Anatomy of mandible

a brief description of the anatomy of the mandible, its muscular attachments and its importance in implant placement

1. Anatomy of mandible And its importance in implant treatment Shashi kiran s 20/06/18

2. introduction The mandible- largest and strongest bone of the face. Horseshoe shaped body which lodges the teeth Pair of Rami

3. Body of the mandible Outer and inner surfaces and upper and lower borders Outer surface Symphysis menti Mental protuberance Mental foramen Oblique line Incisive fossa

4. Inner surface M ylohyoid line Sub-mandibular fossa Sub-lingual fossa Superior and inferior genial tubercles Mylohyoid groove Upper border- sockets Lower border- base, digastric fossa

5. ramus Quadrilateral in shape Lateral and medial surfaces Anterior, posterior, upper and lower borders Coronoid and condylar processes

6. Lateral surface- relatively featureless, bears the oblique ridge in lower half Medial surface- Mandibular foramen, mandibular canal Lingula Mylohyoid groove Upper border- thin, mandibular notch Lower border- base, continuous with posterior border at the angle Coronoid process Condylar process- fibrocartilage- TMJ, neck, pterygoid fovea

7. Attachments and relations Buccinator , depressor labii inferioris , depressor anguli oris Incisive fossa-Mentalis, mentalis slips of orbicularis oris Deep cervical fascia Platysma Masseter Parotid gland

8. Mylohyoid muscle Superior constrictor Pterygomandibular raphe Genioglossus, geniohyoid Anterior belly of digastric Sphenomandibular ligament Medial pterygoid Temporalis Lateral pterygoid Latreal part of the neck- Lateral ligament of temporomandibular joint

9. Foramina, nerves and vessels Mental foramen- mental nerves and vessels Mandibular foramen and canal- IAN and vessels Mylohyoid groove- mylohyoid nerve and vessels Lingual nerve Maxillary artery Mandibular notch- masseteric nerves and vessels Auriculotemporal nerve and superficial temporal artery- neck Facial artery Accessory foramina

10. Alveolar process That portion of maxilla and mandible that forms and supports the tooth socket. Parts- 1. external plate of cortical bone 2. alveolar bone proper (lamina dura) – cribriform plate 3. cancellous trabeculae

11. ossification Mandible is the second bone next to clavicle to ossify in the body. Its greater part ossifies in membrane. The parts ossifying in cartilage- incisive part below the incisors, coronoid and condylar process, and upper half of the ramus above the level of mandibular foramen Each half of the mandible ossifies from only one centre which appears at about the 6 th week of intrauterine life in the mesenchymal sheath of meckels cartilage near the future mental foramen At birth mandible consists of 2 halves connected at the symphysis menti by fibrous tissue. Bony union takes place during the first year of life.

12. Age changes in mandible Infants and children- 2 halves fuse during the first year of life At birth the mental foramen opens below the sockets for the two deciduous molar teeth near the lower border. Mandibular canal runs near the lower border. The foramen and canal gradually shifts upwards Angle- obtuse 140 degrees or more The coronoid process is large and projects upward above the level of the condyle.

13. In adults The mental foramen opens midway between the upper and lower borders Mandibular canal runs parallel to the mylohyoid line Angle- 110-120 degrees In old age Height of the bone is markedly reduced Mental foramen and the mandibular canal are close to the alveolar border Angle- obtuse 140 degrees

14. Mylohyoid muscle Severely resorbed ridge- origin of mylohyoid muscle approximates the crest of the ridge, especially in the posterior mandible. In these cases, surgical manipulation of the crest may injure the muscle. A mandibular periosteal reflection for sub periosteal implant often reflects this muscle to the second molar region. The sub structure of the implant then has a permucosal site in the 1 st molar region and a lingual primary strut above and below the muscle. Surgical manipulation of the tissue of the floor of the mouth- edematous swelling of the sub lingual and the sub mandibular space, echymossis can occur sub- cutaneously or sub- mucosally . In some cases- cellulitis or abcess sub- lingually or sub- mandibularly

15. genioglossus Origin- superior genial tubercle Main protruder of the tongue, branch of hypoglossal nerve During elevation of lingual mucosa and before impression making for a sub periosteal implant, one should be aware of the origin to avoid causing injury. A portion of the muscle can be reflected from the tubercle but should not be completely detached from the tubercle because it may result in retrusion of the tongue and possible airway obstruction.

