Titanium and titanium alloys/ /certified fixed orthodontic courses by Indian dental academy

INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

Metals have been used as Biomaterials for many
centuries.
Around 1565 gold plate was reported to be used to
repair cleft palate defects.
Gold alloys and their substitutes are formed by a
casting process developed by Taggart in 1907.
Since then, cast gold restorations have been
routinely used in clinical dentistry.


With advances in dental porcelain in the 1960s and
the significant increase in the price of gold in the
1970s, alternative alloys such as palladium alloys
and base metal alloys, were developed. The
allergenic and carcinogenic properties of base metal
alloys used in dentistry especially nickel and
beryllium-based alloys, have fueled controversy.


The evolution of titanium (Ti) applications
to medical and dental implants has
dramatically increased in the past few years
because of titanium’s excellent
biocompatibility corrosion resistance and
desirable physical and mechanical
properties.


Titanium has become a material of great interest in
prosthodontics in recent years. A growing trend
involves the use of titanium as an economical and
biocompatible replacement for existing alloys for
fixed and removable prostheses. However, long
term of titanium casting, joining, and porcelain
bonding have to be evaluated before this wonder
metal can be used routinely in clinical dentistry.


Most important deterrent to the use of Ti in
dental application is the fact that it is difficult
and dangerous to cast, The metal oxidizes so
rapidly at elevated temperature that an almost
explosive reaction may occur. So that it needs
to cast titanium alloy in oxygen atmosphere
(vacuum or argon) to prevent excessive
oxidation.

The physical and mechanical properties of pure Ti
and Ti alloys can be greatly varied with the
addition of small traces of other elements such as
oxygen, iron, and nitrogen.
Commercially pure titanium, is available in four
different grades


ASTM 1 to 1V - based on the incorporation
of small amounts of oxygen, nitrogen,
hydrogen, iron, and carbon during purification
procedure.
ASTM committee on materials for surgical
implants recognizes four grades of
commercially pure titanium and two titanium
alloys.

The two alloys are Ti-6Al-4V and Ti-6A1-4V
extra low interstitial (ELI).
Commercially pure titanium is also referred to
as unalloyed titanium. All six of these
materials are commercially available as dental
implants.

Ti-6A1-4V
Several alloys of titanium are used in
dentistry. Of these alloys, Ti 6Al-4V is the
most widely used.
At room temperature, Ti-6A1-4V is a twophase α+β alloy.
At approximately 975°C, an allotropic phase
transformation takes place, transforming the
microstructure to a single phase BCC β-alloy.

Thermal treatments dictate the relative
amounts of the α and β phases and the phase
morphologies and yield a variety of
microstructures and a range of mechanical
properties.


An extremely reactive metal, titanium forms a
tenacious oxide layer that contributes to its
biocompatibility and electro chemical passivity.
This stable oxide with a thickness on the order of
nanoseconds, and it repassivates in a time on the
order of nanoseconds.


However, titanium-based alloys and alloys
containing titanium are prone to gap corrosion
and discoloration in the oral cavity. Therefore
titanium is electrochemically inactivated by
the addition of small percentage of a metal of
platinum group to improve the anticorrosion
properties of the alloys by inducing a firm
passive coating.

Palladium was chosen among the platinum
group metals, as it prevents corrosion of
titanium by the addition of only a small
amount (0.15%).


The lightly held 3d² and 4s² electrons are
highly reactive and rapidly form a tenacious
oxide that is responsible for the metal’s
biocompatibility. The remaining electrons
are relatively stable and tightly bound.


There are three general types of titanium base
alloys, such as alpha alloys, alpha-beta alloys,
and beta alloys, according to the predominant
room temperature phases present in the
microstructure. At temperatures upto 882°C,
pure titanium exists as hexagonal closepacked atomic structure (alpha phase).


Above that temperature, pure titanium
undergoes a transition from hexagonal closepacked structure (alpha) to a body-centered
cubic structure (beta). The metal melts at
1665°C. A component with a predominantly
β-phase is stronger than a component with an
α-phase microstructure.

