The largest portion of a tooth is formed by:

 # The largest portion of a tooth is formed by:

A. Enamel

B. Dentin

C. Pulp

D. Cementum

The correct answer is B. Dentin.

Dentin forms the largest portion of the tooth structure, extending almost the full length of the tooth. Externally, dentin is covered by enamel on the anatomic crown and cementum on the anatomic root. Internally, dentin forms the walls of the pulp cavity (pulp chamber and pulp canals).

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Number of enamel rods in a maxillary molar is about:

 # Number of enamel rods in a maxillary molar is about:

A. 8 million

B. 12 million

C. 20 million

D. 30  million

The correct answer is B. 12 million.

The rods vary in number from approximately 5 million for a mandibular incisor to about 12 million for a maxillary molar. The rods are densely packed and intertwined in a wavy course, and each extends from the dentinoenamel junction (DEJ) to the external surface of the tooth.

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Teeth with longest roots in human dentition are:

 # Teeth with longest roots in human dentition are:

A. Incisors

B. Canines

C. Premolars

D. Molars

The correct answer is B. Canines.

Canines possess the longest roots of all teeth and are located at the corners of the dental arch. They function in the seizing, piercing, tearing and cutting of food. From a proximal view, the crown also has a triangular shape, with a thick incisal ridge. The anatomic form of the crown and the length of the root make these teeth strong, stable abutment teeth for a fixed or removable prosthesis.

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The remnants of epithelial root sheath found in periodontal ligament

 # The remnants of epithelial root sheath found in periodontal ligament are called:

A. Enamel pearls

B. Enamel knots

C. Rests of Malassez

D. Epithelial diaphragm

The correct answer is C. Rests of Malassez.

The development of root does not begin till the enamel and dentin reach the future cemento-enamel junction. In development of root, enamel organ performs a very important function by forming Hertwig’s epithelial root sheath. Hertwig’s epithelial root sheath is molded and assumes tall shape of root by initiation of radicular dentin formation with the help of differentiation of radicular cells into the odontoblasts. Enamel on radicular portion is not formed because of the absence of stratum intermedium. The remnants of the epithelial root sheath are embedded in the periodontal ligament of erupted teeth and are called as epithelial rests of Malassez.

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Basement membrane that separates the enamel organ and the dental papilla

 # The basement membrane that separates the enamel organ and the dental papilla just prior to dentin formation is called the:

A. Advanced bell stage

B. Membrana preformativa

C. Cap stage

D. Enamel knot

The correct answer is B. Membrana preformativa. 

The basement membrane that separates the enamel organ and the dental papilla just prior to dentin formation is called the membrana preformativa.

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The successor of the deciduous teeth develops from:

 # The successor of the deciduous teeth develops from:

A. Lingual extension of the dental lamina

B. Labial extension of the dental lamina

C. Buccal extension of the dental lamina

D. Occlusal extension of the dental lamina

The correct answer is A. Lingual 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).

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Final stage of tooth development

 # What is the final stage of tooth development?

a. Crown formation.

b. Root formation and eruption.

c. Function.

d. Dentinogenesis and amelogenesis.

The correct answer is C. Function.

Crown formation is followed by root formation and eruption. Root formation and eruption are followed by function. Function is the final stage of tooth development. Dentinogenesis and amelogenesis are followed by crown formation.

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