DESCRIPTION

The present invention relates to an orthodontic bracket .

It is known that in the technical sector of orthodontics there exists the need to modify the relative positioning of the teeth along an upper and/or lower dental arch, in order to obtain a correct alignment of the teeth of an arch and/or functionally adequate engagement between upper and lower teeth.

For this purpose (see Fig. 1) orthodontic brackets 1, known for example from US 2015/282897, are commonly used, these being realized in the form of numerous variants which comprise substantially the following main elements:

- a base la, which is cemented onto the tooth so as to be integral therewith;

- a slot lb extending longitudinally along the base and designed to seat an orthodontic archwire 2;

- an orthodontic archwire 2 - or metallic wire - which connects the brackets together and forms the actuating part of the system;

- a vestibular structure which is designed to retain the orthodontic archwire inside the slot and normally consists of two pairs of flanges lc which extend on opposite sides of the slot lb and to which a metal ligature or an elastic ringlet may be fixed so as to pass over the archwire and retain it inside the slot;

fasteners Id for fixing elastic tensioning elements or springs.

For the purposes of the present invention the following terms will also be used:

VESTIBULAR: the part of the tooth and the bracket directed towards the cheeks or the lips;

TIP (of the tooth) : The distal-mesial inclination of the tooth crown relative to the tooth root;

TORQUE (of the tooth) : the radicular-coronal inclination of the tooth relative to the occlusal plane defined by the orthodontic archwire; in the terminology of the sector in particular a "vestibular radicular-coronal" (positive) torque or a "lingual radicular-coronal" (negative) torque are defined .

OCCLUSAL PLANE: the plane where the two dental arches meet, parallel to the plane passing through the orthodontic archwire;

The orthodontic brackets may be non-informed or pre- informed .

Non-informed brackets have a horizontal slot arranged in the centre of the bracket (tip=0) and perpendicular to the base (torque=0) .

To use these brackets, it is required to model the steel wire so as to provide movement information to the tooth and then fasten the wire to the brackets. The pre-informed brackets contain information for the ideal inclination of the tooth which determines during use corresponding forces thereon, in particular :

the tip information provided by the mesial-distal or distal-mesial inclination, when the slot is horizontal at the centre of the bracket the tip=0; the torque information provided by the angle of inclination which the slot has relative to the perpendicular to the plane of the base of the bracket; when the slot extends at 90° relative to the base of the bracket the torque=0;

the degrees of inclination vary from tooth to tooth and refer to the occlusal plane.

Pre-informed brackets are very convenient because they allow one to work using the so-called "straight wire technique" which consists in using nickel- titanium (NiTi) archwires which are pre-formed, i.e. are industrially constructed with the form of an ideal dental arch.

This is possible because NiTi alloys are " superelastic" , have a very great form memory and tend, once deformed, to resume their original form. These archwires are commercially available in different sizes, thicknesses and cross-sections (round, square and rectangular) and are used in coordinated pairs for the two arches; the archwires always have a bigger size than the arch to which they are applied and it is precisely this tendency of the archwire to expand, together with the form- memory, which slowly brings the teeth into the final desired position.

In order to optimize the action of the NiTi archwires the slots of the orthodontic brackets and the ligature system must have as little friction as possible with the metal archwire during the initial stages of the treatment and the greatest possible friction during the final stages.

During the initial stages of orthodontic treatment, the teeth are located at different heights and in different planes and NiTi archwires with a round cross-section and small diameter, normally identified by the numeric codes (014-018), are used. These thin archwires are highly deformable and are therefore able to follow curves and angles, including acute angles, so as to engage with all the brackets in sequence and have the advantage that they slide very easily. After levelling and roughly aligning the arch, it will be possible to use a larger-diameter wire and closer adhesion to the slot will result in more precise alignment of all the teeth .

The orthodontic archwires with a square or rectangular cross-section are instead used with full thickness during the finishing stages in order to give the teeth the right position and torque angle. In short, to obtain functionally correct and aesthetically pleasing positioning of the teeth it is necessary for the wire to work in the three dimensions of space and this is made possible by a wire with a large-thickness rectangular or square cross-section which, once inserted in the slot, transfers to the tooth the information provided by the archwire or the bracket.

The orthodontic brackets with a rectangular cross- section which are used during this stage are large and must be inserted frontally; moreover, they impart forces of reasonable intensity, and therefore the bracket must be strong so that it does not break, and firmly cemented to the tooth so that it is does not become detached.

The known orthodontic brackets, even though they have small dimensions, nevertheless have rough surfaces, with high friction, and a vestibular surface which is very structured owing to the presence of fastening elements and flanges which are constantly the cause of lesions in the mucus of the patients' cheeks.

