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How to reduce fallow time in dentistry

How to reduce fallow time in dentistry

How to Reduce Fallow Time in Dentistry


To minimise aerosol transmission of Covid-19, England’s CDO introduced the concept of fallow time – downtime in the surgery following an aerosol generating procedure (AGP) taking place. 

What does fallow time mean?


This fallow period is designed to allow droplets to settle and be removed from the air. It’s calculated from the point that the AGP ceases. Subsequent patients are not allowed to enter the room until the fallow time has elapsed. The dental team may enter the room, but only with full PPE including an FFP2 or FFP3 respirator mask.

Originally the fallow time period was set at 60 minutes, however SDCEP suggest that the fallow period could be reduced to 20 minutes or even lower depending on mitigating factors. 

Room ventilation


This is the number one factor in the ability to reduce fallow time. Most dental surgeries are neutral pressure rooms (i.e. there is no pressure difference between the surgery itself and the communal areas). The 60 minute recommendation is based on a single room with 6 air changes per hour (ACH). Opening windows and using air conditioning (with recirculation turned off) can increase ACH, and decrease the fallow time needed. The manufacturer of your ventilation systems can advise on the ACH capacity of your equipment, based on the room size.

High volume suction


High volume evacuation is used by 94% of surgeries (Source: BDA) and offers the best solution for removing potentially infectious aerosol particles before they leave the mouth. 

The best systems have exhaust air filters in place. This avoid directing unfiltered exhaust air outside the practice building. 

SDCEP suggest that the use of high volume suction should reduce the fallow time needed by 10 minutes.

Rubber dam

DEHP Rubber Dam

By isolating the work area from saliva and blood in the mouth, rubber dam can help reduce the amount of aerosol generated. SDCEP believe that the use of rubber dam can reduce the fallow time needed by 5 minutes. 

See the full range of rubber dam and accessories from Kent Express here.

Air filtration (Air cleaning)


Products such as the Radic8 VK-401 VirusKiller use a combination of mechanical filters and UV-C decontamination to neutralise air in a single pass. The technology was developed as a response to the 2003 SARS epidemic in South Korea, and test in 2004 showed a near 100% kill rate on SARS-CoV-1 Coronavirus. Radic8 believe that their systems will be equally effective on SARS-Cov-2.

BA EOS350 Extra-Oral Suction Unit

Extra-Oral Suction


Stand-alone units such as the high power BA Optima EOS-350 can help efficiently purify air and capture airborne aerosols. Medical grade triple layer HEPA filters are combined with UV-C lamps to trap then sterilise viruses and bacteria. The units are mobile, lightweight and can easily be moved between surgeries.

Cold fogging


Some practices have introduced cold fogging: a technique that normally involves releasing a solution containing Hypochlorous acid (LOCl). Sometimes a combination of silver ions and hydrogen peroxide is used instead. The droplets are in the form of a mist of particles with less than 20 micrometres diameter. However the BDA has stated that “fogging techniques (with e.g. hypochlorous acid) are not currently recommended as this has not been confirmed as effective for C-19 and the health effects e.g. respiratory issues and long-term health implications for staff are unknown.”

How do I calculate fallow time?


FGDP has released a fallow time calculator built on the latest recommendations.

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