May 2008, Volume 4, Issue 5
Published by AEGIS Communications
The Challenges of Successful Mandibular Anesthesia
John Nusstein; Al Reader; Melissa Drum
Achieving adequate pulpal anesthesia in the mandible can often be a challenge to the clinician. The fear of pain during a dental procedure has been cited as a major reason adults do not seek out dental care.1 Mandibular anesthesia can be especially difficult; therefore, it is important for the dentist to understand the challenges of gaining good pulpal anesthesia in the mandible.
Before reviewing the specifics of local anesthesia, this article provides an overview of some factors that are important to clinical anesthesia. Traditional methods to confirm mandibular anesthesia usually involve questioning the patient ("Is your lip numb?"), soft tissue testing (eg, lack of mucosal responsiveness to a sharp explorer, pinching the lip), or simply commencing with treatment. The problem with these approaches is they may not be effective for determining pulpal anesthesia.2-5 A more objective measurement of anesthesia, in non-painful vital teeth, is obtained with an application of a cold refrigerant on a cotton pellet held with cotton forceps, or by using an electric pulp tester. Clinically, application of cold or the electric pulp tester can be used to test the tooth under treatment for pulpal anesthesia before beginning a clinical procedure.6-11
The cold test or electric pulp tester can also be used to test painful, vital teeth for pulpal anesthesia before beginning the endodontic procedure.6-13 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.6,10,11 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, cold testing adjacent teeth for anesthesia may provide evidence of anesthesia in the working area. 11
Patients who report a history of previous difficulty with anesthesia are more likely to experience unsuccessful anesthesia.14 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 and planned for.
ANESTHETIC SUCCESS—WHAT IS IT?
As a frame of reference in this review, consider the expected outcomes after 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 80/80 readings on the electric pulp tester within 15 minutes of injection and continuously sustain this lack of responsiveness for 60 minutes.2-5,15-19 This objective is equally important to restorative dentistry as it is for endodontic treatment because it allows the provider to start a procedure relatively quickly and gives them time to complete their treatment.
What then is the percentage of anesthetic success? In clinical studies, for the first molar it is 53%, for the first premolar it is 61%, and for the lateral incisor it is 35%.2-5,15-19 It is important to realize that 100% of the subjects in these studies had profound lip numbness.
Anesthetic failure has been defined as the percentage of subjects who never achieved two consecutive 80/80 readings on the electric pulp tester 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 is 17%, for the first premolar it is 11%, and for the lateral incisor it is 32%.2-5,15-19 Again, 100% of these subjects had profound lip numbness.
In most cases after the conventional inferior alveolar nerve block injection, the onset of pulpal anesthesia usually occurs within 10 to 15 minutes.2-5,15-20 However, in some patients onset will be delayed. Slow onset occurs about 19% to 27% of the time in mandibular teeth; about 8% of patients have onset after 30 minutes.2-5,15-20 In contrast to the onset of pulpal anesthesia, the onset of lip numbness occurs usually within 5 to 7 minutes.2-5
The presence of soft tissue anesthesia does not adequately indicate pulpal anesthesia.2-5,15-19 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. Missed blocks occur about 5% of the time, and should prompt the clinician to re-administer the nerve block before continuing with treatment.