Alloying elements are added to stabilize one
or the other of these phases by either raising
or lowering the transformation temperatures.
The elements oxygen. aluminium, carbon, and
nitrogen stabilize the alpha phase of titanium
because of their increased solubility in the
hexagonal close-packed structure.

For example, in Ti-6A1-4V aluminium is an a
stabilizer, which expands the a phase field by
increasing the (α+β) to β transformation
temperature.
Elements that stabilize the beta phase, include
manganese, chromium. iron and vanadium.
They expand the β -phase field by decreasing
the (α+β ) to β transformation temperatures.

Vanadium stabilizes the beta phase of Ti-6A1-4V
alloy, so that it exists as a combination of alpha
and beta phases. The combination of phases
gives the alloy strength.


The ELI alloys are sometimes used. “Extra
low interstitial” describes the low levels of
oxygen dissolved in interstitial sites in metal.
With lower amounts of oxygen and iron
residuals in the ELI alloy, ductility is
improved slightly.


In general, alpha titanium is weldable, but difficult to
form or work with at room temperature.
Beta titanium, however, is malleable at room
temperature and is thus used in orthodontics.
The (α+β) alloys are strong and formable but
difficult to weld.


Thermal and thermo chemical treatments can
refine the post cast microstructures and
improve properties.


Density 4.5g/cm³
(considerably less than gold or Ni-Cr or Co-C r alloys)

Because of the light weight of the titanium
and its strength-to-weight ratio, high ductility,
and low thermal conductivity would permit
design modifications in Ti restorations and
removable prostheses, resulting in more
functional and comfortable use.

The low cost of titanium raw material (USD 22
to 27 per kg) makes titanium material
attractive for dental prostheses.


The environmental resistance of titanium
depends primarily on a thin, tenacious, and
highly protective surface oxide film which
is about 2O - 50 A°. Titanium and its alloys
develop stable surface oxides with high
integrity, tenacity and good adherence.


The surface oxide of titanium will, if scratched or
damaged, immediately reheal and restore itself in the
presence of air or water.
The protective oxide film on titanium mainly Ti02
(rutile), is stable over a wide range of pHs, potentials,
and temperatures, and is specially favoured as the
oxidizing character of the environment increases.


For this reason, titanium generally resists mild
reducing, neutral, and highly oxidizing environments
upto reasonably high temperatures. It is only under
highly reducing conditions that oxide film
breakdown and resultant corrosion may occur. These
conditions are not normally found in the mouth.


The Coefficient of thermal expansion is a most
important factor in bonding of an alloy to
porcelain.
The difference in the coefficient of the expansion
between the alloy and porcelain should be within
±1x10-6 /°C to obtain sufficient bonding strength.


Coefficients of thermal expansion of pure
titanium and Ti-6A1-4V are 10.37 x 10-6
and 12.43 x 10-6 /ºC, respectively, which are
considerably smaller than those of
commercial porcelain materials which is
about 14 x l0-6 /°C.


Titanium is the most corrosion resistant
metallic material for implants in present use,
but, paradoxically, the self formed protective
oxide film on titanium can be affected by
excessive use of the commonest preventive
agents in dentistry, prophylactic polishing and
topical fluoride app1ications.


Adhesion of titanium to methacrylate based
polymer materials can be increased by plasma
treatment.


MECHANICAL PROPERTIES


The mechanical properties of titanium and its
alloys surpass the requirements for an implant
material. Orthopaedic and dental implants
require strength levels greater than that of
bone and an elastic modulus close to that of
bone.


The most commonly used and important
titanium alloy is Ti-6A1-4V, because of its
desirable proportion and predictable
producibility.
The ultimate tensile strength of spongeous
bone is about 83 MPa and cortical bone is
about 117 MPa.


It is important to note that while the modulus of
elasticity of cp grade 1 titanium to cp grade 1V
titanium ranges from 102 to 104 GPa (a change
of only 2%), the yield strength increases from
170 to 483 MPa (a gain of 180%). Reasons for
the changes are related chiefly to oxygen
residuals in the metal.


