Abstract:
The tooth implant includes a conical screw section with a multiple thread, which broadens progressively from the rounded apical end thereof, is adjoined by a multiple micro-thread with a lower pitch. Such an implant has improved primary stability and avoids the injury of anatomical structures and with the micro-thread thereof avoids too high a compression and necrosis. In one example, an abutment with a post is fixed to the implant, which post includes a groove to which various structures can be clipped.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a 35 U.S.C. §§371 national phase conversion of PCT/CH2006/000439, filed Aug. 18, 2006, which claims priority of European Patent Application No. 05405487.9 filed Aug. 22, 2005, the disclosure of which has been incorporated herein by reference. The PCT International Application was published in the German language. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a tooth implant, having a conical fastening portion with a thread which becomes progressively wider from the rounded apical end. A tooth implant of that kind is known from U.S. Pat. No. 6,402,515. The single, progressive thread disclosed therein is provided to improve adhesion of the tooth implant in the bone. 
     There is known from US 2004/101808 A1 an implant system having a double anti-rotational structure between the implant and the abutment. In that case, the implant has a conical shape with rounded apical end. 
     US 2004/219488 A1 discloses what is referred to therein as a micro-thread which follows on from a two-start thread. That micro-thread contains a number of small helical grooves. 
     There is known from WO 2004/098442 a screw-in tooth implant in which groove-like recesses are stamped into a relatively coarse thread, which recesses extend in the direction of the turns of the thread and produce there a so-called micro-thread in order to increase the area of contact between the tooth implant and bone tissue. The threaded pin itself is substantially cylindrical and the thread is not progressive. 
     U.S. Pat. No. 5,403,136 discloses a tooth implant with screw thread, which towards the cervical end has a thread with a decreasing pitch. The main part of the pin is cylindrical and is plane at the apical end. 
     US-A1-2004/0006346 discloses a tooth implant pin that is substantially cylindrical and has a plane apical end. The pin has two different threads, a relatively coarse single thread and then a so-called micro-thread which in this case is in the form of a triple thread. 
     WO 2004/103202 discloses, like the first-mentioned U.S. patent, a conical tooth implant with a progressive thread. 
     SUMMARY OF THE INVENTION 
     Proceeding from that prior art, it is a first object of the present invention to create a tooth implant that, in a combination of various features, provides for minimally invasive insertion, tissue conservation and good primary stability together with good bone adhesion. That object is attained with the tooth implant according to patent claim  1 . 
     It is a further object of the invention to provide a tooth implant that is simple and inexpensive to produce and that includes, in addition to a good anchoring structure, an abutment that simplifies subsequent operations. That object is attained with the tooth implant according to patent claim  5 . 
     Further advantages, such as, for example, good handling, are defined in the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in detail hereinafter with reference to drawings of illustrative embodiments. 
         FIG. 1  shows a tooth implant according to the invention in plan view, 
         FIG. 1B  is a view from the left of  FIG. 1 , 
         FIG. 1A  shows a partial section of  FIG. 1 , 
         FIG. 2  shows an abutment for the tooth implant of  FIG. 1 , viewed from the front, 
         FIG. 3  shows the abutment in accordance with the section III-III in  FIG. 2 , 
         FIG. 4  shows a retaining screw, 
         FIG. 5  shows a closure screw, 
         FIG. 6  shows an abutment screwed to the tooth implant, 
         FIG. 7  shows a snap-on cap, viewed from the front, 
         FIG. 8  shows the snap-on cap in accordance with the line VIII-VIII in  FIG. 7 , 
         FIG. 9  shows a tooth implant ready for despatch, assembled with an abutment and having a snap-on cap. 
         FIG. 10  shows an implementation variant for implementation according to  FIG. 7 , with a transfer part, viewed from the front, 
         FIG. 11  shows the transfer part in accordance with the line XI-XI in  FIG. 10 , and 
         FIG. 12  shows a tooth implant ready for despatch, with a transfer part. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 ,  1 A and  1 B show a tooth implant  1 , preferably made of pure titanium, having the rounded apical end  2 , the progressive multiple thread  3 , in this illustrative embodiment a two-start, self-tapping thread, which becomes wider from the apical end to the other, cervical end  4  and which is adjoined by a micro-thread  5 , similarly a multiple thread, for example a three-start thread. 
