Esthetic orthodontic brackets /certified fixed orthodontic courses by Indian dental academy

ESTHETIC BRACKETS

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

INTRODUCTION
PLASTIC BRACKETS

THE CONSTRUCTION,
MATERIAL PROPERTIES,
BOND STRENGTH,
FRICTIONAL RESISTANCE,
TORQUE PROPERTIES,
BRACKET FRACTURE,
GUIDELINES AND CRITERIA
CONCERNING THE SPECIFIC
APPLICATIONS AND USES,
CONCLUSION.

Orthodontic patients, including a growing population of
adults, not only want an improved smile, but they are also
increasingly demanding better aesthetics during treatment.
The development of appliances that combine both acceptable
aesthetic for the patient and adequate technical performance
for the clinician is the ultimate goal.
There has been a recent trend towards the development of
smaller stainless steel brackets but although these generally
provide the technical performance required by the orthodontist
the aesthetic advantage over conventional sized appliances is
limited.

Lingual orthodontics satisfies the aesthetic criteria but it can be
argued that it produces a decrease in the performance of the
appliance and considerable additional technical difficulties and
time requirement for the orthodontist.
A more recent addition to the orthodontist’s armamentarium is
Invisalign. This esthetically oriented technique uses a series of
clear plastic aligners to treat simple to moderate alignment
cases, especially in the adult patient.
However complex cases still require fixed appliance treatment
and numerous brackets are now available for those clinicians
and patients that are aesthetically oriented. They are the plastic
and ceramic brackets.

Several plastic families, such as acrylics,
nylons, epoxies, polysulfones,
polyphenylene oxides and
polycarbonates were tested as
orthodontic attachments in the oral
environment.
It was found that the unfilled
polycarbonate was the most suitable
material for clinical use.
It is non toxic, Easy to fabricate, It has
high impact strength, Good optical
clarity, Good abrasion and creep
resistance and It has no odor or bad
taste (Newman, 1969a).

Polycarbonate brackets were introduced some
40 years ago (Newman, 1964. 1965. 1971,
1992; Schwartz. 1971) and were initially well
received.
Although plastic brackets were the first esthetic
brackets to be bonded directly to enamel
surfaces (Newman. 1964. 1992).
Between 1986 and 1990, the use of plastic
brackets decreased from 57.8% to 24.3%
(Gottlieb et al.. 199I).

However, later they fell out of favor because of their
clinical disadvantages (Cohl et al.. 1972; Dorbin et al..
1975; Dooley et aI., 1975; Garn. 1976: Rains et al.. 1977;
Gorelick et al, 1978).
After a long period of dormancy manufacturers have
rekindled their interest in improved plastic brackets.
There have been several attempts to reinforce plastic
brackets with the insertion of precision stamped stainless
steel slots, ceramic powder or both (Fischer and
Orlowski. 1975; Aird and Durning. 1986; Feldner et al..
1994).
ln theory, the metal slot should prevent distortion and
reduce bracket friction.

The ceramic filler should reduce staining
and discoloration (Feldner et aI., 1994).
However, there are not enough data to
substantiate these assertions.
In addition to the ceramic filler or metal
slots, some orthodontic manufacturers
tried to reinforce plastic brackets with
glass-fibers.
Newman (1969a) dismissed the use of
these fibers because of their poor
dimensional stability and reduced
resistance to fracture.
New generations of fiberglass reinforced
plastic brackets have been available for
clinical use for over ten years promising
adequate clinical performance (Crow,
1995).


Most of the plastic brackets that are currently available in
the market are composed of high density polycarbonate
plastic.
Some orthodontic companies also manufactured
translucent composite esthetic brackets made of
thermoplastic polyurethanes. clear acrylic or durable
lexan.
Little information has been generated on the physical
properties of the finished products, but the comparison of
the generic materials shows that polycarbonates
demonstrate the lowest mean values of hardness, tensile
strength and fracture toughness compared with stainless
steel and ceramic materials (Swartz. 1988).


