Local Anaesthesia Flashcards
LA is made up of :
And its additions
volume of the glass cartridge
Volume : 2.2ml
Hydrophobic aromatic ring
Intermediate chain - either ester or amide
Hydrophilic amine
Additions
1
* Bisulphite
Preservative - prevents oxidation of vasoconstrictors
further lowers pH - can cause allergies - use plain LA if so
* Methylparabens
Old days
Preservative and bacteriostatic
2
* Sodium chloride
Isotonic solution to prevent osmotic issues in tissue while injecting
* Sodium hydroxide
Neutralises pH by increasing pH to counter bisulphite
* Distilled water
Increases volume
* Nitrogen gas
Space filler that creates bubble
Inert - does not react w vasocon
3
* Vasoconstrictors - adrenaline or fenypressin
Decreases bloodflow to reduce LA absorption into bloodstream, allows higher local conc & prolongs duration of action.
Reduces bleeding at injection site
Common LAs and their active ingredients
2% Lignocaine (Xylocaine): 1:80 000 adrenaline
4% Articaine (Articadent) w 1:100 000 adrenaline - more potent
3% Mepivacaine (Scandonest Plain) - no vasoconstrictor
3% Prilocaine (Citanest): 0.03iu/ml octapressin/felypressin
Principles of diffusion of LA - infiltration and IANB
As RN (base) enters the cell from outside, equilibrium outside shifts to favour more RN formation.
Inside the cell, lower pH than outside causes RN reduction to RNH+ (cation) →
RNH+ binds to sodium channels, causing eqm to shift favouring more RNH+ formation
RN conc decreases → more RN enters cell
RNH+ and RN concentration are determined by
and how are they affected?
pKa of LA
- Higher pKa = lower conc RN = less nerve sheath diffusion
pH of LA solution
pH of injection site
- Lower pH (diseased tissues) = lower RN
Mechanism of action of LA
1) LA first binds to receptors outside nerve membrane
2) LA, in its uncharged base form RN, diffuses through nerve sheath into the nerve
3) Once inside, low intracellular pH causes RN → RNH+ cation, which binds to receptor sites of Na channels embedded in nerve membrane via key amino acids
4) This blocks sodium transduction so ions cannot enter. No membrane depolarisation and no action potential generation occurs.
Choosing site of injection
eg
12
26
33
47
Infiltration (supra-periosteal)
What tooth, what side, which nerves
eg RHS anterior superior alveolar nerves of 12
Palatal
Free endings of nasopalatine nerve
Buccal
Upper teeth: Branches of the dental plexus
- Molars & Premolars –> Middle superior alveolar nerves (and/or post sup alv nerves)
- 13,12,11 → anterior terminal branches (superior alveolar nerves) of dental plexus
Lower teeth:
- Molars & Premolars –> apical branches of inferior alveolar nerve
- 43, 42, 41 –> incisive nerve, branching from IAN
IANB
Inferior alveolar nerve (in the pterygopalatine fossa, past the lingula)
Lingual nerve
Landmarks for IAN block
Locating the tip of the lingula using:
LEVEL - coronoid notch, 1cm above lower occlusal plane, midway btw arches w mouth wide open, buccal pad
ANGLE - contralteral premolars
ENTRY POINT - pterygotemporal depression
Type of LA technique, what’s numbed, and clinical indications
1) Buccal infiltration
- Pulp and root of tooth
- Buccal gingiva including mucoperiosteum
* For Mx exo and resto (w palatal infil), for Md ant exo and resto (w lingual block)
2) Palatal infiltration
- Palatal soft tissues directly arnd adjacent site
* Mx exo and resto (w B infil)
3) IANB
- All ipsilateral teeth
- Ipsilateral hemi-mandible
- Buccal gingiva
- Ipsilateral skin & mucoperiosteum of lower lip, ipsilateral skin of half-chin
* Md post exo and resto, w lingual block
4) Lingual nerve block
- Lingual gingiva and mucoperiosteum
- Anterior 2/3 of tongue general sensation - pain, touch, temp
- Floor of mouth
* Md post exo and resto, w IANB
5) Long buccal nerve block
- Buccal gingiva of molars
- Buccal and alveolar mucosa of Md molars
* Soft tissue manipulation of molars (paired w IANB)
Administration of LA for B infiltration
Type of needle
Insertion site
Procedure
B infil
27 gauge short needle, bevel towards bone
Insert: height of mucobuccal fold above the apex of tooth
1) Prep tissue at injection site: palpate root (root tilt) -> dry w gauze, then triplex → topical LA (Ziagel 5% lignocaine) (~1min) -> test numbness, remove excess topical LA
2) Retract - pull tissues taut
3) Hold syringe parallel to long axis of tooth (not alw possible w post t) - insert needle 2-3mm into the height of the mucobuccal fold. Inject 1/3rd-full carpule of LA.
