This invention relates to tooth prostheses, methods of making tooth prostheses, dentures including the tooth prostheses and methods of making dentures.

Prosthodontics is concerned with treatments to address missing or deficient teeth in patients. One type of prosthodontic device, also referred to herein as an endosteal implant may be used to replace one or more missing teeth by fusing a support member to the jaw bone of a patient, with a core of the prosthesis supporting a crown or a bridge of teeth. An endosteal implant is fixed within a patient's mouth, typically to the jaw through the gums, for example by screws or adhesive, and so is not removable by a patient under normal conditions.

A second type of prosthodontic device is arranged to a replace a patient's missing teeth and contiguous tissue with a prosthesis which is designed to be removed by a wearer, for example nightly. Such removable prostheses, also referred to as dentures herein, may comprise removable partial or whole prosthodontic devices which cooperate with a patient's gums and palate, and with natural remaining teeth (or with other implants) to define partial or complete prosthetic dentition. Such dentures also may also include teeth prostheses which are located in the dental framework in order to form a denture which may be removably worn by a patent with hard wearing prosthetic teeth having a natural appearance.

There are many different types of prosthodontic devices and methods of making such devices. For example, removable prosthodontic devices may comprise a metal framework (e.g. of cobalt/chrome) in combination with cast or moulded plastics parts. However,

disadvantageously, such devices may be heavy, difficult to manufacture to produce an accurate mouth-fit, and have high stiffness and poor load distribution, leading to patient discomfort. Additionally, use of metal may result in relatively high levels of metal ions being introduced into patients' bodies over time. Furthermore, some patients are allergic to metals used in the devices. In addition, manufacture of existing prosthodontic devices, or those which include a combination of metal and plastics, can be time-consuming; and such devices may be aesthetically unattractive. A problem with tooth prostheses is to provide a tooth prosthesis which is natural in appearance and is hard wearing, easily formed into a desired shape and yet which is also light and easily attached to either a dental framework or directly to the jaw of a patient. Typically, tooth prostheses have been made from a core of metal or ceramic material, or from a cast resin material such as acrylic resin, prepared from in-situ reaction of monomers upon moulding, with a dental veneer bonded to the outer face of the core in order to form a crown. It is important that the dental veneer is strongly bonded to the underlying core and remains strongly bonded even after prolonged immersion in the fluids found in the mouth. The presence of metals, or of trace amounts of reactive monomers, in the mouth of a patient are undesirable. It is also desirable to have cores for tooth prostheses which are easily shaped in-situ in a dental surgery, yet which may be strongly bonded to a dental veneer in order to form a crown. It is also desirable to have tooth prostheses which are easily bonded to a dental framework in order to make a removable denture. It is also desirable to have tooth prostheses which are not so excessively rigid that they cause risk of damage to opposing teeth of a patient in use. It is also desirable to have tooth prostheses which are of low weight

It is one aim of the present invention, amongst others, to provide tooth prostheses, dentures and methods which address, obviate or at least partially mitigate at least some of the problems or disadvantages in the prior art, whether identified herein or elsewhere. For instance, it is an aim of exemplary embodiments of the invention to provide a tooth prosthesis and method of making a tooth prosthesis, which has a lightweight, non-toxic and easily shaped core which has suitable strength and resilience and yet which may be soundly bonded to a dental veneer as a crown using conventional dental bonding materials. It is also an aim of the invention to provide alternatives to prior art tooth prostheses, dentures and methods.

According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

Throughout this specification, the term "comprising" or "comprises" means including the components) specified but not to the exclusion of the presence of other components. The term "consisting essentially of or "consists essentially of means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention. Typically, when referring to compositions, a composition consisting essentially of a set of components will comprise less than 5% by weight, typically less than 3% by weight, more typically less than 1 % by weight of non-specified components.

The term "consisting of or "consists of means including the components specified but excluding other components. Whenever appropriate, depending upon the context, the use of the term "comprises" or "comprising" may also be taken to include the meaning "consists essentially of or "consisting essentially of, and also may also be taken to include the meaning "consists of or "consisting of.

Ranges referred to herein, such as "in the range x to y", have the same meaning as "from x to y" and include the values x and y.

The optional features set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the

accompanying claims. The optional features for each aspect or exemplary embodiment of the invention, as set out herein, are also applicable to any other aspects or exemplary

embodiments of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each exemplary embodiment of the invention as interchangeable and combinable between different aspects or exemplary embodiments.

