Dental Asia March/April 2024

USER REPORT
in teeth whitening is hydrogen peroxide
(HP). 1 HP acts as an active oxidising
agent, and can be used directly, or even
indirectly when it is produced during a
chemical reaction involving carbamide
peroxide (CP). 2
and their effects on the enamel surface
are probably clinically irrelevant.
These findings showed that bleaching
procedures are minimally invasive
treatments that are safe for the enamel
surface.
experience a breakage of chemical
bonds, photolysis. Photo-assisted
oxidation is when the oxidation of
molecular bonds in the chromophores
requires a specific activation energy, or
wavelength.
Although the exact mechanism of how
HP bleaches teeth and its associated
effects are not fully understood, it is
known that HP diffuses through the
organic matrix of the tooth structure
because HP has a low molecular
weight. 3 Unfortunately, because the
HP oxidative effect is not only specific
to the long organic chains in coloured
stains, it can also have an effect on
the organic matter of the teeth by this
oxidation. 4,14 Higher concentrations of
CP (35-37%) and HP (30-35%) are used
in professional settings like dental
offices, but at-home bleaching kits
contain formulations with up to 20%
CP and 10% HP. 5
A systematic review by Matis et al.
compared nine studies published on
different tooth whitening systems.
These studies looked at 25 products
used in four different systems.
Although tooth whitening was seen
with all methods, the best system
was a dentist-prescribed overnight
bleaching method. 6
The aim of a study by Abouassi,
Wolkewitz, and Hahn was to evaluate
changes in the surface of the enamel
after bleaching with two different
concentrations of HP and CP. Only
minimal morphological changes
were observed after bleaching with
high concentrations of the agents. 7
Surfaces treated with CP showed
somewhat less alterations compared
to HP. There was no decrease in
enamel micro-hardness in any of the
groups.
The main effect of bleaching on the
morphology of enamel surface is
thought to be related to the oxidation
and subsequent partial lysis of organic
material within the enamel. However,
the differences between CP and HP,
Another study by Tavares et al. tested
the use of light combined with a 15%
peroxide gel in a single office visit
for teeth whitening. 8 Eighty-seven
patients were randomised to receive
peroxide and light, peroxide only, or
light only. The combination of peroxide
gel and light resulted in a significant
increase in lightness and decrease
in yellowness. Tooth sensitivity or
gingival redness were not observed
at the three- and six-month follow-up
visits.
Gottenbos et al. investigated the use
of blue light and HP gel for tooth
whitening. 9 In this study, extracted
teeth were divided into five groups:
Group 1: 9hrs of blue light, 10 hours
of 6% HP gel, and then 6hrs of light
combined with 6% HP gel
Group 2: 9hrs of 6% HP gel, 10hrs of
light, and then 6hrs of light combined
with 6% HP gel
Group 3: 11hrs of light combined with
6% HP gel
Group 4: 8.25hrs of 25% HP gel,
10hrs of light, and then 6hrs of light
combined with 25% HP gel
Group 5: 10.45hrs of light combined
with 25% HP gel
The most significant colour change
was found in groups 1, 2 and 4 that
received 6hrs of light and gel at
the end. This study showed that a
combined treatment with light and HP
gel resulted in better tooth whitening.
De Moor et al. provided an overview
on the chemistry of light accelerated
whitening (LAW) for enhanced
bleaching. 10 Direct photobleaching is a
process involving the chromophores in
the teeth. These chromophores absorb
the light and the excited state can
react with oxygen in the air to become
oxidised, photo-oxidation, or they can
CP is a chemical complex that breaks
down into HP and urea. HP makes up
about one-third of the CP complex. 11
The comparisons between CP and HP
in terms of whitening were studied
by Mokhlis et al. and discussed by
Asmussen. 12 CP has a slower rate of
reaction compared to HP. This slow
breakdown makes it more popular for
in-office whitening procedures. Both
CP and HP are oxidising agents which
whiten teeth but may cause some
sensitivity, and neither of them cause
rebound, which is when teeth appear
to be whiter after a procedure due to
dehydration. An obvious difference
between CP and HP is that CP also
contains urea in addition to HP, while
HP is just composed of hydrogen and
oxygen. As mentioned, HP breaks
down faster than CP. Finally, CP has a
longer shelf life than HP, which needs
cooler temperatures to extend its life.
Because of the differences between
the two chemicals, pros and cons
that come with each whitening agent
are expected. CP is effective and
safe for bleaching teeth because
its longer activity whitens teeth at a
sustained rate and kills bacteria, it
lasts a long time without the need
for refrigeration, and it does not
cause rebound. However, because
CP requires higher concentrations,
these may damage tooth enamel, and
typically the treatment sessions take
longer. In comparison, HP is also a
safe and effective method of whitening
teeth with rapid results, and it also
does not cause rebound. However,
it may also damage tooth enamel,
and as mentioned, it does need to be
refrigerated to extend its shelf life.
Due to the apparent advantages
of CP over HP, determining which
concentrations of CP are more
42 DENTAL ASIA MARCH / APRIL 2024