Much like the skin and other mucosal surfaces, the human oral cavity is densely populated with microbial life that plays a variety of roles in our health and wellbeing. As with any colonized surface, it can also be susceptible to infection from native flora and invasive pathogens. Infections of dental origin—odontogenic infections—are among the most common infections worldwide.
These infections can spread along fascial planes to involve the face and deep neck spaces; in adults, odontogenic infections are the primary cause of deep neck infections. These infections often require interprofessional treatment, with input from dentists, oral surgeons, otolaryngologists, primary care providers, and emergency medicine practitioners.
Anatomy
The pediatric and adult oral cavity contains 20 and 32 teeth, respectively, divided evenly between the maxilla and mandible. Each tooth has between one and three roots that sit within the corresponding socket of the alveolus. The neck of each tooth sits above the alveolus and is surrounded by gingiva in the healthy adult. The crown, covered by enamel, is the visible portion of the tooth. Each tooth is fixed within the socket by periodontal ligaments and supplied by nerves and blood vessels through each root.
There are many potential spaces between the muscles, bones, and fasciae of the face and neck to which odontogenic infections can spread. Deep to the nasolabial fold, the canine space is formed by the insertion of the levator anguli oris muscle; it is bounded posteromedially by the maxilla and levator anguli oris and laterally by the facial skin. The root of the maxillary canine is often long and extends beyond this insertion.
Infection of a maxillary canine can extend from the tooth root into the canine space. Similarly, the buccal space is formed by the insertion of the buccinator muscle on the maxilla and mandible; it is bordered medially by the buccinator muscle and maxilla and laterally by the skin. A maxillary molar root extending superiorly to the insertion can allow for the spread of infection into the subcutaneous tissues of the face.
Infections of the mandibular teeth can lead to infections in three different spaces. The sublingual space is bounded superiorly by the lingual oral mucosa, medially by the extrinsic tongue muscles, inferiorly by the mylohyoid muscle, and anterolaterally by the lingual cortex of the mandible.
The submandibular space is bounded superiorly by the mylohyoid muscle, inferiorly by the neck skin, and laterally by the mandible. The posterior border of the mylohyoid is free, allowing infection to spread between the submandibular and sublingual spaces easily. Finally, the submental space is bounded superiorly by the mylohyoid muscle, inferiorly by the neck skin, and laterally by the anterior bellies of the digastric muscles.
The spread of odontogenic infections of mandibular origin is largely based on the position of the tooth roots relative to the mylohyoid line. The mylohyoid inserts on the superior surface of the hyoid bone and originates from the lingual cortex of the mandibular body at a point known as the mylohyoid line, which is an oblique line that slopes inferiorly from posterior to anterior. Infection spreading medially and inferiorly along dental roots superior to this line will result in infections of the sublingual space; spread along those roots inferior to the line will result in submandibular space infections.
Spread to the submental space is unlikely to occur directly from the tooth root and often occurs due to spread from the submandibular space, sublingual space, or directly from the skin. Infection spreading to the buccal cortex will result in spread to the buccal space or superficial tissues of the neck along the insertion of the platysma on the mandible.
Microbiology
The flora of the oral cavity is diverse, but it is dominated by bacteria, particularly anaerobes and facultative anaerobes. It is estimated that over 700 types of bacteria live within the oral cavity and various types of fungi. The most common bacterial genus by far is Streptococcus, a gram-positive coccus; common species include S. mitis, S. sanguinus, S. salivarius, and S. anginosus.
Other notable gram-positive bacteria include diphtheroids and Clostridium species, a common anaerobic bacterial genus native to the oral cavity. Gram-negative bacteria are also native but are more common in those with poor oral hygiene or diseased states; common gram-negative bacteria in the oral cavity include Prevotella, Fusobacterium, Haemophilus, and Neisseria. Given the diverse bacterial flora of the oral cavity, nearly all odontogenic infections are polymicrobial; treatment is therefore broadly directed even after culture results.
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