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Quiz Bonus Teste - Teste 1
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Multiple choice quiz on this reading: By 1900, the United States had claimed its place as a world power through the Spanish-American War. As the new century began, the country governed subject territories in Puerto Rico, Hawaii, Guam, the Wake Islands, and the Philippines. U.S. troops also occupied Cuba. U.S. businesses reached beyond the country's borders. During the first decade of the new century, the Coca-Cola Company, Quaker Oats, AT&T, the Standard Oil Company, Du Pont, General Electric, and Ford Motor Company seized the opportunity for international sales. After finding international markets, they built factories abroad, taking advantage of lower labor costs in foreign countries. Then they asked for U.S. protection of their investments and interests. Foreign countries invested heavily in Central America. U.S. investors focused on banana plantations and mining, as well as railroads, with little money in government bonds. By 1913, U.S. investments in Central America totaled about $93 million. British investment in Central America peaked at about $115 million in 1913. About $75 million of that total represented railroad holdings, mostly in Costa Rica and Guatemala. The other $40 million was in government bonds, which were worth little or nothing. The Roosevelt Corollary to the Monroe Doctrine From its earliest days, the United States claimed a special interest in the Western Hemisphere. The Monroe Doctrine, issued in 1823, warned European powers to keep their hands off Latin America. In 1902, Britain, Germany, and Italy mounted a naval blockade of Venezuela. They wanted to force the government to repay its debts. All the countries involved eventually agreed to settle the matter by arbitration. The United States stood back and did nothing, but U.S. citizens were clearly uneasy with the appearance of European military forces in "their" hemisphere. In 1904, President Theodore Roosevelt issued a corollary to the Monroe Doctrine, saying that the United States would act as a police officer to keep order in the region. He intended both to keep European military forces out of the hemisphere and to protect U.S. and European investors, exerting whatever pressure or control on Latin American governments that might be necessary to these ends. In 1905, the Dominican Republic owed $40 million in debts to European lenders. In order to prevent the European nations from using military force to collect their debts, Roosevelt used U.S. power. The United States basically took over collection of Dominican customs taxes, declared that $20 million of the debt was unjustified, and began repayment of the rest. Building a Canal The United States needed a canal through Central America, in order to save shipping time and costs. Colombia had the best location for a canal, and the United States negotiated a deal. It would pay Colombia $10 million for a three-mile-wide strip of land and would make annual rental payments of $250,000 yearly, beginning in 1912. Colombia's Senate turned down the deal, and Roosevelt exploded in rage, calling its members "foolish and homicidal corruptionists." Roosevelt considered seizing the land for the canal by military force but soon found an easier way. The province of Panama seceded from Colombia. A U.S. gunship stood off shore, protecting the Panamanian rebels. They formed a new republic under the protection of the United States. The new country of Panama and the United States agreed on a canal treaty within days. The new treaty had similar terms except that the Canal Zone would be five miles wide, instead of three, and the United States would guarantee and maintain the independence of Panama. Revolutions While Roosevelt welcomed the revolution that separated Panama from Colombia, he opposed most other revolutionary activity. So did his successors in office, William Howard Taft and Woodrow Wilson. The U.S. presidents sent troops to put down revolutions in Nicaragua and Haiti, using U.S. military forces to set up new governments in those countries and maintaining military occupations for years. U.S. military interventions were frequent throughout the hemisphere. Dollar Diplomacy President Taft preferred using "dollar diplomacy" to control Latin American countries. In Honduras, for example, U.S.-based banana companies virtually ran the government. Taft supported expanded U.S. investment in South and Central American countries, the Caribbean, and the Far East. He ordered Secretary of State Philander Chase Knox to protect U.S. investments, sending in military troops if necessary. On the World Stage As a world power, the United States did not limit its involvement to the Western Hemisphere. In 1905, President Roosevelt brought Russia and Japan to the negotiating table to end their war over control of Korea and Manchuria. Roosevelt agreed to Japanese annexation of Korea in return for Japan giving up any claim to China, Hawaii, and the Philippines. Roosevelt won the Nobel Peace Prize for settling this dispute. In 1906, Roosevelt's negotiating powers were tested again. This time, he mediated a dispute between the Alliance powers—Germany, Austria-Hungary, and Italy—with the Entente—France, Russia, and Britain—over control of Morocco. The United States backed France and ended the dispute. No longer an upstart, the United States had taken its place as a world power alongside its former colonial ruler.Make mcq quiz with 4 option in which one is correct -'10 Basis of Material Science • .....;;;";;;"~~;;,,;;,,,,;.;.,,;;,,,;,,;.;,.,------------ 6. Temporary materials: Some materials are meant to be placed in the oral cavity for a short period of time for different reasons. • Temporary crowns: While a permanent crown is prepared in the dental laboratory, the patient must wait for few days before it can be fabricated and cemented into place. Does patient experience any problems during this time period? If the tooth is vital (the