Exam 1 Flashcards

Question

Enamel bonding

Answer 1

In enamel bonding, enamel is etched with phosphoric acid. Acid etching preferentially dissolves enamel crystals in each prism. In type I enamel etching, the prism core is preferentially etched Creates mechanical retention; increases SA; removes junk on top of surface; due to hand instruments; breaks down part of enamel, dentin; cleans it up; creates pores- allows materials to have a better interaction Must etch both surfaces (enamel and dentin)- used adhesives (bonding agent- have acid monomers that does the same)- need to clean it up to create better cross linking In Type II, the prism peripherally is preferentially etched. Type III enamel etching results in a uniform or mixed pattern of etching. No difference in micro-mechanical bond strength of the different etching patterns has been established As etching is established, the surface of the etched enamel develops a frosty appearance. This roughened surface provides a substrate for infiltration of bonding agents; After the bonding agents penetrate the roughened enamel surfaces, they are polymerized, forming a micromechanical bond to the enamel surface

Answer 2

Enamel is not a tissue that is uniform in structure. Near the DEJ, enamel is commonly aprismatic, making it more difficult to etch Similarly, fluoride concentration in surface enamel is significantly higher than subsurface enamel, making it more difficult to etch as well

Answer 3

The mineral in all calcified tissues in the body is a highly defective version of the mineral hydroxyapatite (HA). HA has a hexagonal crystal structure, and the formula is Ca10(PO4)6(OH)2. Biological versions of apatites differ from ideal HA found elsewhere in nature in that biological apatite has many more defects and chemical substitutions. Defects and substitutions generally serve to make it less stable and more soluble in acids. The variable composition of HA in enamel and dentin reflects its formative history and other chemical exposures during maturity. Enamel and dentin HA is calcium deficient, carbonate rich, and highly substituted (Mg and Na commonly substitute for Ca; Carbonate substitutes for the phosphate and OH groups) The most beneficial substitution is the fluoride ion (F-), which substitutes for the OH group; Applying fluoride changes HA- makes crystal stronger and less soluble in acids

Answer 4

The most beneficial substitution is the fluoride ion (F-) which substitutes for the OH group; Formula: Ca10(PO4)6(F)2 which is less soluble than HA and more provides more protection against caries

Answer 5

Complex hydrated composite structure composed of an organic matrix and a mineralized component, that forms the majority of the tooth; It is modified by aging, disease and other physiological processes resulting in a wide range of altered forms; The type of dentin you encounter performing restorative procedures may profoundly impact your ability to bond restorative materials to dentin; volumetrically dentin is composed of 50% carbonate rich, calcium deficient apatite, 30% organic material, primarily type I collagen, 20% fluid The tubule lumen is lined by a highly mineralized cuff of peritubular dentin ~0.5-1µm thick. The peritubular dentin, also known as intratubular dentin by some, contains mostly apatite crystals and little or no organic (collagen) matrix; Tubules are separated by intertubular dentin, which has a composite structure, consisting of a matrix of type I collagen reinforced by apatite- this arrangement means that the volume of intertubular dentin in a given area of dentin will vary by location, because tubule density tends to increase as you approach the pulp from the DEJ

Answer 6

The development of teeth and their supporting structures from embryonic tissues; The cells responsible for dentin formation are called odontoblasts- they differentiate from the outer cells of the dental papilla in the Bell Stage of tooth development; the pulp develops from the central cells of the dental papilla; the basement membrane represents the location of the future DEJ; because dentin and pulp have similar embryonic origins, these 2 tissues are commonly referred to as the dentin-pulp complex Odontoblasts continue to make dentin throughout the life of the cell; they can be found on the outer wall of the pulp, immediately medial to the advancing wall of dentin; Because odontoblasts rest just inside the dentin and line the walls of the pulp chamber, the dentin-pulp complex is considered to be a vital tissue

Answer 7

Tubules are a distinct feature of dentin; they represent the tracks taken by odontoblasts as they retreat from the DEJ and appear as tunnels, traversing the dentin from the DEJ to the pulp. The tubules converge as they approach the pulp chamber and therefore tubule density and orientation varies from location to location pain is the only info they send to brain; close the the pulp wider; closer to DEJ, smaller (more difficult to report pain- more time to do restoration than root canal) The content of the tubules are odontoblastic processes and fluid; the extent that the odontoblastic process occupies the tubules has not been conclusively established, but it is believed that it extends to the DEJ

Answer 8

The morphology of dentin varies with location and is altered by aging and disease; Primary dentin is formed by odontoblasts before the tooth erupts while secondary dentin is formed by odontoblasts after tooth eruption; tertiary dentin is reparative dentin that forms quickly and in a very localized manner in response to trauma (caries, cavity prep, attrition, etc. ) [ it is only found under dentinal tubules that have been exposed to trauma, at the outer pupal wall Transparent dentin (sclerotic) is a type of tertiary dentin that develops following trauma, and is characterized by the tubules being partially occluded with mineral (for pulp protection) ; many types of transparent dentin have been described; the nature of the mineralization is both heterogenous and complex, and has been described in detail elsewhere bonding is a problem because the tubules are closed- etching must be different]

Answer 9

When dentin is cut or abraded with a rotary instrument, a smear layer forms (junk on top); the smear layer is a collective term for any debris left on a tooth surface following tooth preparation; This debris consists of chips of enamel and dentin, and organic matter that are resting or burnished onto the surface or into the dentinal tubules; the smear layer serves to occlude the tubules and reduce dentinal permeability, thereby providing a protective effect; however it hinders dental bonding, so it should be either removed or modified before the bonding procedure

Answer 10

Also known as conditioning; removes the smear layer and alters the external lumen of tubules, allowing better infiltration by bonding agents; as dentinal surfaces are conditioned with acid, peritubular dentin is preferentially removed since it has no organic component. The tubule lumen widens with etching creating a funnel shape that can be less retentive due to its flared nature. Longer acid etching of dentin flares the tubule lumen even further

Answer 11

Transparent dentin has a different outcome in conditioning, because the tubules are occluded with mineral- this mineral in the tubules can be very heterogeneous in its response to acid conditioning, depending upon the stimulus which led to its formation; after etching transparent dentin, peritubular dentin is preferentially removed, but the tubules may continue to retain plugs of precipitated mineral which make bonding to transparent dentin even more difficult

Answer 12

Dentin is a composite material, consisting of a mineralized component (HA), and an organic component (type I collagen); acid etching removes the smear layer; acid etching also removes the mineralized component of intertubular dentin, leaving a network of collagen fibrils; engaging this network of collagen fibrils and dentinal tubules with bonding agents forms the micro-mechanical basis for dentin bonding An important element of dentin bonding technique is to keep the demineralized dentin moist; if demineralized dentin is dried, the dentin matrix shrinks and becomes matted, making the collagen fibrils and dentinal tubules difficult to penetrate with bonding agents

Answer 13

Look at slide 73 on PP 1

Answer 14

“The assembly of two tissues with distinctly different elastic moduli requires a complex fusion for long term functional success. Stress transfer in simple bilaminate structures with divergent properties usually induces increased focal stresses at the interface.” “If enamel and dentin at the functional surfaces of a tooth comprised such a simple bilaminate, enamel-initiated cracks would easily cross the DEJ and propagate into dentin.” “In reality, the situation is quite different…multiple enamel cracks…seldom affect the structural integrity of the enamel-dentin complex.” “The explanation lies in…a complex fusion at the DEJ, which can be regarded as a fibril-reinforced bond.” “[At] the DEJ…parallel, coarse collagen bundles (probably von Korff fibers of mantle dentin) form massive consolidations that can divert and blunt enamel cracks through considerable plastic deformation.” “The structure of the DEJ shows two levels of scalloping, which [serves to] increase the effective interfacial area and strengthen the bond between enamel and dentin. The scalloping is most prominent where the junction is subject to the most functional stresses.”

Answer 15

The morphology of the DEJ begins at the earliest developmental stage of the tooth crown; Any other sequence would not allow the creation of such a complex dentinoenamel fusion; During odontogenesis, before the cells of the inner enamel epithelium (IEE) differentiate into preameloblasts, and the outer cells of the dental papilla differentiate into odontoblasts, they are separated by a basement membrane (represents the future location of the DEJ) Once the cells of the IEE differentitate into preameloblasts, they stimulate the outer cells of the dental papilla to differentiate into odontoblasts. The odontoblats then begin secreting dentin matrix on their side of the basement membrane, retreating into the central cells of the dental papilla as matrix and dentin is formed At this point, the basement membrane disintegrates, preameloblasts differentiate into ameloblasts, and the ameloblasts begin secreting enamel matrix. The junction of enamel and dentin is established as these 2 hard tissues begin to form Before enamel forms, some of the developing odontoblastic processes extend into the ameloblast layer; When enamel formation begins, these odontoblastic processes become trapped as enamel spindles. Von Korff fibers in mantle dentin also cross the DEJ into enamel to further integrate these tissues

Answer 16

cracks in enamel do not extend into dentin but instead stop at the scalloped DEJ Have large scallops in molars, but smaller scallops in anterior teeth

Answer 17

Enamel and dentin are oral hard tissues with profoundly different morphological and mechanical properties Bonding dental materials to enamel and dentin is technique-sensitive and requires treating each as a unique tissue Enamel and dentin bonding is micromechanical Natural teeth, through the optimal combination of enamel and dentin, demonstrate the perfect and unmatched compromise between stiffness, strength and resilience Restorative procedures and alterations in the structural integrity of teeth can easily violate this balance

