Local Anesthesia

Signs & symptoms of allergic reactions to LA
Genuine allergy to LA will manifest either as Type 1 or Type 4 hypersensitivity. Signs and symptoms will vary depending on the type of allergy. Type 1 reactions have a rapid onset of symptoms which include swelling, redness, rashes, itchiness, chest tightness, breathing problems. A Type 4 reaction has a delayed onset of symptoms and is usually localized to the site of injection.
Management
If a genuine allergic reaction to LA should occur, the patient should be treated as an emergency for anaphylaxis, according to the guidelines in the respective areas. For the UK, the section on medical emergencies in dental practice in the “Prescribing in Dental Practice” part in the BNF should be referred to. The patient should be sent immediately to the hospital if their condition worsens.The individual should undergo further tests to certify their allergy to the LA or for other possible causes of the adverse reaction.Gate Control Theory in Painless Anaesthesia
The gate control theory explains that pain can be reduced if the touch nerve fibres are stimulated due to non-harmful stimuli.Advancement in techniques used to deliver local anaesthesia are very important. There are types of local anaesthesia that apply vibrations to the skin while the injection is being placed into the skin. This uses the gate control theory to minimise pain to the patient. The high frequency vibrations coming from the device which is attached to the syringe inhibit the pain sensations coming from the needle. They may interfere with the signals of pain by closing the gate in the brain. The nerve fibres that are stimulated are the Ab fibres using pressure or vibration. Other receptors called meissner's corpuscles in the deeper tissues and bone also contribute. This closes a ‘neural gate’ This decreases the patient's feeling of pain.Methods used by dentist to reduce pain during anaesthesia by using the gate control theory are: Warming of the local anaesthetic cartridge, Stretching the oral mucosa, Gentle rubbing of the extra-oral skin.
Myotoxicity
Although complications of myotoxicity in dental anaesthesia are rare, myotoxic injuries are primarily mediated by disturbances in calcium homeostasis. The onset of a myotoxic episode can occur within a few hours to a few days after local anaesthetic (LA) administration. A greater concentration and longer exposure to LA have been found to have a positive correlation with myotoxic effects. It can take human muscles from 4 days to a year to recover from a myotoxic insult. Local anaesthetics used clinically can be ranked in increasing order of their risk of myotoxicity, this includes Lidocaine, Ropivacaine and Bupivacaine.^[35]