Colour coloured modules so that we can ask

change of coloured elastic modules when subjected to various regularly consumed

Cathrine.G1, Dr


1BDS Student, Saveetha Dental College, Chennai

2Professor, Department of Orthodontics, Saveetha Dental College And
Hospitals, Chennai






AIM: The aim of the study is to
see changes in colour when different coloured modules are subjected to commonly
consumed liquids.


OBJECTIVE: To find out whether
commonly consumed food can cause change in colour of elastic modules.


Four different modules were selected for the study. The colour selected was
green, orange, purple and pink and these were put in four different solutions
namely sambar, rasam, milk and limejuice. The modules were kept in the solution
for a period of one week. The control modules were placed in water. At the end
of one week, the modules were taken out. Later the colour of the modules was
compared with the control modules. The variations were noted down and
statistical analysis was done.


BACKGROUND: Modules are small elastic
‘o’ rings that are stretched around the four corners of the bracket to hold the
arch wire in place. There are plenty of colours to choose from. The clear
modules pick up yellow food colouring easily, particularly from curries.
Modules are changed at each visit since it changes colour due to various food


REASON: Many of the young
orthodontic patients want coloured modules for aesthethic reasons however many
times the colour of the modules fade away or they change colour. This study
will give us an idea on which solutions actually bring about changes on which
coloured modules so that we can ask the patients to avoid those drinks or
liquids while using those coloured modules.


RESULT: Significant changes in
colour were not visible even after one week of immersion of the coloured
modules in the liquids. Probably, larger number of samples maybe needed to see
if there are other staining solutions.



Keywords: Colour, Immersion,
Orthodontic, Aesthetic, Modules, etc.





          Biggest problem using coloured
modules is that the colour changes, this becomes more obvious when we use clear
modules for aesthethic purposes. The most common complaints from patients using
modules are that the colour changes to yellow. This is unacceptable because the
patients are wearing ceramic brackets only to reduce the visibility of the
appliance. As this study was conducted to find out whether all the coloured
modules gets stained or lose colour when exposed to some commonly consumed

         Orthodontic elastic ligatures are
composed of polyurethane and can be produced by matrix molding or modular
injection processes (Ardeshna & Vaidyanathan, 2009; Renick et al., 2004). Polyurethanes are not
inert materials, and they decompose when in prolonged contact with enzymes,
water or humid heat (Han et al.,
2011; Mohamed et al., 2011).
There are reports that these ligatures may discolor or stain if the patient
eats certain types of foods or uses mouthwash or lipstick (Ardeshna et al.; Kim & Lee, 2009). This
effect can cause problems because, whereas the ceramic brackets are somewhat
resistant to staining, the aesthetic elastic ligatures do stain.

         Elastic modules have been a common
part of orthodontic practice since their introduction more than 30 years back. These chains,
single ligatures and bands are manufactured by different companies and
available in a variety of different colours to meet the growing global demand
for aesthetic orthodontic appliances. Orthodontists and patients have developed
more relatively and preference for colour selection and more aesthetic
orthodontic treatment. The dentists and patient may chose an aesthetically pleasing
colour for the chains at the time of placement but beyond this initial colour
choice, the susceptibility for discolouration of the modules over time is of
critical concern. Orthodontic elastic modules are made from polyurethane using
a die stamping or injection moulding process. The die stamping process consists
of two steps: the first step uses an extrusion process to produce bulk sheets
of the polyurethane. In the second step the die stamp cuts the sheet into the
final shape and size.

       Concerns have been raised regarding the
quality of the products and whether one company is superior to another in
efficacy or cost-effectiveness. Many studies have been carried out comparing
product performance such as force decay, friction and dimensional changes of
these elastic modules. For example, the question as to whether force delivery is
affected by pigmenting of the elastomer has been studied elsewhere.  Structural conformation and discolouration
have also been examined.

       Although the modules have been reported
to be susceptible to staining in the oral cavity, to the best of our knowledge,
no systematic studies on colour stability of these modules have been reported
previously. The
ability to prevent intrinsic and extrinsic stains of the polyurethanes modules
has become an important challenge, as the oral cavity is exposed to a variety
of media on a daily basis, many of which may stain or alter the surface of
modules causing aesthetic degradation. It is therefore important to know, not
only whether long-term exposure to daily beverages and spices changes the
colour of the module, but also whether it is a change that is perceivable by
the human eye.

        Extended exposure to beverages is known
to cause colour changes of restorative composites and may also cause discolouration of
orthodontic elastic ligature modules. Spices and seasoning are also known to
cause extrinsic staining of teeth. They are essential in processed foods
(prepared foods, snacks, sauces, condiments, salad dressings) and ethnic foods,
especially Mexican, Italian, and Asian.