Answer 18

``` pH Saliva Chewing- occlusion Mechanical loads- depending where food is at (temp too) ```

Answer 19

Must understand the properties of the different materials Polymers- composites (powder/liquid mixed -->activated; light cure) Ceramics Metals In order to conclude that a material is appropriate for clinical use we need to evaluate all kind of properties. In vitro research is just a simulation of what we might get clinically … So… to be able to have a clinical relevance we need to set up clinical trials. In vitro research allow us to standardize measures to compare materials and guiding the interpretation of clinical trials. In the lab we try to simulate as much as we can the clinical conditions. -Size -Shape -Conditions (temperature, proportions, humidity, etc) When we restore a (caries, fractured) tooth it is important to select a materials that is adequate, but we need to take into account the quality of the substrates (enamel, dentin, cementum, proximity to the pulp) that we will restore

Answer 20

``` Mechanical Thermal Electrical Electromechanical Optical ```

Answer 21

When we restore a tooth, we expose that restoration to challenges: chemical- acids (lemonade, OJ) Thermal- different temp Mechanical- wear

Answer 22

One body interacting with another generates a force. Applied - Contact of the bodies - Distance (Eg. Gravity)

Answer 23

Deformation (rigid or deformable and constrained) - Constrained (no movement or translate) = deformation or change its shape - Free of constrains = movement or translate

Answer 24

The force applied on opposing teeth when the jaws are closed; posterior teeth are stronger (surface area, anatomy, muscles) Max occlusal forces ranges from 200- 3500N Occlusal forces are increased in posterior regions and decreased in anterior regions. - Forces on 1st and 2nd molar vary from 400- 800 N. - Average forces on the bicuspids, cuspids, and incisors is about 300, 200, 150 N respectively Children growing up show an increase in force from 235- 494 N with an average increase yearly of about 22N

Answer 25

Patients with dental prosthetic devices decrease occlusal forces. about 65-235 N (partial dentures), about 100 N molars and bicuspids (complete dentures) and about 40 N incisors (complete dentures) dentures cause face changes- lose bone therefore lose strength

Answer 26

Women occlusal forces is about 90 N less than men; facial form and muscles can be predictors of occlusal forces (low angles and square mandibular form=high occlusal forces) Males stronger than female; female have a more delicate facial structure; some people have strong masseters (usually square shaped)

Answer 27

Max occlusal forces and response of underlying tissues changes with: - Age - Anatomic location - Occlusal Scheme (contacts that upper teeth have with lower teeth; as the form and the arrangement of the occlusal contacts in natural and artificial dentition) - Placement of dental prosthesis (removal vs permanent)

Answer 28

When a force acts on a constrained body, the force is resisted by the body and the internal reaction is equal in magnitude and opposite in direction to the applied external force and is called stress (S or σ) The applied force and internal resistance (stress) are distributed over an area of the body stress= Force (N)/area - Pascal (1Pa -1N/m2=1MN/mm2) - mega Pascals (MPa) or millions of Pascals = 1MPa = 106 Pa

Answer 29

A force can be applied from any angle or direction Complex stress= several forces It is rare for forces and stress to be isolated to a single axis Individually applied forces can be defined: Axial- applying load along the axis (occlusion) - Shear- removal of bracket; like cut - Bending- - Torsional- endo files All stresses can be resolved into combinations of 2 basic types: axial and shear

Answer 30

Results from 2 sets of forces directed away from each other in the same straight line; bonding agents (hydrophobic/ hydrophilic)?

Answer 31

results from 2 sets of forces directed toward each other in the same straight line

Answer 32

Compress or shorten

Answer 33

stretch or elongate

Answer 34

2 sets of forces directed parallel to each other, but not along the same straight line A stress that tends to resist the sliding or twisting of one portion of a body over another Ex. orthodontics bracket removal ; like cutting?

Answer 35

Resulting from the twisting of a body ex. endo files

Answer 36

results from an applied bending movement Modulus of rupture, bend strength or fracture strength is a material property, defined as the stress in a material just before it yields in a flexure test. Depending when apply the load you can have different types of stress

Answer 37

Compression- resist to be forced more closely shear- one portion of the body must resist sliding past another

Answer 38

Deformation in a body due to stress Strain = ε = change in the length (ΔL= L-Lo) Strain (ε)= Deformation/Original Length = (L-Lo)/Lo= ΔL/Lo It is reported as a percentage *Lo=Change in length

Answer 39

Amount of deformation (strain) at distinct intervals of tensile or compressive loading (stress) If a bar of a material is subjected to an applied force (F) the magnitude of the force and the resulting deformation (δ) can be measured….. But we can apply the same F to another bar with different dimensions and that other bar will suffer different force-deformation characteristics. If the applied F is normalized by the cross-sectional area (A) of the bar (stress) and the deformation is normalized by the original length of the bar (strain), the resulting stress-strain curve is independent of the geometry of the bar It is better to report the stress-strain curve of a material rather than the force-deformation characteristics. Stress-strain relationship = measure load and deformation and then calculate the corresponding stress-strain Universal testing machine If we assumed that the cross-sectional area of a specimen remains constant during the testing then S-ε curve is engineering S-ε

Answer 40

* Look at graph A=PL proportion limit- will come back to original (marble will have a higher vs glass) – stress and strain are linearly proportional [after exceed PL can not come back (deformation); straight line) B=yield point (constants: 0.1, 0.2. 0.3, 0.5 [doesn’t change the results]; most common is 0.2)- way to calculate in a more accurate way- (constant of the behavior of the material) starts acting like a plastic material Difficult to calculate proportional limit (arrrow in graph) C= ultimate tensile strength- max stress before failure D= fracture point (strength) Elastic limit is not known on this graph Elastic region- can return to original shape, size Plastic- will never return to initial dimensions

Answer 41

Plastic deformation from PL to failure point (FP) The value of the stress at A is known as proportional limit (PL) - (Spl or σpl) below the PL = no permanent deformation, material is elastic in nature. After PL= permanent deformation, irreversable strain occurs = plastic region = non-linear Super elastic materials (exception)

Answer 42

Elastic deformation it is up to the proportional limit (PL) (SEL or σEL) Is the maximum stress that a material will withstand without permanent deformation Elastic limit and proportional limit differ in fundamental concepts -Elastic limit: describes the elastic behavior of the material region) -Proportional limit: deals with the proportionality of strain to stress in the structure (slope) ***So they are different values

Answer 43

The stress at which the materials begin to function in a plastic manner At YS a small defined amount of permanent deformation has occurred in the material. Amount of permanent strain is indicated as 0.1%, 0.2% (often) or 0.5% = offset ``` Stiff material (small elongation) will have a greater offsets than material with larger elongation or deformation. Elastic limit and yield strength define the transition from elastic to plastic behavior ```

Answer 44

Ultimate tensile strength or stress (UTS): Maximum stress that a material can withstand before failure in tension Ultimate compressive strength (UCS): Maximum stress a material can withstand in compression before failure in compression

Answer 45

Point at which a brittle material fractures if the material does not fracture at the point at which the max stress occurs they might elongate resulting in necking

Answer 46

Deformation as a result of the application of a tensile force. Divided in 2: 1. Increase in length of specimen below the PL (0-A) = not permanent 2. Increase in length of specimen after PL (A-D) = permanent Total elongation is reported as a % %Elongation = (Increase in length/original length) *100% An alloy with high value for total elongation can be bent permanently without danger of fracture

Answer 47

The measure of elasticity of a material is descirbed by the term elastic modulus = E; modulus = ratio. E= stiffness of a material within the elastic range. E= stress/strain; E=S/ε Units GPa or MPA (1GPa=1000MPa) To calculate E select 2 stress and 2 strains coordinates in the elastic or linear range . The slope is therefore: (σ1 -σ2 )/(ε1- ε2) Relative rigidity or stiffness of the material within elastic range Young’s modulus of elasticity Elastic modulus = Stress/Strain

Answer 48

During axial loading in tension or compression there is a simultaneous strain in the axial and transverse or lateral directions.(Relative change in lateral dimension and elongation in the longitudinal direction) Tensile loading: as material elongates in load direction = reduction in cross-section known as “necking” during elastic deformation and deformation continues until the material is fractured. Compressive loading: increase in cross sectional within elastic range, the ratio of the lateral to the axial strain is called “Poisson’s Ratio”. Is unitless value because it is ratio of two strains

Answer 49

Ductility: Its ability to be drawn and shaped into a wire by means of tension ex. Orthodontics Eg. Gold and silver: are used extensively in dentistry because are the most malleable and ductile materials

Answer 50

Malleability: Its ability to be hammered or rolled into thin sheets without fracturing Eg. Gold and silver: are used extensively in dentistry because are the most malleable and ductile materials

Answer 51

Resistance of a material to permanent deformation Is an indicator of the amount of energy necessary to deform the material to the PL. Area under the elastic portion of the S-εcurve Units: mMN/m3 or mMPa/m Ex. Mouth guards- need resilient material

Answer 52

Resistance of a material to fracture Indication of the amount of energy necessary to cause fracture. Units: mMN/m3 or mMPa/m includes all aspects of the SS curve

