Improved submergible screw-type dental implant

Technical Field

This invention relates to dental implants and, more particularly, to submergible screw-type implants.

Background Art

Screw-type implants are well known in the art. U.S. Patent No. 3,499,222 of L. I Linkow et al. discloses screwtype implants which may be buried in the alveolar ridge crest bone of a patient in an edentulous region. The implant has a threaded lower portion which may be screwed into an opening created in the bone after the tissue has been displaced. A coronal portion protrudes above the bone and is used to support an artificial dental appliance, e.g. an artificial tooth or bridge.

In more recent year's submergible implants have been created in which the threaded portions of the implants can be completely embedded in the bone. They may then be covered with tissue and allowed to remain in place while new bone grows around the implant and through vent holes in it. Once it is firmly anchored in new bone (3 to 6 months), the tissue is reopened and an upper post portion is screwed into the implant portion and is used to mount the artificial dental device.

GB-A-2 119 258 discloses an implant having having a cilindrically shaped body with at least one vent extending part way into the implant body and having has threads over at least part of its exterior surface for threading into an opening in the bone of a patient. The lower end of the body of this prior art implant is hollow and creates an open interior cavity. Self-tapping threads are located over the outer surface of the cylindrical implant body. The implant body is adapted to be completely buried in the bone of the patient and has an upper section opposite its base which may be engaged by a tool to rotate the implant body into place in the bone. In addition an abutment may be supported on the implant and an artificial tooth may in turn be supported on the abutment. The self-tapping threads of this known implant cause it to be well anchored in the bone and the vents also allow new bone to grow through and into the center cavity to improve the anchoring effect. But when screwing the implant into the bore in the bone the small chips of bone shaved off by the screwing action of the self-tapping threads of the implant body are squeezed between the threads of the body and the surrounding bone which lowers the cutting effectiveness of the threads and causes increased forces necessary to thread the implant into the bore. Also the bone chips created during the self-tapping operation and having the ability to promote faster bone growth because of their autogenous nature, cannot be deposited into the bore and therefore cannot exert a positive influence on new bone growth there.

In the article "Osseointegrated Implants in the Treatment of the Edentulous Jaw" by P.-I. Branemark et al., Stockholm, 1977, Fig. 16 discloses an implant portion of an apical cutter type having a cylindrically shaped body with a cutter at its distal apical end that is adapted to tap into the bone of the base of an opening in the jaw bone. In order to install such implant a bone tap must be used to thread the bone. Thereafter the implant is installed and, as the apical end reaches the bottom of the opening, it taps into the base of the opening to anchor that end. However, when this known implant has been installed the anchoring effect is not always completely satisfactory.

The same article additionally discloses in Fig. 18 an implant portion having threads over its entire length and some channels extending in axial direction over a distal end portion of the implant. However, there is no mention of any self-tapping effect of the threads and also no explanation of the particular purpose of the channels. It is likely that these channels are for the purpose of relieving pressure when the implant is screwed into place and taps blood and other fluids in the opening. As Fig. 18 of this article and the corresponding text fail to state or even suggest any self-tapping action in respect to this implant, it is believed that this known implant also needs an already threaded bore before it can be installed.

Another implant of the apical cutter type is described in "Osseointegration and its Experimental Background" by P.-I. Branemark ("Proceedings of the Toronto Conference on Osseointegration in Clinical Dentistry", September 1983) in Fig. 8 and the corresponding text. This implant is provided with 4 channels extending only over its apical portion. The operation and function of this implant is that of a cutter type with a cuffing end threading action only as the apical end reaches the bottom of the opening. Therefore the opening must again be tapped by a separate tool or bone tap before installation of this implant.

L.I. Linkow and R. Cherchève describe in "Theories and Techniques of Oral Implantology" (Saint Louis, 1970, pages 1, 2, 9 and 157) an implant portion having the features set out an the pre-characterizing part of Claim 1. It is provided with a channel extending longitudinally and through all threads in the implant body. The channels form V-shaped sluiceways, are open at their ends to the upper as well as to the lower section of the implant portion and permit the chips to discharge from and between the threads as the implant is inserted, to enter into and to help fill the channel cavity. Due to the fact that these channels are also open towards the upper section of the implant portion, forces directed upwards and exerted onto the chips in the channel during insertion will cause the chips to be transported upwards in the channels. In this article it is furthermore mentioned that the threads are self-tapping because the spiral portion of the implant is solid and unusually strong. For mounting these implants are forced into openings in soft cancellous bone and essentially crush the bone during insertion. They create trauma to the bone and do not adhere to it very well.

