© Springer-Verlag Berlin Heidelberg 2017
Ove A. Peters (ed.)The Guidebook to Molar Endodontics10.1007/978-3-662-52901-0_3
3. Local Anesthesia
Division of Endodontics, The Ohio State University College of Dentistry, 305 W 12th Ave, Columbus, OH 43210, USA
John M. Nusstein
Pulpal anesthesia is a cornerstone in the delivery of endodontic therapy. It affects not only the dentist’s ability to provide safe, pain-free treatment, but enhances patient compliance and satisfaction. Administration of local anesthesia is one of the first procedures performed by the dentist. This chapter reviews some of the key local anesthetic components and techniques available to providers in the pursuit of providing pain-free dental treatment. This includes both mandibular and maxillary injections, testing for pulpal anesthesia, new technology and drug formulations, and the supplemental techniques that may make all the difference for the provider and patient.
Wallace JA, Michanowicz AE, Mundell RD, Wilson EG. A pilot study of the clinical problem of regionally anesthetizing the pulp of an acutely inflamed mandibular molar. Oral Surg Oral Med Oral Pathol. 1985;59(5):517–21.
This study quintessentially showed the difficulty of anesthetizing mandibular teeth when a state of pulpal inflammation was present and tried to begin to explain why patients report pain during treatment even after a successful inferior alveolar nerve block was delivered.
Profound pulpal anesthesia is of obvious importance in endodontic practice and dentistry in general. It benefits not only the patient, for obvious reasons, but also the dentist who does not have to worry about patient reactions or sudden movement during therapy. There are a number of challenges a clinician must overcome in achieving profound local anesthesia. Diagnosis of the status of the pulp and periapical tissues will affect the anesthetic regimens potentially utilized.
Inflammatory changes within the pulp progress as a carious lesion nears the pulp and may cause chronic inflammation to take on an acute exacerbation with an influx of neutrophils and the release of inflammatory mediators such as prostaglandins, interleukins, and proinflammatory neuropeptides, such as substance P, bradykinin, and calcitonin gene-related peptide (CGRP). These mediators, in turn, can sensitize the peripheral nociceptors within the pulp of the affected tooth which may increase pain production and neuronal excitability These changes may lead to moderate-to-severe pain for the patient and influence the anesthetic strategies needed by the dentist/endodontist to gain profound pulpal anesthesia.
Periapical changes due to infection and chronic inflammation may also impact the anesthesia strategy. The development of an acute apical abscess is the result of pyogenic bacteria from the root canal system spreading to the periapical region and stimulating a strong immune response by the host tissue, with neutrophilic leukocytes dominating the early response. The neutrophils secrete lysosomal enzymes that digest both live and dead cell material. As the neutrophilic response progresses, an accumulation of dead and live neutrophils, disintegrated tissue cells, degraded extracellular matrix, and lysosomal enzymes results in a collection of purulent exudate termed pus. If the involved pathogens are of significant virulence and if the host response is of sufficient intensity, an acute apical abscess may arise. Severe percussion pain or swelling will indicate an acute response within the bone and affect the type of local anesthesia techniques that can be utilized.
Once a pulpal diagnosis is made and a treatment plan developed which includes endodontic therapy, the first step in treatment is local anesthesia. The review of a patient’s medical history may determine which local anesthetic can and cannot be utilized. Patients with uncontrolled hypertension or sensitivity to vasoconstrictors may require the use of anesthetics such as 3 % mepivacaine or 4 % prilocaine. Patients taking nonselective beta-blockers should not receive an injection of an anesthetic containing levonordefrin. A thorough review of the patient’s medical history and drug list will dictate the proper anesthetic choice.
3.2 Topical Anesthesia
The use of topical anesthetic prior to injection has been shown to help reduce the pain of needle insertion in certain locations of the mouth. More popular topical anesthetics include 20 % benzocaine, EMLA (eutectic mixture of local anesthetics – 2.5 % lidocaine and 2.5 % prilocaine), and 5 % lidocaine (Box 3.1).
Box 3.1. Topical Anesthetics
20 % benzocaine
EMLA (2.5 % lidocaine + 2.5 % prilocaine)
5 % lidocaine
These preparations are available as gel, ointment, or spray form, which allows for easy placement at the site of injection. Utilizing a cotton tip applicator, a small amount of topical anesthetic (approximately 0.2 mL) is placed at the injection site and allowed to penetrate for 60 s. Spray forms may be placed on a cotton tip applicator and applied or sprayed directly to the site of injection.
