Laser-assisted dentistry, safety, and cross-infection control: A narrative review

International guidelines and recommendations

Guidelines relating to lasers mainly provide international standards for electrical, electronic, hazard prevention, and biosafety to avoid some tissue damage (eye, non-target oral tissue, and non-target skin). Recommendations are limited or generic when it comes to IPC [1,2,10,51] or are dated [32,51] and are mainly related to reducing aerosol by LD. Two recent documents focused on the ICP benefits of using various laser treatments in daily practice during the COVID-19 pandemic [2,52], and biosafety recommendations related to the type of laser are limited [3]. Knowledge of device functions and the choice of appropriate parameters are important to reduce aerosol and LP formation, as well as the selection of the proper precautions. It is important to choose optimal laser parameters that allow for both concomitant clinical effects and adequate cooling (~8–24 ml/minute), limited aerosol production, and microbial spread by reducing airflow and water spray [1,2,6]. However, the choice is difficult without detailed information for users (IFU) from producers, more interested in clinical efficacy. Concerning health settings, occupational hazards of DHCP caused by surgical LP and indoor air components are an increasing area of interest for international boards involved in ICP [10,51–55] and the CDC’s latest recommendation underscores the need to optimize the use of engineering controls for appropriate indoor air quality [56]. A recent review on the use of lasers in prosthodontics reported that aseptic techniques with strict adherence to the infection control protocols are necessary and it is crucial to prevent any potential cross-contamination or infections [11]. This includes proper sterilization of laser tips or handpieces or any instruments coming in contact during all procedures. Unfortunately, no details have been reported. It is essential that up-to-date guidance on key issues is available, in line with the regulatory framework and improved IFUs from manufacturers and, issued by statutory professional bodies. The laser safety manager and cross-infection control coordinator must work together and have a duty to ensure the safety of patients and the dental team concerning specific dental settings and the classification, type, and use of the laser. The issue of quality (clear guidance), transparency, and review of IFU is emerging [57]. 84% of cross-infection prevention coordinators have had to contact a manufacturer for clarification on the correct cleaning, disinfection, or sterilization of a product and 8% of them have taken the additional step of contacting the Food and Drug Administration for clarifications on the Instructions for Use.

Pre-procedural mouthwash before LD

Data have shown that pre-procedural mouthwashes containing antiseptic agents can help to partially reduce the bacterial or viral burden in the oral cavity or dental aerosols [58]. However, evidence-based efficacy of pre-procedural mouthwash to prevent SARS-CoV-2 and other virus transmission still is lacking [59,60]. The choice of pre-procedural mouthwash for LD deserves some attention. The high temperatures that can occur when using Class IV and certain Class IIIB lasers can themselves cause or contribute to the ignition of flammable dental materials [ethanol (flash point = 14°C), isopropanol (flash point = 11.7°C)] and gases [1]. In the absence of a recommendation, we agree with the indication of precaution described as “No-alcohol based liquids to be used in preparatory or laser-based treatments” to a low-risk assessment [1]. We think that it would be better to use alcohol-free mouthwash [Chlorhexidine digluconate (CHX): 0.05% plus Cetylpyridiniumchloride: 0.05%] or ensure that all oral areas treated with alcoholic mouthwash are completely dry before starting the procedure. This precaution is important because many CHX-based mouth rinses contain 11.6% up to 22.7% alcohol and povidone-iodine-based mouthwash contains 30.5% alcohol (w/v) and ethanol has a flash point of 14°C. In addition, studies are needed on the degradation of CHX by different laser light, increased temperature, and in the presence of other endodontic irrigants to toxic compounds (mainly p-chloroaniline, p-chlorophenylurea, and so on). In particular, P-chloroaniline, is considered to be carcinogenic (Hazardous Substances Data Bank -HSDB-: a database of the National Library of Medicines TOXNET System, 2014).

Indoor air quality during laser dentistry

Indoor air pollution (IAP) is a major cause of diseases (asthma, heart disease, stroke, lung cancer, and possibly dementia) [61] and the occupational consequences of IAP and surgical exposure to LP include irritation of the respiratory tract and eyes, headaches, nausea, and muscle weakness [1,62]. DHCP spend 30%–40% of their time in dental environments and therefore breathe potentially polluted indoor air. Then, researchers and policymakers are increasingly interested in the air quality of dental care facilities [2,4–8,63–65], in the multi-factorial causes and pathological consequences (risk of airborne diseases) of unclean indoor air, and obviously in preventive measures. According to the particle size, PM is classified into:

• coarse particles (particles with aerodynamic equivalent diameter less than 10 µm, PM₁₀)
• fine particles (particles with aerodynamic equivalent diameter less than 2.5 µm, FPs/PM_2.5)
• ultrafine particles [particles with aerodynamic equivalent diameter less than 100 nm, ultra?ne particles (UFPs)].