The characteristic trend of increasing strength
with relatively constant modulus continues
when comparing cp titanium with titanium
alloys. The elastic modulus of the alloys is
slightly higher (113 MPa compared with 104
MPa of cp grade 1V titanium), but the yield
strength increases over 60% to 795 MPa for
ELI alloys and 860 MPa for Ti-6A1-4V
alloys.

Titanium has poor shear strength and wear
resistance, however making it unsuitable for
articulating surface or bone screw applications.


Compared with Co-Cr-Mo alloys, titanium
alloy is almost twice as strong and has half
the elastic modulus. Compared with 316L
stainless steel, the Ti-6A1-4V alloy is roughly
equal in strength, but again, it has half the
modulus.


Strength is beneficial because materials better
resist occlusal forces without fracture or
failure, Lower modulus is desirable because
the implant biomaterial better transmits forces
to the bone.


Titanium and its alloys are inert, have excellent
biocompatibility and predictability.
The non-alloyed titanium elicits an acute
inflammatory response with an increased number of
leukocytes around the implant. However, the
number of inflammatory cells decrease during the
first week and fibroblasts become the major cells in
the interfacial tissue.

During the first week the implant is
surrounded by a fluid space that contains
proteins, erythrocytes. inflammatory cells and
cell debris. One week after insertion of
implants, the size of the fluid space reduces in
non-alloyed titanium, for example, ion
implanted titanium.

The inflammatory cells present in this space
seldom adhere to the surface of the nonalloyed titanium and do not appear activated.
Non-alloyed titanium implants are surrounded
by a thin layer of orderly arranged collagen
and elongated fibroblasts.


Titanium also provides a surface suitable for
the proliferation of several differentiating
tissues. Non-alloyed titanium fixtures which
are inserted in knee-joints after drilling
through the cartilage or synovial tissue heal
within the joints and a direct contact with the
subchondral bone is established 4 to 6 weeks
after insertion.

Non-alloyed titanium can also be used intraarticularly as it causes no inflammation in the
synovial tissue.
Plaque accumulation of titanium or
hydroxylapatite (HA) coated titanium is less
than on natural teeth because of its high
surface energy.


Bone formation and its maturation occurs
faster on HA coated Ti implants than on noncoated Ti implants.
Since enhanced bone growth preceedes by
rapid clotting, so the clotting occurs faster on
the HA-coated Ti implants than on non-coated
titanium implants.

Lost wax
casting


This is a the recently developed investment
for casting titanium inlay, crown and bridge.
Binder - calcia
Refractory -Zirconia


There are 2 types of Calcia and mixing liquid.
1. Saturation type (total expansion 2 ± 3%)
2. Delayed expansion type

Properties
1. Total thermal and setting expansion found was -1 .5 2.5%
2. The maximum thermal expansion is found at - 900 1200°c


Cp titanium
- vacuum casting


Pure titanium melts at 3,035°F (1,668°C) and reacts
readily with conventional investments and gases like
oxygen, nitrogen and carbon. In addition because of
its low specific gravity, titanium flows less easily
that gold alloy when cast in centrifugal casting
machine. Therefore, it must be cast and soldered
with special equipment in oxygen free environment.


New alloys of titanium with nickel that can be
cast by more conventional. methods are being
developed. They release verity little ionic
nickel and bond well to porcelain. New
methods of forming titanium crowns and
copings by CAD/CAM technology avoids the
problem of casting altogether.


Lost-wax casting is one of the most widely
used methods for the fabrication of metallic
restorations outside of the mouth.


Three different types of specially designed Ti
casting systems are presently available namely
A pressure / vacuum casting system with
separate melting and casting chamber
(Castmatic, Dentaurum) .


A pressure /vacuum system with one chamber
for melting and casting (Cyclare, J Morita)
and
vacuum / centrifuge casting system (Tycast.
Jeneric / Penetron, and Titaniumer, Ohara)


The market price for each system
ranges from
USD 20,000 to 30,000.


A new casting machine for casting of titanium
and Ni-Ti alloys was developed by
H.Hamanaka et al in 1989.
The machine consists of an upper melting
chamber and a lower casting chamber with an
argon arc vacuum pressure system.