Plastic brackets are not as hard as ceramics, a fact
which may be an advantage rather than a
disadvantage.
Since it is generally thought that the harder a
material is, the more it will wear an opposing
material softer than Itself (Monasky.1971).
Plastic brackets will not wear or chip enamel. if
occluded upon.


On the other hand, plastic brackets are prone to
distortion or fracture due to their low tensile strength
and fracture toughness (Dorbin et aI., 1975. Aird and
Durning, 1986).
The material properties of the new ranges of cosmetic
brackets have bee considerably improved. but further
studies are needed to analyze their function in clinical
use.


A wide variation exists in the results of different studies on
bond strength with regard to the types of brackets, so that
direct comparison of results is not feasible.
The factors that may contribute to these differences include
-the choice of composite,
-the type of testing equipment used,
-the orientation of the applied force,
-the storage medium of the extracted teeth,
-the bracket material, and
-whether the bracket base has a mechanical or chemical
union to the composite resin (Crow. 1995).

Direct bonding of plastic brackets has been done
principally with adhesives based on methylmethacrylate
and poly-methylmethacrylate (Newman, 1964 1969b:
Miura. 1972; Silverman et aI., 1979: Golden ! 979).
Failure rates for these adhesives were not acceptable.
Although the brackets did adhere initially the application of
deformation forces with time overcome the poor adhesion
of methacrylate to the tooth.
There was also a distressing tendency for the bracket to
slide down the tooth surface until setting occurred
(Newman, 1 969a. 1973: Mizrahi and Smith 1969; Retief et
al.. 1970: Miura et al.. 197!; Cohl et al. 1972; Dijkman,
1972; Silverman et aI., 1972; Lee et 211. 1974).

These materials are not cross-linked and the brackets
may also undergo drifting when subjected to
temperatures slightly higher than those In the mouth
(Rueggeberg et 211.. 1992).
Diacrylate cements used with plastic brackets were found
not to bond well to them without plastic bracket primers
(Nagel. 1973; Faust et al.. 1978 Reyno!ds. 1975: Pulido
and Powers, 1983).
A bonding system, based on a unique thermosetting
combination of mono- and dia-crylates and a high
molecular weight polymeric filler, was developed to
Improve the bond strength of polycarbonate brackets
(Lee et aI., 1974)

At present the new generations of plastic brackets are
suitable for almost all adhesive systems.
No-mix adhesives or light-cure bonding materials with a
supplementary primer are recommended by the
orthodontic companies.
The adhesives with their own plastic primer demonstrated
higher bond strength values than those without plastic
primer (Akin-Nergiz et al.. 1996).
Satisfactory bond strength values were observed for
polycarbonate brackets with no-mix orthodontic bonding
resins and highly filled, self cured diacrylate cements
(Blalock and Powers, 1995 Nkenke e1 al.. 1997).

Glass ionomer cements have also been introduced in
direct bonding of orthodontic brackets.
These cements are less aggressive toward the tooth
enamel and leach fluoride over prolonged periods (Klock
owski et aI., 1989: Cooley et al.. 1989; Fisher-Brandies et
al.. 1991: Fricker, 1992: Ostman-Andersson et al. 1993),
but they have significantly lower- bond strength than the
composite resins (Cook and Youngson, 1988 Rezk-Lega
and1991: Blalock et al.. 1995 Nkenke et al., 1997).


Comparison among the plastic brackets bonded with the
same adhesive revealed differences in bond strength.
Among the factors that may cause these differences are
geometry of the wings, presence of metallic
reinforcement, sharp edges and geometry of the base.
Large and thick bases, rounded contours and provision
for mechanical retention were factor associated with
improved bond strength with the plastic brackets (pulido
and Powers,1983; Nkenke et al.,
The new ranges of plastic brackets offer a mechanical
locking base, providing more bonding surface for
mechanical retention with the adhesive.

