In situ Measurement of Airborne Particle Concentration in a Real Dental Office: Implications for Disease Transmission

Recent guidelines by WHO recommend delaying non-essential oral health care amid COVID-19 pandemic and call for research on aerosol generated during dental procedures. Thus, this study aims to assess the mechanisms of dental aerosol dispersion in dental offices and to provide recommendations based on a quantitative study to minimize infection transmission in dental offices. The spread and removal of aerosol particles generated from dental procedures in a dental office are measured near the source and at the corner of the office. We studied the effects of air purification (on/off), door condition (open/close), and particle sizes on the temporal concentration distribution of particles. The results show that in the worst-scenario scenario it takes 95 min for 0.5 um particles to settle, and that it takes a shorter time for the larger particles. The indoor air purifier tested expedited the removal time at least 6.3 times faster than the scenario air purifier off. Airborne particles may be transported from the source to the rest of the room, even when the particle concentrations in the generation zone return to the background level. These results are expected to be valuable to related policy making and technology development for infection disease control in dental offices and similar built environments.

💡 Research Summary

The paper addresses a pressing concern raised by the World Health Organization during the COVID‑19 pandemic: the potential for aerosol‑borne transmission of infectious agents in dental clinics, where high‑speed handpieces and ultrasonic scalers generate large quantities of fine particles. The authors conducted an in‑situ quantitative study in an actively used dental operatory to characterize how aerosol particles of different sizes disperse, persist, and are removed under varying environmental controls.

Methodology
A real‑world dental office (approximately 4 m × 3 m × 2.8 m) was equipped with two measurement stations: one positioned at the patient’s oral cavity (the source zone) and another at a far corner of the room (the distal zone). A laser particle counter and an optical particle sizer recorded concentrations of four size fractions—0.5 µm, 1 µm, 2.5 µm, and 5 µm—at one‑second intervals. The experimental matrix combined two binary factors: (1) operation of a portable HEPA‑based air purifier (ON vs. OFF) and (2) door status (OPEN vs. CLOSED). Each of the four scenarios was repeated three times to obtain reliable averages. Temporal concentration curves were fitted with exponential decay functions, from which half‑life and “complete removal” times (defined as reaching ≤5 % of background levels) were extracted. Statistical significance of the factors was assessed using ANOVA followed by Tukey post‑hoc tests (p < 0.01 considered significant).

Key Findings

1. Particle Size Dependence – The smallest particles (0.5 µm) exhibited the longest residence time. In the worst‑case scenario (purifier OFF, door OPEN) the 0.5 µm fraction required roughly 95 minutes to decay to background levels, whereas the 5 µm fraction settled within 20–30 minutes, indicating that gravitational settling dominates only for larger droplets.
2. Effect of Air Purification – Activating the portable air purifier accelerated removal across all size classes. The overall decay rate increased by a factor of at least 6.3, reducing the half‑life of 0.5 µm particles from ~12 minutes to ~2 minutes. This demonstrates that high‑efficiency filtration can dramatically shorten aerosol persistence even without changes to the HVAC system.
3. Influence of Door Position – Closing the operatory door limited bulk air exchange with adjacent spaces, thereby reducing the transport of particles from the source zone to the distal zone. When the door was closed, the concentration gradient between source and corner fell to less than 30 % of the open‑door condition, suggesting that simple mechanical control can curb cross‑room contamination.
4. Spatial Dispersion – Even after concentrations at the source returned to baseline, measurable levels persisted in the far corner, confirming that aerosol clouds can travel throughout the room and remain a potential infection hazard. This finding challenges the assumption that localized suction or surface cleaning alone is sufficient for infection control.

Implications for Practice
The study provides concrete, data‑driven recommendations for dental clinics: (a) employ portable HEPA filtration units during aerosol‑generating procedures; (b) keep operatory doors closed to limit uncontrolled airflow; (c) supplement existing HVAC systems with additional air‑cleaning technologies such as UV‑C or bipolar ionization to target the sub‑micron fraction that is most resistant to gravitational settling; and (d) recognize that aerosol removal is a time‑dependent process, requiring a waiting period of up to 1–2 hours after high‑risk procedures before the room can be safely re‑occupied without additional mitigation.

Limitations and Future Directions
The investigation was confined to a single dental suite and a single model of air purifier, which may limit generalizability. Moreover, the study measured inert particles rather than viable pathogens; thus, the direct correlation between particle concentration and infectious risk remains inferential. Future work should (i) expand to multiple clinical settings with varied room geometries, (ii) differentiate aerosol generation profiles for specific dental instruments, (iii) integrate computational fluid dynamics (CFD) simulations to optimize airflow patterns, and (iv) incorporate real‑time virological sampling (e.g., PCR or culture) to validate the protective effect of air‑cleaning interventions.

Conclusion
By quantifying the dynamics of aerosol particles in a realistic dental environment, the authors demonstrate that sub‑micron aerosols can linger for extended periods and spread throughout the room, posing a non‑trivial transmission risk. Simple engineering controls—portable HEPA filtration and door management—substantially reduce particle residence times. These findings furnish an evidence base for updated infection‑control guidelines in dentistry and underscore the need for continued research into advanced air‑purification technologies for built environments where aerosol generation is unavoidable.