It is known that microbial contamination occurs mainly during aerosol-generating dental procedures (AGP); however, the understanding of the level, spread, and half-life of the contamination and the atomization mechanism is still limited [63,66–69]. Recently, data showed that air contamination (78%) is caused mainly by the cooling water from DUWL contaminated with biofilm [70]. In addition to microbial, endotoxin, and mycotoxin, the main indoor air contaminants are: PM of different dimensions (Ø: nanoparticulate (<1 μm); 1–2.5; 2.5–5; 5–10 μm), volatile organic compounds (VOC), CO₂, SiO₂, Be, Hg, heavy metals, As, Cd, and Ni [63]. The levels of CO₂, PM_2.5, and VOC_tot present in the indoor air of dental offices are higher than in other healthcare settings [71,72]. A recent review provides an overview of inhalable PM-induced infectious diseases [73]. Interaction between airborne PM and bacteria makes humans more susceptible to otherwise harmless bacteria, particularly in the upper airways. Pathogenesis induced by PM exposure includes damage to airway epithelial cells, alteration of the immune response, dysregulation of the microbiota, and suppression of the host immune response [73]. Then, opportunistic and/or pathogenic bacteria (such as Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis, P. aeruginosa, or Staphylococcus aureus) commonly found in dental settings may more easily establish respiratory infections and increase occupational risk.

Particulate, bacterial, and fungal aerosol contamination in five wards (pediatric, periodontics, prosthetics, restorative, and endodontics) of a university dental clinic is very complex [74].

Due to clinical benefits for dental practices, LD was proposed as a winning strategy during the COVID-19 pandemic. The contaminated area during Class I cavity preparation procedure is reduced by 70% using Er,Cr:YSGG laser compared to a high-speed turbine [75]. During caries treatment, the laser use reduced aerosol PM by approximately 50% in the patient area and approximately 10% in the dentist area, compared to using a dental turbine; no difference in indoor air contamination has been observed in the dental nurse area [76]. The number of aerosol particles (PM 0.3–10.0 μm) during caries treatment and debonding of the ceramic crown using three tested Er:YAG lasers is significantly reduced compared to conventional handpieces [5]. When HVE is running, the mean level of aerosol particles measured in the manikin’s mouths (the worst place for measurements) was 64.1, 55.1, 29.4–30.6 × 10³, respectively, using a high-speed handpiece, a low-speed handpiece, and three lasers (Morita, Fotona, and LiteTouch). Additionally, using laser plus HVE, aerosol particle reduction is approximately about 45% compared to low-speed handpieces and 55% compared to high-speed handpieces [5]. When using lasers plus a saliva ejector, the reduction is roughly about 45% compared to low-speed handpieces, and 55% compared to high-speed handpieces. Furthermore, in the presence of good office air ventilation and HVE functioning, three Er:YAG lasers did not generate significant changes in aerosol PM levels during the debonding of the orthodontic bracket [5].

However, new data on indoor air contamination by LD do raise some doubts about the real advantages of aerosol prevention and biosafety [2–4,6–8,36,77,78]. The chemical and biological hazards of airborne components generated by lasers have been known since the first position paper on laser safety in dentistry [53]. It is known that explosive processes produce tissue ablation and aerosol formation, while thermal actions that create vaporization, produce a smoke plume, containing water (95%) and 5% containing blood, particulate, and microbial matter [2,6,69]. Nevertheless, the different characteristics of dental lasers (section “The main features of different lasers important for ICP”) influence AGP or smoke plume, and the lack of standard irradiation parameters in clinical applications make very difficult the comparisons between studies. Despite the limited available knowledge, we selected some interesting data in the case of different laser care (endodontic therapy, conventional dental procedures, and surgical care):

