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How Do Topical Anesthetics for Dental Treatments Work?

dentist with patient

How Do Topical Anesthetics for Dental Treatments Work?

One of the formulations we consistently receive requests for is high-powered topical anesthetic gels. There are numerous numbing gels used by dentists for numbing prior to routine dental care, oral surgery, and orthodontic procedures. How do numbing gels work though, and why are some formulations more effective than others?

Anesthetics Designed for Topical Use

A topical anesthetic is not just an injectable anesthetic applied without a needle. Unlike an injected anesthetic, a topical must have excellent permeability in order to penetrate the mucous membrane. In most cases, we add a vasoconstrictor to our formulations in order to slow the dispersal of the anesthetic and increase the amount of time it stays in the area being treated.

The onset of action for a topical anesthetic can be between 30 seconds to 3 minutes, often depending on the patient. The area must be dried before the topical gel is applied, usually with a cotton swab or gauze.

How Topical Anesthetics Work

Topical anesthetics primarily work by blocking nerve signals, which alters the level of pain that a patient can experience. The conduction of nerve impulses is blocked by decreasing nerve cell permeability to sodium ions. The change in permeability increases the threshold of pain, which means it takes more to excite the nerves.

When nerves are operating normally, there is a kind of gate in the nerve that causes ions to flow in and out. The series of gates opening and closing is what carries the message of a stimulus to the brain. When the gates are stopped by a topical anesthetic, the message is no longer able to be carried and there is no sensation of pain. The topical anesthetic makes it so that the nerves do not become excited by something like a needle or a dental instrument.

Topical Anesthetic Ingredients

Benzocaine and lidocaine are the two most common ingredients used in topical anesthetics, mostly due to their low toxicity and efficiency in numbing. Benzocaine is an ester-based anesthetic and lidocaine is an amide-based anesthetic. Although neither type of anesthetic is associated with a high number of reactions, ester-based anesthetic tend to be more frequently associated with an allergic response.

Tetracaine is another ester-based anesthetic that has a longer duration of effect. It can last up to one hour under the right conditions, however the dosage must be limited as it is quickly absorbed into the blood stream. When combined, topical anesthetics can be even more effective. Each of their qualities of potency, absorption, and safety can be combined strategically in one formulation by a compounding pharmacy.

Topical Anesthetic Ingredient Strengths

The percentages of topical anesthetics included in a formulation have been put together based on their absorption rate and potency. For example, in our Profound gel, lidocaine and prilocaine are included in 10% strengths. However tetracaine is included in 4% strength. This is because tetracaine is more potent anesthetic and is also more quickly absorbed. It is important to limit systemic absorption of topical anesthetics to reduce any side effects.

Another formulation we make at our pharmacy is popularly called the Baddest Topical in Town (or BTT 12.5). It is a combination of lidocaine 12.5%, tetracaine 12.5%, prilocaine 3%, and phenylephrine 3% in one anesthetic gel. This provides the highest potency topical anesthetic available to dentists, and is not commercially available.

Side Effects of Topical Anesthetics

Topical anesthetics actually have far fewer incidences of side effects than injected anesthetics. Usually side effects occur because of systemic absorption of an ingredient into the blood. This is not common with topical anesthetics when they are used properly. The majority of patients find that topical anesthetics make their dental visits much easier.

There are useful resources that can help determine the maximum dosage of a topical anesthetic based on a patient’s body weight. However sometimes anesthetic is left on too long, or too much is used, and a patient may experience side effects like rapid heart rate and anxiety. It is important for practitioners to understand the strength of the ingredients they are using on their patients and to always use caution when they are not sure how their patients will react.

Understand Topicals Before You Use Them

Some professionals feel that because they have used topical anesthetics in the past, they are able to effectively use any formulation. Each topical anesthetic formulation is different, however, and has characteristics that may change how it should be used. Understanding fully how topical anesthetics work is essential for all dental professionals. Patients who want to be well-informed about the treatments they receive may also benefit from studying how topical anesthetics work.

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