The effectiveness of a topical anesthetic to reduce the pain of needle insertion has been evaluated in several clinical studies. These have reported no significant difference between 20 % benzocaine compared to a placebo for infiltration injections for the maxillary lateral incisor and that 20 % benzocaine had no effect on needle insertion pain for inferior alveolar nerve block and maxillary posterior buccal infiltration injections. However, results did show that topical anesthetic reduced the amount of needle insertion pain for maxillary anterior infiltrations. Evaluation of the pharmacological and psychological effects of topical anesthesia has shown that, using a placebo application and 20 % benzocaine, subjects who believed that they were receiving an active topical anesthetic anticipated significantly less pain than subjects who thought they were receiving a placebo. Whether injections were preceded by the placebo or the active topical anesthetic did not alter the subjects’ reported pain. No significant difference between 20 % benzocaine and a placebo was also found when used prior to a palatal anterior superior alveolar nerve block. Gill and Orr reported that topical anesthetic application for 1 min is effective for maxillary infiltrations, but had no significant difference when compared with a placebo for an inferior alveolar nerve block . The sum of these studies suggests that the mere knowledge of the patient that they are receiving a topical anesthetic could lower the pain experienced during needle insertion. A survey of 3051 pediatric dentists reported that the majority of dentists used topical anesthetic prior to local anesthetic injections in private practice.
Due to the placebo effect, and since most patients and dentists believe that topical anesthetic reduces the pain of the injection, topical anesthetic should be used, if for nothing more, to have the patient feel that the dentist is attempting everything to make a stressful procedure as comfortable as possible.
3.3 Mandibular Anesthesia
When one considers the challenges of local anesthesia in dentistry, mandibular teeth pose the more severe challenge. The inferior alveolar nerve block (IANB) must be delivered accurately (indicated by soft tissue and lip numbness) to have any chance to attain pulpal anesthesia. Missed blocks (lack of lip numbness) occur about 5 % of the time and should prompt the dentist to re-administer the injection prior to beginning treatment. When one reviews the literature to determine what injection techniques or anesthetic solutions can offer, the dentist needs to be aware of what the definition of “anesthetic success” is utilized. One way used to define anesthetic success for mandibular blocks is the percentage of subjects who achieve two consecutive electric pulp tester (EPT) readings of 80 within 15 min of injection and sustain these readings for at least 60 min. Clinically, this translates into being able to work on the patient no later than 15 min after giving the IANB and having pulpal anesthesia for 1 h. In the available clinical literature, it is reported that, following administration of a successful IANB (lip numbness achieved) using 2 % lidocaine with 1:100,000 epinephrine, for the mandibular first molar, success occurs 53 % of the time, while for the first premolar it is 61 % and for the lateral incisor it is 35 %. Anesthetic failure (the percentage of patients who never achieve two consecutive 80 readings with the EPT during 60 min of testing) for the mandibular first molar is 17 %, 11 % for the first premolar, and 32 % for the lateral incisor. Patients may also be subject to anesthesia of slow onset. These patients generally do not achieve pulpal anesthesia until after 16 min following the IANB. This is reported to occur in mandibular teeth approximately 19–27 % of the time with some patients (8 %) having onset after 30 min. Patients who present a history of anesthesia of slow onset need to be scheduled appropriately earlier than their actual procedure, so that the dentist can give the IANB well before the time it is needed clinically.
3.3.1 Block Technique
The most common injection for obtaining mandibular anesthesia is the inferior alveolar nerve block (Box 3.2).
Box 3.2. Mandibular Anesthetic Blocks
Inferior alveolar nerve block
Vazirani-Akinosi (closed mouth) block
The inferior alveolar nerve (IAN) and lingual nerve are branches of the posterior division of the trigeminal nerve (V3). The lingual nerve provides sensory innervation to the anterior two-thirds of the tongue as well as the floor of the mouth and the lingual gingiva around the molars. The IAN passes medial to the mandibular ramus and enters the mandibular foramen where it eventually branches at the mental foramen and forms the mental and incisive nerves. The IAN provides sensory innervation to the mandibular posterior teeth and buccal soft tissues. Prior to entering the mandibular foramen, the mylohyoid branch splits off and travels downward and forward along the inferior, medial border of the mandible. This nerve innervates soft tissue on the inferior and anterior mandible. It may also innervate the pulps of mandibular molars.
The inferior alveolar nerve block (IANB) is usually administered using a standard aspirating syringe and a 27-gauge 1½-inch needle. The injection site is the soft tissue overlying the medial surface of the ramus, lateral to the pterygomandibular raphe, at a height determined by the coronoid notch on the anterior border of the ramus. With the subject’s mouth wide open, the thumb of the noninjecting hand is placed over the pterygomandibular triangle and then pulled laterally until the deepest depression in the anterior border of the ramus was felt. The first or second finger of the noninjecting hand palpates the posterior portion of the ramus, finding a slight depression. The line between the thumb and the finger establishes the vertical height of the injection site. The direction of the needle insertion is from the contralateral mandibular premolars and is directed parallel to the occlusal plane . The needle is advanced until the bone is sounded, then retracted 1 mm before aspiration and injection into the pterygomandibular space.
