Oral Histology Prelims PDF

In the development of the oral groove or stomodeum, the head fold resulting from craniocaudal elongation caused by the fast developing notochord and the central nervous system plays a crucial and important role....

In the development of the oral groove or stomodeum, the head fold resulting from craniocaudal elongation caused by the fast developing notochord and the central nervous system plays a crucial and important role. DERIVATIVES OF THE BRACHIAL (PHARYNGEAL STAGES IN THE It has been noted that towards the end of the third week, on the ventral side of the cephalic end of the ARCH) DEVELOPMENT OF embryo, an invagination occurs resulting from an apparent pushing in of the ectoderm creating a depression. This depression is the stomodeum or oral groove which is the forerunner or primordium The Boundaries of the Oral The first groove and pouch are involved in the formation of : Stomodeum are: 1. external auditory meatus ORAL STOMODUEM 2. tympanic membrane, Superior boundary – floor of the forebrain; lowest convexity of the prominence of the forehead. Loading… 3. tympanic antrum Inferior boundary – mandibular arch or first branchial arch 4. Mastoid antrum, and pharyngotympanic or eustachian tube. Posterior boundary – buccopharyngeal membrane The second, third, and fourth grooves normally are obliterated by overgrowth of the second Lateral boundary – maxillary process of the primitive mouth. arch forming a transitory cervical sinus that sometimes persists and opens onto the side of the neck (branchial fistula) or on the neck and inside the pharynx (pharyngocutaneous fistula) DEVELOPMENT OF THE EXTERNAL FACE - SEQUENCE OF DEVELOPMENTAL EVENTS Human Face During the third week of development an oropharyngeal membrane (buccopharyngeal , or begins to form during the 4th oral membrane) is first seen at the site of the week of embryonic development. future face, between the primordium of the heart The face develops from five primordia that appear Development of the Face ,Maxilla and By the 6th week the external face is completed. and the rapidly enlarging primordium of the brain. It is composed of ectoderm externally and in the fourth week: the Mandible Loading… endoderm internally. It lies at the beginning of the Between the 6th and 8th weeks digestive tract and breaks down during the fourth week in order to form the opening between the frontonasal prominence, the two maxillary the development of the palate future oral cavity (primitive mouth or subdivides nasal and oral stomodeum) and the foregut. swellings, and the two mandibular swellings. cavities. The oropharyngeal membrane breaks down when This development continues into it stops growing. While tissues around it expand very rapidly, the oropharyngeal membrane’s non- The buccopharyngeal membrane breaks down to the 12th week with completion proliferating cells are gradually pulled apart of the soft palate because they cannot fill the expanding area form the opening to the oral cavity External face forms from two The facial region of a 4-week-old A series of individualized tissue the first pharyngeal arch sources that surround the human embryo, and of a young swellings gives rise to the different child, are shown, seen from parts of the face. gives rise to: oropharyngeal membrane : the tissues of the frontonasal front. These are known as facial processes a pair of mandibular Loading… process that cover the forebrain, predominantly of neural crest The lightly stippled frontonasal process in will give rise to forehead, nose, and midsection (prominences). The following facial processes may be recognized : processes (actually the pharyngeal arch itself), origin of upper lip, 1. the frontonasal process gives rise to: and the tissues of the first (or The mandibular arch darkly 2. a pair of medial nasal processes a pair of outgrowths of the mandibular) pharyngeal arch, of shaded in will give rise to a large (that later contribute to a single arch: the maxillary mixed mesoderm and neural part of the midface and all of the globular [intermaxillary] process), crest origin. lower face. processes (that later give 3. And a pair of lateral nasal processes. rise to a pair of palatal processes) Facial Clefts Development of the face. In the seventh week, the If the processes do not formed in utero when medial nasal processes mold together normally normal development of In the sixth week, the fuse at the midline to a baby's head and neck nasal placodes of the frontonasal prominence form the intermaxillary process. during development, a congenital Loading… are disrupted and parts of the face fail to fuse invaginate to