INTRA-BONE SCREW FOR EXTRA-DENTAL FIXING AND WIRE WITH RESPECTIVE MUTUAL COUPLING MEANS, PARTICULARLY FOR ORTHODONTIC USE

Technical field The present invention relates to an intra-bone screw for extra-dental fixing and to a wire with respective mutual coupling means, particularly for orthodontic use. Background art

Orthodontic devices are used to shift the teeth inside the mouth by applying thereto one or more forces of suitable intensity.

In the orthodontic field it is known to use intra-bone screws, which are designed to be screwed into the bone and in which wires or springs of the commercial type are fixed to the portion that protrudes from the gum: in order to fix the wires to the screw, such screw is provided, at its upper end, with notches, holes or the like which are oriented at right angles to the main axis and to which orthodontic wires are coupled which are fixed to the screw by means of composite resins which surround them and cement them; as an alternative, the wires are anchored to the screw by means of elastic or metallic bindings. Such bindings cause discomfort to the patient due to rubbing against tissues; other times, the wires, cemented by means of composite resins, form porous surfaces which produce an accumulation of bacterial plaque. Both of these connections cause inflammations of the surrounding tissues either due to mechanical irritations or due to bacterial infection of the surrounding tissues.

Another drawback of the background art is the difficulty in creating, with the wire inserted in the oriented notches in the head of the screw at right angles to the long axis of the screw, vectors which are parallel to the axis of the screw. To create these vectors, the wire must be bent adjacent to the notch and then subjected to flexural forces. With this configuration, the

region for contact and fixing of the wire on the head of the screw is too short to withstand dislocation and is difficult to stabilize; such stabilization must necessarily occur by means of bindings or composite resins which cement the wire in the notches. In addition to this, in the background art the wires are rigidly coupled to the screw without any degree of freedom, so as to transmit to the screw also the torsional stresses which tend to screw or unscrew the screw into or from the seat that has formed in the bone, causing its expulsion.

In practice, the rotational moments discharged onto the screw are harmful for the survival of such screw inside the bone tissue, since they cause compression, ischemia and necrosis of the bone cells that surround the turns, consequently causing mobility and loss of the screw. Disclosure of the Invention

The aim of the present invention is to obviate the above cited drawbacks and meet the mentioned requirements, by providing an intra- bone screw for extra-dental fixing and a wire with respective mutual coupling means, particularly for orthodontic use, with which there are no torsional stresses of the screw with respect to the bone, so as to avoid the consequent expulsion phenomena, there is no need for bindings or resins to retain the wire in the screw, avoiding inflammations of the surrounding tissues, and it is possible to create lever arms which work in the three spatial planes, rotating about the head of the screw without ever causing harmful screwing or unscrewing moments affecting the screw device.

Within this aim, an object of the present invention is to provide an intra-bone screw which has a simple structure, is relatively easy to provide in practice, safe in use, effective in operation, and has a relatively low cost.

This aim and this and other objects, which will become better apparent hereinafter, are achieved by the present intra-bone screw for extra- dental fixing and by a wire with respective mutual coupling means, particularly for orthodontic use, characterized in that the head of said screw

has a longitudinal dead hole and in that the end of said wire has at least one bend in order to form a portion which can be inserted by interlocking in said hole.

Brief description of the drawings Further characteristics and advantages of the invention will become better apparent from the following detailed description of a preferred but not exclusive embodiment of an intra-bone screw for extra-dental fixing and of a wire with respective mutual coupling means, particularly for orthodontic use, according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a perspective view of an intra-bone screw according to the invention;

Figures 2A-2E are schematic side views of applications to groups of teeth of the screw according to the invention, used to transmit stresses of different types in order to obtain different effects, in particular: in Figure 2 A, an elastic wire with extrusive effects; in Figure 2B, an elastic wire with intrusive effects; in Figure 2C, a rigid wire and a traction effect due to a helical spring; in Figure 2D, a rigid wire and a pushing effect obtained with a helical spring wound on the rigid wire which works along the direction of the wire; in Figure 2E, a pushing effect obtained with the screw driven in a direction which is substantially perpendicular to the direction of the roots of the teeth;

