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Module 6 Local Anesthesia Budenz: By Lauren McCormick (Reasons for…
Module 6
Local Anesthesia Budenz:
By Lauren McCormick
How to assess anesthesia?
Soft Tissue
question patient
probe the area
Pulpal Tissue
Electric pulp tester
2 consecutive 80/80 readings within 15min of injection
cold test
Onset of Anesthesia
dependent on...
agent used
concentration
diffusion to site
lipid solubility
protein binding to receptor sites
technique used
infiltration
faster onset, simple, safe, good hemostasis w/ vasoconstrictor
BUT multiple injections needed for multiple teeth, shorter duration
block
longer duration
presence of vasoconstrictor
all dental anesthetics are amides
Prilocaine (plain or w/ vasoc.)
Articaine (w/ vasoc.)
Mepivacaine (plain or w/ vasoc.)
Bupivacaine (plain or w/ vasoc.)
Lidocaine (plain or w/ vasoc.)
slows rate of uptake into bloodstream
increase duration of anesthesia
induce localized hemostasis
physiology
diameter (size) of nerve bundle
amount of myelin (lipid) sheath present
Central Core Theory: peripheral fibers anesthetized first, core fibers last
critical length = 3 nodes minimum (5mm)
depends on anesthetic volume, tissue space & density
How they work...
basic, unionized form can pass through nerve membrane (lipid soluble)
acidic, ionized form can't pass through nerve membrane (water soluble)
dependent on....
disassociation rate
transport/perfusion rate
re-association rate
binding rate
Anesthesia Delivery
frequency dependent conduction
vibration stimulates nerves, allows greater anesthetic access to receptor sites to produce better anesthesia
DentalVibe
Accupal
Gate Control Theory of Pain
nociceptors send pain messages to brain via slow conducting thin C nerve fibers
vibration stimuli transmitted by rapid conducting, large A-beta fibers
Reasons for Anesthetic Failures
anatomical/physiological variation
technical errors of administration
patient anxiety
inflammation and infection
causes decrease in pH
less anesthetic can enter nerve due to change in dissociation equilibrium
Normal tissue pH 7.4
Inflammation/infection pH 5.0-3.0
defective/expired solutions
Troubleshooting
"Hot" tooth
give block injection (Gow-Gates highest success w/ 52%)
next, give PDL or intraosseous injection
next give a buccal &/or lingual infiltration w/ articaine
infection present
types
Esters
Procaine
Cocaine
Tetracaine (Pontocaine)
Benzocaine
Chloroprocaine
Metabolism
metabolized in plasma by plasma pseudocholinesterase
product of procaine degradation
para-aminobenzoic acid (PABA)
common ingredient in topical sunscreens
provokes allergic reaction
likely agent for the rare cases of allergic reaction
Amides
Lidocaine (Xylocaine, Octocaine, alphacaine)
2% w/ epi
1-2hrs pulpal anesthesia
3-5hrs soft tissue anesthesia
36mg/cartridge
Bupivacaine (Macaine, Sensorcaine)
0.5% w/ epi
1.5-4hrs pulpal
5-12hrs soft tissue
Mepivacaine (Carbocaine, Polocaine)
3% plain
20-40min pulpal
2-3hrs soft tissue
54mg/cartridge
2% w/ levonordefrin
1-1.5hrs pulpal
3-5hrs soft tissue
Prilocaine (Citanest)
4% w/ epi
1-1.5hrs pulpal
3-8hrs soft tissue
72mg/cartridge
Articaine (Septocaine, Carticaine, Ultracaine)
4% w/ epi
1-1.5hrs pulpal
2-4hrs soft tissue
72mg/cartridge
far less likely to produce allergic reaction
Atypical Drugs
Dyclonine hydrochloride
local anesthetic found in throat lozenges
Diphenhydramine
antihistamine used as local anesthetic (if others are intolerable)
if patient is allergic to both esters and amides
true allergic rxns are rare
usually involve esters, rarely amides
most likely represent misinterpretation of symptoms
vasovagal reaction
effect of epinephrine
intravascular injury
typically due to PABA-like preservatives used in ester compounds
try 1cc hypdermic test injection to evaluate antigen reaction
no cross reactivity between amide and ester agents
it pt is allergic to one, a different class may be substituted
Benadryl
may cause more pain on infiltration
less effective
greater risk of tissue necrosis
usage
short procedures (<1hr)
Mepivacaine 3% plain (infiltration or block)
Prilocaine 4% plain (block)
routine procedures (1-2hr)
Lidocaine 2% w/ vasoconstrictor
Mepivacaine 2% w/ vasoconstrictor
Articaine 4% w/ vasoconstrictor
Prilocaine 4% w/ vasoconstrictor
long procedures (>2hr)
Bupivacaine 0.5% w/ vasoconstrictor (block)
difficult to anesthetize patients
Prilocaine 4% w/ vasoconstrictor
Articaine 4% w/ vasoconstrictor
metabolism
biotransformed in liver by P450 cytochrome enzymes
Articaine has rapid biotransformation in bloodstream (95%) due to ester moiety; completed in liver (5%)
nerve injuries
injury due to direct contact w/ nerve
toxicity injury due to direct contact of anesthetic solution w/ nerve
no guaranteed method to prevent nerve injuries
Method of Action
reversibly blocking nerve conduction
reduces influx of sodium ions into nerve cytoplasm
potassium ions therefore cannot flow out
depolarization of nerve is inhibited
penetrates nerve membrane