The document provides an extensive overview of dental laser physics, detailing the characteristics of laser light, types of lasers, and their interactions with biological tissues. It discusses various effects (photo-thermal, photo-mechanical, photo-electrical) that occur when laser energy interacts with tissues, the mechanisms of biostimulation, and the specific applications of different laser types in dentistry. Additionally, it emphasizes the importance of parameters like pulse duration, energy density, and tissue interaction to minimize thermal damage during procedures.

1. DENTAL
LASER
Physics
Dr . Abdelrahman Mosaad

3. What is LASER
 Light Amplification by Stimulated
Emission of Radiation
 Light
 Amplification
 Stimulated
 Emission
 Radiation

4. Light characteristics :
2.998 * 108 ,, photon is the unit of light
v = f • λ
( v = velocity , f = freq. , λ=
wave length )
 white light formed of …. Different wave
lengths , different directions ,,

6. Photon energy (E)
 E = hc/λ = hf ( eV ) (joule)
( * c : speed of light *h : Planck constant )
= 1.2398/λ λ in ( μm )

8. Laser light characteristics :
- coherent : same phase
- collimated : same direction
- monochromatic : only one wave
length

10. Amplification :
 Increasing the quantity and energy of
photons , so the light photons together
will be able to do !!

11.  How ? By mirrors (2)
 One of the mirrors called the output
coupler is less than one hundred
percent reflective . Light leaks from
the output coupler, and these are the
photons that form the laser beam

12. Amplification in laser cavities

13. Amplification in diode laser

14. Stimulated Emission of
Radiation
- a source is used to pump the e- to
excited state
- the photons are emitted during
transfer of electrons down from the
excited levels of energy

16.  The pumping source could be light
(flash lamp) , laser , electrical
discharge
 Energy is the ability to perform and is
measured in Joules
 The measuring unit for most dental
laser applications is the millijoule (mJ)

19.  The beam will diverge at various rates
depending on the device, the hand
piece, and the tip used

20. Terminology
• Peak Power (PP) : Watts
(Joules/sec)
• Pulse Width/Depth (PD) : Seconds
• Pulse Energy(PE) : W(PP) x
Time(PD) = Joules
• Frequency : Hz (Pulse Per Second)

21. • Average Power : ( PE ) x Hz
• Duty Cycle % : (PD) / (PD + Relaxation Time) x
100
• Energy Density (Fluence) : J = (PE) / Area
• Power Density : W = (PP) / Area

24. * the pulse energy is often calculated by
dividing ( the average power / pulse repetition
rate )
* Power = energy / second
* Pulse rep. rate = pulse / second
•Pulse energy = avrg.power / repetition rate (f)
• = avrg. Power * pulse duration

25. Once the beam reaches the tissue it
will have a specific spot size depending
on the distance from the hand piece and
its specific divergence
The energy density refers to the
actual amount of energy reaching the
tissue within the spot size.

27.  This Energy Density varies considerably
depending on the parameters of energy,
divergence, and distance
Energy density = ( 255/d2 )*power =
( watt/cm2 )
N.B - power in watt
- d is laser beam diameter in mm

28. Types of laser waves
* C.W : continuous wave
* Pulsed : Q-switched
mode-locked

29.  Continuous wave emission mode
means the laser is on the whole time
it is turned on
 Pulsed wave has on and off periods

31. * Q-switching leads to much lower pulse
repetition rates
* much higher pulse energies

34.  Mode locking by :
* acousto-optic modulator
* saturable absorber

36. Tissue Interactions and
Biological Effects
 As the energy reaches the
biological interface one of four
interactions will occur;
 reflection
 transmission
 scattering
 absorption.

39.  Absorption – Specific molecules in the
tissue known as chromophores absorb the
photons
- photo-thermal - photo-mechanical
- photochemical - photoelectrical
 Reflection – The laser beam bounces off the
surface with no penetration or interaction at
all. Reflection is usually an undesired effect

40.  a useful example of reflection is found when
Erbium lasers reflect off titanium allowing for
safe trimming of gingiva around implant
abutment

41. Absorption
- photo-thermal :
- photo-mechanical : 1- photo-disruptive
2- photo-acoustic
- photo-chemical : 1- LLLT ( biostimulation )
2- PDT
- photo-electrical : photo-plasmolysis

43. Transmission
 – The laser energy can pass through superficial
tissues to interact with deeper areas. Retinal surgery
is an example
 The deeper penetration seen with Nd:YAG and diode
lasers is an example of tissue transmission as well.

45. Scattering
– Once the laser energy enters the target
tissue it will scatter in various directions
- This phenomenon is usually not helpful, but
can help with certain wavelengths biostimulative
properties.

