Oral surgery (anatomy/LA) Flashcards
what is anaesthesia?
loss of sensation especially pain induced by drugs
difference between general and local anaesthesia?
GA is when consciousness is lost
LA is when only a specific area of the body is involved
what does the trigeminal nerve supply?
maxillary and mandibular nerves supply the teeth
sensory distribution
branches of the maxillary nerve of CNV
infraorbital (zygomaticofacial, zygomaticotemporal)
posterior superior alveolar
palatine
nasopalatine
branches of the mandibular branch of CNV
lingual, buccal, auriculotemporal
inferior alveolar (mental and nerve to mylohyoid)
other motor branches
the outer cortical plate of maxilla is thin and porous. what does this mean for the LA?
outer bony cortical plate of maxilla is thin and porous, therefore LA can diffuse readily through the plate to the teeth, adjacent teeth and soft tissues
what supplies maxillary incisors and canines?
anterior superior alveolar nerve and nasopalatine nerve
what supplies maxillary premolars?
superior alveolar nerve plexus and greater palatine nerve
apices lie close to surface, therefore solution diffuses readily
what supplies maxillary molars?
posterior superior alveolar nerve and greater palatine nerve
what anaesthesia is used for molars?
infiltration anaesthesia is almost always used, alveolar block not routinely advised
what implications does the density of the buccal bone have on anaesthesia?
due to the density of buccal bone, infiltration anaesthesia is not as effective in the mandible therefore regional inferior alveolar nerve block is used, also called ID (inferior dental) block
where do you place the needle for a mandibularly block, ID block?
place needle 1cm above occlusal place, in front of raphe
why does LA need to occur slowly?
slowly to avoid the nerve and pass the needle slowly
describe anaesthesia to lower 1st premolars - incisors
anaesthetise the mental foramen which usually lies between the apices of the lower premolars
local infiltration around the incisive nerve will produce anaesthesia of incisors
there is an anastomosis between the incisive nerves therefore infiltrations must be given on both sides of the midline
where are lingual infiltrations given?
lingual infiltration must be given as distinct injections in anterior teeth
what anaesthesia should be used for deciduous teeth?
infiltration anaesthesia is highly effective for deciduous teeth due to the presence of multiple vascular canals
what nerve supplies the anterior hard palate?
nasopalatine nerve
what nerve supplies the posterior hard palate?
greater palatine nerve
what considerations for administering palatal anaesthetic?
palatal mucosa is very dense so administer LA under greater pressure.
how do you minimise discomfort to palate when administering LA?
if needle is inserted with the bevel towards the bone and at right angles to the palatal vault.
how to give a painless injection?
warm the cartridge in a cup of hot water
use topical anaesthetic
administer it slowly (pressure hurts)
split the administration
use distraction techniques
what is the mechanism of LA?
LA agents interfere with nerve conduction by reducing the rate of increase of the action potential. they reudce the influx of sodium ions and therefore interfere with the depolarisation phase. thus the critical threshold potential is not reached and no action potentials is ‘fired’, leading to no conduction
what does LA do?
reversibly blocks nerve conduction when applied to a restricted area of the body to enable a procedure to be carried out without loss of consciousness
what is targeted to prevent pain?
voltage gated sodium ion channels to stop generation of APs
what ending do LAs have?
-caine
chemical structure of LA
aromatic ring, amine group, with amide or ester bond linking them
what property does the aromatic ring give?
lipid soluble - will target neurones with a phospholipid bilayer
what property does the amine ring give?
amine groups can exist charged or uncharged. so LA molecules are weak bases and can accept a proton when dissolved in water.
are ester or amide bonds broken down faster?
ester
does ionised or unionised version of LA block VGNa+ channels?
ionised
what is a use dependent block?
the degree of the block is dependent on whether the channels are being used. the ionised molecule blocks open channels. channels are only open if there is stimuli generating APs. thus if there is a more painful stimulus, we may expect more APs. so more open channels = better block
how can pH affect effectiveness of LA?
pH affects ionisation state of molecules
what can cause lower pH?
inflammation - bacteria respire and produce acidic byproducts, lowering pH
affect of lower pH on LA effectiveness
worsens affect of anaesthetic
due to more ionised molecules, so less unionised to cross membrane to bring about blockage action
what are the 5 routes of administration of LA?
