LA Flashcards
Why do we use LA?
- Pain control
- Control bleeding
- Symptom relief for those with facial pain
How does LA work within a nerve cell?
Unionised LA are lipid soluble so can diffuse across the lipid cell membrane.
Once inside the nerve cell, the LA molecule comes ionised due to the pH within the cell being lower and then block the sodium channels.
Why might LA affect cells differently?
Type of sodium channel Myelination or not Size of nerve Length of each nerve Depth of nerve fibre Distribution of Na+ and K+ channels of each nerve Inflamed nerve
What is the structure of an LA molecule?
Hydrophobic aromatic ring
Hydrophilic amine group
What are the two types of LA and where are they metabolised?
Amides - metabolised by the liver
Esters - metabolised by plasma cholinesterases
What is the only type of LA which is an ester?
Benzocaine (used in topical)
What affects the speed of action of the LA?
- Tissue pH
- pKa of anesthesia
- Diffusion distance to nerve
- Concentration of LA
- Lipid solubility
Why do we add a reducing agent to LA?
Prevent degradation of the vasoconstrictor by reducing the amount of oxygen there is to react with adrenaline
Why may some patients need to use prilocaine with felypressin?
- Patients with heart conditions
- Patients who are allergic to other LA types
Why is articaine more effective than lidocaine?
It is double the concentration
Where is articaine metabolised?
Who is this good for?
Metabolised by plasma esterases in surrounding cells (even tho it is an amine).
Good for those with liver disease where the dose needs to be reduced.
Why do we not use articaine for a block?
Higher concentration so said to increase the risk of nerve damage.
What do we use an extra short needle for?
Intra-ligamentary injection
What nerves does the mandibular nerve go into?
Lingual
Buccal
Inferior alveolar
What nerve supplies the maxilla palatal gingiva?
Nasopalatine
Anterior palatine
What supplies the buccal gingiva of the maxillary arch?
Buccal nerve 3-8 and infraorbital nerve 3-1
What technique of LA uses a supra periosteal injection?
Infiltration
Should we bevel our needle towards or away from bone? Why?
Towards - reduce trauma to soft tissue and discomfort for patient
What do we need to make sure we have done before injecting with a buccal infiltration?
Hit bone and then retract before injecting
When we do an maxillary extraction, how much of the cartrige do we give buccally and how much apaltally?
3/4 buccal and 1/4 palatally
Why do we give the palatal infection between the midline raphe and the attached mucosa?
Most fleshy part so is the most comfortable
Why do we give interpapillary injections?
To avoid palatal injections (advance needle towards the palate)
When do we give an intraligamentary injection?
- When the tooth has periodontal infection
Why do we stretch the mucosa before injecting?
Less [painful to penetrate with needle
What LA do we use for extraction of a mandibular second molar?
ID block and long buccal block
What are the main complications of LA?
- Failed LA
- Trismus
- Prolonged anaesthesia
- Pain on injection
- Needle breakage
- Infection
- Soft tissue injury
Why does an abscess affect LA effectiveness?
- Reduced pH of tissue = less dissociation of LA molecules once injected
- Less ionised LA molecules to block to Na+ channels
- Increase in blood supply during infection to the area causing wash out of the anaesthetic
Why it is hard to anaesthetise a tooth with irreversible pulpitis?
- Hyperalgesic pulp (increased pain)
What technique can cause prolonged anaesthesia?
- Inferior alveolar nerve block
What is the difference between prolonged and persistent anesthesia?
Prolonged anaesthesia = lasts days to months
Persistent anaesthesia = permanent nerve damage resulting in change in sensation to area (numb, tingling or burning)
What are some systemic complications of LA?
- Intravascular injection
- Allergy
- Toxicity
- Vasovagal
What teeth does buccal infiltration work in mandibular teeth?
up the second premolar
If we do an intra papillary injection, what other injection can we avoid?
Palatal injection
What question can we ask a patient to see if an ID block has worked?
Is your lip and chin numb?
How do we know if we have our needle in a nerve?
Patient will feel sharp electric shock
What can we inject into which will give the patient a facial palsy?
Parotid gland (facial nerve running through)
What LA do we give for a lower third molar extraction?
ID block & buccal nerve block
When do we need to use block anaesthesia?
- When anesthesia is required over a larger area
- Where bone is porous and LA cannot diffuse in
- If there is an abscess near sight of infection inhibiting a buccal infiltration
What two nerves does a mental nerve anathetise?
- Mental nerve
- Incisive nerve
What soft tissue does a buccal nerve block anaethetise?
Buccal soft tissues distal to second premolar
