Computed tomographic and pathological study of equine cheek teeth infundibular caries
Horbal, Apryle Anne
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Several studies have found equine maxillary cheek teeth infundibular disorders to affect most adult horses. Even infundibulae that appear grossly normal on the occlusal surface may contain areas of caries, defective cementum, or complete absence of cementum subocclusally. These defects can range from possibly insignificant small developmental cemental defects deep in the infundibulum to advanced coalescing infundibular caries leading to dental fracture. The aim of this study was to characterize maxillary cheek teeth infundibular disorders by gross, computed tomographic, and histopathological examinations of affected and control teeth. One hundred maxillary cheek teeth that contained 200 infundibulae were extracted post-mortem from 30 horses, including 82 teeth with and 18 without occlusal surface infundibular caries. The occlusal surface infundibular caries was graded using the modified Honma technique, which found 61.8% of the 82 affected teeth to be affected by Grade 1 caries, 27.9% with grade 2 and 10.3% with grade 3 caries. The rostral infundibulae were more commonly affected by occlusal surface lesions (72% affected) as compared to the caudal infundibulae (64% affected) and also had higher grades of occlusal caries. The Triadan 09 position was greatly overrepresented in the diseased teeth, comprising 50% (41/82) of teeth with visible occlusal caries. There was a significant association between the grade of occlusal infundibular caries present and the Triadan positions of the teeth. All teeth were then imaged by computed tomography (CT) to determine crown and infundibular lengths, and to detect the presence and appearance of any subocclusal infundibular cemental abnormalities. Extensive statistical analysis of dental crown and infundibular lengths were performed, showing that relatively shorter infundibulae are more likely to be diseased. However, this finding can be explained by the predominance of Triadan 09 and older teeth in the diseased group, both of which have lower infundibular depth:crown length ratios. Computed tomography showed 182/200 (91%) infundibulae to have infundibular lesions deep to the occlusal surface. No statistically significant association was found between the presence of subocclusal infundibular defects and age of affected horses, grade of caries, or the presence of visible occlusal infundibular lesions. Teeth affected by occlusal caries were 1.3 times more likely to have subocclusal lesions than teeth without occlusal caries. This study also proposes a relationship between the presence of developmental infundibular cemental lesions and later caries formation. Eight maxillary cheek teeth were then imaged using micro-computed tomography (microCT) which provided much finer details of infundibular lesions. MicroCT images were also used to guide the sites of sectioning of teeth for histopathological analysis, which found that the appearance of infundibular cementum was much more variable than its appearance on standard CT or microCT. The cementum of many infundibulae showed extensive sites of former vasculature that were not filled with cementum. Other areas contained moth-eaten cement which often contained plant material and cellular debris, independent of the appearance of the occlusal surface of the infundibulum. No histological evidence of previous vasculature or of haemoglobin breakdown products were found in infundibular cementum. Major findings and interpretations of this study allow us to conclude: - Many infundibulae are affected by occult subocclusal cemental lesions. These lesions appear to have no association with the presence or absence of apparent occlusal surface infundibular lesions, and also are not more significantly apparent in particular Triandan positions or in horses of a particular age. As the subocclusal cemental lesions appear to be unrelated to the presence of occlusal surface lesions, the relationship between infundibular cemental lesions (both occlusal and subocclusal) and the development of clinical sequelae remains poorly understood. - Even in those infundibulae with no apparent occlusal surface infundibular caries, the subocclusal region often contained hypoplastic cementum and, often, impacted feed material at the most apical aspect of the infundibulum on histological examination. Therefore, there must be a communication between the apical portion of the infundibulum and the occlusal surface for this to occur, even in those that appear unaffected by a vascular channel defect or infundibular caries. - The strict definition of infundibular caries as opposed to normal cementum on the occlusal surface of infundibulae is inadequate to describe the great variation in the appearance and composition of infundibular cementum. Further classification of the subocclusal cemental defects and expectations of normal subocclusal cementum may also be included for a more complete understanding. There should be a standardisation of terminology used to describe normal and defective infundibular regions both on the occlusal surface and subocclusally. - It is likely that subocclusal cemental lesions, particularly areas of apical cemental hypoplasia, become become impacted with feed material even before they are exposed on the occlusal surface, which may allow severe (Grade 2 or 3) infundibular caries to form subocclusally long before that portion of the tooth is exposed. - Analysis of the Hounsfield Units (measurement of density of tissues on CT scan) and their relationship to the histological appearance of the same tissues may allow us to determine if an infundibulum contains normal or hypoplastic cementum, or impacted feed material without more invasive investigatory methods.