Physical Properties

Translucency

opaque

diffused transmission of light: light is transmitted but not dispersed

opaque: no passage of light thru material

Long wave length, low frequency, low energy

short wave length, high frequency, high energy

which is more damaging?

radio, gamma ray, gamma ray

visible spectrum

400-740 n

lower end purple, upper end red

beam of light changes direction upon entering a second medium

refration

no absorption of light: clear like glass

transparaent

diffused transmission of light (light is transmitted but not dispersed)

translucent

no passage of light thru material

opaque

Which is more opaque? dentin or enamel?

dentin

Translucency of enamel

different indices of refraction between prisms and surrounding organic material in enamel → scattering by reflection and refraction → translucency and sensation of depth as scattered light reaches eye

rods sense __

cones sense _-

light intensity: 130 million

color: 7 million

__ types of sensitive cones in retina of human eye?

3: RBG

seeing color

all colors present in white light (source) → surface of object (apple) absorbs all colored light rays except for those corresponding to red. This colored ray is reflected to human eye → sends message to brain (observer/detector)

3 indices of color

hue, value, chroma

hue

dominant color of object (red, yellow, or blue)

natural teeth are in yellow to yellow-red range

Value

teeth?

lightness or darkness of color: 0 black, 10 white

natural teeth 6 to 8

Chroma: teeth?

intensity of color (rich or pale)

0 achromatic (weak), 18 (variable) saturated

Natural teeth toward weak end

Different light sources have different?

color contents

ordinary incandescent/fluorescent/halogen are not pure white light (greater in yellow/blue/red respectively)

CRI

color rendition index: measure of how well a light source renders color compared to standard (daylight)

light source > 90 CRI for color matching

Source related factors affecting color appearance

color content, intensity, surroudnings

Intensity: source related factor, ideal?

low levels of light, rods dominate cones, color perception is lost

high levels: colors wash out

Ideal lumonsity: 1500-2500 lux

Source related: surroundings

modify type of light reaching object

like walls, clothing, lip color: contribute to light incident on teeth

object related factors affecting color apperance

gloss: relative amount of light reflected, high gloss lightens color apperance

surface roughness: smooth vs bumpy surface

observer related factors affecting color apperance

Individual response: normal vision people see different colors, differences between left and right eye

Color vision: 5-8% of men, 0.5% of women color deficient

Optical illusion: adjacent colors influence interpretation of color (darker against light background)

Receptor fatigue?

Application?

causes complementary color to be seen

avoid intense colored backgrounds when color matching: drape patient in light blue or light gray, No lipstick

Munsell color-measuring system

Visual:

• Hue (circumferential)

• Value: vertically

• Chroma: radially:

all coordinates on 3D scale: color in question compared to tabs

Spectrophometry

measurement of relative amounts of reflected or transmitted light at each wavelength of spectrum

CIE

international orgo concerned with light and color

CIE L*a*b* coordinates

• L* in color space represents luminance (value) on numerical scale 0-100 (0 is black)

• Color coordinates A* and B* represent position between red (+a*) and green (-a*) and between yellow (+b*) and blue (-b*)

colorimeters give color measurement values in the coordinates

Metamerism

two color samples appear to match under one light condition but not another

color matchign should be done under two or more diff light sources

Fluorescence

object emits light when illuminated by specific source

near-UV radiation (sunlight, UV, etc) absorbed by teeth and emit visible light

some anterior restorative materials and dental porcelains contain fluoro agents (cerium oxide) to reproduce apperance

UV FOR TEETH

Thermal conductivy

measure of how well heat transferred thru material by conductivity flow

Conductors have higher values (metals)

nonmetals have lower values

thermal diffusivity

rate at which body with nonuniform temp approaches equilibriumd

dental importance of conducvity adn dissuvity

large metal filling/crown in close prox to pulp may cause patient discomfort when hot or cold food produces temp changes

correct by applying thin layer of cement (insulator) between tooth adn metal

coefficient of thermal expansion

denta l importance?

change in length per unit length of a material for 1C change in temp

Contraction and expansion from cold/hot may break margin seal of inaly or fillings

lowest coefficient of thermal expansion for dental materials, highest?

porcelain, composite < sealant < inlay wax

electrical conducivity and resitivity

Dentin? carious teeth?

measurement of materials ability to conduct current

conducvity is reciprocal of resistivity

dentin better conductor than enamel, carious teeth offer less resistance than normal teeth, metals are better conductors:

Corrosion

deterioration of metal by chemical or electrochemical rxn

oral environment is conduicive to corrosive attack

• wet

• salty

• presence of acid and bio agents

• warm

• stresses

3 essnetial components of corrosion

1. anode: surface where corrosion occurs, Oxidation: loss of electrons (metal ions go into solution)

2. Cathode: surface where reduction rxn takes place (consumes electrons)

3. Electrolyte: solution that conducts electricity: supplies ions needed at cathode and carries away corrosion products at anode

electromotive series: which is most ideal, practical? least?

ranking of relative corrosion resistance of metals, ideal in water, and practical (in chloride containg solution): based on thermodynamics

• noble/cathodic: most resistant

  • ideal: gold

  • practical: platinum

• least: active/anodic

  • ideal: titanium

  • practical: iron

gold would be cathode, amalgam would be anode, gold is protected

passivity

certain metals form surface oxide layer that is continuous, relatively impermeable to water: protects from corrosion

• Magnesium, Aluminm, titanium, validium, chromium, zirconium, niobium, Molybdenum, hafnium, tantalum, tungsten

types of corrosion (4)

• uniform: general overall, most common

• Crevice: structural details which result in areas with diff electrolyte composition (oxygen depletion)

  • areas under trapped food

• Stress: stress increases chemical activity of metals

• Galvanic: two dissimilar metals are in physical (electronic) contact and immersed in an ionic conduction fluid medium (saliva)

  • less noble metal is anode and will corode, other is cathodic and protected

galvanic currents

no complete electrical isolation between tooth and metal restoartion

rare postoperative pain due to current flowing thru tooth and pulp still possible

corrosion dental importance

• Release of ions may trigger allergies/rxns

  • mercury from amalgam

  • Nickel and palladiun two common allergens in dental alloys

• esthetics are compromised

• Corrosion products (metal salts and oxides) usually strongly colored

Tarnish and discoloration

Surface discoloration on metal, or slight loss or alteration of surface finish or luster

not necessarily corrosion

metals: oxide, sulfide, surface rxns

Cements and composite: colored substances penetrate material and/or substances continue chemical rxn