Dental implant

Abstract

A dental implant (1) comprises a screw (2) on which there is defined a thread (3) and a head (8), on which there is defined a collar (9) without any thread and which is intended to be positioned in a region of cortical bone (10). Between the collar (9) and the thread (3), the dental implant (1) further comprises at least one cutting edge (11) which is intended to process by drilling the region of cortical bone (10) so as to form a receiving member with optimum dimensions for the collar (9).

Description

[0001] DENTAL IMPLANT

[0002] DESCRIPTION

[0003] The present invention relates to a dental implant having the features set out in the preamble of the main claim.

[0004] In the field of dentistry, it is known to replace extracted or missing teeth by means of dental implants, that is to say, with prosthetic devices which are fixed to the jaw or mandible of the patient.

[0005] These dental implants comprise, in general terms, a screw which is inserted in the bone tissue, a stump, which is fixed at the upper side to the screw and which projects from the gingival tissue, and a dental prosthesis which is fixed to the stump.

[0006] The Applicant has observed that, so that the fixing thereof is stable and durable over time, the dental implant as a whole must also comply, in addition to the biomechanical principles, with the histological and biological characteristics of the implant site.

[0007] There exist three different histological zones which involve the positioning of the dental implant and it is important that in each of these a synergetic relationship is defined with the implant itself, in particular in the region of the respective interface surfaces.

[0008] The implant zones involved are: the medullar bone, which is present in the internal region of the bone tissue, the cortical bone, which is present in the more external region of the bone tissue and the soft connective / epithelial tissue which is external with respect to the bone tissue.

[0009] The medullar bone is the tissue which forms most rapidly (from 30 to 60 micrometres / day) and is very reactive to repair and bone remodelling, thereby being found to be particularly functional for osteo-integration of the dental implant, particularly in the first phases thereof.

[0010] However, the medullar bone develops in a random manner without any predetermined architecture and with biomechanical characteristics which are relatively "poor".

[0011] On the contrary, the cortical bone is an extremely robust tissue and forms slowly (from 0.6 to 1 micrometres / day) and is characterized by a protein / collagen organization which is embedded in a mineralized matrix. Furthermore, it has osteon units, at the centre of which the Havers canals, in which blood vessels and nerves extend, are located as through-channels.

[0012] Therefore, the cortical bone is characterized by a high elasticity modulus and by a vascularization which is relatively weak, although capable of ensuring the equilibrium between re-absorption and remodelling to which the bone is subjected physiologically.

[0013] In one known embodiment, the screw of the dental implant comprises three main portions:

[0014] - a lower portion comprising the thread of the screw;

[0015] - an intermediate portion called the "cortical-periosteal collar" or, for short, collar; and, optionally,

[0016] - an upper portion, called the "frustoconical transmucosal neck" or, for short, neck.

[0017] The collar is defined here as the screw portion which is intended for positioning inside the cortical bone when the dental implant is fixed to the bone tissue.

[0018] The collar is preferably configured to obtain a solid engagement with the cortical bone so as to effectively fix the dental implant to the bone tissue once the osteo- integration process is complete.

[0019] Given the characteristics of the cortical bone, the Applicant has previously observed that the connection of the collar to the interior of the cortical bone is an important and critical element during the installation step for the dental implant.

[0020] In fact, the high elasticity modulus and the poor vascularization of the cortical bone at the time of surgical preparation of the implant site and at the time of insertion of the dental implant can initially bring about a cellular alteration as a result of the cutting of the alveolar preparation and, at a second time, a compression on the surrounding bone structures as a result of the positioning of the dental implant in the cavity.

[0021] In fact, the Applicant has found that, during the positioning step of the dental implant, the thread of the screw may cut into the cortical bone, miniscule bone portions or detritus which can be interposed between the external surface of the dental implant and the cavity becoming detached from the bone tissue, generating excess pressure on the cortical bone.

[0022] On the other hand, the Applicant has found that this detritus can advantageously lead to a more effective osteo-integration as a result of the osteo-conductive, osteogenic and osteo-inductive stimulus thereof.

[0023] Furthermore, the Applicant has observed that, at the time of the dental implant being inserted, there may be promoted a tendency to immediately fracture as a result of compression, or the initialisation of cracks which, over time, if the compression persists, can become wider, leading to the fracture of the cavity with the resultant possibility of loss of the dental implant.

[0024] This results from the high level of fragility of the cortical bone, though it is very tough, as a result of the high mineralization which is typical of this tissue.

[0025] In particular, the Applicant has found that, from the vascular point of view, the insertion of the dental implant often causes in the cortical bone a radial stress in terms of compression in the zones immediately adjacent to the collar, compressing and therefore interrupting as a result of crushing, the already weak periosteal / cortical anastomosis (Havers canals and Volkmann canals) which tend to lead to necrosis and therefore the re-absorption of the cortical bone, bringing about an increasing and undesirable mechanical instability of the dental implant itself.

[0026] In other words, the Applicant has found that there is a correlation, which is also further well substantiated in literature, between the compressing action which is applied by the dental implant to the cortical bone and the loss of bone over time.

