Dentine bonding agents
Dentine bonding agents are materials that originally were made by resins that helped dental fillings attach to the underlying dentin in the tooth. Most of the original dentine bonding agents have been replaced by newer bonding agents.
A cavity is formed whenever the enamel that covers the tooth is worn or chewed away by bacteria, exposing a hole that often extends into the dentin or deeper, softer layer of the tooth. The problem with filling a tooth with a hard enamel-like substance is that the substance is often not easily attached to the dentin, which has much more water content.
Original bonding agents were methylacrylates (adhesives) containing a solvent, such as acetone, and some kind of volatile carrier. The bonding agent flows deeply into the irregularities of the cavity and dentin surface to allow for deeper bonding of the filling. Sometimes acid etching was performed to create an irregular surface on the enamel so that a tighter bond could be made.
Newer bonding agents take into account that dentin is hydrophilic or “water loving” and doesn’t bond well with adhesives. These newer bonding agents create a hybridized dentin layer by taking the mineral out of the tooth dentin at its surface and infusing polymers into it so that it is less hydrophilic. The hybridized dentin is, at a molecular level, a mixture of polymers and harder dental tissues that is resistant to further acid etching and is more amenable to the use of an adhesive to fuse the cavity filling agent with the hybridized dentin layer inside the cavity.