How does the human mouth create suction

Dental aerosols

Extraction and holding technology

The aerosol cloud can be drastically reduced by systematic suction: the germ count drops to a tenth to a twentieth [22]. The Robert Koch Institute (RKI, [23]) also mentions suction technology as protection against contamination. The germ content of the aerosol emerging from the patient's mouth can be effectively reduced by precise suction [24]. The more systematically and precisely the suction technology is carried out, the lower the aerosol cloud will be.

The generic term is suction and holding technology. The primary task of this technology is the suction of solid and liquid substances as well as aerosol from the patient's mouth. Furthermore, the lip, cheek and tongue should be kept away and the patient's head should be kept in an appropriate position. This dual purpose of suction and holding must always be taken into account if only the short term suction technology is used.

When polishing and removing amalgam fillings at high speed, mercury is briefly released [25]. In order to keep this exposure as low as possible, a spray must be used, the turbine or the contra-angle handpiece must be operated with the lowest possible pressure and the optimal suction technology must be used.

The saliva ejector can only remove fluids from the mouth; it is usually required to drain the residual water and saliva in the mouth. The saliva ejector is completely unsuitable for removing the aerosol cloud containing germs and pollutants that is ejected from the patient's mouth when a spray is used.

The suction must be done systematically. It is not enough to "poke around" the mouth with the cannula. The more precisely the extraction technique is carried out, the better the aerosol cloud is extracted. Suction technology as a contamination prophylaxis against microorganisms and pollutants (for example amalgam residues) is an essential part of dental work safety.

However, the aerosol cloud contaminated with droplets cannot be completely removed by suction. Eye and face protection must be worn. To reduce fogging of the glasses, the mask with the integrated metal strip is carefully pressed onto the nose and the skin below the eyes.

The closer the mask is to the face, the better the protective effect against the aerosol that comes in from below [26].


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    As a contamination prophylaxis, suction technology is an essential element of hygienic work safety

Protective masks [2, 27]

Protective systems are required for medical activities where exposure to airborne infectious agents is to be expected. These belong to the personal protective equipment. A distinction is made between:

The Mouth and nose protection (MNS; surgical mask, surgical mask) is primarily used to protect the patient from infectious particles from the mouth and nose area of ​​the treating person. If the filter material meets the normative requirements (DIN standards), it has a good filter effect for viruses, bacteria and fungi. Because of its function, the MNS is a medical device.

It is recommended that those working in the practice also wear an MNS outside of the treatment room [1].

If the mask is pulled down under the chin between treatments, the outer surface of the mask can turn inside out and contaminate the skin of the face. If you pull up the mask again with the already disinfected (gloved) fingers, these would be contaminated again. For psychological reasons, too, you should avoid entering the reception and waiting area with your mask pulled down ("Nikolausbart").

The Respirator (filtering respiratory protective device) serves to protect the worker and has the task of separating the smallest particles (particles) from the inhaled air [2, 28]. FFP masks, masks according to NIOSM (N 95) and KNST are suitable. The particle-filtering half masks ("filtering face piece", FFP; filtering face piece) are divided into the following three classes:

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    FFP1: maximum filter penetration 22 percent, corresponds to coarse filtering,

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    FFP2: maximum filter penetration 8 percent, corresponds to medium filtering,

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    FFP3: maximum filter penetration 2 percent, corresponds to the finest filtering.

With these masks (in contrast to the MNS), not only the filter effect of the mask material is taken into account, but also the tight fit on the wearer's face.

The mask often cannot be precisely adapted to the irregularities of the worker's face; the airflow is hindered by the dense mask material and is therefore directed around the mask and penetrates at the edge of the mask [29]. Masks with malleable metal strips in the nasal area reduce this risk. The ingress of contaminated aerosol through surgical masks is clearly influenced by incorrect wearing of the mask [30]. Even not pressing the nasal clip leads to a significant loss of filtration efficiency [26].