1. Lasers are considered a valuable adjunct treatment in endodontic therapy [1,79,80]. Unfortunately, the evaluation of aerosols during root canal irrigation with all lasers tested showed insignificant differences compared to endodontic needle irrigation alone, and the LP could present the hazard of bacterial spread in simulated endodontic care [81,82]. Because of their strong water absorption, Er:YAG and Er, Cr:YSGG lasers are ideally suited for activating irrigating solution in endodontics by warming (5.5°C–7°C as the limit of acceptable temperature increases on the root surface) and cavitation [1]. Apart from a certain degree of confusion in the terminology used in photodynamic disinfection [1] and the variety of photothermal disinfection protocols, care should be taken to optimize cavitation dynamics, reduce collateral thermal effects on the roots, and avoid carbonization [1]. Importantly, when a liquid is heated and the kinetic energy of molecules increases, there is a reduction in viscosity and surface tension, allowing for better fluid flow and enhanced contact of irrigant solutions with the root canal walls. Unfortunately, this fact could increase the dispersion and airborne particulates, which are removed using HVE supplemented by auxiliary methods.
2. More recently, highly increased levels (+40%) of air (UFP, PM_0.1) are present during some conventional dental procedures (drilling, grinding, root canal filling), but also at very high levels during some laser periodontal treatments (30.000–250.000 UFP counts/cm³) in multi-chair dental clinics [78]. Despite the high variability, the mean and peak concentration of UFP by laser periodontal treatments is double that of those caused by US and like that by classical endodontic filling [78]. In this case, the efficacy of HVE might not be enough [78]. During some laser periodontal treatments, UFP contamination is like those caused by drilling, grinding, and root canal filling. Recently, Karvely investigated the levels of PM₁₀ and PM_2.5 in indoor air during the use of the laser (Er:YAG, 2,940 nm) for the preparation of cavities in human teeth under conditions of insufficient or absent ventilation [36]. During cavity preparation, levels of PM₁₀ and PM_2.5 are 10–15 times higher than contamination in the absence of dental activity. VOC, PM_10, and PM_2.5 levels are higher than what is deemed safe.
3. The risk of LP hazards is expected during the use of all class IV lasers (surgical lasers) and in dental caries management [1]. For example, during Er:YAG laser use, any dentist has perceived the odor that spreads into the surrounding environment. The biological tissues vaporize at 100°C–200°C and the smoke is formed in the shape of a plume. 77% of the particles in the surgical smoke produced by lasers have a Ø < 1.1 μm with an average of 0.07 μm, which falls within the inhalable PM range [77]. The diameter of visible PM is at least 20 μm. Surgical LP (Ø 0.1–5 μm) can spread bacteria viruses, VOC (carbon monoxide, hydrogen cyanide, formaldehyde, benzene, and acrolein), and cancer cells [1,2–4,7,8,53–55,82]. A recent literature review identifies the potential hazards of surgical smoke in dentistry [82]. However, electrosurgical smoke seemed to be potentially more hazardous than laser smoke [82]. Although there is no evidence of lasers used in dental operating rooms, E. coli, Staphylococcus aureus, HPV, HIV, and HBV have been detected in surgical LP produced by simulated experiments, dermatology, and otolaryngology [6,53,68,81]. During the treatment of oral HPV-related lesions, DHCP must consider that the surgical LP is infectious due to its possible contamination with HPV-DNA [83]. VOC are also present when using low-power CO₂ and Nd:YAG lasers [84]. DHCP should always remember that acrylonitrile hydrogen cyanide and many other VOCs are TOXIC, VOLATILE, and ODORLESS. Even if there are limited data on laser-generated air contaminants, including VOCs, in dental settings, it is expected the exposure and then both acute and chronic health effects in DHCW [1,85]. The detailed health effects of chemicals in surgical smoke and their exposure limits have been reported [82].

Recommendations for indoor air quality in dentistry

Waiting for better data on airborne contamination during LD to sustain evidence-based recommendations, the precautionary principle should be applied. Then, contaminated airborne hazards during LD, must be limited by using different procedures (HVAC, ventilation, evacuation (HVE as close as 1 cm from the target site), extraoral evacuation, and portable air purification system). The evidence is rather cloudy on their different efficacy when it comes to the control of dental indoor air when used alone or concurrently, and, above all, during LD [86–96]. It is well known that the evacuation system is designed to remove fluids, air/gas, and particulates with different efficacy. The following data are then expected. Evacuation systems should remove particles as small as 0.3 μm with at least 80% efficiency. However, during carbon dioxide laser surgery and using the HVE at 2 cm, the evacuation ratio decreases by 50% [85]. Then, it is uncertain whether it is effective to stay far away from 4 cm to remove the LP, based on old evidence [1].

More recent data on HVE efficacy are not reassuring: a) PM₁ removal is null at 30 cm, b) PM_>0.5, and PM₁₀ removal is approximately 35% using HVE at 8,5 LPM [97,98]. The efficacy in reducing PM (PM_tot 0.3–10.0 μm) depends on the type of saliva ejector type (intra vs. extraoral), its shape and diameter, and the distance from the source of contamination [76].