Answer 53

The ability to be plastically deformed without fracture, or the amount of energy required for fracture. It is proportional to the energy consumed in plastic deformation

Answer 54

Is the RIGIDITY of an object The extent to which it resists deformation in response to an applied force The more flexible an object is less stiff

Answer 55

The slope of S-ε curve and the magnitude of the stress and strain allow classification of materials with respect to their general properties The properties of stiffness, strength and ductility are independent Materials may exhibit various combinations of these 3 properties *** look at graphs on slide 52

Answer 56

``` Brittle materials are difficult to test because they fracture easily. Grips Slow loading Axial tensile loading Low stress on the material ```

Answer 57

The mechanical properties of many dental materials (alginate, elastomeric, waxes, amalgam, polymers) and substrates (bone, dentin, etc) depend on how fast they are loaded Materials with mechanical properties dependent of loading rate and with viscous and elastic behavior are = Viscoelastic Materials with mechanical properties independent of loading rate = Elastic (strain is produced when load is applied) Other materials exhibit a “Lag” response to load = Viscoresponse.

Answer 58

Same materials are solid dental materials that show some fluid characteristic or many dental materials, such as cements and impression materials are in the fluid state when formed Therefore, fluid (viscous) phenomena are important. Viscosity (η) is the resistance of a fluid to flow and is equal to the shear stress/shear strain rate Or, η = τ/[dε/dt] Units: poise, p (1p= 0.1 Pa; S= 0.1Ns/m2) or centipoise (100cp = 1p)

Answer 59

In this case the strain rate can alter the stress-strain properties Eg. Tear strength of alginate increases ≈ 4 times when rate of loading is increased from 2.5 to 25 cm/min (remove quickly from mouth to increase tear resistance)

Answer 60

Involves cycling loading or loading at high rates (impact). Dynamic Modulus (ED) The ratio of stress to strain for small cyclical deformations at a given frequency and at a particular point on the stress-strain curve. ED=mqp2 m= mass of the loading element q= height/twice the area of the cylindrical specimen p= angular frequency of the vibrations Ex. endo files

Answer 61

Surface Mechanical Properties Resistance to permanent surface indentation or penetration -A measure of the resistance to plastic deformation and is measured as a force per unit area of indentation

Answer 62

Surface Mechanical Properties The resistance between contacting bodies when one moves relative to another. The friction force (Fs) is proportional to the normal force (FN) between the surfaces and the (static) coefficient of friction (μs) Fs=μs FN

Answer 63

Surface Mechanical Properties Is a loss of material resulting from removal and relocation of materials through the contact of two or more materials ``` Types of wear: Adhesive wear Corrosive wear Surface fatigue wear Abrasive Wear ``` Examples: Metals: are susceptible to adhesive, corrosive and three body wear Polymers: are susceptible to abrasive and fatigue wear

Answer 64

formation and disruption of micro junctions.

Answer 65

Secondary to physical removal of protective layer and it is related to the chemical activity of the wear surfaces (common in metals)

Answer 66

free particles with small areas of contact contribute to high localized stress and produce surface cracks.

Answer 67

Involves a harder material cutting into a softer material ex. crowns

Answer 68

Colloid is used now to describe a state of a matter rather than a kind of matter. The main characteristic of colloidal materials is their high degree of microsegmentation. These fine particles also have certain physical properties, such as electrical changes and surface energies that control the characteristics of the colloids.

Answer 69

Substances are called colloids when they consist of two or more phases, with the units of at least one of the phases having a dimension slightly greater than simple molecular size. Size ≈1 to 500 nm in maximum dimensions Colloidal state represent a highly dispersed system of the fine particles They can be fine dispersions: -Gels (hand sanitizer) – Films – Emulsion - Foams

Answer 70

Divided in Sol and Gel Sol resembles a solution, it is made up of colloidal particles dispersed in a liquid. When we add suitable chemicals the Sol can be transformed to GEL = semisolid, jelly like quality. The liquid phase of a GEL or Sol is usually water or an organic liquid such as alcohol. When it is water = hydrosols or hydrogels = hydrocolloids Ex: In dentistry (alginate gels) When the system has an organic liquid as a component = organosol or organogel.

Answer 71

Osmotic pressure is the pressure developed by diffusion of a liquid or solvent through a membrane. Osmotic pressure has been used to explain the hypersensitivity of dentin. The changes in pressure in carious, exposed dentin from contact with saliva causes diffusion throughout the structure that increases or decreases the pressure on the sensory system.

Answer 72

A liquid or gas adheres to the surface of a solid or liquid firmly by the attachment of molecules, decreases their surface free energy Ex. Alginate (viscoelastic material)- don’t want it too wet; external

Answer 73

The substrate diffuses into the solid material by a diffusion process, and the process is characterized by concentration of molecules at the surface (Eg. alginate = swelling) fuses into- in alginate

Answer 74

When adsorption and absorption exist at the same time and it is unknown which one predominates.

Answer 75

Measured in terms of force (dynes) per centimeter of the surface of liquid. Surface tension is a contractive tendency of the surface of a liquid that allows it to resist and external force. The wetting power of a liquid is represented by its tendency to spread on the surface of the solid. And it measure by the degree to which something can be wet.

Answer 76

The perception of color is the result of a physiological response to a physical stimulus. The sensation is a subjective experience, whereas the beam of light, which is the physical stimulus that produces the sensation is entirely objective color of an object is determined on the spectrum and the intensity of the incident light on it and the changes of the light in contact with it as well. Consequently, the color is determined on the reflected light composition (wavelengths). A body, reflecting particular spectrum range to the white light and absorbing the rest, is colored with the color of the reflected light

Answer 77

The eye can distinguish differences in only 3 parameters of color. These parameters are dominant wavelength, luminous reflectance, and excitation purity. The dominant wavelength (λ) of a color is the wavelength of a monochromatic light that, when mixed in suitable proportions with an achromatic color (gray), will match the color perceived.

Answer 78

Electromagnetic radiation resulted in changes of the state of electron cover, including ultraviolet, infrared and x ray radiation

Answer 79

steam of material particles- photons wide spreading as electromagnetic wave

Answer 80

has wavelength in a range of ~380 nm to about 760 nm with a frequency range of ~405THz to 790 THz

Answer 81

When light is refracted by a prism, dispersion causes separation of colors ROYGBV. Consequently, the white light is polychromatic, which is a mixture of the various wavelengths

Answer 82

For an object to be visible, it must reflect or transmit light incident on it from an external source The reflected light intensity and the combined intensities of the wavelengths presented in the incident and reflected light determine the appearance properties- hue, value, and chroma Consequently, to understand the color, we have to know the nature of the optical processes reflection, refraction, and absorption

Answer 83

Reflection of light is either specular (mirror like) or diffuse depending on the nature of the interface

Answer 84

color property, expressed mainly in metals. It depends on quantity of reflected light High brightness- nearly all incident light is reflected

Answer 85

the incident angle is equal to the reflected angle

Answer 86

When the surface roughness is higher than the incident light wavelength

Answer 87

If the surface roughness is commensurable with the incident light wavelength

Answer 88

In dentistry mirror like reflection of ceramic construction can be resulted only if the opaque layer is backed in temperature higher than recommended. After correct backing the opaque porcelain diffusively reflects the light

Answer 89

the change in direction of a wave due to change in its speed. This is commonly observed when a wave passes from one medium to another

Answer 90

the property of the material to let the light pass through it

Answer 91

Is a property of materials that prevents the passage of light. When all the colors of the spectrum from a white light source such as sun light are reflected from an object with the same intensity as received, the object appears white. When all the spectrum colors are absorbed equally, the object appears black. the object does not let the incident light to pass through it. An opaque substance transmits no light, and therefore reflects, scatters or absorbs all of it

Answer 92

absorbs all light

Answer 93

reflects all light

Answer 94

nearly all the light passes through an object

Answer 95

Can be used as a standard for transparency- about 90% of incident light can pass through it

Answer 96

Is a property of substances that permits the passage of light but disperses the light, so objects cannot be seen through the material (Eg. ceramics, resin composite, and acrylics) Not all, but some light passes through it

Answer 97

Matt glass; with transparency coefficient of about 50%

Answer 98

properties of the materials to have different colors in illuminating by different light sources. Metameric colors are color stimuli of identical tristimulus values under a particular light source but with different spectral energy distributions. Under some lights the pairs would appear to match, but under other lights they would be different whenever possible, shade matching should be done in conditions where most of the patients activities will occur. Daylight, incandescent and fluorescent lamps are common sources of light in the dental operatory or aboratory, and each of these have a different spectral distribution. Objects that appear to be color matched under one type of light may appear different under another light source

Answer 99

a pair of objects whose colors match when viewed in a described way but which do not match if the veiwing conditions are changed

Answer 100

opalescent materials- Materials that are able to scatter shorter wavelength of light (Eg. Dental enamel) Mimic the natural appearance of the tooth (Eg. Porcelain veneer, and resin composite) Originating of a rainbow inside a material with little opacity due to the interference of light waves owing to the inside defects and microstructural inhomogeneity. The phenomenon is named after the appearance of opals

Answer 101

is result of interaction of light with enamel prisms- refraction, reflection and interference

Answer 102

the property to absorb the energy and to emit as visible light 2 types: fluorescence and phosphorescence

Answer 103

Is the emission of luminous energy by a material when a beam of light is shone on it Emission of light by a substance that has absorbed light of other electromagnetic radiation of a different wavelength. In most cases, emitted light has a longer wavelength. fluorescence as distinguished from phosphorescence does not persist for an appreciable time after the termination of the excitation process

Answer 104

a specific type of photo luminescence related to fluorescence. Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs and emits it a long time after excitation

Answer 105

Natural tooth structure absorbs light at wavelengths too short to be visible. These wavelengths between 300-400nm are referred to as near IV radiation. Natural sunlight, photo flash lamps, certain types of vapor lamps and UV lights used in decorative lighting are sources containing substantial amounts of near IV radiation. The energy that the tooth absorbs is converted into light with longer wavelengths in which case the tooth actually becomes a light source- the fluorescence process The emitted light, a blue-white color, is primarily in the 400-450nm range Ex. a person with ceramic crown or composite restoration that lack fluorescent agent appear to be missing teeth when viewed under a black light in a night club

Answer 106

(visual method) munsell color system is color space that specifies colors based on 3 color dimensions: hue, value, chroma Hue- measured by degrees around horizontal circles (as you move around the center) Chroma- measured radially outward from the neutral vertical axis (as you move from center outwards) Value- changes from top to bottom; measured vertically from 0 (black) to 10 (white)

Answer 107

describes the dominant colors of an object- red, green, or blue. This refers to the dominant wavelengths present in the spectral distribution. The continuum of these hues creates the color solid Light having short wavelengths (400nm) is violet in color, and light having long wavelengths (700nm) is red. Between these two λ’s are those corresponding to blue, green, yellow, and orange light. This attribute of color perception is also known as hue.

Answer 108

Identifies the lightness or darkness of a color The quality lightness or darkness. That is black is a dark value or low value. White is a light value or high value It increases towards the top to white (value= 10) decreases toward the bottom to dark or more black (value=0) and can be measured independently of the hue. Neutral grays lie along the vertical axis between black and white

Answer 109

represents the degree of a saturation of a particular hue; The quality of a color’s purity, intensity or saturation. Example: A gray color is a neutral – an extreme low chroma Fire-engine red maybe a high-chroma red. Brick red maybe a middle-chroma red It varies horizontally in Munsell system. The higher the chroma, the more intensive the color. Chroma is not considered separately in dentistry. It is always associated with hue and value of dental tissues, restoration and prostheses. In changing the chroma, the value also has to be changed. The higher the chroma, the darker the value

Answer 110

color wheel or circle is an abstract illustrative organization of color hues around a circle, that show relationships between primary colors, secondary colors, complimentary colors, etc. Primary colors- red, yellow, blue secondary colors- green, orange, and violet complimentary colors- pairs of colors that are "opposite" hue in the color wheel ex. Red and green

Answer 111

in the dental operatory or lab, color matching is usually performed by the use of a shade guide to select the color of ceramic veneers, inlays or crowns to be made by a lab tech. Using these shade tabs, one can specify the color characteristics (hue, value, chroma) and translucency to the tech who will produce the proper appearance in the lab. If the tech can see the actual teeth, the probability of achieving an acceptable color match is even greater

Answer 112

most commonly used for determining the teeth color in dentistry. The arrangement of the shades in the VITA classical A1-D4 shade guide is as follows: A1-4 (reddish-brownish) B1-4 (reddish-yellowish) C1-4 (greyish shades) D2-4 (reddish- grey) The chroma increases and the value decreases with increasing the number from 1 to 4

Answer 113

if possible, determine the shade under daylight conditions or standardized daylight lamps, and not under normal indoor lighting conditions. The shade taking environment should preferably be in muted colors. Patients should be asked to remove lipstick or any cosmetic which could have an influence on shade taking. Clothing in pronounced colors should be covered with a grey overall. Make your choice swiftly; always accept your first decision, since the eyes begin to tire after ~ 5-7sec

Answer 114

same principle of arrangement like VITA shade guide- increasing of the number shows increasing the chroma and decreasing the value of the color. All 20 tooth shades are positioned on individual supports that can be removed from the shade guide for detained shade selection. Differences: 5 color groups: 100, 200, 300, 400, 500 Designation- only by number

Answer 115

for the accurate selection of the tooth shade, the surrounding conditions and the correct procedures should be observed. Color of the room: neutral colors (ex. grey) with only minor color effects; artificial light: ideally a daylight lamp (D65) with an illumination of 1200-1500 lux. Daylight: northern light, preferably at 10'o clock in the morning. Patient: cover clothes with a neutral cloth

Answer 116

Carry out shade selection prior to the actual treatment. Prevent the teeth from dehydrating. Determine the amber or grey color type of the patient according to the Ivoclar Vivaddent color typology. Determine the definite base shade of the patient and remove the corresponding shade group. Determine the shade intensity within the shade group. Compare the selected shade once again with the natural tooth

Answer 117

technology (technological process) is combination of different methods and operations for treatment of materials. Technological properties- determine the possibility for treatment of materials in definite conditions: plasticity, fluidity of molten metal, welding ability, etc.

Answer 118

technological and mechanicl property of a material to undergo permanent deformation under load In dentistry, waxes, restorations, and impression materials possess this property. The plasticity of metals and alloys is used in forgin, stamping rolling and drawing processes

Answer 119

ability of a molten metal to flow and fill a channel or cavity Factors influencing the fluidity: chemical composition of the alloy viscosity- the higher viscosity, the lower fluidity of the molten metal Temperature of over heating the molten metal above the melting point- the fluidity increases with its increasing temperature. But the excessive overheating leads to increasing of the molten reactivity resulting in formation of undesired compounds- oxides, nitrides, carbides, etc. The temperature interval of melting- the narrower interval leads to the higher fluidity the pressure on the metal during casting process- the fluidity increases with increasing pressure

Answer 120

method of Kaminski- the test specimen is of mesh type, consisting of 100 squares (10X10 mm) made of wax. The material is of high fluidity if all the squares are filled.

Answer 121

also known as joinability, of a material refers to its ability to be welded. A materials weldability is used to determine the welding process and to compare the final weld quality to other materials. 2 main methods of welding: by melting by pressure

Answer 122

Dental restorative materials are most commonly measured in reflected light using a color measuring instrument or a visual method Instrument Curves spectrol reflectance (%) vs wavelength (nM0 can be obtained over the visible range (405-700nm) with a spectrophotometer integrating sphere

Answer 123

when white light shines on a solid, some of the light is directly reflected from the surface and remains white light This light mixes with the light reflected from the body of the material and dilutes the color. As a result, an extremely rough surface appears lighter than a smooth surface of the same material Ex. unpolished or worn glass ionomers, resin composite restoration

Answer 124

esthetic effects are sometimes produced in restorations by incorporating colored pigments in non metallic materials (resin composites, dentures, ceramic) When colors are combined with proper translucency, restorative materials can be made to closely match the surrounding tooth structure or soft tissue

Answer 125

is the ratio of the velocity in a vaccum (or air) to its velocity in the medium. When light enters a medium, it slows from its speed in air (300,000 km/sec) and may change direction

Answer 126

As light interacts with an object, several phenomena can be observed. Incident light reflected, absorbed, scattered (or backscattered) or transmitted These parameters can all be calculated to more objectively characterize the optical properties of the materials

Answer 127

the fraction of incident light flux lost by reversal of direction in an elementary layer Scattering coefficient, S. S = (1/bX) Ar ctgh [1-a(R+Rg) +RRg/b (R-Rg)], mm-1

Answer 128

The fraction of incident light flux lost by absorption in an elementary layer. The absorption coefficient, K, for a unit thickness of material is define as follows: K= S (a-1), mm-1

Answer 129

Is the light reflectance of a material of infinite thickness, and is defined as: RI=a-b

Answer 130

dental restorations are often used to restore esthetic problems even when carious lesions are not present. The ability of masking depends on optical constants and thickness of the dental materials used

Answer 131

We can measure the temperature of a substance with a thermometer or a thermocouple In dentistry temperature has an important applicability because we need to measure the heat produced during different procedures (Eg. cavity preparation and resin composite polimerarization) because the heat can affect other tissues (pulp and gums) and produce pain or irreversible pulpitis.

Answer 132

