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Fixture

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20120264084 patent thumbnailZoom

Fixture


The present invention relates to a fixture for insertion into a bore hole arranged in bone tissue, comprising a threaded leading portion and a threaded trailing portion located coronally of the leading portion.

Inventors: Stig HANSSON, Anders HALLDIN
USPTO Applicaton #: #20120264084 - Class: 433174 (USPTO) - 10/18/12 - Class 433 
Dentistry > Prosthodontics >Holding Or Positioning Denture In Mouth >By Fastening To Jawbone >By Screw

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The Patent Description & Claims data below is from USPTO Patent Application 20120264084, Fixture.

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TECHNICAL FIELD

The present invention relates to a fixture for insertion into a bore hole arranged in bone tissue, the fixture comprising a threaded outer surface for engagement with the bone tissue.

BACKGROUND OF THE INVENTION

A frequent way today to restore a damaged limb, such as lost tooth, is to install a fixture in the adjacent bone tissue and replace the damaged parts. In this respect, for a successful result, the fixture should become fully stable and correctly joined to the bone. The term osseointegration is used for this joining effect, the basic meaning of this term being the bone tissue growth into the fixture surface. The two major contributors to this joint are a mechanical joint and an organic joint. The former being generally influenced by the macro geometry of the bore into which the fixture is installed, and by the macro geometry of the fixture, and is a direct effect of how well these two work together. The latter one being a continuously evolving and developing effect, particularly during the time immediately after installation, and being generally influenced by how well the micro surface structure of the fixture interacts with the bone tissue.

Due to ingrowth there will be an interlocking effect between the bone and the fixture. Also, the mechanical joint is developed over time since the bone tissue, under ideal conditions, may grow into surface cavities of the fixture, and grow into voids left between the fixture and the bore after installation.

It is furthermore relevant to obtain both a good initial (primary) fixation and a good long-term fixation of the fixture in bone.

There is a continuous endeavour in the industry to further increase the stability of fixtures implanted in bone tissue and to improve the basic conditions during the healing phase after fixture installation. One example is the provision of the fixture surface with different types of structures, such as micro-roughened or blasted structures for increasing the contact surface between the fixture and the bone.

Nevertheless, there is still room for further development of fixtures as regards their stability in bone tissue.

SUMMARY

OF THE INVENTION

An object of the present invention is to provide a dental fixture which has a high stability during the healing phases of the fixture. This and other objects, which will become apparent in the following, are accomplished by means of a dental fixture as defined in the accompanying claims.

According to a first aspect of the present invention, a dental fixture for insertion into a bore hole arranged in bone tissue is provided. The dental fixture comprising a threaded leading portion and a threaded trailing portion located coronally of the leading portion,

wherein the threading of the leading portion has at least one first thread spiral,

wherein the threading of the trailing portion has at least one more thread spirals than the threading in the leading portion,

wherein the threading of the trailing portion and the threading of the leading portion have the same or substantially the same lead,

wherein the profile of at least one of the thread spirals in the trailing portion is, at least along a portion of its extension, substantially the same as the profile of the outermost part of said first thread spiral in the leading portion, and

wherein the at least one thread spiral in the trailing portion having substantially the same profile as the outermost part of said first thread spiral in the leading portion is arranged to follow the spiral path of said first thread spiral.

A dental fixture being provided in the manner described above will provide both a good primary fixation and a good long-term fixation of the fixture in the bone.

By profile of the thread is meant to understand the contour or outline of the thread. Hence, for two threads to have substantially the same profile, the characteristics defining the outer contour of the thread should be similar to each other.

With outermost parts of a thread spiral is meant to understand a part of the thread spiral from the top of the thread towards the thread bottom. The amount of the thread belonging to the outermost part may vary. It may in fact, in those cases where the minor diameter of the macrothreaded section and the microthreaded section is the same, be the entire thread. However, when the minor diameter of the microthreaded section is larger than the minor diameter of the macrothreaded section, the entire macrothread will not be considered to be the outermost part. Instead, the portion of the macrothread belonging to the outermost part is the portion being situated further away from the central axis of the implant, as compared to the distance between the central axis of the implant and the minor diameter of the microthreaded portion. Furthermore, there exist embodiments where there is a curved transition between the threads, i.e. the thread has a bottom radius. In those embodiments, the outermost part of the macrothread is considered to be the part of the macrothread being situated further away from the central axis of the implant than the bottom radius portion of the microthread.

