In: Anesthesia31 Dec 2009
The use of the 80 reading as a criterion for pulpal anesthesia was based on the studies of Dreven et al and Certosimo and Archer. These studies showed that no patient response to an 80 reading ensured pulpal anesthesia in vital asymptomatic teeth. Additionally, Certosimo and Archer demonstrated that EPT readings less than 80 resulted in pain during operative procedures in asymptomatic teeth.
Anesthetic success with the lidocaine IAN block occurred from 20 to 81% of the time. The success rates are similar to those seen in previous studies in which a similar method was used. Therefore, even after a clinically successful block (lip numbness), pulpal anesthesia may not be guaranteed. Theories of anesthetic failure for the IAN block have included accessory innervation, accuracy of needle placement, anesthetic solution migration along the path of least resistance, central core theory, and anxiety and psychological factors.
The buffered lidocaine/hyaluronidase solution did not result in a statistically (P > .05) higher success rate compared with the lidocaine solution (Table 2). Nordqvist felt that hyaluronidase loosened the structure of the connective tissue, thereby allowing the anesthetic solution easier access to the nerve fibers. Studies in the field of ophthalmology have shown that combining hyaluronidase with local anesthetic solutions significantly improves peribulbar infiltrations or retrobulbar blocks. However, other studies have found hyaluronidase did not improve the success of intraocular surgery. It seems that the addition of hyaluronidase to a lidocaine solution, as used in this study, had little effect on the success of the IAN block. Practitioners should consider supplemental techniques (such as intraosseous or periodontal ligament injections) when an IAN block fails to provide pulpal anesthesia for a particular tooth.
Solution deposition had an incidence of around 20% moderate/severe pain ratings (Table 1). The ratings in dicate that an IAN block has the potential to be painful even though the solution was deposited slowly over 1 minute. Other studies of the IAN block have reported similar findings. There were no significant differences between the solutions. Therefore, the addition of hyaluronidase was not found to be any more irritating on injection than the solution without hyaluronidase (Table 1).
The postinjection survey showed there was a much higher incidence of moderate/severe pain and trismus with the hyaluronidase solution (Tables 3 and 4). Hyaluronidase is an enzyme that breaks down the components of the connective tissue. The manufacturer found that the breakdown of dermal tissue appeared to peak in 5 minutes, remained constant for the first hour, and then declined slowly over 5 hours. Further studies showed that reconstitution of the dermal barrier was incomplete at 24 hours, but at 48 hours, the barrier was completely restored. While the pterygomandibular space is different from dermal connective tissue, the high postoperative pain ratings and incidence of trismus clearly show that some adverse effects on the tissue occurred with the injection of hyaluronidase. The postoperative pain ratings and trismus showed improvement by the third day (Tables 3 and 4), demonstrating that the tissue damage was somewhat limited. We recommend that hyaluronidase not be added to local anesthetic solutions for IAN blocks due to its tissue-damaging potential.
We conclude that adding hyaluronidase to a buffered lidocaine solution with epinephrine did not significantly increase the incidence of pulpal anesthesia in IAN blocks and, because of its potential tissue-damaging effects, it should not be added to local anesthetic solutions for inferior alveolar nerve blocks.
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