Relief of palatal injection pain by liposome-encapsulated 2% lignocaine prepared by ultrasonic dental scaler

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Abstract

Injections into the palate are common in dental treatment and are unpleasant for the patient. A liposomal encapsulation technique was developed to improve the efficacy of 2% lignocaine dental injection so that it could be used as a topical anaesthetic. Liposome-encapsulated 2% lignocaine was prepared as needed by sonicating 2% lignocaine hydrochloride dental injection (with 1:100,000 adrenaline) with a lipid mixture using a dental ultrasonic scaler for 1 min. The time to onset and time to take effect were calculated by a pinprick test in the palatal mucosa in 10 normal subjects. In another experiment, the preparation was tested in a further 22 subjects for its pain-relieving effect during a standard palatal injection, and compared with 18% benzocaine/2% tetracaine gel. The results showed that the mean (SD) time to onset and time to take effect of the liposome-encapsulated 2% lignocaine were 39.0 (21.4) and 157.5 (2.3) s, respectively, and the mean (SD) pain score measured on a visual analogue scale (VAS) during injection was 4.1 (2.3) cm. After the application of the gel the corresponding measurement was 4.8 (2.8) cm (p = 0.045). The encapsulation of 2% lignocaine dental injection in liposomes by a dental ultrasonic scaler was effective in improving the efficacy of the anaesthetic for topical application.

Introduction

Injection of anaesthetic into the palatal mucosa is normally painful but necessary for many dental operations on the upper dental arch. To minimise discomfort dentists usually apply a topical anaesthetic before inserting the needle. The most popular topical anaesthetic is 20% benzocaine ointment, or a similar formulation. However, though topical anaesthetics seem to work well on buccal and lingual mucosa, their efficacy on palatal mucosa is less certain. EMLA®, a eutectic mixture of 2.5% lignocaine and 2.5% prilocaine, has been used to anaesthetise palatal mucosa, and has been shown to reduce the pain of palatal injections better than a placebo,1, 2, 3 although it was originally designed for external use. Recently, a thermosetting gel of a mixture of 2.5% lignocaine and 2.5% prilocaine (Oraqix®; Dentsply, USA) has been introduced for intraoral use, and relieves pain during needle pricks on the palatal mucosa more successfully than 20% benzocaine gel.4 It is also effective in reducing periodontal pain during scaling and root planing.5, 6

The efficacy of topical anaesthetics has also been greatly improved by liposome technology. Liposomes encapsulated with lignocaine7, 8 and tetracaine9 are effective in reducing the pain of inserting a needle into the skin. Topical liposomal anaesthetics have also been tested in oral mucosa, and proved to be successful in anaesthetising the buccal mucosa before injection – for example, liposome-encapsulated 1% and 2% ropivacaine,10, 11 and liposome-encapsulated 1.7% tetracaine and 15% benzocaine.12 However, in a crossover study, Franz-Montan et al.11 showed that liposome-encapsulated 1% and 2% ropivacaine were not effective in reducing pain after an injection into the palate.

Lignocaine is a safe and effective local anaesthetic and is also available in dental injection form, which is ready for preparation as it is needed. Sonication is a method used to liposomally encapsulate drugs, which can yield a narrow range of particle sizes.13 As ultrasonic dental scalers are commonly used in dental clinics, we proposed the chair-side use of such devices to liposomally encapsulate 2% lignocaine that is normally used for dental injection, and tested the prepared anaesthetic for its topical anaesthetic effect.

Section snippets

Methods

The study was approved by the Khon Kaen University Ethics Committee for Human Research. Written informed consent was obtained from all subjects. The study was divided into two parts. In the first part the time of onset and the time to take effect of liposome-encapsulated 2% lignocaine were investigated. In the second part the pain-relieving effect of the anaesthetic for palatal injection was compared with that of 18% benzocaine/2% tetracaine hydrochloride gel (OneTouch®, Hager, USA).

First part

Four women and 6 men, mean (SD) age of 24 (1) years, were tested. Mean (SD) time to onset was 39.0 (21.4) s, whereas mean (SD) time to effect was 157.5 (44.3) s. The mean (SD) pain VAS at baseline and at the time at which the drug became effective were 4.6 (2.4) and 0.4 (0.4) cm, respectively (Fig. 2).

Second part

Ten women and 12 men, mean (SD) age 22 (2) years, participated in the experiment. Mean (SD) VAS after the application of the gel was 4.8 (2.8) cm, which differed from the 4.1 (2.3) cm after

Discussion

The palatal mucosa is highly keratinised and many types of topical anaesthetics, other than EMLA®, have failed to anaesthetise it satisfactorily.1, 2, 14 Previous studies have shown that a 5-min application of EMLA® can reduce pain from 5.15 to 3.5 (VAS) during insertion of a needle into the palate,2 and from 3.09 to 1.46 during injection into the palate over posterior teeth,3 compared with a placebo group. Franz-Montan et al.11 recently showed that liposome-encapsulated 2% ropivacaine does not

Acknowledgements

The authors would like to thank all the participants and Khon Kaen University for funding the research. The authors would also like to thank Prof. J.W. Osborn for criticising the first draft of the manuscript and Dr. W. Pitiphat for her assistance in statistical analyses.

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