Dental syringe having an automatically retractable medication carpule and needle cannula

A reusable dental syringe having a hollow cylinder, a prefilled medication carpule to be received within the cylinder, and a hypodermic needle cannula communicating with the carpule and extending outwardly from the cylinder for administering an injection. The syringe also includes a retaining collar which can be moved, against the normal bias of a compression spring, axially and distally through the cylinder and into engagement with the carpule. A slide lock is adapted to lock the retaining collar at the distal position within the cylinder. After a injection has been administered and the carpule emptied, the slide lock may be moved to release the retaining collar from the distal position. The compression spring is now free to return to its normal bias, whereby to drive the retaining collar and the empty carpule connected thereto axially and proximally through the cylinder. Accordingly, the needle cannula is automatically relocated from the outwardly extended position to a retracted position within the cylinder so as to prevent an accidental needle stick and the spread of a contageous, and possibly life threatening, disease.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a reusable dental syringe having a combination 
medication carpule and needle cannula and to a slide lock that is movable 
to either lock the needle cannula at an outwardly extending position 
relative to the cylinder, at which an injection may be administered, or to 
release the needle cannula to be automatically retracted within and 
surrounded by the cylinder, so as to avoid an accidental needle stick and 
the possible spread of disease. 
2. Prior Art 
Syringes of the type having a prefilled carpule of fluid medication and a 
hypodermic needle cannula are well known in the art for injecting such 
medication from the carpule to a targeted tissue area of a patient. At the 
conclusion of the injection, the needle cannula typically remains locked 
in an axially extended position projecting outwardly from the syringe 
cylinder. In some cases, the syringe may be used to treat a patient having 
a communicable disease. Medical workers are especially susceptable to 
accidental and potentially infectious needle sticks due to the careless 
handling and disposing of the syringe after use. The resulting 
mini-accident caused by an accidental needle stick typically requires a 
blood test for such diseases as AIDS and hepatitis. The corresponding cost 
and inefficiency of testing medical workers who have received such an 
accidental needle stick result in considerable waste, which may be 
particularly damaging to a medical facility which is striving for economy. 
The following patent, which has been assigned to the assignee of the 
present patent application, discloses a reusable dental syringe including 
a prefilled medication carpule and means for retracting a needle cannula 
after an injection has been administered: U.S. Pat. No. 4,931,040 issued 
Jun. 5, 1990. 
SUMMARY OF THE INVENTION 
In general terms, a reusable dental syringe is disclosed including a hollow 
cylinder having open proximal and distal ends, a prefilled medication 
carpule to be received within the cylinder, and a hypodermic needle 
cannula communicating with the carpule and extending outwardly from the 
distal end of the cylinder for administering an injection. A hollow 
retaining collar is connected to a radially extending handle. The collar 
extends from the handle into the open proximal end of the cylinder around 
which is formed a radially extending flange. A helical compression spring 
surrounds the retaining collar between the handle and flange. A locking 
tooth projects outwardly from the retaining collar. A slide lock is 
received in and slidable laterally through a slot formed in the flange. 
The slide lock has a central opening through which the retaining collar 
may be reciprocated. The slide lock has at least one catch formed therein 
for selectively engaging the locking tooth of the retaining collar. 
In operation, the handle of the syringe is moved towards the flange, 
whereby to compress the spring therebetween and advance the retaining 
collar axially and distally through the central opening of the slide lock 
and into the cylinder, whereby to engage one end of the carpule. The catch 
of the slide lock engages the locking tooth of the retaining collar to 
retain the collar at the distally advanced position and lock the needle 
cannula in the outwardly extending position relative to the cylinder. A 
detachable piston stem is then depressed for driving an associated piston 
through the carpule for injecting the medication from the carpule into the 
targeted tissue area of a patient via the cannula. 
At the conclusion of the injection, the slide lock is moved through its 
slot, whereby to correspondingly move the catch of the slide lock out of 
engagement with the locking tooth of the retaining collar. The spring is 
now free to return to its relaxed condition, whereby the stored potential 
energy thereof drives the syringe handle away from the syringe flange. 
Likewise, the retaining collar, which is connected to said handle, is 
driven axially and proximally through the central opening of the slide 
lock. The proximal travel of the retaining collar is transferred to the 
carpule for moving the carpule proximally through the cylinder. 
Accordingly, the needle cannula is automatically relocated from the 
axially extended position at which the injection was administered to a 
retracted position at which to be surrounded and shielded within the 
cylinder, whereby to reduce the possibility of an accidental needle stick 
and the spread of a contagious, and possibly life threatening, disease. 
