Abstract:
The present invention relates to a dental implant fixture, and more particularly, to a dental implant fixture which rotates about a central axis thereof, and thus is inserted into a bone tissue constituted by a cortical bone and a spongy bone to form an artificial tooth root, wherein the dental implant fixture includes a first portion, a second portion, and a third portion. The first portion is inserted into the cortical bone and has an outer surface with a first screw thread whereon first vertices and first valleys are alternately arranged. The second portion is disposed beneath the first portion and inserted into the spongy bone, has an outer surface with a second screw thread whereon second vertices and second valleys are alternately arranged. The distance between the adjacent second vertices of the second screw thread is larger than the distance between the adjacent first vertices of the first screw thread. The third portion is disposed beneath the second portion, and has an outer surface with a third screw thread whereon third vertices and third valleys are alternately arranged, and a first cutting part which is hollowed such that the first cutting part is closer to the central axis than the third valleys. The lower outer diameter of the second screw thread is smaller than the upper outer diameter of the second screw thread.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to relates to an implant fixture, and more particularly, to a dental implant fixture that achieves initial fixing force even when inserted into a soft bone tissue like cancellous bone and reduces a time for osseointegration between the dental implant fixture and peripheral bones. 
       BACKGROUND ART 
       [0002]    A screw type implant fixture includes a body having a screw thread formed on an outer surface and is used as a fixing unit to fix a dental or orthopedic prosthesis or the like into a bone. A bone tissue into which a fixture is to be inserted consists of cancellous and cortical bones. The cancellous bone refers to a relatively soft bone tissue of a bone, and the cortical bone refers to a relatively thin film, which is harder than the cancellous bone and generally encloses the cancellous bone. A length of the cancellous bone is usually longer than the cortical bone and thus the inserted fixture is implanted into the cancellous bone. 
         [0003]      FIG. 1  illustrates an implant fixture  100  according to the conventional art. The implant fixture  100  includes a second portion  120  having a large screw thread  121  including peaks  121   a  and roots  121   b  alternating with one another on a central axis of the implant fixture  100 , a first portion  110  disposed above the second portion  120  and including a smaller screw thread  111  than the screw thread  121  of the second portion  120 , and a third portion  130  disposed below the second portion  120  and including a cave cutting portion  131  on the central axis of the implant fixture  100 . A depth of a cave of the cave cutting portion  131  is longer than the bone of the third portion  130  so that the cave cutting portion  131  enables the implant fixture  100  to be easily inserted into a bone tissue at an initial stage. Also, outer diameters D 1  of the first portion  110  and the second portion  120  are the same along the central axis. 
         [0004]    The implant fixture  100  is inserted into an implant hole formed in a bone tissue of the human body using a drill. When the implant fixture  100  is inserted into the bone tissue, the third portion  130  and the first portion  110  are sequentially implanted into a cancellous bone, and the first portion  110  is implanted into a cortical bone. After the implantation is completed, bone tissues near the implant fixture  100  are grown to integrate with a surface of the implant fixture  100  to thereby fix the implant fixture  100 . 
         [0005]    However, the implant fixture  100  according to the conventional art has the following drawbacks. 
         [0006]    First, the second portion  120  of the implant fixture  100  is not inserted into the bone tissue by sufficiently applying a pressure to the bone tissue, and thus the implant fixture  100  does not have a sufficient initial fixing force when the implantation is completed. Thus, bone absorption may occur near the implant fixture  100 . The bone absorption is an atrophy due to a reduction in the amount of a bone tissue near the implanted implant fixture  100 , which deteriorates the fixing force of the implant fixture  100 , thereby hindering the whole stability of the implant fixture  100  or damaging a prosthesis attached to an upper end of the implant fixture  100 . 
         [0007]    Second, when a large implant hole is formed before the implant fixture  100  is inserted, osseointegration takes a long time and the initial fixing force is likely deteriorated as well. More specifically, such a large implant hole causes a bone tissue near the implant fixture  100  and the surface thereof to be far away from each other, which increases the amount of the bone tissue to be grown on the surface of the implant fixture  100 , thereby increasing the total time for osseointegration. 
