Laser safety in dentistry
By Caroline Sweeney, MA, MBA, BSc
Featured in General Dentistry, November-December 2008
Pg. 653-659
Posted on Friday, November 07, 2008
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Although many regulations and standards relating to laser safety are in effect, there continue to be an average of 35 laser injuries per year.1 Laser safety professionals believe that this number under-represents the actual number of injuries and that many more accidents per year occur that are not documented with federal agencies.2 A review of these accidents has determined that failing to wear available eye protection is one of the most frequent contributing factors to laser injuries.1 As the purchase and use of lasers in dentistry continues to grow, so must concern for laser safety. This article provides basic information to advance the safe use of lasers in dentistry and to help establish laser safety protocols for the dental office.
Received: April 1, 2008
Accepted: June 20, 2008
When the topic of laser safety is broached, reactions can range from concern over cost to impatience related to the time-consuming activity of finding the correct pair of laser goggles. Unfortunately, accidents related to laser use have occurred and they are not novel events. In one case, a manufacturer supplied a medical doctor with an extra pair of goggles that were not the correct wavelength-specific product for the laser used. The doctor did not confirm that the product was correct and the beam passed through the goggles, resulting in an eye injury.3 Other medical accidents have included endotracheal tube fires, a CO2 laser inadvertently causing drapes to ignite, and an Nd:YAG laser causing hand burns.1 Although these accidents occurred in the medical setting, this should not diminish their relevance to the dental profession.
When laser energy is emitted, it is absorbed, scattered, reflected, and/or transmitted. Absorption is the main goal for treatment; however, dental structures offer a combination of all four interactions.4 When laser energy is used in dentistry, the intent is for the target tissue to absorb the energy. If the laser energy is not absorbed, it is either scattered (that is, the energy enters the tissue, spreads out, and dissipates) or transmitted (that is, it passes through the target tissue and continues on its beam path). Should the energy beam strike a reflective surface (for example, a mirror), it could reflect and damage an unprotected eye. It is imperative to reduce or avoid the number of reflective surfaces, mirrors, and mouth mirrors during laser use. Finally, the laser beam could be transmitted (through an eyelid, a window, or a curtain) and continue on its path to interact with unprotected eye tissues.
Hazards associated with lasers can vary, depending upon the type of laser and the situation for which it is used. Table 1 identifies some of the major databases that record laser accidents. Rockwell Laser Industries has surmised that the most common factors contributing to laser accidents were failing to wear eye protection, ignorance of potential hazards, and failure to adhere to safety protocols.1 Laser safety programs that are not put into practice can become a very expensive mistake. According to Barat, an assistant who suffered an eye injury claimed that the requirement to wear eye goggles was merely a paper policy and noted that the professor never did. She sued the university for $39 million but settled out of court for $1 million.2
Laser accidents have wide-reaching effects beyond the incident alone; such accidents make it necessary to halt the dental procedure, spend time comforting the injured party, and follow-up with the local hospital and/or ophthalmologist. These accidents also require dentists to file reports with insurance agencies and federal agencies. In some cases, the injury is not experienced immediately and the injured party (for example, a staff member) may return later to report the damage.
To determine the safety protocols associated with different lasers, it is necessary to understand the classification system used for these lasers.
Laser classification
ANSI Z136.1-2007 provides guidance for the safe use of lasers; it has been upheld by the
Class 1 lasers are considered to be incapable of producing damaging radiation levels and offer no risk when they are viewed with the naked eye (compact disc players are examples of a Class 1 laser).6,7 However, Class 1M denotes that the beam is potentially hazardous if it is viewed with an optical instrument, such as eye loupes, cameras, video recorders, or microscopes.
Emissions from Class 2 laser systems (such as laser pointers) range from 400–700 nm. The aversion reaction and/or blink response will afford protection against these low-powered lasers; it is believed that this protective response will occur in less than 0.25 seconds.2 One should not try to overcome the blink response and continue staring into the beam of the laser pointer. A Class 2M laser has the same characteristics as a Class 2 laser but this beam is potentially hazardous if it is viewed with an optical instrument.
