Restoration of dental services after COVID-19: The fallow time determination with laser light scattering

Xiujie Li, Cheuk Ming Mak, Kuen Wai Ma, Hai Ming Wong

Research output: Journal article publicationJournal articleAcademic researchpeer-review

6 Citations (Scopus)


In time, dental health care has slowly expanded beyond emergency treatment to treat oral diseases. How to reduce the cross-transmission risk in dental surgery has raised much more attention. Considering the lack of consistency of fallow time (FT) in its necessity and duration, the highly sensitive laser light scattering method has been proposed to visualize the airborne lifetime and decay rate of suspended particles in the dental surgery environment. The FT is defined as when the number of suspended particles drops to the level that the next patient can safely enter after the aerosol-generating procedures (AGPs). The ultrasonic scaling was performed in the mock-up experimental dental clinic with 6 air changes per hour (ACH), and the instantaneous moments of the droplets were recorded by a high-speed camera. Without any mitigation measures, the estimated FT in the single dental surgery environment with 6 ACH was in the range of 27–35 min, significantly affecting the number of daily dental services. Despite the cooperation of high-volume evacuation (HVE [IO]) cannot eliminate the FT to zero minutes, the equipment could reduce the required FT by 3–11 min for the suspended particles reducing the baseline levels. Owing to the longer airborne lifetime of suspended particles, the relevant protection equipment, especially respiratory protection, is quite essential in dental surgery. The obtained results of this study will provide evidence to establish the revised FT in dental surgery guidelines and protect the health and wellbeing of urban dwellers.

Original languageEnglish
Article number103134
JournalSustainable Cities and Society
Publication statusPublished - Nov 2021


  • Covid-19
  • Dental clinic
  • Fallow time
  • Laser light
  • Suspended particles

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Geography, Planning and Development
  • Renewable Energy, Sustainability and the Environment
  • Transportation


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