Successful Local Anesthesia for Restorative and Endodontic Treatment
School of Dentistry
University of Alabama at Birmingham
John Nusstein, DDS, MS
Professor and Chair, Division of Endodontics
The Ohio State University, Columbus, Ohio
Diplomate, American Board of Endodontics
We have published a number of our anesthesia articles in the Journal of Endodontics. There are a number of reasons for this. The JOE is one of the most respected journals in dentistry. Additionally, in the past, oral surgeons have been the resource for local anesthesia. By publishing our articles in the JOE, the current knowledge endodontists have made us the authorities for local anesthesia. This should come as no surprise since we deal with failures of pulpal anesthesia on a daily basis. We should take advantage of this benefit by working with our referrals regarding the common problems they have with pulpal anesthesia in asymptomatic patients. The following information may be helpful to you and your referring dentists.
IMPORTANT CLINICAL FACTORS RELATED TO LOCAL ANESTHESIA
Before reviewing the specifics of local anesthesia, we would like to provide an overview of some factors that are important to clinical anesthesia.
How do we traditionally confirm anesthesia clinically? Traditional methods to confirm anesthesia usually involve questioning the patient (“Is your lip numb?"), soft tissue testing (e.g., lack of mucosal responsiveness to a sharp explorer), or simply commencing with treatment. The problem with these approaches is they may not be effective for determining pulpal anesthesia.1-4
Objective means of determining pulpal anesthesia in non-painful, vital teeth. A more objective measurement of anesthesia, in non-painful vital teeth, is obtained with an application of a cold refrigerant, or by using an electric pulp tester (EPT). Clinically, application of cold or the electric pulp tester can be used to test the tooth under treatment for pulpal anesthesia prior to beginning a clinical procedure.5-10
Determining pulpal anesthesia in painful, vital teeth. Clinically, after administration of local anesthesia, the cold or electric pulp tester can be used to test painful, vital teeth for pulpal anesthesia prior to beginning the endodontic procedure.5-12 If the patient responds positively to the stimulus, then pulpal anesthesia has not been obtained and supplemental anesthesia should be administered. However, in painful, vital teeth (eg., irreversible pulpitis), the lack of response to pulp testing may not guarantee pulpal anesthesia even if there is vital tissue present in the pulp chamber.5, 9, 10 Therefore, if a patient experiences pain when the endodontic procedure is started, after negative pulp testing, supplemental anesthesia is indicated.
Naturally, if the chamber is necrotic and the canals are vital, no objective test can predict the level of clinical anesthesia. However, as suggested by Hsiao-Wu, et al.10, cold testing adjacent teeth for anesthesia may provide evidence of anesthesia in the working area.
Previous Difficulty with Anesthesia. Patients who report a history of previous difficulty with anesthesia are more likely to experience unsuccessful anesthesia.13 These patients will generally identify themselves with comments such as "Novocaine doesn’t work on me" or "A lot of shots are needed to get my teeth numb." A good clinical practice is to ask the patient if they have had previous difficulty achieving clinical anesthesia. If they have had these experiences, supplemental injections should be considered.
Red Haired Patients. Red hair is a phenotype for melanocortin-1 receptor gene, which is associated with red hair, fair skin, and freckles. There is evidence in medicine that these patients may be more resistant to anesthetic agents.13a,b However in dentistry, red hair was unrelated to success rates of the inferior alveolar nerve block.13c Red hair was associated with higher levels of dental anxiety.13c
MANDIBULAR ANESTHESIA – Restorative Dentistry
Conventional Inferior Alveolar Nerve Block
As a frame of reference, we will review the expected outcomes following administration of a conventional inferior alveolar nerve block, to asymptomatic patients, using 1.8 mL of 2% lidocaine with 1:100,000 epinephrine. While anesthesia requirements vary between dental procedures, the following discussion will concentrate on pulpal anesthesia.
One way to define anesthetic success is the percentage of subjects who achieve two consecutive 80 readings (EPT) within 15 minutes and continuously sustain this lack of responsiveness for 60 minutes.1-4, 20-24 In other words, the objective is to achieve anesthesia within 15 minutes and have anesthesia that lasts 1 hour. This objective is equally important to restorative dentistry as it is for endodontic treatment. What then is the percentage of anesthetic success? For the first molar it was 53%, for the first premolar it was 61%, and for the lateral incisor it was 35%.1-4, 20-24 Therefore, success occurs most often in the molar and premolar teeth. It is important to realize that 100% of the subjects in these studies1-4, 20-24 had profound lip numbness.
Anesthetic failure has been defined as the percentage of subjects who never achieved two consecutive 80 EPT readings at any time during a 60-minute period. These patients have the highest potential for pain during a dental procedure. How often does failure occur? For the first molar it was 17%, for the first premolar it was 11%, and for the lateral incisor it was 32%.1-4, 20-24 Again, 100% of these subjects had profound lip numbness.
In most cases following the conventional inferior alveolar nerve block injection, the onset of pulpal anesthesia usually occurs within 15-16 minutes.1-4, 20-25 However, in some patients onset will be delayed. Slow onset is defined as the percentage of subjects who achieved an 80 EPT reading after 15 minutes. Slow onset occurs about 19-27% of the time in mandibular teeth; about 8% of patients have onset after 30 minutes.1-4, 20-25 In contrast to the onset of pulpal anesthesia, the onset of lip numbness occurs usually within 5-9 minutes.1-4
Duration of pulpal anesthesia in the mandible is very good.1-4, 20-24 Therefore, if patients are anesthetized initially, anesthesia usually persists for approximately 2 1/2 hours with 2% lidocaine with 1:100,000 epinphrine.23
What Does Lip Numbness Mean?
The presence of soft tissue anesthesia (usually measured by “lip numbness” or lack of mucosal responsiveness to a sharp explorer) does not adequately indicate pulpal anesthesia.1-4, 20-24 This is in contradiction to the traditional view. However, the lack of soft tissue anesthesia is a useful indicator that the block injection was not administered accurately for that patient.
How often do missed blocks occur? A missed block is defined as not obtaining profound lip numbness within 15-20 minutes following an IAN block. Pulpal anesthesia will NOT be present with a missed block. We studied missed blocks in over 3,000 asymptomatic subjects and in emergency patients presenting with symptomatic irreversible pulpitis.25a What did we find? The incidence of missed blocks for asymptomatic subjects was 6% for the one-cartridge volume and 4% for the two-cartridge volume. For patients presenting with irreversible pulpitis, the incidence of missed blocks was 8% for the one-cartridge volume and 2% for the two-cartridge volume. In both asymptomatic subjects and patients with irreversible pulpitis, the two-cartridge volume was significantly better than the one-cartridge volume.