The introduction of fallow times after aerosol-generating procedures (AGPs) was one of a barrage of safety measures that enabled dental practices to reopen in 2020, providing reassurance to patients and staff anxious about COVID-19.
Yet, a major downside is that fallow times of up to 60 minutes reduce capacity, hampering dentists’ efforts to provide for the backlog of patients needing oral healthcare.
Fortunately, current guidance includes a useful flow chart showing how to reduce fallow times to as little as 10 minutes with the right set up. This is what you need to know…
When is fallow time essential?
AGPs create a risk for SARS-CoV-2 transmission, so time is needed to allow potentially contaminated aerosols (airborne particles <5 μm) to be removed or diluted, known as Post–AGP Fallow Time.
Procedures using high velocity air and water streams are considered to be AGPs. These include: ultrasonic scalers, high-speed air/electric rotors (>60,000 rpm), Piezo surgical handpieces, and air polishers.
According to official guidance, airborne precautions, including fallow times, are needed when undertaking AGPs on the medium and high-risk pathways.
What are the recommended fallow times?
Within the official guidance published on 20 October 2020, all four UK Chief Dental Officers (CDOs) accepted the recommendations of the Scottish Dental Clinical Effectiveness Programme (SDCEP), including a pragmatic algorithm for determining fallow times based on ventilation and risk mitigation.
The Faculty of General Dental Practice UK (FGDP) and College of General Dentistry (CGDent) similarly updated their guidance.
Key recommendations are:
- No AGPs in a room without natural or mechanical ventilation.
- Baseline post-AGP fallow time of 30 minutes where there is ventilation with 1–5 air changes per hour (ACH) (or where ACH are unknown). Mitigation must also be used, such as high volume suction or a rubber dam.
- Baseline post-AGP fallow time of 20 minutes where there are 6–9 ACH, and 15 minutes where there are ≥10 ACH.
- Use of high-volume suction and a rubber dam reduces the time. With ≥6 ACH, use of both measures reduces the fallow time to a minimum of 10 minutes.
- AGP duration (<5 or ≥5 minutes) may also influence fallow time, which starts when aerosol production ends.
- Where ventilation is poor and suction not used, a fallow time of up to 60 minutes or alternative procedure (e.g. low-speed handpiece or hand scaling) should be considered.
You may find the Fallow Time Calculator useful – built by Flynotes and endorsed by England’s CDO, it incorporates the SDCEP recommendations.
Improving ventilation is key
Some dental surgeries are modern facilities designed for ≥10 ACH. If yours is not one of them, what can you do about it?
Ideally, you want to achieve a total flow rate of ventilation units at least 10× the room volume (ACH ≥10). To increase the total flow rate, consider:
- Mechanical ventilation: to actively extract air (exhausted externally), actively push air into the room, or both. See how one practice in Yorkshire installed mechanical ventilation heat recovery units to achieve 10 ACH.
- Air purification: a supplementary option to enhance ACH and provide reassurance. Either High Efficiency Particulate Air (HEPA) or UV filters can be used to clean the air, while an added extraction arm can capture aerosols close to the source.
Note that effectiveness of recirculating air purification devices varies depending on their air flow rate, air cleaning efficiency, and the room size. Correct positioning and maintenance are essential. Consequently, their flow rate should be halved when calculating ACH, unless they are independently validated.
Does the evidence justify the impact?
SDCEP recommendations were based on rapid review of the available evidence. The conclusions remain unchanged after an updated evidence review in January.
The review acknowledges that evidence for fallow times is very weak. As yet, no confirmed cases of SARS-CoV-2 transmission via dental aerosols have occurred.
Given the lack of data, dental professionals have challenged the need for fallow times, which have numerous negative impacts on dental services, including:
- Severely reduced capacity leading to unmet patient needs: more serious dental problems, increased antibiotics use, potential reduction in oral cancer diagnosis
- Concerns about ability to meet NHS targets for dental activity
- Loss of financial income, expense of ventilation equipment, uncertain practice viability
- Reduced range of services where ACH is suboptimal
- Longer surgery hours with the inconvenience of changing rooms
- Difficulties of planning patient flow
- Disturbance from noisy ventilation
- Staff anxiety and stress.
This list highlights the importance of optimising ventilation to minimise fallow times and safely increase capacity. Please contact us at Dental Defence Society if you need advice about implementing the guidelines.