Patent Publication Number: US-2020289243-A1

Title: Dental abutment blank, method of manufacturing a dental abutment blank and method of manufacturing a dental prosthesis from such a blank

Description:
TECHNICAL FIELD 
     The invention relates to a dental abutment blank, a prosthesis formed from such a blank, a dental arrangement comprising such a blank or a prosthesis and a dental implant and methods of manufacturing a blank or a prosthesis from such a blank. In more detail, the dental abutment blank allows for adjusting the angle of a screw channel in relation to the implant in accordance with the specific patient&#39;s needs. 
     BACKGROUND OF THE INVENTION 
     More commonly, individual dental abutments are manufactured in a CAD/CAM process. Using this process, the implant site is scanned for achieving a 3D-file to be used as a basis for designing dental restoration prosthesis using CAD software. Once the design is set, CAM software is used to guide a NC-controlled milling machine where the final machining is performed. 
     The prosthesis is machined from a blank that is clamped in the milling machine. The blanks need to be clamped so that the abutment-implant interface is orientated according to the scanned file in order for the final prosthesis to fit correctly. 
     Several methods are known in the art for clamping the blanks during machining. For example, the blank may be clamped in the opposite end of the implant connection. 
     Such a method is described in EP 2343025 A2 showing a dental implant abutment blank for tailor-made dental abutments and a method for manufacturing the same. An abutment material is provided including a cylindrical body, a grip at one end of the body, a coupling portion formed on the opposite end of the body. Furthermore, a fastening hole is formed through the grip, the body and the coupling portion. The grip is used for clamping the abutment material to a machine to manufacture a tailor-made abutment. 
     However, this method leaves a cut off peg after machining which must be removed manually. The screw channel must be prefabricated in the blank because the clamping method limits the access and it is not possible to machine the screw channel from the same side used for clamping. 
     Alternatively, the blank may be held with a screw through the abutment-implant connection. This method requires a blank with a screw channel to mount the screw through. 
     Such a method is for example disclosed in US 2008/0254414 A1 showing a dental abutment blank adapted for use with a dental implant, wherein the blank has at least one preformed passage extending between two opposing ends on the blank. Furthermore, a mandrel is disclosed on which the blank may be mounted on when equipped with a dental screw fixation, the mandrel having a longitudinal axis that is either generally perpendicular or parallel (and coaxial) to the at least one passage. 
     Recently, blanks with angled screw channels have been developed to address the problem of structural weakness resulting from a screw channel entrance located on the incisal edge of a dental prosthesis. 
     A blank with an angulated screw channel is for example described in WO 2013/004387 A1 showing a dental component for fixation to a dental implant having a component body with an angulated screw channel and a matching screw, wherein the screw channel wall may be curved. Furthermore, US 2016/0022390 A1 describes a milling blank with a milling section having a feed channel and a securing section having a screw channel for securing the milled abutment attachment to the dental implant. The feed channel may be angled with respect to the screw channel. 
     However, when mounting the blanks having an angled screw channel by the screw to the milling machine, the blanks have to be prefabricated in a large variety of angles and orientations to finally provide a fitting prosthesis. Furthermore, the channel wall thickness might possibly become too thin after milling of the milling section, thereby weakening the prosthesis. 
     Alternatively, some manufacturers produce individual prosthesis from a large block of titanium or cobalt chrome, usually for machining full or partial dental bridges. In this context, the abutment-implant interface is machined in the same operation. However, this usually reduces the accuracy and results in an interface with higher dimensional tolerances compared with a prefabricated interface. 
     SUMMARY OF THE INVENTION 
     Hence, there is a need and thus it is an object of the present invention, to provide a pre-fabricated blank for manufacturing a dental abutment with an angulated screw channel, the blank being versatile with regard to the final application. Furthermore, it is an object of the present invention to provide an efficient method of manufacturing a custom-tailored dental abutment. 
     These objects as well as others, which will become apparent from the following description of the present invention, are attained by the subject-matter of the independent claims. Some of the preferred embodiments of the present invention are defined by the subject matter of the dependent claims. 