49. Chromophores:
 Endogenous light-absorbing chemicals,
which absorb light of specific wavelength
 Proteins diode and Nd:YAG
 HB diode and Nd:YAG
 Melanin argon , KTP & diode
& Nd:YAG
 Water Er:YAG & CO2
 Hydroxy appetite CO2 & Er:YAG

50.  Absorption is the most important
interaction
 Photo-thermal effects occur when the
chromophores absorb the laser energy
and heat is generated.
 This heat is used to perform work such as
incising tissue or coagulating blood.

52.  Photothermal interactions predominate when most
soft tissue procedures are performed with dental
lasers
 Heat is generated during these procedures and great
care must be taken to avoid thermal damage to the
tissues.

53. Photothermal effect :
 When a laser heats oral tissues certain reversible or
irreversible changes can occur:
• Hyperthermia – below 50 degrees C (rev.)
• Coagulation and Protein Denaturation 60+degrees
C
• Vaporization – 100+ degrees C
• Carbonization – 200+ degrees C

55. Photomechanical effect
 Short pulsed bursts of laser light with
extremely high power interact with water in
the tissue and from the hand piece causing
rapid thermal expansion of the water
molecules
 This causes acoustic shock wave that is
capable of disrupting enamel and bony
matrices quite efficiently

58. 1- photo-disruptive : very high peak
power in a very short pulse duration will lead
to bond breakage between tissue cells
2- photo-acoustic : very high peak
power in a very short pulse duration lead to e-
vibrations causing acoustic shock waves
heard as popping sound ,, so a part of tissue
is removed

59.  This shock wave creates the distinct popping
sound heard during erbium laser use
 Erbium lasers’ high ablation efficiency results
from these micro-explosions of superheated
tissue water in which their laser energy is
predominantly absorbed

61.  The tooth and bone are not vaporized but pulverized
instead through the photomechanical ablation process

62. Photo-electrical effect
 Very high power in very short pulse duration (
nano-sec. & femto-sec. ) lead to ionization of
tissue atoms in the tissue forming a cloud of
free electrons and +ve ions called plasma

63.  Thermal damage is very unlikely to happen
as almost no residual heat is created when
used properly, particularly when the concept
of thermal relaxation is considered

64. TRT ( thermal relaxation
time )
 The TRT was defined as the time taken ‘for
the central temperature of a Gaussian
temperature distribution with a width equal to
the target’s diameter to decrease by 50 %’
 This was used to determine the maximum
allowable pulse widths to be used on blood
vessels while minimizing thermal injury to
adjacent tissue

65.  calculated as follows
 TRT = d2 / ( 16 * α )
 d is the target diameter (in millimeter)
 α is the tissue diffusivity (in square millimeter
per second)

66.  https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-
22-13-15686&id=294174
 Eg : dentin trt = 32.6 μs
 Free running Er-YAG pulse = 200 μs
 Q switch Er-YAG pulse = 62 ns , 110 ns

67.  where ( T ) is the thermal relaxation time of
biological tissues, ( α ) is the absorption
coefficient of the tissue to the laser
radiation , ( κ ) is the tissue thermal
diffusivity

68.  At a repetition rate of 3 Hz, 226 mJ pulse energy with
62 ns pulse width has been successfully
accomplished, which should be the best results at 2.94
μm. It has been demonstrated that, with the Q-
switched Er:YAG laser heat damage is unlikely to
happen at all

71.  the crater wall of dental ablation is more
smooth indicating a higher ablation precision,
meanwhile the thermal damage can be
effectively avoided during the hard dental
tissue ablation

72. © 2014 Society of Photo-Optical Instrumentation
Engineers

73.  The dental tissue ablation experimental results reveal that the
ablation effect is essentially different between the free-
running laser and the Q-switched laser.
 The free-running laser has a long pulse in the range of
hundreds of microseconds, during its ablation the excess
heat will diffuse into the surrounding tissue, resulting in very
obvious debris and carbonization.

74.  On the contrary, the pulse width of the Q-switched
laser is much shorter than the tissue thermal relaxation
time. Because the tissue melting occurs almost
instantaneously, this momentary interaction reduces
the debris in the dental tissue.
 Thus, the Q-switched laser exhibits prominent
technique superiority over the free-running laser in the
hard dental tissue ablation.

