Bi-cortical dental implant

Details Bi-cortical dental implant Bi-cortical dental implant

2001-08-09

2002-09-17

O'Connor, Cary E. (Department: 3732)

Dentistry

Prosthodontics

Holding or positioning denture in mouth

C433S075000, C433S174000

Reexamination Certificate

active

06450812

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a tooth replacement, which has an implant member, and to the forming thereof.
BACKGROUND OF THE INVENTION
Dental implants are known. Generally, the process of installing an implant is performed in two steps. During the first step, a bore is drilled vertically through the jawbone. The jawbone is formed of a hard, cortical exterior and a cancellous, sponge-like interior. In a sense, the jawbone can be envisioned as hard crest and side plates that encase the cancellous interior. The bore is drilled through the cortical crest and into the cancellous interior. A generally cylindrical implant member is fitted into the bore, so that its top portion reaches the bone crest. The cylindrical implant member may be a bullet-like cylinder, which has a smooth surface, and which is press-fitted into the bore. Alternatively, the cylindrical implant member may have screw threads around its external surface so as to self-tap its way into the bore. The implant member includes a support structure, for example, a threaded cervix, for supporting a dental prosthesis. During the first step, the cervix is sealed. The bone is then allowed to heal, as the cancellous interior grows around the implant. Often, the implant member is coated with a bone-growth enhancing material, to induce the healing process, which may take several months. During the second step, after healing, the sealant is removed from the support structure of the implant member, and a second member, a dental prosthesis having a crown, which serves as an artificial tooth, and a post, is secured onto the implant member. The post is preformed or cast individually, for example, as a threaded stud that substantially matches the threaded cervix of the implant member. The crown is then cemented onto the post.
A few of the factors, which determine the success of the implant, are as follows:
1. Depth of the bore: For good anchoring, a relatively deep bore of 10-16 mm is generally required. However, for some people, especially older people, a bore deeper than 5 or 6 mm on the lower jaw may make contact with the mandibular canal. For these people, good anchoring with respect to the cancellous bone tissue cannot be achieved.
2. Bacterial penetration: The penetration of bacteria poses additional risk to the bone tissue, and can also lead to local mortality and implant failure. Generally, when the bone heals around the implant member, and the gingival tissue closes on it, there is no bacterial penetration along the interface between the implant member and the bone. However, when the dental prosthesis is installed, the interface surface between the crown and the post, on the one hand, and the implant member support structure, such as the threaded cervix, on the other hand, is susceptible to bacterial penetration.
3. Trauma to the cancellous bone tissue: Excessive vertical or lateral forces by the implants on the cancellous bone tissue can lead to resorption, a phenomenon in which the density and mass of the cancellous tissue decreases, eroding support for the implant.
U.S. Pat. No. 5,611,688 to Hanosh describes a tooth replacement with an expanding implant member. The inserted, or distal portion of the implant member is arranged to expand outwardly into the surrounding cancellous bone.
U.S. Pat. No. 5,951,288 to Sawa describes a tooth replacement with an implant member formed of a shape-memory alloy which is maintained at a cool temperature for easy and non-traumatic insertion. Once in place, the implant member warms to body temperature and expands to anchor itself within the cancellous bone.
U.S. Pat. No. 6,015,294 to Lauks describes a tooth replacement with an implant member having a relatively short cylindrical section and a plurality of wedges extending from the distal portion of the cylindrical section and penetrating the cancellous bone.
These patents, while claiming to solve prior-art problems, still rely on anchoring of the implant member with respect to the cancellous bone, and are generally too deep for those people for whom there is a risk of contact with the mandibular canal or the sinus cavity.
U.S. Pat. No. 5,702,346 to Lazzara describes a tooth replacement with an implant member having a width that is substantially the same as the distance between the cortical plates at the site of installation, so that when the implant member is installed, it is anchored with respect to the cortical plates. However, in general, the bore in the bone is not symmetric, with respect to the two cortical plates, so it is nearly impossible for the center of the bore to be at equal distances from the two cortical plates. Therefore, there may be situations in which Lazzara's implant member is anchored only with respect to one cortical plate, causing an unbalanced load distribution. Furthermore, there may be sections of the bone where the cortical plates close in, and the distance between them narrows. These sections are called undercuts. If an implant member is forced passed undercuts, the cortical plates may crack or puncture.
U.S. Pat. No. 3,981,079 to Lencyzycki describes a tooth replacement wherein the implant member has at least one pre-formed partially threaded lateral channel and is anchored with respect to the buccal cortical plate with at least one lateral screw. The implant member may be hollow or solid. For example, the implant member may be a hollow cylinder, and the partially threaded lateral channel may be two orifices on opposite walls of the cylinder. The distal orifice, with respect to the operator and the buccal cortical plate, has an internal thread, and the proximal orifice has a smooth internal surface, but with a diameter that is slightly larger than that of the distal orifice. Generally, the lateral screw is threaded, self-tapping its way into a lateral channel in the buccal cortical plate and a portion of the cancellous bone tissue. The lateral screw passes freely through the proximal orifice and is threaded into the distal orifice. The lateral screw then advances into the bone, beyond the distal orifice, self-tapping its way through the cancellous bone tissue. Thus the lateral screw is anchored with respect to the buccal cortical plate and with respect to the distal, threaded orifice, but not with respect to the lingual cortical plate.
This arrangement suffers from several drawbacks. Anchoring the implant member with respect to only one cortical plate creates an unbalanced, asymmetric load distribution on the jawbone. In addition, since the cortical plates are wood-like, having little elasticity, the fact that the lateral screw is threaded into both the implant member and the buccal cortical plate prevents re-adjustment and settling of the implant member and may lead to cracking of the cortical plate. The desirable situation is that which maintains the implant member in place, while providing some elasticity for re-adjustment.
U.S. Pat. No. 5,797,741 to Bombard et al. describes a tooth replacement with a solid implant member having a lateral key, whose function is similar to that of the lateral screw in U.S. Pat. No. 3,981,079, hereinabove. In a first embodiment, the lateral key is smooth and cylindrical, for easy insertion, and is arranged to pass through lateral channels, drilled in advance in the jawbone, and through the implant member. The lateral key is thus anchored with respect to the two cortical plates, and load distribution is generally symmetric on the jawbone. However, the tooth replacement described by U.S. Pat. No. 5,797,741 is applicable to the anterior portion of the mouth and would be difficult to install in the posterior portion.
The use of a smooth lateral key has some additional drawbacks:
1. For its insertion, the lateral key is tapped with a mallet, from the buccal side, into the channel drilled in the buccal cortical plate, through the implant member, and into the channel drilled in the lingual cortical plate. The tapping may cause a crack or an incipient crack in the lingual cortical plate. Such a crack is unlikely to be detected; yet it may lead to a lo

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