20. How many teeth (out of 32) in the normal dentition oppose only ONE other tooth?

A. None B. 1

C. 2 D. 4

ANS.D.

Because of the shift of the mandibular teeth in a mesial direction due to the smaller size of the anterior teeth, most teeth have two opposing teeth. That is, they oppose their counterpart in the other arch, and a tooth either mesial or distal to that counterpart. There are two classes of exceptions. One of the exceptions is the mandibular central incisors. These two teeth (#24 and #25) oppose only the maxilary centrals (#8 and #9). The other exception is the maxillary third molars (#1 and #16), which oppose only the mandibular third molars.

Note that the mandibular third molars oppose both the maxillary second and third molars.

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19. The epithelium of the mucous membrane of the mouth is:

A. Simple squamous B. Stratified squamous
C. Simple columnar D. Stratified columnar

ANS.B.

Squamous cells are flattened, pancake-like cells, and when in layers are known as stratified. The stratified squamous cells lining the mucosa of the oral cavity are similar to those lining the outer skin, although less keratinized. They do, however, flake off continuously into the mouth. Simple squamous tissue would be too thin and not allow for the constant flaking and replacement. Columnar epithelium is found in both the respiratory system and other organs of the digestive system.

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18. A wound to the posterior left axillary line, between the ninth and tenth rib, and extending approximately 5 cm deep, will most likely damage

A. Ascending colon B. Duodenum

C. Left kidney D. Spleen

ANS. D.

The spleen follows the long axes of ribs 9 to 11 and lies mostly posterior to the stomach, above the colon, and partly anterior to the kidney. It is attached to the stomach by a broad mesenterial band, the gastrosplemic ligament. Therefore, it is the most likely organ of the group to be pierced by a sharp object penetrating just above rib 10 at the posterior axillary line. Note that the pleural cavity, and possibly the lower part of the inferior lobe of the lung, would be pierced before the spleen. The ascending colon (choice A) is on the wrong side (the right) to be penetrated by a sharp instrument piercing the left side. Most of the duodenum (choice B) is positioned too far to the right to be affected by this injury. Even the third part of the duodenum, which runs from right to left, would still be out of harm's way. In addition, the duodenum lies at about levels L1 to L3, placing it too low to be injured in this case. The superior pole of the left kidney (choice C) is bordered by the lower part of the spleen. However, it is crossed by rib 12 and usually does not extend above rib 11. It would probably be too low and medial to be injured in this case because this penetration is at the posterior axillary line.

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