Know Why It Is The Best For Disinfection For Dental Operatory!


Blog By: Dr. Shivangi, True Value Dental Institute


COVID-19 has put whole of the Dental Fraternity astray. We are scared to open up our practice and start doing the patients. We are not clear how to disinfect our clinic’s environment and operatory and moreover, we are confused about the prevailing methods- fogging, fumigation etc. This article would acquaint with the UV light’s safe use and disinfection.

Although sodium hypochlorite (NaOCl), chlorhexidine and hydrogen peroxide have shown positive results but none of the agents is 100% effective in disinfection for preventing the coronavirus infection in Dental Clinics without causing any side-effects.

Among the various agents used, ultraviolet light (UV-C) disinfection has gained favour due to its efficacy against a broad range of microbial and viral agents found in a variety of environments .1 The potential use of ultraviolet light for airborne disinfection was first demonstrated more than 80 years ago. 2, 3

Due to its harmful effects on human cells and tissues, scientists have found an alternative that is essentially equi-effective at killing antibiotic-resistant bacteria and viruses as conventional germicidal UV lamps4 à Far-UVC (a less known discovery with unconfirmed approval by FDA). It has no harmful effect on human living cells on its exposure.

In this article, we will briefly discuss about UVC and try to acquaint you on Far-UVC light, its exposure time, dosage, and efficacy, method of operation and advantages and applications.

What is UV-C?

  • UVC is a subdivision of UV spectrum of sunlight.
  • Usually, 90% of UVC light do not penetrate the Earth’s atmosphere.5
  • It is considered as germicidal ultraviolet light (UVGI).
  • UV light is invisible electromagnetic radiation with wavelengths shorter than visible light but longer than X-rays i.e., 100 nm to 400 nm.
  • Using the CIE (International Commission of Illumination) classification the UV spectrum is subdivided into three bands:
    • 315 nm to 400 nm à UVA (long wave)
      – useful for printing, curing, lithography, sensing and medical applications
    • 280 nm to 315 nm à UVB (medium wave)
      – useful for curing, tanning and medical applications
    • 200 nm to 280 nm à UVC (short wave)
      – useful for disinfection and germicidal action

Discovery 5

  • In 1878 the sterilizing effect of short-wavelength light by killing bacteria was discovered.
  • By 1903 it was known the most effective wavelengths were around 250 nm.
  • In 1960, the effect of ultraviolet radiation on DNA was established for sterilization purposes.

Method of Operation 5

  • Ultraviolet germicidal irradiation (UVGI) is a disinfection method that uses short-wavelength ultraviolet (ultraviolet C or UV-C) light to kill or inactivate microorganisms by destroying nucleic acids and disrupting their DNA, leaving them unable to perform vital cellular functions.
  • The absorbed energy can result in defects including pyrimidine dimers. These dimers can prevent replication or can prevent the expression of necessary proteins, resulting in the death or inactivation of the organism.
  • UVC causes irreversible damage to nucleic acids (RNA/DNA) of the SARS-CoV2. It selectively renders viruses, bacteria, and parasites unable to replicate.6

UVC Effectiveness

  • The UV light emitted by a source is expressed in watts (W)
  • The irradiation density is expressed in watts per square meter (W/m2).
  • The dose is expressed in joules per square meter (J/m2). (1 joule is 1W.second). 1
UV dose μWs/cm2 = UV intensity μW/cm2 × Exposure Time (seconds)  

It is calculated as:

  • UV intensity is inversely proportional to the square of the distance so it decreases at longer distances.
  • The UV intensity must always be adjusted for distance unless the UV dose is calculated at exactly 1 m (3.3 ft) from the lamp. 7
  • UVC light inactivated the SARS virus at a distance of 3 cm for 15 min.8
  • The effect of UVC light on SARS-CoV at an intensity of  >90 µW/cm2 and a distance of 80 cm, and determined that inactivation of the virus occurred at 60 min.8

Threshold Limit Value (TLV) of UVC:

  • Established to avoid skin and eye injuries among those most susceptible.
  • For 254 nmUV,  TLV is 6 mJ/cm2 over an 8-hour period. 7

Disadvantage of Conventional UVC light 1, 4, 7

  • Travels only in its light path. Less effective if hindrance is present.
  • Skin damageà sunburn, skin cancer by mutation, apoptosis etc.
  • Eyesà photo-keratitis, cataract
  • Degradation of polymer, pigments and dyes.

