Supplemental Anesthetic Techniques for Symptomatic Irreversible Pulpitis

Following the delivery of anesthesia and prior to endodontic access, clinicians should assess the effectiveness of pulpal anesthesia; however, they should also understand that anesthesia can take more time in cases of SIP. According to the literature, the onset of anesthesia can range from as fast as 5 minutes to as slow as 30 minutes in certain patients.⁴

Once a sufficient amount of time has passed, clinicians should test for pulpal anesthesia. Unfortunately, neither self-reporting (ie, asking if the lip feels numb) nor tactile sensation (ie, tapping the gingiva) are accurate predictors of the anesthetization of the pulp itself.¹ According to the endodontic literature, the best measure for the assessment of pulpal anesthesia is thermal testing.⁵ A negative response to the stimulus (ie, cold temperature) during a thermal test is indicative of pulpal anesthesia. However, in cases of SIP or partial pulp necrosis in which small amounts of vital tissue may remain, testing the neighboring teeth may help to confirm the presence of truly profound anesthesia in the region.¹ Finally, it is important to note that although thermal testing is reliable, it does not predict pulpal anesthesia with 100% accuracy.⁵

Clinicians will likely encounter patients who, despite signs of a successful IANB, may not have achieved pulpal anesthesia. Several theories have been proposed to explain the decreased efficacy of local anesthetics in patients with SIP.⁶ One theory suggests that inflamed and/or infected tissues have a decreased pH, which results in less availability of anesthetic in the base form that can penetrate nerve membranes to produce anesthesia.⁶ Investigators have also suggested that inflammation leads to an upregulation of anesthetic-resistant sodium channels in nerve membranes, thereby preventing effective anesthesia. Other theories have proposed that inflammation alters resting membrane potentials and decreases their threshold of excitability. In tissues with a decreased excitability threshold, anesthetic agents are un-able to effectively hinder the transmission of nerve impulses.⁶ The commonality of anesthesia failure in patients with SIP necessitates that clinicians possess strategies to achieve profound anesthesia in patients when initial attempts prove unsuccessful.

In all patients, pulpal anesthesia begins with the administration of traditional nerve blocks. For maxillary teeth, nerve block injections are administered for the anterior superior alveolar (ASA), middle superior alveolar (MSA), and/or posterior superior alveolar (PSA) nerves. For mandibular anterior teeth and molars, both the IANB and a buccal infiltration injection are administered. For mandibular bicuspids, the IANB should be administered as well as a mental nerve block.⁷ According to the literature, lidocaine and epinephrine, articaine HCl and epinephrine (Septocaine^®, Septodont), and mepivacaine HCL (Carbocaine^®, Septodont) possess similar efficacy throughout the mouth and can be used interchangeably.⁸ It is important to note that the use of articaine in conventional nerve blocks should be avoided given its potential for mild neurotoxicity and the subsequent development of parasthesias.⁹

In patients with SIP, the success rate of the IANB can be reduced to less than 30%² and the success rate of maxillary nerve blocks can be reduced to less than 60%.¹⁰ The potential for failure of these techniques necessitates that clinicians possess supplemental strategies to achieve adequate pulpal anesthesia to comfortably care for patients. Table 1 provides an evidence-based algorithm for the use of supplemental techniques in patients with SIP.

Buccal Infiltration

The first technique that clinicians can utilize is a supplemental buccal infiltration with articaine in mandibular molars.¹¹ A comparative study found that this technique was as effective, if not more effective, than other supplemental techniques, and it requires no additional armamentarium. Consequently, clinicians should consider utilizing this technique prior to others in cases of anesthetic failure.

PDL Injection

The intraligamentary injection (ie, periodontal ligament [PDL] injection) is one of the most commonly used supplemental anesthesia techniques.¹ The success rate of the PDL injection technique can increase from 71% (after initial PDL injection) to 92% (after PDL reinjection).¹ To perform this technique, the needle is oriented at a 30° angle to the long axis of the tooth and inserted at the mesiobuccal aspect of each root and advanced until it is located securely between the tooth and alveolar crest. Once in position, 0.2 mL of the anesthetic solution is injected into the tissue under back pressure. Performing the injection with sufficient pressure is critical to its success. Currently, many commercially-available high-pressure syringes and computer-controlled local anesthesia delivery systems exist that can help achieve the necessary back pressure. If successful, the onset of anesthesia will either be immediate or occur within 30 seconds of administration¹²; however, if pulpal anesthesia is not achieved because of failure of the initial injection, reinjection is often required. It is important to avoid using a vasoconstrictor with the PDL technique because it is an intravascular injection and the combination could potentially lead to adverse cardiovascular events.¹⁰

