The nature of modern dental materials has many advantages regarding the long-term health of your teeth. Unfortunately in order to gain many of the advantages, patients commonly note that their teeth become sensitive (temporarily) after getting small fillings. This on/off cold sensitivity usually reverts to normal within a few weeks, but in teeth with extensive decay it can last up to 6 weeks.
In order to understand what a "filling or bonding" truly entails, here is a little dental anatomy background information. The vast majority of the surface portion of a tooth that is visible is covered by enamel. You've probably heard that tooth enamel is the hardest tissue found in the human body. This is true. Enamel is over 95% mineral in composition. Most of this mineral is a compound called hydroxyapatite which, as you probably already know, has a high calcium content.
You may be surprised to learn that teeth are not solid enamel. Only the portion of a tooth nature intended to lie above the gumline is covered by enamel. The bulk of a tooth, both its root and inner aspects, is composed of another calcified material called dentin. Dentin also contains the mineral hydroxyapatite, but to a lesser degree than enamel. Only about two thirds of the content of dentin is mineral so, relatively speaking, dentin is "softer" and also more porous than enamel.
The following is a recent excerpt from The Journal of the American Dental Association regarding the issues dentists face when bonding to natural tooth structure:
"Many clinical problems of dentinal hypersensitivity, microleakage and recurrent caries (decay) are related to dentinal permeablility. The density of [Fig 1] dentin tubules 1.0 millimeter above the cementoenamel junction, or CEJ, at the gingival cavity wall is 49 percent greater than that at the axial wall. Compared with superficial dentin, deeper dentin has more tubules, and the tubule openings are larger. Close to the dentinoenamel junction, or DEJ, under dry conditions, exposed tubules account for 1 percent of the total surface area; these values in deep dentin close to the pulp (tooth nerve) account for 22 percent of the surface area. When dentin is acid-etched (for bonding purposes), these values can increase to 13 percent at the DEJ and 34 percent close to the pulp. (Close to the gumline), cervical dentin also is 3.6times more permeable than occlusal dentin in young adults. Greater amounts of fluid may flow from the pulp, and this pulpal fluid could compromise the adaptability of the restorative material placed at the cut surface of the dentin. This process could be especially detrimental in deeper cavity preparations, in which the tubular diameter is much greater. This excessive surface moisture may result in voids (air bubbles) at the resin-dentin interface. This has been described as "the overwet phenomenon." Extreme conditions of surface wetness or dehydration should be avoided. Failure of resin-based composite to bond to teeth at the dentin gingival margin may be due to a combination of factors such as the configuration factor (C-factor), polymerization (curing) shrinkage and wetness of dentin."
John H. Purk, DDS, MS, PhD
Vladimir Dusevich, PhD
Alan Glaros, PhD
Paulette Spencer, DDS, MS, PhD
J. David Eick, PhD
JADA, Vol. 135, February 2004