Introduction and Anatomy of Local Anaesthesia

• Anaesthesia:

  • Loss of perception of:
  • Pain
  • Touch
  • Pressure
  • Temperature
  • Abolition of motor function

  Analgesia:

  • Loss of perception of pain alone
• Local anaesthetic is somewhere between anaesthesia and analgesia. The pt won't be able to feel pain, touch, or temperature, but will still feel pressure and won't lose motor function. Could also be called local analgesia too.
• Why we have to anaesthetise:

  • Depends on the treatment
  • For restorative dentistry - e.g. fillings, we need to anaesthetise the dental pulp
  • For oral surgery - e.g. extractions, we need to anaesthetise the pulp plus the buccal and lingual tissues
• Methods of pain control:

  • Pharmacological
  • Surface anaesthesia
  • Refrigeration - putting something cold on the skin surface to numb it
  • Topical anaesthetics
  • Local anaesthesia
  • General anaesthesia
  • Out patient drugs - like paracetamol or ibuprofen
  • Non-pharmacological
• It's imperative that we understand the anatomy of the nerve supply to the teeth and supporting structures. So, we need to know:

  • The nerve supply to the tooth (pulp)
  • The nerve supply to the buccal soft and hard tissues
  • The nerve supply to the lingual/palatal soft and hard tissues
• Upper molars (6-8) nerve supply:

  • Pulp - posterior superior alveolar nerve
  • Buccal - posterior superior alveolar nerve
  • Palatal - Greater palatine nerve
• Upper premolars (4-5) nerve supply:

  • Pulp - middle superior alveolar nerve
  • Buccal - middle superior alveolar nerve
  • Palatal - Greater palatine nerve
• Upper canines nerve supply:

  • Pulp - anterior superior alveolar nerve
  • Buccal - anterior superior alveolar nerve
  • Palatal - greater palatine nerve
• Upper incisors (1-2) nerve supply:

  • Pulp - anterior superior alveolar nerve
  • Buccal - anterior superior alveolar nerve
  • Palatal - nasopalatine nerve
• Lower molars (6-8) nerve supply:

  • Pulp - nferior alveolar nerve
  • Buccal - long buccal nerve
  • Lingual - lingual nerve
• Lower anteriors (1-5) nerve supply:

  • Pulp - inferior alveolar nerve/incisive nerve
  • Buccal - mental nerve (inferior alveolar nerve)
  • Lingual - lingual nerve
• Local anaesthetic cartridges contain:

  • Local anaesthetic
  • Ringer's solution (solvent)
  • +/- vasoconstrictor
  • examples of vasoconstrictors = adrenaline or felypressin
  • +/- reducing agent
  • Preservatives - most anaesthetics are now preservative-free to try to reduce allergic reactions
• Vasoconstrictor-containing solutions:

  • More profound anaesthesia
  • More prolonged anaesthesia
  • Reduced operative haemorrhage (useful if doing an extraction)
• Discard a cartridge if:

  • Expiry date passed/unable to read label
  • Cloudy solution
  • Cartridge fractured
  • Large air bubble
• 2% lidocaine (lignocaine) with 1:80,000 adrenaline (epinephrine) is the most common LA to use. The trade name is LIGNOSPAN or XYLOCAINE.
• 3% mepivicaine is plain solution LA (no vasoconstrictor). The trade name is SCANDANEST.
• 4% articaine with 1:100,000 adrenaline is not typically used for regional blocks, but is good for buccal infiltrations in areas with thick bone or infection. The trade name is SEPTANEST.
• Reduce dose or avoid adrenaline:

  • Severe cardiovascular disease
  • With certain drugs
  • Areas of compromise blood supply
• Recording LA used in the pt's notes:

  • ESSENTIAL!
  • Drug - e.g. 2% lidocaine with 1:80,000 adrenaline
  • Amount - e.g. 2.2ml
  • Technique - e.g. right-sided inferior alveolar nerve block
  • DESIRABLE
  • Batch number
  • Expiry date
  • Aspiration positive or negative
• Aspiration is done to check if the needle is inside a blood vessel. It avoids intravascular/intra-arterial injection of LA. If blood enters the cartridge, you know you've hit a blood vessel.
• Reducing discomfort when delivering LA:

  • Topical anaesthesia
  • Stretch tissues - if tissues are pulled taught then the needle penetration will be less painful
  • Distract
  • Sharp needle
  • Position supraperiosteally - needle tip needs to be positioned above periosteum - if needle tip hits bone it should be withdrawn a few mm
  • Aspirate
  • Inject slowly
• Buccal infiltrations:

  • Pulpal and buccal tissue anaesthesia
  • Use long or short needles - 27 or 30 gauge - use short where possible though
  • Inject at least 1.0ml at a rate of 30 seconds per ml
  • Onset 2 mins
  • Duration 45 mins
• Buccal infiltration:

  1. Nerve supplying the maxillary tooth leaves through the apex - idea is to get the needle as close to the tooth apex as possible. Apex is encased in bone, so it's about getting it into the mucosa at the same height as the apex, as close as you can next to the bone.
  2. The local anaesthetic solution will then diffuse across the alveolar bone towards the tooth apex and will then block out the nerve as it exits the tooth apex
• For palatal infiltrations, look midline of palate and gingival margin.

