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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 11  »  Supplementary routes to local anaesthesia
Supplementary routes to local anaesthesia
Routes for local anaesthesia.

J. G. Meechan
The Dental School, University of Newcastle upon Tyne, Newcastle upon Tyne, UK.

Routes for local anaesthesia.
Successful local anaesthesia is the basis for many aspects of dental treatment. One of the problems with local anaesthesia is that it is not 100% successful at the first attempt. Kaufman et al. (1984) reported that 13% of general practitioners experienced failure of local anaesthesia in a 5-day period resulting in up to 10% of treatments having to be abandoned. The most common failures were inferior alveolar nerve blocks. Similar findings amongst dental students have been reported (Milgrom et al. 1984). Unsuccessful local anaesthesia is perhaps most apparent in the management of endodontically involved teeth (Cohen et al.1993). Fortunately, when local anaesthesia fails, this can be managed effectively in most cases. This may involve modification of conventional techniques to overcome anatomical problems such as variations in the location of the mandibular foramen (Afsar et al.1998); for example, the use of ‘high’ blocks such as the Gow-Gates (1973) or Akinosi (1977) techniques (Fig. 1). These latter methods also help to counter any accessory nerve supply from sources such as the mylohyoid nerve which may not be anaesthetized by standard approaches (Wilson et al. 1984, Heasman & Beynon 1986). However, there are other methods which are also useful in overcoming failure in both jaws. This paper describes supplementary intraoral techniques available for administering local anaesthetics to provide pulpal anaesthesia when conventional infiltration and regional block methods prove unsatisfactory.

Figure 1. The Akinosi approach to the inferior alveolar nerve can help overcome problems owing to an ectopic mandibular foramen and collateral supply from other nerves leaving the main branch at a high level (illustration reproduced by kind permission of Oxford University Press).

The Akinosi approach to the inferior alveolar nerve can help overcome problems owing to an ectopic mandibular foramen and collateral supply from other nerves leaving the main branch at a high level

Intraligamentary (periodontal ligament) anaesthesia.
Intraligamentary anaesthesia or periodontal ligament anaesthesia are, in a sense, misnomers. Solution injected via the periodontal ligament reaches the pulpal nerve supply by entering the cancellous bone through natural perforations in the socket wall, not by traveling down the length of the ligament (Fig. 2). Thus, this method is a form of intraosseous anaesthesia. However, the term intraosseous anaesthesia refers to a specific method that is described below.

Figure 2. Intraligamentary and intraosseous anaesthesia deliver anaesthetic into the cancellous space by different routes.

Intraligamentary and intraosseous anaesthesia deliver anaesthetic into the cancellous space by different routes

Prior to the injection, it is recommended that the site of penetration is swabbed with an antiseptic solution. The injection can be performed using either conventional or specialized syringes. The choice of syringe does not affect efficacy (Malamed 1982, Smith et al. 1983).
The needle is inserted at 308 to the long axis of the tooth at the mesio-buccal aspect of the root(s). The needle is forced to maximum penetration until it is wedged between the tooth and the crestal bone, advancement deep into the periodontal ligament is usually not possible (Dreyer et al. 1983). Success is independent of needle gauge (Walton & Abbott 1981, Malamed 1982, Smith et al. 1983). Some authors recommend that the needle bevel should face the alveolar wall (StatusReport 1983) as this reduces the chances of blockage and increases the efficacy of the injection (Kim 1986). On the other hand, Malamed (1997) claims that the orientation of the needle is unrelated to the success of the technique and advocates that the bevel should face the root as this allows easier advancement of the needle. Yet another recommendation is to advance with the bevel facing the root, and then rotate the needle, so that the bevel is facing the bone during the injection (Sykes 1991). Once the needle is correctly positioned, the solution is injected under back-pressure. The amount of solution injected into the periodontal ligament is little. It is recommended that 0.2 mL solution is deposited into the periodontium of each root (Malamed 1997), however, this is simply a recommendation and whether or not this is the optimum volume has not been evaluated. When using the specialized syringes, it is important to maintain the needle in position for about 5-10 s following depression of the lever to allow escape of solution from the cartridge (Roberts & Rosenbaum 1991). Removing the needle from the periodontal ligament too soon will result in loss of solution from the cartridge into the mouth. Walton & Abbott (1981) demonstrated that the most critical factor governing success of the technique is that the injection is performed against resistance. Rapid onset of anaesthesia is a striking feature of intraligamentary anaesthesia. Anaesthesia is achieved within 30 s and can be immediate (Walton & Abbott1981, Khedari1982, Kaufman et al.1983, Status Report 1983).

Duration of intraligamentary anaesthesia.
The duration of intraligamentary anaesthesia is variable. Kaufman et al. (1984) noted the differences in duration between individuals was marked (for example, with lidocaine and 1: 50 000 adrenaline pulpal anaesthesia ranged from 0 to 67 min). Cowan (1986) estimated the duration of pulpal anaesthesia to be around 15 min for single-rooted teeth and rather less for lower molars. Kaufman et al. (1983) reported that the duration of anaesthesia following intraligamental injections was sufficient for cavity preparation, pulpectomy and extractions but some advanced restorative procedures required a second injection after 10-15 min.

Spread of intraligamentary anaesthesia.
Intraligamentary anaesthesia is not a single tooth anaesthetic (Kim 1986). Smith & Walton (1983) have shown that in dogs, solutions injected into the periodontal ligament of one tooth reach the periapical region and pulps of adjacent teeth. D’Souza et al. (1987) found that the spread of anaesthesia to adjacent teeth in humans occurred with both specialized and conventional syringes but that it happened more frequently with the former type. Schleder et al. (1988) reported that spread to adjacent teeth was dependent upon the solution injected, 2% lidocaine with 1:100 000 adrenaline anaesthetizing a greater number of adjacent teeth than plain mepivacaine and lidocaine solutions, a finding confirmed by White et al. (1988).