DENTAL GROSS ANATOMY CASE 4.1 (INFERIOR ALVEOLAR NERVE BLOCK)

HISTORY A 23 yo man went to a dentist to have a mandibular 3rd molar extracted. The patient requested that plenty of anesthetic be given because he was extremely sensitive to pain. The dentist inserted the needle through the mucous membrane on the inside of the patient’s mouth, just lateral to the ridge produced by the underlying pterygomandibular raphe. After penetrating the adjacent muscle the tip of the needle came to rest near the lingula. In a few minutes the patient stated that his gum, lower lip, chin and tongue on the affected side were numb. During the extraction the patient said he felt pain; the dentist injected more anesthetic. The tooth was removed without further incident. As the patient was leaving the dentist’s office he happened to look in a mirror and was surprised to find that he was unable to close his eye and that his mouth sagged on the affected side. He also noticed that his ear lobe was numb. The dentist explained that because of the large amount of anesthetic injected, other nerves in addition to those supplying the teeth had been anesthetized. He assured his patient that these effects would disappear in 3-4 hours.

Name the nerve supplying the mandibular 3rd molar tooth. What is this nerve a branch of (be specific)? In what region of the head does it arise? Name the nerve supplying the mandibular 3rd molar tooth. What is this nerve a branch of (be specific)? In what region of the head does it arise? Inferior alveolar nerve. It is a branch of the posterior division of the mandibular nerve (V3). It arises in the infratemporal fossa.

NERVE SUPPLY OF THE TEETH V3 (POST. DIVISION) INFERIOR ALVEOLAR N.

The pterygomandibular raphe is used as a landmark when giving this type of nerve block. What is the pterygomandibular raphe and what are its bony attachments? The pterygomandibular raphe is used as a landmark when giving this type of nerve block. What is the pterygomandibular raphe and what are its bony attachments? The raphe is a band of connective tissue which separates the buccinator and superior constrictor muscles and serves as a partial origin for each. The raphe extends from the hamulus of the medial pterygoid plate (superiorly) to the posterior end of the mylohyoid line of the mandible (inferiorly).  

Pterygoid hamulus Buccinator m. Pterygomandibular raphe Superior pharyngeal constrictor m. Mandible

PTERYGOMANDIBULAR FOLD CAN BE SEEN AND PALPATED Maxillary anterior teeth Pterygomandibular fold Uvula Dorsum of tongue

What muscle was penetrated by the needle?   The buccinator.

Buccinator m.

What is the lingula of the mandible? What fibrous structure attaches to it? What function does the lingula and the fibrous structure have when giving this type of nerve block? What is the lingula of the mandible? What fibrous structure attaches to it? What function do the lingula and the fibrous structure have when giving this type of nerve block? The lingula is a bony projection on the medial surface of the ramus of the mandible close to the mandibular foramen. The sphenomandibular ligament (running from the spine of the sphenoid to the lingula of the mandible) attaches to it. When the tip of the needle is correctly placed lateral to the ligament, the ligament and lingula make a funnel directing the anesthetic solution into the foramen.

Lingula Mandibular foramen

Sphenomandibular lig.

Why was the patient’s chin and lower lip on the injected side also anesthetized? 5. Why was the patient’s chin and lower lip on the injected side also anesthetized?   Because the mental nerve, a terminal branch of the inferior alveolar nerve, emerges from the mental foramen and supplies the chin and lower lip.

Temporalis fascia and m. Anterior division (V3) (mostly motor) Posterior and anterior deep temporal nn. Posterior division (V3) (mostly sensory) Foramen ovale Masseteric n. Lateral pterygoid n. and m. Auriculotemporal n. Chorda tympani n. Buccal n. Lingual n. Inferior alveolar n. (cut) Mylohyoid n. Mylohyoid m. (cut) Mental n. Inferior alveolar n. (cut) Digastric m. (anterior belly)

Why was the patient’s tongue on the injected side numb? Specifically, what part was affected? Were the tongue muscles paralyzed? Why or why not? Why was the patient’s tongue on the injected side numb? Specifically, what part was affected? Were the tongue muscles paralyzed? Why or why not?   The anterior two-thirds of the patient’s tongue was numb because it is innervated by the lingual nerve which descends just anterior to the inferior alveolar nerve near the mandibular foramen (i.e., the lingual nerve was also anesthetized). The tongue muscles were not affected because they are innervated by XII.

