1671

Post-Bleach Stain Inhibition by Nano-Hydroxyapatite : a Cyclical Staining Test
M.NISHIO, K.FUJITA, T.ISHIZAKI and R.HAYMANSANGI Co., Ltd.Tokyo, Japan
4. Results

3-1. Cyclical Staining Test

1．Aim of Study
Vital tooth bleaching is widely practiced as a non-abrasive means to whiten discolored or badly stained teeth.
But the oxidation action of the bleaching agent is often accompanied by problems of hypersensitivity andrelapsed discoloration believed to result from decomposition not only of the staining substance but also oforganic matrix components, causing microstructural changes to the enamel.

4-1.Cyclical staining test

before bleaching

before bleachingafter bleaching*after bleaching

*

*
*
2

Surface Treatment
0(Renamel or Control,overnight)

after
end ofbleaching cycle 1*

end ofcycle 2(start of test)

end ofcycle 3end ofcycle 1end ofcycle 2

・Spectrophotemetry showed that ⊿a*b* rose sharply in the control group
after even one cycle of CST, whereas in the Renamel-treated group,
although it rose over time, it was significantly lower after 3 cycles, at⊿a*b* = 2.66, than for the control group ( ⊿a*b* = 4.71 ). (Fig. 5)

end ofcycle 3

Fig.4 Change in ⊿a*b* after each step ofcyclical staining and surface treatment test

Staining

2．Materials and Methods

staining andsurface treatment
color-fixing

×3

staining andsurface treatment
color-fixing

stain remover(⊿a*b*(stain remover - bleaching) ) (*p>0.01)

stain remover

Table.1 Change in ⊿a*b* after each step ofcyclical staining and surface treatment test

Color-fixing(oxygen-purge for 1hour)*(10% Polyethylene glycol400 solution for 30min)⊿a*b*Control

cycle 1Treatment with Stain Removercycle 1*cycle14-2. Enamel surface microstructure⊿a*b*

Renamelsurfacetreatment

staining andcolor-fixing

stain
removersurfacetreatment

staining andcolor-fixing

stain
remover

2.12

5.06

4.37

0.35

3.33

1.21

・SEM and SPM observation showed that the enamel surface was coarser
after bleaching than before in all samples. But in samples then treated with
Renamel AfterBleach, a smoothness similar to that of pre-bleach enamel
was restored. Almost no change in surface roughness was seen between
post-bleach enamel and post-bleach enamel treated with the non-hydroxy-apatite control paste (Fig.6&7).
Mean surface roughness after post-bleach enamel treatment was significantly
lower in Renamel-treated specimens (Ra:13.20→8.86nm) than in control
specimens (Ra:13.20→13.93nm). (Fig.7&8)
R

Fig.1 Cyclical staining andsurface treatment test

cycle2

3.29

7.01

4.86

0.41

4.94

1.95

cycle3

4.07

8.07

4.71

0.93

6.01

2.66

* color measurement of tooth surface

cycle 2(⊿a*b*(stain remover - bleaching) )cycle 2Specimens were prepared from sound extracted human teeth without previous restorative treatment, caries
or white-spot lesions. After removing the root, crowns were sliced parallel to the tooth axis with a diamonddisc. A portion of the specimens were prepared for use as standard controls by cutting into 5×5mm blocks,
and successive polishing under running water with #600 and UF 1200 abrasive paper (BUEHLER) to a
standard surface roughness of Ra=approx 8nm, as measured by scanning probe microscope (SPM, SPI4000,SEIKO INSTRUMENTS) The remaining specimens were fixed to a sample stand for colorimetry with quick
self-curing resin (UNIFAST Ⅱ, GC)

R4(Opalescence for 15min×2)(in red wine for 4hours)

2-1. Preparation of tooth specimens

・At the end of 3 cycles, staining was significantly deeper in controls than in
the group surface-treated with Renamel AfterBleach , and exposure of thecontrol group to stain remover showed little effect. In contrast, tooth enamelin the Renamel-treated group retained a glossy, sparsely stained appearance
similar to that of sound enamel (Fig.4)**(surface treatment by Renamel )⊿a*b*Renamel⊿a*b*

We developed a nano hydroxyapatite conditioner, Renamel AfterBleach, designed to restore tooth enamelby mineral replacement, both for professional and home-care use. We examined its effect, in a protocol
designed to allow for both applications, on (1) the return of post-bleach extrinsic stains, using a new cyclicalstaining test (CST) to evaluate relapsed discoloration, and (2) the post-bleach enamel surface, as observed
by SEM and SPM.