``` The arrangement of atoms and molecules in materials is influenced by temperature. As a result, thermal techniques are important in understanding the properties of dental materials Some of the techniques: -Differential thermal analysis (DTA) -Thermo-mechanical analysis (TMA) -Dynamic mechanical analysis (DMA) ```

Answer 133

Is the heat in calories, or joules, J, required to convert 1g of material from solid to liquid state at the melting temperature L=Q/m

Answer 134

Is the quality of heat, in calories, or joules, per second passing through a body 1 cm thick with a cross section of 1 cm^2 when the temperature difference is 1°C. Units: cal/sec/cm2/(°C/cm)

Answer 135

Is the quality of heat needed to raise the temperature of 1g the substance 1°C

Answer 136

Is a measure of transient heat-flow and is defined as the thermal conductivity, K, divided by the product of the specific heat, Cp, times the density, ρ Δ = K/(Cp p) Units: mm2/sec

Answer 137

The change in length (lfinal – loriginal) per unit length of a material for a 1°C change in temperature is called the linear coefficient of thermal expansion, α, and is calculated as follows: (lfinal – loriginal) /[ loriginal) x (°Cfinal - °Coriginal)] = α

Answer 138

The ability of a material to conduct an electric current may be stated as either specific conductance or conductivity, or conversely, as the specific resistance or resistivity

Answer 139

A material that provides electrical insulation is known as a dielectric

Answer 140

Is the voltage developed by any source of electrical energy

Answer 141

The presence of metallic restorations in the mouth may cause a phenomenon called galvanic action, or galvanism. These results from a difference in potential between dissimilar fillings in opposing or adjacent teeth. These filling in conjunction with saliva or bone fluids (electrolytes) make up an electric cell. When two opposing fillings contact each other, the cell is short-circuited, and if the flow of current occurs through the dental pulp, the patient will experience PAIN and corrosion in restorations. Metallic restoration may cause galvanism. The restorations + saliva make up an electric cell and when two opposing restoration contact each other the cell is short circuited and can produce a flow of current affecting dental pulp and producing pain and corrosion in the restorations.