Class 3 lasers are divided into two subclasses, 3R and 3B. A Class 3R laser is potentially hazardous under some direct and specular reflection viewing, provided the eye is stable and focused; however, the odds of actual injury are small.6 Class 3R lasers do not cause skin or fire hazards. A Class 3B laser may be hazardous in some instances involving direct and specular reflection viewing but it is not a fire hazard.6
Class 4 lasers pose eye, skin, fire, diffuse reflection, and plume radiation hazards; they also may produce laser-generated air contaminants. Nearly all dental lasers fall into this category. Table 2 provides an outline of these classifications, examples of associated dental lasers, and details regarding their hazards. Class 3B and Class 4 lasers must be operated by only trained, authorized personnel.8 Within the dental practice, these lasers require written procedural and administrative policies and the appointment of a Laser Safety Officer (LSO).
ANSI Z136.1 details very specific content requirements for laser warning signs. For Class 2 and 2M lasers, warning signs must include the word “caution” and the predominant colors yellow and black. Warning signs for Class 3 and 4 lasers must include the word “danger” and list their name, wavelength, and maximum output; red, white, and black are the predominant colors for these signs. Laser signs must be posted at every possible entrance into the room for the entire operation. When the laser is not in use, the warning signs should be taken down and not left up as part of the office wallpaper.
Terminology
Dentists who work with lasers also should become familiar with the terms Maximum Permissible Exposure (MPE), the Nominal Hazard Zone (NHZ), Nominal Ocular Hazard Distance (NOHD), and Optical Density (OD). According to ANSI, MPE refers to the level of laser radiation to which an unprotected person may be exposed without experiencing adverse biological changes to the eye or skin.6 The ANSI classification system means that it is not necessary to spend hours calculating MPEs directly. The NHZ is the space within which the MPE is being exceeded. For example, if a particular dental laser has an NHZ of seven feet, anyone within a seven-foot radius of this laser will have to wear the applicable protection gear. Once this boundary is established, people outside the boundary do not need to worry about protection. The NHZ can be a critical issue for dental practices whose operatories are accessible by openings rather than doors.
The NOHD defines the distance within which the radiant exposure exceeds the MPE. This space is further defined as the distance along the axis of an unobstructed beam from the laser, fiber end, or connector to the human eye. While it may appear that the NHZ and the NOHD are the same, the NOHD is specific to the eye. Anyone who expects to pass within the NOHD must wear wavelength-specific goggles; keeping one’s eyes closed will not help when high-powered lasers are involved, as the laser beam can transmit through an eyelid and cause damage in less than a quarter of a second.2 The dentist and/or the LSO should consider using barrier methods for open doorways and coating windows with wavelength-specific filters, as laser beams can be transmitted through glass. Should a laser beam’s NHZ extend beyond the operatory opening and into the hallway, other measures should be taken; these steps include marking the hazard zone in the hallways and placing warning signs at those locations. The warning signs are to be removed when the laser is not in use. In addition, protective eyewear that is specific to the laser in operation also must be placed outside the demarcations in the hallway and access to the hallway should be limited for unauthorized persons.
OD refers to the opacity of the laser protective material. According to the Academy of Laser Dentistry (ALD), the OD value should be 5 or higher.7 One also should refer to the manufacturer’s manual for this number as it relates specifically to the laser being used. Fortunately, the dental professional is not required to make these calculations, but dentists should not operate lasers without knowing the distance (in feet or meters) for the NHZ and NOHD or the numerical OD value. Although it has been suggested that the NHZ or NOHD are approximately 10 feet for Class 4 lasers, this number is meant as a guide and an approximation; it must not be taken literally and applied to every Class 4 laser.9 The manual provided by the laser’s manufacturer should always include values for the NHZ, NOHD, and OD as they relate to that laser’s operation. Different manufacturers might establish different numerical values for the same wavelength. For example, two different 810 nm diode lasers could have different NHZ values because their maximum output power (given in W) differs.
