Abstract:
A safety syringe is formed of an inner sleeve receiving a cartridge with liquid, an outer sleeve through which said inner sleeve is telescopically reciprocated, and a plunger assembly that is attached to the inner sleeve and used to eject the liquid. The needle is mounted on a front end of the inner sleeve and in a retracted position is wholly contained within the outer sleeve while in a protracted position the needle is exposed so that it can be used for an injection. Advantageously, in one embodiment, the inner sleeves can rotate with respect to each other causing the needle to rotate both when the needle is extended and when is retracted into the outer sleeve. Another feature of the invention is that in one embodiment the inner sleeve has an internal puncture member for puncturing the cartridge. Therefore, instead of a dental needle with two sharp tips, a standard needle with a single tip and a Luer connection may be used.

Description:
RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of patent application Ser. No. 10/209,415 filed Jul. 31, 2002, which is a divisional application of patent application Ser. No. 09/506,484 filed Feb. 17, 2000 (now U.S. Pat. No. 6,428,517 issued Aug. 6, 2002) and which claimed priority to provisional applications Ser. No. 60/133,397 filed May 10, 1999 and Ser. No. 60/173,374 filed Dec. 28, 1999, all incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     A. Field of Invention  
         [0003]     This invention pertains to a syringe used to inject a therapeutic fluid into human or animal tissues, and more particularly to a syringe that includes a needle movable along a longitudinal axis, which needle is optionally rotating about said axis as well. Importantly, prior to and immediately after the injection, the needle is disposed in a protective sleeve that prevents needle sticks. Preferably, after an injection is completed, a permanent locking mechanism is activated to trap the needle within the sleeve.  
         [0004]     B. Description of the Prior Art  
         [0005]     Traditional dental syringes are metal and designed to accommodate a double-ended needle on the threaded hub of the syringe. A pre-filled glass local anesthetic cartridge fits in the barrel of the syringe. The cartridge is pierced by a sharp working end of the needle that projects into the barrel of the syringe penetrating the diaphragm of the cartridge. It is often necessary for the dentist or other health care provider to provide multiple injections for a single patient throughout a dental procedure or appointment. The standard practice is to recap the needle after initial injection and then uncap and reuse the same needle on the one patient for subsequent injections. Frequently, the cartridge is changed, but the needle is rarely changed for a single patient. In certain situations however, the replacement of a needle may be necessary do to dulling of needle or the need for a different needle length or gauge. This then requires the removal and replacement of the needle. To accomplish this, the user recaps the needle, typically using a one-handed scoop technique or adaptive needle cap holder or add-on shield. The user must still manually manipulate the needle when removing it from the syringe, thus exposing the sharp end that protrudes into the anesthetic cartridge. This procedure provides a risk of percutaneous injury to users when handling anesthetic needles.  
         [0006]     An important goal of dentistry and medicine in general is to insure that during any procedure involving interaction between a dentist or other care giver and a patient, utmost care is taken to protect the care giver from injury and/or infection with diseases. It has been recognized that the use of hypodermic needles, which activity is endemic in the field, is one particularly hazardous area. More particularly, the use of a hypodermic needle in dentistry and other medical fields has been shown to put the user at risk to inadvertent needle sticks, and presents a potential high risk to infection disease transmission for health care workers.  
         [0007]     The use of hollow-core needles is the standard in drug delivery in medicine and dentistry. The use of the hollow-core needle dates back over 150 years when Charles Pravaz, a French general surgeon, patented such a device.  
         [0008]     Currently several auto-retraction type syringes are known that provide increased safety by allowing the protruding needle˜to be retracted into a protective sheath after use. However, these systems where found to be unsatisfactory by the health care provider community. Other syringes are provided with removal caps. Some prior art syringes and needles with protectors are disclosed in the following U.S. patents: U.S. Pat. Nos. 5,120,310; 5,188,613; 5,267,961; 5,389,076; 5,423,758; 5,578,011; 5,632,733; 5,637,092; 5,810,775; 5,030,209; 4,911,693; 4,900,310; 4,813,426; 4,795,432; 4,664,654; 4,695,274; 4,966,592; 4,747,831; 4,900,311; 5,411,487; 5,106,379; 5,713,873.  