Answer 142

Corrosion that is accompanied by a flow of electrons, between cathodic and anodic areas on metallic surfaces

Answer 143

also called electrokinetic potential the potential difference existing between the surface of a solid particle immersed in a conducting liquid (Ex. saliva, water) and the bulk of the liquid

Answer 144

Lose of luster, especially as a result of exposure to air or moisture color change common in cements, resin composite restorations

Answer 145

represents the amount of water absorbed on the surface and into the body of the material during fabrication or while restoration or service ex. dentures= dimensional changes due to water soprtion

Answer 146

Time required for a specimen of X material to attain a specific degree of rigidity compared to the initial time

Answer 147

The general deterioration and change in quality of materials during shipment and storage (temperature, humidity, and time of storage)

Answer 148

when a specimen is tested in compression, failure might occur as a result of a complex stress in the object Compressive forces= shear forces along the cone- shaped area at each end= tensile forces central portion of the mass If we have a cylinder and compression forces are applied =as forces of shear along the cone-shape area at each end and, as a result of the action of the two cones on the cylinder = tensile forces in the central portion of the mass.

Answer 149

When one loads a simple single beam supported at each end with a load applied in the middle (three point bending/ flexure stress) The max stress measured in the test is called the flexural strength= max stress that it can withstand without breaking

Answer 150

normally use to measure the number of bends the specimen will withstand and to compare different composition and dimensions as well as its treatment in fabrication Many dental restorations are subjected to permanent bending The adjustment of removable partial dentures clamps and the shaping of orthodontic wires are two examples of such bending operations.

Answer 151

A test for tensile strength that is only used for materials that exhibit predominately elastic deformation and little or no plastic deformation (brittle)

Answer 152

The maximum stress that a material can withstand before failure in a shear mode load ex. removing brackets in ortho

Answer 153

Results in a shear stress and a rotation of the specimen

Answer 154

Progressive fracture under repeated loading. Is the stress level at which a material fails under repeated loading. Fatigue test are performed by subjecting a specimen to alternating stress applications below its yield strength until fracture occurs (tensile, compressive, shear, bending, and torsion)

Answer 155

a property which describes the ability of a material containing a crack to resist fracture, and is one of the most important properties of any material for many design applications

Answer 156

resistance of a material to fracture

Answer 157

Fractography is the study of the fracture surfaces of materials; helps to define the cause of failures and aid in structural design, as well as to improve existing materials

Answer 158

Tear strength is a measure of the resistance of a material to tearing forces ex. elastomaterial must have very high tear strength

Answer 159

The relative resistance of a material to suffer indentation, scratching or bending Hardness testing is done by applying a standardized force or weight to an indenter Ex. Brinell Hardness Test (spherical indentation piece; Test force F/ Surface area of indentation A), Knoop Hardness Test (diamond shaped, measure H and L), Vickers Hardness Test (pyramid shaped diamond indentor- 4 sided, measure length of the 2 diagonals; test force F/ Surface area of indentation A), Rockwell Hardness Test ( C braile, crate handle, made of conical diamond indentor) , Barcol Hardness Test (handle that must be tested at multiple locations), Shore A Hardness Test (testing rubbers and plastics, use durometer and test 12 different ways)

Answer 160

Many materials have micro or nano structural constituents such as resin composites (indenter needs to be small). Need to create indentations of a smaller size and spatially control the location of the indentation Traditional indentation tests use loads as high as several kilograms and result in indentations as large as 100 μm … Those tests previously mentioned are valuable but they have limitations with recent technologies in the development of dental materials Able to apply loads of ~0.1 to 500 mg- f resulting in indentations of ~1µm in size; eliminates the need to image the indentations to calculate the mechanical properties because the indentation depth is continuously monitored If testing hardness usually using these The nano-hardness of dentin = 696 MPa agrees with Knoop value = 666 MPa. The nano-hardness of enamel = 4.48 MPa higher than with Knoop value = 3.36 MPa. WHY? The smaller indentation used in nano-indentation test in relation to the size of the enamel rods (tiny) Thanks to nano-indentation we obtained the dentin-enamel junction (values which is intermediate to the values for enamel and dentin) elastic modulus (53.2 GPa)

Answer 161

Traditional wear test measures the volume of material lost but don't reveal mechanism of wear Has been studied by 1. service or clinical testing 2. simulated service measurements 3. model systems using various wear machines 4. measurements of related mechanical properties such as hardness 5. exam of the amount and type of surface failure from a single or low number of sliding strokes Important clinical points!!!! - The resistant to wear of the composite resins to abrasion depends on the nature of the filler particles (glass or quartz) and on silanation of the filler. - Enamel is ≈ 5 to 20 times more resistant to abrasion than dentin. Cementum is the least resistant to abrasion. - After a 30 sec prophylaxis the fluoride can be removed from enamel substrate. - Enamel can be remove from 0.6 to 4μm depending on the abrasive.

Answer 162

the time required for the reaction of the material to be completed; sometimes the reaction is too fast so it is needed to have an operator that works fast and sometimes its slow so needs longer time to cpmplete the operation. Proper setting time is very important Measurement- the temperature rise of the mass, because the chemical reaction is exothermic

Answer 163

time after which the material can't be manipulated without creating distortion in the final product

Answer 164

Very important characteristic of materials such as GYPSUM The final setting time is defined as the time at which a material such as alginate can be withdrawn without distortion or tearing.

Answer 165

the time at which a certain arbitrary stage of firmness is reached in the setting process Measurement- measured arbitrarily by some form of penetration test, although occasionally other types of test methods have been designed Ex. Vicat apparatus is commonly used to measure it in gypsum products

Answer 166

Through DMA some properties of materials can be measured, such as dynamic elastic modulus (E') and glass transition temperature (Tg) in polymers This property allows us to predict the strength and structure of the tested material and applicability in the clinical setting

Answer 167

The study of deformation and flow of materials; Working and setting times in cements and direct filling composites have been transitionally determined through rheology, with the increase in viscosity monitored during setting

Answer 168

Another tool to determine temperature transitions in materials Ex. Glass transition temperature (Tg) and melting temperature (Tm)

Answer 169

Fourier transformed infrared (FTIR) spectrosccopy is useful for molecular characterization and for following chemical reactions Vibrational characteristic of the chemical bonds between the atoms can produce interference in electromagnetic waves at highly specific wavelengths

Answer 170

A technique used to determine material density

Answer 171

Abundant in dental literature because they are easy to perform and are not equipment intensive. Can be characterized depending in the area as: - Macro: (4-28 mm2) and Micro; (≈ 1mm2). The tests can be tensile or shear. Limitations: -Stresses at the interface are not uniformly distributed -Results of different studies are not comparable -Bond strength tests lack clinical significance -Stresses at the interface are not uniformly distributed: Debonding occurs due to stress concentration around a critical flaw or void, at the interface that causes a crack to propagate. Results of different studies are not comparable: result values can vary a lot among studies due to differences in bonding substrates, specimen preparation, storage conditions, loading method, operator.

Answer 172

Typical dentin bond strength values are 10-50 MPa. Cohesive and mixed failure 55% of specimen

Answer 173

Typical bond strength values are 10 MPa. Cohesive and mized failur 35% of specimen

Answer 174

Typical bond strength values are 30-50 MPa. Cohesive and mixed failure less than 20% of specimens

Answer 175

Typical bond strength values are 20 MPa. Cohesive and mixed failure 50% of specimens

