The Armamentarium and Basic Injection Technique

The Armamentarium

The armamentarium is composed of:

1. The syringe
2. The needle
3. The local anaesthetic cartridge

The syringe - The syringe has three parts - a screw thread to attach the needle, the plunger to push the contents out of the cartridge, and the ring to allow the dentist control over administering the local anaesthetic. Syringes can be reusable metal or disposable plastic. Most metal syringes allow the dentist to aspirate. Aspiration is useful so that the local anaesthetic isn't inadvertently injected into a vein. This is particularly important if there is adrenaline in the cartridge as adrenaline injected into the vein may cause the patient's heart rate to skyrocket. The plastic syringe has the advantage of being disposable which is desirable from a cross-infection point of view.


The needle - The needle has one end that penetrates the diaphragm of the cartridge and the other end penetrates the person. Needles come in different lengths and diameters. Common lengths are long (41mm), short (25mm) and ultra-short (10mm). The diameters are expressed by the term "gauge". The gauge of a needle is indicating the internal diameter of the needle. Something that confuses me is that the thinner the needle is the larger its gauge is. For example, a 30 gauge is thinner than a 25 gauge! Theoretically the greater the gauge the less painful an injection will be, but in practice patients usually experience the same sensation from 30 gauge to 23 gauge.


The cartridge - The cartridge contains the local anaesthetic and usually a vasoconstrictor like adrenaline. The vasoconstrictor causes the blood vessels adjacent to the injection site to constrict which means that less local anaesthetic gets into the systemic, so less is needed to achieve anaesthesia where needed.

Basic Injection Technique

Commonly used local injection techniques are infiltration, nerve block, intrapulpal, supraperiosteal, intraligamental, and intraosseous.

If the cartridge is below room temperature - as it will be if stored in the refrigerator, it must first be warmed to room temperature. This will make the experience much more comfortable for the patient.

Put personal protective equipment on - gloves, mask, eye wear, etc.

Now load the cartridge followed by the needle into the syringe. Check the flow out of view from the patient and don't spray into the air like you see on the movies. That sort of thing scares patients.

Now that the armamentarium is ready, prepare the patient by tilting them back 45 degrees and adjusting the height of the chair so that the patient's head is at your elbow level.

Dry the area you will be injecting into with some cotton gauze.

Next you may apply topical anaesthetic to the area. Supposedly this will cause anaesthesia 2-3mm into the mucosa if allowed to penetrate for 2 minutes. This topical anaesthetic should make the initial penetration of the needle painless.

While waiting the 2 minutes for the topical to kick in, run through the procedure with the patient.

Now bring the syringe to the patient - keeping it out of their view. Stretch the mucosa you will be injecting into to minimise the pain and tissue damage. Then, making sure you have a good finger/hand rest, insert the needle the length of its bevel into the mucosa. Inject a drop of local anaesthetic - wait a moment - then push the needle into the tissue a little deeper and inject another drop. Continue this process until the target is reached.

Now that the target is reached, aspirate to ensure you're not injecting into a blood vessel, and then slowly deposit the rest of the local anaesthetic (a 2.2mL cartridge should take no less than 2 minutes to inject). While doing this communicate with the patient and observe them for signs of discomfort or reaction to the contents of the cartridge.

If the patient faints (vasodepressor syncope), lie him flat with feet at or slightly above chest level.