In asymptomatic subjects, Steinkruger and co-authors105 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. Therefore, the use of commercial needles with markers to indicate needle bevel is not necessary.
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 incisors89, 106 but plays a very small role in failure with the inferior alveolar nerve block.
Why don't asymptomatic patients achieve pulpal anesthesia with the inferior alveolar nerve block?
The central core theory 107, 108 may be our best explanation. 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. The theory may explain the higher experimental failure rates in anterior teeth with the inferior alveolar nerve block. 1-4, 20-25
Studies That Have Increased the Success of Mandibular Anesthesia in Restorative Dentistry
Use of a Supplemental Articaine Infiltration of the Mandibular First Molar Following an Inferior Alveolar Nerve Block
As discussed previously, Haase and Kanna and co-authors84, 84a found increased success. This approach would be the best for restorative dentistry in the first molar, premolars, and anterior teeth. However, the second molar may require a supplemental intraosseous injection.
Use of the Supplemental Intraosseous Injection
Dunbar,110 Guglielmo,27 Stabile111 and co-authors studied the contribution of the supplemental intraosseous injection after an inferior alveolar nerve block. Using common local anesthetic agents with vasoconstrictors and the Stabident intraosseous system, anesthetic success (no response to pulp testing) was significantly increased for 60 minutes in the first molar. The intraosseous injection was more successful than the periodontal ligament injection109 due to the greater amount of anesthetic solution delivered with the intraosseous injection. Additionally, the intraosseous injection significantly decreased the incidence of slow onset of pulpal anesthesia to 0% when compared to the inferior alveolar nerve block alone (18% incidence).110 Therefore, when pulpal anesthesia is required in asymptomatic teeth, the addition of the intraosseous injection to the inferior alveolar nerve block, in the first molar, will provide a quick onset and a high incidence of pulpal anesthesia for 60 minutes.
Gallatin and co-authors112 found that the use of 3% mepivacaine as a supplemental intraosseous injection following an inferior alveolar nerve block resulted in statistically increased pulpal anesthesia for 30 minutes. The shorter duration of the 3% mepivacaine, when compared to 2% lidocaine with 1:100,000 epinephrine,110 was related to the lack of a vasoconstrictor.
Use of the Supplemental Intraligamentary Injection
Childers and co-authors109 studied the contribution of the supplemental intraligamantary injection after an inferior alveolar nerve block. Using 2% lidocaine with 1:100,000 epinephrine and a high-pressure syringe, anesthetic success (no response to pulp testing) 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.
Speed of Injection and Success
Kanaa and co-authors113 found a slow inferior alveolar nerve block injection (60 seconds) resulted in higher success rates (electric pulp testing) than a rapid injection (15 seconds). However, this was not true for patients diagnosed with irreversible pulpitis.113a
ENDODONTIC ANESTHESIA Success of the Inferior Alveolar Nerve Block
Clinical studies in endodontics,9, 11, 12, 19, 50, 86, 131, 151, 153, 155 in patients with symptomatic irreversible pulpitis, have found success (mild or no pain upon endodontic access or initial instrumentation) with the inferior alveolar nerve block occurred between 19% and 56% of the time. These studies would indicate that anesthesia is often difficult to achieve in irreversible pulpitis with only the inferior alveolar nerve block. In patients presenting with asymptomatic irreversible pulpitis – that is, patients who have no spontaneous pain at the emergency visit, Argueta-Figueroa and co-authors167 found success rates were higher in these asymptomatic patients.
Why does anesthesia fail in patients with painful teeth? One explanation, as we discussed previously, is that conventional anesthetic techniques do not always provide profound pulpal anesthesia. One explanation, as we will discuss soon, 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. Therefore, it is difficult to correlate local influences with failure of the inferior alveolar nerve block. Another explanation for failure is that nerves arising from inflamed tissue have altered resting potentials and decreased excitability thresholds.14, 15 Modaresi, Wallace and co-authors 14,14a demonstrated that local anesthetic agents were not sufficient to prevent impulse transmission due to these lowered excitability thresholds. Another factor would be the tetrodotoxin-resistant (TTXr) class of sodium channels that have been shown to be resistant to the action of local anesthetics.16 A related factor is the increased expression of sodium channels in pulps diagnosed with irreversible pulpitis.17And finally, patients in pain are often apprehensive, which lowers their pain threshold. Therefore, practitioners should consider supplemental techniques - such as intraosseous9, 11, 18, 19 or periodontal ligament injections12 when an inferior alveolar nerve block fails to provide pulpal anesthesia for patients with irreversible pulpitis.
