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57 Cards in this Set
- Front
- Back
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Surface tension |
measured in Force (Dynes) per Centimeter of the surface of liquid. Note: 1 Newton = 100,000 dyne.
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What are the surface tensions of water, alcohol, and mercury at 20 degrees C?
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1) Water: 72.8 dynes/cm, 2) Alcohol: 22 dynes/cm, 3) Mercury: 465 dynes/cm
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What factors decrease surface tension?
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Increasing temperature and presence of impurities
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Surface tension with detergent vs oil
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Great surface tension with drop of water onto oil-covered surface so it DOES NOT spread out and wet surface well; Reduced surface tension with detergent-covered surface, so it spreads out and wets surfaces (hydrophobic chain and hydrophilic head of soap mix with water to decrease surface tension)
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Hydrophilic
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Polar/friendly with water; 1) Describes ability of molecules to transiently bond with water through Hydrogen bonding; 2) Describe ability of liquid to undergo hydrogen bonds with other POLAR solvents ; Ex. Non-oxidized metals
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Hydrophobic
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Non-polar/Fears water; 1) Describes repulsion of molecules from a mass of water (i.e. water prefers to hydrogen bond with itself instead); 2) Indicates a material that DOES NOT FORM HYDROGEN bonds; Ex. paraffins (alkanes), oil, wax, teflon (polyethylene tetra-fluoride)
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Surfactants/ Surface Active Agents
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“Wetting agents” that lower surface tension of a liquid; Amphiphilic molecules (contain BOTH hydrophilic and hydrophobic groups: Long hydrocarbon chain AND ionic head group); Ex: Sodium dodecyl sulfate (SDS) – household detergent, soap, shampoo reduces surface tension of distilled water from 72.8 dynes/cm to 48.3.
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High surface energy
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High surface energy of the substrate increases wetting and results in higher levels of adhesion; Hydrophilic; Ex: Clean metal (no oxides) and Exposed collagen after acid etching in dentistry
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Low surface energy
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Decreases wetting, hydrophobic; Ex: Waxes; Teflon (polyethylene tetra-fluoride)
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Wetting power
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wetting power of a liquid is represented by its tendency to spread on the surface of the solid; Wettability is important in dentistry
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How can wax be used if it gives low wettability?
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a dilute solution of some wetting agent (such as 0.01% aerosol) is first painted on the wax to aid in the spreading
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Relationship between wettability and contact angle?
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The greater the tendency to wet the surface, the lower the contact angle, until complete wetting occurs at an angle equal to zero.; Ex: Teflon is hydrophobic material that doesn’t wet well so it has large contact angle. Clean glass (uncoated with oil) has a much smaller contact angle and is quite hydrophilic.
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Wettability of filler materials
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Filler materials are readily wetted by water and saliva.
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Adhesion
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the force of attachment that develops when two or more substances are brought into intimate contact with one another (i.e. on the molecular level). Interpreted by the force necessary to separate the substances. ; *Note: If it takes a lot of force to separate the 2 surfaces, then it has good adhesion.
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Bond strength
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Amount of force needed to separate 2 substances
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How do you determine the “weak link” on a restoration?
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Depending on location of the cracks, you can identify where the weak link is (adhesive resin, bonding interface, or crack went through dentin since adhesion is too strong that it pulls dentin out?) Cracks always go to the weakest spot (weakest link)
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Chemical adhesion
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bonding at the atomic or molecular level (ionic, covalent or secondary bonding)
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Mechanical adhesion
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interlocking of one phase (adhesive) into another (adherend/substrate). Micromechanical interlocking, or micromechanical retention, plays a key role in enamel and dentin bonding.
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Ideal adhesion
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combination of both chemical and mechanical aspects
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What type of adhesion is most common in dentistry?
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In dentistry, usually just mechanical adhesion. When you acid etch a dentin and open the dental tubules, you then add bonding agent which flow into the tubules, followed by composite and curing. The tubules filled with bonding agent that are cured into resin are called resin tags. Many resin tags micromechanically interlock composite in place. Resin tags are micromechanical retention, NOT chemical bonding!
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2 Examples of bonding to tooth structure
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ORTHO: You don’t want bond of orthodontic cement to tooth to be too strong because meant to be temporary; RESTORATIVE: Want bond to be as strong as possible; your adhesive resin needs to be strong enough to WITHSTAND polymerization SHRINKAGE stress; in additional to CHEWING forces by patients, TEMPERATURE change of food, etc. If the bond cannot withstand these forces, it will develop a MICROCRACK, which will grow and can trap bacteria secreting acid to demineralize tooth structures, going into a continuous cycle. Eventually, leading to SECONDARY CARIES (Primary reason why these restorations fail). – Bonding interface would be the weak link
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What determines quality of bonds?
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Surface properties
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Layers of Dentin bonding (3)
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1) Composite Layer on top, 2) Adhesive Layer with adhesive resin, 3) Hybrid layer on bottom (Adhesive plus collagen)
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Resin tags
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formed when adhesive resin flow into tubules; Aids in micromechanical retention; Etching the tooth surface allows bonding agent to flow into this roughness, increasing surface area and contact areas to give you good bonding.
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Capillary Action
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Nature of penetration of liquids into crevices (or the ability of a substance to draw another one into it); How the adhesive flow into dentinal tubules depends on capillary action. * Low contact angle results in penetration!
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Penetration Coefficient (PC)
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Rate of penetration of liquid into a crevice between 2 solid surfaces; A function of surface tension of liquid, free surface energy of solids, and viscosity of liquid.; Proportional to Surface energy and inversely proportional to viscosity
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What makes pit and fissure sealants successful?
