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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 ITeaching English Introduction to the course: Language learning and teaching A 2 Characteristics of the language learners: Studying a system that aligns with international standards. A3 Cognitive factors in language learning: Addressing questions and obtaining necessary information regarding phenomena such as transfer, interference, and generalization; A4 Inductive and deductive language learning: ability and intelligence; and the phenomenon of systematic forgetting A5 Language learning methods and strategies: Familiarizing with foreign language learning methods, strategies for learning foreign languages, and communication strategies A6 International Assessment System of language skills in CEFR, IELTS, TOEFL: effective methods and strategies used to improve language skills (listening, reading, writing, speaking) A7 Psychological factors in language learning: Exploring various psychological factors such as self-esteem, shyness, risk-taking, anxiety, attitude, and motivation A8 The effectiveness of authentic materials during the learning process: The role of tasks and games in teaching foreign languages A9 Errors in language learning: Discussing types of errors, identifying and describing errors, causes of errors, and fossilized errors A10 Error correction or error analysis approaches: developing students' ability to apply their knowledge in practicing error correction A11 Age-related factors in language learning: Exploring types of comparisonand contrast, focusing on topics such as the age hypothesis and bilingualism, and providing a detailed explanation of these concepts A12 Teaching grammar: Studying grammar teaching methods; deductive and inductive approaches in grammar teaching; A13 Teaching grammar through context: linguistic intuition; language phenomena; using grammatical dictionaries; analyzing grammatical tasks; and designing exercises, tasks, and tests through completing grammarbased activities. A14 Teaching vocabulary. Seeking answers to questions such as 'What is a word?' and 'What does it mean to learn a word?' A15 Teaching vocabulary in context: teaching lexical units/phrases/collocations; introducing new vocabulary; using corpus data for pedagogical purposes; developing students' vocabulary learning strategies A16 Assessing vocabulary tasks: designing vocabulary tasks, exercises, and tests. In international assessment systems such as CEFR, IELTS, and TOEFL, grammar accuracy and lexical resource A 17 Teaching pronunciation: Understanding the importance of pronunciation for successful communication; teaching stress; teaching intonation A18 Modern technologies in teaching pronunciation A19 Error correction methods: watching to various experiences in this area and analyzing video lessons from international experts in the field A20 Analysis of skill integration in language learning: Understanding the stages of developing skill integration; integration of the four language skills; task-based integration; and project-based integration. A21 Teaching listening comprehension A22 Modern technologies in teaching listening comprehension A23 Teaching Speaking A24 Modern technologies in teaching Speaking A25 Teaching Reading A26 Modern technologies in teaching Reading A27 Teaching Writing A28 Modern technologies in teaching Writing A29 The role and importance of translation in teaching a foreign language A30 Module 2. International standards for teaching and assessment Classroom Language: The teacher's actions; the teacher's voice; the teacher's intonation; using the foreign language in the classroom A31 Foreign language environment: asking questions in the foreign language, giving instructions in the foreign language, providing oral explanations in the foreign language, and issues related to the use of the native language in the foreign language class. A 32 Designing curriculum: Studying, analyzing, and working with curricula designed for schools, lyceums, and colleges. A33 Planning lessons and the structure of lesson plans: determining thesequence of lessons, objectives, tasks, and expected outcomes; choosing the lesson structure for planning A34 Designing tasks for different stages of the lesson: Starting the lesson; concluding the lesson; connecting tasks within the lesson A35 Time management: allocating appropriate time for tasks during the lesson; and providing homework assignments A36 Educational materials and resources: Effective use of existing educational materials and resources; anticipating and addressing potential issues Planning and adapting materials: to the situation during teaching and working on lesson planning for groups of students with different abilities. A37 Classroom research: Stages of classroom research, data collection, analysis, and planning; creating/preparing the materials needed for data collection; distinguishing between the positive and negative aspects of the research A38 Data analysis: creating/preparing the materials needed for data collection; distinguishing between the positive and negative aspects of the research. A39 Peer lesson observation: Observing lessons; conducting interviews; questionnaires for teachers and students; maintaining a daily record; discussing problematic situations/events; notes and other aspects; the process of lesson observation: stages of observation; presenting observation results both orally and in writing. A40 Educational materials and national values: important tool for implementing and promoting educational standards, as well as national values. A41 Differences between methods of teaching foreign languages: practical application of modern methods in language teaching; foreign experiences in language teaching: the grammar-translation method; the method of conducting lessons entirely in the foreign language; the audio-linguistic method; and communicative methods. A42 Methods used in the local environment and their analysis: Discussion of the positive and negative aspects of various methods; language and culture; teaching/learning processes; the role of the native language in learning a foreign language; and the psychological foundations of foreign language teaching. A43 Teaching a foreign language through computer technologies A44 Types of independent work and its implementation A45 Principles of Assessment in foreign language teaching А46 Issues in Language Assessment А47 Alternatives in Assessment А48 Test methods. Methods and criteria for assessing language aspects: written expression, reading, listening comprehension, speaking, А49 integrating language skills: vocabulary; grammar; alternative forms of assessment; planning assessment; critical analysis; principles for designingtest tasks: scientific rigor, consistency, conciseness, clarity, informality, logical sequence, and systematic approach. А50 Foreign language for ESP. Studying and analyzing needs; setting objectives for teaching a foreign language in a specific field or professional area; defining teaching approaches in curriculum development; and discussing topics related to these areas. А51 Selecting textbooks, materials and resources А52 Content-based Instruction (CBI) А53 Strategies-based Instruction А54 Lifelong Learning: Teacher development, PreSETT, InSETT А55 The Role of Teaching Practice A56 Organization and implementation of compulsory and non-compulsory course process in foreign language teaching A57 Organization in and outclass activities A58 Defining the goals and content of foreign language teaching at various levels of the education system in the Republic of Uzbekistan: evaluating educational materials; adapting educational materials; creating educational materials; and discussing the role of the foreign language teacher in specialized fields to gain relevant information. 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