Why won't my patient get numb? (Part 2)

In our last post we reviewed a portion of  the Winter 2009 Colleagues for Excellence Newsletter and its discussion of multiple factors that can lead to the failure of our patients to get adequately numb for restorative or endodontic procedures.  In this edition we will review more material from the Newsletter which  focuses on some ways to address failed attempts at anesthesia and also debunks some common myths.
                       
With specific regard to the inferior alveolar nerve block (IANB), it is helpful to keep in mind that while lip numbness usually occurs rather quickly (5-9 minutes), pulpal anesthesia usually requires significantly longer (15-16 minutes).  According to one source (1), in 19-27% of cases, pulpal anesthesia in mandibular teeth takes longer than 15 minutes to achieve after administration of the IANB.  

In light of this information, one important step toward achieving adequate anesthesia is to simply give the anesthetic solution sufficient time to set in.  Additionally, administering the anesthetic slowly (over a period of 60 seconds) rather than quickly (15 seconds) has been shown to be not only less painful for the patient, but also more effective at producing pulpal anesthesia (2).  So when delivering the IANB, remember to slow your roll.                                              
While a second IANB following achievement of lip numbness has not been shown to be helpful, a local infiltration of articaine 4% with epinephrine 1:100,000 following IANB with lidocaine 2% w/ epinephrine 1:100k has been shown to increase pulpal anesthesia.  A 2008 study (3) showed that this method resulted in pulpal anesthesia in mandibular teeth 88% of the time while the success rate was only 71% when the buccal infiltration was done with lidocaine rather than articaine.


Occasionally when lip numbness has been achieved and pulpal anesthesia still eludes us, we as clinicians are tempted to deliver a second cartridge of anesthetic solution via the IANB.  However, studies have shown that if lip numbness is achieved following the first block, adding more solution via a second IANB does not result in better pulpal anesthesia.  The same is true of using an anesthetic formulation with a higher concentration of epinephrine; it does not improve pulpal anesthesia. The perception that a second block results in better pulpal anesthesia is likely the result of the fact that in the time it takes to stop the procedure and administer the second injection, the anesthetic has finally been given sufficient time to fully set in.  Of course, if lip numbness is not achieved after the first attempt, a second cartridge should be delivered.                        

If the patient continues to experience sensation after successful IANB (positive lip sign achieved) and administration of a local infiltration of articaine, an intraligamentary (PDL) or intraosseous injection may be indicated.  While the PDL injection is less successful than the intraosseous injection (3), it is still an excellent adjunct to conventional techniques (IANB and local infiltration) and may be a better option for clinicians unfamiliar with the intraosseous injection technique.  When all else fails, the intrapulpal injection can be utilized for endodontic procedures.  It is particularly effective when back-pressure can be achieved and requires no special syringes or needles. 

Myths:

The Winter 2009 Colleagues for Excellence Newsletter also debunks several myths regarding local anesthesia.  Some of these are listed below.

1.  Contrary to what many of us were taught in dental school, orientation of the bevel (toward or away from the ramus) actually does not affect the success of an IANB (4).

2. Despite popular sentiment to the contrary, studies have consistently failed to show statistically significant superiority of articaine over lidocaine for nerve blocks.

3.  On the question of whether articaine causes paresthesia when used for IANB, conflicting studies have reported different outcomes but the preponderance of the evidence seems to indicate that if articaine is more prone to cause paresthesia, the incidence is extremely low and the authors deem the relationship between use of articaine for IANB and resultant IAN disturbances as "questionable."

4.  Cross innervation does occur in mandibular anterior teeth but it is not the cause of most IANB failures in these teeth.  Rather, these failures are most often due to the anatomy of the IAN bundle (as discussed in the previous blog post).  Therefore, performing an IANB on the contralateral side to the teeth in question is unlikely to produce the desired result (5).

5. "Sticking" or "poking" the soft tissue adjacent to the tooth to be worked on is not a good test to assess the degree of pulpal anesthesia obtained.  Application of a cold cotton pellet to the tooth is a much more useful test of pulpal anesthesia.

    
  
1. Nusstein J, Reader A, Beck M. Anesthetic efficacy of different volumes of lidocaine with epinephrine for inferior alveolar nerve blocks. Gen Dent 2002;50:372-5

2.  Kanaa MD, Meechan JG, Corbett IP, Whitworth JM. Speed of injection influences efficacy of inferior alveolar nerve blocks: A double-blind randomized controlled trial in volunteers. J Endod 2006;32:919-23

3. Haase A, Reader A, Nusstein J, Beck M, Drum M. Comparing anesthetic efficacy of articaine versus lidocaine as a supplemental buccal infiltration of the mandibular first molar after an inferior alveolar nerve block. J Am Dent Assoc 2008;139:1228-35
4. Steinkruger G, Nusstein J, Reader A, Beck M, Weaver J. The significance of needle bevel orientation in achieving a successful inferior alveolar nerve block. J Am Dent Assoc 2006;137:1685-91.
5.  Yonchak T, Reader A, Beck M, Meyers WJ. Anesthetic efficacy of unilateral and bilateral inferior alveolar nerve blocks to determine cross innervation in anterior teeth. Oral Surg Oral Med Oral Pathol Oral Radiol  Endod 2001;92:132-5.