It is advantageous when installing an implant portion in the patent's bone, if the implant is self-tapping in a bore created in the bone. This causes it to be anchored better. Also, it would be advantageous if the bone chips created during a self-tapping operation were deposited into the bore or opening because these chips promote faster bone growth because of their autogenous nature.

Disclosure of the invention

This object can be achieved by the features set out in the second part of claim 1.

The above disadvantage of the known art has been completely overcome by the invention according to claim 1. The provision of at least one-channel extending through said threads on the implant body, being terminated below the uppermost threads, being formed such that it directs bone chips towards the base portion in the bone during insertion and having a serrating edge at a right angle to the circumferential direction of the threads ensures an effective transport of the chips of bone created during the cutting operation, away from the thread engagement into the channel and towards the base of the bore where they can be well deposited and contribute to the desired new bone growth.

Preferred features of the invention are set out in the sub claims .

In order to align the artificial tooth or other dental devices with the other teeth of the patient, it may be necessary to have the post portion at an angle to the implant portion. This may be accomplished by bending the post portion so that its head is at an angle to the threaded shaft. This bending may be accomplished before the post is threaded into the implant portion or afterward. If the post is bent before attachment to the implant, the proper alignment is difficult to achieve. If bent after attachment, there is a danger that too much stress will be put on the implant portion and it will loosen in the bone and fail. Also bending the post may fatigue the metal of the post and cause breakage.

The present invention is directed to a dental implant which, in its preferred form, is of the submergible screw type with a longitudinal channel or slot through the threads so as to improve their self-tapping ability. The implant also has an angled swivelable connector to allow the post for supporting an artificial dental appliance to be positioned in proper alignment with other teeth in the patient's mouth without applying stress to the implant.

In an illustrative embodiment of the invention, the implant portion of the device includes a threaded region that contains a longitudinal channel through a portion of the outer parts of the threads. The channel is wider toward its bottom. One side of the channel is at a right angle to the implant circumference so as to create a cutting edge that assists in the formation of a self-tapping capability for the implant when it is installed in a bore or opening in the patient's bone. The other side of the channel is at an oblique angle to the circumference.

The channel guides bone chips created during the threading of the implant toward the base of the bore in the bone. By terminating the channel below the uppermost threads, epithelial tissue is prevented from growing down into the bone along the channel.

The post or abutment portion of the implant which supports an artificial dental appliance may be a straight portion on to which the appliance is threaded. However, in situations where it must be at an angle to the implant portion, the abutment may be a separate piece from the implant portion and may be attached thereto at an angle by means of a connection portion of the abutment. The connection portion may be in the form of a rotatable beveled collar, a ball and socket joint, or other suitable means that allow the post to swivel about the axis of the implant portion and/or to assume various angles with respect to that axis. Once in place, means are provided for securing the abutment against further movement with respect to the implant portion. As a result the implant can assume a desired angle to assure proper alignment of the artificial dental structure with the other teeth of the patient along the occlusal plane.

