Dental Materials Study Guide PDF

Dental Materials Study Guide Exam 1 SP25 ch.8,9,20,21,27,28 Understand the types, names, and properties of primary and secondary bonds, including their charge and electrons. (pg. 23-27) Primary bonds (Metallic, Ionic, Covalent) are strong bonds between atoms that involve the transfer o...

Dental Materials Study Guide Exam 1 SP25 ch.8,9,20,21,27,28 Understand the types, names, and properties of primary and secondary bonds, including their charge and electrons. (pg. 23-27) Primary bonds (Metallic, Ionic, Covalent) are strong bonds between atoms that involve the transfer of electrons between atoms.Examples below: Ionic (transferring of electrons), Covalent (Sharing of electrons between a pair), Metallic (Electrons are shared by all the atoms that makeup the object). Secondary Bonds (Waals forces) are the results of partial charges from an uneven distribution of electrons around an atom or a molecule. Permanent Dipoles shared electrons of a covalent bond are not shared equally, and one of the bonded atoms is partially positive and the other is partially negative (Unevenly distributed electrons), Hydrogen Bonds ( A stronger dipole bonding pulling of positive or negative ions) Fluctuating Dipole (Uneven distribution of atoms that are always changing, weak attraction). ​ For instance: How is a metallic bond formed, and is it easily broken? Easy to bend? Metallic bonds are similar to covalent bonds in that valence electrons are shared between atoms. The difference is that the electrons in a metal object are not shared by two atoms, they are shared by all atoms that make up the object.The sliding of atoms past each other allows this material to bend, not fracture, and maintain its strength. How do electrons and atoms interact to form it? The electrons are closer to the positive cores than the positive cores are to each other, so the attraction is greater than the repulsion. This results in a weak primary bond in all directions. The enormous number of bonds in a metal results in a strong material. - pg 25-26 (AN) ​ Similar to the last example, covalent bonds involve partially positive and partially negative related atoms. ​ Second: An unequal distribution of electrons surrounding an atom results in a partial charge that creates a bond known Secondary bonds: are a result of partial charges from uneven distribution of electrons around an atom or a molecule. permanent dipoles??? pg 26 (AN) ​ Are you aware of what a replica, positive or negative copy To produce the replica (or positive copy), an impression is made of the prepared tooth or remaining alveolar ridge. The dental impression (or negative copy) is then filled with a material that solidifies to form the replica. If a restoration is constructed on the replica it is called a cast. if the resulting replica is used to study the size and position of the oral tissues it is called a study model or diagnostic cast – pg 10-11 (AN) A cast or study model is positive copy, while an impression is negative copy. The impression is a negative reproduction The replica (the model or cast) is a positive reproduction.(once its poured and trimmed) In an orthodontic office, study models are utilized for treatment planning. For crown or bridge work, casts or dies are utilized. A study model is used to plan treatment and to observe treatment progress (i.e. for orthodontic purposes). A cast is a replica on which a restoration or appliance is fabricated. A cast is more accurate than a study model and is a replica of more than one tooth (such as a quad or full arch) (i.e. used for dentures). A die is a working replica of a single tooth (i.e. for a crown or bridge). pg 130 (NP) Who was given credit for classifying dental restorations and caries? In the late 1800, Dr. G.V. Black classified the most common sites for dental caries pg 17 (AN) ​ Ceramic materials' characteristics include strength, insoluble nature, similarity in color to teeth, and advantages. The disadvantage of dimensional stability and translucency is brittleness. ​ Cross links in dental polymer The chains are linked by convalently boned atoms to form a three-dimensional structure and can no longer slide past each other, resulting in stiff, strong material. Two liquids (oil and water)—not blend, what is it called? Immiscible Emulsion/colloid (lecture wk 1 slide 46) HP The elasticity modulus Modulus of Elasticity = stress / strain, indication of stiffness of a material property The load (stress) and the change in length (strain) are proportional. They always occur together.The modulus of elasticity is characteristic of a material and its atomic bonds. It is the scientific term for the stiffness of a material. The higher the modulus of elasticity= the stiffer the material. p40 (NP) ​ Percolation and thermal expansion coefficients Coefficient of thermal expansion: is a measure of change in volume in relation to the change in temperature (a fractional change in volume or length). Example: if a balloon filled with room temperature air is brought outside on a cold day, the balloon will shrink. Percolation: the process of heating and cooling, and the accompanying opening and closing of the gap. Results in