Comparative Analysis of the Anesthetic Efficacy of 0.5% Ropivacaine Versus 2% Lignocaine Hydrochloride with Adrenaline (1:80,000) for Inferior Alveolar Nerve Block in Surgical Removal of Impacted Mandibular Third Molars

Abstract

Objective

To compare the onset, duration and depth of anesthesia, postoperative pain, duration of analgesia and adverse reaction between 0.5% ropivacaine and 2% Lignocaine hydrochloride with adrenaline (1:80,000) in 40 patients having bilaterally impacted mandibular third molars.

Patients and Methods

A prospective, randomized, single blind study was carried out among 40 patients requiring surgical removal of bilaterally impacted mandibular third molars having similar “difficulty index.” The onset of action, duration and depth of anesthesia, duration of analgesia, postoperative pain and adverse reactions of 0.5% ropivacaine and 2% lignocaine hydrochloride with 1:80,000 adrenaline were evaluated. All patients were infiltrated intradermally with 0.5 ml of 0.5% ropivacaine as test dose to rule out any allergic reaction. The surgical extractions of the impacted third molars were done using the standard surgical procedure.

Results

0.5% Ropivacaine had higher depth of anesthesia, longer duration of action and postoperative analgesic effect than 2% Lignocaine hydrochloride with 1:80,000 adrenaline with no adverse effects.

Conclusion

0.5% ropivacaine is safe, efficacious, clinically acceptable and equally potent local anesthetic agent when compared to 2% lignocaine with 1:80,000 adrenaline in oral and maxillofacial surgery for longer duration of surgeries.

Introduction

Pain control is an essential requirement for minor oral surgeries and local anesthesia is a well established method of achieving this around the jaws. Local anesthetics prevent nociceptive impulses from reaching the central nervous system by reversibly blocking the progress of an action potential.

In 1943, Lignocaine was synthesized by the Swede chemist Nils Lofgren. It is the most popularly used local anesthetic in dentistry and its pharmacodynamic features are the base line in comparative studies with other local anesthetics [1].

The success of a minor oral procedure relies on the potency, duration of action and safety profile of the local anesthetic employed. Local anesthetic with an extended duration of action, shorter onset time and negligible toxicity is an optimal choice.

A common standard option is 2% lignocaine hydrochloride with adrenaline (1:80,000). However, it is not recommended for long procedures or in patients with cardiovascular compromise where adrenaline is not desirable [2].

In 1996, Ropivacaine was clinically introduced. It has a biphasic vascular effect. At low concentrations (0.063–0.5%), it causes vasoconstriction and at higher concentrations (1%), it causes vasodilatation in humans.

Ropivacaine alone is efficient in providing potent prolonged anesthesia without the addition of adrenaline. Therefore, it avoids the undesirable cardiovascular effects associated with adrenaline.

Ropivacaine was also effective in reducing immediate postoperative pain because of its residual analgesic effect that extends for 6 h postoperatively and therefore reduces the need for analgesics in the immediate postoperative phase [3].

The purpose of this present study was to evaluate whether ropivacaine 0.5% could be a better alternative to 2% lignocaine hydrochloride with adrenaline (1:80,000) in the mandibular impacted third molar surgeries.

Patients and Methods

A prospective, randomized, single blind study was done in 40 healthy patients aged between 20 and 50 years having bilateral impacted mandibular third molars with similar “difficulty index” [4] (Fig. 1). The study was conducted in Department of Oral and Maxillofacial Surgery, J.N. Kapoor D.A.V. Centenary Dental College and Hospital, Yamunanagar.

Fig. 1.

OPG depicting bilaterally impacted mandibular third molars with similar “difficulty index”

Patients were excluded if they were known or suspected to be hypersensitive or allergic to local anesthetics, or any ingredients in the anesthetic solution; if they had any coexisting blood dyscrasias, cardiac or neurological diseases or were immunocompromised; if they were pregnant or lactating; or if they were taking central nervous system depressants or any other analgesics preoperatively.