FAR-UVC LIGHT à The Invisible Killer of Covid-19

What is Far-UVC?

  • It has a

-shorter wavelength: 207-222nm

-higher frequency

-higher energy

than UV-C, making its effect on microorganisms different from the regular germicidal UV. 

Mechanism of Operation:

  • Similar in mechanism of action on virus. It kills or inactivates viruses (typically of micron or smaller dimensions) by destroying nucleic acids and disrupting the RNA mechanisms, leaving them unable to perform vital cellular functions.
  • The absorbed energy can result in defects including pyrimidine dimers. These dimers can prevent replication or can prevent the expression of necessary proteins, resulting in the death or inactivation of the organism. 7

Dose, Intensity and Exposure Time 9, 10

  • Dose of 2 mJ/cm2 of 222-nm light inactivates >95% of airborne H1N1 virus.7
  • Dose limit of 222 nm light (International Commission on Non- Ionizing Radiation Protection, ICNIRP) = 23 mJ/cm2 per 8-hour exposure 
  • Exposure limit ~3 mJ/cm2/hour à 99.9% viral inactivation in ~ 25 minutes
  • Increasing the intensity by a factor of 2 would halve these disinfection times, while still maintaining safety.
  • Exposure dose as low as 1.2 to 1.7 mJ/cm2 of 222-nm light inactivates 99.9% of the airborne human coronavirus. 10

Penetration of Far-UVC

  • Traverse microbes that are much smaller in size than human cells à <1µm.11  
  • Unable penetrates the typical human skin cells which are 10-25 µm thick. 12
  • Unable to penetrate through the cornea to the lens as it is 500 µm thick. 13,14

Viral Inactivation (apporx.) 10

Continuous far-UVC exposure at 3 mJ/cm2/hourintensity results in viral inactivation by:

  • 90% à 8 minutes,
  • 95% à 11 minutes,
  • 99% à 16 minutes
  • 99.9% à 25 minutes.

Effectiveness 1

  • The amount of inactivation is directly proportional to the UVC dose which is received.
  • This is the result of its intensity and duration of exposure.
  • The farther away you keep an object from the light source, the less UVC will reach the target, so only a quarter of the UVC remains when the distance doubles.

Source 15

  • An excimer lamp based on a krypton-chlorine (Kr-Cl) gas mixture that emits principally at 222 nm along with a custom bandpass filter (Omega Optical, Brattleboro, VT), used to remove essentially all but the dominant 222-nm wavelength emission.
  • The lamp (High Current Electronics Institute, Tomsk, Russia) is air cooled with a 6,000-mm2 exit window.

Advantage of Far-UVC Irradiation 7

  • It is completely safe on human exposures.
  • Leaves no residuebehind or any potentially dangerous by-products. 1
  • Likely to be effective against all airborne microbes in contrast to the vaccination.
  • Efficiently inactivates drug-resistant and drug-sensitive18 bacteria, without apparent harm to exposed mammalian skin.
  • Strong absorbance in biological materials.
  • Does not have sufficient range to penetrate through living cells even the outer layer (stratum corneum) of the human skin, nor the outer tear layer on the outer surface of the eye – neither of these contains living cells.
  • It is essentially independent of acquired drug resistance.4
  • Does not require additional personal protective equipment.4

Applications of Far-UVC 7

  • Reduction of surgical site infections. 4
  • UV lamps specifically directed over the surgical site can alleviate airborne bacteria or viruses alighting directly from the dental/surgical procedures.16
  • Prevention and reduction of airborne viral and bacterial infections.
  • Limiting the transmission and spread of airborne-mediated microbial diseases at public locations like hospitals, doctor’s offices, schools, airports and airplanes.