When the fixture is inserted into a bore, said first thread of the leading portion will either create a path in the case of a self-tapping fixture or follow a path in the case of a pre-tapped hole through the cortical bone and into the cancellous bone. Since one of the thread spirals in the trailing portion is synchronized with said first thread spiral in the leading portion, the thread spiral in the trailing portion will follow the same spiral path through the bone.

By providing at least one of the thread spirals in the trailing portion, i.e. the thread spiral following the path of said first thread spiral in the leading portion, with a similar or substantially the same geometrical profile as said first thread spiral in the leading portion, at least along a portion of its length, the female threading in the bone will be filled with threads throughout the length of the fixture, or at least for the portions where the profiles are substantially the same. Hence, the fixture will be supported by thread spirals being in contact with the bone throughout at least a large portion of the length of the implant.

The thread spirals in the trailing section are primarily engaged with the hard cortical bone once the fixture has been inserted. By providing more thread spirals at the trailing section, the area of the threads being engaged with the bone increases, as compared to a section having fewer thread spirals. This may be beneficial in terms of improving the initial stability of the implant in the bone.

It may for certain embodiments be an advantage with not providing the entire thread spiral with a thread having substantially the same profile as the first thread spiral. The potential advantage is that it provides for the possibility to e.g. create blood chambers or condensation of the bone at selected positions along the implant. According to one exemplary embodiment, the thread profile is provided so that blood chambers become positioned substantially on the coronal side of the threading. By this, the threads will be in contact with bone on their apical side, hence providing support for the implant when it is impacted by forces from e.g. chewing.

According to one exemplary embodiment, the thread spiral following the path of said first thread spiral in the leading portion has substantially the same profile as said first thread spiral in the leading portion along its entire length. By this, the path of the female threading in the bone in which the thread at the leading portion travels will be filled with threading throughout the length of the fixture. Hence, the fixture will be supported by thread spirals being in contact with the bone throughout the length of the implant. This provides for a good initial stability and a good ability to carry loads and distribute these loads to the bone in a beneficial manner.

The thread spiral following the path of said first thread spiral in the leading portion may, but need not be, continuous with the first thread spiral in the leading portion. Furthermore, the leading and trailing portions of the implant may, but need not be, positioned adjacent each other. It is for example conceivable with another threaded portion between the leading and trailing portion. It is also conceivable with a non-threaded surface between the leading and trailing portion. The non-threaded surface may e.g. be smooth or roughened.

According to at least one exemplary embodiment, the thread spiral in the trailing portion that follows the path of said first thread spiral in the leading portion has the same radius of curvature at the top of the peaks as said first thread spiral. The radius of curvature at the top of the peaks is a geometrical characteristic that influences the profile of the thread.

According to at least one exemplary embodiment, the thread does not have a curvature at the top of the peak. Instead, the top may have a straight extension.

According to at least one exemplary embodiment, the thread spiral in the trailing portion that follows the path of said first thread spiral in the leading portion has the same flank angles, respectively, as said first thread spiral. The flank angles are a geometrical characteristic that influences the profile of the thread.

The flank angle at the apical side of the thread may be similar to the flank angle at the coronal side of the thread. It is however also conceivable with different flank angles at the apical and coronal sides of the thread. The thread spiral in the trailing portion that follows the path of said first thread spiral in the leading portion has the same flank angles, respectively, as said first thread spiral. Hence, in this embodiment the coronal flank angle of the two threads is the same, and the apical flank angles of the two threads are the same, even if there may be different angles at the coronal and apical flanks, respectively.

According to at least one exemplary embodiment, the flanks of the threads have a straight extension.

According to at least one exemplary embodiment, the flanks of the threads have a curved extension. It is for example conceivable with flanks having a concave curvature. It is also conceivable with flanks having a convex curvature.

The different characteristics defining the profile of the thread that have been mentioned above for different exemplary embodiments may of course be combined in any suitable manners.

According to at least one exemplary embodiment, all thread spirals in the trailing portion have substantially the same profile as the outermost part of said first thread spiral in the leading portion. In this embodiment, all threads in the trailing portion are similar to and has the same thread profile as the at least one thread in the leading portion.

