Definition:

Local anaesthesia is defined as a loss of

sensation in a circumscribed area of the

body caused by a depression of

excitation in nerve endings or an

inhibition of the conduction process in

peripheral nerves.

Desirable properties of LA

• Should not be irritating to the tissues to which it is applied

• Should not cause any permanent alteration of nerve

structure

• Systemic toxicity should be low

• Time of onset of anaesthesia should be as short as possible

• The duration of action must be long enough to permit

completion of the procedure yet not so long to require and

extended recovery

• Should be free from producing allergic reactions

• Should be stable in solution and readily undergo

biotransformation in the body

Composition of local

anaestheticsLocal anaesthetic agent:Lignocaine Hydrochloride-2%(20mg/ml)

Reducing agent:Sodium meta-bisulphite-(0.5mg)

Preservative:Methylparaben-0.1%(1mg)

Diluting agent:Distilled water

Fungicide:Thymol

Isotonic solution:Sodium chloride or Ringer’s Solution-6mg

Vasoconstrictor:adrenaline-1:80,000(0.012mg)

To adjust pH-Sodium hydroxide

Nitrogen bubble-1-2mm in diameter and is present to prevent oxygen from being trapped in the cartridge and potentially destroying the Vasopressor.

Actions of :

Vasoconstrictor:Decreased blood flow to the site of injection,absorption of L.A by cardiovascular system is solved,decrease the risk of local toxicity,higher volume of local anaesthetic agent remain in and around the nerve for longer period,thereby increasing the duration of action,vasoconstrictor decreases bleeding at the site of their administration.

Preservative:Stability of modern L.A is maintained by adding caprylhydro-cuprienotoxin which includes xylotox and methyl paraben.

Reducing agent:These act as preservatives for the vasoconstictoragents.Vasoconstrictors are unstable in solution and may oxidize,especially on exposure to prolonged sunlight.Sodiummetabisulphite which competes for the available oxygen is added in the concentration between 0.05% and 0.1%

Vehicle:The isotonic vehicle reduces discomfort during injection.

B.R.I.T:

Bi-Rotational Insertion

Technique:

The operator rotates the needle in a back-

and-forth rotational movement while

advancing the needle through the tissues;

results in less deflection, less force is needed

for needle penetration.

Dosages:

To calculate the recommended dose,the

following must be known:

Concentration of the L.A

Dilution percentages of vasoconstrictors

Standard cartridge volume

Maximum recommended dose

Patients weight and general health

status,including medications.

Maximum recommended

doses:

Lignocaine hydrochloride with

epinephrine:7mg/kg

Articaine:6.4mg/kg

Bupivicaine:6.66 mg/kg

A 100% solution has 1000mg of L.A per ml.Therefore a 2% solution has....

20mg/ml

A cartridge of 2ml,therefore has 40mg of L.A.

M.L.D for lignocaine hydrochloride is 7mg/kg.

For a 70kg man,the maximum dosage of L.A he can recieveis-7*70kg =490mg.

In 1 cartridge there is 2ml of L.A which contains 40mg of L.A,therefore the number of cartridges needed to achieve maximum lethal dose is 12.25 cartridges.(490*1/40)

Anatomical considerations

Branches of maxillary nerve:

Injections used to anaesthetize

the maxillary teeth,soft and

hard tissues:Infiltration(supraperiosteal injection)

Posterior superior alveolar nerve block(PSA)

Middle superior alveolar n.b(MSA)

Anterior superior alveolar n.b(ASA)(Infraorbitalnb)

Greater palatine nb

Nasopalatine nb

2nd division nb(maxillary nb)

Anterior middle superior alveolar nb(AMSA)

Palatal-(PASA)

Infiltration:

Infiltration is a technique used to

achieve pulpal anaesthesia for one or

two maxillary teeth at a time.

The area anaesthetised are the

pulp,bucal soft and hard tissues of the

anaesthetised teeth.

Recommended needle-27 gauge short

Technique:

Site of insertion-Height of the

mucobuccal fold,at the apex of the tooth.

The needle is inserted parallel to the

maxillary bone and inserted till the

needle tip is at or above the apex of the

root.

After two negative aspirations,1/3rd of a

cartridge of L.A is injected.

Posterior superior alveolar

nerve block(PSA

Provides pulpal anaesthesia to the three

maxillary molars and supporting buccal

soft tissue and bone.

In 28% of patients,the mesiobuccal root

of the maxillary first molar is not

anaesthetised by this technique.

Recommended needle-27 gauge short.

