the degree of conversion can be determined as follows:

For conducting the measurements reported in the present text a cylindrical mold (diameter 6mm; height 0.5mm) is placed on top of dentin and filled with the composition. Then, a transparent glass slide is placed on top. Pressure (9 g/cm²) is applied for 10min at 36°C. Then, the pressure is relieved and the samples are stored at 36°C and 100% relative humidity for 24h. Then, slices (thickness 2mm) are cut using an Accutom™ 50 cutting machine to obtain cross-section of the cement dentin interface.

The Raman spectra are acquired with a Witec Confocal Raman microscope using a 488 nm laser. The spectrometer consists of a 600 lines/mm grating dispersed onto a thermo- electrically-cooled CCD (Andor Technologies). Spectral resolution is approx. 8 cm^-1. Spectra are recorded with a 50X/0.95 NA objective. Integration time of a single spectrum is approx. 1 s. Raman spectra are recorded along the cross section of the cured composition which is applied to dentin. 96 data points are recorded along the cross section for statistics.

The spatially resolved monomer conversion is calculated from the Raman line scan data. In order to minimize out-off focus effects the intensity of the acrylic C=C stretching vibration at approx. 1640 cm^-1 is normalized with the intensity of the band at about 1465 cm^-1 which can be attributed to the aliphatic CH deformation vibrations of the cements. The monomer conversion C is calculated according to: C = (1-(A_t/A_t,R)/(Ao/Ao_,R)) ^c 100% where Ao is the intensity of an acrylate double-bond of the uncured monomer resin, and At is the band intensity of the residual acrylate double-bond while the cement cures.

As the general intensities of spectra possibly vary during the time series recording, the band intensities are normalized to the band intensities of a resin specific, inherent internal standard A₍,R and AO,R.

Reduction of Disulfide Bonds

If desired, the reduction or cleavage of disulfide bonds can be determined as follows: Discs of dentin are provided. The dentin discs are either treated with the ascorbic acid component or a composition containing the ascorbic acid component (e.g. for 15 min). As appropriated, the interface (dentin/composition) is etched using phosphoric acid to make the interface accessible for a thiol-specific fluorescent marker. The fluorescence is analyzed with an appropriate instrument, e.g. LSM 510 Meta Confocal Microscope (Zeiss).

As thiol-specific fluorescent markers the following components can be used: e.g. Alexa™ Fluor 488 (ThermoFisher Scientific) or Alexa™ Fluor 546 (ThermoFisher Scientific). Alternatively, the presence of absence of disulfide bonds can also be analysed by

Raman spectroscopy, if desired.

Materials

Examples The following pastes were provided.

The compositions of Part A and Part B were mixed 1:1 by volume to obtain Composition E1.

For comparison Part A and Part B of RelyX™ Unicem 2 AM (3M Oral Care; 3M ESPE) were mixed 1:1 by volume to obtain Composition E2. RelyX™ Unicem 2 AM does not contain an ascorbic acid component.

The composition of Relxy™ Unicem 2 AM can be taken from the respective material data sheets (published).

Example 1 Ascorbyl palmitate powder was rubbed into a freshly prepared (wet) dentin surface and allowed to react for 15min.

Then, the powder residues were removed using a micro brush followed by rinsing with water.

Then, stainless steel rods were cemented using either the composition of E1 or E2 and shear bond strength (SBS) was measured after storage for 24h at 36°C and 100% relative humidity (STD = standard deviation).

ASP treatment of dentin did not significantly increase the SBS value to dentin of the composition of E1 , whereas ASP treatment of the composition of E2 increased the SBS value.

The composition of E1 was not affected by the pretreatment with ASP, because the calcium salt of ascorbyl palmitate (CaASP) was already present in the composition of E1, contrary to the composition of E2, which did not contain neither ASP nor CaASP. Example 2

The degree of conversion (DOC) for the composition of E1 was tested as described above.

For the composition of E1 a high degree of conversion (DOC) in the dentin cement interface was found.

A higher DOC can be correlated to higher shear bond strength as the smear layer is effectively incorporated into the cement.

Claims

1. An ascorbic acid component for use in a method of restoring and/or treating the surface of a prepared tooth in the mouth of a human being or animal, the method comprising the step of bringing the ascorbic acid component or a composition comprising the ascorbic acid component in contact with the surface of the prepared tooth, the surface of the prepared tooth comprising collagen fibers containing disulfide moieties, the ascorbic acid component being applied in an amount and for a time effective to reduce or cleave at least a part of the disulfide moieties contained in the collagen fibers, the method not comprising a step of etching the surface of the prepared tooth with an etchant such as a composition comprising phosphoric acid.

2. The ascorbic acid component for use in a method of restoring and/or treating the surface of a prepared tooth according to the preceding claim, the step of bringing the ascorbic acid component or composition comprising the ascorbic acid component in contact with the surface of a prepared tooth being done for a time period of at least 10 s.

