3 SELF-ASPIRATING DENTAL SYRINGE

Luca Martinelli

The self-aspirating dental syringe

Publication no. 3 - 31st October 2012

1. THE SELF-ASPIRATING SYRINGE

The self-aspirating syringe is so called because the aspiration takes place "automatically", without any need for retracting the plunger.

There are at least two types of self-aspirating syringes, a standard and a "disk" model.

1.1 Standard self-aspirating syringe

 

Pic. 1

1.2 Disk self-aspirating syringe

The structure is identical to the previous one, with the difference that the disk is integral with the vial-holder cylinder, but completely independent with respect of the plunger (It has a through hole that allows the plunger to slide inside it).

 Example of a type of self-aspirating syringe with disk.

Pic. 2

1.3 Loading

The loading is substantially identical to the side-loading syringes except that the vial holder cylinder is to be retracted in order to have the space necessary to insert the tubular vial.

Hold the syringe and retract the plunger;

Pic. 3

Insert the tubular vial into the barrel of the syringe;

Pic. 4

Pic. 5 

When the plunger is retracted, to allow the tubular vial to enter into the barrel, the vial holder cylinder is placed at a rearmost position with respect to the tubular vial, while the plunger is completely out of it (hidden in the handle of the syringe).

Finally, the plunger is released and with it, automatically, also the vial holder cylinder.

When the plunger of the syringe is released the vial holder cylinder (1-Pic. 6) touches the tubular vial (2-Pic. 6) holding it into the barrel.

Pic. 6

The plunger of the syringe (1-Pic. 7) move downwards, until contact with the rubber plunger of the tubular vial (2-Pic. 7).

Pic. 7

Please note that the vial holder cylinder (3-Pic. 7) can not be pushed beyond its natural travel when it is separated from the plunger of the syringe and has no reference points which allow its descent (pressure) in an independent and separate way.

Then insert the needle as usual.

1.4 Operating principle of both "Standard and Thumb-disk" syringes

1.4.1 Physical operating principle

The self-aspiration occurs by variation of tubular vial internal pressure; this takes place when the tubular vial, pushed by the plunger of the syringe or by the vial holder cylinder, opposes the self-aspirating tube located inside the barrel of the syringe.

2 OPERATION

When the diaphragm (2 - Pic. 8) of the tubular vial (5 - Pic. 8) opposes the tube of the syringe (3 - Pic. 8) it undergoes a bending (2 - Pig 8) inwards, this causes an increase in pressure inside the tubular vial (7 - Pic. 8); its release (9 - Pic. 8) causes a drop in pressure inside the tubular vial, and this creates simultaneously an aspiration towards its inside (9 - Pic 8).

Pic.8

Detail of tubular vial in contact with the tube 

Pic.9

The physical operating principle of the two types of self-aspirating syringes (standard and thumb disc) is identical, the difference is the possibility of using two different activation modes.

1.4.3 "Standard" self-aspirating syringe

In "standard" self-aspirating syringes the aspiration is only operated by the plunger of the syringe.

Take as a reference the illustrations in Fig. 8, when pushed, the plunger of the syringe also pushes the rubber plunger of the tubular vial, which in turn pushes the anaesthetic towards the needle, this operation pushes all the tubular vial towards the tube of the syringe.

The diaphragm of the tubular vial thus opposes the tube and undergoes a pressure inwards the tubular vials, increasing its inner pressure; when released, the plunger causes a drop in internal pressure that simultaneously originates an aspiration.

5 Disk self-aspirating syringe

The disc is used when an aspiration is required even before pushing the plunger of the anaesthetic.

The physical operating principle is the same, this is simply and accessory, different mode of activating the self-aspiration.

The vial holder cylinder is integral with the disk (Pic. 10), if the disk is pressed (Pic. 11), the perimeter of the vial holder presses on the perimeter of the tubular vial (Pic. 12) which will be pushed downwards, causing in turn a contrast between the diaphragm and the tube, resulting in the self-aspiration.

Disc/vial holder cylinder (one-piece instrument)

Pic. 10

Pic. 11

               Disc pulled upwards            Disc lowered on the 
                                                          tubular vial
Pic. 12

Finally, in the standard self-aspirating syringe is the plunger that, by pressing on the rubber plunger of the tubular vial, activates the self-aspirating mechanism; in the disk syringe the self-aspiration can also be activated by the disk that, being integral with the vial holder cylinder, presses on the glass edge of the tubular vial (so not on the rubber plunger of the tubular vial) thus pushing and activating the self-aspiration.

1 CLASSIFICATION AND MAIN PARTS OF DENTAL ANAESTHETIC CARTRIDGE SYRINGES

1 CLASSIFICATION AND MAIN PARTS OF DENTAL ANAESTHETIC CARTRIDGE SYRINGES

Luca Martinelli

Basics of dental anaesthetic cartridge syringes

Publication no. 1 - 31st October 2012

 1. CLASSIFICATION AND MAIN PARTS OF DENTAL ANAESTHETIC CARTRIDGE       SYRINGES

The dental cartridge syringes are used to perform local anaesthesia.

