A diastema (plural diastemata, also often called diastemae or diastases) is a space between two teeth. When we speak of diastemata in horses, we usually refer to spaces between the molars of the horse. Periodontitis refers to an inflammation of the ‘periodontium,’ the surrounding tissue around the teeth. In healthy horses, all six molars fit closely together. Each row of molars thus acts as one functional unit, which you might best compare to rough millstones. A horse with diastemata has abnormally large spaces between one or more consecutive molars. These spaces quickly fill up with food particles (see photos). Diastemata are most common in the lower jaw, especially between the back molars, but this condition can occur between all teeth. The diastemata themselves are not painful, but the accumulation of food in these spaces leads to often very painful inflammation of the gums and underlying tissues (periodontitis).