Dentistry – Apparatus – Having intra-oral dispensing means
Utility Patent
1999-05-27
2001-01-02
Wilson, John J. (Department: 3732)
Dentistry
Apparatus
Having intra-oral dispensing means
C604S239000
Utility Patent
active
06168432
ABSTRACT:
BACKGROUND OF THE INVENTION
In the field of dentistry, one method for obturating root canal cavities involves injecting heated thermoplastic material, typically gutta-percha, into the dental cavity with a dental thermoplastic injection device. The injection device is typically a syringe-like instrument having a hollow needle through which the thermoplastic is ejected when the needle is inserted into the dental cavity. The needle is of high thermal conductivity material such as gold, silver, copper or aluminum to assume thermal conductance from a heater in the injection device to maintain the fluidity of the gutta-percha in the needle. See U.S. Pat. No. 4,357,136.
The needle is usually formed from two separate pieces which are joined together. The first piece is a narrow elongate needle portion made of the high thermal conductivity metal such as silver about 1 inch long with a constant diameter between 18 and 30 gauge. The second piece is a threaded hub portion which is brazed to the needle portion. The hub portion allows the needle to be attached to the injection device by screwing the hub portion into the body of the injection device. A drawback with this design is that the joint between the needle and the hub portions may break when the needle is bent within a convoluted dental cavity. Another drawback with the design is that the process for manufacturing the needle is relatively slow and expensive.
SUMMARY OF THE INVENTION
The present invention provides a one piece needle for a dental thermoplastic injection device that does not easily break when bent within a convoluted dental cavity and which is also suitable for manufacture with high speed automated operations.
The present invention is directed to a hollow jointless needle formed from a single piece of conductive metal for injecting thermoplastic material into a dental cavity. The needle extends along a longitudinal axis and includes a flange extending transversely relative to the longitudinal axis for securing the needle to an injection device. The needle has different diameters along its length. Specifically, a first needle portion having a first diameter extends from the flange along the longitudinal axis. A second needle portion extending along the longitudinal axis is a continuation of the first needle portion from a first transition region. In other words, the first transition region connects the second needle portion to the first needle portion. The second needle portion has a second diameter which is smaller than the first diameter of the first needle portion.
In preferred embodiments, the second needle portion is about 20 gauge. In addition, the needle is made from a metal having a coefficient of thermal conductivity greater than about 200 Btu/(hr)(ft
2
) (° F./ft) such as gold, silver, copper and aluminum with silver being the most preferable. The first and second needle portions each have an outer wall with the wall of the second needle portion having a thickness that is less than the wall thickness of the first needle portion. The flange is planar with a thickness which is greater than the wall thickness of the first needle portion and extends perpendicularly to the longitudinal axis.
The larger diameter of the first needle portion reduces stress from the second needle portion to the flange by distributing stress over the larger diameter of the first needle portion. The thicker wall of the first needle portion further distributes stress from the second needle portion to the flange and also maintain a high thermal conductivity along its length.
In one preferred embodiment, the needle further includes a third needle portion extending along the longitudinal axis. The third needle portion is connected to the second needle portion by a second transition region. The third needle portion has a third diameter which is smaller than the second diameter of the second needle portion wherein the third needle portion is about 23 gauge and the second needle portion is about 20 gauge. The outer wall of the third needle portion has a thickness that is less than the wall thickness of the second needle portion.
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Hamilton Brook Smith & Reynolds PC
Wilson John J.
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