3. The ascorbic acid component for use in a method of restoring and/or treating the surface of a prepared tooth according to any of the preceding claims, the ascorbic acid component being used in an amount of at least 0.0001 pmol per mm² treated surface of the prepared tooth.

4. The ascorbic acid component for use in a method of restoring and/or treating the surface of a prepared tooth in particular according to any of the preceding claims, the method comprising the steps of applying the ascorbic acid component to the surface of the prepared tooth as part of or in combination with a composition comprising polymerizable monomers, an initiator and optionally fillers, for enabling the composition to come in contact with collagen fibers containing disulfide moieties being present in the surface of the prepared tooth and reducing at least a part of the disulfide moieties, and allowing the polymerizable monomers to interact with or bond to the reduced disulfide moieties, optionally attaching a dental restoration.

5. The ascorbic acid component for use in a method of restoring and/or treating the surface of a prepared tooth according to any of the preceding claims, the method comprising the steps of applying the ascorbic acid component to the surface of the prepared tooth as part of or in combination with a composition comprising polymerizable monomers, an initiator and optionally fillers, attaching a dental restoration, the method not comprising the step of etching and rinsing the surface of the prepared tooth.

6. The ascorbic acid component for use in a method of restoring and/or treating the surface of a prepared tooth according to any of the preceding claims, the dental restoration comprising a material selected from ceramic, glass ceramic, metal alloy or dental composite.

7. The ascorbic acid component for use in a method of restoring and/or treating the surface of a prepared tooth according to any of the preceding claims, the dental restoration having the shape of an onlay, inlay, veneer, dental crown, dental bridge, root pin, or implant.

8. The ascorbic acid component according to any of the preceding claims for use in a method of restoring and/or treating the surface of a prepared tooth, the ascorbic acid component being applied as part of or in combination with a composition, the composition having a viscosity in the range of 0.01 to 1,000 Pa*s at 28°C and a shear rate of 10 s ¹.

9. The ascorbic acid component for use in a method of restoring and/or treating the surface of a prepared tooth of the preceding claim, the ascorbic acid component being selected from components formed by reacting one or more of the hydroxyl functions of ascorbic acid with a C2 to C30 saturated or unsaturated carboxylic acid, salts and mixtures thereof;

10. The ascorbic acid component for use in a method of restoring and/or treating the surface of a prepared tooth according to any of the preceding claims, the ascorbic acid component being selected from the esters of ascorbic acid with caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic acid, a-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid or docosahexaenoic acid, the salts and mixtures thereof.

11. The ascorbic acid component according to any of the preceding claims for use in a method of restoring and/or treating the surface of a prepared tooth, the ascorbic acid component being applied as part of or in combination with a composition comprising a stabilizer, preferably a stabilizer selected from components comprising a phosphite, sulfite or benzotriazole moiety and mixtures thereof.

12. The ascorbic acid component according to any of the preceding claims for use in a method of restoring and/or treating the surface of a prepared tooth, the ascorbic acid component being applied as part of or in combination with a composition comprising polymerizable components with one or more acidic moieties.

13. The ascorbic acid component according to any of the preceding claims for use in a method of restoring and/or treating the surface of a prepared tooth, the ascorbic acid component being applied as part of or in combination with a composition comprising one or more transition metal components.

14. The ascorbic acid component according to any of the preceding claims for use in a method of restoring and/or treating the surface of a prepared tooth, the ascorbic acid component being contained in a composition comprising ascorbic acid component, preferably in an amount of 0.1 to 2 wt.%, stabilizer(s) selected form sulfite(s), phosphite(s), benzotriazole(s) and mixtures thereof, preferably in an amount of 0.1 to 1 wt.%, photon nitiator, preferably in an amount of 0.01 to 0.2 wt.%, filler(s), preferably in an amount of 40 to 85 wt.%, polymerizable component(s) without acidic moieties, preferably in an amount of 10 to 55 wt.%, transition metal component(s) comprising a copper or iron ions containing salts, preferably in an amount of 0.001 to 0.5 wt.%, organic peroxide(s) having the structure R-O-O-H with R being Ci to C20 alkyl, C3 to C20 branched alkyl, C₆ to C12 cycloalkyl, C7 to C20 alkylaryl or C₆ to C12 aryl, preferably in an amount of 0.5 to 3 wt.%, polymerizable component(s) with acidic moieties, preferably in an amount of 3 to 20 wt.%, additives(s) in an amount of 0.05 to 10 wt.%, wt.% with respect to the weight of the composition.

15. The ascorbic acid component according to any of the preceding claims for use in a method of restoring and/or treating the surface of a prepared tooth, the composition not comprising components comprising a barbituric or thiobarbituric acid moiety, components comprising an aryl borate moiety, components comprising a sulfinate moiety, components comprising a thiourea moiety, components comprising a thiol- or di-thiol moiety.