     Various aspects, advantageous features and preferred embodiments of the present invention as summarized in the following contribute to solving the object of the invention. 
     In one aspect, the present invention provides a dental abutment blank comprising a body having a first end and a second end, a connection section at the first end that is configured to be connected to a dental implant, a channel having a longitudinal axis and defining an opening at the first end, wherein the channel extends through the connection section into the body and has a closed end at a distance from the second end of the body. 
     Thus, the clamping of the blank can be performed directly on or in the abutment-implant connection interface. The machining of the screw channel can be performed in the same operation as the outer contour of the prosthesis is machined. Hence, the milling machine is allowed to have full access to the blank without interfering with a clamping chuck and the prosthesis can be finished in one single operation. Therefore, providing a great number of different blanks with pre-fabricated screw channels having different angulations can be avoided. This reduces the costs of the inventory. Also, a pre-fabricated connection section that forms an abutment-implant connection interface results in improved control of the manufacturing process which enables the production of a more dimensionally accurate interface with a high level of quality. 
     The channel of the dental abutment blank may comprise an end section at or near the closed end having a width and an intermediate section between the end section and the first end of the body having a width greater than the width of the end section. 
     This allows to create an angulated screw channel for inserting a fixation screw, wherein the angulated screw channel has an enlarged portion to facilitate pivoting of the screw when advancing the screw through the angulated screw channel. 
     Furthermore, in the channel of the blank the end section may form a third section with a third width, the intermediate section may form a second section with a second width and the channel of the dental abutment blank may comprise a first section between the second section and the first end of the body having a first width smaller than the second width, and wherein the first width is preferably substantially the same as the third width. By means of this, a seat for the screw may be formed. 
     The length of the first section may be greater than or equal to the length of the connection section. 
     The first and/or the second, and/or the third section of the channel of dental abutment blank may be formed as cylindrical bores having a first, a second and a third diameter, respectively. This may, for instance, facilitate the manufacture of the blank. 
     The closed end of the channel may be formed as a conical bore section. For instance, this may facilitate the manufacture of a prosthesis having an angulated screw channel adapted to the patient&#39;s individual clinical situation with an enlarged section that eases the insertion of a screw. 
     Preferably, between the third section and the second section a transition section is formed that may be tapered, preferably conically tapered, or perpendicular to a central axis of the channel. 
     For instance, this may facilitate the manufacture of a prosthesis having an angulated screw channel adapted to the patient&#39;s individual clinical situation with an enlarged section that eases the insertion of a screw. 
     Preferably, between the first section and the second section a transition section is formed that may be tapered and that may form a screw seat. 
     Preferably, the longitudinal axis of the channel is coaxial to a central axis of the connection section. This design may, for instance, facilitate further machining. 
     The body may comprise a milling section that is substantially cylindrical and a connection section that preferably has a smaller outer diameter than the milling section and protrudes from the milling section. For instance, this design facilitates further machining and clamping from the bottom side, allowing the milling machine to have full access to the blank without interfering with a clamping tool, e.g. a chuck. 
     The connection section may comprise a structure that is configured to be engaged in a form fit manner by a connection section at the implant. For instance, this design may stabilize the connection between the finished prosthesis and the corresponding implant. 
     The connection section may comprise a portion having a polygonal, more preferably a hexagonal outer contour. This design may, for instance, may facilitate the orientation of the outer geometry of the prosthesis in relation to the connection section and the implant. 
     The blank may be made from a material, which is suitable for a dental prosthesis, more preferably from titanium, cobalt, chrome or their alloys or ceramics. A dental prosthesis from such a blank may be stable and well tolerated. 
     In a further aspect, the present invention provides a dental abutment blank comprising a body having a first end and a second end, a connection section at the first end that is configured to be connected to a dental implant, a first channel having a first longitudinal axis (L 1 ) and defining a first opening at the first end, and a second channel having a second longitudinal axis (L 2 ) and defining a second opening at or near the second end, wherein the first channel and the second channel intersect at an intersection plane, so that the second channel extends at an angle relative to the first channel to form an angulated screw channel, and wherein in the wall of the second channel a first recess is provided at an axial position at or close to the intersection plane that enlarges the second channel and that has an angled contour. For example, this design may facilitate the insertion of a screw. 
