Dentosphere : World of Dentistry

# Enamel can act in a sense like a: A. Permeable membrane B. Impermeable membrane C. Semipermeable membrane D. Infrapermeable membrane   The correct answer is C. Semipermeable membrane. Another physical property of enamel is its permeability. It has been found with radioactive tracers that the enamel can act in a sense like a semipermeable membrane, permitting complete or partial passage of certain molecules: 14C-labeled urea, I, etc. The same phenomenon has also been demonstrated by means of dyes. Reference: Orban's CLICK HERE FOR MORE MCQs

 # All primary teeth would have begun to calcify by: A. 14 weeks of intrauterine life B. 18-20 weeks of intrauterine life C. 6 months of gestation D. 6 months of age The correct answer is B. 18-20 weeks of intrauterine life. Calcification of the primary teeth begins in utero from 13 to 16 weeks postfertilization. By 18 to 20 weeks, all the primary teeth have begun to calcify. Primary tooth crown formation takes only about 2 to 3 years from initial calcification to root completion. However, mineralization of the permanent dentition is entirely postnatal, and the formation of each tooth takes about 8 to 12 years. Reference: Wheeler's CLICK HERE FOR MORE MCQs

 # Major salivary buffer is: A. Protein buffer B. Carbonic acid and bicarbonate C. Phosphate buffer D. Albumin The correct answer is B. Carbonic acid and bicarbonate. The maintenance of the physiologic hydrogen ion concentration (pH) at the mucosal epithelial cell surface and the tooth surface is an important function of salivary buffers. The primary effect of these buffers has been studied in relationship to dental caries. In saliva, the most important salivary buffer is the bicarbonate– carbonic acid system. Saliva also contains coagulation factors (i.e., factors VIII, IX, and X; plasma thromboplastin antecedent; and Hageman factor) that hasten blood coagulation and that protect wounds from bacterial invasion. An active fibrinolytic enzyme may also be present.  CLICK HERE FOR MORE MCQs

 # Gingival enlargement can be expected in all of the following patients EXCEPT: A. A patient who has undergone kidney transplant B. A patient with COPD C. An epileptic patient D. Patient on antihypertensive therapy The correct answer is B. A patient with COPD. Gingival enlargement is a well-known consequence of the administration of some anticonvulsants (epileptic patient), immunosuppressants (organ transplant recipient), and calcium channel blockers (antihypertensive). The condition may create speech, mastication, tooth eruption, and aesthetic problems.   CLICK HERE FOR MORE MCQs

 # Which of the following cytokeratin is not found in orthokeratinized epithelium? A. K9 B. K10 C. K11 D. K19 The correct answer is D. K19 Keratins K1, K2, and K10 through K12, which are specific to epidermal-type differentiation, are immunohistochemically expressed with high intensity in orthokeratinized areas and with less intensity in parakeratinized areas. K6 and K16, which are characteristic of highly proliferative epithelia, and K5 and K14, which are stratification-specific cytokeratins, also are present. Parakeratinized areas express K19, which is usually absent from orthokeratinized normal epithelia. CLICK HERE FOR MORE MCQs

 # PDL fibers that prevent extrusion are:  A. Horizontal B. Oblique C. Transseptal D. Alveolar crest fibers The correct answer is D. Alveolar crest fibers. Alveolar crest fibers extend obliquely from the cementum just beneath the junctional epithelium to the alveolar crest. Fibers also run from the cementum over the alveolar crest and to the fibrous layer of the periosteum that covers the alveolar bone. The alveolar crest fibers prevent the extrusion of the tooth and resist lateral tooth movements. The incision of these fibers during periodontal surgery does not increase tooth mobility unless significant attachment loss has occurred. Reference: Carranza's CLICK HERE FOR MORE MCQs

 # Elastic fiber component of periodontal ligament with age: A. Remains same B. Increases C. Decreases D. Either increases or decreases with age The correct answer is B. Increases.  Changes in the periodontal ligament that have been reported with aging include decreased numbers of fibroblasts and a more irregular structure, thus paralleling the changes seen in the gingival connective tissues. Other findings include decreased organic matrix production, epithelial cell rests, and increased amounts of elastic fiber. CLICK HERE FOR MORE MCQs