Causes and Treatment of Odontogenic Infections

Most orofacial infections are of odontogenic origin. Dental pulp infection, as a result of caries, is the leading cause of odontogenic infection. The major pathogens identified in dental caries are members of the viridens (alpha-hemolytic) streptococci family including Streptococcus mutans, Streptococcus sobrinis and Streptococcus milleri. Once bacteria invade the dental pulp, an inflammatory reaction results in necrosis and a lower tissue oxidation-reduction potential. At this stage, the bacterial flora change from predominantly aerobic to more anaerobic flora. Anaerobic gram-positive cocci (Peptostreptococcus) and anaerobic gram-negative rods (Bacteroides, Prevotella, Porphromonas and Fusobacterium) predominate. The infection progresses, forming an abscess at the apex of the root, resulting in bone destruction. Depending on host resistance and bacteria virulence, the infection may spread into the marrow, perforate the cortical plate and spread to the surrounding tissues.

Additionally, the anaerobic bacteria inhabiting the periodontal tissues may provide an additional source of odontogenic infection. The most common anaerobes are Actinobacillus actinomycetemcomitans, Prevotella intermediud, Porphyrommonas gingivalis, Fusobacterium nucleatum, and Eikenella corrodens.

Most odontogenic infections (70%) contain mixed aerobic and anaerobic bacteria. Pure aerobic infections have less than a 5% incidence. Pure anaerobic infections have a 25% incidence. The consensus by researchers is that in early odontogenic infections, bacteria are aerobic with gram-positive, alpha-hemolytic streptococci (S. viridens) predominating. As the infection matures and increases in severity the microbial flora become a mix of aerobes and anaerobes. The anaerobes found are determined by the site of origin; pulpal or periodontal. As the host defenses begin to control the infection process, the flora become predominantly anaerobic.3,4

Thus, the choice of antibiotic is influenced by a number of factors: Stage of infection development and the ability of the patient to take the antibiotic – medical conditions or allergy.

Antibiotics may also be categorized by their method of attack. Bactericidal antibiotics actually kill microorganisms, while bacteriostatic antibiotics slow bacterial growth and depend on the host immune system to eliminate the microorganism. An antibiotic may be bactericidal for one microorganism and bacteriostatic for another. Bactericidals are preferable over bacteristatics in most situations. Bacteriostatics should not be administered to immunocompromised patients whose compromised immune system may be unable to assist in clearance of the microorganism. Common bactericidals used in dentistry are the penicillins and cephalosporins. Common bacteristatics are the macrolides, tetracyclines and sulfonamides.

The ideal antibiotic for treating dental infections would be bactericidal against gram-positive cocci and the major pathogens of mixed anaerobic infections. It would cause minimal adverse effects and allergic reactions and be relatively low in cost.

Table 1. Empiric Antibiotics of Choice for Odontogenic Infections.

Type of InfectionAntibiotic of Choice
Early (first 3 days of infection)Penicillin VK, amoxicillin
Cephalexin (or other first-generation cephalosporin)1
No improvement in 24-36 hoursBeta-lactamase-stable antibiotic:
Clindamycin or amoxicillin/clavulanic acid (Augmentin®)
Penicillin allergyClindamycin
Cephalexin (if penicillin allergy is not anaphylactoid type)
Clarithromycin (Biaxin®)2
Late (>3 days)Clindamycin
Penicillin VK-metronidazole, amoxicillin-metronidazole
Penicillin allergyClindamycin
1 For better patient compliance, second-generation cephalosporins (cefaclor; cefuroxime) at twice daily dosing has been used.
2 A macrolide useful in patients allergic to penicillin, given as twice daily dosing for better patient compliance.

Adapted from Drug Information handbook for Dentistry; Richard Wynn, Timothy Meiller, Harold Crossley, 12th Edition

In the absence of an allergic reaction, penicillin VK is the drug of choice in treating dental infections as it fits most of these criteria. If a patient with an early stage odontogenic infection does not respond to penicillin VK, there is a strong probability of the presence of resistant bacteria. Bacterial resistance to the penicillins is a result of the production of beta-lactamase by the bacteria. In these cases, beta-lactamase-stable antibiotics should be prescribed to the patient. These include either clindamycin or amoxicillin/clavulanic acid (Augmentin®). Another alternative is to add a second drug to the penicillin (e.g., metronidazole Flagyl®). If the penicillin antibiotics prove to be ineffective in management of the infection, culture and susceptibility testing would be indicated to identify the specific bacteria responsible for the infection. The doses for the above drugs may be found in Table 2.

Table 2. Empiric Antibiotics of Choice for Odontogenic Infections.

Penicillin VK≤ 12 years: 25-50 mg/kg body weight in equally divided doses q6-8h for at least 7 days; maximum dose: 3 g/day> 12 years: 500 mg q6h for at least 7 days
Clindamycin08-25 mg/kg in 3-4 equally divided doses150-450 mg q6h for at least 7 days; maximum dose: 1.8 g/day
Cephalexin (Keflex)25-50 mg/kg/day in divided doses q6h
Severe infection: 50-100 mg/kg/day in divided doses q6h; maximum dose 3 g/24h
250-1000 mg q6h; maximum dose 4 g/day
Amoxicillin< 40 kg: 20-40 mg/kg/day in divided doses q8h
> 40 kg: 250-500 mg q8h or 875 mg q12h for at least 7 days; maximum dose 2 g/day
> 40kg: 250-500 mg q8h or 875 mg q12h for at least 7 days: maximum dose: 2 g/day
Amoxicillin/clavulanic acid (Augmentin®)< 40 kg: 20-40 mg/kg/day in divided doses q8h
> 40 kg: 250-500 mg q8h or 875 mg q12h for at least 7 days: maximum dose 2 g/day
> 40 kg: 250-500 mg q8h or 875 mg q12h for at least 7 days; maximum dose: 2g/day