Technique:

Site of insertion-Height of the buccalfold,adjacent to the maxillary second molar,with the syringe held in an upwards,inwards and backwards direction,and inserted to a depth of 16mm

After two negative aspirations,1/2 a cartridge of L.A is injected,over 30 seconds.

Middle superior alveolar

n.b(MSA)

Provides pulpal anaesthesia to the

maxillary premolars and the

mesiobuccal root of the maxillary first

molar,and supporting buccal soft and

hard tissues.

Recommended needle-27 gauge short.

Technique:

Site of insertion-Height of the buccal

fold,adjacent to the maxillary second

premolar.Needle is inserted till its tip is

located way above the apex of the

second premolar.

After 2 negative aspirations,1/2 a

cartridge of local anaesthetic is slowly

injected.

Anterior superior alveolar

n.b(ASA)(Infraorbital nb)

Provides pulpal anaesthesia to five

maxillary anterior teeth-The

incisors,canine and two premolars,and

also anaesthetises the buccal

supporting soft tissue and bone,the skin

of the lower eyelid,the lateral side of the

nose,upper lip.

Recommended needle-25 gauge long.

Technique:

The infraorbital foramen is palpated,lipretracted,the needle is inserted at the height of the buccal fold,adjacent to the maxillary first premolar.

The needle is held parallel to the maxillary bone and inserted till bone is contacted at the roof of the infraorbital foramen.

After 2 negative aspirations,1/2-1/3rd of a cartridge is deposited over 30-40 seconds.

Greater palatine nb(Anterior

palatine nb)

Provides anaesthesia to the posterior

portion of the hard palate and its

overlying soft tissues extending

anteriorly as far as the first premolar and

medially to the midline.

Recommended needle-27 gauge short

Technique:

The greater palatine foramen is palpated(cotton swab may be used for this),the needle is inserted into the soft tissue,just anterior to the greater palatine foramen.

As the needle is advance,L.A is deposited slowly,upon contacting bone,1/4th-1/3rd a cartridge of L.A is deposited,over 15-20 seconds.

Nasopalatine nb

Provides anaesthesia to the anterior

portion of the hard palate,affecting both

soft and hard tissues,from the mesial of

the right first premolar to the mesial of

the left first premolar.

Technique:

Traditional-The needle is inserted,just lateral to the incisive papilla,advanced till bone is contacted,after 2 negative aspirations,0.3 ml of L.A is deposited.

Multipl injection technique-1st injection is an infiltration of 0.3ml to the labial soft tissues between the central incisors.2nd injection is an infiltration to the now limp papilla between the two central incisors.L.A is administered as the needle is advanced,until blanching is noted on the palatal soft tissues.3rd injection is a traditional Nasopalatine nb.

2nd division nb(maxillary nb)

Provides anaesthesia to the pulp of the

teeth of that side of the maxilla,

supporting hard and soft buccal tissues,

the soft tissues and bone of the hard

palate and some of the soft palate

medially till the midline, the skin of the

lower eyelid, lateral side of the nose,

cheek,upper lip.

Recommended needle-25 gauge long.

Technique:

The needle is inserted into the greater

palatine foramen,and advanced to a

depth of 30mm.After 2 negative

aspirations,1.8ml of L.A is deposited

slowly over at least 60seconds.

Anterior middle superior

alveolar nb(AMSA)

Provides pulpal anaesthesia to the

incisors,canine and premolars of that

side,buccal soft tissue and bone,palatal

soft tissue and bone.

Recommended needle-27 gauge short

Technique:

The needle is inserted at a point halfway

along the line between the premolars

and the midline of the palate.

1.4-1.8ml of L.A is slowly deposited.

Palatal-(PASA)

Provides pulpal anaesthesia to both

central incisors,both lateral incisors and

to a lesser degree,both canines,as well

as the labial and palatal soft and hard

tissues of these teeth.

Recommended needle-27 gauge short

Technique:

The needle is inserted lateral to the

incisive papilla,slowly to a depth of 6-

10mm into the incisive canal.Following

negative aspiration,1.4-1.8ml of local

anaesthetic is administered slowly.

Contraindication to local

anaesthetics

Local complication of LA

Needle breakage

Paraesthesia

Facial nerve paralysis

Trismus

Soft tissue injury

Haematoma

Pain on injection

Burning on injection

Infection

Edema

Sloughing of tissues

Post anaesthetic intra oral lesions

Systemic complications

Overdose

Allergy

idiosyncrasy

References:

Malamed, Stanley. Handbook of Local

Anesthesia. 5th Edition. Mosby. 2004

Dr.Vikram Perakath

B.D.S