The Technical Rule for Biological Agents 250 (TRBA 250) points out that "when wearing a beard in the area of ​​the sealing line of respiratory protective equipment, the expected protective effect cannot be achieved because of the poor sealing." Rule 112-190 of the German Social Accident Insurance (DGUV) states that wearers of respiratory masks should not have hair in the area of ​​the sealing contours; The trade association for health and welfare services (BGW, [27]) expresses a similar view.

Another experimental study on the protective effect of face masks [26] confirms that wearing single-layer paper masks only lowers the number of inhaled microorganisms by an average of 40 percent; such masks are to be rejected because of their poor protective effect. Multi-layer surgical face masks (also special stomatological masks and respiratory protection masks of the type FFP2) reduce the number of inhaled microorganisms considerably and are suitable for protecting the worker [27].


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    FFP2 masks are suitable for protecting the worker

Visor or face shield

The TRBA 250 also mentions a visor or face shield as protection against the aerosol. This is problematic in dental treatments that produce an aerosol: the hand that guides the turbine or micromotor and the forearm are like guide rails for the aerosol [31].

The aerosol is thrown up from below and passed between the protective shield protruding below and the face to the mouth and nose; this must be avoided at all costs. Such a protective shield is only acceptable if the mouth and nose underneath are protected by a correctly fitted mouth and nose mask or a breathing mask. This double protection of mask and shield is not infrequently used for the mechanical removal of dental plaque in order to fix the often massive dirt on the shield and not let it get on the mask.

Mouthwash solutions

If the patient rinses and gargles his mouth and throat with disinfecting liquid (oral antiseptics) before treatment, the germ content in the saliva, on the mucous membrane and in the aerosol can be reduced [32, 33]. The rinsing solution should get into the throat as much as possible. A report by the North Rhine Dental Association [34] states that the following antiviral mouthwashes have proven to be particularly effective against SARS-CoV-2: Listerine® cool mint (available in drugstores and supermarkets) as well as Dequonal® and iso-Betadine® Mouthwash 1% (available in pharmacies). Octenisept® is particularly effective (personal communication from Prof. Dr. Lutz Jatzwauk). Presumably, further funds will be mentioned in the future.

Workplace protection and general rules of non-contamination

The aerosol cloud floods the surfaces of the treatment device in front of the patient, especially the floating table above the patient's chest. Therefore, no instruments, containers for cotton wool and medication, stands with rotating instruments, bottles with cold spray and the like should be kept here permanently.

As a common storage area for the dentist and assistant, the floating table is almost indispensable in terms of the work system [3]. Before the treatment, the floating table is empty. The instruments and other work equipment required for the intended treatment are placed on the floating table. After the treatment, everything that is on the floating table must be cleared away and sent to the instrument reprocessing facility or thrown away. The areas of the treatment center that could be contaminated by the aerosol cloud laden with droplets must be disinfected depending on the risk of infection.

The general rules on non-contamination [23, 35] must also be observed with suction technology. This also includes grasping discipline and rational instrumentation [3]. To reduce contamination, the patient's lip and cheek should not be held away with unprotected fingers. Thin-walled, liquid-tight, low-allergen gloves are required. In order to avoid finger contact in the first place, instruments should be used to keep soft tissues away. If gloved fingers keep saliva from soft tissues, an (unnoticed) glove perforation should always be considered. Therefore, the gloved hands should also work with instruments as far as possible. A special retainer [3] or a mouth mirror is suitable for this. These instruments are guided using a special gripping technique, for example, when holding the upper and lower lip and holding the patient's tongue away (detailed illustration: Hilger [3]).


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    Gloved hands should also work with instruments whenever possible

Dental work systematics and posture

From what has been said, the paramount importance of suction technology becomes clear. In order to use these successfully, the basic principles of appropriate patient positioning and correct sitting must be adhered to by the dentist and assistant (extensive information: Hilger [3]). The dental work system also includes the rational instrumentation (mentioned in the RKI guideline [23] as protection against contamination) as well as the special suction technology for treatment without assistance (solo work). Jatzwauk [36] rightly regrets that "the tried and tested suction rules are only inadequately communicated today." Anyone who would like to optimally apply the dental work system can find information in the specialist literature and in corresponding training courses (information from the author)