WHAT IS INSIDE A TOOTH?
From the outside, a tooth looks like a hard, solid substance. But this cut-away illustration reveals that a tooth is really a complex system of specialized tissues.
Enamel - the shiny, hard, white tissue covering the tooth is the strongest tissue in your body. It has to be! Your jaws place as much as 128 pounds of pressure on your teeth when you chew, bite, clench, or grind.
Dentin - this tissue makes up most of the body of the tooth. Even though dentin is hard and feels solid to the touch, it's actually microscopically porous and needs a covering of enamel or an artificial crown to protect it from decay-causing bacteria in your saliva.
Gum - dentists call this the "gingiva." It covers the bone surrounding your teeth. When you brush your teeth after meals and floss daily, you keep this tissue healthy. That's important, because gum disease can cause bone loss. Gum disease can also expose the tooth roots to decay. If root decay affects the pulp, you may need root canal treatment.
Pulp - this soft tissue contains blood vessels, nerves, and connective tissue. The pulp provides nourishment for the tooth during growth and development. Once the tooth is mature, the pulp's only function is sensory. A fully developed tooth can survive without the pulp. If this tissue is damaged, your dentist or endodontist can remove it and save your tooth with endodontic (root canal) treatment.
Root canal containing pulp tissue - this is the passage or channel in the root of the tooth extending from the pulp chamber to the apical foramen (the main opening of the root canal).
Periodontal ligament - like the springs that hold a trampoline to its frame, this tissue supports the tooth and holds it in place in the bony socket surrounding the tooth. This tissue cushions both the tooth and the surrounding bone against the shock of chewing and biting.
Accessory canal - any branch of the main pulp canal or chamber that communicates with the external surface of the root.
Bone - the roots of your teeth are anchored by bone. Healthy teeth stimulate and keep bone tissue healthy and vice versa.
Root - this part of the tooth sits in the bone below the gum. Believe it or not, the root of your tooth is usually twice as long as the crown, the part you see above the gumline.
Crown - this is the part of the tooth you can see above the gumline.
Since childhood, most of our dental concerns have focused on the fear of getting "cavities" due to tooth decay. Tooth Decay (dental "caries") is the decomposition of tooth structure caused by the destructive toxins creating by plaque, a combination of natural bacteria and food debris left on the teeth by inadequate oral hygiene.
Dental caries has been described as a "disease of civilization," especially applicable in the last one hundred years, as man has strayed from diets rich in fruits and vegetables to a high intake of refined sugars. Read the ingredients of today's commercial food products - glucose, fructose, dextrose, etc. - various forms of sugar.
Modern dentistry has succeeded in reducing the incidence of dental caries through water fluoridation, oral hygiene education, and preventive dental care that includes sealants, and conservative restorative treatment. "Cavities" are far less prevalent than they were several decades ago and may now be managed by advanced technology.
BASICS ON DENTAL FILLINGS
Types of Dental Restorations
There are two types of dental restorations: direct and indirect.
Direct restorations are fillings placed immediately into a prepared cavity in a single visit. They include dental amalgam, glass ionomers, resin ionomers and some composite (resin) fillings. The dentist prepares the tooth, places the filling and adjusts it during one appointment.
Indirect restorations generally require two or more visits. They include inlays, onlays, veneers, crowns and bridges fabricated with gold, base metal alloys, ceramics or composites. During the first visit, the dentist prepares the tooth and makes an impression of the area to be restored. The impression is sent to a dental laboratory, which creates the dental restoration. At the next appointment, the dentist cements the restoration into the prepared cavity and adjusts it as needed.
Are dental amalgams safe?
Yes. Dental amalgam has been used in tooth restorations worldwide for more than 100 years. Studies have failed to find any link between amalgam restorations and any medical disorder. Amalgam continues to be a safe restorative material for dental patients.
Is it possible to have an allergic reaction to amalgam?
Only a very small number of people are allergic to amalgam fillings. Fewer than 100 cases have ever been reported. In these rare instances, mercury may trigger an allergic response. Symptoms of amalgam allergy are very similar to a typical skin allergy.
Often patients who are truly allergic to amalgam have a medical or family history of allergies to metals. If there is a confirmed allergy, another restorative material will be used.
Is it true that dental amalgams have been banned in other countries?
No. Erroneous news reporting has confused restrictions in a few countries with outright bans. Dentists around the world are using dental amalgams (silver fillings) to restore teeth that have dental decay. Studies have not shown a link between dental amalgam and any medical disorder.
Is there a filling material that matches tooth color?
