does not interfere with the ability to aspirate blood, but it is worth noting that narrow
needles are more likely to penetrate blood vessels than their wider counterparts.
The choice of syringe used for conventional local anaesthetic injections in children
must allow aspiration both before and during injection. There is evidence that
inadvertent intravascular injection is more likely to occur in younger patients. Positive
aspirate incidences of 20% of inferior alveolar nerve block injections in the 7-12 year
age group have been reported.
One aspect of local anaesthetic delivery that can contribute to discomfort is the speed
of injection. The use of computerized delivery systems such as 'The Wand' permits
very slow delivery of solution (180HFig. 5.8). This is particularly useful when injecting
into tissue of low compliance such as the palatal mucosa and periodontal ligament.
When using conventional syringes the choice of anaesthetic cartridge can also
contribute to the discomfort experienced during injection. The type of cartridge used
should be one that allows depression of the rubber bung at a constant rate with a
constant force. Cartridges that produce a juddering action should not be employed.
181H
Fig. 5.8 The Wand computerized
injection system, which permits slow
delivery of solution.5.6.2 Materials
In the past, heating the contents of local anaesthetic cartridges to body temperature
prior to injection has been advised. There is no sound basis for this recommendation.
There is ample evidence to suggest that patients cannot differentiate between local
anaesthetics between room and body temperature. Indeed, storage of cartridges at
higher temperatures can be detrimental to the solution as this can increase the chances
of bacterial contamination, decrease the activity of epinephrine (adrenaline) in the
solution due to increased oxidation, and finally decrease the pH of the solution (see
further). Cartridges stored in a refrigerator should be allowed to reach room
temperature before use. The pH of the injected solution may affect the discomfort of
the injection. Local anaesthetic solutions vary in their pHs, those containing
vasoconstrictors having lower values. For example, 2% plain lidocaine (lignocaine)
has a pH of 6.8 compared with pH 3.2 for 2% lidocaine with 1 : 80,000 epinephrine
(adrenaline). Thus if minimal sensation is to be produced it may be worthwhile using
a small dose of a plain solution as an initial injection before using a vasoconstrictor-
containing solution as the definitive local anaesthetic.
5.6.3 Techniques
Posterior maxillary buccal infiltrations