Local anaesthesia is frequently used in dentistry and seldom leads to serious local complications. Nevertheless, it is of great importance to be aware of the causes of each local complication and – if necessary – to implement correct treatment. The patient must be informed extensively and, if necessary, be reassured. The incident must also be recorded in detail in the patient’s file. This is especially important if there is a chance of prolonged or even permanent symptoms.
9.1 Needle breakage
Since the introduction of modern disposable needles, needle breakage is a rare complication. Nevertheless, even these needles have a small chance of breaking, especially with mandibular block anaesthesia and tuberosity anaesthesia. This risk increases if the needle is repeatedly bent to facilitate the entrance into the area to be injected. The unexpected movements of a scared patient, such as a sudden jerk of the head, grabbing or moving away the dentist’s hand or suddenly closing the mouth, can also lead to this serious complication. Changing the direction of an incorrectly inserted needle also increases the risk of needle breakage. In such a situation, it is sensible to pull back the needle almost completely and then insert it again in the correct direction.
If the needle does break and the proximal part of the needle is still sticking out of the mucosa, the end may be taken with tweezers or mosquito artery forceps and cautiously removed. However, if the broken part of the needle is no longer visible the patient must be referred quickly to an oral and maxillofacial surgeon in a well-equipped hospital (Box 9.1). In the meantime, the patient must be instructed not to talk and to swallow as little as possible, since such movements may allow the needle to move deeper into the tissues.
- Try to remove the needle with a fine haemostat.
- Mark the place of insertion of the needle with a waterproof marker.
- Inform the patient and advise to avoid jaw movements.
- Contact the oral and maxillofacial surgeon immediately.
- Contact your defence union and discuss the case with colleagues.
- Arrange immediate assessment of the patient.
- Arrange immediate radiographic examination (OPG and CT-scan).
- Discuss treatment modalities with the patient, parent or carer.
- Arrange surgical exploration.
9.2 Pain during administration
Even during a calm and slow injection, the patient sometimes feels some discomfort or a burning sensation when the needle is introduced through the soft tissues. An increase in tissue pressure from injecting too quickly or injecting a too-large volume is unpleasant for the patient and must of course be avoided. A pronounced pain sensation is, however, usually the result of unintentionally pricking an anatomical structure, e.g. a tendon or muscle, the periosteum, a nerve or blood vessel.
Pricking the periosteum is usually the result of an incorrect position of the bevel of the needle. The bevel should be placed parallel to the bone surface, to avoid the sharp point of the needle pricking the tight and highly innervated periosteum and tearing it away from the underlying bone. During the administration of mandibular block anaesthesia the inferior alveolar nerve or the lingual nerve can be inadvertently touched. The patient will experience this as a shot of pain or a sensation like an ‘electric’ shock in the lower jaw or the tongue and will react by suddenly pulling away the head. If this occurs, the needle must be pulled back slightly and, if necessary, the direction of insertion must be altered before injecting the anaesthetic fluid. Such contact of the needle with a nerve does not automatically mean that sensation disorders will occur, but the patient must be informed of the possibility and, if necessary, should be regularly checked. It is good to realise that the occurrence is not an indication of a poor injection technique, but simply a risk that is inevitably related to the administration of block anaesthesia.
A shot of pain may also occur if the artery wall is touched, resulting in the phenomenon of ‘blanching’ (see Section 9.7).
9.3 Insufficient anaesthesia
The most prevalent causes of failure of local anaesthesia are an incorrect injection technique and an injection into inflamed tissue or a blood vessel. For maximal anaesthesia, the anaesthetic fluid must be deposited near the nerve or, in infiltration anaesthesia, as close as possible to the bone surface in the apex region of the element that is to be anaesthetised. In the case of block anaesthesia in the lower jaw, the vertical aspect of the position of the mandibular foramen must be taken into account. If the direction of the needle is too low and the anaesthetic fluid is injected below the level of the foramen, there will be no anaesthetic effect, partly due to the effect of gravity. If infiltration anaesthesia is given in an inflamed area, the local anaesthetic will be less effective due to the lower pH of the tissue. In that case, adequate anaesthesia can be achieved by infiltration at a distance or by block anaesthesia.
During the insertion of the needle it is important to take care that the slanted part of the needle (the ‘bevel’) points to the tooth that is to be anaesthetised. Otherwise the fluid will move in the wrong direction, to a place far from its goal. Since diffusion must occur over a larger distance, this could lead to insufficient or even lack of anaesthesia. The same applies if the anaesthetic fluid is deposited in a muscle due to incorrect position of the needle. In that case, diffusion of the fluid is also hindered by the barrier of muscle tissue. An intravascular injection, resulting in injection of local anaesthetic into the bloodstream, is another cause of insufficient anaesthesia. A diffusion problem caused by a local haematoma can also play a role here. Less frequent causes are individual anatomical variations, for example, in the density of the cortical bone or divergent nerve pathways. A good example of the latter is an occasional accessory branch of the inferior alveolar nerve that first runs ventrally and the/>