Patent Publication Number: US-2019175307-A1

Title: Anchoring assembly for a dental prosthesis

Description:
The present invention generally relates to supporting structures for dental prostheses and in particular to a support assembly comprising a plurality of implants that may be fitted in the upper and/or lower jawbone of a patient, as well as a plurality of connecting rods arranged between the implants. 
     It is well known that replacing missing teeth with dental implants prevents bone resorption. In fact, dental implants perform the same function as the natural roots of the teeth, thus allowing to maintain the shape and anatomy of the jawbone as well as to prevent natural migration of the teeth and gingival retraction. 
     It is known that dental implants are assembled surgically and generally comprise a prosthesis or crown that replaces a natural tooth and is fixed on an implant by way of a suitable connecting member called “abutment”. 
     Also known are anchoring assemblies wherein a complex dental prosthesis, e.g. having the shape of a whole dental arch, is mounted on a plurality of implants that are surgically fitted in the jawbone and protrude from the gum. The prosthesis may be fixed on the implants directly or by way of a suitable superstructure mounted on the implants, which serve as supporting members or “pillars”. 
     The use of anchoring assemblies is extremely useful in elderly patients whose bone structure is weakened due to bone resorption or osteoporosis and cannot therefore be fully exploited to insert individual implants that replace the roots of natural teeth. 
     Known anchoring assemblies for dental prostheses comprise a plurality of implants and a superstructure made up of a plurality of connecting arms configured to be fixed between subsequent implants, more particularly at the ends of the abutments that protrude from the gum. The connecting arms have a telescopic structure that can be adjusted to the actual distance between subsequent implants once they have been surgically fitted into the jawbone. Moreover, the ends of the arms and the ends of the individual implants are configured so as to form spherical couplings that allow the arms to be oriented depending on the inclination the implants reach in vivo once they have been fitted into the jawbone. In fact, it is not generally possible to obtain a perfectly vertical arrangement of the implants due to the condition of the bone structure of the upper or lower jawbone, and because the implants are fitted surgically in spaces that are generally small and poorly accessible. In addition to this, the manual ability of a dentist greatly affects the result of an intervention. 
     Anchoring assemblies of this type for dental prostheses are described e.g. in patents U.S. Pat. No. 5,219,286 and EP 1357853. 
     Also known are assemblies having a structure similar to the anchoring assemblies, but that are used to take dental records in view of the manufacturing of a final dental prosthesis once a number of implants have been surgically fitted in the jawbone. 
     In this case, the telescopic arms of the superstructure are not mounted on the abutments of the implants, but on special pins that form an extension of the implants and serve to keep them in place when the dental record is made. It is known in fact that this operation requires to use a plastic material that is pressed against the implants and made to cure in situ. The resulting dental record serves as a model for the manufacturing of a monolithic superstructure on which a dental prosthesis will be permanently mounted. The monolithic superstructure is usually made starting from a metal block that is processed by numerical control machines. 
     Unlike the anchoring assemblies described in patents U.S. Pat. No. 5,219,286 and EP 1357853, a superstructure comprising telescopic arms and respective pins is therefore only a provisional element used to manufacture a final monolithic superstructure. An example of a superstructure of this type is described in U.S. Pat. No. 6,905,336. 
     Despite the availability of various types of anchoring assemblies for dental prostheses, there is still a need to improve their configuration so as to facilitate assembly of a superstructure on a number of implants to be surgically fitted in the jawbone, which is an object of the present invention. Said object is achieved by an anchoring assembly whose main features are specified in the first claim, while other features are specified in the remaining claims. 
     An idea of solution underlying the present invention is to provide an anchoring assembly whose superstructure includes telescopic arms mounted on pins that are in turn fixed on the abutments of the implants. According to the invention, the telescopic arms are mounted on the pins by way of perforated blocks fitted therein. The pins include an outer thread and through holes of the blocks have a corresponding internal thread. 
     Thanks to this combination of features, by rotating the pins around their axes with relative to the abutments it is possible to raise or lower the arms relative to the abutments and thus to adjust their position and inclination until a desired arrangement is reached, for example, until they are substantially parallel to the gum. By locking the configuration of the superstructure so achieved by way of suitable glues, the superstructure can be removed from the implants and integrated in a dental prosthesis. 
     The main advantage of the invention is to simplify the mounting of an anchoring assembly and to ease adjusting of its components, these operations being typically performed inside a patient&#39;s mouth, where there is little room and access for the hands of a dentist. 
     Another important advantage of the invention is that after locking the configuration the superstructure of the anchoring assembly, the superstructure can be directly integrated in a dental prosthesis, there being no need to machine a final superstructure from a block of material. This results in a remarkable reduction of the costs for the manufacturing of a dental prosthesis. 
     According to an embodiment of the invention, each abutment is formed integrally with the respective dental implant, which provides the advantage of reducing the number of components a dentist has to handle and install in the mouth of a patient. 
     Depending on the position of the implant in the upper or lower jawbone, the axis of the abutment may be aligned or inclined relative to the axis of the implant, thus allowing to exploit the patient&#39;s bone structure in an optimal way so as to ensure the stability of the dental prosthesis immediately after surgery and over time. 
    
