Walsh, Laurence J.

University of Queensland eSpace

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P ublished data clearly support thevalue of lasers in many fields ofdentistry. The challenge for the
practitioner is knowing when, where, and
what armamentarium to use in any given
situation, since not all laser wavelengths
are necessarily useful in every clinical sit-
uation. The current range of applications
for lasers in dentistry is so broad that to
cover the field in any depth requires a
large textbook. (The book “Oral Laser
Applications”, co-authored by LJ Walsh,
was published by Quintessence in July
2006, and is a useful source of contempo-
rary information on laser dentistry). 
Two examples of applications of lasers
attracting current interest which I will dis-
cuss in this article are photomechanical
effects for creating analgesia for hard and
soft tissue procedures; and biostimulation
for promoting rapid integration of
implants. Despite their obvious differ-
ences, in terms of mechanisms, both rely
on the effect of lasers on membranes - the
cell membrane and the inner mitochon-
drial membrane, respectively.
Laser-induced analgesia
Early work with free-running pulsed
Nd:YAG lasers in the early 1990’s showed
that pulsed laser radiation which could pen-
etrate dentine was responsible for part of
the desensitizing effect on cervical dentine,
the remainder of this effect being a partial
occlusion of dentinal tubules. Subsequent
studies of laser-induced analgesia with the
free-running pulsed Nd:YAG and Er:YAG
laser by Orchardson and Zeredo, respec-
tively using rodents showed conclusively
that there was a dramatic blockage of neu-
ronal activity and a corresponding increase
in the pain threshold of teeth after laser irra-
diation. The effect had a clear dose
response for its onset, declined after 15-20
minutes, and was also associated with
blockade of late-phase neurogenic inflam-
mation (which is driven by the effects of
neuropeptides). These effects were iden-
tical to those noted in clinical practice
when preparing cavities with erbium lasers
(Er:YAG and Er,Cr:YSGG). The animal
studies however removed all possibility of
placebo effects and psychogenic influ-
ences, and demonstrated that there was a
fundamental reversible alteration occurring
in the nociceptive response caused by the
laser treatment, which suppressed nerve
firing for a given level of stimulus.
Clinically, the blockade with shorter
exposures is more selective for depolariza-
tion of A delta fibers (rapid, sharp, well
localized pain) than for C fibers, which
explains why some patients notice low
level photomechanical shock waves
(“mini-earthquakes”) but not discomfort.
Laser analgesia is known to be induced at
sub-ablative settings, which give high pen-
etration of both teeth and soft tissues (e.g.
through to the pulp via the attached gin-
gival and alveolar bone). Because of some
persisting C fiber activity, some patients
notice cooling effects in their teeth during
lasing due to evaporative energy loss (the
thermodynamics dictate that with a net
energy loss, pulpal cooling of up to 7
degrees Celsius may occur). These mild
sensations would be more likely to occur
in younger patients, and in previously
unrestored teeth with rapidly progressive
caries on the buccal surfaces of canine and
premolar teeth, as these have the shortest,
straightest, and widest dentine tubules in
adult patients, and the least secondary den-
tine (Figure 1). Achieving reliable laser
analgesia as a pre-emptive step in such
cases involves using the lower energies
and higher pulse frequencies which give
the penetrating analgesic effect rather than
surface ablation of tooth structure.
Since microscopic studies on both ani-
mals and humans had shown the laser
analgesia effect was molecular, not histo-
logical, the intellectual issue then arose of
the targets involved. An obvious explana-
tion could be that low level stimulation of A
delta fibers by laser pulses could initiate
gate control, in a pattern similar to trans-
cutaneous or trans-mucosal electrical
stimulation. However, when investigating
this effect, changing the frequency of
Laser dentistry: Membrane-based 
photoacoustic and biostimulatory 
applications in clinical practice
BY PROFESSOR LAURENCE J. WALSH
THE CUTTING EDGE
Figure 1. Before and after photographs of the treatment of deep caries with an
Er:YAG laser in a young patient with the “worst case” scenario of an unrestored
canine tooth with rapidly progressive caries on the buccal surface. A gingivoplasty
has also been undertaken to gain access to all the margins - note the lack of bleeding.
The margins show laser etching.
6 4 -  D e n t a l  P r a c t i c e S e p t e m b e r / O c t o b e r  2 0 0 6
pulsing the laser suggested that a resonance
effect was occurring, since there were core
frequencies which were effective, as well
as harmonics of these (10 Hz, 20 Hz, etc).
The putative target for a photo-acoustic
effect identified by the author was the Na/K
ATPas pump. The work of Rice at NYU
has shown that this is a hollow tubular pro-
tein which spans the cell membrane of
nerves, and establishes the gradients in
sodium and potassium which are essential
for propagating an impulse down a nerve
through membrane depolarization and
repolarization. The term “bioresonance”
has been coined by the author to explain
how partial spatial dissociation of the beta
domain of this ion channel protein (which