75. Photochemical effect
 occur when photon energy causes a
chemical reaction.
 These reactions are implicated in some of
the beneficial effects found in biostimulation

77.  Molecular targets can be cytochrome c
oxidase (with absorption in the NIR) or
photoactive porphyrins.
 Cellular targets are mitochondria with the
effects of increased adenosine triphosphate
production, modulation of reactive oxygen
species, and initiation of cellular signaling

79.  The primary photo-acceptor within (redIR) is mixed valance (
partially reduced ) cytochrome -c- oxydase
 The primary photo-acceptor within (bluered) is avoprotiens ( eg.
NADH dehydrogenase )

81.  The results of photochemical effect may be:
• Increased cell proliferation and migration
(particularly by fibroblasts).
• Modulation in the levels of cytokines, growth
factors, and inflammatory mediators.
• Influence on the activity of second
messengers (cyclic adenosine
monophosphate, Ca2+, nitric oxide).

82. • Increased tissue oxygenation.
• Increased healing of chronic wounds and
improvement in injuries and carpal tunnel syndrome, pain
reduction, and impact on nerve injury.

83. Photo-biomodulation or
Biostimulation
 refers to lasers ability to speed healing, increase
circulation, reduce edema, and minimize pain
 Many studies have exhibited effects such as increased
collagen synthesis, fibroblast proliferation, increased
osteogenesis, enhanced leukocyte phagocytosis, and
the like with various wavelengths

84. Known also as ( LLLT ) or
( cold laser )
 The exact mechanism of these effects is not
clear
 it is theorized they occur mostly through
photochemical and photo-biological
interactions within the cellular matrix and
mitochondria.

85. Theories of photo-biomodulation
(1 o reactions )
1) change redox properties ( photo oxidation
of cytochrome -c- oxydase
2)N.O. theory : activation of e- flow in
cytochrome c oxydase  increase O2 binding
and respiration  antagonize the N.O.
production

86. 3) super oxide anion theory : activation of respiratory
chain  increase production of super oxide anion
4) singlet oxygen theory : Irradiation of photo-
acceptors  generation of singlet oxygen which stimulate
DNA and RNA synthesis

87.  5) transit local heating hypothesis : transient
increase in temperature  structural changes initiates
the biostimulation activity

88. 2o reactions
 1 ) photo-acceptor
control over the ATP of the intercellular
matrix
 2 ) (AP-1) & (NF-kb)
are transcription factors which are regulated
by cellular redox state which is altered by laser

89.  N.B.
stimulation = increase oxidants conc. &
decrease antioxidant conc.
Inhibition = decrease oxidants conc. &
increase antioxidants conc.

90.  Use lower dose and less time LLLT in cases
of wound healing ( eg. 2 j/cm2 )

91. Limitations of
LLLT 1 ) always stimulates the cells with less growth
rates
 2 ) limited to G1 phase of cell cycle
 Cell cycle : ( 24hrs )
 G0 resting phase ( 2hrs )
 G1 ready for DNA synth. (10hrs )
 S DNA replication ( 5-6 hrs )
 G2 ready for mitosis ( 3-4 hrs )
 M mitosis ( 2 hrs )

92. Biomodulation refers to
lasers ability to :
 speed healing
 increase circulation
 reduce edema
 minimize pain
 increased collagen synthesis
 fibroblast proliferation
 increased osteogenesis
 enhanced leukocyte phagocytosis

93. Types of Dental Lasers
 The dental lasers in common use today are Erbium,
Nd:YAG, Diode, and CO2.
 Each type of laser has specific biological effects and
procedures associated with it

95. Erbium lasers
 built with two different crystals, the Er:YAG
(yttrium aluminum garnet crystal) and
Er,Cr:YSGG ( chromium sensitized yttrium
scandium gallium garnet crystal).
 They do have different wavelengths, Er:YAG
has 2940 nm and Er,Cr:YSGG has 2780 nm

97.  The erbium lasers are hard and soft tissue
capable and have the most FDA clearances
for a host of dental procedures.
 Their primary chromophore is water, but
hydroxyapatite absorption occurs to a lesser
degree.

99.  Photothermal interactions predominate in soft
tissue procedures and photo-disruptive in
hard tissue procedures.
 Thermal relaxation is excellent and very little
collateral thermal damage occurs in tissues
when proper parameters are followed.

101.  Tooth preparation is quite efficient with
erbium devices and many procedures can be
done without local anesthesia
 Smear layer is virtually eliminated and the
laser has a significant disinfecting effect on
the dentin and enamel to be restored.

103.  Bone cutting with erbium lasers results in minimal thermal
and mechanical trauma to adjacent tissues.
 Studies have demonstrated the atraumatic effect and
excellent healing response following erbium resection of
bone.
 Very short laser pulses of 50 to 100 microseconds are
typically used for hard tissue procedures.

