Antibiotics are among the most often prescribed medications in dental practices.


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Antibiotics are understood as medications that either kill or hinder the growth of microorganisms such as viruses, bacteria, fungi, or parasites.

When antibiotics are prescribed, the individual should strictly differentiate between preventive and a therapeutic administration.

Preventive administration is especially considered before surgeries in order to minimize the threat of wound infections post-surgery. In this case, the objective is to establish a certain antibiotic level in tissues that may possibly be contaminated during the procedure. It should prevent the attachment or reproduction of microorganisms and immediately kill contaminating pathogens. Many studies have shown that such a prophylaxis can be performed on short notice, i.e. for the purpose of administering the antibiotic once or twice.

If, however, an infection has already occurred in terms of the attachment, invasion, or reproduction of the pathogen, and the immunological reaction of the host, then antibiotics must be applied therapeutically.

When should antibiotics be administered therapeutically?

Antibiotics are indicated in case of infections

  • in which a bacterial genesis is ascertained or at least probable
  • if a local rehabilitation of the place of infection is not possible or insufficient

Prescribing antibiotics is particularly necessary in cases of dental infections where a danger of spreading or generalization exists. Signs of spreading include general symptoms such as fever, soft tissue swelling, swelling of the eyelids, or lockjaw.

Viral infections, pains or swelling due to unclear causes such as tumors and simple periodontal and chronic abscesses are not indications for antibiotics.

A pathogen detection and resistance determination prior to the initial administration of antibiotics is practical for antibiotic therapy. Exceptions to this are acute infections requiring immediate antibiotics, as well as a typical pathogen-specific disease pattern. The latter normally applies to dentogenic infections, in which a pathogen and resistance determination is not required.

Classification of Antibiotics

There are a multitude of substances available for antibiotic therapies. By now, even specialists have difficulty surveying this flood of substances. Therefore, it is helpful to divide antibiotics into different classes that provide information not just about the basic chemical structure of a substance, but also about their other characteristics (e.g. tolerance and costs). However, there are also considerable differences within individual antibiotic classes with regard to the range and intensity of the effects of the individual substances.

Range of Effects and Intensity

The range of effects of an antibiotic includes all those microorganisms, which – due to the mechanism of their action – can basically be reached by the substance. Antibiotics are distinguished between those covering a broad range, e.g. with an effect on gram-negative and gram-positive bacteria, on cocci, rods, as well as on anaerobic and aerobic microorganisms, and antibiotics with a small range of effect such as those that are only effective on gram-positive microorganisms.

Depending on the mechanism of the action, a distinction can be made between bactericidal (bacteria killing) and bacteriostatic (bacteria inhibiting) antibiotics. Antibacterial action is determined in vitro through the determination of the minimal inhibitory concentration (MIC) and the minimal bactericide concentration (MBC).

The MIC is the concentration of the antibiotic that is needed to inhibit the growth of a stem. The MBC is the concentration of the antibiotic that is needed to kill 99.9 % of the germs in a pathogen population. Every antibiotic, then, has a characteristic range of effect. Types of germs outside that range are resistant.

However, the term resistance is relative insofar as germ types are also designated “resistant” if they can only be killed in the living organism by means of antibiotic concentrations that cannot be achieved (difference between microbiological and clinical effectiveness).

After oral administration, antibiotics are absorbed to varying degrees, partially depending on food intake. Elimination takes place either through renal clearance or through metabolization in the liver.

Antibiotics may have allergic, poisonous, and biological side effects. Allergies to antibiotics (penicillin in particular) are not rare as up to 10 % of the population suffers from these. The risk of allergization is highest in skin applications and lowest in oral administration.

As a rule, allergic reactions take the form of skin reactions (erythema, exanthema, edema). These should be differentiated from skin rashes, which result from the infection itself. So-called anaphylactic reactions are rare and are virtually absent as part of oral administration.

Poisonous side effects may occur in cases of absolute overdosage or due to accumulation in case of an impaired metabolism or elimination. Due to the wide therapeutic range, the risk of poisoning is very low in most antibiotics.

Biological side effects are understood as the impairment or shift of the physiological germ flora in the oral cavity and colon.

Range of Pathogens

Petrischale mit Bakterienkultur


There are a multitude of different microorganisms to be found in the oral cavity, which may lead to a local infection in the area of the oral cavity, but also to infections of other organs in terms of a focal disease (e.g. endocarditis).


Dentogenic infections consist primarily of aerobic and anaerobic germ combinations, which can sometimes consist of more than 10 different types of pathogens. In such cases, anaerobes attain bacterial counts of up to 105 times the number of the aerobes. They also surpass them considerably with regard to diversity. Germs not belonging to the physiological resident flora of the mouth, such as Escherichia coli, Proteus mirabilis, Streptococcus faecalis, or Clostridium only account for a very small share of all proven bacteria stems.

This suggests that infections in the oral and maxillofacial area are mostly caused by the normally present germs of the mouth and throat cavity and not from the outside.

Since anaerobic germs are often hard to grow in a microbiological culture medium, their verification is not always possible, so that the suspicion is often just made clinically and a microbiological verification cannot be achieved. Clinical clues for anaerobic infections are:

  • Foul smell
  • Aerogenic detection in the tissue in terms of an emphysema
  • Lack of success with treatment after the administration of an antibiotic that is ineffective against the anaerobes


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