WO2014115090A1

WO2014115090A1 - Method for obtaining endodontic posts

Info

Publication number: WO2014115090A1
Application number: PCT/IB2014/058469
Authority: WO
Inventors: Angelo SONAGLIA
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-01-28
Filing date: 2014-01-22
Publication date: 2014-07-31
Anticipated expiration: 2015-07-28
Also published as: ITRM20130047A1

Abstract

Method for obtaining endodontic posts to be inserted inside a canal cavity placed inside any one root of a tooth of a patient. The endodontic post is directly obtained from a block made of a glass or carbon fiber reinforced resin matrix. The optical scanning of the cavity of the endodontically-treated tooth present in the mouth of the patient, in which the endodontic post is to be inserted, is carried out by means of a common optical scanning device. The block is provided with a size more than suitable for the endodontic post to be obtained. The block is glued to a common metallic holding device adapted to allow the machining in a cutter. The machining of the block in the cutter is carried out on the basis of digitalized information of the dental cavity previously obtained and digitally transferred to the cutter. The endodontic post with the desired personalised form specific for the operation to be performed is extracted from the cutter.

Description

METHOD FOR OBTAINING ENDODONTIC POSTS

Description Field of the art

The present invention relates to the field of dentistry or dental technology, specifically the methods for manufacturing "customized" posts and the use of such endodontic posts.

Prior art

An endodontically-treated tooth, due to a carious lesion or any one degenerative disease, loses part of its physical-chemical-mechanical characteristics.

From the literature we know that if the tooth loses two or more walls, or if the residual walls have thickness < 2 mm, the use of a post and core becomes necessary in order to give support, retention and stability to the subsequent prosthetic restoration, crown or inlay, or to the preserving restoration in the case of a reconstruction.

The selection of the post is therefore of fundamental importance because it must stabilize the restoration over the long term, facilitating the integrity and the function thereof over time. The tooth devitalized and reconstructed with a post is considered to be a system composed of multiple separate components glued to each other, in which the forces that affect the tooth tend to be concentrated above all at the level of the interfaces; in such a manner, it is possible to cause a separation of the post, if these forces are greater than the adhesion force, or a fracture of the post, if the post is constituted with insufficiently strong materials, or the breakage of the tooth itself, due to the excessive hardness of the post.

In substance, the posts used in dentistry can be divided into two large groups:

The prefabricated posts;

The personalized posts.

The prefabricated posts can be made of metal, of carbon fibers, quartz fibers or glass fibers. Metallic posts, widely used in the past, are extremely strong but due to their excessive hardness (Young's modulus 210 GPa for those made of steel), they have in turn also led to the fracture of the tooth and for this reason in recent years have been increasingly substituted by more flexible posts, such as those formed by carbon fibers (Young's modulus 110 GPa), and above all by those made of glass fibers (Young's modulus 42GPa) or another type. The prefabricated posts made of carbon fiber and glass fibers are immersed in a resin matrix with a modulus of elasticity more similar to that of the dentin (Young's modulus 18.6 GPa). The endodontic posts made of carbon fiber are constituted by a resin matrix, which represents about 36% by weight, in which fibers are immersed with diameter equal to a few microns, such fibers previously subjected to silanization processes. There are essentially two procedures applied for obtaining fiber posts: a) creating suitable molds in which the epoxy resin is introduced under pressure, coming to fill all the spaces present between the pretensioned and uniformly distributed fibers; b) the fibers are directly immersed inside the resin. The endodontic posts like all the materials used in the dental field are subjected to the regulations of biological evaluation of medical devices. Such regulations have as objective that of being an overall reference document for the selection of tests that allow being able to evaluate the biological responses in relation to the safety of the devices and the medical materials. According to the above-indicated regulations, the endodontic posts are devices communicating with the outside, with prolonged exposure over time, since they are intended to remain in contact with biological tissues, representing a situation of potential high risk if the material used does not have ideal tolerability characteristics. The results of the tests carried out have shown for all post types that can be found on the market, independent of whether they are metallic or made of plastic polymers, characteristics of cytotoxicity and genotoxicity compatible with clinical use. Indeed, even if the cytotoxicity test with direct contact has shown a minimum percentage of cellular death - a factor which suggests a valid biocompatibility of the products - it should not be forgotten that the endodontic posts should never be placed in contact with vital biological tissues, but only positioned inside the endodontic space, and not contiguous with tissues of the oral cavity, nor with periapical tissues. Such situation is ensured by the presence of the apical seal in the canal filling, as well as by the material with which the restoration or core is made. It follows that among the various properties of the posts, biocompatibility and genotoxicity are perhaps less important than other characteristics, such as mechanical, physical and chemical characteristics that affect the strength, stability and lesion of the dental structures. These are the characteristics that the present patent application intends on developing, by describing an innovative endodontic post adapted to combine the advantages of the glass fiber with the personalization of the embodiment. It must be underlined that the posts currently on the market rarely tend to create problems of biocompatibility since they tend to not come into contact with the biological fluids, and hence prevent the release of substances or particles that are potentially toxic, irritating and mutagenic. Nevertheless, the conventional materials used up to now for the achievement of the posts have, among the positive characteristics, a good level of tissue tolerability and poor mutagenicity as can be inferred from the experimental data present in the literature. Indeed, there are no statistically significant differences between the posts made of carbon fiber and glass fiber produced by the two largest producer companies that are currently available on the market. Therefore, the clinical selection of the use of one type of endodontic post over another type essentially depends on other factors, such as mechanical strength, aesthetic requirements and the type of polymerization, rather than on the biocompatibility, a valid characteristic in all types of posts on the market. The commercial posts currently available on the market, whether metallic or polymeric, are however provided with various standardized shapes obtained in large series and are constituted by materials provided with characteristics that are slightly different each time. They can have cylindrical, frustoconical, oval or sub-oval shape, though substantially their shape is simple and linear, lacking bends, projections and recesses. Their external surface can be smooth, slightly notched or rough, but in any case they are produced in series with standardized size and profiles.

