Local anesthesia is the most commonly used drug in the dental office. It's an essential tool for making sure patients are comfortable while their dentist or hygienist does the work that is needed. But while local anesthetics are common, they aren't without their complexities. Choosing the right agent for the job requires an understanding of their different pros and cons, as well as an awareness of the different patient conditions that could influence a practitioner's choice of drug and decisions around how to use it. What are the ideal properties of a local anesthetic? It should be potent and reversible. It should act quickly and over the duration required for the procedure being done. It shouldn't cause any system or allergic reactions, or localized reactions for that matter. It should be easily metabolized and excreted. It should be inexpensive and have a long shelf life. There are a number of available agents that meet these criteria. Generally speaking, there are two types of anesthetics used in dentistry — amides and esters — and each one comes with its own set of concerns and considerations for use. Amides, which are all injectable, include drugs like lidocaine, articaine and mepivacaine. These drugs are metabolized in the liver. Patient conditions that could be of concern when using amides include low hepatic blood flow, which could prevent a person from metabolizing amides at a normal rate, as well as hypotension, congestive heart failure and cirrhosis. Esters are topical agents and include tetracaine, procaine, cocaine and benzocaine. As opposed to amides, which rarely cause allergic reactions, esters can cause allergic reactions in some patients. The choice of what anesthetic to use largely comes down to two factors: how long you need the drug to work for, and the medical history of the patient.
Having a thorough understanding of a patient's medical history is essential before selecting a specific type and dose of anesthetic. This starts with taking a patient's blood pressure. While clinicians should take the blood pressure of all their patients simply as a matter of health screening, it is vital that they record a patient's blood pressure before administering local anesthesia. According to current guidelines, normal blood pressure is 120/80 or lower, with 120/80 to 129/80 considered elevated, and levels above that considered high. Local anesthesia cannot be given to patients with blood pressure of 200/115 or higher. Other conditions that may influence decisions around local anesthesia include heart failure or whether a patient has had a bypass, stroke or heart attack. Traditionally, the practice has been to avoid giving local anesthesia to patients who have experienced such cardiovascular events within the previous six months, but that has changed as linkages between oral health and cardiovascular health have become more clear. Clinicians should consult with a patient's cardiologist to determine if moving ahead with anesthesia and treatment within that six-month window is safe and warranted. Another key factor to consider is other drugs — both prescription and recreational — that a patient may have in their system. It is essential that prior to administering local anesthesia, clinicians ask their patients whether they have taken any recreational drugs in the last 72 hours and record their answer in their chart. If they have taken recreational drugs in that period, they can't be given anesthesia. Prescription medications and even, in some cases, those that are over the counter, can also present issues. For instance, patients taking acetaminophen can run into problems when given large doses of the amide prilocaine. Drug interactions are also an important factor to take into account when deciding whether or not to use injectables that include epinephrine. As a vasoconstrictor, epinephrine offers several benefits when administering local anesthesia. It slows absorption of the drug, keeping it in the targeted area longer, which prolongs its effectiveness and reduces systemic effects. On the other hand, epinephrine can cause a temporary lack of blood supply to the injection site and can cause increased heart rate, anxiety and sweating in patients. Given these effects, epinephrine shouldn't be used in patients with significant cardiovascular disease. Additionally, the sodium metabisulfite typically included in an epinephrine cartridge may cause an allergic reaction in some patients. More significantly, epinephrine can interact with beta-blockers and tricyclic antidepressants. Administration of a synthetic epinephrine is absolutely contraindicated in patients on tricyclic antidepressants. Having a thorough understanding of a patient's medical and drug history and taking care to observe best practices when administering local anesthesia will make its use as effective and safe as possible. Even so, overdoses and emergency situations can occur, and every office that uses local anesthesia should have a plan in place to deal with them if and when they do arise. Emergency preparation is key to making sure everyone in an office knows what their role is during such an event.
Beyond choosing the most appropriate anesthesia for a patient, correct administration of that anesthesia is key for optimizing its effectiveness while also reducing the potential for toxicity. Start off with as low a dose as will be effective. More isn't necessarily better. When injecting a drug, aspirate first to make sure you aren't injecting into a blood vessel, which will speed the movement of the drug to the brain and heart. Also, administer the drug slowly. One cartridge should take one minute to inject. Additionally, clinicians should never anesthetize a patient's entire mouth but should instead work on one side of the face at a time. Anesthetizing by arch as opposed to side of the face is problematic because it can produce a gag reflex (in the case of a fully anesthetized maxillary arch) or difficulties speaking or swallowing (in the case of the mandible). Also important is correct application of the topical anesthetic used to treat a site prior to injection with an injectable drug. These topical drugs are most effective on mucous membranes and work to a depth of around 2 to 3mm and for a duration of 10 to 15 minutes. To apply, dental professionals should first dry the area being targeted and then place the topical anesthesia, giving it one minute to work on mucous membranes and two minutes on palatal areas and then wiping it off. Apply the anesthesia without rubbing, as rubbing will tear away the top layer of skin and cause the patient more pain the next day.
When thinking about local anesthesia, practitioners need to consider the risks and benefits for each patient individually, taking into account medical conditions and other drugs they might be using. They need to also carefully consult the product information and stay up to date on the latest guidelines in the field, consulting when necessary with anesthesia experts. Local anesthesia is a vital tool in dentistry, and choosing the right drugs for the person and the procedure is fundamental to good practice.
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