|Year : 2006 | Volume
| Issue : 4 | Page : 155-160
|Evaluation of three topical anaesthetic agents against pain : A clinical study
R Nayak, P Sudha
Dept. of Pedodontics and Preventive Dentistry, Manipal College of Dental Sciences, Mangalore, India
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| Abstract|| |
AIM : To compare pain responses of children during local anaesthetic infiltration at bilateral buccal sites prepared with topical application of EMLA 5% cream, benzocaine 18% gel or lignocaine 5% ointment and also to find out the rapidity of onset of action of these agents. METHODS : 60 healthy children aged 6 to 12 years old, received bilateral buccal infiltration following application of topical anaesthetic agents applied in a double blind design. Pain responses were compared based on subject self report using visual analogue scale (VAS) and operator assessment using Sound -Eye -Motor (SEM) scale. RESULTS : Benzocaine gel had the rapidest onset of action. EMLA 5% cream proved to be superior in pain reduction compared to benzocaine and lignocaine. Taste acceptance was better with benzocaine gel. Further studies are required for EMLA cream with an improved formulation more suitable for mucosal application before its routine use in dentistry.
Keywords: Topical anesthetics, Eutectic mixture of local anesthetics, pain, visual analogue scale, sound-eye-motor scale
|How to cite this article:|
Nayak R, Sudha P. Evaluation of three topical anaesthetic agents against pain : A clinical study. Indian J Dent Res 2006;17:155-60
|How to cite this URL:|
Nayak R, Sudha P. Evaluation of three topical anaesthetic agents against pain : A clinical study. Indian J Dent Res [serial online] 2006 [cited 2014 Sep 18];17:155-60. Available from: http://www.ijdr.in/text.asp?2006/17/4/155/29871
| Introduction|| |
Pain control is an integral part of modern dentistry . In pediatric dentistry, it forms an important part of child behavior guidance and helps in positive acceptance of dentistry by the child patient . Needle injection of local anaesthetic is the commonest modality of pain control used today. However it is ironical that the pain control measure itself is a source of fear and anxiety for dental patients, more so for the child. Hence, it is important to resort to a pain free method of administering local anesthesia for a child patient. Pediatric dentists are on a constant search of tools for painless administration of local anesthesia. Topical anesthetics are a boon to them in their attempts.
Topical anesthetics control pain perception and hence alter the pain reaction of an individual . They act by blocking the transmission of signals from the terminal fibers of the sensory nerves. Their effects are limited to the control of painful stimuli occurring on or just beneath the mucosa .
Various agents are available today for topical analgesia. While lignocaine serves as the gold standard , benzocaine is also known for its excellent surface anaesthetic properties . EMLA (Eutectic mixture of local anesthetics) was introduced into the anesthetic armamentarium in the 1980s for dermal analgesia . The earliest reported study on use of EMLA for mucosal application was by Holst and Evers . From then on several studies reported the mucosal use of this drug with conflicting results ,,,,,,,,,,,.
Hence this study was carried out with the following aims and objectives:
a) To study the rapidity of onset of action of EMLA 5%, benzocaine 18%, and lignocaine 5%.
b) To evaluate the efficacy of these drugs in reducing the pain associated with intraoral injections.
| Materials and methods|| |
Three topical anaesthetic agents were used in this study. 5% EMLA cream (Astra Pharma Inc. Ontario), lignocaine hydrochloride ointment (lignox 5%, Warren Pharmaceuticals Pvt. Ltd.), and benzocaine 18% gel (Topicale, Premier Dental Products co.) [Figure - 1]
This study was conducted at Manipal College of Dental Sciences, Mangalore on 90 healthy children between age 6 to 12 years in two phases. The approval of institutional ethical committee was obtained before begining the study.
Phase 1 was conducted to find out the rapidity of onset action of the three agents used in the study viz EMLA cream, lignocaine ointment, and benzocaine gel.
