Superior Position of the Mandibular Foramen and the Necessary

Superior position of the IN BRIEF • Provides an overview of inferior dental block (IDB) techniques and reasons for PRACTICE mandibular foramen and failure. • Focuses on anatomical variation and accessory innervation as reasons for local anaesthesia failure with reference to a the necessary alterations in case study. • Alternative IDB techniques are discussed, namely the Akinosi and Gow-Gates the local anaesthetic technique: techniques. a case report

R. Holliday1 and I. Jackson2 VERIFIABLE CPD PAPER

The inferior alveolar nerve block or inferior dental block (IDB) is one of the most common techniques of delivering dental anaesthesia, with several million being administered each year. When conventional techniques fail the dentist should have the skills and confidence to use alternative techniques to achieve anaesthesia. The aim of this paper is to discuss the possible reasons for failure, with particular reference to local anatomy. The benefit of alternative techniques is highlighted by the use of an interesting case study, involving a superior position of the mandibular foramen.

INTRODUCTION While the direct and indirect techniques The inferior alveolar nerve block or infe- will provide effective local anaesthesia in rior dental block (IDB) is one of the most the vast majority of cases, they do not common techniques of delivering dental allow for all eventualities, for example, anaesthesia, with several million being variation in the location of the mandibu- administered each year.1 Good dental lar foramen. Two alternative approaches, anaesthesia is essential for delivering pain- namely the Akinosi technique and the free dentistry and the highest quality of Gow-Gates technique, may therefore be patient care. Varying success rates have utilised, either at the outset, where vari- been reported and the possible reasons for ations in local anatomy have been recog- failure include:2 nised, or following a failed conventional • Poor anaesthetic technique attempt at achieving anaesthesia. • Anatomical variations Each of these techniques and their Fig. 1 A right ¼ dental panoramic tomography demonstrating a radiolucent • Presence of acute infections potential applications will be described band with corticated margins ascending • Patient immaturity in more detail. To highlight the clinical almost the entire length of the ascending • Inability to introduce the needle to the relevance, the following case study high- ramus to the condylar neck appropriate site lights a scenario whereby the Akinosi • Reduced patient pain threshold. technique was utilised to achieve effective local anaesthesia before removal of a Two techniques of delivering IDBs are lower third molar. taught at undergraduate level in the UK: the direct technique, also known as the CASE STUDY Halstead technique, and the indirect tech- A 28-year-old Caucasian female with no rel- nique. The key features of these techniques evant past medical history was referred to are summarised in Table 1. a primary care-based specialist in oral surgery for the surgical removal of an impacted lower right third molar, owing to a history 1*Senior House Officer in Oral and Maxillofacial Surgery, NHS Forth Valley, Forth Valley Royal Hospital, Stirling of recurrent pericoronitis. Clinically, this Road, Larbert, FK5 4WR; 2Specialist Oral Surgeon, Lo- tooth was partially erupted with an inflamed thian Salaried Dental Services, Chalmers Dental Centre, operculum and the tooth appeared to be Fig. 2 Suspected position of the mandibular 3 Chalmers Street, Edinburgh, EH3 9EW foramen demonstrated (dotted red circle) *Correspondence to: Mr Richard Holliday distoangularly impacted. A dental pano- Email: [email protected] ramic tomograph (Fig. 1) confirmed that the Refereed Paper lower right third molar was indeed distoan- path of the mandibular canal was noted to Accepted 4 November 2010 DOI: 10.1038/sj.bdj.2011.145 gularly impacted. In addition, the position be unusual. A radiolucent band with corti- ©British Dental Journal 2011; 210: 207-211 of the mandibular foramen and resulting cated margins was noted to ascend almost