On the other hand, polycarbonate brackets form a
chemical bond with composites containing monoacrylate
rather than diacrylate, thus increasing the bond between
resin and bracket (Crow. 1995).
Bond failure interrupts the continuity of fixed orthodontic
treatment. Many workers have studied the bond strength of
polycarbonate brackets (New-man; 1969a; Miura et al.,
1971: Cohl et al., 1972 Reynofds, 1975; Garn.1976; Moser
et 211.. 1979; Pulido and Powers. 1983).
Although bond failures occur, Reynolds and von
Fraunhofer (1977) indicated that the bond strength of
polycarbonate brackets was superior to that of metallic
brackets.

Gwinnett (1988) found that the mean shear bond
strength of various plastic ceramic and metallic brackets
were not statistically different and Harris et al. (1992)
indicated acceptable strengths for clinical use for ceramic
and plastic brackets, although plastic brackets had a
wider range of sheer/peel bond strength values than the
other brackets.
In the same study the highest values were recorded for
metal brackets.
Chaconas et al. (1991) observed that ceramic filled
plastic brackets and polycrystalline ceramic brackets
exhibited greater resistance to tensile force than
monocrystalline ceramic brackets.

The new fiber-glass plastic brackets showed lower bond
strength than metal (Manhartsberger et aI., 1989) and
ceramic brackets bonded with two-paste composite
(Crow, 1995).
It was found that the mean shear bond strength of
fiberglass brackets was lower than those shown by Moser
et al. (1979) and Beech and Jalaly (1981), who
demonstrated higher shear values for their polycarbonate
attachments (Crow, 1995).
Miura et al. (1971) considered that 5.1 MPa shear
strength gave satisfactory performance over a two year
period for polycarbonate brackets, which is equivalent to
the mean value of fiberglass plastic brackets bonded with
no-mix composite (Crow. 1995).

Several variables have been demonstrated to affect the
magnitude of friction between bracket and wire including
the material,
size and shape of the wire,
the material, width and slot-size of the bracket,
the ligature material and
the presence of salivary lubrication (Angolkar et a!.,
1990).


The effect of bracket material on bracket-wire friction has
been investigated by Riley et al. (1979).
These investigators compared the frictional force
generated by wires in plastic brackets with that produced
in stainless steel brackets and noted that plastic brackets,
especially in combination with steel ligatures, were
associated with larger frictional force.
The dynamic frictional force of sliding between different
modern orthodontic brackets and arch wires was
investigated and it was found that polycarbonate brackets
showed the highest friction compared with the other
brackets (Tselepis et aI., 1994).


Glass-fiber reinforced plastic brackets showed comparable
frictional forces to other plastic materials and steel
(Milleding et al., /993).
Orthodontic companies suggest that plastic brackets with
incorporated metal slots have considerably reduced
frictional resistance than other plastic brackets due to their
smoother slot surfaces.
However, there was no distinct trend in frictional resistance
between the plastic brackets with and without the metal
slot inserts (Bazakidou et aI., 1997).


Plastic brackets due to their viscoelastic nature are
renowned for not adequately torquing teeth.
It was found that pure polycarbonate brackets had an
unacceptable amount of deformation and creep when
subjected to torquing forces (Dorbin et al., 1975).
Higher torque as well as lower deformation values were
reported, by placing self-curing adhesive over the wire
and bracket thereby producing a reinforcing component to
the system (Dorbin et aI., 1975).


Although this is not clinically feasible, it demonstrated the
possibility of improving the torque capability of plastic
brackets (Feldner et al.. 1994).
This concept of reinforcement consequently led to the
incorporation of a metal slot or ceramic particles into the
plastic matrix of the bracket.
Metal slot reinforcement appears to strengthen the matrix
adequately so that torque, comparable to metal brackets,
can be applied (Feldner et aI., 1994).


