local anaethesia- how and why

Question 1

What is LA used for?

Answer 1

Prevent pain during treatment
Post-surgical relief/acute pain
Localisation of pain- diagnosis
Reduce surgical haemorrhage (vasoconstrictor)

Question 2

Why is GA not used in dental practices?

Answer 2

Requires intensive care facilities
Greater risk
Patient must be starved and accompanied
Must have consent
Restricted post-op activities for patient
Contraindicated in some patients w underlying medical problems

Question 3

When is GA permitted?

Answer 3

Some children, uncooperative patients, patients w extreme anxiety, significant surgery

Question 4

Why is LA used?

Answer 4

Safe
Easy to use- single operator, less hassle for patient
Economical
Patient cooperation- to check occlusion etc
Long operating time
Haemostasis
Few medical contraindications

Question 5

When is LA contraindicated?

Answer 5

Unmanageable patients
Injections in acute infection
Possible risk of bleeding w IA block in haemophilia/other bleeding disorders
Allergies

Question 6

What are the types of local anaesthetic?

Answer 6

Surface/topical
Infiltrations
Regional block

Question 7

What are surface LAs?

Answer 7

5% lidocaine ointment
10% lidocaine flavoured spray
Jet injection
Ethyl chloride

Question 8

What are infiltration LAs?

Answer 8

Between mucosa and periosteum
Effective w thin alveolar bone and vascular channels
Sub-periosteal- painful
Intra-osseus- rarely used

Question 9

What is a regional block?

Answer 9

In mandible due to thick cortical w no vascular channels

Question 10

What is needed for LA?

Answer 10

Syringe-
~cartridge- breech or side-loading
~aspirating system- avoids intravascular injections
~all/part disposable needle

Cartridge-
~1.8 or 2.2ml sterile LA in glass/plastic tube
~single patient use
~blister packed

Aspirating-
~positive aspiration
~self aspiration- passive

Question 11

What is an aspirating system?

Answer 11

LA shouldn’t go into blood stream so if needle goes into blood vessel-

Self aspirating-
~put negative pressure on system so if blood is pulled back into syringe, reposition needle

Positive aspirating-
~uses O-ring
~put positive pressure on ring to create negative pressure to see if blood is pulled back into syringe

Question 12

What needle is used for LA?

Answer 12

Sterile/single patient use
Flexible stainless steel-
~30 gauge (0.3mm OD), short 19mm for infiltration
~27 gauge (0.4mm OD), long 34mm for regional block
Double bevel
Always leave some of needle exposed when penetrating into tissues
Handle and dispose w care, avoid bending

Question 13

How is LA administered?

Answer 13

Patient- comfortable, relaxed, well postioned, aware of what to expect
Operators- stable, good visibility
Equipment- ready and out of sight
Tissues stretched taut
Insert needle slowly during stretch and advance to appropriate position w bevel away from bone
Aspiration
Inject slowly-
~1ml/15s for infiltration
~2ml/20s for IA block (loose tissue)
Ask if numb/probe or bur cautiously initially
Avoid injecting into foraminae

Question 14

What are the branches of the maxillary nerve?

Answer 14

Posterior superior alveolar nerve 
~leaves in pterygomaxillary fissure just before infra-orbital canal
Middle superior alveolar nerve
~50% present in patients
Anterior superior alveolar nerve
~leaves within infra-orbital canal

Question 15

How is LA deposited in the maxilla for routine dentistry?

Answer 15

1-2ml buccally over apex of tooth adjacent to bone
Effective <2 mins, wait ~4 mins, by 6-8 mins assume failures
Avoid floor of nose anteriorly- painful
Avoid malar buttress above 6 (bone is dense w/o vascular channels) so do a bit of local above 5 and 7 instead

Question 16

If LA needs to be used for extractions or palatal surgery?

Answer 16

Anterior (greater) palatine nerves
~through palatine canal and palatine foramen
Nasopalatine nerve
~along nasal septum and through incisive canal to anterior palate

Needle 90 degrees to tissues behind tooth
Midway between gingiva and midline of palate
Tissues tightly bound so inject v slowly
Infiltrate a small amount
Nasipalatine block is difficult- papilla v sensitive, avoid canal if possible

Question 17

How might a regional block be administered in the maxilla?

Answer 17

Posterior superior dental block-
Mouth partly closed, cheek retracted
Long, wide needle adj to mesial upper right 8
Must aspirate due to pterygoid plexus- commonest site for haematomas

Infra-orbital block-
IO foramen palpated, lip reflected w thumb, inject long needle through sulcus adj to second premolar- depth 1.5-2cm, approx 1ml
Extra oral approach is v rare

Question 18

What is an intraligamentary injection?

Answer 18

Patients w contraindications for other anaesthetics
30 gauge needles, fine and short, special syringe (pistol/pen)
Insert approx 2mm along periodontal ligament of each root
Inject slowly (0.2ml/30s) max 0.4ml/root- must feel resistance
Fast onset, high success rate
Only w healthy gingivae
Avoid injecting adjacent teeth due to crestal bone