Insert for fixing of dental prostheses

The present patent application for industrial invention relates to an insert for stable fixing of dental prostheses.

The peculiarities and advantages of the invention will be more evident after a short description of the prior art.

A dental implant technique is traditionally used to remedy the loss of teeth that may have fallen spontaneously, or traumatically removed or extracted by the dentist.

According to said technique, a basically cylindrical metal pin (technically defined as "implant") is inserted in the patient's bone by the dentist and acts as root for the false tooth.

Once such an implant has stabilized in the bone, a basically conical metal stem, normally defined as "stump", is fixed, generally by means of a screw.

Such a stump is adapted to support the dental prosthesis (the so-called "crown"), i.e. the ceramic-coated metal capsule that exactly reproduces the missing tooth.

Also the crown is fixed to the stump by means of a screw that, after crossing an axial hole obtained on the stump, is engaged in the implant.

Then the crown is cemented on the stump, also in order to conceal the installation recess of the fixing screw.

An alternative to this technology is the so-called screwed prosthesis, wherein the stump is already integrated in the prosthetic crown.

In such a context the upper opening of the axial hole of said stump remains visible on the upper side of the prosthetic crown.

This allows for inserting the screw used to fix the screwed prosthesis to the implant.

In both technologies, after being deeply engaged into the implant, the head of the screw is disposed on the bottom of said axial hole of the stump. Then the hole is filled with a typical hardening paste for dental use, which is intended for numerous uses in the oral cavity.

So the hardening paste incorporates the head of the fixing screw that is housed on the bottom on the axial hole.

It was assumed that, after setting, the cement paste could firmly lock the fixing screw in place inside the hole of the stump, in such way to prevent it from accidentally loosening because of the inevitable mechanical stress suffered by the entire prosthetic tooth during mastication.

It is easy to understand that, in case of even partial loosening of one of said screws, the prosthetic tooth would move uncontrollably, impairing functionality and practicality of use.

However, the choice of using the hardening paste to prevent the progressive disengagement of the fixing screw from a corresponding prosthetic tooth has proved a rather unreliable solution.

Regardless of the use of such hardening paste, the current prostheses normally tend to loosen and lose stability inside the patient's oral cavity.

US 5 704 788 discloses a dental implant comprising a hexagonal shaft engaged in a notch of the head of a screw used to secure a stump of the implant.

The specific purpose of the present invention is to innovate the foregoing technology in order to specifically prevent that such a dental prosthesis is impaired, in terms of stability and efficacy of use, by the progressive loosening of the screw that ensures fixing to the implant.

More precisely, it was assumed that such a result could be achieved by means of a locking insert adapted to be engaged inside the typical axial hole of a stump, in such manner to be prismatically coupled with the head of the screw housed on the bottom in order to prevent loosening.

Practically, such an insert can be compared to the tip of a screwdriver, since it consists in a short rod having total length slightly lower than the depth of the axial hole of the stump and provided with lower pointed end. With reference to the installation of said insert, it must be noted that the same is inserted deeply into the axial hole of a stump, after tightening the fixing screw on the bottom of the latter.

Then the tip of the insert is exactly coupled with the notch obtained on the head of the screw, in such a condition that the entire insert is housed for its entire length inside the axial hole of the stump.

Successively, the hole is filled with the traditional hardening paste to block the insert in the position given during installation, thus preventing the loosening of the screw used for prismatic coupling of the insert.

Obviously, if the rotation of such an insert inside the axial hole is prevented by the hardening paste, the same will be true for the fixing screw joined to said insert.

The above explains the reason why the hardening paste finally ensures a perfect blocking action.

As a matter of fact, according to the prior art, the hardening paste only incorporated the head of the fixing screw of the stump, thus holding only for the very short height of said head.

According to the present innovative technology, instead, the hardening paste can hold for the entire height of the insert of the invention and consequently for the entire height of the axial hole of the stump.

For explanatory reasons the description of the invention continues with reference to the attached drawing, which only has an illustrative, not limiting value, wherein:

- figure 1 is an axonometric view of the insert of the invention;

- figure 2 is a front view of said insert;

- figure 3 is a side view of said insert;

- figure 4 is a top view of said insert;

- figure 5 is a cross-sectional view with a vertical plane of a typical stump for dental prostheses provided with the insert of the invention.

Referring to the figures, the insert of the invention (1 ) basically consists in a rod (2) with substantially rectangular section, provided in lower position, with interposition of a basically cylindrical connection collar (3), with a narrower and thinner end (4).

Moreover, it must be considered that such an insert (1 ) can be indifferently made of metal, hard plastic or any other suitable material.

As shown in Figures 2, 3 and 4, the lateral edges (4a) of said lower end (4) are provided with a basically V-shaped sharp profile with outward facing vertex.

Such an insert (1 ) is intended to be inserted for its entire length into the basically cylindrical axial hole (F) of a traditional stump (M) for dental prostheses.

In such a situation said collar (3) guarantees the exact centering of the insert (1 ) inside the corresponding axial hole (F).

In particular, such an advantageous condition is obtained because the collar (3) is provided with slightly lower diameter than the circular section of the axial hole (F).

After introducing the insert (1 ) into the corresponding hole (F) of the stump (M), the tip (4b) of the lower end (4) is prismatically coupled with the head of the screw (V) lying approximately on the bottom of the hole (F).

Following to such a coupling, the insert of the invention (1 ) and the corresponding screw (V) are perfectly joined.

Now, it is simply necessary to cast hardening paste (P) inside the hole (F), in such a way that it firmly incorporates said rod (2) above the collar (3), as expressly shown in Figure 5.

Once the hardening paste (P) has set, the entire insert (1 ) loses the possibility of rotating inside the hole (F), thus preventing the accidental loosening of the screw (V) to which it is joined by means of said mutual prismatic coupling.

When the head (T) of the screw (V) is of type provided with a traditional rectilinear diametral notch, the necessary anti-rotation prismatic coupling with the insert of the invention (1 ) is obtained when said tip (4b) of the lower end (4) is exactly engaged into said rectilinear diametral notch. Instead, when the fixing screw (V) is an Allen screw, the notch obtained on the head of the screw is shaped as a traditional hexagonal cavity (E), as expressly shown in Figure 5.

In such a case the anti-rotation prismatic coupling between the insert of the invention (1 ) and the hexagonal cavity (E) is obtained in view of the exact engagement of said V-shaped lateral edges (4a) of the lower end (4) of said insert (1 ) into two diametrically opposite corners of said hexagonal cavity (E).