If Chapter 18 gave us the wiring of the cranial nerves,
this chapter teaches us something far more practical:
How to interrupt that wiring - safely, deliberately, and effectively.
This is not just anatomy.
This is applied anatomy - where knowledge becomes intervention.
PART I - WHAT IS ANAESTHESIA, REALLY?
From page 312:
Anaesthesia = loss of sensation due to drugs, injury, or disease
Mechanism
Local anaesthetics:
Stabilise nerve membranes
Block conduction of impulses
Prevent transmission of sensation
Fibre Sensitivity (Clinical Gold)
Order of blockade:
Pain fibres (small, unmyelinated) → first
Touch/proprioception → later
Motor → last
Pain disappears first -
because it travels along the most fragile pathways.
PART II - TWO STRATEGIES: INFILTRATION VS BLOCK
1. Infiltration (Local)
Inject near nerve endings
Small, localised effect
2. Nerve Block (Trunk Anaesthesia)
Inject near nerve trunk
Large region anaesthetised
A Third Concept: Plexus Anaesthesia
Injection into connective tissue over periosteum
Relies on diffusion through bone
Works best where bone is thin (maxilla)
The difference is simple:
Infiltration whispers
Plexus spreads
Blocks silence entire conversations
PART III - THE MAXILLA: WHERE DIFFUSION WORKS
From pages 312–314:
Maxillary bone:
Thin cortical plate
Allows anaesthetic diffusion
Nerve Supply
Anterior superior alveolar
Middle superior alveolar
Posterior superior alveolar
Key Insight
Plexus anaesthesia is ideal in maxilla
Especially effective except around first molar region
Clinical Image (Page 315)
The diagram shows:
Needle placed near premolar apex
Pink-highlighted area showing spread across teeth
This visually reinforces:
Diffusion-based anaesthesia works when anatomy allows it.
PART IV - THE MANDIBLE: WHERE DIFFUSION FAILS
From page 316:
Mandibular bone:
Thick cortical plate
Prevents diffusion
Consequence
Plexus anaesthesia limited to incisors
Trunk (nerve block) required
The mandible teaches a hard lesson:
when structure resists, strategy must change.
PART V - MAXILLARY NERVE BLOCKS (THE PRECISION MAP)
Posterior Superior Alveolar (PSA) Block
From page 317:
Anaesthetises molars
But may miss mesial root of first molar (~28%)
Clinical risk:
Nearby artery → hematoma (page 318 image)
Infraorbital Block
From page 318–319:
Covers incisors → canine (and often premolars)
Access via infraorbital foramen
Critical warning:
Too deep → orbital complications (eye muscle paralysis)
Palatal Blocks
Greater Palatine
Posterior hard palate
Nasopalatine
Anterior palate
From pages 320–321:
Nasopalatine block anaesthetises both sides
Painful due to tightly bound mucosa
The palate is not forgiving -
it demands slow, deliberate technique.
PART VI - MANDIBULAR NERVE BLOCKS (THE CORE SYSTEM)
Inferior Alveolar Nerve Block
From page 322:
Target: mandibular foramen
Anaesthetises:
Teeth
Gingiva
Often lingual nerve as well
Key Landmarks
Retromolar pad
Pterygomandibular fold
Clinical Reality
From page 323:
Failure rate: 15–20%
Positive aspiration: 10–15% (highest)
This is not a simple injection -
it is navigation through variable anatomy.
PART VII - SUPPLEMENTARY BLOCKS
Buccal Nerve Block
Buccal gingiva of molars
Mental Nerve Block
Lower lip, chin, anterior gingiva
Incisive Nerve Block
Pulp of anterior teeth
From pages 323–326:
Mental and incisive nerves = terminal branches of inferior alveolar nerve
Clinical Insight
Mental block → soft tissue
Incisive block → pulpal anaesthesia
PART VIII - THE MOST IMPORTANT SAFETY STEP
Aspiration
From page 311 & 314:
Pull back syringe before injecting
If blood appears → DO NOT inject
Why it matters
Intravascular injection → toxicity
Can affect:
Heart
Brain
Local tissue
This is the moment of pause -
where precision becomes safety.
PART IX - WHAT THE TABLES SHOW (PAGE 313)
The tables map:
Which block → which tooth
Pulp vs gingiva vs palate
Key takeaway:
No single technique covers everything
Combination strategies are often required
Anaesthesia is not a single act -
it is a carefully choreographed sequence.
Key Takeaways
Local anaesthesia blocks nerve conduction
Pain fibres are blocked first
Maxilla → diffusion works (plexus)
Mandible → requires nerve blocks
Each block targets a specific anatomical pathway
Aspiration is critical for safety
Clinical success depends on anatomy + technique