Various evidence based studies suggest that Far-UVC has numerous applications in germicidal as well as disinfection of surfaces. Thus it can be utilized in the dental practice effectively against coronaviruses17 and to disinfect the dental operatory per se without any serious harmful effect on the human living cells on its exposure.

This small video (Available from: https://youtu.be/4iJuSNI3Y98 ) by the Center for Radiological Research, Columbia University depicts the power of light in preventing the airborne spread of coronavirus and influenza virus. 18




  1. Chitguppi R. How to use Ultraviolet light (UVC) to fight COVID-19 effectively in dental clinics: Dr Ajay Bajaj. Dental Tribune South Asia. 2020 May 12
  2. Wells, W. F. & Fair, G. M. Viability of B. Coli Exposed to Ultra-Violet Radiation in Air. Science 82, 280–281 (1935).
  3. Reed, N. G. The history of ultraviolet germicidal irradiation for air disinfection. Public Health Rep 125, 15–27 (2010).
  4. Buonanno, M. et al. Germicidal Efficacy and Mammalian Skin Safety of 222-nm UV Light. Radiat. Res. 187, 483–491 (2017).
  5. World health Organization. Coronavirus disease (COVID-2019) situation reports, (2020). Available from: https://www.who.int/emergencies/diseases/novel-coronavirus-2019/situation-reports
  6. Keil SD, Ragan I, Yonemura S, et al. Inactivation of severe acute respiratory syndrome coronavirus 2 in plasma and platelet products using a riboflavin and ultraviolet light-based photochemical treatment. Vox Sang. 2020 Apr 20;10.1111/vox.12937.
  7. Ultraviolet germicidal irradiation. Wikipedia. Available from: https://en.wikipedia.org/wiki/Ultraviolet
  8. Darnell ME, Subbarao K, Feinstone SM, et al. Inactivation of the coronavirus that induces severe acute respiratory syndrome, SARS-CoV. J Virol Methods. 2004;121(1):85-91;10.1016/j.jviromet.2004.06.006
  9. Welch D, Buonanno M, Grilj V, et al. Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases. Sci Rep. 2018 Feb 9;8(1):2752;10.1038/s41598-018-21058-w.
  10. Buonanno  M, Welch D, Shuryak I, et al. Far-UVC light efficiently and safely inactivate airborne human coronaviruses. Research Square. 2020 April 27; Preprint;10.21203/rs.3.rs-25728/v1.
  11. Metzler, DE., Metzler, CM. Biochemistry: The Chemical Reactions of Living Cells. 2nd. San Diego: Academic Press; 2001.
  12. Lorian V, Zak O, Suter J, Bruecher C. Staphylococci, in vitro and in vivo. Diagn Microbiol Infect Dis. 1985; 3(5):433–44. [PubMed: 4028668]
  13. Doughty MJ, Zaman ML. Human corneal thickness and its impact on intraocular pressure measures: a review and meta-analysis approach. Surv Ophthalmol. 2000; 44(5):367–408. [PubMed: 10734239]
  14. Kolozsvari L, Nogradi A, Hopp B, Bor Z. UV absorbance of the human cornea in the 240- to 400-nm range. Invest Ophthalmol Vis Sci. 2002; 43(7):2165–8. [PubMed: 12091412]
  15. Sosnin EA, Avdeev SM, Kuznetzova EA, Lavrent’eva LV. A bacterial barrier-discharge KrBr Excilamp. Instr Experiment Tech. 2005; 48:663–6.
  16. Buonanno M, Pehrson GR, Bigelow AW, et al. 207-nm UV Light – A Promising Tool for Safe Low-Cost Reduction of Surgical Site Infections. I: In Vitro Studies. Plos One. 2013 October;8(10);10.1371/journal.pone.0076968
  17. Chitguppi R. An evidence based approach: Effect of far UVC light on coronaviruses in aerosols: A step-wise summary in Q&A format. Dental Tribune South Asia. 2020 May 13;10.13140/RG.2.2.21318.09282
  18. Brenner DJ. Using the Power of Light: Preventing the Airborne Spread of Coronavirus and Influenza Virus. Center for Radiological Research. 2020 Feb.

Dr. Shivangi

Research Team


Email: truevaluedentalinstitute@gmail.com

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