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Potential Contamination Of High-Speed Dental Handpiece By Spray Impact On The Mouth Surface

M. Sanches (1), A.S.H.O Moita (1,2), M.R.O. Panão (3)

(1) IN+, Center for Innovation, Technology and Policy Research, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal

(2) CINAMIL, Centro de Investigação Desenvolvimento e Inovação da Academia Militar, Academia Militar, Instituto Universitário Militar, Lisboa, Portugal

(3) ADAI, LAETA, Mechanical Engineering Department, University of Coimbra, Coimbra, Portugal

Portable dentistry devices allow medical dentists to perform procedures on patients in their homes. However, considering the recent pandemic context, these procedures raise concerns regarding the potential of infection since high-speed dental handpieces use water sprays to cool the rotating tool. The water spray droplets impacting the mouth of an infected patient can, thus, become a contamination source. Therefore, to produce reliable data to develop numerical models of aerosol propagation, this work uses a Phase-Doppler Interferometer to characterize the water spray before impact and the application of spray impact models indicates that 80% of droplets are in the conditions to deposit on the mouth's soft tissues and 19% of droplets should rebound. While a mere 1% expects to generate splashing events, the liquid film stripping and the complex 3D flow emerging from dragging the surrounding air generates a spray exiting the mouth. This spray is different from the original, thus, it is the result of shear-driven film stripping. The mathematical function that best describes all sprays was the Log-Normal and this work explains it as the result of an exponential drop size diversity growth rate (Φ). Therefore, while the characteristic size is reasonably understood in its physical meaning, the standard deviation (s) acquires one, i.e., it is a measure of the constant drop size diversity growth rate (s ≡ Φ). This could be a relevant insight to the physical interpretation of fitting a Log-Normal probability density function to describe the distribution of drop sizes in sprays. Finally, a scale analysis of the rebound contact time using a simple diffusion model, indicates that these droplets can also become contaminants agents.

20th Edition
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