The injection rate should be slow; research has shown that a slower injection rate is more comfortable for the patient (1 cartridge over 60 s) and may lead to more successful blocks. The standard inferior alveolar nerve block will anesthetize the inferior alveolar nerve, mental nerve, and usually the lingual nerve as well. This would include pulpal anesthesia of mandibular molars, premolars, and incisors on the injected side, along with the associated supporting bony and periodontal structures to the midline. It would also anesthetize the buccal and labial soft tissues and chin to the midline. A long buccal injection can be given if soft tissue anesthesia is required of the buccal gingival tissues next to the molar teeth for rubber dam clamp placement. Onset of pulpal anesthesia will range from 5 to 19 min and is slower than the onset of lip numbness (4–6 min).
Other injection techniques have been developed and advocated in attempting to block the inferior alveolar nerve. The Gow-Gates technique  has been reported to have a higher success rate than a conventional IANB, but other well-controlled clinical studies have not been able to confirm this. The Vazirani-Akinosi technique (closed mouth) [4, 5] also has not been shown to be superior in terms of achieving profound anesthesia compared to the conventional IANB technique. Therefore, replacing the conventional IANB injection with these techniques will likely not improve success in attaining pulpal anesthesia in mandibular teeth.
Inaccuracy of the IANB injection has been cited as a contributor to failed mandibular pulpal anesthesia. Hannan et al.  used medical ultrasound to guide an anesthetic needle to its target site for the IANB. This group reported that accurate injections could be attained by this method, but it did not result in more successful pulpal anesthesia. Simon et al.  studied the anesthetic effectiveness of an IANB after using a peripheral nerve stimulator to locate the inferior alveolar nerve at the injection site. The technique was no more successful than the conventional injection technique. Therefore, the accuracy of the injection technique (needle placement) is not the primary reason for anesthetic failure with the IANB. Needle deflection as related to the needle bevel direction (toward or away from the mandibular ramus) has also been shown not to affect the anesthetic success rate of the IANB.
Accessory nerves have also been implicated as a potential reason for the failure of the IANB. The incisive nerve block at the mental foramen has been shown to improve anesthetic success of the IANB in first molars and premolars, but the success rate was not as good as other supplemental anesthetic techniques (to be discussed later). The mylohyoid nerve is the accessory nerve most often implicated as the cause for mandibular anesthesia failure. However, Clark and coauthors , when combining the IANB with a mylohyoid injection after locating the mylohyoid nerve with a peripheral nerve stimulator, found no significant improvement in mandibular anesthesia when the mylohyoid injection was added.
3.3.2 Local Anesthetic Compounds for Mandibular Anesthesia
Lidocaine with epinephrine is still considered the standard to compare all other local anesthetics too. The emergence of 4 % articaine has decreased the use of lidocaine in many countries. When one looks at the literature, no local anesthetic has significantly improved the success rate of the IANB. Research comparing various local anesthetic agents such as 3 % mepivacaine plain (Carbocaine, Polocaine, Scandonest), 4 % prilocaine (Citanest Plain), 4 % prilocaine with 1:200,000 epinephrine (Citanest Forte), 2 % mepivacaine with 1:20,000 levonordefrin (Carbocaine with Neo-Cobefrin), 4 % articaine with 1:100,000 epinephrine (Septocaine) to 2 % lidocaine with 1:100,000 epinephrine for the IANB in patients with normal pulps showed that there was no difference in success rates. Therefore, changing local anesthetic agents may not be of benefit for endodontic procedures. When confronted with the increased difficulty of achieving anesthesia due to a diagnosis of symptomatic irreversible pulpitis, clinical studies have also failed to show any superiority of 3 % mepivacaine or 4 % articaine with 1:100,000 epinephrine over 2 % lidocaine with 1:100,000 epinephrine for the IANB. The use of a buffering agent, such as sodium bicarbonate to increase the pH of the anesthetic solution, has also not been found to improve success rates of pulpal anesthesia clinically .
Increasing the volume of local anesthetic delivered during the IANB, therefore increasing the amount of anesthetic in the pterygomandibular space and potentially exposing the nerve to more anesthetic, has also been found not to increase the incidence of pulpal anesthesia in asymptomatic patients or those diagnosed with symptomatic irreversible pulpitis. Increasing the concentration of epinephrine (1:50,000) in hopes of keeping the anesthetic agent at the injection site longer showed no advantage in the IANB.
The duration of pulpal anesthesia utilizing 1.8 mL 2 % lidocaine with 1:100,000 epinephrine or 0.5 % bupivacaine with 1:200,000 epinephrine has been reported to be 2.5 h and 3–4 h, respectively. Therefore, adequate time is available for the dentist to complete endodontic therapy. The actual duration of pulpal anesthesia for anesthetics has not been studied.
The choice of local anesthetic may therefore be more a preference of the provider, medical condition of the patient, or even the desired duration of anesthesia. A volume of 3.6 mL (two cartridges) may improve achieving a successful IANB block (lip numbness), but may not improve the success rate of pulpal anesthesia.