4) Withdrawal of syringe + safe disposal
Administration of LA for P infiltration
Type of needle
Insertion site
Procedure
27 gauge short 25mm needle; bevel towards bone
Insert: site of max tissue thickness (ie at attached gingiva 5-10mm from free gingival margin)
Bevel to bone
1) Pt positioning: ask pt open mouth wide, extend neck, turn head either left or right for better visibility
2) Prep tissue - dry w gauze, then triplex → topical LA (~1min) -> test numbness, remove excess topical LA
3) Place bevel of needle against soft tissue at injection site. Penetrate mucosa - advance needle 2-3mm. Up to 1/8 of carpule (usually a few drops enough)/ once you see palatal tissue blanching if using LA w adrenaline
4) Withdrawal of syringe + safe disposal
Procedure for IANB
Type of needle
Insertion site
Procedure
27 gauge long 40mm needle
Insert: pterygotemporal depression, 1cm above Md occlusal plane, angle of insertion: contralateral 2nd premolar
Bevel orientation less critical
1) Position the pt - recline pt at 45 deg so occlusal plane is parallel to floor
2) Prep tissue - dry w gauze, then triplex → topical LA (~1min) -> test numbness, remove excess topical LA
3) - Palpate: Define coronoid notch by palpating for medial border of ramus
- Right ramus with left index finger, slide finger in retromolar area between external and internal oblique ridges. Pterygomandibular fold will be 5mm medial to finger.
- From angle of contrateral lower premolar, parallel to occlusal plane, insert needle in the pterygotemporal depression, arnd 1cm above Md occlusal plane.
4) Advance needle w minimum force until it touches bone (2/3rd to ¾ of needle length)
Withdraw slightly, aspirate, inject 3/4 of carpule
5) Move barrel towards midline, withdraw half the amt of inserted needle, aspirate, inject for lingual nerve (1/4 of capsule)
6) Withdrawal and safe disposal of needle
Testing for anaesthesia
1) Start w non-anaesthetised side - push onto ST w gentle pressure using end of mirror handle/tip of tweezers
2) Repeat on anaesthetised tissue
3) Ask pt if feels diff & how it feels
Failure of IANB
Reasons
1) Operator technique
Most likely the cause if ipsilateral is not numbed at all - chip lip teeth
* Height too low - pt not opening wide enough
* Inadequate stretching - cannot locate pterygotemporal depression
* Swung too: medially and inferiorly/laterally/posteriorly/superiorly
* ‘Electric shock’ - needle contacting IAN
2) Insufficient volume
* At least entire carpule for adults 3/4 IANB, 1/4 LN
3) Timing
* Inject too quickly - ballooning of tissues, v uncomfortable. Inject 1ml/min
* Didn’t allow time for LA to diffuse (can take 5-10min sometimes). [Pulpal anaesthesia may take longer due to dense covering of t apex]
Infil 2-3min onset
IANB 4-5min onset
4) Anatomical variation
Most likely the cause if there is partial anaesthesia - chin lips but not teeth. Eg accessory nerves and foramena, bifid IAN, different ramus or coronoid notch height, obstruction by ligaments/processes
5) Other patient factors
* Anxiety - lowered pain threshold
* Inflammation:
- Inflammation - delays onset of LA
- Increased blood supply in area → increases rate of absorption and clearance
- Prostaglandins - lower threshold of nerve activation - more sensitive - lower LA effectiveness
Examples of anatomical variation –> IANB failure
- Accessory nerve/foramena
– Nerve to mylohyloid having a sensory component as well as its normal motor
– Contralateral incisive nerve can supply lower anteriors- causes 3-3 to be not fully anaesthetised - Bifid IAN: presence of secondary branch of IAN - bifurcation before it enters the foramen - normal IANB technique insufficient in blocking conduction frm both branches.
- Mandible:
–prognathism,
–Width of ramus -inferiorly positioned in children - affects location of lingula - Obstruction
Sphenomandibular ligament obstructing lingula
Rare - stylohyoid ligament/styloid process
Local complications
Complication
Signs and symptoms
Management
1) Haematoma: dmg to blood vessel - bleeding, clot forms
–> Can lead to trismus + intra/extraoral facial bruising and swelling
* Apply localised pressure ~2min to stop bleeding
* Ice may be applied to region immediately
* Consider analgesics
* Record in dental record, advise pt risk of trismus
* Do not apply heat to area for at least 4-6h - may increase size of hematoma - apply moist heat the next day
* Discolouration shd resolve in 7-21d
2) Temporary Facial paralysis/Ocular complications
-> LA deposited in parotid gland - anaesthetise facial nerve
=> facial drooping
Inability to close one eye → risk of corneal ulceration
* Reassure pt it is temporary, advise not to rub eyes
* Cover affected eye w eyepatch
* Keep under observation until better
* Inform next-of-kin to bring pt home, not ok to drive home alone
* If not recovered after 12h, med review
3) Nerve damage
-> Dpd on severity - neuropraxia > axonotmesis > neurotmesis
-> Paraesthesia: tingling and prickling sensation
Dysaesthesia: painful and burning sensation
Damage to lingual nerve -> altered taste
* Paraesthesia resolves within ~8wks, if more refer to oral surgeon
* Reassure pt and book in for reassessment
4) Soft tissue trauma
Self-inflicted trauma (lip biting)
Prolonged topical gel application → sloughing of tissue (desquamation)
Prolonged ischaemia → sterile abscess.
-> Localised pain and swelling. Sterile abscess usually on H/P after Pa infil
* Appropriate post-op, written if necessary
* Warm saltwater rinses
* OTC antiseptic gel eg SM33
5) Trismus - locked jaw
-> Damage to medial pterygoid muscle: by intramuscular injections, repeated needle injections
=> Prolonged spasm of the jaw muscles → reduced mouth opening, pain assoc w mouth opening
* Reassure pt that trismus is temporary
* Usually self-limiting (no tx needed) and improves within 48-72h wup to 6wks for complete recovery
* Pt may seek heat therapy (20min/h), warm saline rinse, soft diet, jaw exercises
* Analgesics - check MHx
* Avoid further dental tx until area has fully healed
* Review in 7-14d, consider referral to OM if unresolved
