Dental Ceramics

Origin of the Term: The term “ceramic” originates from the Greek words ‘keramos, keramikos, keramenes,’ meaning “made of clay.” Early Ceramics: Initially, ceramics were used for making household and decorative items. They were made from kaolin, had a weak, porous, and opaque structure. Transparency and strength were achieved by mixing...
A dental doctor wearing blue gloves and a mask holds a dental model
Dental Ceramics
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  • Origin of the Term: The term “ceramic” originates from the Greek words ‘keramos, keramikos, keramenes,’ meaning “made of clay.”
  • Early Ceramics: Initially, ceramics were used for making household and decorative items. They were made from kaolin, had a weak, porous, and opaque structure. Transparency and strength were achieved by mixing kaolin with other minerals like silica and feldspar, forming what is known as ‘porcelain.’
  • Etymology of ‘Porcelain’: The word ‘porcelain’ derives from the Medieval Italian word ‘porcella,’ referring to the white, shiny surface inside an oyster shell.
  • Use in Dentistry: The use of ceramics in dentistry dates back to the 18th century. In 1723, French dentist Pierre Fauchard considered using porcelain for dental applications, initiating the first efforts in this field.

Structure of Dental Ceramics:

  • Composition in Dentistry: Although dental porcelain is similar to general ceramic structure, the proportions and firing systems differ. Dental porcelain is composed of silicon tetraoxide (SiO4), which contains chemical bonds between four oxygen (O-) atoms and a central silicon (Si4+) atom.
  • Basic Components:
    • Feldspar: Consists of a mixture of potassium aluminum silicate and sodium aluminum silicate. It provides natural translucency and forms the main structure of the porcelain. It constitutes about 60% of porcelain powder.
    • Quartz (Silica): Quartz, with its silica (SiO2) structure, serves as a filler in the matrix. It prevents shrinkage during firing, provides stability, controls the thermal expansion coefficient, and increases the durability of the porcelain. During firing, it remains free, helping to preserve the shape of the restoration. Quartz makes up 10-30% of the porcelain powder.
    • Kaolin in Dental Ceramics: Kaolin, a dehydrated aluminum silicate (AI2O3 2SiO2 2H2O), is also known as China clay. It is heat-resistant and provides elasticity to the porcelain paste. Its sticky nature helps bind other materials together, facilitating the modeling of the porcelain. Due to its opaque property, it is only present in 1-5% of the porcelain powder.

These components and their specific properties make dental ceramics an essential material in restorative dentistry, offering durability, aesthetics, and biocompatibility.

Other Components in Porcelain Structure:

  • Fluxes or glass modifiers that lower the melting point and increase the coefficient of thermal expansion in porcelain: calcium oxide (CaO), sodium oxide (Na2O), and potassium oxide (K2O).
  • Intermediate oxides that increase viscosity reduced by glass modifiers: aluminum oxide (Al2O3).
  • Glass-forming oxide used to facilitate the glass-making process: boron oxide (B2O3).
  • Various color pigments: metal oxides such as iron, nickel, copper, titanium, manganese, cobalt, zirconium, and tin.
  • Various agents that enhance opacification or fluorescence properties.

Classification of Dental Ceramics: Dental porcelain systems are classified based on their melting temperatures, chemical structures, and fabrication techniques.

  • Classification Based on Melting Temperatures:
  • High-temperature porcelains
  • Medium-temperature porcelains
  • Low-temperature porcelains
  • Very low-temperature porcelains

Dental Ceramics – Classification According to Melting Temperatures:

  1. High Heat Porcelains:
  • Firing temperatures are around 1315-1370°C.
  • They contain a very low amount of flux (less than 15% shrinkage).
  • Used in the making of artificial teeth and, rarely, high heat-fired jacket crowns due to their transparency, durability, and minimal dimensional change characteristics.
  • Medium Heat Porcelains:
  • Firing temperatures are around 1101-1300°C.
  • They contain more flux compared to high heat porcelains, melt at lower temperatures, and show more than 15% shrinkage.
  • Used in the making of body porcelain.
  1. Low Heat Porcelains:
  • Firing temperatures are around 850-1100°C.
  • Used in jacket crowns, metal-backed crown porcelains, alumina porcelains, various coloring and polishing powders.
  • Contain 95% flux, have shorter firing times, and exhibit 30-35% shrinkage.
  • They have very little or no kaolin in their composition.
  1. Ultra-Low Heat Porcelains:
  • Fired at temperatures below 850°C.
  • Some ultra-low heat porcelains are used with titanium and titanium alloys in inlay-onlay and precision-linked crowns due to their low shrinkage coefficients.
  • Lower firing temperatures reduce the risk of metal oxide release.