According to another exemplary embodiment, the profile of the thread spirals in the trailing portion are different from each other, or from one of the other thread spirals in case of more than two thread spirals. Characteristics of the thread spiral defining its profile is e.g. thread height, curvature radius at the top of the thread (if any), flank angle, flank extension, flank curvature, thread width, transition between adjacent threads and major diameter of the implant. By this, it is possible to e.g. provide one thread spiral that creates a blood chamber between itself and the bone, or a thread spiral that creates condensation of the bone as it is being inserted.

According to at least one exemplary embodiment, the profile of one of the thread spirals in the trailing portion, that does not follow the path of said first thread spiral in the leading portion, alters along the thread.

A thread spiral of the trailing portion that does not follow the path of a thread spiral in the leading portion will cut into the bone between the female thread path of the thread spiral or spirals of the leading portion. The thread spirals may be either self-tapping or enter into a pre-tapped bore. It may for certain embodiments be beneficial if the profile alters along the tread spiral or spirals. Characteristics of the thread spiral defining its profile is e.g. thread height, curvature radius at the top of the thread (if any), flank angle, flank extension, flank curvature, thread width and major diameter of the implant. By alternating one or more of the characteristics along the length of the thread spiral it is possible to create e.g. blood chambers between the thread and the bone at certain positions, and to create a tight fit between the thread and the bone at other positions. It is also e.g. possible to create a tight fit between the thread and the bone at certain positions and to create a condensation of the bone at other positions, or to create a fixture which alters between providing blood chambers and condensation of the bone along its length.

According to one exemplary embodiment, more than one thread spiral in the trailing portion has a different or a varying profile along the length of the respective thread spiral. It is not necessary that the characteristics of the thread spirals that vary, varies in the same manner. Hence, one of the thread spirals may e.g. be designed to create blood chambers and one of the thread spirals may e.g. be designed to create condensation of the bone.

According to at least one exemplary embodiment, the smallest spacing between adjacent peaks of the threading in the trailing portion is smaller than the smallest spacing between adjacent peaks of the threading in the leading portion.

When measuring the axial spacing between adjacent peaks, the smallest spacing between adjacent peaks in the trailing portion is smaller than the smallest spacing between adjacent peaks in the leading portion. When measuring the axial spacing between adjacent peaks, the measurement is to be taken between the tops of the peaks and not in the valleys.

If the thread in the leading portion has one thread spiral and the thread in the trailing portion has two thread spirals that are evenly distributed, the axial spacing between adjacent peaks in the trailing portion will be substantially half the distance between adjacent peaks in the leading portion. If the thread in the leading portion has one thread spiral and the thread in the trailing portion has three thread spirals that are evenly distributed, the axial spacing between adjacent peaks in the trailing portion will be approximately a third of the distance between adjacent peaks in the leading portion.

However, there also exist fixtures in which the thread spirals are not evenly distributed. There also exist fixtures being provided with a major thread being provided with minor threads at its top. In these cases, the distance between the major threads should be measured separately, and the distance between minor threads should be measured separately. Hence, one should not mix between the two different thread types in one portion of the fixture when measuring the smallest axial distance.

According to at least one exemplary embodiment, the number of thread spirals in the threaded trailing portion is a multiple integer of the number of thread spirals in the leading portion.

In order to be able to provide a thread spiral in the trailing portion following the path of a thread spiral in the leading portion, it is beneficial if the number of thread spirals in the trailing portion is a multiple integer of the number of thread spirals in the leading portion. Hence, if there is provided one thread spiral in the leading portion, the number of thread spirals in the trailing portion may be two, three, four and so on. If there is provided two thread spirals in the leading portion, the number of thread spirals in the trailing portion may be four, six, and so on. If there is provided three thread spirals in the leading portion, the number of thread spirals in the trailing portion may be six, nine, and so on.

According to one exemplary embodiment, the number of thread spirals in the threaded trailing portion is not a multiple integer of the number of thread spirals in the leading portion. It is possible to provide an implant in which the number of thread spirals in the trailing portion is not a multiple integer of the number of thread spirals in the leading portion, and in which one of the thread spirals in the trailing portion follows the path of one of the thread spirals in the leading portion. This is for example conceivable if the thread spirals are not evenly distributed, i.e. the axial distance between adjacent thread spirals differ from one another, along the length of the implant.

