Question

Joseph, a 24-year old male, has gone to the dentist for treatment of apical periodontitis, an inflammatory condition of the periodontal tissue. Upon administration of lidocaine for local anaesthesia, his dentist realises that he has not been sufficiently numbed by the injection. Regarding the anaesthetic, explain i) how lidocaine aims to achieve anaesthesia, and ii) the most likely reason as to why it did not achieve a sufficient effect

Answer 1

I. Lidocaine is a local anesthetic

It act by blocking nerve conduction, by decreasing the entry of Na+ ions during upstroke of action potential. When the concentration of lidocaine increases rate of rise of action potential and depolarization decreases causing slow conduction. Finally local depolarization fail to reach threshold potential and lead to conduction block. Patient feel anaesthetized.

II. Periodontitis is a inflammatory condition. Local anesthetic like lidocaine fails to afford adequate pain relief in inflamed tissues such as infected tooth. Reasons are

1.inflammation lower the ph of tissues. So greater fraction of lidocaine become ionized. Ionized form cannot diffuse in to axolemma.

2.blood flow to the inflamed tissue is very high so local anesthetic get removed rapidly from site.

3.inflammatory products will reduce action of listening.