The present invention relates to a dental root canal obturation material for endodontics treatment.

Endodontics is the dental specialty that deals with the tooth pulp and the tissues surrounding the dental root of a tooth.

In the course of endodontic treatment, obturation of the dental root canal system with a dental root canal filling material after dental root canal disinfection is essential to prevent re-infection of the disinfected dental root canal space, entomb remaining micro-organisms and prevent entry of periapical tissue fluid into the dental root canal space.

The following definition shall apply throughout the, specification and the claims. Radiodensity or radiopacity (the two terms will be used indifferently) refer to the relative inability of electromagnetic radiation, particularly X-rays, to pass through a particular material. Radiolucency indicates greater transparency or "transradiancy" to X-ray photons. Materials that inhibit the passage of electromagnetic radiation are called radiodense or radiopaque, while those that allow radiation to pass more freely are referred to as radiolucent. Radiopacity refers to the relatively opaque white appearance of dense materials or substances on radiographic imaging studies, compared with the relatively darker appearance of less dense materials. The Hounsfield scale is a quantitative scale for describing radiodensity. However, in the following, radiopacity will be measured in mm Al/mm according to the norm ISO 6876:2003 which is the standard norm for endodontic dental root filling material. A material has a radiopactiy of x mm Al/mm if 1 mm thick of the said material has a radiopactiy equivalent to x mm thick aluminium.

In medical imaging, artefacts are misrepresentations of tissue structures seen in medical images produced by modalities such as ultrasonography, X-ray computed tomography and magnetic resonance imaging. These artefacts may be caused by a variety of phenomena such as the underlying physics of the energy- tissue interaction (for example ultrasound-air), data acquisition errors (such as patient motion), or a reconstruction algorithm's inability to represent the anatomy. There is a risk mistaking these artefacts for actual pathology if the practitioner doesn't recognize them.

It is commonly perceived that the specific characteristic of radiopacity of the dental root canal filling materials is desirable when obturating dental root canals. It is important to achieve firm condensation of the material against the dental root canal surface, and the radiopacity of the material allows the operator to visualise the material on the intra-oral radiograph and to an extent confirm that the material fills the entire dental root canal system.

Radiographs may be taken of the treated tooth in the course of treatment, and for subsequent post operative follow-up visits. The presence of the radiodense material makes it possible to visualise the dental root canal filling material using two dimensional intra oral or plain film radiography, as the radiopaque filling material is easily viewed against the background of the imaged dental root or bone. However, inevitably these two dimensional 'shadowgraphs' lack the three dimensional detail, and do not really adequately give the true picture of the dental root canal system, as they can't reveal void or extra canal for example.

Three dimensional imaging of the jaws is becoming increasingly popular in dental surgery environments. This is largely due to increasing access to Cone Beam Computed Tomography (CBCT) technology. CBCT is an example of a relatively low dose three dimensional imaging technique, which is rapidly gaining acceptance in endodontics. Access to, and further developments in this new technology, particularly in terms of dose reduction, mean that it will gain more widespread and common usage in endodontic therapy.

Dental root canal systems often follow curving or complex courses making two dimensional radiographs very difficult to interpret. Three dimensional imaging and CBCT have offered an exciting new approach to endodontic diagnosis, and will reveal voids and extra canals. However, the nature of the beam, the image acquisition and the reconstruction process of current CBCT imaging units lead to many imaging artefacts adjacent to a radiodense structure. Artefacts such as beam hardening, partial volume and photon starvation will lead to dark patches, bright streaks and dark bands. Highly radiodense structures will intensify these artefacts. Some software corrections are available. However their usefulness is limited, since there use induces a loss of detail around the radiopaque structure, which is often the area of interest for the diagnosis.

Gutta-percha based, and more recently polymer/resin based dental root canal fillings are common dental root canal filling materials used to obturate dental root canal systems. Radiopaque fillers, commonly in the form of metal salts, are used to impart radiopacity to these materials. Current dental root canal filling materials thus have a radiodensity of approximately 6 to 12 mm Al/mm, with the minimum fixed by the norm ISO 6876:2003 being 3 mm Al/mm.