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the entire length of the ascending ramus to the condylar neck. It was agreed that this Table 1 Summary of the inferior dental nerve block (IDB) techniques was most likely to represent the mandibular IDB technique Specific Technique details Anaesthesia canal with a superiorly positioned mandibu- indications achieved Inferior alveolar lar foramen (Fig. 2). However, a grooving Thumb on coronoid notch nerve of the medial aspect of the ramus of the Another finger on posterior mandibular border mandible may also have explained this appearance, with the mandibular foramen Long (35 mm) 27 gauge needle Direct Approach from the lower premolars of the itself lying in a normal position just above Conventional conventional opposite side technique the occlusal plane. It was felt unnecessary to or ‘Halstead’ Puncture site: a position lateral to the ptery- Lingual nerve confirm the true position of the mandibular gomandibular raphe and medial to the thumb foramen with a CT scan. (ramus) at a level half-way up the thumbnail (1 cm above the occlusal plane of the molars) At the time of treatment a direct tech- Needle inserted until bony contact, usually nique IDB was administered using 2.2 ml 20-25 mm Inferior alveolar of 2% lignocaine with 1:80000 adrena- Similar to direct technique nerve line. After approximately five minutes, no Needle is initially positioned over the molars of signs of inferior alveolar nerve anaesthesia the same side Indirect Conventional were achieved. The Akinosi technique was Needle advanced 10-15 mm conventional technique then utilised to deliver a further 2.2 ml of Needle swung over to the premolars of the Lingual nerve 2% lignocaine with 1:80,000 adrenaline. opposite side Subsequently, complete anaesthesia of Needle advanced further until bony contact is achieved as in the direct technique the inferior alveolar nerve was achieved Inferior alveolar Nervous patients Mouth closed within approximately two minutes. We nerve suspect the more superior positioning of Trismus or ankylosis Cheek retracted Lingual nerve the Akinosi technique delivered the local Large tongues Long (35 mm) 27 gauge needle anaesthetic solution closer to the man- Akinosi Puncture site: the retromolar mucosa, parallel to dibular foramen, although we cannot rule the maxillary occlusal plane to the level of the Superior position of maxillary mucogingival junction Long buccal nerve out the possibility that the anaesthesia mandibular fora- Advanced ~25 mm until the hub is at the level of men anticipated achieved was as a delayed effect of the the distal aspect of the upper second molar tooth direct technique nerve block. Surgical No bony contact end point removal of 48 was completed uneventfully. Inferior alveolar Mouth open wide nerve DISCUSSION Neck extended in a similar position to the palatal Lingual nerve injection The mandible is one of the most variable Mandible held in a similar fashion to the Inferior Long buccal nerve bones in the body. Geographically two of dental block the most variable measurements are the Two planes are imagined for needle orientation height (superoinferiorly) and the width 11 Alpha plane – passes through the corners of the Gow-Gates Superior position mouth and the lower border of the tragus of the ear (anteriorposteriorly) of the ascending (high man- of mandibular ramus.3 Dental nerve blocks are based on dibular block) foramen anticipated Beta plane – contains the tragus in its relationship with the side of the face. This assesses the diver- anatomic norms and statistical averages of gence of the mandibular ramus and the needle In some cases, should be parallel to this plane the auriculotem- nerve pathways and bone structure. Any poral nerve variation from the ‘average patient’ can Approach from the opposite corner of the mouth result in failed anaesthesia, as suggested Needle slide across the mesio-palatal cusp of the in our case study. Anatomic variations that maxillary second molar on the injection side 1 Puncture site: just distal to the maxillary second could predispose to IDB failure include: molar • A wide flaring mandible Extraoral palpation of the condyle • A wide ramus mandibularis in the Intraoral palpation of the angle between the anterior-posterior direction Modified coronoid process and the coronoid notch Same as conven- Gow-Gates At the level of the sigmoid notch, the needle • A long ramus mandibularis in the tional Gow-Gates technique17 penetrates the mucosa, tangent to the posterior superior-inferior direction border of the coronoid process, and is advanced • Bulky musculature or excess adipose toward the fingertip placed on the condylar head tissue until bony contact is achieved • An abnormal position of the mandibular foramen. foramen. The position of the mandibu- anteroposteriorly and two thirds of the lar foramen has been found to vary but way down a line joining the coronoid The case study discussed shows an is predominantly located on the medial process to the angle of the mandible.4 The abnormal position of the mandibular surface of the ramus, at a midpoint position changes in relation to the occlusal