Non-target tissue hazards
The primary purpose of the laser-tissue interaction is the absorption of laser radiation, which causes a temperature increase that denatures tissue proteins.10 The build-up of carbonized tissue at temperatures above 200°C generally is accepted as damage and not as an intended result. It is necessary to document the parameters of the dental procedure, as well as the amount of time that the laser was used. It also is important to recognize that a laser might be absorbed by something beyond the intended target tissue. For example, at the time of this writing, a 10,600 nm CO2 laser has FDA clearance for soft tissue surgery; however, it also is highly absorbed in hydroxyapatite and can have unintentional effects on tooth and root structures.
Eye hazards
Laser users’ surprisingly common reluctance to wear the required protective eyewear is supported by the alarming number of eye injuries.11 Peer pressure can be a factor in this instance; if no one else in the room is wearing the safety goggles, it may be difficult to go against the existing organizational culture. Laser damage to the eye can lead to headaches, excessive watering of the eyes, and floaters (swirling distortions caused by dead cells that detach from the retina and choroid and appear as swirling distortions after one blinks because they are floating in the vitreous humor) shortly after the exposure (see Table 2).2
Retinal damage may go unnoticed because the retina lacks pain receptors; however, damage to this area can result in blindness, an inability to distinguish color, or diminished reading, working, and/or night vision.2 Sometimes an audible pop can be heard at the time of the exposure.2 The energy of a laser can be intensified 100,000 times on the retina due to the focusing effects of the lens and cornea.
Protective eyewear (either goggles or inserts for the users’ loupes) must be specific to the laser wavelength that is being used and must have side shields. The wavelength and OD value must be permanently inscribed on the goggles or side shields. The color of the lens on the goggles or inserts is no indication of the wavelengths for which they are suited. A given pair of goggles may list a variety of wavelengths and the OD value varies, depending on the wavelength. For example, a pair of goggles that lists only two wavelengths, one above the other (for example, 810 nm and 2,780 nm), protects the wearer from those two particular wavelengths and no other. If the inscription reads 810–2,780 nm, then all wavelengths between these outer ranges are covered.
No single goggle or insert covers the entire range of dental lasers from 810 nm to 10,600 nm; such a lens would be too opaque to see through. If the manufacturer’s manual states that a Nd:YAG 1,064 nm laser eye protection must have an OD of 7, then goggles whose inscription lists an OD of 7 for 810 nm and an OD of 5 for 1,064 nm will not offer adequate protection. The filter that coats the goggles and inserts can decrease visual acuity during laser procedures. The temptation to lift the protective eyewear during laser operation to observe the tissue interaction more closely must be avoided and performed only when the laser is in the safe “stand-by” mode.
The protective film on goggles and inserts will degenerate over time; improper storage, cleaning, and handling will accelerate that degeneration. Surface disinfectant sprays are too harsh and can scratch the protective coating. The Standard Proficiency Certification course from the ALD recommends washing protective eyewear with antibacterial soap and drying the eyewear with a soft cotton cloth. Inserts and goggles must be inspected frequently for any cracks, peeling, blisters, cloudiness, occlusions, frostiness, discolorations, crazing, and scratches that could reduce or eliminate the protection these goggles provide.
Dentists should put applicable laser goggles on patients as soon as they are seated in the chair. Patients are not to remove these goggles until they are ready to leave or until a change of laser warrants different protective eyewear. The dental team should have their eyewear close at hand and put it on prior to the start of the laser procedure; the goggles should remain on until the laser process is completed. Furthermore, it must be documented that laser goggles were used during the procedure; writing “LGU” (an abbreviation for Laser Glasses Used) is sufficient.
Skin hazards
Skin protective equipment with a close weave is required when the MPE is exceeded during use of a Class 3B or Class 4 laser.5 Given the OSHA requirement for personal protective equipment in dentistry, the dental team usually does not expose skin; however, patients might. Damage resulting from dental lasers can range from excessively dry skin to blisters and burns (see Table 2).
