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Questions to Prof Christoph Hämmerle, University of Zürich

How to respond to the corona pandemic in the dental office

Dental patients cannot be treated while wearing masks. Are dental professionals therefore at a high risk of contagion? What are the most important measures for dealing with the new situation? Prof Christoph Hämmerle provides answers.


Professor Hämmerle, is there a higher risk for dental professionals to become infected with Covid-19?

Prof. Hämmerle: Currently, there is insufficient data to confirm or reject this assumption. It is important to note that the risk of infection in a dental practice mirrors the prevalence of the disease in the general population.


What treatment steps involve particular risk?

Prof. Hämmerle: In addition to the general risks of disease transmission via coughing, shaking hands with an infected person etc. there are some special risks in the dental practice. These include aerosols produced during dental treatment that could bear infectious agents and improper sterilization of instruments.


How big is the risk of aerosols?

Prof. Hämmerle: The volume of water flow through a red counter angle handpiece is about 50 ml per minute. The unstimulated saliva production is about 0.4 ml per minute, stimulated about 2 ml per minute. So, the saliva is diluted about 25 to 100 times. Is this still enough to produce infectious aerosols? We don’t yet know. Therefore, we should avoid these procedures wherever possible.


What are the most important measures implemented by the dental clinics at the University of Zurich?

Prof. Hämmerle: The protective measures already start prior to entering the practice. We do an interview by telephone before the appointment to make sure that the patient neither has any symptoms nor is a risk patient, e.g. taking immunosuppressive medication. Then, there is a second interview upon entering the practice including a health status questionnaire and we check the temperature of the patient.

Then there are several protective measures already in the entrance and waiting area: There are physical barriers between the patients and welcoming desk in the entrance hall, accompanying persons are not allowed, there are no journals or newspapers in the practice, the chairs in the waiting room are separated and each patient is provided with a mask.


And during the treatment?

Prof. Hämmerle: On one hand we enhanced the personal protective equipment – so, disinfect hands and surfaces, wear masks, wear goggles, shields, gloves, hats & gowns. And we allow more time – an additional 15 minutes – between patients for disinfection, cleaning and ventilating operatories.  

On the other, we have patients rinse with antimicrobial agents before we start treatment and, as I said before, we avoid aerosols.


What agents would you recommend for pre-procedural mouthwash?

Prof. Hämmerle: Two mouthwashes can be recommended based on scientific literature: 0.5-1% percent hydrogen peroxide solution for 1 min or povidone iodine 0.2 percent solution. Chlorhexidine is not effective against a virus with a lipid wall. 


Are there also recommendations for anti-microbial substances to be used in water for air rotors?

Prof. Hämmerle: No.


Is an air-purifier necessary?

Prof. Hämmerle: There is no data indicating benefits from such equipment.


Which surgical masks are recommendable for the staff in a dental practice?

Prof. Hämmerle: FFP-2 masks without valve are recommendable.


How do you deal with risk patients, e.g. elderly patients, patients with diabetes, cardiac disease etc?

Prof. Hämmerle: We manage high-risk patients separately in special operatories, usually in the early morning or later afternoon and we allow even more time for ventilation and cleaning between patients.


Will the University of Zurich consider frequent Covid-19 tests for all the staff and patients/visitors? And how frequent would it be?

Prof. Hämmerle: A positive effect of testing can only be achieved if enough tests are done. So local intensive testing will not be of any benefit. Extensive testing strategies should be developed as soon as we have low infection numbers. It’s not an easy task for scientists to come up with a good recommendation.

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Marco Mafra wrote:

Thank you for sharing your experience with us, prof Hämmerle!