The main features that have been developed are
as follows:
1) The melting and casting chambers are
evacuated to a higher degree by means of an
oil diffusion pump.
2) In the casting chamber, a heater has been
placed to control the mold temperature; it
may be moved up and down with use of the
lever outside the chamber.

3) Two types of copper crucibles have been
developed - one a split type and the other a
tilting type that are changeable.
4) A device for direct suction has been placed
at the bottom of the mold for improved
castability.
5) The vaccum tank and the compressed argon
gas tank have been set to operate more
efficiently.

6) With use of the water-cooled electrode and
double D.C. electric sources, the capacity for
melting alloy is about 100g.
7) A new control system was developed.
In this system, after a mold and metal are set
on the machine, the upper and lower
chambers are evacuated.

Then, argon gas is fed into the upper chamber
when the “start” button is pushed, and an
electric arc begun automatically at the given
pressure. After the alloy melts down, the new
control system can be started when the “cast”
button is pushed.


At first. the upper chamber is exhausted for 0
to 1.0 seconds , and then the copper crucible
splits or tilts to drop the molten metal. From
0.01 to 0.05 seconds later, the compressed
argon gas is injected into the upper chamber.
This control system works automatically in
accordance with a given program.

Advantages of this machine are:
As gas in the mold is removed by the mold
being heated under a high vacuum, the
reaction between the molten metal and the
mold decreases.


The new control system and the two types of
crucibles developed proved very useful for
prevention of internal macro-defects in
castings and for improvement of castability.
Mechanical properties and castability of pure
titanium are improved.


The initial application of titanium to dentistry
was machined Ti dental implants. As an
alternative to lost-wax casting, the Procera
system (Nobelpharma) with titanium
machining has been developed by Andersson
et al for the fabrication of unalloyed titanium
crowns and fixed partial dentures.

The external contour of a titanium crown or coping
can be shaped out of a solid piece of titanium by a
milling machine, while the internal contour of the
titanium crown is spark eroded with a carbon
electrode.
Single titanium crowns can be fabricated with this
method, and multiple unit fixed prostheses can be
made by laser welding individual units together.


Information on the marginal fit of titanium crowns
was unavailable until quite recently. Meyer and
Schafers evaluated cast titanium inlay and partial
veneer crowns. Heterogeneous results did not
satisfactorily withstand comparison to conventional
methods. The authors questioned the clinical
application of titanium casting.


Ida et al reported that, in more than 100 cast
titanium crowns made, the fit was inferior to
that of silver-palladium crowns but superior to
that of nickel-chromium crowns. The criteria
used to determine fit were not described.


Blackman et al examined the fit of 20 cast
titanium copings divided into two equal groups
with 45 and 90 degree shoulders. The surface of
marginal discrepancy was greatest with the 90
degree configuration.
Casting shrinkage occurred particularly along
the horizontal axis in the plane of the shoulder.
It was concluded that Ti crown copings can be
cast with acceptable fitting accuracy.

Different methods to join titanium have been
investigated.
Yamagishi et al examined the mechanical
properties of Nd:YAG laser welds of titanium
plates (1mm thick) and found that there is a
significant relationship between three-point
bending strength and the irradiation
atmosphere, the irradiation intensity, and the
combination of atmosphere and intensity.

Laser welding is effective when performed in
an argon environment. At the same time, the
results are markedly different with various
intensities of irradiation.


Roggensack et al studied the bending fatigue
behavior of titanium joined by laser and plasma
welding. No significant differences in fatigue
strength could be found between the two methods
of welding. Extreme loads led to earlier fatigue in
the plasma welded specimens.


Even after the recent developments and
improvements in casting technology, the
challenge of using titanium casting for
prosthesis still presents major difficulties.
The mechanical properties of cast titanium differ
significantly from those of the parent metal.


Also, the outer 100 to 200 micro meter of the
surface has greater hardness and reduced
ductility than the core material. Titanium’s
high-fusing temperature and chemical activity
are considered primarily responsible for these
casting problems.