An orthodontic bracket according to the preamble of Claim 1 is described in KR 2013 0132037.

The technical problem which is posed therefore is that of providing orthodontic brackets which are less traumatic, which help promote periodontal health, which move the teeth assisting also the muscular forces present in the mouth, but which at the same time are also able to produce adequate torque forces indispensable for obtaining effective correction of the position of the teeth.

In connection with this problem it is also required that these brackets should have small dimensions, be attractive, easy and inexpensive to produce and assemble and be able to be easily, but stably fitted to all teeth of the dental arch and allow low-friction operations, i.e. avoid the application onto the archwires of means which create friction, such as elastic or metal ligatures, and that they should exert low forces.

These results are obtained according to the present invention by an orthodontic bracket according to the characteristic features of Claim 1.

An orthodontic bracket according to the invention comprises a base 10 for attachment to a tooth of the dental arch, extending in a longitudinal widthwise direction X-X and vertical heightwise direction Z-Z, and a body 20 integral with the base 10, which has a substantially continuous vestibular surface 21; between the base 10 and the body 20 there being formed a first slit 30a parallel to the base surface 10 and open towards the outside along a coronal or gingival flank 10a of the bracket; said first slit 30 is connected to a second slit 30c; 130c which extends inside the body 20 towards the vestibular surface 21 with a blind end inside the body 20, and in a mesial-distal direction, the second slit 30c; 130c being open towards the outside along a mesial flank.

Preferably, the point where the first slit 30a and the second slit 30c are joined together and/or the blind end of the second slit 30c have a recess 30b extending towards a body part 30 opposite to the opening of the first slit 30a.

Preferably, said second slit 30c; 130c has a mesial- distal development with a given inclination of between 0° and 30°, and preferably between 10° and 20°, relative to the longitudinal direction X-X and, during use, to the orthodontic archwire, able to provide tip information of the bracket.

The second slit 30c may also have an inclination in the coronal or gingival direction relative to the perpendicular to the longitudinal-vertical plane X- Z of the base 10, ranging between 10° and 35°, preferably between 15° and 30°, able to provide torque information of the bracket.

The second slit 30c; 130c inside the body 20 has preferably a polygonal cross-section with corner edges able to seat orthodontic archwires 2 of corresponding cross-section.

The bracket according to the invention has preferably a groove 40 extending in the bracket part opposite to the opening towards the outside of the first slit 30a with a section 40a along a mesial flank, a section 40b along a gingival/coronal flank and a section 40c extending along a distal flank and/or a seat 50 with a circular form cut into both the mesial and distal flanks of the body 20 for seating one end of a spring 51. According to a preferred embodiment, the bracket has a tunnel with a blind distal end, for inserting one end of the orthodontic archwire 2.

Preferably, the second slit 30c; 130c which is open outwards on the mesial flank, passes through the body 20 in the mesial-distal direction or has a blind distal end.

Further details may be obtained from the following description of non-limiting examples of embodiment of the subject of the present invention, provided with reference to the accompanying drawings, in which :

Figure 1 : is a perspective view of an orthodontic bracket according to the prior art;

Figure 2 : is a perspective view of an orthodontic bracket according to the present invention;

Figure 3: is a side view of the orthodontic bracket according to Fig. 2;

Figure 4 : is a view from above of the orthodontic bracket according to Fig. 2;

Figure 5: is a view the rear of the orthodontic bracket according to Fig. 2;

Figures 6a, 6b : are respectively a cross-sectional view and a cut-away view of variations of embodiment of the bracket according to the invention;

Figure 7 : shows schematic views of embodiments of the progression of the inclination of the slit relative to the occlusal plane;

Figure 8 : is a schematic view of the orthodontic bracket according to the invention in the specialized variants for different teeth of the arch;

Figure 9: is a schematic cross-sectional view similar to that of Fig. 7 with a single orthodontic archwire inserted;

Figure 10: is a schematic view of the orthodontic brackets provided with double orthodontic archwire; Figure 11 : is a cross-section along a vertical plane of one of the brackets according to Fig. 10. As shown in Figures 2-6 and assuming solely for the sake of easier description and without a limiting meaning, a set of three orthogonal reference axes with respective directions, i.e.

longitudinal direction X-X along the width of a base 10 of the bracket and, during use, substantially parallel to the direction of extension of the orthodontic bracket;

transverse direction Y-Y extending in an anterior- posterior direction and substantially parallel to a thickness of the bracket between the base 10 and a vestibular surface thereof;

vertical direction Z-Z along the length/height of the base 10 and, during use, substantially parallel to a gingival/coronal direction of the tooth;

as well as a mesial part of the bracket corresponding to the part directed towards the centre of the arch and a distal part opposite to the mesial part, the orthodontic bracket according to the invention comprises essentially:

a rear base 10, which is preferably polygonal, for attachment to the tooth;

