Patent Publication Number: US-2011070557-A1

Title: Dental implant

Description:
FIELD OF THE INVENTION 
     This invention relates to an endosseous implant for prosthesis embedded in the bone tissue of a living body, and in particular, to an endosseous dental implant. 
     BACKGROUND OF THE INVENTION 
     Endosseous dental implants are widely used in dental surgical procedures for restoration of one or more teeth in a patient&#39;s mouth using a prosthetic tooth that is secured to a dental abutment united with the dental implant anchored in the jawbone. 
     Generally, the procedure for restoring a tooth includes several stages. In the beginning, an implant cavity of dimensions adapted to those of the implant is created by to drilling a hole of increasing diameter. Then, the dental implant is inserted into the hole, typically by screwing, although other techniques are known for introducing the implant in the jawbone. After the implant is initially installed in the bone, a temporary healing cap is secured over the exposed proximal end of the implant. The patient&#39;s gums are then sutured over the implant to allow the implant site to heal and to allow desired cicatrization of the bone and osseointegration with the implant to occur. This healing phase for conventional implants can take from four to ten months. 
     Thereafter, the surgeon reaccesses the implant by making an incision through the patient&#39;s gum tissues. The healing cap is then removed, exposing the proximal end of the implant, and a dental abutment designed to be used as support for the tooth prosthesis is united with the implant. Sometimes, prior to the final abutment, a temporary dental abutment is attached to the implant for a certain time period for control the healing and growth of the patient&#39;s gum tissue around the implant site. In a modified procedure, an abutment component can be either integrally formed with the implant or attached to the implant during the previous stage, i.e. together with the introducing of the implant in the jawbone. It should be noted that the terms “proximal” and “distal” are used herein with reference to the dental surgeon of the dental implant. 
     The final stage in the restorative procedure involves fabricating and placement of a cosmetic tooth prosthesis to the abutment. 
     The dental implant typically includes a threaded body portion and a collar portion. The body portion is configured to extend into and osteointegrate with the jawbone. The top surface of the collar portion typically lies flush with the crest of the jawbone. The dental abutment typically lies on the top surface and extends through the soft tissue of the gingiva, which lies above the jawbone. 
     One of the problems associated with mounting implants within a hole drilled in the jawbone is associated with poor immediate immobilization of the implants. In to attempting to remedy the disadvantage, self-screw threaded (self-tapping) implants has been designed to be screwed into bone. Owing to their self-screw threading character, such implants make it possible to obtain a better intimate contact with the bone and consequently to increase the primary stability of such implants. 
     A typical self-tapping implant has a distal end for tapping threads in the bone, a proximal end for connecting to a prosthesis, and a threaded section usually arranged near the distal end, for engaging the threads tapped in the bone. The body of the implant near the tapping distal end usually includes several grooves or flutes that extend upwardly on the sidewall of the implant along the longitudinal axis of the implant. Each flute includes a cutting edge that scrapes off bone as the implant is rotated into the hole. The cutting edges form threads along the bone for engaging the threaded section of the implant. 
     Despite that the self-tapping implants generally create a more intimate contact with the surrounding bone than non-tapping implants, conventional self-tapping implants also possess numerous disadvantages. For example, irregularities or defects may be formed on the bone around the entrance of the hole at the implantation site. Such irregularities occurring as a result of the surgical procedure, further may inhibit bone integration with the implant. As another disadvantage, bone fragments and shavings (bone debris) resulting from the cutting operations tend to accumulate at the cutting edge while the implant is being tapped into the bone. This bone debris decreases the effectiveness of the cutting edge and further increases the insertion torque required to insert the implant. Moreover, the accumulated bone debris may cause compression of the bone removed which results in necrosis of the bone cells. 
     In attempting to remedy these disadvantages, U.S. Pat. No. 5,897,319 to Wagner et al. describes a self-tapping dental implant for implantation into bone. The implant includes multiple flutes disposed around the tapping end. Each flute has a helical configuration. During tapping, bone chips are directed upwardly and away from the tapping end. 
