Loading...
chapter 4: Liquid and Solids
Quiz by edkasa chemistry
Customize this quiz to suit your class
Instantly translate to 100+ languages
Tag the questions with any skills you have. Your dashboard will track each student's mastery of each skill.
Give this quiz to my class
Chapter 4 : Solids and liquidsMake 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 IMost of the functions of a eukaryotic cell are controlled by the nucleus, shown in Figure 4-12. The nucleus is filled with a jellylike liquid called the nucleoplasm, which holds the contents of the nucleus and is similar in function to a cell’s cytoplasm. The nucleus houses and protects the cell’s genetic information. The hereditary information that contains the instructions for the structure and function of the organism is coded in the organism’s DNA, which is contained in the nucleus. When a cell is not dividing, the DNA is in the form of a threadlike material called chromatin. When a cell is about to divide, the chromatin condenses to form chromosomes. Chromosomes are structures in the nucleus made of DNA and protein. The nucleus is the site where DNA is transcribed into ribonucleic acid (RNA). RNA moves through nuclear pores to the cytoplasm, where, depending on the type of RNA, it carries out its function. Nuclear Envelope The nucleus is surrounded by a double membrane called the nuclear envelope. The nuclear envelope is made up of two phos- pholipid bilayers. Covering the surface of the nuclear envelope are tiny, protein-lined holes, which are called nuclear pores. The nuclear pores provide passageways for RNA and other materials to enter and leave the nucleus. Nucleolus Most nuclei contain at least one denser area, called the nucleolus (noo-KLEE-uh-luhs). The nucleolus (plural, nucleoli) is the site where DNA is concentrated when it is in the process of making ribosomal RNA. Ribosomes (RIE-buh-SOHMZ) are organelles made of protein and RNA that direct protein synthesis in the cytoplasm. The nucleus of a cell is surrounded by a double membrane called the nuclear envelope. The nucleus stores the cell’s DNA. FIGURE 4-12 Nuclear envelope Nucleolus Nuclear pores DNA (chromatin) Copyright © by Holt, Rinehart and Winston. All rights reserved. 80 CHAPTER 4 MITOCHONDRIA Mitochondria (MIET-oh-KAHN-dree-uh) (singular, mitochondrion) are tiny organelles that transfer energy from organic molecules to adenosine triphosphate (ATP). ATP ultimately powers most of the cell’s chemical reactions. Highly active cells, such as muscle cells, can have hundreds of mitochondria. Cells that are not very active, such as fat-storage cells, have few mitochondria. Like a nucleus, a mitochondrion has an inner and an outer phos- pholipid membrane, as shown in Figure 4-13. The outer membrane separates the mitochondrion from the cytosol. The inner membrane has many folds, called cristae (KRIS-tee). Cristae contain proteins that carry out energy-harvesting chemical reactions. Mitochondrial DNA Mitochondria have their own DNA and can reproduce only by the division of preexisting mitochondria. Scientists think that mito- chondria originated from prokaryotic cells that were incorporated into ancient eukaryotic cells. This symbiotic relationship provided the prokaryotic invaders with a protected place to live and pro- vided the eukaryotic cell with an increased supply of ATP. RIBOSOMES Ribosomes are small, roughly spherical organelles that are respon- sible for building protein. Ribosomes do not have a membrane. They are made of protein and RNA molecules. Ribosome assembly begins in the nucleolus and is completed in the cytoplasm. One large and one small subunit come together to make a functioning ribosome, shown in Figure 4-14. Some ribosomes are free within the cytosol. Others are attached to the rough endoplasmic reticulum.Some substances, such as macromolecules and nutrients, are too large to pass through the cell membrane by the transport processes you have studied so far. Cells employ two other transport mecha- nisms—endocytosis and exocytosis—to move such substances into or out of cells. Endocytosis and exocytosis are also used to transport large quantities of small molecules into or out of cells at a single time. Both endocytosis and exocytosis require cells to expend energy. Therefore, they are types of active transport. Endocytosis Endocytosis (EN-doh-sie-TOH-sis) is the process by which cells ingest external fluid, macromolecules, and large particles, including other cells. As you can see in Figure 5-7, these external materials are enclosed by a portion of the cell’s membrane, which folds into itself and forms a pouch. The pouch then pinches