The disadvantage of such conventional commercial posts is that they are not adapted to the particular anatomic form of a given patient, so that when they are inserted in the affected cavity, it is the wall of the cavity itself that must be adapted, more or less slightly, to the standardized shape of the endodontic post. Of course, the dentist will select the most advantageous shape from among the various posts at his disposition, but in any case such form will never correspond with the optimal one that perfectly copies the form of the cavity in which the endodontic post must be inserted. Hence, even if they have various shapes, for example oval, cylindrical and frustoconical and different sizes, the standard posts made of fiberglass or other materials are unable to be adapted to the infinite anatomic variables.

The adaptation is therefore carried out by operating on the tooth with calibrated cutters, however to the detriment of the dental substance, with consequent further weakening of the tooth itself. Nevertheless, there often remains an excessive tolerance between the post and the tooth to be treated. This undesired space is currently filled with cement. However, the cement is in turn a further weak point of the system, since the greater the quantity of cement interposed between the tooth and the post, the greater its contraction will be during hardening. The contraction of the cement is indeed tied in a directly proportional manner to its mass and hence the more cement is used, the greater the probability of separation of the post itself once the cement has been consolidated.

In addition, the posts on the market, in order to be sufficiently retentive for the subsequent restoration, must be further modified by the dentist with composite material, which must achieve the so-called actual retentive support "core". This step may cause the insertion of further errors or weak points, such as the contraction of the core or partial or total separation of the composite with consequent loss of the restoration.

Instead, the non- standardized posts or the personalized posts currently available on the market are specially created for each single patient. After the endodontic treatment, the dentist takes the mold of the canal with plastic polymers according to the conventional technique, normally resin, pastes with silicone, polyether or hydrocolloid base. From the impression obtained, a small model is developed that accurately replicates the form of the tooth itself and a post is then made on this model that is adapted with extreme precision to the radicular cavity. This technique allows obtaining the maximum precision and the minimum tolerance between the post and the canal, allowing a considerable reduction of the accumulation of cement and the disadvantages connected thereto. Currently, however, the personalized posts can only be made with metals, ceramics and zirconium. As stated above, such materials are provided with a high Young's modulus and are hence considerably harder than the dentin. The excessive hardness of these materials, under the masticator loads, could even lead to the fracture of the tooth, with consequent extraction of the element.

Object of the invention

The innovation introduced by the present industrial invention patent application consists of combining the merits of the aforesaid techniques using personalized posts, hence specially made and customized for each patient, deriving however from a preformed block made with materials having a modulus of elasticity that approaches that of the dentin in a manner so as to prevent the fracture of the tooth yet conferring a good strength in order to avoid the fracture of the post. These blocks could be constructed in carbon fiber or better yet made of glass fiber, associating the merits of these materials with those deriving from the personalized posts. The shape of the post, object of the present invention, will be adapted with extreme precision to the infinite anatomic variables of each single tooth, in a manner so as to best dissipate the occlusal forces, drastically reducing the thickness of cement to be placed in the post-tooth interface. Moreover, the personalized post thus achieved is a single piece termed "post and core". Two important advantages derive from this:

- time savings by the dentist, who after the cementing of the post no longer has to reconstruct the core;

- improved physical-mechanical characteristics which derive from the use of a "monolithic" post and core, constituted by only one material.