     In order to enhance the growth of living bone tissue, the metal implants can be coated with biologically-compatible materials. For example, U.S. Pat. Appl. Pub. No. 2008/020349A1 describes a bone implant comprising a solid structure provided with an osteogenic layer comprising calcium phosphate in the form of particles (dihydrate and/or alphahemidrate) with a weight average particle size comprised between 10 micrometers and 250 micrometers. This coating provides a larger bone volume for ensuring a good fixation of the artificial tooth or teeth or dental prosthesis. 
     In order to maximize the effects of bone growth, the implant can be provided with grooves, holes, recesses, and other features into which bone growth may proceed. For example, U.S. Pat. No. 5,759,034 to Daftary describes a dental implant that includes a plurality of spaced apart transverse annular grooves and a longitudinal groove on the implant&#39;s wall. The longitudinal groove extends upwardly from the distal end to the middle of the implant. The transverse annular grooves and the longitudinal groove provide a greater surface area into which bone growth is formed to prevent the implant fixture from vertical and rotational movements within the jawbone. 
     U.S. Pat. No. 5,676,545 to Jones describes a dental implant that includes at least one helical channel (flute) formed within the threaded portion of the implant. The helical channel is designed to carry bone-fragment crumbs and other bone shavings away from the distal end and distribute them throughout the threaded portion of the implant. The threaded portion of the implant also includes diametrical holes through the implant at various levels along the axis of the implant and connecting to the helical channel. The purpose of the holes is to provide receptacles for packing crumbled bone tissue prior to installation of the implant and avenues for bone tissue growth after installation. 
     U.S. Pat. No. 5,366,374 to Vlassis describes a dental implant that has an elongated, substantially cylindrical body, a distal hollow internal chamber and an open distal end. The distal end has a series of dentate ridges that form a rotary cutting surface for trephining the bone. Proximally there is provided a dental handpiece adapter. At least one spiral osteogroove is disposed on the external surface of the body, extending from the distal portion generally toward the proximal portion and communicating with a recessed osteoreservoir. At least one osteovent is situated in the osteogroove, and has a leading bevelled margin to promote the ingress of bone fragments therethrough into the internal chamber. 
     U.S. Pat. No. 5,871,356 to Guedj describes a dental implant that has a tubular distal section with a cylindrical wall that turns around an axis, and is provided with an outer thread and defines an inner holding volume for bone material. The cylindrical wall has at least one distal indentation that forms a front cutting edge at the ring-shaped base. 
     SUMMARY OF THE INVENTION 
     Despite the known techniques in the area of endosseous implants for prosthesis embedded in the bone tissue, there is a need in the art for, and it would be useful to have a novel dental implant, which has improved osteointegration properties and encourages bone tissue growth in and around the implant thereby achieving greater attachment security over longer periods of time. 
     It would be advantageous to have a dental implant that can provide a greater surface area into which bone growth is formed to prevent the implant fixture from vertical and rotational movements and to further support the implant fixture within the jawbone. 
     It would also be advantageous to have a dental implant that will be mechanically strong in order to resist the stresses to which it is subjected during installation and use. 
     It would still be advantageous to have a dental implant that will less traumatize the jawbone, thereby decreasing the healing phase after insertion of the implant. 
     It would further be advantageous to have a dental implant that will be biologically compatible with the bone tissue in order that it may facilitate bone growth in and around the implant. 
     The present disclosure satisfies the aforementioned need by providing a novel endosseous dental implant for anchoring in a jawbone to support an abutment for mounting a dental prosthesis. 
     According to one embodiment, the dental implant comprises a collar portion, a mid portion integrally connected to the collar portion, and a base portion integrally connected to a mid portion. 
     The collar portion is located at an open proximal distal end having an axial opening, and is configured to secure the abutment to the dental implant. It should be noted that in the description and claims that follow, the terms “proximal” and “distal” are used with reference to the dental surgeon of the dental implant. The axial opening extends into a blind hole proceeding from the proximal end into the interior of the implant. The blind hole includes an internally-extending chamfered zone located near the proximal end, that is followed by a wrench-engaging zone adapted for engaging with a tool that screws the implant into the jawbone, that is in turn followed by an abutment post receiving chamber zone, that is followed by an internally-threaded zone having a threaded surface configured to receive a bolt used to secure the abutment to the dental implant. 