It was observed that significantly less bracket slot angle
changes due to creep can occur when using metal slot
reinforced plastic brackets (Alkire et a1.. 1995).
Ceramic reinforcement does not appear to have any
significant clinical effect on strengthening the polycarbonate
matrix and is unable to withstand heavy clinical torquing
forces, without excessive distortion (Feldner et al.. 1994).
It was suggested that in cases which require substantial
amounts of torque. such as Class II, division 2, plastic
brackets proved inferior to metallic and ceramic brackets
(Kastrup-Larsen et al.. 1993).

The breakage of plastic brackets during clinical use is a
major problem.
These brackets are not often able to withstand typical
orthodontic pressures and to transfer them as controlled
moving forces onto the teeth.
In practice, the fracture of brackets is often caused by
occlusal and torquing forces (Rains et aI., 1977).
Bracket fracture as a cause of appliance failure was
reported during clinical trials (Cohl et aI., 1972; Garn, 1976;
Pulido and Powers. 1983; Aird and Durning, 1986).


Even if this extreme phenomenon does not occur, the
strength of these forces may be dissipated by deforming
the bracket (Dorbin et aI., 1975).
In comparison to metal brackets, plastic brackets possess
inadequate strength to withstand all intra-oral and extra
oral orthodontic forces (Dooley et al.. 1975).
Aird and Durning (1986) found that 7.4% of the examined
polycarbonate brackets fractured during orthodontic
therapy.


The fractures were classified into three groups.
slot-wing fracture.
Broussard slot fracture and
stalk base fracture.
It was concluded that arch wire-bracket interactions, stainless steel ligaturing, auxiliary arch mechanics and certain
features of bracket design contributed to bracket fracture.
Moser et al. (1979) reported defects of both cylindrical and
irregular outline within fractured brackets.
They concluded that where a material flaw terminated at a
failure, bracket failure could result during clinical tooth
movement.

Bracket failure may also occur during the
debonding process.
This was observed for ceramic-filled plastic
brackets (Gwinnett. /988; Harris et 31.,
1992), but not for fiberglass plastic brackets
(Crow, 1995).
Ligating wires onto fiberglass brackets may
be difficult because of wing fractures
(fv1anhartsberger et al.. 1989).
Rains et al, (1977) investigated the areas of
potential weakness within plastic brackets
and suggested that an Increase of material
at critical stress points of a bracket, may
improve Its efficiency.

Bracket – Plastic standard edgewise
Manufacturer – Ortho Organizers
Composition – Plastic
Prescription – Standard edgewise
Slot size – 0.018”, 0.022”
Special Bonding – Primer required
Special features – Strong, Durable and stain
resistant contemporary design, smooth, rounded
edges for patient comfort, Extra large tie wings for
maximum strength.


Bracket – Silkon mTM
Manufacturer – American Orthodontics
Composition – Plastic with “ceramic like” filler
Prescription – Roth style
Slot size – 0.018”, 0.022”
Special Bonding – no
Special features – injection molded, Non-porous, stain
resistant surface, Particle mechanical lock base, low
profile cuspid/bicuspid hooks available

Bracket – Elegance SL
Manufacturer – Dentaurum
Composition – fiberglass reinforced polycarbonate with metal
slot
Prescription – Standard edgewise & Roth
Slot size – 0.018”, 0.022”
Special Bonding – no
Special features – transparent composite, fully integrated metal
slot, contoured mechanical/chemical retention base, Rhomboid
design with torque-in base, integrated metal cuspid hooks
available.

There is no doubt that plastic brackets represent a major
improvement for orthodontic patients. However, when
compared to metallic and ceramic brackets, they have a
number of limitations and detrimental clinical
characteristics.
The new generations of plastic brackets offer favorable
optic qualities.
Un like ceramic brackets they do not need special
bonding adhesives and equipment and they present far
less danger of debonding complications and enamel
damages. Also their low price contributes to profitability.


There seems to be need for further Improvement of their
mechanical properties, as they are inferior to metallic
brackets regarding bond strength, frictional resistance.
torque control and bracket fracture.


Thank you
Leader in continuing dental education


Esthetic orthodontic brackets /certified fixed orthodontic courses by Indian dental academy

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