Test 1 - Dental Materials (MCQs) PDF

# Test 1 - Dental Materials (MCQs) 1. is seen as force over area, whereas is deformation over length. - a. Stress, strain - b. Dimensional change, strain - c. Strain, stress - d. Elastic modulus, elastic limit 2. The average biting force for bicuspids is. - a. 222-445 - b....

# Test 1 - Dental Materials (MCQs) 1. is seen as force over area, whereas is deformation over length. - a. Stress, strain - b. Dimensional change, strain - c. Strain, stress - d. Elastic modulus, elastic limit 2. The average biting force for bicuspids is. - a. 222-445 - b. 400-890 - c. 133-334 - d. 250-450 3. G.V. Black introduced an acceptable amalgam formula in; - a. 1846 - b. 1855 - c. 1874 - d. 1895 4. The ability of a material to sustain permanent deformation without rupture under compression is known as. - a. Brittleness - b. Ductility - c. Malleability - d. Fatigue strength 5. The Knoop hardness number for dentin is. - a. 130 - b. 100 - c. 95 - d. 75 6. All the following are factors affecting adhesion except. - a. Interpenetration - b. Wettability - c. Macro-mechanical interlocking - d. Viscosity Feedback 7. Which of the following is/are gypsum accelerator/s? - a. Sodium chloride - b. All the following - c. Sodium sulphate - d. Potassium sulphate 8. Which of the following does not occur when a beam of light strikes an object? - a. Transmission - b. Scattering - c. Dispersion - d. Absorption 9. The maximum stress that a material will withstand without permanent deformation is known as. - a. Fatigue strength - b. Elastic limit - c. Yield strength - d. Proportional limit 10. A liquid that becomes less viscous and more fluid under repeated applications of pressure is referred to as. - a. Thermoplastic - b. Dilatant - c. Thixotropic - d. Pseudoplastic 11. Which of the following is not a mechanical property that deals with plasticity? - a. Ductility - b. Percent elongation - c. Elastic modulus - d. Yield strength 12. Which one of the following is not a synthetic polymer? - a. Polysporenes - b. Bakelite - c. Perspex - d. Nylon 13. The strength of color or the degree of saturation of color is known as; - a. Value - b. None of the following - c. Hua - d. Chroma 14. A measure of the rate at which a temperature disturbance at one point in a body travels to another point is knowns as; - a. Thermal conductivity - b. Thermal expansion - c. Thermal diffusivity - d. Heat flow 15. The slow deformation of a material under constant stress is referred to as; - a. Flow - b. Stress relaxation - c. Resilience - d. Creep 16. The first ADA seal of acceptance was used in - a. 1955 - b. 1946 - c. 1908 - d. 1931 17. The elastic limit is the same as the of a material. - a. Ultimate strength - b. Proportional limit - c. Yield strength - d. Yield point 18. is a result of two sets of forces directed parallel to each other but not along the same straight-line axis. - a. Shear - b. Tension - c. Torsion - d. Compression 19. Tests for the microhardness of material are. - a. Shore A and Vickers - b. Brinnell and Rickwell - c. Rockwell and Knoops - d. Knoops and Vickers 20. All the following are methods for adhesive bonding except. - a. Diffusion - b. Fenestration - c. Mechanical - d. Chemical # Part B short answers 1. List four properties of an ideal restorative material. - a. Must be biocompatible - This means that when placed in the mouth, it should not cause harm to any of the surrounding tissue in the oral cavity and by extension to the individual. - b. It should bond permanently to tooth structure/tissues (enamel and dentine) or bone - c. It should match the natural appearance of tooth or other visible tissues. - d. Exhibit similar properties to the tooth tissues which are enamel and dentine. - e. Must be able to initiate the tissue repair process or regeneration of missing/damaged tissues. 2. Explain the various types of electrochemical/wet corrosion providing an example of each. - a. Galvanic corrosion occurs when there are combinations of dissimilar metals in direct physical contact. E.g., An amalgam restoration existing on a lower tooth and opposing, is the upper tooth with a gold inlay. This forms an electrical circuit because saliva acts as an electrode and there is a potential difference between the amalgam and gold restorations; when these teeth are brought into contact, this short circuit through alloys allows for sharp pain to result in galvanic shock. - b. Stress Corrosion occurs during immense fatigue or excessive cyclic loading. Therefore, when the application of stress increases, the internal energy of an alloy is created through a micro-strained field that is associated with the dislocation or displacements. E.g., Excessive burnishing of the margins in metallic crowns or amalgam restorations. - c. Concentration Cell Corrosion occurs when they are variations in the electrolytes or in composition of the given electrolyte within the system. This occurs where the potential difference is associated with the difference in the concentration of the solution causing corrosion at different parts of the metal surface. E.g., The accumulation of food debris over a metallic restoration. One type of electrolyte is formed under the food debris and another in saliva, this causes the electrochemical corrosion to occur under the layer of food debris on the metallic restoration. 