What is a local anesthetic?

Local anesthetics are one of the safest, most reliable ways to achieve anesthesia in dentistry. Local anesthetics contain three parts – an aromatic group, an intermediate chain, and a secondary or tertiary amino terminus. The portion known as the ‘intermediate chain’ is the basis for the classification of anesthetic, which is divided into two groups. These two groups are known as amides and esters.

Because esters are more common to cause allergic reactions, they are rarely (if not at all) used for local anesthesia in dentistry. These are anesthetics such as butacaine, procaine, and cocaine.

Amides are now the most commonly used anesthetics. They can easily be remembered by this rule: ‘If the local anesthetic has two ‘i’s’ in its name; it is an amide.’ The amides used today are:

• Lidocaine
• Prilocaine
• Bupivicaine
• Articaine
• Mepivacaine

Anesthetics are commonly paired with epinephrine, a vasoconstrictor. As the local anesthetic is injected into tissues, the epinephrine acts to constrict blood vessels around it, minimizing the amount of anesthetic that is taken into the blood stream and even further localizing the anesthesia into the indicated area.

What dictates what type of local anesthetic we use?

There are various factors that determine which type of local anesthetic we use – whether a patient has hypertension, the types of drugs patients are taking, and the duration of the procedure are all important factors.

If a patient is hypertensive, using epinephrine with the anesthetic may be contraindicated, as it could result in a hypertensive crisis. With this in mind, having an anesthetic on hand that does not contain epinephrine is essential. The anesthetic that can be used in this situation is Mepivicaine – it has minimal vasodialative effect for those who are hypertensive. It’s important to understand that Mepivicaine is often found with vasoconstrictors such as levonordefrin (instead of epinephrine) – if this is the case, be wary that levonordefrin can trigger hypertension in those who use selective beta blockers.

If you are planning to do a procedure that is exceptionally long, you may choose to use Bupivicaine, which is known to have a long duration of effect. This anesthetic is not great for maxillary infiltrations, though, due to it’s high pKa value.

If you are attempting a restoration on the mandible, and would like to use infiltrations, you may want to use Septocaine (Articaine). Septocaine has a great ability to infiltrate dense bone, such as that found in the mandible. It also has a very short half-life, meaning it is eliminated from the body faster. There is debate whether Septocaine should be used in nerve blocks, though, and caution should be advised when apply nerve blocks with Septocaine, as well as those patients that are pregnant

If you are looking for a run-of-the-mill anesthetic, Lidocaine might be the anesthetic you’re looking for. Unfortunately, Lidocaine has to be used with a vasoconstrictor, such as epinephrine, and this may be contraindicated in someone who has high blood pressure.

To summarize:

• Any anesthetic with a vasoconstrictor should be used with caution on those who are hypertensive
• Carbocaine (Mepivicaine) should be used with those who are hypertensive
• Septocaine is a great #1 choice due to its low half-life and infiltrating ability, but should be used with caution during blocks and those who are pregnant
• Lidocaine is O.K.

References:

(n.d.) Pharmacodynamics of LA. Dr. Anthony Caputo. A.T. Still Missouri School of Dentistry and Oral Health.

(n.d.) Local Anesthesia Review. Dr. Robert Fuszner. A.T. Still Missouri School of Dentistry and Oral Health.