A first aspect of the invention provides a tooth prosthesis comprising a core of a composition comprising a polymeric material, the core having an outer face and a dental veneer as a crown bonded to the outer face of the core, wherein the polymeric material comprises, a repeat unit of formula (I):

The symbols t1 and w1 independently represent 0 or 1 and v1 represents 0, 1 or 2. The composition, also referred to herein as the first composition, may consist or consist essentially of the polymeric material, or may include, for instance from 60 to 100%, say from 75 to 100% of the polymeric material, with from 0 to 40%, say from 0 to 25% of other materials. The composition may include, for example colourants (e.g. pigments, ceramics, metal oxides (eg. titanium dioxide)) or fillers (for example reinforcing or wear enhancing fillers or fibres, bioactive fillers such as bioglasses, soluble glasses, zeolites containing antibacterial agents such as silver ions, nanosilver, ceramics such as hydroxyapatite (HA) or substituted HA or treatment agents such as antibiotic doped HA or compounds favourable to the gingiva, diagnostic agents such as radiopaque fillers such as barium sulphate, aesthetic fillers such as reflective agents and light refracting agents, fillers conveying some taste or flavour altering or enhancing effect or breath freshening effect). The composition may include, for instance, 0-10 wt%, suitably 0-6 wt% of colourants. Colourants may be selected so the composition is white. Colourants may be employed so that the colour is graduated. In one embodiment, the composition includes no colourant. When a filler is included in the composition, it may suitably be included to improve the mechanical properties and/or bonding characteristics and/or biological acceptability of the composition. However, it has been found that cores for tooth prostheses with excellent mechanical properties can be made without requiring addition of filler. Preferably, the composition comprises at least 80 wt%, at least 90 wt% or at least 94 wt% of the polymeric material. Suitably, the composition may comprise hydroxyapatite as adjunct, for instance as up to 25% by weight of the composition. This may improve the biological compatibility of the tooth prosthesis, for instance when used as an endosteal implant, and may encourage growth and fixation of bone in the jaw to the attachment means of the tooth prosthesis.

The polymeric material preferably consists essentially of a repeat unit of formula I. Preferred polymeric materials comprise (or consist essentially of) a repeat unit wherein t1 =1 , v1 =0 and w1 =0; t1 =0, v1 =0 and w1 =0; t1 =0, w1 =1 , v1 =2; or t1 =0, v1 =1 and w1 =0. More preferred polymeric materials comprise (or consist essentially of) a repeat unit wherein t1 =1 , v1 =0 and w1 =0; or t1 =0, v1 =0 and w1 =0. The most preferred polymeric material comprises (or consists essentially of) a repeat unit wherein t1 =1 , v1 =0 and w1 =0 (in other words the polymeric material is most preferably a polyetheretherketone, PEEK, homopolymer). In preferred embodiments, the polymeric material is selected from polyetheretherketone, polyetherketone, polyetherketoneetherketoneketone and polyetherketoneketone. In a more preferred embodiment, the polymeric material is selected from polyetherketone and polyetheretherketone. In another preferred embodiment, the polymeric material is

polyetheretherketone, such as homopolymeric polyetheretherketone.

The polymeric material may have a Notched Izod Impact Strength (specimen 80mm x 10mm x 4mm with a cut 0.25mm notch (Type A), tested at 23°C, in accordance with ISO180) of at least 4KJm ^"2 , preferably at least 5KJm ^"2 , more preferably at least 6KJm ^"2 . The Notched Izod Impact Strength may be less than 10KJm ^"2 , suitably less than 8KJm ^"2 . The Notched Izod Impact Strength may be at least 3KJm ^"2 , suitably at least 4KJm ^"2 , preferably at least 5KJm ^"2 . The impact strength may be less than 50 KJm ^"2 , suitably less than 30KJm ^"2 .

The polymeric material suitably has a melt viscosity (MV) of at least 0.06 kNsm ^"2 , preferably has a MV of at least 0.09 kNsm ^"2 , more preferably at least 0.12 kNsm ^"2 , or at least 0.15 kNsm ^"2 . Advantageously, the MV may be at least 0.35 kNsm ^"2 and or at least 0.40 kNsm ^"2 An MV of 0.45 kNsm ^"2 has been found to be particularly advantageous in the manufacture of accurate, strong cores. MV is suitably measured using capillary rheometry operating at 400°C at a shear rate of 1000s ^"1 using a cylindrical tungsten carbide die, 0.5mmx3.175mm in size (diameter x length of die). The polymeric material may suitably have an MV of less than 1 .00 kNsm ^"2 , preferably less than 0.5 kNsm ^"2 .

