Evaluation of pulpal anesthesia and injection pain using IANB with pre-heated, buffered and conventional 2% lignocaine in teeth with symptomatic irreversible pulpitis—a randomized clinical study

Study design, ethical approval, and clinical trial registry

This double-blind randomized clinical study was approved by the Sumandeep Vidyapeeth Institutional Ethics Committee (SVIEC/ON/DentBNPG18/D19047; date of approval 22/11/2019), India. The protocol was developed and registered at the clinical trial registry of India (CTRI/2020/09/027796). The current superiority trial was reported according to Consolidated Standards of Reporting Trials (CONSORT) guidelines (Schulz, Altman & Moher, 2010). Written informed consent was obtained from all participants in this study.

Sample size

In a one-way ANOVA study, sample sizes of minimum 60, 60 and 60 were obtained from the three groups whose means were compared. The total sample of 180 subjects achieves 80% power to detect differences among the means versus the alternative of equal means using an F test with a 0.05 significance level. The size of the variation in the means is represented by their standard deviation which is 30.0 the common standard deviation within a group is assumed to be 1.13. Between groups, the one way analysis of variance with multiple comparison tested at 5% level. The sample size formula used was: (Zalpha +Zbeta)²*Sqrt(n*delta²/2kS²), where Zalpha = 1.96; Zbeta = 0.84; n = total number of groups = 3; delta = mean difference = 30.0; k = degrees of freedom = n-1 = 2; S = standard deviation = 1.13.

However number of patients enrolled in the study were 252 divided into in following three groups: (A) preheated 2% lignocaine, (n = 84); (B) buffered local anesthesia, (n = 80); and (C) conventional 2% lignocaine, (n = 88).

Selection criteria

Patients were selected as per the inclusion: patients among 18 to 60 years of age with mandibular hot teeth (Symptomatic irreversible pulpitis), having actively experienced moderate to severe pain on a visual analog scale (VAS) scale of five or more were included in the study. Exclusion criteria: Patients with known hypersensitivity to Lignocaine and sodium bicarbonates, who had undergone cardiac surgery in the last six months, pregnant or lactating females, or with necrosed teeth with sinus or swelling, severe periodontitis and poor oral hygiene, cracks, fracture, and open apex were excluded from the study.

Randomization and allocation concealment

A postgraduate student assessed the eligibility of five hundred and twenty-one patients based on clinical examinations, radiographs, and pulp sensibility tests. Clinically tooth having spontaneous/lingering pain/nocturnal pain with moderate to deep carious lesion and absences of tenderness on percussion and delayed response to the electric pulp test (EPT) were taken for further radiographic examination. Tooth with radiolucency involving enamel, dentin, and approaching pulp was selected. All the radiographs were taken with a long cone and paralleling technique using a positioning indicator device. Two hundred and fifty-two patients meet the selection criteria and agreed to participate in the trial. Co-investigator implemented the random sequence generation and allocation concealment. Randomization was done by computer randomization (https://www.randomizer.org/) and patients were assigned into three groups.

The allocation concealment ratio was 1:1:1. This was done by inserting the LA cartridges in sequentially numbered sealed opaque envelopes. The envelopes were marked with the randomization code. As soon as the patient was placed in the intervention group, the number was noted in the patient’s case sheet and decoded at the end of the trial. 

Blinding

The entire procedure was double-blinded to avoid bias. The primary investigator and the patient both were blinded to the groups allotted. The operator directly received an aspirating metal syringe loaded with the cartridge of lignocaine; pre-heated lignocaine or buffered lignocaine with a 27-gauge needle attached to the tip of the unit.

Clinical procedure

Patients were sensitized to a (1 to 10-point) VAS scale. This scale was given to the patient to choose thrice: the first time was before the injection, second time after receiving the injection, and the third after entering the pulp chamber and a pre-operative VAS score was recorded. Pre-operative pulp sensibility test was recorded using the electric pulp test (EPT). The patient was explained about the test and the tooth was checked first followed by the affected tooth. Patients were asked to indicate when a tingling sensation occurs to him/her, and the response of the affected tooth was noted down in numbers.

For group A—The preparation of preheated local anesthesia was done according to method described by Allen, Bunce & Presland (2008) and Davidson & Boom (1992). A 1.8 ml cartridge of commercially accessible 2% lignocaine hydrochloride with 1:80,000 adrenaline (Lignospan special, Septodont Healthcare India) was placed in a composite warmer (12 VDC, 2000Mpa, 24W0 power supply; AR Heat), for 4 min. Two cartridges were placed in the heating slot of the warmer and the thermostat is set in such a way that a temperature of 42 °C was obtained for the anesthetic liquid. The rubber cap of the second cartridge was removed and a thermometer was used to check the temperature of the anesthetic solution, as it is ascertained at 37 °C (body temp), the first 1.8 ml cartridge was administered to the patient.

