Odontogenic infections have.two major origins: (1) periapical, as a result of pulpal necrosis and subsequent bacterial invasion into the periapical tissue, and (2) period on trial periodontal as a result of a deep periodontal pocket that allows inoculation of bacteria into the underlying sof tissues.
Of these two, the periapical origin is the most (ommon in odontogenic infections. Necrosis of the dental pulp as a result of deep caries allows a pathway for bacteria to enter the periapical tissues. Once this tissue has become inoculated with bacteria and an active infection is established, the infection will spread equally in all directions but preferentially along the lines of least resistance. The infection will spread through the cancellous bone until it encounters a cortical plate. If this cortical plate is thin, the infection erodes through the bone and enters the soft tissues. Treatment
of the necrotic pulp by standard endodontic therapy or extraction of the tooth will resolve the infection. ‘Antibiotics alone may stop the infection, but the infection is likely to recur when antibiotic therapy is ended
and the tooth is not treated. When the infection erodes through the cortical plate of the alveolar process, it appears in predictable anatomic locations. The location of the infection from a specific tooth is determined by the following two major factors: (1) the thickness of the bone overlying the apex of thetooth and (~) the relationship of the site of perforation of bone to muscle attachments of the maxilla and mandible. Fig. 1-5-1 demonstrates how infections perforate through bone into the overlying soft tissue. In Fig. 15-1, A, the-labial bone’ overlying the apex of the tooth is thin compared with the bone on the palatal aspect of the tooth. Therefore’ as the infectious process spreads it goes into the labial soft tissues. In Fig. 15-1, B, the tooth is severely. flared, Which results in thicker labial bone and a  relatively thinner palatal bone. In ·this situation as the infection spreads through the bone into the soft tissue, the infection is expressed as a palatal abscess.
Once the infection has eroded through the bone, the .precise location of the soft’ tissue infection will be determined by the position of the perforation relative to the muscle attachments. In Fig. 15-2, AI the infection has eroded through to the labial aspect of the tooth and infe

FIG. 15~-1 When infection erodes through bone, it will enter soft tissue through thinnest bone. A, Tooth apex is near thin labial bone, so infection erodes labially, B, Right apex is near palatal aspect, so bone will be perforated.
FIG. 15~-1 When infection erodes through bone, it will enter soft tissue through thinnest bone.
A, Tooth apex is near thin labial bone, so infection erodes labially, B, Right apex is near palatal
aspect, so bone will be perforated.

rior to the attachment of the buccinator muscle, which results in an infection that appears as a vestibular abscess.  In Fig. 15-2, B, the infection has eroded through the bonesuperior to the attachment-of the buccinator muscle and will be expressed as an infection of the buccal space. Infections from most maxillary teeth erode through  he labiobuccocortical-plate. They also erode through the bone below the attachment of the muscles that attach to the maxilla, which means that most maxillary dental abscesses appear initially as vestibular abscesses. Occasionally, a palatal abscess from a severely inclined lateral incisor or palatal root of a maxillary first molar will occur. Likewise, on occasion a long maxillary canine-tooth will
erode thrugh the bone superior to the insertion of the  levator anguli oris and will cause a canine space infection.More commonly, the maxillary molars will have  infections that erode through the bone superior to the’
insertion of the buccinator muscle, which result in a buccal space infection. In the mandible, infections of the incisors, canines, and premolars usually erode through the labiobuccocortical plate and above the associated musculature, resulting in vestibular abscesses. Molar teeth infections erode
through the linguocortical bone more frequently than the anterior teeth. First-molar infections will drain either buccally or lingually. The second molar can perforate either buccally or lingually (but usually lingually), and
third molar infections almost always erode through the linguocertical plate. The mylohyoid muscle will determine whether infections that drain lingually go into the sublingual or submandibular space. The most common odontogenic infection is a vestibular abscess (Fig. 15-3). Occasionally, patients do not seek treatment for these infections, and the process will rupture spontaneously ‘and drain, resulting in resolution of the Infection.The infection will recur if the site of spont aneous drainage closes. Sometimes the abscess establishes a chronic sinus tract that drains to the oral cavity (Fig. 15-4). As long as the sinus tract continues to drain, the
patient will experience no pain. Antibiotic administration  administration will usually cause a cessation of the drainage, but when .antibiotics are stopped, ·the drainage will recur. Definitive treatment of a chronic sinus tract requires treatment of the original problem, that is, the necrotic pulp treated by endodontic therapy or by extraction of the tooth.



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