     A second recess may be provided at an axial position farther away than the first recess in a direction towards the second opening in the wall of the second channel and that has an angled contour. With this, the insertion of a screw might be further facilitated. 
     The contour of the first and the second recess may be triangular in a plane parallel to the longitudinal axis (L 2 ) of the second recess. For instance, this embodiment may be easy to be manufactured when using a blank with a widened blind bore described above. 
     In a further aspect of the present invention, the first and the second channel first may have walls that face each other at an angle and opposite walls that face away from each other and wherein the first and the second recess are provided at the wall that face away from each other. Likewise, this embodiment for example may be easy to be manufactured when using a blank with a widened blind bore described above. 
     The first channel may comprises a first section at the first end of the body having a first width and a second section between the first section and the second channel having a second width greater than the first width. With this design, a seat configured to receive the head of a screw may be provided. 
     The first, and/or the second section, and/or the second channel may be cylindrical bores having a first, a second and a third diameter, respectively. The dental abutment blank with an angulated screw channel may be further be formed by a body, and/or a connection section, and/or a material as mentioned above. 
     In a further aspect, the present invention provides a dental prosthesis formed from a blank described above. The dental prosthesis may have an angulated screw channel adapted to the implant site of a patient and may be finished in one single operation. 
     In a further aspect, the present invention provides an arrangement comprising a blank or prosthesis mentioned above together with a screw, an implant, and optionally a crown. 
     In a further aspect, the present invention provides a method of manufacturing a dental abutment blank comprising the steps of providing a dental abutment blank comprising a body having a first end and a second end, a connection section at the first end that is configured to be connected to a dental implant, a channel having a longitudinal axis and defining an opening at the first end, wherein the channel extends through the connection section into the body and has a closed end at a distance from the second end of the body; widening the width of the first channel at a distance from the first and the second end. This methods may easily allow obtaining a dental abutment blank suitable for being prepared to a dental prosthesis having an individually adapted angulated screw channel. 
     In a further aspect, the present invention provides a method of manufacturing a dental prosthesis from a dental abutment blank, the blank being defined as described above comprising the steps of holding the blank at the connection section, and preferably milling the blank. This method allows the milling machine to have full access to the blank without interfering with a clamping tool. 
     Furthermore, the following steps may be comprised: preparing a second channel at the second end to form a screw channel together with the first channel, the second channel having a longitudinal axis L 2  that is angled with respect to the longitudinal axis L 1  of the first bore, wherein the preparation step of the second channel takes place before, after or during the milling step. Further to what was described above, this method may allow preparing an angulated screw channel adapted to a patient&#39;s implant site, wherein the prosthesis can be finished in one single operation together with the milling. 
     Additionally, the method may comprise the step of providing a centering support in the milling machine, the centering support having an outside surface that is engaging an inside surface of the connection section. This may allow clamping and simultaneously stabilizing the connecting section for milling and/or preparing the screw channel. 
     In a further aspect, the present invention provides a method of clamping a dental abutment blank or a dental prosthesis in a chuck, the dental blank or prosthesis being defined by any of the preceding items and the chuck comprising a centering support; the method comprising the steps of: engaging an outside surface of the connection section with at least two jaws of the chuck; engaging a wall portion of the channel at or near the second first end of the dental abutment blank or prosthesis with an outside surface of the centering support. This may allow clamping and simultaneously stabilizing the connecting section for milling and/or preparing the screw channel as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective side view of a dental abutment blank according to the invention. 
         FIG. 2  shows a schematic cross sectional view of a dental abutment blank with a blind hole according to a first embodiment, wherein the section is taken in a plane including a central longitudinal axis of the blank. 
