Ceramics

Question 1

What are ceramics?

Answer 1

Compounds between metallic and nonmetallic elements with bonds that are either totally ionic or combination of ionic and covalent

Question 2

Advantages and disadvantages of ceramics

Answer 2

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

Question 3

Physical forms of bioceramics

Answer 3

Micro-spheres, thin layers or coatings on a metallic implant, porous networks, composites with a polymer component, large well polished surfaces

Question 4

4 Types of implant-tissue respone

Answer 4

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

Question 5

4 Classifications of tissue attachment on ceramics

Answer 5

Type 1: Nearly Inert
Type 2: Porous Ingrowth
Type 3: Bioactive
Type 4: Resorbable

Question 6

Type 1: Nearly Inert

Answer 6

dense, inert, nonporous ceramics which attach bone by tissue growth into surface irregularities or by press fitting; morphological fixation

Question 7

Type 2: Porous Ingrowth

Answer 7

porous inert ceramics which attach by bone ingrowth into pores resulting in mechanical attachment of bone to material; biological fixation

Question 8

Type 3: Bioactive

Answer 8

dense, nonporous surface-reactive ceramics which attach directly by chemical bonding with bone; bioactive fixation

Question 9

Type 4: Resorbable

Answer 9

dense, nonporous or porous resorbable ceramics which are slowly resorbed and replaced by bone

Question 10

Processing of ceramics

Answer 10

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

Question 11

Classifications of bioceramics

Answer 11

Inert ceramics: Alumina and Zirconia
Biodegradable ceramics: calcium phosphate
Bioactive ceramics: glass ceramics
Pyrolytic carbon

Question 12

Two most commonly used structural bioceramics & applications

Answer 12

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)

Question 13

Alumina properties

Answer 13

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

Question 14

Zirconia properties

Answer 14

Compared to alumina, zirconia has:

higher flexural strength, fracture toughness, better reliability, lower Young’s modulus, lower hardness

Question 15

Calcium Phosphates properties and applications

Answer 15

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

Question 16

Bone mimicry properties of calcium phosphates

Answer 16

Interconnecting porosity
Biodegradablility
Bioactivity
Osteoconductivity
Osteoinductivity

Question 17

Bone mimicry: Interconnecting porosity

Answer 17

macroporosity formed by adding porogens with foaming methods; microporosity depends on sintering temperature

Question 18

Bone mimicry: Biodegradablility

Answer 18

acidic buffer somewhat mimics the environment during osteoclastic activity

Question 19

Bone mimicry: Bioactivity

Answer 19

allows the material to directly bond with new forming bone

Question 20

Bone mimicry: Osteoconductivity

Answer 20

ability of the material to serve as a scaffold or template to guide formation of the newly forming bone along with their surfaces

Question 21

Bone mimicry: Osteoinductivity

Answer 21

ability of the material to induce de novo bone formation without the presence of osteogenic factors

Question 22

Calcium hydroxyapatite uses

Answer 22

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

Question 23

Example of bioceramic coatings

Answer 23

hydroxyapatite coatings applied to metallic implants to alter the surface properties; without coating body would sense a foreign body

Question 24

Glass ceramics

Answer 24

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

Question 25

Glass ceramics applications

Answer 25

Orthopedics: bone plates and screws, hip components, coatings for controlled implant/tissue interfacial response, space filling of diseased bone, vertebral prostheses, vertebra spacers
Dentistry: crown and bridge, implant coatings, ridge maintenance, brackets for orthodontics, glass ionomer cements and adhesives

Question 26

Pyrolytic Carbon

Answer 26

man-made and not found in nature, produced by pyrolysis by decomposing to hydrocarbon to permit graphite to crystallize, very compatible to blood