- a body 20 integral with the base 10 and with a substantially continuous vestibular surface 21; preferably, the vestibular surface has a continuous rounded form, but it is envisaged that it may also have the form of a polygonal surface which approximates as far as possible a rounded surface. Between the base 10 and the body 20 there is formed a slit 30 which comprises a first slit 30a extending parallel to the longitudinal-vertical plane of the base 10 and passing through the body 20 in the vertical direction Z-Z, which first slit is connected to a second slit 30c which extends inside the body 20 towards the vestibular surface 21 and extends inside the body 20 in a mesial- distal direction, being open at least on the mesial side and preferably passing through the body 20 in said mesial-distal direction.

The first slit 30a is open towards the outside along a flank 10a of the bracket; preferably the said flank of the bracket is coronal or gingival. The second slit 30a will have the blind anterior- vestibular end inside the body 20.

According to the preferred modes of implementation (Fig. 6) it is envisaged that:

-) the point where the first slit 30a and the second slit 30c are joined together has a recess 30b,

-) the blind end inside the bracket of the second slit 30c has a similar recess 30b,

the two recesses extending towards the part of the body 20 opposite to the opening of the first slit 30a and able to increase the stability of positioning of the orthodontic archwire 2 after insertion thereof.

According to preferred embodiments, it is envisaged that the blind slit 30c which extends in the vestibular direction inside the body 20 has different inclinations relative to the longitudinal-vertical plane X-Z of the base 10, corresponding to different torque information of the bracket which determine forces necessary for the different teeth to which the said bracket must be fitted.

In particular, the second slit 30c may have an inclination of between 10° and 35°, preferably between 15° and 30°, in the coronal/gingival or gingival/coronal direction relative to the perpendicular to the longitudinal-vertical plane of the base, where there is a torque = 0.

According to a further preferred embodiment (Figs. 6b, 7) it is envisaged that the second slit 30c may have a mesial-distal extension with an inclination, relative to the longitudinal direction X-X and during use to the plane determined by the orthodontic archwire, ranging between 0° and 30°, preferably between 10° and 20°, in order to obtain the tip information of the bracket which determines the forces for correction of the tip, particularly useful for movement of the canine teeth and of the incisors.

Preferably, the vestibular edges 30ai and 30a ₂ of the first slit 30a are rounded and/or flared to allow attachment of an elastic.

Preferably, the slit 30 has a width of between 0.45 and 0.50 mm.

According to a further variation of embodiment, it is envisaged that the slit section 30c, 130c inside the vestibular body 20 has a polygonal cross- section with corner edges, so as to allow the seating of orthodontic archwires of corresponding cross-section which, if suitably positioned with diagonals staggered relative to those of the seat, will allow the torque effect associated with the archwire to be added to the torque effect derived from the inclination of slit 30c of the orthodontic bracket according to the invention.

In the bracket part opposite to the opening towards the outside of the first slit 30a, the bracket according to the invention has a groove 40 extending with a section 40a along a mesial flank, a section 40b along a gingival/coronal flank and a section 40c extending along a distal flank.

The mesial section 40a and distal section 40c of the groove 40 extend as far as the point 30b where the slits 30a and 30c are joined together.

Preferably, the rear surface 10b of the base 10 has incisions 11, or alternatively, a surface which is made rough in order to favour improved adhesion to the surface of the tooth, obtained by means of adhesives and/or cement.

The rear surface 10b may be concave following a radius of curvature, for better engagement with the surface of the tooth.

Preferably, also escapeways 12 for excess adhesive are provided; preferably the escapeways are open towards the side of the base 10 opposite to that of the opening of the first slit 30a so as not to soil it with adhesive residues which would block the entrance and prevent sliding of the orthodontic archwire .

In a preferred embodiment of the bracket according to the invention, said bracket also has a seat 50 with a circular form cut into the opposite mesial and distal flanks of the body 20, the seat being suitable for receiving one end of a spring 51 which can be used to space from each other two adjacent teeth, independently of the other movements of the teeth of the associated arch, as will become clear below .

Depending on the tooth to which it is applied, the opening towards the outside of the first slit 30a may for example be gingival or coronal.

In one embodiment for attachment to second molars, the bracket of the invention has, in addition to the slit, a tunnel with a distal blind end. This feature does not allow the thin archwires to migrate such that one end comes out of the distal part of the bracket of the last molar.