         [0008]    Third, when an implant hole is not formed using a drill in a desired direction in a straight manner before the implant fixture  100  is implanted, if a thread has a stumpy peak cross section as shown in the conventional art, the implant fixture  100  is implanted in a wrong direction. More specifically, the implant fixture  100  follows a direction of the implant hole and has difficulties in changing a direction thereof to a desired direction or moving a position thereof. When the implant fixture  100  is implanted in a wrong position, it is necessary to remove the implant fixture  100  from the wrong position, form a new implant hole, and insert the implant fixture  100  into the new implant hole. 
       DETAILED DESCRIPTION OF THE INVENTION 
     Technical Problem 
       [0009]    The present utility model provides a dental implant fixture capable of achieving initial fixing force in a cancellous bone, preventing bone absorption after implantation, and being inserted into a desired direction. 
       Technical Solution 
       [0010]    According to an aspect of the present invention, there is provided a ˜˜ 
       ADVANTAGEOUS EFFECTS 
       [0011]    According to the dental implant fixture of the present invention described above, an outer diameter of a second screw thread implanted into a cancellous bone increases toward an upper side thereof, thereby achieving initial fixing force by applying a pressure to a bone tissue near the cancellous bone, and accordingly, preventing bone absorption after implantation. 
         [0012]    The dental implant fixture formed with screw threads has a sharp cross section as a whole, so that the dental implant fixture can be inserted in a desired direction even when an implant hole is erroneously formed using a drill, thereby preventing a re-surgical operation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The above and other features and advantages of the present utility model will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
           [0014]      FIG. 1  illustrates an implant fixture according to the conventional art; 
           [0015]      FIG. 2  illustrates an implant fixture according to an embodiment of the present invention; 
           [0016]      FIG. 3  illustrates the implant fixture of  FIG. 2  viewed at a different angle; 
           [0017]      FIG. 4  is a rear view of the implant fixture of  FIG. 2 ; 
           [0018]      FIG. 5  is a cross-sectional view of the implant fixture of  FIG. 2 ; 
           [0019]      FIGS. 6 through 8  are schematic views illustrating the implant fixture of  FIG. 2 , being implanted into a bone tissue; 
           [0020]      FIG. 9  illustrates an implant fixture according to another embodiment of the present invention; and 
           [0021]      FIG. 10  is a cross-sectional view of the implant fixture of  FIG. 9 . 
       
    
    
     BEST MODE 
       [0022]    Exemplary embodiments of the present utility model will now be described in detail with reference to the attached drawings. 
         [0023]      FIG. 2  illustrates an implant fixture  1  according to an embodiment of the present invention.  FIG. 3  illustrates the implant fixture  1  of  FIG. 2 , viewed at a different angle.  FIG. 4  is a rear view of the implant fixture  1  of  FIG. 2 .  FIG. 5  is a cross-sectional view of the implant fixture  1  of  FIG. 2 .  FIGS. 6 through 8  are schematic views illustrating the implant fixture  1  of  FIG. 2 , being implanted into a bone tissue  40 . 
         [0024]    The implant fixture  1  of the present embodiment is inserted into the bone tissue  40  consisting of a cortical bone  41  and a cancellous bone  42  so as to form an artificial tooth root. The implant fixture  1  has a cylindrical shape and an outer surface on which a screw thread is formed. When the implant fixture  10  rotates about a central axis C, the implant fixture  1  is inserted into the cortical bone  41  and the cancellous bone  42  to form screw roots at an inner surface of an implant hole formed in a bone tissue using a drill in advance. The implant fixture  1  may be formed of titanium or any other type of metal material that is not rejected by the human body. 
         [0025]    The implant fixture  1  includes a first portion  10 , a second portion  20 , and a third portion  30 . 
         [0026]    The first portion  20  refers to a portion of the implant fixture  1  that is mostly inserted into the cortical bone  41  when the implant fixture  1  is inserted (the first portion  20  may also be partially implanted into the cancellous bone  42 ), and forms an upper side of the implant fixture  1 . A first screw thread  11  is formed on an outer surface of the first portion  10 . The first screw thread  11  has a spiral form, and includes first peaks  11   a  and first roots  11   b  alternating with one another in a direction of the central axis C. 
