83.Which of the following will cause reduction of the size of the pulp chamber in mid-life?

A. Formation of primary dentin
B. Formation of secondary dentin
C. Internal resorption
D. External resorption
E. Pulp fibrosis

The correct answer is B. Primary dentin (choice A) surrounds the pulp chamber when the tooth is
first formed and erupts. It is the initial dentin that makes up the base of both the crown and root. If the
young tooth has a given size pulp chamber, further dentin formation, secondary dentin, later in life, will
begin to fill the chamber with dentin, making it smaller. Internal resorption (choice C) is loss of dentin,
resulting in a larger pulp chamber. External resorption (choice D) involves the exterior of the root and
does not change the pulp chamber size. Pulp fibrosis (choice E) would change the histology of the cells in the chamber, but not the chamber's size


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82.Towne’s projection is a:

a. A-p view b. P-a
c. Lateral d. Panoramic

Ans: a. Antero-posterior view

This view is primarily used to observe the occipital area of skull and sometimes the

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81.In restoring a mandibular first molar, lingual cusps are important for which movement?

A. Centric occlusion B. Protrusive
C. Retrusive D. Working E. Nonworking

ANS. D. To answer this question, place your own teeth in centric occlusion(maximum intercuspation). Notice that the occlusion is held in place by the lingual cusps of maxillary teeth and the buccal cusps of mandibular teeth. Mandibular lingual cusps are not in contact. In protrusion, the anterior teeth act to separate the maxilla and mandible as the mandible moves forward. The anterior teeth act as guides in retrusion as well (try it). So far the mandibular lingual cusps are not involved. If you make a left working movement (slide your mandible left), notice that the mandibular lingual cusps on the left, drag against the lingual side of the maxillary lingual cusps. In the nonworking side (in this case, the right side), the mandibular lingual cusps move AWAY from contact.


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