         FIG. 3  shows a schematic cross sectional view of a dental abutment blank with a widened blind hole according to a further embodiment, wherein the section is taken in a plane including a central longitudinal axis of the blank. 
         FIG. 4  shows a schematic cross sectional view of a dental abutment blank with an angulated screw channel and recesses according to a further embodiment, wherein the section is taken in a plane including a central longitudinal axis of the blank. 
         FIG. 5  shows a schematic cross sectional view of clamping a dental abutment blank according to a further embodiment in a chuck with a centering support according to the invention, wherein the section is taken in a plane including a central longitudinal axis of the blank. 
         FIG. 6  shows a schematic cross sectional view perpendicular to the cross section of  FIG. 5  of clamping a dental abutment blank in a chuck at a connection section of the blank. 
         FIG. 7  shows a schematic cross sectional view of an individual dental abutment with an angulated screw channel according to the invention mounted to a dental implant, wherein the section is taken in a plane including a central longitudinal axis of the implant and the prosthesis. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A dental abutment blank according to a first embodiment is shown in  FIGS. 1 and 2  in form of a single tooth replacement abutment. The dental abutment blank comprises a body  1  having a first end  1   a  and an opposite second end  1   b . The body  1  includes at the second end  1   b  a milling section  2  that may be substantially cylindrical having a cylinder axis that defines a central longitudinal axis C 1  of the body and further includes a connection section  3  at the first end  1   a . The milling section  2  is configured to be machined to achieve the final outer geometry of the prosthesis, in particular to be milled in a milling machine. The connection section may be pre-fabricated and serves as abutment-implant connection interface. As depicted in  FIGS. 1  and  2 , the connection section  3  has a central longitudinal axis, that is coaxial with the cylinder axis of the milling section  2 . Alternatively, the milling section  2  may be eccentric relative to the connection section  3 . An outer diameter and an axial length of the milling section  2  may be greater than an outer diameter and an axial length of the connecting section  3 . 
     As can be seen from  FIG. 1 , the connection section has a substantially polygonal outer contour with flat outer surface portions  31 . In this embodiment, the contour is hexagonal. However, also other forms of contours are conceivable, for example a triangular, quadrangular, pentagonal, heptagonal, or octagonal. Furthermore, the connecting section  3  may comprise an engagement structure  3   a  that is configured to be engaged in a form fit manner by a connecting section at a dental implant (not shown). The engagement structure  3   a  may consist of protrusions and/or indentations at the edges of the polygon that are configured to engage corresponding recesses and/or protrusions at the connections section of the dental implant. 
     Optionally, a transition section  2   d  may be formed between the milling section  2  and the connection section  3  for abutment at the dental implant. The transition section  2   d  may have an outer diameter smaller than the diameter of the milling section  2  and greater than the outer diameter of the connection section  3 . 
     As shown in particular in  FIG. 2 , in a first embodiment, the dental abutment blank comprises a channel in the form of a blind bore  4  that defines an opening at the first end  1   a  and that extends completely through the connecting section  3  into the milling section  2  up to a distance from the second end  1   b . The bore  4  may have a circular cross-section. However, the channel may also have a polygonal, oval, irregular or otherwise shaped cross-section. Referring to  FIG. 2 , the bore  4  has a longitudinal axis L that is coaxial with the central longitudinal axis C 1  of the body. Preferably, the closed end  5  is located substantially in the middle of the milling section  2 . Further preferred, the closed end  5  is conically shaped. The dental abutment blank  1  is configured to be machined at the milling section  2  including the forming of a screw channel for inserting the screw while being held at the connection section  3 . 
