FIELD OF THE INVENTION

The present invention relates to the technical sector concerning dental implants. DESCRIPTION OF THE PRIOR ART

Dental implants (also known as endosseous implants), are medical devices of a surgical type used for functionally and aesthetically rehabilitating a loss or congenital absence of one or more teeth, enabling support of a prosthetic replacement by means of a direct bone support with a biological process known as osseointegration.

Dental implants, also known as fixtures or screws, are the part that the dentist inserts internally of the bony part of the mandible and/or maxilla and have a cylindrical or conical shape.

The surface of the external vertical face of the implant is not smooth, but is characterised by a threading that following the insertion of the screw internally of the bone makes the implant solid in the dental cavity, i.e. in the cavity present in the maxillary/mandibular bone which originally contained the tooth and subsequently the screw of the implant.

Dental implants of known type can be subdivided into two categories: one-stage implants and two-stage implants.

The one-stage implant comprises a body forming a lower threaded portion, corresponding to the root portion of the tooth to be replaced, and an upper rigid stump to which a dental crown is anchored, corresponding to the upper part of the tooth.

The one-stage implant is indicated for all cases in which there are no particular operating difficulties; in fact, with a single operation the screw provided with the stump is inserted into the bone.

Differently, each two-stage implant comprises: a body, having a blind hole in the head portion and inferiorly forming a threading; a secondary component, or stump, which stabilises with the insertion of the stump in the hole realised in the body by means of an internal connection, for example by screwing, or a connecting screw that stabilises the body-stump coupling.

The two-stage implant is indicated in a case of an increase in the bone dimension (raising the sinus, crest or expansion of the crest), and its use required two surgical operations, one for positioning the implant and, following osseointegration, a second for applying the healing screw which repairs the soft tissue (gum) around the implant.

The dentist will decide, on the basis of the situation the patient presents orally, which type of implant to use.

All dental implants have a morphological constraint deriving from the need to screw the implant internally of a surgical cavity (realised by the dentist, in the surgical step, with appropriate rotary burrs) or into the healed bone or at the centre of the extraction site, i.e. in the bone part located in the dental cavity or cavities (cavities destined to house the roots of the tooth) following an extraction; the known implants, therefore independently of the tooth, or rather the conformation of the root that it will replace, and of the support (crown) which it will have to support, always have a circular section.

In a case in which the implant is positioned to replace a tooth, following an extraction, the dentist will have to position the implant at the centre of the extraction site, i.e. will have to realise the surgical cavity between the dental alveoli, preposition and screw the implant to the available bone tissue.

In this situation there can be cases with a bone deficit for preceding gum/bone resorbances due to inflammatory processes, so the dentist will have to realise the surgical cavity, screw the implant into the cavity, fill the spaces around the implant with fragments of natural bone or granules of synthetic bone, to prevent migration of the implant itself and, thereafter, suture the gum to maintain the implant in the bone up to obtaining the osseointegration of the implant.

Further, to position an implant it is necessary: to have a thickness of bone tissue that is sufficient to enable anchoring the implant while preserving the stability thereof; to have a sufficient soft tissue around the plant, following the osseointegration of the implant, to prevent bacteria, normally present in the oral cavity, from invading the underlying tissues.

In a case where there is not sufficient soft tissue about the implant the plaque, tartar and bacteria act by insinuating into the space between the gum and the implant (i.e. in the gum pockets) and inflaming and damaging, initially, the gum and thereafter the bone tissue supporting the implant.

In these situations it is very likely that there will be gum recession and a risk to the grip of the implant.

In fact, a part of the implant will no longer be completely integrated in the available bone tissue and therefore a part will be uncovered and not protected by the gum tissue and not completely supported by the bone tissue; in this situation the implant is not able to support the relative masticating loads, causing the fracturing of the stump screw.

In the worst cases, the plant can even be lost, as the thickness of the bone tissue will no longer be sufficient to maintain the plant solidly stable and therefore there will be a need to increase the dimension of the bone tissue before positioning a new implant, using known methods.

