Introduction
Odontomas are the most common tumor-like lesions of the human jaw. Nevertheless, from a histopathological perspective it has still not been clarified whether odontomas should be regarded as developmental malformations or true neoplasms. Morphologically, odontomas are characterized by changes in the arrangement of the dental hard substances resulting in partial or complete loss of the typical tooth shape. In the horse, odontoma-related structural changes of the tooth shape often lead to a loss of the integrity of the cheek tooth arcades. This subsequently results in clinically relevant pathologies like diastemata and/or abnormal wear patterns.

Material and Methods
Extracted teeth (n = 25) were submitted from 22 horses (male = 12, female = 8, n/a = 2) aged 2 to 13 years for further macroscopic and microscopic evaluations to the Institute of Veterinary-Anatomy, -Histology, and -Embryology. All teeth were extracted because of clinical pathological findings. From 20 upper pre/molars, 2 upper incisors, 1 lower incisor, 1 canine and 1 conglomerate of dental hard substances pictures were taken using a stereomicroscope. Afterwards all teeth were sectioned using a diamond micro-band saw. The specimens were decalcified for 4 to 6 weeks using buffered EDTA-solution. Following decalcification, all samples were embedded in paraffin wax and afterwards stained with toluidine blue or hematoxylin eosin for histological examinations.

Results
Despite a wide range of morphological changes from total loss of the dental shape to only minor abnormalities of the typical enamel ridge pattern, in all teeth the observed structural changes were due to a focal or general increased formation of dental hard substances. Microscopically, the mineralized hard substances as well as related cell populations showed a well differentiated and histomorphologically normal appearance. However, their stratigraphic alignment appeared disarranged.

Discussion
According to the microscopical findings of well differentiated but disarranged dental substances, the examined equine odontomas are regarded as so-called hamartomas rather than true neoplasms. Hamartomas are defined as an overgrowing, less-organized tissue in a particular anatomical location. In contrast to neoplasms, hamartomas do not show any invasive growth characteristics and have no potential to metastasize. Thus, after a successful and complete extraction of an equine odontoma, a recurrent new formation is not to be expected. However, due to the characteristic structural changes of odontomas, extraction might be complicated.