     A second embodiment of a dental abutment blank  1 ′ is shown in  FIG. 3 . Equal features will not be repeated. In this embodiment, the channel has a widened intermediate section. More in detail, the bore  4  comprises three different bore sections. A first bore section  4   a  is formed at the first end  1   a  and has a diameter d 1  and a length  11 , a third bore section or end section  4   c  is formed at the closed end  5  and has a diameter d 3  an a length  13 , and an intermediate second bore section  4   b  is formed between the first bore section  4   a  and the third bore section  4   c  and has a second diameter d 2  and a length  12 . The second bore section  4   b  is widened in relation to the first and the third bore sections  4   a  and  4   c . More in detail, the second diameter d 2  is greater than the first diameter  11  and also greater than the third diameter  13 . In this embodiment, the first bore section  4   a  extends in an axial direction through at least the whole connection section  3 . The second bore section  4   b  has a greater length  12  than the first bore section  4   a , which in turn has a greater length  11  than the third bore section  4   c . However, other ratios of the lengths of the bore sections may also be contemplated depending on, for instance, the shape of the intended prosthesis or the length and shape of the fixation screw. 
     Between the first  4   a  and the second bore section  4   b , a first transition section  4   d  may be formed that is tapered towards the first bore section  4   a . In the embodiment shown in  FIG. 3 , the transition section  4   d  is conically tapered. The transition section  4   d  is configured to form a support surface for a head of a screw, in other words a screw seat, as will be explained in the context of an arrangement according to the invention below. 
     Between the second  4   b  and the third bore section  4   c , a second transition section  4   e  may be formed that narrows towards the third bore section  4   c . In the embodiment shown in  FIG. 3 , the transition section  4   e  narrows conically. However, also other forms or a perpendicular transition between the first  4   a  and the second bore section  4   b  are conceivable. However, also other forms or a perpendicular transition between the second  4   b  and the third bore section  4   c  are conceivable, as for example illustrated in  FIG. 5  below, the abutment blank  1 ′″ without transition section  4   e  representing a third embodiment  1 ′″ of the invention. 
     A fourth embodiment will now be described with reference to  FIG. 4 . Equal features will not be repeated. The dental abutment blank  1 ″ comprises a first channel in the form of a first bore  4 ′ having a first longitudinal axis L 1  and defining a first opening at the first end  1   a , and a second channel in the form of a second bore  4 ″ having a second longitudinal axis L 2  and defining a second opening at the second end  1   b . The first bore  4 ′ and the second bore  4 ″ intersect at an intersection plane P, so that the second bore extends at an angle α relative to the first bore  4 ′ when measured relative to the first bore axis L 1 . In other words, the first channel and the second channel form an obtuse angle β=180°−α. In this embodiment, a is approximately 200 and β is about 100°. However, depending on the clinical situation, also other angles may be contemplated, preferably angles α between about 10° and about 300. 
     Resulting from the angulation, the first  4 ′ and the second bore  4 ″ have wall portions  6  and  7 , respectively that face each other at the angle β, and opposite walls portions  8  and  9 , respectively, that face away from each other. In the wall of the second bore  4 ″ a first recess  10  is provided at an axial position at or close to the intersection plane P that enlarges the second bore  4 ″ at the wall portion  9  facing away from the wall portion  8  of the first bore  4 ′. The first recess  10  may have a triangular contour in a cross sectional plane, the plane including the axis L 1  and L 2  and the central longitudinal axis C 1 . In a perspective view, the first recess  10  may comprise a conical wall section. 
     Furthermore, a second recess  11  may be provided at the wall portion  9  of the second bore  4 ″ that faces away from the wall portion  8  of the first bore  4 ′. The second recess  11  may be provided at an axial position farther away than the first recess  10  in a direction towards the second opening at the second end  1   b . Likewise, the second recess  11  may have a triangular contour in a cross sectional plane, the plane including the axes L 1  and L 2  and the central longitudinal axis C 1 . Accordingly, the second recess  11  may comprise a conical wall section in a perspective view. As described more in detail below, the first recess  10  and the second recess  11  may be the result of the manufacturing process of the dental abutment blank in such a manner that the first recess  10  emerges from the transition of the widened second bore section  4   b  to the third bore section  4   c  in the second embodiment described with reference to  FIG. 3 . The second recess  11  emerges from the transition of the third bore section  4   c  to the closed end  5  as shown in  FIG. 3 . 
