A Randomized Clinical Trial to Compare the Efficacy of Alkalinized Local Anesthesia in Inferior Alveolar Nerve Blocks: A Study of 100 Cases

Introduction

Local anesthetics have been a key component of dental treatment since the beginning of 20^th century.¹ Local anaesthetic administration is a prerequisite for pain reduction while performing any minor surgical procedure.² Local anesthetics are now being administered in anesthesiology, emergency department (ED), lumbar puncture and intravenous cannulation. Additionally,for post-procedure pain control, longer-acting local anesthetics have also been administered.³

The incorporation of a vasopressor, commonly epinephrine, to lignocaine causes prolongation of anesthetic effect by reduction in blood flow to anatomic area and dispersion of drug away from the position of injection. 2% Lignocaine Hydrochloride with 1:200,000 concentration of adrenaline is effective from 2 to 3 minutes following administration, lasting for 45 minutes to 1.5 hours.⁴

The pH of local anesthetics without epinephrine is about 5.5. On adding epinephrine to lignocaine, the pH value lowers. Hence sodium bicarbonate can commonly be used to maintain the alkalinity of the solution. When it interacts with the hydrochloric acid in local anesthetics, sodium bicarbonate creates water and carbon dioxide (CO₂ ).⁵ The dissolved carbon dioxide, during needle penetration, rapidly diffuses through the tissues and turns off the nociceptor responsible for initiating pain impulses.²

Several ways to decrease the pain of local anaesthetic administration include topical local anaesthesia, use of thin needle, slow injection, injecting during needle withdrawal and altering the temperature of anaesthetic solution. There is overwhelming evidence that buffered local anaesthetics cause less pain during injection.⁶

The only drawback with adoption of this technique is that the buffered lignocaine solutions are relatively unstable.⁷ Hence, on-spot fresh preparation of buffered solution is required which may lead to increase in treatment time and makes it less applicable at the time of emergencies.

As the advantages of buffered solutions are greater than its feasibility, a study was proposed in our department involving alkalinization of local anaesthesia with 7.5% sodium bicarbonate aiming to evaluate its effect on pain during injection, the onset and duration of anaesthesia with inferior alveolar nerve block.

Materials and Methods

The study took place in the Department of Oral and Maxillofacial Surgery at Chhattisgarh Dental College & Research Institute, Rajnandgaon. The study was approved by the Institutional Ethical Committee accompanied with trial registration in the ICMR (Indian Council of Medical Research). This study included 100 patients who had to undergo tooth extraction under local anaesthesia in the mandibular region and were arbitrarily divided into two equal groups of 50 cases each. Group A was the control group in which the patients included were administered lignocaine hydrochloride with 1:80,000 adrenaline solution by injection and Group B comprised of study group in which patients were given lignocaine hydrochloride with 1:80,000 adrenaline solution mixed with 7.5% sodium bicarbonate by injection for attaining local anesthesia (LA).

Armamentarium

The materials most importantly included were 7.5% sodium bicarbonate ampule, disposable syringe (10 mL & 2 mL) & needle (27 gauze), 2% lignocaine HCL with 1:80,000 adrenaline, digital clock for recording time and mandibular extraction forceps as per the need (Figures 1-5).

The case selection procedure focused on detailed case history, clinical and radiological examination (Intra oral periapical radiograph/Orthopantomogram) with acknowledgement of existence or absence of infection. The patients in the age group of 18-60 years who gave consent for the study, with an indication for mandibular tooth extraction were included in the study. Patients who did not present positive subjective symptoms after administration of local anesthetic solution were also covered. Patients under any medications which would alter the pain perception, medically compromised patients with systemic illnesses, pregnant or lactating women, and patients contraindicated for lignocaine with adrenaline were eliminated from the study.

Initial sensitivity testing was done for both carbonated lignocaine and lignocaine hydrochloride. Following standard protocols, patient’s preparation followed by administration of mandibular nerve block (inferior alveolar nerve block) was done. Intra operative assessment of time of deposition, pain during deposition through VAS (Visual Analogue Scale),⁸ time of onset of local anaesthesia and duration of the procedure was done. Extraction of the indicated mandibular tooth was performed atraumatically (Figure 6). Post-operative assessment was done through telephonic conversation or assessment card.

Statistical analysis

The statistical analysis was carried out using IBM SPSS (Statistical Package for Social Sciences), statistical version 21. The analysis included frequency table, bar, pie chart, association of variables based on Chi-square. All quantitative variables were estimated using measures of central location “mean” and measures of dispersion (standard deviation). For normally distributed data, mean was compared using independent t-test (for two groups). For non-normality distributed data, median was compared using Mann Whitney U test (for two groups). For relationship, Pearson correlation method was used using Chi square test.