Temporalis fascia and m. Anterior division (V3) (mostly motor) Posterior and anterior deep temporal nn. Posterior division (V3) (mostly sensory) Foramen ovale Masseteric n. Lateral pterygoid n. and m. Auriculotemporal n. Chorda tympani n. Buccal n. Lingual n. Inferior alveolar n. (cut) Mylohyoid n. Mylohyoid m. (cut) Mental n. Inferior alveolar n. (cut) Digastric m. (anterior belly)

INNERVATION OF TONGUE MUSCLES XII Styloglossus m. Genioglossus m. Hyoglossus m.

What is the relationship between the sensory nerve identified above (#6) and the mandibular 3rd molar? Is this nerve liable to be injured by the clumsy extraction of this tooth? What is the relationship between the sensory nerve identified above (#6) and the mandibular 3rd molar? Is this nerve liable to be injured by the clumsy extraction of this tooth? The lingual nerve lies just posterior and inferior to the mandibular 3rd molar. Yes.

Lingual n. 3rd Molar

Describe the innervation of the gingiva of the mandibular teeth. In view of your answer, should the dentist have anesthetized any other nerve before performing this extraction? Describe the innervation of the gingiva of the mandibular teeth. In view of your answer, should the dentist have anesthetized any other nerve before performing this extraction? Buccal gingiva opposite molars supplied by buccal nerve. Buccal gingiva opposite premolars, canine and incisors supplied by mental nerve. Entire lingual gingiva supplied by lingual nerve. Yes, the dentist should have also anesthetized the buccal nerve.

INNERVATION OF TEETH & GINGIVAE Good summary slide for students to study.

What caused the patient’s facial paralysis and loss of sensation in his ear lobule? 9. What caused the patient’s facial paralysis and loss of sensation in his ear lobule?   Because a relatively large amount of anesthetic was injected some of it spread into the nearby parotid gland and adjacent tissues. Since VII pierces the parotid gland it was anesthetized, thus causing facial paralysis. The nearby great auricular nerve which supplies the ear lobule was also affected.

INFERIOR ALVEOLAR NERVE BLOCK Medial pterygoid m. Parotid gl. & facial n. Sphenomandibular ligament Lingual n. Inferior alveolar n. Pterygomandibular raphe Ramus of mandible Temporalis m. insertion Masseter m. Buccinator m.

What complication might have arisen if the dentist had injected too far laterally? Too far medially? (Hint: what muscle might be pierced?) What complication might have arisen if the dentist had injected too far laterally? Too far medially? (Hint: what muscle might be pierced?) When the tip of the needle is properly placed it lies in the pterygomandibular space between the medial pterygoid muscle (medially) and the ramus of the mandible (laterally). Thus, if the needle is too far lateral it may come into contact with the mandible (or the insertion of the temporalis muscle) in which case the anesthetic is unlikely to be effective. If the needle is too far medial it may enter the medial pterygoid muscle. Bleeding within the medial pterygoid can cause reflex spasm of the muscle (trismus). The patient may be unable to open his/her mouth as a result. (Note: Even correctly placed injections may sometimes percolate through the inferior orbital fissure and cause transient visual disturbances by affecting the nerve supply of the extraocular muscles).

INFERIOR ALVEOLAR NERVE BLOCK Medial pterygoid m. Parotid gl. & facial n. Sphenomandibular ligament Lingual n. Inferior alveolar n. Pterygomandibular raphe Ramus of mandible Temporalis m. insertion Masseter m. Buccinator m.

END OF CASE 4.1