The main strategies (patient placement position; the position of air purification system) to prevent the spread of pathogens are shown in the section “dental facilities” of the latest recommendations [30,56], in addition to the ANSI/ASHRAE/ASHE Standard 170–2021 guidance on ensuring that ventilation systems operate properly, and other options to improve indoor air quality [97]. Concerning indoor air quality, the recommended levels of CO₂, PM_2.5, and VOC are < 800 ppm, 5 µg/m³, and <150 ppm, respectively [71,72]. For general dentistry, the current recommendation for ventilation, in terms of air changes per hour (ACH), is at least 6 for dental rooms, and 15 during the AGP [98]. The operation of ventilation and portable air purifiers is recommended up to 2 hours after the end of dental work. We also would like to briefly focus on indoor air quality monitoring systems [99], generally called sensors, which we are evaluating in our dental practices to control indoor air quality by CO₂, VOC, and PM levels [76,100,101] and to check if the mitigation strategies (HVAC system, HVE use, ventilation, portable HEPA air purification systems, patient orientation) are working properly [102,103]. In addition to engineering control, they are useful for controlling the maintenance costs associated with HEPA filters on air filtration units. Three sensors are shown. They have reasonable costs (350–1000 €), but different parameters, range of use, and the check of specific VOC, partly suitable for LP detection (Table 3) [104–106]. Alternatively, airborne microbiological testing (by culture-based methods and MALDI-TOF MS) can be used [107]. These procedures are time-consuming, tedious, and more expensive for private dental practices, and the relationship between airborne bacteria and PM is unclear [108]. Wells–Riley equation has been used extensively to quantify the risk of indoor airborne infection, and the average indoor CO₂ concentration should be kept below 700 ppm to control the risk of indoor airborne infection [109]. To delve deeper into the topic, we recommend the sections “better IFU and research priorities” to readers.

Table 3. Examples of sensors for indoor air quality and use in private dental settings [76,100,101]. [Click here to view]

Uses of PPE

PPEs are at the bottom of the hierarchy of defense and the last line of defense against IPC for all DHCP; for this reason, their quality related to filtration or isolation is determinant. In terms of occupational safety, PPE includes disposable clinical gloves, disposable well-fitting (tight face-fit) filtering facepiece (FFP) respirators, face shields/goggles/protective eyewear, and fire-resistant gowns. During LD, the main problem is related to the choice of surgical mask and FFP. During the COVID-19 pandemic, face masks were recommended by most documents (94%), with 91% also specifying the use of goggles or face shields [110]. Face masks (Type II or Type IIR) represent a mitigation strategy to lower airborne disease transmission. The use of N95/FFP2, which removes at least 95% of particles as small as 0.3 μm, is recommended during AGPs [56,111] and surgical procedures, in poorly ventilated areas according to NIOSH recommendation [112].

There is ambiguity regarding aerosol-generating lasers (erbium, chromium: yttrium, scandium, gallium garnet [Er,Cr:YSGG]; erbium-doped yttrium aluminum garnet [Er:YAG]; CO₂ -9. 3 nm) and AGPs are “non-risk stratified for transmission” [113]. Although they are not yet included in the dental equipment known to generate aerosols and airborne contamination (ultrasonic scaler, high-speed dental handpiece, air/water syringe, air polishing, and air abrasion), we consider it reasonable that an N95 mask or FFP2 should be used to limit the inhalation of contaminated LP, in line with recent data reported in the section “Indoor air quality during laser dentistry”.

Fluid-resistant surgical facemask for routine care and FFP3 or hood for AGPs is recommended as respiratory protection for healthcare workers during the prevention of 24 suspected or confirmed pathogens showing droplet/airborne routes of transmission [114]. The major international and national health organizations, including the WHO, the European Centre for Disease Prevention and Control, the US CDC and Prevention, and Public Health England, have identified guidance on the reuse or prolonged use of surgical masks or FFP respirators only during the COVID-19 emergency. Surgical masks and FFP/N95 respirators are now considered disposable medical devices.

However, the effectiveness of these PPEs relies heavily on correct usage and a secure fit to the individual’s face. A false form of protection is to cover an N95-FFP respirator with an overlying face mask [115]. Face shields may reduce the inhalation of harmful aerosol particles for a short time, and, to a different extent, concerning the dimension of the particles [65]. When considering the choice and the use of FFP, we must consider that dental lasers have inherent antimicrobial properties and are expected to kill viruses or non-sporulating bacteria with which the beam comes in contact at temperatures in the range of 50°C–60°C [1]. This conclusion does not consider that many bacteria grow in oral biofilm and are much more resistant than planktonic bacteria. Periodontal pathogens are well known to be very resistant, highly adhesive, and biofilm-forming, and little is known about their thermostability [116]. Finally, temperatures (60°C–100°C), normally used for adjunctive nonsurgical periodontal and peri-implant disease laser therapy, do not affect the viability of spores [117,118] and unknown effects on some hyperthermophile infectious agents, multi-drug-resistant (MDR) microorganism, or those having sporulation genes or sulfate-reducing metabolism [119]. Then, it is not surprising that there is low-level evidence that adjunctive use of diode laser for scaling and root planning may provide some additional benefit in terms of reduction of red complex bacterial count and improvement in clinical periodontal parameters [12–16]. So much so that, different nanomaterials have been proposed for the photothermal killing of MDR bacteria to increase laser clinical efficacy [120].