         [0009]     Other systems are also known (e.g., U.S. Patent Application Publications 2002/0169421 and 2002/0068921 published Nov. 14, 2002 and Jun. 6, 2002, respectively) and U.S. Pat. Nos. 5,207,646 and 6,413,236. However, these systems are awkward to use and explicitly describes means for preventing needle rotation.  
         [0010]     Generally, these prior art references have either one or more of the following deficiencies.  
         [0011]     1) Hollow core needle that is rigidly affixed to the end of a syringe-, tubing or handle. The protruding needle presents a risk of inadvertent needle stick to the operator.  
         [0012]     2) Existing auto-retracting syringes are difficult to use  
         [0013]     3) Cannot be locked permanently to prevent reuse.  
         [0014]     In the past 15 years regulatory agencies such as OSHA have attempted to improve the use and safety of needles in the health care industry. With the rise of infectious diseases, i.e., hepatitis and AIDS, protection of the health care workers has become a needed priority. It is supported in the medical/dental literature that inadvertent needle sticks represents a significant risk to our health care providers.  
         [0015]     The proposed invention has been designed to eliminate the potential of inadvertent needle sticks after and during use.  
         [0016]     For example, various medical organizations have suggested and several states have instituted rules for the protection of care givers while providing injections to patients. More specifically, rules have been promulgated requiring that injection needles on syringes be provided which can be easily removed prior to an injection and re-installed immediately after an injection.  
         [0017]     Another related problem addressed by the present invention pertains to the deflection or bending of needles as they are inserted into the tissues of a patient. This deformation occurs because the needle is usually flexible because of its relatively small cross-sectional area and cannot resist effectively the axial and radial forces present during the insertion. This deflection is undesirable because it provides additional resistance during the insertion, to the movement of the needle and/or syringe, makes it difficult to guide the needle to a particular site preselected by the care giver. Moreover, if a needle is deflected, bent or otherwise deformed during insertion, it may cause more paint to the patient, trauma to the local tissues and other undesirable effect. It has been discovered (as disclosed in co-pending patent application Ser. No. 60/173,374 filed Dec. 28, 1999), incorporated herein by reference, that these disadvantages are eliminated or at least alleviated if the needle is rotated about its longitudinally about its axis as it is advanced along the axis into the patient tissues. Other syringes do not allow the use of a rotational insertion and removal technique to be used during a power assisted injection process.  
       SUMMARY OF THE INVENTION  
       [0018]     This syringe described herein overcomes the known disadvantages of existing syringes. It is a capable of both intermittent locking during use as well as permanent locking after use. In addition, an optional design configuration utilizes a single ended medical Luer-lock needle in combination with a standard local anesthetic cartridge enhancing the safety to the operator. An additional benefit of this device is an innovative design element in the barrel of the syringe that guides the needle into translation/rotation during injection, resulting in the reduction of force needed to penetrate the patient&#39;s tissue and also reduces needle deflection. Needle deflection in local anesthetic injections has been associated with increased failure rates. This same feature of simultaneous rotation/translation of needle will also result in a reduced amount of force to remove the needle from the patients&#39; tissues, once again aiding in the safety and comfort to both the operator and patient. An auto-aspiration design is an innovative safety element in one of the potential designs of this device. The inclusion of this feature ensures greater safety for patients during the use of this device. Currently, no dental syringe is available with these features.  
         [0019]     Because of the potential for nerve damage during dental anesthetic injections, it is desirable to have proper aspiration during certain injections. This helps prevent damage that may result in permanent loss of feeling and function in areas of the mouth, tongue and lip.  
         [0020]     Because of its design, the subject syringe can be manufactured with fewer components then other syringes currently available in the marketplace.  
