Saliva Test for Streptococcus Mutans

Detection of excessive salivary contamination with Streptococcus mutans (S. mutans, mutans streptococci), the most important caries germ, is considered an indication of a patient’s increased caries risk because salivary contamination correlates with the presence of S. mutans in plaque (dental plaque). There are several diagnostic parameters that can help determine a patient’s individual risk of developing caries, such as:

  • Assessment of caries experience (e.g., existing fillings).
  • Assessment of oral hygiene
  • Presence of initial carious lesions (visible whitish decalcification).
  • Determination of the salivary flow rate
  • Saliva test for S. mutans
  • Saliva test for lactobacilli

Saliva tests offer the advantage that they can provide preventive indications of an expected carious event. Thus, their results have an impact on the prophylactic program established for a patient. Nevertheless, it must be remembered that the caries risk depends on many factors and is subject to time-dependent fluctuations, so that the results of a saliva test represent a snapshot. In terms of their significance, they are inferior to clinical predictors such as discolored fissures (pits in the occlusal relief of posterior teeth) and chalky decalcification on smooth surfaces of the teeth.

Indications (areas of application)

The indication to examine saliva with regard to the bacterial count for cariogenic mutans streptococci arises in the context of individual prophylaxis:

  • Individual preparation of a preventive (precautionary) prophylaxis program: The results of the saliva test are incorporated into the recommendations that the patient receives for fluoridation measures, dietary changes and recall intervals (interval between dental visits)
  • To monitor the progress of individual prophylaxis measures.
  • For monitoring the progress of germ-reducing measures such as a fortnightly chlorhexidine therapy, which serves to reduce the germs of mutans streptococci.

Contraindications

  • Saliva testing for S. mutans must not take place during or after the patient has received antibiotic therapy less than 14 days ago
  • An antibacterial mouth rinse must not be used in the 12 hours before testing.

Before the examination

First, a saliva sample is collected, usefully in conjunction with a determination of the saliva flow rate, for which the patient chews on a kerosene pellet for five minutes and collects the resulting saliva in a cup. The amount produced allows conclusions to be drawn about the natural cleansing ability of saliva by rinsing the teeth. The saliva sample can also be used to determine the buffer capacity of the saliva, which, like the amount of saliva produced, allows conclusions to be drawn about the caries susceptibility of the dentition. Since one would like to get comparable results over longer periods of time, the following recommendations exist from the manufacturer’s side (KariesScreenTest by Aurosan), which refer to the behavior at least one hour before the test:

  • Do not eat
  • Drink nothing
  • Do not chew gum
  • Do not smoke
  • Do not brush teeth

The procedure

Easy-to-use culture medium carriers coated on both sides in sample tubes are offered by Ivoclar Vivadent (CRTbacteria):

  • The carrier side coated with blue agar (culture medium) is used for bacterial count testing of S. mutans.
  • The carrier side coated with light agar is used for the bacterial count examination of lactobacilli.
  1. The agar carrier is taken from the sample tube.
  2. A NaHCO3 tablet is placed on the bottom of the tube. The sodium bicarbonate releases CO2 (carbon dioxide) during the incubation period of the saliva sample and thus ensures a low-oxygen atmosphere.
  3. The protective films are removed from the agar surfaces without touching them.
  4. Saliva is applied to the agar surfaces with a pipette, excess saliva is allowed to drip off by holding it at an angle.
  5. The tube is sealed after insertion of the agar carrier.
  6. Incubation of the upright sample is performed in the incubator cabinet for 48 hours at 37 °C. An incubation period extended by one to two days does not affect the number of germ colonies.
  7. Reading of colony density is done visually by comparison with a reference map. The classification is only in two risk classes:
Risk class CFU (colony forming units) per ml saliva
Low < 105
high > 105

Modification of the procedure:

With good oral hygiene, a low bacterial count of mutans streptococci can be expected. Nevertheless, the dentition may have risk sites, for example, caused by rotational and crowded teeth or located in the region of the posterior molars (molars), which are more difficult to access for adequate oral hygiene. In these cases, the procedure can be modified as follows to refine the diagnosis:

  1. Plaque is collected from the tooth surfaces of the problem areas using a fine brush.
  2. The brush is used to carefully spread the sample on the blue agar surface without scratching it.
  3. To release enough CO2, the NaHCO3 tablet must be moistened with a drop of water.
  4. The procedure continues as described.

After the examination

The incubated culture media can be used as visual aids in the motivational interview with the patient.