Copy of biomaterials in orthodontics /certified fixed orthodontic courses by Indian dental academy

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Biomaterials
in
Orthodontics
INDIAN DENTAL ACADEMY
Leader in continuing dental education


Contents
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Introduction
Structures and properties of materials
Orthodontic wires
Orthodontic brackets
Etching agents, Adhesive resins & Cements
Elastomeric ligatures & Chains
Impression materials
Prophylactic agents
& Miscellaneous

Introduction
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Knowledge of fundamental principles
governing the relationship between
composition, structure and properties is central
to an understanding of orthodontic materials.
Because wide array of metallic, ceramic and
polymeric materials are used in the
profession, and new materials are continuously
being introduced. It is essential that the
scientific basis for selection and proper use of
materials for clinical practice be thoroughly
understood

Structure
and
properties of materials

Metals
Stainless steel:
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F. Huaptmeyer in 1919
These family of steels contain more than 12% of
chromium which owes for its success
Relatively high Chromium content in SS→ favors the
stability of BCC unit cells of ferrite
Ni, Cu, Mn, N→ favors an FCC structure of austenite
Other additives are
- carbon, Silica, Sulfur, Phosphorus, Manganese
Heat treatment of these stainless, which promotes the
precipitation of some elements added.

Stainless steels are classified
according to the American Iron and
Steel Institute
Various steels are:
Austenitic steels (300 series)
 Martensitic steels (400 series)
 Ferritic steels
 Duplex steels
 Precipitation-hardenable (PH) steels
 Cobalt containing alloys
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Manganese containing steels

BCC

FCC


AUSTENITIC STEELS (300 SERIES )
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Austenitic FCC structure is unstable at lower temperature.
Austenizing elements (Ni, Mn and N) are added, the highly
corrosion resistant solid solution phase can be preserved even
at room temperature.
The 300 series steels are used for most attachments because of
there corrosion resistance.

MARTENSITIC STEELS (400 SERIES)

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In Microstructure of these steels is the same as that of iron at
room temperature (BCC).
These steels are stronger but less corrosion resistant alloys
Such stainless steels should be used only for a short contact
with oral environment
It is used for sharp instruments and resistant edges

Ferritic steels
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Chromium is substituted for some of the iron atoms in the BCC
unit cells
Modern “Super ferritics” contain 19% to 30 % chromium and are
used in several nickel free brackets. These are highly resistant to
chlorides and alloys contain small amounts of aluminum and
molybdenum and very little carbon.

Duplex steel
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It consists of an assembly of both austenite and ferrite grains.
They also contain molybdenum and chromium and lower nickel
content
The duplex structure results in improved
toughness and ductility.. These steels have been used for the
manufacture of one-piece brackets (Eg: Bioline “low nickel”
brackets).

PRECIPITATION-HARDENABLE
STEELS
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These steels can be hardened by heat
treatment, which promotes the precipitation of
some elements added.
PH 17-4 stainless steel is widely used for
“mini” brackets.
PH 17-7 stainless steel is used to manufacture
Edgelock brackets (Ormco)


Titanium
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The unparalleled tissue tolerance and biocompatibility of titanium
have made it the leading metal for dental implants. .
Most alloys used in orthodontics contain potentially toxic nickel,
chromium, and cobalt. .
Titanium alloy are highly corrosion resistant
They are strong but not as stiff as stain less steel, hence needed to
be compensated by over size
It exists in alpha and beta forms; beta form is stable above 1620
deg c . But can be stabilized at lower temperature
Titanium oxide film has high affinity which may be the cause for
its high frictional resistance.
It is used to make intermediate arch wires and can be welded .

Beta –titanium

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Introduced BY BURSTONE AND GOLDBERG
Commercial name – TMA (Titanium Molybdenum
Alloy)
beta-stabilized titanium
Composition
Titanium
– 77.8 %
Molybdenum – 11.3 %
Zirconium – 6.6 %
Tin
– 4.3 %
A clinical advantage of β - titanium is its excellent
formability which is due to the BCC structure of beta
stabilized titanium
Zirconium and zinc - contribute to increased strength
and hardness.

Ceramics
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The first ceramic used was aluminum oxide or alumina,
followed by zirconia
alumina and zirconia can be found as tridimensional
inorganic macromolecules & are esthetically pleasing
The ionic crystalline structure accounts for its hardness and
compressive strength which exceeds that of the metals, but
they have poor flexure strength
Alumina is quite stable at normal conditions but zirconia
under goes phase transformation from the tetragonal
structure to monoclinic structure when cooled through 1100
-1200 range. with a volume change of approximately 3
%that can cause fracture of ceramics

A l 3+

b 2"

A l3+

O
O

O

2-

2-

b1

2-

2

A l3+

O
Al

3+

1

3+

O

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3

A l3+

Al

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b"
2-

2-

O

b'
2-

Small addition of yttrium oxide and hot isostatic
pressing can be employed to achieve very small grain
size yttrium oxide partially stabilized zirconia
This transformation toughness results in high facture
toughness 9- 10mpa.m1/

Organic polymers
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Are natural allies of medicine because they enter the
composition of living tissues.
To be used in the oral cavity these materials must be nondegradable, stable and should not be mutagenic or
carcinogenic
The first organic polymer to be used in orthodontics were
rubber and its sulfur cross linked derivatives like vulcanite
Polymers truly adequate for dental purpose were only
discovered in late 1930 s’
Polymethy-methacrylates and polyurethanes by Obeyer in
1937
Polycarbonates and polysulfones has made possible
manufacturing esthetic attachment.
The discovery of epoxies and cyanoacrylates led to the
convenient use of adhesives

Structure and composition
 Even though the chemical composition is the
same the materials exhibit different properties
this is basically determined by the polymer
chain length. small chains and residual
monomer can be detrimental to their properties
 The polymeric chains may be linear branched
or three dimensional
 with the increase in the side chains the
polymer becomes stiff
 Polymer shrinkage occurs due to excess
monomer

Handling
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The chemical degradation of the polymer and their
precursor often takes place well in advance of their
delivery
Among the most sensitive products are polyurethane
elastomers.when these materials are subjected to light
high temperature, ph variations, solvents, or even air
polyurethanes degrade and become brownish.
To control these undesirable effects various additives
are need, like the initiators, accelerators ,polymerization
inhibitors, plasticizers and uv –stablizers.

