When most people think of a "filling", they imagine an item made out of some sort of material, either metal or plastic that is placed directly in a hole in a tooth, carved to resemble the original shape of the tooth, and then allowed to harden inside the hole to restore the form and function of the tooth. Of course, it also must relieve the pain associated with the cavity. In fact, these "direct" restorations, though far and away the most common types due to their lower cost are only one half of the equation.
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Another type of restoration, less common due to their much higher cost, are called "indirect" restorations. These "fillings" justify their expense by being more durable (in other words, properly cared for, they should last longer than regular indirect restorations), and also more esthetic (better looking because they are actually built by a laboratory technician on a lab bench without the difficulties imposed by the time constraint and the poor access the dentist faces working in a patient's mouth). Indirect fillings, made in a dental laboratory, are known as inlays and onlays.
Indirect fillings used to be more common when gold and ivory were the principal dental materials. With the advent of porcelain laboratory produced restorations, most dentists today prefer the superior strength and esthetics of "full coverage" of the tooth in the form of crowns or veneers rather than simply filling cavities with laboratory processed gold or porcelain fillings.
The types of direct fillings
There are three major types of direct filling materials; silver amalgam, composite (combination of glass/porcelain particles in a plastic matrix) and temporary filling materials. (There are also three major types of indirect filling material; gold, fused porcelain and composite.) (There is an indirect form of composite which some dentists use.)
Resin Composite fillings (sometimes called "porcelain" fillings)
Composite fillings are what people think of when they say "white fillings" or "porcelain fillings". We call them tooth colored fillings to distinguish them from amalgam, gold and temporary filling materials. There are a number of different formulations of composite filling, but the type most commonly used today is made of microscopic glass, or porcelain particles of varying shapes and sizes (depending on the intended use) embedded in a matrix of acrylic. The glass particles account for between 60% and 80% of the bulk of these materials, so these restorations could more properly be called porcelain fillings.
The glass particles give the composite restoration their color (and their stiffness in the unset state). The acrylic is the plastic matrix that holds the glass particles together. Most composite restorations today are "light cured" which means that the acrylic remains fluid until a very bright light is shined on it causing it to harden. Light curing allows the dentist time to work with the material, building and shaping it correctly, and when ready, to harden it immediately with the light. The light curing also makes for a more color stable restoration. The new tooth colored composite restorations do not get yellow or brown with age as the older ones did.
The before and after images of the tooth above are impressive, but do not tell the whole story. In fact, a tooth that is built in more than 50% restorative material is inherently weak and should be prepared for a crown. This does not mean that all badly damaged teeth should be crowned immediately. In fact the decay in this one was quite deep. Deep decay places the nerve in jeopardy, so a plain filling may serve as a good intermediate restoration to test whether the nerve will die before a final crown is placed on the tooth.
The porcelain particles also give the restoration a great deal of resistance to wear. Amalgam fillings will probably always wear less than composite restorations, however the recent advances in particle formulation and shape have made the newest posterior composites quite competitive for filling back teeth. Five to seven years is average. Composites are even stronger than amalgams in shear strength which makes them better for overlaying large biting areas.
Composite fillings have been used in front teeth for years, but only recently has the technology in composite formulation improved enough to allow their common use in back teeth. Prior to acrylic/glass composites, other types of composites were used in areas where esthetics was important. This is why even in the early twentieth century people were not forced to have silver amalgam fillings in their front teeth. However, even in the 1980's the technology had not yet advanced enough to allow the routine use of composite to restore chewing areas of the back teeth.
Composite resins are still not as popular with dentists for repairing back teeth as old-fashioned amalgam. In fact, only about 25% of dentists currently use them routinely for restoring posterior teeth. The reasons for this are that they are not as wear resistant as amalgam restorations, they are more technique sensitive than amalgam, and there is a tendency for more prolonged tooth sensitivity to cold after the restoration is done. On the other hand, as the materials continue to improve, they have become tougher and more wear resistant while improvements in placement technique have reduced cold sensitivity. However, the greater difficulty in placing these restorations remains a deterrent for many dentists, and continues to keep the cost of the service higher than for an a comparable amalgam restoration.
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 dieing nerve, and the only solution to this problem is either to perform a root canal treatment 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.
Temporary filling materials
When a patient presents at my office with pain attributable to a cavity, we sometimes place a temporary filling in the tooth and reappoint the patient for a final permanent filling at another visit. Sometimes, this is done in order to save time, especially if we have slipped the emergency patient between two regularly scheduled patients. Sometimes it is done in order to save money.
Temporaries are the least expensive (and most temporary) way to fill a tooth. Temporary fillings can be done quickly, because they are usually inserted without any of the time consuming rituals associated with a permanent filling. The patient is anesthetized, the decay removed and the temporary filling is mixed and inserted, generally simply by pushing it into the cavity preparation with a gloved finger. The patient bites into it while it is still soft in order to adjust the height, and the patient leaves the office without even waiting for a final set on the material. In a phrase, a temporary is "fast and cheap'.
But there is another reason that may indicate that a temporary is the best way to treat the patient, even if time or money is not an issue. Temporary fillings are different from permanent amalgam or composite fillings because they are "sedative" fillings. This means that they tend to soothe an inflamed nerve in a tooth, and may make the difference between the tooth needing a root canal (or an extraction), or simply filling the tooth later on, after the nerve has calmed down. Sometimes a temporary filling is the best course to relieve pain.
Temporary fillings are made of two major components: Oil of clove (eugenol), which has been used for centuries to relieve toothaches, and Zinc Oxide which is an excellent disinfectant. The oil and oxide mix together to make a stiff paste that eventually hardens into a waterproof substance which soothes the nerve of the tooth and kills germs while protecting the cavity like a hard band aid.
Zinc Oxide and Eugenol is not very durable, and it wears away after just a few weeks, but it works to relieve pain, calm the nerve and protect the tooth until an appointment can be made to get it filled permanently.
Never plan to keep a temporary filling more than 6 months. They are not meant to last that long, and while the eugenol lulls the patient into a false sense of security, the restoration wears rapidly and begins to leak. If you wait too long, the nerve could die, the temporary filling will wear away, the tooth will decay further, and then you will need a root canal or extraction.