[0027] Furthermore, the Applicant has observed that in some known dental implants the thread of the screw also extends in the region of the collar in order also to securely engage with the dental implant by means of screwing in the region of the cortical bone.

[0028] Dental implants of this type are described, for example, in the Korean Patent KR. 20150068555 and in the European Patent Application EP 2510899.

[0029] In particular, in both the solutions described here, there is provision for the thread provided in the region of the collar to have a different pitch and a smaller extent (for example, equal to half) with respect to the one provided in the lower portion of the screw which is intended to engage with the medullar bone. In these technical solutions, there is provided between the two threads with different pitches a self-tapping cutter in order to allow the passage from one thread to the other without the screw getting stuck.

[0030] However, the Applicant has found that in such solutions the engagement between the thread and the cortical bone can be the cause of excess overpressures in the cortical bone, bringing about the undesirable effects described above.

[0031] On the other hand, the Applicant has observed that the collar cannot be positioned in a cavity with an excessively high diameter which could lead to expansion of the times necessary for the osteo-integration; furthermore, the possibility of effective engagement between the collar and the cortical bone would be less, with a relevant reduction in the stability of the implant in the time period necessary for the osteo-integration (so-called primary stability).

[0032] Therefore, the Applicant has recognized that, in order to ensure the correct and effective installation of a screw of a dental implant, it is necessary to position the collar inside the cortical bone so as to prevent, or at least to greatly limit, the formation of localized excess pressures, but ensuring the stability of the connection thereof to the cortical bone and, furthermore, without impairing the subsequent step of osteo-integration.

[0033] However, achieving this object requires an extremely high precision in forming the receiving seat of the collar which cannot be ensured by drilling operations before the installation of the implant, even less with manual tools.

[0034] Therefore, the Applicant has perceived that the receiving seat of the collar can be defined with precision by the same screw during the screwing movement thereof inside the bone tissue, providing the screw itself with elements which allow them to operate as a tool in the formation of a receiving member which is suitable for allowing effective and stable fixing of the collar in the bone tissue, preventing the generation of localized excess pressures and the development over time of the disadvantages mentioned above.

[0035] Finally, the Applicant has found that a dental implant comprising a screw which is provided with at least one cutting edge which is interposed between the thread and the collar, and which is advantageously configured to process the region of cortical bone in which the same collar is intended to be positioned, is capable of operating as a coaxial drill bit with respect to the screw and is directed along the same advance trajectory as the screw.

[0036] In this manner, the receiving seat for the collar can be formed in an extremely precise manner by the screw itself, so as to have optimum dimensions to prevent localized excess pressures on the cortical bone and, at the same time, to ensure optimum stability of the implant, at the same time maintaining reduced times for osteo-integration.

[0037] In a first aspect thereof, therefore, the present invention is directed towards a dental implant comprising a screw which is configured to engage in a cavity which is formed in a bone tissue.

[0038] Preferably, the screw comprises a thread which is configured to engage at least in a medullar region of the bone tissue.

[0039] Preferably, the thread extends along a rotation axis of the screw between an upper end of the thread and a lower end of the thread.

[0040] Preferably, the screw comprises a head which extends from the upper end of the thread.

[0041] Preferably, a collar is defined on the head.

[0042] Preferably, the collar is intended to be positioned in a region of cortical bone of the bone tissue. Preferably, the collar does not have any thread.

[0043] Preferably, the screw comprises at least one cutting edge.

[0044] Preferably, the cutting edge is formed on the head and is interposed between the collar and the upper end of the thread.

[0045] Preferably, the cutting edge is intended to process the region of cortical bone after the passage of the thread in order to provide it to receive the collar.

[0046] As a result of these features, the dental implant of the present invention is itself able to define the correct and best seat for receiving the collar inside the region of cortical bone.

[0047] In particular, the provision of the cutting edge between the thread and the collar further advantageously allows the removal, completely or partially, of the helical tips which are formed in the cortical bone by the thread of the screw during its passage through it. In other words, the cutting edge is configured to at least partially eliminate the counter-thread which is generated by the passage of the screw through the cortical bone.

[0048] The processing by drilling of the region of cortical bone facilitates the partial penetration and the positioning of the collar, preventing (or limiting in a controlled manner, if considered advantageous) the contact with interference with the region of cortical bone and the resultant generation of over- pressures which could be the cause of necrosis of the bone tissue and therefore subsequent instability of the dental implant. Furthermore, the processing by drilling of the region of cortical bone is advantageously carried out at the same time as the insertion movement of the screw in the medullar bone so that, in fact, the final definition of the receiving seat for the collar is automatically carried out by the specific insertion operation of the dental implant in the bone tissue.

[0049] It may be noted that a screw portion, for example, the collar, is considered to be "without any thread" both in the absence of thread and in the presence of a thread where this thread is not suitable for engaging in a screwing manner with the bone tissue, for example, when it has a diameter less than the hole which is defined by the processing by drilling of the cutting edge.

[0050] In the above-mentioned aspect, furthermore, the present invention may have one or more of the preferred features which are described below.

[0051] Preferably, the cutting edge is directed towards the thread and extends between an axially internal end and an axially external end thereof in a direction which is inclined with respect to the rotation axis.