Brief description of the drawings

The foregoing and other features of the present invention will be more readily apparent from the following detailed description and drawings of illustrative embodiments of the invention, in which: <ul id="ul0001" list-style="none" compact="compact"><li>Fig. 1 is a schematic cross section of the side of a patient's face showing the alveolar ridge crest with a screw type implant according to the present invention installed therein;</li><li>Fig. 2 is an enlarged view of an illustrative embodiment of the implant portion of the device of Fig. 1 with an external hex projection this embodiment does not comply with the language of claim 1 insofar as the channel is required to terminate below the uppermost threads;</li><li>Fig. 3 is a top view of the implant portion of Fig. 2 showing the external hex portion;</li><li>Fig. 4 is a cross-sectional view through the implant portion of Fig. 2 along line 4-4 showing the cross-sectional shape of the channel according to the present invention;</li><li>Fig. 5 is an implant portion of a screw-type implant according to the present invention with an internal hex recess;</li><li>Fig. 6 is a illustrative embodiment of a completed screw-type implant with an angularly positioned threaded shaft attached thereto;</li><li>Fig. 7 is a cross-sectional view of a ball and socket connection portion of an abutment according to the present invention;</li><li>Fig. 8 illustrates a further modification of the ball and socket joint of Fig. 7;</li><li>Fig. 9 illustrates a further modification of the ball and socket joint of Fig. 7;</li><li>Fig. 10 is a ball and socket joint connection portion with a stationary ball;</li><li>Fig. 11 is a side view of a healing collar according to the present invention; and</li><li>Figs 12 and 13 are front and side sectional views of an artificial tooth with an abutment according to Fig. 7.</li></ul>

Description of Illustrative Embodiments

The present invention contemplates at least a two part screw-type dental implant, i.e, an implant portion 10 which is buried in the bone of the patient and a post or abutment portion 20 which is attached thereto and which supports an artificial tooth structure 30. As shown in Fig. 1, an implant screw portion 10 is located in a bore in the aveolar crest 11 at an angle that causes it to be in the center of the thickest portion of good available bone. The abutment 20 is attached both the implant portion 10 and the artificial tooth 30, and is set so that the tooth is at an angle to the implant which causes the tooth to be in proper alignment.

In Figs. 2 and 3 the screw implant portion 10 of Fig. 2 is illustrated in more detail. This implant portion 10 contains threads 13 which extend over the middle region of the implant portion. These threads may have a flat bottom and be angled up to form a Christmas tree shape in cross section. The lower half of the implant portion 10 contains a cavity 14 (shown in dotted line). Also, spaced about the lower end of the implant are holes or vents 16, 16a and 16b, which penetrate from its exterior to the interior cavity 14. The purpose of these vents is to allow new bone to grow through and into the center cavity in order to firmly anchor the implant in the patient's bone. The upper surface 17 of the implant portion defines a threaded aperture 19 which is used to connect the abutment 20 to the implant portion 10. The projecting structure 12 which forms surface 17 has a hexagonal shape as shown more clearly in Fig. 3. This hexagonal shape allows a tool, e.g. a wrench, to be used to rotate the implant portion so as to thread it into the patient's bone.

According to the present invention a channel 18 is cut through the threads 13 and possibly into the outer casing of the implant portion 10. As depicted in dotted line in Fig. 3 and in cross-section in Fig. 4, the channel 18 is one of three channels 18, 18a, 18b in a typical implant portion. These channels are made to intersect the respective vents 16, 16a and 16b which are spaced at angles of 120° about the circumference of the implant portion 10. The channels do not extend completely toward the upper surface 12 in order to prevent tissue from growing down along the channel, and to prevent the incursion of food and bacteria. It should be particularly noted in Fig. 4 that the channels 18 have one edge which is at about 90° to the circumference of the implant, i.e. surface 18', and another more obliquely shaped edge, i.e. surface 18''.

During installation of the implant, an incision is made in the gum tissue of the patient and the underlying bone is exposed. Then a drill or burr is used to make an opening or bore hole in the bone which is slightly larger in diameter than the implant portion body 10, but which is not as wide as the threads 13. A wider counterbore may be provided to accommodate a protection collar as explained subsequently. Next the implant is inserted up to the first thread in the opening in the bone. A tool, such as a wrench, is used to engage the hex portion 12 and to rotate the implant. The threads 13 are made to be self-tapping so that the implant portion will begin to screw down into the patient's bone. If necessary, a bone tap can be used to create grooves in the hard upper cortical bone prior to insertion of the implant portion. The right angle surface 18' of the channel also has self-tapping properties so as to ease the insertion of the implant, once it has reached the depth of the channels 18. Further turning of the implant causes the right angle surface 18' to scrape off bone as the implant is being threaded and to push the resulting bone chips forward. This causes the bone chips to fall through the channels 18 are made wider towards the vents 16.

