Anaesthesia is traditionally, and still is in many places today, given by injection. Children's aversion to dental procedures stems from their fear and anxiety around needles. This article discusses the recent advances in local anaesthesia with its advantages and disadvantages. 

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Introduction

To eradicate pain during treatment usually anaesthesia has to be administered. The word Anaesthesia is a compound word from the Greek words an- (“without”) and aesthesis (“sensation”).

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Topical anaesthetics

The form of anaesthesia obtained by direct application of the drug to abraded skin or mucous membrane (Monheims 7th edition). It is used to anaesthetise small wounds and intact mucous membranes for simple procedures.

Mechanism of action

1. It reversibly blocks nerve conduction near the site of administration.
2. They act on free nerve endings in the dermis or mucosa producing temporary loss of sensation in a limited area.

Types of topical anaesthetics

According to the vehicle used, topical anaesthetics are classified as:

1. Non-aqueous or water-insoluble
2. Aqueous or water-soluble

A. Non-aqueous or water-insoluble: These anaesthetics are insoluble in water but they are soluble in vehicles such as alcohol, polyethylene glycol, propylene glycol or carboxymethylcellulose. Anaesthetics belonging to this group are Benzocaine and Lidocaine base.

Combinations of benzocaine:

• Orabase: A combination of benzocaine, gelatin, pectin & sodium carboxymethylcellulose.
• Cetacine: It contains 14% benzocaine, 2% butamen, 2% tetracaine Hcl.

B. Water soluble topical anaesthetics: These anaesthetics are soluble in water. It rapidly get absorbed into blood stream and thus reported to have more toxic properties like allergic reaction, methamoglobinemia etc. So it is not recommended to be sprayed on mucous membrane.

The anaesthetics belonging to this group are:

• Benzyl alcohol
• Tetracaine hydrochloride
• Lidocaine hydrochloride

Combinations of tetracaine hydrochloride:

• Tetracaine, adrenaline (epinephrine), and cocaine (TAC)
• Lidocaine, epinephrine, and tetracaine (LET)
• S-caine patch™ and local anaesthetic peel the patch

Combinations of lidocaine hydrochloride:

1. Eutectic mixture of local anaesthetics (EMLA): An oil-in-water emulsion mixture. It is composed of lignocaine 2.5% and prilocaine 2.5% in an emulsion in which the oil phase is a eutectic mixture of lignocaine and prilocaine in a ratio of 1:1 by weight.
2. Betacaine-LA
3. Oraqix

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Recent advances in topical anaesthesia

1. Precooling (Cryo Anaesthesia)

The application of cold to localised parts of the body to block local nerve conduction of painful impulses. Topical cold application stimulates myelinated A fibres, activating inhibitory pain pathways which in turn raises the pain threshold.

Advantages :

1. Produces immediate anaesthesia as it suppresses both pain and pressure.
2. An easy, reliable, and effective technique.
3. Is comfortable, safe and physiologically active.
4. It is cost-effective.

Disadvantages: Short-acting: 2-5 min.

2. Lontophoresis

A method of enhancing the transport of topically applied drugs using mild electric current to increase the permeability of charged drugs through the skin.

Advantages:

1.  Patient acceptance is very high.
2. Provide rapid and effective anaesthesia compared to topical anaesthesia alone.

Disadvantages:

1. It may irritate skin at greater current densities or after prolonged use.
2. Sometimes mild electrical sensation can be uncomfortable for some patients.
3. Equipment is expensive and bulky.
4. Cannot be applied to huge body surface regions.

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Delivery systems in local anaesthesia

1. Transcutaneous electric nerve stimulation (TENS)/ electronic dental anaesthesia

1. A non-pharmacological method which is widely used for the management of acute and chronic pain.
2. Use of electric current produced by a device to stimulate nerves for therapeutic purposes.

Indications:

1. Can be used successfully in pediatric patients. Since the equipment contains no syringes, it will impart positive behaviour in children and reduce their fear.
2. Used to alleviate chronic pain of TMJ syndrome, trigeminal neuralgia and post-herpetic neuralgia.
3. Can be used in patients with xerostomia by increasing the salivary flow rate.

