J. 0. AKINOSI, B.D.s., F.D.S.R.C.S.

Transcription

1 British Journal of Oral Surgery 15 ( ) A NEW APPROACH TO THE MANDIBULAR NERVE BLOCK J. 0. AKINOSI, B.D.s., F.D.S.R.C.S. Department of Oral Surgery and Pathology, College of Medicine, Lagos University, P.M.B , Lagos Summary. A new method for the block anaesthesia of the oral branches of the mandibular nerve is described. Only one penetration of the oral mucosa is made in this injection at a site which is relatively painless and which results in a more rapid onset of anaesthesia. This method is also of value when trismus or ankylosis is present and is free of common complications. Introduction Conventional methods for achieving an inferior alveolar nerve block are relatively easy. These techniques, however, rely on the presence and identification of certain anatomical landmarks such as the teeth, the mucosal elevation due to the pterygomandibular raphe and the apex of the buccal pad of fat. Difficulties may be experienced in edentulous patients, in cases where the raphe is not prominent and particularly in cases where opening is limited. Anatomical variations in the shape and size of the mandible may make accurate localisation of the mandibular fossa difficult. The width of the ascending rami and their divergance determine the position of the mandibular foramen and this varies from one individual to another. As a result of these variations coupled with operator-mediated errors, a failure rate of at least 5 per cent is to be expected when the conventional method is used (Bremer, 1952; Gow-Gates, 1973). Inaddition to the above, failure to achieve anaesthesia may be due to a number of other factors which include inadequate dosage of anaesthetic solution and the presence of supplementary innervations, which may together raise the failed inferior dental anaesthesia rate to over 15 per cent (Northop, 1949). As a result of these deficiences, various other methods which claim superiority over the conventional methods have been described for the inferior dental nerve injection (Gow-Gates, 1973; Cannel1 & Cannon, 1976; Rood, 1976). This communication describes a technique which is markedly less painful and which even though it cannot claim a higher efficacy rate over other methods is remarkable because of its ease of administration and the more rapid onset of anaesthesia, faster than in most methods as yet described. In addition, this method has the added advantage that it can easily be employed in cases in which the jaw opening is limited. Materials and Method The materials required for this injection are in no way different from those normally used for giving the inferior dental block injection. They include the standard cartridge syringe with a 27 g disposable long needle (about 3.5 cm or 13 in length) a cartridge of 2 per cent local anaesthetic solution containing 1: adrenaline, a pair of Spencer Wells artery forceps, a surface anaesthetic spray and a container and applicator for a suitable antiseptic solution. (Received 16 December 1976; accepted 14 January 1977) 83

2 84 BRITISH JOURNAL OF ORAL SURGERY FIG. 1. Young patient receiving the injection. Note the relaxed appearance. FIG. 2. Outline of area of lip and face which became numb following injection.

3 MANDIBULAR NERVE BLOCK 85 auriculotemporal n. inferior ahreolar n.. lingual n., FIG. 3. A schematic diagram showing the relationship of the main branches of the mandibular nerve and the relationship of the needle during injection. The patient is seated in a semi-reclining position with the head, neck and shoulders well supported. When the mouth is open, the pterygo-mandibular elevation of the oral mucosa can be easily identified extending from the retromolar area of the mandible upwards and backwards to join the tissues immediately posterior to the upper third molar. The cheek is then freely distended using the fingers of the left hand and the mucosa immediately buccal and distal to the upper third molar is wiped with a 0.5 per cent chlorhexidine tincture or any other suitable antiseptic. A few seconds later the area is dried and a small amount of a surface anaesthetic solution is sprayed into the area and in about one minute the patient is ready for his injection. The dentist stands in front and to the right of the patient. The teeth are closed to aid relaxation of the cheek muscles which are then well distended for good vision. The needle is positioned at the level of the maxillary marginal gingivae and with the barrel parallel to the maxillary occlusal plane, the syringe is then advanced and the needle then penetrates the tissues in the embrasure between the vertical ramus and maxillary tuberosity (Fig. 1). Between 2.5 cm and 3 cm of the needle is buried in the tissues at this site and about 1.5 cc to 2 cc of anaesthetic solution is slowly deposited. The needle at this point lies in the pterygo-mandibular space having passed through the buccinator muscle. It is in close relationship with the main branches of the mandibular nerve in this situation and are easily reached by diffusion of the anaesthetic solution. The needle is then slowly withdrawn. Results When correctly given, the patient experiences altered sensations in the tongue and lip from about 40 seconds after the injection and surgical anaesthesia is obtained in about 14 minutes. The anaesthesia involves the sensory divisions of the mandibular nerve excepting the auriculotemporal branch. The branches which are affected are the