Intraosseous Injection

Another supplemental technique that is available to clinicians is the intraosseous injection. An intraosseous injection often induces pulpal anesthesia within 10 to 20 seconds,¹² and its efficacy can be increased with reinjection (80% success after initial injection versus 98% success after reinjection).¹ It involves perforation of the alveolar mucosa and cancellous bone and subsequent delivery of anesthetic solution into the cancellous bone adjacent to the affected tooth.¹² This technique is commonly administered via the use of commercially available devices that utilize a trephine (eg, Stabident Intraosseous Anesthesia Delivery System, Fairfax Dental Inc.; X-Tip^™ Intraosseous Anesthesia Delivery System, DENTSPLY Maillefer; IntraFlow^™ HTP Anesthesia Delivery System, Pro-Dex Inc). Prior to perforation, it is important to first infiltrate the gingiva with 0.2 mL of anesthetic solution to produce gingival anesthesia. Subsequently, a safe point of perforation that will not risk root involvement is determined. This site is located 2-mm apical to the intersection of two imaginary perpendicular lines: a vertical line bisecting the interdental papilla of the affected tooth and a horizontal line along the gingival margin of the adjacent teeth. Once gingival anesthesia is achieved, the trephine is inserted at the point of perforation and advanced with a high-speed handpiece until the cancellous bone has been penetrated, which is indicated by a characteristic "give" of the trephine. Subsequently, a traditional anesthetic syringe is introduced into the perforation, and 1.0 mL of anesthetic solution is gradually administered into the cancellous bone over a period of 2 minutes.¹² In many ways, the intraosseous injection technique is similar to the PDL injection technique. As with the PDL injection technique, due to the rapid entry of anesthetic solution into the circulation, the use of vasoconstrictors should also be avoided when using the intraosseous injection technique.¹⁰

Intrapulpal Injection

Another supplemental method of achieving anesthesia, the intrapulpal injection technique, is indicated primarily in teeth diagnosed with SIP that have not responded to other supplemental techniques (eg, buccal infiltration, PDL injection). This occurs in as many as 5% to 10% of mandibular teeth with SIP (Figure 1 and Figure 2). Similar to the PDL injection, the intrapulpal injection proves most effective when administered under back pressure.¹ To facilitate this, clinicians should use a small round bur to create an opening into the pulp chamber that is just large enough to ensure a tight fit of the needle. However, if a large opening to the pulp chamber already exists, the needle should be inserted into the canal until a tight fit is achieved. Upon encountering resistance, 0.2 mL of anesthetic solution should be deposited into the root canal system.¹² As with the PDL injection, the onset of pulpal anesthesia after an intrapulpal injection can be immediate. One disadvantage of the intrapulpal injection technique is its potential to induce moderate to severe pain, which can be caused by the pulp exposure prior to anesthetic administration as well as the process of injection itself.¹ In cases where an intrapulpal injection cannot be administered or where all other supplemental injection techniques (including intrapulpal) fail to produce profound anesthesia, a reappointment with premedication may be recommended to increase both patient comfort and anesthetic efficacy.

In addition to anesthetic techniques, other injectable and oral medications can also be used to enhance anesthesia in cases of SIP. A recent systematic review and network meta-analysis revealed that the medications that were most effective in significantly increasing anesthetic success were, in order of descending efficacy: dexamethasone, nonsteroidal anti-inflammatory drugs (NSAIDs), and tramadol. The data indicated that premedication using acetaminophen coadministered with NSAIDs demonstrated similar efficacy when compared with the use of NSAIDs alone. Although dosages are often tailored to the individual patient, the review found that the most effective dosages for anesthetic premedication included 0.5 mg of dexamethasone, 10 mg of ketorolac, 20 mg of piroxicam, 400 mg of ibuprofen with 500 mg of acetaminophen, and 50 mg of tramadol.¹³

Sedation techniques may also be considered to enhance patient comfort, especially when anxiety or a gag reflex complicates a patient's ability to tolerate endodontic treatment. Although orally administered benzodiazepines have not been shown to be effective in enhancing local anesthesia,¹⁴ inhaled nitrous oxide has analgesic properties that can enhance pulpal anesthesia (Figure 3 and Figure 4). When combined with nitrous oxide, traditional nerve blocks such as the IANB have been shown to significantly increase success rates (ie, from 28% to 50%) among patients with SIP.¹⁵ Given its sedative and analgesic effects, nitrous oxide may be an optimal supplementary anesthetic agent for an apprehensive patient with SIP.¹⁵

Overcoming the challenge of achieving profound anesthesia in teeth that are diagnosed with SIP requires clinicians to be familiar with an armamentarium of supplemental anesthetic techniques. Several methods, ranging from anesthetic injections to premedication to conscious sedation, can be used to enhance pulpal anesthesia. The evidence-based algorithm provided in Table 1 can help guide clinicians in the selection of techniques that are individualized to their patient to facilitate comfortable endodontic treatment.

Shraya Sharma
DMD Candidate, Class of 2020
Harvard School of Dental Medicine
Boston, Massachusetts

Brooke Blicher, DMD
Upper Valley Endodontics
White River Junction, Vermont

Assistant Clinical Professor
Department of Endodontics
Tufts University
School of Dental Medicine
Boston, Massachusetts

Clinical Instructor
Department of Restorative Dentistry
and Biomaterials Science
Harvard School of Dental Medicine
Boston, Massachusetts

Rebekah Lucier Pryles, DMD
Upper Valley Endodontics
White River Junction, Vermont

Assistant Clinical Professor
Department of Endodontics
Tufts University
School of Dental Medicine
Boston, Massachusetts

Jarshen Lin, DDS
Director of Predoctoral Endodontics
Department of Restorative Dentistry
and Biomaterials Science
Harvard School of Dental Medicine
Boston, Massachusetts

Clinical Associate
Department of Oral and
Maxillofacial Surgery
Massachusetts General Hospital
Boston, Massachusetts