It is not your fault! If there is one important fact that you need to remember, it is that patients DO NOT always achieve pulpal anesthesia in endodontics, but it is not your fault.
Success of Maxillary Molar Infiltration in Patients with Irreversible Pulpitis.
Endodontic clinical studies of maxillary, posterior buccal infiltrations in patients presenting with irreversible pulpitis have shown success occurs from 54% to 88% of the time.9,157,158 Srinivasan et al.85b found articaine was superior to a lidocaine formulation for maxillary buccal infiltrations in patients with irreversible pulpitis. However, the numbers were small in this study. Rosenberg, et al.85 and Sherman et al.85a found no significant differences between an articaine solution and a lidocaine solution when used as a maxillary infiltration, supplemental infiltration after inferior alveolar nerve blocks, or Gow-Gates injection in patients with irreversible pulpitis. However, the numbers were small in these studies. While some authors have found a difference between articaine and lidocaine,159 others have not.160,161
Kanaa and co-authors158 found no significant difference in success (no pain on access) between articaine (76% success) and lidocaine (70% success).
Success with Articaine for Inferior Alveolar Nerve Blocks in Patients With Irreversible Pulpitis.Success rates for the inferior alveolar nerve block using 4% articaine with epinephrine have ranged from 26% to 87%50b-i. Claffey and co-authors50 found an articaine solution had a success rate of 24% and a lidocaine solution had a success rate of 26%, with no significant difference between the solutions. Neither solution resulted in an acceptable rate of anesthetic success in patients with irreversible pulpitis. Tortamano and co-authors50a found similar results in patients with irreversible pulpitis.
Primary Infiltrations for Mandibular Anesthesia in Patients with Irreversible Pulpitis
Aggarwal and co-authors73a found a primary buccal plus lingual infiltration of articaine had only a 27% success rate in mandibular first and second molars for patients presenting with irreversible pulpitis.
SUPPLEMENTAL INJECTIONS Supplemental injections are essential when, as frequently occurs, anesthesia from conventional injections is inadequate and the pain is too severe for the endodontist or dentist to proceed. There are four such supplemental techniques – infiltration of 4% articaine for mandibular posterior teeth, the intraligamentary injection, the intraosseous injection, and the intrapulpal injection.
If the patient has profound lip numbness and experiences pain upon endodontic access, repeating the inferior alveolar nerve block does not solve the problem.156 Kanaa and co-authors156 found only a 32% sucess rate for a repeat inferior alveolar nerve block. Clinicians may think that another injection is helpful because the patient sometimes achieves pulpal anesthesia after the second injection. However, the patient may just be experiencing slow onset of pulpal anesthesia. That is, the second injection does not provide additional anesthesia – the first injection is just “catching up” due to the slow onset of pulpal anesthesia.
Supplemental Infiltrations of Articaine for Mandibular Anesthesia in Patients with Irreversible Pulpitis
Supplemental Buccal, Lingual, or Buccal Plus Lingual Infiltrations of Articaine
While the infiltration of articaine is effective in restorative dentistry as a supplemental technique (following the inferior alveolar nerve block),84,84a its use in endodontically involved teeth will not result in predictable pulpal anesthesia.86,151,153 Success rates in studies have ranged from 38% to 84%,50b,50e,86,86b,151,152,153,156,162,162a with the majority of studies reporting success rates less than 60%.50b,86b,167,151,152,153,162 The reason for the higher success rates in some studies is related to not using patients with failed inferior alveolar nerve blocks. Therefore, it was not known how many of the patients would have been successfully anesthetized with the inferior alveolar nerve block alone. This omission in study design could have affected the results. There will be no difference between 1.8 mL and 3.6 mL of 4% articaine for supplemental buccal infiltrations.50d
Buccal infiltration alone, buccal plus lingual infiltrations alone (or following an inferior alveolar nerve block) will not result in complete pulpal anesthesia.86a,86b,86c,152,157,162,163
Therefore, the intraosseous and intraligamentary injections are the preferred techniques for supplemental anesthesia, with the intrapulpal injection being indicated when the intraosseous or intraligamentary injections are not successful.
