Evaluation of the efficacy of nitrous oxide inhalation sedation on anxiety and pain levels of patients undergoing endodontic treatment in a vital tooth: A prospective randomized controlled trial.

CONTEXT: Anxiety and fear of pain are the two major deterrents for which patients avoid dental treatment. Local anesthetic, which forms the foundation for the delivery of pain-free endodontic treatment, does not serve the purpose in anxious patients and requires augmentation with other pharmacological agents. AIMS: The aim of this study is to observe the effectiveness of nitrous oxide in alleviating patient anxiety and pain during endodontic treatment of a vital tooth. SETTINGS AND
DESIGN: The present in vivo study was conducted on sixty healthy patients from the Outpatient Department of Genesis Institute of Dental Sciences and Research, Ferozepur, Punjab, India. SUBJECTS AND METHODS: Sixty anxious patients having irreversible pulpitis in their lower molar were selected and divided into two groups, namely control group and intervention group, with thirty patients placed in each group. In control group, access opening and pulp extirpation was done under local anesthesia only, whereas in intervention group, access opening and pulp extirpation was done under local anesthesia and nitrous oxide sedation. The anxiety levels of patients, before and after the treatment, were measured using the Modified Dental Anxiety Scale. Pain felt by the patients during administration of local anesthesia and during access opening was measured using the Visual Analog Scale. STATISTICAL ANALYSIS USED: The data were analyzed using ANOVA and paired t-test, and graphical analysis of the data was done.
RESULTS: Significant reduction in anxiety and pain levels of patients during endodontic access opening including significant reduction in pain during administration of local anesthesia was observed under nitrous oxide sedation.
CONCLUSIONS: Conscious sedation with nitrous oxide is a useful technique to add to the armamentarium used in the treatment of teeth with symptomatic irreversible pulpitis. Copyright:

INTRODUCTION

Avoidance of dental treatment because of anxiety and fear of pain is acknowledged to be the major deterrent to oral health.[1] Dental treatment has been ranked fifth among the commonly feared situations. One of the dental procedures which is feared by many people is endodontic treatment.[2] Mandibular molars are usually anesthetized by inferior alveolar nerve block (IANB). The overall success rate for IANB in patients presenting with symptomatic irreversible pulpitis ranges from 15% to 57%. Studies have attempted to increase the success of IANB through buffering, varying anesthetics and dosing, the use of the Gow–Gates and Vazirani–Akinosi techniques, and preoperative medications. In general, the results have not proven to be completely effective.[3] In addition, a higher level of anxiety may manifest as increased pain intensity.[1]

Various oral pharmacological agents such as benzodiazepines (diazepam and midazolam) are available to reduce patient anxiety. However, oral sedation has a relatively unpredictable effect, making its use more difficult. Of all approaches, the most commonly used and the safest form of conscious sedation is nitrous oxide sedation.[4]

Nitrous oxide gas is not new to either anesthesia or dentistry. It has an impressive safety record and is excellent for providing conscious sedation and relative analgesia for apprehensive dental patients. It has analgesic, sedative, and hypnotic properties.[4] It might make endodontic treatment painless and also improve the efficacy of IANB.[5]

No study has investigated the efficacy of nitrous oxide in alleviating anxiety and pain during endodontic treatment in patients with irreversible pulpitis. Therefore, the purpose of this prospective, randomized study was to determine the effectiveness of nitrous oxide in alleviating patient anxiety and pain during endodontic treatment of a vital mandibular tooth with irreversible pulpitis.

SUBJECTS AND METHODS

The present randomized controlled study was conducted on sixty healthy patients from the Outpatient Department of Genesis Institute of Dental Sciences and Research, Ferozepur, Punjab, India.

The following inclusion criteria were used to select patients for the study:

Age >18 years

Patients requiring root canal treatment of a vital mandibular molar with irreversible pulpitis

Anxious and fearful patients selected on the basis of scoring on the preoperative Modified Dental Anxiety Scale (MDAS)

Patients in American Society of Anesthesiologists Category I or II

Patients willing to accept nasal hood and showing no impediments to adequate nasal breathing

Nonpregnant patients.

A prior consent of the patients was obtained, and a thorough health history of the patients was recorded. To ensure vitality of tooth, electric pulp test and cold test were performed, and a preoperative radiograph of the affected tooth was taken.

The patients were requested to fill the MDAS pro forma before treatment. The MDAS (as described in study by Clark and Brunick[6]) was used to assess the anxiety levels of patients. For clinical purpose, the researchers have established a cutoff MDAS score of 19 and above as a strong likelihood of patient being anxious for dental treatment, so patients with MDAS score >19 were selected for the study.

The Heft–Parker visual analog scale (VAS)[7] was used to access pain perceived by the patients. Every patient was made to understand VAS so that he/she could objectively rate pain on VAS.

