Fundamentals of technique The importance of a quiet, confident, and friendly manner towards all patients so physical comfort is also essential for the co-operation of the patient and the ease of operation of the dental surgeon. The patient should be seated in a semi-reclining position with the back and legs supported and with head rest in the nape of the neck. Most adult patients will respond to the dental surgeon's endeavors to gain the patient his or her confidence and so premedication will not be required for the administration of a local anaesthetic for a relatively simple procedure. Types of local anaesthesia For descriptive purposes it is convenient to sub-divide local anaesthesia on an anatomical basis into topical, infiltration, and regional techniques. Topical or surface anaesthesia: is obtained by the application of a suitable anaesthetic agents to an area of either skin or mucous membrane which it penetrates to anaesthetize superficial nerve-ending. It is most commonly used to obtain anaesthesia of mucosa prior to injection. Spray: containing an appropriate local anaesthetic agent are particularly suitable for this purpose because of their rapidity of action. The active ingredient is 10% lignocaine hydrochloride. When used as a spray it is very easy to spread the solution, and its effect, much more extensively than is desired. The onset time of anaesthesia is about 1 minute and the duration round about 10 minute. Ethyl chloride: when sprayed on skin or mucosa volatilizes to rapidly produces anaesthesia by refrigeration. This phenomenon is of clinical value only when spray directed at a limited area until snow appears.\This technique is of limited value is occasionally used to produce surface anaesthesia prior to incision of a fluctuant abscesses. Fig. 1 Fig. 1 1 Ointment: containing 5% lidocaine hydrochloride can be used for a similar purpose but take 3- 4 minutes to produce surface anaesthesia. Amethocaine and benzocaine are included in ointments are particularly useful when applied to tender gingivae prior to deep scaling. An emulsion: containing 2% lignocaine hydrochloride is also available. It is useful when taken an impression and following a gingivectomy. One teaspoonful should be used round the mouth and oro-pharynx for 1-2 minute and any excess spat out immediately and is quite safe if swallowed. Jet injection : is a technique in which a small amount of local anaesthetic solution is propelled as a jet into the sub-mucosa without the use of a needle. Fig. 2 Fig. 2 Infiltration anaesthesia Anaesthetic solution deposited near the terminal fibers of any nerve will infiltrate through the tissue to reach the nerve fibers and thus produce anaesthesia of a localized area served by them. Fig. 3 Fig. 3 2 This infiltration technique is subdivided into: A. Sub-mucous injection: in this technique the solution is deposited just beneath the mucous membrane. Whilst this is unlikely to produce anaesthesia of the dental pulp it is often employed either to anaesthetize the long buccal nerve prior to the extraction of teeth or for soft tissue surgery. B. Supra-periosteal injection: in some sites, such as the alveolar processes of maxilla the outer cortical plate is thin and perforated by tiny vascular canals as cancellous bone. In these areas when anaesthetic solution is deposited outside the periosteum, it will infiltrate through the periosteum, cortical plate, and medullary bone to the nerve fibers. By this means anaesthesia of the dental pulp can be obtained by injecting along side the approximate position of the tooth apex. The supra-periosteal injection is the technique most frequently used in dentistry. Fig. 4 Fig. 4 C. Sub-periosteal injection: In this technique the anaesthetic solution is deposited between injection is painful. D. Intra-osseous injection: in this technique the solution is deposited within the medullary bone. The procedure is carried out by the use of bone drills and needles especially designed. After giving the ordinary way anaesthesia a very small incision is made through the muco-periosteum at the chosen site of injection to provide access for the introduction of a bur or fine reamer. A small hole is made through the outer cortical plate of bone. It must be near the apex of the tooth concerned without damage to the root of the tooth. Fig. 5 3 Fig. 5 E. Intra-septal injection: This modified version of the intra-osseous technique is sometime when difficulty in gaining complete anaesthesia, or when an immediate denture is to be fitted and supra-periosteal techniques are best avoided. Fig. 6 Fig. 6 Regional (block) anaesthesia Anaesthetic solution deposited near a nerve trunk will, by blocking all impulses, produce anaesthesia of the area supplied by that nerve. Although this technique may be used in maxilla and mandible. The used of infiltration technique in mandible is unreliable due to the density of the outer cortical plate of bone. By placing the anaesthetic solution in the pterygomandibular space near the mandibular foramen, regional anaesthesia over the whole distribution of the inferior alveolar nerve on that side is obtained. Fig. 7 4 Fig. 7 Periodontal ligament technique Nerve anaesthetized terminal nerve endings at the site of injection at the apex of the tooth. The bone, mucosa, apical, and pulpal tissue in the area of injection. Indication: 1. Pulpal anaesthesia of 1-2 teeth. 