ABSTRACT: Equine odontoclastic tooth resorption and hypercementosis (EOTRH) is a relatively recently described dental disorder, commonly found in horses above the age of 15 years old (Carsten Staszyk et al. 2008). The disease was first categorised as EOTRH in 2008, following the identification of clinical cases involving severe resorptive lesions and cementomas forming on the lower portion of equine incisors (Kreutzer et al. 2007) (Baratt 2007). The two main disease indicators are resorptive lesions caused by odontoclasts and hypercementosis, characterised by reparative/irregular cementum deposition, forming bulbous-like features (Schätzle, Tanner, and Bosshardt 2005). Horses with severe EOTRH often present dysphagia, pain whilst eating and behavioral changes, which may lead to further unrelated complications (Earley and Rawlinson 2013). Some suggested that Warmbloods and Thoroughbreds are more commonly diagnosed (Sykora et al, 2014; Smedley et al, 2015; Lorello et al, 2016; Earley et al, 2017), although others state there are no appar¬ent breed associations (James, 2022; Tretow et al, 2023). Furthermore, in a limited group of Icelandic horses, a diagnosis was established in 72.2% of cases (Tretow, Hain, and Bienert-Zeit 2023). While radiography is the primary diagnostic method for EOTRH after clinical examination, recent studies have indicated that this approach may lack sensitivity for early disease detection, potentially impeding treatment if the condition has advanced significantly (Albers, Bienert-Zeit, and Staszyk 2022). A comparable ailment observed in cats is Feline Odontoclastic Resorptive Lesions (FORL). In this species there was a prevalence of 29% , and similar to EOTRH, it exhibited an elevated risk associated with age (Gorrel 2014). The underlying causes of EOTRH are not yet fully understood with many potential factors considered, including age, sex, breed, diet and environment (Pearson et al. 2013). One of the first theories suggest a sequence of events beginning with periodontal inflammation leading to resorptive lesions and subsequent cementum production (Carsten Staszyk et al. 2008). Other studies found gram-negative bacteria (Treponema, Tannerella) were more commonly identified in the gingival crevicular fluid of diseased horses, highlighting the potential importance of the oral microbiome in disease aetiology (Sykora et al. 2013). Current treatment involves extraction of affected teeth. However there is an increased likelihood of neighboring teeth developing EOTRH (Rahmani et al. 2019). Presently there are no reported disease modifying treatments available to treat EOTRH and symptom management and pain reduction are the current gold standard approaches (Foster 2013). Whilst the cementum of teeth is the most effected dental tissue other types of dental tissues include dentine, enamel, pulp and the periodontium. The latter consists of cementum, periodontal ligament and alveolar bone. Compositionally cementum is similar to bone with 55% organic material and 45% inorganic hydroxyapatite (Tziafas 2005). It covers the entire length of equine teeth, potentially explaining the hyperactivity of cementum-producing cells (cementoblasts) in EOTRH [C. Staszyk, Suske, and Pöschke (2015)](Bosshardt 2005). Coronal cementum acts as a support to enamel, whilst cementum nearer to the roots is primarily an interface between tooth and the periodontal ligament (PDL). Finally a third type of cementum is present within the infundibulum near the coronal surface of the tooth. Irregular cementum has been shown to be deposited during EOTRH at both resorbed and non-resorbed surfaces along the tooth-PDL interface. Proteomic tools have been utilised to analyse clinical samples in both normal and disease-specific states. Specifically in dental tissues proteomics has been used to map proteomes of enamel, dentin, cementum and pulp in human teeth [Green et al. (2019)](Widbiller et al. 2019)[Giovani et al. (2020)](Eckhardt et al. 2014). As well as this human dental diseases, such as gingivitis, caries and periodontal disease have all been investigated with a similar approach [Gonçalves et al. (2011)](Wang et al. 2018)(Hartenbach et al. 2020). There have been no studies performed to identify potential pathological distinctions between the cementum tissues from healthy horses and those with EOTRH. We hypothesised that global protein changes in horses with and without EOTRH would increase the understanding of underlying pathways and disease mechanisms enabling insight into aetiologies. In addition, by understanding the pathophysiological mechanisms related to EOTRH this could provide treatment targets to delay or prevent disease progression. To investigate protein profiles we used unbiased label-free mass spectrometry-based proteomics.
Emily Clarke 