Taking all from the IPC point of view, we cannot be sure that laser-assisted treatments destroy all periodontal bacteria and render what is produced without danger of cross-infection. Then, the choice and the correct use of PPE, in particular the adaptation to the face of the surgical face mask, FFP2 or FFP3, is important for DHCP during dental care. Recently, some researchers pointed out criticalities in the use of FFP2 masks related to different professional roles within the overall group of HCWs, stressing the need for an FFP2 human-centered design that accounts not only for physical needs but also for workload and task variability [121]. Finally, DCHP must be vigilant to avoid buying misrepresented respirators, which are all respirators that are falsely marketed and sold as NIOSH-approved respirators or have fake CE marks [122].

Hand hygiene

Hand hygiene is the main standard precautions [29,30,32,55]. Despite the relevant cost-savings associated with hand hygiene, compliance with hand hygiene remains low (educators: 63.7%–78.4%; students: 35.1%–45.8%) in dental school, and violations are significant, even during the COVID-19 pandemic [123,124] and increased attention to limit transmission. Unless hands are visibly soiled, an alcohol-based hand rub (ABHR; 70%–90% alcohol mixture) is preferred to soap and water in most clinical situations due to evidence of better compliance compared to soap and water [125,126]. Because of fire hazards [1], before LD, DHCP must ensure that all alcohol has evaporated and the ABHR bottle is perfectly closed and far from the laser beam. An open bottle of ABHR causes an early alarm for VOC using an AQ sensor [104].

Reconditioning of LSE

During laser care, LSE is needed for both the patient and DHCP [1]. They must have a CE marking, writing down compliance with the PPE regulations and the desired characteristics for laser beam protection [127]. According to PPE Regulation EU 2016/425, manufacturers must specify a rated shelf life and operational life for their products. Indicatively, safety glasses can technically last up to 3 years if they have not been compromised [128]. This creates added costs regarding laser treatments because of the need to replace them following IFU. Polycarbonate lenses are the most popular type used in LSE. They contain a wavelength-absorbent dye and a coating on the surface to limit scratches; scratches can cause the beam to burn through the filter material more quickly, thus causing ocular damage. The LSE would be reconditioned after use avoiding procedures that could cause the filters to crash and damage the elasticized band, required to secure the eyewear around the head. Some indications for LSE reconditioning are present in IFU from different producers, but they are unclear. In general, hand washing is allowed only with a gentle household cleanser. However, immersion or soaking is forbidden. Alternatively, alcohol (about 20% isopropanol) impregnated wipes could be used, while bleach is not recommended as it can damage the lens [129]. In general, it is advisable to be careful when using alcohol-based disinfectants compatible with synthetic materials and to follow the IFU. An IFU does not allow the use of harsh or acidic cleaners isopropyl alcohol or disinfectants [130]. Most LSEs can be adversely affected by disinfectant solutions (solutions of 70% alcohol) indicated for SARS-CoV-2 inactivation [131]. Products for cleaning and/or disinfection with a hydrogen peroxide (pH 2-3) base are never considered in IFU. Never use abrasive cloth or paper-based textiles and never place LSE in a steam autoclave, even when using the “plastic material cycle”. In general, IFU are scarce and focus more on material stability than IPC. See the section “Clinical contact surface disinfection” for the selection criteria for a disinfectant for clinical contact surfaces (as LSE).

Standards for the reconditioning of laser accessories

We agree with those indicated in the “standard 7” of recent guidance [52]. Steam sterilization must become the standard for the reconditioning of laser accessories (fiber, handpieces, and tips) in dentistry. Because improper reconditioning can damage equipment and accessories, producers must give clear indications in the IFU on cleaning, disinfection, and steam sterilization. Recently, some laser handpieces, in particular scalpels and laser handpieces, have some important features (autoclavable design, improved cleanability, reduced porosity of surface, and anodized finishing) leading to easier reconditioning phases. Currently, available handpieces are designed to meet the requirements for sterilization between patients and the ADA recommendations [10]. The main weaknesses of ICP in the three main phases of reconditioning (cleaning, disinfection, and sterilization) [132–134] are:

