Topical Anaesthetic Agents for Intraoral Use

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Table of Contents

Introduction
Water-Insoluble Topical Anaesthetics
Examples: Benzocaine, Lidocaine base
Examples: Benzyl alcohol, Pontacaine, Lidocaine hydrochloride
Evidence for Effectiveness of Intra-oral Topical Anaesthetic Agents
Works Cited

Introduction

Topical anaesthetics are drugs that are applied on the skin or mucosal surfaces to reduce pain. Their use in dental practice is prominent due to their ability to reduce pain while administering injection needles for anaesthesia.

Topical anaesthetics can be divided into water-insoluble and water-soluble (Monheim 160).

Water-Insoluble Topical Anaesthetics

Most of the topical anaesthetic agents are insoluble in water, but soluble in vehicles like alcohol, polyethene glycol, propylene glycol, or carboxymethylcellulose, which make them surface applicable (Monheim 160). These agents generally remain in contact with the surface for a longer duration with prolonged activity (Monheim 160). Also, toxicity is negligible owing to poor absorption into circulation, except for local irritation and allergy on prolonged use (Monheim 160).

Examples: Benzocaine, Lidocaine base

Benzocaine (Ethyl aminobenzoate)

It is a simple ester of aminobenzoic acid that cannot form soluble anaesthetic salts due to the absence of a basic nitrogen group (Monheim 160). Hence, it is suitable as an injection and is only used as a topical anaesthetic (Monheim 160). It is a popular topical anaesthetic agent with the commonly used brand name Hurricane and is used in many preparations of topical anaesthetics (Monheim 160).

Lidocaine base

Lidocaine (diethyl-2,6-dimethylacetanilid) is the first nonester local anaesthetic used in dentistry (Monheim 146). It was first synthesized in 1943 by Lofgren (Monheim 146; Yagiela 48). Lidocaine base is water-insoluble and is used at a concentration of 5% (Monheim 161). Maximum surface anaesthesia is achieved in 15 seconds and the general duration of action is 30 minutes for a single application (Monheim 161).

A 10% lidocaine base aerosol spray with discharge dose-adjusted at 10 mg per spray is a flavoured preparation that causes excellent anaesthesia of 15 minutes within 10 to 15 seconds of application (Monheim 164).

Water-Soluble Topical Anaesthetics

They have a great disadvantage in terms of toxicity due to their rapid absorption into circulation (Monheim 164). Moreover, the vascular nature of mucous membranes causes rapid absorption of the agent over a wide area (Monheim 164). To be effective, the intended mucosal area should be dried with a cotton swab before application of the agent to prevent dilution with saliva and, then a cotton pledget moistened with the agent should be kept in place for 10 to 15 seconds (Monheim 164).

Examples: Benzyl alcohol, Pontacaine, Lidocaine hydrochloride

Benzyl alcohol

It is an aromatic alcohol that is used in 4% or 10% solutions for topical anaesthesia (Monheim 164). It has a shorter duration of action and is less toxic than benzocaine (Monheim 164).

Pontacaine (Tetracaine hydrochloride)

2% pontacaine is a very potent water-soluble topical anaesthetic agent with a great potential for systemic toxicity (Monheim 164). Its duration of action is longer up to 45minutes to 1 hour when applied on dry mucosa (Monheim 164). However, a combination of benzocaine that has a rapid onset and brief duration and tetracaine hydrochloride results in rapid and long-lasting action within 30 seconds (Monheim 164).

A commonly used combination of tetracaine is called Cetacaine that contains 14% benzocaine, 2% butamben and 2% tetracaine dissolved in propylene glycol (Monheim 165). The water solubility of tetracaine and the insolubility of the other two agents results in the longest duration of anaesthesia with the shortest latent period than each agent alone (Monheim 165). A spray of not more than 1sec and a maximum dose of 20 mg or 1 ml of 2% solution is recommended for tetracaine (Monheim 165).

Lidocaine hydrochloride

Its water solubility makes it more penetrating and toxic than lidocaine base (Monheim 165). It is generally used as a 2% or 4% concentration, and the maximum recommended dose is 200mg (Monheim 165). In patients with gag problems during dental procedures, a flavoured 2% viscous lidocaine syrup is used as an oral rinse or gargle (Monheim 165).

With cotton pledgets, the maximum recommended dose is 1 to 5 ml or 0.3 to 0.6 mg/kg with the overall amount not to exceed 300 mg or 4.5 mg/kg (Monheim 165).

EMLA

The eutectic mixture of local anaesthetics (EMLA) is meant to use in place of lidocaine or benzocaine sprays (Malamed 129). It is mainly useful to apply on intact skin while the others can be effective only on mucous membranes or damaged skin (Malamed 129). It is a combination of 2.5% lidocaine hydrochloride and 2.5% prilocaine hydrochloride (Leshaw 191). It is available as a 5% cream and is 95% effective when applied properly (MacKenzie & Young 30; Leshaw 191). It is an emulsion with sufficient moisture and lipid solubility to penetrate effectively through intact skin without the need to dissolve in alcohol that causes skin irritation (MacKenzie & Young 30). The problem with EMLA is that it should be applied under occlusion for 45 to 60 minutes at the site of needle insertion before the procedure (Malamed 129).

Though it is mainly intended for use on intact skin, Holst and Evers demonstrated its efficiency in blocking the pain of needle insertion through oral mucosa (Malamed 129).

Evidence for Effectiveness of Intra-oral Topical Anaesthetic Agents

Various studies have been conducted to determine the effectiveness of different topical anaesthetic agents when used intraorally.