         [0021]     Briefly, a safety syringe constructed in accordance with this invention includes two telescoping sleeves and a plunger assembly. Means are provided to selectively interlock the two sleeves in either a protracted and a retracted position. A cartridge filled with a liquid is disposed in the inner sleeve and is in fluid communication with a needle coupled to the inner sleeve. A user can advance the needle out of the outer sleeve . Preferably, as the needle is advanced it is rotated about its longitudinal axis at the same time for an angle of between 25 and 270 degrees. In one embodiment, the liquid is expressed as the needle is moving and rotating forward. In another embodiment the needle is advanced and rotated until it reaches the protracted position, and then the liquid is injected. In either case, at the end of the injection, the inner sleeve is withdrawn from the outer sleeve causing the needle to rotate as it retracted into the outer sleeve.  
         [0022]     Once the needle is retracted into the second sleeve means provided on the outer sleeve are used to permanently capture the needle so that it cannot be removed.  
         [0023]     In an alternate embodiment, means are provided that selectively urge the cartridge away from the needle thereby providing aspiration.  
         [0024]     In an alternate embodiment, means are provided to puncture a membrane on the cartridge to provide access for the liquid. In this embodiment, a single ended standard medical needle can be used instead of a dental needle that possess a double ended needle with two sharp points. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0025]      FIG. 1  shows an orthogonal blown up view of a syringe constructed in accordance with this invention;  
         [0026]      FIG. 2  shows an orthogonal view of the syringe of  FIG. 1  with the needle protracted;  
         [0027]      FIG. 3  shows an orthogonal view of the syringe of  FIG. 1  with the needle extended;  
         [0028]      FIG. 4  shows a side view of the push rod for the syringe of  FIGS. 1-3 ;  
         [0029]      FIG. 5  shows a side view of the push rod guide cap for the syringe of  FIGS. 1-3 ;  
         [0030]      FIGS. 6 and 6 A show a side view of the inner sleeve for the syringe of  FIGS. 1-3 ;  
         [0031]      FIG. 7  shows a side view of the outer sleeve for the syringe of  FIGS. 1-3 ;  
         [0032]      FIG. 8  shows an enlarged partial cross-sectional view of outer sleeve of  FIG. 7 ;  
         [0033]      FIG. 8A  shows a second enlarged partial cross-sectional view of the syringe taken along lines  8 A- 8 A in  FIG. 7 ;  
         [0034]      FIG. 8B  shows an enlarged partial top view of the outer sleeve of  FIG. 7 ;  
         [0035]      FIG. 9  shows an enlarged partial cross-sectional view of the syringe of  FIGS. 1-3  with the inner sleeve being pushed into the outer sleeve;  
         [0036]      FIG. 10  shows a cross-sectional view of the syringe in the protracted position;  
         [0037]      FIG. 11  shows a partial cross-sectional view of the inner sleeve with a rim providing aspiration;  
         [0038]      FIG. 12  shows a partial cross-sectional view of the inner sleeve with a coil spring providing aspiration; and  
         [0039]      FIG. 13  shows a partial cross-sectional view of the inner sleeve with integral flexible fingers providing aspiration.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0040]     Referring first to  FIGS. 1-10 , a safety syringe  10  constructed in accordance with this invention includes a plunger assembly  12 , an inner sleeve  14 , and an outer sleeve  16  terminating at its distal end with an aperture  20 . Briefly, a cartridge  18  filled with a desired liquid is inserted into the inner sleeve  14  and the inner sleeve  14  is the closed by inserting therein an end of the plunger assembly  12 . A coil spring  22  is positioned on one end of the inner sleeve  12 , a standard dental needle assembly  24  having a needle tip  25  is attached to the inner sleeve as shown in  FIG. 2 . The syringe  10  is then operated by forcing the inner sleeve  12  and its cartridge  18  through the outer sleeve  14  so that a portion of the needle assembly  24  exits through aperture  20 . As the needle assembly exits through the aperture, the liquid within the cartridge is expressed through the needle and therefore the injection may be started as soon as the needle tip appears through the aperture. Preferably, as the needle tip  25  is advancing toward its final position shown in  FIG. 3 , it is simultaneously rotated about its longitudinal axis.  
