GROWTH AND DEVELOPMENT OF TONGUE AND SALIVARY GLANDS
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INDIAN DENTAL ACADEMY
Leader in continuing dental education
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CONTENTS
INTRODUCTION DEFINITION OF GROWTH AND DEVELOPMENT DEVELOPMENT OF TONGUE ANOMALIES OF TONGUE DEVELOPMENT OF SALIVARY GLANDS ANOMALIES OF SALIVARY GLANDS PROSTHODONTIC CONSIDERATATIONS SUMMARY REFERENCES www.indiandentalacademy.com
Introduction
Tongue is a muscular organ in the floor of the mouth associated with a function of taste, speech, mastication and deglutition. The tongue also influence the path of eruption of teeth. The salivary glands are important organs of oral cavity which produces saliva, essential fluid required for normal mastication, swallowing and digestion. Hence it is essential to study the growth and development of tongue and salivary gland. www.indiandentalacademy.com
Definition of growth: Krogman : Increase in size, change in proportion and progressive complexity. Todd: An increase in size. Moyers: Quantitative aspect of biological development per unit time. Definitions of development: Todd: Development is progress towards maturity. Moyers: Development refers to all the naturally occurring unidirectional changes in the life of an individual from its existence as a single cell to its eloboration as a multifactorial unit terminating in death. Thus, it encompasses the normal sequential events between fertilization and death.
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DEVELOPMENT OF TONGUE
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During the early 4th week of I.U.L. the lateral part of mesoderm of ventral foregut region becomes segmented to form a series of 5 distinct bilateral mesenchymal swellings called as pharyngeal arches. Pharyngeal clefts: Arches are seperated by deep grooves called pharyngeal clefts. Pharyngeal pouch: are outpocketings appearing along the most cranial part of foregut.
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DEVELOPMENT OF TONGUE
Tongue arises from the ventromedial wall of the primitive oropharynx from the inner lining of the first four branchial arches. Development of tongue can be studied under the following headings
Anterior 2/3rd (or the body of tongue) Posterior 1/3rd(base of the tongue) Musculature and connective tissue Papillae and taste buds. The nerve supply www.indiandentalacademy.com
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Anterior 2/3 of the tongue rd
During the 4th week of IUL, paired lateral swellings appear on the internal aspect of the 1st brachial arches Tuberculum impar is a median eminence whose caudal end has a pit called the foremen caecum
These lateral swellings rapidly enlarge, merge with each other and overgrow the tuberculum impar to form the body of the tongue
A U shaped sulcus, the linguogingival groove develops in front of the oral part, which allows it to be free and highly mobile except at the region of the lingual frenum where
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Posterior 1/3 of the tongue rd
The base of the tongue is initially indicated by two midline elevations that develop caudal to the foremen caecum The copula The hypobrachial eminence As the tongue develops, the hypobranchial eminence,overgrows the second branchial arch to become continous with the body of the tongue. The site of union b/w the the body and base of the tongue is delineated by a V shaped groove, called the sulcus terminalis. www.indiandentalacademy.com
Musculature and connective tissue ď Ž
Branchial arch mesenchyme forms the connective tissue and the lymphatic and the blood vessels of the tongue
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Tongue musculature` ď Ž
During the 5th to 7th week of the IUL, 3-4 occipital myotomes, migrate anteriorly to form the musculature of the tongue.
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Papillae of the tongue ď Ž
Papillae are projections of mucous membrane on the dorsum of the tongue Circumvalate papillae Fungiform papillae Filliform papillae Foliate papillae
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Taste buds ď Ž
Taste buds are located on the dorsum of the tongue and are associated with the papillae Taste buds appear around 8th week of IUL Taste buds arise by inductive interaction b/w the epithelial cells and the invading gustatory nerve cells
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Nerve supply of the tongue ď Ž
Development of tongue from the branchial arch explains its nerve supply Sensory supply Ant 2/3rd-Lingual nerve for general sensation.chorda tympani for the special sensation Post 1/3r Glossopharyngeal nerve Posterior most part -vagus nerve Motor supply All the intrinsic and extrinsic muscles except the palatoglossus are supplied by the hypoglossal nerve. Palatoglossus –pharyngeal plexus
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Arterial supply: It is chiefly derived from the lingual artery a branch of external carotid artery. The root of the tongue is also supplied by tonsillar and ascending pharyngeal artery. Venous drainage: The deep lingual vein is the principal vein of the tongue. Lymphatic drainage: The tip of the tongue drains into submental nodes. The remaining part of the anterior 2/3rd drains into the submandibular nodes. The posterior 1/3rd of the tongue drains into jugulo-omohyoid nodes www.indiandentalacademy.com
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Structure of the tongue
The bulk of the tongue is made of muscles Intrinsic muscles Extrinsic muscles
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The oral part of the dorsum of the tongue has numerous papillae associated with the taste buds. The pharyngeal part of the dorsum of the tongue is rich in lymphoid follicles that is collectively called the lingual tonsil. Mucous glands are also present. www.indiandentalacademy.com
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The inferior surface of the tongue shows the frenulum linguae,deep lingual veins and the plica fimbriata
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The entire tongue is in the mouth at birth .Its post 1/3rd desends into the pharynx by the age of 4yrs. The tongue normally doubles in length,breadth and thickness from birth to adolesence reaching maximal size at about 8yrs.
