Odontogenic maxillary sinusitis caused by odontogenic infections

Regarding the aetiology of usual odontogenic maxillary sinusitis, because of an increase of personal hygiene awareness in Japan, it has become rare that untreated dental diseases (i.e. dental caries) cause odontogenic maxillary sinusitis.^{Reference Sato2–Reference Sato, Chitose, Sato, Sato, Ono and Umeno7} Instead, most teeth that cause odontogenic maxillary sinusitis have already received dental treatment, especially root canal treatment, that is, endodontics.^{Reference Sato2–Reference Sato, Chitose, Sato, Sato, Ono and Umeno7} Consequently, it is important that the teeth always be suspected as the cause of odontogenic maxillary sinusitis, even if a dental procedure has already been performed.^{Reference Sato2,Reference Sato3}

When the root canals of teeth are incompletely filled with a filling material during endodontics, insufficient root canal treatment causes pulpitis and pulp necrosis in the root canal at the root apex.^{Reference Sato2–Reference Sato4} Pathological studies of the problematic teeth (those causing the odontogenic maxillary sinusitis) show pulp necrosis and apical lesions after root canal treatment.^{Reference Sato2,Reference Sato3} Pulp inflammation causes apical lesions (apical periodontitis); consequently, odontogenic infection such as alveolar osteitis occurs.^{Reference Sato2,Reference Sato3} When the odontogenic inflammation is constantly presented at the floor of the maxillary sinus, the maxillary sinus is at risk of becoming inflamed.^{Reference Sato2,Reference Sato3}

Odontogenic maxillary sinusitis precipitated by maxilla or maxillary sinus lesions

As mentioned above, the pathophysiology of the usual odontogenic maxillary sinusitis is well understood. However, atypical odontogenic maxillary sinusitis caused by odontogenic infections precipitated by the maxilla or maxillary sinus lesions is not well known.

Dental caries cause pulpitis in the pulp chamber, and pulpitis and pulp necrosis progress from the root canal to the root apex (Figure 4). However, there is another atypical pathophysiological condition of pulpitis and pulp necrosis. An inflammation around the root apex causes pulpitis in the root apex and root canal via the apical foramen, and pulpitis and pulp necrosis progress from the root apex, root canal and pulp chamber, that is, pulpitis and pulp necrosis are ascending (Figure 4).

Fig. 4. Progress of pulpitis and pulp necrosis caused by ascending pulpitis.

Sato reported an atypical pathophysiology of odontogenic maxillary sinusitis caused by odontogenic infections precipitated by the maxilla or maxillary sinus lesions.^{Reference Sato8,Reference Sato9} The pathological findings of the odontogenic infections are ascending pulpitis and pulp necrosis precipitated by the maxilla or maxillary sinus lesions, after which, ascending pulpitis and pulp necrosis cause apical lesions and odontogenic maxillary sinusitis.^{Reference Sato8,Reference Sato9} The maxillary sinus lesions are acute maxillary sinusitis and retention cysts, and maxilla lesions include post-operative maxillary cysts and odontogenic cysts.^{Reference Sato8,Reference Sato9}

Odontogenic maxillary sinusitis precipitated by maxillary sinus retention cysts

Figure 5 shows the pathophysiology of odontogenic maxillary sinusitis caused by odontogenic infections precipitated by retention cysts in the maxillary sinus. When the root apex protrudes into the maxillary sinus and is covered by a retention cyst occupying the floor of the maxillary sinus, compression resorption and periodontitis of the root apex occur. Furthermore, pulpitis progresses from the root apex to the root canal (ascending pulpitis) (Figure 4). Once the ascending pulpitis and pulp necrosis occur, secondary apical lesions also occur. When secondary odontogenic inflammation such as apical periodontitis is constantly present at the floor of the maxillary sinus, the maxillary sinus is exposed to the potential danger of inflammation.^{Reference Sato2,Reference Sato3} The inflammation and infection from tooth roots can spread through the maxillary alveolar bone and sinus mucosa, thereby causing sinus inflammation and infection (secondary odontogenic maxillary sinusitis) (Figure 5).

Fig. 5. Pathophysiology of odontogenic maxillary sinusitis caused by odontogenic infections precipitated by the maxilla or maxillary sinus lesions such as retention cysts. The main pathophysiology of odontogenic maxillary sinusitis caused by odontogenic infections precipitated by the maxilla or maxillary sinus lesions is ascending pulpitis and pulp necrosis.

Diagnosis of odontogenic infections caused by maxillary sinus retention cysts

Regarding the clinical symptoms, when persistent facial pressure and cheek pain continues even though there are no lesions in the tooth crown (except dental restoration), tooth root or periodontal tissue, the tooth should be suspected to have periodontitis and pulpitis around the root apex. In addition, when the tooth has percussion pain, the tooth should be suspected to have periodontitis and pulpitis around the root apex.

Cone-beam CT scanning is extremely accurate and useful in the diagnosis of odontogenic maxillary sinusitis.^{Reference Sato10–Reference Shahbazian, Vandewoude, Wyatt and Jacobs12} This study showed that cone-beam CT scanning is also extremely accurate and useful in the diagnosis of odontogenic infections caused by retention cysts of the maxillary sinus, in addition to physical examination. Furthermore, the relationships between the retention cysts and the apex of the affected teeth can be observed using cone-beam CT scanning. The retention cysts occur on a mucosal surface of the maxillary sinus floor, and they surround the root apex of the teeth protruding into the maxillary sinus.

Dental evaluations by plain dental radiography frequently fail to detect odontogenic infections caused by retention cysts of the maxillary sinus. The relationship between the retention cysts and the apex of teeth can be accurately observed using cone-beam CT scans.

Optimal timing of sinus surgery

As mentioned above, there is an atypical pathophysiology of odontogenic maxillary sinusitis caused by odontogenic infections precipitated by maxillary sinus lesions such as retention cysts. The pathological findings of the odontogenic infections are ascending pulpitis and pulp necrosis precipitated by maxillary sinus lesions.^{Reference Sato8,Reference Sato9}

Functional endoscopic sinus surgery is highly indicated when a maxillary sinus retention cyst causes periodontitis and pulpitis of the root apex. In the present case series, the upper three-quarters portion of retention cysts was removed; however, the lower one-quarter portion of the cyst wall attached to the floor of the maxillary sinus and root apex were left intact under nasal endoscopy, to avoid injuring the apical foramen and dental nerve. The results of the present study showed that the treatment outcome was exceptionally good once the drainage of the retention cysts was successfully restored after surgery.

Regarding the optimal timing of FESS, The procedure should be performed before the periodontitis and pulpitis of the root apex progress to ascending pulpitis and pulp necrosis. In other words, FESS should be performed while the affected tooth is still vital. This surgical indication aims to prevent odontogenic maxillary sinusitis caused by odontogenic infections that are precipitated by maxillary sinus lesions such as retention cysts.