Overall. The authors explore the reasons why the conventional inferior alveolar nerve block fails and describe several alternate techniques. They also present the protocol used in their office to achieve mandibular anesthesia.

Conclusions. Several alternatives to the inferior alveolar nerve block are available. Clinicians should investigate them, rather than repeat the inferior alveolar nerve block after it has failed.

Practice Implications. Mastering anesthetic techniques maximizes success in the dental office. It enables clinicians to provide better and more comfortable treatment to patients.

	FAILURE OF CONVENTIONAL INFERIOR ALVEOLAR NERVE BLOCK

TOP ABSTRACT FAILURE OF CONVENTIONAL INFERIOR... WHAT TO DO IF... CONCLUSION REFERENCES

 
There are a number of reasons for the comparatively high failure rate of this block, as listed below²:

– anatomical: accessory nerve supply (mylohyoid nerve, cervical cutaneous nerve C1, C2, auriculotemporal nerve), variable course of nerve, variation in foramen position, bifid alveolar nerve or bifid mandibular canal;

– pathological: trismus, infection, inflammation, previous surgery;

– pharmacological: chronic alcohol abuse, chronic narcotic drug abuse;

– psychological: fear, anxiety, apprehension;

– poor technique: this is the most common reason for failure of the conventional inferior alveolar nerve block. We emphasize the three most commonly occurring problems with this technique.

Inadequate mouth opening. The target area for this block is the mandibular sulcus, which is at the level of the coronoid notch and above the mandibular foramen.³ When the mouth opening is not adequate, the inferior alveolar nerve, which descends from above, is relaxed and away from the medial wall of the ramus. Consequently, it is at a distance from the target area, which leads to inadequate anesthesia. When the mouth opening is adequate, the nerve is flush against the medial wall of the ramus and at the target area.³ Hence, the patient reports experiencing almost immediate onset of anesthesia. This is why the block does not work in cases of trismus and the closed-mouth block needs to be administered.

Improper needle placement. A common mistake is to insert the needle too far forward or backward of the target area.² Clinicians need to insert the needle just medial to the pterygomandibular raphe such that it approaches from the opposite side of the premolar region and bisects the thumbnail (or fingernail) placed at the deepest portion of the coronoid notch.¹ The needle is inserted to a depth of 20 to 25 millimeters.¹

Haste. Malamed¹ recommends waiting three to five minutes after the injection before starting the procedure. We believe these minutes can be used to build rapport with the patient and make him or her feel at ease. While waiting for a mandibular block to take effect, the practitioner should ask the patient to sit up. This postural change often facilitates the onset of anesthesia.¹

	WHAT TO DO IF THE CONVENTIONAL BLOCK FAILS?

TOP ABSTRACT FAILURE OF CONVENTIONAL INFERIOR... WHAT TO DO IF... CONCLUSION REFERENCES

 
Repeat the block. If the conventional block fails, most general dental practitioners tend to repeat the block. Although this is effective in a few cases, repeated injections in the same area can lead to postinjection pain and even trismus.¹ Alternatives to the conventional block may be useful in this situation and are discussed below.

Closed-mouth block (Vazirani/Akinosi block). This technique is most useful when the patient cannot open the mouth completely, as is the case with trismus (Figure 1).^4,5 It is a simple technique that is comfortable for the patient.¹ After the patient closes his or her mouth, the clinician advances a syringe fitted with a 35-mm needle parallel to the maxillary occlusal plane at the level of the cervical margin of the maxillary molars. The needle is inserted medial to the anterior border of the ramus and buccal to the maxillary alveolus. The clinician then advances the needle until the hub is level with the distal surface of the maxillary second molar. After performing aspiration, he or she then deposits a 1.8-milliliter cartridge of local anesthetic solution. This technique does not block the buccal nerve in some cases, so a separate buccal nerve block may be required to achieve anesthesia of the tissues buccal to the mandibular molars.¹

View larger version (94K): [in this window] [in a new window]   Figure 1. Closed-mouth block (Vazirani/Akinosi technique).

Gow-Gates block. The Gow-Gates block was developed by a general dentist (Figure 2).⁶ It is technically more difficult than the conventional and closed-mouth blocks, but has a higher success rate.¹ The point of mucosal penetration is higher than it is with the conventional inferior alveolar nerve block. This truly is a mandibular block, because it blocks almost all the branches of the mandibular branch of the trigeminal nerve.¹

View larger version (91K): [in this window] [in a new window]   Figure 2. Gow-Gates block.