Results

It was a randomized prospective clinical study conducted during the period 2019-2021. The study patients were within the age range of 18-60 years. The analysis of age distribution was done by Chi square test and no significant difference was found i.e. p=0.92 (p >0.05). It was interpreted that both the groups were comparable with respect to age (Table 1, Graph 1).  

In Group A, the age ranged from 18-60 years (mean age - 30.06±14.26 years) and in Group B, the age ranged from 18-59 years (mean age - 32.1±15.18 years). On using the unpaired t test, the difference in mean age was insignificant i.e. p=0.49 (p >0.05). This also reveals that both the groups were comparable in terms of age of the subjects included (Table 2, Graph 2).

In the present trial, the commonly extracted mandibular tooth in Group A was left first premolar while it was right first premolar in Group B (Table 3).

The study included a total of 33 males and 67 females. Group A consisted of 16 male patients (32%) and 34 female patients (68%), while Group B consisted of 17 males (34%) and 33 females (66%). On statistical analysis, no significant difference was established in gender distribution among both the groups as the difference was found to be insignificant p=0.81 (p >0.05) (Table 4, Graph 3).

Pain during injection, onset and duration of anaesthesia and related complications were evaluated both intra operatively and post operatively in all the patients included in both the groups.

Pain during injection

The pain was assessed on administration of local anesthesia by Visual Analog Scale. The pain score for Group A was 3.29±1.02 and for Group B was 4.64±1.12. The unpaired t test resulted in a p value of <0.001 suggesting a significant difference and the pain experienced was significantly low in patients in whom buffered local anesthesia was administered i.e. Group B (Table 5, Graph 4). 

Onset of subjective symptoms

The time of onset of subjective symptoms was calculated from the point of retrieval of the needle after injection till the first numbness felt at the corner of mouth (below lower lip). Two patients out of 100 did not present positive subjective symptoms but experienced objective symptoms and were included in our study. Intraoperatively, the mean time for the onset of subjective symptoms was assessed and the test showed a p value of 0.64, indicating that the comparison was insignificant (p>0.05) (Table 5, Graph 5).

Onset of objective symptoms

The time of onset of objective symptoms was assessed by running a periosteal elevator or probe intra orally through the attached gingiva between mandibular canine and premolars. Mean time was analyzed through unpaired t test and the p value resulted was 0.85, indicating an insignificant difference between the groups (p >0.05) (Table 5, Graph 6).

Duration of anesthesia

The estimation of duration of anesthesia after extraction extended till the time sensation was first felt by the patient post operatively. The time was recorded by patient and was informed through telephonic conversation or by filling post-operative assessment card provided following extraction. Six out of 100 patients did not revert due to their unreachable network and some did not even receive the call. Based on collected data, no statistical significant difference was found in the duration of anesthesia among the two groups with p value 0.4 (p >0.05) (Table 5, Graph 7).  

Complications

There was no evidence of occurrence of intraoperative and post-operative complications such as allergy, bleeding, wound healing, nerve damage and dry socket in our study. None of the complications were significant amongst both the groups with respect to all the parameters included (Table 5).

Discussion

The oral cavity is richly supplied with nociceptive neurons and is associated with sensory gratification and physical attractiveness. Patients are most likely to judge dentists and oral surgeons based on pain avoidance at the time of treatment. Moreover, to provide a comfortable treatment experience to patients and to combat the prior notion, many factors were considered for painless injection technique but mostly buffering of local anesthetic solution is well accepted and practiced.

On 26^th November 1884, Hall encountered sensitivity in left upper incisor tooth and started his dentistry to try the effects of cocaine. A needle was passed through the mucous membrane of his mouth to a point as close as possible to the infra-orbital foramen, and a small quantity of the substance was injected which resulted in complete anesthesia of the left half of the upper lip and cheek. Anesthesia lasted for 26 minutes and reduction in sensation was observed for another 10 to 15 minutes. This was how the first step towards invention of anesthetic effect took place.⁹ There are several factors that influence pain on administration of local anaesthesia, like acidity of the solution, speed of injection due to increase in volume within tissues, size of the needle, type of anesthetic solution used and temperature of the solution.¹⁰ Hence painless injections can be attained by injecting the solution slowly, reducing the acidity by altering the pH of the solution, decreasing needle size or increasing the temperature of solution.

