Retractable dental syringe

Details Retractable dental syringe Retractable dental syringe

1999-10-01

2001-04-24

Yasko, J (Department: 3763)

Surgery

Means for introducing or removing material from body for...

Treating material introduced into or removed from body...

C604S195000, C604S218000

Reexamination Certificate

active

06221055

ABSTRACT:

FIELD OF THE INVENTION
The present invention is a retractable medical device, more particularly, a retractable device that employs a removable medicine container that is well suited for dental use.
BACKGROUND OF THE PRIOR ART
Conventional syringes have a barrel and a closely fitting piston which draws fluid into the barrel via a needle in front of the barrel. Fluid is drawn into the barrel through the needle, the air is expelled and an injection is made by depressing the plunger. Many of these medical devices have been designed to retract the needle by various mechanisms because of the continuing danger of exposed needles contaminated with infectious agents. With the increase of dangerous communicable diseases such as AIDS, it has become critical to eliminate needle stick injuries to medical personnel. Intensive efforts have been directed to development of retractable syringes which are safe, effective and practical, which can be mass produced at low cost.
Seemingly ignored in all this activity is the smaller but still significant group of syringes which employ a pre-filled cartridge of fluid medication and a double ended hypodermic needle communicating with the cartridge for injecting the contents of the cartridge. The pre-filled syringe cartridges are referred to as “carpules”. They are typically cylindrical tubes with a puncturable membrane in front and a piston seal at the rear which is pressed forward by some form of plunger. The most common of these are the carpule syringes used by dentists in freezing the gums of their patients prior to their performing dental work on their teeth. Typically, the syringe enclosures with which such pre-filled syringe cartridges are used are not easily capable of retracting the needle into a protective enclosure to avoid inadvertent and potentially harmful needle sticks. Consequently, most syringes used for this purpose by dentists have a fixed needle which must be sheathed.
The relatively few attempts that have been made to produce a retractable needle syringe have produced results not altogether satisfactory. Weltman, U.S. Pat. No. 3,306,290; Sullivan, U.S. Pat. No. 5,330,430; and Haber, U.S. Pat. No. 4,820,275 among other things suffer from the deficiency that the device is necessarily much longer than the stroke the plunger itself would require in order that the outer shell house both needle and cartridge. Stanners, U.S. Pat. No. 5,330,440, although it doesn't suffer from the length deficiency, employs special thread engaging plugs in both ends of the carpule and plunger. These threaded connections must be mechanically connected together to withdraw the needle to the back of the special carpule. Retraction is done manually by disengaging a catch.
Although the needles can be retracted, these devices do not provide instantaneous retraction of the needle automatically at the end of an injection by further depression of the plunger while the needle is still in the patient's tissue. A slow controlled manual retraction of the needle is undesirable. Unintended movement of the syringe could damage tissue. Carpule syringe devices that would meet the above objections and which enable instantaneous retraction by continuation of the same motion used for the injection would be a significant improvement. These and other objects are the subject of the present invention.
SUMMARY OF THE INVENTION
The present invention is a single use retractable medical device which employs a modified carpule having a two-part sliding piston seal in back and a sliding seal in front. The retractable medical device is especially well suited for use as a dental syringe and one embodiment employs a thumb ring at the back of the plunger as is typical with dental syringes. The syringe is designed to retract after the injection by the simple expedient of continued depression of the plunger without moving the syringe away from the patient. The retraction parts and most of the needle are retracted into the carpule. All of the needle is retracted into the housing instantaneously upon depression of the plunger after the injection.
The carpule is unconventional mainly in the closures at the front and back end. The carpule has a cylindrical wall defining a fluid chamber and a front end with an opening into the fluid chamber and an open back end. A slidable front seal is lodged in the opening of the front end. The conventional carpule has no need for a sliding seal to cover the opening of the front end which is punctured by a rearwardly extending needle when the carpule is inserted. The modified carpule has a two-part sliding piston seal lodged in the open back end. The piston seal comprises an outer rim portion in sliding sealed contact with the wall of the fluid chamber and a slidably removable core portion. The sliding piston seal is moved by a plunger to the front of the fluid chamber to dispense all fluid. When driven in a retraction direction, the sliding front seal removes the core of the piston seal and traverses through the rim portion to enter the chamber along with following portions of a retraction mechanism.
The retractable medical device has a tubular housing having a wall defining a front end portion, a main body portion, an open back end and an inner surface defining a hollow interior. A retraction mechanism is mounted in the front end portion of the housing. The retraction mechanism comprises a needle holder having an elongated body with a front, a back and a widened part of the body spaced behind the front. Needle portions extend from the front and back of the needle holder. A spring is mounted under the widened part of the needle holder to apply retraction force thereto.
A releasable “push ring” is grippingly mounted around the widened part of the needle holder along a longitudinal interface. The push ring extends radially outwardly to the inner wall of the housing. Outer edges of the push ring are preferably in sliding gripping contact with the housing to hold the needle holder in place against the retraction force provided by the spring. The housing wall may be provided with stops behind the push ring to prevent rearward motion of the push ring and retraction mechanism. One form of push ring is a separable member shaped like a disc with a relatively straight walled opening in the center and a rounded outer edge. Another form of separable member is essentially an “O” ring which is donut shaped or still further a donut shaped “O” ring with a relatively straight walled central opening and a curved outer edge. The push ring/separable member holding the needle in place is not required to perform a sealing function for fluid due to the fact that the carpule holds the medicinal fluid. This means that the push ring/separable member could have a hub and spoke design or segmented structure of many different kinds.
A carpule of the type described above is inserted into the housing with the front seal in contact with the back end of the needle holder and punctured by the needle. The front of the carpule faces the push ring. One form of plunger is adapted to progressively receive the carpule while entering the housing and pressing the slidable piston forward to dispense fluid through the needle. Another form of plunger is received within the carpule in the manner of an ordinary syringe plunger in its housing.
On one form of plunger, a wall part presses the outer rim part of the piston seal so that the core portion can slide rearwardly relative to the rim portion during retraction without being obstructed by the plunger. This form of plunger also has another wall part which presses against the outer edge portions of the push ring when the piston seal is fully depressed to the front of the carpule at the end of an injection. This outer wall part is outside the carpule near the wall of the tubular housing. It engages the outer part of the push ring after the carpule is emptied. Retraction occurs by further depression of the plunger to move the push ring from a widened part of the needle holder while dislodging the front seal and the separable core part of the piston

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