6.2 Injection Techniques, Anatomical Landmarks & Nerve Blocks

Injection Techniques, Anatomical Landmarks & Nerve Blocks

Neuroanatomy of the Trigeminal Nerve (CN V)

Safe and effective administration of local anesthesia requires a thorough understanding of the trigeminal nerve (Fifth Cranial Nerve, CN V). The trigeminal nerve is the primary sensory nerve of the head and face and the motor nerve for the muscles of mastication. It divides into three distinct sensory divisions within the trigeminal (Gasserian) ganglion:

1. Ophthalmic Division ($V_1$): Sensory only; exits skull via Superior Orbital Fissure.
2. Maxillary Division ($V_2$): Sensory only; exits skull via Foramen Rotundum into the Pterygopalatine Fossa.
3. Mandibular Division ($V_3$): Mixed sensory and motor; exits skull via Foramen Ovale into the Infratemporal Fossa.

CN V (Trigeminal)
├── V1 (Ophthalmic) -> Superior Orbital Fissure (Sensory)
├── V2 (Maxillary) -> Foramen Rotundum (Sensory)
└── V3 (Mandibular) -> Foramen Ovale (Sensory & Motor)

Maxillary Anesthesia Techniques ($V_2$ Branches)

Maxillary bone (maxilla) is porous and thin compact bone compared to the dense cortical bone of the mandible. Consequently, local infiltration (supraperiosteal injection) is highly successful in the maxilla. However, nerve block techniques are indicated for multi-tooth quadrant treatment or localized surgical procedures.

Maxillary Nerve Blocks (V2)
├── PSA: Molars (except MB root 1st molar 28%), Buccal periodontium
├── MSA: Premolars & MB root 1st molar, Buccal periodontium
├── ASA / IO: Incisors & Canine, Facial periodontium, Lip/Nose/Eyelid
├── Greater Palatine: Hard palate 1st premolar to soft palate
└── Nasopalatine: Anterior hard palate canine-to-canine

Posterior Superior Alveolar (PSA) Nerve Block

• Target Nerve: Posterior Superior Alveolar nerve as it enters the PSA foramina on the posterior surface of the maxilla.
• Areas Anesthetized: Maxillary 3rd, 2nd, and 1st molars (entire tooth structure except the mesiobuccal root of the maxillary 1st molar in ~28% of the population, which is innervated by the MSA nerve), along with buccal periodontium and overlying bone.
• Landmarks: Mucobuccal fold, maxillary tuberosity, zygomatic process of maxilla, apex of maxillary second molar.
• Needle & Technique: 25- or 27-gauge short needle. Penetrate at the height of the mucobuccal fold above the 2nd molar. Advance the needle in three planes simultaneously:
  • Superiorly (45° to occlusal plane)
  • Posteriorly (45° to long axis of 2nd molar)
  • Medially (45° toward midline)
• Depth of Insertion: 16 mm (approximately 3/4 length of short needle). In small adults or children, depth must be reduced to 10-14 mm to avoid over-insertion.
• Complications: Highest incidence of hematoma among all dental injections. Over-insertion can puncture the dense pterygoid plexus of veins or the maxillary artery in the infratemporal fossa, causing rapid extraoral swelling and bruising distal to the zygomatic arch.

Middle Superior Alveolar (MSA) Nerve Block

• Target Nerve: Middle Superior Alveolar nerve (present in ~72% of individuals).
• Areas Anesthetized: Maxillary 1st and 2nd premolars, mesiobuccal root of the maxillary 1st molar, and surrounding buccal periodontium and bone.
• Landmarks: Mucobuccal fold above the apex of the maxillary second premolar.
• Technique: Insert short needle at the height of the mucobuccal fold above the 2nd premolar, keeping the syringe parallel to the long axis of the tooth. Insert 5-8 mm until needle tip is above the apex of the 2nd premolar. Aspirate and deposit 0.9-1.2 mL.

Anterior Superior Alveolar (ASA) / Infraorbital Nerve Block

• Target Nerve: ASA nerve and Infraorbital nerve branch.
• Areas Anesthetized: Maxillary central incisor, lateral incisor, canine, premolars, and mesiobuccal root of 1st molar; facial periodontium; lower eyelid, side of nose, and upper lip.
• Landmarks: Mucobuccal fold above 1st premolar, infraorbital notch, infraorbital foramen.
• Technique: Locate infraorbital foramen by palpating the infraorbital notch on the inferior orbital rim and moving finger 8-10 mm inferiorly. Insert needle into mucobuccal fold above 1st premolar, advancing parallel to long axis of tooth until bone of infraorbital ridge is contacted (~16 mm). Maintain finger pressure over foramen during injection and for 1-2 minutes post-injection to direct solution into infraorbital canal.

Greater Palatine (GP) Nerve Block

• Target Nerve: Greater Palatine nerve exiting the greater palatine foramen.
• Areas Anesthetized: Posterior portion of hard palate and overlying soft tissues from the 1st premolar posteriorly to the soft palate, medially to the palatal midline.
• Landmarks: Greater palatine foramen (located at junction of maxillary alveolar process and palatine bone, usually distal to 2nd or 3rd molar), palatal vault.
• Technique: Apply firm pressure with a cotton swab for 30 seconds directly over foramen to produce pressure anesthesia. Insert short needle at a 90° angle to the palatal bone from the opposite side of mouth. Deposit 0.45-0.6 mL solution slowly. (Palatal tissues are tightly bound; fast injection causes intense pain).