Selected patients were then randomly divided into two groups, namely control group and intervention group, with thirty patients placed in each group. In control group, access opening and pulp extirpation was done under local anesthesia only. In intervention group, access opening and pulp extirpation was done under local anesthesia and nitrous oxide sedation.

In patients of control group, anesthetic gel was placed passively at the site of inferior alveolar nerve block (IANB) injection for 60 seconds, using a cotton tip applicator. Following this the IANB was administrated in the manner described by Jorgensen and Hayden[8] by using a standard aspirating syringe and a 27G 1¼” needle. The solution given was 3.6 mL of 2% lidocaine with 1:100,000 epinephrine (xylocaine; Astra Zeneca LP, York, PA, USA). The patients were instructed to rate the injection pain on the VAS scale. Fifteen minutes after the injection, the tooth was isolated with a rubber dam, and endodontic access was performed. Each patient was instructed to definitively rate any pain felt during access opening using a VAS similar to the one used to rate injection pain [Table 1]. After pulp extirpation and thorough irrigation, the chamber was closed, and temporary restoration was done. The patients were instructed to fill a final MDAS on the basis of anxiety felt throughout the treatment and were then discharged after giving postoperative instructions [Table 2].

Table 1

Readings of pain perceived by patients (on the visual analog scale) during administration of local anesthesia and during access opening

Control group		Intervention group
During administration of local anesthesia	During access opening	During administration of local anesthesia	During access opening
114	54	0	23
85	54	36	23
85	36	54	36
85	23	0	0
114	23	0	0
85	54	23	0
114	23	23	23
85	85	0	0
85	54	0	23
54	0	23	0
54	23	0	0
114	85	23	0
114	23	0	0
114	85	54	36
85	36	0	0
85	0	54	54
54	0	0	0
114	36	0	0
114	23	0	0
54	36	23	0
23	0	23	0
54	0	23	23
114	36	23	0
54	0	54	23
114	54	54	36
85	23	23	36
54	23	23	0
114	36	54	0
23	0	36	23
114	23	23	0

Table 2

Comparison of anxiety levels of patients (on the Modified Dental Anxiety Scale) before and after treatment

Control group		Intervention group
Preoperative	Postoperative	Preoperative	Postoperative
23	17	18	11
17	12	23	12
15	11	20	9
17	10	21	5
21	12	19	8
19	13	22	6
17	9	21	6
23	15	19	6
22	13	20	10
18	11	17	7
16	6	20	9
25	15	17	7
19	10	22	7
20	19	17	11
19	12	24	8
19	11	18	12
17	11	23	7
17	13	23	7
22	15	22	6
16	11	22	10
18	7	23	7
17	12	18	8
17	12	19	8
19	12	20	16
23	14	24	14
17	10	23	16
17	11	18	11
21	13	19	12
20	8	17	11
22	11	21	6

The intervention group patients were asked to complete a preoperative, written psychomotor skill test, that is, Trieger Dot Test (as used by Newman et al.[9]). The score of the test was recorded to be compared with similar postoperative test as an objective measurement to ensure the complete recovery of cognitive functions of the patient.

In patients of intervention group, a 6 L/min flow rate of 100% oxygen was established, and the patients adjusted the nasal hood for comfort [Figure 1]. The patients were instructed to breathe through their nose. After 5 min of 100% oxygen, the nitrous oxide/oxygen was titrated during a 5-min period until an ideal sedation level was reached. Malamed[10] states that an ideal sedation will be achieved when the patient experiences some or all of the following: a feeling of light-headedness, a feeling of warmth throughout the body, numbness of the hands and/or feet, a feeling of euphoria, and a feeling of lightness or heaviness of the extremities. The range of nitrous oxide concentration was 30%–50%, which, according to Malamed, is the concentration typically required for analgesia. Once this level was achieved, the patient was maintained at this level for 5 min before the injection of local anesthetic. Rating of pain during local anesthesia injection and access opening [Figure 2] was done in a manner similar to control group [Table 1]. After treatment, the patient was put on 100% oxygen for at least 5 min. Postoperative anxiety was rated using the MDAS [Table 2] after complete recovery of the patient as determined by the postoperative Trieger dot test. Patients were then discharged after giving postoperative instructions and asked to report for a recall visit.

Figure 1

Nitrous oxide and oxygen being delivered to patients through a nasal hood

Figure 2

Local anesthesia administration and access opening done under local anesthesia

RESULTS

The anxiety levels of patients, before and after treatment, and pain perceived by the patients, during administration of local anesthesia and access opening in a mandibular molar with and without nitrous oxide sedation, were recorded and put to statistical analysis using ANOVA and paired t-test.

A statistically highly significant reduction was observed in postoperative anxiety score of patients in intervention group as compared to those in control group, even though there was no significant difference in preoperative anxiety of these patients.