US2016/0193017 describes a dental implant, an upper portion of which has a stump for stabilising a dental crown to the implant, comprising: a profiled core realised using a biocompatible material that is non-bioresorbable, having a relative external vertical face and externally conforming a threading for anchoring the implant to the surgical cavity; a cladding layer made of a hydroxyapatite, which adheringly envelops an external vertical face of the profiled core at the threading. In the implant described in US2016/0193017, the whole working cavity is substantially occupied by the profiled core.

SUMMARY OF THE INVENTION

The aim of the invention is to provide a dental implant formed in such a way as to obviate the drawbacks cited in the preamble, and in particular an implant the conformation of which is associable to the conformation of the implants of traditional type so as to enable insertion thereof following the standard surgical protocol.

A further aim of the invention is that it provides a dental implant realised by a combination of known elements that enable a simple anchoring of the implant, by stimulating the new formation of the bone tissue.

A further aim of the invention is that it provides an implant conformed in such a way as to include a portion that can be designed on the basis of the anatomical characteristics of the tooth to be replaced.

A further aim of the invention is to provide an implant conformed in such a way as to facilitate osseointegration thereof in the bone tissue, and increase the support surface for the dental crown.

A still further aim of the invention is to describe a dental implant which is reliable, functional and relatively inexpensive with respect to the advantages that it provides. The above-mentioned advantages of the invention are attained according to the contents of the claims.

In the present invention the term "resorbable material" is understood to mean a material that is at least partly resorbable by the human body, i.e. a material that is at least partly bio-resorbable, which comprises at least a component that is totally bio-resorbable and, optionally, an osseo-integratable component, for example hydroxyapatite. Alternatively the at least partly bio-resorbable material can be totally bio-resorbable.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics of the invention are specified in the following with particular reference to a preferred, but not exclusive, embodiment, with reference to the accompanying tables of drawings, in which:

- figure 1 is a large-scale perspective view of a dental implant of the invention; - figures 1A, 1B illustrate two views from above of the dental implant of the invention in two different embodiments;

- figure 2A is a perspective view of the implant of figure 1 , showing the internal part of the implant;

- figure 2B is a perspective view of the implant-dental crown assembly;

- figure 3 is a section and partially exploded view of the implant-dental crown assembly, corresponding to a premolar, following insertion of the implant in the bony part of a patient;

- figure 4 is a partly-sectioned view of the implant-dental crown assembly, in which the osseointegration of implant of figure 3 is highlighted;

- figure 5 is a partly-sectioned and partially exploded view of the implant-dental crown assembly, corresponding to a premolar, following insertion of the implant in the bony part of a patient;

- figure 6 is a section view of the implant-dental crown assembly, in which the osseointegration of the implant of figure 5 is shown.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A dental implant, an upper portion of which has a stump (5) for stabilising a dental crown (6) to the implant, comprises: a profiled core (3) realised using a biocompatible material that is non-bioresorbable, having a relative external vertical face; a cladding layer (4) made of a resorbable material, which adheringly envelops an external vertical face of the profiled core (3) and externally forms anchoring means (F); the anchoring means (F) being realised entirely of the resorbable material and the implant (1 ), being insertable in a working cavity (C), realised on healed bone or at a centre of the dental cavity or cavities following a dental extraction, is anchorable to the working cavity (C) via the anchoring means (F).

The plant (1 ) is advantageously maintained for the time compatible with the surgical cavity: in fact, with this plant 1 the overall quantity of biocompatible non- bioresorbable material, for example titanium, introduced in a surgical cavity (C), is reduced, as it is replaced by resorbable material by means of the cladding layer (4) that is destined to be resorbed by the healed bone which will grow in time to surround the implant 1.

In other words, with the above-described implant (1 ), the surgical cavity (C) will be occupied by biocompatible material, which will be such during the whole time of permanence of the implant (1 ) in the patient's mouth, and by resorbable material which will be bio-resorbed by the human body.