off from the cell membrane and becomes a membrane-bound organelle called a vesicle. Some of the vesicles fuse with lysosomes, and their con- tents are digested by lysosomal enzymes. Other vesicles that form during endocytosis fuse with other membrane-bound organelles. Two main types of endocytosis are based on the kind of material that is taken into the cell: pinocytosis (PIEN-oh-sie-TOH-sis) involves the transport of solutes or fluids, and phagocytosis (FAG-oh-sie-TOH-sis) is the movement of large particles or whole cells. Many unicellular organisms feed by phagocytosis. In addition, certain cells in animals use phagocytosis to ingest bacteria and viruses that invade the body. These cells, known as phagocytes, allow lysosomes to fuse with the vesicles that contain the ingested bacteria and viruses. Lysosomal enzymes then destroy the bacteria and viruses before they can harm the animal. CYTOSOL EXTERNAL ENVIRONMENT During endocytosis, the cell membrane folds around food or liquid and forms a small pouch. The pouch then pinches off from the cell membrane to become a vesicle. FIGURE 5-7 vesicle from the Latin vesicula, meaning “bladder” or “sac” Word Roots and Origins www.scilinks.org Topic: Endocytosis Keyword: HM60505 mb06se_homs02.qxd 5/18/07 11:03 AM Page 105 106 CHAPTER 5 1. Explain the difference between passive trans- port and active transport. 2. What functions do carrier proteins perform in active transport? 3. What provides the energy that drives the sodium-potassium pump? 4. Explain the difference between pinocytosis and phagocytosis. 5. Describe the steps involved in exocytosis. 6. How do endocytosis and exocytosis differ? How can that difference be seen? CRITICAL THINKING 7. Analyzing Information During intense exercise, potassium tends to accumulate in the fluid surrounding muscle cells. What membrane protein helps muscle cells counteract this tendency? Explain your answer. 8. Evaluating Differences How does the sodium- potassium pump differ from facilitated diffusion? 9. Relating Concepts The vesicles formed during pinocytosis are much smaller than those formed during phagocytosis. Explain. SECTION 2 REVIEW Vesicle Cell membrane EXTERNAL ENVIRONMENT CYTOSOL During exocytosis, a vesicle moves to the cell membrane, fuses with it, and then releases its contents to the outside of the cell. FIGURE 5-8 INSIDE OF CELL Vesicle OUTSIDE OF CELL Exocytosis Exocytosis (EK-soh-sie-TOH-sis) is the process by which a substance is released from the cell through a vesicle that transports the sub- stance to the cell surface and then fuses with the membrane to let the substance out of the cell. This process, illustrated in Figure 5-8, is basically the reverse of endocytosis. During exocytosis, vesi- cles release their contents into the cell’s external environment. Figure 5-8 also shows a photo of a vesicle during exocytosis. Cells may use exocytosis to release large molecules such as pro- teins, waste products, or toxins that would damage the cell if they were released within the cytosol. Recall that proteins are made on ribosomes and packaged into vesicles by the Golgi apparatus. The vesicles then move to the cell membrane and fuse with it, deliver- ing the proteins outside the cell. Cells in the nervous and endocrine systems also use exocytosis to release small molecules that control the activities of other cells.Lipids are large, nonpolar organic molecules. They do not dissolve in water. Lipids include triglycerides (trie-GLIS-uhr-IEDZ), phospho- lipids, steroids, waxes, and pigments. Lipid molecules have a higher ratio of carbon and hydrogen atoms to oxygen atoms than carbohydrates have. Because lipid molecules have larger numbers of carbon-hydrogen bonds per gram than other organic com- pounds do, they store more energy per gram. Fatty Acids Fatty acids are unbranched carbon chains that make up most lipids. Figure 3-10 shows that a fatty acid contains a long carbon chain (from 12 to 28 carbons) with a carboxyl group, —COOH, attached at one end. The two ends of the fatty-acid molecule have different properties. The carboxyl end is polar and is thus hydrophilic or attracted to water molecules. In contrast, the hydro- carbon end of the fatty-acid molecule is nonpolar. This end tends not to interact with water molecules and is said to be hydrophobic (HIE-droh-FOH-bik), or “water fearing.” In saturated fatty acids, such as palmitic acid, which is shown in Figure 3-10, each carbon atom is covalently bonded to four atoms. The carbon atoms are in effect full, or saturated. In contrast, linoleic acid, also shown in Figure 3-10, has carbon atoms that are not bonded to the maximum number of