Exam 1 Flashcards

Question

Phosphoric acid on enamel

Answer 1

Commonly used in enamel bonding Eliminates smear layers associated with cavity preparation Dissolves persisting layers of prismless enamel in deciduous teeth Differentially dissolves enamel crystals in each prism

Answer 2

* Odontoblasts * 50 vol% mineral (less mineral than enamel) * Carbonate-rich, calcium deficient apatite * 30 vol% organic * Type I collagen * 20 vol% fluid * Similar to plasma * Largely found in tubules that connect to pulp

Answer 3

outer is less dense, then middle, then inner

Answer 4

Tubules filled with mineral deposits In front of a progressing caries lesion due to loss of overlying dentin Tubules filled with minerals are much more difficult to etch with acid

Answer 5

Enamel is more dense Enamel has higher modulus of elasticity--\> more rigid

Answer 6

* Polymicrobial communities * Complex * Surface-adherent * Spatially organized * Bacteria surrounded by polysaccharide matrix * Dental plaque * Oral biofilm on teeth and biomaterials * Dental plaque that is pathogenic causes disease * We will always have a biofilm and not all biofilms cause disease

Answer 7

Hydrophobicity-hydrophilicity Surface free energy Surface charge Surface roughness Pellicle formation

Answer 8

In vivo, in situ, and in vitro

Answer 9

* Pounds: the weight of an object * Weight=mass x acceleration due to gravity * Units of mass * slug (English) * kilogram-kg or gram-g (metric/SI) * Units of force * Pound-force (English) * dyne-d or Newton - N (metric/SI) * kilogram force-kgf * Metric prefixes * kilo - k - 1000 - 10 3 * mega - M - 1,000,000 - 10 6 * giga - G-1,000,000,000-10 9 * centi - c - 0.01 - 10 -2 * milli - m - 0.001 - 10 -3 * micro - µ - 0.000001 - 10 -6 * nano- n-0.000000001–10-9

Answer 10

* Molars * 400-800N * Premolars * 200-500N * Incisors * 100-300N Lower in child and geriatric patients Lower in patients with removable dental appliances-dentures Mandible is a lever system→ the further you get from the hinge, the less force there is

Answer 11

* If a force acts upon a body and that body does not move-it is constrained-there must be developed in the body an equal and opposite force of reaction→ stress * Stress and applied load are different * Stress is the reaction to the applied force * Stress= Reaction Force/Area=σ * Units * Pounds per square inch (psi) * Newtons per square meter (N/m2) or pascal (Pa) * MPa=1x106 Pa

Answer 12

Shear- 2 equal but oppositely directed forces separated by a distance act upon a body-place in shear-shear forces-shear stress Torsion-twisting of a cylindrical shape around its axis-screws that retain implant superstructures to the implant embedded in bone Torque=force x length of lever over which it acts (foot-pounds, inch-pounds, meter-newtons) Bending-flexure of a beam shaped object-complex stress

Answer 13

Strain (ε) = (L-L_O)/L_O = ΔL/L_O L_O= original length No units Type of strain is related to type of stress: compressive, tensile, shear, complex

Answer 14

Calculate engineering stress→ engineering= based on original area σ=force/original area= F/a_O _{Calculate engineering strain} _ε=ΔI/I_o

Answer 15

Highest stress where stress and strain proportional

Answer 16

Highest stress where the behavior of the material is completely elastic Up to this point, if the force is removed that material will return to its original

Answer 17

* The stress at which a material deforms plastically and there is a defined amount of permanent strain * Difficult to accurately determine proportional limit or elastic limit * Practical definition- accept a small amount of plastic deformation * Commonly 0.1% or 0.2% plastic strain * Stress is determined at which this occurs * Define yield strength at the % offset strain chosen

Answer 18

* =stress/strain at or below elastic limit * Units same as stress; GPa, PSI * =initial slope of stress-strain curve * Stiffness or rigidity * E=stress/strain=σ/ε=(P/A)/(Δl/l_O) * Flexibility= 1/E * Maximum flexibility=strain at elastic limit

Answer 19

* A property related to the ability of an object to withstand applied force without fracture or excessive change in shape * A prerequisite of any structural material * Within limits, larger--\>stronger * Physical limitations * Large objects may fail due to their own weight * Geometric constraints * In restorative dentistry, the size and shape are determined by the natural dentition

Answer 20

The highest possible stress that can be withstood by a material without failure

Answer 21

The stress level at which the material finally breaks Some materials actually fracture at a stress level below the UTS or UCS

Answer 22

* For elastic deformation only→ always positive * Specimens in tension or compression will exhibit deformation at right angles to the principle strain * v=-εy/εz * εy= transverse strain * εz= longitudinal strain * 0.25 \< v \< 0.5 for most materials

Answer 23

* E=elastic modulus or Young’s modulus * In uniaxial tension or compression * G=the shear modulus * In shear * Assuming Poisson’s ratio= 0.3 * G=E/2(1+v)=E/2(1+0.3)=0.38E * v= Poisson's ratio * G ~ 40% * Note: elastic deformation is easier in shear!!!

