Infections of Odontogenic Origins

   Odontogenic infections refer to infections originating within the teeth. These can be divided into endodontic or pulpal infections that develop in the tissues within a tooth, and periodontal infections that can originate in the soft tissues surrounding the teeth.
  Endodontic Infections
  1. Dental Caries
  Dental caries is commonly referred to as tooth decay or cavities. Worldwide, this condition is one of the most common chronic infectious diseases (Aas et al., 2008).

While the occurrence of dental caries is common, the mechanism for their etiology is still being determined. Three hypotheses have been put forward to explain how bacteria cause dental caries.
The nonspecific plaque hypothesis posits that the overall contribution of all the bacteria in the oral cavity creates the conditions necessary for tooth decay. This is based on the idea that the quantity of plaque, regardless of the bacterial source, is the key determinant in the formation of dental caries.

Advances in the study of microbiology have refuted this hypothesis, although plaque removal is still the most recommended way to prevent caries (Rosier et al., 2014).
The specific plaque hypothesis proposes that only select bacterial species are actively pathogenic. This is supported by the observations that bacterial species have been identified in the oral cavity of individuals with dental caries, but are not found in similar populations of individuals without caries (Aas et al., 2008). Finally, the ecological plaque hypothesis asserts that dental caries occur following environmental changes that shift the balance of the normal microbiome. This hypothesis accounts for the virulent growth of specific bacterial species following an antibiotic treatment that alters normal bacterial levels (Rosier et al., 2014).
  Route of access
      Bacteria cause dental caries first by demineralizing the outer tooth enamel and invading the soft underlying dentin (Lopez-Piriz, Aguilar, & Gimenez, 2007).
    Chipped or ground-down surfaces of teeth can provide easy access to this soft tissue. Deep pulpal tissue then undergoes necrosis and bacteria can continue degrading structures until they exit through the apical foramen or foramina.
    Additionally, gingival recession can provide a route of access to pulpal tissues, including the roots of adjacent teeth. Infections that reach the apical regions of a tooth are capable of spreading to the surrounding tissues and can result in systemic infections.
    Therefore, it is important to treat pulpal infections expediently in order to prevent further damage to the surrounding tissue.
  Bacterial Causes
  Dental caries can be caused by many bacterial species, with a higher proportion of anaerobic bacteria associated with the condition.  

The most common of these anaerobic bacteria are Prevotella intermedia, Fusobacterium nucleatum, Porphyromonas endodontalis, Porphyromonas gingivailis, and Selenomonas sputigena, whereas the most common aerobic bacteria viridans streptococci and Streptococcus anginosus.
  Bacterial Causes
  Dental caries can be caused by many bacterial species, with a higher proportion of anaerobic bacteria associated with the condition.

The most common of these anaerobic bacteria are Prevotella intermedia, Fusobacterium nucleatum, Porphyromonas endodontalis, Porphyromonas gingivailis, and Selenomonas sputigena, whereas the most common aerobic bacteria viridans streptococci and Streptococcus anginosus. (Lopez-Piriz et al., 2007; Robertson & Smith, 2009).

As evidenced by the varying hypotheses for what kinds of bacterial populations cause dental caries, it is not trivial to identify which bacterial species are responsible. Factors including immunocompetency of the host and bacterial populations in specific microdomains further complicate this analysis (Ji & Choi, 2013).