Figure 3 is a perspective view of a screw according to the invention; Figure 4 is a perspective view of the screw coupled to a wire whose diameter is similar or identical to the diameter of the hole;

Figures 5 and 6 are perspective views of the screw coupled to a thin elastic wire;

Figure 7 is a perspective view of the screw coupled to a wire having substantially the same diameter as the hole and is fitted with a helical spring

in order to transmit forces which are oriented along the direction of the wire;

Figure 8 is a side view of a screw coupled to a longitudinal thin elastic wire; Figure 9 is a side view of a screw coupled to a thin elastic wire with three bends;

Figure 10 is a side view of a screw coupled to a substantially rigid wire;

Figure 11 is a side view of a screw coupled to a thin elastic wire with three bends;

Figure 12 is a side view of a screw coupled to a thin elastic wire with a single bend;

Figure 13 is a perspective view of a screw coupled to a thin elastic wire with three bends. Ways of carrying out the invention

With reference to the figures, the reference numeral 1 generally designates an intra-bone screw for extra-dental fixing and a wire with respective mutual coupling means, particularly for orthodontic use, according to the invention. The screw 1 comprises a threaded and frustum-shaped portion 2, which is designed to be screwed into the bone of the gum, and a portion 3, which remains outside the bone, passes through the gum and advantageously has a portion 4 which is shaped like a parallelepiped with a hexagonal cross-section, protrudes from the gum and is surmounted by a tubular portion 5 which has a reduced diameter and is crossed in an upper region by two mutually opposite slots 5a, 5b or by a horizontal groove on the outer circumference of the cylinder; an axial hole 6 of the tubular portion 5 protrudes inside the screw with a blind portion; the hole 6 has a cylindrical cross-section and smooth walls. The reference numeral 7 generally designates a wire of the type used

in orthodontics, which can have various diameters and can be made of different materials: the end of the wire 7 has at least one bend to form a portion which can be inserted by interlocking in the hole 6.

The hole 6 can have a diameter which is substantially identical to the diameter of the wire, and in this case the bend is a single one, designated by the reference numeral 8, and is substantially at 90°: a bent end 9 is coupled to the head hole of the screw so that the wire adheres perfectly to the walls of the hole (Figure 4).

Figure 5 illustrates a screw with a head hole whose diameter is slightly larger than twice the diameter of the wire 7.

There are two bends: a first one, designated by the reference numeral 10, is substantially at 90°, and a second one, designated by the reference numeral 11 , is at 180° and forms a U-shaped terminal which is inserted and mated elastically in the hole of the screw without transmitting torsional stresses to the screw.

In Figure 6, the diameter of the hole of the screw is more than twice the diameter of the wire; like the wire 7 shown in Figure 5, the wire 7 in Figure 6 has a first bend and a second bend, designated by the reference numerals 10 and 11, respectively at 90° and 180°, and has a third 90° bend 12 which forms a tab 13 which can be fixed to a contiguous tooth, the U- shaped portion being inserted with slight forcing in the hole of the screw practically without transmitting torsional stresses to the screw.

The wire is made of elastic metal alloy, and if its elasticity is activated, its free end is adapted to transmit a force which is parallel to the major axis of the screw and has an intrusive or extrusive direction with respect to the gum (Figures 2A, 2B, 2C, 2D).

Figure 8 is a side view of a screw which is coupled to a thin longitudinal elastic wire, of which configurations 15 in which it can work elastically are shown in broken lines. Figure 9 is a side view of a screw which is coupled to a thin elastic

wire with three bends, of which configurations 15 are shown in broken lines in which the two ends of the wire can work elastically.

Figure 10 is a side view of a screw which is coupled to a substantially rigid wire which acts as a guide for the spring M so as to push in the direction of the arrow A.