form the By the 10th week, the malformation, together, creating facial intermaxillary process and/or cranial nasal pits and the lateral forms the philtrum of the known as a facial cleft, and medial upper lip. will occur at that differences. nasal processes. boundary  At the end of the fourth week, two ectodermal Simultaneously, paired maxillary processes thickenings: nasal placodes, appear on the develop near the base of the first frontonasal process. They are the precursors of the olfactory epithelium, responsible for the pharyngeal arch (mandibular arch). Development of sense of smell. They enlarge and grow ventrally and During the fifth week, lateral nasal and medial medially, surrounding the future oral nasal swellings that surround the nasal placodes cavity. appear on the frontonasal process. These four nasal processes grow forward, while the nasal The maxillary processes grow rapidly, first meeting the lateral nasal processes, and Mandible placodes remain relatively stationary. This gives the impression that the nasal placodes then the lower extension of the medial “invaginate”. nasal processes. They actually stay behind and come to lie in This lower extension is known as the blind nasal pits, surrounded by the nasal globular or intermaxillary process processes. PREPARED BY DR. MA. EMILY P. NAVARRETTE and will give rise to the midstructure This is the first step in the development of the (philtrum) of the upper lip nasal cavities. 2 TYPES of OSSIFICATION The Mandible Mandible and the maxilla form from the tissues of the first branchial arch the mandible forming within the mandibular process, maxilla within the the mandible is a membrane bone, INTRAMEMBRANOUS CARTILAGENOUS maxillary process. developed in relation to the nerve of the Bones that are develop directly from Formed first from the mesenchymal tissue first arch and almost entirely independent embryonic mesenchymal tissue. which later on ossify to form the bone. of Meckel's cartilage. Loading… Example Cranial vault , mandible and clavicle Loading… The mandible has neural, alveolar, and muscular elements and its growth is assisted by the development of secondary cartilages. Site of initial osteogenesis related to mandible formation. Bone formation extends from this In human beings, Meckel's cartilage anteriorly and posteriorly along Meckel's cartilage has a close positional relationship to the developing mandible. The two cartilages of each side do not meet at the midline sixth week of embryonic development, a condensation of Anteriorly, this spread of new bone formation occurs but are separated by a thin band of mesenchyme. mesenchyme occurs in the angle formed by the division of along the lateral aspect of Meckel's cartilage, At 6 weeks of development, this forming a trough that consists of lateral and medial cartilage extends as a solid hyaline The mandibular branch of the trigeminal nerve (the nerve the inferior alveolar nerve and its incisor and mental plates that unite beneath the incisor nerve cartilaginous rod surrounded by a of the first arch) has a close relationship to Meckel's branches. cartilage, beginning two thirds of the way along the length This trough of bone extends to the midline, where it fibrocellular capsule, from the of the cartilage. 7 weeks of development , intramembranous ossification comes into approximation with a similar trough developing ear region (otic capsule) begins in this condensation, forming the first bone of the formed in the adjoining mandibular process. At this point the mandibular nerve divides into lingual and mandible. From this center of ossification, bone formation to the midline of the fused inferior alveolar branches, which run along the medial and The two separate centers of ossification remain mandibular processes spreads rapidly anteriorly to the midline and posteriorly separated at the mandibular symphysis until shortly lateral aspects of the cartilage, respectively. after birth. toward the point where the mandibular nerve divides into The inferior alveolar nerve further divides its lingual and inferior alveolar branches. The trough soon is converted into a canal as bone into incisor and mental branches more anteriorly forms over the nerve, joining the lateral and medial plates Fate of Meckel’s cartilage the incus and malleus of the inner ear and the there is a backward extension of ossification along the lateral aspect of Meckel's e ramus of the mandible develops by a by 10 weeks of development, the sphenomalleolar ligament. cartilage to the point where the mandibular nerve divides into the inferior alveolar rapid spread of ossification posteriorly rudimentary