As a result of this structure, bone chips created during the implant procedure tend to accumulate at the base of the implant in the patient's bone. Because of the autogenous nature of these bone chips they promote the growth of new bone in the area and speed the formation of new bone around and through the implant such that it is anchored in place more rapidly.

In Fig. 5 there is shown an implant portion 10 which is nearly identical to that shown in Fig. 1. The principle difference is that, rather than having a hexagonal projection useful for applying torque to the implant, a hexagonal recess 12ʹ is provided. In addition, the threaded aperture 19' is made somewhat smaller and is located at the base of hexagonal recess 12'. As explained previously, the threaded aperture 19' is used for attaching the implant portion of the device to the abutment portion. One embodiment of such an attachment is shown in Figure 6.

In Figure 6 the upper part of the implant portion 10 is shown partly broken away and partly in section. It is shown partly broken away to exhibit the interior cavity 14 and the threads 13. Towards the upper part of the implant portion it is shown in cross section. This implant portion is like that shown in Fig. 5 with a hexagonal recess 12' for rotating it into position in the bone. As shown in Figure 6 the screw type implant portion 10 is connected to an abutment portion 20 that includes a transitional collar 21, an angled threaded shaft 24, and a tooth support cylinder 31. The threaded shaft 24 has its lower end screwed into threaded aperture 19' in the implant portion 10. The upper end of the threaded shaft, which is set at an angle to the lower end, is received within a threaded aperture 35 in tooth support cylinder 31. This cylinder 31 contains a recessed portion 32 which may be utilized in fixing on to the cylinder via cement or some other convenient and well known method, a porcelain, plastic, or other dental tooth-colored veneering material in the form of an artificial tooth.

The transitional collar 21 is located between the upper end of the implant portion 10 and the cylinder 31. This collar has an angled upper surface 25 and a perpendicular lower surface 23. The angle of the upper surface is made to equal the angle of the upper part of the angled shaft 24. While collar 21 surrounds threaded shaft 24, it does not engage its threads.

During an installation procedure the implant portion 10 is located in the patient's bone as previously described. The gingival tissues can then be replaced over the implant portion and several weeks or months allowed to pass while new bone grows around and through the implant portion. However, alternatively the artificial tooth can be connected to the implant immediately. Whichever manner is chosen, the attachment is accomplished by selecting an angled shaft and transition collar which have an angle which will cause the artificial tooth to be correctly aligned with the other teeth of the patient. Therefore the dentist or oral surgeon must be provided with a variety of such shafts and collars which are at standard angles. Also during the insertion procedure the surgeon must appropriately angle the opening in the bone so it penetrates a reasonably thick area of good bone. This may require that the opening in the bone be drilled at an angle in order to avoid penetrating a nearby sinus cavity, passing completely through the bone, or contacting a nerve bundle. However, in selecting the angle at which the implant is buried, care must be taken to make sure that this angle will accommodate one of the standard angles available with the threaded shafts and collars, e.g. 10, 20 or 30 degrees, so as to result in alignment between the new artificial tooth and the remaining teeth of the patient.

Once the threaded shaft 24 is engaged with the implant portion 10, the collar 21 is slipped over the free end of the shaft. Then the shaft is rotated so that it is firmly secured in the implant portion and is extending in the proper direction. With the collar in place over this shaft, the cylinder portion 31 is threaded over the open or free end of the shaft until it makes tight contact with the upper surface of the collar and begins to squeeze the collar between the cylinder and implant portions. Notches and recesses 22 and 27 are provided in the mating surfaces such that, once the parts are screwed together, these notches and recesses engage each other and prevent unintentional unscrewing of the portions of the implant. With this firm attachment completed, the artificial tooth can then be attached over the abutment cylinder 31.

In Figure 6 the level the patient's bone is shown as dotted line 70. Since the implant portion is submerged in the bone, the line 70 intersects the lower portion of the transitional collar 20. The gum tissue line 72 is towards the upper portion of the transitional collar. As a result the collar acts a barrier to prevent the encroachment of bacteria and food into the interior portion of the collar and the hex recess of the implant portion.

