Dentistry – Prosthodontics – Holding or positioning denture in mouth
Reexamination Certificate
1999-12-03
2002-04-02
Lewis, Ralph A. (Department: 3732)
Dentistry
Prosthodontics
Holding or positioning denture in mouth
Reexamination Certificate
active
06364663
ABSTRACT:
SCOPE OF THE INVENTION
The invention concerns a tooth implant that can be inserted in the jaw in an operation with a rotationally-symmetrical implant body that has a rough surface, and a method to make the implant.
STATE OF THE ART
Prior-art tooth implants have a rotationally-symmetrical implant body that can be designed as a cylinder or cone or as a stepped shape. The implant body consists of titanium that is very biologically compatible with the bone tissue. The surface of the implant body, such as a coating with hydroxylapatite (DE A 38 39 724), promotes stable healing where it contacts the bodily tissue. It is also prior art that the surfaces of the implant body are exposed to an acidic etching process after the natural titanium oxide layer is removed to attain an essentially uniform roughness over the entire surface (WO 96/16611).
By treating the surface of the implant body, contact with the surrounding bone tissue is made easier, and the participating implant surface is increased. A titanium plasma coating (TPC) is prior art that is created by thermal spraying titanium onto the titanium implant. In addition, a process is used that treats the surface by coarse sand blasting to create macroroughness in the titanium. This process is followed by acid etching that generates evenly-distributed micropits in the sand-blasted surface (Cochran et al., “Bone response to unloaded and loaded titanium implants with a sand-blasted and acid-etched surface”, Journal of Biomedical Materials Research, Vol. 40, 1998, p.1).
The osteons of the bone only collect slightly on the surface of the implant body or not at all. The biomechanical integration of the implant is hindered.
The goal of the invention is to design the surface of the implant to improve the bone deposition and hence achieve long-term biomechanical integration of the implant in the jawbone. The subject of the invention is also a method to produce such a surface.
SUMMARY OF THE INVENTION
According to the invention as defined in claims
1
,
12
and
27
, the surface of the implant body has numerous groove-shaped recesses that follow its lengthwise axis or are at a sharp angle to it.
The histology of bone reveals a lamellar structure that is composed of an outer general lamella with embedded osteocytes that are 2-3 micrometers large, osteons (Havers systems) with special lamella 20-300 micrometers large, intermediate lamellae that contain dead and partially transformed osteons, and an inner general lamella. The osteons are surrounded by collagen that form helically around the Havers channel like a tree structure and are embedded in the bone substance. The osteons are aligned according to the static tasks of the bone.
The invention allows the osteons of the bone to attach to the groove-shaped recesses of the implant surface and grow along the implant. The size of furrows formed by the trough-shaped recesses is adapted to the size of the osteons, and the furrows accept the parts of the osteons that come into contact with the implant. As a result and due to the pressure acting on the implant, compact bone is formed around the implant in the spongiosa area of the bone that better absorbs the forces acting on the implant and provides a stable and permanent seat for the implant.
This effect is reinforced in that there are numerous, small, densely-distributed concave recesses in the trough-like recesses. The concave recesses accept the osteocytes of the bone tissue surrounding the implant and hence support the contact between the implant and bone.
Crosswise groove-like recesses improve the osteon deposition. A first set of grooves is provided that runs in a first direction at a sharp angle to the lengthwise axis of the implant body, and a second set of grooves is provided that runs in a second direction at a sharp angle to the lengthwise axis of the implant body and that cross the first grooves. The trough-like recesses are advantageously close together and have a concave profile whose edges run into the perimeter of the implant body. Such a surface structure offers favorable conditions for osteons to collect during the healing phase and additionally secure against axial shifting and rotation of the implant after healing.
In another embodiment of the invention, the surface of the implant body along its lengthwise axis is divided into numerous sections that are separated by radial bands. The perimeter of the sections has numerous groove-shaped recesses that run in the direction of the lengthwise axis of the implant body or at a sharp angle to it. The bands assume the function of barriers during the healing and healed stages against any foci descending from the head of the implant. The diameter of the sections can differ and decrease stepwise toward the bottom end of the implant body. The diameter of the implant body narrows in the area of the radial bands. Likewise, the surface structure of the sections can also differ. These features essentially contribute to a fixed seat for the implant in the jawbone and offer favorable conditions for the deposition of osteons in the grooves of each of the sections.
A procedure to manufacture a tooth implant according to the invention provides that numerous groove-shaped recesses that run along the lengthwise axis are created in the surface of the implant body by a material removal process in one of the smooth implant bodies preformed into the desired shape. The material removal process is advantageously carried out by a digitally-controlled laser beam. Instead of a laser beam, a focused ion beam can be used. Alternately, the material removal process can also be carried out by a precision milling machine.
In another step, troughs or “lagoons” are introduced into the surface of the implant body that are small in comparison to the groove-shaped recesses. This step can consist of acid etching. The head and in certain cases the foot of the implant can be covered with an acid-resistant coating. A digitally-controlled laser beam can also be used to introduce the troughs or lagoons so that the same material removal process can be used to create both the groove-shaped recesses and troughs or lagoons.
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Cochran, D.L. et al.; “Bone response to unloaded and loaded titanium implants with a sandblasted and acid-etched surface: A histometric study in the canine mandible”; Journal of Biomedical Materials Research, v. 40, 1998, pp. 1-11, John Wiley & Sons, Inc.
Kudirka & Jobse LLP
Lewis Ralph A.
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