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plane with age, for example, children having a lower position and older edentulous patients a higher position. A study of lateral cephalometric radiographs showed the mandibular foramen to be ~4 mm below the occlusal plane at 3-years-old, rising to the level of the occlusal plane at 9-years- old and to ~4 mm above the occlusal pane in adulthood.5 A dental panoramic tomograph can be Fig. 5 Akinosi technique demonstrated clinically. Observe the mouth closed position useful in predicting the site of the mandibular foramen. This factor alone is not justification for an exposure6 but if a radi- ograph has already been exposed then the information should be utilised. Occasionally, variations in the position of the mandibular foramen can be overcome Fig. 3 A left ¼ dental panoramic tomography demonstrating a superior position by subtly altering conventional approaches of the mandibular foramen. Anaesthesia was to dental local anaesthetic techniques. For achieved with a direct IDB technique with a example, a direct IDB technique with a slightly elevated point of entry slightly elevated point of entry was success- fully utilised to achieve local anaesthesia Fig. 6 Akinosi technique. Observe the position of the syringe parallel to the in the case shown in Figure 3, despite the maxillary occlusal plane and with the hub mandibular foramen clearly lying in a more adjacent to the distal aspect of the upper superior position than would normally be second molar tooth expected. However, in more extreme cases two further approaches, the Akinosi tech- hence intravascular injections, possibly nique and the Gow Gates technique, may due to the relatively avascular nature of be considered. the site which only has a few small vessels, The Akinosi technique, also known as in comparison to the pterygomandibular the Vazirani-Akinosi or the closed mouth Fig. 4 Akinosi technique. Observe the lack of triangle which has the inferior alveolar a bony contact technique, was first described in 1960.7 nerve, vein and artery and the pterygoid In a single injection, anaesthesia of the plexus.11,12 This reduced vascularity also inferior alveolar, lingual and buccal nerves nerve block techniques, the Akinosi tech- reduces the need for a vasoconstrictor,13 is achieved. This technique requires the nique does not rely on bony contact as the particularly useful when vasoconstrictor patient to have their mouth closed which end point. Rather the needle is advanced use should be limited due to medical con- forms a position of muscular and aponeu- until the hub is at the level of the distal ditions. Penetration of the medial ptery- rotic relaxation, permitting a nearly pain- aspect of the upper second molar tooth, goid muscle is avoided and hence incidents less injection to be made.8 The tissue is the needle having entered the tissues to a of post injection trismus are reduced.11,12 also of a rather loose areolar type in this depth of approximately 25 mm. For experienced operators high success area which allows for easy accommodation The Gow-Gates technique, also known rates have been achieved14 but for inexpe- of the solution without pain.8 It is useful as the high mandibular block, was devel- rienced operators high failure rates have with nervous patients, those with trismus oped in 1947 but not presented in the lit- been reported.15 This is likely to be due to or ankylosis and those with large tongues erature until 1973.10 In a single injection, difficulties with appropriate visualisation interfering with the standard direct or indi- anaesthesia of the inferior alveolar nerve, and alignment of the extraoral reference rect techniques. A lower incidence of posi- lingual nerve, long buccal nerve, possi- planes and the intraoral puncture points, tive aspirations has been reported with the bly the auriculotemporal nerve and other which have been described as ‘impossible’ Akinosi technique (2%) compared to the accessory nerves is achieved. The target by some authors.16,17 Zandi et al. describe standard technique (22%).9 area for deposition of local anaesthetic, a device that facilitates the Gow-Gates Figures 4, 5 and 6 demonstrate the in this technique, is the latero-anterior technique to unfamiliar practitioners to approach required. With the mouth closed surface of the condylar neck, just below achieve higher success rates.15 Shinagawa the dentist retracts the tissues of the cheek. the insertion of the lateral pterygoid mus- demonstrated an alternative Gow-Gates A long (35 mm) needle is advanced into cle. This local anaesthetic deposition site technique, with altered reference planes, the retromolar mucosa, parallel to the offers several advantages over the stand- which gives an effective injection site.17 maxillary occlusal plane but at a height ard technique’s deposition site, inside the The conventional and ‘altered reference coincident with the mucogingival junc- pterygomandibular triangle. There is a planes’ techniques are described in Table 1 tion. In contrast to other inferior dental lower incidence of positive aspirations and and illustrated in Figures 7 and 8.