Answer 24

ability to be drawn into a wire under tensile stress

Answer 25

* Limitation on use of brittle materials * tensile strength much lower than compressive * brittle materials are not ductile * Enamel is brittle * Temperature dependence of ductility * Some metals, most plastics * At low temperatures ductile materials can become brittle * Importance of ductility * Workability, safety

Answer 26

* % elongation * Put broken ends of specimen together and measure Lf * 100(Lf-Li)/Li * 100 x (length after fracture-initial length)/initial length

Answer 27

* Ductile Materials * Most metals and alloys * Pure gold is the most ductile of all materials * Brittle materials * Ceramics, tooth enamel, cements, many resins, dental amalgam * Klc \< 2.0 MN m-3/2 * Klc is a measure of the resistance of a material to crack extension under predominantly linear-elastic conditions

Answer 28

ability to deform under compression instead of tension

Answer 29

* Material will break where there are flaws or defects because the area that the load is being spread across goes down a little * Strength is the stress value where it breaks * Stress concentration fractures: * Surface finish (crack size) * Internal flaws * Geometric stress risers-design * Bonded interface between 2 materials with different elastic modulus values * Bonded interface with different thermal expansion coefficients * Load applied to small area- Hertzian point load

Answer 30

most important property for brittle materials in tension- measure of stress required to make a crack grow

Answer 31

* Usually compressive strength tests performed for convenience * May not be clinically relevant * Crushing strength of gypsum, dental cements * Uniaxial tensile test very difficult for brittle materials * Grips cause stress concentration and premature failure * One solution: the indirect tensile test, “diametral compression test for tension” * actually tested in compression

Answer 32

Tensile strength= (2P)/(pi\*D\*t) P=load at fracture, D=diameter, t=thickness Note: a successful diametral test results in a fracture along the dotted line with 2 half cylinders resulting

Answer 33

Material will fail if maximum tensile stress exceeds tensile strength occlusal-gingival height of the connector--\> enters the equation for the 3 point bending stress at d² ^{Max stress decreases with an increase in the connector height squared}

Answer 34

Resistance to tearing force (combination of tension and torsion) Useful for describing elastomeric polymers

Answer 35

Energy need to deform the material to the proportional limit Resillience = area under elastic part of stress strain curve =½ \* prop limit \* strain at PL = prop limit2/ (2E) Units N/m2 = N\*m/m3 = j/m3 energy volume

Answer 36

maximum energy required to fracture-elastic and plastic No general formula Units N/m2 = N\*m/m3 = j/m3 energy volume

Answer 37

stiff--\> steep slope ductile--\> long plastic deformation brittle--\> short plastic deformation strong--\> takes high stress to deform plastically resilient--\> large area under elastic portion of curve flexible--\> less steep slope

Answer 38

For small cyclical deformations at a given frequency and particular point on the stress strain curve

Answer 39

* A very rapidly applied force * Very difficult to measure * Best described by energy transferred * Related to resilience and toughness * If no permanent deformation takes place: * Impact energy=kVR=(kVP2)/(2E) * R=resilience=P²/2E, V=volume, k=shape constant, P=proportional limit, E=elastic modulus

Answer 40

* Failure of a brittle material after constant stress experienced over a long time * Usually, a result of environment and applied load leading to crack growth * Corrosion * Ceramics and water * Impact of surface finish

Answer 41

* Magnitude varied with time in a periodic manner * Can produce failure at stresses below UTS or even below proportional limit * dynamic fatigue * cyclic load causes crack growth * important clinically * implants * removable partial denture framework * endurance limit: where it won't break no matter how many more cycles