     According to one embodiment of the present invention, the collar portion has a substantially cylindrical unthreaded shape. 
     According to a further embodiment of the present invention, a part of the wrench-engaging zone, the entire post receiving chamber zone, and the internally-threaded zone are resided within the mid portion. 
     The mid portion is integrally connected to the collar portion. The mid portion includes external helical treads turning around an external wall of the mid portion. 
     According to a further embodiment, the mid portion includes at least one flute having a self-tapping cutting edge. For example, the flute can extend at least half of the length of the mid portion. 
     According to still a further embodiment, the mid portion is tapered with contraction towards the base portion. For example, the contraction of the mid portion starts from the end of the collar portion. The contraction of the mid portion can, for example, be axially symmetric with a tapering angle from about 2° to about 10°. Alternatively, the contraction of the mid portion can be asymmetric with respect to a longitudinal axis of the dental implant. 
     The base hollow portion is integrally connected to a mid portion and located at an open distal end of the implant. The base hollow portion comprises a wall that defines an internal storage volume for an osseous tissue of the jawbone. The base hollow portion further comprises a plurality of openings arranged in the wall. The openings pass through the wall and enter the internal storage volume. The base hollow portion is unthreaded and tapered with contraction towards the distal end. 
     According to one embodiment of the present invention, the openings have a circular shape. The circular openings can, for example, be arranged in one or more rows. The rows can, for example, be distributed and equally spaced along the length of the hollow base portion. The circular openings in each row can, for example, be equally spaced. 
     According to one embodiment of the present invention, the area of the openings in the wall of the base portion should not exceed 60% of the total area of the wall. Preferably, the area of the openings in the wall of the base portion is in the range of about 50% to 60% of the total area of the wall. 
     According to one embodiment of the present invention, the openings are slot openings. The slot openings can, for example, extend along at least a part of the length of the base portion between the mid portion and the distal end of the base portion. 
     The dental implant of the present invention can be effectively screwed through the jaw bone to smoothly transmit torque from the proximal end of the dental implant to the distal end. 
     There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows hereinafter may be better understood. Additional details and advantages of the invention will be set forth in the detailed description, and in part will be appreciated from the description, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
         FIG. 1A  is a schematic side elevation view of an endosseous dental implant, according to one embodiment of the present invention; 
         FIG. 1B  is a schematic longitudinal cross-sectional view of the dental implant of  FIG. 1A ; 
         FIG. 1C  is a schematic proximal end cross-sectional view of a portion of the dental implant of  FIG. 1A  taken along the line B-B′; 
         FIG. 1D  is a schematic transverse cross-sectional view of the dental implant of  FIG. 1A  taken along the line A-A′; 
         FIG. 2A  is a schematic side elevation view of an endosseous dental implant, according to another embodiment of the present invention; and 
         FIG. 2B  is a schematic longitudinal cross-sectional view of the dental implant of  FIG. 2A . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The principles of the method for the medical device according to the present invention may be better understood with reference to the drawings and the accompanying description, wherein like reference numerals have been used throughout to designate identical elements. It being understood that these drawings which are not necessarily to scale and proportions, are given for illustrative purposes only and are not intended to limit the scope of the invention. Examples of constructions, materials, dimensions, and manufacturing processes are provided for selected elements. Those versed in the art should appreciate that many of the examples provided have suitable alternatives which may be utilized. 
     Referring to  FIGS. 1A and 1B  a schematic side elevational view and a longitudinal cross-sectional view of an endosseous dental implant  10  is illustrated, correspondingly, according to one embodiment of the present invention. It should be understood that the dental implant  10  is not bound to the scale and proportion illustrated in  FIGS. 1A and 1B , and in other drawings. Generally, the dental implant  10  includes a collar portion  11 , a mid portion  12  integrally connected to the collar portion  11 , and a base portion  13  integrally connected to a mid portion  12 . Thus, the base portion  13  together with the collar portion  11  and the mid portion  12  form a one-piece fixture of the dental implant  10 . 
