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Fillings and Core Buildups

What are Fillings and Core Buildups?

Fillings are among the most frequently prescribed and versatile of all dental restorations. In a procedure known as cavity preparation, the dentist uses any of a variety of dental drills (also called burs), microabrasion devices, or laser tips to remove damaged tooth structure, and any tooth material that has been weakened or undermined by decay. Applying their knowledge of ideal tooth shape (morphology), dentists replace the missing tooth structure with filling material of various types.

Fillings are placed into teeth following the removal of tooth decay (caries), and filling material can also be used to restore chipped or partially broken teeth to their normal contour and function.

When performed traditionally, a mixture of silver, zinc, copper and mercury known as amalgam is used to fill the back teeth, and sometimes even the front ones if the decay is on a surface that is not visible when the patient smiles. Although they can be bonded into the tooth with modern dental adhesives, silver fillings are held into the tooth primarily by mechanical interlocking features cut into the tooth by the dentist.

If replacement of multiple silver fillings is recommended, it’s a good idea to understand what’s involved and why it’s important. Diagnostic photographs of failing (for example, cracked) fillings can help you to understand why replacement may be needed. If you are having it done for cosmetic reasons, it’s important to understand the risks.

Large four-surface silver filling that is still in excellent shape.

Figure 1: A large silver filling in a lower molar tooth. (Image courtesy Byron J. Greany, DDS)

Figure 1 shows a large silver filling in a lower molar tooth. These fillings have been the workhorse of dentistry for many years, and when properly placed and cared for, can provide decades of service. Placing silver fillings in the presence of significant moisture (for example, saliva) can cause them to outgas, resulting in pitting and voids that reduce their service life. That’s why it’s important to isolate the teeth with a rubber dam or cotton rolls when placing silver fillings in them.

The debate surrounding the use of mercury in silver fillings continues. Because of silver amalgam’s durability, track record for long term success, ease of use, similar wear properties to natural tooth enamel, and relative inexpense, it continues to be widely used and endorsed as safe for most patients. If you have questions about the safe use of silver for you or your child, talk it over with your dentist. There are generally other options available.

Beginning in the 1960’s a process known as dental bonding was developed. Since its inception, dental bonding has continued to improve in strength and durability, allowing teeth to be more conservatively restored. Modern bonding materials may allow teeth that have been structurally compromised to be repaired with long-lasting and cosmetically pleasing fillings. A tooth-colored material known as composite resin is currently used to restore many cavities—even those found in the back teeth (Figures 2, 3, and 4).

Dental caries (tooth decay, or cavities) has infected this lower molar tooth.

Figure 2: Tooth decay (caries) has created a cavity in this partially prepared lower molar tooth.

Figure 2 shows where tooth decay (caries) has created a cavity in this partially prepared lower molar tooth. Blue caries detection dye has been used to identify less obvious areas of decay. Use of caries detection dye helps the dentist remove all of the decay without removing too much tooth structure.

Tooth cavity preparation for a composite resin filling dental restoration.

Figure 3: The decay has been removed.

Figure 3 shows the cavity prepared for a filling. The decay has been removed, and the preparation stained with dye to verify complete caries removal. No dye is visible, because the decay has all been removed. If the decay is very deep into the tooth, the dentist may place a layer of base material (an insulation layer) over the yellow dentin floor. Some cavities require very thin base layers called liners.

Bases and liners can reduce post-operative sensitivity in the tooth, and promote formation of reparative dentin (a calcified substance cells in the tooth produce to protect the pulp from damage). Some dentists apply desensitizing agents to the exposed dentin before filling the cavity. All of these techniques are considered to be part of the filling process.

A 1-surface composite resin filling in a lower permanent molar (note rubber dam).

Figure 4: A tooth-colored composite resin filling has been placed in the prepared cavity.

In Figure 4, a tooth-colored composite resin filling has been placed in the prepared cavity. Well placed and well taken care of, it should provide many years of service.

The process of placing a Filling or Core Buildup

Before teeth are filled

When you have fillings done, the dentist will review your health history. If you have replacement joints (for example, total knee replacement, hip replacement, etc.), you may be pre-medicated with antibiotics for the procedure. If you have certain types of heart murmurs or replacement heart valves, you may also need to take an antibiotic pre-medication prior to the procedure.

If you are anxious about dental procedures, your dentist may recommend sedating you for the procedure. There are several methods of relaxing patients for dental treatment, including oral anti-anxiety pills; inhaled anti-anxiety medication like nitrous oxide; and intravenous anti-anxiety medication.