[0052] In particular, the cutting edge extends in a direction which is inclined with respect to the rotation axis of the screw so as to diverge away from the thread. In other words, the axially internal end of the cutting edge is nearer the thread with respect to the axially external end of the cutting edge.

[0053] In this manner, the cutting edge acts as the primary cutter of a drill bit, removing during the axial advance movement thereof the portions of cortical bone having a distance from the rotation axis of the screw less than the axially external end of the cutting edge, particularly the tips of the thread which is generated by the passage of the screw.

[0054] The axial advance of the cutting edge therefore defines in the cortical bone a cylindrical hole which has a diameter equal to the external diameter of the cutting edge (corresponding to the distance of the radially external end thereof from the rotation axis of the screw).

[0055] It will further be noted that the axial advance of the screw is determined by the configuration of the thread so that an axial movement thereof equal to the pitch of the thread itself corresponds to each complete revolution of the screw about the individual rotation axis.

[0056] Preferably, the cutting edge extends in a direction inclined with respect to the rotation axis about an angle between 55° and 70°, more preferably approximately 60°.

[0057] In this manner, the inclination of the cutting edges is optimum for ensuring a good capacity of self-alignment with the screwing direction of the screw and for providing a reduced resistive torque, promoting the screwing action of the operator.

[0058] Preferably, there is formed between the cutting edge and the upper end of the thread a discharge groove, which extends circumferentially between the upper end of the thread and the lower end of the head.

[0059] In this manner, the cutting edge is completely separate from the thread, providing the cutting edge with the space necessary both for correctly performing the individual function and for facilitating the process of obtaining cutting edges during the construction of the head.

[0060] Preferably, the diameter of the discharge groove is substantially equal to or less than the diameter of the core of the screw in the region of the thread.

[0061] Preferably, the discharge groove has a width between 0.6 mm and 1 mm, more preferably equal to the dimension of the pitch of the thread, for example, 0.8 mm.

[0062] Preferably, the axially internal end of the cutting edge has a distance from the rotation axis of the screw which is equal to or less than the core of the screw or, in other words, equal to or less than the valley of the thread of the screw. In this manner, the cutting edge is capable of removing without getting stuck at least some of the tips of the thread formed on the cortical bone by the passage of the screw.

[0063] In a preferred embodiment of the invention, the axially external end of the cutting edge has a distance from the rotation axis of the screw equal to or greater than the external diameter of the thread.

[0064] In this manner, the cutting edge is capable of removing the tips formed in the cortical bone by the passage of the thread over the entire radial extent thereof. In an alternative embodiment, the axially external end of the cutting edge has a distance from the rotation axis of the screw less than the external diameter of the thread.

[0065] In this manner, the cutting edge removes the tips formed in the cortical bone by the passage of the thread only over a portion of the radial extent thereof.

[0066] Naturally, the radial extent of the cutting edge and consequently the quantity of cortical bone to be removed may advantageously be selected as a function of the dimension of the collar located above and the type of connection desired between the collar and cortical bone.

[0067] As mentioned above, in fact, the drilling processing operation carried out by the cutting edge which is configured according to the present invention allows the formation in the cortical bone of a seat for the collar with dimensions which are very precise. In this manner, the degree of interference or play desired between the collar and the cortical seat can also be selected with accuracy and reliability. In fact, it is always possible to define on the collar, whatever the configuration thereof, an external diameter corresponding to the diameter of a geometric cylinder which is coaxial with the rotation axis, which circumscribes the collar, of the screw.

[0068] In a preferred embodiment, the cutting edge has a maximum distance from the rotation axis of the screw which is greater than or equal to the radius of the geometric cylinder.

[0069] In this manner, the connection between the collar and the corresponding seat formed in the cortical bone may be a "precise" connection or a connection with Play.

[0070] In an alternative embodiment, the cutting edge has a maximum distance from the rotation axis of the screw which is less than the radius of the geometric cylinder.

[0071] In this manner, the connection between the collar and the seat which is formed in the cortical bone is carried out with interference which, as a result of the precision of processing carried out by the cutting edge, can be calibrated with extreme precision.

[0072] In a preferred embodiment, the cutting edge projects from the geometric cylinder by an extent between 0.02 mm and 0.1 mm, more preferably between 0.03 mm and 0.07 mm, and in a highly preferable manner approximately 0.05 mm.

[0073] In this manner, radial compressions are avoided between the collar and the cortical bone and the dimension of the cavity obtained by means of widening by drilling the region of cortical bone is optimized.

[0074] In fact, as a result of smaller projections, the effective removal of bone tissue could not be ensured, and consequently pressure zones could remain between the collar and the bone tissue, while with greater projections the collar could be too far from the walls of the respective seat and could therefore reduce the stability of the dental implant and increase the times for osteo-integration.

[0075] In a preferred embodiment, the cutting edge has a curvilinear profile, which is preferably concave with respect to the advance direction of the screw.

[0076] Preferably, the thread has a decreasing diameter from the upper end towards the lower end.

[0077] Preferably, the thread, in the region of the lower end, comprises at least one thread portion which alternates with at least one recessed portion, more preferably three thread portions alternating with three recessed portions which are equidistant from each other, and which is configured to form a self-tapping cutter in the region of the thread portion.