CHOICES TO IMPROVE ANESTHESIA IN THE MANDIBLE
Alternate Anesthetic Solutions
McLean and co-authors have shown that 3% mepivacaine plain and 4% prilocaine plain are as effective as 2% lidocaine with 1:100,000 epinephrine in an inferior alveolar nerve block.3 Hinkley and co-authors have shown that 4% prilocaine with 1:200,000 epinephrine and 2% mepivacaine with 1:20,000 levonordefrin are also equivalent to 2% lidocaine with 1:100,000 epinephrine in an inferior alveolar nerve block in achieving pulpal anesthesia.5 Articaine has a reputation of providing an improved local anesthetic effect.21 The available literature indicates that articaine is equally effective when statistically compared to other local anesthetics for an inferior alveolar nerve block.22-30 When comparing the anesthetic efficacy of 4% articaine with 1:100,000 epinephrine to 2% lidocaine with 1:100,000 epinephrine for inferior alveolar nerve blocks, Mikesell and co-authors found that the two solutions were not significantly different.29 Tofoli et al found that 4% articaine with 1:100,000 epinephrine was equivalent to 4% articaine with 1:200,000 epinephrine in inferior alveolar nerve blocks.31
One proposed method to increase anesthetic success is to double the injection volume of local anesthetic solution. However, increasing the volume of 2% lidocaine with epinephrine to 3.6 mL (two cartridges) does not increase the incidence of pulpal anesthesia with the inferior alveolar nerve block.2,19,32-34 A second approach may be to increase the concentration of epinephrine. However, when evaluated in clinically normal teeth, there was no advantage to using a higher concentration (1:50,000) of epinephrine in an inferior alveolar nerve block.16,35
For patients with symptomatic mandibular teeth, Cohen et al, in a clinical study of patients with irreversible pulpitis, found that 3% mepivacaine and 2% lidocaine with 1:100,000 epinephrine were equivalent for inferior alveolar nerve blocks.13 Claffey and co-authors compared the anesthetic efficacy of 4% articaine with 1:100,000 epinephrine to 2% lidocaine with 1:100,000 epinephrine for inferior alveolar nerve blocks in patients experiencing irreversible pulpitis in mandibular posterior teeth. The success rate (none or mild pain upon endodontic access or initial instrumentation) for the inferior alveolar nerve block using the articaine solution was 24% and for the lidocaine solution success was 23%. There was no significant difference between the articaine and lidocaine solutions.30
The Gow-Gates technique36 has been reported to have a higher success rate than the conventional inferior alveolar nerve block.37,38 However, experimental studies have failed to show that the Gow-Gates technique is superior.20,39-42 The Vazirani-Akinosi37,43 technique has also not been found to be superior to the standard inferior alveolar injection.39,44-46
Labial or lingual infiltration injections of a lidocaine solution alone are not very effective for pulpal anesthesia in mandibular teeth.25,26,47 Adding a labial infiltration (1.8 mL of 2% lidocaine with 1:100,000 epinephrine) to a conventional inferior alveolar injection increases the success of anterior pulpal anesthesia.48 Meechan et al reported that using 1.8 mL of 2% lidocaine with 1:100,000 epinephrine for either a buccal or buccal plus lingual infiltration of the mandibular first molar resulted in a 32% to 39% success rate (no response to pulp testing).49 Adding a labial or lingual infiltration injection, using 1.8 mL of 2% lidocaine with 1:100,000 epinephrine, after an inferior alveolar nerve block does not significantly result in more profound anesthesia in the first molar.50
A recent study showed articaine was significantly better than lidocaine for a primary buccal infiltration of the mandibular first molar (Figure 1). Articaine only had a 64% success rate (two consecutive 80/80 readings with the electric pulp tester).51 However, another recent study found an 87% success rate (two consecutive 80/80 readings with the electric pulp tester) for a primary articaine buccal infiltration of the mandibular first molar vs a 57% success rate for a lidocaine solution (Figure 2 ). The duration of pulpal anesthesia declined over 60 minutes for both anesthetic solutions.52
Adding an infiltration injection of articaine after an inferior alveolar nerve block resulted in an 88% success rate (that is, two 80/80 readings within 10 minutes after the injections and sustaining the 80/80 readings up to 60 minutes) for articaine vs a 71% success rate for lidocaine (Figure 3 ).53 Therefore, and this is important, if the patient has pain after a clinically successful inferior alveolar nerve block (lip numbness), adding a cartridge of articaine should help to provide profound pulpal anesthesia.
POSSIBLE REASONS FOR THE LOW SUCCESS RATE
Judging from clinical and anatomical studies,54,55 the mylohyoid nerve is the accessory nerve most often cited as a cause for failure with mandibular anesthesia. Clark et al compared the inferior alveolar nerve block alone to a combination injection of the inferior alveolar nerve block plus the mylohyoid nerve block, which was aided by the use of a peripheral nerve stimulator. The investigators found that the mylohyoid injection did not significantly enhance pulpal anesthesia of the inferior alveolar nerve block (Figure 4 ).33 Therefore, the result of the study does not lend much credibility to the notion that the mylohyoid nerve is a major factor in failure with the inferior alveolar nerve block.
