Lasers: Physics Lecture 2

Modes of operation--pulsed and continuous--are different how?

Pulsed Wave: Thermal relaxation between energy pulses. Continuous Wave: NO thermal relaxation between energy pulses

Wavelengths in dental lasers: which ones are pulsed and which ones are continuous waves and which are both?

Pulsed: Er: YAG, Er,Cr:YSGG Continuous: CO2 Both: Nd:YAG and diodes

Delivering Laser Energy: conducted through what 3 things?

Quartz fibers. Hollow wave guides. Articulated arms.

"Hot Needle" effect

shrinkage only

The ___the focal spot, the higher the power density.

smaller

Applications of diode lasers

soft tissue, periodontal therapies, tooth whitening

Heat/Cold Thresholds: Welding

70-90 celsius (158-194 F)

What is actually occurring to make a laser?

Man-made single-photon wavelength produced when an excited atom becomes stimulated, thus emitting a photon.

Laser Energy: what does 'watt' mean?

A unit of power

___ is MOST important type of tissue interaction. Irradiation volume area that is biostimulated.

Absorption. WE want to control how much energy is going into tissue

Undesirable tissue interactions can be what 3 things?

Coagulation (excess clotting.) Charring (tanning.) Edema (swelling.)

Heat/Cold Thresholds: Carbonization, Charring, Blackening

200 + celsius (392 f)

Heat/Cold Thresholds: Hyperthermia

37-50 celsius. (95-122 f)

Biostimulation (LLLT) increases what 4 things?

1. Circulation. 2. Collagen formation. 3. Fibroblastic Activity. 4. Osteoblastic Activity.

Heat/Cold Thresholds: Coagulation

60 degrees + celsius. (149 F)

Heat/Cold Thresholds: Tissue Vaporization

100-150 celsius (212-302 f)

Power density affected by what 3 things?

1. Distance from the source. 2. Settings on the laser. 3. Diameter of the tip of the fiber.

IONIZING factors--6 (really about the way energy is disrupting and changing molecules)

1. Higher frequency ultraviolet radiation. 2. Can break chemical bonds. 3. Shorter wavelengths. 4. Gamma Rays, Ultra-Violet Rays, X-rays. 5. Dubbed the "harmful radiation" and may disrupt DNA structure 6. Can penetrate biological tissues

NON-IONIZING factors--6

1. Lower frequency audible and ultraviolet radiation. 2. Longer wavelengths. 3. Microwaves. 4. Radio waves 5. Infrared heat waves 6. Vaporize biological tissue through thermal energy

All of these factors must be involved for lasers to effect tissues:

1. Power Density (Watts/Cm2). 2. Cooling. 3. Duration of Exposure. 4. Specific Wavelength. 5. Emission Mode. 6. Tissue Characteristics--lighter and tighter the more painful because it's not being absorbed well.

Laser Features--5

1. Programmable preset functions. 2. Rheostat foot control wired or wireless, hand-held (pen laser). 3. Pulse, continuous operating modes. 4. Adjustable aiming beams and volume (to hear it). 5. Fiber management systems (or disposable tips).

Parameters of lasers

1. Radiation wavelength. 2. Power (energy) density. 3. Operation mode: Pulsed or Continuous Wave (CW)

___ is the only laser that is not commonly used in dentistry. It's not infrared.

Argon

Wave scale or light spectrum: where do most dental lasers operate?

Between ultraviolet and infrared light. Right beneath where visible light is. We think this is why we get biostimulation.

What is the delivery system always for a diode laser?

Delivery system: optic fiber

Who first postulated lasers in 1916 and theorized that you can stimulate portions of the electromagnetic field to amplify light

Einstein

How the Diode works

Electromagnetic energy absorbed by a carbonized tip. Molecules in tip vibrate and produce energy. Tip gets hot (instant). Heat is reconverted into electromagnetic energy (incandescence). Tip emits infrared light.

Tissue effects are influenced by:

Emission wavelength. Tissue optical properties (what color is the tissue.) Time of exposure--how much time spent under exposure. Laser energy.

Do all the numbers for the wavelengths of the different dental lasers.

Er: YAG--2940 nm ErCr: YSGG -- 2780 nm Nd:YAG--1064 nm CO2--10,600 nm Diodes--655 nm - 980 nm

With power density relationships, the greater diameter the tip of the optic fiber means what?

Greater diameter means less powerful energy. Example: 150 micron fiber has a HIGHER power density than a 500 micron fiber.

What other things may alter laser tissue effects? Think about things presenting different colors in the mouth.

Healthy tissue behaves different than infected, purply gums because color is different. Blood has a very specific color that is predictable. How much saliva is present. Melanin in skin. Margin line on a crown.

Biostimulation (LLLT) is what?

Low-level laser therapy: Cold lasers, Biomodulation. Using light to speed, enhance and promote healing. Wound healing/tissue repair big for us, though can do pain relief, inflammation, edema, chronic diseases.

Laser Energy: measured how?

Joule: a measure of energy

Diodes will indeed kill what main periodontitis character?

Kills PG, thankfully

What is the main target for absorption for Nd: YAG, CO2, diodes?

Melanin Hemoglobin Some water

What is diode mode like?

Mode: continuous wave and pulsed

What are 4 laser radiation characteristics?

Monochromatic: Very precise color or wavelength. Collimated: Very directional, can be focused. Coherent: Synchronized in phase--predictable Measured in nanometers.

Laser Energy: what does one watt mean in terms of joules?

One watt = one joule for one second. Power Density: watts/cm2

Lasers and Tissue interact in what 4 ways?

Reflection--doesn't penetrate, bounces off. Absorption--goes in specific direction into tissue. Transmission--how it travels through things. Scatter--hits and goes all over.

What is a laser, very simply put?

Single color of light.

Power density is?

The amount of power being delivered to the tissue. Distance from the source changes the way the wavelength works.

Wavelength is? What is it measured in? What's that equation we must know?

The distance from wave crest to wave crest. Measured in nanometers. nm = 10-9 (1 billionth of a meter)

Remember: no mode is particularly better, it is dependent upon what?

The procedure and patient. Like a pulsed wave good for cutting through softer tissue and continuous would be better at hard tissue.

What's a photon?

elemental quanta/quantum (quantity) of radiant energy.

What is the main target for absorption for Er:YAG and Er,Cr:YSGG?

Water (typically used just for hard tissue because of this absorption into water.) Hydroxyapatite

Diode Lasers wavelengths and spectrum.

Wavelengths: 810nm, 940nm, 980nm. Electromagnetic spectrum: near infrared, visible.

"Knife" effect

cutting with no coagulation; coagulation happens when heat interacts with tissue, like cooking meat.

Most lasers today are in the ____ spectrum, right before visible light

infrared

Absorption characteristics exist for what body molecules for diode lasers?

melanin, hemoglobin, water.

Do diodes emit as much energy as Nd: YAG?

nope. Pulse duration is much longer than Nd: YAG (1064 nm) Less peak power, thus less bacterial kill. Does not reach ablation threshold (when tissue heats up and coags) of Nd: YAG. Still enough power to damage tissue.

With diodes, is the active medium solid?

yes, solid (semi-conductor)