[0078] In this manner, the advance of the screw cuts into the bone tissue the seat (the nut) in which the thread of the screw engages.

[0079] Preferably, the head of the screw is constructed in one piece with the thread. Preferably, the collar is cylindrical.

[0080] In this manner, the collar may abut the region of cortical bone in a homogeneous manner over the entire lateral surface of the seat which is formed by the processing of the cutting edge, increasing the stability of the dental implant.

[0081] In a preferred embodiment, the diameter of the geometric cylinder which circumscribes the collar is equal to the maximum external diameter of the thread. Preferably, a plurality of cutting edges which are arranged along the circumferential perimeter of the head are formed on the head.

[0082] More preferably, these cutting edges are provided at regular intervals.

[0083] Preferably, the cutting edges are configured identically to each other.

[0084] Preferably, the cutting edges are arranged in a co-planar manner in a plane which is substantially perpendicular to the rotation axis of the screw. The provision of a plurality of cutting edges on the circumferential perimeter of the head affords the possibility of defining, in an optimum manner, the depth of the cut which is carried out by each cutting edge on the cortical bone during the advance movement thereof.

[0085] Given that the axial movement of the cutting edge for each rotation of the screw is imposed by the pitch of the thread of the screw, in fact, the quantity of bone material which is removed by each cutting edge for each complete rotation of the screw will be a function of the pitch of the thread and of the number of cutting edges present.

[0086] In this manner, the depth of cut (or "passage depth") of each cutting edge may be dimensioned in an optimum manner for preventing excessive lesions and possible fractures of the cortical bone during the drilling step.

[0087] Preferably, the number of cutting edges formed on the head is such as to bring about a depth of passage for each cutting edge no greater than 150 micrometres, more preferably no greater than 100 micrometres.

[0088] The Applicant has observed that this characteristic allows the removal of a shaving of bone which is substantially continuous and segmented. This type of shaving has the advantage of preventing lesions and fractures in the wall of cortical bone adjacent to the cutting operation and, furthermore, allows a fragmented shaving which, in a manner advantageously received in positions adjacent to the screw, may promote the subsequent osteo-genesis process, to be obtained.

[0089] Preferably, there are at least 5 cutting edges formed in the head, more preferably there are between 8 and 15 and even more preferably there are 9. The Applicant has observed that with this number of cutting edges there is obtained, for a pitch of the thread of approximately 0.8 mm, a passage depth which is sufficiently low and, at the same time, a number of cutting edges which is not excessive which would substantially complicate the production process for the screw.

[0090] Furthermore, it is preferable for the number of cutting edges to be odd in order to have a better balancing of the tearing forces which would tend to redirect the insertion direction of the screw.

[0091] Preferably, the at least one cutting edge is formed on a respective fin which projects radially from a central body of the head of the screw.

[0092] In this manner, the cutting edge is formed in a screw portion which is separate from the other components of the screw and may be configured with the shape and the dimensions which are considered most suitable without external constraints which are dictated, for example, by the formation of the thread or the collar.

[0093] Preferably, the fin extends between a first end which is distal with respect to the thread and a second end which is proximal with respect to the thread and the cutting edge is formed on the second end of the fin.

[0094] In this manner, the fin can advantageously act as a conveying element for the detritus which has just been generated by the cutting edge.

[0095] Preferably, the fin extends longitudinally in a direction which is inclined with respect to the plane perpendicular to the screwing direction of the thread (this being defined by the direction of the helix of the thread when developed in a plane) by an angle between -30° and +30°, more preferably by an angle between 0° and +20°.

[0096] It is specified that the above-mentioned angle is considered to be positive when the longitudinal direction of the fin (considered to be orientated positively from the fin in a direction away from the thread) forms an acute angle with the screwing direction (considered to be orientated positively in the screwing direction of the thread), while this angle is considered to be negative when the longitudinal direction of the fin forms an obtuse angle with the screwing direction. In this manner, the fin may convey the detritus which is generated by the processing operation carried out by the cutting edge in a preferred direction.

[0097] In fact, by regulating in a suitable manner the inclination thereof with respect to the screwing direction of the thread, it is possible to urge the flow of detritus away from the thread (and therefore away from the cutting edge towards the outer side of the bone tissue) or, conversely, to urge the flow of detritus towards the interior so as to retain it at least partially in an accumulation between the head of the screw and the bone tissue.

[0098] In a first embodiment, the fin extends longitudinally in a direction which is substantially perpendicular to the screwing direction of the thread.

[0099] In this manner, the fin receives the detritus which is generated by the processing of the cutting edges without conferring thereon a preferential urging direction in the axial direction during the screwing.

[0100] In other words, during the screwing, the detritus is not conveyed outwardly or pressed towards the interior of the cavity, but instead is removed from the portion of bone tissue which has just been processed and moved at the same time as the movement of the dental implant.

[0101] In another embodiment, the fin extends longitudinally in a direction which is inclined by approximately from 8° to 11° with respect to the thread of the screw. In this manner, the detritus is lightly forced to remain in the region of the head of the screw, generating a minimum accumulation which may promote the subsequent process of osteo-integration, but leaving the possibility of being discharged outwardly if the accumulation is excessive.