With reference to figures 1 , 2A, reference numeral 1 denotes a dental implant comprising: a profiled core (3) forming the natural profile of a dental root, realised using a biocompatible material, for example titanium, the external surface of which exhibits a roughness (not illustrated); a central blind hole (30), realised in the head portion of the core (3), for example having first anchoring means (31 ), for example a nut screw; a cladding layer (4), which adheringly envelops the external vertical face of the core (3) and externally forms a threading (F) and, as illustrated in the embodiment of figures 1A, 1 B, and 2A, having, above the threading, a transversal section with a circular profile.

As the surgical cavity (C) typically has a transversal section with a circular profile, the above-mentioned characteristic enables easily screwing in implants, according to the invention, in which the profiled core (3) has the conformation of the root which it will have to replace and therefore does not have a circular profile.

The cladding layer (4) has a thickness that decreases from bottom-up in proportion to the dimensions of the profiled core (3), and is made of a resorbable material, being a polymeric biomaterial, for example polylactic acid and hydroxyapatite.

With reference to figure 4, in which the profiled core (3) forms a monoradicular tooth for the external face, what is meant is the external surface of the root that the profiled core (3) forms, while, with reference to figure 6, in which the profiled core (3) forms a pluri-radicular tooth for the external face, i.e. the sum of the external surfaces of the roots that the profiled cores (3) form.

The plant (1 ), as illustrated in figures 2B, 3, 5, further comprises: a stump (5), interiorly forming second anchoring means (51 ), for example a screw portion, which couple removably with the complementary first anchoring means (31 ), and superiorly a support (52) (figure 2B), which following the coupling with the implant (1 ) extends from the head portion of the core (3) vertically upwards; a dental crown (6) which will be stabilised, according to the background art, to the support (52) of the stump (5) (two-stage implant).

In a variant (not illustrated) a support extends vertically upwards from the head portion of the profiled core, in a single body, which support defines the stump to which the dental crown will be anchored (one-stage implant).

The dental implant (1 ) of the invention, like known implants, is used either following a dental extraction, with the preparation of a surgical cavity (C) in the centre of the dental cavity or cavities, or following the realisation of the cavity in a healed bone site, following, in both situations, the standard surgical protocol. In both cases, according to the tooth that the implant will replace, the corresponding implant is chosen, i.e. the implant having a profiled core (3) forming the root of the tooth that it will go to replace.

The implant specialist surgeon, in the presence of different situations that emerge, will decide whether the positioning of the implant can be either submerged under the gum (G) following an extraction, or left to emerge from the gum (G) in the case of a mature bone, i.e. a zone in which the tooth has been extracted a long time previously and the bone tissue (O) and the gum tissue have completely reformed. In the case of a submerged implant a healing screw (not illustrated as of known type) is inserted in the central hole (30) flush with the implant and the gum tissue is sutured so as to completely cover the implant (1 ) and the healing screw; in a case where the implant is left to emerge from the gum (G) a healing screw (not illustrated) is inserted in the central hole (30), which healing screw (30) emerges from the gum and is kept there up until the osseointegration of the implant (1 ) has taken place.

In both situations, during the osseointegration period the cladding layer (4), due to the technical characteristics of the material with which it is realised, will stimulate the new growth of the bone tissue with a contemporary gradual resorption of the cladding layer (4).

Following complete osseointegration, therefore, the cladding layer (4) will be completely resorbed while the bone tissue and the gum tissue will naturally have regrown around the core (3).

The dental implant (1 ) of the invention has particularly advantageous characteristics.

The fact of including an externally threaded cladding layer (4) with a circular profile is advantageous, as it enables the implant (1 ) to be positioned in the surgical cavity following the standard surgical protocols; in fact, following the preparation of the surgical cavity (C) the implant is simply screwed into the bored surgical cavity.

The primary stability of the implant, in fact, is obtained during the first surgical step, and is necessary for avoiding micro-movements which might lead to the formation of fibrous tissue around the implant and the consequent fibro-integration which over time leads to a progressive loss of stability and increase in connected complaints (pain on pressure, inflammation of the soft tissues etc.).

The primary stability is guaranteed by the bone that surrounds and delimits the implant site and this stability depends on the design of the implant and on the way in which the implant site is prepared.