The polymeric material may have a MV in the range 0.09 to 0.5 kNsm ^"2 , preferably in the range 0.14 to 0.5 kNsm ^"2 , more preferably in the range 0.4 to 0.5 kNsm ^"2 .

The polymeric material may have a tensile strength, measured in accordance with IS0527 (specimen type 1 b) tested at 23°C at a rate of 50mm/minute of at least 20 MPa, preferably at least 60 MPa, more preferably at least 80 MPa. The tensile strength is preferably in the range 80-1 10 MPa, more preferably in the range 80-100 MPa.

The polymeric material may have a flexural strength, measured in accordance with IS0178 (80mm x 10mm x 4mm specimen, tested in three-point-bend at 23°C at a rate of 2mm/minute) of at least 50 MPa, preferably at least 100 MPa, more preferably at least 145 MPa. The flexural strength is preferably in the range 145-180MPa, more preferably in the range 145-164 MPa.

The polymeric material may have a flexural modulus, measured in accordance with IS0178 (80mm x 10mm x 4mm specimen, tested in three-point-bend at 23°C at a rate of 2mm/minute) of at least 1 GPa, suitably at least 2 GPa, preferably at least 3 GPa, more preferably at least 3.5 GPa. The flexural modulus is preferably in the range 3.5-4.5 GPa, more preferably in the range 3.5-4.1 GPa.

The polymeric material may be amorphous or semi-crystalline. It is preferably crystallisable. It is preferably semi-crystalline. The level and extent of crystallinity in a polymer is preferably measured by wide angle X-ray diffraction (also referred to as Wide Angle X-ray Scattering or WAXS), for example as described by Blundell and Osborn (Polymer 24, 953, 1983).

Alternatively, crystallinity may be assessed by Differential Scanning Calorimetry (DSC).

The level of crystallinity of the polymeric material may be at least 1 %, suitably at least 3%, preferably at least 5% and more preferably at least 10%. In or preferred embodiments, the crystallinity may be greater than 25%. It may be less than 50% or less than 40%. Preferably the prosthodontic device includes a framework having the aforementioned levels of crystallinity. The main peak of the melting endotherm (Tm) of the polymeric material (if crystalline) may be at least 300°C.

The tooth prosthesis of the first aspect of the invention may be adapted for retention in a patient as an endosteal implant. For instance, the tooth prosthesis may be adapted for retention by comprising a support post, which may, for instance, be in the form include a peg, post, pillar, screw or the like, arranged for fastening the tooth implant into a hole formed in a patient's jaw. The tooth prosthesis of the first aspect of the invention may alternatively or additionally be adapted for retention in a prosthodontics framework, such as the framework of a removable denture. For instance, the tooth prosthesis may be adapted for retention by comprising a support post, which may, for instance, be in the form include a peg, post, pillar, screw or the like, arranged for fastening the tooth implant into a hole formed in a dental framework of a removable denture.

The core and the support post may be of a unitary construction. In other words, the core and support post may both be of the same composition comprising polymeric material according to formula (I) and may be formed together in a monolithic fashion, for instance by moulding, for instance injection moulding of a melt, or by milling from a blank of the composition.

Where the support post and the prosthodontics framework comprise or consist essentially of the same, or a similar polymeric material, adhesion, or bonding or welding of the support post to the framework may be enhanced as a result of the same or similar polymeric material being used.

Preferably, the outer face of the core is a roughened outer face. The roughened outer face may have an Ra from 0.06 to 7.0 micrometres, where Ra is the roughness average of a surface, expressed in micrometres. This is the arithmetic mean of the absolute departures of a roughness profile from the mean line of a measurement carried out along an arbitrary line along a surface. Ra is suitably measured by a mechanical contact method by means of a stylus drawn in a straight line over the surface with the height of the stylus measured at regular intervals along the surface, wherein the stylus tip has a diameter of 2 micrometres in accordance with DIN EN ISO 4288 and DIN EN ISO 3274, using a Perthometer SP6 surface profilometer.

More preferably, the roughened outer face may have an Ra from 0.5 to 2.0 micrometres. It has been found that such roughness values provide good bonding between the core and the dental veneer. For instance, Al ₂ 0 ₃ particles may suitably be used as abrasive particles for blasting the outer surface in order to provide roughening. Alternatively or additionally, sulphuric acid etching or tribochemical treatments may be applied.

Any suitable dental veneer may be used, and these are widely available commercially.

However, it has been found that optimal bonding occurs when the dental veneer comprises silica, for instance at least 10% by weight of silica. The dental veneer may be a pre-formed veneer or may be formed in-situ on the outer face of the core.