This radiodensity of current obturation materials leads to strong artefacts while using techniques such as CBCT, which inhibits accurate diagnosis in the area of the dental root canal, particularly at the peripheral part of the radiodense material.

At present there is no obturation material specifically designed for use with three dimensional imaging systems alone, or in conjunction with current conventional radiographic systems. It is therefore the aim of the present invention to provide such a dental root canal obturation material optimised for visualisation and evaluation of endodontic results using three dimensional imaging technologies such as Come Beam Computed Tomography (CBCT) and Computed Tomography (CT). Another aim of the present invention is to provide a dental root canal obturation material optimised for visualisation and evaluation of endodontic results using three dimensional imaging technologies that further allows for the material to be recognised using a traditional two dimensional imaging technique to avoid misdiagnosis from operator unaware that a dental root canal has been adequately treated.

To this end, there is provided a dental root canal filling material for endodontic treatment, characterised in that it comprises a central portion and a peripheral portion, the central portion having a higher radiopacity than the peripheral portion.

In the following, a central portion of a material will designate an internal portion of the material as opposed to a peripheral portion. Moreover, the use of the adjective "central" doesn't imply that the central portion has a particular shape or position other than being a non peripheral portion. Thus, a central portion of the material could have any suitable shape at any position inside the material as long as it is not a peripheral portion.

The radiopacity of the peripheral and central portions of an obturation material according to the invention can be adapted by adjusting the quantity of radiopacifiers (such as metal salts, tungsten) and the amount and type of fillers present in each portion. The peripheral and/or central portions of the obturation material may consist of gutta-percha, polyamide or other thermoplastic polymers, combined with inorganic filler. The chemical composition of the filler can be used to adjust radiopacity of the central and/or peripheral portions of the obturation material, as well as radiopacifiers such as metal salts (barium salts, bismuth salts), oxides (zirconium oxide, bismuth oxide), or metals (tungsten).

According to the invention, a central portion of the material has a higher radiopacity than a peripheral portion of said material.

An ideal material from the perspective of diagnosis and analysis with the aid of three dimensional radiographic imaging techniques would have a peripheral portion having a lower radiodensity, typically lying in the region of 1 to 3 mm Al/mm giving it a radiopacity lying between that of dense cortical bone, dentine (1 mm Al/mm) and enamel (1 .8 mm Al/mm). Of course a radiopacity of 2 to 6 mm Al/mm would also reduce artefacts in the area of diagnostic, i.e. around the dental root canal walls and the said peripheral portion of the material, compared to materials having a still more radiodense peripheral portion.

On the other end, this invention provides for the incorporation of radiopaque components designed to impart a distinct radiopaque 'signature' in a central portion of an obturation material. This signature will then be visible using a traditional two dimensional imaging technique and will help the practitioner recognise a treated tooth and the particular type of material that has been used. Moreover, different types of signature could highlight different types of obturation material: a first signature could indicate that traditional gutta-percha was used to treat the tooth, while a second signature could indicate that another thermoplastic polymer was used.

These radiopaque components designed to render the central portion of the material more radiopaque than a peripheral portion may take the form of fine particles, strands, fibres, wires, formed objects, or any structure intended to be clearly recognizable, and also resolvable by the use of two dimensional 'conventional' radiographs.

Such structures combined into a central portion of a traditional obturation material will impart a distinct signature appearance when viewed in a radiograph. These signature structures must be sufficiently radiopaque to be visible with a two dimensional imaging technique, while a peripheral portion of the said obturation material remains radiolucent allowing for a good visualisation of the dental root canal surface without artefact with a three dimensional imaging technique.

This may be achieved by introducing strands of a more conventional form of dental root canal filling material formulation (for example, gutta-percha of standard radiopacity), into a central portion of a more radiolucent material. Such a combination might be used to create a 'cone' or 'point' also having a distinctive striped or variegated appearance. One preferred approach to manufacture would be to form a cone comprising of a relatively radiopaque central portion and an exterior peripheral portion of a relatively radiolucent material. The following table highlights examples of quantitative description of the obturation material according to the invention:

Several preferred embodiments of the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 is a cross-sectional view of a tooth illustrating its root canals, one of which being obturated by a dental root canal obturation material according to the invention.

Figure 2a is a cross-sectional view of a first embodiment of a dental root canal obturation material according to the invention.