     The micro-thread  5  is adjoined towards the cervical end  4  by a tapered portion  5 A and the implant has an inwardly oriented chamfer  4 A. Both measures make better bone adhesion possible and thus prevent bone resorption and promote growth of connective tissue at the cervical end of the implant. When an abutment having an outwardly curved shoulder is used, the effective biological width is increased with the tapered portion and the chamfer. 
     The rounded apical end largely prevents injury to anatomical structures such as the floor of the sinus, the floor of the nose, the mandibular nerve or the mucosa when the tooth implant is being screwed in. 
     The tooth implant  1  further has a conical shape which tapers towards the apical end  2 , which increases the primary stability in comparison with a cylindrical tooth implant shape when being screwed into a straight cavity, and results in perfect adaptation in the cervical region. 
     The progressive multiple thread considerably improves the primary stability. A high mechanical primary stability is the most important prerequisite for immediate and early loading of the tooth implant. By virtue of the progressive thread, micro-movements of the inserted tooth implant are largely prevented and, as a result, incorporation of the implant and osseointegration are promoted. 
     In the cervical region, the progressive thread becomes a multiple micro-thread in order to avoid excessively high compression and necrosis in the corticalis. The tooth implant further has in the apical region cutting channels  6 , for example two, which also serve as relief channels for the bone chips. 
     It will be apparent from  FIGS. 1A and 1B  that the tooth implant has at the cervical end a hexagon socket  7  adjoined by a bore  8  with thread. 
       FIGS. 2 and 3  show an abutment  9  which may be fastened to the tooth implant by means of a retaining screw  10 , see  FIG. 4 . The abutment is preferably also made of pure titanium and has a connecting portion  11  constructed as a hexagonal element which fits into the hexagon socket  7  of the tooth implant. That hexagonal element  11  is adjoined by a multifunctional post  12  which, starting at the connecting portion, has a platform  13  and tapers from there towards the end. Close to the platform  13 , there is a circumferentially extending groove  14 , and two opposing flat portions  15  are disposed longitudinally of the post. 
     The groove in the cervical region of the post makes it possible to use a snap-on technique for various parts, which is simple to manage, very precise and time-saving. That applies especially to the transfer, to the fastening of the temporary crown or to impression-taking with a multifunctional snap-on cap, see  FIGS. 7 to 9 . In addition, the groove serves to enable optimum distribution of the fastening cement when the final restoration is being inserted. 
     As is apparent from  FIG. 2 , the abutment is constructed as a sleeve and has a continuous bore with two different diameters. Viewed from the cervical end  16 , the diameter of the bore  17  is greater than that of the adjoining bore  18 , thereby forming a shoulder  19  on which the head of the retaining screw is supported. Disposed at the cervical end there is a hexagon socket  25  by means of which the implant together with the abutment is screwed into the bone by a hexagon screwdriver. 
     The retaining screw  10  serves to fasten the abutment to the tooth implant and is constructed accordingly. In  FIG. 4 , described from left to right, the retaining screw comprises a head  20  with a hexagon socket  21 , a cylindrical portion  22  and a shoulder  23  therebetween and, adjoining the cylindrical portion, a thread  24  corresponding to the bore with thread  8  in the tooth implant. 
     From  FIG. 6 , a combination of the tooth implant with the abutment, it will be apparent that the retaining screw  10  extends through the abutment and can be screwed into the tooth implant with a hexagon screwdriver. The shoulder  23  of the retaining screw  10  is supported during that operation on the shoulder  19  of the abutment, with the result that as the retaining screw is screwed in, the abutment and the tooth implant are pulled together and secured. 
     As will be apparent from the combination shown in  FIG. 6 , the abutment post  12  has a smaller diameter than that of the tooth implant in order to assist the attachment of soft and hard tissue and, in the long term, prevent bone resorption risk of infection. The multifunctional post  12  is to be used as standard for all tooth implants of this system, even in the case of different diameters, and serves
         a) as a transfer post from the double sterile packaging into the predrilled cavity,   b) for screwing into the predrilled cavity,   c) as a temporary post and   d) as the final post.       

