Thursday, September 8, 2011

Factors influencing tooth whitening

Type of bleach
The majority of contemporary tooth whitening studies involve
the use of either hydrogen peroxide or carbamide peroxide.
This latter material is an adduct of urea and hydrogen
peroxide which on contact with water breaks down to urea
and hydrogen peroxide. For example, a 10% (w/w) carbamide
peroxide gel would yield a maximum of 3.6% (w/w) hydrogen
peroxide. In general, the efficacy of hydrogen peroxide
containing products are approximately the same when
compared with carbamide peroxide containing products with
equivalent or similar hydrogen peroxide content and delivered
using similar format and formulations, either tested in vitro
or in vivo. For example, Nathoo et al. demonstrated in a
clinical study that a once a day application of either a 25%
carbamide peroxide gel or a 8.7% hydrogen peroxide gel both
gave a statistically significant tooth shade lightening after 2
weeks use compared to baseline, but found no statistically
significant differences between products.
An alternative source of hydrogen peroxide is sodium
percarbonate and this has been used in a silicone polymer
containing product that is painted onto the teeth forming a
durable film for overnight bleaching procedures. The
peroxide is slowly released for up to 4 h and gave significant
tooth colour improvement after 2 weeks versus baseline.
However, the relative clinical or in vitro efficacy of sodium
percarbonate versus hydrogen peroxide tested in the same
product format and conditions has not been reported.
A tooth bleaching system based on sodium chlorite
applied to the tooth surface and activated under acidic
conditions has been described in the literature, however,
no efficacy data has been reported to date. Similarly, other
potential vital tooth bleaching systems have been outlined in
the literature with limited supporting evidence for their
efficacy. These include sodium perborate, peroxymonosulphate, peroxide plus metal catalysts and oxireductase
enzymes. The long-term acceptability and relative
efficacy of these alternative tooth bleaching systems requires  
significant further research

Concentration and time
 Two of the key factors in determining overall tooth whitening
efficacy from peroxide containing products are the concentration
of the peroxide and duration of application. For
example, Sulieman et al. compared the in vitro tooth
bleaching efficacy of gels containing 5–35% hydrogen peroxide
and found that the higher the concentration, the lower the
number of gel applications required to produce uniform
bleaching. Similar results were found by Leonard et al. who
compared the in vitro tooth bleaching efficacy of 5%, 10% and
16% carbamide peroxide gels and found the whitening was
initially faster for the 16% and 10% than the 5% concentration.
However, the efficacy of the 5% approached the higher
concentrations when the treatment time was extended. In a
clinical study using custom made bleaching trays, Kihn et al.
showed that a 15% carbamide peroxide gel gave significantly
more tooth whitening than a 10% carbamide gel after 2 weeks
use. This result was confirmed in another clinical study
reported by Matis et al. However, in this latter study, by
extending treatment time to 6 weeks, the differences in
tooth lightness were no longer of statistical significance. The
initial faster rate of bleaching for higher concentrations of
carbamide peroxide has also been observed when bleaching
tetracycline stained teeth in vivo over a 6 months period.85systems. Typically, an image of the anterior teeth is
captured under controlled lighting conditions by a digital
camera together with suitable calibration tiles or standards
and then subsequently analysed via computer software to
determine the colour of the individual teeth, often expressing
them in terms of CIE Lab values. For example, after 14 days use
of a 10% carbamide peroxide tray-based system, the mean
change from baseline in L* and b* were 2.07 and 1.67,

Heat and light     

The rate of chemical reactions can be increased by increasing
the temperature, where a  8C rise can double the rate of
reaction. The use of high-intensity light, for raising the
temperature of the hydrogen peroxide and accelerating the
rate of chemical bleaching of teeth was reported in 1918 by
Abbot.Other approaches for heating the peroxide have
historically been described to accelerate tooth bleaching, such
as heated dental instruments.However, excessive heating
can cause irreversible damage to the dental pulp.Contemporary
approaches and literature has focussed on accelerating
peroxide bleaching with simultaneous illumination of
the anterior teeth with various sources having a range of
wavelengths and spectral power, for examples, halogen curing
lights, plasma arc lamps, lasers and light-emitting diodes.
For some light sources, significant increases in pulpal
temperatures have been measured using in vitro models
during tooth bleaching.The light source can activate
peroxide to accelerate the chemical redox reactions of the
bleaching process. In addition, it has been speculated that
the light source can energise the tooth stain to aid the overall
acceleration of the bleaching process. Some products that
are used in light activated bleaching procedures contain
ingredients that claim to aid the energy transfer from the light
to the peroxide gel and are often coloured materials, for
examples, carotene and manganese sulphate.
Case studies have demonstrated the efficacy of light
activated peroxide tooth bleaching systems. However,
the literature evidence from in vitro and clinical studies
for the actual effect of light on tooth bleaching versus a
suitable non-light control is limited and controversial. An in
vitro study using naturally coloured extracted human teeth
showed that the application of various light sources significantly
improved the whitening efficacy of some bleach
materials, but not for others. Other in vitro studies have
clearly shown significant tooth whitening benefits for peroxide
plus light versus suitable control conditions
However, these studies artificially stained the tooth specimens
with, for examples, black tea, coffee, tobacco and red
wine, i.e. ingredients commonly found to promote extrinsic
stains. These chromophores are likely to be different to that
which may be found naturally inside the tooth.
Tavares et al. conducted a tooth whitening clinical study
to compare 15% hydrogen peroxide gel illuminated with a gas
plasma light source versus 15% peroxide alone versus placebo
gel plus light, all treatments lasting 1 h. The change in Vita
shade from baseline for peroxide plus light, peroxide alone
and placebo plus light were 8.35, 5.88 and 4.93, respectively,
with peroxide plus light being significantly different to the
other two groups. In contrast, Hein et al.demonstrated no
additional effect of any of the three light sources tested over
the bleaching gel alone for three commercial products in asplit mouth clinical design. Thus, further work is clearly
required in order to unequivocally demonstrate the additional
efficacy benefit of light activated tooth whitening systems
versus their non-light activated controls.


Michael Griffin said...

There are a lot of factors that can turn people's teeth yellow. I believe bleaching is a great way to bring back our teeth's pearly white color. Ahh, yes. Bleaching efficiency varies in concentration and time, depending on the patient's dental condition.

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