What type of cement is considered most harmful to pulpal tissue?

Zinc phosphate cement is considered the most harmful to pulpal tissue due to its high acidity when mixed. This acidity can potentially irritate the dental pulp if the cement is used inappropriately or if it comes into contact with the pulp itself. When zinc phosphate cement is mixed, it creates an acidic environment that can lead to pulp necrosis if not properly isolated from the dental pulp.

The other types of cements have properties that are less damaging to pulpal tissue. For example, glass ionomer cement releases fluoride, which can be beneficial and has a neutral pH, making it less irritating. Resin cements also have better biocompatibility and less acidity compared to zinc phosphate. Calcium hydroxide, on the other hand, is often used as a pulp capping material because it promotes the formation of reparative dentin, which is protective to the pulp.

These characteristics underscore why zinc phosphate is recognized as the most harmful cement when it comes to pulpal health.