Thirty healthy children between 6 to 12 years of age and a mean age of 8.9 years who attended our pedodontic clinic were chosen for this part of the study. The sample selected was independent of sex, race, and ethnic characteristics.
The selected children had a normal healthy gingiva, were free from any systemic diseases and did not report of any allergy to any of the components of the drugs to be used in the study. Written, informed consent was obtained from the parents of the participating subjects prior to the start of the study.
The thirty selected children were divided into 3 groups of 10 children each. Each group was assigned to one of the three test agents as follows.
Group 1 - Lignocaine ointment
Group 2 - EMLA cream
Group 3 - Benzocaine gel
The gingiva in relation to the maxillary right central incisor was chosen as the test site in all the subjects. This site was chosen due to ease of access and isolation so that the time of onset of action of the drugs could be accurately determined. Following isolation, the test area was dried using sterile gauze. Approximately 0.5 gm of the test agent was applied to the area using a cotton applicator. Care was taken to see that no undue pressure was exerted on the tissue during the application of the drug. The area was checked for the onset of surface anaesthesia every 30s for a period of 3 minutes. The blunt end of a periosteal elevator was used to check for objective signs of surface anesthesia. The children were instructed to indicate pain by raising their right hand. Also, the investigator noted eye signs of discomfort. Time was regulated using a stop clock. The time of onset of surface anesthesia was noted in seconds. Following the 3-minute period, the test area was wiped free of the agent. The mucosa was inspected for any signs of local irritation. An average time of application for each agent was derived from this phase of the study.
This part of the study was conducted to evaluate the efficacy of the three topical anaesthetic agents in reducing the pain of intra oral injections.
A dental examination of 250 school children was undertaken for the purpose of subject selection and seventy healthy children were chosen. The chosen subjects had mobile deciduous teeth or deep carious lesions in two different areas of the mouth that could be treated under infiltration anesthesia.
The following exclusion criteria were observed during sample selection.
- History of allergy to any of the components of the agents to be used in the study
- Abscess in the area of the study
- Bleeding disorders
- Immunocompromised subjects
- Presence of genetic/systemic diseases that may compromise the health of the oral mucosa
- Extremely anxious and fearful subjects
- Presence ofperceptual motor problem
- Presence ofbehavioral problems.
Further detailed examination excluded 10 extremely anxious children, 6 of whom had abscess in the test sites. Finally 60 healthy children who fulfilled the requirements of the study were selected. The subjects were between 6 to 12 yrs of age. No gender, race, or ethnic characteristics were considered and only those children in need of dental treatment under local anesthesia and meet the age criteria were selected. Written informed consent was obtained from the parents of the participating subjects prior to the start of the study.
Design of the study
The study was conducted in a double-blind manner in which one investigator delivered the topical anaesthetic while another investigator carried out the evaluation.
Each topical anaesthetic agent was assigned a code as follows:
A - EMLAcream
B - Benzocaine gel
C - Lignocaine ointment
In order to confirm to the double blind design of the study, the coding, the application, and data maintenance were entrusted to two trained investigators.
The sixty selected subjects were divided into 3 groups of 20 children each as follows.
Group 1 - EMLA Lignocaine
Group 2 - Benzocaine Lignocaine
Group 3 - EMLA Benzocaine
Two agents were used in one subject at a time. Changing of the application turns against any possibility that the order of application of the agent could affect the responses of the patients to the visual analogue scale was done. The investigator was also unaware of which agent was applied on which side in the subject.
The duration of application of each agent was derived form the first phase of the study as: 2 minutes for lignocaine and benzocaine and 3 minutes for EMLA cream.
The areas to be infiltrated on the buccal aspect were chosen as the test sites.
The test areas were dried using a sterile gauze piece following adequate isolation. A trained assistant applied 0.5 gm of the test agent for the stipulated time to the sites using a cotton applicator. Following this application the test areas were wiped free of the surface anaesthetic such that no traces of the test agent could be identified.
