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| stripping teeth of enamel leads to tooth sensitisation |
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material substance that occupies space and has weight
divisions (atom, molecule, compound), properties (chemical and physical) and states (solid, liquid, gas) |
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| crystalline lattice structure |
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| definite shape but no fixed anatomical position |
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| tendency to chere, and defined by container |
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| moves like liquid, expands indefinitely |
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internal resistance to external force being place on an object;
measured in F/Area units; PSI or Pascals (N/m2)
measurable quantity
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| forces on an object are directed toward one another |
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| forces are directed away from one another (pull apart) |
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| forces on an object are directed in such a manner to twist, rotate or deform the object by sliding one part parallel to the other (harmful to the human dentition) |
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@font-face { font-family: "Cambria"; }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0in 0in 10pt; font-size: 12pt; font-family: "Times New Roman"; }div.Section1 { page: Section1; } measure of the change in length due to applied force. Measure in terms of deformation or change in dimension per unit dimension; strain is unitless number
@font-face { font-family: "Cambria"; }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0in 0in 10pt; font-size: 12pt; font-family: "Times New Roman"; }div.Section1 { page: Section1; } (percentage of change: DL/L x 100%) |
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| maximum stress before fracture; stress-strain curve is at its highest point |
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| plastic/permanent deformation |
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| the object will never return to initial state |
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falls around the deformation range; "when the object gives."; atomic cracks form after ultimate strenght
industry standard giving manufacturer a range as to when the material tends to fail; 0.2% offset below the linear portion of the stress-strain curve |
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| measured at its point of fracture |
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| elstic modulus (Young's Modulus) |
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| measure of materials stiffness; stress/strain until no longer proportional |
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| stress proportional to strain; at stresses that exceed the proportional limit the object no longer retains its orginal shape |
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| strain associated with stress at the proportional limit |
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| strain associated with stress at the proportional limit |
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| small but permanent dimensional change |
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| low ductility; less stress to achieve deformation |
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| ability of a material to withstand permanent deformation under tensilee stress without fracture |
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| ability of a material to withstand permanent deformation under compressive stress without fracture; predominate in metal; metallic component |
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| amount of deformation a material can withstand without rupture when a tensile stress is applied |
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| amount of deformation a material can withstand w/o rupture when a compressive stress is applied |
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| ratio of axial to lateral strain within the elastic range; reduction of cross-section is proportional to the elongation during elastic deformation |
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| degree of hotness or coldness measured on a definite scale |
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heat in calories, or joules, required to convert 1 g of a material from solid to liquid state at the melting temperature
L=Q/m (Q = total heat absorbed) |
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| transmission of heat; quantity of heat in calories of joules, per second passing through a body 1-cm thick with a across section of 1 cm2 when the termpature difference is 1 celsius degree |
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| quantity of heat needed to raise the temperature of 1 g of the substance 1 degree |
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measure of transient heat flow and is defined as the thermal conductivity, divided by the product of the specific heat;
rate at which body with a non-uniform temperature approaches equilibrium
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o Delta = K / (Cpr) mm2/sec
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| linear coefficient of thermal expansion |
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measure of change in length per unit lenght when the temperature is raised 1 degree higher
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o (DL/L)/( Dt)
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| light passes completely through an object |
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| light not allowed to pass at surface or incompletely below surface |
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| light entering does not leave |
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| colors under a fluorescent light source differ under a natural light source |
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| : emission of visible light as a result of absorption of radiation from some other source |
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| 2 dissimilar metal placed in oral cavity can create a battery cell; galvanic cell can cause galvanic shock |
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| face-centered space lattice |
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| composes gold, copper, silver, and platinum |
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| hexagonal close-packed space lattic |
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| Zn structure (anti-oxidants are rust protectors) |
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| permanent deformation under constant load in crystalline materials |
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| permanent deformation under constant load in amorphous materials |
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| area beneath the linear portion of the stress-strain curve; energy to deform material permanently |
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| total area under the stress-strain curve; energy to cause fracture |
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| material resistant to identation |
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| standard hardness test; 172-130 degree elongated diamond used for micro-identation tests; thin plastic/metal sheets; brittle materials |
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| BHN, Brinnell Hardness Tester |
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| metals and alloys; fixed ball diameter and fixed load; 1.6 mm ball diameter - load of 123 N; force/area |
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| vickers hardness tester (VHN) |
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| 136 degree diamond pyramid; measures small areas, very hard materials; Vickers can be altered |
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| developed as a rapid method of determing hardness, the superficial method is used to measure hardness of plastics used in dentistry; place load on plastic and make measurement |
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| studies depth of cure of resin composites; spring loaded needle 1 mm in diameter |
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| shore A durometer used to measure relative hardness of elastomers |
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| used to measure the properties of microphase (0.1-5000 mg) |
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| study of flow of liquids; in relation to viscosity; viscosity decreases rapidly as temperature is increased |
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| bonding between unlike materials |
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| bonding between similar materials |
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| material used as a binding agent |
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surface to which the adhesive is applied
greater the surface energy of the adherend, the more readily the adhesvive reacts with the adhesive |
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| ideal adhesive has a contact angle that approaches, but can never attain zero degrees |
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| reduction in surface tension of all liquids as the temperature is increased |
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| reduce the surface tension in water |
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| surface attachment of molecules; 2 substances cohere, two unlike substance adhere |
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| substance absorbed diffuses into solid material and not noted of a concentration of molecules at the surface |
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absorption and adsorption taking place at the same time
water absorbed on the surface and absorbed into the body of the material |
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| penetration of liquids into narrow crevices is known as capillary action (flowable composite) |
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| rate of penetration of a liquid into a crevice |
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| adhesion of liquid bridges between solids; isolated capillaries from reservoir |
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| placed on the posterior of children's dental caries; also placed on adult teeth |
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| calcium sulface dihydrate |
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| fluffy, porous, least dense |
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| densest of the raw gypsum; strongest and least amount of water required to make product set |
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impression plaster; inelastic material; requires different fillers and retarders, used with patients with no undercut areas
water/poser ratio: 50 cc water/100 grams
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| plaster of parish; made through open kettle method; weaker than stone |
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occurs under steam or autoclave pressure in presence of water;
alpha hemihydrate, made w/ water/powder: 30 cc water/100 gram |
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| dental model stone, makes didagnostic cast; maxillary and mandibular replica of patient's mouth |
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| die stone; 20 cc water/100 grams type IV |
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| high-strength dental sotne; 18.62 cc water/100 gram |
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| impression material used today |
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| longer, more rapidly the gypsum is mixed the shorter the setting time |
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| warmer the water, decreases the setting tme |
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| higher temperature, reduces setting time |
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| all gypsum products expand during setting (0.1 to 0.3 percent) |
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| measured by Vicat penetrometer |
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| time-time at which the material can separate from the impression without fracture |
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| shows relatively high compressive strenght; brittle procuts |
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| ZnO; setting runs to conclusion |
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