The equine periodontium: the (re)model tissue

Recent developments in equine dentistry

Equine dentistry is a rapidly developing clinical specialty. It has benefitted from key advances in anatomical and physiological research, development of equipment and instrumentation, utilisation of standing sedation and anaesthesia protocols, a change towards minimally invasive surgical techniques, and the introduction of restorative and endodontic techniques translated from techniques used in human and canine dentistry. Anatomical research has provided further insight into the endodontic system of incisors and cheek teeth and how it changes throughout development with age. Studies of the periodontium have demonstrated a rich vascular supply and repair capacity. Routine dental visits are increasingly being performed utilising sedation and clinical instruments for routine examinations. Equipment has become more efficient, battery-operated and miniaturised giving benefits to both equine dental maintenance work and advanced techniques, assisting the transition to minimally invasive techniques, and the development of endodontic and restorative dentistry. Diagnosis has also benefitted from advances in equipment such as patient-side digital radiography systems, high definition oroscopy, and small diameter flexible fibrescopes that are capable of visualising inside a pulp canal. Dental units combining endodontic high- and low-speed drills, suction and air or water flush are becoming increasingly used and adapted for equine use. Sedative combinations and standing anaesthesia protocols have meant that revisions of traditional techniques, as well as novel techniques, can be performed with almost no requirement for general anaesthesia. Equine dentistry can only continue to advance in this way if there is early identification of dental disease through clinical oral examinations, leading to a system based on prophylaxis, as in human dentistry. This necessitates a change in attitude of the public and industry in general to a proactive approach, with early intervention based on examination and diagnostic findings of practitioners and not necessarily based on the clinical signs displayed by the patient.

The Equine Gingiva: A Histological Evaluation

Equine periodontal disease in horses has long been recognized as a painful disease, leading to a poor condition. The disease is widespread and attracts growing attention in equine dental medicine. The understanding of the underlying etiological and pathological mechanisms of equine periodontal disease is necessary to develop effective prophylactic and treatment options. As a first step, a thorough description of the histological features of the healthy equine gingiva is required. Specimens were taken from six horses (3 mares, 3 geldings, age: 0.5–26 years). The animals were euthanized for reasons not related to this study. Heads were dissected and gingival specimens, including parts of the adjacent teeth, alveolar bone and the periodontal ligament, were obtained from several positions of the dentition. Histological sections were evaluated via light microscopy, with special attention to the structural components of the gingiva, i.e., the gingival sulcus, the epithelium, and the components of the lamina propria (LP). Although the equine gingiva showed the same structural components as described in humans and dogs, the equine junctional epithelium was adapted to the equine dental anatomy and attached to the equine-unique peripheral cementum. Leucocytic infiltrations (LI) of the LP, sulcular epithelium (SE) and junctional epithelium (JE) were frequently seen. The amount of LI was not associated with a macroscopically visual pathology (e.g., diastema or food entrapment) in the respective position. The gingival sulcus depth had an average depth of <1 mm.

Molecular Characteristics of the Equine Periodontal Ligament

The equine periodontal ligament (PDL) is a fibrous connective tissue that covers the intra-alveolar parts of the tooth and anchors it to the alveolar bone-it, therefore, provides a similar function to a tendinous structure. While several studies have considered the formation and structure of tendons, there is insufficient information particularly on the molecular composition of the PDL. Especially for the equine PDL, there is limited knowledge concerning the expression of genes commonly regarded as typical for tendon tissue. In this study, the gene expression of, e.g., collagen type 1 alpha 1 (COL1), collagen type 3 alpha 1 (COL3), scleraxis (SCX), and fibrocartilage markers was examined in the functional mature equine PDL compared with immature and mature equine tendon tissue. PDL samples were obtained from incisor, premolar, and molar teeth from seven adult horses. Additionally, tendon samples were collected from four adult horses and five foals at different sampling locations. Analyses of gene expression were performed using real-time quantitative polymerase chain reaction (qRT-PCR). Significantly higher expression levels of COL1 and 3 were found in the mature equine PDL in comparison with mature tendon, indicating higher rates of collagen production and turnover in the mature equine PDL. The expression levels of SCX, a specific marker for tenogenic-differentiated cells, were on a similar level in functional mature PDL and in mature tendon tissue. Evidence of chondrogenic metaplasia, often found in tendon entheses or in pressurized regions of tendons, was not found in the mature equine PDL. The obtained results justify further experiments focused on the possible use of equine PDL cells for cell-based regenerative therapies.

A new understanding of oral and dental pathology of the equine cheek teeth

Equine dental disease has a high prevalence. Because of developmental, functional, and anatomic differences, limited inference can be made from brachydont dental pathology to that of equine cheek teeth. This article reviews the pathology of equine cheek teeth and their associated oral tissues, with specific information on periodontitis, pulpitis, maxillary infundibular changes, dental fractures, dental overgrowths, mucosal ulceration, and the regenerative capacity of equine teeth.