6R

(surface treatment by placebo)*Bleaching
RRenamel group

Control group

Human Extracted Tooth⊿a*b*Controlb*L*652-2. Bleaching and enamel surface treatment

60412

All specimens were bleached 3 times with Opalescence Xtra Boost (ULTRADENT, 38% H2O2), according
to the maker's instructions, after which specimens intended for use as standard controls were immersed ineither Renamel AfterBleach (SANGI) or an identical paste without nano hydroxyapatite (placebo) for 3days' enamel surface treatment. Specimens intended for colorimetry were subjected to the same respective
surface enamel treatments, but for 8 hours at 37℃.

32A
356R

11Acycle 3cycle 3

1-6

A52-5-4-3-2-12 03132

456a*A-1

5. Conclusion-22-32-3. Cyclical staining test (CST, Fig.1)

148

Fig.3 Digital camera images showing
tooth enamel surface during cyclical staining

-42-5

3

After bleaching and enamel surface treatment, specimens for calorimetry were immersed in red wine at 37℃
for 4 hours' staining, followed by 1 hour in an oxygen-purge incubator (Fig.2, flow: 2L/min) for color-fixing,
and 30 minutes in a 10% polyethylene glycol 400 solution for potential stain-removal.The specimens werethen sonicated for 5 minutes, washed in distilled running water, and immersed in their respective enamelsurface treatment agent (Renamel or non-hydroxyapatite containing control) overnight, before washing with
distilled water for a further round of staining. The cycle of staining and surface treatment was repeated 3times, to achieve a clear, easily evaluated level of stain, and at the same time assess the effect on the staining
process of continuing enamel surface treatments.
Color was measured for each specimen at the start and end of each cycle, using a Fast-Spectrophotometric
Color Meter (CMS-35Fs, MURAKAMI), and also recorded by digital camera (EOS Kiss Digital, CANON).

3-6

Fig.5 Comparison of L*,a*,b* at the end of each cycle

Fig.2 Color-fixing

Control group
Renamel group

A After Bleaching 1
A After Bleaching 1

Removal-1

2 Removal-2

3Removal-3

Removal-1

2 Removal-2

3Removal-3

3-2. Observation of Enamel Surface Microstructure
Control

Control
252-4. Observation of enamel surface microstructure

Control
Renamel20**50×50μm

Standard control specimens in three groups - before bleaching, after bleaching, and after bleaching followedby 3 days' enamel surface treatment - were prepared by standard method for comparative observation byscanning electron microscope (SEM)(S-4500, HITACHI)(observation conditions : vacc 5kV, emission 10μA).
The three groups were also compared by observation under a scanning probe microscope (SPM), whichallows both repeated observation of the same site in the same specimens and quantification of surface
roughness (Ra). (observation conditions : scannning area 50×50μm, dynamic force mode.)200

150Ra(nm)〔nm〕

69195.77

Mean surface roughness(Ra) : 13.94nm
50×50μm

50×50μm
200Renamel〔nm〕

069195.77

Mean surface roughness(Ra) :before bleaching

8.2nm

before bleachingafter bleaching

200

Renamel

069195.77

RWe concluded that Renamel AfterBleach, containing nano hydroxyapatite,
is an effective agent for use after bleaching, restoring a smooth surface tothe enamel and inhibiting relapse of extrinsic tooth stains.

105

Mean surface roughness(Ra) : 13.20nm

after bleaching

Statistical analysis was performed using Student's t-test.

0200

before bleachingafter bleachingafter post-bleach treatment〔nm〕

Fig.7 SPM observation ofenamel surface after each treatment
post-bleach treatment

・Treatment of post-bleach enamel with Renamel AfterBleach, containing
nano hydroxyapatite, appears effective in inhibiting early relapse of
post-bleach stains.
Mean surface roughness of post-bleach enamel treated with Renamel was
significantly lower than that of controls, indicating that stain inhibition
was related to the enamel-restorative action of nano hydroxyapatite,which is almost the same substance as tooth enamel.
R〔nm〕

50×50μm

Fig.6 SEM observation ofenamel surface after each treatment

・The cyclical staining method appears effective as a model for evaluating
post-bleach discoloration relapse in the presence of continuing surface
enamel treatments.
Oxygen-fixing produced a clear stain profile, which was confirmed byboth the stain removal challenge, and repetition of the cycle three times.

069195.77

Mean surface roughness(Ra) : 8.86nm

post-bleach treatment

Fig.8 Mean surface roughness (Ra) of
tooth enamel surface after each treatment(*p<0.01)

84th General Session & Exhibition of the IADR /June,2006
E-mail:nishio@sangi-j.co.jp