Dental Ceramics
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Dental ceramics hold the promise of a restorative material, that can realistically duplicate teeth, to the extent that the layperson may find it difficult to differentiate. One might argue that composite resins have a similar esthetic potential.
- However, there is a difference— dental ceramics are far stronger, durable, wear-resistant, and virtually indestructible in the oral environment.
- They are impervious to oral fluids and absolutely biocompatible. They do have some drawbacks which will be discussed subsequently.
- Because of their huge potential, it is still a fast-growing area in terms of research and development.
- Thanks to continuing research, these materials once restricted to restoring single crowns have now expanded to include long-span fixed partial dentures.
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Dental Ceramics Uses And Applications
- Inlays and onlays.
- Esthetic laminates (veneers) over natural teeth.
- Single (all ceramic) crowns.
- Short and long-span (all ceramic) FDP.
- As a veneer for cast metal crowns and bridges (metal ceramics).
- Artificial denture teeth (for complete denture and partial denture use).
- Ceramic posts and cores.
- Ceramic orthodontic brackets.
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Evolution Of Dental Ceramics
Ceramics are among the oldest materials known to man. Ceramic objects dating back to 20,000 years have been found in China.
The history of glass dates back to 3500 BC in Mesopotamia. The term ‘glass’ was first developed during the late Roman Empire.
Ceramics comes from the Greek word ceramics, which means pottery, and keramos, which means potter’s clay.
- An esthetic and durable material that could accurately reproduce missing teeth or teeth structure had always been a dream.
- Prior to the use of porcelain, crowns were made entirely of gold or other alloys.
- As demands for esthetics increased, the tooth-colored resin was used as a veneer over the metal in the esthetic areas.
- Around the early 1900s, porcelain crowns were introduced to dentistry by Charles Land (grandfather of aviator Charles Lindbergh) who coined the term porcelain jacket crowns (PJC).
- The restoration was extensively used after improvements were made by EB Spaulding and publicized by WA Capon.
- While not known for its strength due to internal micro cracking, the porcelain “jacket” crown (PJC) was used extensively until the 1950s.
- These early crowns were made of feldspathic porcelains which generally were materials of poor strength.
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- They were also very difficult to fabricate and did not fi well (poor margins).
- To reduce the risk of internal microcracking during the cooling phase of fabrication, the porcelain-fused-to-metal (PFM) crown was developed in the late 1950s by Abraham Weinstein.
- The bond between the metal and porcelain prevented stress cracks from forming.
- This led to the era of metal-ceramics. Prior to this, metal FDPs were veneered (covered) with tooth-colored acrylic in order to hide the metal.
- These veneers did not last very long and had to be replaced often. Besides they could not be used to cover the occlusal surface because of their poor wear resistance.
- The metal-ceramic crowns and fixed dental prostheses were instantly accepted because of their superior esthetics, wear resistance, and strength.
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- The ceramic could be used to veneer the occlusal surface as well. Since the margins were in metal, the marginal fi was highly accurate.
- In spite of the success of the metal-ceramic restorations, they did not represent the final solution.
- The underlying opaque-covered metal did not allow the natural passage and reflection of light as in natural teeth.
- Under certain lighting conditions, these crowns appeared dense, dark, and opaque.
- The margin of the restoration appeared to be dark, even when hidden below the gums as it sometimes showed through the gums (the gums developed a bluish discoloration).
- Some manufacturers did attempt to solve this problem by introducing ‘shoulder porcelains’. A portion of the metal was removed from the labial margin (metal-free margin) and replaced with shoulder porcelain.
- However, this still did not entirely solve the problem of translucency. The first breakthrough at developing a stronger all-ceramic restoration came in 1965.
- McLean and Hughes introduced an alumina-reinforced core material which improved the strength of the porcelain.
- However, they were still not strong enough for posterior use and of course, the problem of marginal adaptation still remained.
- The 1990s saw the reemergence of the all-ceramic crown as well as small fixed partial dentures.
- The strength of the restorations had been improved through the introduction of newer porcelains and fabrication techniques.
- The marginal adaptation and fit had also improved considerably when compared to the first-generation all-porcelain crowns.
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- The new generation ceramics included castable glass ceramics, injection molded ceramics, glass infiltrated core ceramics, CAD/CAM (computer-aided design, computer-aided machining) ceramics, etc.
- With the increase in strength, the use of all ceramic restorations gradually expanded to include posterior crowns and bridges.
- A major reason for this was the introduction of stabilized zirconia and CAD/CAM.
- Ceramic technology continues to evolve because of the high demand for esthetic tooth-colored restorations.
Evolution Of Dental Ceramics Definition
- Compounds of one or more metals with a nonmetallic element, usually oxygen.
- They are formed of chemical and biochemical stable substances that are strong, hard, brittle, and inert nonconductors of thermal and electrical energy (GPT- 8).
Classification Of Dental Porcelains
The wide variety of ceramic systems available in the market makes the classification of ceramics a challenging task. The manufacturer provides equipment and materials compatible for the particular system. They are usually not interchangeable.
According To the Firing Temperature
- High fusing – 1300 °C or above
- Medium fusing – 1101 °C to 1300 °C
- Low fusing – 850 °C to 1100 °C
- Ultra-low fusing less than- 850 °C
According To Type
- Feldspathic porcelains
- Leucite-reinforced glass ceramics
- Tetrasilicic flormica based glass ceramics
- Lithia disilicate-based ceramics
- Alumina reinforced ceramics
- Spinel reinforced ceramics
- Zirconia reinforced ceramics
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According To Its Function Within The Restoration
- Core ceramics – Supports and reinforces the restoration in all-ceramic restorations
- Opaque ceramics – Masks or hides the metal or underlying core ceramic. Bonds ceramic to an underlying metal
- Veneering ceramics
- Body or dentin – Simulates the dentin portion of natural teeth
- Incisal – Simulates the enamel portion of natural teeth
- Gingival – Simulates the darker gingival portion of teeth
- Translucent – Simulates translucent incisal enamel seen sometimes in natural teeth
- Stains – Used to color ceramics to improve esthetics
- Glaze – Imparts a smooth glossy surface to the restoration
According To Microstructure
- Glass-ceramics
- Crystalline ceramics
- Crystal containing glasses
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According To the Fabrication Process
- Condensable ceramics
- Slip-cast glass-infiltrated ceramics
- Heat-pressed (hot isostatic) ceramics
- Castable ceramics
- Machinable ceramics
- Various combinations of the above
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