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Poly urethanes are further hydrophilic. water
and especially saliva hydrolyses them
The polymer surface may develop crazes an
lodge micro-organism , and become
unpleasant
Biocompatibility
Adhesives, sealants and restorations contain
various additives, aromatic amines , peroxide,
inhibitors and uv –stabilizers
Some of them are potentially toxic,
carcinogenic www.indiandentalacademy.com

Implants

Implants materials
The materials commonly used for implants can
be divided into 3 categories:
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Biotolerant - stainless steel, chromium-cobalt
alloy.
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Bioinert
- titanium, carbon and
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Bioactive - vetroceramic apatite hydroxide,
ceramic oxidized aluminum.

Titanium Implants
Advantages of titanium
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Commercially pure titanium is the material
most often used in implant logy.
It consists of 99.5% titanium, and the
remaining 0.5% is other elements, such as
carbon, oxygen, nitrogen, and hydrogen.
Osseo integration
no allergic or immunological reactions
Mechanical characteristics -very light weight,
excellent resistance to traction and breaking .

Orthodontic wires

Orthodontic wires , which generate
the bio-mechanical forces
communicate through brackets for
tooth movement , are central to the
orthodontic practice. In the rational
selection of wires for
particular
treatment, the orthodontist should
consider a variety of factors.

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Low stiffness, good spring back and
produce light forces

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highly formable and Ability and ease of
joining.

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Low coefficient of friction
Corrosion resistance
Cost and biocompatibility

Stainless steel wires –
Austenitic stainless steel
 excellent formability & corrosion resistance
 Stainless steel alloy used for orthodontic wires are
18-8 austenitic type, containing approximately 18
% chromium and 8 % nickel and less than 0.20
percent carbon.Nickel,
 Heat treatment of 400 – 500 degree c ……residual
stress, heat treatments above 650 degrees c
……..precipitation of chromium carbide at the
grain boundaries
 The free hand soldering should be done rapidly
with a well controlled torch and use of flux .
 spot welding often causes localized loss of wrought
microstructure

Cobalt chromium nickel wires
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Elgiloy 1950 .
It is available in four tempers that are color coded –
blue (soft) , yellow (ductile) , green (semi resilient)
and red (resilent)
Composition is 40 % Co, 20% Cr, 15 % Ni, 7 % Mo,
and 16% Fe.
Corrosion resistance & lower elastic force delivery
The eigiloy blue as received wire can easily
manipulated into desired shapes and then heat
treated to achieve considerable strength and
resilience.
Elgiloy has been used for making fixed lingual quad
helix appliance

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Has excellent formability.

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Spring characteristics are similar to those
of stainless steel.

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Can be soldered, but technique is
demanding.

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Corrosion resistance of the wire is
excellent.

Beta titanium
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TMA by Burstone and Goldberg
highest friction owing to substantial cold
welding or mechanical abrasion.
Ion-implantation - causes surface hardening
and can decrease frictional force by as much
as 70% and improve compressive strength,
fatigue resistance and ductility of the wires
Katherine Kula and proffit in AJO 1998
concluded that there was no significant
difference when ion implanted TMA wire
when compared to unimplanted TMA wire in
sliding mechanics clinically.

Properties
 Corrosion resistant and biocompatible
 Deflection
2 ( S.S) = TMA
 Beta titanium is ductile
 Allows direct welding of auxiliaries to an
arch wire without reinforcement by
soldering.
 Beta titanium wires are the most expensive
of all the orthodontic wire alloys but the
increased cost is offset by its combined
advantageous properties.

Nickel titanium wires
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Introduction
Andreasen and Hillman in 1971.
Nitinol- Buehler.
Naval Ordinance Laboratory, its place of
origin.
NiTi, Nitinol, Orthonol, Sentinol and
Titanal
Good spring back and flexibility
large deflections but low forces

Composition
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Nitinol is approximately 52 percent nickel,
45 percent titanium, and 3 percent cobalt.
With proper heat treatment, the alloy
demonstrates significant changes in
mechanical properties and crystallographic
arrangement.
Have a stabilized martensitic phase formed
by cold welding, were the shape memory
effect has been suppressed.

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Two major NiTi phases are:
1. Austenitic Niti - a ordered BCC structure
occurs at high temperatures / low stress.
2.Martensitic NiTi- distorted monoclinic,
triclinic or hexagonal structure and forms at low
temperatures / high stress.
shape memory effect is associated with a
reversible martensite to austenite transformation,
which occurs rapidly by crystallographic twinning
When these alloys are subjected to high
temperatures, detwinning occurs, and the alloy
reverts to the original shape or size - shape
memory effect.

Kusy has classified nickel titanium wires as
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Martensite stabilised alloys- Nitinol.
Martensite active alloys- employ the
thermoelastic effect for shape memory. alloys
such as Neo-Sentalloy and Copper Ni-Ti
Austenitic active alloys (SIM) These alloys
are the super elastic wires that do not possess
thermoelastic shape memory at the
temperature of the oral environment such as
Nitinol SE

Shape memory effect

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Hurst and Nanda in AJO 1990 -specific TTR
depends on the chemical composition of the alloy and
its processing history.
Memory is set in the material by holding it in the
desired shape while annealing it at 450° F to 500° F
for 10 minutes
Once a certain shape is set, the alloy can then be
plastically deformed at temperatures below its TTR.
On heating through the TTR, the original shape of
the alloy is restored.
To obtain maximum shape recovery, the deformation
should be limited to 7% or 8% , below TTR .
Buehler and Cross- shape-memory phenomenon was
related to the inherent capability of a nickel-titanium
alloy to alter its atomic bonding as a function of
temperature

Superelasticity / Pseudoelasticity
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In response to temperature variations, the crystal structure
undergoes deformations
On activation, the wire undergoes a transformation from
austenitic to martensitic form due to stress
The different loading and unloading curves produce the
remarkable effect the force delivered by the austenitic NiTi
wire can be changed during clinical use by merely releasing
the wire and retying it.
Deflection generates a local martensitic transformation and
produces stress-induced martensite (SIM).
In orthodontic clinical applications, SIM forms where the
wire is tied to brackets on malaligned teeth so that the wire
becomes noticeably pliable in the deflected areas, with
seemingly permanent deformation

Clinical usage
 The high springback of nitinol is useful in circumstances that
require large deflections but low forces
 This results in increased clinical efficiency of nitinol wires
since fewer arch wire changes or activations are required.
 for a given amount of activation, wires made of titanium alloys
produce more constant forces on teeth than stainless steel
wires. A distinct advantage of nitinol is realized when a
rectangular wire is inserted early in treatment. This
accomplishes simultaneous leveling, torquing, and correction
of rotations.
 Andreasen and Morrow - fewer arch wire changes, less
chairside time, reduction in time required to accomplish
rotations and leveling, and less patient discomfort.
 Since hooks cannot be bent or attached to nitinol, crimpable
hooks and stops are recommended for use.
 Cinch-backs distal to molar buccal tubes can be achieved

Chinese Ni Ti wire
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Chinese NiTi wire is applicable in situations
where large deflections are required
Used in conditions were teeth are badly
malaligned and in appliances designed to
deliver constant forces.
There is a force difference if the appliance is
left in place throughout the deactivation or if
it is removed and retied. If the force levels
have dropped too low for a given type of tooth
movement, then the simple act of untying and
retying can increase the magnitude of the
force.

