Classification of Hydraulic Cements Used in Dentistry

Since their introduction in clinical dentistry, hydraulic cements have gained popularity. Their applications are diverse and their usefulness is due to their hydraulic nature. These materials require water to set and reach their optimal physical and mechanical characteristics, do not deteriorate when wet, and form calcium hydroxide as a by-product of the hydration reaction. All these characteristics are important for a number of clinical applications. The first hydraulic cement was a simple mixture of Portland cement, as used in the construction industry, with bismuth oxide to increase its radio-opacity. Regardless of being a hydraulic calcium silicate, it was initially incorrectly labeled as a phosphate cement misleadingly called "mineral trioxide aggregate." Since then, beneficial clinical applications have led to the development of a number of materials with a different base, alternative vehicles, and incorporating modifiers of various kinds. Given the variety, and possible confusion, a rational classification of hydraulic cements used in dentistry is necessary. The classification is primarily dependent on the clinical context in which the materials are used as this informs the user about the environment and possible interactions. Secondly, a classification based on the material constitution is given as knowledge of its chemistry will help predict behavior, identify risks, and thus facilitate selection and handling.