Dental anesthesia

Although several different medications are available, the most commonly used local anesthetic to prevent pain in the area around a tooth is lidocaine (also called xylocaine or lignocaine).

Commercially used LA in dental practice has a low pH of 3–4, this is advantageous as it will extend the shelf life of the product and prevent early oxidation.

Intraligamentary or periodontal ligament anaesthesia is a technique used primarily for endodontic treatment and to supplement inferior dental blocks where they may have failed.

This technique involves 'the deposition of at least 0.2ml of local anaesthetic solution for each root of the tooth' [10] diffusing into the marrow spaces surrounding the teeth.

Interligamentary anaesthetic may be complicated by poor operator technique where rapid injection and excessive volume is used; this could lead to sensitivity to biting and percussion.

[11] Research has shown that the rate of onset of anaesthesia in the patients was between 15 and 20 second; this provides an advantage compared to that of inferior alveolar dental block.

[12] Other advantages include a decrease in overall trauma in comparison to conventional blocks therefore being an ideal procedure for extractions and endodontic treatment in children.

Intrapulpal anaesthesia involves the direct placement of anaesthetic agent using a small needle (of 25 or 27 gauge) into the pulp chamber; it is injected under pressure leading to brief yet intense discomfort.

The technique involves direct deposition of anaesthetic agent into the papilla with associated tissue blanching at site of injection.

A jet injection aims to create a release of pressure strong enough to push a liquid medication dose through a small orifice.

When something is said to have an "absolute" contraindication this underlines that under no circumstance would that LA be selected to administer to that specific patient as it poses a potential life-threatening risk e.g. allergy.

The main contraindication of Prilocaine is that it has a short half life and it possesses a mild cytotoxic effect, therefore should be avoided in pregnancy.

[23] The dose of local anesthesia is often reduced when a patient has any systemic health implications or habits which may cause an interference.

The variety of techniques associated when giving a local anaesthetic can affect the success and if done incorrectly lead to a possible fracture of the needle tip.

It is extremely rare for the needle to fracture whilst giving an injection intra-orally unless an inadequate technique is adopted.

Provided a dentist performs proper aspiration to avoid intravenous injections, local anesthetics containing epinephrine (adrenaline) are safe to use during pregnancy.

The epinephrine causes vasoconstriction which in turn reduces systemic distribution of the anesthetic as well as prolongs its action in addition to decreasing bleeding at the operating site.

Unfavourable reactions to LA are commonly due to a hyperemotional response to a perceived danger within someone's mind, and it could be demonstrated in several ways.

Examples are temporal loss of consciousness, sweating, flush, change in heart rate or blood pressure, panic attack, hyperventilation, of which may be mistaken as allergic reactions.

[30] It is important to ensure that children and adolescents experience less anxiety and fear to aid acceptance of future dental treatment.

A study compared different methods to increase the acceptance of delivery of local anaesthetics to patients aged between 2–16 years old.

[30] Signs and symptoms mainly involve the nervous system e.g. aggressive behaviour, drowsiness, speech alteration, disorientation etc.

Type 1 reactions have a rapid onset of symptoms which include swelling, redness, rashes, itchiness, chest tightness, breathing problems.

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.

The gate control theory explains that pain can be reduced if the touch nerve fibres are stimulated due to non-harmful stimuli.

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.

Local anaesthetics used clinically can be ranked in increasing order of their risk of myotoxicity, this includes Lidocaine, Ropivacaine and Bupivacaine.

[35] Issues can also arise with use of nitrous oxide in patients who have had pneumatic retinopexy (alone or in conjunction with a vitrectomy), commonly used to treat retinal detachments.

Nitrous oxide is 34 times more soluble than nitrogen and will cause an extreme expansion, raising the intraocular pressure to dangerous levels.

Such high intraocular pressures cause ischemia of the central retinal artery, leading to irreversible vision loss.