Placement of a restorative material in dentin produces the possibility of pulpal injury. In vitro studies have shown that the constituents of dental biomaterials have toxic potentials. In the clinical setting, there may be an immediate reaction of the pulp to, for example, acid etching and to the placement of a bonding agent; however, in most cases the remaining dentin serves as protection against long-term or permanent damage to the pulp. Important factors for long-term pulpal outcome are microleakage with possible bacterial penetration and leakage products from restorative materials. Both factors are influenced by the cavity depth, i.e., the remaining thickness of sound dentin.

Responses of the pulp–dentin organ to dental restorative biomaterials.
Dahl JE, Ørstavik D.
Endodontic Topics 2010, 17, Issue 1, pages 65–73. doi: 10.1111/j.1601-1546.2010.00250.x.