Occlusal fissures in equine cheek teeth: μCT and histological findings.

Fissures on the occlusal surface of equine cheek teeth are commonly encountered during oral examination. Generally, their presence is considered abnormal but their aetiopathogenesis and clinical impact on pulp disease is still undetermined. The aims of this research were to study the extent of occlusal cheek teeth fissures using high-resolution X-ray computed tomography (μCT) imaging and their histological characteristics. Twenty-seven teeth (of 15 horses) were scanned using μCT imaging to analyse fissure extent. Histological examination of a subset of teeth (n=7) was performed. Forty-three type 1 fissures (35 type 1a, eight type 1b) were identified. The mean length of the fissure of type 1a and type 1b on the occlusal surface was 3.47+/-1.60mm and 13.64+/-7.40mm, respectively. Their mean depth was 13.22+/-10.76mm and 7.42+/-6.42mm, respectively. Potential risk factors associated with fissure depth were identified using a multivariable mixed model The location of the fissure and Triadan number were significantly associated with fissure depth. Fissures could be identified on histological sections with the presence of organic material inside the fissure, microorganisms in the continuation of the fissure extending into the dentinal tubules and the presence of reactionary dentine. This study suggests that fissures can provide a pathway for microorganisms to enter the dentinal tubules, potentially resulting in local pulpal inflammation. It appears that in healthy teeth, vital odontoblasts react by producing reactionary (tertiary) dentin, which lacks patent tubules and thus provides a proper seal.