Complete history of all the patients were taken along with general physical and clinical examination and an informed consent was signed by the patients, prior to the surgical procedure.

The choice of local anesthetic for the first operation was randomized (by the toss of a coin), and the other local anesthetic was given for the second side. All patients were infiltrated with 0.5 ml of 0.5% ropivacaine (Ropin 0.5%, Neon Laboratories Ltd.) (Figure 2) intradermally as test solution to rule out any allergy reaction.

Fig. 2.

Ropivacaine ampoule

A classical direct inferior alveolar with long buccal and lingual nerve bock of 3 ml (2 ml for inferior alveolar nerve block, 0.5 ml for lingual nerve block and 0.5 ml for long buccal nerve block) was administered using a 26 gauge needle and a standard surgical procedure was used for extraction of impacted third molars.

We recorded intraoperatively, time of onset of anesthesia, depth of anesthesia (using HP VAS [5]) and postoperatively, duration of anesthesia, duration of analgesia and adverse effects associated with ropivacaine or lignocaine hydrochloride with adrenaline (1:80,000).

Postoperatively, the patients were provided with a questionnaire [1] that had to be filled up after they were discharged. The questionnaire contained all the questions regarding the postoperative analgesia, adverse effects associated with anesthesia and time of intake of rescue analgesic. The patients brought back the questionnaire on the 3rd postoperative day.

Analysis of Data

A database was constructed using Microsoft Excel (Microsoft, Redmond, WA). The statistical analysis was done with the help of SPSS (statistical package for social sciences) version 21.0 and Epi-info version 3.0 statistical Analysis Software. The significance of differences was assessed using Unpaired “t” test, Chi-square test, Shapiro–Wilk test, as appropriate.

Results

Forty patients were included in this study, of which 19 were males and 21 were females. The average age of the study patients was 31.85 ± 8.57 years (range 20–49 years).

The mean time taken to achieve soft/hard tissue anesthesia was significantly more with ropivacaine in comparison with Lignocaine (Table 1).

Table 1.

Time taken to achieve soft/hard tissue anesthesia (in seconds)

	Ropivacaine		Lignocaine		Mean difference	t test value	p value
	Mean	SD	Mean	SD
Subjective	127.80	34.46	78.58	34.84	49.23	6.353	0.001*
Needle stick test	190.68	43.46	126.06	36.43	64.63	7.207	0.001*
Loss of proprioception	247.13	44.26	170.58	41.98	76.55	7.936	0.001*
Electric Pulp test	300.93	42.02	207.55	40.66	93.38	10.099	0.001*

Unpaired t test

*Significant difference

The depth of anesthesia of 0.5% ropivacaine was found to be higher than 2% lignocaine with adrenaline (Table 2).

Table 2.

Depth of anesthesia

	Ropivacaine		Lignocaine		Mean difference	t test value	p value
	Mean	SD	Mean	SD
Soft tissue incision	0.00	0.00	0.00	0.00	0.00	0.000	1.000
Flap elevation	0.00	0.00	0.00	0.00	0.00	0.000	1.000
Osteotomy	2.45	1.46	6.95	3.95	4.49	− 2.533	0.041*
Suturing	0.33	0.24	1.00	0.42	− 0.67	− 1.734	0.108

Unpaired t test

*Significant difference

The mean duration of anesthesia (hours) and duration of postoperative analgesia (hours) were 8.27 ± 0.67 h and 10.94 ± 0.98 h for ropivacaine and 2.92 ± 0.58 h and 3.86 ± 0.67 h for Lignocaine, respectively (Table 3).

Table 3.

Duration of anesthesia and postoperative analgesia (in hrs)

	Ropivacaine		Lignocaine		Mean difference	t test value	p value
	Mean	SD	Mean	SD
Duration of anesthesia (h)	8.27	0.67	2.92	0.58	5.35	38.258	< 0.001*
Duration of postoperative analgesia (h)	10.94	0.98	3.86	0.67	7.08	37.803	< 0.001*

Unpaired t test

*Significant difference

None of the patients were found allergic to any of the anesthetic agents (Table 4).

