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10 Implant Tribune Italian Edition - Settembre 2016 Ricerca & Clinica < pagina 9 A literature review was conducted to assess the anatomy of the an- terior mandible, through a search in electronic databases, namely MEDLINE (PubMed), Embase and the Cochrane Library. Boolean op- erators and truncation were used for the search. The search terms used were “(anatomy OR vessel* OR muscle OR artery) AND anterior AND mandible”. The inclusion cri- teria were case reports, anatomical studies on cadavers or radiographic studies of the anatomy of the floor of the mouth and the anterior man- dible, performed in humans. The exclusion criterion was anticoagu- lated patients. Results Bony anatomy and musculature of the sublingual region Among the soft tissues surround- ing the mandible are the floor of the mouth (made of up the sublingual region and the tongue itself), and the mental and genial areas. The sublingual region is limited below by the mylohyoid muscle, laterally by the hyoglossus, genioglossus and geniohyoid muscles, above by the mucosa of the floor of the mouth, and anteriorly by the body of the mandible (Fig. 1). The mandible in the symphyseal area is dropshaped and tilted toward the lingual area. The mandibular symphysis is the medial area of the mandible that results from the endochondral os- sification and the subsequent mer- gence of Meckel’s cartilage in the 24th week of intrauterine life9 . At that time, the musculature forms, affecting the development and sub- sequent growth of the mandible10. In this region, the mental spines stand out where the quadratus labii inferioris muscle forms. The supe- rior and inferior mental spines are located on the mandible’s inner side (Fig. 2). The genioglossus muscle originates from the superior mental spine, while the geniohyoid muscle originates from the inferior mental spine (Figs. 1 & 2). The digastric fos- sa, from which the anterior digas- tric muscle originates, is located on the mandible’s inner side, near the lower edge in the paramedian loca- tion (Fig. 3). Sublingual artery The sublingual artery follows a me- dial course to the mandible within the sublingual gland and supplies the mylohyoid muscle (Fig. 4). It is at the level of this muscle that the sublingual artery issues branches that anastomose with the submen- tal artery11 . The artery ends in the mental spine. Submental artery This artery is a branch of the facial artery. It passes together with the mylohyoid nerve along the inferior surface of the homonymous muscle to the anterior region, where it sup- plies the anterior digastric muscle (Fig. 5). At this anterior level, the per- forating branches of the submental artery pierce the mylohyoid mus- cle to anastomose with perforating branches of the sublingual artery12 . Vascular anastomosis There are many anastomoses of the arteries involved in the sublingual region. An anastomosis found be- tween the lingual and the submen- tal arteries runs along the bottom flange of the mandibular body and through the mylohyoid muscle (Fig. 6). Anastomoses between both sub- lingual contralateral arteries in the symphysis are frequent too (Fig. 7). In summary, the mandibular sym- physeal area is supplied by multiple vascular structures from different origins and presents a variability dependent on the anastomosing relationships established by the terminal branches of these struc- tures13-15 . Discussion The sublingual region is well vas- cularized, with several anastomo- ses that can impair hemostasis if bleeding occurs7 . Treatment can be uncomfortable for the patient, so the priority is to prevent trau- ma occurring through good an- atomical knowledge of the area and proper planning of the sur- gery. Regarding the bony anatomy and musculature of the anterior mandible, the mental spines are located in the mandible’s inner side. Some studies highlight its morphological variability, for ex- ample the variability in the dis- tance from the mental spine to the inferior border of the mandible or to apices of the mandibular inci- sors16 . The genioglossus and genio- hyoid muscles originate from the mental spines, so this variability may increase the risk of damage to these structures when dental implants are placed in this area. The digastric fossa is located on the mandible’s inner side, near the lower edge in the paramedian lo- cation. Therefore, an injury caused by piercing of the mandibular cor- tical bone, for example when plac- ing a dental implant, may affect different muscles depending on whether the implant preparation is in the medial or paramedian loca- tion in relation to the mandibular symphysis17 . Three arteries supply this anatomical region: (a) the sub- lingual artery, which is a branch of the lingual artery; (b) the submen- tal artery, which is a branch of the facial artery; and (c) the chin ar- tery, which is the terminal branch of the inferior alveolar artery. The lingual and facial arteries are both branches of the external carotid artery and the inferior alveolar artery is a branch of the maxillary artery11 . Katsumi et al. classify the arterial supply to the floor of the mouth into four types18 . In Type I, the sublingual region is supplied by the sublingual artery. In Type II, it is supplied by the sublingual and submental arteries. In Types III and IV, it is supplied by the submental artery (the difference between the last two being that in Type III the deep lingual artery— which supplies the tongue—orig- inates from the lingual artery, and in Type IV it comes from the submental artery). The sublingual artery is the main supply of the sublingual region. Anatomical and radiographic studies have identi- fied lingual vascular canals in the mandible where the sublingual artery pierces the mandibular lin- gual cortical plate (Figs. 6 & 8)19-21 . The frequency of lateral lingual canals in the area of the mandib- ular incisors varied between 33.1% and 100.0% and in the area of the canines between 69.0% and 80.0% of the cases19-21 . The location of the lingual canals coincided with the most frequent sites of clinically important bleeding during im- plant placement. The diameter of the canals was on average 1.2 mm, which is enough to produce severe sublingual bleeding22 . > pagina 11 Fig. 2 - Anatomical structures of the sublingual space. Sagittal plane. Fig. 3 - Musculature of the mandible and sublingual artery piercing the mandibular lingual plate. Fig. 4 - Anatomical photograph of the arterial supply of the floor of the mouth. Fig. 5 - Course of the facial and submental arteries.