The following description of the filling procedure may vary from patient to patient, and dentist to dentist, depending on unique individual circumstances and preferences. However, the steps will generally resemble the following:

On the day of, or prior to treatment, your dentist will generally review the procedure, its risks and anticipated benefits with you. Ask any questions you may have ahead of time. Understanding the procedure, and any options you may have will lead to the best possible treatment outcome.


A dental team member will frequently apply a topical numbing gel to the anesthetic injection site, to help reduce injection discomfort. Sometimes cavity preparations can be accomplished without any anesthetic. You should discuss that with your dentist. If local anesthetic is administered, you will generally feel just a slight pinch, if anything. After that, the area will begin to tingle, and then “go to sleep”, normally for a couple of hours. Injections for lower molar teeth can produce a bit more discomfort, because the nerves to be numbed are deeper under the skin.

If the patient is a child, don’t tell them in advance that they’re “going to get a shot.” Most of the time, children who are not pre-conditioned to fear a procedure by an adult will be unaware of the injection. Most dentists who treat kids are pretty good at talking a young patient through what to expect without making them fearful.

Isolation of the teeth

Once the tooth or teeth are numb, the dentist or dental assistant may isolate the area with a rubber dental dam or other barrier. Although these are sometimes awkward to place, they can enhance the procedure and the treatment outcome greatly. Rubber dams prevent contamination of the filling with saliva and warm, moist, exhaled air, which can impair the bond between the filling and the tooth. Rubber dams also prevent the patient from having to swallow bacteria-rich decay and old filling material. They protect the tongue and cheeks from injury by dental instrumentation. You can think of rubber dams as a surgical drape. Patients often express concerns that they won’t be able to breathe or swallow if a rubber dam is used; however, neither is the case. If you anticipate difficulty breathing through your nose, an external nasal dilator (for example, BreatheRight Strips®) may help.

Decay removal/Cavity preparation

When good isolation is achieved, the dentist will remove the tooth decay with a dental handpiece, a laser handpiece, or an abrasion handpiece. The type of device to be used reflects the dentist’s philosophy and training to a large extent; however the goal is always to remove bacterially infected and weakened tooth structure. When all of the obvious decay has been removed, and the preparation shape has been idealized to retain a filling, the dentist may use a caries detection dye, which will stain areas of less obvious decay. It helps the dentist remove all of the decay without removing excess tooth structure. Some dentists may use a cavity disinfecting solution like chlorhexidine, which can kill tooth bacteria and help remove tooth cuttings known as smear layer for a better bond.

If the cavity is deep, the dentist may apply a base layer or liner to insulate or medicate the tooth pulp. Some dentists use desensitizing varnishes. If the filling is to be bonded into the tooth, the cavity will be etched for a short time with a phosphoric acid solution. Any of a variety of adhesives and adhesive primers will be applied. The filling will be placed, and, in the case of composite resin fillings, will be cured (polymerized) with a blue light. It will then be polished, and following removal of the isolation barrier, the bite will be checked and adjusted if necessary.

Dental acid etch solution is used to prepare enamel and dentin as the first step in the bonding process.

Figure 1: Dental acid etch solution is applied to the prepared enamel and dentin as the first step in the bonding process. Often, a de-sensitizing agent will be applied to the prepared dentin prior to acid etching.

Dental bonding

Dental bonding is a technique used by dentists to firmly attach fillings, crowns, inlays, onlays and veneers to the teeth (Figures 1 and 2). Virtually all bonding systems combine the following steps: An acid solution is applied to the tooth to produce a microscopically roughened surface. Under a microscope, acid-etched tooth structure resembles Velcro®, with linear filaments projecting from the tooth surface.

A liquid adhesive solution is applied, which contains long strands of resin polymers that entangle themselves among the linear filaments of enamel. When the polymer strands of the dental adhesives are exposed to light of a certain wavelength, they begin to form molecular bonds (cross-links) with one another, effectively locking themselves in among the enamel filaments. Tails of the polymer strands are left protruding from the tooth’s surface on every wall of the prepared tooth.

A dental curing light produces blue wavelength light to cure the photopolymer composite resin filling.

Figure 2: A blue light source (approximately 460 nanometer wavelength) is used to harden tooth-colored, composite resin filling material in these lower molar teeth.

The dental restoration (fillings, crowns, etc.) is also treated to produce a similar surface. When the restoration is placed in the tooth and exposed to the curing (polymerizing light), the polymer strands from the tooth and restoration cross-link, producing an ultra strong chemical bond. Different materials have been developed to enhance the process, but they all work in essentially this way.

Bonding has ushered in a new era of minimally invasive dentistry, in which teeth can now be fixed without the need to cut away healthy tooth structure, just to hold a filling or crown onto the tooth.

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Author: Thomas J. Greany, D.D.S. / Editor: Ken Lambrecht

This page was last updated on December 17, 2018.

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