     The dental implant  10  is fabricated of any suitable biocompatible material. For example, the implant  10  may be formed from a titanium alloy and may have any one of various surface coatings or surface textures, such as an as-machined surface or microtextured surface to promote osteointegration. The portions of the implant that are to be in intimate contact with the bone can, for example, be titanium plasma sprayed. When desired, these portion can be coated with hydroxyl-apatite, tricalcium phosphate or any other suitable material that increases the surface area of the implant&#39;s body. Texturing of the threaded surface can be accomplished by a variety of processes known to those skilled in the art, such as grit-blasting with an abrasive medium, or etching with a strong acid. 
     Referring to  FIGS. 1A ,  1 B and  1 C together, the collar portion  11  has generally a cylindrical unthreaded shape and includes an axial opening  111  arranged at a proximal end  112  of the dental implant  10 . It should be noted that in the present description and claims that follow, the terms “proximal” and “distal” are used with reference to the dental surgeon of the dental implant. The collar portion is configured to support an abutment (not shown), which lies on the proximal end  112  of the dental implant  10 . 
     When desired, as shown in  FIGS. 1A ,  1 B and  1 C, the collar portion  11  can include a relatively small mouth region  113  in which an outer surface  114  of the collar portion  11  tapers inwardly with contraction towards the uppermost edge of the proximal end  112 , whereas an inner surface  115  of the of collar portion  11  tapers outwardly with expansion towards the uppermost edge of the proximal end  112 , thereby forming a chamfered zone  116  in the vicinity of the axial opening  111 . These features are created for decreasing the sharpness of the uppermost edge of the implant at the end, and thereby enhancing its atraumatic characteristics. 
     According to the embodiment shown in  FIGS. 1A and 1B , the axial opening  111  extends into a blind hole having four distinct zones proceeding from the proximal end  112  into the interior of the implant  10 . The internally-extending chamfered zone  116  (corresponding to the mouth region  113 ) is followed by a wrench-engaging zone  117 . The wrench-engaging zone  117  has a multi-sided, wrench-engaging surface  1170  that is adapted for engaging with a tool (dental hand-piece) that screws the implant into the bone. The wrench-engaging zone  117  is followed by a post receiving chamber zone  118 , which, in turn, is followed by a more deeply recessed internally-threaded zone  119  having a threaded surface  1190 . The post receiving chamber zone  118  is configured to fit a post of the abutment (not shown), and in some arrangements can include anti-rotational features (not shown), for example, flat sides, grooves, and or indentations, so as to prevent the abutment from rotating with respect to the dental implant  10 . The internally-threaded zone  119  is configured to receive a bolt (not shown) used to secure the abutment to the dental implant  10 . 
     The most deeply arranged zones can be extended from the internal part of the collar portion into the internal part of the mid portion  12 . As shown in  FIGS. 1A and 1B , a part of the wrench-engaging zone  117 , and the entire post receiving chamber zone  118  and the internally-threaded zone  119  are resided within the mid portion  12 . 
     The mid portion  12  has external threads  121  helically turning in a clockwise direction around an external wall  122  of the mid portion  12 . The threads  121  can have any desired configuration known to a person versed in the art. According to the embodiment shown in  FIGS. 1A and 1B , the mid portion  12  also has a helically shaped flute  123  having a self-tapping cutting edge  124 . When desired, more than one flute can be disposed on the mid portion  12 . For example, an implant having a larger diameter than those shown in the figures, may utilize two or more separate flute sections. The overall length of the flute  123  may vary. As shown in  FIGS. 1A and 1B , the flute  123  extends about half of the length of the mid portion  12 , and does not extend through the entire length of the mid portion  12 . However, when desired, the flute  123  may extend from the base portion  13  of the implant towards the collar portion  11  completely through the mid portion  12 . According to the embodiment shown in  FIGS. 1A and 113 , the mid portion  12  is tapered with contraction towards the base portion  13 . The contraction is axially symmetric with a tapering angle from about 2° to about 10° with respect to an axis O of the dental implant. The contraction can start from the end of the collar portion  11 , however other embodiments are contemplated. It should be understood that the contraction towards the distal end can be either symmetric or asymmetric with respect to the longitudinal axis O of the dental implant. 