         [0027]    In this regard, a screw thread disposed in the lowest end of the first screw thread  11  may have a cutting surface  12  approximately in parallel to a plane including the central axis C. The cutting surface  12  can be inclined toward the plane within about 30°. 
         [0028]    More specifically, the number of screw lines of the first portion  10  increases, compared to that of the second portion  20 , and thus a new screw thread is generated at a starting portion of the first screw thread  11 . The conventional newly generated screw thread has a gradual protruding shape, which increases a cutting resistance in a process of inserting an implant fixture and thus a cutting becomes generally difficult. However, in the present embodiment, the cutting surface  12  formed in the lowest end of the first portion  10 , which is an initial portion of the first screw thread  11 , can facilitate cutting. 
         [0029]    The second portion  20  is disposed below the first portion  10 . In detail, the second portion  20  is integrally coupled to the first portion  20 . However, the present invention is not limited thereto, and another structure may be disposed therebetween. Most of the second portion  20  is inserted into the cancellous bone  42  (a part of the second portion  20  may also be implanted into the cortical bone  41 ), thereby forming a lower portion of the implant fixture  10 . A second screw thread  21  is formed on an outer surface of the second portion  20 . The second screw thread  21  has a spiral form. The second screw thread  21  includes second peaks  21   a  and second roots  21   b  that alternate with one another in the direction of the central axis C. Distances (pitches; S 2 ) between the adjacent second peaks  21   a  of the second screw thread  21  are greater than distances (pitches; S 1 ) between the adjacent first peaks  11   a  of the first screw thread  11 . That is, the cross-sectional size of the second screw thread  21  is greater than that of the first screw thread  11 , and thus the second screw thread  21  is referred to as a ‘macro-screw thread’. On the other hand, the cross-sectional size of the first screw thread  11  is smaller than that of the second screw thread  21  and thus is referred to as a ‘micro-screw thread’. 
         [0030]    As described above, the sizes of the first screw thread  11  and the second screw thread  21  vary due to the quality of bones into which they are respectively implanted. For example, the first portion  10  that is implanted into the cortical bone  41  that is relatively hard includes a dense number of screw threads for concentration of stress in a contacting portion between the first portion  10  and the cortical bone  21 , thereby uniformly distributing the entire stress to a peripheral bone tissue  40 . On the other hand, the second portion  20  inserted into the cancellous bone  42 , which is relatively soft, is formed with a size that increases an amount of bone tissue being captured to thus obtain sufficient fixing force. 
         [0031]    An outer diameter D 22  of a lower side of the second screw thread  21  is smaller than an outer diameter D 21  of an upper side thereof. The outer diameters may continuously increase upward, but the present invention is not limited thereto, and the outer diameters may discontinuously increase upward. As described above, the outer diameter D 22  of the lower side of the second screw thread  21  and the outer diameter D 21  of the upper side thereof are different from each other in order to apply a pressure to the cancellous bone  42  due to an increase in the outer diameters during a process of inserting the second portion  20  into the cancellous bone  42 , thereby obtaining sufficient fixing force. 
         [0032]    In this regard, the second portion  20  is formed tapering. More specifically, if an inclination angle between the central axis C and a first straight line I 1  that connects the second peaks  21   a  disposed in the upper and lower sides of the second screw thread  21  on a plane (refer to the cross-sectional shape of  FIG. 5 ) passing through the central axis C is θ′, θ′ may be between 0.5° and 3°. If the inclination angle θ′ between the central axis C and a first straight line I 1  is less than 0.5°, less pressure may be applied to the peripheral bone tissue  40  during the process of inserting the second screw thread  20 . If the inclination angle θ′ between the central axis C and a first straight line I 1  is greater than 3°, extreme pressure may be applied to the peripheral bone tissue  40 , which causes damage to bones. 
         [0033]    Also, both of the outer diameters the first portion  10  and the second portion  20  may be increased. More specifically, all the first peaks  11   a  of the first screw thread  11  and all the second peaks  21   a  of the second screw thread  21  may be disposed on the same plane. 
