Lasers in Dentistry

by Ricki Lewis, Ph.D.

       Lasers are now part of our lives in many ways. They are in our
computer printers and compact disc players, they record prices at
the supermarket check-out, they light up rock concerts, and they
guide weapons and measure distances between planets. Lasers have
also revolutionized many surgical procedures, minimizing bleeding,
swelling, scarring, and pain. And now they're beginning to blaze a
new trail in dentistry.
       The potential benefits of laser use in dentistry include
procedures done on soft tissues of the mouth. Because laser
techniques cause less pain than traditional methods, they are also
likely to reduce the fear that many people have of the dentist. At
the very least, lasers in some dental applications would eliminate
the noise of the instruments that to some patients are nearly as
disturbing as the physical discomfort.
       However, it may be quite a while before you can have your
cavities drilled or root canals cleaned with a painless flash of a
laser. "FDA has cleared for marketing certain lasers for soft
tissue use, such as gingivectomies [removing excess gum tissue],
but not for hard tissues," says Gregory Singleton, D.D.S., senior
dental officer in the Center for Devices and Radiological Health at
FDA. The hard tissues include tooth and root, while soft tissues of
the mouth refer to the gums, the ligaments and fibers that bind
tooth to socket, and the tissue supporting the tongue.
       So far, lasers seem to be living up to their promise in the
latter area. "For soft tissue surgery, lots of patients report less
postoperative pain. There are sealed off nerve endings, so recovery
is less painful," says Marilyn Miller, D.M.D., co-director of the
Princeton Dental Resource Center in Princeton, N.J. But she adds
that healing may be slightly slower, because the laser also seals
off blood vessels, which would bring in clotting factors to help
heal cut tissues.

Laser Basics
       Since the mid-1960s, lasers have proven to be powerful
surgical tools. The word "laser" is an acronym for "light
amplification by stimulated emission of radiation," which means
that the intense and narrow beam of light is of one wavelength.
Ordinary "white" sunlight, in contrast, is a continuum of light of
many wavelengths, corresponding to the colors of the visible
spectrum plus the infrared (heat) and ultraviolet wavelengths that
sandwich them. Sunlight passing through a prism separates into its
component colors; a laser light remains a single color.
       A medical laser device includes a source of electricity,
mirrors to direct the beam, a crystal or gas that is stimulated to
emit the light, and tubing to deliver the light energy. The nature
of the material through which the light passes determines the
specific properties of the laser--and therefore what it can do in
the human body. Instrument design is tailored to specific uses.
Many dental lasers, for example, include long narrow tubing so that
the dentist can use it in the narrow confines of a person's mouth.

Types of Dental Lasers
       FDA has cleared four types of lasers for dental use: carbon
dioxide, Nd:YAG, argon, and holmium:YAG.
       A carbon dioxide (CO2) laser uses CO2 gas. Watery tissue
absorbs this type of laser energy, which doesn't penetrate very
deeply, but vaporizes surface cells. A CO2 laser leaves a residue
of carbon, called char. If a dentist leaves char in place, it
serves as a biological dressing, maintaining sterility.
       Because the beam from a CO2 laser is invisible, a second laser
beam, based on the elements helium and neon, adds a red beam, so
the dentist can see the laser energy.
       A CO2 laser is used in gingivectomies, biopsies, and removal
of benign and malignant lesions (see accompanying article). A CO2
laser is particularly good for a frenectomy. "The frenum--the
tissue under the tongue--is tight in some people, and it can be
quickly loosened up with laser treatment," says Michael Yessik,
president of Incisive Technologies, a laser manufacturer in San
Carlos, Calif.
       For lesions extending into tissue deeper than the 0.1
millimeter that the CO2 laser penetrates, a neodymium:yttrium-
aluminum-garnet (commonly called an Nd:YAG) laser is appropriate.
As with the CO2 laser, an accompanying red beam makes the energy
visible. A jet of cool water or air limits possible heat damage
that can result when a super-heated gas, called a plasma, forms on
the tissue surface as it is being treated. An Nd:YAG laser can harm
thin tissue, such as the gum in the lower front of the mouth. The
CO2 and Nd:YAG lasers are used in some of the same procedures that
remove soft tissue.
       The argon laser is based on gas of the element argon, and
emits a bluish-green light. It is cleared for marketing for a
different application--curing composite resins. These tooth-colored
materials are used in reconstructing chipped teeth, filling
cavities in visible areas of the mouth, or sealing teeth to protect
them from decay. The dentist paints on the composite, and then
focuses a narrow beam of light to harden, or cure, it. The intense
light alters the physical properties of the composite, linking its
small molecules into longer ones, which adds great strength. Robert
Pick, D.D.S., clinical associate professor at Northwestern
University Dental School, writes that he thinks the argon laser
will soon become the standard method for curing dental composite
resins, replacing ultraviolet light.
       Another device used on soft tissues is the holmium:YAG laser.
Oral and maxillofacial surgeons have used it experimentally to
surgically remove the damaged disc separating the condyle of the
mandible from the base of the skull. The disc can be damaged due to
trauma or chronic inflammatory diseases such as osteoarthritis that
can cause symptoms commonly known as temporomandibular joint (TMJ)
syndrome. (An oral and maxillofacial surgeon is a dentist
specializing in correcting abnormalities of the jaws and face with
surgical procedures.) TMJ syndrome can cause facial pain,
headaches, pain in front of the ear, noise when the jaw opens, ear
congestion, dizziness, ringing in the ears, difficulty swallowing,
nervousness, insomnia, difficulty chewing, sensitive teeth, numb
fingertips, and backache.