Figure 2b is a cross-sectional view of a variant of the first embodiment of a dental root canal obturation material according to the invention illustrated in figure 2a.

Figure 3a is a cross-sectional view of a second embodiment of a dental root canal obturation material according to the invention.

Figure 3b is a cross-sectional view of a variant of the second embodiment of a dental root canal obturation material according to the invention illustrated in figure 3a.

Figure 4 is a cross-sectional view of a third embodiment of a dental root canal obturation material according to the invention. Figure 1 is a cross-sectional view of a tooth 22 that has been endontically prepared for root canal obturation by first removing a portion of the crown 23 to form an access opening 24. The access opening 24 permits the pulp and infected tissue (not shown) to be removed from the tooth 22 and to expose the interior portions of the root canals 25 (two in the tooth pictured in figure 2). The root canals 25 are then commonly subjected to mechanical shaping operations e.g. reaming, filing, to obtain a root canal 25 with relatively long and tapered walls 26. Prior to the introduction of an obturation material 10 into the canals 25, the said canals are irrigated with cleaning and etching solutions to remove the residual pulp and any dentin 27 dislodged from the tooth 22 during the mechanical shaping of the root canals 25. An obturation material 10 can then be introduced into the canals 25. The positioning of the obturation material 10 and the obturation procedure are well known to the skilled person of the art and will not be further described.

Some embodiments of a dental root canal obturation material according to the invention will now be described in further detail.

Figure 2a illustrates a first embodiment of a dental root canal obturation material according to the invention. The dental root canal obturation material is provided in the form of a cone 100 made preferably of gutta-percha or any other suitable thermoplastic polymer having a lower radiopacity than commonly used known obturation materials. Preferably, the radiopacity of the cone 100 is in the range of 1 to 6 mm Al/mm. According to this first embodiment, the said cone 100 contains a thin wire 102. The said wire 102 is preferably made of a biocompatible radiopaque metal and has a higher radiopacity than the radiopacity of the cone 100. Preferably, the thin wire 102 has a radiopacity of 6 mm Al/mm or above. The thin wire 102 could be made of one of the following metals: titanium, titanium alloys, stainless steel, gold, cobalt, tungsten, nickel-titanium alloys, cobalt- chromium alloys or tantalum. In a variant, the thin wire 102 could also be a yarn of ceramic or glass having a radiopacity higher than the radiopacity of the cone 100. The wire 102 is placed in a central portion 101 of the cone 100 and has preferably a diameter of 0.1 mm or less. The thin wire 102 acts like a characteristic signature and because it is more radiopaque than the cone 100, it will appear as a bright stripe in the darker radiolucent material of the cone and thus will be clearly recognisable using a two dimensional radiographic imaging technique. The thin wire should be thick enough to be visible on a two dimensional X-ray image but should be thin enough so as not to create artefact in the area of diagnostic interest, i.e. the dental root canal surface 26 and a peripheral part of the cone 103, while using a three dimensional imaging technique.

In a variant of the first embodiment, illustrated in figure 2b the thin wire 102' has a helical shape. All the characteristics described above regarding the first embodiment are applicable.

Figure 3a illustrates a second embodiment of the invention. In this embodiment, the dental root canal obturation material has the form of a cone 110 that can be made of gutta-percha, polyamide or other thermoplastic polymers for example. A central portion 112 of the cone is radiopaque. Preferably, the central portion has a radiopacity greater that 3 mm Al/mm and is made of gutta-percha combined with a radiodense filler, such as zinc oxide.

The cone 110 according to this second embodiment presents a peripheral portion 111 , which is the part of the obturation material that will be in contact with the dental root canal walls 26. The said peripheral portion 111 is less radiopaque than the central portion, having preferably a radiopacity lesser than 6 mm Al/mm. The peripheral portion 111 is preferably made of the same material as the central portion 112, such as gutta-percha, polyamide or other thermoplastic polymers but combined with a radiolucent filler such as magnesium oxide or calcium oxide.

Thus the more radiopaque central portion 112 of the cone 110 will be clearly visible using a two dimensional imaging technique while a less radiopaque peripheral portion 111 of the cone 110 will permit to obtain a clear three dimensional image with no artefact in the area of diagnostic interest that is around the said peripheral portion 1 1 1 of the cone 1 10 and the dental root canal walls 26.