So new techniques like spark erosion (electro
erosion) and machine duplication termed
“copymilling” have been introduced.
Ti-6A1-4V is one of the superplastic alloys that
exhibits excellent elongation (more than
1,000%) at a temperature of 800°C to 900°C.


This super plasticity deformation is obtained
by grain-boundary sliding or dislocation with
a fine-grain structure (diameter 4 to 10 micro
meters).
Ti-6A1-4V is applied to denture framework
fabrication.


The retention of acrylic resin to the titanium
base is an important consideration.
Noriyuki Wakabayashi et al confirmed that
bond strength between a denture-base resin
containing an adhesion-promoting monomer
and Ti-6Al-4V alloy that had been airborne
particle abraded using aluminum oxide
particles was statistically equivalent to that
between the same resin and a cobaltchromium alloy casting.

Commercially pure (cp) titanium and titanium
alloys containing aluminum and vanadium, or
palladium (Ti-O Pd), should be considered
potential future materials for removable
partial denture frameworks.


Their versatility and well-known
biocompatibility are promising; however,
long-term clinical studies are needed to
validate their potential usefulness.
Currently, when cp titanium is cast under
dental conditions, the material properties
change dramatically.

During the casting procedure, the high
affinity of the liquid metal for elements such
as oxygen, nitrogen, and hydrogen results in
their incorporation from the atmosphere.


The usefulness of Ti as a metal for removable partial
denture (RPD) and complete-denture frameworks
has been evaluated. Removable partial denture
frameworks that were 0.70 mm thick had better
castability than did 0.35 mm thick RPD frameworks,
suggesting that if Ti is used for RPD frameworks, a
thicker wax pattern is needed than is used in casting
of a conventional denture framework with Co-Cr
alloys.


In the same study, Ti commonly failed to cast
perfect mesh specimens, but Co-Cr alloys did
not have this problem.


The biocompatibility of titanium is well
known in its clinical application in dental and
craniofacial implants.
Its use has been recently extended to include
metal ceramic crowns.
Titanium copings can be fabricated by casting
or by machine milling.

The low coefficient of thermal expansion
(CTE) of titanium (about 9 x 10-6/ºC)
compared to those of the conventional lowfusing porcelains (about 13 x 10-6/°C) raised
the concern of thermal compatibility.


Porcelains manufactured to bond to titanium
are currently commercially available. The
Procera porcelain (Procera, Nobelpharma:
Goteborg, Sweden) was formulated for
machine-milled crowns processed through the
Procera technique, while the Duceratin
porcelain (Degussa, South Plainfield NJ) was
formulated for cast titanium crowns.

The strength of porcelain-fused-to-metal
structures is related to mechanical properties
of the metal framework, the veneering
porcelain, the porcelain-metal interface, and
their interactions.


There is abundant literature on the adherence
of oxides formed at high temperatures on gold
alloys, Ni-Cr, and Co-Cr alloys. The
oxidation mechanisms and reasons for
development of a non-adherent oxide layer
while not perfectly understood, are well
characterized for Ti and its alloys.

Kirmura et al reported the oxidation effects of the
porcelain-titanium interface reaction. They
concluded that the conventional degassing
procedure is not suitable for porcelain-titanium
restorations and that the cycle should be below
800°C to minimize the metallic oxide formation
on the Ti surface.


The use of metals for implants dates back to
ancient times. It was not until the 1930s,
however, that improvements in metal
technology led to an era of expanded surgical
use of metallic implants.


A successful long-term implant requires
biocompatibility, toughness, strength, corrosion
resistance, wear resistance, and fracture resistance.
Titanium alloys of interest to dentistry exist in three
forms: alpha, beta, and alpha-beta. These types
originate when pure titanium is heated, mixed with
elements such as aluminium and vanadium in certain
Concentration and cooled.


Titanium and its alloys are important in dental
and surgical implants because of their high
degree of biocompatibility, their strength. and
their corrosion resistance.


Pure titanium, theoretically, may form several
oxides. Among these . TiO, Ti02 and Ti2 03. Of
these, TiO2 is the most stable and therefore
the most commonly used under physiologic
conditions. These oxides form spontaneously
on exposure of Ti to air.


