Dentistry – Prosthodontics – Holding or positioning denture in mouth
Reexamination Certificate
1999-08-03
2001-04-24
Wilson, John J. (Department: 3732)
Dentistry
Prosthodontics
Holding or positioning denture in mouth
C433S174000
Reexamination Certificate
active
06220860
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a dental implant for rotation into the bone tissue of a jaw bone of a partially or totally edentulous patient consisting of a body which has an axis of rotation and on which is provided a circumferentially-oriented roughness comprising a series of circumferentially-oriented peaks which are axially spaced apart by troughs and angularly inclined to the axis of rotation.
BACKGROUND OF THE INVENTION
Dental implants of this type are for use as the anchoring members of dental prosthesis. To this end, the dental implant is inserted into a bore-hole drilled into the bone tissue of a jaw bone (maxilla or mandible) at a site where the dental prosthesis is required by rotating the dental implant into the bore-hole. The convention in the art is for the circumferentially-oriented roughness on the dental implant to take the form of a screw thread and in this case the bore-hole will typically be (i) provided with internal threads in advance, or (ii) left un-tapped with the dental implant being provided with a self-tapping capacity, e.g. by the provision of one or more axially-extending cutting recesses or notches in the screw thread.
A superstructure having the prosthetic part of the prosthesis is then secured to the dental implant. The superstructure will typically consist of a spacer or transmucosal component which engages to the dental implant to bridge the gingiva overlying the maxilla or mandible at the dental implant site and the prosthetic part, e.g. a crown, bridge or denture, is then secured to the spacer. There are various other forms that the superstructure can take as is known in the art. For instance, the prosthetic part may be secured directly to the dental implant.
The long-term integrity of the prosthesis is highly dependent on the successful osseointegration of the dental implant with the bone tissue of the maxilla or mandible, that is to say, the remodelling of the bone tissue in the maxilla or mandible into direct apposition with the dental implant. A study on the factors which affect the osseointegration of dental implants was undertaken by Professor Per-Ingvar Br{dot over (a)}nemark and co-workers and the results were published in a book entitled “
Osseointegrated Implants in the Treatment of the Edentulous Jaw: Experience from a
10-
Year Period
”, Almqvist & Wiskell International, Stockholm, Sweden, 1977. It was found by Br{dot over (a)}nemark et al that successful osseointegration depends upon inter alia the use of biocompatible materials for the dental implant, for example titanium and alloys thereof, and the surgical procedure adopted, for example leaving the dental implant unloaded for several months before adding the superstructure.
Dental implants having a circumferentially-oriented roughness have some notable advantages in promoting successful osseointegration with the adjacent bone tissue, a major one being as a result of the fact that the main loads on the dental implant in the clinical situation are axial loads. These dental implants are very well suited to support axial loads and this may be particularly important in the initial stages of the osseointegration process in which it is important that the dental implant is fully stable and as immovable as possible in the bore-hole (primary fixation). One can consider this to be due to the bone tissue growing into the troughs between adjacent peaks of the circumferentially-oriented roughness on the dental implant.
In Applicant's prior International patent application publication WO94/07428 there is disclosed a dental implant consisting of a body which has a coronal end surface, an apical end surface and a generally cylindrical section which extends apically from a position in close proximity to the coronal end surface. The outer peripheral surface of the generally cylindrical section is presented by one or more screw threads each of height no more than 0.2 mm, so-called microthreads. The use of microthreads enables the dental implant to be both tapped and screwed into a bore-hole provided in a jaw bone.
It would be an advantage to provide a dental implant with a circumferentially-oriented roughness which commences close to the coronal end surface of the dental implant as in WO94/07428 but which has a trough-to-peak height greater than that of microthreads.
SUMMARY OF THE INVENTION
According to the present invention there is thus provided a dental implant for rotation into the bone tissue of a jaw bone consisting of a body having an axis of rotation, a coronal end surface, an apical end surface and a generally cylindrical section, the generally cylindrical section having a coronal edge coincident with, or in close proximity to, the coronal end surface and an outer peripheral surface which extends apically from the coronal edge towards the apical end surface, the outer peripheral surface being presented by a circumferentially-oriented roughness comprising a series of circumferentially-oriented peaks which are axially spaced apart by troughs and oriented at an inclined angle to the axis of rotation, the height from the troughs to the peaks throughout the circumferentially-oriented roughness being greater than 0.2 mm.
The advantage of providing a dental implant with a circumferentially-oriented roughness which has a height greater than 0.2 mm at, or in close relation to, the coronal end surface of the dental implant is that when the dental implant is implanted in the bone tissue of a jaw bone the bone tissue adjacent the entry point of the dental implant into the jaw bone will interface with the roughness. Axial loading applied to the dental implant by a superstructure mounted thereon will then be transmitted through this bone-roughness interface and counteract bone tissue resorption at the entry point (marginal bone tissue resorption) which can inter alia undermine the stability of a dental implant.
In an embodiment of the invention such as the one hereinafter to be described the coronal edge of the generally cylindrical section is spaced from the coronal end surface of the body by no more than approximately 4% of the distance between the coronal and apical end surfaces of the body. The coronal edge of the generally cylindrical section may be spaced from the coronal end surface of the body by a coronal section of the body having an outer peripheral surface not presented by a circumferentially-oriented roughness. The outer peripheral surface of the coronal section may be smooth or perhaps roughened such as if the implant were grit blasted or etched to produce micropits.
In an embodiment of the invention such as the one hereinafter to be described the height from the troughs to the peaks throughout the circumferentially-oriented roughness is uniform and preferably approximately 0.3 mm.
In an embodiment of the invention such as the one hereinafter to be described each peak has a pair of opposed flank surfaces and the facing flanks of each adjacent pair of peaks are connected by a curved surface.
In an embodiment of the invention such as the one hereinafter to be described the circumferentially-oriented roughness is formed by one or more screw threads. Alternately, the circumferentially-oriented roughness may be formed by a series of axially spaced-apart circumferential lines of beads with the beads in each line optionally being circumferentially spaced-apart.
In an embodiment of the invention such as the one hereinafter to be described the outer peripheral surface of the generally cylindrical section extends apically from the coronal edge over a major proportion of the distance between the coronal edge and the apical end surface of the body.
In an embodiment of the invention such as the one hereinafter to be described the generally cylindrical section has an apical edge which is spaced coronally from the apical end surface of the body by no more than approximately 20% of the distance between the coronal and apical end surfaces of the body and the outer peripheral surface of the generally cylindrical section extends to the apical edge. The apical edge may be s
Astra Aktienbolag
Bumgarner Melba
White & Case LLP
Wilson John J.
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