Dental Ceramics – Classification According to Fabrication Techniques:

  • Metal-Supported Dental Porcelains
  • Metal-Free Dental Porcelains:
  • Traditional powder-liquid porcelains
  • Castable porcelains
  • Computer-aided (CAD-CAM) fabricated porcelains
  • Heat and pressure pressed porcelains
  • Infiltrated porcelains
  • Metal-Supported Dental Porcelains:
  • Metal-supported porcelain systems meet the requirements of crown and bridge prostheses by enhancing aesthetic characteristics and fracture resistance.
  • These porcelains contain high alkaline to increase the coefficient of thermal expansion. The addition of soda and potassium is necessary for porcelain to adapt to the metal substructure.
  • To ensure adequate bonding to the metal substructure, the metal surface must be clean and have a sufficient oxide layer.
  • More metal oxide is added to the porcelain powder to mask the metal color and minimize the thickness of the opaque porcelain.
  • Metal-supported porcelain restorations consist of a metal substructure placed on the prepared tooth and porcelain fired on top of it.
  • The application of porcelain on the metal substructure involves creating an oxide layer on the metal surface and applying opaque porcelain.
  • Firing temperatures vary according to the used metal substructure.

Advantages of Metal Supported Porcelain:

  • They are more durable.
  • They are aesthetic when the gingival tissue is thick or the margins are finished with porcelain.
  • They can be used in cases of toothlessness in the anterior and posterior regions, in the construction of multi-member bridges, implant-supported dentures and when tooth color needs to be masked.

Disadvantages of Metal Supported Porcelain:

  •  It requires excessive tooth preparation because it contains both metal and porcelain.
  • Allergic and toxic effects may occur against the metal infrastructure.
  • There is a tendency for corrosion and oxidation.
  • Gray discoloration may occur in the gums due to reflection.
  • Due to the light-proof and opaque structure of metal, adequate aesthetics may not be achieved.

Dental Porcelains Without Metal Support:

  • Since metal-supported prostheses cannot fully meet aesthetic expectations, all-ceramic restorations are preferred due to their excellent aesthetic properties, biocompatibility and high resistance to discoloration.

    Aesthetic Advantages of Full Ceramics:

  • They provide depth in color.
  • Their light transmittance and light reflection characteristics have optical properties similar to the enamel and dentin tissues of natural teeth.
  • They have translucent properties similar to natural teeth.
  • The marginal discoloration problem observed in metal-supported restorations is not observed in these systems.

Disadvantages:

  • Compared to metal-supported porcelain crowns, it requires more attention and detail in tooth preparation, laboratory procedures and clinical practice procedures.
  • Due to its mechanical properties, not every all-ceramic system may be suitable for long and posterior bridge restorations.
  • It is not as economical as metal-supported systems and often requires special equipment for their construction.They have a very low resistance to tensile forces and a fragile structure.

Dental Porcelains Without Metal Support – Construction Techniques

  1. Porcelain Produced with Traditional Powder-Liquid Mixture:

  • Feldspathic porcelain was developed by increasing the crystalline content in order to obtain higher strength.
  • These porcelain powders are diluted and applied in layers on the ‘refractor day’ material and the form of the restoration is created.
  • Refractory day material allows porcelain to be transported directly to the furnace without the need for platinum foil application.
  • Examples: Optec HSP, Hi-Ceram, Cerestore, Mirage II, Ceramco and Ceramco II, Cerinate, Finesse, Duceram LFC.
  1. Castable Porcelains:

  • Castable porcelains are obtained by crystallizing glass by applying heat and turning it into ceramic.
  • During the vitrification reaction, crack formation is prevented by the force applied to the crystallized particles, and the material becomes more durable and homogeneous.
  • Lost wax and centrifugal casting techniques are used.
  • Examples: Dicor, Cerapearl, CCPG Castable Calcium Phosphate Glass Ceramics, OCC Olympus Castable Ceramics.
  1. Porcelains Prepared with Computer Aided (CAD/CAM):

  • CAD/CAM refers to computer-aided design and manufacturing.
  • Homogeneous ceramic ingots used in CAD/CAM systems aim to reduce microporosity, homogeneity problems and shrinkage problems caused by firing at high temperatures in other ceramic systems.