        The important clinical issue about
elastomers is force delivery and force degradation of these materials over
time. The force exerted by elastomers depends on the initial force and force
decay rate, many studies reported 50-70% force loss in the first 24 hours.

        The objective of this study was to
evaluate the colour change of elastic coloured modules immersed in sambar,
rasam, milk and limejuice. The study examined whether colour changes of elastic
modules due to dietary media exposure.


          In the present study, we investigated four
different modules (Green,
Orange, Purple, Pink). A
study was conducted using these coloured modules placed in commonly consumed
food like sambar, rasam, milk and limejuice. The above solutions were selected
because these are commonly consumed liquids in South Indian population. The
modules were cut down into pieces and then they were kept in solutions (sambar,
rasam, milk and limejuice) for one week. Simultaneously, modules were kept in
water as control. After one week, the modules were taken out and compared with
control for colour change. Statistical analysis was done and tabulated.


           Similar studies were done which
includes immersion of coloured elastic modules in the other staining solution
such as red wine, artificial saliva, coffee and coca cola. There were
significant colour change and the colour change was detected using a
spectrophotometer. The color change (?E*ab) can also be calculated using the
following equation: DE*ab = (DL*)??+ (Da*)??+ (Db*)?1?2

           The changes in the color parameters
(DL*, Da* and Db*) were calculated by subtracting the final values from the
initial values (dry discs). Prior to each measurement, the discs were washed
with distilled water to avoid the possibility of reading solution residues
deposited on the surfaces of the discs.

           The statistical significance
(p=0.05) of the effect of the different solutions on different brands of
elastic ligatures was tested by one-way or two-way repeated measures analysis
of variance (ANOVA, post hoc analysis – Fisher PLSD test). The statistical
analysis was performed using the software SPSS 15.0 (SAS Institute Inc., Abacus
Concepts, Cary, North Carolina, USA).

            This study can also be performed in
vivo and has shown significant changes in results. The study has already been
conducted in United States including 25 orthodontic patients and different
orthodontic modules were used as follows,

» Morelli
(Sorocaba, São Paulo, Brazil)

» Uniden
(Sorocaba, São Paulo, Brazil)

» TP (La
Porte, Indiana, USA)

American Orthodontics (Sheboygan, USA)

(Bohemia, NY, USA)

» 3M
Unitek (St. Paul, Minnesota, USA)

Orthosource (North Hollywood, USA)

Tecnident (Porto Alegre, RS, Brazil)

          Multiple comparisons were used to detect
significant differences in various studies that are the other shortcoming of
the study.

           Luciane Q. Closs, Sônia Paczko,
Patricia Zardo, Telmo Ojed and Caroline Dias have conducted similar studies and
they used four high pigment beverages coffee, red wine, cola and black tea All
samples were immersed for 15 minutes, three times a week, in four high-pigment
beverages: coffee (3 Corações, Três Corações, Brazil), red wine (Cabernet
Sauvignon, Viu Manent Winery, San- tiago de Chile, Chile), cola (Coca-Cola, Rio
de Janeiro, Brazil), and black tea (Classic, Twinings of London, London, United
Kingdom). Immersion duration was set at 15 minutes based on the mean time
usually required to consume such drinks.

            Between immersion sessions, modules
were kept immersed in artificial saliva (20 mmol/L NaHCO3, 3 mmol/L NaH2PO4, and 1
mmol/L CaCl2 at
neutral pH) at 37_C
(002 CB incubator, Fanem, São Paulo, Brazil). One group of control elastomeric
modules was not exposed to any pigment but was kept immersed in artificial
saliva throughout the study period. The temperatures of the different solutions
varied so as to simulate real-life conditions: coffee and tea were used hot, at
an average temperature of 80_C; cola was used ice-cold, at an average of 10_C; and red
wine was used at an average temperature of 18_C.






1: Coloured modules used
in the Study



These are the coloured modules used in the study – Green, Orange,
Purple, Pink.



FIGURE 2: Control – coloured bands used in the study



These are the coloured bands kept in water as control in the study




FIGURE 3: Coloured modules (Green,
Orange, Purple, Pink) and sambar














FIGURE 4: Coloured modules (Green,
Orange, Purple, Pink) and rasam















FIGURE 5: Coloured modules (Green,
Orange, Purple, Pink) and milk



















FIGURE 6: Coloured modules (Green,
Orange, Purple, Pink) and limejuice









FIGURE 7: Before immersion of coloured
modules (Green, Orange, Purple, Pink) in the liquid





FIGURE 8: Coloured modules (Green,
Orange, Purple, Pink) immersed in all four liquids










FIGURE 9: Coloured modules (Green,
Purple, Orange, Pink) after immersion in sambar, rasam, milk and limejuice over
a period of one week.







