Page 12 - ADITI 2018 Newsletter - Volume 2

Thus, an attempt is made to maximize the area for
interlocking potential by making more space for
bonding agent. Brazing alloy is used to join wing and
the base and mesh to the base. Brazing filler alloy is
applied in between the bracket base and the wing
interface. Most stainless-steel alloys can be brazed
with any one of several different filler metal families,
including Ag, Ni, Cu and Au. Initially, stainless steel
brackets were brazed using silver based filler alloys
which is the most frequently used brazing filler.
Cadmium was added to lower the melting
temperature and improve wetting. Silver based
brazing alloy introduces a galvanic corrosion with
release of metallic ions with Copper and Zinc the
most easily leached out element from the silver
brazing alloys. This galvanic corrosion is the main
reason for progressive dissolution of the brazing filler
metal leading to detachment of wing from the bracket
base during treatment. To overcome this problem
gold based brazing materials have been developed.
However, this may lead to dissolution of stainless
steel, which is less noble than the gold alloys and may
be the reason for in-vivo corrosion of bracket bases as
well as for Nickel leaching from stainless steel alloys. indentations are incorporated in the bracket design
When gold based brazing alloy are used there is
minimal alloying with stainless steel base metal
therefore exhibiting good ductility, strength and
corrosion resistance. Brackets travel through a
brazing furnace to complete the process.
Brackets go through a final finishing step giving them
a smooth polished finish
Color-coding is applied prior to final inspection. All
brackets are inspected for quality assurance
throughout the manufacturing process and prior to
packaging.
The advantages of MIM includes:
·Very complex-shaped parts can be manufactured
with or without very little secondary finishing.
Undercuts in the parts, which are not possible with
conventional sintering processes, can be realized
with the MIM Process without problems.
·The surface of MIM parts is far superior to that of
precision cast parts. Thereby, finishing and polishing
costs can be eliminated or substantially reduced.
·The MIM process reaches densities of between 96%
and 100% of the theoretical material density
·The MIM process allows an accuracy of better than
+/-0.3% of the required dimensions.
The disadvantages of MIM are:
· High initial tooling and machinery cost.
· Part design restrictions.
· Small runs of parts can be costly
MIM is the least expensive mainly due to material
savings during the production cycle because runners
and sprues can be easily recycled and reused.
Casting is the most expensive because it is estimated
that 90% of the metal used is wasted in sprues and
runners. MIM allows the use of any alloy for the
production of orthodontic brackets, which is not
always the case with the other processes. As single-
piece appliances, MIM brackets are expected to be
free of the corrosion consequences associated with
the galvanic couple of brazing alloys with stainless
steel (SS).
One-piece brackets
The brackets are usually manufactured in two pieces
i.e. bracket top portion is fabricated separately either
by casting or MIM technique, the mesh is attached
latter with brazing as discussed. However to cut down
on the cost and reduce the number of steps in
production, a few companies fabricate one piece
brackets, where instead of separate mesh,
itself. The brackets made as one piece are very rigid
as there is no flexibility between mesh and the bracket
top. Therefore during removal of the brackets the
bond between rigid bracket base and adhesive does
not break leading to fracture of enamel leading to
permanent damage to the tooth surface.
The biocompatibility concerns deriving from the
application of Nickel containing alloys in the oral
cavity of humans for extended periods of time have
provoked the fabrication of alternative materials.
Thus, non-metallic, nickel-free alloys or steels with
reduced nickel content have been tried in
orthodontics. Titanium (Ti) has been recently
introduced as an alternative material in the production
of metallic orthodontic brackets. The reason
underlying the choice of this metal resides in its
proven biocompatibility, lack of allergenicity and
increased corrosion resistance. Laser welding is also
being used. The main advantage of this method is that
two alloys with different stiffness can be used, the
absence of an intermediate phase and potential
corrosion risk optimize the prospective performance
of final products.
Dr. Sohinderjit Singh :Prof & Head
Dept. of Orthodontics & Dentofacial Orthopedics
Himachal Institute of Dental Sciences
Paonta Sahib H.P.