An opaque paste comprising silica may be located between the dental veneer and the outer face of the core. Such opaque pastes are commercially available for use in bonding crowns to cores of tooth prostheses, and are used to provide a realistic tooth-like appearance to the crown. It has been found that the use of an opaque paste comprising silica may improve the bonding of the dental veneer to the core of the dental prosthesis of the invention. The bonding layer may be located on the outer face of the core, between the outer face of the core and the dental veneer. Preferably, the bonding layer may comprise reactive phosphate or silane moieties.

For the polymeric material, it is preferred for t1 =1 , v1 =0 and w1 =0. In other words, the polymeric material is preferably a PEEK polymer, such as a PEEK homopolymer.

A second aspect of the invention provides a method of forming a tooth prosthesis by bonding dental veneer, as a crown, to a core of a composition comprising a polymeric material,

wherein the wherein the polymeric material is or comprises a repeat unit of formula (I):

wherein t1 and w1 independently represent 0 or 1 and v1 represents 0, 1 or 2, wherein the method comprises: a) forming the core, having a predetermined shape, from the composition of polymeric material;

b) subjecting an outer face of the core to a surface treatment whereby the outer face is transformed into a roughened outer face; and

c) bonding the dental veneer to the roughened outer face. For the method of the second aspect of the invention, the bonding of the dental veneer may comprise applying a bonding layer to the roughened outer face and bonding an inner face of the dental veneer to the bonding layer. An opaque paste layer comprising silica may be applied between the bonding layer and the inner face of the dental veneer to attach the inner face of the dental veneer to the bonding layer.

The outer face of the core may be roughened by sulphuric acid etching and/or by blasting with abrasive particles. For instance, Al ₂ 0 ₃ particles may suitably be used as abrasive particles.

The outer face may suitably be roughened to an Ra from 0.06 to 7.0 micrometres. The outer face may preferably be roughened to an Ra from 0.5 to 2.0 micrometres by blasting with abrasive particles.

Suitably, the abrasive particles may have a weight-based median particle diameter from 30 to 100 micrometres. This may be measured using a Malvern particle sizing apparatus based on light scattering and making the assumption that the particles are spherical in nature and of uniform density.

The abrasive particles may be silica-coated abrasive particles, whereby the roughened outer face of the core may be at least partially silica-coated as a result of interaction with the abrasive particle surfaces during blasting. A third aspect of the invention provides a tooth prosthesis obtained or obtainable by the method of the first aspect of the invention.

A fourth aspect of the invention provides a method of forming a denture comprising:

providing a tooth prosthesis according to the first aspect of the invention, the tooth prosthesis further comprising an attachment means of the composition comprising the polymeric material, providing a dental framework of a second composition comprising a second polymeric material which is or comprises a repeat unit of formula (I):

wherein t1 and w1 independently represent 0 or 1 and v1 represents 0, 1 or 2, the dental framework arranged to engage with the attachment means; and

attaching the tooth prosthesis to the dental framework at the attachment means. The tooth prosthesis may be attached or bonded to the dental framework by any suitable means, but is preferably welded to the dental framework by ultrasonic welding.

The attachment means may comprise an attachment post and the dental framework may be arranged to engage with the attachment post by comprising a female member adapted to accept the attachment post mated therein.

Preferably, the second polymeric material (i.e. of the dental framework) is the same polymeric material as the first polymeric material. Suitably, the second composition may consist or consist essentially of the second polymeric material. The first and second polymeric materials are preferably a PEEK polymer, such as a PEEK homopolymer.

For a better understanding of the invention, and to show how exemplary embodiments of the same may be carried into effect, reference will be made, by way of example only, to the accompanying diagrammatic Figures, in which:

Figure 1 schematically depicts the stages in the formation of a core for an embodiment of a tooth prosthesis according to an aspect of the invention from a blank of polymeric material;

Figure 2 schematically depicts the bonding of a crown of dental veneer to the core of Figure 1 to form the tooth prosthesis of the embodiment; Figure 3 schematically depicts the attachment of the tooth prosthesis of the first embodiment to a dental framework of polymeric material in order to form an embodiment of a denture according to an aspect of the invention.

The PEEK used as core was the following material, referred to hereinafter simply as PEEK: PEEK-OPTIMA (Trade Mark) LT1 - polyetheretherketone (PEEK) of melt viscosity (MV) 0.45 kNsm ^"2 . Alternatively the two other variants of PEEK-OPTIMA® (Trade Mark) LT2 and LT3 of melt viscosity (MV) in the range between 0.45 and 0.15 could also have been used.

