Tooth fillings, Inlay, Onlay

Dental Filling Materials

Today, several dental filling materials are available. Teeth can be filled with gold; porcelain; silver amalgam (which consists of mercury mixed with silver, tin, zinc, and copper); or tooth-colored, plastic, and materials called composite resin fillings. There is also a material that contains glass particles and is known as glass ionomer. The location and extent of decay determines the type of filling. Let us discuss all the types of fillings.

Silver Amalgam

 Silver amalgam is a combination of one part liquid mercury with one part of a metallic alloy which mainly contains silver and tin. It has been used for over 150 years to restore decayed teeth and the mixture sets relatively fast to form a hard alloy. However its use has stirred controversy from the earliest days. To make the amalgam, mercury is mixed with the other metals to form a paste that can be filled in the tooth cavity.

Advantages of silver amalgam

1. Durability -- silver fillings last at least 10 to 15 years and usually outlasts composite (tooth-colored) fillings.
2. Strength -- can withstand chewing forces
3. Expense -- is less expensive than composite fillings

Although dental amalgam is extremely strong and durable and may still be considered a material of choice for some fillings in the back teeth, it has some drawbacks.

1. It is not tooth-colored so it is very visible; even more so in front teeth.
2. It does not adhere to the surface of the tooth cavity, so dentists have to drill out relatively large holes in the teeth to securely fasten the filling.
3. It contains mercury that is toxic in some forms. There is concern that mercury could be released during placement, normal corrosion and wear, and removal of a filling, and that it could lead not only to local effects in the mouth but also to effects in the body as a whole, for instance on the nervous system.
4. Discoloration -- amalgam fillings can create a grayish hue to the surrounding tooth structure
5. Allergic reactions -- a small percentage of people, approximately 1%, are allergic to the mercury present in amalgam restorations.

Cast Gold Fillings

 Until recently, gold was considered to be the esthetic restoration for posterior teeth, as it does not discolour the teeth and the colour gold was considered less objectionable than other materials. As we have become more aware of esthetics in dentistry, we also have developed new techniques, even with gold, which do not destroy the beauty of a smile.

Advantages of gold fillings

1. Durability -- lasts at least 10 to 15 years and usually longer; doesn't corrode.
2. Strength -- can withstand chewing forces
3. Gold Supports and Protects the Enamel Margins of the Tooth.
4. Gold Does Not Absorb Oral Fluids : Saliva and other oral fluids will not penetrate the surface of a gold casting
5. Gold Does Not Produce tooth discoloration: Gold castings do not produce discoloration of the tooth, which may occur from ion penetration with silver amalgams.
6. Gold Castings Can Be Cemented Successfully Without Adhesive Bonding.
7. Wear of the Gold Restoration Is Similar to Normal Wear of Tooth Structure.
8. Gold Does Not Liberate Toxins.

Disadvantages of gold fillings

1. Expense -- gold cast fillings are expensive; up to 10 times higher than cost of silver amalgam fillings.
2. Galvanic shock -- a gold filling placed immediately next to a silver amalgam filling may cause a sharp pain (galvanic shock) to occur. The interaction between the metals and saliva causes an electric current to occur. It's a rare occurrence, however.
3. Aesthetics –Many patients do not like metal "colored" fillings and prefer fillings that match the rest of the tooth.
4. Gold Castings Require Considerable Care, Skill and Technique From the Operator. It also requires multiple sittings.

Composite Fillings

Resin composite fillings are made of ceramic and plastic compounds. Since resins mimic the appearance of natural teeth, these fillings have been used in front teeth for years. When they first appeared, however, resin compounds weren't strong enough to be used in back teeth, where high-pressure grinding and chewing require greater durability.

Advantages of Composite Fillings

1. Aesthetics -- the shade/color of the composite fillings can be closely matched to the color of existing teeth. Composites are particularly well suited for use in front teeth or visible parts of teeth.
2. Bonding to tooth structure -- composite fillings actually chemically bond to tooth structure, providing further support.
3. Versatility -- in addition to use as a filling material for decay, composite fillings can also be used to repair chipped, broken, or worn teeth.
4. Tooth-sparing preparation -- sometimes less tooth structure needs to be removed compared with amalgam fillings when removing decay and preparing for the filling.

Disadvantages of Composite Fillings

1. Lack of durability -- composite fillings wear out sooner than amalgam fillings (lasting at least five years compared with at least 10 to 15 for amalgams); in addition, they may not last as long as amalgam fillings under the pressure of chewing and particularly if used for large cavities.
2. Increased chair time -- because of the process to apply the composite material, these fillings can take a longer time to place as compared to amalgam fillings.
3. Expense -- composite fillings cost much more than amalgam fillings.
4. Chipping -- depending on location, composite materials can chip off the tooth

In addition to tooth-colored, composite resin fillings, two other tooth-colored fillings exist -- ceramics and glass ionomer cement.

 A relatively recent development in tooth coloured filling material is ceramic whose colour and translucency mimic natural tooth. Ceramic is most often made of porcelain. After tooth preparation an impression is taken which is sent to a lab for fabrication.  It is then bonded permanently to the tooth with dental cement. It generally lasts more than 15 years but can cost as much as gold fillings. By bonding the filling and the tooth together the strength

Glass ionomer fillings:

Glass ionomer is made of acrylic and a specific type of glass material. This material is most commonly used for fillings below the gum line and for fillings in young children. Cavity preparation is done in the usual way. Glass ionomers release fluoride, which can help protect the tooth from further decay. However, this material is weaker than composite resin and is more susceptible to wear and prone to fracture. Glass ionomer generally lasts five years or less with costs comparable to composite resin.

Ceramics

 A relatively recent development in tooth coloured filling material is ceramic whose colour and translucency mimic natural tooth.

Ceramic is most often made of porcelain. After tooth preparation an impression is taken which is sent to a lab for fabrication.  It is then bonded permanently to the tooth with dental cement. It generally lasts more than 15 years but can cost as much as gold fillings. By bonding the filling and the tooth together the strength increases exponentially.

Ceramic fillings, because they are made by dental technician, can be made to look extremely natural. They are more resistant to staining than composite resin material but are also more abrasive. They are mainly used for inlays, onlays and veneers.

Large tooth defects wherein direct tooth fillings might not withstand the chewing forces, inlays and onlay fillings are considered. 

Dental Inlays are indirect fillings made of metal and or ceramic material. The defective tooth is prepared to receive an inlay. Inlay is fabricated in the lab and then fixed over the tooth. They provide a much higher standard of support to the defective tooth.

Dental Onlays: When the tooth defect is more extensive and one or more cusps are lost, Onlays are the treatment of choice. The tooth is suitably prepared and an impression is made which is then sent to the lab. They prepare the onlay which will be fixed by the dental surgeon.

Dental crowns are a variant of onlays as they cover all the cusps of the treated tooth. A cusp refers to the raised points on the crowns of teeth. Our canine teeth for instance contain a single cusp, while premolars contain two and molars normally possess either four or five cusps.