How long does local anesthesia last?

How long does local anesthesia last

Local anesthetics are given at the surgical site to numb the tissue without loss of consciousness. An ideal local anesthetic numbs the tissues during the procedure and wears off soon after the surgery. Before going into the details of how long does your local anesthesia last, you should know:

  • How does local anesthesia work?
  • What anesthetic techniques are used to numb teeth?
  • How is local anesthetic given?
  • How many injections are given during a dental procedure?
  • How long does local anesthesia last?

Let’s get started:

How does local anesthesia work?

Local anesthetic is contained in a water-based solution in the cartridge, and when injected into the tissues, it is converted into fat-soluble molecules. These activated molecules enter the nerves and block their electrical conduction. 

which techniques are used to numb teeth

The local anesthetic is frequently given in two forms for different dental procedures.

Infiltration anesthesia: Local anesthetic is given near the site that needs to be operated. In the mouth, it is injected into the tooth’s gums, which need to be treated. This type of anesthesia is known as infiltration and is given to the front teeth and premolars.  

Nerve block: Nerve block is required in molars as they are supplied by more than one nerve. Also, the dense lower jaw bone in the molar region doesn’t allow penetration of local anesthetic drugs to the nerves supplying the teeth. A nerve block is given a distant to the surgical site before the nerve branches. 

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What is the procedure for giving a local anesthesia?

The injection site is cleaned with wet sterile gauze, and the injection is given near the surgical site. 

Infiltration anesthesia numbs the tissues in 5 -10 seconds. However, nerve block takes 3-5 min to become effective. The anesthetized tissues are pricked with a sharp instrument (dental probe) to check if the anesthetic is working. The doctor or dentist then proceeds with the operation. 

You may need some additional dose of anesthesia if the procedure takes longer and the anesthetic effect wears off. 

How many injections are given during a dental procedure?

The amount of anesthetic injection given to patients is determined according to their body weight. 

For most dental procedures, for an average-weight adult, one cartridge is given for the infiltration anesthesia—half cartridge on the outer and inner sides of gums. However, a nerve block requires 1.5 cartridges. Molars also require infiltration anesthesia on the outer gum side to block the long buccal nerve.

The amount and duration of anesthetic required for a procedure may vary with dose, weight, presence of infection, and use of a vasoconstrictor.

How long does local anesthesia last?

The local anesthetic is selected, which should profoundly numb the tissues during the procedure and diminishes after the surgery. The drugs with moderate duration (1-4 hours) of action are well suited to be used as a local anesthetic so the procedure can be performed without any additional injections during the procedure nor the effects of the drug last long after the procedure. 

Duration of lidocaine

There are different types of medications used for local anesthesia. Lidocaine is the most common drug used for local anesthesia because it is least likely to cause allergic reactions (0.1-1%). 

It is given in inhalation, injection, spray, or cream forms because of its high safety profile. 

It has a moderate duration of action. Lidocaine slightly dilates the vessels, so to prolong the anesthetic duration, it is combined with a drug (epinephrine) that narrows the vessels. 

It is used in dentistry at a concentration of 1:100000 epinephrine. At this concentration, the local infiltration injection numbs the teeth for 60 mins and soft tissues (gums) for 2-3 hours. However, nerve block makes the tooth pain-free for 65-90 min and soft tissues for 3-4 hours. 

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Factor influencing the duration of local anesthesia

Presence of infection 

The duration of anesthesia is affected by the degree of infection. A local anesthetic agent is injected into the body in the inactive, water-soluble form. It activates when converted into fat-soluble form at the body pH of 7.4 (normal pH). Therefore, It is challenging to anesthetize a patient with acute infection because of the low tissue pH (5.4). Less amount of anesthetic agent gets activated in the acidic environment. For that reason, dental surgical procedures are often deferred till the infection resolves.

Also, a nerve block may be effective in infections as it is given away from the site of infection. You may also require a large drug dose that lasts less than the average expected time. 

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Use of a vasoconstrictor 

The duration of local anesthesia banks on the redistribution of the drug into the system. 

The use of vasoconstrictors such as epinephrine in local anesthetic cartridges prolongs the duration of the anesthetic. It narrows the blood vessels at the injection site and delays drug entry into the blood circulation. 

In patients with heart disease (cardiac arrhythmias) and high blood pressure, anesthetic cartridges without epinephrine are used as their vessels are already narrow.  

In pregnant women, cartridges without epinephrine are used as lidocaine, the only anesthetic safe for the baby. So, the drug effect wears off rapidly.  

Medical conditions 

It is broken down in the liver and should be used cautiously in patients with liver disease.

In severe liver disease, drug metabolism is reduced, leading to toxic reactions. Lidocaine breakdown products (metabolites) are sedatives. 