Turning to Figure 1 , a blank of polymeric material (PEEK) is formed into a core 2 for a tooth prosthesis, also including an attachment post 4. The core 2 and attachment post 4 are formed in this embodiment by computer-aided milling, and as a unitary structure from the blank by milling away of unwanted material. The core 2 has an outer face 3. The outer face 3 is roughened by blasting with 50 micrometre Al ₂ 0 ₃ particles using an air pressure of 2 Bar to form a roughened outer face 5 having an Ra of 0.96 micrometres in this embodiment. Figure 2 shows how a crown of dental veneer 6 may be bonded to the roughened outer face 5 of the core 2 by applying a bonding layer (not shown), such as a primer to the roughened outer face 5 of the core 2 and then applying the dental veneer 6 which is polymerised in situ. An opaque paste may be applied in addition to, or instead of, the primer before the dental veneer is bonded to the core 2.

In Figure 3, the resulting dental prosthesis 1 1 is shown being inserted into a walled female member 9 forming part of a dental framework 10 which is formed from the same polymeric material as the unitary core 2 and attachment post 4 for this embodiment. The dental prosthesis 1 1 may be secured in place as part of a denture with the dental framework 10 by ultrasonic welding of the wall of the female member 9 to the attachment post 4.

The following experimental examples were carried out in order to better demonstrate the principles of the invention.

Polyetherketone (PEEK, Juvora, GB) plates were milled to the following dimensions: thickness 3 mm, length 20 mm, width 10 mm. The PEEK surfaces were either untreated, chemically etched (H ₂ S0 ₄ 98% in water for 1 min; H ₂ 0 ₂ :H ₂ S0 ₄ 1 :1 for 30s), blasted with ΑΙ ₂ 0 ₃ (50/120μηι median diameter, Harnish & Rieth, G) or activated with silica-modified alumina oxide treatment (Rocatec 30μηι/1 10μηι, 3M, USA). Blasting with abrasive was at an air pressure of 2-3 Bar. Table 1

Surface roughness Ra was determined using a Perthometer SP6, Perthen, Germany as described hereinbefore. After surface treatment, the PEEK surface was bonded to a cylinder of commercial dental veneer (d= 5mm, height 4mm) using commercial primer/bonder and with or without the use of a commercial opaque paste. Shear bond strength (SBS) was determined following ISO TR 1 1405. Specimens were fixed in a shear bond device, which allowed the loading die to strike the composite cylinder with a distance of 0.1 mm between chisel and PEEK plate. This technique was used for avoiding cantilever effects on the bonded surface. The crosshead speed was 1 mm/min (Zwick 1446; Zwick, Ulm, Germany). For investigating the influence of storage and aging, the specimens were either stored in distilled water maintained at 37°C for 90 days, or thermally cycled for 12,000 cycles in distilled water alternating between 5°C and 55°C. The holding time of each bath was 2 min. The entire thermal cycling process lasted 17days. As a control PEEK was sandblasted and veneered without primer and without use of opaque paste between the PEEK and the veneer.

Table 2 shows the SBS achieved using various commercially available dental veneer systems bonded to the core of PEEK.

Table 2

Acceptable SBS was found for several commercial systems bonded to PEEK (with SBS in excess of 5 MPa after 24 hours, in excess of 8 MPa after 12,000 thermal cycles and in excess of 1 1 MPa after 90 day storage). Surface roughness was found to play an important role for adhesion of the dental veneer. Bonding (Primer) treatments giving good results contained phosphate moieties or silane moieties in the primer and the presence of opaque paste, although not essential, was effective at improving bonding.

Although a few exemplary embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims. For example, the dental veneer 6 may be a pre-formed crown which is bonded to the core 2 rather than polymerised in situ. As an example, the product family Visio.lign (see the third entry in the table) includes a veneer Novo.lign which is a pre-formed tooth crown.

For example, the core 2 may be formed by melt moulding of the PEEK rather than by milling.

In summary, tooth prostheses are disclosed as having a core of a composition comprising a polymeric material comprising a repeat unit of formula (I):

wherein t1 and w1 independently represent 0 or 1 and v1 represents 0, 1 or 2, and a dental veneer bonded thereto as a crown. Also disclosed are dentures including the tooth prostheses and methods for forming the tooth prostheses and dentures.

The tooth prostheses are easy to form, highly biocompatible and can be used as endosteal implants and dentures based on dental frameworks comprising similar polymeric materials.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.