anesthesia pt2

Middle Superior Alveolar (MSA) Block

• Presence & Innervation

  • MSA nerve absent in approximately $72\%$ of individuals.
  • When absent, area supplied mainly by anterior superior alveolar (ASA) nerve with contribution from posterior superior alveolar (PSA); all are branches of the superior dental plexus.
  • Block targets maxillary premolars (1st & 2nd) – pulps, buccal periodontium, and gingiva.
  • Palatal periodontium/gingiva for these teeth require greater palatine (GP) block if anesthesia is needed.

• Target Area

  • Nerve trunk superior to apex of maxillary second premolar.
  • Located within the height of the maxillary mucobuccal fold.

• Injection Site & Technique

  • Palpate mucobuccal fold above apex of 2nd premolar (Fig. 9.10).
  • Insert needle parallel to long axis of tooth, advancing until tip lies superior to apex without contacting bone (reduces trauma).
  • Deposit solution; withdraw.

• Signs of Successful Anesthesia

  • Harmless tingling/numbness of upper lip.
  • Absence of discomfort during procedure.

• Complications & Risk

  • Very low positive aspiration rate.
  • Over-insertion rare; hematoma uncommon.

Anterior Superior Alveolar (ASA) Block

• Innervation & Use

  • Anesthetizes ASA nerve → maxillary anterior teeth (canine to central incisor) & associated labial periodontium/gingiva to the midline in one quadrant.
  • Often combined with MSA block; can replace IO when only anteriors involved.
  • Larger area than a single supraperiosteal injection; considered a true nerve block.

• Crossover-Innervation

  • ASA fibers may overlap across midline → contralateral central incisor region.
  • If patient feels discomfort, consider:
  • Bilateral ASA blocks, or
  • Supraperiosteal injection above apex of contralateral central incisor.

• Palatal Soft-Tissue Supplement

  • For palatal periodontium/gingiva → nasopalatine (NP) block required.

• P-ASA (Palatal-ASA) Variant

  • Computer-controlled device delivers solution via incisive canal → simultaneously anesthetizes ASA & nasopalatine nerves.
  • Produces bilateral anesthesia of anteriors (labial + palatal) without upper-lip/muscle numbness; valuable for cosmetic dentistry (immediate smile-line assessment).
  • Depth/duration may be variable.

• Target Area

  • ASA nerve trunk superior to apex of maxillary canine.

• Injection Site & Technique

  • Height of maxillary mucobuccal fold, superior to canine apex, just medial & parallel to canine eminence (Fig. 9.13).
  • Needle angled $\approx 10^{\circ}$ off line parallel to long axis of canine (Fig. 9.14).
  • Advance above apex without bone contact; deposit.

• Success Indicators / Risk

  • Tingling/numbness of upper lip.
  • Low aspiration rate; hematoma rare.

Infraorbital (IO) Block

• Coverage

  • Single injection anesthetizes infraorbital nerve + ASA + MSA, therefore:
  • Maxillary anteriors and premolars (pulps, facial periodontium, gingiva) to midline.
  • Extra-oral branches → lower eyelid, lateral nose, upper lip.
  • Palatal tissues still require NP (anterior) + GP (posterior) blocks; PSA may be added to complete quadrant.

• Crossover-Innervation

  • Same ASA contralateral overlap considerations; bilateral IO or supplemental supraperiosteal may be required.

• Anatomical Landmarks

  • Infraorbital foramen: Slightly inferior to midpoint of infraorbital rim at the zygomaticomaxillary suture.
  • Palpable depression produces soreness when pressed.
  • Useful linear alignment on ipsilateral face (Fig. 9.15):
    $\text{supraorbital notch} \rightarrow \text{pupil} \rightarrow \text{infraorbital rim midpoint} \rightarrow \text{infraorbital foramen} \rightarrow \text{labial commissure}$

• Injection Site & Depth Estimation

  • Height of mucobuccal fold above apices of maxillary first premolar (Fig. 9.17).
  • Pre-measure depth: finger on foramen + finger on injection site.
  • Depth varies with:
  • Height/depth of mucobuccal fold.
  • Superior/inferior position of foramen.

• Technique

  • Insert parallel to tooth long axis, advance toward foramen while