Yes. Composite resins are tooth-colored, plastic materials (made of glass and resin) that are used both as fillings and to repair defects in the teeth. Because they are tooth-colored, it is difficult to distinguish them from natural teeth. Composites are often used on the front teeth where a natural appearance is important. They can be used on the back teeth as well depending on the location and extent of the tooth decay. Composite resins are usually more costly than amalgam fillings.
What's Right for Me?
Several factors influence the performance, durability, longevity and expense of dental restorations. These factors include: the components used in the filling material; where and how the filling is placed; the chewing load that the tooth will have to bear; and the length and number of visits needed to prepare and adjust the restored tooth. The ultimate decision about what to use is best determined by the patient in consultation with the dentist. Before your treatment begins, discuss the options with your dentist.
If my tooth doesn't hurt and my filling is still in place, why would the filling need to be replaced?
Constant pressure from chewing, grinding or clenching can cause dental fillings, or restorations, to wear away, chip or crack. Although you may not be able to tell that your filling is wearing down, your dentist can identify weaknesses in your restorations during a regular check-up.
If the seal between the tooth enamel and the restoration breaks down, food particles and decay-causing bacteria can work their way under the restoration. You then run the risk of developing additional decay in that tooth. Decay that is left untreated can progress to infect the dental pulp and may cause an abscess.
If the restoration is large or the recurrent decay is extensive, there may not be enough tooth structure remaining to support a replacement filling. In these cases, your dentist may need to replace the filling with a crown.
AMALGAM IN DETAIL
Amalgam Use and Benefits
Dental amalgam, in widespread use for over 150 years, is one of the oldest materials used in oral health care. Its use extends beyond that of most drugs, and is predated in dentistry only by the use of gold. Dental amalgam is the end result of mixing approximately equal parts of elemental liquid mercury (43 to 54 percent) and an alloy powder (57 to 46 percent) composed of silver, tin, copper, and sometimes smaller amounts of zinc, palladium, or indium.
Because of a general decline of dental caries among school children and young adults, the use of dental amalgam began to decrease in the 1970s. There are also changes in patterns of dental caries, largely the result of topical and systematic fluoride, sealant use, improved oral hygiene practices and products and possibly dietary modifications. In 1990, over 200 million restorative procedures were provided in the United States; of these, dental amalgam accounted for roughly 96 million, a 38 percent reduction since 1979. This trend is expected to continue.
There are also reports that carious lesions today are generally smaller, easier to treat, and managed by more conservative treatment that retains tooth structure. Because of this decrease in the frequency and size of dental caries, there has been a relative increase in the use of alternative dental restorative materials. The most commonly used and less expensive of the alternate materials, however, cannot be used for large lesions and need more frequent replacement. Also, there are currently many serviceable dental amalgam restorations that will need replacing in the future. Approximately 70 percent of the resotrations placed annually are replacements. Most of these replacements will require amalgam or other metallic materials, because compositie materials often lack sufficient strength or durability to be considered adequate substitutes.
Advantages and Disadvantages of Amalgam Fillings
Used for well over a century, dental amalgam is the most thoroughly researched and tested restorative material among all those in use. It is durable, easy to use, highly resistant to wear and relatively inexpensive in comparison to other materials. For those reasons, it remains a valued treatment option for dentists and their patients. Because amalgam fillings can withstand very high chewing loads, they are particularly useful for restoring molars in the back of the mouth where chewing load is greatest.
Disadvantages of amalgam include possible short-term sensitivity to hot and cold temperatures after the filling is placed. The silver-colored filling is not as esthetically pleasing as one that is tooth-colored, especially when the restored tooth is near the front of the mouth, visible when the patients laughs or speaks. And lastly, to prepare the tooth, the dentist may need to remove more tooth structure to accommodate an amalgam filling than for other types of direct fillings.
Today, dental amalgam is used in the following situations:
- in individuals of all ages,
- in stress-bearing areas and in small-to moderate-sized cavities in the posterior teeth,
- when there is severe destruction of tooth structure and cost is an overriding consideration,
- as a foundation for cast-metal, metal-ceramic, and ceramic restorations,
- when patient commitment to personal oral hygiene is poor,
- when moisture control is problematic with patients,
- when cost is an overriding patient concern.
It is not used when:
- esthetics are important, such as in the anterior teeth and in lingual endodontic-access (root canal) restorations of the anterior teeth,
- patients have a hisotry of allergy to mercury or other amalgam components,
- a large restoration is needed and the cost of other restorative materials is not a significant factor in the treatment decision.
