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EQUINE VETERINARY EDUCATION / AE / MARCH 2016
Case 1 and the diagnosis of a hypercementotic form of EOTRH was confirmed (Fig 8).
Discussion
Both cases presented were diagnosed with a hypercementotic form of EOTRH that was evident grossly, radiographically and confirmed histopathologically. The two cases differed significantly in terms of severity suggesting there may be a wide range of presentations for this condition.
Clinical signs The equine hypsodont tooth is typically composed of three types of peripheral cementum (Kilic et al. 1997b). Peripheral enamel is directly surrounded by a thin layer of primary cementum that contributes to the amelocemental junction (Mitchell et al. 2003). A thicker layer of secondary cementum is deposited over the primary cementum and it is into this material that the periodontal ligament (PDL) attaches and provides anchorage of the tooth (Mitchell et al. 2003). Tertiary cementum (or clinical crown cementum) is produced and
deposited at the subgingival level. Once erupted, this material becomes a structural component of the clinical crown providing support for the hard but brittle enamel ridges (Mitchell et al. 2003, Staszyk et al. 2015). Equine peripheral cementum at the occlusal level is
known to be thicker on the palatal aspect of maxillary CT compared with the buccal surface (Kilic et al. 1997a, Mitchell et al. 2003). The opposite is found on the mandibular CT where thicker peripheral cementum is present on the buccal surface compared with the lingual border (Mitchell et al. 2003). In both cases, there was an exaggeration of this normal
pattern with cementum deposits showing visible incremental lines. These features suggest that a transition occurs where normal clinical crown cementum deposition becomes unregulated and disproportionate. This macroscopic finding has been confirmed by the histological demonstration of high amounts of irregular cementum. It is emphasised that the presence of exaggerated amounts of irregular clinical crown cementum was the only visible sign of cheek tooth EOTRH in Case 1, apart from radiological signs. Contrary to Case 1, the
a)
d)
b)
e)
c)
f)
Fig 8: EOTRH in cheek teeth of a 38-year-old Shetland pony mare (Case 2). a) Radiograph showing bulbous enlargements of all cheek teeth and blunting of the dental roots. b) Extracted 411, lingual view. The tooth is covered by irregular cementum (irC). Dark stained areas indicate presence of necrotic tissue. c) Extracted 411, horizontal section, root tip. Incremental lines indicate continued deposition of irregular cementum causing hypercementosis. Dark stained necrotic areas reaching into the irregular cementum indicate ongoing resorption of tooth substances. d), e), f) Extracted 411, histological sections demonstrating typical microscopical features of EOTRH: d) Odontoclastic resorption (red arrowheads). e) Reactive deposition of reparative/irregular cementum indicated by presence of wavy reverse and incremental lines (blue arrowheads). f) Presence of hypercementotic areas composed or cellular and acellular irregular cementum. Green arrowheads: cementoblast lacunae. Blue arrowheads: reversal and incremental lines.
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