2 palate.pdf

development of face and palate Dr Sandeep Gupta Assistant Professor  Learning objectives At the end of the lecture student should – Know about the germ layers and formation of various components of orofacial structures – Know about the process of development of palate...

development of face and palate Dr Sandeep Gupta Assistant Professor  Learning objectives At the end of the lecture student should – Know about the germ layers and formation of various components of orofacial structures – Know about the process of development of palate – Know about process of development of tongue Embryo at 4-5 weeks (Lateral view)  Introduction Face is derived from the following structures that lie around the stomodaeum (4th week): 1. Fronto-nasal process 2. 1st Pharyngeal (mandibular) arch of each side: (a) Maxillary process (b) Mandibular process  Formation of mandibular & maxillary processes (4th week) The single fronto-nasal prominence ventral to the forebrain. The paired maxillary prominences develop from the cranial part of first branchial arch. The paired mandibular prominences develop from the caudal part of first branchial arch.  Five facial primordia appear as prominences around the stomodeum: FNP The single frontonasal prominence The paired maxillary prominences The paired mandibular prominences  1 Frontonasal prominence 2 Maxillary prominences 2 Mandibular prominences Stomatodeum  Further development of face Formation of nasal placodes and lens placodes (4th week). Nasal placodes sinks below to form nasal pits (5th week). Elevations of the nasal pits form the medial and lateral nasal processes. Nasal placodes are primordia of the nose and nasal cavities.  Derivatives of Facial Components  Fronto-nasal prominence forms the: Forehead and the bridge of the nose Frontal and nasal bones  Maxillary prominences form the: Upper cheek regions and most of the upper lip Maxilla, zygomatic bone & secondary palate Mandibular prominences fuse and form the: Chin, lower lip, and lower cheek regions Mandible The lateral nasal prominences form the alae of the nose The medial nasal prominences fuse and form the intermaxillary segment Development of Palate The medial nasal swellings enlarge, grow medially and merge with each other in the midline to form the intermaxillary segment. Human embryo: 7 weeks  Intermaxillary Segment Gives rise to the: Philtrum of lip Premaxillary part of the maxilla, that bears the upper 4 incisors and the associated gums. Primary palate (region of hard palate just posterior to the upper incisors).  Palatogenesis Begins at the end of the 5th week. Gets completed by the end of the 12th week. The most critical period for the development of palate is from the end of 6th week to the beginning of 9th week. The palate develops from two primordia: The Primary palate The Secondary palate  The Primary Palate Begins to develop:  Early in the 6th week.  From the deep part of the intermaxillary segment, as median palatine process. Lies behind the premaxillary part of the maxilla. Fuses with the developing secondary palate.  The primary palate represents only a small part lying anterior to the incisive fossa, of the adult hard palate Primary palate Hard palate Secondary palate Soft palate  The Secondary Palate Is the primordia of hard and soft palate posterior to the incisive fossa. Begins to develop:  Early in the 6th week.  From the internal aspect of the maxillary processes, as lateral palatine process.  In the beginning, the lateral palatine processes project inferomedially on each side of the tongue. With the development of the jaws, the tongue moves inferiorly. During 7th & 8th weeks, the lateral palatine processes elongate and ascend to a horizontal position above the tongue. Tongue  Gradually the lateral palatine processes:  Grow medially and fuse in the median plane.  Also fuse with the: Posterior part of the primary palate & The nasal septum  Fusion with the nasal septum begins anteriorly during 9th week, extends posteriorly and is completed by 12th week. Bone develops in the anterior part to form the hard palate. The posterior part develops as muscular soft palate Embryological subdivisions of the palate Development of Tongue  Formation of tongue 1st,2nd, 3rd, 4th pharyngeal arches Median swelling-tuberculum impar Two lateral swellings –lingual Caudal medial swelling-hypobrachial eminence  Anterior 2/3 of the tongue Formation: median and lateral tongue buds that arise from the floor of the 1st pharyngeal arch and then grow rostrally. thus it is formed by fusion of -- tuberculum impar, two lingual swellings The tongue buds are then invaded by occipital myoblasts that form the intrinsic muscles of the tongue.  Thus anterior 2/3rd of tongue is supplied by lingual branch of mandibular nerve and chorda tympani nerve Posterior 1/3rd of tongue is supplied by glossopharyngeal nerve (nerve of 3rd arch) Most posterior 1/3rd of tongue is supplied by superior laryngeal nerve (nerve of 4th arch)  Musculature of tongue is derived from occipital myotomes--explains nerve supply by hypoglossal nerve, nerve of these myotomes.  Posterior 1/3rd of tongue Formed from cranial part of hypobranchial eminence ( copula) The second arch mesoderm gets buried below the surface. The third arch mesoderm grows over it to fuse with mesoderm of first arch. posterior one third of tongue thus formed by third arch mesoderm. posterior most part of tongue is derived from fourth arch  Thus swellings from the floor of the 3rd and 4th pharyngeal arches overgrow the 2nd arch and fuse with the anterior 2/3 of the tongue. Posterior 1/3 of the tongue is derived from the 3rd and 4th arches Intrinsic musculature is also derived from occipital myoblasts. The line of fusion of the anterior 2/3 and posterior 1/3 of the tongue is indicated by the terminal sulcus. Thank You