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Local Anesthetic Failure and Prevention in Dentistry

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Local anesthesia is pivotal to dental surgeries and post-operative healing of the oral tissue. Read the article to know why an anesthetic failure occurs and its prevention in dentistry.

Medically reviewed by

Dr. Infanteena Marily F.

Published At February 15, 2022
Reviewed AtDecember 23, 2022

Why Is Local Anesthesia Needed in Dentistry?

The dental surgeon mandatorily gives local anesthesia (LA) for simple dental procedures like deep scaling and root planing to surgical procedures like:

This is because the surgical procedures can be done only by pain control or by numbing the affected area. When the local anesthesia is given, the operator can successfully access and perform the procedure effectively on the patient (endodontic or oral surgical, or periodontal surgeries). According to traditional research, the failure of a local anesthetic to penetrate effectively is deemed around 5 to 15% of the total number of LA injections given by dental surgeons to patients. The dental surgeon cannot be held responsible solely for the success or failure of local anesthesia.

When Is Local Anesthetic Failure Possible?

Even after giving the required anesthetic dosage for dental surgical procedures, multifactorial causatives lead to anesthetic failure. They are,

1. Variation in the Anatomy of the Teeth:

The dental surgeon cannot visualize the nerves directly. Only the approximate anatomic landmark would be accessible to anesthetize. In edentulous patients, that is, patients of older age with missing teeth in one or more areas, the landmarks may be obliterated to induce adequate anesthesia. In children and adolescents, especially in the growth spurt stage, the landmarks may vary slightly from individual to individual. In some patients, due to excess buccal pad of fat or thicker mucosal lining in the maxillary or mandibular areas (where the anesthetic needs to be given), the efficaciousness of anesthetic to act directly in that area injected tends to reduce. Hence for multiple causes varying from person to person, anatomic variations in the oral cavity pose a challenge to the dentist to inject an adequate amount of anesthetic directly.

2. Chronic Alcoholism and Smoking:

Chronic alcoholics are individuals who consume alcohol at least once daily or even those individuals with an increased frequency of alcohol intake in a week from a prolonged period. Patients often do not mention the detrimental habits of smoking, tobacco or quid chewing, or chronic alcoholism to the dentist, which may complicate the risk of anesthetic failures. This warrants a thorough medical history from the patient before starting a surgical procedure. As the local anesthetic mainly acts by inhibiting peripheral nerve conduction, the alcohol content consumed is certainly known to interfere with a room of local anesthetic, slowing its mechanism considerably.

In chronic alcoholics with liver damage and multi-organ damage, the consequences of alcohol, even mistakenly before or after a procedure, would be life-threatening. Especially prior to a dental surgical procedure, the doctor avoids forewarning these individuals to avoid alcohol and smoking habits (if present) 24 hours before and preferably for up to one week till the area surgically operated heals well. Smoking similarly alters the healing period of post-extraction sites and can cause dry socket,gingivalis bleeding, inflammation, and halitosis.

3. Iatrogenic Errors:

The dentist should avoid operator-based errors (as the nerves cannot be directly visible and approximate anatomic landmarks can only be visualized externally) like depositing the solution into a blood vessel or deep tissue or space. Another major reason is not being able to give an adequate amount of anesthesia, so the patient may not feel numb adequately for the operator to proceed ahead with the procedure painlessly.

4. Anxiety or Apprehensiveness of the Patient Itself:

These patients may raise fears about the dental procedure, making the dentist difficult to operate on. This is especially true in dental phobias, meaning fear of dental procedures or distinctive dentists. These patients can be calmed down by adopting voice control and showing them the difference between an anesthetized area and a non-anesthetized area to make them understand. Explaining the procedure in detail can make the comprehensive patients also alleviate their fears to an extent.

5. Issues With Anesthetic Solutions:

There will be a risk of anesthetic failure if there are storage-related issues with the anesthetic solution, such as indirect exposure to sunlight or heat instead of storing it in a cold environment. Expired anesthetic solutions also cannot act properly, leading to failure, and such errors should be avoided by the dental operator.

6. Certain Genetic Syndromes and Sodium Channel Disorders:

Some examples of resistance to local anesthesia are genetic defects pertaining to sodium channels in the body, tetrodotoxin-resistant channels, mutations, certain anemias, or specific syndromes like the Ehler Danlos syndrome associated with joint hypermobility. In these cases, the dentist should modify the dosage and technique (like the intraligamentary or periodontal ligament anesthesia for usually one or two single-rooted teeth) until the patient's pain is tolerable.

Inflammation - This is a major impediment to the success of local anesthesia. The pharmacodynamic and pharmacokinetic activity of the anesthesia circulating for a specified period in the localized area is affected. This is attributed to the hypothesis of inflammatory acidosis that would potentially occur in people suffering from systemic diseases or inflammatory disease or even in people suffering from oral inflammatory lesions. The interaction to the lipid bilayer is impacted, and the excitability threshold and the Ph of the site are lowered in these inflammatory conditions leading to anesthetic failure. Also, the acidic conditions of the infected or pus-filled area hinder the mechanism of action and passage of the anesthetic molecule to the pulp or the root canal of the tooth to be anesthetized.

In these cases, the dental surgeon may consider preoperative antibiotic prophylaxis to minimize or reduce the source of infection and then choose to operate. In patients suffering from localized dental-related inflammation like apical periodontitis, periodical abscess, gingival abscess, etc., the anesthetic time to produce the effect may be prolonged for the same reason.


