THE LONG AND SHORT OF IT - Teacher Tina RDH

THE IMPORTANCE OF NEEDLE SELECTION

One of the keys to a successful injection is needle selection. Putting the correct needle on your syringe will help you hit your target just right.

There are two measurements of the needle to consider, length and gauge.

To hit the right spot, you need to have the length to get there. The length should be appropriate for the depth of injection. The long needle is about 32 mm in length which is perfect for most of the mandibular injections, but not the best option for an injection in which minimal penetration is needed, like a PDL. An extra-short, about 10 mm long, would be ideal for this one.

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Don’t forget the important safety rule of not “hubbing the needle”. The hub (where the needle and adapter meet) is the weakest point of the needle. While it is rare, there have been enough cases in which a needle has broken during the injection. When a needle breaks while it is in the tissue, the mucosa can have a rebound effect, and the tissue slides up the needle a few millimeters. If the tissue is at the hub or close to it, the tissue will “swallow” the needle. Then all of a sudden you are dealing with a plethora of other issues…NO THANK YOU! So, for those deeper injections like the mandibular blocks or the IO, grab a long needle.

Let’s be safe!

The other aspect we often forget about and is just as important to an accurate injection, is the gauge. The needle gauge is based on lumen size (diameter of the hole). The different gauges commonly used in dentistry are 25, 27, and 30.

One would think that the lower the number, the smaller the lumen of the needle. However, it is the exact opposite. A 30-gauge needle has a smaller opening while a 25-gauge is larger. Check out the diagram to see the size difference.

While the length of the needle helps us reach the target point, it is the gauge of the needle that will help us get there accurately. The larger the gauge of the needle the less flexible it is. The needle is less likely to bend, which increases the success rate (you get straight to the point). This means that when giving an injection that has a significant depth to the targeted deposition, a 25-gauge needle will not bend or flex as much.

For example, when giving the IA injection, you may need to readjust the syringe during insertion to avoid premature contact with the bone. When you readjust, the needle can bow a little. I know you have probably seen the needle do this outside of the tissue, but it even happens when the needle is deep into the mucosa, and even if you don’t need to readjust. With a smaller gauged needle, like the 30, the needle is more likely to bend, like a rainbow. This means the opening will not be at the targeted deposition site. Alas, one reason why a 30-gauge long needle is a rarity in the dental office.

Also, the larger lumen provides the opportunity for a more accurate aspiration. Due to the larger diameter, it is easier for the fluid to flow into the needle. As the diameter of the lumen decreases fluid resistance increases. This makes the act of aspiration harder (it can even cause the harpoon of the syringe to become dislodged from the rubber stopper, WHOOPS!). Some may think that the use of a 25-gauge needle causes a higher rate of positive aspiration. When what is being observed is a more accurate indication of vascular penetration.

IT DOESN'T FEEL TO BAD EITHER

Often clinicians will select a needle size to help reduce the pain of the initial injection. The pain perception for needle size is reported to have no difference between a 25, 27, or a 30-gauge. According to Malamed, a study was conducted assessing the patient’s awareness of needle size based on pain perception. The participants were injected over the maxillary anterior teeth (without any topical) and could not tell any difference in the needle size. Now that is an interesting research study…I wonder how they were able to get the volunteers for that one.

As a side note, to reduce the sensation of the needle insertion the use of topical anesthetic and pulling the tissue so it is tight will allow for an easier time for you and your patient.

So next time you are setting your syringe up make sure to consider the length and gauge of your needle. Making the correct selection will help you hit your best shot.

CHEERS,

Tina

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Reference:

Are you confused when choosing the correct Hypodermic needle for your patient? Well your fear and trepidation is about to dissolve. This article will explain all the different types of needle gauge available at RayMed and how they should be used.

As the hypodermic needle gauge increases, the width of the needle decreases. So a 16g needle will be larger in width when compared to a 30g needle. Secondly the length of the needle is a important factor when selecting your desired needle. Our selection of needle offers a wide range of length ranging from 8mm to 40mm. 

There are four types of injections 

1. Intramuscular injection
2. Intradermal injection
3. Subcutaneous injection
4. Intravenous injection

Intramuscular injection deliver the substance directly inside the muscles, the needle is kept 90 degrees with the skin when the needle is inserted into the skin. The length of needle is usually long so a suitable choice of gauge will be 20g-23g. Some clinicians don't mind using needle gauge 25g-29g as the needle length is 13mm to 16mm. The Z track method is used for a intramuscular injection. 

An intradermal injection is where the needle is injected just beneath the dermis, below the epidermis of the skin. Absorption is the slowest and its preferred use is to test for skin allergies as the reaction is clearly visible. Preferred needle gauge for a intradermal injection ranges from 25g to 30g as the needle width is small 0.5mm to 0.3mm and a length of 8mm to 13mm. 

Subcutaneous injection are well known for a the injection of insulin for people suffering with diabetes, again the chosen needle gauge ranges from 25g to 30g as they are the most efficient in delivering the liquid in between the skin and muscles.  

Intravenous injection is where the needle is injected directly into the veins and hence the bloodstream. You will notice most NHS staff while doing intravenous injection using the needle gauge between 20g and 25g. The needle width and length makes it very efficient for the injection. These can also be used for injection in the deltoids. 

Aesthetics clinics providing anti wrinkle injections are known to using hypodermic needle gauge 25g to 30g. As most of the Botox is applied to the face the needle length is required to be around 13mm with a very fine width. Our range of needles are incredible for the Aesthetic industry. 16g to 23g can be used for the withdrawal of liquids before injection.

Our products are CE marked and sterile fit for humans and animals, veterinary professional can use any of our hypodermic needles. Animals with thick skin can use 16g to 21g with a longer needle length in order to pierce the tough skin. Farm animals requiring vaccination have bought from us on many occasions. Diabetic cats and dogs may use the 25g needle. It consists of a width of 0.5mm and length 16mm, ideal for insulin injection on cats. 

Our hypodermic needle range have triple bevelling resulting in a sharp stainless steel needle fit for all types of skin, the easy to identify colour code allows you to choose the correct needle for effortless injection. All needles are STERILE, totally non- toxic and non-pyrogenic, ready for medical use. Now you know what a hypodermic needle is and how to choose the correct gauge. 

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