atoms to which they can bond. Instead, they have formed double bonds within the carbon chain. This type of fatty acid is said to be unsaturated. Triglycerides Three classes of lipids important to living things contain fatty acids: triglycerides (fats), phospholipids, and waxes. A triglyceride is composed of three molecules of fatty acid joined to one molecule of the alcohol glycerol. Saturated triglycerides are composed of saturated fatty acids. They typically have high melting points and tend to be hard at room temperature. Common dietary saturated triglycerides include butter and fats in red meat. In contrast, unsaturated triglycerides are composed of unsaturated fatty acids and are usually soft or liquid at room temperature. Unsaturated triglycerides are found primarily in plant seeds where they serve as an energy and carbon source for germinating plants. Phospholipids Phospholipids have two, rather than three, fatty acids attached to a molecule of glycerol. They have a phosphate group attached to the third carbon of the glycerol. As shown in Figure 3-11, the cell membrane is made of two layers of phospholipids, called the lipid bilayer. The inability of lipids to dissolve in water allows the mem- brane to form a barrier between the inside and outside of the cell. Hydrophilic “head” Phospholipids Hydrophobic “tail” Phospholipids Water Water The lipid bilayer of a cell membrane is a double row of phospholipids.The “tails” face each other.The “head” of a phospholipid, which contains a phosphate group, is polar and hydrophilic.The two tails are two fatty acids and are nonpolar and hydrophobic. FIGURE 3-11 H C H C O OH H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H C H H H H C H H C H H C H H C H H C H C O OH H C H H C H H C H C H C H C H H C H H C H C H H C H H C H C H H H H C H Fatty acids have a polar carboxyl head, highlighted in purple, and a nonpolar hydrocarbon tail, highlighted in green. FIGURE 3-10 Palmitic acid Linoleic acid mb06se_bchs02.qxd 5/18/07 10:49 AM Page 59 60 CHAPTER 3 1. Compare the structure of monosaccharides, dis- accharides, and polysaccharides. 2. How are proteins constructed from amino acids? 3. How do amino acids differ from one another? 4. Describe a model of enzyme action. 5. Why do phospholipids orient in a bilayer when in a watery environment, such as a cell? 6. Describe how the three major types of lipids differ in structure from one another. 7. What are the functions of the two types of nucleic acids? CRITICAL THINKING 8. Applying Information Before a long race, run- ners often “carbo load.” This means that they eat substantial quantities of carbohydrates. How might this help their performance? 9. Recognizing Relationships High temperatures can weaken bonds within a protein molecule. How might this explain the effects of using a hot curling iron or rollers in one’s hair? 10. Applying Information You want to eat more unsaturated than saturated fats. Name examples of foods you would eat more of and less of. SECTION 2 REVIEW Waxes A wax is a type of structural lipid consisting of a long fatty-acid chain joined to a long alcohol chain. Waxes are waterproof, and in plants, form a protective coating on the outer surfaces. Waxes also form protective layers in animals. For example, earwax helps pre- vent microorganisms from entering the ear canal. Steroids Unlike most other lipids, which are composed of fatty acids, steroid molecules are composed of four fused carbon rings with various functional groups attached to them. Many animal hor- mones, such as the male hormone testosterone, are steroid com- pounds. One of the most familiar steroids in humans is cholesterol. Cholesterol is needed by the body for nerve and other cells to func- tion normally. It is also a component of the cell membrane. NUCLEIC ACIDS Nucleic acids are very large and complex organic molecules that store and transfer important information in the cell. There are two major types of nucleic acids: deoxyribonucleic acid and ribonucleic acid. Deoxyribonucleic acid, or DNA, contains information that deter- mines the characteristics of an organism and directs its cell activi- ties. Ribonucleic (RIE-boh-noo-KLEE-ik) acid, or RNA, stores and transfers information from DNA that is essential for the manufactur- ing of proteins. Some RNA molecules can also act as enzymes. Both DNA and RNA are polymers, composed of thousands of linked monomers called nucleotides (NOO-klee-uh-TIEDS). As shown in Figure 3- 12, each nucleotide is made of three main components: a phosphate group, a five-carbon sugar, and a ring-shaped nitrogenous base.Chapter 4110.31.b.17.C Topic: Reading/Vocabulary Development