Which material is best for forming a dentine bridge?

Correct answer: D. Calcium hydroxide

• A. Zinc oxide-eugenol is sedative and palliative but does not induce a bridge; eugenol is in fact cytotoxic to pulp cells at higher concentrations.
• B. Resin-modified glass ionomer shares that limitation and its resin component adds pulpal irritation potential.
• C. Conventional glass ionomer is a good liner and base with fluoride release, but it has no bridge-inducing capacity.
• D. Correct. Calcium hydroxide's high pH causes a superficial layer of necrosis and then stimulates odontoblast-like cells to lay down reparative dentine — the dentine bridge. It is also strongly antibacterial for the same reason.

Note: MTA and the newer bioceramics now bridge as well or better than calcium hydroxide, with less tunnel defect formation — but calcium hydroxide is the classic answer when MTA is not among the options.