mandible is formed almost fibrocellular capsule persists as the and lingual nerves. into the mesenchyme of the first arch, entirely by intramembranous ossification, sphenomandibular ligament turning away from Meckel's cartilage. and Meckel’s cartilage degenerates to Loading… From this point where the nerve divides to the midline, medial and lateral alveolar plates of bone develop in relation to the forming tooth germs subdividing This point of divergence is marked by the lingula in the adult mandible, the point at make place for new bone From the lingula forward to the division of the alveolar nerve into its incisor and mental branches, Meckel's cartilage degenerates. the trough of bone. which the inferior alveolar nerve enters the teeth come to occupy individual compartments, which finally are enclosed the body of the mandible. totally by growth of bone over the tooth germ. In this way the body of the mandible essentially is formed  tooth eruption. These cartilages 2.Increase are over all length of the in the 2.mandible. post, half of the ramus to the level of anterior Anterior alveolar half of the ramus space to the level posteriorly for of inferior permanent referred mandible to as secondary to distinguish them from dental It starts when the deciduous tooth germ foramen. alveolar molars nerve. appears at about 4 months of development, the primary Meckel’s cartilage. reach the early bell stage surmounting the anterior border and top of the two in 3.Increase number, a of They haveappear theininter different the condylar histologic distance structure connective from tissue the primary cartilages in that their cells are larger, The bone of the mandible begins to grow coronoid process. betweenandthe lesstwo ends of matrix intercellular Meckel's cartilage but are is formed. I secondary cartilage on each side of the tooth germ Coronoid cartilage is a transient growth cartilage entirely independent of it. The most impt,center of growth is the and disappears long before birth. By this growth the tooth germs come to condylar cartilage They are obliterated within the first year after birth. be in a bony trough which also includes It gives rise to: Small islands of cartilage also may appear as variable the alveolar nerves and vessels It shifts the mandible forward and and transient structures in the developing alveolar downward Growth of Mandible Coronoid process Anterior half of the ramus to the level of inferior Growth of the Alveolar Process processes. Subperiosteal bone formation and Vertical septa of bone develop between the adjacent tooth germs keeping each The growth of this cartilage contributes to: alveolar nerve. Undergo endochondral ossification and give rise to: Condylar symphysis The distanceofbetween Cartilage mandible. the 2 arches increases resorption tooth separates in its bony crypt. coronoid cartilage Alveolar process grows rapidly during Symphyseal cartilages 1, increase in height of the ramus creating a space for teeth to erupt Enlarged and fused within 1st year of life. tooth eruption. 2.Increase in the over all length of the I secondary cartilage At the same time bone apposition occurs at the Deposition on ext. surface of the 3.Deposition mandible at the lower border of appears at about 4 months of development, mandible,resorption on the inner surface mandible and chin result to strengthening The most impt,center of growth is the crest shaped Carrot of the alveolar cartilageprocess appearsand at the fundus 14 wks of the in utero condylar cartilage inalveolus. the condyle region and occupies most of the resultthe surmounting toanterior increaseborder transverse width and top of of the two in 3.Increase of number, of theininter the mandible appear the condylar distance connective tissue further growth of the mandible until birth is influenced strongly by the appearance of three developing ramus, coronoidmandible process. between the two ends 4. Bone remodeling of Meckel's cartilage but are with development It shifts the secondary mandible (growth) forward cartilages and and the The deposited bone at the fundus of the alveolus entirelyand independent development Coronoid Deposition cartilage isona transient posterior growth border of ramus cartilage function ofoftongue it. and muscles of downward of muscular attachments. It counts later act as an to the active bodyofofgrowth center the mandible. until theThis age of These secondary cartilages: and angle and disappears long before birth. mastication. They are obliterated within the first year after birth. 