The great thing about dental fillings is the ease and speed with which they correct a problem. You can walk into your dentist's office with a cavity, and walk out before too long without the cavity, safely treated with a dental composite tooth-coloured filling or a dental amalgam metal filling. Needing additional work on a filling is a rare occurrence, but it's not completely impossible. It's mostly deeper or larger fillings that are more likely to experience complications, but these complications can certainly be reversed.

Tooth Trimming

Dental fillings are one of the most common elements of general dentistry. Although they're extremely effective in treating many forms of tooth decay, there are some limits to their effectiveness. This is compounded by the fact that tooth trimming is generally required prior to a filling. This trimming is the removal of the decayed portion of your tooth, along with the margins of this decay. So, in order to place a filling, a certain portion of your tooth's enamel must first be removed. 

Deeper Cavities

When a cavity extends into a tooth (as opposed to primarily affecting its surface area), the subsequent trimming must be more expansive before the filling material can be applied. In some instances, the depth of the cavity will affect your dental pulp. This is the nerve inside the tooth, housed in a pulp chamber at the centre of the tooth. The filling material might not yet have breached the pulp chamber, but this can still be a possibility. When the pulp chamber becomes compromised, pulp necrosis (nerve death) can be the end result. In this instance, a root canal may be your best option because the cavity was simply too deep to be corrected with a standard filling.

Larger Cavities

When a cavity takes up a relatively large amount of the tooth's surface area, a dental cavity will still be the preferred initial treatment. However, when the size of the cavity requires a correspondingly large filling, the overall structural integrity of the tooth can be affected. This puts the tooth at risk of fracturing. Clearly, a fractured tooth must be avoided. Your dentist might opt to replace a composite tooth-coloured filling with an amalgam metal filling, which is self-sealing and can be sturdier when a larger surface area is to be filled. Alternatively, the tooth could be sealed with a dental crown, containing both the tooth and its filling. 

The failure of a filling isn't something you need to be particularly concerned about, but it's important to be aware that deep or large cavities may require some follow-up work.