104.  Erbium lasers are excellent soft tissue
devices as well. parameters differ from hard
tissue uses are much longer pulse durations
(300-1000 microseconds = 0.3 – 1.0
millisecond ) and less or no water spray.
 Though slightly more thermal than the hard
tissue settings, there still is quite a bit of
thermal relaxation and minimal heat
penetration into underlying tissues.

107.  Erbium lasers can also be used to safely scale root
surfaces during periodontal procedures which has the
added benefit of root surface decontamination.

108. Nd:YAG Lasers
 Nd:YAG lasers were the first types of true pulsed
lasers to be marketed exclusively for dental use in
1990. (nidmium yttrium aluminum garnet crystal )
They are a near infrared wavelength of 1064 nm.
 This wavelength is absorbed by pigment in the
tissue, primarily hemoglobin and melanin.
 Photothermal interaction predominates and the
laser energy here can penetrate deeply into tissues.

110.  Contact and non-contact mode are both
utilized depending on the procedure being
performed.
 Nd:YAG also have excellent biostimulative
properties.
 Nd:YAG lasers have the unique capacity to
stimulate fibrin formation. This effect is
maximized when the pulse duration is set at
650 microseconds.

113.  These lasers are primarily used for
periodontal treatments.
 effective debridement and disinfection of
periodontal pockets
 Bacterial decontamination contributes to
resolution of periodontal infection

115.  They also have the ability to stimulate fibrin
formation with longer pulse duration settings
 this phenomenon is utilized to biologically
seal treated pockets and act as a scaffold for
reattachment.
 The ability to form fibrin is also utilized when
forming clots in extraction sites which can
help prevent alveolitis and enhance
osteogenesis.

116.  Nd:YAG lasers can also be used for multiple
soft tissue procedures
 The deep penetration and the near infrared
wavelength of these lasers also make them
ideal for photo-biomodulation procedures

117. Diode Lasers
 Diode lasers are becoming quite popular due
to their compact size and relatively affordable
pricing.
 A specialized semiconductor that produces
monochromatic light when stimulated
electrically is common to all diode lasers.
 Diode lasers can be used in both contact and
non-contact mode and can function with
continuous wave or pulse modes.

119.  Diode lasers are invisible near infrared
wavelengths and current machines range
from 805–1064 nm.
 One exception is the Diagnodent caries
diagnostic laser which uses a visible red
wavelength of 655 nm.
 Diode lasers are soft tissue only

121.  The chromophores are pigments such as
hemoglobin and melanin, similar to the
Nd:YAG absorption spectrum.
 Photothermal interactions predominate
whereby diode tissue cutting is via thermal
energy.

123.  They are quite effective for a host of intraoral
soft tissue procedures such as gingivectomy,
biopsy, impression troughing, and
frenectomy.
 Diode lasers also exhibit bactericidal
capabilities and can be used for adjunctive
periodontal procedures .

125.  They also are used for laser assisted tooth
whitening.
 Diode lasers have excellent photo-
biomodulation (LLLT )properties as well.

127. CO2 Lasers
 CO2 Lasers have been available in medicine
since the early 1970’s and have been used in
dentistry for more than 26 years (since 1990).
 The CO2 gas is in a chamber with nitrogen
and helium and the active medium is pumped
with an electrical current. They are a 10,600
nm infrared wavelength, which is highly
absorbed by water.

129.  Articulated arms or hollow waveguides are
used to transmit CO2 laser beams and quartz
optical fibers cannot be used.

131.  They are a 10,600 nm infrared wavelength,
which is highly absorbed by water.
 Articulated arms or hollow waveguides are
used to transmit CO2 laser beams and quartz
optical fibers cannot be used.
 CO2 lasers are very efficient and exhibit
excellent hemostasis.

133.  The traditional CO2 are currently for soft
tissue uses only.
 They are continuous wave lasers that can be
operated in gated wave modes, including
what are termed “superpulsed” modes.
 These superpulsed gated modes offer
improved surgical control with less charring of
tissue.

134.  CO2 lasers are excellent tools for incising
tissue for multiple purposes. Incisional and
excisional biopsies, frenectomy,
gingivectomy, pre prosthetic procedures, and
the like are all achieved with excellent
hemostasis.

136.  Sutures are rarely needed with CO2 and the controlled
thermal effects and sealing of nerve endings often
makes for a very comfortable post-operative
experience for the patient.
 CO2 is also very effective for ablation and vaporization
of leukoplakia and dysplasia.

137.  A hard tissue capable CO2 laser has become available
recently. This laser’s CO2 molecule uses an oxygen
isotope that creates a beam at 9300 nm.