Welcome to the second part of the lecture on clinical anatomy. Previously, we have discussed the importance of the structure of the maxilla. And now, we will talk about the mandible. Ian, how do you avoid implant surgical complications? We could avoid surgical complications by proper assessment of the ridge morphology, and relevant structures before implant surgery. If we know where they are, we could stay away from them by proper incision designs, flat managements, and osteotomies. To assess the anatomy, a panoramic radiograph is very useful. It gives you the information of the bone height, and the location of the important structures like the sinuses, the mandibular canal, and mental foramen. For a standard implant case, it is quite sufficient. However, for patients with moderate or severe bone resorption, we would recommend a CT scan for evaluation, because it shows a three-dimensional view of the atrophic ridge. Bone quality could also be assessed and classified into different types. In addition, detailed representations and localizations of the bony structures such as the septae in the sinuses, foramen, and intra-osseous channels for nerves and blood vessels are possible. For the structures that we cannot assess preoperatively, such as the nerves and blood vessels in the soft tissues, we could only estimate where they are with the information obtained from human cadaver dissections or other imaging studies. Mandible is a U-shaped bone, formed by the fusion of two separate halves at the mental symphysis. From the side, we can see a vertical ramus, and a horizontal body, joined by the angle of the mandible. The body is further divided into the upper alveolar bone and the lower basal bone. There are two bony extensions on the ramus. One is the coronoid process, while the posterior one is the condylar process, which forms the temporomandibular joint with the temporal bone above. The ramus can be viewed from lingual. Midway from its vertical height, there is a bony projection called a lingula. Below this, is the mandibular foramen, which leads to a bony canal called the mandibular canal. It travels anteriorly, and deviates sharply towards the buccal at the premolar region to exit as the mental foramen. Anterior to this opening is a canal called incisive canal where the nerves and blood vessels serve the anterior teeth. If the mandible is cut at different regions, it can be shown that the mandibular canal takes up a lingual position initially, but gradually becomes more buccal in the premolar region. Besides, the lingual outline of the mandible is also more concave in the second molar region than in the first molar region. The nerves of the mandible that we would encounter during implant surgeries are the lingual nerve, and the inferior alveolar nerve. They are both sensory branches of the trigeminal nerve. The lingual nerve passes the lingual bony cortex at the posterior mandible, before descending to the base of the tongue. The nerve supplies the sensation and taste of the anterior 2/3 of the tongue, and the sensation of lingual gingivae. The lingual nerve could be damaged during implant placement of the lower second molar, which would cause sensory disturbance of the tongue, and impairment of taste. To avoid this complication, before making the incision, we shall palpate the lingual plate because the soft tissue can be thick and mask the bony morphology there. The crestal incision needs to be directed toward the external oblique ridge distally, and the lingual mucoperiosteum shall be raised carefully and be protected before drilling and implant insertion. The inferior alveolar nerve enters the mandibular foramen at medial side of the ramus, and travels through the mandibular canal. It then branches into mental and incisive nerves at premolar region. Before the mental nerve exits through the mental foramen, it sometimes forms loop anteriorly. The nerve supplies the lower lip, chin, and the lower teeth. Trauma to the nerve would cause different degrees of neurosensory disturbances. The inferior alveolar nerve could be injured during implant placement and bone graft harvesting at the posterior mandible by drilling or by compression of implant body. Moreover, direct trauma of mental nerve could occur during relieving incisions and flat manipulations near to the mental foramen. The external carotid artery gives off branches to supply the mandible by the maxillary, facial, and lingual arteries. Maxillary artery is a long artery, with many branches which supplies the maxilla, nasal cavity, and muscles of mastication. A branch called the inferior alveolar artery supplies the mandible and the mandibular teeth. It enters the mandibular foramen, and travels in the mandibular canal, and branches to become the mental artery at the mental foramen. The terminal branch of it is the incisive branch, that supplies the incisors and canines. The external carotid branches off at two points. The first one is the facial artery, and runs superficially across the face. Another one, the lingual artery, that supplies the deep structures, like the tongue, and also the floor of the mouth. The lingual artery has three main branches. Also lingual supplies the posterior 1/3 of the tongue. The deep lingual can be seen by sticking out one's tongue. The last one is the sublingual, which goes forward at the base of the tongue. It has branches that penetrate the lingual plate and form anastomosis with incisive blood vessels. The floor of the mouth is bounded by the mylohyoid muscle. The muscle attaches to the mylohyoid line of the medial side of mandible, passing downward and unite medially. Posteriorly, it attaches to the hyoid bone. Above the muscle lies the sublingual salivary gland, which is closely associated with the Wharton's duct of the submandibular gland. The superficial and deep parts of the submandibular gland lie at the posterior edge. The branches of the sublingual and submental arteries are present anteriorly. Normally, the contents of the floor of mouth is quite distant from the alveolar crest. In the atrophic mandible, however, the structures become relatively superficial. Implant at the anterior mandible could be risky, if the arteries are damaged. This may cause a haematoma at the floor of mouth, which could displace the tongue backward and compress the airway. Injury of the sublingual gland is also possible. If it is damaged, mucus extravasation could occur, and cause a swelling at the floor of mouth. The swelling could sometimes herniate through the mylohyoid muscle, causing submandibular swelling, which is known as plunging ranula. We hope these overviews have helped you in understanding anatomy in relation to implant surgery. Good luck and Good-bye.