When an implant is introduced into the body,
complex reactions begin to take place at the
oxide/bio environment interface. The oxide
film grows as ions diffuse outward from the
metal and inward from the environment. The
oxide that forms in the body may therefore, be
somewhat different than that which forms in
air.

The rate of formation and composition of this
film is important. Titanium, both as a pure
metal and as an alloy, is easily passivated,
forming a stable Ti02 surface oxide that makes
the metal corrosion resistant. This oxide will
repair itself instantaneously on damage such
as might occur during insertion of an implant.

The normal level of Ti in human tissue is 50
ppm. Values of 100 to 300 ppm are frequently
observed in soft tissues surrounding Ti
implants. At these levels, tissue discoloration
with Ti pigments can be seen.


This rate of dissolution is one of the lowest of
all passivated implant metals and seems to be
well tolerated by the body. The clinical
significance of this data is substantiated by
more than 20 years of clinical experience with
pure Ti and Ti 6A1 4V alloys.


This reactive group of metals and alloys (with
primary elements from reactive group metallic
substances) form tenacious oxides in air or
oxygenated solutions. Titanium (Ti) oxidizes
(passivates) upon contact with room
temperature air and normal tissue fluids.


This reactivity is favourable for dental
implant devices. In the absence of interfacial
motion or adverse environmental conditions,
this passivated (oxidized) surface condition
minimizes biocorrosion phenomena.
In situations where the implant would be
placed within a closely fitting receptor site in
bone, areas scratched or abraded during
placement would repassivate in vivo.

This characteristic is one important property
in vivo. This characteristic is one important
property consideration related to the use of
titanium for dental implants. Some reports
show that the oxide layer tends to increase in
thickness under corrosion testing and that
breakdown of this layer is unlikely in aerated
solutions.

Bothe et al. studied the reaction of rabbit bone to 54 different
implanted metals and alloys and showed that titanium
allowed bone growth directly adjacent to the oxide surface.
Leventhal further studied the application of titanium for
implantation.
Beder et al., Cross et al., Clarke et al., and Brettle were able
to expand indications of these materials.
In all cases titanium was selected as the material of choice
because of its inert and biocompatible nature paired with
excellent resistance to corrosion.

Proper implant configuration can help
effectively control or alter force transmission
to remain within physiologic limits of health.
The basic metallurgic properties of titanium,
particularly its ductility,
allow it to be strong and malleable,
permitting fabrication of optimal dental
implant configurations with little compromise.


Relatively high strength is required in a
prosthetic metal so it can withstand the
mechanical forces and stresses placed on it
during short-and long-term function without
undergoing unintended permanent deformation
or fracture.


However, a lower toughness specific to
deformation is desired so that one can shape the
implant during the manufacturing process, and
when appropriate, bend it to accommodate the
anatomic conditions found at the host site. These
conditions vary, system by system.


The strength values for the wrought soft and
ductile metallurgic condition (normal root
forms and plate form implants) are
approximately 1.5 times greater than the
strength of compact bone. In most designs
where the bulk dimensions and shapes are
simple, strength of this magnitude is adequate.

Commercially pure (cp) titanium and alloys of
titanium exhibit good elongation properties.
Elongation is directly related to malleability.
Low elongation can result in implant fracture
during processing or manipulation at the time
of insertion.


Titanium and its alloys exhibit moderate yield
strengths. Yield strength relates to the
magnitude of stress at which a metallic material
shows initial permanent deformation. When the
yield strength is exceeded, the shape of the
implant is altered.


Finally, the tensile strengths, the point at
which metallic material can fracture in
response to an applied load, should be
sufficiently high for functional stability of a
properly designed dental implant.


In general, titanium and its alloys have
outstanding strength-to-weight ratios; good
yield, tensile, and fatigue strength; and
adequate toughness for dental implant
systems.


The alloy of titanium most often used is titaniumaluminum-vanadium.
The wrought alloy condition is approximately 6
times stronger than compact bone and thereby
affords more opportunities for designs with thinner
sections (e.g., plateaus, thin interconnecting regions,
implant-to-abutment connection screw housing,
irregular scaffolds, porosities).