 

Stages of CAD/CAM Systems:

  1. Scanning a Three-Dimensional Surface:

  • A three-dimensional computer model of the surface is obtained with the help of an optical or analog surface scanning device.
  • CAD software combines the data obtained from the scan to create a three-dimensional surface model.
  1. Three Dimensional Computer Aided Design:

  • Scans are reviewed electronically using appropriate software.
  • The physical design of the prosthesis is made on the model created with three-dimensional CAD software.
  1. Production:

  • After the model is created, the selected porcelain block is placed in the cutting section of the device and processed.
  • Occlusal adjustment is made, the restoration is polished, its inner surface is roughened and cemented with adhesive cement.
  1. CAD/CAM Restoration Techniques:

  • Copy Milling: The wax modeling prepared on the model is scanned with a scanner and scraped from the porcelain block (eg: Celey, Mikrona).
  • CAD/CAM: After scanning the preparation or measurements and transferring them to the computer, the restoration is shaped by engraving the porcelain blocks (eg: Procera, Nobel, Biocare).

Porcelains Pressed Under Heat and Pressure:

  • These products are available in the form of ceramic ingots and are produced by pressing under heat and pressure into the cavity created by the lost wax technique.

IPS Empress I System:

  • The glass porcelain system, shaped under heat and pressure, was developed by Wohlwend at the University of Zurich in 1983 and was introduced to the market by Ivoclar and Vivadent in 1991.
  • IPS Empress I system is strengthened by homogeneously distributing 35-40% of 1-3μm sized leucite crystals (SiO2 Al2O3 K2O) into the glass porcelain matrix.
  • Leucite crystals increase the fracture and bending resistance by preventing the progression of microcracks formed in the glass matrix.
  • In this system, wax modeling alumina is transferred to a phosphate-bonded investment in a special piston mold, then leucite-strengthened glass porcelain tablets reach the viscous alumina feature in a special oven at 1150°C and are transferred under pressure to the negative space of the restoration.
  • The final color of the crown is achieved by applying surface coloring to the restoration using colorless porcelain or by using colored dentin tablets and applying the layering technique with veneer porcelain material.
  • IPS Empress I system offers high aesthetic quality with light transmittance and color characteristics close to natural teeth. It is used in the production of laminate veneers, inlays, onlays and single crowns.
  • However, its use is not indicated on teeth that are colored or on which metal post core has been applied, or on implant-supported dentures using metal abutments, due to their high translucency.

IPS Empress II:

  • Developed in 1998, IPS Empress II consists of 60% of the main crystalline phase lithium disilicate (SiO2-LiO2).
  • It is three times more durable (300-400 MPa) than IPS Empress I, has higher bending resistance and offers excellent aesthetic properties thanks to its high translucency.
  • It is indicated for the application of three-member bridges in the anterior region, three-member bridges and single-crown restorations in the posterior region that extend up to the second premolar region and have a body as wide as one premolar.

 

Other Examples:

  • IPS Empress Esthetic
  • IPS e.max
  • IPS e.max Press
  • IPS e.max CAD

Infiltrated Porcelains:

  • Infiltrated porcelains consist of porous aluminum oxide powder and glass that infiltrate the porous structure at high temperatures.
  • These two components are used as the core structure and the superstructure is prepared with feldspathic layering porcelain.

In-Ceram System:

  • In-Ceram system, which is prepared by melting and infiltrating glass particles onto the sintered oxide infrastructure, has three types: In-Ceram Alumina, In-Ceram Spinell and In-Ceram Zirconia, depending on the chemical content of the prepared infrastructure.

Zirconium Ceramics:

  • The first biomedical study on zirconium was conducted in 1969 and it began to be used in dentistry in the early 1990s.
  • Zirconium is used in various applications in dentistry due to its high tensile strength, tissue friendliness and low grain diameter. These include implant abutment material, core material in fixed restorations, post-core material and orthodontic bracket.
  • Zirconium exists in 3 main phases: monoclinic, cubic and tetragonal. Pure zirconium is in the monoclinic phase at room temperature, passes into the tetragonal phase above 1170 °C, and into the cubic phase at temperatures higher than 2370 °C.
  • “Partial stabilized zirconium” is obtained by adding stabilizing oxides (CaO, MgO, CeO2, Y2O3) to pure zirconium. The most commonly used biomaterial is yttrium tetragonal zirconia polycrystal (Y-TZP).

Production and Classification:

  • Y-TZP blocks are classified into 2 main groups: semi-sintered and fully sintered.
  • Semi-sintered blocks have a porous structure and are shaped 20-30% larger than normal by “green machining” and are sintered at 1350-1500°C to reach the desired size and density.
  • Fully sintered blocks have high density and are subjected to direct milling process.
  • Differences according to systems: While semi-sintered Y-TZP blocks are used in Lava and Cercon systems, fully sintered Y-TZP blocks are preferred in DCS-Precident and DC-Zircon systems.
  • Micro cracks may occur during the milling process of semi-sintered blocks, but this problem does not occur in fully sintered blocks and better edge fit is achieved. Fully sintered blocks are more difficult to mill.

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