Tooth development l Oral histology & biology MCQs for dental students

 

Tooth development l Oral histology & biology MCQs ( multiple choice question ) for dental students

 Tooth development

Key Points

1. The embryonic connective tissue concerned with tooth development is termed ectomesenchyme due to the migration of the neural crest cells in it.
2. The lingual extension of the dental lamina gives rise to the enamel organ of the successional teeth central and lateral incisors, canines and premolars.
3. The distal extension of the dental lamina gives rise to the enamel organ of the non-succedaneous teeth permanent molars.
4. The remnants of the dental lamina are called the cell rests of Serres.
5. Vestibular lamina is also known as the lip furrow band.
6.  Stellate reticulum is also called enamel pulp and it acts as a shock absorber to protect the inner enamel epithelial cells.
7. The enamel knot acts as a signalling centre and determines the morphology of the cusp.
8. The bell stage marks the morphodifferentiation of the crown and histodifferentiation of the ameloblasts and odontoblasts.
9. The stratum intermedium exhibits a high degree of metabolic activity and synthesizes proteins essential  for enamel formation.
10. After the formation of the dental matrix, the inner enamel epithelial cells (ameloblasts) receive nutrition from the capillaries of the dental follicle.
11. The basement membrane that separates the enamel organ and dental papilla just before the dentin formation is called the membrana preformativa.
12. The shape of the crown is formed by the differential mitotic division of the inner enamel epithelial cells.
13. The infolding that occurs in the inner enamel epithelium during crown pattern determination is due to the differential rates of mitotic division.
14. The reversal of polarity of the ameloblasts is the alignment of nuclei towards the stratum intermedium and the Golgi complex towards the dental papilla.
15. Hertwig’s epithelial root sheath outlines the future root and is responsible for the shape, length, size and number of roots.
16. During root development, the plane of the epithelial diaphragm remains fixed and the lengthening of the root is accompanied by the movement of the crown in an axial direction.
17. The remnants of Hertwig’s epithelial root sheath are called the cell rests of Malassez.
18. A cell becomes histodifferentiated when it undergoes functional and morphological changes and acquires its functional assignment.
19. The dentinoenamel and dentinocemental junctions are the blueprints which decide the morphology of the crown and the root, respectively.

INTRODUCTION in tooth development

• The development of the tooth involves many complex biological processes, including epithelial mesenchymal

• interactions, morphogenesis and mineralization. In human beings, 20 deciduous and 32 permanent teeth develop from the interaction between the oral epithelium cells and the underlying mesenchymal cells.

• The basic developmental process is similar for all teeth but each developing tooth develops as an anatomically distinct unit. Vitamins, minerals and hormones affect tooth development. Vitamin A is important for epithelial growth, vitamin C for connective tissue development and vitamin D is essential for calcification.

PRIMARY EPITHELIAL BAND

• The oral ectoderm is neural crest or ectomesenchyme in origin. It is lined by stratified squamous epithelium. The initial oral cavity develops after the rupture of the buccopharyngeal membrane at the fourth week of intrauterine life. The interaction between the oral epithelium and the underlying mesenchymal cells results in tooth development.

• After thirty-seven days of development, a continuous band of thickened epithelium forms around the mouth in both the future upper and lower jaws. This occurs from the fusion of separate plates of thickened epithelium. These bands of the epithelium are roughly horseshoe-shaped structures. These correspond in position to the future dental arches in the presumptive upper and lower jaws  The primary epithelial band forms as a result of a change in orientation of the plane of the dividing cells .

Dental Lamina

• At the sixth week of gestation period, certain areas of basal  cells of the oral ectoderm proliferate more rapidly than the adjacent cells. The primary epithelial band forms two subdivisions called the dental lamina and the vestibular lamina. The dental lamina is a band of epithelium that has invaded the underlying ectomesenchyme along both the horseshoe-shaped future dental arches

• Deciduous dentition develops directly from the dental lamina at the eighth week of fetal life, whereas the permanent molars develop from a distal extension of the dental lamina.

• The initiation of the permanent first, second and third molars occurs at the fourth month of intrauterine life, one year after birth and five years after birth respectively. The lingual extension of dental lamina is called successional lamina. Successional lamina is responsible for the development of permanent incisors, canine and premolars.

• The successional lamina is active from the fifth month in utero (for the permanent central incisor) to ten months of age (second premolar).

Vestibular Lamina

• Facial (labial and buccal) to dental lamina another thick band of epithelium develops in the maxillary and mandibular dental arches. It is called as the vestibular lamina or the lip furrow band. It develops somewhat later and independently . It later hollows out and forms the oral vestibule between the alveolar portions of the jaws and the lips and cheeks.

• The oral epithelium in the lower jaw forms an epithelial invagination separating the tongue from the developing alveolar process termed the linguoalveolar sulcus.

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