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The success rates of these alternative techniques (Akinosi and Gow-Gates) are not significantly different to standard IDB techniques although the onset of pulpal anaesthesia is slower, due to the thicker nerve bundle at more proximal posi- tions.18,19 When specifically looking at irreversible pulpitis, the Gow-Gates technique has given significantly higher success rates compared to the standard IDB.20 The Akinosi technique and buccal-plus-lingual Fig. 7 Gow-Gates technique. Observe the deposition of the anaesthetic close to the Fig. 8 The Gow-Gates technique infiltrations technique had statistically head of the mandibular condyle demonstrated clinically similar success rates to the conventional IDB technique with irreversible pulpitis.20 There is no difference in pain on injection nerve just before the mandibular fora- anaesthetic techniques and are beyond the between standard IDB, Akinosi and Gow- men. However the position of branching scope of this publication. Local or ana- Gates techniques.18 is variable and the mylohyoid branch may tomically related complications can be As a point of interest, a further IDB tech- escape anaesthesia, especially with shield- divided into the following types: injuries nique is available which utilises an extra- ing from the pterygomandibular fascia and to blood vessels, trauma to muscles and cranial approach. This involves a point sphenomandibular ligament.25 If profound injuries to nerves. of entry inferomedial to the lower border anaesthesia is not achieved from an IDB The Akinosi and Gow-Gates techniques of the mandible just anterior to the angle then it may be necessary to provide an have a more superior anaesthetic depo- and via the sigmoid notch.2 However, this additional mylohyoid nerve block. To sition site than the standard IDB, with a approach is not recommended for den- achieve this, a simple infiltration of the closer proximity to the maxillary artery tists, with the risk of intracranial deposi- soft tissues over the distal lingual root and therefore an increased risk of vascu- tion of solution resulting from incorrect surface of the tooth requiring treatment lar injury. In order to decrease the risk of needle position. or just under the lingual mucosa in the intravascular injection an aspiration in Accessory innervation may also be a area of the tooth has been reported as two planes technique has been suggested.29 cause of failed local anaesthesia, particu- successful.26,27 An infiltration in the ret- Aspirating before and after rotating the larly of a mandibular molar. Sutton studied romolar area also achieves this effect and needle 45 degrees prevents the vessel wall the innervation of mandibular teeth and additionally anaesthetises any accessory occluding the needle tip, thus giving a listed the following as involved nerves: mandibular nerves entering the foramen more accurate aspiration. The temporalis mylohyoid, transverse cervical, facial, at the coronoid process. and medial pterygoid muscles are the most buccal, auriculotemporal, great auricular, The problem of accessory innervation commonly damaged during the standard posterior superior alveolar and lingual.21 is reduced when using the Gow-Gates IDB. The more superior position of the Studies into the presence of accessory technique because the local anaesthetic is Gow-Gates technique increases the possi- foramen in the mandible have shown deposited at a deeper site than the stand- bility of the lateral pterygoid muscle being that the average mandible has 36 fora- ard IDB technique and more proximally involved although, as previously men- men22 with the largest accessory foramen along the nerve. This allows the mandibu- tioned, incidents of trismus are reduced being located on the lingual surface in lar division of the trigeminal nerve to be due to avoidance of the medial pterygoid an area superior to the genial tubercles.23 anaesthetised before it separates into its muscle. Nerve damage following inferior Dissections and clinical studies have indi- branches and hence the accessory branches dental nerve blocks is rare, estimated to cated that the mylohyoid nerve may enter are anaesthetised. occur perhaps once in a full-time practi- some of these foramen to provide innerva- Alternative local anaesthetic techniques, tioner’s career.30 70% of these injuries are tion to the mandibular teeth22 and it has in addition to nerve blocks, include intra- to the lingual nerve and high concentra- also been shown that, other than the infe- ligamentary, intraosseous and intrapulpal tion solutions such as 4% articaine should rior alveolar nerve, the mylohyoid nerve techniques. More recently infiltrations be avoided.30 has the greatest incidence of involvement with articaine have become popular and of innervation of mandibular teeth.21 a buccal infiltration in the mandible has CONCLUSION The mylohyoid nerve is a mixed nerve been shown to be as effective as an IDB In the few situations where the standard providing motor innervation to the mylo- or able to achieve anaesthesia when an IDB technique fails to achieve sufficient hyoid and anterior digastric muscles and IDB fails.28 anaesthesia, alternative techniques such sensory innervation to the teeth and a Complications of delivering local anaes- as the Akinosi and Gow-Gates tech- small area of the chin, although this is thetic can be divided into general and niques can be utilised. They give effective highly variable.24 The mylohyoid nerve local. General complications, for exam- anaesthesia via a non-painful injection is usually anaesthetised during the IDB ple psychogenic reactions (for example, with some advantages over the standard as it branches from the inferior alveolar fainting), and toxicity relate to all local techniques, such as eliminating accessory

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