         [0034]    If a width of the first roots  11   b  of the first screw thread  11  is d′ and a width of the second roots  21   b  of the second screw thread  21  is d, d may be less than d. If d′ is greater than d, the number of screw threads formed in the first screw thread  11  is less than that of the second screw thread  21 , and thus the first portion  10  cannot achieve sufficient supporting force after implantation. 
         [0035]    Also, if a vertical distance between one of the first roots  11   b  of the first screw thread  11  and the first peak  11   a  adjacent to the first root  11   b  is b′, b′ may be greater than 0.20 mm, and may be preferably greater than 0.25 mm. If b′ is smaller than 0.20 mm, the size of the first screw thread  11  is extremely small, and thus supporting force between the peripheral bone tissue  40  and the first screw thread  11  can deteriorate. 
         [0036]    Further, the distances the first screw thread  11  and the second screw thread  21  move per one rotation along the central axis are set to be the same. If the distances they move along the central axis are different, a greater rotational torque is required during implantation, and this may apply a strong pressure to the peripheral bone tissue  40  and cause cracks therein. The moving distance may be between 0.5 and 2.5 mm. 
         [0037]    An inner diameter (or a bone diameter; D 23 ) of the second screw thread  21  may be smaller than an inner diameter D 13  of the first screw thread  11 , preferably by 0.1 and 1.5 mm. The number of lines of the first screw thread  11  per lead (a distance that a peak of a screw thread moves in the central axis direction C when the implant fixture  1  makes one rotation with respect to the peak) may be greater than that of the second screw thread  21  per lead, preferably by more than 200%. More specifically, if the second screw thread  21  has one line, the first screw thread  11  may have two or more lines, and if the second screw thread  21  has two lines, the first screw thread  11  may have four or more lines. 
         [0038]    A second cutting portion  22  is formed in the second screw thread  21  of the second portion  20 . The second cutting portion  22  extends from the lower side of the second portion  20  to the upper side thereof. The second cutting portion  22  extends upward and is not parallel to the central axis C, unlike a first cutting portion  32  of the third portion  30  that will be described. Specifically, the second cutting portion  22  has an inclined shape, and, more specifically, coils in spiral form and extends upward. The second cutting portion  22  formed in the second screw thread  22  can facilitate an insertion from the third portion  30  to the second portion  20 . That is, unlike the conventional art, the outer diameter of the second portion  20  increases upward, which slightly increases a torque during a process of inserting the second portion  20  into the peripheral bone tissue  40 . The formation of the second cutting portion  22  facilitates inserting the second portion  20 . 
         [0039]    The maximum depth of the second cutting portion  22  may be less than a vertical distance (a height of the second screw thread  21 ; b) from one of the second peaks  21   a  of the second screw thread  21  and the second roots  21   b  adjacent to the second peak  21   a , and more preferably, by 0.5 and 1.0 times. When the minimum depth of the second cutting portion  22  is smaller than 0.5 times the height of the second screw thread  21 , a cutting effect is reduced, and when the minimum depth of the second cutting portion  22  is greater than 0.8 times the height of the second screw thread  21 , the second cutting portion  22  may not sufficiently smooth the peripheral bone tissue  40 . 
         [0040]    The second screw thread  21  has a sharp screw thread shape, compared to the conventional art, and preferably a cutting edge shape. 
         [0041]    More specifically, the shortest distance a (refer to  FIG. 5 ) between the adjacent second roots  21   b  of the second screw thread  21  may be less than the vertical distance (the height of the second screw thread  21 ; b) from the second peaks  21   a  of the second screw thread  21  to the second roots  21   b  adjacent to the second peak  21   a , more preferably, b/a (i.e. height/width) is between 0.9 and 1.5. That is, the height is greater than the width so that the second screw thread  21  has a sharp shape like a blade as a whole. Thus, when the second screw thread  21  rotates, the peripheral bone tissue  40  is easily cut and the implant fixture  1  is inserted into the peripheral bone tissue  40 . Meanwhile, if b/a is less than 0.9, the second screw thread  21  is stumpy or is not sharp, and thus a sufficient cutting effect is not obtained, and if b/a is greater than 1.5, the second screw thread  21  is extremely thin and has a low strength, and thus a somewhat strong bone tissue is likely to easily damage the second screw thread  21  when rotating. 