Copper Ni – Ti wires
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In 1994 copper Ni –Ti wires were introduced by the
ormco corporation.
It is available in three temperature variants: 270 C,
350 C and 400 C corresponding to the austenite
finish temperatures
Shape memory behaviors is reported to occur for
each variant at temperatures exceeding the specified
temperature.
The addition of copper to nickel titanium enhances
the thermal- reactive properties of the wire, thereby
enabling the clinician to provide optimal forces for
consistent tooth movement.

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Composition
They are composed of
Nickel
– 44%
Titanium – 51%
Copper – less than 5%
Chromium – 0.2 – 0.3%
Kusy - wire contains nominally 5-6 wt% of copper
and 0.2-0.3 % of chromium.
The 27deg C variant contains 0.5% of chromium to
compensate for the effect of copper in raising the Af
above that of the oral environment.
The addition of copper to Ni-Ti not only modifies the
shape memory , but also increases the stability of
transformation and also helped to control hysteresis
width and improved corrosion resistance.

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Uses of copper Ni - Ti wires
27°C Copper Ni-Ti generates forces in the high range of
physiological force limits and produces constant unloading forces
that can result in rapid tooth movement. Engagement force is
lower than with other superelastic wires. This variant would be
useful in mouth breathers.
35°C Copper Ni-Ti generates mid-range constant force levels
when the wire reaches mouth temperature. Early ligation is easier
with full-size archwires due to the lower loading forces. When
earlier engagement of full-size wires and sustained unloading
forces at body temperature are desired, 35°C Copper Ni-Ti is the
ideal wire. This variant is activated at normal body temperature.
40°C Copper Ni-Ti provides intermittent forces that are activated
when the mouth temperature exceeds 40°C. It is useful as an
initial wire and can be used to engage severely malaligned teeth
(such as high cuspids) without creating damaging or painful levels
of force or unwanted side effects. It is also the wire of choice for
patients scheduled for long intervals between visits when control
of tooth movement is a concern. This variant would provide
activation only after consuming hot food and beverages.

Japanese Ni-Ti wires
Classic NiTi alloy wire used in clinical
orthodontics is the work-hardened type wire
called Nitinol.
 The Japanese NiTi alloy wire possesses
excellent springback property, shape memory,
and super-elasticity.
 Super-elasticity is especially desirable because
it delivers a relatively constant force for a long
period of time, which is considered a
physiologically desirable force for tooth
movement

Orthodontic brackets


Orthodontic brackets bonded to
enamel provide the means to
transfer the force applied by the
activated arch wire to the tooth.


TYPES OF BRACKETS
A) METAL BRACKETS
1) Stainless steel brackets
2) Gold-coated brackets
3) Platinum-coated brackets
4) Titanium brackets
B) PLASTIC BRACKETS
1) Polycarbonate brackets
2) Polyurethane-composite brackets
3) Thermoplastic-polyurethane brackets
C) CERAMIC BRACKETS
1) Monocrystalline alumina (Sapphire)
2) Polycrystalline alumina
3) Polycrystalline Zirconia (YPSZ)

Stainless steel brackets
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The bracket material used for metal brackets is of Aisi type
316L austentic stainless steel ,to stabilize the austentic
structure at room temperature nickel is added
This Ni leaches out in the oral environment leading to
biocompatibility problems.
These brackets have 16 -18 Cr ,10-14 Ni ,2-3 Mo and a
maximum of 0.03 C. The content of Cr is comparative less and
Cro does not form that effective film compared to Tio .
A 2205 stainless steel alloy than contains half the amount of
nickel found in 316L alloy has recently been proposed by
Oshida and colleagues. The 2205 stainless steel alloy has a
duplex microstructure consisting of martensitic and deltaferrectic phases, and is harder then the 316L alloy. Moreover,
the 2205 alloy demonstrates substantially less corrosion then
316L alloy

Titanium brackets
Pure titanium bracket (Rematitan-DENTAURUM) is a
one-piece construction requires no brazing layer, and
thus it is a solder- and nickel-free bracket.
 These brackets appear grey and have greater
coefficient of friction then stainless steel
 According to Hamula et al in JCO 1996, the
problems of nickel sensitivity, corrosion, and
inadequate retention of SS brackets has been solved
with the introduction of new, pure titanium bracket
(Rematitan).

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A computer-aided laser (CAL) cutting
process generates micro- and macroundercuts, making it possible to design an
“ideal” adhesive pattern for each tooth.
Single-piece construction allows the lowest
possible bracket height, This makes the
miniaturized appliance even less conspicuous
A low bracket profile can be helpful in
assessing lip balance during treatment,
especially in cases of lip insufficiency and
protrusion.

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Titanium also has low thermal conductivity,
and thus alleviates the sensitivity to extreme
temperature changes often experienced by
patients wearing metal appliances.
It imparts none of the metallic taste of
stainless steel brackets.
Such brackets may provide an alternative
to SS brackets for those who are concerned
with nickel toxicity

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Composition
A commercially pure (cp) medical grade 4 Ti
(designation DIN 17851-German standards) is
used as the basis for the manufacture of titanium
brackets.
Composition is
Titanium - over 99%
Iron
- < 0.30%
Oxygen
- < 0.35%
Nitrogen - < 0.35%
Carbon
- 0.05%
Hydrogen - 0.06%

Surface characteristics
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The surface texture of the Ti brackets is much
rougher than that of the SS brackets.
These are the reasons for significantly more
plaque accumulation and a more marked change
of color with titanium brackets.
Titanium brackets are a suitable alternative to
conventional metal brackets in many aspects.
Their biocompatibility, absence of nickel, good
corrosion resistance, superior dimensional
stability, comparable frictional characteristics and
decreased conspicuousness along with low thermal
conductivity make these brackets a suitable
alternative to conventional S.S brackets specially
in nickel sensitive patients.