  Direct needle halfway between midline and gingival margin - and slightly posterior to the tooth you want to anaesthetise (if 3rd molar though, then it should be at the same level, not posterior).
• The nasopalatine nerve exits maxilla at incisive foramen to supply palatal tissues of anterior palate. Therefore a nasopalatine nerve block gives anaesthesia to the anterior hard palate. Do this by advancing needle into incisive papilla. Like with palatal infiltration, not a lot of tissue space, so lots of pressure needs to be applied to ensure solution is injected. Uncomfortable procedure for patients.
• For an infraorbital nerve block, aim for the infraorbital foramen, where the infraorbital nerve exits. Inject about 1.5ml.
• Buccal infiltrations in the mandible:

  • Deciduous teeth
  • You can use buccal infiltrations in the mandible, but not as commonly as in the maxilla; mandibular buccal bone is very thick and dense and tends to prevent LA from diffusing through to the tooth apex - can be used in children with deciduous molar teeth and thinner mandibular bone
  • Combined with lingual infiltrations for adult lower incisors
  • Buccal infiltrations work in the anterior mandible; the bone there is thinner and allows the LA to diffuse through
  • For long buccal nerve; it's sat in soft tissue (no hard tissue to get in the way)
• Buccal infiltrations can be used to anaesthetise the mandibular molars if articaine is used.
• For lingual infiltrations in the mandible, you end up injecting into the fold between the mandibular bone and the floor of the mouth.
• Block techniques in the mandible:

  • Inferior alveolar (+ lingual) nerve block (IANB) (IDB)
  • In the mandible you'll most commonly use block techniques - most common one is IANB (inferior alveolar nerve block) - a modification can be added in to anaesthetise the lingual nerve - can be called IANB, but most commonly called an IDB (inferior dental block)
  • Long buccal nerve block
  • Mental and incisive nerve block
• Inferior alveolar nerve block injection:

  • Using long 27 gauge needle
  • Aim - deposit LA solution close to mandibular foramen (because that's where the inferior alveolar nerve enters the mandible)
  • Anaesthetise:
  • Inferior alveolar nerve
  • And therefore, mental nerve (because it's a branch of the inferior alveolar nerve and it's a block injection)
  • (+/- lingual nerve)
  • Onset approximately 5-8 minutes
  • Duration approximately 60 minutes
  • Pretty much always use lidocaine for IDB
• Most of the time with an IDB, the lingual nerve will be anaesthetised too, but a modification can be added to ensure this if that's necessary. The lingual nerve sits close to the inferior alveolar nerve, so it's easy to see why both nerves can be anaesthetised.
• Needle hits the lingula when doing an IDB (a small projection of bone that sits above the mandibular foramen).
• An artery and vein sit close to the IAN; it's a neurovascular bundle - therefore important to aspirate for all injections, but particularly for this one; it's really easy to be in the artery/vein and wouldn't know if didn't aspirate. The medial pterygoid muscle is also sat close to the injection sites, and can quite often be caught. The needle will penetrate the buccinator muscle to reach the right area.
• The pterygomandibular depression is downwards from and mesially to the pterygomandibular raphe - the point of insertion is typically within this depression. You also want to palpate the coronoid notch.
• Giving an IDB:

  • Pt position (put them in a position where you can clearly see what you're doing)
  • More upright so tongue doesn't cover landmarks
  • Pt opens mouth wide
  • This makes the landmarks much clearer to see and makes it more comfortable for the patient
  • Tell them to concentrate on opening their mouth as wide as they can
• Giving an IDB:

  • Observe/palpate landmarks
  • Premolars and raphe
  • Internal oblique ridge (feel for it)
  • Move thumb into coronoid notch once internal oblique ridge has been found - this pulls and stretches the tissues, which will make the process more comfortable for the patient
  • Pull/stretch the tissues
• Giving an IDB:

  • Introduce needle
  • Advance needle until it hits bone:
  • Approximately 25mm of needle penetration
  • Don't use short needle
  • Supraperiosteal, since this technique requires you to hit bone
  • So once you've hit bone, withdraw the needle a few mm
  • Aspirate
  • Inject
• Adding a lingual block to an IDB:

  • This would be done after an IDB, but before the needle is completely withdrawn
  • Lingual nerve = about halfway between inferior alveolar nerve and the point of needle insertion
  • Withdraw the needle halfway
  • Inject most of the remainder of the cartridge at that site
  • Continue to inject as you withdraw - this ensures the lingual nerve is actually hit with LA
• Indirect IDB technique:

  • Needle hits bone at 25mm for direct technique
  • Hit bone too early, or didn't hit bone at all...
  • Instead of removing the needle and trying again, the indirect technique would be used
  • It's a way to reposition the needle
  • NEVER to to the hub of the needle; if the needle fractures off, there's no excess needle to hold on to, and the pt would need surgery to have it removed