A variant of the second embodiment is illustrated in figure 3b. In this variant the central portion 1 12' of the cone 1 10 is made of gutta-percha, any other thermoplastic polymer or other suitable material. Preferably, in this variant, the central portion 1 12' is made of the same material as the peripheral portion 1 1 1 . The central portion 1 12' is then made more radiopaque than the peripheral portion 1 1 1 by adding particles, strands or fibres 1 13 of a highly radiodense material. Preferably, these particles, strands or fibres 1 13 have a radiopacity of 3 mm Al/mm or above. They can be glass particles. The radiopacity of these particles strands or fibres 1 13 can be adjusted by adding metals such as titanium, chromium, barium, tantalum, lanthanum, tungsten or their oxides. Preferably, the greatest dimension of these fibres or particles 1 13 should be between 10 pm and 2 mm, most preferably between 10 pm and 100 pm. All the characteristics described above regarding the second embodiment are applicable. With this variant, the central portion will appear as a spotted portion using a two dimensional imaging technique, the particles strands or fibres 1 13 being clearly visible due to their high radiopacity.

Figure 4 illustrates a third embodiment of a dental root canal obturation material according to the invention. In this embodiment, the dental root obturation material is a carrier based material 120 comprising a plastic carrier 122. The carrier 122 comprises a handle 123 to facilitate manipulation and insertion of the obturation material 120 into the root canals 25. The handle 123 can be cut off or detached any other way once the carrier based obturation material 120 is correctly positioned into the root canals 25. The plastic carrier 122 is preferably made of a thermoplastic polymer or vulcanised elastomer. The plastic carrier 122 can more generally be made of any suitable polymeric material; one possibility is for example a cross-linked polyisopren. On the plastic carrier 122 is coated an obturation material 121 such as gutta-percha, polyamide or another thermoplastic polymer or any other suitable material. The plastic carrier 122 is radiopaque having a higher radiopacity than the obturation material 121 . For example, the plastic carrier 122 could contain radiopaque fillers or a radiodense signature such as the thin wire 102 or the particles or fibres 1 13 described above. The obturation material 121 can be combined with some radiolucent filler so that the said material 121 is less radiopaque than the carrier 122. Hence, the carrier 122 acts as a signature and will be clearly visible using a two dimensional imaging technique, while the presence of artefact closer to the dental root canal walls 26 will be reduced using a three dimensional imaging technique.

The list of suitable substances that can be used to make an obturation material according to the invention mentioned above and comprising gutta-percha, polyamide or other thermoplastic polymers is not exhaustive. It will be evident to the skilled person of the art that any suitable substance can be used as a base component of an obturation material according to the invention.

Other components without influence on radiopacity of the material such as colorants can be added to the obturation material according to the invention. In particular, particles of bioactive glass can be added, preferably to the peripheral portion of an obturation material according to the invention since these particles are known to promote bone growth.

Although several embodiments of a dental root canal obturation material according to the invention have been described, they all share the same essential characteristics and advantages. A dental root canal obturation material according the invention presents at least a central portion that is more radiopaque than a peripheral portion of said material. Preferably, the peripheral portion which is substantially radiolucent has a radiopacity of 1 mm Al/mm to 6 mm Al/mm, while the radiopaque central portion has a radiopacity of 3 to 12 mm Al/mm. Although all described and illustrated embodiments comprise a central portion extending substantially along the longitudinal axis of the obturation material, it is clear that the central more radiopaque portion of the obturation material according to the invention can have any suitable form and dimensions allowing it to fulfil its purpose: being visible using a two dimensional imaging technique and being more radiopaque than a peripheral portion of the material to not create artefacts in the area of diagnostic interest using a three dimensional imaging technique.

Hence, the central radiopaque portion of the obturation material according to the invention acts like a signature indicating immediately to a practitioner if a dental root canal has been treated and can provide detail on the particular obturation material used. On the other hand, the low radiopacity of a peripheral portion of the said material will allow the practitioner to clearly visualise the material in the area adjacent to the dental root canal walls 26, which is the area of diagnostic interest.