One should be careful with metal-tipped cannulas, as fiber-optic breaks inside these cannulas can go undetected. Thermal energy from the fiber could heat the metal tip, which in turn could burn a patient’s lip—and a patient may not notice the damage if he or she has been anesthetized for the procedure. Practitioners must know and observe tissue interaction during a laser procedure. If the target tissue demonstrates no change, it is possible that the fiber has broken and is not delivering thermal energy to the target site. The entire dental team must be vigilant on-site during the procedure to monitor for adverse events that may occur outside the primary dental structures. The FDA has produced a newsletter concerning electrical dental handpieces that have caused patients to suffer third-degree burns that resulted in corrective plastic surgery.12 Dental lasers also can cause fabric to burn.
Laser plume
As tissue interaction occurs, the resultant smoke plume not only hinders vision but contains debris that may include bacterial spores; cancer cells; viruses, such as the human papilloma virus (HPV), human immunodeficiency virus (HIV), and herpes; and such chemicals as hydrogen cyanide, formaldehyde, acrolein, and benzene.13 This debris may contain toxic gases (such as carbon monoxide and dioxide) and particulate organic and inorganic matter. This debris is commonly referred to as laser-generated air contaminants.
As far back as 1989, the FDA accepted that many surgical instruments (such as handpieces and electrosurgical equipment) contribute to airborne contaminants.14 Dentists should be concerned about surgical debris hazards in general, as few research studies have been performed on this issue.14
A 1998 study by Gelskey et al concluded that it could not identify compounds in the vapor emissions that resulted from using an Nd:YAG laser on extracted tooth structures but did recommend additional research.15 More recent studies concerning the laser plume have revealed that inhaled nanoparticles are far more toxic than microsized particles of the same element, contributing to lung damage and the formation of amyloid plaques.2 The most recent ANSI Z136.3 (2005), concerning the safe use of lasers in health care facilities, reports that the hazard area for laser-generated air contaminants may exceed the NHZ for the laser.16
Exposure to laser-generated air contaminants can produce a variety of symptoms, including coughing, watery/burning eyes, nasal congestion, nausea, vomiting, chest tightness, fatigue, abdominal cramping, and flu-like symptoms.13
Routine dental personal protective equipment (PPE) is an accepted safety measure for infection control during dental procedures, but additional measures—such as high volume evacuation and masks that are capable of filtering to 0.1 µ—should be present when lasers are used. Claymen and Kuo recommended keeping the evacuation system within 4 cm of the target site.17 However, other studies have said that the evacuation tube should be as close as 1 cm and that the evacuation ratio was 50% lower when the tube was 2 cm from the target site.18
Fire hazards
Given the thermal component of lasers, there is a risk of a fire if the heat generated through the laser beam makes contact with combustible materials and/or gases. A revision of ANSI Z136.3 (2005) allows dentists to use nitrous oxide and oxygen as long as a closed circuit delivery system is used and the scavenging system is connected to the high-speed evacuation system.19 Endotracheal tubes should have a wavelength-specific reflective coating to prevent the laser beam from burning a hole in the tube and combusting with the gases. Patients who are oxygen-dependent and carry a portable oxygen tank should either place their oxygen tank outside the NHZ during the laser portion of the procedure or should avoid the laser during the dental process.
In addition, dentists should avoid using aerosol products, alcohol-based topical anesthetics, alcohol-soaked gauze, or any other alcohol-based materials within the NHZ, as the laser could ignite such flammable elements. Patients should be advised to avoid using oil-based lip products and gels (two oil-based products, petroleum jelly and cocoa butter, frequently are found in lip balms), particularly if the laser is used to reduce a herpes lesion on the patient’s lip.
Although fire codes require that all dental practices have easy access to a working portable fire extinguisher, operating procedures also should occur near a source of water, such as a sink. A syringe of saline solution should be kept on the dental tray when a procedure could lead to an airway fire. Smoke damage and burns to the trachea and lungs can occur if the laser used in a procedure punctures the endotracheal tubes and ignites with the anesthetic gases.
Infection control
According to the CDC, critical items that are used to penetrate soft tissue or bone (such as quartz tips, optic fibers, and sapphire tips) possess the greatest risk for transmitting infection and should be sterilized by heat between patients.20 The CDC does not allow dentists to use a high-level disinfectant solution to wipe fiber-optic materials that make direct contact with tissues, teeth, and bones.