The modulus of elasticity of the alloy is
slightly greater than that of titanium, being
about 5.6 times that of compact bone.
The alloy and the primary element (Ti) both
have titanium oxide (passivated) surfaces.
Information has been developed on the oxide
thickness, purity, and stability as related to
implant biocompatibilities.

In general, titanium and alloys of titanium
have demonstrated interfaces described as
“osseointegrated” for implants in humans.
Also, surface conditions where the oxide
thickness has varied from hundreds of
angstroms of amorphous oxide surface films
to 100% titania (Ti02 rutile-form ceramic)
have demonstrated osseointegration.

Titanium plasma sprayed coating (TPS)
The first rough titanium
surface introduced

Plasma flame spraying technique

Coated with titanium powder
particles in the form of
titanium hydride


Porous or rough titanium surfaces have been
fabricated by plasma spraying a powder form
of molten droplets at high temperatures in the
order of 15,000 ºC, an argon plasma is
associated with nozzle to provide very high
velocity 600 m/sec partially molten particle c
titanium powder (0.05 to 0.1mm diameter)
projected onto a metal or alloy substrate.

The plasma sprayed layer after solidification
(fusion) is often provided with a 0.04 to
0.05mm thickness.


When examined microscopically, the coatings
show round or irregular pores that can be
connected to each other.
These types of surfaces were first developed
by Hahn and Palich, who reported bone
ingrowth in plasma spray titanium hybrid
powder and plasma spray-coated implants
inserted in animals.

In addition, porous surfaces can result in an
increase in tensile strength through ingrowth
of bony tissues into three dimensional
features, High shear forces determined by the
torque testing methods and improved force
transfer into the periimplant area have also
been reported.

Hydroxyapatite coating by plasma spraying was
brought to the dental profession by deGroot.
Kay et al. showed with scanning electron
microscopy (SEM) and spectrographic analyses that
the plasma-sprayed HA coating could be crystalline
and could offer chemical and mechanical properties
compatible with dental implant applications.


Thomas showed an accelerated bone formation and
maturation around HA-coated implants in dogs when
compared with non-coated implants.
HA coating can also lower the corrosion rate of the
same substrate alloys.
Cook et al. measured the HA coating thickness after
retrieval from specimens inserted in animals for 32
weeks and showed a consistent thickness of
50micrometer, which is in the range advocated for
manufacturing.


The bone adjacent to the implant has been
reported to be better organized than with other
implant materials and with a higher degree of
mineralization. In addition, numerous
histologic studies have documented the greater
surface area of bone apposition to the implant
in comparison to uncoated implants, which
may enhance the biomechanics and initial
load-bearing capacity of the system.

HA coating has been credited with enabling
HA-coated Ti or Ti alloy implants to obtain
improved bone-to-implant attachment
compared with machined surfaces.


Implants of solid sintered hydroxyapatite have been
shown to he susceptible to fatigue failure. This
situation can be altered by the use of a CPC (calcium
phosphate coating) along metallic substrates.
Although several methods may be used to apply
CPC coatings, the majority of commercially
available implant systems are coated by a plasma
spray technique.


A powdered crystalline hydroxyapatite is
introduced and melted by a hot, highvelocity region of a plasma gun and
propelled onto the metal implant as a
partially incited ceramic.


One advantage of CPC coatings is that they
can act as a protective shield to reduce
potential slow ion release from the Ti-6A1-4V
substrate.
Also, the interdiffusion between titanium and
calcium, and phosphorus and other elements
may enhance the coating substrate bond by
adding a chemical component to the
mechanical bond.

Cranial prosthesis:
Titanium has been recently used in fashioning
cranial prostheses (Gordon and Blair, 1974)
This metal is a strong but light material that is soft
enough to be swaged in a die-counterdie system.
Moreover it can be strain hardened and thus become
stronger with manipulation. Sheets that are 0.6 1mm
thick are adequate and its radiodensity permits most
radiographic studies.


