Mechanisms of Atomization from Rotary Dental Instruments and Its Mitigation

Abstract

Since the onset of coronavirus disease 2019, the potential risk of dental procedural generated spray emissions (including aerosols and splatters), for severe acute respiratory syndrome coronavirus 2 transmission, has challenged care providers and policy makers alike. New studies have described the production and dissemination of sprays during simulated dental procedures, but findings lack generalizability beyond their measurements setting. This study aims to describe the fundamental mechanisms associated with spray production from rotary dental instrumentation with particular focus on what are currently considered high-risk components—namely, the production of small droplets that may remain suspended in the room environment for extended periods and the dispersal of high-velocity droplets resulting in formites at distant surfaces. Procedural sprays were parametrically studied with variables including rotation speed, burr-to-tooth contact, and coolant premisting modified and visualized using high-speed imaging and broadband or monochromatic laser light–sheet illumination. Droplet velocities were estimated and probability density maps for all laser illuminated sprays generated. The impact of varying the coolant parameters on heating during instrumentation was considered. Complex structured sprays were produced by water-cooled rotary instruments, which, in the worst case of an air turbine, included droplet projection speeds in excess of 12 m/s and the formation of millions of small droplets that may remain suspended. Elimination of premisting (mixing of coolant water and air prior to burr contact) resulted in a significant reduction in small droplets, but radial atomization may still occur and is modified by burr-to-tooth contact. Spatial probability distribution mapping identified a threshold for rotation speeds for radial atomization between 80,000 and 100,000 rpm. In this operatory mode, cutting efficiency is reduced but sufficient coolant effectiveness appears to be maintained. Multiple mechanisms for atomization of fluids from rotatory instrumentation exist, but parameters can be controlled to modify key spray characteristics during the current crisis.

Virus transmission by ultrasonic scaler and its prevention by antiviral agent

“…The concentration of log 3.25±0.59 TCID 50 /ml was measured in LS. This observation is in accordance with a recent paper, stating that mixing the introduced coolant with real saliva also requires consideration (Sergis et al 2020). In our case, with virus titration control in saline suspension and splatter collected directly at the USS, the concentration reduction was 0.87 log, which is near 10x dilution and goes perfectly with the ratio of virus suspension and irrigant flow.…”

“…The EAV predominantly spreads via larger droplets (splatter) that, according to ballistic laws, reach the near surrounding area, as infected droplets consistently infected cells on plates up to the distance of 45 cm (16 th well) from the USS tip. These observations are in accordance with a recent review (Sergis et al 2020) stating that contaminants settle to a great extent on the operator’s dominant arm, eyewear, and chest of the patient, and to a lesser extent on the non-dominant arm and chest of the operator and assistant. To the best of our knowledge, this is the first proof of the contribution of an USS action to the spread of the virus via droplets to the environment.…”

“…Using a high vacuum evacuator or similar device, as they are usually used in a clinical setting, would considerably reduce the spread of splatter and aerosol (King et al 1997; Holloman et al 2015). Similar to a recent study on atomization from rotary dental instruments (Sergis et al 2020), the generalization of our findings into the wide variety of clinical settings is difficult due to variability of USS devices and their operating parameters, including power setting tip selection and irrigant flow rate. Even larger differences may be found between dental procedures (Allison et al 2021).…”

“…The measures range from pre-procedure mouth-rinse, use of personal protective equipment, high volume evacuation, air purification (ventilation, filtering, air disinfection), and surface disinfection. Personal protective equipment can protect the dental care providers; however, the contamination of clinical environments by sprays still necessitates periods of “fallow time” between appointments to protect patients and staff (Sergis et al 2020). A special concern was raised for open plan clinic environments, reporting a safe distance of 5m (Holliday et al 2021) Although preprocedural mouth-rinse is included in most recommendations (Clarkson et al 2020), its effectiveness is questionable as no scientific clinical evidence exists for reducing the viral load (Carrouel et al 2020).…”

British Society for Oral & Maxillofacial Pathology news

“…Researchers at Imperial College London and King's College London have measured and analysed aerosol generation during dental procedures and suggested changes to prevent contamination in the first place, to improve safety for both patients and the dental practice workforce. 1 They suggest that dentists avoid using dental drills that use a mixture of air and water as the abrasion coolants, and carefully select and control drill rotation speeds for those instruments that only use water as a coolant. Parameters have been identified that would allow some procedures such as dental fillings to be provided while producing 60 times fewer aerosol droplets than conventional instrumentation.…”