         [0042]    In addition, with regard to the cross-sectional shape of the second screw thread  21 , if a width of a top of the second peaks  21   a  of the second screw thread  21  is c, and a width of the second roots  21   b  adjacent to the second peaks  21   a  is d, c may be less than d, more preferably, c:d is 1:2˜1:6, and most preferably, c:d is 1:3˜1:5 (refer to  FIG. 5 ). With regard to a screw angle, if an angle between a straight line vertical to the central axis C and an inclination surface of the second screw thread  21  is θ, θ may be 5°˜35°, and most preferably, 15°˜20° (refer to  FIG. 5 ). The screw thread can have a sufficient sharp is shape of the above ratio of c:d and the above range of θ. 
         [0043]    The first screw thread  11  and the second screw thread  21  may be continuously connected to each other. More specifically, as shown in  FIG. 3 , the second screw thread  21  is continuously connected to the first screw thread  11 , and the first screw thread  11  is continuously connected to the second screw thread  21 . The continuous connection of the first screw thread  11  and the second screw thread  21  can result in a natural implantation of the implant fixture  1  without an instant increase in implantation torque. 
         [0044]    The third portion  30  is disposed in a lower side of the second portion  20 , and includes a third screw thread  31  having an outer surface on which third peaks  31   a  and third roots  31   b  alternate with one another, and the first cutting portion  32  caved approaching the central axis C. The third portion  30  is the lowest end of the implant fixture  1  and is an entrance portion that is implanted into a bone tissue  40  at an initial stage. More specifically, the third portion  30  is inserted into the bone tissue  40  at an initial stage to form a female screw thread inside the bone tissue  40 . The first cutting portion  32  that is deeply caved enables the third portion  30  to be easily inserted into the bone tissue  40 . 
         [0045]    The first cutting portion  32  vertically extends upward from a lower end of the third portion  30 . More specifically, the first cutting portion  32  extends upward in parallel to the central axis C. The first cutting portion  32  is caved in deeper than the third roots  31   b  so that the first cutting portion  32  easily cuts a peripheral bone tissue of an implant hole located at a lower end of the implant fixture  1 . 
         [0046]    The shapes of the first cutting portion  32  and the second cutting portion  22  vary in order to improve surface roughness of the peripheral bone tissue  40  by minutely cutting the peripheral bone tissue  40 , which has been roughly cut using the first cutting portion  32 , with the second cutting portion  22 . That is, as the second cutting portion  22  rotates, the peripheral bone tissue  40  that has been cut roughly using the first cutting portion  32  may be smoothed. 
         [0047]    The dental implant fixture  1  according to the current embodiment of the present invention has the following effects. First, as illustrated in a left side of  FIG. 6 , an implant hole having a diameter h 1  is formed in the bone tissue  40  with a drill so as to insert the implant fixture  1  in the implant hole. In detail, the dental implant fixture  1  is inserted into the implant hole while rotating around the central axis C. In this regard, the first cutting portion  32  disposed in the lowest end of the dental implant fixture  1  forms a female screw groove in the peripheral bone tissue  40 , and simultaneously the third portion  30  is inserted into the implant hole at the same time. After the first cutting portion  32  is inserted, the second cutting portion  22  is inserted, thereby cutting and smoothing the bone tissue  40  and smoothing the peripheral bone tissue  40  at the same time. After the second portion  20  is completely inserted, the first portion  10  is inserted, and here, a cutting edge formed in the lowest end of the first portion  10  cuts the peripheral bone tissue such that the first portion  10  is easily inserted into the implant hole. The implant fixture  1  that is completely inserted into the bone tissue is shown in a right side of  FIG. 6 . 
         [0048]    Also, the outer diameter of the second screw thread  21  increases upward so that a pressure applied to the peripheral bone tissue  40  gradually increases upward. Therefore, when the implant fixture  1  is inserted, the pressure is applied to the cancellous bone  42 , thereby increasing fixing force. Further, the fixing force regarding the cancellous bone  42  is maintained, and, at the same time, a partially concentrated stress regarding each screw thread is distributed, bone absorption is prevented, and osseointegration is improved. 