The tested solution was not able to cause significant colour change in the
aesthetic elastic modules.

The rasam and limejuice solution caused the greater colour change compared to
the other two solutions.

The significant changes in colour were not visible even after one week of
immersion of the coloured modules in the liquids. Probably larger number of
samples maybe needed to see if there are other staining solutions.





           In the oral environment, the
clinical behavior of the ligatures is problematic. When stretched beyond their
elastic limit and maintained under constant tension, polyurethanes exhibit an
undesired characteristic known as load relaxation (Huget et al.). The degradation of the
polyurethane elastic ligatures in the oral environment may be associated with
the process of color change undergone by the ligatures, and this process may be
reduced by determining its cause (Kim & Lee). In this context, the
concentration and frequency of consumption of certain products in the diet can
alter the staining caused by these products. In addition, considering that
elastic ligatures manufactured by different manufacturers differ, variations in
staining have been described in the literature (Renick et al.). Ardeshna & Vaidyanathan evaluated the color change
of different colors of elastic ligatures. These authors found that white and
transparent ligatures had the highest DE values, suggested that the deposition
of pigments from the solutions studied likely occurred on the surface of the
ligatures and hypothesized that changes in the surface texture and morphology
might contribute to the observed differences found among ligatures from
different manufacturers.

The results of this study show that significant colour change of the
elastic modules may occur under exposure to dietary liquids in the oral cavity
and this is also one of the known clinical shortcomings of elastic modules.

The complete study was done in vitro hence there is no significant
difference, the same study if done in vivo may show significant colour change
due to various factors including saliva, plaque, calculus and also habits which
directly influence the colour change od coloured elastic modules. The
above-mentioned factors play a vital role in colour change of the coloured
elastic modules, which cannot be included in vitro and this is considered to be
the most important shortcomings of the study.

           Clinically, aesthetics is a
significant reason for the selection of coloured modules in orthodontic
practice and staining of elastic modules is therefore a major concern for both
patients and dentists. This study done is an important criteria to select a
module, taking into account the overall performance profile of the elastic module
based on its colour, processing method and brand, as well as the individual’s
own dietary intake habits. Clinicians can use such criteria for elastic modules
for improved aesthetic concern of the modules used in clinical practice.

           However, some important limitations
of the study that also needs to be considered. Pigment uptake is potentially
related to the water uptake and the resulting swelling of the polymer. The
surface area to volume ratio of the samples may strongly influence the water
uptake and the results of this study may not therefore represent the absolute
changes in colours of the elastic modules, however, we are interested in the
relative changes of the coloured elastic modules and the relative changes will
be reflected by the ranked differences.

            Controls were used to detect
significant differences in this study. Since the experimental design of the
coloured elastic modules involved four outcomes. Such a large number of control
with the same data may increase the chance of a type I error by incorrectly
identifying a significant difference where none exists. For this reason, we
used visual observations of differences to confirm the most important
statistical test outcomes of interest, where possible.

            Colour plays an important role in
many aspects of dentistry, particularly shade matching of restorations and
tooth whitening products. Several studies have been carried out on the staining effects of
beverages namely, coffee, tea and wine, which are normally associated with
adult tooth stain on composite restorations and tooth bleaching.

            This investigation was an in vitro study
and some additional differences with clinical situations must be listed out.
For example, there was no consideration of the surrounding area such as shade
of the tooth, metal, etc.    


            Four coloured modules used in the study
had very minimal colour change. Probably, larger number of samples maybe needed
to see if there are other staining solutions. Dentists should make patients
aware of the intake of beverages and spices on the colour stability of their
selected modules. Darker colour modules may be preferred to clear modules to
avoid excessive colour degradation through dietary media such as beverages and
food spices. Patients consuming large amounts of spices or coffee should avoid
clear modules made by extrusion processing because of their tendency to dis colour
or staining.


So we
conclude as follows,

1. Exposure
of clear and coloured elastomeric modules to spices and beverages such as
coffee, tea causes significant discolouration in vitro whereas in our study
sambar, rasam, milk and limejuice comparatively showed less discolouration.  

2. The
degree of discolouration varies with the original colour of the module. Clear
and lighter coloured modules exhibited more change than darker colours whereas
in our study only coloured modules were used which ends as a shortcoming.  

Studies have shown that spices and coffee had the most effect and cola the

4. From
an aesthetic point of view, elastomers of darker shades and colours should be
preferred and patients should be made aware of the effect of spices in food and
coffee on colour change.






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