Gold coated brackets
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Recently gold-coated steel brackets have been
introduced and rapidly gained considerable
popularity.
Brackets are now available with 24 karat gold
plating, plated with 300 micro inches of gold.
Gold-coated brackets may be regarded as an esthetic
improvement over stainless steel attachments, and
they are clean and thus more hygienic than ceramic.
Patient acceptance of gold-coated attachments is
generally positive. Significant side effects in the form
of corrosion or allergic reactions have not been
observed clinically.

Platinum coated brackets
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The result is a bracket with greater abrasion
resistance than gold.
A smoother, harder surface than stainless steel
for reduced friction and improved sliding
mechanics is achieved.
By combining platinum metal and an exclusive
implantation process, a barrier has been created
against the diffusion of nickel, cobalt, and
chromium.
Platinum has been found to be superior to all
other known metals

Nickel free brackets
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Made of Cobalt chromium (CoCr) dental
alloy
One-piece construction (without solder) by
metal injection molding technique
Laser structured bracket base for retention


Plastic brackets
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Unfilled polycarbonate 1970 s.
creep deformation, discoloration
ceramic reinforced, fiberglass and metal slotreinforced polycarbonate brackets were introduced.
while metal slot reinforced
polycarbonate brackets reported problems with the
integrity of the slot periphery.
The beneficial effect of these brackets due to their
low modulus of elasticity they tend to peel of during
debonding like the metal brackets.

Various plastic brackets were:
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Polycarbonate brackets (E.g.Elation)
Reinforced polycarbonate brackets ( D B
fibre )
Polyurethane-composite brackets
(E.g.Envision)
Thermoplastic-polyurethane brackets
(E.g.Value line)


Polycarbonate brackets
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Various reinforced polycarbonate brackets:
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Polymer fiber reinforced polycarbonate brackets
Fiberglass reinforced polycarbonate brackets
Ceramic reinforced polycarbonate brackets
Metal slot reinforced polycarbonate brackets
Metal slot and ceramic reinforced polycarbonate
brackets

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Bonding mechanism of plastic brackets is mainly
mechanical retention

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Disadvantages

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Polycarbonate brackets undergo creep
deformation when transferring torque loads
generated by arch wires to the teeth
Discoloration of first generation unfilled
polycarbonate brackets during clinical aging.
They absorb water to a slight extent and tend to
weaken in the course of about one year (Newman
1973).

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Ceramic brackets
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Ceramics used for the manufacturing of ceramic
brackets were Alumina and Zirconia. Both can be
found as tridimensional inorganic macromolecules.
Types of ceramic brackets
Monocrystalline (Sapphire)-Inspire ,Starfire TMB
Polycrystalline Alumina-Allure, Mxi, Clarity
Polycrystalline Zirconia (YPSZ) ) Hi-Brace

Bonding mechanisms :
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Mechanical retention employing large
recesses.
Chemical adhesion facilitated by the use of a
silane layer.
Micromechanical retention through the
utilization of a number of configurations,
including protruding crystals, grooves, a
porous surface, and spherical glass particles

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Strength of the brackets can be increased
by eliminating the surface flaws that can
serve as the sites of stress concentration and
fracture initiation. Decreasing the grain size
also increases the strength of polycrystalline
brackets. The polycrystalline zirconia
brackets manufactured by injection
molding technique followed by isostatic
pressing in partially stabilized zirconia 5
%wt yttrium oxide

RECYCLING OF ORTHODONTIC
BRACKETS AND ITS EFFECTS
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Several in-office bracket-reconditioning methods
have been introduced since 1980,

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Grinding - Wright and Powers (1985)
Sandblasting - Millet et al (1993), Sonis (1996)
Direct flaming
Buchman method - Buchman (1980)
BigJane machine method - Buchman (1980)

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Buchman (1980) concluded that as
temperatures are increased in thermal
treatment, the hardness and tensile strength
are decreased and the microstructures
illustrate corresponding susceptibility to
metallic intergranular corrosion.
Matasa et al (1989) described that heating
method used for reconditioning metal brackets
causes intergranular corrosion. He also
enumerated the effects of heat on brackets
like, structural metal weakening, vertical slot
obstruction, steel corrosion and base clogging

Enamel Etching

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Traditionally slots were welded to the bands and
cemented to the crowns, before the introduction of
etching agents and adhesive resins, which
demanded extra arch width ,time of the clinician,
compromised oral hygiene and esthetics
With the introduction of acid etching (Bonocore)
opened new vents for bonding brackets to the
teeth. Etching of enamel creates microporosities
with in the enamel and reduces the surface tension
that allows resins to penetrate and polymerize
with in the etched enamel rods (mechanical
bonding)

Enamel etching with acids
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Type and concentration of acid

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Orthodontic bonding of brackets to teeth does not require high bond
strength (6-8 mpa), as need in restorative dentistry. Various studies have
shown that etching with 10%-37% phosphoric acid has provided
adequate bond strength.
Some studies have also shown that even treating the enamel with 2%
phosphoric acid have been able to provide adequate bond strength.
The use of 10% maleic acid for etching results in lower bond strength.

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Duration of etching

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No difference in bond strength was detected between 15 second and 60
second etching with 37% phosphoric acid
However shorter etching time results in decreased bond strength (0 – 5
seconds)
Scanning electron microscopy showed that etching with 37% phosphoric
acid for atleast 30 seconds produces more optimal etchin pattern than
etching for 15 seconds.













Resin composite does not bond well to un
etched enamel; however, hybrid inomer
orthodontic cements have a bond strength
ranging from 8 to 25 mpa .
Hybrid inomer cements have better bond
strength to enamel than sand blasted metal
bracket base.
And these cements lack cohesive strength
Use of pumice before etching to clean the
enamel of surface deposits has shown no
alteration in bond strength

Iatrogenic effect of etching









Fracture or cracking of the enamel during
debonding
Porosities caused by etching may cause
staining of tooth
Loss of enamel. (10- 20 um)
Resin tags retained in the enamel after
debonding may get discolored.
Alternate methods for etching enamel

Acidic primer
Composition
 Acid(phenyl-p)
 HEMA
 And dimethacrylate




Although they are expensive ,comparable
bond strength can be attained
It also reduces the chair time

Air abrasion






Also known as micro etching is a tecnique
in which particles of aluminum oxide are
propelled against the surface of enamel
causes abrasion of the enamel surface
Micro etching metals is an effective way of
increasing bond strength of brackets
Microetching of enamel produces only 50 %
of the bond strength to that of acid etching