Success as a Primary Injection
For use as a primary injection, good success rates have been reported for restorative procedures. However, when compared to the inferior alveolar nerve block, the primary intraligamentary injection resulted in higher pain scores during treatment.114 There is more difficulty in achieving adequate pain control in extractions and endodontic treatment.115, 116 Malamed116 reported a 50% success rate in endodontics when the intraligamentary injection was used as a primary technique. Kaufman et al.,117using a high-pressure syringe, found a 79% success rate in performing vital pulpectomies. Higher success rates have been shown in posterior teeth than anterior teeth.77, 118
Success as a Supplemental Injection in Endodontics
The success of supplemental intraligamentary injections in achieving pulpal anesthesia for endodontic procedures has been reported to be 50 to 96%.12, 119, 120 Walton and Abbott119 reported a 63% success rate of the supplemental intraligamentary injection during endodontic and restorative procedures. Re-injection, if the first intraligamentary injection failed, was shown to be successful in 71% of the patients for an overall success rate of 92%. Smith et al.120 reported similar results. Cohen et al.12 studied endodontic patients with irreversible pulpitis and found that a supplemental intraligamentary injection was 74% successful. Re-injection increased success to 96%. The intraligamentary injection will not be successful in mandibular anterior teeth.77, 118
Fan and co-authors86a found a 83% success rate with a supplemental intraligamentary injection of articaine in patients with irreversible pulpitis. However, Fan’s study did not use patients with failed inferior alveolar nerve blocks. Therefore, it was not known how many of the patients would have been successfully anesthetized with the inferior alveolar nerve block alone. This omission in study design could have affected the results. Kanaa and co-authors158 and Zarei and co-authors164 found a 48% and 70% success rate, respectively, for the intraligamentary injection after a failed inferior alveolar nerve block in patients with irreversible pulpitis.
Recently, Bangerter and co-authors,120a in a survey of endodontists (response rate of only 33%), found the intraligamentary injection was used more often than other intraosseous techniques – with older endodontists using the intraligamentary injection more often. The reported finding may be because many endodontists have not been taught the newer intraosseous systems.
Technology for the Intraligamentary Injection – The CCLAD
Recently, a computer controlled local anesthetic delivery system (CCLAD) has been introduced which can be used to administer an intraligamentary injection. The Wand, CompuDent, STA (CompuDent, Milestone Scientific Inc., Deerfield, IL) local anesthesia computer-controlled injection system accommodates a standard local anesthetic cartridge that is linked by sterile micro tubing to a disposable, pen-like handpiece with a Leur-Lok needle attached to the end. The device is activated by a foot control, which automates the infusion of local anesthetic solution at a controlled rate. A slow or fast flow rate is initiated and maintained by a foot pedal control. The fast rate delivers 1.4 ml of solution in 45 seconds. The slow rate delivers 1.4 ml of solution in approximately 4 minutes and 45 seconds. The slow rate is used for the intraligamentary injection.
Success of the Primary Intraligamentary Injection, Using the CCLAD, in Asymptomatic Vital Teeth
An experimental study121 compared the anesthetic efficacy of the primary intraligamentary injection of 1.4 mL of 4% articaine with 1:100,000 epinephrine and 1.4 mL of 2% lidocaine with 1:100,000 epinephrine, administered with computer-controlled local anesthetic delivery system, in the mandibular first molar. Successful pulpal anesthesia (two consecutive 80 readings with an electric pulp tester) was obtained 86% of the time with the articaine solution and 74% of the time with the lidocaine solution. There was no significant difference between the articaine and lidocaine solutions. The duration of pulpal anesthesia for the first molar ranged from 31 to 34 minutes – which is longer than the 10 minutes recorded in a similar study using a pressure syringe and 0.4 ml of a lidocaine solution.118 Therefore, there is an advantage to using the computer-controlled local anesthetic delivery system to increase the duration of pulpal anesthesia. However, the clinician must be aware that anesthesia does decrease slowly over the hour.
Nusstein et al.122 determined the anesthetic effectiveness of the supplemental intraligamentary injection, administered with a computer-controlled anesthetic delivery system, in mandibular posterior teeth diagnosed with irreversible pulpitis when the conventional inferior alveolar nerve block failed. Success of the intraligamentary injection (none or mild pain upon endodontic access or initial instrumentation) was obtained in 56% (30 of 54) of the patients. The results were somewhat disappointing because the computer-controlled anesthetic delivery system should have been capable of delivering approximately 1.4 mL of anesthetic solution via of the intraligamentary injection by consistently maintaining a precise flow rate.
Intraligamentary Injection, Using STA (Single Tooth Anesthesia) Technology
The STA device uses dynamic pressure-sensing (DPS) technology which allows continuous feedback during the intraligamentary injection.123 Lights on the STA unit give audible and visual indicators which indicate the correct pressures involved to deliver the anesthetic solution by intraligamentary injection. Therefore, it transforms a “blind” intraliamentary injection with a syringe into an accurate pressure-sensing injection with the STA unit. However, no studies have been performed to evaluate this new technology.