Broadening Clinical Perspectives on Inferior Alveolar Nerve Blocks

Failures of the traditional or Halsted inferior alveolar nerve block (HIANB) have been discussed globally. Successful HIANBs require aligning relevant and sometimes difficult-to-visualize penetration sites and needle pathways with key technique aspects. Even when optimal sites are located, profound anesthesia may not result. Mehta¹ notes, “If you numb three to five patients with inferior alveolar nerve blocks on any given day, the statistical probability of running into [failure] happens almost every other day.”

Many clinicians have perfected their HIANB techniques and rarely experience failures. While this level of achievement is commendable, there remains a small window of failure. According to Madan et al,² “In certain cases … this nerve block fails, even when performed by the most experienced clinician.” When using common techniques, confirmed by contact with the medial ramus near the mandibular foramen, profound anesthesia is not assured. While contacting bone is a common safety step to avoid penetration into the parotid gland, it does not necessarily ensure optimal deposition sites. A variety of factors can impact the development of anesthesia, such as accessory innervation, fibrous tissue resistance and deflection, and variability in the locations of neural, vascular, and bony structures and landmarks.

The abundance of alternative mandibular block techniques in the literature (20 were reviewed for this discussion), highlights the pervasive nature of mandibular anesthesia failure. In addition to the conventional HIANB and two well-known alternatives, this discussion will report key features of a few mandibular block techniques from the global literature. In addition, short needle approaches will be discussed.

HALSTED INFERIOR ALVEOLAR NERVE BLOCK FAILURE

The HIANB is a common approach to anesthesia in the mandible.^3,4 Despite widespread use, failure rates ranging from 15% to 20% or more — even after a second injection — have been reported.^5,6 Some studies suggest even higher failure rates. Potocnik and Bajrović⁷ note that “even when a traditional inferior alveolar technique is employed, clinical studies show that [it] fails in approximately 30% to 40% of cases.”

Numerous sources describe alternative techniques that demonstrate higher success rates, such as the Gow-Gates and Vazirani-Akinosi nerve blocks (97.5% and as high as 95.7%, respectively).^6–10 Although these techniques are reportedly more effective than the HIANB, they may not have been included in dental curriculum and, even when included, are less frequently performed compared to the HIANB.¹¹ A study of Harvard School of Dental Medicine graduates, for example, reported that despite instruction in the HIANB, Gow-Gates and Vazirani-Akinosi blocks, most graduates did not incorporate Gow-Gates or Vazirani-Akinosi techniques into their anesthesia routines. The researchers estimated that only 3.7% to 16.1% used Gow-Gates blocks and 0.0% to 3.8% used Vazirani-Akinosi blocks as their method(s) of choice for achieving mandibular anesthesia.¹¹

Most failures occur because anesthetic solution is not deposited into optimal locations within the pterygomandibular space. The most common reasons cited for failure include technique errors related to inaccurate assessment of landmarks and syringe position.^3,9 Deposition posterior and/or inferior to nerves, anatomic barriers and variations, accessory innervation, needle deflection, armamentarium issues, and numerous other challenges have been cited, as well.^3,9,12–20

In a study of 132 mandibles, Kilarkaje et al¹⁷ reported the relationship between the mandibular foramen and mandibular molar occlusal and alveolar crestal planes increases in height with age. As Gow-Gates²¹ noted, individual anatomic variations of mandibular foramina are described as being located higher than expected in a significant percentage of patients. Gow-Gates also commented that criticism of the HIANB technique “is based on unpredictable results from its use and the false premise that pulpal anesthesia is consistently attained by depositing the anaesthetic solution at the lingula.”²¹

GLOBAL PERSPECTIVES ON ALTERNATIVE TECHNIQUES

While the Gow-Gates and Vazirani-Akinosi techniques are well-known, from a global perspective there are many lesser-known alternatives to inferior alveolar nerve anesthesia. This article will present several examples to provide insight. It should be noted this review is a limited discussion and is not intended to provide instructions, or illustrations, for performing these techniques.

Kahlil²⁰ discusses seven alternative HIANB techniques, two of which were described by Thangavelu et al.²² The first requires patients to open widely. Approaching from the contralateral side, needle insertion is ~8 to 10 mm posterior to the anterior border of the ramus and continues 6 to 8 mm until contact with bone. The syringe is then moved to the midline and the needle is advanced, making multiple contacts along the ramus. These repeated bony contacts may result in periosteal trauma. At a depth of 21 to 24 mm, the syringe is moved back to the contralateral side. The reported technique success rate is 95%.

The internal oblique ridge is the key landmark for the second Thangavelu et al²² technique. Approaching from the contralateral premolars, with the thumb over the retromolar area, insertion is 6 to 8 mm above the midpoint of the thumb and 2 mm posterior to the internal oblique ridge. Insertion continues until contact with bone. Both inferior alveolar and lingual nerves are anesthetized. The reported success rate is 95%.

A technique described by Boonsiriseth et al²³ makes use of the HIANB penetration site; however, the syringe is aligned directly over the occlusal surfaces on the side to be anesthetized. With this technique, 30 mm needles are recommended and no bony contact with the ramus occurs.

Palti et al²⁴ describe the intersection of two wires to predict the location of the mandibular foramen. One wire is positioned over the permanent first molar (or over the second primary molar), along the mesiobuccal groove and midpoint of the mesial slope of the distolingual cusp. The other wire is positioned over the contralateral occlusal plane.

Galdames et al²⁵ recommend depositing anesthetic in the retromolar triangle, essentially accessing the inferior alveolar nerve via neural and vascular canals communicating with the mandibular canal. The success rate of this technique is reported to be 72%. While less successful than the HIANB, it is described as useful in patients on anticoagulant therapy or with bleeding disorders, such as hemophilia.