Answer 176

``` Mercury Dilatometer Bonded Disk AcuVol Managing Accurate Resin Curing (MARC) test Cavity configuration Factor (C-Factor) ```

Answer 177

The materials used in dentistry must be able to withstand the stress and strain caused by repetitive forces of mastication. The design of dental restorations is particularly important to probide the best properties of the restorative material. Stresses in dental structures have been studied by alot of techniques such as: brittle coatings analysis, strain gauges, holography, 2 and 3D photoelasticity, finite elements analysis and other numerical methods

Answer 178

was developed to evaluate the stresses developed at the bonded interface due to resin composite polymerization while bonded to cavity walls Devices and methods: Tensilometer Tensometer crack analysis

Answer 179

50% mineralized apatite crystals 20% water 30% organic matrix (collagen fibrils) composites are hydrophobic

Answer 180

Water content varies from superficial to deep dentin Diameter and number of tubules increases near pulp 20,000 tubules/mm^2 at DEJ 45,000 tubules/mm^2 close to pulp The composition and properties of dentin vary with location Resin tags (adhesion) travel within dentin (form cross linking)

Answer 181

American National Standards Institute (ANSI)/ American Dental Association Standards Committee of Dental Products any standard developed and approved by this committee are reviewed by the Council of Scientific Affairs of the ADA. Federal Specifications and Standards regulates requirements of federal government service agencies for the purchase and use of materials. 1963 a program for international specifications was established by FDI World Dental Federation and the International Organization for Standardization (ISO). American Dental Association (ADA)

Answer 182

Ability of a material to elicit an appropriate response (continue doing what that tissue did originally) in a given application in the body- implication of function

Answer 183

Tissue compatability as a whole

Answer 184

individual cells being compatible

Answer 185

Context is key ex. mineralization occurs at one location over another Examples of inappropriate responses that don't have biocompatability : 1. cell/tissue death 2. inflammation 3. fibrosis 4. Tumor formation- dividing inappropriately (CONTEXT)

Answer 186

"In glass;" experiments using isolated populations of cells cheapest to do Direct in vitro test- relevant cells (primary/cell line) placed directly in contact with material; simplest cytotoxicity/proliferation: Do cells die? proliferate normally? Ex. dye exclusion (trypan blue) observation of morphology, cell number Functionality: Do cells differentiate, make proteins or otherwise change their behavior? Ex. MTT assay, BrdU assay Mutagenesis: Do cells change their core genetic function in response to a material? Ex. Ames (bacterial) and Styles (mammalian cell) tests [tumor formation] These divisions are fairly artificial, often an experiment setup covers multiple categories

Answer 187

"Out of the living"; experiments performed using whole tissues extracted from organisms Removal of whole tissues and exposure to material; increased physiological relevance but much more complex, making analysis more difficult Ex. cut mandible; culture- cells stay where they are suppose to- apply materials for testing Not totally relevant because removed from vasculature Ex. rats have continuous ameloblast because continually grow cells- we do not; material broken down by cells; taking a whole tissue- regeneration possibility- watch what happens

Answer 188

"In the living" experiments performed in whole, live organisms, cost most, most complex Material placed into an animal system; Not necessarily in a clinically relevant location ex. sticking enamel in random places; usually smaller animals like rats, mice, hamsters Ex. dorsal sub-cutaneous injection (implantation tests, mucous membrane irritation tests, placment of material into bone etc.) ex. material in the back of the rat Increased complexity of system (why did organism die? more things to consider) analysis more difficult physiological relevance always in question

Answer 189

in vivo experiments using a material within its clinical context ex. putting amalgam where it's suppose to go In dentistry, mini-pigs and dogs are common. Direct clinical application of material in a full living system. Prohibitive cost, last ages, huge ethical and legal to do; other types of testing used initially to "screen" materials Clinical trials- usage test in humans (no in vivo testing- HAS to be in relevant location) Ex. how type 2 diabetes and bone healing (after implant) relate in rats (in clincally relevant location) colagen, stem cells; culture new pulp- regrew pulp in dog teeth ``` Ex. dental pulp irritation test: tissue necrosis, inflammation material directly on pulp- class V defect created ``` Mucosa and gingival usage test: tissue necrosis, inflammation material placed next to soft tissue to see if affected

Answer 190

(less complex to more complex) Single cell --> tissue (multiple types of cells) --> organ (specialized tissue working together) --> organism (made of all these organs together; most complex)

Answer 191

Cells placed directly on material; choice of a relevant cell type important ex. pulp derived cells for pulp capping materials Can tell us many things about the basic compatability of material, BUT very limited in terms of complexity (single cells) Ex. resin composite- how do pulp cells react to it? Does not tell you if histocompatability is present- talking about one cell rodent incisors continually grow Ex. How many cells grow over time over different types of materials? those that have more cell growth- cytocompatible

Answer 192

cells placed on the opposite sides of a relevant barrier to a material; Ex. dentin slab, diffusion of material over agar; allows assessment of a material's impact on cells through a barrier- quite relevant in dentistry Ex. bonding to dentin vs putting directly on pulp Diffusion across detin- can't get through dentin= compatible

Answer 193

Results from in vitro, ex vivo, in vivo, and usage tests over time result in an overall idea of biocompatability Ex. Zinc oxide cement testing: toxic to cells directly, but caused minimal disruption in usage tests (when in location in question) (because zinc does not penetrate dentin) pyramid is a good abstract way to think of this: Progress of testing increases as you go up: bottom--> up: Unspecific toxicity (primary) , specific toxicity (secondary), clinical trials (usage)

Answer 194

Dental materials are typically medical devices; 1976 Medical Device Regualtion Act: basic safety assurances, some requirements for safety/efficacy testing ANSI/ADA Specification 41 (current 2005): outlines standard practices for ensuring biological safety of devices, NOT "pharmacologically active medicaments" ISO 10993/ ISO 7405;2008 give similar international standards for testing ``` Initial tests: 1) In Vitro: Cytotoxicity Hemolysis Mutagenesis Carcinogenesis 2) In Vivo: Physiological Distress Death; Horrible, Boring Death Zombification ``` Secondary testing: In Vivo: Inflammatory/Immunogenic reactions in soft/hard tissues Final testing: Usage Tests: Large Animals (primates) Clinical Trials* *with FDA approval

Answer 195

Dental pulp reactions: restorative and bleaching agents- can bleach get into pulp? what effects if it does? Oral soft tissue reactions Reaction of oral tissues to implants: ceramics, metals and alloys, and resorbable materials ex. pulp capping materials Does it cause cell death/growth?

Answer 196

Dentin: tubules key consideration: how well can stuff diffuse into pulp odontoblasts key: make dentin- make it continuously throughout life of tooth

Answer 197

Teeth as living organs: can respond to external stimuli by producing new dentin critical that material bonds tightly with dentin to prevent microleakage microleakage of bacteria, food, saliva, etc. causes pulpal irritation (causes pain/root canal) and can lead to reestablishment of caries Want odontoblasts to keep making dentin after restoration Want to recreate DEJ New dentin to form in response to restorative material- protecting pulp Want restoration to stimulate odontoblasts --> form dentin

Answer 198

Dentin bonding: attachment of restorative material to dentin Better bonding= better dentin formation, less microleakage Bonding difficult due to organic components of dentin (primarily collagen type I like bone) After cutting/site preparation, a 'smear layer' of debris remains Etchant removes this layer, allowing better attachment to material (ex. EDTA, citric acid, sodium hypochlorite and many more) because exposes tubules- better adhesion (BUT open door into pulp-affect diffusion into pulp)

Answer 199

exposes collagen present in dentin, allowing direct contact with materials, particularly resin composite- 'hybrid layer' Removal of smear layer through etching (decreases mineralization in the area) directly exposes pulp to material via dentinal tubules; removal increases the potential for microleakage; etchant (acids) themselves may have cytotoxicity when they contact the dental pulp 0.5mm of dentin generally sufficient to prevent diffusion into pulp-depends how deep prep is Release of sequestered bioactive factors in dentin through acid etching too- increases chances of making dentin

Answer 200

Consider rainbow Jello- each layer sets and forms a barrier maintaining the positon of the previous layer In the same way, multiple barriers between the pulp and a potentially cytotoxic material can reduce penetration of that material the ability of a material to penetrate dentin is often a good indicator of how biocompatible it is minimizing microleakage is also vital for protecting the pulp: the layer of Jello must form a good seal Cytotoxicty of material is directly proportional in its ability to get to pulp Like Building a restoration- ex. Lining material (barrier) build on top of that – keeping material that may be cytotoxic material away from pulp Liners may cause minor irritation but not as much as putting direct composite Bleaching agents- harmful to pulp if left on for too long Important of dental bridge!

Answer 201

Combined organic/inorganic components, thus "resin composites" (polymer +filler) Generally speaking, these are also cytotoxic (to pulp) freshly set resins are more cytotoxic, this decreases over time and a thicker dentin barrier Dentin bridge formation also decreased pulp exposure to resin restoration (build more dentin) Use of basement materials and bonding agents helps reduce pulp irritation- no contact, no irritation Resin based restoratives can shrink slightly as they cure- not ideal- can enhance microleakage

Answer 202

Resin composites are intersting as they can form a hybrid layer with exposed collagen on an etched surface; basically the polymer can chemically attach collagen, allowing a tight association with dentin; this generally is good, but this hybrid layer is susceptible to enzymatic attack. However, this means enzymes capable of degrading extra cellular matrix can degrade the attachment of the material to the tooth ***Resin + collagen intertwined- good biochemical attachment; but bad because anything that affects collagen will affect this seal- degradation of ECM- root cause of restoration failures