         [0049]      FIG. 7  is a schematic view illustrating the implant fixture  1  of  FIG. 2 , being implanted into the bone tissue  40  when an implant hole having a diameter h 2  smaller than the diameter h 1  of the implant hole of  FIG. 6  is formed. In the conventional implant fixture having a stumpy screw thread as a whole, it is difficult to insert the conventional implant fixture into the implant hole having the small diameter h 2 . This is because an excessive implantation torque is required. If the conventional implant fixture is excessively inserted into the implant hole having the small diameter h 2 , a crack may occur in a bone tissue. Thus, it is necessary to additionally broaden the diameter h 2  of the implant hole using a drill. 
         [0050]    Also, since the implant fixture  1  of the present embodiment has a sharp screw thread as a whole, the implant fixture  1  easily cuts the peripheral bone tissue  40  like a drill blade when the screw thread rotates, thereby easily inserting the implant fixture  1  in the implant hole. That is, it is unnecessary to broaden the diameter h 2  of the implant hole. The implant fixture  1  can obtain the same fixing force as that of an initial stage regardless of a diameter of a drill hole by reducing the sensitivity of the implant hole, and, in particular, can be sufficiently implanted into the implant hole owing to a sharp shape even if the implant hole has a small diameter. 
         [0051]    Further, referring to  FIG. 8 , when an implant hole is formed in a direction different from a desired direction, if the implant fixture  1  is inserted into the implant hole after placing the implant fixture  1  in the desired direction, without forming a new implant hole in the desired direction, the implant fixture  1  can be implanted in the desired direction while the screw thread in the sharp shape cuts the peripheral bone tissue  40 . That is, it is advantageously unnecessary to form a new implant hole. 
         [0052]    According to the present embodiment, a concentrated stress to the cortical bone  41  is spread to the cancellous bone  42  so as to uniformly distribute the stress to the implant fixture  1  as a whole, thereby preventing bone absorption of the cortical bone  41  and improving osseointegration. 
         [0053]    The present invention has the following modification. 
         [0054]      FIG. 9  illustrates an implant fixture  1  according to another embodiment of the present invention, and  FIG. 10  is a cross-sectional view of the implant fixture of  FIG. 9 . 
         [0055]    Although the distances S 1  between the adjacent first peaks  11   a  of the first screw thread  11  and the distances S 2  between the adjacent second peaks  21   a  of the second screw thread  21  are different from each other in the previous embodiment, the distances S 1  and the distances S 2  are the same in the present embodiment. In this regard, the width d′ of the first roots  11   b  of the first screw thread  11  may be between 0.3 mm˜0.6 mm. The distances S 1  and the distances S 2  are the same, and the width d′ of the first roots  11   b  is maintained within a predetermined range in order to produce a sufficient roughness since powders having fine sizes (generally diameters between 0.25 mm˜0.5 mm) used for a surface treatment obtain a sufficient bone width in the second portion  20 , thereby sufficiently contacting the second roots  21   b . Meanwhile, if a bone width of the first portion  10  is small like the conventional art, since the width d′ of the first roots  11   b  is narrow, the powders have difficulties in sufficiently contacting the bone surface. However, in the present embodiment, the distances S 1  and the distances S 2  are the same, and the width d′ of the first roots  11   b  is maintained within a predetermined range so as to obtain a sufficient width of the first roots  11   b , so that the powders can sufficiently contact the surface of the first roots  11   b . If the surface roughness is sufficiently obtained, a junction between the implant fixture and the peripheral bone tissue increases. 
         [0056]    Further, the distances S 1  and S 2  may be between 0.6 mm˜1.0 mm, more preferably, 0.7 mm˜0.9 mm, and most preferably, 0.8 mm. The implant fixture of the present embodiment is similar to the implant fixture  1  described with reference to  FIG. 2  in terms of function and structure, and thus the detailed description will not be repeated. 
         [0057]    In the previous embodiment, although the width d′ of the first roots  11   b  of the first screw thread  11  is less than the width d of the second roots  21   b  of the second screw thread  21 , the widths d′ and d may be the same. 
         [0058]    While this invention has been particularly shown and described with reference to embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The embodiments should be considered in descriptive sense only and not for purposes of limitation. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.