Which is used in a deep cavity preparation to prevent thermal shock?

In deep cavity preparations, the primary concern is to protect the pulp from thermal shock caused by temperature changes during restorative procedures. A dental base serves this purpose effectively by providing insulation against thermal variations.

Dental bases are typically made from materials like zinc oxide-eugenol or glass ionomer, which not only insulate but also support the restoration and protect the pulp from irritants and microleakage. Their thickness and thermal properties help buffer the effects of temperature fluctuations that occur during procedures such as filling or when exposing the tooth structure to materials that may conduct heat.

The other options, while serving important roles in cavity preparations, do not primarily focus on insulating against thermal shocks. Varnishes may provide temporary sealing but do not offer sufficient thermal insulation. Desensitizers are mainly used to alleviate sensitivity by closing dentinal tubules rather than protecting against thermal changes. Cavity liners can provide some thermal protection but are often thinner and less effective compared to an appropriate dental base. Thus, for preventing thermal shock in deep cavity preparations, using a dental base is the most appropriate choice.