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Dental Biomaterials Date: 21/3/09 Student No.: ………………..…. I. Student name: ………………… What are the characteristic of the ideal dental materials? 1 II. In the following multiple-choices questions, one or more of the responses may be correct. 1. Which of the following conditions could lead to corrosion in restorative dentistry? a. b. c. d. A composite contaminated with iron during handling in the dental laboratory. A chemical attack of a metal by components in food or saliva. Polished amalgams that have become dull and discolored with time. Adjacent restorations constructed of dissimilar metals. 2. An amalgam has a force of 111N applied over contact area of 0.645 mm2 , which of the following is the stress applied to the amalgam? Would you expect the amalgam to fracture? (Note, the ultimate compression strength of amalgam over 300 MPa) a. b. c. d. 17.2 MPa 1720 MPa 172 MPa No will not fracture 1.72 MPa 3. Which of the following statements are true? a. The yield strength is always slightly higher than the proportional limit. b. Above the stress associated with yield strength, a material no longer functions as an elastic solid. c. Above the stress associated with the yield strength, a material will be permanently deformed, even after the applied force is removed. d. Most restorations are not classified as clinical failures until fracture has occurred. 4. Which of the following are example of Galvanism in restorative dentistry? a. A piece of aluminum foil from a backed potato becomes wedged between two teeth and contact a gold restoration. b. A temporary plastic crown contacts a gold restoration. c. A temporary aluminum crown contacts a gold restoration. d. A metallic taste is a frequent complaint of patients. 2 5. Adhesion of composite restoration with tooth surface by using acid etching and bonding agent consider as: a. b. c. d. Mechanical retention. Chemical retention. Micro-mechanical retention Combination of micro-mechanical and chemical retention. 6.The restoration material used to restore a small portion of an anterior tooth should have which of the following properties? a- Esthetic b- High strength c- Durability d- Ease of casting 7. Full denture bases are usually made from which of the following materials? a- Composite restorative resin b- Gold alloys c- Acrylic resin d- Ceramic 8. Which of the following conditions could lead to microleakage between tooth and restoration: a. Difference in Co-efficient of thermal expansion between a restoration and tooth structure. b. Difference in surface hardness between restoration and tooth structure. c. Poor adhesion between restoration and tooth surface. d. Difference in melting temperature between restoration and tooth structure. 3 9. Which of the following statements are true? a. The initial setting time characterizes the start of the chemical reaction of model plaster. b. The initial setting time of model plaster can be detected clinically by the phenomenon know as loss of gloss. c. Common practice allows the plaster cast to harden for 45 to 60 minutes. before removal of it from impression. e. The setting time of gypsum can be altered easily by the operator with the use of accelerator. 10. Increasing the water-powder ratio of high-strength stone would do which of the following? a. b. c. d. Lengthen the initial setting time. Increase the 1 hour compressive strength. Increase the setting expansion. Increase the amount of excess water used to mix the material. 11. A pattern wax might be used to do which of the following: a. b. c. d. Make corrective impression. Form a mold around an impression. Form a general size and contour of a restoration. Useful for bite registration. 12. Which of the following is true of residual stress? a. Is developed in wax when it is cooled under stress. b. Results in a uniform dimensional change that can be compensated for in the casting process c. Can be minimized by the manipulation of wax at a temperature as high as is practical d. Can cause warpage that increases at higher storage temperatures and during longer storage times. 4