16. Medial pterygoid Medial pterygoid bounds the pterygo mandibular space medially. This space is entered when an IANB is admistered Infection of this space is dangerous because of its proximity to parapharyngeal space and the potential spread of infection to mediastinum. Mandibular nerve

17. Temporalis Origin from temporal fossa and inserts into the coronoid process and anterior border of the ramus Retromolar triangle- surgical exposure of mandibular ramus medially would involve this triangle which may lead to transaction and post op pain. Incisions placed on the anterior ascending ramus should be placed below the insertion of the two tendons of the muscle. Retractor and elevator, mandibular nerve

18. mentalis Origin- mental tubercles, insertion- skin of the chin Complete reflection of the mentalis muscle for the purpose of extension of a sub periosteal implant may result in witch’s chin due to failure of muscle re attachment. If the muscle is completely detached to expose the symphysis, then an elastic bandage is applied externally to the chin for 4 days to help in re attachment. Facial nerve

19. masseter This muscle can easily be deflected during surgery to expose bone for ramus extension needed for lateral support for a sub periosteal implant. The space between the masseteric fascia and the muscle is a potential surgical space known as the masseteric space into which infection may spread causing myositis and trismus. Mandibular nerve

20. Inferior alveolar nerve In an excessively resorbed ridge, mental foramen with its contents can be found on the crest of the ridge. While making incisions or reflection of mucosa in this region, care should be taken to avoid injury to these vital structures. Knowledge of the position of the mandibular canal in vertical and buccolingual dimensions is of paramount importance during site prep for implants

21. Lingual nerve Because this nerve lies just medial to the retromolar pad, incisions in this region should remain lateral to the pad. And the mucosal reflection should be done with the periosteal elevator in constant contact with bone to prevent injury to the nerve. Improper reflection of a lingual mucoperiosteal flap may injure the lingual nerve and produce ipsilateral paraesthesia or anaesthesia, loss of taste, and reduction of salivary secretion.

22. Long buccal nerve The nerve courses between the 2 heads of lateral pterygoid and precedes medial to the medial tendon of the temporalis to gain access to the buccinator . The nerve supplies the skin of the cheek and runs down to the level of the external oblique ridge, penetrates the buccinators and spread its branches under the cheek mucosa alveolar mucosa and attached gingiva opp molar teeth An implantologist planning to access the ramus for the purpose of excising block graft should be aware of the buccal nerve and avoid injuring it. In addition, surgical manipulation in this area (insertion of sub periosteal implant) may injure this nerve

23. Blood supply of the mandible Major artery- inferior alveolar artery Incisive branch is often severed during the harvest of a mono cortical symphyseal block of bone for grafting resorbed ridges Changes with age Reversal of flow Atherosclerotic changes- tortuous and narrow Arteries that supply blood after the interruption – mental artery, mandibular branch of sub lingual artery, facial artery These anastomoses are critical in procedures with mucoperiosteal flaps.

24. conclusion The surgical anatomy of the maxilla and mandible provide the foundation required to safely insert dental implants. The anatomy is also a requisite to the understanding of complications that may inadvertently occur during surgery such as injury to blood vessels and nerves This information also provides the operator the confidence needed to deal with these complications.

25. references Bd Chaurasia’s Human Anatomy 2 nd edition Carranza’s clinical periodontology 10 th edition Contemporary implant dentistry, Carl E Misch , 3 rd edition