Answer 203

Zinc dependent proteases, present in both dentin and pulp; play a major role in matrix remodeling (normal physiological) and response to foreign bodies (introduced materials); released from dentin which is demineralized, secreted from microbial sources and cells; produced by many cell types (ex. fibroblasts, odontoblasts, osteoblasts, macrophages, neutrophils) increased expression often associated with inflammation. They are also secreted in the saliva. Bacteria create conditions which activate host MMPs and can interfere with the function of MMP inhibitors, TIMPs (Tissue Inhibitors of Matrix Metalloproteases) Inhibition currently topical in dentistry (chlorhexidine, galardin)- preventing breakdown of organic matrix near restorations (hybrid layer/dentin bridge) Thus, mechanical/physical forces are not the only considerations, but also biological reactions to materials 70% of work is replacing restorations that have failed MMP- cause degradation of ECM (collagen)- useful for tissue remodeling sequestered in dentin- inhibited , but activated by destruction of tissue, etc. Ex. Microleakage- bacterial biofilm on restoration- biofilm secretes acid -->releases MMP from endogenous tissues- bad for restoration- breaks collagen matrix that hybrid layer is linked with Shrinkage --> microleakage -->MMP --> inhibitors of TIMPS (bacteria does this) --> activate MMPs more Acid production activates MMP; destroys collagen/ hybrid layer

Answer 204

"corrosion products" released from amalgams are the primary consideration over time, particularly mercury. In vitro:mercury= cytotoxic, copper= cytotoxic (much worse) In vivo implantation: high copper amalgams cause severe tissue responses Usage tests: amalgams very well tolerated, high copper amalgams similar to older low copper restorations generally amalgams don't cause pulpal damage, but can cause pulp inflammation in deep, unlined restorations, resulting in pain Thermal/electrical conductivitiy can also cause discomfort, depending on cavity depth, and lining (want lining becuase conduction of heat) There is initial microleakage around margins, which diminishes as corrosion products build up Resin composites shrink due to polymerization reaction Amalgam- less leaky over time ; always have leaky margin- pulp irritation, but seal Last a long time, biohazard

Answer 205

Serve to attach restoration to tooth; generally are toxic, however are safe if exposure is minimized; repeated washes to remove unbound elements (remember the tubules) ``` Resin based bonding agent examples: Hydroxyehtyl methacrylate (HEMA) Bis-GMA Urethane dimethacrylate (UDMA) Triethylene glycol dimethacrylate ``` Dentin barrier generally protects pulp- thinner dentin barrier= increased cytotoxicty (liner) can get through dentin so allow them to set and then wash them off

Answer 206

Polyacrylic acid used as cement, lining material, base and restorative material; release fluoride as they set In vitro: cytotoxicity reported, reduces over time (when set, release acid, but reduced over time) usage test: doesn't cause sustained adverse reactions in pulp tissue- polyacryclic acid is relatively large and doesn't diffuse through dentin may etch the dentin, potentially releasing bioactive factors which enhance dentin bridge formation, but also MMPs

Answer 207

Liners and Non-resin cements; frequently used as a lining material (not very cytotoxic) In vitro: high pH, cytotoxic. better when combined with resin (Dycal) Usage test: direct exposure to pulp causes immediate necrosis. Necrosis is significantly reduced/eliminated when combined with resin; Resin- calcium hydroxide used as a pulp capping material; may release bioactive factors from dentin, although mechanism is unclear Resin- buffer- puddy Top layer of pulp died- fossilized- creation of layer They are buffered- don’t cause much pulp irriation Resin, calcium OH, dentin

Answer 208

Liners and Non-resin cements; zinc based cements used as lining cements in restorations; In vitro: zinc phosphate( cytotoxic, perhaps due to leaching of zinc ion, although dentin is an effective barrier); zinc polyacrylate (possibly less cytotoxic); ZOE (eugenol has cytotoxic effects, although this is buffered effectively by the dentin. Also has anesthetic properties) Usage test: zinc phosphate (causes necrosis in direct contact with pulp) zinc polyacrylate and ZOE (mild inflammation, which resolves relatively quickly) these materials don't strongly stimulate the formation of a dentin bridge

Answer 209

MTA: mineralized trioxide aggregate: modified Portland cement, the main soluble component is calcium hydroxide In vitro: not cytotoxic, increases cell proliferation/migration and synthesis of mineralized matrix specific proteins usage test: does not cause pulp necrosis, appears to encourage dentin bridge formation Not bad for pulp; drive proliferation/migration Pulp capping material (difficult in adults)

Answer 210

Almost all contain peroxide; In vitro: As you might imagine, high levels of cytotoxicity These agents can rapidly transverse enamel, dentin, and come in contact with pulp; also capable of burning gingiva and causing soft tissue damage Caused by poorly formed trays – get black triangles Don’t bleach tooth under stress

Answer 211

The restoration is in contact with oral soft tissues; buffered by the oral cavity, but not a dentin barrier; a main concern is the formation of bacterial plaques on the external surface of the material (more bacteria= more inflammation in surrounding tissues); areas where saliva doesn't frequently wash, gingival pockets, under fixed appliances, etc. Cements: generally well tolerated after they set Resin composites: can be highly cytotoxic to fibroblats in direct contact (PDL) and cause an inflammatory response Amalgam: can be cytotoxic, generally copper and zinc > silver or mercury in vitro Most materials not good for oral soft materials- isolation of an area

Answer 212

Materials designed to be biodegradable; release bioactive molecules, stimulate a particular response from surrounding cells or simply be vulnerable to remodeling; many types, including polyactic acid, polyglycolic acid, collagen, starch, cellulose, synthetic peptides, and many more. Generally, these are biocompatible, non- cytotoxic. Resorption by a combination of physiological conditions, phagocytosis by cells and digestion by cell products ex. matrix metalloproteinases

Answer 213

a. Low fluoride in water reduced caries incidence b. Introduce fluoride to community water to get exposed during teeth formation. Fluoride as a dietary supplement; high risk patients; Trying to expose them to prevent caries incidence. c. Systemic and topical fluorides for 50 years have decreased prevalence of caries on smooth surfaces d. Pits and fissures of posterior teeth are more resistant to fluoride uptake because of irregular occlusal surface. Retention of food and can’t brush well here either so starting carious lesion. e. Sealant-fill irregularities to reduce risk of carious lesion. Make smoother surface to clean easily

Answer 214

a. Common sealant= Bis-Gma resin and are light cured, but some available as self cured b. Sealants are more fluid so they can penetrate pits and fissures easily and etched areas on the enamel which promote retention of sealant c. Fumed silica added to provide stiffness and improve wear resistance

Answer 215

a. Apply sealant to pit and then cure with light for 20 sec b. Sealants applied to thin sections so time is enough c. Advantage of light cured sealant-working time controlled by operator (most are light cured; ex. diketone and aliphatic amine)

Answer 216

a. During polymerization there’s a surface layer of air inhibition that varies in depth w/ different commercial products b. Make sure to apply enough material to coat all pits/fissures w/ a thick layer to ensure complete polymerization c. Uncured, air inhibited layer can easily be removed after curing (with a prophy cup in a rotary hand piece) using an abrasive pumice with a handpiece. It’s more effective than wiping

Answer 217

Sealants are circumscribed by enamel and are not subjected to occlusal stress so their mechanical properties are less important that those of resin composite restoratives. a. Add ceramic or glass filler particles (up to 40% by weight) and all properties except tensile strength show improvement (improved elastic modulus, wear resistance, more visible on clinical inspection) b. Modulus of elasticity shows the most improvement and the increased rigidity makes the filled material less subject to deflection under occlusal stress c. Filler added to improve wear resistance and make material more visible on clinical inspection d. Optimal adhesion of sealant to enamel-occurs when sealant has high surface tension, good wetting, and low viscosity i. These properties allow sealant to flow easily along the enamel surface e. A drop that spreads readily produces a low contact angle f. This highly wetted surface is conducive(more likely) to a strong adhesive bond g. Polymer tags-formed when the resin flows into the surface irregularities made by acid etching and are responsible for the mechanical bond that retains the sealant to enamel h. Durability of the sealant bond related to stresses induced by: . Shrinkage of the resin during curing, Thermal cycling, Deflection from occlusal forces, Water sorption, Abrasion j. Sealants have variety of features so must select carefully k. Most current materials are light cured instead of self cured because easier controlled rate l. Tooth colored or clear resins available for natural look m. Also available in opaque or tinted material to make recall exam easier n. New color reversible, photosensitive sealants developed i. They are similar to light cured sealants in resin composition and filler loading ii. Photosensitive pigments are added that change to green and pink when exposed to dental curing light iii. Color change lasts 5-10 min to help determine whether the sealant covers the pit/fissures o. Increasing number of sealants are marketed claiming that they release fluoride. Release is highest in first 24hrs after placement and then tapers (may not be sufficient to provide extended clinical protection against caries

Answer 218

Study with light cured sealant showed retention rate of 42% and effectiveness of 35% in caries reduction over 5yrs Similar study with filled resin sealant showed retention of 53% and effectiveness of 54% over 4yrs Results of quicker setting unfilled resin-> retention rate 80% and effectiveness of 69% after 3 yrs. The longest published study on sealant effectiveness is a 15 year evaluation of a self cured unfilled material which showed 27.6% complete retention and 35.4% partial retention. Study comparing fluoride releasing sealant (91% retention) vs non-fluoride sealant(95%)...and yet the caries incidence was the same for both groups (10%) Almost all studies show a direct correlation btw sealant retention and caries protection Therefore important to use materials that are retentive to enamel, resistant against occlusal wear, and easily applied with little surface contamination opportunities Current evidence indicates sealants are most effective on occlusal surfaces where pits/fissures are defined