It is possible to obtain this innovative result by fabricating blocks made of glass fibers which can be quickly modeled by the dentist himself, by means of digital scanner and cutter, or alternatively by the assigned dental technician by means of the impression of the tooth sent by the dentist, which after casting will be scanned by a suitable laboratory apparatus and then obtained from said glass fiber block. Hence, the present invention intends to remedy the aforesaid drawbacks of the prior art by describing an innovative endodontic post adapted to overcome all the current problems and provided with an ideal Young's modulus, with a form compatible with that of the tooth to be treated and which can be quickly and inexpensively obtained.

Description of the invention

The present inventive concept intends to describe an innovative method and the product thus obtained for the machining of the polymer blocks, from which a personalized endodontic post is obtained; the concept is inspired by the already known machining technique which serves to obtain manufactured prosthetic items starting from a polymer block of raw material, usually with cylindrical or cubic form. In the prior art, said block or cube of raw material to be machined is usually stably fixed, by means of mono-component or bicomponent adhesive, to a metallic structure adapted to be mounted on a common cutter, which obtains from said block the form of the crown or filling most adapted to the patient. Up to now, blocks or cubes made of zirconium or silicate ceramic, composite blocks or in only resin have been used.

According to the present invention, such prior art adapted for the large-series production of standardized endodontic posts is instead adapted for obtaining personalized posts made of glass fiber with matrix obtained for example with the known resinous bis-GMA matrix. This material, i.e. the matrix mixed with the glass fiber, has an optimal modulus of elasticity for attaining endodontic posts, since it is similar to that of the dentin associated with a suitable fracture strength, therefore it does not damage the teeth. In addition, given that it is precisely shaped to the space that it must occupy, it further reduces the mechanical stresses to which the tooth and the root are subjected during mastication. The product thus obtained allows postponing the reconstruction of the core, saving time and increasing the quality of the manufactured product. Specifically, according to the technique introduced with the present invention, starting from a common block made of glass fiber and matrix, for example, starting from a block with parallelepiped shape, it is possible to obtain a suitably personalized endodontic post with particular physical characteristics: size, shape, modulus of elasticity or other, adapted to be perfectly inserted in the cavity present in the tooth of the patient to be treated. According to the present industrial invention application, thus starting from a raw block made of glass fiber with matrix, e.g. resinous bis-GMA matrix, said raw material block - fixed with adhesive for example on its metallic support - is transferred into a common cutter of known type. The cutter operates based on the digitalized information that is supplied thereto, on the basis of a digitalized impression of the dental cavity detected by an optical scanning device placed in the mouth of the patient, where the post will be subsequently inserted. For such purpose, the dental cavity was first meticulously cleaned, then carefully explored and precisely surveyed with conventional impression materials such as resin, silicones, polyethers and hydrocolloids, or with a common optical scanning device. Such optical scanning device - all the useful information having been obtained for making said endodontic post of personalized type - will transmit such information via data processing to the cutter device which starting from the block of raw material, will achieve the endodontic post provided with the characteristic size detected in the patient's cavity, in a manner so as to be adapted to be perfectly inserted inside said cavity. Thus, the present invention allows attaining a personalized endodontic post that is perfectly adapted to the particular anatomic shape of each single patient who must receive it and in the long term does not give rise to problems of biocompatibility and mechanical problems by virtue of the fact that it is made of a material - i.e. glass fiber in bis-GMA matrix or in another resin matrix - such to have a modulus of elasticity close to that of the dentin.

Preferably, according to the present invention, the percentage by weight of the glass fiber with respect to the matrix (bis-GMA matrix) can widely vary, on the condition that the modulus of elasticity of the finished endodontic post does not undergo unacceptable variations or at least variations overly distant from those of the tooth, or it is not excessively weakened, so as to render it overly fragile and fracturable.

Therefore, while in the prior art the material block from which the endodontic post is obtained was made of composite, stratified ceramic or simply in ceramic, according to the present invention such block is made of glass fiber mixed with resin matrix (bis-GMA matrix).