Immediately following this, the investigator administered infiltration anesthesia on both the test sites one after another. I ml of 2% Xylocaine with vasoconstrictor was injected using a 26 gauge needle to each of the test sites. The needle was concealed in an attempt not to create a fear-promoting situation that could alter the subject's pain perception. The use of fear promoting words was also avoided. During the injection procedure, the investigator as well as another trained person observed the response of the child The sound eye motor scale designed by Wright et al  was used. The subjects response was graded on a scale from 0-3 [Table - 1].
Each child quantified the pain perceived during the injection using a 10-point visual analogue scale (VAS). The VAS used in the present study was about the size of a small plastic ruler [Figure - 1]. One side of the VAS consisted of an interval scale ranging from 0-100 in millimeters. On the opposite side of the VAS were the caricatures of five faces ranging from a smiling face to a weeping face. One end of the scale had "no pain" written on it while the other end had "worst pain imaginable" written on it. A slit in the center of the scale harbored a movable pointer, which the child moved to quantify the experienced pain/discomfort [Figure - 2]. No instructions were given regarding the procedure or the use of VAS to the child prior to the study in order to eliminate bias due to anticipated pain. The pain score for each of the test sites was recorded.
All the obtained data were subjected to statistical analysis. Following the calculation of mean and standard deviation, the analysis was done using Dunnet's "t" test.
| Results|| |
In phase I of the study, it was found that benzocaine gel had the rapidest onset of action [Table - 2].
In phase 2 of the study the efficacy of the topical anaesthetic agents in reducing pain of intraoral injections was evaluated using VAS and SEM scale.
Infra group comparison showed EMLAto be significantly efficient as compared to benzocaine and lignocaine [Table - 1],[Table - 2],[Table - 3]. The mean scores of group 1, 2, and 3 are depicted in graph 4.
| Discussion|| |
In the phase 1 of the present study, the rapidity of onset of action of EMLA cream benzocaine gel and Lignocaine ointment were studied on 30 patients. Gel (18% benzocaine) showed the most rapid onset of action of 75s±15.81. Literature supports the fact that benzocaine has a rapid onset of action . This property is attributed to its low dissociation constant (pKa = 3.4). Topical anaesthetic drugs that have apKa less than physiologic pH blossom, as sufficient local anaesthetic base can be provided to permit diffusion through the mucous membrane to the free nerve endings . However, the above result did not support the manufacturers claim of 10-second application.
Lignocaine 5% ointment showed the mean time of onset of action of 105s as against the 15s suggested in literature . Cawson and Spector recommend 1-2 minutes of contact with the mucosa for lignocaine since it has a relatively weak surface anaesthetic activity .
EMLA cream had the slowest onset of action (I 38s±1 5.49). The slow onset of action of this preparation can be attributed to its low viscosity and consequent difficulty in localizing it to the site of application.
Holst and Evers recommended an application time of 5 minutes to be the tolerable limit of practical usefulness for EMLA cream . Haasio et al recommended a four minute application and found that the maximum analgesic effect is reached at 13±8 minutes . Vickers and Punnia Moorthy used a 2-minute application time and observed a significant reduction of pain on needle penetration . Meechan and Webery recommended that ideally, a topical anaesthetic be applied for 2 minutes time .
In the present study, a topical application for a minimum of 1 minute was observed to be essential for obtaining a reasonably good surface anesthesia. This is in accordance with the recommendations ofthe ADA and FDA .
The blunt end of a periosteal elevator was used to check the onset of anaesthesia. Roghani, Duperon and Barcohana  evaluated the efficacy of commonly used topical anesthetics using a specially designed instrument with a ball-ended tip. Since the purpose of our study was only to find out the time of onset of action of the topical anesthetic, the periosteal elevator was used.
