WRITTEN BY
Pamela S. Stein, DMD, and Jennifer K. Brueckner, PhD
No one can argue that profound anesthesia is an absolute necessity in endodontics. Pulp extirpation, enlarging the canal when vital tissues are present, and at times even obturation can be extremely painful if successful anesthesia is not achieved.
Most patients have a preconceived idea that root canals are terribly painful. As clinicians we should counter these fears with patience, understanding, and reassurance that we will make every effort to make the visit comfortable. Ensuring minimum patient discomfort depends largely upon the dentist’s knowledge, skills, and armamentarium related to local anesthesia. In preparing this article, we looked to the experts in both endodontic and local anesthesia literature to bring you clinical pearls for achieving the greatest depth of local anesthesia possible for your endodontic patients.
Anesthetizing for endodontics
A variety of factors influence the types of local anesthesia that are needed for endodontic therapy, including anatomical variations, pulpal inflammation, and the individual patient’s tolerance for pain and level of anxiety.1 Anesthesia should be given at each endodontic appointment, even in patients with necrotic pulps or periradicular lesions, as some vital tissue may remain near the apices.2
Table 1 outlines routine injections given for endodontic treatment.1 Lingual infiltrations, as indicated in the table for mandibular teeth, should be given directly beneath the tooth. In addition, infiltrations into the alveolar crest of the furcation of mandibular molars and into the septum between adjacent mandibular teeth may be beneficial.1 Note that the primary injection listed for mandibular incisors is infiltration. Incisor infiltration may also be used to supplement conventional blocks. Research by Clark et al. has shown that supplementing inferior alveolar nerve (IAN) blocks with labial infiltrations significantly improves pulpal anesthesia in mandibular lateral incisors, while supplementing with lingual infiltrations significantly improves pulpal anesthesia in mandibular central incisors.3
Many endodontists begin anesthetizing with two cartridges, particularly in the mandible when utilizing IAN blocks. Using two cartridges instead of one, in infiltration of maxillary molars, has been shown to speed onset and increase duration.4
Lip anesthesia should be obtained within 90 seconds after an IAN block and may serve as an indication to the dentist to begin the access procedure. However, lip anesthesia does not necessarily indicate that the tooth is anesthetized.5,6,7,8 In addition, if lip anesthesia follows a slower progression, such as 10 to 15 minutes, supplementary injections will likely be necessary.1
Utilizing a two-step injection technique may minimize the discomfort of many injections. This may be accomplished by drying the site for injection and placing topical anesthetic for one to two minutes, followed by injecting a small amount of a “plain” anesthetic just below the mucosal surface (the pH of nonepinephrine anesthetic approaches almost neutral pH producing minimal discomfort).9 After a couple of minutes, the block injection is given with an epinephrine-containing anesthetic, advancing the needle virtually painlessly to the full depth of the target site.2 If the patient has suffered the previous night with a toothache, a long-acting agent such as marcaine may be employed to allow for a few hours of rest.10
Why local anesthetics fail in pulpitis
Most clinicians have experienced difficulty in achieving adequate local anesthesia in patients with painful pulpitis.11,12,13,14 Managing patients with the so-called “hot tooth” is a challenge, because the tooth is overly sensitive to temperature changes and pressure, despite repeated injections accompanied by the standard signs and symptoms of numbness.14,15
Several potential mechanisms have been implicated in the etiology of local anesthesia failure in inflamed tissues. A reduction in local pH in inflamed tissues may make local anesthetics less effective, particularly when they are administered by infiltration techniques.14,16 pH is lowered in regions of infected tissue due to the build-up of acidic byproducts of bacterial metabolism and neutrophilic lysis.17 Such pH changes may interrupt the anesthetic’s ability to penetrate the myelin sheath to reach the nerve’s plasma membrane,18 although this concept has been challenged by some researchers.19,20
A second explanation is that increased vascularity, or hyperemia, exists in the presence of infection, thereby accelerating uptake of local anesthetic from the infected pulp and shortening its effective duration of activity.21 As with the pH change hypothesis, this theory accounts for failure of solution deposited in the area of inflammation but does not elucidate how regional blocks fail in acute inflammation.14
A third contributing factor may be inflammation-mediated changes in the nerves’ morphological and physiological properties. Najjar11 proposed that inflammation changes the morphology of the axonal membrane and its myelin sheath along the entire length of the nerve, thereby presenting a potential barrier to penetration of anesthetic solution. Sensory nerve fibers in the inflamed pulp may also experience physiological reductions in their resting potentials and excitability thresholds, which extend along the length of the affected nerve such that the anesthetic cannot completely block impulse transmission.12,19,20
Finally, accessory innervation of mandibular teeth may also preclude an acceptable level of anesthesia in endodontic therapy. The mylohyoid nerve may convey sensory fibers that innervate posterior mandibular teeth.22,23 Variations in the position of the mandibular foramen and lingula can make the inferior alveolar nerve difficult to anesthetize in some patients.24,25 In addition, bifid mandibular divisions of the trigeminal nerve have been reported, although this anomaly is relatively rare.26 ■
References
1 Weine FS. Endodontic therapy, 6th ed; St. Louis: Mosby 2004.
2 Walton RE, Torabinejad M. Principles and practice of endodontics, 2nd ed; Philadelphia: W.B. Saunders 1996.
3 Clark K, Reader A, Beck M, Meyers W. Anesthetic efficacy of an infiltration in mandibular anterior teeth following an inferior alveolar nerve block. Anesth Prog 2002; 49:49-55.