3. Explain the various theories of setting for gypsum products. - a. Colloidal theory - This theory states that when the hemihydrate power is mixed with water, it enters a colloidal state via a sol-gel state which is basically moving from solution to a gel. In this solution state, the hemihydrate particles are saturated and hydrated to form the dihyrate by entering an active state. Additionally, as the measured amount of water is consumed, the mass gets converted into a solid gel. - b. Hydration theory This theory states that rehydrated plaster particles are joined together through hydrogen bonding to the sulphate groups to form the set material. - c. Dissolution Precipitation theory - this theory states that based on the dissolution of plaster and instant recrystallization of gypsum, is perceived by the interlocking of the crystals to form a set product that is compact and rigid. 4. List and describe four factors that would affect good bonding. - a. The cleanliness of the surface - surfaces should be free of debris and contaminants to have good bonding occurs. - b. Penetration of the surface - The liquid adhesives such as sealants and other bonding agents must be able to penetrate the crevices created by the acid etching process. - c. Chemical reactions - This occurs when there is a formation of a strong chemical bond across the prepped surface to increase the number of attachment sites or to increase the surface area. - d. Shrinkages of Adhesives - The liquid adhesives solidify by processes such as solvents evaporation and polymerization that results in shrinkage because of poor bonding. The adhesive may pull away from the substrate or the stress created can weaken the bond. Shrinkage occurs towards the centre of the adhesive mass and if light cured, it occurs towards the light source. - e. Thermal Stresses - If the adhesive and substrate have different thermal expansion coefficients, changes in temperature will produce stresses in the bond. E.g., Porcelain enamels are bonded to alloys at high temperatures and then cooled to room temperature. - f. Corrosive Environments - The presence of water or corrosive liquid or vapor will often lead to deterioration of an adhesive bond. E.g., Acrylic resins will initially adhere to clean un-etched tooth enamel, but the bond deteriorates upon storage in water. 5. What makes dentin a challenge when it comes to adhesive bonding? - a. Dentine is a living tissue that is made up of mainly organic materials and its tubular nature provides varying areas in which dentinal fluid may flow to the surface and adversely affect adhesion. - b. The presence of the smear layer on the cut dentine surface tends to make bonding difficult, this can have possible side effects on the pulp especially in cases where the cavity is large and near the pulp. This smear layer is removed by acid etching so that it does not interfere with the formation of a bond when the adhesive is applied. 6. Classify dental materials providing examples for each. - a. Preventative dental materials - these aim to provide resistance to the progression of active carious lesions and can include things like antibacterial mouthwashes, varnishes, pits and fissure sealants, fluoride releasing cements. - b. Restorative dental materials - this category basically describes a synthetic component being used to repair or replace tooth structure, these repairs can be done directly or indirectly. Direct restoration refers to materials that are used intraorally, or if something is fabricated it is done on the teeth or tissues in the oral cavity. E.g., Filling restoration, dental sealants, or the application of fluoride treatment and indirect restoration refers to everything that is used extra orally. E.g., Cases where dentures are made; it is done indirectly over a model. - c. Auxiliary dental materials - The auxiliary materials refer to things that are used when making dental prosthetics. E.g., dental wax used to take a bite for a patient doing an upper and lower complete prosthesis. - d. Temporary Restorative dental materials - these are used to restore teeth for a short period of time. E.g., IRM temporary filling material or a temporary crown after a tooth was prepared for a dental crown. 7. List and describe the various types of gypsum products and provide an example of how each is used in dentistry. - a. Type 1 - Impression plaster: this material was previously modified with the addition of chemical flavors to enhance its taste, so that it could have been used to take impression for patients with edentulous ridges to make complete removable prosthesis. - b. Type II - Dental Plaster (Bata hemihydrate): This is the weakest and least expensive of all the gypsum that was heated directly in a container in the formation of porous and irregular particle size present in the powder. It is used to make complete or partial removable prosthesis. It can also be used as an articulator; this is an instrument that is used to hold a cast together. - c. Type III Dental Stone (Alpha hemihydrate): This is the strongest and more expensive than plaster; it was made under calcination of steamed pressure in a controlled environment that result in the releasing of water and the formation of uniform and less porous particles. It is used to make casts for diagnosis purposes in cases where a patient having ortho treatment, a cast can be made to study the movement progression of the teeth. - d. Type IV - Dental Stone (High Strength/modified hemihydrate) – made by calcining of chloride solution to result in a very dense and cuboidal shaped particles with a reduce surface area; it is used to make inlays and other dental prosthesis. - e. Type V - Dental Stone (High Strength, High Expansion) - This is the same as the type IV, but it has added accelerator and retarders. It is best used to make dental prosthesis such as inlays and onlay and to achieve the just right fit, because of its high expansivity.