What is fallow time in dentistry?

July 22, 2020

What is fallow time in dentistry?
What is the fallow time for aerosols in dentistry

Fallow means dormancy or latency. In dentistry fallow time is also referred as settle time or stand-down period. In times of COVID-19, it becomes very crucial in the dental office to reduce the number of infective micro-organisms in the dental surgery. Dentists carry out a lot of treatment procedures which involve aerosols. So how is fallow time related to such procedures in the times of COVID-19?


Aerosols are particulate matters which are less than 50 micrometers in diameter. These aerosols are large enough to house the Covid-19 causing microorganisms (Sars-Cov-2) which are likely to be emitted from the patient himself/herself, the dental health care personnel or the person accompanying the patient. Following the completion of any treatment plan involving aerosols, the infective microorganisms are likely to have travelled to various surfaces in the dental room. Before the dentist calls in the next patient, it is important to allow the dental surgery to be left in solitude for a certain time period. No human should be allowed to enter the premises for the dental operatory following the completion of the Aerosol Generating Procedure (AGP).


This time period has to be at least 20 minutes and can be as high as 120 minutes. In order to make the air within the operatory free from any viral or bacterial pathogens, the air change per hour (ACH) needs to be high in quantity. This is the amount of air that gets displaced by various means of ventilation in a given area. The faster this form of air circulation takes place, the lesser will be the fallow time. In the phase of a pandemic it is crucial for dentists to install certain equipment that accelerates the change in air circulation or the ACH after an AGP has been performed. Here are a few points to consider:


• Heating, Ventilation and Air Conditioning (HVAC) units should be regularly filtered or should be replaced if old

• High Efficiency Particulate Air (HEPA) filter needs to be installed in the dental operatory. This is a machinery that is retrofitted to the HVAC units. These units have the ability to filter particles as small as 0.3 micrometers. They are often used in hotels, factories, hospitals, etc.

• The most economical solution is to install an extraction fan. By means of negative pressure, the extraction fan will displace the air within the operatory. Though it is relatively cheaper, the mode of action of the extraction fan is slower than the above mechanisms

• Charcoal filters can also be used to get rid of any unwanted odor in the dental operatory. However, it should be noted that these filters are minimally effective in removing viruses and bacteria

• UV-C filters are also used in many dental offices. These filters are ozone-free in nature and emit UV rays to kill the microorganisms. However, the major drawback of this system is that it needs immense precision in its placement else these filter lamps won't be able to assert their maximum effect.


Considering the above options, it is easy to say that HEPA filters are the most effective ones. The best of these which meet the criteria of the European Standards can filter out 99.99% of microorganisms. However, not only are they expensive but they also need to be checked for maintenance every 6 months. Considering the miniature size of the Sars-Cov-2, HEPA filters would be the most effective ones. However, not all dental offices would be comfortable in opting for HEPA units. In these cases, the dentist should consider increasing the fallow time.


An increased fallow time might have a scatter of effects. The dentist would see lesser number of patients in a given day which might mean that the cost of treatment would be increased. Dentists will give more importance to the patients whose dental pain needs to be relieved. Having said that, it is also essential that amidst the pandemic, enough importance is given to the fallow time depending on the total surface area of the dental operatory and the type of air purifier or air filter installed. As for dentists, there are certain formulations that they can check for which can help them in determining the fallow time based on the dimensions of their dental office. Patient compliance is supreme given the relatively higher fallow time in the time of a pandemic.


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