Post operative discomfort after fillings (why they sometimes cause prolonged sensitivity to cold or pressure)
When any type of filling is done on a tooth, some sensitivity to cold and pressure is normal. This often lasts for as much as a month after the filling is done. The amount of post operative discomfort associated with any given filling depends on the depth and extent of the cavity preparation which in turn depends upon the depth and extent of the original area of decay or of the old filling which is to be replaced.
In many instances the living nerve in the tooth is not especially healthy at the time the filling is done, and the trauma caused by removal of the decay or the old filling can push the nerve over the edge causing an irreversible pulpitis (inflammation of the nerve) which will lead to the eventual death of the nerve. Situations in which the nerve of the tooth remains exquisitely sensitive to cold, or hurts spontaneously without an external stimulus may have a dying nerve, and the only solution to this problem is either to perform a root canal or extraction on the tooth.
A second problem that can cause prolonged sensitivity to cold or pressure on a recently filled tooth is hyperocclusion. This is a technical term that means that the filling is simply too “high” and strikes the opposing teeth with too much force when the patient closes his mouth. This can cause very severe sensitivity to cold and sensitivity to pressure, especially pressure applied to the side of the tooth. This is a very common problem because the patient is generally numb when the dentist carves the top of the tooth. The patient may not be closing into his normal bite and the dentist may miss a high spot. The solution to this problem is to return to the dentist for an occlusal adjustment, which means that the dentist determines what spots on the tooth are high and grinds them down.
Finally, removal of an old filling or decay may reveal a crack in the floor of the cavity preparation. This can lead to cracked tooth syndrome which means that the tooth hurts whenever pressure is applied to one or more cusps (points) of the tooth. Cracked teeth happen all the time in dentistry, and they are one of our most challenging diagnostic problems. The sudden appearance of cracked tooth syndrome does not mean that the dentist did something wrong. It is generally due to a pre existing crack which suddenly allowed the tooth segments to spring apart when the old filling was removed, or when the dentist cut a new surface in order to remove decay. The management and prognosis for cracked teeth is complex and I urge you to read the page I have provided to explain it.
Composite fillings present unique technical challenges to the dentist which he or she does not face when placing an amalgam filling. These difficulties are the primary reason why many dentists refuse to place composite fillings in back teeth. The technique for composite fillings is more demanding than that used for amalgam fillings. Iatrogenic (dentist caused) problems associated with composite fillings are generally due to one or more of the following:
Under cured composite–Modern composite filling material begins as a paste which is placed in the cavity preparation after a proper bonding technique has been performed. The paste is packed into the tooth and then hardened using a very bright light which triggers a chemical reaction causing the paste to harden into a very hard tooth colored filling. As light curing became more and more perfected, both the composition of the filling material and the construction of the curing lights evolved over time. Newer curing units (lights) are extremely bright while the older units were much less bright. A brighter light means deeper and faster curing of the composite. Many of the older curing lights were perfected before composite had evolved enough to be placed into back teeth. Because of the depth of the fillings in back teeth, many of these older lights are not bright enough to cure the full depth of a posterior composite filling. This problem can be overcome by filling the tooth in thin increments and curing each increment thoroughly before placing the next increment. On the other hand, the newer arc lights, and laser curing units, which are much more expensive than the older standard units are so bright that they can cure to a greater depth quite quickly. (The newest curing unit in dentistry uses LED’s which are less bright, but concentrate the light energy into wavelengths that are more likely to harden the composite.) If the composite used to fill your tooth was not cured enough, your tooth will remain sensitive for a very long time. The only solution for this problem is to remove the filling and replace it with a properly cured composite or an amalgam.
Shrinkage stress–All plastics tend to shrink when they transform from the liquid to the solid phase (similar to the way water tends to expand when frozen). Modern composites have been formulated to minimize this problem, both chemically and by using very dense concentration of glass particles as fillers. The glass, of course does not shrink, and much of the contraction caused by the hardening acrylic matrix is counteracted by the close packing of the glass particles. (See my page on dental composites for more on this.) Even so, some microscopic shrinkage always happens, and this, when combined with the powerful bonding techniques available today, can cause the vertical walls of the preparation to be drawn together which can produce prolonged sensitivity to cold. If the dentist suspects that this is the case, it is sometimes possible to release the stresses using a simple technique called “slicing”, in which the dentist cuts a vertical groove from the top of the filling to the floor of the preparation from mesial (front) to distal (back) through the filling. This allows the cusps on either side to rebound relieving the stress. The groove is then refilled with composite and the filling is then as good as new. This procedure is fast and easy and saves a lot of time and trauma to the patient (as well as the dentist).
Some dentists believe that light cured composites always shrink toward the light source. If this is true, then some of the shrinkage away from the walls of the cavity preparation, and to a to a certain extent away from the floor of the cavity preparation (see next paragraph) can be avoided by the use of a thin light-guide placed on the tip of the curing light. This concentrates the light and allows the dentist to shine the light for a few seconds on each cusp of the tooth instead of directly on the filling material itself. Thus, the light channels down the enamel and dentin of the tooth and causes the initial set of the material to draw toward the cavity prep walls rather than toward the chewing surface of the restoration.
Another way to avoid shrinkage away from the walls of the prep is to use clear plastic matrix bands. (A matrix band is used to contain the filling material inside of the tooth in areas where the walls of the tooth have been breached in order to remove decay. If a matrix band were not used in these cases, the filling material would penetrate between adjacent teeth under the gum line, and would also bond adjacent teeth together. Most dentists use metal bands due to their ease of use. Click on the image to see how one popular type of matrix, an Automatrix®, is placed on a tooth.) A clear plastic matrix allows the curing light to be directed through the plastic from the side of the tooth. This would cause the composite to be drawn toward the cavity prep walls and eliminate the shrinkage away from them. Not too many dentists use a clear plastic matrix due to the difficulty (some may say “near impossibility”) of placing a thin piece of pliable plastic between the tight contacts between two adjacent teeth.
Shrinkage away from the floor of the cavity preparation–As mentioned above, light cured composites always shrink toward the light source. Since the light source is usually directed from the top of the tooth, the composite tends to shrink toward the light, often causing the filling material to pull away from the floor of the cavity preparation allowing a tiny void to form underneath the filling between the bottom of the filling and the tooth surface. This void eventually fills with fluid and can cause hydrostatic pressure in the dentinal tubules which leads to sensitivity to pressure on the filling. This is the most common reason for pain when biting on a newly done composite filling. The only solution for this problem is to redo the filling. The dentist can often avoid this problem by placing the composite in increments that cover only part of the floor, or by the use of a self curing glass ionomer base used under the composite.