    
     
       Further advantages and features of the anchoring assembly according to the present invention will become clear to those skilled in the art from the following detailed and non-limiting description of embodiments thereof with reference to the attached drawings, wherein: 
         FIG. 1  is a perspective view showing an assembly according to the invention for the anchoring of a dental prosthesis; 
         FIG. 2  is a perspective exploded view of the anchoring assembly of  FIG. 1 ; 
         FIG. 3  is a front view showing a partial longitudinal section of the anchoring assembly of  FIG. 1  wherein the implants are fitted in a jawbone; 
         FIG. 4  shows a detail IV of  FIG. 3 . 
     
    
    
     Referring to the figures, an anchoring assembly according to the invention for the anchoring of a dental prosthesis is generally indicated by reference numeral  100 . 
     The anchoring assembly  100  includes a plurality of dental implants  110 , for example four in the embodiment shown in the drawings. 
     Each dental implant  110  comprises a threaded portion  111  intended to be fitted in a hole formed in the upper or lower jawbone B of a patient, and an abutment  112  intended to protrude from the jawbone B as well as from the gum G upon surgical fitting of the dental implant  110  into the jawbone B. 
     The dental implant  100  also comprises a superstructure that is assembled on the implants  110  and serves to support a dental prosthesis (not shown). 
     The superstructure comprises a plurality of pins  120  every one of which is configured to be mounted on an abutment  112 . For this purpose, each abutment  112  has a threaded hole  113  configured to receive a screw  114  and each pin  120  comprises a cavity  121  through which the screw  114  can be fitted. In order to allow assembly of the parts to be mounted, the cavity  121  has a shoulder  122  suitable to receive a head of the screw  114 . 
     As shown in the drawings, each abutment  112  has a free end featuring a frustoconical shape. Correspondingly each pin  120  comprises an end portion  123  having a matching frustoconical shape, which facilitates assembly of the pin  120  on the abutment  112 . 
     In the embodiment shown in the drawings, wherein the assembly  100  comprises four dental implants  110 , the axes of the abutments  112  that are arranged in the middle and are intended to be fitted in the front portion of the upper or lower jawbone are substantially aligned with the axes of the respective implants  110 . The axes of the abutments  112  that are arranged aside and are intended to be fitted into the rear portion of the upper or lower jawbone are instead inclined relative to the axes of the respective implants  110 , for example by 17° or 30°. It is well known that the choice of the angle between the axes of the abutments and the axes of their respective implants depends on the position they have in the upper or lower jawbone and allows to exploit the jawbone structure of a patient in the most effective way so as to ensure stability of a dental prosthesis immediately after surgery, i.e. the so-called primary stability, and over time, i.e. the so-called secondary stability. 
     According to a preferred embodiment of the invention, each abutment  112  is formed integrally with the respective dental implant  110 , which offers the advantage of reducing the number of components a dentist has to handle and install in the small room available in the oral cavity of a patient. 
     The superstructure of the anchoring assembly  100  also comprises a plurality of blocks  130  each having a through hole  131  allowing them to be mounted on a respective pin  120 . 
     The superstructure of the anchoring assembly  100  finally comprises a plurality of telescopic arms  140  configured to be mounted between the blocks  130  in turn mounted on the respective pins  120 . The telescopic arms  140  include at least one male element  141  and at least one hollow female element  142  whose cavity matches the shape of the male element  141 . 
     In order to allow mounting of the arms  140  on the blocks  130 , the blocks comprise matching coupling means configured to define a spherical coupling. 
     The use of a spherical coupling allows the arms  140  to be oriented according to the inclination the implants  110  take in vivo as a result of their insertion into the bone. As explained in the introduction, it is generally not possible to obtain a perfectly vertical arrangement of the implants, due to the condition of the upper or lower jawbone structure, and considering the fact that implants are fitted surgically in a small and poorly accessible room. In addition to this the manual ability of a dentist greatly affects the result of an intervention. It is therefore advantageous to configure the connection of the arms  140  so that they can be inclined so as to be adapted to the real position of the implant  110 . 
     In the embodiment shown in the drawings the coupling means include, for example, spherical cavities formed in one between the blocks  130  and the respective arms  140  and corresponding spherical elements formed in the other one between the blocks  130  and their respective arms  140 . 