The slide lock may be moved out of engagement with the retaining collar to 
permit the proximal relocation of the retainning collar and the automatic 
retraction of the cannula into the cylinder by laying either side of the 
syringe on a flat surface (e.g. an instrument tray, a table, or the like) 
so that the lock is contacted and moved laterally through its slot by said 
flat surface. The combination carpule/cannula may then be ejected from the 
cylinder and discarded.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The reusable dental syringe which forms the present invention and the 
retractable medication carpule and needle cannula thereof are best 
described while referring to the drawings where such a dental syringe 1 is 
illustrated. The presently disclosed dental syringe 1 preferably includes 
certain elements that are common to a commercially available syringe. Such 
a commercially available dental syringe is sold under the name CARPUJECT 
by Winthrop-Breon Corporation of New York. However, it is to be expressly 
understood that the teachings of this invention are not limited to the 
above-mentioned syringe and other syringe configurations could be employed 
in combination with the present invention to achieve the advantages 
offered thereby. 
Referring initially to FIGS. 1 and 2 of the drawings, the preferred dental 
syringe 1 is shown including a hollow, elongated cylinder 2 having open 
proximal and distal ends. A prefilled medication carpule 4 is removably 
snap fit within the hollow interior of cylinder 2 (best illustrated in 
FIG. 2). The front face of the cylinder 2 is removed so that a health care 
worker will have visible access to the entire carpule 4 being carried 
therewithin. A window 5 is removed from the opposite face of cylinder 2 to 
aid the health care worker in ejecting an empty carpule therefrom after an 
injection has been administered. Carpule 4 is a disposable, medication 
filled cartridge of the type that is available from the above-named 
manufacturer, as well as from other sources. Carpule 4 has an associated 
hypodermic needle cannula (designated 6 in FIGS. 3 and 4) and a removable 
needle shield 8 which preserves the sterility of of the cannula while 
preventing an accidental needle stick prior to the administration of the 
injection. 
Carpule 4 also has an associated piston 9 which is adapted for axial 
movement therethrough to expulse the medication from the carpule during 
the administration of an injection. A screw threaded fitting 10 projects 
outwardly from piston 9 for connection to a piston stem so as to complete 
a piston assembly. 
The proximal end of the syringe cylinder 2 terminates at an integral, 
radially projecting flange 11 under which the fingers of a health care 
worker are placed during the administration of an injection. Spaced above 
and arranged in parallel alignment with the flange 11 is a radially 
projecting handle 12 having a hollow retaining collar 14 integrally formed 
with and extending therefrom. The inside diameter of retaining collar 14 
is slightly larger than the outside diameter of carpule 4, so that one end 
of the carpule may be received within and retained by collar 14. A helical 
compression spring 16 surrounds retaining collar 14 between the flange 11 
and the handle 12. A locking tooth 18 having an inclined end projects 
outwardly from one of the sides of retaining collar 14. The side of 
retaining collar 14 from which locking tooth 18 projects and the opposite 
side thereof are formed as flat, planar surfaces (best depicted in FIG. 
2). A longitudinally extending guide slot 20 runs along the top of 
retaining collar 14. The purposes of and advantageous effects provided by 
the compression spring 16, locking tooth 18, and guide slot 20 will be 
described in greater detail hereinafter. 
An elongated piston stem 21 is received through a hole in handle 12 and the 
hollow interior of retaining collar 14 to be detachably connected to the 
piston 9 of carpule 4. The piston stem 21 has a screw threaded receptacle 
(not shown) which is adapted to be rotated into engagement with the screw 
threaded fitting 10 of piston 9 at the interior of syringe cylinder 2, 
whereby to complete a piston assembly for selectively controlling the 
axial movement of piston 9 through carpule 4 during the administration of 
an injection. 
Syringe 1 is provided with a slide lock 22 by which to automatically lock 
(and subsequently release) the medication carpule 4 at a distally advanced 
position within cylinder 2 so that the needle cannula 4 is retained at an 
outwardly extended position relative to cylinder 2 for the purpose of 
penetrating the skin of a patient so that an injection can be efficiently 
administered. More particularly, the slide lock 22 is shown as a generally 
rectangular member having a central opening 23 (best illustrated in FIG. 
2) surrounded by an outer frame. Slide lock 22 is sized to be received 
within a correspondingly sized slot 24 which extends transversely through 
flange 11. To this end, a centering spring 26 is connected between the 
slide lock 22 and a tab 28 which is affixed (e.g. at the bottom) of 
syringe cylinder 2. Centering spring 26, which may be a straight piece of 
wire, or the like, performs the multiple functions of preventing the 
removal of slide lock 22 from its slot 24, permitting the slide lock 22 to 
slide laterally a controlled distance through slot 24, and automatically 
centering the central opening 23 of slide lock 22 so that the locking and 
releasing of the carpule 4 may be reliably achieved in a manner which will 
soon be disclosed. 