In the above example, by increasing the external diameter of the implant (1 ) the external cladding (4) facilitates and guarantees the stability, as, following the positioning thereof, the cladding layer (4) will initially abut the wall of the dental cavity or cavities, thus eliminating the spaces between the wall of the implant and the wall of the cavity or cavities, and preventing micro-movements or involuntary migration of the implant: with this novel technical solution it is not necessary to fill the gaps with synthetic or natural bone, with all the advantages that brings.

At the moment of positioning the implant (week 0) there is the maximum primary stability, which is guaranteed by the pre-existing bone of the patient.

The process of healing begins immediately following surgery, which involves both the osteoblasts, which produce the new bone matrix, and the osteoclasts, which eliminate the residues produced during the surgical step.

The cladding layer (4) realised using a polymeric biomaterial and due to its technical characteristics stimulates the new growth of the bone tissue, independently of the density and the quantity of the patient's bone.

The new bone matrix is subject to progressive mineralisation and maturation so as to guarantee the secondary stability of the implant.

The cladding layer (4) is gradually resorbed contextually with the osseointegration of the implant, maintaining or reconstituting the peaks of bone (P) (figures 4, 6) and consequently the gum crests (R) against the head of the implant; thus preventing liquid infiltrations which in many cases are what determine the inflammatory processes and the bacterial colonisation which lead to gum recession and subsequently to the reduction of the bone tissue with a consequent detachment of the implant due to peri-implantitis.

A further advantage attributable to the implant (1 ) relates to the transmission of masticating loads to the osseointegrated implants which is characterised by significant biomechanical differences with respect to natural teeth.

The natural tooth is connected to the bone by the collagen fibres of the periodontal ligament which enable intrusion up to 50-100 pm; the implant, on the other hand, is in direct contact with the bone.

The elasticity of the implant depends on the elasticity of the bone and the transmission of the masticating loads into a plant depends only to simple non- specialised nerve endings present in the surrounding bone tissue; with the present invention the new bone growth, stimulated by the biomaterial of the cladding layer (4) and therefore with the well-osteointegrated implant (1 ), the control action on the entity and the direction of the masticating loads with respect to the implants of the prior art is optimised.

The fact that the core (3) is profiled to define the standard conformation of the tooth that the implant (1 ) will go to replace, is another technical-functional aspect which enables obtaining a greater distribution of the masticating loads on the implant-crown assembly, as the design of the connection with respect to the biological profiles of the corresponding natural tooth and, therefore, the stump and the crown will be supported by a base, the conformation of which is identical to the standard conformation of a corresponding natural root.

A further advantage associated to the conformation of the core (3) derives from the fact that in a stump-implant connection of a conical type, the coupling between the stump and the implant is stable to guarantee an adequate resistance to mastication stresses: the two components will not be subject to rotary, torsional or flexional movements, as following complete osseointegration the core (3), which simulates the conformation of the natural root of the tooth, replaces the natural root of the tooth and carries out the same function.

Obviously, since during the whole time of installation of the implant (1 ) in the patient's mouth, the profiled core (3) must replace the natural root of the tooth, the profiled core (3) is made of a non-bioresorbable biocompatible material. In other words, the non-bioresorbable biocompatible material is not resorbed by the bone tissue, nor by the gum during the new growth of the bone tissue.

A further advantage of the implant (1 ) derives from the fact that, it can be realised perfectly corresponding to the natural conformation of the root of the tooth of each single patient; in fact, following a pre-operational CT scan (computed axial tomography) the shape of the core (3) can be found with the same dimensions as the original root of the tooth which the implant will replace.

The fact that the external surface of the core is rough, for example sanded or micro-punched or the like, following osseointegration increases adherence of the bone tissue to the core (3).

In variants that are not illustrated, alternatively to the threaded profile (F) the cladding layer 4 can comprise anchoring means, known to the expert in the sector, which enable, in known ways, stabilising the implant (1 ) to the surgical cavity (C) realised during the surgical step.

It is understood that the above has been described by way of non-limiting example and that any modifications of detail, and variants of form and dimensions of the described elements all fall within the protective scope, as claimed in the following.