[0102] This configuration is found to be particularly advantageous for promoting the filling of any recesses adjacent to the fin, which are configured as containment vessels for the detritus.

[0103] Preferably, the fin comprises a front side and a rear side with respect to the screwing direction of the screw.

[0104] Preferably, the cutting edge is defined by the intersection of the front side with the second end of the fin.

[0105] In this manner, the front side of the fin acts as a leading "chest" of the cutting edge and the inclination thereof with respect to the advance direction of the cutting edge defines the upper rake angle of the cutting edge, while the inclination of the second end of the fin with respect to the advance direction of the cutting edge defines the lower rake angle of the cutting edge.

[0106] Preferably, the front side of the fin is inclined with respect to the rotation axis of the screw so as to form an upper rake angle of the cutting edge between -20° and +20°, more preferably between -15° and +15°.

[0107] In a greatly preferred manner, the front side of the fin is inclined with respect to the rotation axis of the screw in a variable manner along the development of the cutting edge, in particular it has a negative rake angle in the region of a radially internal portion thereof and a positive rake angle in the region of a radially external portion thereof.

[0108] Preferably, the second end of the fin is inclined with respect to the rotation axis of the screw so as to form a lower rake angle of the cutting edge greater than + 10°, more preferably between +10° and +15°. With consideration of the helix angle of the thread which defines the cutting direction of the cutting edge, the second end of the fin is inclined with respect to the rotation axis of the screw about an angle between 70° and 75°, for example, approximately 73°.

[0109] This advantageously prevents the detritus from being flattened by the second end of the fin against the bone tissue underneath during the screwing of the screw.

[0110] Preferably, the fin comprises a tip which extends between the front side and the rear side of the fin and which is defined as the radially outermost portion of the fin.

[0111] In this manner, the intersection between the tip and the front side defines a secondary cutter, the function of which is to scrape the cylindrical surface of the wall of the cortical bone which is processed by the cutting edge and to retain the detritus inside a potential containment recess which is provided downstream of the fin.

[0112] Preferably, the tip extends from the second end of the fin as far as the first end of the fin.

[0113] Preferably, the tip has a constant distance from the rotation axis of the screw. Preferably, the inclination between the front side and the tip is such as to form an upper rake angle of the secondary cutter greater than 30°, for example, approximately 40°.

[0114] Preferably, the inclination between the front side and the tip is such as to form a lower rake angle of the secondary cutter which is substantially zero.

[0115] In this manner, the tip is in fact supported on the wall of the cortical bone acting as a guide for the advance movement of the screw. The secondary cutter is not in fact called upon to further cut the cortical bone, but only to trim the wall which has already been processed by the cutting edge.

[0116] However, the lower rake angle which is substantially zero allows the tip to effectively withstand any radial loads which are applied by the operator during the manoeuvre for screwing the screw, generally carried out manually, by being supported against the wall of the cortical bone without cutting it.

[0117] The tip preferably has a width between 0.03 mm and 0.1 mm, more preferably approximately 0.05 mm.

[0118] In this manner, the tip provides a support surface for the wall of the cortical bone which is sufficiently extensive, but while maintaining reduced friction which does not increase the torque necessary for screwing the screw into the bone tissue.

[0119] Preferably, at least one recess which is capable of containing the detritus of the processing operation carried out by the cutting edge is formed in the head of the screw.

[0120] In this manner, the detritus generated by this processing operation is collected in the recess so as to prevent the compression of the cortical bone surrounding the collar. The presence of the detritus between the head of the screw and the cortical bone further promotes the process of osteo-integration.

[0121] Preferably, the at least one recess is delimited laterally by two adjacent fins.

[0122] Preferably, the at least one recess is closed at the upper side towards the collar. In this manner, possible localized over- pressures which are caused by the presence of detritus between the collar and the cortical bone are prevented.

[0123] Preferably, the at least one recess has a recessed bottom with respect to the geometric cylinder which circumscribes the collar. Preferably, the at least one recess has a recessed bottom with respect to the core of the screw.

[0124] Preferably, the recessed bottom has a depth between 0.2 mm and 0.4 mm, more preferably approximately 0.3 mm, with respect to the geometric cylinder of the collar and / or the core of the screw.

[0125] In this manner, the recess has a sufficient volume for containing at least some of the quantity of detritus which is generated by the processing of the cutting edges, promoting the subsequent osteo-integration step.

[0126] In some embodiments, the head comprises a neck which is intended to be positioned above the region of cortical bone.

[0127] Preferably, the neck has a frustoconical shape.

[0128] In some embodiments, the screw does not have a neck.

[0129] Preferably, the head of the screw has a rough surface which can promote the osteo-integration.

[0130] Preferably, a hole which extends axially and which is open in the region of the upper end of the head of the screw is present inside the central body of the head of the screw. More preferably, the hole is shaped so as to be connected to a handling tool which allows the screw to be screwed in the cavity.

[0131] Preferably, the dental implant comprises a stump which is fixed to the head of the screw at the side opposite the thread by means of an additional screw which is received in the hole.

