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Dental Biomaterials
1. The notion of biomaterials. Their properties.
Biomaterials play an essential part in modern dentistry. It play a vital role in the
restoration of the diseased or damaged tooth structure and despite providing reasonable
outcomes.
Tensile strength, yield strength, elastic modulus, corrosion, creep, and hardness are some
of the most vital properties of biomaterials that should be thoroughly investigated and
evaluated before implantation.
2. Electrical properties (galvanization).
The electrical current discharged from a tooth when two or more different metals coexist
within the slightly acidic saliva is known as oral galvanism.
The classic example of dental galvanism is that of a silver amalgam placed in opposition
or adjacent to a tooth restored with gold. These dissimilar metals in conjunction with
saliva and body fluids constitute an electric cell.
3. Color selection. Dimensions of color.
the order of color selection is value first, then chroma, and finally hue. Color matching
should be done in a systematic manner to achieve precision, consistency, and
predictability, all of which are critical in aesthetic dentistry.
The interaction of three dimensions known as hue, chroma, and value can be used to
express colors.
Hue is a color dimension that is easier to distinguish because it matches the color's name.
Due to the modest variance between dental hues, which are mainly limited to variations
between shades of yellow and orange, is regarded as the least chromatic dimension in
dentistry.
The degree of saturation, intensity, purity, or amount of a pigmented shade determines
chroma, which make it hard to compare this dimension between distinct hues.
It varies from one tooth to the next and between sections of the same tooth in natural
teeth.
The value is a more immediately recognisable colour dimension that represents the
reflected light from the item. The value dimension is more essential than the hue and
chroma dimensions because minor differences in value are easier to spot than small
variances in hue and chroma.
4. Mechanical properties (strength, resilience, flexibility) of biomaterials biomaterials.
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Mechanical properties are physical properties that a material exhibits upon the application
of forces. Examples of mechanical properties are the modulus of elasticity, tensile strength,
elongation, hardness and fatigue limit.
All mechanical properties are measures of the resistance of a material to deformation, crack
growth, or fracture under an applied force or pressure and the induced stress. An important
factor in the design of a dental prosthesis is strength, a mechanical property of a material,
which ensures that the prosthesis serves its intended functions effectively and safely over
extended periods of time. In a general sense, strength is the ability of the prosthesis to resist
induced stress without fracture or permanent deformation (plastic strain). Plastic
deformation occurs when the elastic stress limit (proportional limit) of the prosthesis
material is exceeded. Although strength is an important factor, it is not a reliable property
for estimating the survival probabilities over time of prostheses made of brittle material
because strength increases with specimen size and stressing rate, decreases with the number
of stress cycles, and is strongly affected by surface processing damage. Thus, strength is
not a true property of a material compared with fracture toughness, which more accurately
describes the resistance to crack propagation of brittle materials.
Mechanical properties are expressed most often in units of stress and/or strain. The
stressing rate is also of importance since the strength of brittle materials increase with an
increase in the rate at which stress is induced within their structures. They represent
measures of (1) elastic or reversible deformation (2) plastic or flexible deformation (3) a
combination of elastic and plastic-deformation
5. Characteristics of the compressive pressure. Impact strength.
Compressive Strength refers to a material's resistance to Compressive Stress, which is
caused by any force applied to the stone mass.
The typical strength of concrete is defined as the strength below which no more than 5%
of the test results should fall. This compressive strength value is controlled for design
reasons by dividing by a factor of safety, whose value varies depending on the design
philosophy applied.
6. Metals and metal alloys. Definition
Metals are opaque, lustrous elements that are good conductors of heat and electricity. Most
metals are malleable and ductile and are, in general, denser than the other elemental
substances.
Metal alloys are blends of two or more metals that have been melted together.
7. Alloys for fixed dentures (noble, base).
Cobalt-chromium alloys are now commonly used for fixed dentures and single crowns.
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A noble metal alloy is a device composed primarily of noble metals, such as gold,
palladium, platinum, or silver, that is intended for use in the fabrication of cast or porcelain-
fused-to metal crown and bridge restorations.
A base metal can be the primary metal in an alloy. An example is iron in steel. A base metal
can be a metal or alloy to which a plating or other coating is applied. An example is steel
or iron in galvanized steel.
8. Alloy casting, welding and bonding, alloy recycling.
Casting alloys. They are substitutional solid solution alloys which do not contain any noble
metals.
In dentistry, welding between abutment elements, during construction of the metal
framework or even after ceramics application, has been used by the vast majority of dentists
to solve problems related to laboratory distortions that are reflected in prostheses' misfit in
the marginal area.
Alloys are advantageous compared with pure metals in physical and mechanical properties
because of engineering the optimum influence from each constituent. For example, pure
gold is ductile, malleable, and soft, which is not desirable for prosthetic applications such
as crowns
9. Acrylic resins. Types.
There are three types of acrylic resin denture teeth in common use: homogenous, layered
and polycarbonate coated. The type of denture teeth used has been shown to affect the bond
strength. Homogenous acrylic resin teeth had higher bond strength than crosslinked teeth
10. The properties of heat activated acrylic resins (structure, porosity, volume change,
thermal expansion, shrinkage during curing, thermal shrinkage, biological
properties).
properties Heat activated acrylic resin materials are most widely used for the fabrication
of denture prosthesis. Flexural strength, impact strength and surface hardness are some of
the desirable mechanical properties of denture prosthesis materials.
Structure An acrylic resin is a thermoplastic or thermosetting plastic substance typically
derived from acrylic acid, methacrylic acid and acrylate monomers such as butyl acrylate
and or methacrylate monomers such as methyl methacrylate.
Porosity in an acrylic resin denture base is often attributed to the presence of residual
monomer.
Volume change Acrylic resins marketed as index and pattern materials have a
polymerization shrinkage of 6.5% to 7.9%. Eighty percent of the change appears before
17 minutes at room temperature. Altering the powder-to-liquid ratio by adding more liq-
uid significantly increases the shrinkage.
Shrinking during curing Heat cure acrylic resins are the most commonly used denture
base materials. The important limitation is they may act as reservoir of microorganisms.
The adherence of microorganisms can be reduced by chemical modification of the
surface charge of denture base resin.
Biological properties