         [0041]     After the injection is complete, the inner sleeve can be released and the coil spring  22  causes the needle assembly  24  to be rapidly withdrawn into the outer sleeve  14 . The syringe can be reused, or alternatively, a permanent lock mechanism can be activated to trap the needle assembly  24  within the outer sleeve  16 . The whole syringe  10  can then be discarded safely since the needle tip  25  is not exposed. Details of the syringe elements and how they interact to provide the described functions are provided below.  
         [0042]     The plunger assembly  12  consists of an elongated push rod  30  (shown in  FIG. 4 ) and a guide cap  40  (shown in  FIG. 5 ). Push rod  30  has a shaft  31  attached at one end to a finger ring  32  or other similar means for engaging the thumb or finger of a health care provider. At the opposite end, shaft  31  has a reduced diameter portion  33  formed with preferably two O-rings  34 . The end face  36  may be provided with a hook or a barb  37 . The two O-ring design is somewhat preferable because it provides a suitable frictional grip and therereby the following advantages: 
        1. Two O-ring design allows the plunger to be properly stabilized within the anesthetic cartridge at two axially spaced contact points within the glass cartridge. With a single O-ring design the plunger may pivot within the inner surface of the glass cartridge making the plunger unstable during use.     2. The two O-ring design provides increased frictional drag of the plunger as it is moved within the glass cartridge. This serves 2 additional important purposes: 
            a. The increased drag of the two O-rings ensures a slower rate of delivery because of the increased friction force encountered against the glass cartridge while depressing the plunger thus ensuring that the anesthetic solution will be expressed at a slower rate producing a more comfortable injection for the patient. It is well documented in the dental and medical literature that a slower injection is a more comfortable injection for the patient.     b. The increased drag of the two O-ring design enables the glass cartridge to be removed simultaneously with the plunger assembly as the plunger assembly is disconnected or withdrawn from the inner cylinder. This can add in the efficiency of removal or replacing the cartridge at the end of the injection.    
               
 
         [0047]     The design of the plunger is not limited to a two o-ring design and may use more or less number of O-rings to accomplish the same objectives. It is also conceivable that another type of “gasket component” could be used such as a flexible collar that is made from a soft material such as silicone, but not limited to silicone, to achieve a similar outcome.  
         [0048]     Between its two ends, rod  30  supports the push rod cap  40  shown in more detail in  FIG. 5 . The cap  40  is formed with a short sleeve  41  formed with two snap tabs  42 . Cap  40  can be glued to the rod  30 , can be held in place by two O-rings (not shown) or the push rod  30  and the cap  40  can be molded unitarily.  
         [0049]     As discussed above, the cartridge  18  holds a desired liquid such as an anesthetic. Typically, such a cartridge has a cylindrical glass or plastic sidewall  44  ( FIG. 1 ), with a rubber piston  38  at one end, and a rubber membrane  46  encased in a metal sheath at the other end.  
         [0050]     The inner sleeve  14  shown in detail in  FIGS. 6 and 6 A is formed with a cylindrical sidewall  48  with an open mouth  50 A at one end, and a closure  50  at the other end. The closure  50  includes a shoulder  52  surrounding a hub  54 . The cylindrical wall  48  is formed with one or more elongated (preferably two) windows  56 . In addition, the wall  48  with two similarly shaped transversal openings  58 A,  58 B, one near each end of sleeve  14 . The two openings  58 A,  58 B are angularly offset from each other. The sleeve  14  is further provided with two additional openings or depressions  60  spaced peripherally about wall  48 , preferably opposite to each other. These openings  60  are formed with a flexible tongue  60 A. As seen in  FIG. 6A , the tongues  60 A are formed so that their ends normally extend outwardly of the surface  48 . Between openings or depressions  60  there is butterfly-shaped opening  61 . Wall  48  is also formed with a pin  62 .  