4 86 BRITISH JOURNAL OF ORAL SURGERY inferior alveolar, the lingual and the long buccal nerves. The area of anaesthesia obtained is similar to that achieved when conventional methods are used (Fig. 2). Surgical anaesthesia is obtainable in the mandibular teeth from the third molar to the canine on the injected side and simple surgical procedures such as dental extractions and soft tissue surgery in the buccal or lingual sulcus as well as in the lower lip can be performed without pain. Of a total of 100 consecutive injections given to patients requiring routine mandibular extractions only seven were unsuccessful at the first attempt and of these, five were successful at the second attempt. This injection technique, which can be called the tuberosity approach to the mandibular nerve, is based on a knowledge of the anatomy of the pterygo-mandibular space. The lingual nerve passes upwards and backwards through the space a little in front of the inferior dental nerve. The two nerves are joined by the long buccal nerve which arises from the cheek and buccal mucoperiosteum and crosses the anterior border of the ascending ramus to traverse the upper part of the pterygo-mandibular space. In this upper part, the three trunks come to lie in close proximity suitable for simultaneous injection (Fig. 3). This technique of injection has many advantages over the old method. The patient is less likely to be apprehensive since the injection is not made into the throat and particularly as he is not required to open his mouth fully. The tissues in the retromolar area of the maxilla are rather lax when the mouth is in the semi-open or closed position and the penetration of the needle is, therefore, relatively painless. A further advantage is the rather loose areolar tissue deep in the space into which the solution is easily accommodated without pain. The average patient is rather afraid of injections particularly when several injections have to be given. The old method for the injection of branches of the mandibular nerve involves three separate manoeuvres one for each nerve and at least two separate needle pricks. The technique described here has the important advantage that only one prick of the needle is required together with a more rapid onset of analgesia. The dental surgeon should feel safer giving this injection since neither his equipment nor his finger lie between the patient s teeth and are, therefore, unlikely to be bitten should the patient suddenly find himself in a mood for vengeance. The conventional technique is often unsuitable for anaesthetising the area of the lower third molar particularly in the presence of acute alveolar abscess or a pericoronitis in this area. This is because inflammatory changes may extend to the injection site and trismus may be present limiting adequate mandibular opening. The use of the tuberosity approach would allow surgical procedures to be carried out in these circumstances. Last, but by no means least of the advantages, is the relative safety of the needle in this area from the danger of fractures. Difficulties may be experienced with this method when either a deformity exists or a tumour is present in the area of the maxillary tuberosity. The absence of teeth in the upper quadrant may also create some problems, but this can always be overcome by the utilisation of the alveolar ridge in place of the gum margin. When dealing with children, short needles (3.175 cm) should be used. This technique has not been found reliable in children as it has been in adults, but this may be due to the difficulty experienced in estimating the depth to which the needle should penetrate in the growing child. Although this injection has been in use in our clinic for over four years, not a single significant complication has so far been recorded. Post-anaesthetic infection has not

5 MANDIBULAR NERVE BLOCK 87 occurred in any of our cases. This may be explained by the relative cleanliness of the tuberosity area when compared with the corresponding mandibular site. Acknowledgements I thank Mrs T. M. Lawal for her secretarial assistance, the staff of the Medical Illustration Unit, Lagos University Teaching Hospital, for the photographs and the Medical Artist, London Hospital Dental School, for Figure 3. Bremer, G. (1952). Oral Surgery, Oral Medicine, Oral Pathology, 36, 321. Cannell, H. & Cannon, P. D. (1976). British Dental Journal, 141, 48. Gow-Gates, G. A. E. (1973). Oral Surgery, Oral Medicine, Oral Pathology, 36, 321. Northop, P. M. (1949). Journal of the American Dental Association, 38, 444. Rood, J. P. (1976). British Dental Journal, 140, 413.