     In the embodiment shown in the drawings, cavities  132 ,  133  are shown in each block  130  on substantially opposed sides relative to the through hole  131 , and ball elements  143 ,  144  having matching diameters are respectively formed at the opposite ends of the arms  140 . 
     In the embodiment shown in the drawings, the coupling means are configured to be snap-fitted to each other and for this purpose the ball elements  143 ,  144  include diametric slots that allow to reduce their size thereby allowing them to be snap-fitted into the spherical cavities  132 ,  133  formed in blocks  130 . 
     It will be appreciated that this feature does not limit the invention. However, the provision of snap-fits is preferred because it simplifies assembly and provides a tactile and sound feedback once the parts are assembled. 
     According to the invention, the pins  120  comprise an outer thread  124  and the through holes  131  of the blocks  130  have a corresponding internal thread  134 , which allows to accurately adjust the position of the blocks  130  along the pins  120  and, consequently, to accurately adjust the position of the arms  140  relative to the implants  110 . 
     In other words, according to the actual arrangement the implants  110  reach when they have been inserted surgically into the upper or lower jawbone of a patient, it is possible to finely tune the position of the blocks  130  and of the arms  140  that form the superstructure together with the pins  120  so as to define the best possible configuration of the superstructure either in view of the design of a new dental prosthesis or in the aim of reworking an existing prosthesis. 
     From an operational point of view, once the implants  110  are inserted surgically into the upper or lower jawbone, the pins  120  are provisionally locked on the abutments  112  by the screws  114  and the blocks  130  are screwed on the pins  120 . The dentist then assembles the arms  140  on the blocks  130  by employing the coupling means, for example the snap-fit means described above, thus completing the superstructure of the anchoring assembly  100 . 
     Once all the components of the anchoring assembly  100  have been mounted, the dentist loosens the screws  114  and rotates the pins  120  about their respective axes relative to the abutments  112 . Thanks to the threaded coupling between the pins  120  and the blocks  130  the rotation of the pins  120  causes the arms  140  to be raised or lowered with respect to the abutments  112  and, thanks to the spherical coupling means, it is also possible to adjust the inclination of the arms  140  relative to the blocks  130  and to the pins  120  so as to arrange them substantially parallel to the gum G. During these adjustment steps, the telescopic arms  140  are extended or shortened depending on the relative distance between pins  120  set by the dentist. 
     Once the desired configuration of the superstructure has been achieved, the dentist tightens the screws  114  in the respective threaded holes  113  of the abutments  112  and then locks the blocks  130  on the pins  120 , as well as the male and female elements  141 ,  142  of the arms  140 , by way of a suitable glue. 
     For this purpose, the male and female elements  141 ,  142  of the arms  140  may advantageously comprise textured surfaces, such as e.g. grooved, knurled and the like, whose function is to increase the gripping surface and promote adhesion of the glue. In the embodiment shown in the drawings, the male elements  141  of the arms  140  are provided e.g. with a plurality of grooves forming a helical pattern. 
     Once the mutual positions of the components of the superstructure are blocked, the superstructure is disassembled from the implants and delivered to a dental technician so as to be integrated in a dental prosthesis. 
     According to a further aspect of the invention, the arms  140  may have the shape of an arch suitable to match the contour of a dental prosthesis according to the natural curvature of the upper and/or lower jawbone of a patient. The provision of arch-shaped arms also allows to better adapt the arms to different distances between subsequent implants, while minimizing the risk that they interfere with the internal space of the dental arch, which would be negatively perceived by the patient and would result in aesthetic problems. 
     Moreover, the anchoring assembly  100  may advantageously comprise one or more auxiliary elements  150  for anchoring respective dental prostheses. The function of the auxiliary elements  150  is to increase the gripping surface for the mounting of the dental prostheses. 
     The auxiliary anchoring elements  150 , that are for example rod-shaped bodies in the embodiment shown in the drawings, are configured to be mounted on the female elements  142  of the telescopic arms  140 , for example by way of a snap-fitting, a threaded connection or equivalent coupling means. 
     The invention has herein been disclosed with reference to preferred embodiments thereof. It will be appreciated that further embodiments based on the same inventive idea may exist, all of which are encompassed in the scope of protection of the claims set forth below.