Contraindications:

1. In apprehensive patients, this technique requires patient cooperation.
2. Cannot be used in patients with cardiac pacemakers.
3. Cannot be used in patients with a history of aneurysm, stroke and transient ischemia.
4. Have the potential to trigger seizures, so it cannot be used in epileptic patients.
5. Cannot be used in pregnant patients.

Mechanism of action: Analgesic effect of TENS is based upon two main theories Gate control theory and the endogenous opiod theory.

Classification: Depending upon the frequency of stimulation, it is classified into two categories:

1. High-frequency transcutaneous electric nerve stimulation (TENS) uses a frequency of greater than 50 Hz.
2. Low-frequency transcutaneous electric nerve stimulation (TENS) uses a frequency of less than 10 Hz.

2. Jet injection

1. Was introduced by John. F. Roberts in 1933.
2. The first dental study using a needless jet injector was reported by Margetis et al in 1958.

Indications:

1. Commonly used in pediatric patients and has a high success rate.
2. Increased anaesthetic effect in children as they have less bone density.
3. Used for vasoconstriction or post-operative analgesia after oral surgical procedures.
4. For nasopalatine and greater palatine block.
5. Used for mass vaccination.
6. In cases where we need surface and pulpal anaesthesia.

Contraindications: Cannot be used in epileptic patients.

Trade names: Syrijet, Med-Jet H III

3. Computer-controlled local anaesthetic delivery system (C-CLAD)

Indications:

1. Used in pediatric patients as it renders painless anaesthesia.
2. In adult patients to produces anaesthetic effects during pulp capping, endodontic procedures, and extractions.
3. For painless palatine injections.

Contraindications:

1. In highly apprehensive patients they might get anxiety about seeing the bulky set up.
2. In intellectually disabled children.

Trade names:

1. Compudent
2. Comfort control syringe
3. Single tooth anaesthesia
4. Quick sleeper
5. Sleeper one

A. Compudent/Wand

1. Was originally known as Wand. Later on, subsequent versions were introduced in market as Wand Plus and then CompuDent.
2. Good alternative to administer small quantities of anaesthetic solution continuously during needle insertion, which anaesthetize tissue immediately ahead of advancing needle.

B. Comfort control syringe

1. Introduced by Dentsply International, USA in 2001.
2. It is thought to be a substitute for Wand.

C. Single Tooth Anaesthesia System (STA)

1. Newest dental computer-controlled local anaesthetic delivery system.
2. Introduced by Milestone Scientific Inc, USA in 2007.
3. In addition to computer control, it uses vibration to decrease pain.
4. This device also incorporates dynamic pressure –sensing technology that provides a constant monitoring of the exit pressure of the local anaesthetic solution.

D. Quick sleeper

1. Introduced by Dental Hi-Tec, France in 2011.
2. Introduced as an alternative for Wand.
3. After acceptance of Quick Sleeper, newest model Quick Sleeper S4 which is 40% lighter and 19% reduced in diameter compared to previous models is also introduced in market.

E. Sleeper one

1. Was introduced by Dental Hi-Tec, France.
2. The design of this device is similar to Quicksleeper.
3. Lightest handpiece makes operator to hold comfortably and pen like appearance is helpful to use in front of pediatric patients.

4. Vibrotactile devices

1. Pain relief by vibratory stimulation is a method for relief of pain.
2. The technique of pinching and shaking the cheek has been followed to distract the brain from the discomfort of used anaesthesia.

Indications:

1. In paediatric patients, distraction and pain reduction are created by vibrating massages.
2. Indicated in cases where topical anaesthesia is undesirable.

Contraindications:

1. Contraindicated in epileptic patients.
2. In severe neurological disorders patients.
3. In some areas, we need profound anaesthesia.

Devices which work on this concept:

1. Currently, there are four vibrotactile devices available in the market.
2. They are VibraJect, DentalVibe, Accupal and Single tooth anaesthesia.

5. Intraosseous anaesthetic system

It has been employed for more than a century in clinical dentistry.The original technique was too invasive. It requires elevation of the gingival flap to gain access to the buccal cortical bone for perforation with a small round bur.

Available devices: Stabident, X-Tip, Intra Flow

Disclaimer- The views and opinions expressed in this article are those of the author and do not necessarily reflect the official policy or position of M3 India.

About the author of this article: Dr Neha Kalantri is a practising dentist from Nashik.