# Photocuring ihatethisclass 1

olola's version from 2016-12-12 00:32

## Section

at 0.5mm depth, what percentage of top surface irradiance remains? (aka relative loss of light)39-43%
at 2m depth, what percentage of top surface irradiance remains? (aka relative loss of light)1-8%
for soft-start curing, you should increase exposure duration by how much?1.5% increase to make up for the initial reduced light intensity
Compare percentage light loss values at similar depths between light (A2) and dark (A4) composite shadesTHERE IS NO DIFFERENCE IN PERCENTAGE LIGHT LOSS. There is NO difference b/t shades Universal to Gray; but you have to increase exposure duration for "remarkably darker" shades
what 2 clinical techniques can be used to overcome the great loss of irradiance seen at the depths of composites?1- increase power output 2-increase exposure duration
state how light loss though the composite compares to that through wet dentinvery SIMILAR loss of light at similar thicknesses of composite and tooth structure
what is Radiant excitance/emittance?radiant power/flux EMITTED from a surface (mW/cm^2) (to be used instead of Power Density or Irradiance when describing the output from a curing light)
In general, for composites, "Depth of Cure" values should ____ to pass the ISO testexceed 1.5 mm (scraped depth of cure values divided by 2)
T/F Because a light is emitting a high amount of energy means that it has a high potential for curingFalse Just because a light is emitting a high amount of energy does not necessarily mean that it has a high potential for curing. Must consider the relationship b/t the spectral emission from the light and the spectral absorbance needs of the photoinitiator
xenon arc units (PAC)broad banded (350-550nm)
QTH light"Quartz-Tungsten-Halo", broad banded (350-550nm), passes only blue light and absorbs infrared radiation
maximum absorption for CQ is at465-470 nm
Multipeak LED lights"considered" broad band due to multiple spectral outputs (390-410, 420-480nm), what we use in clinic "VALO"
T/F? The absorption of CQ is linearFalse NOT LINEAR. absorption of CQ greatly changes with wavelength, peaking around 470nm
if a light unit does not match the absorption of CQ well, you can make up for it how?1- increased intensity output (might heat up pulp though), 2-longer exposure duration
Blue LED lightnarrow spectrum, will only cure CQ initiation (420-480nm)
Does doubling the exposure time from 5 to 10 seconds result in twice the thickness of cured composite segments?No
irradiance delivered in an area during a specified time: irradiance multiplied by exposure duration- in units of mJ/cm^2) (light energy/surface area)Radiant Exposure
which wavelengths pentrate composite greater?LONGER wavelengths (470nm, Blue) penetrate composite greater than shorter ones (400nm, violet)
how are measured depths in lab not indicative of what one would obtain in a tooth clinically?HIGHER depth of cures would be found CLINICALLY b/c of the reflective and translucent nature of tooth
T/F? Light loss obeys the Inverse Square LawFalse light curing tip does NOT act like a point source radiating 360 degrees in space
Is light coming from the curing tip divergent or collimated?Divergent due to this, the concentration of light over a specified area (Irradiance) will decrease with increasing tip distance, depending on how wide an angle the light is bent coming out the end. Thus, the curing tip of the VALO light does NOT have to be held directly against the composite surface, b/c light does NOT fall off as fast as expected from the inverse square law
describe the VALO curing lights used in clinicMultipeak LED, Non-light guided, Lensed (less divergent, more collimated)
How far out did the tip have to be before 50% of the tip end light level was lost for the VALO light in each curing mode (conventional and high-power), and which type tip looses light at a greater rate?Conventional power AND High power tips lost 50% of light at 7-8mm Change in output intensity mode of the unit does NOT affect the rate at which light is lost - At each time distance, the irradiance using the high output level is proportionally greater than when using the conventional mode
what types of light can cause premature composite curing?Operatory light, Black light (UV light), Fluorescent lighting that is NOT found in offices (distances are too great to cure). CQ has a large UV absorbance but UV light is not used to cure anymore due to potential eye damage and possibility of changing the microbio flora of a patient's mouth
what is "Dark cure"?continued slow rx when light is turned off, polymerization is NOT complete when light stops, occurs within 20 min from curing but will slowly plateau up to 24 hours and increase no more. NO NEW RADICALS are formed during this phase
when does most of composite shrinkage occur during a light exposure?VERY EARLY into the exposure
what happens to cured composite when re-irradiated?A very small expansion (due to heating from the light), then rapid shrinkage when light went back off (due to cooling back to room temp). The same effect is present in the mouth when pts eat or drink hot and cold food
what's the point of using a soft-start method?to slow the photocuring rx rate so that stresses can be relieved as a result of composite flow from an unbonded surface - results in stress reduction at tooth/resin interface and enhanced marginal integrity
units of light intensity associated with the ability of humans to perceive lightLux (equivalent to 1 lumen/m^2), "foot-candles", measures Illuminance
human eye is much more sensitive to what colors?Yellow-Green, ~550nm
T/F? Lumens as a unit of measurement are used to gauge the abilty of a dental curing unit to provide power to a photochemical reactionFalse Lumens are INAPPROPRIATE b/c the values are adjusted for the disproportional response of the eye to wavelength
Units of irradiance for dental curing lights is what?mW/cm^2
State the proper uses of hand-held radiometers in a clinical dental environmentShould NOT be used to obtain absolute readings; only to be compared, to indicate intensity level changes with use. A drop in intensity level could either arise from problems in the curing source (the bulb, LED chip), from debris or damage to the light guide, or from damage to a filtering system.
Light intensity adjusted for the non-linear response of the human eye to different wavelengthsIlluminance (Lux, foot-candles)
Light measurement for purposes of absolute power measurement - NOT related to eye responsivenessRadiant Flux (Watts)