According to at least one exemplary embodiment, the threading in the leading portion has at least a first and a second thread spiral, and wherein one of the thread spirals in the trailing portion follows the path of said first thread spiral in the leading portion.

In those embodiments where the leading portion is provided with two thread spirals, i.e. a double thread, a first thread spiral in the trailing portion may follow the path of the first thread spiral in the leading portion.

According to one exemplary embodiment, a second thread spiral in the trailing portion may follow the path of the second thread spiral in the leading portion. These two thread spirals in the trailing and leading portion, respectively, may also have the same profile so that the female threading in the bone is being filled, thereby providing support for the fixture along the length of the implant.

According to at least one exemplary embodiment, a second thread spiral in the trailing portion does not follow the path of the second thread spiral in the leading portion.

According to at least one exemplary embodiment, the fixture is self-tapping. There exist different manners in how to provide an implant with self-tapping capabilities, it is for example possible to provide the implant with cutting means extending from the apical end into the threaded leading portion. However, it is also possible for an implant to be self-tapping even if it does not comprise any cutting means.

According to at least one exemplary embodiment, the fixture is provided with separate cutting means adapted for cutting a female thread in the bone that corresponds to the profile of at least one of the thread spirals at the trailing portion.

Providing separate cutting means at the trailing portion provides for the opportunity to cut out a female thread for the threading of the trailing portion. By this, the trailing portion may be inserted into the bone with the amount of bone being crushed during insertion being reduced.

The cutting means at the trailing portion may preferably begin at the apical end of the trailing portion, and extend coronally into the trailing portion.

According to at least one exemplary embodiment, the cutting means provided for cutting a female thread in the bone corresponding to the profile of the thread spirals at the trailing portion extends over at least one turn of all thread spirals at the trailing portion. With extending over at least one turn of all thread spirals, it is meant to understand that it extends over an axial length corresponding to the axial extension of one full rotation of the thread spirals. Hence, if the thread at the trailing portion is a double-thread, the cutting means extend over at least both threads, if the thread is a triple-thread, the cutting means extend over at least all three threads, and so on. The cutting means, may, but does not need to, extend over several rotations of each one of the thread spirals. By this, a female thread corresponding to the thread of the trailing portion will be cut in the bone and the bone will thereby not have to be subject to the strong impact that could otherwise be a risk when a thread is pressed into bone that has not been properly prepared.

According to at least one exemplary embodiment, the cutting means provided for cutting a female thread in the bone corresponding to the profile of the thread spirals at the trailing portion is provided to cut a female thread corresponding to both the outer and inner diameter of the thread at the trailing portion. By this, a female thread corresponding to the thread of the trailing portion will be cut in the bone and the bone will thereby not have to be subject to the strong impact that could otherwise be a risk when a thread is pressed into bone that has not been properly prepared.

Furthermore, depending on the configuration of the cutting means in relation to the profile of the thread in the trailing portion, e.g. the shape and minor and major diameter of the cutting means, it is possible to design fixtures in which a desired rate of condensation of the bone occurs. Obviously, a desired rate of condensation may be zero condensation.

According to at least one exemplary embodiment, the depth of the threads in the leading portion is larger than the depth of the threads in the trailing portion. A configuration according to this embodiment has proven to be beneficial in terms of load distribution to the bone, thereby providing for good initial and long-term stability of the fixture.

According to at least one exemplary embodiment, the major diameter of the fixture is similar in both the leading portion and the trailing portion.

According to at least one exemplary embodiment, the major diameter of the fixture is greater in the trailing portion than in the leading portion. By providing the trailing portion with a larger major diameter than the leading portion, a condensation of the bone surrounding the trailing portion will occur when the implant is inserted into the bone, in the case of a straight cylindrical bore hole.



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Device and method intended for holding a prosthesis in dental implantology
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Fixture and a fixture set
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stats Patent Info
Application #
US 20120264084 A1
Publish Date
10/18/2012
Document #
13444975
File Date
04/12/2012
USPTO Class
433174
Other USPTO Classes
International Class
61C8/00
Drawings
10



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