pulp is alive), the patient is likely to experience pain and sensitivity while eating and drinking, also it looks unesthetic. What can be done to solve this problem? A temporary crown is placed before the patient leaves the clinic. It is constructed and luted in the same appointment in which the crown preparation is done. Temporary crowns are not very strong or esthetic but they serve adequately till the permanent crown is ready to be cemented. • Temporary restorations: Sometimes it is difficult to decide immediately the best line of treatment for a particular tooth. The exact condition of the pulp may not be obvious to the dentist from the patient's symptoms. A dentist removes all or part of the decay and then places a temporary restoration to have time to observe the behaviour of the pulp or to give the pilip time to heal before deciding the further treatment required. Classification based on Location of Fabrication 4,9 Materials can be classified based on the location of fabrication into: • Direct restorative materials. • Indirect restorative materials Direct restorative materials: They include those materials which are used to restore cavity preparations directly in the oral cavity (Box 1.5). Box 1.5: Examples of direct restorative materials Amalgam, composites, glass ionomer and other materials, which set by chemical reactions in the mouth. Indirect restorative materials: It includes those restorations which must be fabricated outside the mouth, indirectly on a cast/ model/ die, because their processing condition would harm oral tissues. Materials used in the construction of such prosthesis are called indirect restorative materials (Box 1.6). Box 1.6: Examples of indirect restorative materials Gold inlays, crowns of metal, ceramic and polymers, which are processed at elevated temperatures. Some indirect composite restorations can be processed under specific wavelength of light, e.g. Ceramage. Classification based on Longevity of Use 1. Permanent restorations: These restorations are not planned to be replaced for a particular time period. Though they are referred to as permanent, actually they are not, e.g. fillings, crowns, bridges and dentures do not last forever (Fig. 1.5). 2. Temporary restorations: These restorations are planned to be replaced in a short period of time, such as few days to weeks. For ~ Permanent C/) c c -.2 0 c- :;::; Cll co Interim ~ Q; 0 .8ll::1iJ C/) o~ Cll a:: c:=:J Temporary Time period Fig. 1.5: Diagram depicting the time period of use of a restoration. (Arrow in permanent restoration depicts that such restorations are not planned to be replaced for a long period of time.) Introducton to Dental Materials Dental materials Box 1.7: Characteristics of metals 1. High thermal and electrical conductivity 2. Ductility (pure metals are very soft and they can be bent without breaking) 3. Opacity (they do not transmit light) 4. Luster (they have a surface that strongly reflects light and appears bright and shiny) 5. They tend to dissolve to some extent in water or other aqueous solutions, producing cations. 6. All metals are white (actually gray) except for gold, which is yellow, and copper, which is reddish. 7. All metals are solid at room temperature except mercury, which is liquid at room temperature and is used with silver alloys as amalgam. 8. All metals have high melting temperatures because of high strength of the metallic bond that holds the atoms together. 3. Polymers 4. Composites Composites are mixtures of two or more of the first three classes in which the different components remain distinct from one another in the final structure. A common example is composite resin. Fig. 1.7a: Three-dimensional structure of iron (metal) Metals Metals are the oldest of the three classes of materials that have been used as dental materials. Metals are characterized by metallic bonds (Box 1.7) which will be discussed in the next chapter. Metals solidify with their atoms in a regular or crystalline arrangement (see Chapter 2), often in the form of a cube (Fig. 1.7a). example, temporary fillings done in a tooth during root canal treatment, which have to be replaced within 2-4 days during subsequent visits. They are used to protect the tooth and provide function till the final restoration is done. 3. Interim restoration: At times, dental treatment requires "long-term" definite temporary restorations or "interim" restorations. For examle, a 7-year-old child, met with trauma and fractured one of his central incisors. A large composite build- up may serve his immediate requirement until the root formation is completed and a permanent crown is placed. 5 Classification based on the Chemical Nature of the Material These are the atoms that make up a material and the way they are bonded together determine the properties of that materiaLS Weak bonds make for weak materials and vice versa (Table 1.4). Materials can be classified into different categories based on their primary atomic bonds (Fig. 1.6): 1. Metals 2. Ceramics Fig. 1.6: Classification of dental materials based on chemical nature 12 Basis of Material Science Box 1.9: Benefits of ceramics in dentistry 1. Many ceramic oxides are used as pigmenting agents. These oxides produce good range of colors. Due to this characteristic, we are able to match almost any tooth color with good esthetic results. 2. They are inert, i.e. not chemically reactive. This quality provides ceramics with good bio- compatibility. 3. Ceramic materials are translucent, like natural teeth. This translucency gives the ceramic crown a more natural appearance than any other dental material. Fig. 1.7b: Internal arrangement of tetrahedral structure of ceramic (silica) four large oxygen atoms surround smaller silicon atom Ceramics A ceramic is a compound formed by the union of a metallic and a non-metallic element (Box 1.8). Most of these materials are oxides, formed by the union of oxygen with metals such as silicon, aluminum, calcium and magnesium (Fig.1.7b). Ceramics may be simple or complex. Examples of simple ceramics are alumina and silica. Examples of complex ceramics are feldspar (potassium aluminum silicate) and kaolin (hydrated aluminum silicate). Ceramics may be crystalline or non- crystalline (i.e. amorphous). Porcelain is a specific type of ceramic used extensively in dentistry (Box 1.9). Box 1.8: Characteristics of ceramics 1. High melting points. 