     The base portion  13  is hollow inside and located at an open distal end  131  of the implant  10 . An opening  132  formed at the distal end  131  extends through the base portion  13  thereby creating a blind hole. The hollow base portion  13  has a wall  133  defining an internal storage volume  134  for an osseous tissue of the jawbone (not shown). The base portion  13  is unthreaded outside and tapered continuously from the mid portion  12  with contraction towards the distal end  131 . It should be noted that the dental implant  10  includes the threads only on the mid portion whereas the collar portion  11  and the base portion  13  have unthreaded external surface. In practice, implants having such a feature can cause fewer traumas to the jawbone than implants having completely treated surface. Accordingly, that can result in decreased healing time after implantation of the implant  10 . 
     Referring to  FIGS. 1A ,  1 B and  1 D together, the hollow base portion  13  has a plurality of openings  135  arranged in the wall  133 . Each opening  135  passes through the wall  133  and enters the storage volume  134 . The openings  135  have a circular shape of a predetermined diameter and generally are arranged around the hollow base portion  13  in one or more rows. The rows of the openings  135  are distributed along the length of the hollow base portion  13  and equally spaced, although other arrangements of the rows are contemplated. In each row, the circular openings  135  are equally and symmetrically spaced with respect to the axis O, although other arrangements of the openings in rows are contemplated. 
     The main purpose of the openings  135  is to enable the osseous tissue of the jawbone to penetrate and grow into the internal storage volume  134  after implantation during the healing time period, thereby securing the dental implant in position in the jawbone. The surface area for bone growth is increased, since bone tissue can grow not only around the implant, but also within the internal storage volume  134 . The increased surface area promotes osseointegration. 
     It should be noted here that contrary to the present invention, in the prior art dental implants which may also include openings in the implant&#39;s wall (for example, in the dental implants described in U.S. Pat. Nos. 5,366,374 and 5,871,356), the openings in the wall as well as the internal chamber in the implant are formed for collecting bone shavings, and fragments formed during the rotation of self-tapping cutting edges and sharp ridges adapted to trephine the bone. On the other hand, since the dental implant  10  does not include threads on the base portion  13 , it will not trephine and in any other way damage the bone at the distal end of the implant; thereby the implant  10  causes fewer traumas to the jawbone. Accordingly, the healing time required after implantation of the implant can be decreased. 
     It should be understood that the larger openings in the wall  133  can provide greater penetration and growth of bone tissues within the internal storage volume  134 . However, the size of the openings is bound by the strength of the implant  10 . In other words, the implant should be mechanically strong in order to resist the stresses to which it is subjected during installation and use. The strength of the implant should be greater than the level of strain induced in the implant by an external force, e.g., by occlusal load. It is known that occlusal forces in young males can range from 222 N in the incisor region to 522 N in the molar region. 
     In its simplest form, stress imparted on an implant is equal to the magnitude of a force distributed over an area over which the force acts (Stress=Force/Area). Stress can be represented as either normal stress (perpendicular to the plane on which the force acts) or shear stress (parallel to the plane on which the force acts). 
     Hooke&#39;s law relates normal stress and normal strain according to the following formula: 
       σ=Eε,  (1)
 
     where: σ is the normal stress, E is the modulus of elasticity and ε is the normal strain. 
     A similar relationship exists between shear stress and shear strain according to the following formula: 
       τ=Gγ,  (2)
 
     where: τ is the shear stress, G is the modulus of rigidity and γ is the shear strain. 
     Referring to  FIGS. 1A ,  1 B and  1 D together, the weakest section of the implant is along the line A-A′. 
     A stress imparted on implant  10  in this section, can be estimated according to the following formula: 
       σ A-A′   =F/A   A-A′   =F /{[π( D   1   2   −D   2   2 )/4 ]−[nd ( D   1   −D   2 )/2]};  (3)
 
     where: A A-A′  is the area of the implant&#39;s surface at the level of the line A-A′; D 1  is the outer diameter of the base portion  13  at the level of the line A-A′; D 2  is the diameter of the internal storage volume  134  at the level of the line A-A′; n is the number of openings at the level of the line A-A′; and d is the diameter of the openings. 