controls its function) closes the lumen of
the “pipe” and thus prevents repolarization
for a short period of time (Figure 2).
Using water mist to couple laser energy
into soft tissues, analgesia can be exploited
for soft tissue procedures as well as for
cavity preparation. Animal studies by
Zeredo’s group have confirmed that
Er:YAG laser incisions to lip, gingiva,
mucosa, and tongue are less painful than
with scalpel, when both are undertaken
without local anaesthesia, scientifically val-
idating the clinical experience of many laser
dentists who undertake minor procedures
such as gingivoplasty during cavity prepara-
tion without causing discomfort (Figure 3).
Biostimulation
The second laser application under the
spotlight is low level laser therapy (LLLT),
also known as soft laser or biostimulation.
This effect is a photochemical effect caused
by the action of visible red (633-635 nm) or
near infrared (810-830 nm) light on the
electron transport chain in mitochondria,
which activates NADPH oxidase (and other
enzymes) in the inner mitochondrial mem-
brane, and causes a broad activation of
normal cellular functions. Exploiting this
to accelerate bone behaviour in terms of
integration and regeneration around
implants is attracting current interest. Many
clinical studies (including randomized con-
trolled clinical trials) have shown that
LLLT is of proven benefit in wound healing
for soft tissues, accelerating closure of oral
mucosal soft tissue wounds by facilitating
the healing process at the level of both the
microvasculature and fibroblasts. Max-
imum benefit with LLLT occurs with
repeated dosages, with the best effects
being obtained when the treatment is
applied daily or every second day.
Recent work has shown that LLLT may
accelerate metabolism and/or mineraliza-
tion during early bone healing. For
example, in a rabbit tibia model, Khadra has
shown that LLLT stimulates the mechanical
strength of the interface between the
implant and bone after a healing period of 8
weeks. Histomorphometric and mineral
analyses showed that the irradiated implants
had greater bone-to-implant contact than
the controls. Using the same model, Lopes
noted that LLLT improved bone healing
such that the loading time could be reduced
to 30 days after LLLT, while Guzzardella
demonstrated greater implant-bone contact
area and greater bone microhardness.
Animal studies using primates have exam-
ined the effects of low-energy laser
irradiation on osteocytes and on bone
resorption at bone sites used for implant
placement. When sites are irradiated imme-
diately after drilling before inserting
implants, osteocyte viability measured after
5 days was higher compared to non-irradi-
ated control sites, implying that LLLT may
have positive effects on the integration. In
contrast, the rate of bone resorption was not
affected by laser irradiation.
Further studies are underway to deter-
mine the benefits of LLLT with various
implant placement techniques in humans.
Given the expansion of implant dentistry
and laser dentistry in recent years, it is
logical to anticipate the concurrent use of
both technologies in clinical practice as
the evidence base consolidates.
Further reading
• Moritz A, et al. Oral Laser Applications. Quintessence, 2006.
• Mount GJ, et al. Preservation and restoration of teeth, 2nd edn.
Brisbane: Knowledge Books and Software. 2005. pp.119-143.
• Forrest-Winchester K, Walsh LJ. Perio 1992; 13:37-43.
• Walsh LJ. Aust Dent J. 2003; 48:146-155.
• Orchardson R, Whitters CJ. Lasers Surg Med. 2000; 26:241-9. 
• Orchardson R, et al. J Dent.1998; 26:421-6. 
• Orchardson R, et al. Lasers Surg Med. 1997;21:142-8.  
• Zeredo JL, et al. OSOMOPORE 2005;100:31-5. 
• Zeredo JL, et al. Brain Res. 2005;1032:149-53. 
• Zeredo JL, et al. Lasers Surg Med. 2003; 33:169-72.  
• Rice WJ, et al. Biophys J. 2001; 80:2187-2197.
• Walsh LJ. J Oral Implantol. 1992; 18:335-340.
• CB Lopes, Photomed Laser Surg. 2005; 23:27-31.
• M Khadra, Swed Dent J (Suppl). 2005;(172):1-63.
• M Khadra, Clin Oral Implants Res. 2005; 16:168-75. 
• GA Guzzardella, Clin Oral Implants Res. 2003; 14:226-32. 
• Dortbudak, Clin Oral Implants Res. 2002; 13:288-92. 
Professor Laurence J. Walsh is the tech-
nology editor of Australasian Dental
Practice magazine. He is also a noted
commentator on and user of new technolo-
gies and is the Head of The University of
Queensland School of Dentistry.
THE CUTTING EDGE
CPD POINTS AVAILABLE
Continuing Education credits are 
available on this article for subscribers
by answering the questionnaire at
www.dentalpractice.com.au
Figure 2. Two molecular models of the NaK pump, showing
external, transmembrane (TM) and inner cytoplasmic parts,
based on the work of Bill Rice and David Stokes at NYU. The red
domain on the right image is the beta domain. For an animation
of the pump working, see www.mark-hilge.com/nak/nak-atpase_f.htm
Figure 3. Gingivoplasty in an orthodontic patient undertaken
without LA using the Er:YAG laser. Note how the soft tissue
contours match those immediately after surgery. The patient did
not undertake any mechanical or chemical oral hygiene during
the 2 weeks after the surgery.


Laser dentistry: membrane-based photoacoustic and biostimulatory applications in clinical practice

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Laser dentistry: membrane-based photoacoustic and biostimulatory applications in clinical practice

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