Cross innervation from the contralateral inferior alveolar nerve has been implicated in failure to achieve anesthesia in anterior teeth after an inferior alveolar injection. Experimentally, cross innervation occurs in incisors but plays a very small role in failure with the inferior alveolar nerve block.34,56
Needle deflection has also been theorized as a cause for failure with the inferior alveolar nerve block.57-59 Various authors, using in vitro methods, have reported that beveled needles, when passed through substances of varying densities, will deflect toward the non-beveled side; that is, the needle will deflect away from the bevel.57-62 In asymptomatic subjects, Steinkruger and co-authors found the orientation of the needle bevel (away or toward the mandibular ramus) for an inferior alveolar nerve block did not affect anesthetic success or failure (Figure 5 ).63
It has been theorized that an inaccurate injection contributes to inadequate mandibular anesthesia. Hannan et al used a medical ultrasound unit to guide needle placement for inferior alveolar nerve blocks. While they found that the nerve block administered with ultrasound was accurate, it did not result in more successful pulpal anesthesia (Figure 6 ).15 Therefore, accuracy of needle placement is not the primary reason for anesthetic failure with this block. Two studies performed 30 years ago reached similar conclusions. Berns and Sadove,64 and Galbreath and Eklund65 used radiographs to locate the mandibular foramen and found that accurate needle location did not guarantee successful anesthesia. Twenty-five percent of accurate blocks resulted in anesthetic failure. The authors speculated that migration of the anesthetic solution followed the path of least resistance and this was determined by facial planes and structures encountered in the pterygomandibular space. These studies provide an important clinical point: the lack of pulpal anesthesia is not necessarily a result of an inaccurate injection.
PULPAL ANESTHESIA FAILURE
The central core theory66,67 may be our best explanation as to why patients fail to achieve pulpal anesthesia with an inferior alveolar nerve block. The theory states that nerves on the outside of the nerve bundle supply molar teeth while nerves on the inside supply anterior teeth. The anesthetic solution may not diffuse into the nerve trunk to reach all nerves to produce an adequate block, even if deposited at the correct site (Figure 7 ). The theory may explain the higher experimental failure rates in anterior teeth with the inferior alveolar nerve block but not posterior teeth.2-5,15-20
Endodontic patients who are in pain and have pulpal pathosis have additional anesthetic problems. There are a number of explanations for this failure. One explanation is that conventional anesthetic techniques do not always provide profound pulpal anesthesia. Another explanation relates to the theory that the lowered pH of inflamed tissue reduces the amount of the base form of anesthetic to penetrate the nerve membrane. Consequently, there is less of the ionized form within the nerve to achieve anesthesia. However, this explanation of local influences on the anesthetic solution does not explain the mandibular molar with pulpitis, which is not readily blocked by an inferior alveolar injection administered at some distance from the area of inflammation. Another explanation for failure is that nerves arising from inflamed tissue have altered resting potentials and decreased excitability thresholds.68,69 Wallace and co-authors demonstrated that local anesthetic agents were not sufficient to prevent impulse transmission as a result of these lowered excitability thresholds.68 Another factor would be the tetrodotoxin-resistant class of sodium channels that have been shown to be resistant to the action of local anesthetics.70 A related factor is the increased expression of sodium channels in pulps diagnosed with irreversible pulpitis,71 or increased central sensitization that may amplify incoming signals from sensory nerves. Finally, patients in pain are often apprehensive, which lowers their pain threshold.