Data regarding the efficiency of topical anesthetics is sparse and results are contradictory. Phase 2 of the present study was conducted to study the efficiency of EMLA, lignox, and benzocaine in reducing pain of intra oral injections. 60 participating subjects were divided into 3 groups of 20 patients each and the study was conducted in a double blind manner using visual analogue scale and sound eye motor scale for subjective pain measurement and objective ratings respectively.
Certainly pain is difficult if not impossible to quantify. Huskinson has stated that "pain is a personal psychological experience and an observer can play no legitimate part in its direct measurement" .
Because of the developmental, cognitive, and emotional differences between adults and children, assessment of pain is even more difficult in children. Generally two techniques that are useful in pain measurement are selfreport and observation of behavior. Variations of these techniques are useful for estimating pain intensity in children .
The visual analogue scale and its variations have proven to be useful in children over ages of 6 or 7 years and reasonable validation data are available in this regard ,. Pain assessment is more difficult in patients under the age 6 years since they usually have not developed the cognitive skills necessary for the use of VAS . Hence, in the present study, children above 6 years of age were chosen.
Sound eye-motor scale designed by Wright et al  was used as the observational scale. Its use is justified since none of the existing observational scales are feasible for measuring pain in a dental situation.
In the present study, interrater reliability with SEM scale was seen and there was slight deviation in implementation. Sounds and movements accompanied one another and rarely were desparate responses were seen. However the application of this scale in younger children may be difficult as their response to painful situations may not only be dependent on the pain experienced during the procedure but may also be influenced by many other factors.
No prior instructions were given to the participating subjects regarding the procedure or use of VAS to avoid bias due to anticipated pain. This helped in a better appreciation of the efficiency of the agents on objective observation by the investigators. The needle was concealed during the procedure since the site of the needle may produce a fearful situation for the child and may alter his response to the pain.
In the present study, EMLA cream was found to be superior to Topicale and Lignox with regards to pain reduction. Holst and Evers reported superiority of EMLA 5% over Xylocaine 5% . EMLA was found to be superior to NUM and Xylocaine 5% by Vickers and Punnia Moorthy . Tulga and Mutlu reported that vision gel was superior in performance compared to EMLA 5% . In the present study, the result could be differed due to 18% content ofbenzocaine used as against the 20% used by Tulga and Mutlu. However Meechan and Donaldson stated that EMLA and lignocaine 5% were equally effective .
In this study it was observed that EMLA cream had a low viscosity and was difficult to handle. Localization of the drug solely to the injection was difficult. To overcome this difficulty, Svenson and Peterson have recommended use of orahesive bandages . However, Tulga and Mutlu reported difficulty in sticking these bandages on to the mucosa .
Despite these technical difficulties, the superiority of EMLA cream in the present study could be attributed to its high pH of 9.6. This is in accordance with Setnikar who stated that increasing the pH increases the potency of the topical anaesthetic agent . Also, a combination of two drugs in a single agent could have contributed to the increased efficiency .
A placebo was not used in the study since it would have been irrational to carry out pain provoking procedure in children without making an effort to control pain adequately.
No adverse effects were observed with any of the agents during in the course of the present study. Also it was observed that, no subject gave a zero pain score for any of the agents.
| Conclusions|| |
Based on the results of our study, the following conclusions can be drawn:
- Benzocaine 18% had the rapidest onset of action (75 seconds) followed by lignocaine 5% (105 seconds) and EMLA cream (138 seconds).
- In spite of its slow onset of action, EMLA cream proved to be superior in pain reduction followed by benzocaine 18% and lignocaine 5% with VAS and SEM scale.
As the numbers of studies on this subject are sparse and the clinical results are mixed, an attempt has been made to explain the results on a pharmacological basis. However, further studies are required for EMLA cream with an improved formulation more suitable for mucosal application before its routine use in dentistry.
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Dept. of Pedodontics and Preventive Dentistry, Manipal College of Dental Sciences, Mangalore
[Figure - 1], [Figure - 2]
[Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5]
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