Laser: A Boon during the COVID Pandemic in Aerosol Mitigation – A Systematic Review

Abstract

The scientific community was always intrigued by the indoor air quality in dental offices. The unexpected emergence of the COVID pandemic has put greater challenges on dental professionals. Shortly after the declaration of coronavirus as a pandemic by the World Health Organization in March 2020, the American Dental Association abstained the dental society from providing routine dental procedures. An evidence-based review of the literature was conducted electronically using three databases, PubMed, Science Direct, and Google Scholar between January 2005 to December 2021. Three articles were selected for the qualitative analysis out of 41 screened articles from the databases. The evidence suggests that there is a significant reduction in aerosol generation with laser when compared to conventional treatment modalities. Laser-assisted treatment procedures bring the dentist and patients a step closer to providing safe dental treatments and reducing the risk of transmission of disease.

INTRODUCTION

The air quality of health-care spaces has always been of importance to the scientific society. There is a risk of significant contamination from the emission of gases and particulate matter from the hospital equipment as well as infectious agents and microorganisms.^[1] Dental clinics and hospitals soar the risk of cross-contamination due to the “chemical air pollution” generated by the dental equipment and treatment procedures.^[2] The unexpected emergence of the COVID pandemic has put greater challenges on dental professionals.^[3] Shortly after the declaration of coronavirus as a pandemic by the World Health Organization (WHO) in March 2020, the American Dental Association abstained the dental society from providing routine dental procedures. Similar regulations for dental procedures were announced in various countries around the globe refraining the dental offices from nonemergency care.^[4] These restrictions were put forth based on the literature evidence demonstrating aerosolization of oral microorganisms and the SARS-COV2 virus. The aerosols hence generated harbor potent infectious agents putting the public as well as the dentist at a greater risk of contracting the disease.^[5]

AEROSOLS IN DENTISTRY

The majority of the dental treatments are mainly performed in a “wet environment” implying the saliva, blood, water coolant, patient’s normal breath, coughing, and gagging of the patient. These procedures produce “bioaerosols” in and around the dental operating spaces.^[6] In a series of studies on aerobiology in Dentistry, Micik et al. used the term “aerosols” and “splatter.”^[7–11] They defined aerosols as particles <50 μm in diameter. An aerosol is a collection of solid or liquid particles suspended in a gas, such as air.^[12] It is a heterogeneous system with particle sizes varying between 0.001 and 100 μ. These particles are small enough to stay suspended in the air for a prolonged time during which they can enter the respiratory passage. This specter of “aerosol-cloud” produced during tooth preparation, scaling, and air polishing is even conspicuous to the naked eyes. The smaller particles of an aerosol (0.5–10 μm in diameter) have the potential to penetrate and lodge in the smaller passages of the lungs and are thought to carry the greatest potential for transmitting infections. The virus typically has smaller dimensions and can easily float in the air. On analysis of negative-stained SARS-CoV-2 articles by electron microscopy, different researchers have had varying results, but the diameter of the virus has been found to range between 50 and 140 nm.

van Doremalen etal.^[13] estimated the stability of SARS-CoV-2 in aerosols and various surfaces and found that these viruses remain viable for up to 3 h in aerosols. The estimated half-life of SARS-CoV-2 in aerosols was around 1.2 h with a range of 0.64–2.64 h and 7 h on plastic surfaces and 6 h on stainless steel. WHO in its review in 2009 stated that viral infectious diseases are transmitted at an alarming rate in indoor spaces through aerosols.^[14] A retrospective study by Micik etal.^[9] for SAR-CoV-2 implied airborne transmission as the most likely mechanism compared to direct and indirect contact with contaminated surfaces.^[15] The dentist has the moral obligation of treating the patients safely and avoiding the spread of infection. The production of aerosols cannot be put to a stop but can be significantly reduced by utilizing “laser-assisted Dentistry.”

LASERS ASSISTED DENTISTRY

In this unsettled period of COVID pandemic, “laser-assisted Dentistry” is indeed a ray of hope to the dentist as well as the public. Lasers can be mainly divided into:

1. Aerosol-producing laser (erbium, chromium: yttrium, scandium, gallium garnet [Er,Cr:YSGG]; Erbium-doped yttrium aluminum garnet [Er:YAG]; CO₂–9.3 nm)
2. Nonaerosol producing (neodymium-doped yttrium aluminum garnet [Nd:YAG], CO₂–10.3 nm, diodes).