Laser etching








The application of laser energy on the enamel
surface causes localized melting and ablation.
Removal of enamel results primarily by micro
explosion of entrapped water in the enamel
Laser etching is done by neodymium-yttriumaluminum garnet
Laser typically produces low bond strength
compared to acid etching

Crystal growing solution









A proposed alternative to etching for retention of
adhesive is to grow crystals on the enamel surface
This technique is called crystal bonding
The potential advantages of crystal bonding
include easy debonding, less residual adhesive left
on the tooth, and less enamel damage.
It includes application of poly(acrylic acid)
solution containing sulfate ions,which cause
growth of calcium sulfate dehydrate crystals on
the enamel
It produces 60-80 %0f bond strength compared to
acid etching Acidic primers

Bonding agents


Based on the polymerization initiation
mechanism:







Chemically activated (self cured ) :two paste
or one paste
Light cured ( photo cured )
Dual cured (chemically activated and light
cured
Thermo cured

Chemically activated orthodontic
adhesive systems














These adhesives employ benzoyl as an initiator and tertiary
aromatic amine such as dimethy-p-toluidene as activator
Initiation occurs from the mixing of the paste and liquid
components of these systems and free radicals are formed by
multi step processes
Chemically cured two phase systems:
Polymerization is initiated by mixing of liquid and paste
Clinical handling is laborious; time consuming
Properties
Increased exposure of the components to the air induces
oxygen inhibition
Mixing introduces defects due to trapping of air and
formation of voids
Concise (3M)

Chemically cured one phase system














Application of the liquid component on the enamel and on the
bracket base.
No mixing is involved
Clinical handling: - efficient application ;limitation in time
requirements
Properties
Limited data is available on the bond strength and degree of
curing
Inhomogeneous Patten of curing due to the sandwich involved
Enamel bracket sides of the polymer is more polymerized than
the middle of the bracket
System 1(ormco)
Unite (3M)


Visible light cured
The photo initiator in these systems is
camphoroquinone and a reducing amine
 Polymerization is initated by exposure to light
curing source
Clinical handling
 Provides increased working time and bracket
placement time.
 Curing should be done from the incisal and cervical
margins
Properties
 The degree of cure of a stain less steel brackets
bonded with light cured adhesive is comparable to
that of a transparent aesthetic bracket



Dual cure
Polymerization is initiation is achieved by through
exposure to light and the reaction progress following
a chemically cured pattern
Clinical handling
 Combines the disadvantages of handling both light
cured and chemical cured materials.
 Most time consuming application
Properties
 Increased degree of cure and bond strength ,but of
questionable clinical significance
 Ideal for bonding molar tubes



Moisture active
Polymerization – cyanoacrylate, no liquid
component is involved. Polymerization is
initiated on exposure to water
Clinical handling
 One step procedure-intentionally the surface
of the tooth must be wetted
 One of the study has shown acceptable bond
strength
 Smart bond (Gestenco)


Moisture resistant







Primer compatible with the use of the
adhesive
Clinical handling
Application of primer on wet enamel
surface
Trans bond MIP(3M)

Microbial alteration and caries
prophylaxis




Individuals with malocclution have many
retion site owing to the irregularities of
teeth .more retion sites are introduced when
orthodontic appliances are bonded and
banded to teeth. Oral hygine is thus
markedly more difficult to maintain for
orthodontic patients




Table 6.1


Caries prophylaxis aspect of orthodontic treatment





Fluoride is the most caristatic agent know
The mechanism of action of fluoride is generally
believed to be due to its effect in plaque film
around the mineral crystallites, by inhibiting
demineralizing and increasing remineralizing of
mineral lost during the caries processes
Rationale caries prophylactic measures for
orthodontic patient is prevention of caries lesion
developed during orthodontic treatment

Fluoride tooth pastes
Fluoride toothpaste is the basis for all caries
prevention. Most tooth pastes contain sodium
fluoride, monofluorophosphate, stannous fluoride
 The fluoride concentration may vary, but the
maximum concentration allowed is 0.15 %.fluoride
concentration less than 0.1 % should not be
recommended for orthodontic patients
 The cariostatic effect of fluoride will improved
significantly if oral hygiene is improved
 The anionic agent sodium lauryl sulphate is a
popular detergent
 It increases the permeability of the oral mucosa and
increases the nickel sensitivity and has been reported
for helping in development of ulcers





Stannous fluoride has a plaque inhibiting effect in
addition to the anticaries action. the stannous ion
is responsible for the plaque inhibiting effect.
Stannous inhibit the adsorption of plaque bacteria
to the enamel by bonding to the phosphate
polymer lipoteichoic acid present on the surface of
gram positive bacteria. Stannous fluoride also
interferes with the acidogenicity of the plaque. It is
possible that tin atoms bound to the surface of the
bacteria also block the sucrose from entering the
cell and there by preventing acid formation
Detergents and surface active agents are
incorporated in to the tooth paste and mouth
rinses to lower the surface tension and loosen and
penetrate the deposits and emulsify and suspend
the debris

Fluoride supplements
High and long lasting cariogenic challenge
 For average orthodontic patient it was found that tooth pastes
alone were inadequate to stop caries and there fore
recommended the use of fluoride mouth rinses (0.05 % NaF )
daily
 An improved cariostatic effect can be achieved by use of
fluoride in combination with antibacterial agents like
chlorhexidine, triclosan and zinc
 Topical fluoride in the form of varnishes or gels may be
recommended
 Solution of titanium tetra fluoride inhibits the development of
lesions associated with fixed appliances more efficiently than
other conventional preparation ,its mechanism of action is
probably due to retentive, titanium rich. Glaze like coating
formed on the treated enamel

Fluoride releasing bonding agents











Fluoride reservoir that does not depend on patient co operation
.and fluoride is deposited in an area immediately adjacent to the
caries susceptible areas.
Gass inomer cements, and resin modified glass inomer cements
In studies simulating oral environment, it was found that the
fluoride availability from glass inomer cements is PH-controlled.
glass inomer cements take up fluoride from the oral environment
and released .
It is seen that much fluoride is released during the first few days
to weeks. Short term studies have shown that here is reduction in
incidence of caries but long term effect shows there was a
significant reduction in the release of fluoride
Fluoride releasing sealants are also available s