With the embodiment of Figure 6 fixed angles are provided to the dentist and he must work with the standard angles and the angle which he creates for the bore in the patient's bone, in order to assure proper alignment of the teeth. In some patients who have had serious bone disease, the amount of available good bone is limited and the dentist has only a limited amount of freedom in selecting the angle at which the bore for the implant is made. Also with the embodiment of Figure 6 it is necessary for a dentist to keep a stock of various angled shafts and collars. The difficultly presented by the type of implant in Figure 6 is overcome by the implant shown in Figure 7.

In Figure 7 the angled shaft and transition collar are replaced with a ball and socket joint which allows for the setting of the angled relationship between the implant portion and the abutment portion at any selected angle within the range of motion of the ball and socket joint, e.g. up to 30-40 degrees. In Fig. 7 the threaded cavity 19 receives the threaded shaft of a lower or inner abutment casing 42. This casing has a generally Y-shape with the lower portion being the shaft that extends into and engage the threads of cavity 19. The upper portion of casing 42 has a hemispherical surface 45 such that it can receive a ball 46. An upper or outer casing 44 screws onto outer threads of the inner casing 42 such that ball 46 is trapped within the abutment casing, but is free to rotate therein so as to create a ball and socket joint.

A relatively large set screw 48 penetrates the ball completely. This set screw 48 has an internal threaded cavity 55 which passes through an upper hexagonal projection 56. Once the implant portion 10 has been located in the bone at the optimal angle, the ball 46 is rotated such that the center axis of the set screw is at the proper angle for mounting of an artificial tooth in line with other teeth in the patient's mouth. Then the hexagonal portion 56 is rotated with a wrench or other tool so the set screw comes into extreme frictional contact with the hemispherical surface 45 of inner casing 42. This prevents further rotation of the ball and the set screw.

The artificial tooth structure in the embodiment of Figure 7 has an interior cylinder 50, about which the porcelain, plastic or other dental material is formed to create the artificial tooth structure. This cylinder 50 with the artificial tooth structure mounted thereon, is placed on top of the hexagonal projection 56 and is then attached thereto by means of a screw 52 which passes through the cylinder 50 and into the threaded aperture 55 in set screw 48.

The bone line 70 is shown in Figure 7 as being approximately mid-way through the lower abutment casing 42, while the gum line 72 is just below the upper edge of the outer or upper casing 44. Thus, the bone does not interfere with the setting of the proper angle for the abutment and the tissue is not likely to contact moveable adjustment parts.

The arrangement of Figure 8 is a modification of that shown in Figure 7. In this arrangement the set screw 48, which has a threaded recess 55 at its end in Fig. 7, is replaced with a set screw 49 that has a further screw thread 59 on the opposite side of the hex projection 56. This additional screw thread is used to mount an artificial tooth support cylinder 53 which has an interior threaded cavity. However, this device is essentially located and fixed in position in the same manner as the implant of Figure 7. One difference with this implant of Figure 8 is that the artificial tooth support cylinder 53 may extend down to and in contact with the outer casing 44. This is done above the gum tissue line 72 as shown in the figure. Because of the contact between the cylinder and the casing 44, food and bacteria are prevented from entering between these two parts and the likelihood of infection is reduced. However, this arrangement allows for somewhat less range of angular adjustment. In particular the arrangement of Fig. 7 is capable of an angular adjustment range of approximately 37 1/2°, while that of Fig. 8 is limited to about 30°.

As a further alternative, the set screw 48, rather than having a projecting threaded portion located above the hexagonal adjustment nut 56, may have a projecting cylinder which is internally threaded (not shown). Thus either a male or female connection of this type may be used without difficulty.

In order to get increased angular adjustment, an arrangement such as that shown in Fig. 9 may be used. The abutment arrangement of Figure 9 is essentially the same as that of Figure 7; however, the ball and socket joint are made smaller and the ball sits higher in the socket joint. Further, the set screw 54 of Fig. 9 is made to have a beveled surface 57 such that a greater angular rotation may be made before it contacts the upper part of the outer casing 44. With this arrangement nearly 45 degrees of angular adjustment can be achieved.

The abutment cylinder 50 has a recess 51 to receive the outer end of the set screw 54. This allows for greater stability when it is attached to the set screw by means of attachment screw 52. The cylinder 50 is also angled in the same manner as the surface 57 of the set screw 54 so that it does not bind against the upper abutment casing 44 and limit angular rotation.

