 Hello everyone. In this lecture we shall discuss armamentarium of local anesthesia. Main equipment necessary for the administration of local anesthetic include the syringe, the needle and the local anesthetic cartridge. In addition, you may also need topical antiseptic, topical anesthetic, applicator sticks, cotton gauze and a hemostat. The first equipment is the syringe. The syringe is the vehicle whereby the contents of the anesthetic cartridge are delivered through the needle to the patient. The syringe types available in the industry can be classified into non-disposable syringes, disposable syringes, safety syringes and computer controlled local anesthetic delivery systems. In the non-disposable category, you have bridge loading, metallic cartridge type aspirating syringes. Pressure syringes and eject injectors. American Dental Association criteria for acceptance of local anesthetic syringes are given here. The syringes must be durable and able to withstand repeated sterilization without any damage. They should be capable of accepting a wide range of cartridges and needles. It should be permittable for repeated use. They should be inexpensive, self-contained, lightweight and simple to use with one hand. It should also provide effective aspiration and it should be built in such a way that any blood in the cartridge can be easily observed. Now let's have a look at the different components of bridge loading, metallic cartridge type syringe. Here is the assembled syringe and here is the disassembled one. As you can see in the figures, there is a syringe barrel which is metallic. This is the piston with the harpoon at its end, a pointed harpoon at its end. Then you have the finger, a grip, a thumb ring and a needle adapter. So the term bridge loading implies that the cartridges inserted into the syringe from one side of the barrel. Here is the syringe barrel and the cartridges inserted through the side. So there is a hinge mechanism which is operated to insert the cartridge into the syringe barrel. The needle is attached to the barrel of the syringe at this point which is the needle adapter. The needle, from the needle adapter it passes into the barrel so that it penetrates the diaphragm of the local anesthetic cartridge which is inserted into the barrel prior to insertion of the needle. The cartridge also has two ends. So the one end of the cartridge will be penetrated by the needle and the other end which has a silicone rubber stopper is penetrated by the harpoon which forms the tip of the piston. How does this syringe become an aspirating type of syringe? When a negative pressure is exerted on the thumb ring by the administrator the blood will enter into the needle and it will be visible in the cartridge. If the needle tip is within the lumen of a blood vessel that is called negative pressure that is if the administrator pulls the piston with the harpoon behind then it creates a negative pressure which will take the blood within the cartridge if it is within the blood vessel. And if the administrator applies a positive pressure that means if he pushes the piston forward towards the needle side it is then called positive pressure. By this way the local anesthetic solution can be deposited at the desired target site. With commonly used bridge loading metallic cartridge type syringes an aspiration test must be carried out purposefully by the administrator before or during drug deposition. However the studies have shown that many dentists don't purposefully perform an aspiration test before injection of an anesthetic drug therefore to increase the ease of aspiration self-aspirating syringes were developed. As mentioned earlier the cartridge which is inserted into the syringe battle has two diaphragm ends one of which is penetrated by the needle and the other which rests on the tip of the piston. So self-aspirating syringes use the elasticity of the rubber diaphragm in the anesthetic cartridge to obtain the necessary negative pressure for aspiration. Unlike in the aspirating syringes the piston itself aspirating syringes don't have a sharp harpoon but the metallic plunger here is blunt and flat and the cartridge diaphragm rests on this metal projection inside the syringe that directs the needle into the cartridge. So any pressure acting directly on the cartridge through the thumb disc or indirectly through the plunger shaft which is the metal projection over here at the piston. So this pressure acting on the cartridge distorts the rubber diaphragm at the piston end of the cartridge which produces a positive pressure within the anesthetic cartridge. That means any pressure given through from the thumb ring over here will push this plunger towards the rubber diaphragm on the cartridge so that a positive pressure is created within the cartridge and when this positive pressure which is given is released it then produces a negative pressure within the cartridge which permits aspiration. The point to be understood here is that the positive pressure created within the cartridge which then gets converted into negative pressure in order to aspirate is produced by this metallic plunger alone or it is produced by the pressure given from the thumb ring. It is found that the thumb ring produces twice as much negative pressure as the plunger shaft which is this metal projection. So the use of self self aspirating dental syringe permits easy performance of multiple aspirations throughout the period of local anesthetic deposition. This is a plastic disposable syringe. So this syringe contains a lure lock screw on needle attachment mechanism and it has no aspirating tip. Aspiration can be done by pulling the plunger of the syringe before or during injection because there is no thumb ring. Aspiration with a plastic disposable syringe needs the use of both the hands. In addition these syringes don't accept dental cartridges therefore the needle attached to the syringe must be inserted into a vial or a cartridge of local anesthetic drug and an appropriate volume of solution should be removed. The next component in the armamentarium is the needle. The needle permits local anesthetic solution to move from the cartridge into the tissues surrounding the needle tip. Most needles used in dentistry are stainless steel and are disposable. All needles have these components in common the bevel, the shaft or the shank, the hub and syringe penetrating end. The bevel defines the point or the tip of the needle. It is manufactured as long medium or short bevel. It is found that the greater the angle of bevel with the long axis of the needle, the greater will be the degree of deflection as the needle passes through the soft tissues of the mouth. The shaft or the shank of the needle is a long piece of tubular metal