02.08.2015

Comment on a case report – Advanced diagnostic imaging and surgical treatment of an odontogenic retromasseteric abscess in a guinea pig (J Small Anim Pract 56, 134-137 2015)

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Full-Article at Wiley Online Library

Abstract: A two-year-old guinea pig presented for difficulty chewing. Examination and diagnostic imaging, including computed tomography and magnetic resonance, revealed an odontogenic retromasseteric abscess associated with a mandibular cheek tooth. Treatment included removal of the abscess and marsupialisation of the surgical site for repeated debridement and healing by second intention. Unique features of this case included the use of advanced diagnostic imaging and utilisation of marsupialisation for surgical correction.

Here some critical comments on this paper:

“most striking abnormality was a large, non-painful palpable mass”. This seems to show how “indolent”and “tough” small mammals often are. Human beings, dogs and cats would react differently. These animals tend to suffer silently without showing pain?

“Physical examination showed slight malocclusion of the occlusal plane of the incisor teeth”………….. “The lateral radiographic projection showed an abnormal occlusal plane of the incisor teeth”. In my opinion, there is not only a slight malocclusion of the occlusal plane of the incisor teeth visible, but also a marked elongation of the clinical crowns of both mandibular incisors (red arrows) which occlude abnormally based on that (unphysiological immediate contact) (red circle). Since in most cases with an unilateral abscessation of one or more lower cheek teeth the incisors also show a laterally sloped occlusal plane (as a consequence of the cheek tooth asymmetry), a more detailed description of the occlusal surfaces of all incisors might have been useful. This is missing, unfortunately, although this guinea pig suffers from an apparently advanced secondary incisor malocclusion.

“Intraoral evaluation with an otoscope was unremarkable“ and “Endoscopic intraoral inspection was unremarkable, and there were no abnormalities associated with the right mandibular M3”. It might have been very interesting to add intraoral images of the affected molar (M3) to confirm this statement. In nearly all cases infected cheek teeth show some kind of pathology on their occlusal plane (abnormal appearance of dental folds). These pathological findings are sometimes very subtle, with just a tiny aberration from normal pathology, but in principle, clearly visible on a detailed intraoral examination. Since the last right molar is obviously much thicker on the lateral radiograph (in comparison to the other cheek teeth), this statement must to be doubted. Especially, since the occlusal plane of this tooth also rises slightly upwards most caudally. This should be an abnormal intraoral finding.

“The left oblique projection was unremarkable”. In my opinion, this is not correct. The dental structure of both caudal left molars (M2 and M3) is highly abnormal, since the multiple physiological intradental lines are missing and both teeth additionally show an increased radiodensity along their entire length (white arrows). Furthermore, the occlusal plane between the second and third molar appears “stepped” and the approximal space seems widened. These are important findings that need further diagnostic steps to be able to inform the owner correctly about the severity of the malocclusion. Both teeth are a ticking bomb.

Another pathology not mentioned in the text, is the bilaterally thickened wall of the bulla tympanica (blue arrows). As long as an otitis media is not ruled out, this might influence longterm prognosis and therefore seems to be an important information for the owner and the attending veterinarian. A thickened wall of the bulla is often the result of chronic Bordetella infections. So taking thoracic radiographs prior to any surgery seems indicated to rule out a lung infection that might negatively affect anaesthesia (higher risk).

“The right oblique projection showed a radiotransparent area caudal to the right mandibular third molar (M3), consistent with periapical infection” (yellow arrow):

I would not name it a “periapical” infection but a far advanced “periodontal” infection with secondary bone lysis. It does not seem to be a typical example of an apical infection to me. But I agree, this last molar is highly infected and therefore it needs to be removed. And here I come to my problem with this case report since this tooth has not been extracted. This is absolutely incomprehensible for me and not state of the art.

Other radiographically visible findings that are not mentioned or discussed in the text are: the caudally rising occlusal plane (black dotted line and black arrow) and the highly abnormal structure of the last cheek tooth (M3) with the unphysiological augmentation/widening of its dental body (green line) (so-called macrodont). Such a highly altered cheek tooth can not be worn off normally by its much smaller antagonist. So in the longterm, the opposite tooth always gets involved as well. This maxillary cheek tooth is healthy at the beginning and it can stay healthy in the longterm provided that its abnormally changed antagonist is extracted. Based on the specific chewing motions in guinea pigs the clinical crown of the left upper cheek tooth (M3) can be worn off normally by the remaining last but one mandibular cheek tooth (M2). But in this case the authors conclude the article with this statement: “Extraoral extraction was not considered, as this required a more aggressive disruption of the masseter muscle, and in this specific case incurred the risk of additional fractures of the mandible and the condylar process and damage to the temporomandibular joint”.

My comments on this are: Not extracting an infected cheek tooth also increases the risk of a mandibular fracture since the peridental bone lysis will continue to progress unstoppably – even if antibiotics are applied. For a retrograde access to the last molar the masseter does not need to be aggressively disrupted, as its greatest part can remain unaffected. And the muscle tissue surrounding the infected tooth is highly altered anyway. But even if a radical resection of the muscle might be needed, I can say that the entire masseter muscle can be removed without any problems (own experience). The other chewing muscles can compensate that. 

Otherwise, I agree that the mandible can break, in principle. A certain risk is certainly given. But with such a far advanced periodontal infection the cheek tooth can certainly be mobilized relatively easily. To facilitate mobilization and retrograde extraction of the tooth parts of the alveolar bone can be carefully resected with a bur. 

Overall I guess that a trauma of the temporomandibular joint during the molar extraction is very unlikely. The joint is too far away from the extraction site. Whereas secondary pathology caused by spread of infection is very likely. And this seems to emphasize the importance of tooth extraction.

 

 

It is interesting to see that an iatrogenic injury to the TMJ during surgery seems to be feared, but on the other hand the radiographically visible pathology near the TMJs is ignored or not mentioned and discussed in detail, respectively. The dorsoventral view depicts except for the small radiolucent area and the lysis of the angular process that are mentioned by the authors (thick yellow and white arrow) more pathological findings that seem to be very important: the thickened walls of both bullae (blue arrows) and a wide lateral shift of the caudal part of the right mandibular ramus (processus angularis) (red dotted arrow and red line). Just compare it with the other side (red dotted double arrow). This is indicative of a secondary TMJ pathology (mostly soft tissue affected) and needs further diagnostic steps as a locked jaw is a common consequence of that in the longterm. The periodontally and apically infected last molar (M3) shows radiographic signs of an extreme apex elongation and bone perforation (green arrow). In principle, prognosis is poor in such cases.