The aerosol-producing lasers or the high-power laser or the tissue cutting lasers produces laser plumes. According to the academy of laser Dentistry “laser plumes” or aerosols are produced due to laser-tissue interaction. Several ex vivo studies have demonstrated lower aerosol generation with laser procedures when compared with air-turbine handpieces and ultrasonics. Grzech-Leśniak and Matys^[3] extensively studied aerosol production with lasers (Er:YAG and Er:YSGG) to that of high-speed handpieces and demonstrated a significant reduction of aerosols with lasers. Laser-assisted treatment procedures therefore bring the dentist and patients a step closer to providing safe dental treatments and reducing the risk of transmission of disease. This systematic review was done to evaluate the effectiveness of laser as an alternative to high-speed handpieces in terms of aerosol or particulate matter production.

MATERIALS AND METHODS

Registration and reporting

The protocol for the study was registered with the Open Science Framework. PRISMA statement for transparent reporting of systematic reviews and meta-analysis was followed for the conduct of the report.

Eligibility criteria

Study design

1. Experimental studies including those involving modeling studies and manikins
2. Studies mimicking dental setups
3. Clinical trials
4. Studies pertaining to laser and aerosol mitigation strategies.

Population/intervention/comparison/outcome

Dental procedures involving aerosol generation are done on phantom heads or mannequins or clinical stimulation units. Procedures involved teeth preparation performed on extracted tooth or typodont. Studies included the use of laser tooth preparation as a mitigation strategy in aerosol production. Aerosol production was compared when using high/low-speed handpieces and laser systems with various parameters. The outcome was measured by the aerosol count or concentration or surface area in the procedural environment.

Exclusion criteria

1. Studies in languages other than English
2. Studies not relevant to dental clinical settings
3. Case studies or letter to the editors or commentaries.

Search strategy

An evidence-based review of the literature was conducted electronically using three databases, PubMed, Science Direct, and Google scholar. The search strategy was a timeline between January 2005 and December 2021. Previously conducted systematic reviews and cross references were also evaluated for potential studies. The keywords used were: “Coronavirus,” “COVID-19,” “SARS-COV-2,” “transmission,” “Contamination,” “infection control,” “dentistry,” “tooth preparation,” “laser,” “aerosol,” “splatter,” “mitigation,” “lasers,” and “high/low speed handpieces.” These MeSH terms or keywords were used for the search in combination with Boolean terms, AND and OR.

Screening process

Two investigators (KK and PM) independently carried out the search. Studies were initially screened by reading the title and the abstract. The duplicates were removed and the full text of the remaining articles was screened for the eligibility criteria by both the investigators. Any disagreements were resolved by discussion until they reached a consensus or were resolved by a third reviewer (HP).

Data extraction

A preplotted standardized form were used to extract the following: first author’s name and year of publication, study design, study objective, study comparison, laser parameters, and conclusion. The two investigators independently conducted this data extraction [Table 1].

Table 1: Characteristics of the included study

Risk of bias assessment and level of evidence assessment

The assessment of the quality of the papers was performed using Newcastle–Ottawa quality assessment scale [Table 2]. The level of evidence was rated in accordance with the “Oxford Centre for Evidence-based Medicine” ranking criteria as follows: level 1 (systematic review of randomized trials), level 2 (randomized trial), level 3 (nonrandomized controlled cohort/follow-up study), level 4 (case-series, case–control, or historically controlled studies), and level 5 (mechanism-based reasoning) [Table 1].

Table 2: Quality assessment of the studies using Newcastle–Ottawa Quality Assessment Scale

RESULTS

The initial search based on the keyword and MeSH terms in the 3 databases yielded 41 studies. Eighteen articles were excluded by the screening of title and abstract. The records that fulfilled the eligibility criteria were 23. Nine duplicates were removed. The remaining 14 articles were assessed for full text. Of the 14 articles assessed for eligibility criteria and data extraction, 11 studies were excluded due low quality or data could not be extracted. A total of 3 studies were included for the qualitative analysis [Figure 1].

Figure 1: Study selection

Characteristics of the included studies

Among the 3 included studies, 2 studies used Er: YAG laser and 1 study employed Er: YSGG laser. The studies were conducted in Greece, Spain, and Poland and were published in the year 2021. All the 3 included studies were in vitro experimental studies. Descriptive characteristics including technical details of these 3 studies are illustrated in Table 1. The included studies demonstrated heterogeneity with respect to the methodology and outcomes, hence a narrative summary of laser and aerosol production in the studies were hence undertaken.