4 Mikesell A, Reader A, Beck M, Meyers W. Analgesic efficacy of volumes of lidocaine in human maxillary infiltration (Abstract) J of Endod 1987; 13:128.
5 Vreeland D, Reader A, Beck M et al. An evaluation of volumes and concentrations of lidocaine in human inferior alveolar nerve block. J of Endod 1989; 15:6.
6 Chaney M, Kerby R, Reader A et al. An evaluation of lidocaine hydrocarbonate compared with lidocaine hydrochloride for inferior alveolar nerve block. Anesth Prog 1992; 38:212.
7 Nist R, Reader A, Beck M, Meyers W. An evaluation of the incisive nerve block and combination inferior alveolar and incisive nerve blocks in mandibular anesthesia. J of Endod 1992; 18:445.
8 McLean C, Reader A, Beck M, Meyers W. An evaluation of 4% prilocaine and 3% mepivacaine compared with 2% lidocaine (1:100,000 epinephrine) for inferior alveolar nerve block. J of Endod 1993; 19:146.
9 Weathers AK. Top 10 systems for taking the stress out of endodontics. Dent Today 2002; 21:66-73.
10 Pitt Ford TR, Rhodes JS, Pitt Ford HE. Endodontics: problem-solving in clinical practices. 1st ed; London: Martin Dunitz 2002.
11 Najjar TA. Why can’t you achieve adequate regional anesthesia in the presence of infection? Oral Surg 1977; 44:7-13.
12 Brown RD. The failure of local anesthesia in acute inflammation. Brit Dent J 1981; 151:47-51.
13 Wallace JA, Michanowicz AE, Mundell RD, Wilson EG. A pilot study of the clinical problem of regionally anesthetizing the pulp of acutely inflamed mandibular molar. Oral Surg 1985; 59:517-521.
14 Fleury AAP. Local anesthetic failure in endodontic therapy: the acute inflammation factor. Compend Contin Educ Dent 1990; 11:210-216.
15 Pitt Ford TR. Harty’s endodontics in clinical practice, 5th ed; London: Wright 2004.
16 Wong MKS, Jacobsen PL. Reasons for local anesthesia failures. JADA 1992; 123:69-73.
17 deJong RH, Cullen SC. Buffer-demand and pH of local anesthetic solutions containing epinephrine. Anesthesiology 1963; 24:801-807.
18 Malamed SF. Management of pain and anxiety. In: Cohen S and Burns RC Editors. Pathways of the Pulp. 7th ed; St. Louis: CV Mosby 1998.
19 Rood JP. Some anatomical and physiological causes of failure to achieve mandibular anesthesia. Brit J Oral Surg 1977; 15:75-82.
20 Rood JP, Pateromichelakis S. Local anesthetic failures due to an increase in sensory nerve impulses from inflammatory sensitization. Journal of Dentistry 1982; 10:201-206.
21 Meechan JG, Robb ND, Seymour RA. Reasons for failure. In: Pain and Anxiety Control for the Conscious Dental Patient, Oxford, UK: Oxford University Press 1998.
22 Frommer J, Mele FA, Monroe CW. The possible role of the mylohyoid nerve in mandibular posterior tooth sensation. J Am Dent Assoc 1972; 85:112-117.
23 Chapnick L. A foramen on the lingual of the mandible. J Can Dent Assoc 1980; 46:444-445.
24 Bremer G. Measurements of special significance in connection with anesthesia of the inferior alveolar nerve. Oral Surg 1952; 5:966-988.
25 Young J. General morphology and location of the mandibular foramen as it relates to local anesthesia. Fla Dent J 1978; 49:23-25.
26 Grover PS, Lewis L. Bifid mandibular nerve as a possible cause of inadequate anesthesia in the mandible. J Oral Maxillofac Surg 1983; 41:177-179.
Jennifer K. Brueckner, PhD
Dr. Brueckner is an assistant professor of anatomy and neurobiology at the University of Kentucky College of Medicine, where she directs the dental gross anatomy course. With a strong interest in dental education, she currently serves as councilor in the anatomical sciences section of the American Dental Education Association. Contact her at [email protected].
Pamela S. Stein, DMD
Dr. Stein is an assistant professor of anatomy and neurobiology at the University of Kentucky College of Medicine. A board-certified lecturer on the topic of local anesthesia, she recently co-authored “The Anatomy of Local Anesthesia,” a multimedia tutorial software program to be distributed to dental students nationwide. Contact her at [email protected].