For group B—The preparation of buffered local anesthesia was done according to a previous study (Saatchi et al., 2015). The buffered local anesthetic solution has a shelf-life of one week, but it was prepared fresh once every two days for maximum efficacy. Under sterile conditions, 0.18 ml from a 1.8-ml cartridge of 2% Lignocaine with 1:80,000 adrenaline was drawn and replaced with 0.18 ml 8.4% sodium bicarbonate using a 1 ml plastic syringe and stored in the refrigerator. The cartridge was inverted five times to mix the solution. As a result, no precipitation was formed. It was shaken until the solution was clear; this ensured that the sodium bicarbonate was completely dissolved. The cartridge was then loaded into a metal syringe and injected.

For group C—Preparation of conventional group – Conventional nerve block with 1.8ml of 2% lignocaine with 1:80,000 adrenaline was injected. IANB in all the three experimental groups was given with a metal syringe with 27-G, a 1.5-inch needle attached to a standard aspirating dental injection syringe about 1 mm, and 1.8 ml of the solution was deposited slowly (2 min). Immediately after injection, VAS was used to evaluate the injection pain for all the experimental groups.

All the patients were asked to wait for 15 min for the profound anesthesia to be achieved. Subjective symptoms like tingling sensation, numbness of lower lip, buccal and lingual periosteum on the respective side of jaw were considered, whereas objective symptoms like EPT (Parkell Gentel Pulse vitality tester) of concerned tooth was done, negative response to EPT was considered as effective anesthesia. Those patients who do not showed subjective and objective symptoms were given supplementary intra-ligamentary injections and were excluded from the study (consort flow chart).

Isolation was performed with the help of a rubber dam fifteen minutes after the injection. Excavation of caries was done along the walls of the tooth and lastly, the pulpal roof was prepared. Access cavity preparation was done with help of endo access bur to design the access cavity. After entering the pulp chamber and intra-operative VAS score was recorded as intra-operative reading. Further, the endodontic treatment was performed as per the standard methods and protocol by the primary investigator.

Statistical methods

The obtained data were tabulated and statistically analyzed using SPSS version 21 and p-value and Chi-square Value, one way ANOVA with Tukey’s post hoc test, and paired t-test were applied. For the statistical test between the group, a one-way analysis of variance with multiple comparison tests at the level of significance was set as 5%.

Demographic data

The patients enrolled in the clinical trial are presented on the CONSORT 2010 flow diagram (Fig. 1). Total of 252 patients were included in present study of which 11 patients were dropped out as lip numbness was not achieved after 15 min of INAB and considered as failure due to the wrong technique. So, 241 patients were included for final evaluation. Out of the total enrolled patients, 119 were male, while 122 were female. The age of 41 patients was between (18–25) years of age, 82 patients were between (26–36) years, 66 patients were between (37–46) years of age and the remaining 52 patients were between (47–60) years of age.

Pre-Intra operative VAS score

The mean pre-operative pain using a 10-mm Visual Analog Scale (VAS) was 7.28 mm ± 1.26 mm, for Group A. For Group B mean VAS score was 6.88 mm ± 1.23 mm, and for Group C score was 6.88 mm ± 1.24 mm (Table 1). On comparing the means of all three groups no statistical difference was found in the pre-operative pain values. While the mean of Intra-operative pain for Group A was 1.59 mm ± 1.03 mm, for Group B 1.69 mm ± 1.07 mm, and Group C was 3.54 mm ± 2.34 mm. This shows that all three local anesthetic agents were highly effective in reducing pain (P value <0.001).

Table 2 shows an inter-group comparison between all the three experimental groups for the reduction in intra-operative pain, there was no statistically significant difference (P = 0.183) between Group A (Preheated LA) and Group B (Buffered LA). Whereas there was a highly significant difference (P < 0.001) between Group A (Preheated LA)—Group C (Conventional LA) and between Group B (buffered LA)—Group C (Conventional LA). This indicates that buffered and preheated local anesthetic solutions are more efficient in reducing pain in patients with symptomatic irreversible pulpitis in comparison to conventional 2% local anesthetic agents.

Pain on injection

The mean pain on LA administration using VAS (Visual Analog Scale) for Group A was 1.35 mm ± 1.09 mm, Group B was 2.08 mm ± 1.27 mm, and Group C was 3.19 mm ± 0.93 mm. Table 3 shows the mean difference between Group A and Group B was −0.73 mm ± 0.17 mm and between Group A and Group C was −1.84 mm ± 0.17 mm stating that there statistically significant difference between the groups (P value <0.001). Correspondingly comparing Group B with Group C showed a mean difference of −1.11 mm ± 0.17 mm and a p-value of <0.001 thus indicating there was a statistically significant difference between them concerning pain on injection. This shows that preheated LA showed the least pain on injection followed by buffered and conventional LA.