Oral And Maxillofacial Surgery, Oral medicine and radiology

Complications of Local Anesthesia

Local Anesthesia is useful in many dental treatment procedures and there are many complications associated with the administration technique and also with the composition of certain components of the agent present like allergic reactions and other conditions which are divided into Local and Systemic. One of the most common Complication seen in Syncope which can be caused due to many reasons and the Dentist should be ready at all times to deal with it in a rapid manner.

Some localized complications due to Local anesthesia are – Anaesthetic Necrosis which is is seen as a localized necrosis of soft tissue surrounding the injection site. The complications can be as simple as the above mentioned necrosis or some times severe systemic complications like Cardiac Arrest which can be seen if proper history of the patient is not collected before going ahead with the administration of LA Agent.

Complications due to Local Anesthesia:


Any deviation from the normally expected pattern during or after the securing of regional analgesia is termed as a complication due to Local Anesthesia.

In this image a case of Occulomotor palsy which is seen as a complication of inferior alveolar nerve block when it is given into the parotid gland and affects the Facial nerve.

Complications / Adverse Effects of Local Anesthesia are classified into 3 types:

1) Primary or Secondary:

A Primary complication is one that is caused and manifested at the time of anesthesia. A Secondary complication is one that is manifested later, even though it may be caused at the time of insertion of the needle and injection of the solution.

2) Mild or Severe:

A mild complications is one that exhibits a slight change from the normally expected pattern and reverses itself without any specific treatment. A Severe complication manifests itself by a pronounced deviation from the normally expected pattern and requires a definite plan of treatment.

3) Transient or Permanent:

A Transient complication is one that, although severe at the time of occurrence, leaves no residual effect. A Permanent complication would, of course, leave a residual effect, even though mild in nature.

Complications / Adverse Effects may be further divided into 2 groups:

1. Those attributed to the solutions used:

This group includes those complications that result from the absorption of the anesthetic solution:

  • Toxicity
  • Idiosyncrasy
  • Allergy
  • Anaphylactoid reactions
  • Infections caused by contaminated solutions
  • Local irritations or tissue reactions caused by the solution

2. Those attributed to the insertion of the needle:

This group includes those complications attributed to the insertion of the needle:

  • Syncope (fainting)
  • Muscle Trismus
  • Pain or Hyperalgesia
  • Edema
  • Infectious
  • Broken Needles
  • Prolonged anesthesia other than from the anesthetic solution
  • Hematoma
  • Sloughing
  • Neurological complications

Complications can also be divided based on Local and Systemic Effects:

1. Local Complications:

  • Needle Breakage
  • Pain on injection
  • Burning on injection
  • Persistent anesthesia (Paresthesia)
  • Trismus
  • Hematoma
  • Infection
  • Edema
  • Slugging of tissue
  • Soft tissue injury (lip, cheek, tongue, palate)
  • Facial Nerve Paralysis
  • Postoperative intraoral lesions – Recurrent Aphthous Stomatitis, Herpes Simplex
  • Visual Disturbance
  • Intravascular injection
  • Failure to obtain anesthesia

2. Systemic Complications:

  • Toxicity due to overdose
  • Allergy
  • Idiosyncrasy
  • Syncope
  • Drug interaction
  • Serum hepatitis
  • Occupational dermatitis
  • Respiratory arrest
  • Cardiac arrest
  • Hyperventilation


  1. Dear Varun, thank you so much for this information. I had a root canal done less then two weeks ago and i am still suffering from severe adverse effects. I went to the Dentist who performed the root canal and he denied knowing what is wrong. i know he is lying to me. When he gave me the second local injection it was excruciating.I nearly jumped out of the seat. I believe he hit something and from reading yr explanations I think i know what happened. i am looking for an honest dentist who will tell me exactly what is wrong as i am still suffering the effects of the badly given injection. I have persistant swelling and pain inside my mouth on my lower right jaw. I dont know if he hit the nerve a muscle?? it is injury to something and it may be a hematoma? but the ass denied he knew what it was. what did he think it would just go away and i would forget it? The lesson for all u new dentists here is to be honest, because now that he wasnt honest with me I will persue this to the full extent, whereas if he had been honest and helped me get treatment right away, it could have ended differently,

  2. Dear Hillary, it is generally alright to touch the nerve while giving local anaesthesia.. however,the dentist should have pulled it back and then deposited the solution.. local anaesthesia, like all other medical procedures are deemed to have some complications, and some of them can be attributed to the operators mistake.. hope you forgive him, and hope he admitted that it was a mistake on his part as well

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