20increases yrs, the distance between the mandibular The growth of this cartilage contributes 1. the condylar cartilage canal and the apices of the premolars and two Resorption It gives rise to: on ant.border ramus and Small islands of cartilage also may appear as variable to: It gives rise to: 2, coronoid cartilage molars. coronoid process result to adjust ramus and transient structures in the developing alveolar Symphyseal cartilages Development of Alveolar Process Growth of Mandible Growth of the Alveolar Process 1, increase in height of the ramus 1.Condyle head and neck of the mandible Coronoid process 3. symphyseal cartilage. This means alveolar process aids the height of the width,add to length of mandible increase processes. These cartilages 2.Increase are over all length of the in the 2.mandible. post, half of the ramus to the level of anterior Anterior alveolar space half of the posteriorly ramus for of to the level permanent inferior Undergo endochondral ossification and give rise to: mandible referred to as secondary to distinguish them from dental It starts when the deciduous tooth germ foramen. alveolar molars nerve. the primary Meckel’s cartilage. symphysis The distanceofbetween mandible. the 2 arches increases reach the early bell stage two in 3.Increase a of They haveappear number, theininter different the condylar histologic distance structure connective from tissue creating Enlargeda and space for teeth fused withinto1st erupt year of life. the primary cartilages in that their cells are larger, The bone of the mandible begins to grow I secondary cartilage betweenandthe lesstwo ends of matrix intercellular Meckel's cartilage but are is formed. At the same time bone apposition occurs at the entirely independent of it. on each side of the tooth germ The most impt,center of growth is the crest of the alveolar process and the fundus of the They are obliterated within the first year after birth. By this growth the tooth germs come to condylar cartilage alveolus. be in a bony trough which also includes Small islands of cartilage also may appear as variable It shifts the mandible forward and The deposited bone at the fundus of the alveolus the alveolar nerves and vessels and transient structures in the developing alveolar downward counts later to the body of the mandible. This Growth processes. of the Alveolar Process Subperiosteal bone formation and Vertical septa of bone develop between the adjacent tooth germs keeping each The growth of this cartilage contributes increases the distance between the mandibular canal and the apices of the premolars and two to: Undergo endochondral ossification and give rise to: Condylar symphysis The distanceofbetween Cartilage mandible. the 2 arches increases resorption tooth separates in its bony crypt. coronoid cartilage Alveolar process grows rapidly during Symphyseal cartilages 1, increase in height of the ramus molars. Development of This means alveolar process aids Alveolar the height of the Process creating a space for teeth to erupt Enlarged and fused within 1st year of life. tooth eruption. 2.Increase in the over all length of the mandible. At the same time bone apposition occurs at the Deposition on ext. surface of the 3.Deposition mandible at the lower border of It starts when the deciduous tooth germ appears at about 4 months of development, mandible,resorption on the inner surface mandible and chin result to strengthening crest shaped Carrot of the alveolar cartilageprocess appearsand at the fundus 14 wks of the in utero reach the early bell stage inalveolus. the condyle region and occupies most of the resultthe surmounting toanterior increaseborder transverse width and top of of the two in 3.Increase of number, of theininter the mandible appear the condylar distance connective tissue coronoidmandible process. The bone of the mandible begins to grow developing ramus, between4. the Bonetwo ends of Meckel's remodeling cartilage but are with development on each side of the tooth germ The deposited bone at the fundus of the alveolus entirelyand independent Coronoid Deposition cartilage isona transient posterior growth border of ramus cartilage function ofoftongue it. and muscles of It counts later act as an to the active bodyofofgrowth center the mandible. until theThis age of By this growth the tooth germs come to and angle and disappears long before birth. mastication. They are obliterated within the first year after birth. 20increases yrs, the distance between the mandibular be in a bony trough which also includes canal and the apices of the premolars and two Resorption It gives rise to: on ant.border ramus and Small islands of cartilage also may appear as variable the alveolar nerves and vessels It gives rise to: molars.