Table 4.

Adverse effects (local and systemic)

Adverse effects	Ropivacaine	Lignocaine
No	40	40
	100.0%	100.0%
Local	0	0
	0.0%	0.0%
Systemic	0	0
	0.0%	0.0%
Total	40	40
	100.0%	100.0%

Chi-square value = 0.000, p value = 1.000

Chi-square test

^#Non-significant difference

Discussion

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage. International Association for the Study of Pain (IASP) defined pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in term of such damage” [6–8].

Anesthetic agents have been in use for dental pain management since early 1844, when nitrous oxide was first used for sedation during tooth extraction. Modern chemical local anesthetic agents came in 1904–1905 when Alfren Einhorn discovered procaine, but with the discovery of Lidocaine in 1943 by Lofgren, the field for local anesthesia entirely changed [1].

Lignocaine is the local anesthetic most widely used for pain control, since its pharmacokinetic characteristics and low toxicity compared with other ester type anesthetics makes it safe for use in dental procedure. However, such an immediate acting anesthetic does not provide analgesia during the periods of most intensive postoperative pain experienced (6–8 h) leading to an increased consumption of postoperative analgesics.

Despite the “gold standard” status of lignocaine hydrochloride, which is the most commonly used local anesthetic in dental practice, many clinical trials have proven the efficacy of newer long-acting amide local anesthetic, ropivacaine, which differs chemically from lignocaine in having a propyl group on the piperidine nitrogen atom. Ropivacaine is the first amide-type local anesthetic with a pure S-enantiomeric configuration having high pKa and relatively low-lipid solubility. The chemical structure of the local anesthetic agent affects the potency and toxicity levels of the anesthetic agent [7].

The time of onset of soft and hard tissue anesthesia was calculated from the time of injection of local anesthesia till the appearance of tingling sensation and numbness on the ipsilateral side if the tongue and lower lip (subjective symptoms) and the absence of pain on—insertion of a needle into the mucosa (onset of soft tissue anesthesia), insertion of a probe into the periodontal ligament space (loss of proprioception) and electric pulp testing of the mandibular first premolar (onset of pulpal anesthesia). Evaluation for onset of anesthesia was carried out after every 30 s.

In the present study, the mean time of onset of subjective anesthesia (Table 1) for ropivacaine was 127.80 s and for lignocaine was 78.58 s. Hence, onset of ropivacaine was found to be longer by about 49 s, and the difference was found to be significant which coincided with the study of various authors [2, 9, 10].

Lignocaine has pK_a of 7.7 and ropivacaine has pK_a of 8.1. Due to lower pK_a of lignocaine, it has rapid onset of action as compared to ropivacaine resulting in large number of lipophilic free base molecules that are able to diffuse through the nerve sheath thereby lowering the onset time [1].

The mean time taken for objective onset of soft tissue anesthesia (Table 1) by needle stick test with ropivacaine (190.68 s) and lignocaine (126.05 s) was found to be 64.63 s with onset being longer for ropivacaine and the difference has been found to be significant.

The mean time taken for loss of proprioception with ropivacaine was 247.13 ± 44.26 s as compared to 170.58 ± 41.98 s with lignocaine. So, the mean time taken for loss of proprioception in ropivacaine administered patients was 77 s more than that of lignocaine patients.

No studies could be found comparing the time of onset of anesthesia with objective evaluation specifically using needle stick test or loss of proprioception as done in the present study.

The mean time of onset of pulpal anesthesia for ropivacaine was 300.93 s and 207.55 s for lignocaine. The difference was found to be about 93.38 s with patients of ropivacaine achieving delayed pulpal anesthesia than those of lignocaine. The difference was found to be significant in the present study and was in agreement with the study done by Axelsson et al. [11]. The reason for longer onset of soft and hard tissue anesthesia with ropivacaine is its poor diffusion through the soft tissue and bone as compared to lignocaine.