The central opening 23 of slide lock 22 is sized to accommodate the 
retaining collar 14 therethrough (also best illustrated in FIG. 2). As 
will soon be described, the retaining collar 14 is adapted for reciprocal 
movement through central opening 23 to control the relocation of 
medication carpule 4 and its associated cannula 6 relative to syringe 
cylinder 2. A guide pin 30 (best shown in FIG. 2) extends downwardly from 
handle 11 for receipt in the longitudinal guide channel 20 at the top of 
retaining collar 14. Guide pin 30 rides through guide channel 20 during 
the reciprocal movement of the retaining collar 14 through the central 
opening 23 of slide lock 22 for the purpose of limiting the proximal 
travel of retaining collar 14 and, thereby, preventing the inadvertent 
removal of collar 14 from the cylinder 2 through the open proximal end 
thereof. That is to say, the axial distance travelled by retaining collar 
14 in a proximal direction through cylinder 2 at the conclusion of an 
injection (which travel will be imparted to carpule 4 and cannula 6) is 
dependent upon the length of guide channel 20 through which the guide pin 
30 will ride. 
As is best shown in FIG. 2, a pair of detents 31 and 32 are located 
adjacent one another on the same side of the outer frame of slide lock 22. 
A catch 34 is formed between detents 31 and 32. As will be described in 
greater detail when referring to FIGS. 3 and 4, the detents 31 and 32 and 
catch 34 of slide lock 22 cooperate with the locking tooth 18 of retaining 
collar 14 when such collar 14 moves distally through the central opening 
23 of slide lock 22 to automatically lock (and subsequently release) the 
medication carpule 4 an its associated needle cannula 6 at an outwardly 
extended position relative to syringe cylinder 2 so that an injection may 
be administered. 
The operation of the dental syringe 1 of the present invention is now 
described while referring to FIGS. 2-4 of the drawings. In FIG. 2, the 
combination medication carpule 4 and needle cannula 6 is shown removed 
from its shipping container and snapped into engagement with the interior 
of the syringe cylinder 2 such that needle cannula 6 extends outwardly 
through the open distal end thereof. The cannula 6 is initially surrounded 
and protected by the needle shield 8. The carpule 4 is loaded into 
cylinder 2 so as to be spaced axially and distally from the hollow 
retaining collar 14. Therefore, the locking tooth 18 of collar 14 is 
spaced proximally from slide lock 22 and compression spring 16 is relaxed. 
Moreover, the piston stem 21 is detached from the piston 9 of carpule 4. 
In FIG. 3, the piston stem 21 is shown after it is rotated (in the 
direction of reference arrow 38) through the hollow retaining collar 14 
and into contact with the threaded end of piston 9 so as to complete a 
piston assembly for driving the piston through the medication carpule 4 
and expulsing the medication therefrom via cannula 6. The health care 
worker may locate his index and middle fingers below the flange 11 and his 
thumb upon handle 12 so as to apply an axial and distally directed force 
(in the direction of reference arrow 40) for moving handle 12 towards 
flange 11. Thus, the coil spring 16 is compressed between flange 11 and 
handle 12. The integral retaining collar 14 of handle 12 is 
correspondingly moved axially through the central opening 23 of slide lock 
22 and into syringe cylinder 2 (via the open proximal end thereof), 
whereby the guide pin 30 rides through longitudinal guide channel 20 and 
an end of carpule 4 is received within and retained (by means of a 
friction fit) at the hollow interior of collar 14. Such friction fit 
between retaining collar 14 and carpule 4 may be enhanced by an integral, 
spring-like tongue 42 which extends inwardly of collar 14 for engaging the 
carpule. 
By virtue of the present invention, the carpule 6 is automatically locked 
in the outwardly extending position relative to the open distal end of 
cylinder 2, so as to permit the health care worker to relocate his thumb 
from the handle 12 to the piston stem 21 for controlling the movement of 
piston 9 through carpule 4. More particularly, the axial movement of 
retaining collar 14 through slide lock 22 correspondingly moves the 
locking tooth 18 of collar 14 into contact with the catch 34 which is 
located between the detents 31 and 32 of lock 22. The continued axial 
movement of retaining collar 14 into cylinder 2 and towards carpule 4 
causes catch 34 to ride up the inclined end and over the top of locking 
tooth 18, whereby to also cause lock 22 to slide laterally (as shown in 
phantom) through its transverse slot 24 in flange 11 and thereby stress 
the centering spring 26. The lateral movement of slide lock 22 through 
slot 24 aligns said lock so that locking tooth 18 can pass through the 
detent 32 formed therein. When retaining collar 14 is moved through the 
cylinder 2 and into engagement with an end of carpule 4, the locking tooth 
18 will have travelled across and dropped behind the catch 34. The energy 
stored within centering spring 26 will return slide lock 22 to its 
original position in slot 24 as spring 26 returns to its pre-stressed 
configuration. With the catch 34 of slide lock 22 located behind the 
locking tooth 18 of retaining collar 14, the proximal travel of collar 14 
(and the carpule 4 connected thereto) through cylinder and lock 22 is 
blocked. Therefore, the needle cannula 6 is locked in the outwardly 
extending position relative to cylinder 2 so that an injection may be 
administered. 