1. A clear indication that plastic delivery tips (called mini tips or disposable tips) are single-use;
2. Cleaning procedures of autoclavable tips and laser handpieces (often made of anodized aluminum alloy), with attention to the type of detergent/enzymatic cleaning solution with a neutral pH and to the limited compatibility with alkaline cleaners (normally used in washer-disinfectors);
3. Many questions on cleaning procedures of optic fibers. Does it clean immediately after use or within a maximum of 1 hour after the LD? Does it use enzymatic and/or low-foaming detergents? Should aldehyde-based disinfectants be avoided to prevent occupational hazards (asthma) and the reduction of the light transmission of the laser fiber or its damage [133]?
4. According to many IFUs, the laser fiber can be inserted in tabletop autoclaves EN 13060 Class B. In general, the cycle for thermolabile items is indicated (normally 121°C for 15 minute). However, the IFUs do not report the maximum number of steam cycles that guarantee the main optical and mechanical properties of the fibers and the connector. It should be noted that so far little data has been reported on the possible effects of sterilization on optical fiber properties [134]. In a steam autoclave, the fibers are exposed to the combination of high temperature and highly concentrated water vapor; this may cause cracking of the polymer coatings and/or deterioration of the glass cladding surface. The strength of the laser fiber also depends on the different coatings of the fiber (i.e., double acrylate, polyimide, silicone/PEEK, and fluoroacrylate/ETFE hard coating). Considering the properties of the laser fiber, the average strength of the fiber was found to be stable when the fibers were exposed to 20 cycles in a gravity autoclave (132°C for 8 minutes) [134]. However, multiple autoclaving cycles caused stress corrosion cracking of the acrylate fiber and slight changes in fiber spectral attenuation for silicone/PEEK and 200/HCS/ETFE fibers alone [134].

Environmental IPC: from the clinical contact surface disinfection to the use of transparent barriers

Clinical contact surface disinfection

DHCPs need to adopt surface disinfection (spray disinfectant/wipe/spray disinfectant decontamination method) [135] in the cases of:

1. Large-diameter erbium fiber-optic cable that is not designed for steam sterilization;
2. Frequent use of the fiber and handpiece compared to the slowness of the reconditioning process;
3. Protective housing around the laser, including the control panel and articulating arm (if applicable), the dental cart, and countertops.

Following IFU, special care must be dedicated to the disinfection of laser devices, buttons, and touch screen, and their accessories before and after their use, and by selecting the appropriate disinfectant [fast active (1–2 minutes contact time), a broad spectrum of activities, compatible (containing 20% alcohol or less) for plastic, metals, and laser fibers] [135].

The use of transparent barriers

Further precautions must be taken, including the use of disposable transparent barriers (food use barriers, medical grade barriers, adhesive disposable protective film) for two main reasons. First, the aim is to protect the laser tips and avoid direct contact with oral tissues during low-level laser PBM; alternatively, the tip should be sterilized. Second, to shield the dental laser cart and countertop instrument, in particular, the switch on/off from environmental contamination and the contaminated glove touch of the clinicians at the end of LD. The reduction of laser output power (at red and infrared wavelengths) by using two latex-free protective materials [polyethylene and polyvinyl chloride (PVC)] has been reported by Nogueira Rodrigues et al. [136]. PVC is the most suitable for the protection of the tip of low-power lasers (both red and infrared wavelengths) because its main absorbance is in the range of 200–300 nm, while polyethylene absorbance has peaks at 720 nm, about 732 nm, about 1190 nm, and 1,250 nm [136].

Selection criteria for disinfectant for contact surfaces in dental clinics

IFU of lasers and its accessories contains limited indication about the importance of disinfection efficacy. The 2003 CDC guideline for dentistry specifies that after each patient the clinical contact surfaces (as LSE) must be cleaned and disinfected with a certified low-level (against HIV and HBV) or medium-level (against TBC) disinfectant when the surface is visibly contaminated with blood or other potentially infectious materials [32]. The list of the EPA can help DHCP with the choice of disinfectants [137]. The EPA (Environmental Protection Agency, USA) regulates the claims on?disinfectant product labels and periodically updates different Lists (indicated with S, C, D, E, F, N, Q, and K) for disinfectants. Each is a searchable and sortable list of products for use against specific infective agents or groups of them. For example, list N contains disinfectants for use against SARS-CoV2 and its variants, and the recent list S those against HIV, HBV, and HCV.

There are not so many appropriate commercial disinfectants (fast active (1-2 minute contact time), with a broad spectrum of activities, and compatible with plastic materials (containing 20% alcohol or less) [135]. Ensure that all areas treated with commonly used disinfectants, and potentially flammable liquid preparations are completely dry before starting LD. Be careful to use the commonly used disinfectants for clinical contact surfaces, because of ethanol and isopropanol concentrations are often in the range of 35%–62% and 1%–35%, respectively [135].

Limitations

The limitations of the present narrative review are the limited number of current studies and recommendations and the heterogeneity of the data specifically regarding ICP in LD, which makes a quantitative assessment of the data by meta-analysis impractical.