The ceramic currently used in the prior art is often too hard, creating structural problems at the root of the tooth itself, above all during mastication. The present invention offers the possibility to quickly and directly form, on a common raw block, a personalized endodontic post entirely made of glass fiber and matrix. The glass fiber in the bis-GMA matrix does not give rise to drawbacks due to its optimal modulus of elasticity, as stated above, and moreover the implant operation for the endodontic post is less invasive by virtue of its perfectly personalized ("customized") form, obtained by the exploration or rather preliminary optical scanning of the introduction cavity. The entire operation of survey of the cavity of the tooth of the patient, the transmission of the detected data to the cutter device, the positioning of the glass fiber and matrix block provided with the metallic portion with stem glued on a face thereof in a manner so as to be manageable by the cutting machine, the operation of cutting the block, its separation from the metallic stem portion, so as to obtain the personalized endodontic post, can be carried out in a short time period and directly within any one dentist office, making the aforesaid technique extremely well-focused, quick and inexpensive.

Brief description of the drawings and of several particular embodiments of the invention The present invention will now be illustrated only for exemplifying and non-limiting purposes on the basis of several drawings:

- Fig. 1 shows a block 3 made of raw material whose oblong form is suited for the obtainment of a post, i.e. a block 3 made of solid glass fiber according to the present invention not yet machined, whose base 9 is fixed - for example by means of gluing - to a metallic portion 2 with stem, for the mounting of the raw block 3 on the cutter so as to be able to execute the desired machining. - Fig. 2 shows a possible personalized form of the endodontic post 1 ready to be inserted in the root of a tooth obtained from the raw block 3 of Fig. 1 after the machining in the cutter. The recess 5 is observed along with the irregular shape of the tip 10.

- Fig. 3 shows a different form of endodontic postl, with respect to Fig. 2, in which the section rather than being circular as in Fig. 2, is substantially oval or elliptical at least at the base 7. In this case, the endodontic postl has a lateral recess 5.

- Fig. 4 shows a further form of said endodontic post 1, with respect to the previous figures, such endodontic post 1 having rather irregular form and section, with a lateral projection 6, a pair of irregular recesses 5 with form slightly different from Fig. 3. In Fig. 4, it is noted that the endodontic post 1 has a substantially irregular progression, and the base 7 of said endodontic post 1 also has irregular form.

The solid material block 3, shown in Fig. 1 (not in scale), can have by way of merely non- limiting example the dimensions: bl x b2 x h = 1cm x 1.5cm x 3cm, where "bl" and "b2" are the sides of the base of the block 3, and "h" indicates its height. The base of the block 3 is that connected to the metallic part 2 for fixing to the cutter (not shown in the figure).

From the figures, it is inferred that the endodontic post 1 can be perfectly custom-made and is precisely adapted to the relative introduction cavity (not shown) of each single patient. The present invention is also easily extended to the obtainment of other dental prostheses, such as crowns or fillings made of glass fiber mixed with resin matrix and/or combinations thereof.

Claims

1. Method for obtaining endodontic posts to be inserted inside a canal cavity placed inside any one root of a tooth of a patient, characterized in that said endodontic post (1) is directly obtained from a block (3) of solid raw material, and in that it comprises the following steps:

- the optical scanning of the cavity of the endodontically-treated tooth present in the mouth of the patient, in which the endodontic post (1) is to be inserted, is carried out by means of a common optical scanning device,

said block (3) of solid raw material is provided, with size more than suitable for the object to be obtained, i.e. the endodontic post,

- such block (3) is fixed to a common metallic sealing device (2) adapted to allow the machining in a cutter, by means of gluing;

- the machining of the block (3) in the cutter is carried out, on the basis of digitalized information of the impression of the tooth or of the dental cavity or of a combination thereof, previously obtained and digitally transferred to the cutter;

- the endodontic post (1), made of glass fiber and resin matrix, or carbon fiber, provided with the desired personalized form, specific for the operation to be performed is extracted from the cutter.

2. Method according to the preceding claim, characterized in that said block (3) is fixed, for example glued with a mono-component or bicomponent glue, to a metallic support (2), adapted to allow stably mounting said block (3) on the cutter in a manner so as to allow said cutter to machine said block (3) with precision.

3. Method according to any one of the preceding claims, characterized in that said resin matrix is the bis-GMA, UDMA or HDDMA matrix and that the fibers inserted in the resin matrix can be glass fibers, quartz fibers, or carbon fibers or a combination thereof.

4. Method according to any one of the preceding claims, characterized in that the modulus of elasticity of the glass fiber made of resin matrix that constitutes the block (3) is most similar to that of the dentin, at the same time maintaining a good fracture strength.

5. Method according to any one of the preceding claims, characterized in that the endodontic post (1) can have a form that is substantially cylindrical, conical, oval or the like, with smooth or notched surface (5), and/or with projections (6) and lateral inlets (4), and possibly it can also have a structured surface.

6. Personalized endodontic dental post made of glass fiber and resin matrix, characterized in that it is achieved with exactly the same form as the cavity that is required to receive it.