After the metal prosthesis is shaped, trimmed,
and polished, tissue acceptance of the implant
is enhanced by anodizing it in a solution of
80% phosphoric acid, 10% sulphuric acid,
and 10% water (Gordon and Blair, 1974).


Titanium trays offer the best combination of
strength and rigidity with the least bulk of any
implant material currently available for
restoration of mandibular defects. Titanium
frameworks are also used for rehabilitation of
maxillary and mandibular defects like cleft
palate.

The osseointegration technique allows the
placement of titanium implants in to the orbital
bony resin that are capable of supporting a facial
prosthesis.
The osseointegration procedure, allows titanium
implants in to bone to project through the skin,
providing points of attachment for prosthetic
devices .


Titanium implants are used for retention of
bone anchored Hearing Aid (BAHA) .


Based on their physical properties and
biocompatibility, titanium and its alloys have
emerged as the metals of choice in dental implant
industry.
The application of titanium to fixed and removable
prostheses is still in the developmental stages.
Concerns regarding castability, porcelain bonding,
and joining have been reported.


Some reports in the literature have indicated
problems with castability and porosity.
Others have shown that clinically acceptable
titanium castings can be produced.
Problems associated with porcelain bonding
and titanium joining need to be resolved.


Attempts to substitute gold alloys with
titanium for dental prostheses by the dental
industry, laboratories and clinicians, have
been a slow process.
At present time, use of titanium restorations
or prostheses is low because of lack of
knowledge of the material among dentists and
long-term c1inic follow-up.

Titanium is a useful biomaterial. It will
probably continue to dominate the implant
market in the future. Titanium is economical
an readily available, but the technologies of
machining, casting, welding and veneering it
for dental prostheses are new.


Increased use of titanium in prosthodontics
depends on research and clinical trials to
compare its effectiveness, as an equivalent or
superior metal, to existing metals. The future
of titanium in dentistry looks promising.


William J. 0’Brien: Dental materials and their selection
Robert G. Craig: Restorative dental materials.
John F McCabe: Applied dental materials.
E.C.Coombe: Notes on dental materials.
Kenneth J Anusavice: Science of dental materials.
E.H. Greener: Material science in dentistry.
Bernard G. N. Smith: The clinical handling of dental material.
Carl. F Misch :Contemporary implant Dentistry.
Charles. M. Weiss, Adam Weiss: Principles and practice of
implant Dentistry.


AKAGI. K, OKAMOTO. y, MATSUURA. T,
HORIBE. T
“Properties of test metal ceramic titanium alloys”,
J Prosthet Dent 1992; 68: 462-7.
ANDERSSON.M, BERGMAN. B, BESSING. C,
ERICSON. G, LUNDQUIST. P, NILSON. H
“Clinical results with titanium crown fabricated with
machine duplication and spark erosion”,
Acta Odontol Scand 1989 ; 47 : 279-286.

BALTAG. 1. WATANABE. K. KUSAKARI. H., MIYAKAWA. 0,
“Internal porosity in circumferential clasps of a clinical framework design”,
J Prosthet Dent 2002: 88: 15 1-8.

BERG. E, DAVIK.G, HEGDAHL.T,
“Hardness, strength, and ductility of prefabricated titanium rods
used in the manufacture of spark erosion crowns”,
J Prosthet Dent 1996; 75: 419-425.
BERG. F. WAGNER.W,C. Davik. G, Dootz. E.R, “Mechanical
properties of laser-welded cast and wrought titanium”,
J Prosthet Dent 1995; 74: 250-7.


BLACKMAN. R, BARGHI. N. TRAN. C,
“Dimensional changes in casting titanium removable
partial denture frameworks”,
J Prosthet Dent 1991: 65: 309-15.
B. Kasemo,
Biocompatibility of titanium implants:
Surface science aspects
J Prosthet Dent June 1983 volume 49 number 6.

Gregory R. Parr , Richard W. Toth, et al
Titanium: The mystery metal of implant
dentistry. Dental materials aspects
J Prosthet Dent 1985,Vol54,No.3,410-414.


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