Answer 42

Liquids-flow Crystalline solids-creep Amorphous solids-flow

Answer 43

study of flow of liquids under applied stress

Answer 44

incompressible and incapable of supporting a tensile stress

Answer 45

shear stress

Answer 46

* the resistance a liquid exhibits to flow * viscous liquids * Tar, molasses, honey * Dental resin composites (in unpolymerized state) * low viscosities * water, alcohol, acetone * cavity varnish * usually decreases with increasing temp * may depend upon shear strain rate * may depend upon previous shear history-thixotropic * units: centipoise (cP=mPa\*sec) * water at 20C ~1.0cP=1.0mP

Answer 47

* Newtonian→ linear * Zinc phosphate cement, water * Pseudoplastic * Glass ionomer, rubber impression material * Thixotropic * The change in viscosity of a material with time * Prophy pastes * Dilatant * Heavily filled resin composite, microfilled composite * Thermoplastic materials * Become plastic on heating and harden on cooling, and are able to repeat these processes

Answer 48

* time dependent plastic deformation of a crystalline solid under a static stress (only at temperatures that approach melting point) * Thermally activated; only significant at temperatures \> 0.8 Tmp oK * T\> 0.95Tmp at ceramic firing temperature * Sag-distortion of cast metal substructure * 37oC is \> 0.9Tmp for Sn-Hg component * ADA specification #1 * Creep \<3% over 3 hours at 36 MPa

Answer 49

* Time dependent deformation of noncrystalline solids under static pressure * Flow rates are very dependent on T * Resins, waxes * Thermoplastic polymers * non crystalline solids (supercoiled liquids with no melting point)

Answer 50

viscoelastic behavior

Answer 51

* reduction in stress in a material subjected to a constant strain, wheras creep is the increase in strain in a material under constant stress * Temperature dependent * Dental waxes * Heavily deformed crystalline materials * Orhto wire

Answer 52

sensitive to how rapidly it is strained Impression materials

Answer 53

* Resistance to indentation * Fast and easy to measure * Indirectly related to other properties * Strength, proportional limit, ductility * Good for quality control or comparing very similar materials * Microhardness versus macrohardness

Answer 54

* both good for ductile material: beforms permanently without breaking * Brinell * Spherical indenter * BHN=load/projected area (BHN=Brinell hardness #) * Not good for brittle or elastic materials * rockwell * Can also be micro Spherical or conical indenter Depth of penetration measured Not good for brittle or elastic materials

Answer 55

* Vickers * 136o diamond pyramid indenter * VHN load divided by projected area calculated from lengths of diagonals * Good for materials except highly elastic ones * Used for tooth structure * Knoop * Asymmetric diamond pyramid * Good for all materials including elastic * Long diagonal used to calculate area * Used for tooth structure

Answer 56

spring loaded indenter, measures depth of penetration: Depth of cure of restorative resins Softer materials

Answer 57

spring loaded indenter, measures depth of penetration: Rubbery materials such as impression materials, denture liners and maxillofacial prosthesis elastomeric materials

Answer 58

The ability of one material to be plastically deformed by scratching with another material Correlate- diamond burs used to scratch away tooth structure Used since 1820 Scale of 1-10 Talc=1 (soft) Diamond=10 (hard)

Answer 59

* A liquid or gas firmly adhering to the surface of a solid or liquid * Related to surface free energy * Two identical materials in contact-cohesion-direct gold * Two different materials in contact-adhesion * Adherend * Adhesive

Answer 60

diffusion process into a liquid

Answer 61

adsorption and absorption

Answer 62

* Surface energy-interface between different phases-solid, liquid, gas * Cohesive force (bonds) unbalanced at surface of solids * Adhesive forces can develop * Primary-chemical reaction-gases like oxygen on metal surface-chemisorption * Secondary-physical forces-inert gases on metal surface-physisorption * Soap spreads out more and lowers surface tension * The cohesion between water and surface -active agent is less than that between water and water

Answer 63

* Required for maximum adhesion * Related to interfacial energies * Contact angle * Balance of forces at interface

Answer 64

Dimensional change→ change in temperature affects dimension Linear coefficient of thermal expansion 𝝰=𝝙I/(IO \* 𝝙T) (units 1/^oC) Relationship: aV=2𝝰 If thermally induced stress→ margin opening→ unacceptable

Answer 65

* Rate of steady state heat conduction through unit area of material with unit thickness with 1oK temperature difference-units: watts/(m\*K) * Lower thermal conductivity * Insulator- tooth structure * High thermal conductivity * Conductor-most metals * Sensitivity, pain, pulp damage * Thermal diffusivity * How fast temperature changes-most common dental problem * Non steady state * Eating, drinking hot or cold substances (0oC-65oC) * 5.5oC increase in temperature can cause pulp damage