The dentist introduces the needle across the contralateral mandibular canine and directs it across the mesiopalatal cusp of the ipsilateral upper second molar; the needle is advanced until bony contact is made. This point of bony contact is the condylar head, just below the attachment of the lateral pterygoid muscle. The dentist withdraws the needle slightly and, after aspirating, deposits a full cartridge of anesthetic. The patient should keep the mouth open for a few minutes until he or she reports experiencing signs of inferior alveolar anesthesia.

Intraligamentary injection. The intraligamentary injection can be used as a primary or secondary technique (Figure 3).⁷ It has limitations, such as short duration, but can be used to overcome a failed alveolar nerve block.² Although special syringes and needles are available, the intraligamentary injection technique is equally effective when a standard 27-gauge needle is used.

View larger version (90K): [in this window] [in a new window]   Figure 3. Intraligamentary injection.

Approximately 0.2 mL of anesthetic solution is injected per root under pressure.⁸ This technique is advantageous for patients with bleeding disorders, since injection into potential spaces, such as the pterygomandibular space, is avoided.⁸ However, it requires multiple insertions for multi-rooted teeth. The solution must be injected slowly, since rapid injection can cause pain and even extrusion of teeth.⁸

Intrapulpal injection. This technique can be most useful in endodontics.⁹ Unlike other techniques, the intrapulpal injection achieves anesthesia as a result of pressure, not as a result of the local anesthetic solution. Saline has been reported to be as effective as an anesthetic solution when injected intrapulpally.⁹

After locating a small access cavity into the pulp, the clinician selects a needle that will fit snugly into it. A small amount (0.1 mL) of anesthetic is injected under pressure. The patient will experience some transient discomfort during the injection. Onset of anesthesia is rapid. When the operative site is too large to allow a snug needle fit, the clinician should bathe the exposed pulp in a small amount of local anesthetic for about one minute before introducing the needle as far apically as possible into the pulp and injecting under pressure. This technique is a vital adjunct when the conventional block fails.

Intraosseous injection. As with the intraligamentary injection, the intraosseous injection method can be performed using conventional or specialized equipment.¹⁰ The site of injection is the interradicular bone,² and radiographs are useful in locating it. The clinician infiltrates the gingiva in the area of penetration with a small volume of anesthetic. The region to perforate is within the attached gingiva, about 2 mm below the gingival margin of adjacent teeth in the vertical plane bisecting the interdental papilla.

The perforation can be made with a sterile bur on a slow-speed handpiece, which is advanced until the obvious penetrating feeling into the cancellous space occurs. The dentist removes the perforator, advances a 6-mm 30-gauge needle through the defect into the cancellous bone and administers 0.2 to 0.5 mL of solution slowly. Plain 2 percent lidocaine solution is preferred because lidocaine with epinephrine can cause palpitations.⁸ Although aspects of intraosseous anesthesia (such as increased risk of postoperative pain, discomfort and infection) preclude its use as a primary technique, it may be a useful adjunct to an inferior alveolar nerve block.¹¹

Other anesthetic techniques are available, such as intraseptal injection and extraoral techniques, but these are of limited clinical value and are not discussed here.

Figure 4 illustrates the protocol followed in our clinic for achieving local anesthesia in the mandible. However, this is meant to be a guide only. Every practitioner must develop his or her own protocol based on knowledge and mastery of techniques.

View larger version (43K): [in this window] [in a new window]   Figure 4. Anesthesia protocol used in the authors’ clinic.

	CONCLUSION

TOP ABSTRACT FAILURE OF CONVENTIONAL INFERIOR... WHAT TO DO IF... CONCLUSION REFERENCES

View larger version (136K): [in this window] [in a new window]   Dr. Gautam Madan is in private practice as a consultant oral and maxillofacial surgeon, B-10, Nobles, Opp Nehru Bridge, Ashram Road, Ahmedabad, India 380009, e-mail "gautammadan{at}yahoo.com". Address reprint requests to Dr. Gautam Madan.

View larger version (143K): [in this window] [in a new window]   Dr. Sonal Madan is in private practice as a consultant oral and maxillofacial surgeon, Ahmedabad, India.

View larger version (124K): [in this window] [in a new window]   Dr. Arjun Madan is in private practice as a consultant orthodontist, Ahmedabad, India.