Which of the following is a disadvantage of calcium hydroxide?

The selected response is correct because calcium hydroxide, while beneficial in many dental applications, has inherent limitations in its mechanical strength, particularly when used in deeper cavities. When relying solely on calcium hydroxide as a lining material, it may lack sufficient durability to withstand the forces exerted by occlusion or pressure from filling materials. Consequently, in deeper cavities where stronger reinforcement is needed, it is typically advisable to use a base material alongside calcium hydroxide to provide added strength and support.

The other options highlight characteristics of calcium hydroxide that are advantages rather than disadvantages. While it promotes dentine remineralisation—which is beneficial for tooth health—it does not serve as a hindrance. Its compatibility with various filling materials makes it a preferred choice in many dental procedures, as it doesn't adversely affect the bonding process. Additionally, while its sedative properties can be an asset for alleviating postoperative discomfort, they do not constitute a disadvantage. Thus, the appropriate context of calcium hydroxide’s limitations in deeper cavities supports why the chosen option correctly identifies a disadvantage.