Topical anesthetics are effective to a depth of 2-3mm and are effective in reducing the discomfort of the initial penetration of the needle into the mucosa. Although flavored topical anesthetics are currently available, it may be still disagreeable to patient and the length of application time may increase apprehension in some pediatric patient. Topical anesthetics are available in gel, liquid, ointment, patch and pressurized spray forms. When applying topical anesthetics to the soft tissue, use the smallest effective amount to avoid anesthetizing the pharyngeal tissues.
The most common topical anesthetics used in dentistry are those with benzocaine or lidocaine.
Ethyl aminobenzoate (benzocaine) is an ester local anesthetic. It is available in up to 20% concentrations. It is poorly absorbed into cardiovascular system. It remains at the site of application longer, providing a prolonged duration of action. Localized allergic reactions may occur following prolonged or repeated use, and it is reported to inhibit the antibacterial action of sulfonamides.
It is not known to produce systemic toxicity in adults but can produce local allergic reactions. The Food and Drug Administration (FDA) has raised concern regarding the use of benzocaine and compounded topical anesthetics containing mixture of amides and esters.2 This compound may cause methemoglobinemia, a rare but serious and potentially fatal condition. Children younger than 2 years appear to be at particular risk. In the most severe cases, methemoglobinemia can result in death. Patients who develop methemoglobinemia may experience signs and symptoms such as pale, gray or blue colored skin, lips and nail beds; headache; lightheadedness; shortness of breath; fatigue; and rapid heart rate.
Most of the cases reported were in children younger than 2 years who were treated with topical benzocaine gels for the relief of teeth pain. The signs and symptoms can occur after a single application or multiple applications and can begin within minutes and hours of application.
Lidocaine is available as a solution or ointment up to 5% and as a spray up to 10% concentration. It has a low incidence of allergic reactions but is absorbed systemically and can combine with an injected amide local anesthetic to increase the risk of overdose. A metered spray is suggested if an aerosol preparation is selected.
Systemic absorption of a lidocaine topical anesthetic must be considered when calculating the total amount of anesthetic administered.