The efficacy of the two anesthetics was compared on the basis of depth of the anesthesia between the ropivacaine and lignocaine, which was inversely proportional to intraoperative pain. It was measured with the help of Heft Parker Visual Analog Scale which consists of a long horizontal line of 170 mm, anchoring the verbal descriptors “no pain” and “worst pain imaginable” during soft tissue incision, flap elevation, osteotomy and suturing.

In the present study (Table 2), proportional differences in HP VAS scores for Osteotomy was found to be higher in lignocaine indicated lower depth of anesthesia than in ropivacaine. It is because of higher lipid solubility and a higher dissociation constant (pK_a—8.1) of ropivacaine which decreases the diffusion of larger number of free base molecules through the nerve membrane and thereby increasing the potency of the drug. [12]

The duration of anesthesia was calculated from the time of onset of numbness and tingling post-injection till the reappearance of sensation in the area. Above-mentioned questionnaire was given to the patient to note down the return of sensation in the area.

In the present study, the mean duration of anesthesia was 8.27 ± 0.67 h for ropivacaine and 2.92 ± 0.58 h for lignocaine. The difference was found to be about 5.35 h with ropivacaine having a longer duration than Lignocaine (Table 3).

The present study coincides with studies conducted by various authors [9, 10, 13] who observed similar results with mean duration of anesthetic effect for 0.5% ropivacaine.

Duration of the effect of an anesthetic is proportional to its degree of protein binding. The protein binding capacity of ropivacaine is 94% in contrast to lignocaine which is 65%. The longer duration of ropivacaine as compared to lignocaine is because of its greater protein binding capacity [1, 14].

The duration of analgesia was calculated as the number of hours, the patient was free from the pain after the administration of anesthesia till the reappearance of pain sensation.

The mean duration of postoperative analgesia for ropivacaine was 10.94 ± 0.98 h as compared to that of lignocaine (3.86 ± 0.67 h) with the mean difference of 7.8 h (Table 3). The mean duration of anesthesia was significantly more for the ropivacaine and favors the study conducted by Brkovic et al. [13].

As per the present study, we can say that ropivacaine offers better postoperative analgesic effect clinically with a significant reduction in postoperative analgesic requirement.

After the procedure, the patient was told about various adverse reactions that can occur by lignocaine and ropivacaine and were manifested as local adverse effects (prolonged anesthesia, paresthesia, hematoma, trismus, facial palsy, tissue sloughing and ulceration) or systemic adverse effects (drowsiness, nausea, vomiting, shallow breathing, headache and sweating). The patients were asked to document any of above mentioned postoperative adverse effects on the questionnaire provided by the surgeon.

None of the patients reported any side effects in ropivacaine and lignocaine during the study. This shows that both lignocaine and ropivacaine have a safety profile in appropriate concentrations (Table 4).

On the basis of these preliminary results of this clinical study, ropivacaine, at 0.5% concentration seems to be suitable for achieving inferior alveolar nerve block during mandibular third molar surgery, demonstrating satisfactory intensity of local anesthesia and prominent postoperative analgesic potency superior to that of lignocaine. Accordingly, ropivacaine could be recommended for use in oral surgery when a long-acting anesthetic is indicated. Moreover, its prolonged duration of anesthesia without need for added vasoconstrictor could be an attractive advantage over lignocaine.

Therefore, ropivacaine is safe, efficacious, clinically acceptable and equally potent local anesthetic agent when compared to 2% lignocaine with 1:80,000 adrenaline in oral and maxillofacial surgery for longer duration of surgeries.

Compliance with Ethical Standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical Statement

Obtained for experimentation with human subjects from patients as well as from ethical committee. (F/Ethical/1593). The study design was approved by the Board of Studies of the University.

Informed Consent

An informed consent was obtained from all the patients.