Local Anesthesia is a very integral part of almost every Dental Treatment performed which is used in making treatment procedures painless for the patient. Having good understanding of the composition of LA is important for treatment planning and to avoid any complications of LA such as allergies, etc. Local Anesthesia is used in a wide range of treatments ranging from a Simple Extraction to Wisdom Tooth removal, Rootcanal treatment, Flap surgery, Implant placement or some simple procedures like tooth cutting in a vital tooth and some cervical abrasion cases as well. So it is important to know everything about the Local Anesthetic agent which is being administered as it contains substances which some patients might be allergic to.
Some of components of the agent are known to be allergic to certain types of patients and it is also important to keep in mind that any patients with any heart disease should not be administered the Vasoconstrictor like adrenaline or Epinephrine. Some patients are known to be allergic to the preservative in the LA Agent and it is important to give a test dose before giving the Nerve block to check for any allergic reactions – Complications of Local Anesthesia.
Composition of Local Anesthetic agent
1) Local anaesthetic agent : Lignocaine HCL – 2% (20 mg/ml)
2) Vasoconstrictor : Adrenaline – 1:80,000 (0.012 mg) or Epinephrine
3) Reducing Agent: Sodium Metabisulphite – 0.5 mg
4) Preservative: Methylparaben – 0.1% (1mg)
5) Isotonic Solution: Sodium Chloride – 6 mg
6) Fungicide: Thymol
7) Vehicle: Ringer’s Solution
8) Diluting Agent: Distilled water
9) To adjust pH: Sodium Hydroxide
10) Nitrogen Bubble: 1-2mm in diameter and is present to prevent Oxygen from being trapped in the cartridge and potentially destroying the Vasopressor or vasoconstrictor.
Actions of each component of Local Anesthetic agent:
Vasoconstrictor function: Decrease blood flow to the site of injection, absorption of local anesthetic into the cardiovascular system is solved,decrease the risk of local toxicity, higher volume of local anesthetic agent remain in and around the nerve for longer period, thereby increasing the duration of action, vasoconstrictor decreases bleeding at the site of their administration.
Preservative : Stability of modern local anesthetic solution is maintained by adding caprylhydro-cuprienotoxin which includes xylotox and methyl paraben.
Reducing agent : These act as preservatives for vasoconstrictor agents. Vasoconstrictors are unstable in solution and may oxidize, especially on a prolonged exposure to sunlight. Sodium metabisulphite which competes for the available oxygen is added in the concentration between 0.05% and 0.1%
Vehicle : All the above solutions and local anesthetic agent are dissolved in a modified ringer solution. This isotonic vehicle minimizes discomfort during injection.
Why is Nitrogen Bubble present in the cartridge: 1-2mm in diameter and is present to prevent Oxygen from being trapped in the cartridge and potentially destroying the Vasopressor or vasoconstrictor, so this is the function of Nitrogen Bubble in the LA cartridge.
We see many patients who ask “what do dentists use to numb teeth or mouth” before performing a procedure and the answer is dental anesthetics which help in making dental procedures painless be it related to the tooth or the gums and other soft tissue in the mouth or oral cavity. Having proper knowledge about the Allergic Reactions to LA and also we should have good knowledge about the amount of LA to be given to avoid Local Anesthesia Toxicity due excess LA administration.