micro-leakage, tooth sensitivity, and recurrent decay. Example: When the mismatch is great, the restoration will shrink with cold beverages, opening gaps between the restoration and the tooth. When the tooth heats up again and expands, the gap is closed. ​ Relationship between stress and strain: illustration of the monkeys in the textbook: Larger springs can support a larger load without additional elongation. The load (stress) and the change in length (strain) are proportional. They always occur together. Dental Ex: ​ Examples of aqueous elastomeric materials include Define thermal conductivity-The rate of heat flow through a material solubility-ability of a material to dissolve in liquid Mohs's hardness (enamel = 5–6): measure of relative resistance to scratching ​ gelation: is the process by which gelatin, such as Jell-O, changes from a liquid state to a semisolid state when it cools. ​ Elasticity: The phenomenon of when a force is removed on an object, it returns back to its original position. Scientists and engineers have extensively investigated this phenomenon of change in shape and return to the original shape. ​ Syneresis: is the process when hydrocolloid materials contract slightly after setting and exude (discharge) water. Syneresis occurs very slowly but it is a second reason to pour hydrocolloid impressions as soon as possible. An illustration of Physically set impression substance (what distinguishes agar from alginate?) Alginate is irreversible, whereas agar is Jello that turns liquid when heated. Dental ceramic characteristics Ceramic materials are colored to match the appearance of the patient’s natural teeth and the materials are also translucent meaning that some light passes through, as in natural teeth. Ceramic material are strong when compressed because the atoms are forced together but ceramic material are weak and brittle when pulled or bent. ​ Standing location -Where is the right-handed operator's position for the Maxillary alginate impression? Mandible? Ch 27 (pg 341) kz Maxillary: On the side/ in back of patient, 11 o’ clock position Mandible: On the side/ in front of the patient, 7 o’ clock position When does the alginate setup, mixing, and working time begin? For what length of time? A suitable power to liquid ratio is necessary to achieve a good or desired outcome. Alginate setup: patient tray, basic set up, impression tray (mand/max), rope wax, wax bite registration, premeasured alginate , disposable cup, mixing bowl, spatula, water measuring cup, patient bib, ziplock baggie, disinfectant, paper towels, clinician PPE Mixing time: 1 min. Initial settting time is 3-4mins Working time:. calculated by by adding the mixing and setting times. ​ The best way to determine the initial gypsum set? The most reliable was to determine the initial set is by observing the “loss of gloss” on the surface of the mixed material. Gypsum usually takes 30-45 min to completely set (final setting time for gypsum). BEST TIME is to let it set overnight. Dry strength: what is it? A product made of gypsum that does not include water is referred to as having a surplus of water. Dry strength is the strength that is measured when the excess water is not present in the sample. Dry strength may be two or more times the wet strength. Usually the cast must sit in a dry environment OVERNIGHT to approach these values. p135 (NP) ​ The textbook's recommended method for mixing gypsum Use powder to The preferred method of mixing is to add the measured water into the mixing bowl first, followed by gradual addition to the pre weighted powder. Hand mixing: done in flexible, plastic or rubber bowl with stiff-bladed spatula. Mix should be smooth/homogenous and free of air bubbles. Mix by using a wiping motion against sides of bowl. Vibrator: use to reduce bubbles in mix. pg 136 (NP) The best elastomeric substance that is liquid is: Liquid silicone rubber ​ What is the classification of vinyl polysiloxanes and additional silicone dental material? Polysulfides, Condensation silicones, polyethers and additional silicones are all used for most dental procedures full dentures, partial dentures, inlay, crown and bridge work. The setting process for all listed above is chemical and are elastic.​ When a material experiences stress that exceeds its yield strength, the strain is proportionate to the stress, and the material cannot get back its former shape. Becomes stretched ​ What is the term for the rate at which heat moves through a material—​ a mix of ceramic and polymer? Thermal conductivity Important things to know: -Alginate materials are IRREVERSIBLE, because they do not reverse to their original state -Alginate materials are not as accurate as reversible hydrocolloid materials but are EASIER TO USE. potassium sulfate and borax? Both can be added to gypsum to affect setting speed. Potassium sulfate works as an accelerator, borax works as a retarder. Improved stone? Type IV, alpha-hemihydrate, pink stone. strongest, most expensive. Stress? Strain? Elasticity ? Dry strength ? most advantageous elastomeric material : PVS, polyvinyl siloxane indicator of the initial set of gypsum products : loss of gloss ? DONE, Mrs. Bui Review worksheets