         [0051]     Referring to  FIGS. 7, 8 , and  8 A, the outer sleeve  16  is formed with a cylindrical outer wall  70  with a mouth  72  at one end and opening  20  at the other. A finger collar  74  is formed around mouth  72  having about the same diameter as the push rod cap  40 . Adjacent to collar  74  there is a control lever  76 . The control lever  76  includes a curved arm  78  shaped and sized to be operated with a finger (like the trigger of a pistol) and a tong  80  extending inside the outer sleeve  16 . The control lever  76  is preferably molded unitarily with the outer wall  70  and collar  74  in such a manner that it can be slightly pivoted when pulled by a finger as indicated by arrow A to cause the tong  80 A to rise outwardly of the sleeve  14 , as indicated by arrow B. When the arm  78  is released, the tong moves back to the position show in  FIG. 8 . As seen in  FIGS. 7 and 8 B, axially spaced from the control lever  76  there is a tab  80 . This tab  80  is supported by a frangible strip  82  attached to the sidewall  70  and includes a tooth  84  extending into the sleeve  16 . Two or more tabs  80  may also be provided.  
         [0052]     Optionally, the sidewall  70  can be formed with two elongated windows windows  56 A having generally the same size and shape as windows  56  on the inner sleeve. The purpose of the two sets of coinciding windows  56 ,  56 A is as follows: 
        1. The oral cavity is a moist and humid environment and it is possible that the humidity encountered by the device may result in a fogging effect of the materials used thus hampering the ability of the user to see the cartridge  18  contained within the syringe assembly  10 . However, in some instances (for example, aspiration) it is important that user be able to see the contents of the cartridge  18 . The two set of elongated windows  56 ,  56 A are conincident to ensures that proper ventilation is provided to prevent the fogging or clouding when being used.     2. In addition, the windows allows the sleeves to be molded of a material that is not translucent and is relatively opaque but still enables the user to see cartridge  18      3. The windows may be used to remove the cartridge from the sleeve  14 .        
 
         [0056]     Advantageously, sleeve  16  also includes two fingers  86 . Each finger  86  includes a respective inwardly extending projection  88  as shown in  FIGS. 8A and 8B .  
         [0057]     The sleeve  16  also includes a helical channel  90 . The channel is disposed on the inner surface of sleeve  16  and is sized and shaped to receive pin  62 . Preferably, the sleeve  18  includes a rib  92  forming channel  90 , although, if the sleeve  16  is thick enough, rib  92  may not be necessary. The sleeve  16  is preferably made from a molded plastic material.  
         [0058]     Returning to  FIGS. 1-3 , initially, the syringe  10  may be supplied in two parts: sleeves  14  and  16  form one part, the plunger assembly  12  forms another part and the health care provider supplies the needle and the cartridge. The sleeve  14  is disposed in the protracted position of  FIG. 3 , so that it is essentially all the way inside sleeve  16 . The two sleeve are being biased by the spring  22  is compressed between the two sleeves, however they are maintained in this protracted position by the tongue  80 A being disposed in hole  58 A and thereby engaging the inner sleeve.  
         [0059]     A user applies an injection to a patient using the syringe  10  as follows. First, he attaches an appropriate needle  24  by mounting on hub  54 . In this position, the needle tip  25  extends outwardly, as shown in  FIG. 2 , while the inner needle end  25 A extends inside the sleeve  14 . Next, the user pulls the lever  76  causing the tongue  80 A to disengage from the sleeve  14 . As a result, the spring  22  causes the sleeve  14  outward to the retracted position and shifting the needle into the sleeve  16  so that it is no longer exposed. Sleeve  14  moves back until the tongues  60 A come into contact with the inwardly extending projections  88  on fingers  86 . Thus, tongues  60 A, fingers  86  and projections  88  are slightly flexible to allow the sleeve  14  to be inserted into sleeve  16 , but once the sleeve  14  is inserted, these elements cooperate to form a stop that prevents the sleeve  14  to be removed from sleeve  16 . Moreover, the control lever  76  also engages the sides of opening  58 B thereby capturing sleeve  14  in the retracted position.  
         [0060]     Next, the user inserts a cartridge  18  into sleeve  14 . The user pushes the cartridge all the way, causing the needle end  25 A to penetrate the membrane  46  and is immersed in the liquid contained therein.  
