Ceramics play a major role in the day to day life and there is no exception that it rules the medical field. Ceramic is a class of inorganic products and it is a nonmetallic polycrystalline material. It has the properties of heat and corrosion-resistant and it is also hard and brittle. The raw materials are structured and shaped through the sintering process.

The process of forming a structural solid material through the heat and pressure, without the involvement of melting is known as sintering.

The fine powders are generally mixed with a binder and made into the desired shape and then sintered. If there is no chemical reaction occurs during this process, then we would have the starting material in the final body but if there is any reaction, then it is known as reaction sintering. So here the final product would have different chemical components as it has undergone chemical reaction.

Generally ceramics are classified into two types as classical ceramics that include pottery and sanitary ware etc., and advanced ceramics that include implants. Bioceramics is a class that is generally used to repair the damaged bone tissue. These bioceramics can directly interact with the surrounding tissues and it can also induces the new tissue regeneration. Bioceramics are classified into various types that is mentioned below:

BIOCERAMIC TYPES

Here bioinert ceramics and bioactive ceramics are elaborated in this blog

BIOINERT CERAMICS:

  • Alumina
  • Zirconia
  • Carbides and nitrides
  • Quartz
  • Porcelain

The most commonly used materials for bioinert ceramics are alumina and zirconia. Carbides and nitrides are used for dental applications. Alumina(Al₂O₃) is the most used compound for technological ceramic devices and biomedical products. It is pressed and sintered at 1600 degrees Celsius. Less than 0.5% of MgO is added during the sintering to limit grain growth. To promote the grain growth less than 0.1% of SiO2 along with alkali metal oxides is used.

The single crystal alumina is referred to as “Sapphire”. “Blue Sapphire” is the alumina with the impurities of Fe and Ti whereas “Ruby” is the alumina with 1% of Al3+ replaced by Cr3+ that yields the red color.

PROPERTIES OF ALUMINA:

  • Excellent wear resistance
  • Low friction coefficient
  • Biocompatibility
  • Excellent corrosion resistance
  • Inert in a physiological environment.
APPLICATIONS:
  • Hip implants
  • Total joint prosthesis,
  • Dental crowns,
  • Cochlear implants, and
  • Maxillofacial applications.

Zirconia is nothing but the white crystalline oxide of zirconium and it is a monoclinic crystalline structure. It is stable at room temperature. When it is not stable, suitable additives are added to obtain the stable phase by cooling after heating. Pure zirconia is not useful to produce the ceramics.

The properties of zirconia include:

  1. Low wear resistance
  2. High fracture toughness. It is used in the applications of femoral head, artificial knee, dental etc.,

Carbides are composed of carbon. It’s mechanical performance depends on the composition. It is used as a coating for surgical implants. It has high melting temperature. At high temperature it exists in three forms namely alpha phase, beta phase and gamma phase. Nitrides are the compound of nitrogen. Generally TiN, TaN are used in biomedical applications which has alpha phase.

The advantages of nitrides over carbides are

  1. Easily obtained and used widely than carbides
  2. Very high tribological performance
  3. They have low thermal expansion coefficient than carbides.

Quartz is the most common mineral found on the earth and its natural form of silicon dioxide is found in wide range of varieties and colours. During firing process, it is dissolved in the viscous feldspar. Porcelain is materials that don’t fit into classical ceramics and so is termed fritted porcelain. They are generally categorized into three categories: hard-paste, soft paste, and bone china. Kaolin is the primary material from which the porcelain is made. The properties of porcelain include

PROPERTIES OF PORCELAIN :

  1. Whiteness,
  2. Hardness,
  3. Low permeability
  4. Elasticity, and
  5. High durability. Al2O3 is used to avoid excess brightness and to improve toughness. Materials such as TiO2, ZrO2, ZrSio4 , and CeO2 are used to adapt the white tone for the teeth. These are generally used in the applications of artificial teeth.

Porcelain is widely used because of its aesthetic appearance.

BIOACTIVE CERAMICS

Coming to bioactive ceramics, these ceramics are generally used to induce specific biological activity for repairing damaged organs. Calcium phosphates and hydroxyapatite are generally used but in rare cases, tricalcium phosphate is used. It is mainly used in bone and the main function is to sustain the growth of the bone. These materials are subjected to bio resorption and can exhibit biostabilty

Osteoinduction, osteoconduction, and osseointegration are the most important properties of bioactive ceramics.

From the name, it is understood that osteoinduction is the process by which osteogenesis is induced. Osteogenesis is nothing but the formation of bone. This type of phenomenon is regularly seen in the process of bone healing. This enhances bone regeneration and this osteo induction implies the recruitment of immature cells and preosteoblasts are developed due to the stimulation of these immature cells. The majority of bone healing such as fractures depends on osteo induction.

Osteo conduction is the growth of the bone on a surface. This phenomenon is generally seen in bone implants. This provides a suitable scaffold for the deposition of the new bone. But it does not induce bone formation in the soft tissue. Low biocompatibility materials such as copper, silver and bone cement shows no osteo conduction.

Osseointegration/osteointegration is the direct structural and functional connection between ordered, living bone and the surface of load-carrying implant. It is the stable anchorage of an implant. A fixture is Osseo integrated if it provides stable and immobile support of the prosthesis under loads without pain or inflammation.

Tricalcium phosphate, Hydroxyapetite, and calcium phosphate ceramics are some of the examples of bioactive ceramics. Tricalcium phosphate(TCP) is slowly bioresorbed.

PROPERTIES OF TCP:

  1. White, crystalline powder
  2. Odorless
  3. Tasteless
  4. Moderately soluble in water.
  5. Not very chemically reactive. Bioresorbable ceramics would have the capability of high osteoinduction.

APPLICATIONS OF TCP:

  1. Calcium phosphate bone cements
  2. Bone graft substitutes
  3. Implant material

Hydroxyapetite(HA) looks similar to the stable product that is present in the bone.

PROPERTIES OF HYDROXYAPETITE:

  1. Biostable
  2. Biotolerable
  3. Biocompatible
  4. Good bioactivity
  5. Thermodynamically stable
  6. Good adhesion and surface attachment. These properties of HA made it used to a greater extent.

APPLICATIONS OF HYDROXYAPETITE:

  1. Bone regeneration
  2. Bone repair
  3. Scaffolds
  4. Coatings on orthopedic and dental implants.

Calcium phosphate ceramics are mainly used for the surgical applications on the bone. The ceramic behaviour depends on the chemical nature and the structure. It does not have high mechanical resistance. These ceramics are incorporated into scaffolding materials. Phosphates build complex class of chemical compounds.

Thus various types of ceramics and its application are explained here. HAPPY READING!!!

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