[0132] Preferably, the dental implant comprises a dental prosthesis which is fixed to the stump at the side opposite the screw.

[0133] The present invention will be described below in accordance with a preferred embodiment thereof which is provided by way of non-limiting example and with reference to the appended drawings, in which:

[0134] - Figure 1 is a perspective view of a dental implant which is constructed according to the present invention;

[0135] - Figure 2 shows a longitudinal section of the dental implant of Figure 1;

[0136] - Figure 3 is a perspective view of the screw of the dental implant of Figure 1;

[0137] - Figure 4 is a general view of the dental implant of Figure 1 in the insertion step into the bone tissue;

[0138] - Figure 5 shows a detail drawn to an enlarged scale of Figure 4; and

[0139] Figure 6 is a front view, drawn to an enlarged scale, of a portion of the screw of the dental implant of Figure 1.

[0140] With reference to the appended Figures, there is generally designated 1 a dental implant which is constructed according to the present invention.

[0141] The dental implant 1 is intended to be fixed to a bone tissue 5 which can be equally well the bone of the maxilla or the bone of the mandible in order to replace one or more teeth which are missing.

[0142] The dental implant 1 comprises, in terms of the main components thereof:

[0143] - a screw 2 which in turn includes a thread 3 which extends between an upper end 6 and a lower end 7 along a rotation axis X of the screw 2 and a head 8 which extends coaxially from the upper end 6 of the thread 3,

[0144] - a stump 26 which is removably fixed to the head 8 of the screw 2, and

[0145] - a dental prosthesis 30 which is connected to the stump 26 according to techniques which are known per se in the sector.

[0146] The screw 2 is configured to engage with the thread 3 thereof in a cavity 4 which is formed in the bone tissue 5 and in particular in a region of medullar bone 10a thereof. The thread 3 has a diameter which decreases from the upper end 6 as far as the lower end 7 and in the region of the lower end 7 has threaded portions which alternate with three recessed portions 23 which define on the respective threaded portions self-tapping cutters.

[0147] The overall dimensions of the screw 2 in terms of length and diameter as well as the geometric characteristics of the thread 3 thereof are a function of the specific application of the dental implant 1 and are conventional per se.

[0148] In the embodiment illustrated here, for example, the screw 2 has a core with a diameter of approximately 3.2 mm, from which the thread 3 extends up to a maximum external diameter of approximately 3.75 mm, with a pitch of approximately 0.8 mm, defining a helix angle of slightly less than 4°.

[0149] The head 8 and the thread 3 are made from titanium and are preferably obtained in one piece by means of suitable processing operations of turning and milling.

[0150] The head 8 comprises a central body which extends between a lower end 18 in contact with the upper end 6 of the thread 3 and an upper end 8a which is axially opposite the thread 3.

[0151] The head 8 comprises a collar 9 which is intended to be positioned in a cortical bone region 10 which is defined in the bone tissue 5.

[0152] The collar 9 is defined in a central region of the head 8 and has a cylindrical shape which is coaxial with the thread 3 and an external diameter which is equal to the external diameter of the thread 3 of the screw 2.

[0153] The geometric cylinder which circumscribes the collar 9 coincides in this case with the external surface of the same collar 9.

[0154] The collar 9 has a substantially smooth surface without any thread.

[0155] The head 8 at the side axially opposite the thread 3 further comprises a neck 9a which is intended to be positioned above the region of cortical bone 10 in the region of the gingival tissue. The neck 9a is formed in a frustoconical manner so as to promote the engagement thereof with the stump 26 and the dental prosthesis 30.

[0156] There is formed inside the central body of the head 8 a hole 25 which extends axially and which opens at the side of the upper end 8a of the head 8, which is shaped so as to be connected to a handling tool which allows the screw 2 to be screwed in the cavity 4.

[0157] There is further formed in the hole 25 a suitable thread for allowing the screwing of an additional screw 27 which removably retains the stump 26 which is engaged in the head 8.

[0158] The stump 26 projects from the bone tissue together with the dental prosthesis 30 which is fixed thereto.

[0159] In the region of the lower end 18 of the head 8, there is further provided between the collar 9 and the upper end 6 of the thread 3 a plurality of fins 12, for example nine, which are identical to each other and which are arranged at regular intervals along the entire circumferential perimeter of the head 8 in a plane perpendicular to the rotation axis X.

[0160] Each fin 12 extends between a first end 13 which is distal with respect to the thread 3 and a second end 14 which is proximal with respect to the thread 3 and comprises a front side 15 and a rear side 16 with respect to the screwing direction F of the screw 2.

[0161] Each fin 12 further comprises a tip 21 which is defined as the radially outermost portion thereof which connects the front side 15 to the rear side 16 of the fin 12. The tip 21 of the fin 12 extends longitudinally in a longitudinal direction of the fin 12 which is denoted T in Figure 6 and which is inclined by an angle of approximately 13° with respect to the rotation axis X and which is particularly inclined by an angle C of approximately +9° relative to the perpendicular R. to the screwing direction S of the thread 3. The tip 21 further has a width of approximately 0.05 mm and an axial dimension of approximately 0.9 mm.