There is still important work to be done on ICP during LD in the future. In the dental setting, recommendations, guidelines, and legislation concerning standard precautions for ICP must be evidence-based or based on international best practices. Recommendations, guidelines, and regulations should then be developed in consultation with the dental team and extended to the laser safety manager and the IPC coordinator who are experts in clinical LD and updated on current laser technologies and ICP. We need to encourage dental staff to speak up and report adverse events, near misses, and technical difficulties during the decontamination and sterilization of laser parts or accessories. The Dental Patient Safety Foundation is a way to report patient safety events (adverse events, near misses, or unsafe conditions) safely, voluntarily, and confidentially [138]. This is a strategy to know errors and develop evidence-based recommendations. Regarding ICP during LD, research on aerosol generation is minimal [6]. Future research should include routine real-time monitoring of LP with appropriate sensors, which will provide valuable information to clarify the influence of different lasers and the relationship between LP, its composition (i.e., in terms of VOC, PM, and CO₂), and potential toxicity and development of respiratory disease in DHCP. At the same time, the chemical toxicity and microbiological hazard of LP should be assessed using in vitro cellular studies and a lung-on-a-chip model, and finally at the organ level in animal models. Data are needed on amalgam melting by LD and the possible release of mercury vapor and laser fiber resistance [1].

Perspectives

In the reported sections, we reported the standard infection control precautions, the current limitation for application during LD, and if known, hazard severity. The summary of key and specific recommendations for ICP in LD, the rationale, and open questions are shown in Table 4. This table is expected to strengthen the operative applicability of those reported.

Table 4. Summary of key and specific recommendations for ICP that are expected to strengthen its practical applicability, rationale and open questions concerning ICP in LD. [Click here to view]

Better IFU and research priorities

As part of sound recommendations or best practices against IPC in LD, better, unambiguous IFU and deeper knowledge are needed. Recently, the WHO reported global research priorities for antimicrobial resistance in human health. In panel 5, infection prevention and control shows a high research priority score (0.90) [139].

We think that better and more clear IFUs from producers, in line with the requirements of the Regulations EU 2017/745, are needed for:

• The reconditioning (cleaning-disinfection-sterilization) of dental laser components, parts, and accessories;
• Laser fiber and connector stability after steam autoclave cycles;
• The reconditioning of LSE and its shelf life and working life according to PPE Regulation [93].

For the evidence-based recommendation for ICP, research priorities are :

• To clarify the ambiguity of AGP and non-AGP (with and without modifying factors) [113] during the use of lasers in dentistry;
• To quantify the air and aerosol contamination using different types of lasers and different clinical protocols;
• To select evidence-based standard activities for better air quality on the components of LP, particularly those caused by laser-assisted endodontics, periodontics, and surgery, focusing on microorganisms, VOC, and PM contamination;
• To develop air sensors suitable and sensitive enough to identify the main VOCs produced by LD;
• To verify the efficacy of FFP2 and surgical mask during LD.

Looking to the future, molecular biology tests, sensors for indoor air quality in dental settings, and artificial intelligence (AI) will be very useful approaches to investigation. AI is profoundly transforming dentistry. For our specific objective, it is expected to improve the diagnostic accuracy of microbially caused oral diseases, while molecular biology plus AI the extent of bacteremia after LD. Mainly, AI will be useful for monitoring the application of standard precautions (e.g., procedure and duration of hand washing, disinfection, and so on) or the quality of indoor air interfaced with automatic ventilation modulation systems.

Infectious risk and cross-infection hazard in dentistry: a look to the future

Predicting infectious hazards is very complicated. Nevertheless, the outlook for infectious risks is alarming [140–142] and SARS-CoV2 different variants continue to go on spreading. Climate and land-use changes are predicted to increase the frequency of zoonotic spillover events, which have been the cause of most modern epidemics. Meadows’s group estimated that some pathogens (SARS Coronavirus 1, Filoviruses, Machupo virus, and Nipah virus) would cause four times the number of spillover events and 12 times the number of deaths in 2050, compared with 2020 [140]. So the real question is, not if there will be a pandemic, but when there will be. Other causes of disease emergence are: changes in human demographics and behaviors (i.e., HIV, tubercolosis, and Mpox clade 2), international travel and commerce (SARS, mPox clade 1), health care technology (Enterococcus, HCV, HBV, and so on), and microbial changes (infections with antibiotic-resistant strains). In addition, we live in a very dynamic word for infective agents [143]. The 2024 WHO BPPL covers 24 pathogens, spanning 15 families of antibiotic-resistant bacterial pathogens. Remarkable among these are Gram-negative bacteria resistant to last-resort antibiotics, at least three of them are of dental interest (drug-resistant strains of Mycobacterium tuberculosis, P. aeruginosa, and Staphylococcus aureus). But on the podium of the winners of the 2024 BPPL update, there are also Klebsiella pneumoniae and Acinetobacter baumannii, which are “new entries” for ICP in dentistry [143–145]. Fungal infections are continually increasing and oral Candida infection is certainly the most widespread mycosis in denture wearers, immunosuppressed patients, and patients with saliva secretory dysfunctions. Candida albicans and Candida auris are included in the WHO fungal pathogens priority list [146] and also C. auris seems to be present in denture wearers and adheres to dental implant materials [147]. The risk of new pandemics will recur, and the economic consequences are of concern to all economic and healthcare activities, including dentistry. Dentistry is also concerned with emerging pathogens (i.e., Enterovirus, Candida auris, measles virus, and so on) [142,148,149] and many of them could be a hazard for elderly and susceptible persons. Some NHS and epidemiologists reported that measles outbreaks is expected in the near future [149]. The new mutations of SARS-CoV-2 virus indicate that it remains a bit of a wild card, where it is always hard to predict what he will do next. Dental care-associated infections do not seem so rare in the last years [33,49,148–152]. The prospect caused by new SARS-CoV2 variants and the long-term presence of SARS-CoV2 in many tissues during Long COVID is not reassuring [153]. Antimicrobial resistance is a global public health hazard with serious economic consequences [49,50]. Photodynamic and photothermal therapy seems a promising strategy to combat antimicrobial-resistant bacteria [21,22,154].