     Moreover, the first bore  4 ′ comprises a first bore section  4   a ′ at the first end of the body  2  having a diameter corresponding to the first bore section  4   a  described with respect to  FIG. 3 , and a second bore section  4   b ′ between the first bore section  4   a ′ and the second bore  4 ″ having a second diameter greater than the first diameter. 
     The blanks described above are made from a material, which is suitable for a dental prosthesis. Preferably, the blank is made from titanium, cobalt, chrome or their alloys or ceramics. 
     According to the present invention, the dental abutment blank embodiments described above may be manufactured as will described in the following. It should be understood that each embodiment of the dental abutment blanks described above per se represents a blank for manufacturing a customized dental prosthesis. At the same time, the embodiments represent, in chronical order where reasonable—intermediate products for the manufacture of a customized dental prosthesis to be connected to a dental implant, the prosthesis having an angulated screw channel. 
     First, to obtain the blank according to the first embodiment as depicted in  FIG. 2 , a body is provided having a cylindrical milling section  2  and a pre-fabricated connecting section  3  provided at the first end  1   a  that is configured to be connected to a dental implant. Then, the blind bore  4  is prepared, preferably by drilling. 
     To obtain the dental abutment blank as depicted in  FIG. 3  or alternatively, as depicted in  FIG. 4 or 5 , the blind bore  4  is widened, e.g. by a turning tool, such that an intermediate second section  4   b  is formed as described above. Optionally, the above described transition sections  4   d  and/or  4   e  are formed—either before or after preparing the intermediate bore section  4   b -between the first bore section  4   a  and the second bore section  4   b  section and/or the second bore section  4   b  and the third bore section  4   c , respectively. The blanks described above may form pre-fabricated dental abutment blanks to be machined further to form a customized prosthesis. 
     Furthermore, to obtain the blank as depicted in  FIG. 4 , a second bore  4 ″ may be prepared at or near the second end  1   b  as described above, for example by drilling, to form the angulated screw channel. 
     It should be noted that also other manufacturing methods may be contemplated for manufacturing a blank according to the invention, for example additive manufacturing methods, such as laser sintering or laser melting or electron beam melting 
     In a next step, either one of the blanks according to the embodiments mentioned above is held in a milling machine and is further machined, preferably milled, to obtain a dental prosthesis according to a patient&#39;s individual needs. 
     Preferably, the skilled person, for instance a clinician or dental technician, has scanned the implant site before milling to obtain an individual 3D-file that is further used as a basis for designing the dental restoration prosthesis using a CAD software. Once the design is set, a CAM software may preferably be used to guide an NC-controlled milling machine. 
     For holding the blank in the milling machine, the connecting section  3  of the blank  1  is clamped in a clamping tool, preferably in a chuck, more preferably in a three jaw chuck  12 , by engaging the hexagonal contour of the connecting section  3  with the jaws  13  of the chuck as illustrated in  FIGS. 5 and 6 . Preferably, a centering support  14  is provided inside the chuck  12  that engages an inside surface of the first bore  4   a ′ of the connecting section. Preferably, the centering support  14  is configured to engage the first bore  4   a  in a form-fit manner. Furthermore, the centering support  14  may have a length that allows extending into the body beyond the connecting section. 
     Hence, the blank  1  is clamped according to the invention from the outside and simultaneously is supported and centered from inside. By means of this, it possible to hold the blank  1  firmly during machining without deforming the connecting section  3  that may have a relatively thin wall. Hence the rotation speed during machining needs not to be reduced. Furthermore, clamping on the connecting section hexagon provides a method of orientating the connecting section  3  in relation to the outer geometry of the prosthesis to be machined. 
     Preferably, the second bore  4 ″ described above is prepared at any time before, during or after the milling operation. Preferably, the angle α of L 2  relative to L 1  is chosen such that it optimally matches the design of the prosthesis to be manufactured with regard to the wall stability of the second bore, the chewing surface and the implant site. 