[0162] The tip 21 belongs to a cylindrical surface which is coaxial with the rotation axis X so that the distance thereof from the rotation axis X remains constant over the longitudinal extent thereof.

[0163] The front side 15 is inclined with respect to the tip 21 in the region of the intersection between the two surfaces by approximately 40°.

[0164] A discharge groove 20 which extends circumferentially between the head 8 and the thread 3 is further formed between the respective second ends 14 of the fins 12 and the upper end 6 of the thread 3.

[0165] The discharge groove 20 has a diameter substantially equal to the core of the screw, in this case approximately 3.2 mm, and an axial dimension (substantially defining the width of the groove) of approximately 0.8 mm.

[0166] According to a main aspect of the present invention, the intersection of the front side 15 with the second end 14 of each fin 12 defines a respective cutting edge 11 which is intended to process by drilling the region of cortical bone 10 of the bone tissue 5 during the advance movement of the screw.

[0167] Each cutting edge 11 therefore faces towards the upper end 6 of the thread 3 and extends between an axially internal end 11a which is positioned near the upper end 6 of the thread 3 and an axially external end lib which is axially spaced apart from the upper end 6 of the thread 3. The axially internal end 11a is positioned in the region of the discharge groove 20, therefore having a distance from the rotation axis of approximately 3.2 mm, while the axially external end lib projects from the external diameter of the thread 3 and therefore also from the geometric cylinder which is defined by the collar 9 by approximately 0.05 mm.

[0168] Each cutting edge 11 further extends in a direction A which is inclined by approximately 60° with respect to the rotation axis X, following a curvilinear profile, which is concave with respect to the advance direction F of the screw 2. The inclination of the front side 15 and the second end 14 of the fin 12 with respect to the advance direction F of the cutting edge 11 define the upper rake angle and the lower rake angle of the cutting edge 11, respectively.

[0169] With consideration of the helix angle of the thread 3 and the inclination of the fin 12 (defined above in relation to the tip 21), and the curvilinear profile of the cutting edge 11, there is obtained an upper rake angle which in the radially internal portion of the cutting edge 11 is approximately -11° and in the radially external portion of the cutting edge 11 is approximately +11°.

[0170] The second end 14 of the fin 12 is substantially planar and is inclined with respect to the rotation axis X of the screw 2 by approximately 73° so as to define a lower rake angle of approximately +13° taking account of the helix angle of the thread 3.

[0171] There is further formed between each pair of adjacent fins 12 a respective recess 19 which is able to contain the detritus of the processing operation in such manner as to prevent the compression of the region of cortical bone 10 surrounding the collar 9 and to allow the regrowth thereof by promoting the osteo-integration. Each recess 19 is laterally delimited by two fins 12 which are adjacent and is closed in the upper region towards the collar 9.

[0172] Each recess 19 has a recessed bottom with respect to the geometric cylinder which is defined by the collar 9 by an extent of approximately 0.3 mm.

[0173] The head 8 of the screw 2 further has a tissue-like surface micro-processing (texturized) which can promote the subsequent step of adhesion with the surrounding organic tissues.

[0174] The dental implant 1 of the present invention is operated in the following way.

[0175] The screw 2 is inserted in the cavity 4, which is previously formed in the bone tissue 5, according to implant techniques which are known per se. The diameter of the cavity 4, which is determined according to specific clinical criteria, is slightly less than the external diameter of the thread 3 so that the screwing movement of the screw 2 in the cavity 4 brings about the formation of a counterthread in the bone tissue 5, the effect of which is to increase the retention force of the screw 2.

[0176] The screw 2 is therefore screwed in the screwing direction F inside the cavity 4 until it is introduced into the medullar region 10a.

[0177] By the screwing movement being continued, when the lower end 18 of the head 8 reaches the region of cortical bone 10, the cutting edges 11 of the fins 12 begin to cut into the region of cortical bone 10 and particularly the tips of the counter-thread which are formed by the passage of the thread 3.

[0178] The cutting edges 11 generally operate in the manner of a drill bit, removing the material of the region of cortical bone 10 in a progressive and continuous manner so as to process the region of cortical bone 10, generating a cylindrical housing 24 in which the projecting collar 9 is positioned. The number and dimensions of the cutting edges define a depth of passage less than 0.1 mm so that the swarf removed by each cutting edge is preferably continuous and segmented, producing detritus which is conveyed from the front side 15 of the fin 12 inside the recess 19 adjacent thereto, where it can remain with a specific margin of space so as not to cause over- pressures in the region of cortical bone 10 and, at the same time, to promote the subsequent process of osteo-integration of the screw.

[0179] The provision of an adequate lower rake angle prevents possible phenomena of crawling of the second end 14 on the bone tissue which has just been processed (so-called "chasing") which would cause an increase in the resistive torque for the screwing.

[0180] It will further be noted that the provision of the tips 21 with a rake angle which is substantially zero allows them to be supported on the walls of the cortical bone, substantially acting as a guide during the screwing movement of the screw 2.