Elastomeric ligatures and chains








Elastomeric products are used in
orthodontics as ligatures and as continuous
modules for the engagement and the
retraction.
Despite the popularity, there has been some
concern about the force degradation
exhibited by the elastomeric chains
Efforts have also been directed to minimize
plaque retention capacity of elastomeric
chains. Fluoride releasing elastomeric
ligatures has been introduced to minimize
the risk of demineralization of enamel
margins

Composition and structure








The elastomeric ligature and chains are
polyurethanes, which are thermosetting polymers
possessing a –(NH)-(C=O)-O-stural unit formed by
condensation polymerization.
The cross linking between the chains must be
relatively few to facilate large extension with the
failure of primary bonds.
The glass transition temperature of biomedical
polyurethanes range from -50 to -80 deg. C
The difference in energy between the rigid and
rubber states corresponds to increase in the amount
of molecular motion experienced by the polymer
after undergoing the glass transition temperature







Greater the glass transition temperature more rigid
is the polymer and generates more force.
The two main methods of processing the modules
are injection molding technique and die stamping.
The die stamping polymers are found to be more
consistent in physical properties.
It is said that pigments added to the elastomers also
effect the physical properties of polymer, however
the general studies has shown that there is no
difference between the conventional and the colored
elastomeric materials.

Fluoride releasing polyurethanes







Advances in the field of elastomerics include the
introduction of products with
fluoride releasing features
It was thought a reliable means of long term
fluoride releasing areas adjacent to the bracket
margins would be paramount significance.
Though it was thought such fluoride release is
beneficial it is said to hamper the properties of
elastomers and early degrading of elastomer


Elastomeric chains




Significant differences in their force decay
characteristics have been reported. These
differences may be attributed to several factors ,
variation in manufacturing techniques, variations
in additives incorporated in the basic
polyurethane polymer, variation in morphology or
dimensional characteristics .
Many in vitro studies that have measures the
force degradation rate of he elastomerics modules
……the census of these studies is that elastomerics
modules experience a steeps decline in force ,
ranging from 40 to 50 % during the first 24 hrs
which continues at a lower rate for nest 2 to 3
weeks.







Traditionally these modules have been used for
retraction of anterior teeth to close extraction spaces
as well as midline diastemas
with the advent of Super elastic ni ti coil springs
which can deliver low constant forces , use of
elastomerics has diminished significantly
Then there has been a criticism related to lack of
mechanical control of teeth Engaged with
elastomerics chains , because loss of directional
control of moments leads occasionally to undesirable
mesio-distal or bucco-lingual rotations as describes
previously that the elastometic chains loose almost
half the applied force





very early , some investigators have proposed that
this deficiency can be counteracted by application of
higher initial force of 3 to 4 times the desired force
level .Some other investigators felt that the
application of orthodontic force up to 4 times the
optimal level for tooth moment may have
unpredictable outcomes on biological processes
Several studies have also dealt with the use of
prestreaching to eliminate the force loss by
elastomerics modules . 2 methods have been
suggested , one is instantaneous pre stretching
technique by young and et el other is the extended
time technique by Brantley et al but evidence has
also shown that it only eliminates about 10 % of
force decay

Cements in orthodontics













In orthodontics application of cements is
limited to luting of appliances,
for acceptable performance the luting agent
should have a variety of properties :
Adequate working time and setting time.
high tensile
Compressive
Shear strength
Resistance to dissolution
Clinically acceptable bond strength low
adhesive remnant index score on debonding,
and anti carigenic potential

Zinc phosphate cement


Once zinc phosphate cements were widely
used for cementation of orthodontic bands.



These cements are available as hand mixed
powder and liquid system although some
encapsulated products are marketed

Composition
 The principal constituent of cement powder is zinc
oxide.
 A small quantity of Magnesium oxide which
improves mechanical properties and color stability.
Small amounts of additives such as Silica or alumina
which also improves mechanical properties.
 Approximately 10% fluoride in the form of stannous
fluoride for anti cariogenic effect.
 The liquid is an aqueous solution of phosphoric acid
in concentrations from 45% to 64% buffered by 2 to
3% of aluminum phosphate and 1 to 9% of zinc
phosphate.
 Buffered by a small quaintly of 2-3% of aluminum
phosphate .

Properties.
 The powder to liquid ratio for the cement strongly
affects the working and setting times.
 A thin consistency (low viscosity)is essential when
the cement is used as a luting agent, to ensure
adequate flow during cementation of orthodontic
bands.
 A reasonable working time for zinc phosphate
cements ranges between 3 and 6 minutes, and the
setting time should be between 5 and 9 minutes.
 For optimum results the powder should be
incorporated into the liquid in small Proportions
and a relatively slow rate to achieve the desired
consistency, the exothermic setting reaction is
retarded











In contrast, rapid mixing of the cement powder and
liquid causes substantial heat evolution, with
considerable decrease in working and setting time.
Mixing over a large area of the glass slab also results
in a lower temperature increase from the setting
reaction
Cooled and dried mixing slab retards the reaction
rate.
Care must be taken not to cool the slab below dew
point, since condensation from the air can cause
contamination by water.
The film thickness should be around 20 um Since
adhesion has not been documented to develop
between zinc phosphate cements and orthodontic
bands, retention of the bands is attained by
mechanical interlocking.

Properties
 Initial setting takes place at 4-7 minutes it attains up to 50 %of
the final strength which is attained at 24 hours. Exhibits
compressive strength of 80 – 140 mpa tensile strength of less
than 5 mpa
 Solubility
 During the first 24 hours of cementation significant solubility
of the cement has been reported as much as 0.04 -3.3 %by
weight and decreases due time .
 High powder liquid ratio decreases the solubility of the cement
Draw backs
 Zinc phosphate is brittle.

It has a relatively high solubility in the mouth and it does not
adhere to tooth substance.

Zinc phosphate relies on mechanical interlocking for its
retentive effect.

It does not provide any chemical bonding to tooth or metal
surfaces.