         [0061]     Next, the user inserts the plunger assembly into the sleeves. More particularly, he pushes the rod  30  into the sleeve  14 . The rod  30  and the sleeve  14  are dimensioned so that as the end  36  of rod  30  comes into contact with the piston  38 , the inner surface of the sleeve  14  telescopically fits over short sleeve  41  and a frictional engagement is created between the sleeve  14  and the snap tabs  42 . The assembled syringe is shown in  FIGS. 2 and 8 . If the rod  30  has a barb  37 , the barb penetrates and engages the piston  38 .  
         [0062]     The syringe could be used in two modes. In one mode, the user holds the syringe with the thumb extending through ring  32  and two fingers trained around finger collar  74 . One finger is used to release the sleeve  14  by pushing control lever  76 . The user then squeezes the syringe between his fingers and thumb together in a normal fashion. As the user is squeezing the syringe three events occur simultaneously. First, the piston  38  is pushed by rod  30  into the cartridge  18  causing the liquid to be expressed through needle  25 . Second, the sleeve  14  with cartridge  18  starts moving forward so that the needle starts extending outwardly of aperture  20 . Once a substantial portion of the needle tip  25 A is visible, the injection can be started. Third, as discussed above, the pin  62  is disposed in groove  90  so that as the sleeve  14  advances through sleeve  16  groove  90  forces the sleeve  14  and needle  24  through pin  62  to rotated about their common longitudinal axis. In other words, the needle  24  is translated and rotated simultaneously while the liquid is ejected and injected. This composite motion continues until the sleeve  14  reaches it initial protracted position. At this position, the control lever  76  again engages the sleeve  14  through opening  58 A.  FIG. 9  shows an intermediate position with the plunger assembly  12  and sleeve  14  advancing, and  FIG. 10  shows the syringe during this final, intermediate locked position. Once this position is reached, the user can just continue injecting the patient. As disclosed in my earlier applications, this three-fold action is very advantageous because it reduces the pain normally associated with the injection, reduces tissue damage, and so forth.  
         [0063]     Once the injection is complete, the user stops squeezing the syringe and activates the control lever  76  again. Once again, the needle  24  jumps back into the outer sleeve. Because pin  62  still engages groove  90 , during this motion, the needle is still caused to translate and rotate simultaneously thereby reducing pain and trauma, and also reducing unnecessary tissue damage. The user can now remove the plunger assembly and the spent cartridge, replace the cartridge in the inner sleeve and start a new injection. This operation is facilitated by the fact that there are one or more (preferably two) O-rings  34  engage the sidewall of the cartridge and stabilize the plunger assembly as it is being withdrawn from the inner sleeve, and when the plunger assembly is removed, the cartridge is pulled out and discarded at the same time. However, if it becomes too difficult to remove the cartridge, the user can remove the cartridge by hand by pushing it axially through windows  56 .  
         [0064]     After the injection is completed, the plunger assembly is discarded together with the spent cartridge. As discussed above, the control lever  76  is used to selectively and temporarily lock sleeve  14  in either the retracted or protracted positions. However, recently some authorities have recommended or mandated that the needle should be immobilized after one use so that it and the syringe cannot be reused. In the present invention, after the sleeve  14  is pushed into the retracted position, tab  80  is pushed inward causing it to bend and engage the sidewalls of hole  61 . The frangible strip  82  is permanently deformed by this action so that it is no longer flexible and cannot be used to retract tab  80 . This tab  80  permanently engages hole  61  and does not allow the sleeve  14  to be shifted or removed from sleeve  16 . In this manner, the needle  24  is captured within sleeve  16 .  
         [0065]     In a second mode of operation, the user first squeezes the push rod cap  40  and the finger collar  74  together. This action causes the inner sleeve to move into the outer sleeve, as described above, without the liquid being injected. When the inner sleeve reaches the Protracted position ( FIG. 3 ), the needle can then be inserted into a patient tissue and liquid can be injected in the normal manner. After the injection is completed, the needle can be retracted into the outer sleeve, as described above.  
