Tooth development 2 l Oral histology & biology MCQs for dental students

 

tooth development 2 l Oral histology MCQs ( multiple choice question ) for dental students

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Tooth development

The bell stage is characterized by the following four layers of epithelial cells

a. Inner enamel epithelium

b. Stratum intermedium

c. Stellate reticulum

d. Outer enamel epithelium

Inner Enamel Epithelium

• Inner enamel epithelium consists of a single layer of tall columnar cells, which differentiate into specialized cells called ameloblasts, before amelogenesis . These are characterized by high glycogen content. The diameter and length of ameloblasts is five microns and 40 microns respectively.

• Ameloblasts are attached to each other by junctional complexes and to stratum intermedium by the desmosomes. Inductive influences of ameloblast on the underlying ectomesenchymal cells of dental papilla result in development of odontoblasts.

Stratum Intermedium

• Stratum intermedium is the layer of squamous cells present in between the inner enamel epithelium and stellate reticulum . These cells are intimately attached by desmosomes and gap junctions. They have a high degree of metabolic activity due to developed cytoplasmic organelles, acid mucopolysaccharides, glycogen deposits and an enzyme, alkaline phosphatase. Stratum intermedium is essential for the development of enamel because it contains new ameloblasts and is essential for the formation and calcification of enamel.

• It is absent in the root part of the tooth. Inner enamel epithelium and stratum intermedium are considered as a single functional unit.

Stellate Reticulum

• The star-shaped cells of the stellate reticulum have long processes, which anastomose with the processes of adjacent cells. There is continuous expansion in the size of the stellate reticulum because of increased amount of intercellular fluid. Just prior to the beginning of enamel formation, at the height of the cusp or incisal edge, the stellate reticulum collapses and gets mixed up with the cells of the stratum intermedium.

• This decreases the distance between the ameloblasts, which are centrally situated, and the blood capillaries situated near the outer enamel epithelium. This change, which starts at the height of cusps shows gradual cervical progression .

Outer Enamel Epithelium

• In the initial stages of development of enamel organ, the cells of the outer enamel epithelium are single-layered, and cuboidal in shape. Before enamel formation begins, outer enamel epithelium is folded. The capillary network develops in between the folds from the dental sac and provides a rich blood supply to the avascular enamel organ.

• This rich nutritional blood supply is required for the intense metabolic activity of the avascular enamel organ. The dental papilla is mesenchymal in nature. Under inductive influences of epithelium, the dental papilla develops the odontoblasts. The development of odontoblasts occurs and laying down of dentin starts before the inner enamel epithelium lays down the first layer of enamel matrix .

Dental Lamina

• The dental lamina proliferates lingually at its deep end and gives rise to the enamel organ of the permanent teeth. It happens in all teeth except the permanent molars.

Dental Papilla

• The dental papilla is covered by the enamel organ. The mesenchymal peripheral cells of the papilla differentiate into specialized cells called odontoblasts, which produce dentin. First, they are cuboidal-shaped and are then elongated to become columnar in shape and produce a thin layer of predentin.