Clinical settings

The experimental settings varied in the three selected studies. In one study, the clinical settings were duplicated using extracted teeth on a manikin. The clinical procedures were performed on the extracted teeth using Er: YAG Laser and high-speed handpiece and aerosol concentration was measured using PC200 laser counter 2 cm from the manikins, operator’s and assistant’s mouth.

Another study evaluated aerosol production by Er:YSGG laser and high speed turbine in a transparent box. The aerosol measurement was done by taking digital images of the fluorescent material with the help of ultraviolet light in a dark room. The air quality in another ex vivo study measured particulate matter production with Er:YAG laser using the standard method by EN legislation. The measurements were carried out in both stimulated environments of a small private clinic and hospital settings.

Procedure performed

Two among the 3 included studies performed class I cavity preparation and Class II preparation in the other study. A saliva ejector (SE) was used in two of the studies. In addition to SE, one study employed a high-volume evacuator (HVE) and another study used a rubber dam. One study did not employ any suction devices during the cavity preparation.

Laser parameters

Er:YAG (2940 nm) laser was employed in two studies and Er:YSGG (2780 nm) laser in another study. The tip diameter varied from 600 μ to 1 mm, frequency 10–50 Hz, energy 55–450 mJ and power 2–6 Watts. The water spray settings varied in individual studies and subgroups in those studies [Table 1].

DISCUSSION

Lasers have been widely used in Dentistry over the past 3 decades. With the introduction of laser in Dentistry in the late 1980s this technology was widely accepted by the dentist all over the globe due to its merits such as the absence of smear layer during tooth preparation, bactericidal nature, absence of noise and tissue selectivity, and the wavelength of the laser.^[7] Various treatments including tooth cutting, endodontic procedures such as access cavity preparation and irrigation, orthodontic procedures like debonding and soft-tissue management are effectively performed with lasers. The other added advantages of laser include low cutting pressure and less vibration when compared to cutting with a bur and minimal or no need for local anesthesia.^[16,17]

The production of heat and debris by the rotary instruments during function mandates the use of water coolant, resulting in aerosol production. Toroğlu etal.^[18] using the high-speed air-turbine, found a significant increase in environmental aerosols after 5 min of removing excessive adhesive material after brackets debonding. Harrel etal.^[19] demonstrated considerable aerosol and splatter production even in the absence of water coolant. Virdi etal.^[20] in their systematic review have stated that the use of rotary handpieces, high-speed handpieces and scalers contribute to the maximum aerosol production in Dentistry. The use of photonic energy for cavity preparation also employs water coolant that can contribute aerosol production/laser plumes. According to the Academy of Laser Dentistry, “laser plumes” or aerosol is produced due to laser-tissue interaction. Ex vivo studies on laser have demonstrated lower aerosol generation with laser procedures when compared with air-turbine handpieces and ultrasonics.

Grzech-Leśniak and Matys.^[3] extensively studied aerosol production with lasers (Er: YAG) to that of high-speed handpieces and demonstrated significant reduction of aerosols with laser. They validated that caries excavation with low as well as high-speed handpieces and SE brought about the maximum amount of aerosol particles. They observed that application of Er: YAG lasers decreased aerosol generation around two times compared to both conventional handpieces. Here Er: YAG laser of three different manufactures were employed with different laser parameters [Table 1]. Grzech-Leśniak and Matys.^[3] demonstrated hard tissue lasers when used in conjugation with HVE demonstrated significant reduction in aerosols than when used with SE. SE is primarily meant to prevent the pooling of saliva and coolant water during tooth preparation. They do not possess the power to limit the aerosol spread. However, HVE primarily reduces the splatter and aerosols and are compulsory during the use of aerosol generating procedures.^[21]

The aerosol or laser plumes produced during any procedures are mainly dependent on the laser water/air parameters and water coolant supply. Two among the three studies evaluated the significance of water/air ratio in aerosol production.^[3,22] Abdelkarim-Elafifi etal.^[22] used 80% and 40% of water respectively in the two laser groups for cavity preparation. The results of this study demonstrated that high speed turbine contaminated 70% and 73% additional surface area while using 80% and 40% water, respectively. The water and air ratios mainly impact the photothermal effects on the adjacent tissues. Variation in the air/water spray, results in lower or air and water supply and is conveyed and aimed toward the laser beam to a lesser or greater extent.^[23] Higher the air/water percentage plays a paramount role in tissue ablation, significantly impacting the laser-tissue interaction and enhancing the tissue cooling and cleansing action. However higher this ratio, greater the aerosol production.^[22] A reduction in power with reduced water and increased pulse repetition rate can compact for the heat dissemination. Conventional handpieces demand specific air pressure to function and cannot be modified leading to significant aerosol production. Laser handpieces hence have an upper hand over conventional handpieces over aerosol production and heat dissemination over the adjacent tissues.