At this time, the health care worker removes the needle shield 8 to expose 
the cannula 6 for penetrating the targeted tissue area of the patient. The 
health care worker may then use his thumb to apply an axial and distally 
directed force to the piston stem 21 for driving the piston 9 through the 
carpule 4 and thereby expulsing the medication therefrom via cannula 6. 
Referring to FIG. 4, the combination medication carpule 4 and cannula 6 is 
shown safely and completely retracted within the interior of the cylinder 
2 of dental syringe 1 after the medication has been expulsed from the 
carpule. The foregoing may be advantageously and automatically 
accomplished whenever the syringe 1 is laid on a flat surface (e.g. an 
instrument tray, a table, or the like), so that slide lock 22 is moved 
into contact with and displaced by such flat surface. More particularly, 
the engagement of slide lock 22 by a flat surface will cause the lock to 
slide laterally (as indicated in phantom) through its slot 24 in flange 
11. Accordingly, the slide lock 22 is relocated in slot 24 so that one of 
the detents 31 or 32 formed in the outer frame thereof will be moved into 
alignment with the locking tooth 18 of retaining collar 14 to permit tooth 
18 to pass therethrough. The potential energy stored within the helical 
spring 16 (which was previously compressed between flange 11 and handle 12 
during the movement of retaining collar 14 through cylinder 2 and into 
receipt of carpule 4) automatically drives the retaining collar 14 axially 
and proximally through the cylinder 2 and the central opening 23 of slide 
lock 22 (in the direction of reference arrow 44), such that spring 16 
returns to its relaxed, pre-compressed condition and handle 12 returns to 
its axially spaced location relative to flange 11. Inasmuch as retaining 
collar 14 is connected to the carpule 4, the proximal movement of collar 
14 is also transferred to carpule 4, whereby to cause the needle cannula 6 
to be retracted proximally within and surrounded by the syringe cylinder 
2. 
By forming slide lock 22 with a pair of detents 31 and 32, either side of 
the syringe 1 may be placed in contact with a flat surface. That is, lock 
22 is adapted to slide laterally and in opposite directions through its 
slot 24. The locking tooth 18 will then be aligned with one or the other 
of the detents 31 or 32 depending upon the end of the slide lock 22 that 
is moved into contact with the flat surface and the corresponding 
direction in which said lock slides. The ability of slide lock 22 to slide 
in opposite directions permits the needle cannula 6 to be released from 
its outwardly extended position after use and retracted into the cylinder 
2 without requiring any special action on the part of the health care 
worker, other than to position syringe 1 such that either end of slide 
lock 22 is moved into contact with a flat surface. Of course, the health 
care worker can also activate slide lock 22 with his thumb, rather than by 
contact with a flat surface. 
The automatic relocation of cannula 6 from the outwardly extended position 
relative to cylinder 2 reduces the likelihood of an accidental needle 
stick and the spread of the contageous, and possibly life threatening, 
disease. The combination carpule 4 and cannula 6 may be removed from the 
cylinder 2 and discarded after the piston stem 21 is rotated out of 
engagement with the piston of an empty carpule 4. The health care worker 
may use the open window 5 through cylinder 2 to assist him in ejecting the 
carpule/cannula combination for disposal. 
It will be apparent that while a preferred embodiment of the invention has 
been shown and described, various modifications and changes may h=made 
without departing from the true spirit and scope of the invention. By way 
of example, a second locking tooth or lock-out 46 may project outwardly 
from the retaining collar 14 in spaced, axial alignment with the first 
tooth 18 thereof. Like the first tooth, the second tooth 46 has one 
inclined end. As the retaining collar 14 is driven proximally through 
cylinder 2 and past the central opening 23 of slide lock 22 to 
automatically retract needle cannula 6, the catch 34 of slide lock 22 will 
ride up the inclined end, travel across the top, and drop behind tooth 46. 
With the catch 34 located behind the locking tooth 46 (best shown in FIG. 
4), the distal relocation of collar 14, and the carpule 4 which is 
connected thereto, is blocked. Therefore, the needle cannula 6 cannot be 
inadvertently returned to extend outwardly from the distal end of cylinder 
2 (as shown in FIG. 3) for subjecting a health care worker to an 
accidental needle stick.