Highlights of the Report on Dental Amalgam
Dental amalgam has been used as a dental restorative material for over 150 years. Amalgam remains popular because it is strong, durable and relatively inexpensive. Roughly 200 million restorative procedures performed in 1990 used amalgam. Nonetheless, amalgam use is declining because the incidence of caries is decreasing and because improved substitute materials are now available for certain applications.
Dental amalgam, an inter-metallic compound, contains elemental mercury that is emitted in minute amounts as vapor. Becuase vapor emitting from amalgam restorations can be absorbed by the patient through inhalation, ingestion, or by other means, concerns have been raised about possible toxicity. At present, there is scant evidence that the health of the vast majority of people with amalgam is compromised, nor that removing amalgam filings has a beneficial effect on health. It also is recognized that a total conversion from dental amalgam to alternative materials would cause a significant increase in U.S. health care costs. Nonetheless, the possiblity that this material, as well as currently available alternatives, could pose health risks cannot be totally ruled out becuase of the paucity of definitive human studies.
Given the limitations of existing scientific data, a research program should be designed and implemented to fill as many gaps as possible in current knowledge about the potential long-term biological effects of dental amalgam and alternative restorative materials. The Public Health Service (PHS) should be a leader in this effort.
The PHS should also educate dental personnel and consumers about the risks and benefits of dental amalgam. An educational program should include information on all restorative materials to help dentists and their patients make informed dental treatment decisions, and encourage dental care providers to report adverse reactions. Such a program should promote the use of preventative measures such as fluoride and dental sealants to prevent caries and thus further reduce the need for dental restorations.
To exert greater control over dental amalgam use, the Food and Drug Administration (FDA) should regulate elemental mercury and dental alloy as a single product. To help dentists identify patients who may exhibit allergic hypersensitivity to all restorative materials, including dental amalgam, the FDA should require manufacturers to disclose the ingredients of these materials in product labeling.
Sweden, Denmark, and Germany have proposed restrictions on dental amalgam use to diminish both human exposure to and environmental release of mercury and not becuase of any documented health effects associated with exposure to dental amalgam.
The U.S. Public Health Serice believes it is inappropriate at this time to recommend any restrictions on the use of dnetal amalgam, for several reasons. First, current scientific evidence does not show that exposure to mercury from amalgam restorations poses a serious health risk in humans, except for an exceedingly small number of allergic reactions. Second, there is insufficient evidence to assure the public that components of alternative restorative materials have fewer potential health effects than dental amalgam including allergic-type reactions. Third, there are significant efforts underway in the U.S. to reduce the amount of mercury in the environment. And finally, as stated previously, amalgam use is declining due to a lessening of the incidence of dental caries and the increasing use of alternative materials.
THE BEST CHOICE: COMPOSITE FILLING MATERIALS
Non-metal, non-toxic dentistry is truly a reality of today.
Advances in modern dental materials and techniques increasingly offer new ways to create more pleasing, natural-looking smiles. Researchers are continuing their often decades-long work developing esthetic materials, such as ceramic and plastic compounds that mimic the appearance of natural teeth. As a result, dentists and patients today have several choices when it comes to selecting materials used to repair missing, worn, damaged or decayed teeth.
The advent of these new materials has not eliminated the usefulness of more traditional dental restoratives, which include gold, base metal alloys and dental amalgam. The strength and durability of traditional dental materials continue to make them useful for situations where restored teeth must withstand extreme forces that result from chewing, such as in the back of the mouth.
If you are restoring a tooth for the first time then composite filling materials will not only strengthen the tooth as well as provide greater longevity and beauty than the mercury/silver ones but, more importantly it is far less damaging to the healthy tooth.
The majority of initial composite fillings require only minimal natural tooth removal and not only restore decayed areas but also seal up weak spots so decay will not penetrate the other surface groves.
Sealed surfaces ARE protected as long as the sealant lasts. When it wears out it can easily be reapplied until the child grows out of this cavity prone period. However, the composite sealant must be placed before decay begins. On the average 36% of the children today are cavity free. However, those children raised in the southwest are much more likely to be cavity free than those from the northeast. No single cause can be found for these differences.
Composite fillings are a mixture of acrylic resin and finely ground glasslike particles that produce a tooth-colored restoration. Composite fillings provide good durability and resistance to fracture in small-to-mid size restorations that need to withstand moderate chewing pressure. Less tooth structure is removed when the dentist prepares the tooth, and this may result in a smaller filling than that of an amalgam. Composites can also be "bonded" or adhesively held in a cavity, often allowing the dentist to make a more conservative repair to the tooth.