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ANOMILIES OF THE TONGUE
Aglossia Microglossia Macroglossia Bifid tongue Ankyloglossia Lingual thyroid Fissured tongue Median rhomboid glossitis www.indiandentalacademy.com
ANKYLOGLOSSIA
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LINGUAL THYROID
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FISSURED TONGUE
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MEDIAN RHOMBOID GLOSSITIS
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Development of salivary glands www.indiandentalacademy.com
DEVELOPMENT OF SALIVARY GLAND
All salivary glands show a similar pattern of development They originate from oral epithelial buds invading the underlying mesenchyme.
The origin of epithelial bud is belived to be ectodermal in parotid and minor saliavary gland and endodermal in submandibular and sublingual glands.
The connective tissue stroma and blood vessels form from the mesenchyme
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GLAND
ORIGIN
I.U.LIFE
PAROTID GLAND
CORNERS OF THE STOMODEUM
6TH WEEK
SUBMANDIBULAR GLAND
FLOOR OF THE MOUTH
END OF 6TH WEEK
SUB LINGUAL GLAND
LATERAL TO SUBMANDIBULAR PRIMORDIUM
8TH WEEK
MINOR SALIVARY GLAND
BUCCAL EPITHELIUM
12TH WEEK
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STAGES OF DEVELPOMENT
STAGE I: Bud formation :Induction of oral epithelium by underlying mesenchyme
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STAGE -II Formation and growth of epithelial cord.
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STAGE III: Initiation of branching in terminal parts of epithelial cord and continuation of glandular differentiation
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STAGEIV: Dichotomous branching of epithelial cord and lobule formation
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STAGE V:Canalization of presumptive ducts.
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STAGE VI: Cytodifferentiation
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Serous acini
Mucous acini
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Terminal tubules – intercalated ducts Striated ducts Intracalated ducts Myoepithelial cells Full differentiation of functional secretory components is apparent at birth but its not complete until the onset of solid diet and the presence of masticatory stimuli www.indiandentalacademy.com
Types:
MAJOR SALIVARY GLANDS
Parotid gland Submandibular gland Sublingual gland
MINOR SALIVARY GLANDS
Buccal Labial Lingual Palatine Glossopalatine
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GLAND
LOCATION
DUCT
SECRETION
Parotid
Ant to the Stensons duct external acoustic meatus
Purely serous
Submandibular
Submandibular triangle
Whartons duct
Predominantly serous
Sublingual
Floor of the mouth
Bartholins duct
Predominantly mucous
Minor salivary glands
Beneath the epithelium
Directly into the mouth
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Nerve supply
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Developmental anomalies
Aplasia Hyperplasia Atresia
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Prosthodontic considerations
Tongue plays an important role in the stability of lower denture. Macroglossia – Stability of the denture is reduced,hence Surgical trimming is indicated Microglossia – Inadequate lingual seal. Bifid tongue - Surgical reconstruction is required. Ankyloglossia – Poor registration of the lingual seal. Frenectomy is indicated. Aplasia Denture produces soreness and irritation Lack www.indiandentalacademy.com of retention of the denture
Tongue position is important to the prognosis of mandibular denture:
Wright classification of tongue position:
Class I : The tongue lies in the floor of the mouth with the tip forward and slightly below the incisal edges of the mandibular anterior teeth. Class I position is ideal for construction of mandibular denture.
Class II: The tongue is flattened and broadened but the tip is in a normal position.
Class III: The tongue is retracted and depressed into the floor of the mouth with the tip curled upward, downward or assimilated into the body of the tongue. www.indiandentalacademy.com
SUMMARY ď Ž
ď Ž
The tongue develops from the first 4 branchial arches. Salivary gland originate from the oral epithelial buds invading the underlying mesenchyme.
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REFERENCES
Chaurasia B.D. – Human Anatomy, 3rd Edition, 1996
James K.Avery, ‘Oral Development and Histology’, ed.1,Balteimor, 1990, B.C.Decker. Keith L. Moore – Clinically oriented anatomy. 3rd edition. Moore & Persaud – The Developing Human, Clinically Oriented Embryology, 5th Edition, 1993. Murray Brooker – Clinical embryology: A color atlas and text. Shafer W.G. – Text Book of Oral Pathology, 4th Edition, 1983
Sperber G.H. – Craniofacial Embryology, 4th Edition, 1989. Tencate A.R. – Oral Histology, 3rd Edition, 1989 Sheldon Winkler – Essentials of complete denture prosthodontics. 2nd edition.
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