Choosing the Best Laser
       The challenge to dentists is finding the best laser type and
strength for a particular application. Lasers can vary in chemical
basis (CO2, Nd:YAG, argon, holmium:YAG, and others), wavelength of
emitted light, power, whether it is applied continuously or in
short  pulses, and whether the laser is applied directly (a contact
laser) or through a tip of some sort (non-contact).
       The effect of a particular laser must be evaluated for each
type of dental tissue--such as enamel, dentin, pulp, bone, and
gingiva. Light can have one of four fates when it hits a tissue--it
may be absorbed, reflected, scattered within the tissue, or
transmitted. This is important, because light energy that is
transmitted or scattered may harm surrounding tissue. Reflected
laser light dissipates so quickly that it does no damage.
       Whether or not anesthesia is needed for soft tissue dental
laser procedures depends on the duration of the treatment and the
amount of tissue removed. CO2 laser procedures may require local
anesthesia, but Nd:YAG treatment usually does not.
       "About 70 to 80 percent of procedures using dental lasers are
done without anesthesia. It depends on the power level needed to
perform the procedure," says Yessik.

Safety Measures
       Several precautions to dental staff and patient must accompany
laser use. Everyone in the room must wear protective glasses--dark
green tinted for argon and YAG lasers, and clear for CO lasers. Wet
gauze pads are placed in the patient's mouth surrounding the
treated area. Reflective surfaces, such as instruments and mirrors,
are covered so that stray light beams cannot ricochet around the
room.
       It is very important that all anesthetic gases be removed from
the room. They are explosive, and could be ignited by a laser beam.
The dentist must also suction off vaporized soft tissue, and the
smoke, or laser "plume," emitted during procedures. The plume can
carry viruses. This is one reason that some dentists do not like to
use a laser to remove herpes lesions in the mouth. Treatment with
a CO2 laser provides rapid pain relief and speeds healing.

Zapping Away Cavities--Not Yet
       If you dream of having a cavity treated with a painless,
soundless zap of a laser, you will have to wait awhile. Although
lasers have great potential for one day replacing the drill, there
is still too much danger of their damaging the pulp under the
enamel, according to Gerard Kugel, D.M.D., assistant clinical
professor of restorative dentistry at Tufts University School of
Dental Medicine in Boston. The problem is the amount of heat
generated in hard tissue treatment.
       "It may take a different intensity or type of laser energy to
remove debris from soft tissue than to remove the hard calculus or
plaque from a tooth's root," says Dennis Mangan, Ph.D., director of
the Periodontal Research Program at the National Institute of
Dental Research in Bethesda, Md. (A periodontist specializes in
diseases of the gums and supporting structures of the teeth.) Also,
a laser could not produce the uneven edges carved intentionally
with a drill so that dental amalgam or other filling materials can
be retained properly. Lasers could not be used to repair existing
fillings either, because they would vaporize the amalgam component
mercury, which would make it highly toxic.
       But dental researchers are actively investigating the safety
and efficacy of lasers for hard tissue applications on freshly
extracted human teeth and in animal and human trials.
       Researchers at the University of California at San Francisco 
School of Dentistry carried out one human study using a pulsed
Nd:YAG laser at relatively low power. They used the laser on 163
cavities in 97 people at three private dental clinics in 1987 and
1988. At follow-up three years later that included 35 participants,
the areas where the laser had removed decay had all remineralized
well, with no complications.
       Still, much more study is needed before the dentist's drill
becomes a thing of the past. "The FDA feels there is not enough
support for use of lasers on hard tissues, and dental
organizations, such as the American Dental Association, do not
support non-FDA-approved laser procedures," says Miller.

A Look Ahead
       Despite the slow evolution of lasers in dentistry, researchers
say the day will indeed come when a variety of lasers play a more
prominent role in maintaining a healthy mouth. "And it won't be
just one laser that will do all dental procedures. Researchers
envision a laser unit in which you can switch on or off different
types of lasers depending upon the procedure," says Miller.
       "It's an exciting technology, and patients are really
intrigued at the idea of a laser. The lay press exaggerated, saying
now we can throw away dentists' drills. But research is showing
that we will be able to do that--eventually,fl she says. flBut we
haven't yet found the right laser."

Ricki Lewis is a freelance science writer in Scotia, N.Y., and
author of college biology texts.

Some Current Dental Laser Procedures
       Replacing conventional soft tissue dental surgery with lasers
often eliminates the need for sutures and anesthesia. Today lasers
can:
fl      Remove excess gum tissue, which can develop as a side effect
of taking certain drugs, poor oral hygiene, or orthodontia, in a
procedure called gingivectomy.
fl      Expose dental implants, replacement tooth roots made of steel
or titanium surgically embedded in the jawbone, which can become
covered with too much soft tissue. A CO2 laser can quickly expose
the implant for the dentist to work on.
fl      Relieve the pain of aphthous ulcers, mouth sores. Both CO2 and
Nd:YAG lasers can relieve the pain instantly--used on low power,
without an anesthetic.
fl      Remove excess tissue under the tongue in less than two
minutes, in a procedure called frenectomy.
fl      Biopsy or sample tissue from a lesion to see whether it is
cancerous. A laser biopsy does not require suturing and heals well.
This is particularly useful on the tongue, where bleeding can be
profuse.
fl      Remove soft tissue in the mouth to even out wrinkles that form
when a person smiles.
fl      Hasten clotting of bleeding caused by other procedures. 
--R.L.