     The following values of the parameters of the implant  10  were selected for estimations: D 1 =0.26 cm; D 2 =0.15 cm; d=0.07 cm; n=6 and π≅3.14. Substitution of these values into formula (3) provides the values of σ A-A′ ≅180 MPa for the load F=222 N (occlusal forces in the jaw incisor region) and σ A-A′ ≅420 MPa for the load F=522 N (occlusal forces in the jaw molar region). 
     These values of σ A-A′  can be compared to the values of a yield strength of the materials used for the fabrication of implants. For example, the yield strength for Titanium ASTM Grade 4 and Titanium Alloy: Ti 6Al 4V-EL1 is 480 MPa and 760 MPa, correspondingly. These values are less than the estimated values for σ A-A′ . Accordingly, the dental implant  10  having the above characteristics selected for the estimation can be fabricated from these materials. 
     It was estimated that for conventional materials used for fabrication of dental implants, in order to withstand the external load, the area of the openings in the wall  133  of the base portion  13  should not exceed 60% of the total area of the wall  133 . Preferably, the area of the openings in the wall of the base portion is in the range of about 50% to 60% of the total area of the wall. 
     It should be understood that the shape of the openings in the wall of the base portion  13  is not bound to a circular shape. Referring to  FIGS. 2A and 2B , a schematic side elevation and longitudinal cross-sectional views of an endosseous dental implant  20  are illustrated, correspondingly, according to another embodiment of the present invention. This embodiment differs from the implant ( 10  in  FIGS. 1A-1D ) in the fact that the hollow base portion  13  includes a plurality of openings  235  which are in the form of slots arranged in the wall  133 . The slot openings  235  extend along the length of the hollow base portion  13 , and are symmetrically spaced with respect to the axis O, although other arrangements of the slots are contemplated. Each slot opening  235  passes through the wall  133  and enters the storage volume  134 . 
     The overall length of the slot openings  235  may vary. As shown in  FIGS. 2A and 2B , the slot openings  235  extend substantially along the entire length of the base portion  13  between the mid portion  12  and the distal end of the base portion  13 . However, when desired, the slot openings  235  may extend only a part of the length of the base portion  13 , and do not extend along the entire length of the base portion  13 . 
     As such, those skilled in the art to which the present invention pertains, can appreciate that while the present invention has been described in terms of preferred embodiments, the concept upon which this disclosure is based may readily be utilized as a basis for the designing of other structures and processes for carrying out the several purposes of the present invention. 
     Although the collar portion  11  of the implant shown in  FIGS. 1A ,  1 B,  2 A and  2 B has a cylindrical shape, when desired the collar portion  11  can be inwardly or outwardly tapered with contraction or expansion towards the proximal end  112 . 
     Although a preferable configuration of the axial opening  111  arranged at a proximal end  112  of the dental implant  10  is shown in  FIGS. 1A ,  1 B,  2 A and  2 B, the dental implant can also have another configuration of the axial opening that is different than the configuration shown in these drawings. It should be understood that this configuration depends on the tool (dental hand-piece) utilized for axial rotation of the implant during implantation. 
     It should be noted that the application describes threads and flutes that spiral in a clockwise direction about the implant. However, when desired, these threads and flutes may also be configured to spiral in a counter clockwise direction about the implant. 
     Although the openings arranged in the wall of the hollow base portion  13  are shown in the circular shape in  FIGS. 1A and 1B  and the form of slots in  FIGS. 2A and 2B , generally the opening can have any desired shape and be distributed along the wall&#39;s surface in any fashion. Examples of the shape suitable for the openings include, but are not limited to, oval, polygonal, semi-circular, D-shape, and various combinations thereof. Preferably, the area of the openings in the wall of the base portion is in the range of about 50% to 60% of the total area of the wall. 
     It should be understood that the dental implant of the present invention is not limited to medical treatment of a human body. It can be successfully employed for medical treatment of animals as well. 
     Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. 
     It is important, therefore, that the scope of the invention is not construed as being limited by the illustrative embodiments set forth herein. Other variations are possible within the scope of the present invention as defined in the appended claims. Other combinations and sub-combinations of features, functions, elements and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or a related application. Such amended or new claims, whether they are directed to different combinations or directed to the same combinations, whether different, broader, narrower or equal in scope to the original claims, are also regarded as included within the subject matter of the present description.