In Fig. 7-9 the ball rotates with the set screw during angular adjustment. However, as an alternative, the ball may remain stationery and the abutment casing may rotate as shown in Figure 10. In Figure 10 a threaded ball joint 60 has a projecting threaded shaft 61 which is received in threaded recess 19 of the implant portion 10. Various size protection washers or collars 65 can be located about the finial part 67, which connects the ball to the threaded shaft, in order to cover the upper surface of whatever implant portion is used, thereby preventing bacteria and food from entering the bore. The opening in the bone can be countersunk as indicated by dotted line 70 so the collar can extend out beyond the implant portion upper surface, and bone can grow over part of the upper surface of the collar.

A two-part casing 62, 64 is mounted on the ball 60. The casing includes outer casing portion 62, which secures the remote end of the ball, and an inner casing 64, which provides the main hemispherical surface against which the outer casing holds the ball in a rotatable manner. These two casing parts can be threaded together or attached to each other in any convenient manner. Their attachment, however, is such that the casing may rotate freely on the ball.

At the opposite end of ball 60 from the screw threads is a hexagonal recess 63, which is the means by which this threaded ball joint is screwed into the threaded recess 19 of the implant portion. In this arrangement the gum line 72 is shown about 1/3 up from the base of the ball joint, but below the lower extension of casing 62.

A hexagonal projection 66 is provided on the inner casing 64. This projection can be used to rotate the inner casing 64 so that the ball is squeezed between it and the outer casing 62 so that swiveling can be prevented when the arrangement is at the proper angle. A conventional cylinder 50 for a dental prosthesis is attached to the inner casing 64 by means of a screw 52. This screw 52 penetrates a threaded aperture in the inner casing.

Installation of submergible implants is generally a two stage procedure. During the first stage the implant portion is buried in the bone and the tissue is restored in place over it. Time is allowed to pass while new bone grows about, and often over, the implant. The tissue is then reopened at the start of the second stage. If bone has grown over the submerged implant, it must be removed by a burr before the abutment can be installed. If the bone grows into the threaded aperture for the abutment, however, removal of this bone may be very difficult. Consequently, it is conventional to install a thread cap having a low height into the aperture during the first stage. However, bone also grows over this cap and it must be removed in order to replace the cap with the abutment. Removal of such bone may cause some loosening of the implant portion.

With the present invention, the collar 65 is used with a screw 68 as a temporary cap as shown in Fig. 11. Even if bone grows up over the edges of the collar 65, there is no need to remove it because it becomes part of the permanent abutment. In particular cover screw 68 is removed during the second stage operation, which may require the removal of a small amount of bone that has growth over the screw. Then the cover screw 68 is replaced with threaded shaft of abutment ball 60 which has the abutment casings 62, 64 already installed. Thus the collar 65 which is anchored in bone, need not be freed from from the bone as in prior art caps, but becomes part of the final abutment structure.

Figs. 12 and 13 show front and side sectional views of an incisor of a patient which is supported by an implant according to the present invention. As can be seen, particularly from Fig. 13, the patient's upper front jaw bone has only a thin amount of good bone 11 and this bone is at an angle to the regular alignment of the other incisors in the patient's mouth. Utilizing the present invention, implant portion 10 is located in the center of the main portion of this bone. After this implant portion 10 is firmly anchored in good bone, either immediately after its insertion or after several weeks or months have been allowed to pass, the abutment portion is installed. The abutment portion is a ball and socket joint like that in Fig. 7 having a set screw 48 which locks the ball 46 at the proper angle. The cylinder 50 of the artificial tooth support is then attached to the set screw via an attachment screw 52. As shown in cross section in Fig. 13, cast metal 58 surrounds cylinder 50 and a porcelain or plastic dental material 70 forms the tooth structure about the metal.

Besides being used to mount a single tooth, the implants according to the present invention can be used as supports for a permanent bridge or a removable bridge. In the case of a removable bridge the abutment cylinder is in the form of small copings which can be spaced throughout the edentulous span of a patient. These copings support a bar onto which the bridge structure may be screwed or clipped.