When the tip is a disposable fiber-optic, it must be disposed of in a sharps container. As the fiber is cleaved, all cleaved parts must be put into the sharps container. When a plastic canula is used to shape and hold the fiber-optic at the end of the handpiece, it can be disposed of with regular waste. Remaining coils of fiber-optic lengths are sealed in sterilization bags and put through the autoclave process according to the manufacturer’s instructions. Particulate matter must be cleaved off or wiped off the tip or fiber-optic prior to sterilization, for the same reasons that instruments are cleaned through ultrasonic systems prior to being placed in the autoclave/chemiclave. Laser handpieces are to be heat-sterilized and cleavers that contact blood/tissue on fibers should be sterilized by heat (or in cold sterile solution for 24 hours).20
The remaining components of the dental laser do not make direct contact with tissue, teeth, or bone. Noncritical instruments (including the control panel of the laser, the articulating arm, and the hollow waveguide) can be wiped down with a high-level disinfectant. At present, one Er:YAG manufacturer (HOYA ConBio) uses a large fiber-optic as its delivery system; however, this fiber-optic does not come in direct contact with tissue, teeth, and/or bone, unlike the fiber optic in the diode lasers.
Laser safety officer
The ANSI Z136.1 (2007) designates that an LSO must be appointed wherever Class 3B and Class 4 lasers are in operation.6 This person has the authority to monitor, control, and enforce adherence to safety protocols. The LSO has the authority to shut down laser operation in the event of non-compliance or safety concerns with the equipment and/or environment. If the LSO generally works in a non-management position, the dentist must ensure that other team members realize that the LSO has certain authorities. The administrative control duties of the LSO are listed in Table 3.
At present, only the ALD provides Standard and Advanced Proficiency certification in dental laser wavelengths. Many manufacturers will provide a certificate of training on their respective devices/models. The training received at the ALD Standard Proficiency level is sufficient for any dentist, office manager, hygienist, or assistant to become the designated LSO.
Engineering controls
Engineering controls refer to the safety mechanisms that the manufacturer has put in place to reduce the hazard potential of the laser. These include an on/off key or password protection (to prevent the laser from being turned on when authorized personnel are not present); safety interlocks (a mechanism on the panels and protective housing on the laser) that cannot be removed for servicing without rendering the laser inoperative; remote interlock jacks; a connector that will shut down the laser when the connecting door of the device is opened during laser use; a guarded footswitch (to prevent a person from accidently stepping on the switch and initiating the laser); an emergency stop button; software diagnostics (the laser’s own internal system, to identify an element that is not working correctly or attached properly); a system time-out (for example, if the laser is in operational mode and has not been activated within a specified time frame, the laser will switch its mode to “stand-by”); audible warning sounds; and visible warning devices (for example, a yellow light to indicate that the laser is powered up but not emitting and a red light when the laser is in operational mode). It should be noted that engineering controls are always preferred over administrative controls because of the human element involved with administrative controls.6
Summary
Lasers have offered exciting opportunities and outcomes to dentists. It would be sad to dampen enthusiasm for this technology due to careless and avoidable accidents. Failing to adhere to safety protocols can result in permanent damage. Time invested in education and the construction of sound operating polices should result in safe laser use becoming second nature to dentists and should free practitioners to enjoy using this technology.
Author information
Ms. Sweeney is chair of the Safety Committee for the
References
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13. Laser plumes—Health care facilities. Available at: http://www.ccohs.ca/oshanswers/phys_agents/laser_plume.html. Accessed March 6, 2008.
14. Bauman N. Is laser plume a health hazard? OR Manager 1989;5(1):1,7.
15. Gelskey SC, White JM,
16. American National Standard for safe use of lasers in health care facilities.
17. Claymen L, Kuo P. Lasers in maxillofacial surgery and dentistry.
18. Fisher RW. Laser smoke in the operating room. Biomed Tech Today 1987:191-194.
19. American National Standard for safe use of lasers in health care facilities.
20. Guidelines for infection control in dental healthcare settings—2003. MMWR Weekly Report 2003;December 19:1-61.
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General Dentistry, November-December 2008 , Volume 56 , Issue 7
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