The study patients were administered 1.8 mL of local anesthetic solution within one minute for inferior alveolar block. The reduced pain during injection was achieved by adding sodium bicarbonate to the LA solution. The warming of local anesthetics up to body temperature is believed to decrease the amount of pain experienced during injection and several reports advocated this.¹¹

Elevation of pH of LA by addition of sodium bicarbonate was first proposed by Louis Bignon in 1892. Use of excessive alkalizing agent causes precipitation of the unionized base.¹² Sodium bicarbonate is an alkalinizing agent which increases the concentration of plasma bicarbonate, buffers excess hydrogen ions, raises pH of blood, thereby reversing the clinical signs of acidosis.¹³

Alkalinisation of local anesthetic solution produces less stinging pain during deposition. The injected solution is absorbed quickly by the normal tissues, increasing the rate of diffusion, thus causing rapid onset of action. When excessive solution is added, pH rises too far and uncharged basic form further gets precipitated. Therefore, alkalinized local anesthetic solutions should be freshly prepared before injection.¹⁴

The study used freshly prepared alkalinized LA solution by mixing 7.5% sodium bicarbonate which increases the pH of local anesthesia to a more physiological one. Once opened, the unused portion of the 30 mL vial was discarded and a new lignocaine vial was used for subsequent patients. Since NaHC03 is less expensive and easy to use, it was not necessary to use the solution as multidose in different patients.

7.5% sodium bicarbonate was added to LA solution in a dilution of 1/10 (3 mL of sodium bicarbonate to 30 mL of local anaesthetic solution). This increased the pH from 3.05 to 7.38, resulting in availability of lipophilic uncharged lignocaine molecules (RN), also called the base, to be readily available for diffusion into the neural membrane as the solution was close to physiological tissue pH of 7.4. Thus it reduced the pain caused by the injection itself. Most patients were given local anaesthetic solution with sodium bicarbonate that showed no pain during injection.

Erramouspe,¹⁵ Martin,¹⁶ Davies¹⁷ and Sarvela et al.,¹⁸ concluded that using alkalinized solutions reduced pain during injection of local anaesthesia and our study results confirmed the same. However, Chow et al., inferred no change in the intensity of pain using alkalinized solutions.¹⁹ Many studies have also reported that the combination of lignocaine hydrochloride with long acting local anesthetic does increase the duration of action and decreases patient discomfort.^15-18,20

Gros,²¹ Ritchie,²² and Kashyap et al.,⁶ concluded that addition of sodium bicarbonate to solutions of lignocaine reduced the onset of anaesthesia, and was effective in reducing pain during injection. But according to the current study results, there was no significant difference encountered in the onset of subjective and objective symptoms after buffered lignocaine administration. Moreover, on comparison with buffered local anesthesia, no significant difference was observed in duration of anesthesia post extraction.

Complications most likely encountered at the time of administration of local anesthetic solution include hypersensitivity, allergy, over dosage, toxicity, hematoma, trismus, paresthesia, or neuralgia. Mostly to prevent intra operative complications, sensitivity test was done prior to local anesthesia administration (buffered or non-buffered).²³

Palanivel Indu et al.,²⁴ and Tirupathi SP²⁵ did not mention any of the complications related to alkalinization of local anesthesia. Among 100 patients included in the present study, not a single complication was encountered intraoperatively or post operatively in any of the study subjects.

A limitation of buffering is that it results in manipulation of concentration of 2% lignocaine used in alkalinized group. On addition of 7.5% sodium bicarbonate to 2% lignocaine, the concentration of lignocaine in buffered solution becomes 1.8%. Thus, this study supports the finding that alkalinization of local anesthesia causes decreased concentration of lignocaine but still results in less pain on administration.

Pain is considered as a subjective finding. When patients with high pain threshold are allocated into the non-buffered lignocaine group or vice versa, there might be some bias in the study outcome. As the buffered lignocaine used is not previously manufactured but had to be freshly prepared by the operator, the study had to follow blinding of two parties only (patient and interpreter), rather than three. This could have resulted in bias in the study results which was overcome by incorporation of larger sample size.

Conclusion

On weighing the patient’s anxiety and apprehensiveness with operators ease during administration of LA, comfort throughout treatment is considered to be of prime importance. This was the main motivational thought to proceed with this study. The study hence concluded that addition of 7.5% sodium bicarbonate to 2% lignocaine and 1:80,000 adrenaline reduces pain and burning sensation experienced by the patient during injection, thus providing comfort to the patient. However, the onset of anaesthesia was not improved using buffered lignocaine in normal tissues. The cost effectiveness of the solution also recommends its use. The only drawback is the need for fresh preparation of alkalinized solution at the time of administration. Pre-formed buffered lignocaine injections are available in the market as well but are not cost effective. More randomized controlled trials with adequate sample size should be carried out to validate decreased onset and increased duration of anesthesia in buffered local anesthetics for extraction socket.

Conflict of Interest

1. Competing Interests and Funding: No funding was received for conducting this study. The authors have no competing interests to declare that are relevant to the content of this article.

2. Ethical approval: Ethical approval was waived by the local Ethics Committee of University in view of the retrospective nature of the study and all the procedures being performed were part of the routine care.

3. Consent to participate and publish: Informed consent was obtained from all individual participants included in the study and to publish the data in journals.

Acknowledgements

I would like to acknowledge all my contemporaries, seniors, juniors and nursing staff members for co-operation and help which led to smooth and successful completion of our research.