Ceramics Flashcards
(26 cards)
What are ceramics?
Compounds between metallic and nonmetallic elements with bonds that are either totally ionic or combination of ionic and covalent
Advantages and disadvantages of ceramics
Advantages: inert or bioactive in body high wear resistance high modulus/stiffness & compressive strength esthetic for dental applications Disadvantages: brittle low tensile strength poor fatigue resistance
Physical forms of bioceramics
Micro-spheres, thin layers or coatings on a metallic implant, porous networks, composites with a polymer component, large well polished surfaces
4 Types of implant-tissue respone
Toxic –> surrounding tissue dies
Nontoxic + biologically inactive/nearly inert –> fibrous tissue of variable thickness forms
Nontoxic + biologically active/bioactive –> interfacial bond forms
Nontoxic + dissolves –> surrounding tissue replaces material
4 Classifications of tissue attachment on ceramics
Type 1: Nearly Inert
Type 2: Porous Ingrowth
Type 3: Bioactive
Type 4: Resorbable
Type 1: Nearly Inert
dense, inert, nonporous ceramics which attach bone by tissue growth into surface irregularities or by press fitting; morphological fixation
Type 2: Porous Ingrowth
porous inert ceramics which attach by bone ingrowth into pores resulting in mechanical attachment of bone to material; biological fixation
Type 3: Bioactive
dense, nonporous surface-reactive ceramics which attach directly by chemical bonding with bone; bioactive fixation
Type 4: Resorbable
dense, nonporous or porous resorbable ceramics which are slowly resorbed and replaced by bone
Processing of ceramics
1) compounding: mix and homogenize ingredients into slurry or clay
2) forming: clay or slurry is made into parts by pressing into mold; sintering
3) drying: formed object dried at room temperature until “green”, leathery state
4) firing: heated to drive off remaining water; porous parts formed by adding a second phase that decomposes at high temperatures
Classifications of bioceramics
Inert ceramics: Alumina and Zirconia
Biodegradable ceramics: calcium phosphate
Bioactive ceramics: glass ceramics
Pyrolytic carbon
Two most commonly used structural bioceramics & applications
Alumina
Applications: orthopedics (femoral head, porous coatings for femoral stems, knee prosthesis); dental (crowns and bridges)
Zirconia
Applications: orthopedics (femoral head, artifical knee); dental (crowns and bridges)
Alumina properties
smaller grain size and porosity –> higher strength; high hardness, low friction, high wear resistance with no generation of wear particles, excellent corrosion resistance, low fracture toughness and tensile strength
Advantage : biocompatible
Disadvantage: non-adherent fibrous membrane at interface; interfacial failure can occur, leading to implant loosening
Zirconia properties
Compared to alumina, zirconia has:
higher flexural strength, fracture toughness, better reliability, lower Young’s modulus, lower hardness
Calcium Phosphates properties and applications
Different forms exist depending on Ca:P ratio, presence of water, impurities and temperature; excellent biocompatibility; high elastic modulus; structure resembles bone mineral good for bone replacement; coating of metal implants to promote bone ingrowth; most stable form is crystalline hydroxyapatite
Uses: drug-delivery systems; repair material for bone damaged trauma or disease; void filling; repair of vertebrae, maxillofacial and dental defects
Bone mimicry properties of calcium phosphates
Interconnecting porosity Biodegradablility Bioactivity Osteoconductivity Osteoinductivity
Bone mimicry: Interconnecting porosity
macroporosity formed by adding porogens with foaming methods; microporosity depends on sintering temperature
Bone mimicry: Biodegradablility
acidic buffer somewhat mimics the environment during osteoclastic activity
Bone mimicry: Bioactivity
allows the material to directly bond with new forming bone
Bone mimicry: Osteoconductivity
ability of the material to serve as a scaffold or template to guide formation of the newly forming bone along with their surfaces
Bone mimicry: Osteoinductivity
ability of the material to induce de novo bone formation without the presence of osteogenic factors
Calcium hydroxyapatite uses
Gained acceptance as bone substitute; repair of bony defects, repair of periodontal defects, maintenance or augmentation of alveolar ridge, ear implant, eye implant, spine infusion, adjuvant to uncoated implants; closely related to collagen making it a logical candidate for induction of a host response
Example of bioceramic coatings
hydroxyapatite coatings applied to metallic implants to alter the surface properties; without coating body would sense a foreign body
Glass ceramics
polycrystalline solid prepared by controlled crystallization of glass (brittle); silica based materials; bioactivity depends on relative amounts of SiO2, CaO, and Na2O; cannot be used for load bearing applications; ideal as bone cement filler and coating due to its biological activity