Zinc polycarboxylate cements:



These cement were introduced by smith in
1968 and these cements were the 1 st dental
materials developed with an adhesive
potential to enamel and dentin and it has
the desirable properties of zinc phosphate
and zinc oxide eugenol

Composition










The zinc polycarboxylate is available in powder liquid
formations, the powder consists of zinc oxide with 10 % of
magnesium oxide or tin oxide , silica , alumina , or bismuth
salts and small quantities of stannous fluoride may be
incorporated in some brands
The presence of fluoride in these cements also increases the
strength while controlling the setting time,
The liquid is an aqueous solution of a homopolimer o acrylic
acid or co polymers acrylic with other unsaturated carboxylic
acids such as etaconic and maelic acid .
The acid concentration is 40 %by wt. it has a relatively high
molecular wt which may increase the strength of the material .
undesirable effects such as short shelf life and difficulties in
manipulation occur because of high viscosity









Mixing of the polycarboxylate cements should be
completed rapidly within 30 to 40 seconds.
The working time varies from 2 to 5 minutes at
room temperature and setting time ranges from 6
to 9 minutes at 37 degree centigrade.
The powder should be rapidly incorporated into
the liquid in large quantities to optimise the
working and setting time.
The working time of polycarboxylate cement can
be extended by lowering the temperature of the
mixing slab and storing the powder in a
refrigerator.











Refrigeration of liquid is avoided because gelation
may occur from formation of hydrogen bonds.
The cement mixture should be used while it still
has a glossy surface appearance.
Although the polycarboxylate cement mixture has
a thicker consistency than that for zinc phosphate
cement its flows readily when loaded, yielding an
appropriate film thickness of 20 μm.
The fully set cement at 24 hours after mixing has
compressive strength ranging from 48 to 80 Mpa.
Tensile strength ranging from 8 to 12 MPa.
Modulus of elasticity of zinc polycarboxylate
cement is between 3 to 6 GPa.

Solubility






The solubility of these cements in water is low ,
ranging between .1 % to .6%by wt.
some products incorporating stannous
fluoride exhibit higher solubility because of
fluoride release .
These cements have low resistance to
dissolution under acidic conditions such as
lactic acid citric acid.depending upon the pH
of the environment.

Bonding
 These cements are capable of bonding with
surfaces of metallic restorations, prostheses
and appliances particularly nickelchromium, silver-palladium and stainless
steel alloys
Disadvantages
 High viscosity.
 High intraoral solubility
 Short setting time.

Glass inomer cement
History
 Glass ionomer cements was first
introduced by Wilson and kent in 1972
 It is referred to as polyalkenoate cement
,also known as ASPA(Alumino-silicate poly
acrylate)


Glass ionomer cements can be classified based
on use as:
 Type I or luting cements.Glass particle size
is 13 to 19 microns.Powder to liquid ratio is
approximately 1.5:1.
 Type II or restorative cements.Particle size
of upto 50 microns.Powder to liquid ratio is
approximately 3:1
 Type III. Chemically set liners/bases or pit
and fissure forms.
 Type IV.Visible light activated liners/bases

Glass ionomer cement was introduced to orthodontics in 1986.
Composition
 GIC powder is an acid soluble Calcium flouroalumino silicate
glass.
 Main constituents include silicon dioxide, aluminium
oxide,calcium flouride, aluminium phosphate, aluminium
flouride and sodium flouride.
 The liquid for GIC is an aqueous solutions of polyacrylic acid
in a concentration of about 50%.
 The liquid was quite viscous and tended to gel over time.
 The other acids were in the form of itaconic acid, maleic acid
and tartaric acid.These acids tend to increase the reactivity of
the liquid, decrease the viscosity and reduce the tendency for
gelation.
 These acids can be freeze dried into powder and added to glass
powder or water, to extend the working time.


Properties
 The luting glass ionomer cements have working
times 3 to 5 minutes and setting time 5 to 9 minutes.
 The water based glass ionomer cements have longer
working and setting times compared to polyacid
containing cements.
 The margins of setting cement should be protected
from moisture contamination with a varnish
 Compressive strength ranges between 90 and 140
MPa.
 Tensile strength is 6 to 8 MPa.
 Modulus of elasticity is 3.5 to 4 GPa.
 The flexural strength (9 to 20 MPa) and fracture
toughness are higher for glass ionomer cements than
for all other typeswww.indiandentalacademy.com
of luting cements











The solubility in water of the fully set cement is
considerably lower than that of zinc polycarboxylate
and zinc phosphate.
Their early susceptibility to moisture within 4 to 10
minutes after the start of mixing is very high.
Prior to application of glass ionomer ,the enamel
surface for bonding may be conditioned with an
aqueous solution of polyacrylic acid having a
concentration in the range of 10 to 40%.
GlC act as a reservoir of fluoride,providing a
possible means to minimise the potential of
subsurface enamel demineralisation.
The initially elevated level of fluoride release is
attributed to higher elution occuring before the
cement has set. the cement,finally attaining a low
constant level

Hybrid resin inomers
Since the early 1990's,hybrid resin/glass
ionomer products have been introduced for
clinical purposes.
They may be categorised as:
 Resin modified glass ionomers
 Compomers (polyacid modified resin
composites)
 Ionomer modified composite



RESINMODIFIED GLASS IONOMERS
COMPOSITION








The powder of resin modified glass ionomer cements, consists
of either the glass composition used for conventional glass
ionomer cements barium aluminosilicate glass is also
incorporated in some products.
Significant alteration have been made in the liquid
component of RMGIC's
The most prominent changes are the replacement of water by
a water-HEMA (Hydroxyethyl methacrylate)mixture and the
incorporation of photoinitiators or chemical initiators for free
radical polymerisation.
In some products,methacrylate based monomers BisGMA,
TEGDMA and UDMA are added to the polyacrylic acid
solution ; The final hardening and strengthening is enhanced
by the formation of polycarboxylate salt matrix.

Properties
 Resin modified glass ionomer cements have longer working
time and undergo rapid setting after light curing.
 The desirable film thickness for luting applications may be
obtained with a lower powder to liquid ratio.
 The enamel surface should first be pumiced,rinced and
dried without desiccation taking place.
 The powder should be incorporated into liquid in large
portions and rapid spatulation for 10 seconds is suggested;
the usual working time is upto 20 seconds.
 A more rapid rate of strength development for these
materials may be attained by photopolymerisation, which
presumably accelerates the setting process.
 RMGIC appear to provide significantly higher bond
strength than the conventional GIC and a decreased
probability for bond failure.











The fluoride release from RMGIC has a relatively constant
rate, characterized by a substantially lower initial ion elution
compared to other types of glass ionomer cements.
Resin modified glass ionomer cement demonstrate superior
compressive and tensile strength, fracture toughness and are
more resistant to permanent deformation and dissolution in
wet environment, even during the early setting stage.
A more rapid rate of strength development for these materials
may be attained by photopolymerisation, which presumably
accelerates the setting process.
RMGIC appear to provide significantly higher bond strength
than the conventional GIC and a decreased probability for
bond failure.
The fluoride release from RMGIC has a relatively constant
rate, characterized by a substantially lower initial ion elution
compared to other types of glass ionomer cements.