Childers and co-authors72 studied the contribution of the supplemental periodontal ligament (PDL) injection after an inferior alveolar nerve block. Using 2% lidocaine with 1:100,000 epinephrine and a high-pressure syringe, anesthetic success was significantly increased for 23 minutes in the first molar. The short incidence of anesthesia was related to the small amount of anesthetic solution administered. The success of supplemental intraligamentary injections in achieving pulpal anesthesia for endodontic procedures has been reported to be 50% to 96%.13,73,74
The intraosseous injection allows placement of a local anesthetic solution directly into the cancellous bone adjacent to the tooth to be anesthetized. Dunbar,75 Guglielmo,76 Stabile,77 and their co-authors studied the contribution of the supplemental intraosseous injection after an inferior alveolar nerve block in asymptomatic patients. Using common local anesthetic agents with vasoconstrictors and the Stabident® intraosseous system (Fairfax Dental Inc, Miami, FL), anesthetic success was significantly increased for 60 minutes in the first molar (Figure 8 ). The intraosseous injection was more successful than the PDL injection because of the greater amount of anesthetic solution delivered with the intraosseous injection.72 In patients diagnosed with irreversible pulpitis, Nusstein et al found that a supplemental mandibular intraosseous injection, using the Stabident system, of 1.8 mL of 2% lidocaine with 1:100,000 epinephrine was 91% successful in gaining total pulpal anesthesia for posterior teeth diagnosed with irreversible pulpitis.10
Parente et al used the Stabident intraosseous injection in patients with irreversible pulpitis when conventional local anesthetic techniques failed. They found an initial supplemental intraosseous injection, using 0.45 to 0.9 mL of 2% lidocaine with 1:100,000 epinephrine, was successful in 79% of posterior mandibular teeth. A second intraosseous injection increased success to 91%.78
Nusstein et al also used an X-tip® (DENTSPLY, York, PA) supplemental intraosseous injection in patients with irreversible pulpitis when a conventional inferior alveolar nerve block failed. The X-tip injection site was 3 mm to 7 mm apical to the mucogingival junction of the mandibular molar or premolar tooth and 1.8 mL of 2% lidocaine with 1:100,000 epinephrine was administered. They found that six of the 33 (18%) X-tip injections resulted in backflow of the anesthetic solution into the oral cavity—none were successful in obtaining anesthesia. Twenty-seven of the remaining 33 X-tip injections (82%) were successful.79
An infiltration injection of articaine after an inferior alveolar nerve block if the patient has pain after a clinically successful inferior alveolar nerve block (lip numbness), should help to provide profound pulpal anesthesia, as discussed previously.
In about 5% to 10% of mandibular posterior teeth with irreversible pulpitis, supplemental injections, even when repeated, do not produce profound anesthesia; pain persists when the pulp is entered. This is an indication for an intrapulpal injection. The major drawback of the technique is that needle placement and injection are directly into a vital and very sensitive pulp; the injection may be moderately to severely painful.10 The advantage of the intrapulpal injection is that it works well for profound anesthesia if given under back-pressure.80,81 Onset will be immediate and no special syringes or needles are required. The methods for this technique can be found in many excellent endodontic textbooks. Strong back-pressure has been shown to be a major factor in producing anesthesia.80,81 Depositing anesthetic passively into the chamber is not adequate; the solution will not diffuse throughout the pulp.
As one can see, mandibular anesthesia remains a challenge in dentistry and especially endodontics. The clinician needs to develop strategies to overcome this challenge and provide the most comfortable procedure for the patient that is possible. There are a number of options for dentists today and continued research in the area of dental local anesthesia may provide even more options for success in the future.
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|Figure 1 Articaine vs lidocaine with inferior alveolar nerve block injection: incidence of pulpal anesthesia (80/80 reading on electric pulp tester) of mandibular first molar over time.||Figure 2 Articaine vs lidocaine with buccal infiltration injection of mandibular first molar: incidence of pulpal anesthesia (80/80 reading on electric pulp tester) of mandibular first molar over time.|
|Figure 3 Articaine vs lidocaine with buccal infiltration injection of mandibular first molar following inferior alveolar nerve block injection: incidence of pulpal anesthesia (80/80 reading on electric pulp tester) of mandibular first molar over time.||Figure 4 Mylohyoid injection vs inferior alveolar nerve block injection vs combined injections: incidence of pulpal anesthesia (80/80 reading on electric pulp tester) of mandibular first molar over time.|
|Figure 5 Effect of needle bevel direction (toward or away from ramus) during inferior alveolar nerve block injection: incidence of pulpal anesthesia of mandibular first molar over time.||Figure 6 Ultrasound-directed vs conventional inferior alveolar nerve block injection: incidence of pulpal anesthesia of mandibular first molar over time.|
|Figure 7 Central core theory for anesthetic failure of the inferior alveolar nerve block injection.||Figure 8 Conventional inferior alveolar nerve block injection with and without supplemental intraosseous injection: incidence of pulpal anesthesia of mandibular first molar over time.|
|About the Authors|
John Nusstein, DDS, MSAssociate Professor and Head
Al Reader, DDS, MS
Melissa Drum, DDS, MS