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Crown And Bridges : Types Of Materials

 What Types Of Materials Are Available In Fabrication Of Crown And Bridges?

The type of materials that are recommended for your crown or bridge will depend on a number of factors, including which tooth the crown or bridge will be used on, whether you grind your teeth and if you are allergic to metal. Before choosing the material for your crown or bridge, it’s crucial to consider the pros and cons of each option. Crown and bridge can be constructed by a variety of materials; dental alloy, dental porcelain or porcelain fused to metal.

Ceramics are actually earthenware/ stoneware. Ceramic material which has been blended with other materials such as silica and feldspar to produce translucency and extra strength is termed porcelain. Dental porcelain materials are used by a dental technician to fabricate lifelike restorations. Overall, dental porcelain have excellent aesthetics properties, high strength and good biocompatibility. Dental porcelain’s high aesthetic qualities of translucency and tooth like colour; redeem them very suitable for crowns and bridges construction especially in the aesthetic zone. Dental porcelain is a very strong and hard material capable of sustaining biting forces. However dental porcelain is brittle and can fracture when subjected to sharp impact or excessive biting force. Dental porcelain should be highly polished and smooth to avoid wearing out of the opposing restoration.

Porcelain can be classified based on their basic compositional categories.

Leucite reinforced porcelain such as IPS Empress, is a monolithic restoration, meaning the material is the same throughout the restorations. Leucites scatter light naturally and have a translucent and lifelike appearance but lack of strength when used in certain clinical situations. It is used to fabricate veneer and single unit anterior and premolar crowns.

Lithium disilicate porcelain marketed as IPS E.Max, is typically monolithic but can also be made as restoration layered with veneering porcelain. This system allows for computer aided design and manufacturing (CAD/CAM) by milling the restorations from dense ceramic blocks. Due its high strength, lithium disilicate can be used for crowns and short span bridges in the anterior and premolar areas.

Alumina based porcelain such as Procera and In-Ceram, have a high-strength alumina oxide core that can be used to fabricate anterior and posterior crowns.

Restorations from zirconia based porcelains such as Lava, are fabricated using CAD/CAM technology. Due to extremely high strength, it can be used for both anterior and posterior crowns and bridges. Implant abutments can also be made with zirconia-based materials. While crowns made from solid zirconia are very strong; due to lack of colour selection and blending, they provide moderately esthetic results. 

Dental alloys have been used for a very long time in the mouth. In fixed prosthodontics, dental alloys are used for the construction of inlays/onlays, crowns, bridges, post and implant. In removable prosthodontics metal alloys are used to fabricate metal-based dentures.

Dental alloys can be classified into three groups; precious metal (high noble alloys), semiprecious metal (noble alloys) and non precious metal (non noble) depending on the metal’s composition.
Gold alloy that fall into precious metal category is one of the strongest materials available. It’s resistant to wear, making it a great choice for the patients who grind their teeth.

The classification system for metal alloy is based upon the metal’s composition.

Precious metal alloy group has a composition that is over 60% noble metal (gold, palladium and/or platinum), of which more than 40% must be gold. Examples of precious metals are gold, platinum, rhodium, ruthenium, iridium and osmium. Gold alloy provides a strong and biocompatible restoration and does not corrode in the mouth. The relative high strength of cast gold alloys allows for minimal reduction of tooth structure to achieve adequate thickness for the restoration.

The semiprecious metal group has at least 25% noble metal content.

The non precious metal group is also referred to as base metal. They often comprise of large percentages of cobalt, chromium, nickel or beryllium. These elements that corrode more than precious alloys; are alloyed with precious metals as they have significant effect on the properties of the alloy such as increasing strength, decreasing flexibility and increasing wear resistance of the alloy.

Porcelain fused to metal restoration is made with a strong metal substructure and the porcelain is bonded to the metal to mimic the look of a natural tooth. With the metal substructure, the strength and durability of these restorations can be increased. The natural tooth colour of porcelain masks the unnatural appearance of the underlying metal to provide excellent toothlike colour and appearance. A porcelain fused to metal crown or bridge is a good option for any location in the mouth.

The comparison between dental porcelain and dental alloy can be summarized in the table below.

Comparison between dental porcelain and dental alloy

Factors

Porcelain

Precious metal

Non precious metal

General description

Porcelain, ceramic or glass-like fillings and crowns

Alloy of gold, copper and other metals resulting in a strong, effective filling, crown or bridge

Alloys of non noble metals with silver appearance resulting in high-strength crown and bridges

Principal uses

Inlays, onlays, crowns and veneers

Inlays, onlays, crowns and fixed bridges

Crowns, fixed bridges and partial denture

Leakage and recurrent decay

Sealing ability depends on materials, underlying tooth structure and procedure used for placement

The commonly used methods used for placement provide a good seal against leakage. The incidence of recurrent decay is similar to other restoration

Durability

Brittle material, may fracture under heavy biting loads.
Strength depends greatly in quality of bond underlying tooth structure.

High corrosion resistance prevents tarnishing. High strength and toughness resist fracture and wear

Cavity preparation consideration

Because strength depends on adequate ceramic thickness, it requires more aggressive tooth reduction during preparation. However, with the latest technology and ceramic systems on the market, it allows for minimal tooth reduction to be done.

The relative high strength of metals in thin sections require the least amount of healthy tooth structure removal

Resistance to wear

Highly resistance to wear , but ceramic can rapidly wear opposing teeth if its surface become rough

Resistance to wear and gentle to opposing teeth

Resistance to fracture

Prone to fracture when placed under tension or on impact

Resistance to wear and gentle to opposing tooth

Biocompatibility

Well-tolerated

Well-tolerated

Well-tolerated but some patients may show allergic sensitivity to base metals

Thermal conductivity

Low thermal conductivity reduces the likelihood of discomfort from hot and cold

High thermal conductivity may result in early post placement discomfort from heat and cold

Aesthetics

Color and translucency mimic natural tooth appearance

Metal colours do not mimic natural teeth

Relative costs

Higher; requires at least two visits and laboratory services

Higher; requires at least two visits and laboratory services

Adapted from Direct and indirect restorative materials JADA, Vol. 134, April 2003

References:

  1. Shenoy A, Shenoy N. Dental ceramics: An update J Conserv Dent. 2010 Oct-Dec; 13(4): 195-203
  2. ADA Council on Scientific Affairs: Direct and indirect restorative materials JADA, Vol. 134, April 2003
  3. Ceramics in Dentistry – Part I – Classes of Materials |ID| dentalageis.com
  4. Warden HN, Shika G, Jessie V, Karen S. Dimension of Dental Hygiene: Advances in All-Ceramics Restorations
  5. http://pocketdentistry.com/21-alloys-used-in-dentistry/

 

Last Reviewed : 23 January 2017
Writer : Dr. Aswani bt. Che Ahmad
Accreditor : Dr. Roshima bt. Mohd Sharif