Fillings are specially selected dental materials used to fill cavities or defects in teeth as the result of either tooth decay or damage by excessive force. Different types of materials including metals, composite resins, porcelain and zirconia have been used. As the strength, durability, biocompatibility and aesthetic properties are vastly different, the choice of filling material depends on clinical and patient factors including cost. The decayed portion is first removed and the remaining tooth structure then prepared by shaping the cavity and refining the margins before inserting the filling.
Types of Dental Fillings
01. Traditional Filling Materials – Amalgam
The commonest filling used was amalgam, which is a mix of silver, other metals and mercury. It has been in use for more than 100 years as it is a low-cost option that is both strong and durable. However, its use has been reduced due to concerns over the mercury content and the poor cosmetic outcome. While we do not advocate routine replacement of these fillings, we have not used amalgams in the clinic for more than 30 years. The substitute for amalgams when the fillings are small are tooth coloured resin materials. For large cavities, crowns may be required.
02. Conventional Tooth Coloured Filling Materials
- Composite Resins
Composite resins are mouldable plastic materials placed to repair cavities in teeth It is today the mainstay for most fillings as it closely matches the colour of teeth. The procedure involves removing the decayed portion of the tooth followed by roughening of the sides of the cavity. An acid is used to gently etch the tooth surface to create micropores on the tooth surface. The resin is then bonded to the tooth and hardened by shining a blue light. However, they are not as strong and are less suitable for larger fillings. In general they last between 2-3 years.
03. Adhesive Filling Material
- Glass Ionomer Cement
Another common material, “glass ionomer” cement, is used to seal the sides of teeth which have become sensitive as a result of abnormal shearing off of outer enamel near the gum margins of patients who grind their teeth. Minimal tooth preparation is required and the tooth lightly cleaned with a special liquid to condition the tooth surface. These fillings are simple to use and are effective but seldom last for more than 2-3 years.
04. Metal Fillings
Gold and non-precious metals have also been used to replace parts of teeth which have fractured off. They are stronger than silver amalgams and plastic materials and are suitable for use on patients who grind their teeth. Two visits are required. In the first visit the tooth is prepared and a mould is made and sent to the laboratory for processing. The metal is then melted at high temperatures to the desired share and form required. Also termed an “inlay”, they are cemented in place on the second visit. Their use has been superceded due to the patients preference for porcelain fillings.
05. Porcelain Fillings
Porcelain fillings are a popular option due to its strength, relative durability and cosmetic appearance. However, it is a more costly option. As with traditional fillings, the decayed section of the tooth is first removed and cleaned. A mould is made of the remaining tooth and sent to the laboratory for processing. Using modern computer-based techniques, a filling can be made within hours. These fillings last longer than composites but do not as long as full metal filling. On the balance however, it is the preferred material of choice today. The average lifespan is 7-10 years
06. Zirconia Fillings
Another material commonly used is Zirconia which is even stronger than porcelain but is opaque and less aesthetic. However, recent developments in material science has resulted in newer zirconia products which are a compromise between strength and appearance and can nearly match the cosmetic result of porcelain while retaining significant strength. These fillings are preferred in patients with high biting forces or who grind their teeth. They are preferred in areas where the filling is visible. It should be noted that the last molar teeth in the lower jaw are visible when one smiles.
What do the terms inlay and onlay mean?
An inlay is a tooth filling which is made in the dental laboratory to fit the mould of a tooth cavity. It is then returned to the clinic for the dentist to cement. As the filling fits within the boundaries of the tooth it is termed an inlay. An onlay is a type of inlay where the underlying tooth structure is more extensively broken down and a much larger part of the tooth needs to be covered or overlaid by the replacement filling material, hence the term “onlay”.
How are Computer designed and manufactured fillings made?
The tooth is scanned and a filling custom designed using digital technology. Pre-fabricated blocks of filling materials such as porcelain, zirconia or plastics are trimmed to exact specification in a laboratory using precision tooling in a “milling” machine. The process is highly automated. The end-product is then heat treated to harden it and produce a smooth or glazed surface. The dentist then attached the fillings using a special biocompatible cement. Porcelain and plastic fillings can be made within hours while Zirconia fillings will need an extra day to process.
When are fillings required?
Fillings are required when teeth are decayed, or when a part of it has chipped, worn down or broken off. In general, composite resin fillings are useful for smaller chips and cavities while metal, porcelain or zirconia are more suitable for larger fillings or when the tooth is badly broken down. Tooth coloured restorations are usually used to restore our front teeth or the back teeth which are visible when we smile. Adhesive fillings are used to prevent teeth sensitivity. If the cavity or defect is too large, a crown may be needed.
What is Tooth Decay (Dental Caries)
Tooth decay is the result of the action of acids produced by the bacteria which accumulates on teeth which are not thoroughly cleaned. These penetrate the tooth surface causing cavities. If this lies within the outer enamel layer, there is little pain. When it reaches the second layer (the dentine), the pain begins. If it reaches the innermost part of the tooth (the pulp) that houses the nerve and blood supply of the tooth, the pain is usually severe and the term “pulpitis” is used. Infection can then spread from the pulp to the jawbone through narrow passages within the root called the root canals.
How do you fill or repair a fractured tooth?
Teeth may fracture following a traumatic injury or as a result of strong bite forces over time. Depending on the extent of damage, the tooth can either be repaired or removed. The tooth is assessed and the smaller portion of the cracked tooth is removed. If the remaining tooth structure is sound, the tooth can be filled. The tooth is first roughened and a liquid (an acid) used to create micro-pores on the tooth surface. A thin layer of a special bonding agent is applied before a resin filling is attached and hardened using a special blue light source. Larger fractures may require a crown.