In Nooh’s and Abdullah’s²⁶ technique, the syringe is aligned over the contralateral premolars and the needle is inserted 15 mm above the occlusal plane and advanced to bony contact. After contact with the ramus, the syringe is relocated to the side of injection over the teeth. The needle is then advanced 30 to 34 mm while remaining in contact with bone. Nooh and Abdullah claim this technique has fewer complications and lower positive aspiration and failure rates than the HIANB.

Takasugi et al²⁷ describe depositing anesthetic solution between the medial pterygoid and temporalis muscles near the anterior border of the ramus, within the pterygomandibular space. This technique is referred to as an anterior inferior alveolar nerve block. Takasugi et al use computed tomography scans to predict syringe location and angle. With the syringe on the contralateral side, the needle is inserted 10 mm above the occlusal plane to a depth of 10 mm. Success is approximately 75%.

LOMA LINDA INFERIOR ALVEOLAR NERVE BLOCK — A SHORT NEEDLE TECHNIQUE

The Local Anesthesia Manual issued by the Loma Linda University School of Dentistry describes an inferior alveolar nerve block technique accomplished with short, 25-gauge needles.²⁸ Key anatomic landmarks include the depth of the coronoid notch, internal oblique ridge, mandibular occlusal plane, pterygomandibular raphe and medial ramus. Inserting the needle to 5 mm, 0.5 ml of anesthetic is deposited for a lingual block. The needle is then advanced — maintaining contact with the ramus — until contact is lost over the lingular notch. Up to 1.0 ml of anesthetic is deposited after contact is lost. The success rate is estimated to be 80% to 85%.

SHORT NEEDLE INFERIOR ALVEOLAR AND LINGUAL NERVE BLOCK DISCUSSION

A short needle approach for inferior alveolar nerve blocks is used by many clinicians. This method follows HIANB penetration site landmarks, inserting short needles of varying gauges to depths anywhere from three-fourths to the full length of the needle (i.e., to the hub). Many learn the technique from colleagues, use it routinely, and anecdotally claim great success.

Despite the technique’s apparent success, deep insertions with short needles and routine penetrations to needle hubs are well-documented safety concerns.^3,13,16 When reviewing the risks associated with short needles in deep penetrations, researchers have reported that needle diameter is a significant predisposing factor in needle fracture.^13,16 In 31 of 40 cases (77.5%) where diameter was mentioned, 30-gauge needles were involved. While reliably effective, concerns persist over risks associated with deep insertions to the hub of short, and particularly small diameter, needles.³

Using cadavers with intact tissues, Menke and Gowgiel²⁹ compared 25-gauge, 25 mm short needles versus 25-gauge, 36 mm long needles to determine which best approximated the location of the inferior alveolar nerve. Measuring penetration depths from the mucous membrane at the pterygomandibular raphe to the inferior alveolar nerve, the range was found to be 12 to 19 mm. This depth was noted to be within the limits of the short needles used in the study. The authors further observed that needle deflections were more frequent when long needles were used, and that long needles were more likely to deflect in a posterior direction from the mandibular foramen.²⁹ Galbreath and Eklund³⁰ provided evidence that depositions posterior to the foramen are likely to result in lower success rates (~50%) compared to depositions anterior to the foramen (~80%).

The penetration site recommended for the short needle inferior alveolar and lingual nerve block (SNIALB), based on Gow-Gates’ observation of false premise, is ~2 to 3 mm higher than Halsted penetration site (Figure 1).^21,31 At this height, the insertion site is moved ~2 mm medially due to the curvature of the ascending pterygomandibular raphe (Figure 2). The average penetration depth (16 mm) reported by Menke and Gowgiel²⁹ is increased to 18 mm to accommodate this change (Figure 3).

The SNIALB nerve block approach described in Table 1 differs significantly from most other techniques previously discussed. It relies on a high penetration site and shallow insertion depth to deposit solution close to the inferior alveolar nerve. This single deposition site routinely anesthetizes both the inferior alveolar and lingual nerves. Bony contact is not expected. If it occurs, the insertion depth should be decreased prior to deposition. Addressing concerns of inserting needles to the hub and/or the potential for needle fracture, at the recommended insertion depth of 18 mm, 7 mm of a 25 mm, 25-gauge needle (preferred) are exposed (Figure 4).

CLINICAL STUDY: SHORT NEEDLE INFERIOR ALVEOLAR AND LINGUAL NERVE BLOCKS

Menke and Gowgiel²⁹ noted disagreement in the literature regarding the depth of penetration of needles for inferior alveolar nerve blocks. Their study of the actual depths of penetration from the mucous membrane of the penetration site to the inferior alveolar nerve were conducted using cadavers with intact tissues. Anatomic studies that did not account for soft tissue were described by the team as “not totally helpful to a clinician who is administering an inferior alveolar nerve block.”²⁹ A blinded randomized controlled trial comparing the SNIALB to the HIANB is currently under way.

CONCLUSION

Achieving profound anesthesia with a traditional HIANB occurs, on average, 80% to 85% of the time or less. While the HIANB typically succeeds on repeat injection, failure is not uncommon. Clinicians who are unfamiliar with, or reluctant to perform, Gow-Gates or Vazirani-Akinosi blocks often rely on alternatives to supplement anesthesia. In this case, the SNIALB technique may prove clinically relevant.

References

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FIGURES 1, 2 AND 4: COURTESY LOCAL ANESTHESIA FOR DENTAL PROFESSIONALS; FIGURE 3 COURTESY KATHY BASSETT, RDH, MEd

From Decisions in Dentistry. February 2023;9(2)32-35.