[0181] Advantageously, as a result of the projection of the cutting edge 11 with respect to the external diameter of the collar 9, the housing 24 obtained by the drilling processing carried out by the cutting edges 11 has a slightly greater diameter than the collar 9 so that, once the screwing step is finished, the collar 9 remains positioned at the level of the region of cortical bone 10 without pressing thereon. In this manner, the formation of over- pressures generated by the collar 9 on the bone tissue 5 and the consequent formation of necrotic tissue which could involve the removal of the bone tissue 5 and could affect the stability of the dental implant 1 are prevented.

[0182] It will further be noted that, as a result of the minimal projection of the cutting edges with respect to the diameter of the geometric cylinder which is defined by the collar 9, it is located in a position very close to the tissue of the region of cortical bone 10 so as to ensure an efficient stability, including lateral stability, of the dental implant 1 and, at the same time, reduced times for the osteo- integration thereof.

[0183] In order to comply with additional and contingent requirements, a person skilled in the art may apply to the above-described dental implant a number of additional modifications and variants which are still included within the scope of protection of the present invention as defined by the appended claims.

Claims

Claims1. A dental implant (1) comprising a screw (2) which is configured to engage in a cavity (4) which is formed in a bone tissue (5), the screw comprising:- a thread (3) which is configured to engage at least in a medullar region (10a) of the bone tissue (5) and which extends along a rotation axis (X) of the screw(2) between an upper end (6) of the thread (3) and a lower end (7) of the thread(3);- a head (8) which extends from the upper end (6) of the thread (3) along the rotation axis (X),- a collar (9) which is defined on the head (8) and which does not have any thread and which is intended to be positioned in a region of cortical bone (10) of the bone tissue (5); at least one cutting edge (11) which is formed on the head (8) and which is interposed between the collar (9) and the upper end (6) of the thread (3), the cutting edge (11) being configured to process the region of cortical bone (10) after the passage of the thread and in order to provide it to receive the collar (9).

2. A dental implant (1) according to claim 1, wherein there is formed between the cutting edge (11) and the upper end (6) of the thread (3) a discharge groove (20) which extends along the circumferential perimeter of the head (8).

3. A dental implant (1) according to claim 1 or 2, wherein the cutting edge (11) faces towards the thread (3) and extends between an axially internal end (11a) and an axially external end (lib) thereof in a direction (A) which is inclined with respect to the rotation axis (X) by an angle between 55° and 70°, preferably approximately 60°.

4. A dental implant (1) according to claim 3, wherein the axially external end of the cutting edge (11) has a distance from the rotation axis (X) equal to or greater than the external diameter of the thread (3).

5. A dental implant (1) according to any one of the preceding claims, wherein on the collar (9) there is defined a maximum external diameter which corresponds to the diameter of a coaxial geometric cylinder which circumscribes the collar (9) and the cutting edge (11) has a maximum distance from the rotation axis (X) greater than or equal to the radius of the geometric cylinder.

6. A dental implant (1) according to claim 5, wherein the at least one cutting edge (11) projects from the geometric cylinder by an extent between 0.02 mm and 0.1 mm.

7. A dental implant (1) according to any one of the preceding claims, comprising a plurality of cutting edges (11) which are arranged at regular intervals along the circumferential perimeter of the head (8).

8. A dental implant (1) according to claim 7, wherein the plurality of cutting edges (11) comprise at least 5 cutting edges (11).

9. A dental implant (1) according to claim 8, wherein the plurality of cutting edges (11) are formed by a number of cutting edges (11) between 8 and 15.

10. A dental implant (1) according to any one of the preceding claims, wherein the at least one cutting edge (11) is formed on a respective fin (12) which projects radially from a central body of the head (8) of the screw (2).

11. A dental implant (1) according to claim 10, wherein the fin (12) extends between a first end (13) which is distal from the thread (3) and a second end (14) which is proximal to the thread (3) and the cutting edge (11) is formed on the second end of the fin (12).

12. A dental implant (1) according to claim 10 or 11, wherein the fin (12) extends longitudinally in a direction (T) which is inclined with respect to a plane (R.) perpendicular to a screwing direction (S) of the thread (3) by an angle (C) between -30° and +30°, preferably between +8° and +11°.

13. A dental implant (1) according to claim 11 or 12, wherein the fin comprises a front side (15) and a rear side (16) with respect to the screwing direction of the screw (2) and the cutting edge (11) is defined by the intersection of the front side (15) with the second end (14) of the fin (12).

14. A dental implant (1) according to claim 13, wherein the front side (15) is inclined with respect to the rotation axis (X) of the screw (3) so as to form an upper rake angle of the cutting edge (11) between -20° and +20°.

15. A dental implant (1) according to any one of claims 11 to 14, wherein the second end (14) of the fin (12) is inclined with respect to the rotation axis (X) of the screw (3) so as to form a lower rake angle of the cutting edge (11) greater than +10°.

16. A dental implant (1) according to any one of the preceding claims, wherein there is formed in the head (8) at least one recess (19) which can contain the detritus of the processing of the cutting edge.

17. A dental implant (1) according to claim 16, wherein the at least one recess (19) is laterally delimited by two adjacent fins (12).

18. A dental implant (1) according to claim 16 or 17, wherein the at least one recess (19) has a bottom (22) which is recessed with respect to the geometric cylinder and has a depth between 0.2 mm and 0.4 mm.

Images