Answer 66

h=thermal diffusivity cm2/sec k=thermal conductivity c_p=specific heat ρ=density h=k/(c_pρ)

Answer 67

* its thickness divided by the square root of diffusivity→ thickness is more important than h * Z=t/h1/2 * Z=insulating ability * h=thermal diffusivity * t=thickness * Insulators protect pulp from temperature change * E.g. resins, cements * Insulators used for denture base-patient loses sensation of hot or cold food and drink

Answer 68

Porcelain (more amorphous) vs. teeth (more crystalline)

Answer 69

400-750nm (red is high, blue is low)

Answer 70

wavelength and intensity

Answer 71

200-400nm UVA 315-400 UVB 280-315: sunburn, skin damage UVC: ionizing, germicidal

Answer 72

Specular-mirrorlike-glare Diffuse- scattered light-contains most of the color information for the object Reflectance spectrum

Answer 73

red, green, blue cones

Answer 74

most affect red and green 1/12 men, 1/200 women

Answer 75

Light levels-color vision requires threshold value for illumination- B&W vision more sensitive Surroundings Fatigue- after image (the longer you stare at something, the more the color shifts) Size of object Viewing angle

Answer 76

* Hue- primary wavelengths * Red, green, blue, etc. * Value-lightness→ we are most sensitive to * Black and white * Chroma-saturation

Answer 77

looks different under different lights An object can only reflect wavelengths present in the incident light An object may appear very different if viewed under illumination with different spectra 2 objects with different reflectance spectra may appear similar or different depending upon the illumination-metamerism

Answer 78

type of illuminant used

Answer 79

Absorption of short wavelength light and re-emission of longer wavelengths

Answer 80

Enamel and dentin strongly absorb 360-380nm UV and emit 450nm blue light (just below visible range) * “Vital” appearance under illumination with a significant UV component-including sunlight * Some artificial light, photoflash lamps, “black light”

Answer 81

* Color rendering index (CRI) * Illuminant compared to “an ideal” illuminate * Historically, sunlight has been used * Artificial illuminant as designated by CIE * Perfect match: CRI=100 (try to get \>90) * Full spectrum illumination- color rendering index CRI\>90, color temp\>5500oK * Natural daylight * 2 light sources with different spectral content * Color matching in clinic→ shade guides are used to communicate color to lab

Answer 82

color rendering index CRI\>90, color temp\>5500oK

Answer 83

* Safety of patient * Hypersensitivity and allergy issues * Benefits of use must outweigh the risks * Safety of the staff * Chronic exposure (e.g. amalgams, latex, resin-based materials HEMA TEGDMA, camphoroquinone) * Legal liability * Regulatory compliance (e.g. elimination of mercury from dental waste)

Answer 84

ability of a material to elicit an appropriate response in a given application in the body

Answer 85

Biomaterials are not biologically inert Biocompatibility is a dynamic process Biocompatibility is a property of a material and its environment

Answer 86

Critical adverse effect: lowest exposure level with event Critical concentration: critical amount that causes effect

Answer 87

Patch test Remember: toxicity=dose dependent, allergy=dose independent

Answer 88

by wear, dissolution or corrosion Dissolution vs. corrosion (difference between chemical concentration gradients and electrical current gradients)

Answer 89

cyclic stresses

Answer 90

materials' composition, amount of ion/molecule, etc.

Answer 91

* Different composition from the bulk (metal and resin composites) * Titanium alloys (TiO2 layer) * Roughness increases the release allergens, mutagens, toxins * Rough surface * Promotes corrosion * Increase the release of ions may lead to adverse effects * Acidic beverages= degradation of ceramics, increase roughness * Unfinished surfaces

Answer 92

Chemical nature of components Physical nature of components types/locations of patient tissues exposed to the device Surface characteristics of the material Amount and nature of substances eluted from material

Answer 93

Process of forming a direct structural and functional interface between live bone and an artificial implant surface without any intervening fibrous connective tissue

Answer 94

(acid sensitive) Excellent chemical durability Acidic beverages and/or auxiliary dental products (acidulated phosphate fluoride, APF) Important issue: bonding protocol toxicity of HF--\> burns, dangerous protocol Dilute solutions deeply penetrate before dissociation, thus causing delayed injury and symptoms

Answer 95

Initial test- in vitro, using cells Secondary test-in vivo test, using animals Usage test-tested in situation identical to its intended clinical use

Answer 96

red=proportional and elastic limit blue=max flexibility green=resistance purple=toughness yellow=yield strength pink=tensile strength