Local anesthetics are expelled from the body through urine and are avoided in patients with kidney failure or advanced kidney damage. 

which procedures require local anesthesia 

The oral procedures requiring local anesthesia are:

  • Root canal treatment
  • Deep cavity filling
  • Periodontal surgery 
  • Bone grafts 

Other minor procedures requiring local anesthetic injection are:

  • Biopsy 
  • Pacemaker placement
  • Minor skin surgeries such as wart removal 

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What are the side effects of local anesthesia 

You can experience one or more of the following side effects:

These symptoms resolve once the drug is excreted from the body. Call the emergency room or the doctor’s office if symptoms get worse. 

What Things you need to avoid during anesthesia 

Avoid the following things until the anesthetic completes wears off:

  • Infiltration anesthesia only numbs a small area where it is given, but a nerve block given for the lower molars numbs your tongue and lips. So, be careful not to drink any hot drink or bite your tongue or lip.
  • It is best to take rest of the day off and take some rest 
  • Take medicines approved by your health care professional to avoid any drug interactions
  • Abstain from alcohol for 24 hours  

FAQ’s

How long does local anesthesia last in hand?

Local anesthesia is used to anesthetize hand for several procedures such as fingertip surgeries, hand lacerations, repair of rupture tendons, foreign body removal, wound disinfection, tumor removal for biopsy, and fracture stabilization. 

The 2% lidocaine with or without epinephrine in a concentration of 1:100,000 used to numb the hand lasts for 10 hours and 5 hours, respectively. The addition of epinephrine prolongs the anesthetic’s duration of action. 

How long does local anesthesia last in mouth?

The duration of anesthesia in the mouth is given for procedures such as root canal treatment, tooth extraction, bone augmentation for denture or implant placement, smoothening bone spurs, and tissue removal for biopsy. 

The procedures involving soft tissues only require less anesthetic to numb the tissues and keep them numb for longer. Numbing teeth and bones require more anesthetic and last for a shorter duration. 

The injection may be given near the operated site (infiltration) or remote (nerve block) to the surgical site. The remote anesthetic injection blocks the nerve conduction from the larger nerve trunk and numbs the larger area for a longer duration.

The soft tissues like the tongue, cheek, and gums recover the sensations 2-4 hours after the injection, and bone and teeth 2-3 hours post-injection. 

How long does local anesthesia stay in your system?

The half-life of lidocaine, the most commonly used anesthetic, is 1.5 to 2 hours. 70-90% of the drug is broken down in the liver into inactive molecules that lack anesthetic action. Some molecules do possess weak anesthetic activity. The drug enters the blood 10 to 30 minutes after the injection, and the drug-related adverse effects are likely to appear 15-30 minutes after the injection.

Patients with a history of congestive heart failure and liver impairment show delayed lidocaine metabolism and require reduced dosage to prevent drug toxicity.   

How long does local anesthesia last after tooth extraction?

The anesthesia in the upper and lower front teeth wears off within 1 to 2 hours after the injection. However, it takes 2-3 hours to go away completely in lower molars. Moreover, the injection in the lower molars also numbs the lips and tongue, so make sure not to bite them or eat hot or cold food. Wait until all the sensations return. 

How long after local anesthetic can you eat?

You can eat after all the sensations in the mouth return to normal. Eating can hurt you, so please ensure not to eat or drink any hot or cold food. The local anesthetic effect may last for 3-4 hours. However, you can sip plain water or juice if you feel low or hungry. 

Can you drive after local anesthetic?

It is best not to drive or operate heavy machinery after local anesthesia. However, the drug injected in the mouth enters the circulation slowly 10-30 min after the injection. The blood can take it anywhere.

The anesthetic drug entering the brain can cause drowsiness.  However, the amount of drugs entering the brain is so small that it doesn’t affect consciousness. 

You may become drowsy if injected with a large dosage of anesthesia, for instance, in acute infections. 

So, it is safe to relax and rest for 24 hours after the injection and avoid driving and operating heavy machinery. 

Can you speed up the local anesthetic wearing off?

Yes, you can. But it is best to wait for the local anesthetic to wear off. A local anesthetic numbs the tissues to make the procedure painless. It also eliminates the pain felt after the procedure for few hours. Be prepared for the pain at the surgery site after the local anesthetic wears off. 

Your dentist may prescribe you pain medication for pain relief. However, the numb lips and tongue can be frustrating, wanting you to get rid of it asap. 

Walking or increasing physical activity increases the circulation in the muscles allowing the drug to enter the circulation and decreasing its concentration at the surgery site. 

It is often advised to take rest and limit your physical activity after the surgery. So, stay put and let the local aesthetic go away. 

Can your body reject local anesthesia? 

Yes, there are certain cases when the body fails to respond to the local anesthesia. On average, 7% of all local anesthetic injections fail to numb the tissues, and 10% in lower molar nerve block.  

An acute (severe) infection makes it difficult to achieve local anesthesia. The acidic environment doesn’t let the anesthetic convert into its active form. 

Other reasons are 

  • Anatomic variations 
  • Anxiety 
  • Technical errors

Can you sleep after local anesthetic? 

Yes, you can sleep after local anesthesia. It is advisable to take some rest and relax after the surgery. Sleep eases your body and initiates the healing process. Your doctor may advise you to take pain medication after the procedure so you won’t feel after the anesthesia wears off. 

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