Dental Implant and Osseointegration
Some investigators have passivated Ti and Ti alloys twice to reduce ion release,
and they claim that this process yields superior osseointegration. One can
consider titanium oxide (TiO2) or such other oxide ceramics as Al2O3 and ZrO2
as tooth root materials. Ironically, even these “metal” implants are virtually
“ceramics” coated by an oxide layer. Single-crystal alumina can also be used.
The bone substitutes would have osseo- or osteointegration during the healing
process. However, direct apposition of bone on the surface of an implant without
intervening collagen membrane formation is termed osseointegration. To have
such a tissue–implant interface, first, there should be minimal relative motion
between the two; second, there should be minimal mismatch of modulus or
compliance; and, third, the implant surface material should be highly
biocompatible. In orthopedics, osseointegration cannot be easily achieved due
to the first two factors. Other researchers have suggested that the implant–bone
interface undergoes fibroosseous integration or biointegration. Both processes
describe the same collagen membrane formation at the interface. The presence
of collagen membranes at the interface is key evidence of these processes.
Membranes are usually formed in response to mechanical loading (relative
motion) on the surface, and the presence of foreign matter. The interface can
change over time, and initial osseointegration may become fibro-osseous
integration due to infection, implant wear products, and overloading of implant
during mastication. Moreover, a dental implant is exposed to the “exterior” of
the body since the crown protrudes into the mouth. This makes it
atranscutaneous or percutaneous implant, which introduces the added burden of
sealing an implant to prevent invasion by foreign organisms.
The metals (Ti and Ti6Al4V) used in Branemark-style implants have many
favorable features. They are easy to machine, have high strength, toughness, and
low modulus, are easily passivated, etc. However, such metals as zirconium
should be explored for possible use in dental implants, as they have
characteristics similar to those of titanium in terms of high oxidizability and
good mechanical properties.
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Ceramic for dental
In Dental science, ceramics are referred to as nonmetallic, inorganic structures
primarily containing compounds of oxygen with one or more metallic or semimetallic elements. They are usually sodium, potassium, calcium, magnesium,
aluminum, silicon, phosphorus, zirconium & titanium. Ceramics have excellent
intraoral stability and wear resistance adding to their durability. Basically
ceramics are used as indirect restorative materials such as crowns and bridges,
Inlays and dental implants. Recently ceramic braces are used in orthodontics.
Dental cements are basically glasses. Initially, silicate cements were introduced.
The cement powder contains a glass of silica, alumina and fluorides. The liquid,
on the other hand, is an aqueous solution of phosphoric acid with buffer salts.
The cement powder and liquid are mixed together resulting in an acid-base
reaction. Fluoride ions are leached out from the set cement, which is responsible
for the anti-cariogenic property exhibited. Cements are direct restorative
materials – i.e. manipulated and placed onto teeth directly, unlike other
restorations that are made outside and fixed to teeth, called indirect restorations.
They are highly advantageous as they are quick to set, release fluoride leading
to anti cariogenic action, esthetic and chemically bond to tooth material.
Classification of dental ceramics Based on Composition
Dental ceramics can classified according to their composition to:
Silicates ceramic are characterized by amorphous glass phase, containing
predominantly silica.
Oxide ceramics: It is notable that only oxide ceramics are used in dentistry,
since nonoxide ceramics are difficult to process. Oxide ceramics contain a
principal crystalline phase like Alumina. Zirconia has very high fracture
toughness.
Glass ceramics: These are type of ceramics that contains a glass matrix phase
& at least one crystal phase such as Carbides nitrides.
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