Though iatrogenic errors may be possible by the dental surgeon, they may not be the reason for anesthetic failure. Consideration of the patient's anatomic landmarks, systemic and oral conditions, habits, and anxiety before the procedure will help prevent local anesthetic failure in the dental setting.

Frequently Asked Questions


Can a Failure of Local Anesthetic Be Overcome or Not?

The best treatment to overcome the failure of local anesthesia will be the repetition of the injection. And this will result in the success of the treatment. During the second attempt, in the case of repeated block injection, it will be easy for a doctor to palpate bony landmarks at the second attempt because this method will make the needle carefully penetrate the tissues painlessly.


How Can One Define Local Anesthesia in Dentistry?

Local anesthesia can be defined in dentistry as an injection consisting of an anesthetic solution adjacent to the nerves, giving sensation to a region of the oral cavity where the treatment is given.
Lidocaine, articaine, prilocaine, mepivacaine, and bupivacaine are the common local anesthetic drugs used in dental treatment. These drugs will provide a numbing of the site of injection that will last for 30 to 60 minutes.


What Is the Importance of Local Anesthesia in Dentistry?

In dentistry, local anesthesia will play a major part in pain-control techniques. Pain can be easily prevented and eliminated during dental treatment, benefiting patients, doctors, and dental hygienists. Tremendous therapeutic advances are seen in the dental profession through LA because the action of LA will enable impossible dental treatments into possible mode.


Name the Three Examples of Local Anesthesia?

Local anesthesia can be injected or put on the skin during medical, surgical, or dental procedures to lessen pain. Lidocaine (also known as lignocaine), mepivacaine, and prilocaine are the three examples of local anesthesia.


Name a Few Complications of Local Anesthesia?

Paresthesia, ocular complications, allergies, toxicity, and methemoglobinemia are a few complications of local anesthesia. However, the risks involved with local anesthesia decrease the chances of adverse events, leading to improved patient care.


List the Contraindications of Local Anesthesia in Dentistry?

The use of local anesthesia is contraindicated to individuals who are known to be allergic to a local anesthetic agent or an ingredient present in the anesthetic solutions. So the main contraindication to local anesthesia will be an allergy. Sepsis, local infection, and bacteremia, used to avoid the spread of infection, are termed absolute contraindications for local anesthesia. In addition, people should avoid steroids because they inhibit bone healing in an intra-articular fracture.


What Happens to an Individual When Anesthesia Fails?

When anesthesia fails in a few cases, individuals can raise or lower their limbs or even speak to tell the doctor that the anesthesia is not working before the surgeon uses their scalpel. But this type of response is not seen in people who have undergone neuromuscular blocks.


Name Some Factors That Affect the Local Anesthetic Activity?

Some factors will influence the activity of local anesthesia. It includes the lipid solubility of the local anesthesia, pKa, pH of the surrounding tissue, the bond present in the intermediate chain, its length, and the protein binding capacity of a particular type of anesthesia are in doubt nowadays.


What Tips Are Used to Make Anesthesia More Efficient?

To improve or make the anesthesia more efficient given below are the five tips for the individual:
 - Every time should start on time.
 - For the pre-admission testing process, ownership should be established.
 - Everyone should follow the leader.
 - One should merge pain management.
 - Keep it rolling, maximizing efficiency.


Is Anesthesia Failure Commonly Seen or Not?

Anesthesia awareness is still considered a mystery for years onwards. But there are a few rare extreme experiences like Penner's, seen in around 5 percent of people who wake up on the operating table and also there are possible in many more cases. In general practice overall, local anesthesia fails in seven percent of cases, and ten percent of cases of an inferior alveolar block is seen. Infection and wrong selection of local anesthetic solutions, mistakes on the technical side, variations in anatomy with accessory innervation, and patient anxiety are the possible causes of failure of LA.


Can Anesthesia Have Serious Complications in Individuals?

The serious complication seen in individuals with anesthesia is hypotension (low blood pressure). Usually, many healthy patients can tolerate this transient hypotension, but there are reports that cardiac arrest is seen during the placement of spinal or epidural anesthesia. So extra care must be taken in patients having cardiac history while receiving neuraxial anesthesia.


What Awareness Can Be Given to an Individual to Prevent Anesthesia?

Getting appropriate counseling and sharing their experience will reduce the fear or trauma experienced by an individual.
To reduce the risk of anesthesia awareness given below are the few steps to reduce it:
 - Depression.
 - Smoking or frequent use of alcohol.
 - Heart or respiratory problems.
 - Use of herbal supplements or some medications.


Can Teeth Be Commonly Damaged Through Anesthesia?

During anesthesia, mostly three or any teeth can be damaged. And the most frequently affected teeth will be the anteriorly placed maxillary incisors. Again, the left is more often damaged than the right, reflecting that the right-handed laryngoscope blade is most commonly used in all anesthesia.


Are Risk Factors Seen for Local Anesthetic Toxicity?

The type of local anesthesia and dose, the injection site, the patient's death, more aged people, and muscle mass in a small size or limited quantities are the few variables that increase the risk of toxicity. And the toxicity is also associated with the lipophilicity of local anesthesia. And also, risk factors in patients include kidney or liver compromise and respiratory and metabolic acidosis.
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Dr. Achanta Krishna Swaroop
Dr. Achanta Krishna Swaroop



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