         [0066]     In some instances, it may be recommended that the syringe be aspirated at the beginning of the injection. For this purpose, in one embodiment of the invention, shown in  FIG. 11 , the inner sleeve is provided with an annular rim  96  on the end wall of sleeve  14  positioned adjacent to the membrane  46 . During injection, the cartridge  18  is pushed forward so that the membrane  16  bears against rim  96 . The membrane is soft and resilient and therefore it is deformed by the rim  96 . If aspiration is desired, the user releases the finger ring and the rim pushes the membrane  46  and cartridge  18  toward the right, away from needle  24 . This action causes the syringe to aspirate some blood or other body fluid. When injection is resumed, the membrane  46  is pushed back, against the rim  96 . In an alternate embodiment of the invention, instead of, or in addition to the rim  96 , the sleeve  14  is provided with a coil spring  96 A. Again, if the finger ring  32  is released, the spring  96 A causes the cartridge  18  to pull back and aspirate. In another embodiment shown in  FIG. 13  the inner sleeve  14  is formed or molded with integral flexible fingers  96 B on its inner wall as shown. The fingers  96 B are bent forward by the cartridge  18  while the plunger assembly is advanced. When the plunger assembly is released, the fingers spring back, causing the cartridge to move backwards, away from front end of the inner sleeve  12 .  
         [0067]     In another advantageous embodiment shown in  FIG. 12 , the sleeve  14  is provided on its end wall with a hollow spike  98 . The spike is sized and shaped to penetrate the membrane  46  when the cartridge  18  is pushed into the sleeve  14 . The inner lumen of the spike is in communication with the hub  54 . In this embodiment, instead of using a dental needle with two needle tips, a needle assembly  27  can be used with a single hollow needle  27 A that receives the liquid from cartridge  18  through spike  98 . Again, the needle assembly  27  is provided with a Luer lock so that it can be readily mounted onto the hub  54 . Thus, the needle  24  could be a standard needle.  
         [0068]     While it is preferable to have the needle rotate as it is advanced out of the outer sleeve and retracted back into the outer sleeve, obviously safety syringe can be modified to eliminate this rotation, for example, by omitting the pin  72 , the groove  90 , or both.  
         [0069]     Obviously, the safety syringe provides numerous advantages not found in the prior art. More specifically, the safety syringe prevents or at least reduces the sharps injuries from exposed needles. Moreover, by reducing or eliminating exposure to sharp needles, the safety syringe also reduces the risk to exposure to blood and other potentially infections substances. The syringe meets the requirements set forth for this purpose by various state and federal agencies for preventing sharps injuries and exposure to potentially contaminated or infectious substances.  
         [0070]     The syringe is highly innovative and includes many desirable characteristics not currently available in other syringes, in the dental or medical market place. These features include a smaller and compact size, one-handed operation from a single position on the device, reduced needle insertion force, reduced needle deflection, integrated aspiration function, selectively intermittent or permanent locking the needle within the syringe. These features provide the following advantages:  
         [0071]     a. The compact design insures that the syringe can be used by health care providers having various hand-sizes;  
         [0072]     b. One-handed operation insures that that syringe is operated reliably and consistently;  
         [0073]     c. Multiple injections can be performed on the same patient safely, without requiring the recaping of the needle in between injections;  
         [0074]     d. The intermittent locking reduces the risk of accidental needle stick during normal use;  
         [0075]     e. Permanent locking insures that the needle can be safely disposed while it is completely encapsulated and captured within the outer sleeve.  
         [0076]     At least one study has shown that at the present health care practitioners are reluctant to use other types of safety syringes because these syringes lack the following features and therefore they are more difficult and less convenient to use: 
        Needle visibility;     Cartridge visibility;     Difficulty in breaking down and disposing after use;     Difficulty in replacing needle during multiple injections.        
 
         [0081]     Moreover the study has also shown that the following characteristics are desirable for a safety needle: 
        Passivity (little or no user manipulation required to activate safety feature)     Reliability of the safety feature;     Ability to exchange the cartridge quickly and efficiently;     Visibility of the needle tip and cartridge.     Adaptability to various hand sizes     Easy and safe breakdown;     Cost savings.        
 
         [0089]     The safety syringe contains all these desirable characteristics.  
         [0090]     Numerous modifications may be made to this invention without departing from its scope as defined in the appended claims.