Dentistry – Prosthodontics – Holding or positioning denture in mouth
Patent
1995-10-05
1998-06-30
Lucchesi, Nicholas D.
Dentistry
Prosthodontics
Holding or positioning denture in mouth
A61C 800
Patent
active
057724377
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a screw-type securing element, made of titanium, for permanent anchoring in bone tissue, in particular for permanent anchoring of artificial teeth and dental bridges in the jawbone. The securing element has an outer threaded portion which at its far top merges into a smooth conical and/or cylindrical portion. The front part of the screw is preferably provided with one or more recesses whose margins adjoining the circular symmetrical surface of the securing element form cutting edges permitting self-tapping when the element is being screwed into the bone tissue.
BACKGROUND OF THE INVENTION
Screw-type securing elements, made of titanium, for replacing lost teeth have been shown to have many advantages. The outer thread of the securing element provides a natural positive locking in the bone and gives initial stability, and also distributes the load favorably to the surrounding bone tissue. Recent long-term clinical follow-up studies have underlined the fact that threaded securing elements are in this respect more advantageous than the unthreaded ones. The position of the boundary area where the thread merges into a smooth, cylindrical or conical surface is for this reason of great importance with regard to the function of the securing element, i.e. the implant. This position usually determines where, on the securing element, long-term stabilizing of the bone tissue occurs.
To obtain initial stabilizing of the securing element, and to place the latter in a predetermined position, it is already known to have the thread end with a flange. The flange means that there is a possibility of mechanical resistance with increased initial stability and results in more reliable positioning. The initial stability is considered to be important for ensuring incorporation, and the improved positioning in the axial direction affords greater protection against penetration into the nerve channel of the mandible.
The flange also makes it possible for the soft tissue to seal off the oral cavity directly against the fixture, and any bacterial leakage through the spacer piece does not reach the bone level. The flange can thus be regarded as a first part of the spacer system attached to the fixture (or a first part of the implant part penetrating the soft tissue).
However, when the thread is being chased, the flange represents an obstacle to the runout of the thread cutter, for which reason a turned recess is usually formed under the flange to lift the cutter out without damaging the flange. However, this means that approximately one thread turn is lost on the securing element, which leads to the marginal bone height lying correspondingly further down on the securing element. This loss is critical in some cases, since it means that it is not possible to use the outermost bone edge, which normally has the best mechanical properties. It is also important, particularly in the case of thin bone, that the thread be fully used to obtain good initial stability of the implanted securing element.
An alternative production procedure is to allow the thread cutter to be drawn out only radially, but this results in an increasingly shallower thread, which does not fit in the already threaded hole, and an undefined flange is obtained. Thus, this method also does not solve the problem of how to fully use the outermost bone edge.
The loss of marginal bone height is especially critical in the use of a small number of implants in the molar areas of the jaw, since an unfavorable loading can occur in this region, especially in the case of an individual molar. A considerable increase in the strength of the implant can, of course, be obtained simply by increasing the dimensions of the implant, but it is far from certain that the existing bone volume will permit this. Omitting the flange, and allowing the thread to run right to the top, is not an optimal solution either, considering the advantages which a flange affords, namely being a counterstay for the initial tightening, and an active, sealing
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Johansson Ulf
Langer Burton
Rangert Bo
Lucchesi Nicholas D.
Nobel Biocare AB
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