Airborne transmission of pathogens

First, it is important to note that R₀, referred to as the reproduction number, is a mathematical term that indicates how contagious an infectious disease is; R₀ is in the range 0–18. For measles, poliomyelitis/rhinovirus/small pox, SARS-Co-V2, and influenza H1N1, the estimated R₀ values are 18, 6, 3, and 1.5, respectively.

Then, numerous respiratory and other viruses replicate in the oral cavity and are transmitted via aerosol or “droplet nuclei” (5–100 μm) and mainly at a distance of >1 to 2 m away from the infected individual and via droplets (>100 μm) [155]. Droplets can travel less than 1 meter, and fall to the ground in under 5 seconds. SARSCoV, influenza-, parainfluenza-, metapneumo-, rhino-, adeno-, and respiratory syncytial viruses are transmitted by aerosols and droplets, as well as direct and indirect contact (fomites). Other diseases spread by respiratory and oral fluids are: tubercolosis, diphtheria, pneumonia, meningitis, sinusitis, conjunctivitis, bacterial bronchitis, CMV disease, mononucleosis, measles, rubella, and mumps. In particular, mycobacterium and rubeola (measles) virus are considered aerosol transmitted. Aerosols produced by an infected individual may contain infectious viruses, and studies have shown that viruses are enriched in small aerosols. The transport of virus-laden aerosols is affected by the physicochemical properties of aerosols themselves and environmental factors (temperature, relative humidity, ultraviolet radiation, airflow, and ventilation). Aerosols up to 100 mm can be inhaled. Depending on their size, they deposit in different regions of the respiratory tract, based on one of several key mechanisms (inertial impaction, gravitational sedimentation, Brownian diffusion, electrostatic precipitation, and interception). Aerosols >5 mm deposit primarily (87% to 95%) in the nasopharyngeal region. Only aerosols that are sufficiently small (0.001–2 μm, mainly in the range 0.001–0.3 μM) can reach and deposit in the alveolar region. Recent data shows that ambient CO₂ concentration correlates with SARS-CoV-2 aerostability and infection risk [156]. Higher aerostability results also from a moderate increase in the atmospheric CO₂ concentration (e.g., 800 ppm).

Recently, Zemouri’s group showed data on the modeling of the transmission of Coronaviruses, Measles Virus, Influenza Virus, Mycobacterium tuberculosis, and Legionella pneumophila in Dental Clinics (ref) in a high scenario [(The DHCP does not wear a medical face mask, nor covers the nose with the medical face mask and works in poor indoor air quality (>1,500 PPM CO₂)] and low-risk scenario (The DCHP wears an FFP-2 mask and works in good indoor air quality (400–800 PPM CO₂) [157]. The high-risk scenario leads to the highest transmission probabilities of measles virus (100%), coronaviruses (99.4%), influenza virus (89.4%), and M. tuberculosis (84.0%). The low-risk scenario leads to transmission probabilities of 4.5% for the measles virus and 0% for the other pathogens. From the sensitivity analysis, the transmission probability is strongly driven by indoor air quality, followed by patient infectiousness, and the least by respiratory protection from medical face mask use. Nevertheless, in-depth studies are necessary to evaluate the influence of saliva composition on the decay of viral viability and viral transmission.

Up to now, great progress has been made in understanding the adverse effects of ambient fine and ultrafine PM on human health [73,158]. However, more studies are needed on the effects of them on various organs and their specific action mechanisms.

Finally, it is known that DHCPs work and are exposed in an area within 1.5–2 m of the source of contamination (patient’s head). We think that the data reported in the section “Indoor air quality during laser dentistry”, relating to aerosol and PM production during LD, do not allow us to exclude the hazard of airborne transmissible infections.