which runs from the tip of the needle through the hub and continuing to the piece that penetrates the syringe or the cartridge. The two factors that needs to be considered with the shank are the lumen or diameter of the needle and also the length of the shaft from point to the hub. The hub is a plastic or a metal piece through which the needle attaches to the syringe. The syringe penetrating end of the needle extends through the needle adapter and it perforates the diaphragm of the local anesthetic cartridge. So these are the parts which form a needle. As mentioned earlier when needles are selected for use in various injection technique there are two factors which must be considered. They are the gauge and length of the needle. Gauge refers to the diameter of the lumen of the needle. The smaller the number the greater the diameter of the lumen. For example a 30 gauge needle has a smaller internal diameter when compared to a 25 gauge needle. The smaller diameter needles are less traumatic to the patient than needles with larger diameter. The most commonly used needles in dentistry are 25, 27 and 30 gauge needles. Coming to the length. Dental needles are available in two lengths mainly long which is approximately 40 millimeters and short needles which are approximately 25 mm. The needles should not be inserted into the tissues till their hub unless it is absolutely necessary. The weakest portion of the needle is at the hub so that the needle breakage occurs. Long needles are preferred for all injection techniques requiring penetration of significant thickness of soft tissue. There are several clinical problems pertaining to needle insertion. Pain on insertion is mainly due to use of dull needle. Therefore this can be avoided by using sharp new disposable needles and application of topical anesthetic at the site. Bending of needle can make them weak and lead to needle breakage. So never attempt to force a needle against resistance. Smaller gauge needles are more likely to break than larger gauge needles. Pain on withdrawal of the needle is more likely that they occur when the needle tip forcefully contacts a hard surface like bone. So here also needle should never be forced against resistance. Injury to the patient or administrator. It happens mainly due to carelessness or inattention by the administrator. Even sudden unexpected movement of the patient can also cause injury. Therefore the needle should remain capped until it is to be used and it should be made safe immediately after withdrawal from the mouth. A new approach to reducing needle deflection has been described as bi-rotational insertion technique or BRIT technique. In this technique the operator rotates the needle in a back and forth rotational movement while advancing the needle through soft tissue. So this technique is similar to that of entrodontic instrumentation. It has been demonstrated that deflectional bending of a needle can be minimized or even eliminated regardless of the length or gauge of the needle as long as the insertion was performed using BRIT technique. Dental cartridge is a glass cylinder containing the Luchelin esthetic drug along with other ingredients. A pre-filled 1.8 ml dental cartridge consists of four parts. Cylindrical glass tube, stopper, aluminum cap and a diaphragm. Stopper is located at the end of the cartridge that receives the harpoon of the aspirating syringe. Stopper was initially mixed with paraffin wax in order to produce an air tight seal around the against the glass walls of the cartridge. Glycerin was also added to act as a lubricant. Today silicone stoppers are used hence eliminating the need for paraffin and glycerin. Aluminium cap is located at the opposite end of the cartridge from the rubber plunger. It fits around the neck of the glass cartridge thereby holding the diaphragm in position. Diaphragm is a semi-permeable membrane usually made up of latex rubber through which the cartridge end of the needle penetrates. The perforation of the needle is synchrically located and round thus forming a tight seal around the glass chamber. Contents of a dental cartridge include local anaesthetic agent which aids in conduction blockade, vasopressor, sterile water which acts as a solvent, sodium chloride to maintain the isotonicity of solution, sodium metabysulfite which is an antioxidant to vasopressor, methylparaben, a preservative which is no longer used due to its allergic nature. Some of the clinical problems related to dental cartridge includes bubble in the cartridge. A small bubble of approximately 1 to 2 mm in diameter is formed in the dental cartridge. This bubble is composed of nitrogen gas which was bubbled into the local anaesthetic solution during its manufacture. This was to prevent oxygen from being trapped inside the cartridge. The stopper can become extruded if a cartridge is frozen and the liquid inside expands. In this case the solution is considered unfit for use. Burning sensation on injection. Burning sensation can be caused as a normal response to the pH of the blood. Also cartridge containing sterilizing solution, an overheated cartridge or a cartridge containing a vasopressor has lower pH which results in burning sensation. Corroded cap or a rusted cap. Aluminium cap on a local anaesthetic cartridge can be corroded if it is immersed in disinfecting disinfecting solutions which contain quaternary ammonium salts like benzalconium chloride. In this case the cartridges shouldn't be used and discarded. The leakage of local anaesthetic solution into the patient's mouth during injection occurs if the cartridge and the needle are prepared improperly or the needle puncture of the diaphragm is not centric. If it is a void or eccentric it can cause leakage of solution during injection. Broken cartridge is another clinical problem related to cartridge and the most common cause is mishandling of cartridge during shipping. How will you carefully handle local anaesthetic armamentarium? After each use thoroughly wash and rinse the syringe free of any local anaesthetic solution, saliva or any other foreign matter. You may autoclave the syringe in the same manner as other surgical instruments. After every five autoclavings dismantle the syringe and lightly lubricate all the threaded joints especially where the piston contacts the thumb ring. You may clean the harpoon with a brush after every use. The needles must never be used on more than one patient. Needles should be changed after three or four tissue penetration in the same patient. It should be covered with a protective sheet when not being used and it must be properly disposed after every use. Some of the things you need to keep in mind while handling syringe, needle and a cartridge. That's all for this lecture. Thank you.