This occurrence, which is very frequent, gives rise to many emergency situations which the dental surgeon is required to deal with since the end of the archwire acts on the cheek like a needle and cannot be managed by the patient.

When the seventh molars are not present, the bracket may be mounted on the sixth molars.

The blind end of the tunnel functions as a stop: when it is required to expand the arch it is sufficient to cut the archwire so that it is a little longer and insert it into the tunnel.

The teeth of the anterior sector will be displaced forwards and the seventh molar will be retracted a little. This latter effect, if not desired, may be avoided by a continuous ligature between molars and premolars .

Some non-limiting examples of embodiment of the orthodontic bracket according to the invention envisage the following features:

UPPER CENTRAL INCISORS: horizontal rectangular base; angle of inclination of the second slit = - 15° relative to the perpendicular to the longitudinal vertical plane X-Z (torque) ; opening of the first slit 30a on the coronal side; tip information = 0-10°.

UPPER LATERAL INCISORS: Square base, angle of inclination of the slit relative to the perpendicular to the plane X-Z = -15°; opening of the slit 30a on the gingival side; tip information = 10°-20°, preferably 17-20°.

UPPER AND LOWER CANINES: square base with curvature of radius 10 mm; flexing angle relative to the perpendicular to the plane X-Z = 0°; opening of the slit 30a on the gingival side; tip = 10-20°, preferably 12-15°.

UPPER AND LOWER PREMOLARS: Square base with curvature of radius 10 mm; flexing angle of the slit (torque) = +10°, coronal opening of the slit 30a. UPPER AND LOWER FIRST MOLARS: Rectangular base (horizontally) ; flexing angle relative to the perpendicular = +15°; gingival opening of the slit 30a.

SECOND MOLARS: Rectangular-horizontal base; angle of inclination of slit relative to the perpendicular to the plane X-Z = +15°; gingival opening of the slit 30a.

Preferably, for use on the second (seventh) molars, the second slit 30c has a blind distal end able to prevent the orthodontic wire from damaging the patient's cheek.

CENTRAL LOWER INCISORS: vertical rectangular base; angle of inclination of the slit relative to the perpendicular to the plane X-Z = +15° ; opening of the coronal slit 30a;

LATERAL LOWER INCISORS: Vertical rectangular base; angle of inclination of the slit (torque) = +15°. The lower incisors are the same, but two have a coronal/gingival opening of the slit 30a for allowing it to be turned upside down should a negative torque be required.

The structure of the bracket according to the invention allows the bracket to be positioned (see Fig. 7) with the opening towards the outside of the slit 30a alternately gingival or coronal, so as to form a path for the orthodontic archwire 2 such that the latter is kept in the correct position without the need for auxiliary ligatures.

However, should a ligature be necessary, it is possible to use the groove 40 to which the wire or the elastic which tie the orthodontic archwire 2 may be secured.

As schematically shown in Figs. 10,11 it is also envisaged being able to fit two orthodontic archwires, i.e. a first fixed wire 2a and a second operationally expanding wire 2b.

Preferably, the first wire 2a is a non-expanding archwire, for example made of braided steel, which is arranged at the joining point between the two slits 30a, 30c and remains fixed since it is tied at the rear; the second wire 2b is a NiTi archwire which is positioned at the blind end of the horizontal slit 30c where it will remain also owing to its tendency to expand and/or to the presence of any recesses 302b.

When the fixed archwire 2a is fixed at the rear with two distal folds (closed archwire) , it becomes a rotational fulcrum and allows the NiTi archwire to apply the torque which, guided by the respective inclinations of the slit 30c, causes the teeth to assume the correct inclination because all the blind ends of the slits will be aligned in the same plane. It is therefore clear how the orthodontic bracket according to the invention is of the pre-informed type for straight-wire, low-friction and self- ligating - and even non-ligating - technology, but at the same time is able to manage correctly the torque with light forces, also by means of archwires with a square cross-section, owing to the polygonal form of the second slit, being at the same time able to avoid traumas owing to the smooth vestibular surface, without conventional archwire ligature systems.

The bracket is also highly attractive, easy to clean and able to reduce to a minimum the accumulation of bacterial plaque.

Owing to the receding profile it cannot be easily detached during chewing and is able to conceal very well any metallic or elastic ligatures.

The construction material may be ceramic, glass, metal, polycarbonate, resin or composite material. The colour, imitation white, may also be coloured for use on children. Strass or decorative elements may be applied onto the vestibular surface.

Although described in connection with a number of embodiments and a number of preferred examples of embodiment of the invention, it is understood that the scope of protection of the present patent is determined solely by the claims below.