topical anaesthesia
infiltration
nerve block
epidural
spinal
describe topical anaesthesia
Anaesthetising surfaces. Nerve terminals are branching to cover the skin area. Not very effective since skin is made up of many layers and is dense so it is difficult for the LA molecules to diffuse across the skin.
describe infiltration anaesthesia
LA is injected into the skin. Sometimes done as multiple injections so all of the neurones supplying that area are anaesthetised. Can be used in some forms of dental work for anaesthetising one tooth.
describe nerve block anaesthesia
Injection given quite proximally so it is targeting quite a large mixed nerve so all of the axons are affected within that nerve.
what happens if LAs are injected into vessels or are given at too high doses?
in bloodstream can circulate body and block all VGNa+ channels. in heart can interfere and cause heart attack.
what happens if LA enters CNS?
affect neurones in brain causing tremor, convulsions, respiratory failure
what happens if LA enters CV system?
cardiac muscle means heart might not contract as well
blood vessels may not contract, might dilate, decreasing BP
what else is found in LAs?
neutral e.g., saline to prevent bacteria growth, sterile
why are vasoconstrictors administered with LA?
LA will affect the blood vessels in that region. We want to keep LA in that region so constricting the blood vessels can reduce flow so stop it from being easily enterable into the circulation. This decreases unwanted effects in other regions and increases duration of action since it reduce rate at which LA is metabolised in the body, so a lower dose can be given.
why must we be cautious of vasoconstrictor administration area?
administering into extremity could cut off blood flow from this area
examples of vasoconstrictors
adrenaline/felypressin
what LA do we use?
lidocaine (medium duration)
what can cause hypersensitivity from LA?
A variety of other agents are in the solution to preserve it. Some can cause hypersensitivity reactions, e.g. redness around injection site. This is non-specific because it is not due to the LA molecules themselves.
describe the nerve, numbs and placement of an ID block
nerve - inf alveolar nerve
numbs - ipsilateral lower molars, half lips, half tongue
placed - pterygomandibular raphe
describe the nerve, numbs and placement of a long buccal nerve block
nerve - long buccal nerve
numbs - soft tissue on buccal side in mandibular molar region
placed - distobuccally to last molar in mucosal membrane
describe the nerve, numbs and placement of a mental block
nerve - mental nerve
numbs - chin, lower lip, labial gingiva, premolars and anterior teeth
placed - base of buccal sulcus between 4+5
describe the nerve, numbs and placement of a supplementary lingual nerve block
nerve - lingual nerve
numbs - lingual tissue
placed - lingual mucosa surrounding teeth to be extracted
what does an anterior superior alveolar nerve block?
buccal tissues of incisors and canines
what does an anterior middle alveolar nerve block?
buccal tissues of premolars
what does an anterior posterior alveolar nerve block?
buccal tissue of molars
where can the nasopalatine nerve/greater palatine nerve block be placed?
palatal infiltration adjacent to each tooth
maximum safe dosage of lidocaine
4.4mg/kg 7 cartridges
contraindications of lidocaine
severe liver disease
maximum safe dosage of prilocaine
6mg/kg 6 cartridges
contraindications of prilocaine
pregnancy, young infants, kidney/liver/heart disease
maximum safe dosage of mepivacaine
4.4mg/kg
how long does mepvicaine last?
30 mins
max safe dosage of bupivicaine
1.3mg/kg
max safe dosage of articaine
7mg/kg
What are the constituents of LA cartridge?
Anaesthetic agent
Vasoconstrictor
Preservative (usually methylparaben)
Reducing agent (usually sodium metabisulphite)
Fungicide (thymol)
Vehicle (modified Ringer’s solution)
What are the constituents of LA cartridge?
Anaesthetic agent
Vasoconstrictor
Preservative (usually methylparaben)
Reducing agent (usually sodium metabisulphite)
Fungicide (thymol)
Vehicle (modified Ringer’s solution)
What are the properties of an ideal LA?
Safe (therapeutic dose)
Reversibility of action
Reliable
Potency
Adequate shelf life
Non-irritable
Compatible pH
Adequate duration
Rapid onset
Penetration of mucous membranes
Sterility (saline)