Power distributed over an area (same as excitance or incident irradiance)Radiant Emittance (mW/cm^2)
Define the phrase “irradiance” and state the units of measurement and indicate if that value is uniformly distributed over the tip end.Light output applied over a defined area (mW/cm^2). However, irradiance is NOT uniformly distributed across the tip end in dental curing lights, and thus is not uniformly distributed over the target upon which the light falls.
Camphorquinone absorption peak occurs at ____, but effective absorption ranges from ___?470nm; 425-490nm
to gauge effective cure potential for all kinds of composites, the curing radiometer should really provide an indication of the energy emitted between ____?380-490nm
What are the components in a Chemically activated polymerization?Oxidizer- Benzoyl Peroxide, Reducer- Amine; activated by mixing
components required for creating a free radical in Visible light-cured resinsOxidizer- Photoinitiator (CQ as an a-diketone), Reducer- Photoaccelerator (DMAEMA); activated by light
what is the key controlling influence in initiation of the polymerization process?Control of free radical formation
number of cycles per secondFrequency (Hz) inverse relationship b/t frequency and wavelength
compare the energy of UV light to visible lightUV light has HIGHER ENERGY b/c higher frequency/shorter wavelength
electronic transitions: not ionizing ground state to excited statevisible light
electronic transitions: ionizing ability to release electron from orbitUV light (the energy contained by photons in the UV band is sufficient to totally remove an outer electron completely from an atom, thus creating an ion. Creation of an ion has serious biological implications, as it may lead to mutations and alters homeostasis)
3 stages of photo-activation and main factors influencing each stage1- raise to high energy state (wavelength, intensity), 2- collision with reducing agent (duration), 3- formation of free radical (polymerization initiation)
does composite get damaged if over-exposured?NO You cannot overexpose a composite to degrade its physical properties. But heat to pulp and on exposed mucosal surfaces is a concern.
describe the shrinkage forces during a Chemical curecuring stresses relieved at top surface, stress at tooth/resin interface minimized, shrink toward their bulk mass
describe the shrinkage forces during a Light cure, conventional levelCuring stresses develops at: margin, tooth/resin interface, within tooth. But if bonding is optimal b/t ALL bonded boundaries (enamel and dentin) and the restorative material, then the curing vectors would be toward the prep walls and NOT toward the light
describe the shrinkage forces during a Light cure, high levelCuring stresses develops at: margin, tooth/resin interface, within tooth. Use of very intense curing light sources will result in high stress formation from fast curing and the material will actually cure TOWARD the light, creating even more marginal gaps.
point at which developing polymer is hard enough to transmit stressesGlass Transition point (Tg) at this point the polymer matrix has developed sufficient stiffness so that the shrinkage caused by further curing does not result in polymer flow but is instead transmitted across the polymer to the bonded interface
T/F? Composite continues to polymerize until it is completely curedFalse does NOT "totally" cure due to increased viscosity, steric hindrance, inability to heat the material above ambient conditions
C-Factor?ratio of bonded surface area to the free unbonded area. While polymer poorly formed, flow can relieve stress from shrinkage
factors that influence restoration thicknessLight intensity, Free radical formation, Extent of cure, Incremental thickness, Tip-to-tooth distance
Describe the Halogen cycle1- Hot filament emits tungsten, 2-Tungsten deposits on bulb envelope, 3- Halogen redeposits tungsten on filament
advantages and disadvantages of LEDlow cost, narrow spectral output (can match CQ), long life expectancy (5-10 yrs), easily powered by batteries, becoming more intense, communications and data storage. // Disadvantages- narrow spectral output, heat generation (lowers source life, fan, heat in target)
what are alternative photoinitiators used for?in bleaching colors, when inicisal translucency needed, do NOT need accelerator, UV absorbers; Lucerin TPO, PPD, Ivocerin
electromagnetic spectrumhas both an electric and magnetic component traveling in a specific direction, energy is sinusoidal with respect to time, energy travels at the speed of light regardless of its frequency
distance traveled by a single cycle of energywavelength (nm)
For dental applications, wavelengths b/t ____ are used for photopolymerization380-500nm (violet + blue light) Newer materials contain photoinitiators that absorb energy b/t 380-450nm (aka only Violet light)
differences of interactions of photons of infrared, visible light, uv light when interacting with matterInfrared- photons interact with atoms by increasing the amplitude that bonds vibrate (result is heat), Visible light- orbital electron absorbs the energy contained in the photon and moves to a higher energy shell, then drops back down to supply a photon of lower energy and small amt of heat, UV- energy contained by photons is sufficient to totally remove an outer electron completely from an atom creating an ION
mechanisms of radical formation1- Absorption of radiation by CQ (raises molecule to triplet state where it is very reactive), 2- Collision with tertiary amine (only when CQ is in excited triplet state AND collides with amine can a free radical be formed from an exiplex), 3- Initiation of polymerization (once free radical is formed, polymerization rx will start and propagate/terminate)
All contemporary resin-based restorative materials undergo what kind of polymerization?free radical, vinyl polymerization
what polymerization happens after the dark reaction is complete?after "dark rx" has completed (first 15-20 min plateauing at 24 hrs) there is NO additional curing of the polymer; rx does NOT slowly continue until all monomer is used. It ceases and leaves unreacted methacrylate groups present
define "depth of cure" phenomenon in light activated materials and factors that cause itAttenuation of light energy within a composite the extent of cure decreases dramatically from the surface closest to the light. Coloring agents and fillers decrease depth of cure. But more light penetrates a composite the better it is cured since it becomes more dense and RI increases.
T/F? All resin-based materials shrink when curedTrue