2. Brittleness, which means they cannot be bent or deformed (no sliding) to any extent without actually cracking and breaking. 3. They are poor conductor of heat and electricity. 4. They are chemically inert. 5. They have excellent esthetic result in terms of matching natural teeth. Fig. 1.8: Stucture of synthetic polymer Polymers They are the latest addition (early to mid- 1900s) to dental materials. Most of the polymers are nowadays synthesized by humans. Polymers are giant, long-chain organic molecules (Fig. 1.8). Polymers are characterized by covalent bonds within each molecule, giving them tremendous strength in a single direction. Try to break a nylon rope by pulling it! They are poor conductors of heat and electri- city. Most polymers have a structure containing thousands of carbon atoms linked together like beads on a string. Others, such as silicone polymers are formed with silicon-oxygen bonds. Introducton to Dental Materials Table 1.4: Characteristics of different materials 13 Characteristics Bond Properties Crystal structure Metals Metallic bonding High strength and hardness, high electrical and thermal conductivity BCC, FCC, or HCP unit cells Ceramics Ionic or covalent bonding, or both High hardness and stiffness, electrically insulating, refractory, and chemically inert Crystalline or amorphous Polymers Covalent bonding Low sensitivity, high electrical resistivity, and low thermal conductivity, strength and stiffness vary widely Amorphous and crystalline Composites Composites are combinations of any of the basic ceramic, metallic and polymeric materials (Box 1.10). Each material that makes up composites is called a phase. Their properties tend to be somewhere between those of their basic constituents and are used to enhance their performance, longevity and handling chracterstics. Box 1.10: Types of composites in dentistry 1. Ceramic - metallic composite: Tungsten carbide bur. 2. Metal - polymer composite: Die materials in dental laboratory. 3. Ceramic - polymer composite: Enamel, dentin, bone and restorative composites. A composite is a kind of "combination" of materials, which compliment each other. The properties lacking in one material are compensated by those of the other material. For example, restorative composite has two phases, namely resin and fillers. Teeth and bones are examples of natural composites. Enamel is a composite of hydroxyapatite (which is a ceramic material) and protein (which is a polymer). EVALUATION OF DENTAL MATERIALS Most manufacturers of dental materials maintain a quality assurance programme (As per international standard like ADA specifications) and materials are thoroughly tested before being released into the market for dental practitioner (Fig. 1.9). Laboratory Evaluations Most ADA/ ANSI specifications involve laboratory tests. The tests performed as per these specifications are useful but they all are performed in vitro, (carried out in the laboratory away from the clinical conditions) which have a lot of limitations in clinical practice.lO Clinical Notes 1. For example, most of the direct restorative materials are tested for their compressive strength but ultimately the material is subjected to a combination of compressive, tensile and shear stresses, which may decide the final success or failure of the material under masticatory load. 2. Similarly upper dentures mostly fracture along the midline because of bending. Hence a bending or transverse strength ~B-a-s-is-o-f-M-a-t-e-ria-I-S~c-ie-n-c-e-------------- ---------. test is far more meaningful for denture base materials than a compression test. Clinical Trials The majority of new materials are subjected to extensive clinical trials normally in co-operation with a dental college or hospital departments prior to their release. CONCLUSION As the number of available materials is going up, it is important that the dentist remains more aware about new products so that their judgement about the selection of material remains successful. Materials which have not been thoroughly evaluated should be avoided, specially with clinical dentistry falling under Consumer Protection Act (CPA). I Research and development I iI Manufacturer/analysis Ideal requirements for clinical use: Thermal, optical, mechanical, chemical, biological Available materials and their properties are evaluated Launch of new I product Choice and selection of material by the dentist Critical assessment based on clinical performance I I H feedback to IQuiz Bonus - Pré-testePré Quiz - BonusBonus QuizChapter 3 Bonus QuizLONG QUIZ IN DRESSMAKING (BONUS QUESTIONS)Create a vocabulary quiz checking understanding with the following words: loose ends a task is due overdue attain procrastination cluttered desk figure out enterprise entrepreneur entrepreneurship distraction disruption outcome digression digress (v) headset circle back facilities bonus benefits rivalry competition commute daycare level-headed comply with sth wear and tear laughing stock track record to play the blame game breach accomplish take advantage of boast about emotionally draining tempting seductive death penalty capital punishment resonate noise-cancelling headphones get rid of sth put sth off postpone thrive on adrenaline rush commitment break down superficial surveillance addicted to sth sedentary lifestyle tense stay alert notifications come down to enhance artificial intelligence confidential regardless of tireless efforts chin wag flossing compulsive over-exercising rapture comprehensive school weep circle back wrap up cutting-edge bargaining rivalry differentiation hazard crucial retain raise the bar head to head make a killing ahead of the curve to drop the ball ballpark figure