One potential 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 block1, 24, 87-89.
Increasing the Epinephrine Concentration
A second approach for increasing the success of inferior alveolar nerve blocks is 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.21, 90
Does the combination of 3% mepivacaine plain (Carbocaine) plus 2% lidocaine with epinephrine improve anesthesia and reduce the pain of anesthetic injection for the inferior alveolar nerve block?Three percent mepivacaine plain has a higher pH and concentration than 2% lidocaine with epinephrine. In theory, using 3% mepivacaine initially for an inferior alveolar nerve (IAN) block would decrease the pain of injection, provide faster onset, increase success, and possibly potentiate the effect of a second cartridge of 2% lidocaine with epinephrine. Lammers and co-authors90a found The combination of 3% mepivacaine plus 2% lidocaine with 1:100,000 epinephrine was equivalent to the combination of two cartridges of 2% lidocaine with 1:100,000 epinephrine in terms of injection pain, onset time, and pulpal anesthetic success for the IAN block.
Diphenhydramine as a Local Anesthetic Agent
Diphenhydramine (Benadryl) has been advocated for patients who are allergic to commonly used local anesthetics. Two studies91, 92 found diphenhydramine was less effective than lidocaine for extractions. Willett and co-authors93 found the combination of lidocaine/diphenhydramine with epinephrine and diphenhydramine with epinephrine were significantly less effective for pulpal anesthesia than lidocaine with epinephrine for inferior alveolar nerve blocks. They also found that the diphenhydramine solutions were more painful upon injection and had a high incidence of moderate postoperative pain.
Hyaluronidase decreases the viscosity of the injected tissue permitting a wider spread of injected fluids. Ridenour and co-authors93a found that adding hyaluronidase to a lidocaine solution with epinephrine did not statistically increase the incidence of pulpal anesthesia in inferior alveolar nerve blocks. Another problem we found was the combined lidocaine/hyaluronidase solution resulted in a significant increase in postoperative pain and trismus.
Adding Demerol to a Local Anesthetic
Investigational and clinical studies in medicine have shown meperidine (Demerol) has a local anesthetic effects and may not compete for the same binding site as lidocaine. Therefore, there is a potential for enhancement of a local anesthetic effect if lidocaine is combined with meperidine. However, Goodman and co-authors93b found that a meperidine/lidocaine combination was inferior to the use of a lidocaine solution alone in inferior alveolar nerve blocks.
How about Carbonating a Local Anesthetic?
Experimentally, hydrocarbonated anesthetic solutions are supposedly more effective due to the trapping of the anesthetic within the nerve. Additionally, CO2 has a synergistic relationship to local anesthetics and a direct depressant action on nerves. However, Chaney and co-authors93c were not able to demonstrate a superior effect of lidocaine hydrocarbonate in inferior alveolar nerve blocks. A hydrocarbonated solution has a higher concentration of carbon dioxide than a solution buffered with sodium bicarbonate.
Buffering a Local Anesthetic
There are a number of studies in medicine that have found a faster onset of anesthesia and less pain with buffered anesthetic solution. Whitcomb and co-authors93d compared the degree of pulpal anesthesia obtained with 2% lidocaine with 1:100,000 epinephrine/sodium bicarbonate (8.4%) versus 2% lidocaine with 1:100,000 epinephrine in an inferior alveolar nerve block. They reported that buffering 2% lidocaine (with 1:100,000 epinephrine) with sodium bicarbonate did not statistically increase anesthetic success, provide a faster onset, or decrease pain of injection when compared to unbuffered 2% lidocaine with 1:100,000 epinephrine for an inferior alveolar nerve block.
OnPharma has introduced a new system that buffers a local anesthetic solution using a unique dispensing system. A recent study170a using the Onpharma system for IAN blocks found a quicker onset time and less pain with injection for a buffered lidocaine formulation – which is completely different than Whitcomb’s study.93d Hobeich and co-authors170b found buffering did not result in faster onset times or decreased pain of injection for maxillary infiltration.
Studies Evaluating Mechanisms of Failure with the Inferior Alveolar Nerve Block Accessory Innervation
Judging from clinical and anatomical studies,94, 95 the mylohyoid nerve is the accessory nerve most often cited as a cause for failure with mandibular anesthesia. Clark et al.88 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. 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.
Accuracy of the injection
It has been theorized that an inaccurate injection contributes to inadequate mandibular anesthesia. Hannan and co-authors 20 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. Another study used a peripheral nerve stimulator to locate the inferior alveolar nerve but it was not any more successful than a standard block.22 Therefore, accuracy of needle placement is not the primary reason for anesthetic failure with this block. Two studies performed thirty years ago reached similar conclusions. Berns and Sadove,96 and Galbreath97 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 fascial planes and structures encountered in the pterygomandibular space. These studies provide an important clinical point – the lack of pulpal anesthesia is not necessarily due to an inaccurate injection.
Needle deflection has been theorized as a cause for failure with the inferior alveolar nerve block.98-100Various authors,98-103 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. Recently, Hochman and Friedman100 developed a bi-directional needle rotation technique using the computer-assisted Wand (CompuDent, Milestone Scientific Inc., Deerfield, IL). The bi-directional technique rotates the Wand handpiece assembly and needle in a manner similar to rotation of an endodontic hand file. The technique was found to reduce needle deflection during needle insertion. Kennedy et al.104 compared the anesthetic efficacy of the conventional inferior alveolar nerve block, administered with the needle bevel oriented away from the mandibular ramus (so the needle would deflect toward the mandibular foramen), to the bi-directional needle rotation technique, administered using the computer-assisted Wand anesthesia system, in patients diagnosed with irreversible pulpitis. There were no significant differences between the success rates (50% for the conventional and 56% for the bi-directional technique) of the two techniques. Neither technique resulted in an acceptable rate of anesthetic success in patients with irreversible pulpitis.