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“Hey Doc, I’m Hard To Freeze”

Thanks to local anesthetics, the vast majority of dental procedures should be painless. But several factors can affect the efficacy of local anesthesia.

Let’s face it, dentistry is not an easy job. Besides the clinical knowledge and expertise required, managing patients' fear is an essential part of being a good dentist. Anticipation of pain during dental procedures, whether based on past experience or related stories is perhaps the most common fear for patients. And while one can appreciate this prior to the introduction of local anesthetics (LA), today the vast majority of treatments should be painless.

Perhaps the most alarming situation for dentists occurs when a patient, following administration of a local anesthetic, yells or violently jerks the head during treatment. Not only is this traumatic for the patient but for the dentist as well. Unlike the mad dentist portrayed in the film “Little Shop of Horrors,” dentists do not want to cause harm.

While several factors can affect efficacy of local anesthesia, in my over forty years of practice one stands out above all others. But first a brief history.

The use of local anesthetics in dentistry became widely available in the early 1900’s when Novacaine was introduced. Subsequently in the late 1940’s, a safer product Lidocaine became the gold standard and is widely used to this day. The pain blocking mechanism of action for the “caine'' class is through their binding to and temporarily inactivating sodium channels to nerve cell membranes, essentially preventing local signals from being transmitted to pain centers in the brain. For upper teeth, infiltration through thinner jaw bone is used whereby each tooth is individually anesthetized by administering the agent at root's end. For lower teeth in adults and older children, infiltration of anesthetic through the denser mandibular bone to individual teeth is not feasible hence the agent must target the main branch, or inferior alveolar nerve located posteriorly in the jaw. So why doesn’t it always work?

The Root Of The Problem

Failure rate to achieve adequate anesthesia is between 7-10% , more often in lower teeth. And while rare cases of genuine resistance to local anesthetics have been reported, local factors are mostly responsible. Here are some of the most common ones. 


Local anesthetics are alkaline drugs with a pH similar to the body's normal pH of 7.4. It is in this environment that they are most effective. Infections such as a dental abscess lower the pH of surrounding tissues and reduce the agent's ability to enter cellular membranes. Often, infections must be treated with antibiotics prior to dental work in order to achieve adequate local anesthesia.


As any sufferer can tell you, an inflamed dental nerve can cause excruciating pain. While the  mechanisms inhibiting local anesthetic efficacy are not fully understood for a hot tooth, the most common explanation is a combination of pulpal tissue pathologies including inflammatory acidosis. Taking an oral anti-inflammatory such as Ibuprofen prior to treatment may facilitate better anesthesia, but often an injection directly into the affected pulp is the only solution and though briefly painful, generally well accepted by patients who haven’t slept for days.


It is not uncommon for people to be fearful of dental treatments and a highly anxious patient can be very challenging for the dentist. High anxiety can result in hypersensitivity to a variety of stimuli including pain. Despite outward signs of anesthesia, like a numb lower lip and tongue, local anesthetics may not be effective for some patients due to fear and apprehension. Sedation, and when indicated general anesthesia, are often good options for such individuals who need not suffer needlessly.

The “Missed Block”/Operator Error

The Mandibular or Inferior Alveolar nerve block requires precise skill, and as we all know, not all dentists are created equal. Experience is essential, particularly as jaw anatomy can vary greatly among populations. Size, shape, amount of fatty tissue, and variations in where the nerve exits the mandible all contribute to potential complexity of administration. The anesthetic must be delivered to a precise landmark posteriorly in the mouth where the mandibular nerve exits the foramen. A bit too high, low, anteriorly or posteriorly mispositioning of the needle can all lead to failure. Even in the most experienced hands, locating the landmark, all done by feel, can be very challenging, and any dentist who says they never miss a block is full of horseradish

So here’s a situation that pops up in my office every once in a while. A new patient comes in and within seconds of sitting in the chair says “I just want to warn you Doc I’m hard to freeze.” This triggers an alarm bell in my head. Typically, most people don’t remember if it was top or bottom teeth, but I mostly assume the lower arch where operator technique is paramount. After reassuring the patient that it is unlikely they are truly resistant, I carefully administer the local anesthetic and in most cases achieve good anesthesia. Once done, the patient often looks at me as if I’m Gandalph from Lord of the Rings, but I explain to them that some people’s jaw anatomy can vary, making correct needle placement challenging.

Perhaps a previous dentist had difficulty in finding the proper location and being frustrated told the patient, “You’re hard to freeze.” Et voila, you’ve created a dental phobic who believes they’re physiologically atypical. In these instances, it’s better to readminister another dose while repositioning the needle, but if still unsuccessful, explain to the patient that it’s best to reschedule during which time the dentist can brush up on technique. It’s never a good idea to proceed while telling patients to “hang in there.” Dentistry can be stressful enough without causing pain. And as all dentists know, a pain free patient is a happy one!


Dr. Mark Grossman is a practicing dentist and likes to take a bite out of nonsense when it comes to dental issues.

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