     With reference to  FIG. 7 , an arrangement  15  according to the invention is described in the following. The arrangement  15  comprises a single tooth abutment prosthesis  100 , whose milling section has been milled into a milled section  200   c  having a tooth-like form, the prosthesis  100  having a first end  100   a  and a second end  100   b , an angulated screw channel comprising a first bore  400 ′ and a second bore  400 ″ corresponding to the bores described in the context of  FIG. 4  above, and further comprises a screw  16  having a shank  17  with a threaded section and a screw head  18  that is configured to be inserted trough the angulated screw channel, and an implant  19  to be implanted in a patient&#39;s jaw bone and optionally a screw or cement-retained crown (not shown) that is configured to fit onto the prosthesis  100 . 
     The implant  19  comprises a first end  19   a , an opposite second end  19   b  and a bore  20  defining an opening at the second end  19   b , the bore  20  ending at a distance from the first end  19   a  and comprising an internal thread  21  that is configured to engage the threaded section of the screw  17 . Furthermore, a recess  22  is provided at the opening that is configured to engage the connecting section  3  of the prosthesis  100  preferably in a form-fit manner. Furthermore, an outside surface is provided at the second end  19   b  of the implant  19  that engages a surface of the prosthesis  100 , preferably a surface of the transition section  200   d  of prosthesis  100  between the milled section  200   c  and the connection section  300 . 
     In more detail, the shank  17  of the screw  16  has a maximum diameter that is smaller or equal to the diameter of the smallest bore section, i.e. the first bore section  400   a ′ of the first bore  400 ′. In the embodiment shown in  FIG. 7 , a conically tapered section  400   d ′ is provided between the first bore section  400   a ′ and the second bore section  400   b ′ of the first bore  400 ′ that tapers towards the first bore section  400   a ′ and forms a screw seat. Accordingly, the screw head  18  preferably comprises conically tapered section that matches the conically tapered section of  400   d ′. Furthermore, the diameter of the screw head  18  is selected such that the screw can be inserted through the second bore  400 ″ into the first bore  400 ′ until the screw head rests in the screw seat  400   d′.    
     During surgery, the implant  19  may be inserted into the jaw bone of a patient, followed by mounting the prosthesis  100  by engaging the connection section  300  with recess  22 . Thereafter, the screw  16  is inserted into the prosthesis  100 . As depicted in  FIG. 7 , the screw shank  17  has to be pivoted to follow the angulated screw channel during insertion. More in detail, when the screw head  18  arrives at the axial position of the second recess  111 , the screw can be pivoted easier as the second recess provides an enlarged space for the screw head. After further advancement, the screw head  18  enters the first recess  110  which provides again space for pivoting. Hence the enlargement of the screw channel facilitates the insertion of the screw. Once the screw head  18  abuts against the screw seat  400   d , the screw is tightened and locks the prosthesis  100  with respect to the implant  19 . 
     Various modifications of the above described embodiments may be contemplated. For example, only one or more than two recesses for enlarging the screw channel may be provided. To achieve this several bore sections of the first bore, with different diameter could be provided a portion of which remains in each case when the second bore is formed. 
     Moreover, the screw channel consisting of the first and second channel in the form of the first and second bores may have a cross-section other than a circular cross-section. The screw seat may have another shape, for example a spherical shape. The screw head and the screw seat may or may not have a matching shape. 
     The second channel needs not to be angulated relative to the first channel, so that the screw channel at a whole is straight. However, the dental abutment blank is most suitable for angulated screw channels. 
     For the connection section any shape may be contemplated that permits holding the blank for machining. The blank may also clamped from inside the connection section i.e. from inside the first bore. 
     Although all embodiments described above are illustrated by reference to a single tooth replacement abutment blank and/or prosthesis, it should be understood that the dental abutment according to the invention also includes abutment blanks for bridge based prostheses. Contrary to a single prosthesis that is only mounted to one implant, the implant mounted bridge is an abutment that is mounted to multiple implants installed in the jaw bone of a patient. Depending on the clinical situation, the pre-fabricated bridge abutment blank may comprise multiple blank bodies and/or bores—either having a blind bore or already having an angulated through bore as described above.