Requirements and test methods of syringes are specified in EN ISO 9997 rule.

Dental cartridge syringes are so called as they use an anaesthetic placed in a tubular vial whose appearance resembles a firearm cartridge.

With these syringes it is possible to perform intra-oral anaesthesia such as:

1   by infiltration (submucosa, para-periosteal, intra-osseous, intra-ligament, intra-papillary);

2   by conduction (truncal or plexus).

1.1 Classification according to the type of aspiration

The dental cartridge syringes are classified according to the following types:

Type 1: non-aspirating;

Peripress type

Fig. 1

Examples of some types of non-aspirating syringes.

Type 2: aspirating. 

Type 2a: with aspiration due to the plunger puling from the needle;

                              

Fig. 2

Examples of some types of aspirating syringes.

The couplings of the tubular vial rubber plunger are many and distinguished by shape and type depending on the manufacturer, the choice must then be made by the dentist.

Fig. 3 

Examples of some types of anchor of the syringe plunger for coupling to the tubular vial rubber plunger   

Type 2b: Self aspirating due to the deflection of the tubular vial rubber diaphragm.

Fig. 4

Examples of some types of self aspirating syringes.

                                   

The syringes may be fitted with 1.8 ml tubular vial or with a longer barrel (a tube housing the cartridge) and plunger, 2.2 ml tubular vial, the threading of the needle is of the metric type, but also syringes with "Imperial" (in this case often the name is also used to refer to the syringe itself) or Whitworth thread type are available, and some make it possible to interchange the tip.

1.2 Classification according to the loading system

There is also a classification according to the type of loading of the tubular via, as follows:

1 - Side-loading syringes;

Fig. 5

Example of some side-loading syringes

1 - Rear-loading syringes;

Fig. 6

Example of a type of rear-loading syringe

      1 - Front-loading syringes.

Fig. 7

Example of some front-loading syringes

Beyond the various types of syringe, the choice between them depends on the type of anaesthesia that must be performed.

In the case of anaesthesia by infiltration the front-loading syringes of the type shown in Fig. 7 can be used, but of course all the other syringes.

The anaesthesia by conductions requires an aspirating syringe and therefore all those not allowing aspiration are to be excluded.

1.3 The main parts of the syringe

Fig. 8

Example of aspirating syringe

 

Fig. 9

Example of self-aspirating syringe

2. CONSTITUENT MATERIAL

Generally, dental cartridge syringes are made of nickel-plated brass (formerly chrome) with parts made of other metals, is now increasingly used stainless steel, typically an AISI 303 or 304 type.

Some syringes have constructional details such as the finger grip and the handle of the plunger black coloured, obtained by laying surface deposits, or made of plastic material (mostly polypropylene) as well as the protective tubes (explosion-proof) of the vial.

However, there are types of syringes made of "plastic", usually disposable.

                                                  

Fig. 10

Example of syringe made of plastic material.

                

3. INSERTING THE TUBULAR VIAL NTO THE VARIOUS TYPES OF SYRINGE

3.1 Side-loading syringes

 After having retracted the plunger of the syringe, insert the tubular vial and then the anchor of the syringe plunger into the rubber stopper of the tubular vial, then insert the needle into the syringe, leaving it covered.

  Fig. 11

  3.2 Rear-loading syringes

Open the hinge of the syringe and after having bent the barrel fits the tubular vial, from the side of the aluminium capsule, close the syringe and align the plunger proceeding as in the previous case.

Open the hinge of the syringe and after having bent the barrel fits the tubular vial, from the side of the aluminium capsule, close the syringe and align the plunger proceeding as in the previous case.

Fig. 12

3.3 Front-loading syringes

Unscrew the barrel of the syringe, insert the tubular vial and re-tighten the barrel to the handle, slightly push the plunger and insert the needle.

Please remember that in the "pen" syringes without the retracting button of the plunger rack, the latter must be completely removed from the front and then re-inserted from the rear.

It should be added that the syringes fitted with rack deliver an "x" amount of anaesthetic per each "click" made.

This amount is not the same for all syringes (it depends on the manufacturer) since the quantity is determined by the distance that the plunger covers into the barrel and therefore into the tubular vial.

Since the size of the rack geometry is known, the amount of anaesthetic in a tubular vial could be divided depending on the number of "clicks" a syringe allows, but undoubtedly the best procedure is that involving the information directly given by the manufacturer, it must be considered that, in principle, the amounts of anaesthetic delivered with a "gun" syringe corresponds to about 0.20 ml per "click" and about 0.05/0.06 ml in case of a "pen" syringe.

Obviously, these values vary from model to model depending on the different constructive geometry, it is then important to get the information from the manufacturer of the syringe.