The laser tips used and water coolant system in the handpieces also influences the aerosol production.^[3] The laser systems employed will have a single discharge channel as in AdvErL Evo laser or multiple discharge channel as in LightWalker and LightTouch laser. In addition to the variations in the laser tips, differences in the laser water coolant systems also influence the aerosol production. When the water is transported through a single discharge channel, it results in comparatively lesser aerosol production than when compared to water discharge through three channels. Er: YAG lasers with these variations in the tips designs and water coolant systems demonstrated higher aerosol reduction when compared to high-speed handpieces.

Er: YAG laser when used for hard tissue cutting produces significant particulate matter in the working environment.^[2] Karveli etal. species the importance of ventilation during laser procedures as this significantly reduces the particulate matter in the indoor air. The use of a physical ventilation and high suction devices significantly compacts these challenges. However, in their research with laser and particulate matter production, by Karveli etal. there was no comparison done with the conventional handpieces.

Any dental treatment despite following utmost protection protocols inherently produces aerosols and splatters. Photonic sources of energy can be employed in this current scenario of COVID pandemic. The past 2 years have been a major challenge for dentists worldwide, with the pandemic putting constraints over the treatment procedures and risks of spreading infection. Dentist has the moral obligation of treating the patients in the safest manner and avoiding the spread of infection. The clinical set ups are now equipped with air cleaning systems such as high efficiency particle absorbing filters to improve the air quality and mitigate spread of infection. The use of lasers provides an added benefit in mitigating aerosol production and cross-infection.

Laser Dentistry can be well utilized by the “dental out-reach programs” targeting the socioeconomic backward classes. The pandemic has deprived the backward class of the society of basic amenities as well as health facilities. Community-based programs employing “laser” can effectively help the dentist as well as the patient. Employing laser can mitigate the aerosol production thereby protecting the service provider. The application laser in Dentistry varies significantly based on the wavelength employed. Apart from cavity preparation, lasers can be employed for caries prevention, dentinal hypersensitivity, bleaching, and for diagnosis of lesions of dental hard tissues.^[16,24,25] The property of laser fluorescence can be employed for caries detection in addition to visual examination in dental outreach programs. According to the goals set by the WHO, for effective caries diagnosis adequate diagnostic aids have to be employed in dental outreach programs.^[26] Laser diagnoses have a better detection potential of the incipient carious lesion and are highly specific.^[27] Lasers can demonstrate the internal structure of teeth and any de-arrangements in the microstructural organization can be evaluated by an experienced dentist. The ability of laser for caries prevention adds further benefits for its employment in outreach programs.^[28] Studies provide evidence that laser can be well employed in fearful and anxious children as it is relatively painless compared to regularly used caries detection and removal techniques.^[29–31] With the advantages of minimal aerosol production, caries detection and prevention lasers can be effectively used in school-based programs and services.

While using lasers safety rules as well as protocols should be followed by the health-care providers. All the procedures must be performed under rubber dam to avoid viral contamination from mouth and saliva. Darker rubber dam sheets tend to absorb higher laser energy and metal clamps tend to reflect the laser light. For the dentist and assistant protection gloves and gowns to be used along with Google, eyeglasses, face shields, and FFP2 or FFP3. A suction system with a high-flow volume and good filtration, positioned at the closest distance from the surgical site to avoid nosocomial viral dissemination.

Limitations

The research done on laser procedures and aerosol production is minimal. Further studies and clinical trials have to be undertaken to establish the significance of aerosol and particulate matter production by lasers. The studies compiled consisted of only tooth preparation. The widespread use of lasers in the field of endodontic, prosthetic, orthodontic, and surgical treatment procedures have to be evaluated for aerosol production and mitigation. Another major disadvantage of laser is its cost-effectiveness.^[32] The major reason for the lack of effective use of laser in dental practice is its cost and maintenance. With further advancements in laser technology and cost-effectiveness, “the future” holds good for laser Dentistry.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.