     The two flat portions  15  of the post serve on the one hand to cement the crown in a manner securing it against rotation and to obtain correct axial alignment. This makes precise transfer possible. 
     The posts are preferably coded, for example by giving them a bicolour marking, to avoid confusion. The flat surfaces may in that case be left untreated or uncoloured. 
     To obtain a stable press-fit between abutment and tooth implant, the hexagonal element  11  and the hexagon socket  7  of the tooth implant have a conicity of from 0.5° to 7°. This also makes exact transfer possible, since it is not possible for wobbling to occur, as is unavoidable in the case of straight surfaces owing to the necessary tolerance. 
     The biological width, the connective tissue covering at the cervical implant end, is according to Tarnow and other authors from 1.5 to 3.5 mm. The previously prepared shoulder  40  on the fastening portion of the abutment of approximately from 1.7 to 2.1 mm, preferably 1.9 mm, above the end of the tooth implant takes that biological width of the soft tissue into account, which provides considerable advantages for long-term success from an aesthetic and a functional point of view. That effect is assisted by the tapered portion  5 A and the chamfer  4 A at the cervical end of the implant. 
     The described abutment having the post with a circumferentially extending groove for a snap-on technique is advantageous not only in respect of the implant  1  described in the introduction but also in respect of other types of implant, in which case, however, the connecting portion has to be of an appropriate form and may have, instead of a hexagonal element, other coupling means. 
     If the tooth implant is to grow in without the abutment, it is essential to seal its opening  7  and  8 . There is used for that purpose the closure screw  27  of  FIG. 5 , which has a countersunk head  28  with a hexagon socket  29  and a thread  30  that fits into the thread  8  of the tooth implant. 
     In the packaging ready for despatch shown in  FIG. 9 , that closure screw is screwed into a corresponding recess  32  at the rear portion of a snap-on cap  31  and is secured by means of a cover  33 . 
     The multifunctional snap-on cap  31  is made from a burn-out plastics material and, as its name reveals, it is able to perform various functions:
         a) it may serve as an introduction aid for transfer from the sterile packaging into the predrilled cavity and for screwing-in of one to two turns.   b) it may serve as a base for the temporary crown which can be fitted exactly. Fastening of the crown is effected by means of the described snap-on technique and temporary cement.   c) it may serve as an impression cap in conjunction with prefabricated laboratory tooth implants to obtain exact transfer. The shape of the snap-on cap is matched to the post of the abutment.   d) it may serve as a pre-modelled crown base for the dental technician and as a base for the final restoration after the technician has milled away the receiving ring  34 .       

     The snap-on cap altogether makes possible an economical workflow in the collaboration between dentist and dental technician, saving time and affording high precision. 
     The snap-on cap has at its apical end  35  a bore  36  with a neck  37  which corresponds to the groove  14  of the abutment post. Accordingly, the snap-on cap may be snapped onto the abutment post in order to be securely fixed there. In addition, at its periphery it has a bead  26 . 
     So that the snap-on cap may be used as a screwing-in aid it must be held in a manner securing it against rotation relative to the abutment post. That is achieved by means of the snap-on cap having in the inner bore  36  two opposing flat surfaces  38  which cooperate with the two flat portions  15  of the abutment post. 
     The closure screw  27  is inserted in a receiving ring  34  of the cap, which ring has a flat portion  39  which serves to secure a crown. 
       FIGS. 10 to 12  show a transfer part  41  which may be directly connected to the implant  1  and not to the abutment as in the previous example. For that purpose, the transfer part has at its apical end  42  a hexagonal element  43  which consists of two halves  43 A and  43 B, the halves being separated by a gap  43 C, as a result of which they are resilient. That hexagonal element corresponds to the hexagon socket  7  of the implant and may similarly have a conicity of from 0.5° to 7°. 
     The remaining configurations and features as well as advantages and possible applications of the transfer part  41  correspond to those of the snap-on cap  31  shown in  FIGS. 7 to 9 . That applies also to the receiving of a closure screw  27 . In  FIG. 12 , the implant with the transfer part is shown partly in section.