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Define thermal conductivity:
amount of heat that passes per second through a body 1m thick, area of 1m2, temp gradient is 1K
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Materials with low thermal conductivity are:
enamel, dentin, porcelain, cements, resins, and GP
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Define specific heat:
amount of heat to raise temp of 1Kg of substance by 1K (water is high, metal 10% of)
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Metals in terms of specific heat and thermal conductivity?
low specifc heat, high conductivity (heat and cool more rapidly)
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Define thermal diffusivity?
thermal conductivity divided by specific heat times density
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Define the linear coefficient of thermal expansion (LCTE):
change in length per unit length of material for a 1K change in temperature
gold, GI, porcelain equal to dentin
GP is not, it contracts, therefore you need compaction pressure as it cools
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What is the washed field technique?
Tooth surface is expose to air-water spray for 5 seconds before cutting. 1 second up and 4 seconds cut afterwards.
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Pulpal reactions to restorative procedures may be caused indirectly, not to excessive heat production, how?
1. rate of expansion of dentinal fluid creates shear forces tearing the cell membrane
2. Evaporative fluid flow, outward flow that is so fast it tears membranes
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Dental procedures can elevate pulpal temps:
9-15C
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During tooth preparations what determines the amount of frictional heat produced?
- 1. force to bur
- 2. cooling effficency of irrigant
- 3. prior wear/design of bur (fissure vs. diamond)
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What chemical mediator can be used as a marker of tooth pulpal insult?
NOS
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Operative variables rated in protection of pulp? bur speed, smear layer removal, RDT, resotrative materials?
RDT>bur speed>smear layer removal
not restorative material
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System B range of 200-600C produced what temp increase in root surface? Floren 1999 study
1.04C-5.78C
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WVC shown to increase apical temp by only __C and cervical temps by only __C.
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Hydrated mineralized dentin denature temp?
170.4C
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Dehydrated dentin denature temp?
186.5C
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Demineralized hydrated dentin denature temp?
65.5C
can happen with MTAD irrigant, which demineralizes up to 10um deep
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What temp rise causes irreversible damage to PDL?
10C for greater than a minute
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What Laser stand for?
light amplification by stimulated emission radiation
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Laser differ from coventional light, how? 3
monochromatic (single wavelength)
very low divergence (collimated)
coherence (photons in phase)
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Which lasers emit invisible light?
CO2 ER:YAG and Nd:YAG
Excimer are visible
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Lasers will do four things when interacting with tissue
- 1. through (no injury)
- 2. reflect (no injury)
- 3. scattered (less intense, less precise)
- 4. absorbed (converted to thermal energy)
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Most effective laser on tissues with high water content and is highly absorbed by all biologic hard and soft tissues?
CO2 will damage pulp
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Most effective laser on pigmented or vascular tissues?
Argon
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Laser interacts with pulp very well, all vascularized tissues?
Nd:YAG
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Which lasers would be ideal for cleaning and shaping root canals?
Nd:YAG, argon, Er:YAG, Er:YSGG, and excimer
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Extent of interaction of laser energy with tissue will be determined by: (2)
1. specific wavelength
2. optical characterisitcs of the particular target tissue
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Clinician controls four parameters with laser use:
- 1. power density
- 2. energy density
- 3. pulse reptition
- 4. continous vs pulsed energy and direct contact or no contact with target tissue
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Four approaches to reducing pulpal temp rise with lasers?
- 1. cooling air water spray
- 2. brief pulse
- 3. excimer lasers that operate in the UV range with short pulses
- 4. occlusion of dentinal tubules (done with Nd:YAG and excimer lasers)
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Limitation of laser use in root canals?
- 1. light emitted at end instead of side
- 2. guide must be small ~.2um
- 3. stiff but no brittle
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First ype of laser used in densitry?
Ruby lasers
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CO2 laser and dentin permeability?
inc 1.4-24 fold with removal of plugs and smear layer
creates severe thermal damage
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The laser that harms the hybrid layer creating by bonding with dentin adhesive?
Er:YAG
vaporizes exposed collagen fibrils
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Name laser: little thermal damage, improved cutting efficency
Nd:YAG
vaporizes water so rapidly to create microexplosions, mechanical ablation
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Name laser: UV range photons, reduced heat absorption and reduced dentin cracking
Excimer lasers, photoacoustic distruction
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Two mechanisms for dentinal tube occlusion by lasers for hypersensitivity?
1. melting and fusing dentin or the smear layer or coagulating proteins in tubes
2. directly reduce neuronal activity
Nd:YAG most studied
65%-72% reduction (air/probing)
combined with Fl varnish, 90% reduction
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Another term for airborne particle abrasion?
kinetic cavity preparation
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