| Topical Anesthetics in the Dental Office
Topical anesthetics are applied directly on the skin or mucous membranes to relieve pain or itching caused by dental injections and procedures, hemorrhoids, insect bites, sunburn, cuts or poison ivy. Topical anesthetic preparations containing benzocaine are available in grocery and drug stores to ease pain from teething, braces, canker sores or toothache.
Dentists commonly use topical anesthetics for several purposes:
- To prevent or reduce the pain caused by injecting an anesthetic
- To prevent the gag reflex (the tendency to gag when something touches the back of your throat) when you are having an X-ray, or when a tray is being placed in your mouth to take an impression or give you a fluoride treatment
- To decrease discomfort during scaling and root planing or the removal of stitches
- To relieve pain from a complication of tooth extraction called dry socket
Topical anesthetics are applied as ointments, gels or sprays, or through an adhesive patch. Some topical anesthetics have flavors, including cherry, watermelon, banana, bubble gum, mint, strawberry, raspberry and pina colada.
Most topical anesthetics are the same drugs as injectable local anesthetics, but topical anesthetics usually are given in higher concentrations because not all of the anesthetic will work its way through the tissue.
Before giving you a topical anesthetic, your dentist will review your medical and dental history for possible allergic reactions to an anesthetic or to other ingredients. In addition, your dentist will ask whether you have certain rare medical conditions, such as hereditary methemoglobinemia, that would require some topical anesthetics to be used with extreme caution.
To apply the anesthetic, your dentist will dry the area with a gauze pad. He or she will apply the anesthetic with an applicator (usually a cotton swab), holding the anesthetic on the area to be numbed for two to three minutes. Your dentist also may apply the topical anesthetic using a spray. He or she then will rinse or wipe the area. The anesthetic also can be applied in the form of an adhesive patch.
Topical anesthetics numb the nerves 2 to 3 millimeters below the surface. They usually are effective for 15 to 30 minutes, enough time for you to receive an injection or have stitches removed.
Many of the anesthetics used in the dental office also are in over-the-counter products, such as gels to relieve oral pain and sprays to relieve sunburn or sore throat pain. Over-the-counter products have lower concentrations of anesthetic, compared with the products used in the dentist's office. Here are some common topical anesthetics.
Lidocaine comes in an ointment and as an anesthetic patch. It commonly is used to reduce pain during an injection. Viscous lidocaine (a thick liquid) can be used to relieve pain from dry socket (alveolar osteitis), a complication of tooth extraction.
After lidocaine is applied, it takes about 3 minutes for the area to become numb, and the numbness lasts about 15 minutes. Anesthetic preparations containing lidocaine are approved for in-office use only when used directly in the mouth. Over-the-counter products that contain lidocaine, such as ointments to treat cold sores, should not be used in the mouth.
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| Anesthetic patch in use |
In 1996, the U.S. Food and Drug Administration approved an anesthetic patch for use in dentistry. The patch is a small adhesive strip that contains lidocaine and is placed in the mouth for up to 15 minutes. The anesthesia takes 2 to 5 minutes to work and lasts for about 30 minutes after the patch is removed.
The patch works just as well as (and sometimes better than) lidocaine ointment, but it is somewhat safer because it produces a lower level of anesthetic in the blood. The level is about 11% of the levels that results from a typical injection of lidocaine, and about 50% of the level produced by applying lidocaine ointment.
Benzocaine commonly is used as an ointment or liquid and contains from 7.5% to 20% anesthetic. It is used to reduce the pain of injections, and works similarly to lidocaine ointment. In addition, it is the only topical anesthetic available over the counter that is specifically intended for the temporary relief of toothache pain and the discomfort from canker sores, braces, teething and dentures.
Tetracaine is a powerful topical anesthetic. Because it dissolves in water, it spreads through the body's tissues faster than other anesthetics do. Tetracaine is used with benzocaine to reduce the gag reflex before taking impressions or X-rays. The onset of numbness is very rapid (within 1 minute) and lasts for about 15 minutes. This anesthetic combination is given in the form of a spray and must be used cautiously because tetracaine easily penetrates the mucous membrane in the mouth and enters the bloodstream. Overdoses can lead to severe toxic reactions, including death.
This compound is used in many over-the-counter lozenges for relieving sore throat pain. It also is used in the dental office, most commonly in liquid form. Dyclonine hydrochloride takes up to 10 minutes to produce numbness, but it can be used in people who are allergic to other topical anesthetics.
EMLA (eutectic mixture of local anesthetics) is a combination of lidocaine and prilocaine in liquid form. Currently, EMLA is approved only for anesthesia on intact skin, and not inside the mouth. This is because EMLA reaches the bloodstream rapidly after it is applied in the mouth. There are no dosing guidelines for dental use. However, studies have tested EMLA in the mouth and found that it provided better anesthesia than 5% lidocaine ointment for certain procedures, including injections. A form of EMLA for use specifically in the mouth is being developed.
Dental topical anesthetics have not been shown to affect developing infants, nor do they show up at significant levels in breast milk. If you are pregnant or nursing and you are concerned about topical anesthetics, consult your dentist.
Topical anesthetics have some limitations:
- Applying them across a large area can cause them to be toxic. This is particularly a danger for tetracaine, because it is so easily absorbed.
- Some people are allergic to the drugs, flavorings or other ingredients.
- Most topical anesthetics have not been tested in very young children (under 1 to 2 years of age) or the elderly.
The risk of receiving a topical anesthetic is usually quite low. However, risks include:
Allergic reactions
These are rare and usually are mild, although severe reactions have been reported. A mild allergic reaction can include swelling and raised welts on the skin that can itch or burn. Some allergic reactions are delayed up to two days after the anesthetic is given.
Toxicity resulting from too much anesthetic
Symptoms can include:
- Blurry vision
- Unusual nervousness or restlessness
- Dizziness or lightheadedness
- Headache
- Ringing or buzzing in the ears
- Shivering
- Drowsiness
- Difficulty breathing
- Seizures (with more severe toxicity)
Excessive amounts of benzocaine have caused methemoglobinemia, a condition in which hemoglobin (a substance in red blood cells) is converted to an inactive form that does not carry oxygen. Mild forms of this condition may not produce any symptoms. More severe cases can cause fatigue, a bluish or grayish cast to the skin and difficulty breathing. This is a relatively uncommon condition and has occurred primarily in three situations:
- In the operating room where doctors have applied excessive amounts of benzocaine or a combination tetracaine/benzocaine spray to the back of the throat before placing breathing tube or a special tube to view the stomach or heart. Methemoglobinemia is far more likely to occur in this situation in elderly, debilitated patients.
- In teething infants, if parents have disregarded the manufacturer's dosing directions and applied excessive amounts of benzocaine liquid or gel throughout the entire mouth.
- In young children who have accidentally ingested toxic amounts of benzocaine.
Follow the manufacturer's instructions for all drugs and keep all medications out of the reach of young children. For mild cases of methemoglobinemia, close observation of the patient is usually all that is needed. In more severe cases, methylene blue dye is injected into a vein and acts as an antidote.
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