Nasopalatine (NP) Nerve Block

• Target Nerve: Nasopalatine nerves exiting the incisive foramen bilaterally.
• Areas Anesthetized: Palatal mucoperiosteum and hard palate of anterior maxilla from the lingual of the right canine to the left canine.
• Landmarks: Incisive papilla (located in midline posterior to central incisors).
• Technique: Apply pressure anesthesia to incisive papilla for 30s. Insert short needle lateral to incisive papilla at a 45° angle. Advance 4-5 mm until bone is contacted. Deposit 0.45 mL slowly.

Mandibular Anesthesia Techniques ($V_3$ Branches)

Because the adult mandible consists of dense, thick cortical bone (especially in the molar region), infiltration anesthesia is ineffective for adult mandibular teeth. Regional nerve blocks are required.

Mandibular Nerve Blocks (V3)
├── IA Block: Mandibular teeth to midline, Body of mandible, Mental/Incisive areas
├── Lingual Block: Anterior 2/3 tongue, Floor of mouth, Lingual periodontium
├── Buccal Block: Soft tissue/periosteum buccal to mandibular molars
├── Mental Block: Lower lip, chin, buccal mucosa anterior to mental foramen
└── Incisive Block: Premolars & Anterior teeth pulpal anesthesia + Mental areas

Inferior Alveolar (IA) Nerve Block

• Target Nerve: Inferior Alveolar nerve before it enters the mandibular foramen on the medial surface of the ramus.
• Areas Anesthetized: All mandibular teeth in the quadrant to midline; body of mandible; buccal periodontium anterior to 1st molar; lip and chin (via mental nerve branch).
• Key Anatomical Landmarks:
  1. Coronoid Notch: Greatest concavity on anterior border of ramus.
  2. Pterygomandibular Raphe: Tendinous strip extending from hamulus to mylohyoid line.
  3. Mandibular Occlusal Plane: Height reference line.
  4. Lingula: Bone spine guarding mandibular foramen.
• Needle & Technique: 25- or 27-gauge long needle (32 mm).
  • Height of Insertion: 6-10 mm superior to mandibular occlusal plane (parallel to occlusal surfaces).
  • Syringe Barrel Position: Positioned over the contralateral premolars.
  • Penetration Site: In pterygomandibular space, 3/4 of distance between coronoid notch and pterygomandibular raphe.
  • Depth of Insertion: Advance needle 20 to 25 mm (approx 2/3 to 3/4 of long needle) until bone is gently contacted.
• Troubleshooting Needle Position:
  • If bone is contacted too early (<15 mm): Needle tip is positioned too far anteriorly on ramus. Withdraw needle slightly, swing syringe barrel more anteriorly toward midline, re-advance to correct depth.
  • If bone is NOT contacted (>25 mm): Needle tip is positioned too far posteriorly into the parotid gland. DO NOT INJECT. Deposition into parotid gland causes transient facial nerve paralysis (CN VII drooping). Withdraw needle, move syringe barrel more posteriorly over molars, re-advance until bone is contacted at 20-25 mm.

Lingual Nerve Block

• Target Nerve: Lingual nerve running anterior and medial to IA nerve in pterygomandibular space.
• Areas Anesthetized: Anterior two-thirds of tongue, floor of mouth, lingual gingiva and periosteum of mandibular teeth in quadrant.
• Technique: Administered during withdrawal of the IA block needle. After depositing solution for IA block, withdraw needle to approximately half its insertion depth (10-12 mm), re-aspirate, and deposit 0.2-0.4 mL of solution.

Buccal (Long Buccal) Nerve Block

• Target Nerve: Buccal branch of $V_3$ crossing anterior border of ramus.
• Areas Anesthetized: Soft tissue and periosteum buccal to mandibular molar teeth.
• Landmarks: Mucobuccal fold distal and buccal to most posterior molar, retromolar fossa.
• Technique: Insert long or short needle into retromolar mucosa distal to last molar. Advance 1-4 mm until bone contacted. Deposit 0.2 mL.

Mental & Incisive Nerve Blocks

• Target Nerve: Mental nerve (exiting mental foramen) and Incisive nerve (continuation inside canal).
• Areas Anesthetized:
  • Mental Block: Soft tissue of lower lip, chin, and buccal mucosa anterior to mental foramen.
  • Incisive Block: Pulpal anesthesia of premolars, canine, and incisors, plus soft tissue of mental block.
• Landmarks: Mental foramen (located at apex of mandibular 1st and 2nd premolars in mucobuccal fold).
• Technique: Insert short needle into mucobuccal fold above mental foramen (~5-6 mm). For Incisive Block, apply digital pressure over foramen for 2 minutes post-injection to force anesthetic into mental foramen for pulpal distribution.

Gow-Gates & Vazirani-Akinosi Mandibular Blocks

• Gow-Gates Technique: True mandibular nerve block. Targets lateral side of condylar neck below lateral pterygoid muscle. Anesthetizes entire $V_3$ sensory distribution (IA, lingual, buccal, mental, incisive, mylohyoid, auriculotemporal nerves). High success rate (~95%), minimal aspiration risk (1%).
• Vazirani-Akinosi Technique: Closed-mouth mandibular block. Indicated for patients with severe trismus or limited jaw opening. Targets soft tissue of pterygomandibular space at height of maxillary mucogingival junction.