In teeth where chewing loads are high, composite fillings are moderately resistant to wear, but less so than amalgam fillings. The cost is moderate and depends on the size of the filling and the technique used by the dentist to place it in the prepared tooth. The time required to place a composite filling is usually longer than what is required for an amalgam filling. Composite fillings require a cavity that can be kept clean and dry during filling and they are subject to stain and discoloration over time.
Glass ionomers are tooth-colored materials made of a mixture of acrylic acids and fine glass powders that are used to fill cavities, particularly those on the root surfaces of teeth. Glass ionomers can release a minute amount of fluoride that may be beneficial for patients who are at high risk for decay. When the dentist prepares the tooth for a glass ionomer, less tooth structure is removed; this may result in a smaller filling than that of an amalgam.
Glass ionomers are primarily used as small fillings in areas that need not withstand heavy chewing pressure. Because they have a low resistance to fracture, glass ionomers are mostly used in small non-load bearing fillings (those between the teeth) or on the roots of teeth.
Resin ionomers also are made from glass filler with acrylic acids and acrylic resin. They also are used for non-load bearing fillings (between the teeth) and they have low to moderate resistance to fracture.
Ionomers experience high wear when placed on chewing surfaces. Both glass and resin ionomers mimic natural tooth color but lack the natural translucency of enamel. Both types are well tolerated by patients with only rare occurrences of allergic response.
INDIRECT RESTORATIVE MATERIALS
Sometimes the best dental treatment for a tooth is to use a restoration that is made in a laboratory from a mold. These custom-made restorations, which require two or more visits, can be crowns, inlays or onlays. A crown covers the entire chewing surface and sides of the tooth. An inlay is smaller and fits within the contours of the tooth. An onlay is similar to an inlay, but it is larger and covers some or all chewing surfaces of the tooth. The cost of indirect restorations is generally higher due to the number and length of visits required, and the additional cost of having the restoration made in a dental laboratory. Materials used to fabricate these restorations are porcelain (ceramic), porcelain fused to metal, gold alloys and base metal alloys.
All-Porcelain (Ceramic) Dental Materials
All-porcelain (ceramic) dental materials include porcelain, ceramic or glasslike fillings and crowns. They are used as inlays, onlays, crowns and aesthetic veneers. A veneer is a very thin shell of porcelain that can replace or cover part of the enamel of the tooth. All-porcelain (ceramic) restorations are particularly desirable because their color and translucency mimic natural tooth enamel.
All-porcelain restorations require a minimum of two visits and possibly more. The restorations are prone to fracture when placed under tension or on impact. Their strength depends on an adequate thickness of porcelain and the ability to be bonded to the underlying tooth. They are highly resistant to wear but the porcelain can quickly wear opposing teeth if the porcelain surface becomes rough.
Another type of restoration is porcelain-fused-to-metal, which is used to provide strength to a crown or bridge. These restorations are very strong and durable.
The combination of porcelain and metal creates a stronger restoration than porcelain used alone. More of the existing tooth must be removed to accommodate the restoration. Although they are highly resistant to wear, porcelain restorations can wear opposing natural teeth if the porcelain becomes rough. There may be some initial discomfort to hot and cold. While porcelain-fused-to-metal restorations are highly biocompatible, some patients may show an allergic sensitivity to some types of metals used in the restoration.
Gold alloys contain gold, copper and other metals that result in a strong, effective filling, crown or a bridge. They are primarily used for inlays, onlays, crowns and fixed bridges. They are highly resistant to corrosion and tarnishing.
Gold alloys exhibit high strength and toughness that resists fracture and wear. This allows the dentist to remove the least amount of healthy tooth structure when preparing the tooth for the restoration. Gold alloys are also gentle to opposing teeth and are well tolerated by patients. However, their metal colors do not mimic natural teeth.
Base metal alloys
Base metal alloys are non-noble metals with a silver appearance. They are used in crowns, fixed bridges and partial dentures. They are highly resistant to corrosion and tarnishing. They also have high strength and toughness and are very resistant to fracture and wear. Some patients may show allergic sensitivity to base metals and there may be some initial discomfort from hot and cold. The metal color does not mimic natural teeth.
Crowns, inlays and onlays can be made in the laboratory from dental composites. These materials are similar to those used in direct fillings and are tooth colored. One advantage to indirect composites is that they do not excessively wear opposing teeth. Their strength and durability is not as high as porcelain or metal restorations and they are more prone to wear and discoloration.