On comparing VAS reading during local anesthesia, there was a highly significant reduction in pain perceived by patients during the administration of IANB under nitrous oxide sedation.

A significant reduction in pain perceived during access opening was observed under nitrous oxide sedation [Table 3].

Table 3

Mean data collected during the study

	Control group	Intervention group	P
Total number of patients	30	30	-
Mean preoperative anxiety	20.27	20.67	0.384 (NS)
Mean postoperative anxiety	11.87	9.10	<0.01 (S)
Mean pain perceived during local anesthesia	85.23	21.63	<0.001 (HS)
Mean pain perceived during access opening	31.60	11.97	<0.001 (HS)

NS: Nonsignificant, S: Significant, HS: Highly significant

DISCUSSION

The anxiety evoked by dental treatment can be successfully controlled by slightly depressing the level of consciousness in many patients. Thus, sedation is a method that dentists can use to reduce the fear of dental treatment; in addition, it is suggested for patients who may have difficulty in achieving profound anesthesia. It also prevents the neurophysiologic consequences of stress. The use of conscious sedation might make endodontic treatment painless and also improve the efficacy of IANB.[5]

To minimize the bias in recording the anxiety and pain levels of patients undergoing endodontic treatment, only highly anxious patients were included in this study.

Although the exact mechanism of action of nitrous oxide is not known, it is known that nitrous oxide does not work through a single mechanism. Research indicates that nitrous oxide activates its analgesic effect by causing the release of endogenous opiate peptides with subsequent activation of opioid receptors and by the inhibition of N-methyl-D-aspartate (NMDA) glutamate receptors. NMDA typically incites an excitatory response in the nervous system; therefore, by blocking this effect, nitrous oxide creates the desired analgesic effect. An advantage of nitrous oxide in the current study is that it targets both opiate and NMDA receptors to provide analgesia. The anxiolytic effect involves the activation of the gamma-aminobutyric acid A receptor through the binding site for benzodiazepines. The anxiolytic effect of nitrous oxide involves three key enzymes, namely nitric oxide synthase, soluble guanylyl cyclase, and cyclic guanosine monophosphate-dependent protein kinase.[11] The inhibition of any of these enzymes blocks the anxiolytic effect of nitrous oxide.

The concentration of 30%–50% nitrous oxide was chosen for this study for two reasons. Jastak and Donaldson[12] theorized that a 30% dose of nitrous oxide is equivalent to a 10–15-mg dose of morphine. Second, a dose range of 25%–50% nitrous oxide has been commonly used in previous studies evaluating nitrous oxide sedation and analgesia during painful procedures.[8131415]

A significant reduction in the anxiety level of patients was seen in the nitrous oxide group in this study [Graph 1]. This result was in correlation to the study by Zacny et al.[16] who studied mood changes during nitrous oxide inhalation in patients with different levels of preoperative dental anxiety. The results of their study suggested that nitrous oxide reduces dysphoria and elevates mood in all patients.

Graph 1

Significantly lower postoperative Modified Dental Anxiety Scale score in intervention group

On comparing VAS reading during local anesthesia also, there was a significant decrease in the number of patients in “moderate pain” and “severe pain” categories [Graph 2]. These results were in concurrence with a study by Jacobs et al.[17] who determined the effect of nitrous oxide on pain during three mandibular block techniques. They concluded that the patients in the group that received N2 O:O2 and then the local anesthetic demonstrated a statistically significant reduction in pain on injection than those in other groups who received the local anesthetic only.

Graph 2

Significant decrease in the number of patients in “moderate pain” and “severe pain” categories in intervention group. Most of the patients in intervention group experienced no pain or mild pain during local anesthesia injection

A significant reduction in pain perceived during endodontic access cavity preparation under nitrous oxide sedation was also observed in this study [Graph 3]. This correlates with the study result by Stanley et al.[18] who found that the success rate for the IANB was 50% for the nitrous oxide control group and 28% for the placebo group. A more effective IANB along with reduced anxiety must have played an important role in reducing pain during access cavity preparation.

Graph 3

Marked reduction in pain perceived by patients in intervention group during access opening. Most of the patients in it experienced either “no pain” or had only “mild pain” during access opening

The results show that nitrous oxide sedation did alleviate the anxiety and pain of patients during endodontic access opening including a significant reduction in pain during administration of local anesthesia, and therefore, it might be a useful technique to add to the armamentarium used in the treatment of teeth with symptomatic irreversible pulpitis. Furthermore, if a patient presents with irreversible pulpitis of a mandibular tooth and severe anxiety, this study points out that nitrous oxide sedation is preferable to oral sedation, as with nitrous oxide sedation, the dose is titratable and the patient would not require a driver to accompany him/her as he/she would not be sedated beyond the length of the treatment appointment.

CONCLUSIONS

Nitrous oxide sedation is a highly safe, efficacious, and convenient way to provide painless endodontic treatment to the patients.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.