“Most of the injectable local anesthetics we use in dentistry today are amide anesthetics, like lidocaine, articaine, mepivacaine, prilocaine and bupivacaine,” says Dr. Nkansah. “They’re metabolized differently from ester anesthetics, and they tend to be safer when they’re exposed to the systemic circulation.” Ester anesthetics are broken down rapidly in the bloodstream by plasma cholinesterases and are more likely to cause true allergic reactions because their metabolism produces PABA, a known allergen. In contrast, amides anesthetics are metabolized primarily in the liver and have a much lower incidence of allergy. Understanding this distinction helps guide drug selection, especially in patients with an allergy history or hepatic impairment. The choice of a specific local anesthetic depends on the clinical procedure and patient-specific factors. Dr. Nkansah emphasizes that dentists must consider what task they are performing, how long treatment will take and whether postoperative pain control is needed. “The dental arch matters as well, since anesthesia in the maxilla and mandible presents different challenges,” Dr. Nkansah says. “Duration of numbness is another key variable, particularly when deciding whether anesthesia should wear off quickly or persist into the postoperative period.” In addition to structural differences, drug formulations differ in part based on the presence of vasoconstrictors, which significantly influence duration of effect and systemic absorption. Lipid solubility, potency and concentration also affect clinical decision-making. “Dosage is especially important in children, since weight-based toxic thresholds are reached sooner,” says Dr. Nkansah. Conversely, longer-lasting drugs, such as bupivacaine, may be useful when extended postoperative analgesia is desired. “There is sometimes a misunderstanding about what is the ‘best’ local anesthetic,” he says. “What is ‘best’ depends on the patient and their specific treatment needs. Articaine is widely used and effective, but like every other local anesthetic, it has its limitations.” Articaine’s 4% concentration has been associated in some studies with an increased risk of paresthesias, particularly after mandibular nerve blocks.1 Why Local Anesthesia Sometimes Fails Dr. Nkansah emphasizes that missed blocks are a normal part of practice. Failures happen most often in the mandible, especially around the first molar. “Maxillary anesthesia is usually easier,” Dr. Nkansah explains, “because the bone is more porous, so you can often inject near the tooth and get good diffusion.” In the lower jaw, anesthesia is more difficult because the bone is thicker and less permeable. Dentists often rely on inferior alveolar nerve blocks, but these can be challenging because the nerve cannot be seen directly and anatomy varies from patient to patient. “Accuracy is actually the problem, not because we’re not aiming correctly, but because the nerve might not run where we think it does,” Dr. Nkansah says. Accessory nerves can also play a role. If branches such as the lingual, buccal or mylohyoid nerves contribute to innervation, incomplete anesthesia may occur even when the main block seems successful. Infection makes things harder still. Dr. Nkansah notes that inflamed tissue reduces anesthetic effectiveness, and once a pain pathway is activated, it becomes much more difficult to shut down. Dosage and Prevention of Toxicity Dr. Nkansah emphasizes that local anesthetics are very safe when used correctly, but they are not risk-free. “There’s no such thing as a non-toxic drug,” he says. Dentists calculate safe limits mainly using a milligramper-kilogram formula. For most injectable anesthetics, the maximum dose is usually around 7-8 mg/kg. One important exception is bupivacaine, which is more toxic, especially to the heart, so it must be given in lower maximum amounts. Dentists often rely on inferior alveolar nerve blocks, but these can be challenging because the nerve cannot be seen directly and anatomy varies from patient to patient. 33 Issue 3 | 2026 | Supporting Your Practice
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