Melusine Tretow (1995) graduated as a veterinarian at the University of Veterinary Medicine Hannover, Germany, in 2020. Since then, she has been working as an equine vet in a German veterinary practice (Tierarztpraxis für Pferde Eyendorf) in combination with a research project as part of her thesis entitled “Aetiological study on the prevalence of Equine Odontoclastic Tooth Resorption and Hypercementosis (EOTRH) in older Icelandic horses in Germany.”

Background
The dental syndrome Equine Odontoclastic Tooth Resorption and Hypercementosis (EOTRH) is a painful, progressive dental disease with an unknown aetiology. A multifactorial genesis is suggested, involving horse feeding, mechanical stress of the ageing dentition/ periodontal ligament as well as inflammatory and microbiological factors. EOTRH could also be related to age, breed, and sex. Moreover, genetic linkage and metabolic and endocrine disorders like Pituitary Pars Intermedia Dysfunction (PPID), Equine Metabolic Syndrome (EMS) and nutritional secondary hyperparathyroidism may also have an influence. Further theories based on under- or oversupply of vitamins and trace elements. The quite often painful nature of EOTRH emphasises the need for a better knowledge of the underlying pathomechanism and risk factors. A comparative analysis of anamnestic, haematologic, biochemical and endocrine values in EOTRH affected and non-affected horses has not been described.

Methods
The study contained anamneses, clinical and radiological examinations of the rostral oral cavity as well as blood analyses of Islandic horses. Data of 151 horses, aged 15 years and older were collected. Anamnestic data were collected using an owner-completed questionnaire. A CBC was performed and plasma concentrations of calcium, inorganic phosphate, zinc, selenium, vitamin A, 25-hydroxy-vitamin-D3, ACTH, Insulin, free thyroxine, triiodothyronine and total thyroxine were measured. A detailed examination of the rostral oral cavity was performed, and incisor teeth were assessed radiographically using a standardised scoring system for evaluation. Based on the results, the study population was separated into ‘EOTRH affected’ (n=109) and ‘EOTRH healthy’ (n=23) horses. A staging system enabled further differentiation into suspicious (Stage 1), mild (Stage 2), moderate (Stage 3) or severe (Stage 4) EOTRH-affected versus Stage 0 (EOTRH healthy). To assess the correlations between EOTRH diagnosis and collected data, logistic regression analysis was performed.

Results
EOTRH is strongly represented in the Icelandic horse population analysed (>70 % EOTRH-affected horses). A correlation between the results of the blood tests and EOTRH could not be proven. However, age, place of birth and sex showed a significant influence. Furthermore, the assumption that higher acid feeds (haylage, silage) causes or enhances EOTRH was not confirmed. The way in which the roughage is fed (floor, nets or hayracks) does not appear to have any influence either. Likewise, the quality of the water supply (drinking or trough water) does not correlate with the onset of EOTRH. Analysis of clinical findings revealed statistically significant associations between non-age correlating bite angle, fistulae, gingival swelling, gingival recession as well as gingivitis and radiographic EOTRH diagnosis. Meanwhile, no statistic association was found between the occurrence of calculus or tooth mobility and EOTRH diagnosis.

Take home message
EOTRH is a dental disease of high practical relevance due to its widespread prevalence. In the Icelandic horse population studied, many of the previously assumed factors thought to cause or promote EOTRH could not be proven. Older age, male sex and being imported or born in Germany are risk factors. There is a clinical symptom complex that is indicative of the presence of EOTRH: non-age correlating bite angle, bulbous enlargement of gingiva, gingival recession, fistulae and gingivitis. This combination of findings considering severity and age should prompt a radiographic examination to confirm EOTRH diagnosis and start treatment in time.