Answer 219

Handling characteristics of a sealant depend on composition of material and surface it’s applied to (read manufacture instructions). Optimal preparation of the 2 aspects leads to->close adaption of the sealant to the tooth enamel, a strong seal against the ingress of oral fluids and debris, and long term material retention

Answer 220

Penetration of sealant to bottom of pit is important Wettability of the enamel by the sealant is improved by etching(some suggest pretreatment with silanes) Must fill pit/fissure without voids- air/debris trapped in there prevents it from being completely filled Must control viscosity of sealant to get optimal results. Viscosity determines the penetration of resin into the etched areas of enamel to provide retention of sealant Etching the pit/fissure for specified time(15 to 30sec) w/ 35-40% phosphoric acid is recommended. Acid etchant should be flushed with water and dried. If you don’t rinse well then phosphate salts remain on surface and will interfere w/ bond formation Enamel surface should not be rubbed during etching and drying because the developed roughness can be destroyed Important to isolate the site throughout the procedure to get optimal tag formation and clinical success If saliva contaminates during treatment, the surface needs to be rinsed and the etch needs to be reapplied Acid etching enamel-should appear white and dull w/ rough(chalky) texture. If appearance isn’t uniform then you need to etch for 30 more seconds Etched area should extend beyond anticipated area for sealant application-reduce leakage and bonding of margins (completely cover all exposed pits and provide a smooth transition along the inclines of the enamel cusp) Place light cured bonding agent on etched enamel before placing sealant-> improves retention Single step etching provide weaker bond to uncut enamel than to cut enamel

Answer 221

Depending on viscosity and setting time, sealant may best be applied with a thin brush, ball applicator, or syringe Avoid buildup of excess material- could interfere with occlusion Place sufficient amount of material to cover all exposed pits Overworking light cured sealants on tooth surface during application can introduce air voids that appear later as surface defects Air inhibited surface layer should be wiped immediately after curing, and inspect the coat for voids or areas of incomplete coverage Defects can be covered at this time by repeating the entire reapplication procedure (including acid etch and applying fresh sealant only to areas with insufficient coverage) After sealant is applied and cured, occlusion should be checked and adjusted to get rid of premature contacts Possible problems: air or debris, control of viscosity (penetration of the sealant) and sealants can penetrate a depth of 25-50µm

Answer 222

Have been tested for ability to function as a fissure sealant because ability to release fluoride/ provide caries protection on tooth surfaces at risk Viscous property and difficult to gain penetration to the depth of a fissure Lack of penetration makes it difficult to obtain mechanical retention to the enamel surface to the same degree as with BIs- GMA resins More brittle and less resistant to occlusal wear Studies show lower retention rates than resin sealants but greater fluoride deposition in enamel surface (greater potential for later caries protection after sealant loss) Areas with high risk kids- conservative caries management technique used to seal caries in a fluoride rich environment establishing some remineralization Ex. Atraumatic restorative treatments- opening a lesion, removing soft surface decay and filling or sealing surface with highly filled glass ionomer with fast set time

Answer 223

For preventive resin restorations, cavity liners, restoration repairs and cervical restorations Packed in syringes/ compules for direct application to pit/fissures Trapping of air in sealant must be avoided They have a higher filler content compared to most resin sealants then they have better wear resistance- provide good retention/ caries resistance after 24 months

Answer 224

Slowly release fluoride so used in cervical restorations (esthetics not critical) Recommended for patients with high caries risk

Answer 225

Glass ionomers supplied as powders (not shades?) (Ion leachable aluminosilicate glass) of various shades and a liquid (water solution of polymers and copolymers of acrylic acid) Material sets because of metallic salt bridges between Al and Ca ions (when powder and liquid are mixed, the glass surface gets attacked by acid. Then Na, F, Al and Ca ions leached into aqueous medium) Reaction is slow Chelation effect with Ca on exposed surface- adhesive bond Surfaces of new restorations should be protected from saliva with protective coating

Answer 226

Elastic modulus that is similar to dentin Bond strength to dentin of 2-3 MPa Expansion coefficient comparable to tooth structure Low solubility Fairly high opacity Fluoride is released slowly from glass providing anticariogenic effect Retention of glass ionomers in areas of cervical erosion are better than for composites even though bond strength to dentin is lower (75% retention rate after 5 years) Pulp reaction to glass ionomer is mild GI surface might look rough but fewer Streptococcus mutans exist in plaque next to a glass ionomer restoration Packed in bottles and vacuum capsules- mechanical mixing Liquid in unit dose capsule is forced into powder by a press and mixed Mix then injected into cavity prep (must be done quickly or else physical properties will be low and adhesion lost Maintain isolation, use proper etch procedure, protect restoration from saliva, delay final finishing for a day or longer Population that benefits for GI: the elderly, patients with xerostomia, kids with high caries risk

Answer 227

Used in lower stress bearing restorations | Recommended for patients with high caries risk

Answer 228

Powder is similar to glass ionomer/ liquid has monomers, polyacids, water Placing a bonding agent before decreases fluoride uptake by dentin/enamel RMG set by combined acid-based ionomer reaction and light cured resin polymerization of 2 hydroxyethyl methacrylate

Answer 229

Bond to tooth structure without use of bonding agent Flexural strength is almost double of standard glass ionomer Release more fluoride than compomers/ composites but same as glass ionomers Glass and Hybrid ionomers recharge after exposed to fluoride treatments or dentifrices Plaque next to resin modified glass ionomer had higher fluoride than that next to compomer restoration

Answer 230

Mixing of unit dose capsules makes uniform mix with fewer larger air voids Need optimum powder/liquid ratio for long term maintenance Set immediately when light cured, finished 5-10 min after initial set Finishing with wet environment then recoating with protective varnish/bonding agent helps maintain color/surface texture

Answer 231

Used to line the dentin walls of a deep cavity Provide thermal insulation Sandwich technique- use this to seal dentin releases fluoride; then cover with resin composite Use to relieve stresses that occur with shrinkage of composite during curing Lining cements release fluoride ions and are radiopaque

Answer 232

Used for lining specific areas of deep cavities or for direct pulp capping (have antibacterial action) Initially a paste that then hardens (has a base paste [calcium tungstate, tribasic calcium phosphate, zinc oxide in glycol salicylate] and catalyst paste [CaOH, Zinc oxide, zince stearate in ethylene toulene sulfonamide] that are mixed) CaOH and salicylate are responsible for setting reaction Important properties of these cements: mechanical/thermal properties, solubility, antibacterial activity and pH Can create secondary dentin bridges when applied to direct pulp exposure Have low values of tensile/compressive strength or elastic modulus Restrict usage to specific areas not critical to support restoration Setting time varies between 2.5-5.5 min, but compressive strength increases over 24 hour period Solubility necessary to achieve therapeutic properties Acid etching procedures and varnish must be done with care Free CaOH in excess stimulate secondary dentin close to pulp/ show antibacterial activity Mostly used in direct pulp capping, specifically deep spots of a cavity prep Light cured resin modified glass ionomers are better for general lining of cavities (fluoride release, decreased solubility, and superior mechanical properties)

Answer 233

Deliver fluoride topically to surface of teeth in those at risk for caries Used routinely after prophylaxis 5% NaF (2.26% F or 22,600ppm) 1% difluorsilane (0.1% F or 1000ppm) Fluoride is dissolved in organic solvent that evaporates when applied when exposed to moisture leaving thin film of material covering all exposed tooth surfaces CaF deposited on tooth→ converted to fluorapatite (remineralization) Advantage is extended time of exposure on tooth surface (hours before wears) research study: release of F up to 6 months after restoration with RGM+Fluoride varnish Efficient at treating young kids at risk for caries (reduction up to 70%) Potential Use for prevention of root caries in older populations

Answer 234

Natural repair process for carious lesions Elevated levels of fluoride in toothpaste effective in rehardening root caries lesions Concept of caries balance Pathological factors: 1. Acid producing bacteria 2. Frequent consumption of fermented carbohydrates 3.Below normal salivary flow and function Protective factors: 1. Normal salivary flow and components 2. Fluoride 3. Antibacterials - Salivary components required for remineralization are CALCIUM AND PHOSPHATE. FLUORIDE enhances remineralization

Answer 235

Calcium phosphate added to toothpaste, varnishes, and gum Ex. Calcium phosphate remineralization technology based on Casein phosphopeptide- amorphous calcium phosphate (CPP-APC) effective in remineralizing enamel subsurface lesions by stabilizing high levels of Ca and phosphate ions Sugar free gun in a RTC after 24 months showed a reduction in caries progression of 18% Bioactive glass (calcium sodium phosphosilicate) originally developed as a bone- regenerative material, has been show to deposit onto dentin surfaces and mechanically occlude dentinal tubules when delivered in a dentifrice but when combined with fluoride, increases remineralization of caries lesions still in the mouth

Answer 236

Composite resin are thicker so withstand restoration Sealant still has to be able to withstand occlusal forces-has to be viscous. Withstand thermal changes. Set time. Isolate tooth Clean tooth without using fluoride Etching with phosphoric acid 35-40% for 20 seconds wash /rinse/dry Should look frosty/white looking to see if it’s ready. 1mm out of edges to make sure boundaries are covered Apply sealant with ball and tip or syringe Cured for 20 seconds Check for occlusion- using articulating paper 15 year study showed 27%retention Glass ionomer-releases fluoride.more brittle.higher viscosity than sealant/resins. Sandwich technique- put glass ionomer then cover with composite Use for kids and older pple(taking drugs that affect salivary flow)

Exam 1 Flashcards

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