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wetting of sealants and the flow of these sealants into areas (want good wettable surface and low viscosity)
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How to measure shear bond strength on dentin
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A metal ring is placed on surface with a hole in the middle, stimulating Class I cavity after etch, prime, and adhesive, light cure steps were done. Then add composite onto hole as a Class I restoration and light cure. After mounting to pinning device, you use chisel to push the metal ring off. The bonding here is only from Class I composite to the dentin. You measure the force needed to push ring off, you know contact area, and you can get the shear bond strength.; *Compared this to commercial bonding agents containing antibacterial substances to try to get antibacterials but not compromise bonding strength; Results similar for both
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Advantage of adding nanoparticles to a bonding agent
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Nanoparticles of amorphous calcium phosphate can neutralize acid (to avoid damage) and can release ions to remineralize existing lesions; Also use of nanoparticles so bonding agent can get into small tubules
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Microtensile dentin bonding strength
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Cut one tooth into many rods and torn each rod into fracture. For the same bonding agent, result from microtensile test is higher than shear bond strength; i.e. microtensile of 60MPa equivalent to shear bond testing of 30MPa.
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Color
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Perception of a physical stimulus (light) resulting in a physiological response, which is subjective
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3 Things that influence perception of color
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1) Objective component (Wavelength of light, color of the incident light), 2) Subjective component (physiological sensation), 3) Color of background if object is translucent (i.e. for dentin and enamel)
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Range of visible light
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(400-700nm); Violet has shortest wavelength of 400nm. Red is longest, 700nm. Blue, green, yellow and orange are in between.
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3 Parameters of color
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1) Hue, 2) Chroma, 3) Value
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Hue
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the basic color we see. Aka dominant wavelength of the light spectrum corresponding to the perceived color
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Primary colors
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Red, Green, and blue/violet; All other colors are a combination of these; Ex: yellow = green + red
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Chroma
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intensity/purity of the color or degree of saturation (also regarded as purity). Number represents excitation purity from 0 to 1; Higher # of chroma, Higher apparent concentration of hue
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Value
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relative lightness/ luminous reflectance; Lower value implies darker (black = 0, reflect no light), while Higher value implies lighter (white =100, reflect all light)
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Color arrangement diagram
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Hue is the circle, Chroma is the radius (Ex: How red is it? – grey closer to center of circle, then increasingly red); Value is vertical Z axis and color gets lighter as you go up |
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-b* vs +b*
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-b* IS more blue side of circle and +b* is more yellow side
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-a* vs +a*
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-a* is more green side of circle and +a* is more red
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Color of Teeth/Composite materials
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typically on the lighter side (whitish, ~50 Value), negative a* (toward green side), negative b* but some could be somewhat positive onto yellow side, but close to 0
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CIE Color Standard 1931
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Commission Internationale d’Eclairage (International Commission on Illumination) defined a standard system for color representation |
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XYZ Tristimulus coordinate system |
Defines the relative amount of the 3 basic colors (Red, Green, Blue) that combine to represent the target color; Amount of desired color = Desire color/ total amount of mixture that make up the whole light [Any PURE Basic Color = 1 = 100%] |
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Munscell scales
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similar to CIE L*a*b*, but Values is from 0 to 10 instead of to 100. Chroma is 0 (most gray) from center to 18 (most saturated) farthest from center. Hue is measured from 2.5 to 10 in increments of 2.5. |
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Effects of surface thickness
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With Increase in thickness, there is Higher absorbance and Increased opacity; Note: The perceived color of enamel is dependent on its thickness and the color of the underlying dentin. In addition, restoration thickness will also influence its apparent color.
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Effect of rough surface
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result in diffuse reflection and interference bet. incident light and reflected light. [Rough surfaces will appear lighter and have less distinct color. It scatter more light so less light get into material.] ; *Things are less opaque when it absorbs less light
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Opacity
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the property of a material that prevents the passage of light. Highly opaque implies minimal transmission, by reflection or absorption; e.g. – complete reflection of white light (full spectrum) results in a white object. Complete absorption of all wavelengths results in black object.
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Translucency
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is a property of substances that permits the passage of light but disperses the light, so objects cannot be seen through the material. In between opaque and transparent. e.g. enamel, ceramics, resin composites, and acrylics. Enamel is more translucent than dentin.
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Transparency
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allow the passage of light so little distortion takes place and objects may be clearly seen through them. i.e. glass
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Fluorescence
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Emission of luminous energy by a material when a beam of light is shone on it; Wavelength of emitted light is usually longer than the incident spectrum
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Emission of sound tooth structure
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Sound tooth tissue irradiated at 365 nm (UV light) emits polychromatic light with highest intensity in the blue region (450 nm)
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Index of Refraction (n)
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defines the reduction in velocity of light within the medium with respect to that in vacuum. n ≥ 1. Speed of light in air or vacuum is different than in dentin. LIGHT WILL SLOW DOWN IN DENTIN. ~1.5 to 1.6 for typical dentin material and enamel for refractive index.
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What occurs when there is Refractive index mismatch between resin and filler particles
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results in opacity due to dispersion of light.
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Ti-core
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, a core build-up material. It is a titanium and lanthanide reinforced composite resin material that matches the strength of dentin. Ex: Ti-Core Gray Self-cure and Ti-Core flowable dual cured composite resin.
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Opacity of Ti-Core
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Titanium is opaque when put as filler particle.
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Refractive index of ceramic particles
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Ceramic particles, such as alumina, zirconia, and silicon nitride, have refractive index mismatches between resin matrix and the fillers. The resulting composite is opaque and not esthetic; *Sometimes we use these materials for crown prep since it won’t be seen and we can distinguish between the build up and dentin. |