Figure 11 is a side view of a screw which is coupled to a thin elastic wire with three bends, with a terminal portion of the wire which is wound so as to form a helical spring 14 which pulls in the direction of the arrow B.

Figure 12 is a side view of a screw which is coupled to a thin elastic wire with a single 180° bend, which forms two terminals which protrude coaxially from the screw and of which configurations 15 in which the terminals can work elastically are shown in broken lines.

Figure 13 is a perspective view of a screw which is coupled to a thin elastic wire with three bends, which form two terminals which work on a plane which is perpendicular to the axis of tlie screw and of which configurations 15 in which they can work elastically are shown in broken lines.

The operation of the invention is as follows: the coupling of the end of the wire to the hole of the head of the screw, which occurs without the aid or interposition of bindings or cementing resins, is free to rotate without transmitting moments which tend to loosen or tighten the screw: this reduces the possibility of losing the screw.

If instead one uses wires which adhere perfectly to the walls of the hole, the more rigid wire having a larger diameter can become a guide or core around which a cylindrical helical spring M winds, being thus guided so as to push longitudinally with respect to the wire (Figure 7).

With the invention it is possible to create an anchoring device mainly for orthodontic apparatuses which uses a wire whose diameter is similar or identical to the diameter of the hole on the screw. In this case, the wire is rigid and does not produce elastic arms; only once an end thereof has been

accommodated in the hole of the screw does the opposite end of the wire, which protrudes from the hole, get retained and locked on the orthodontic apparatus.

A "screw- wire" and orthodontic apparatus anchoring unit is thus created which allows the wire to remain free to rotate about the screw, but the rigidity of the wire prevents said wire from disengaging from the axial hole of the screw and allows to perform the anchoring task for the orthodontic appliance.

It has thus been shown that the invention achieves the intended aim and objects, in particular the insertion of the orthodontic wire coaxially to the axis of the screw. If said wire is made of elastic metallic alloy, even without creating any bends, with a wire which has a simple rectilinear shape, and if its elasticity is activated, its free end will be adapted to transmit a force which is parallel to the major axis of the screw and an intrusive or extrusive orientation with respect to the gum. The walls of the dead hole produce sufficient and simple retention on the wire, with a system which is easy to provide in practice and effective in operation.

Moreover, there is no need for any binding or cementing paste to stabilize the wire with respect to the screw. With reference to Figures 2A-2E, some of the possible applications are illustrated: in Figure 2A, one has extrusive effects, with the elastic wire which flexes upward by means of the screw on the right, and pushes with its tip by means of the left screw; in Figure 2B, there is an intrusive effect; in Figure 2C, there is a pulling effect caused by the helical spring, which acts by traction; in Figure 2D, there is a pushing effect obtained with a helical spring wound on a rigid wire acting by compression, in the direction of the wire, on a ring which is fixed to the tooth to be moved;

in Figure 2E ₅ there is a pushing effect obtained with the screw inserted in a direction which is substantially perpendicular to the direction of the roots of the teeth on which it has to work and with the elastic wire working on a plane which is perpendicular to the length of the screw (Figure 13).

Attention is called to the extreme versatility of the screw according to the invention, which can be screwed into the gum with any orientation and in which the wire can perform pushing actions without transmitting torsions to the screw in any direction (centrifugal or centripetal with respect to the head of the screw, for example by means of helical springs guided along the rigid wire), or with an elastic wire which can transmit moments or axial stresses on planes or in directions which are orientated in any way in space at 360° with respect to the axis of the screw.

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

All the details may further be replaced with other technically equivalent ones.

In the exemplary embodiments that follow, individual characteristics, given in relation to specific examples, may actually be interchanged with other different characteristics that exist in other exemplary embodiments.

Moreover, it is noted that anything found to be already known during the patenting process is understood not to be claimed and to be the subject of a disclaimer. In practice, the materials used, as well as the shapes and dimensions, may be any according to requirements without thereby abandoning the scope of the protection of the appended claims.

The disclosures in Italian Patent Application No. PR2006A000040, from which this application claims priority, are incorporated herein by reference.