Dentistry – Prosthodontics – Holding or positioning denture in mouth
Patent
1991-03-13
1992-03-03
Wilson, John J.
Dentistry
Prosthodontics
Holding or positioning denture in mouth
433181, A61C 1312
Patent
active
050927728
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to dental prostheses, such as bridges and partial dentures, and in particular to connectors for attaching such prostheses to natural teeth.
DESCRIPTION OF THE PRIOR ART
Prostheses such as a dental bridge or partial denture, comprise an artificial tooth or teeth, known as a "pontic", which extends along the line of the dental arch and is supported on each side by a suitably prepared sound natural tooth, an "abutment tooth". A variety of different connectors are known for securing a pontic to abutment teeth.
The abutment teeth usually have to be prepared by surgery, and in one method they are reduced to parallel sided pillars. A dental bridge is constructed by a technician with caps that fit precisely over the abutment teeth on either side of the pontic, and the bridge is secured using dental cement. This method has a major disadvantage that high bending stresses arise in use on the pontic and the abutment teeth, which are liable to damage the abutment teeth, or may result in the dental cement shearing and the bridge being dislodged. Such bending stresses can arise in the first instance because of imperfections of fit, but even if this is avoided, movements of the abutment teeth, in use, and with the passage of time, give rise to substantial stresses. Of particular importance, of course, are the occlusal loadings that are applied in mastication and there have been many proposals to provide dental prostheses with supports that have stress-breaking capabilities, ie. that reduce these bending stresses.
One arrangement has been proposed (U.S. Pat. No. 1664433) using a crown on the abutment tooth which allows relative vertical movements between the pontic and the abutment tooth, so that direct occlusal pressure can be transmitted to the gums beneath the pontic, but it makes no provision to prevent bending and torsional strains being transmitted to the abutment tooth.
Connectors are also known in the form of pin and socket joints, the pin projecting from the pontic to fit closely in a socket that has been cemented into a cavity formed in the abutment tooth. Such connectors may make it easier to insert and remove the prosthesis, but they can also transmit excessive stresses to the abutment tooth. As examples there may be mentioned U.S. Pat. No. 1,614,325 and U.S. Pat. No. 3,019,528.
In WO 86/07251 I describe pontics having a pin and socket joint. In one case, the pin of the joint has an enlarged head of rectangular cross-section, the edges of that head being formed as cylindrical segments and each opposite pair of edges providing bearing surfaces with a common central axis. In another case, cylindrical segmental bearing surfaces project inwards to engage a prismatic pin. These arrangements permit relative translational movement varying the spacing between the pontic and the abutment tooth as well as pivoting about axes transverse to the direction of said movement, so providing a stress breaking function.
The same patent specification also suggests that a pin and socket joint can employ a pin mounted in the pontic and slidable along its own axis into and out of a socket cemented in an abutment tooth. If this arrangement is combined with a pin and socket joint offering limited rotational freedom as mentioned in the preceding paragraph, there are obtained a number of advantages. There is a limited freedom of displacement of the pin within the socket allowing the pontic and the abutment tooth to move relative to each other, in particular under an occlusal load. The forces transmitted from the pontic to the. abutment tooth are reduced, therefore, while the pontic is positively retained in position. Moreover, to the extent that the pin and socket are capable of relative rotational and axial displacement, less skill is required when preparing abutment teeth for the prosthesis, while axial displaceability of the pins allows the prosthesis to be removed and replaced.
There are instances, however, in which the methods of connection using displaceable pins as taught by WO86/072
REFERENCES:
patent: 2705366 (1955-04-01), Van Dyk
patent: 3019528 (1962-02-01), DePietro
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