Career et al. conducted a study in 2005 to compare the effectiveness of clove and 20% benzocaine gel versus placebo in reducing the pain of needle insertion (747). They used four substances namely homemade clove gel, 20% benzocaine gel, a placebo that resembled clove and a placebo that resembled benzocaine (747 & 8). They applied these agents on the maxillary canine buccal mucosa of 73 adult volunteers (Alqareer et al. 747 & 8). Pain response was noted with a 100 mm visual analogue pain scale (Alqareer et al. 747). The results showed that clove and benzocaine gels had lower mean pain scores, indicating that both were effective in reducing pain (Alqareer et al. 747). Moreover, the absence of any significant difference between the pain scores of clove and benzocaine indicated that both could be used interchangeably (Alqareer et al. 749).

Fukayama et al. made a comparative study on the effectiveness of 20% benzocaine and 60% lidocaine gel (157-61). They applied these agents separately on the alveolar mucosa of the upper incisor apices of 20 healthy males for 20 minutes and subjected the area for three different stimulations to assess pain response (Fukayama et al. 157). The stimulations are, in order, insertion of 30-G dental infiltration needle with resin stopper 2 mm from the tip of the needle into the labial gingival, 30-G needle insertion to the alveolar bone, and a 30-second infiltration injection with 0.9 ml of 2% lidocaine containing 1/80,000 epinephrine using the same needle as the first stimulator (Fukayama et al. 157 & 8). The pain rating score and the visual analogue scale showed that 60% lidocaine was more effective as a topical anaesthetic before infiltration anaesthesia (Fukayama et al. 158-60).

On the other hand, Rosivack et al observed the effectiveness of benzocaine 20% and lidocaine 5% and concluded that both were effective topical anaesthetic agents without significant difference between them (290-2). However, no statistically significant differences in heart rate were found between the two and the placebo (291).

In a study by Gazal et al. to find the effectiveness of topical bupivacaine in reducing distress after extraction in children, they found that topical bupivacaine did not reduce distress after extraction (425-431). They applied swabs soaked with bupivacaine and sterile water separately on exposed teeth sockets in two different groups of children (Gazal et al. 425). The preoperative, postoperative and 15-minute postoperative mean distress scores did not show any difference between the two conditions (Gazal et al. 429 & 30).

Meechan in a study on EMLA concluded that a 15-minute application of EMLA effectively worked as a sole anaesthetic agent for soft tissue biopsy of palatal mucosa in a needle-phobic patient (32-4). Meechan, however, pointed out that the original formulation of EMLA was not appropriate for its intraoral use, and that its low viscosity mandates the use of custom splints to maintain the agent in position (Meechan 33).

Another study conducted by Nakanishi indicated that topical anaesthesia might reduce the pain of needle insertion in the anterior mandibular mesiobuccal fold, but not very effective in the area of an inferior alveolar nerve block (14-19). The determination of pain threshold by an algometer and assessment of pain by a visual analogue scale revealed that topical anaesthetic was more effective than placebo in reducing needle insertion pain in the mandibular canine area, but not as effective in the pterygotemporal depression (Nakanishi et al. 14-19).

In a yet interesting study by Kramp et al., prilocaine HCl was found to be more effective than mepivacaine and lidocaine in reducing needle insertion pain (52-5).

All in all, water-insoluble topical anaesthetics are widely approved due to their low potential toxicity. Several studies have resulted in different inferences on the relative effectiveness of various topical anaesthetic agents in intra-oral use.

Works Cited

Alqareer, Athbi, Asma Alyahya and Lars Andersson. “The Effect of Clove and Benzocaine Versus Placebo as Topical Anesthetics.” Journal of Dentistry 34 (2006): 747-750.

Rosivack, R. Glenn, Samuel R. Koenigsberg and Kathryn C. Maxwell. “An Analysis of the Effeciveness of Two Topical Anesthietcs.” Anesth Prog 37 (1990): 290-292.

Leshaw, Steven M. “Advances in Local Anesthesia.” The Western Journal of Medicine 156.2 (1992): 191.

Fukayama et al. “Comparison of topical anesthesia of 20% benzocaine and 60% lidocaine gel.” Oral Surgery Oral Medicine Oral Pathology 94 (2002): 157-161.

Gazal, G. et al. “A Double-blind Randomized Controlled Trial Investigating the Effectiveness of Topical Bupivacaine in Reducing Distress in Children Following Extractions Under General Anaesthesia.” International Journal of Paediatric Dentistry 14 (2004): 425-431.

MacKenzie, Terrance A. and Earle R. Young. “Local Anesthetic Update.” Anesth Prog 40 (1993): 29-34.

Yagiela, John A. “Local Anesthetics: A Century of Progress.” Anesthesia Progress (1985): 47-56.

Meechan, J. G. “The Use of EMLA® for an Intraoral Soft-tissue Biopsy in a Needle Phobic: A Case Report.” Anesthesia Progress 48 (2001): 32-34.

Kramp, Louis F. et al. “Evaluation of Prilocaine for the Reduction of Pain Associated With Transmucosal Anesthetic Adminitstration.” Anesthesia Progress 46 (1999): 52-55.

Malamed, Stanley F. “What’s New in Local Anesthesia?” Anesthesia Progress 39 (1992): 125-131.

Monheim, Leonard M. Monheim’s Local Anesthesia and Pain Control in Dental Practice. Mosby-Year Book, 1983.

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