2. Situation in which regional block are contraindicated. 3. Aid in the diagnosis of pulpal discomfort. 4. As an adjunctive technique following nerve block if partial anaesthesia is present. Contraindication: 1. Infection or acute inflammation in the area of injection. 2. Patient who requires sensation for psychological comfort. Advantages: 1. Avoid anaesthesia of lip tongue and other soft tissues. 2. Minimum dose of local anaesthesia is required. 3. Rapid onset of profound pulpal and soft tissue anaesthesia. 4. Less traumatic than conventional block technique. Disadvantages: 1. Excessive pressure or rapid injection may break the glass cartridge. 2. A special syringe may be required. 3. Excessive pressure can produce focal Technique: 1. A 27 gauge short needle recommended. 2. Area of insertion: the long axis of the tooth to be treated on its mesial or distal of the root. 3. Target area: is the depth of gingival sulcus. 5 Intrapulpal injection This technique is used when pain control is required for pulp extirpation in the absence of adequate anaesthesia from other techniques. Techniques of maxillary anaesthesia The oral cavity is one of the most sensitive parts of the body. Sensory nerve-endings are present in the dental pulp, the periodontal ligament, the alveolar bone, the muco-periosteum, and the mucous membrane. There are several methods of obtaining local anaesthesia. The type of local anesthesia and the dose is depended on two factors are the site of deposition of the drug and the operative intervention, so all type of topical anaesthesia, all type of infiltration injection, infra-orbital nerve block injection, posterior superior alveolar nerve block injection, periodontal ligament injection, and rarely used anterior superior and middle superior alveolar nerve block injection. The maxilla can be divided to three area anterior, middle and posterior area. Fig. 8 Fig. 8 Anaesthesia of the permanent anterior teeth The central, lateral incisor, and canine teeth are innervated by the anterior superior alveolar nerve. These teeth may be anaesthetized together with their supporting tissues and muco- periosteum by infiltration injection by depositing about 1ml. of local anaesthetic solution near the apex of tooth concerned. The ease with which the floor of the nose may be penetrated due to miscalculation of the length of the root or the depth of the labial sulcus. Fig.9 6 Fig. 9 The infra-orbital block injection: since infiltration injections are so effective in the maxilla, block injection is seldom required. However, the infra-orbital block injection may be of value if numerous extractions or extensive surgery are to be undertaken in the anterior teeth regions. It may also be employed for anaesthetizing an anterior teeth where the used of infiltration injections are precluded by the presence of infection at the site of injection. This technique is based upon the fact that solution deposited at the orifice of the infra-orbital foramen pass along the canal to involve both the anterior and middle superior alveolar nerves thus producing anaesthesia of the incisor, canine, and premolar teeth and their supporting structures. Either an intraoral or extraoral approach may be employed for the infra-orbital block. The intraoral technique is more popular and allows the needle to kept out of the patient's sight. Technique: The infra-orbital ridge is palpated and the infra-orbital notch located with the tip of the 1st finger, which is then moved slightly downwards to lie directly over the infra-orbital foramen. With the finger-tip maintained in that position the thumb reflects the upper lip and expose the site of injection which the tip of long needle is inserted just above the reflection of the mucous membrane over the apex of the 2nd premolar. The needle is advanced in line with the long axis of the 2nd premolar to a depth of 1.5-2 cm, where the correct position of the tip of the needle overlying the foramen is confirmed when the injection of solution is felt beneath the fingertip. The deposition of 1 ml suffices in most instances. Fig. 10 7 Fig10 Anaesthesia of the premolar teeth The mesio-buccal root of the 1st molar, both premolars, and the buccal supporting tissues and muco-periosteum related to them are innervated via the middle superior alveolar nerve. Infiltration techniques are usually employed to anaesthetize these structures. Deposition of 1 ml of solution suffices to anaesthetize the both premolars teeth but may not be adequate for the 1st molar because the buccal bone of the zygomatic process is dense and is perforated by comparatively few vascular canals.