Ireland's Dental Magazine October 2015

Local anaesthetics

Comfortably numb L

ocal anaesthetics interrupt neural conduction by inhib- iting the influx of sodium ions through channels within neuronal membranes. When

the neuron is stimulated, the channel is activated and sodium ions can diffuse into the cell triggering depolarisa- tion. Following this sudden change in membrane voltage, the sodium channel assumes an inactivated state and further influx is denied while active transport mechanisms return sodium ions to the exterior. After this repolarisation, the channel

assumes its normal resting state. Local anaesthetics have the greatest affinity for receptors in the sodium channels during their activated and inactivated states rather than when they are in their resting states2.

PHARMACOLOGY Local anaesthetics consist of three components which contribute necessary clinical properties: • Lipophilic aromatic ring – improves lipid solubility of the compound

• Intermediate ester/amide linkage • Tertiary amine.

Articaine consists of an amide group and an ester link. It has a thiophene ring instead of a benzene ring as seen in the chemical structure of lignospan. The thiophene ring improves it’s lipid solubility. Articaine therefore in some studies shows better potential for penetrating through the neuronal sheath and membrane when compared with other local anaesthetics3.. The dissociation constant of an anaesthetic affects its onset of action. The lower the pKa values, the greater the proportion of uncharged base molecules can diffuse through the nerve sheath. Articaine has a pKa of 7.8, wheras lignospan has a pKa of 7.9. This proves important when a local anaesthetic is administered to anaesthetise inflamed tissues, where the ph of the tissues is reduced4

. Articaine has a half-life of 20 minutes, whereas lignospan 24 Ireland’s Dental magazine

has a half-life of 90 minutes. Therefore, articaine presents less risk for systemic toxicity during lengthly dental treatments when additional doses of anaesthetic are administered5

.

COMPARISON BETWEEN ARTICAINE AND LIGNOSPAN Some studies argue that there is no

significant difference in pain relief provided by 2 per cent lignospan and 4 per cent articaine where both formulations contain adrenaline6

. However,

a recent systematic review demonstrated a different conclusion7

. This review

showed that when considering successful infiltration anaesthesia, 4 per cent articaine solution containing adrenaline was almost four times greater than a similar volume of 2 per cent lignospan also containing adrenaline. Other studies have stated that 4 per cent articaine offers superior levels of anaesthesia in the anterior maxillary region when compared to 2 per cent lignospan, however this level of superiority appears less significant in the maxillary molar region8

.

There is evidence to support that articaine is more effective in the maxillary posterior region when compared with lignospan when tissues are inflamed9

.

However, there is insufficient evidence to suggest a similar level of superiority for mandibular teeth, where the solution has been administered with the inferior alveolar nerve block techniqueı0

. The additive administration of lignospan

using the IANB technique and buccal infiltration with articaine could potentially increase the level of pulpal anaesthesia achieved in the mandibular molar and premolar areaıı

in 4 per cent articaine is considered critical in achieving it’s profound anaesthesiaı2 Brandt et al demonstrated that articaine was superior when administered using the

. The Wand

Dr Laura Fee explores the controversies surrounding local anaesthetics and the medically complex patient

inferior alveolar nerve block technique (IANB)7

. However, it must be stressed that

the potency of the agent administered via the inferior alveolar block was considerably lower than the potency administered by the infiltration technique. It was shown that neither articaine or lignospan demonstrated superiority over the other when administered to symptomatic teeth. It is important to recognise the limitations in this study of comparing a 4 per cent solution of articaine with a 2 per cent solution of lignospan7

.

Other studies also reported no difference between articaine and lignospan when using the IANB technique while treating symptomatic teethıı-ı3

Interestingly, it has been demonstrated that 4 per cent articaine with ı:ı00,000 adrenaline administered using the buccal infiltration technique had

a significantly faster onset of pulpal anaesthesia when compared with the inferior alveolar nerve block. Therefore, dentists can consider the use of articaine administered by a buccal infiltration as an alternative to the inferior alveolar nerve block when anaesthetizing the mandibular first moları4

. Another study

also concluded that articaine delivered by buccal infiltration alone was more effective than lignospan administered by the inferior alveolar technique when anaesthetising mandibular first molar teethı5

.

PARAESTHESIA In 20ı0, Garisto et al reported 248 cases of paraesthesia after dental treatmentı6

. The inclusion of adrenaline .

.

Most cases involved mandibular nerve blocks and, in 89 per cent of cases, the lingual nerve was damaged. paraesthesia was shown to be 7.3 times more likely with 4 per cent articaine when compared with lignospan. Similar findings were reported by Hillerup et al who demonstrated greater neural toxicity of 4 per cent compared to

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