Compomers










These are supplied as anhydrous single pastes and contain
major ingredients of both resin composites and glass
ionomers,except for water.
Exclusion of water ensures that initial setting occurs only by
polymerisation and is essential in preventing premature
setting of the material in the container
An acid base reaction may occur later as the material absorbs
water invivo.This cannot take place without appreciable
water diffusion.
By the time this has occured,the self limiting visible light cure
generated network will have a sufficient cross link density to
suppress extensive reaction, although the water does provide
a measure of plasticization.
Flouride release is minimal.However strength and ease of
handling are superior

IONOMER MODIFIED COMPOSITES
 These set only by a polymerisation mechanism but
contain ion leachable glasses in an attempt to
achieve flouride release.
 Developments involving the use of glass ionomers
as luting agents has been the introduction of selfcured hybrid resin/glass ionomer products
 These cements have several advantages compared
to traditional glass ionomer luting agents
 They have greater tensile strength and are less
brittle.
 In addition,they release at least as much flouride
as traditional glass ionomers,are less soluble and
are less sensitive to moisture contamination and
desiccation.

IONOMER MODIFIED COMPOSITES
 These set only by a polymerisation mechanism but
contain ion leachable glasses in an attempt to achieve
flouride release.
 Developments involving the use of glass ionomers as
luting agents has been the introduction of self-cured
hybrid resin/glass ionomer products
 These cements have several advantages compared to
traditional glass ionomer luting agents
 They have greater tensile strength and are less
brittle.
 In addition,they release at least as much flouride as
traditional glass ionomers,are less soluble and are
less sensitive to moisture contamination and
desiccation.

Impression materials






There are a variety of impression materials
for general dentistry but orthodontic
purposes
the routinely used impression materials are
alginate less commonly polyvinylsiloxanes


Alginate hydrocolloid
Components:
Diatomaceous earth
K alginate or Ca alginate
K sulfate
Na phosphate
Ammonium salts & CLX
Glycol
Others











Functions
Filler
Alginate gel
Plaster setting
Retarder
Disinfectants
Render the powder dust
less
Provide taste and color


Properties of the impression materials and
relation ship to clinical use
Properties before insertion into the patient
mouth


Material cost and shelf life



Ease of preparation and use

Properties while in the patients mouth







Biocompatibility
Patient acceptance
Flow
Wetting of oral structures
Setting dimensional change
Setting time


Properties during the removal from patient
mouth




Flexibility
Tear strength
Creep compliance


Properties after removal mouth


Dimensional stability



Immunity and disinfection



Compatibility with die material


Polyvinysiloxane


Component
Siloxane oligomer
Oligomer with
terminal vinyl group
+ Platinum acid crystal
+ Filler

Function
Mech & chem.
inertness
for cross linking
Catalyst
Improve the
handling


Bonding to non conventional
surfaces




With the ever increasing adult patients
undergoing orthodontic treatment situations
arise were many of these patients have
restored teeth. Although banding can one
alternative for bonding these teeth but
sometimes it may become necessary to bond
these teeth for esthetics and better hygiene.
The materials commonly used for restoration
teeth are ceramics, cast alloys, composites,
amalgam restoration, acrylic resins

Bonding to ceramics


A variety of ceramic materials are used to restore
teeth, it becomes extremely difficult for the
clinician to identify the chemical composition but
what becomes important is the external
restoration of the ceramic. The principal
veneering material used is leucite containing
feldspar.. How ever there are other materials like
fluorine mica silicate in dicor castable alloy
systems .these type of ceramics all the color is
obtained from the external layer hence can be
problematic. All other ceramic achieve there color
from the internal ceramic layer.

The protocol for bonding the ceramic surfaces is as follows











The glaze is first removed by sand blasting , using 50 um
aluminum oxide for 2 to 4 seconds
The ceramic surface is then etched with 9.6% HF acid for two
minutes
Subsequently followed by two to three layers of silane coupling
agent on the etched surface and followed by drying.
Then two layers of unfilled resins are applied as thin coating
Then the bracket is finally bonded to the prepared ceramic
surface with highly filled bisGMA resin.
It is said that if the color of ceramic and integrity of the
restorations not to be altered and further chances of
rebonding are there then it is advised not to follow the above
protocol

Alternative surface preparation that have
been found to achieve satisfactory results
 mechanical roughening with stones and
diamond
 sand blasting
 chemical roughening with hydro fluoric
acid
 and chemical coupling with the use of saline

Bonding to casting alloys
 A proper surface preparation and special
adhesives are required for acceptable bonding to
the casting alloys. although roughening the surface
of the alloy with stone increases the bond strength.
 intaoral sand blasters provide better results
 Research has shown that tin plating the noble
alloys increases the bond strength
 In the recent years adhesives that chemically bond
to metal surface have been developed. The
commercial products superbond C & B and C &
B metabond .
 Other commercial products like panavia EX and
panavia21 and bis-GMA
 Intermediate resins are also used

Bonding to dental amalgam
 Sand blasting of the surface the restoration
followed by use of adhesives4-metabisGMAand intermediate resins improves the
bonding to the dental amalgam
Bonding to composite resins
 The uppermost resin composite has to be
removed with a diamond bur then the surface
is etched with37% phosphoric acid.silination
follows before the application of an unfilled
resin and bonding

Bonding of acrylic resins





The surface is first wetted with methyl
methacrylate for three minutes then the
brackets then can be bonded using a
bonding agent and resin composite
Or it can be embedded in a Pmma
restoration+ Glass ionomer cements

Dental Solder




Brazing : it is the joining of metal parts by a
filler metal at temperature below the solidus
temparature of the metals being joined and
above 450 deg c
Soldering :it is the joining of metal parts by a
filler metal at temparature below the solidus
temparature of metals being joined and below
450 deg c

Solder

hard solder

Soft solder


Lead tin alloys



Gold solder

Not used



Silver solder

Composition
Gold solder
 Gold:-45 to 81%
 Silver:- 8 to 30 %
 Copper :- 7 to 20 %
 Tin:- 2 to 4 %
Silver solder
 Silver:- 10 to 80 %
 Copper :- 15 to 50 %
 Zinc :- 4 to 32%





Properties
These have high melting temperature
Greater strength and hardness


Conclusion
Whether to surrender to the
manufacturer

or drive away the bull…..

Thank you
For more details please visit


Copy of biomaterials in orthodontics /certified fixed orthodontic courses by Indian dental academy

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