Walsh, Laurence J.

University of Queensland eSpace

126 Australasian Dental Practice November/December 2007
D entures, removable orthodontic retainers,mandibular advancement and occlusalsplints and other oral appliances develop
extrinsic staining from a variety of sources,
including components of the diet, and products
used for oral hygiene. Biofilms of bacteria and
fungi form on the surface of appliances and under
appropriate conditions of pH and mineral concen-
tration, these biofilms may serve as foci for the
accumulation of calculus.
Denture cleaning products may utilise several
modes of action:
• Physical abrasion;
• Surfactant effects to dissolve biofilms;
• Dissolution of calculus by acid erosion;
• Decolourisation of surface stains via oxidation
reactions; and/or
• Removal of loose deposits by effervescence.
This short report illustrates how digital image
analysis can be used to assess the chemical
cleaning capability of denture cleaning products, in
particular to discriminate the direct chemical effect
from the mechanical action added by the user after
soaking the appliance. Two commonly used den-
ture cleaning products (Cal-Dent, Elbaford, West
Chermide, Brisbane, Australia; and Steradent Extra
Strength, Dentsply, UK) were compared in terms of
their ability:
1. To remove stains (wine, tea, coffee, chlorhexi-
dine) on maxillary complete dentures;
2. To alter the level of acidity of a solution (pH); and
3. To cause corrosion of metallic denture components
in acrylic partial dentures.
Methodology
Effect on staining
A total of 41 identical full upper dentures were con-
structed from the same master cast (Figure 1),
using the same batch of acrylic resin and identical
Chemical cleaning 
of oral appliances
By Professor Laurence J. Walsh
“digital image
analysis can be
used to assess
the chemical
cleaning 
capability of 
denture cleaning
products, in 
particular to 
discriminate the
direct chemical
effect from the
mechanical action
added by the user
after soaking the
appliance...”
Figure 1. Control unstained denture. Note the 
calibration bars on the left side of the image.
Figure 2. Dentures immersed in one of the 
staining solutions (in this case, green tea).
clinical | EXCELLENCE
November/December 2007 Australasian Dental Practice 127
acrylic teeth. One denture was completely
untreated and served as a control. The
other 40 were divided randomly into 4
groups of 10 each and stained by immer-
sion for 14 days at room temperature (22
degrees Celsius) in a sealed container
containing 1 litre one of the following
solutions (Figure 2):
1. Wine (Galway vintage Shiraz 2000,
Yalumba Wineries, South Australia;
13.5% ethanol) (Figure 2);
2. Green tea (Dilmah, Sri Llanka, 5 tea
bags in 1000 mL);
3. Coffee (Malongo café Moulo ground
coffee (Zimbabwe), 5 heaped teaspoons
in 1000 mL); and
4. Savacol (0.2% chlorhexidine in 11.5%
ethanol; Colgate Oral Care, Australia).
The tea and coffee solutions were pre-
pared in the usual way using boiling water
and the dentures placed in the solution
when the water temperature had cooled
below 60 degrees Celsius. Each of the 4
staining solutions was agitated gently
every second day during the 14-day
staining period.
Using a positioning jig, each denture was
then photographed in a moist state, after
shaking off excess staining solution (Figure
3). The images were captured using a 3.34
megapixel digital camera (Nikon Coolpix
995) mounted on a fixed stand with a con-
stant camera-target distance of 45 cm, using
an electronic flash under conditions of con-
stant artificial ambient lighting. Each image
included two colour calibration bars to
serve as internal reference points. Checking
of these internal controls by animating the
photographs in sequence, and by digital
image analysis, did not reveal any
detectable variation in the lighting condi-
tions during the study.
After the baseline photographs were
obtained, the 10 dentures in each group
were then allocated into 2 subgroups 
of 5 each.
Figure 3. Residual staining from wine on
FU denture, after Steradent; occlusal view.
Figure 5. Control unstained denture, beside a denture stained with red wine.
Figure 6. DOTCAM2 analysis showing selection of the denture after digital subtraction.
Figure 7. Histogram analysis of luminosity
using Adobe Photoshop software.
Figure 4. Residual staining from wine,
after Steradent; buccal view, showing per-
sisting stain in the gingival margin region.
clinical | EXCELLENCE
Two sachets of Cal-Dent™ powder were
added to 500 mL of hot (60 degree Celsius)
water in a 2-litre plastic container, and 5 den-
tures placed in the solution to fully submerge
them, with the tissue fitting surface placed
toward the bottom of the container. After 30
minutes, the dentures were removed one at a
time, the Cal-Dent solution rinsed off for 5
seconds, and photographs taken as before.
Each denture was then brushed lightly with a
wet Oral B 30 soft toothbrush without any
paste, for 20 seconds in total (10 seconds
each on both the tissue and oral surfaces), to
remove loosened material. The dentures
were then re-photographed.
This sequence was followed for den-
tures stained with wine, tea, coffee and
chlorhexidine.
Two tablets of Steradent™ (UK) were
added to 500 mL of hot (60 degree Cel-
sius) water in a 2-litre plastic container
and 5 dentures placed in the solution to
fully submerge them, with the tissue fit-
ting surface placed toward the bottom of
the container. After 10 minutes, the den-
tures were removed one at a time, rinsed,
photographed, bushed and re-pho-
tographed as before. This sequence was
followed for dentures stained with wine,
tea, coffee and chlorhexidine.
The matched images were analyzed using
DOTCAM2, an image analysis method
which is not affected by variations in
lighting between images of the same object
under different conditions (See The Cutting
Edge in this edition). The non-denture com-
ponent of each image was subtracted
digitally and a histogram analysis performed
of the approximately 500,000 pixels repre-
senting the denture surface, using Adobe
Photoshop™ version 6 software (Figsures 6
and 7). Histogram analysis was performed
with data for the luminosity (brightness)
channel. The possible range of luminosity
values is 0 to255, with zero representing
black, and 255 representing white. Thus, a
higher luminosity value indicates a brighter
denture surface and thus corresponds to
better removal of staining.
Luminosity data for the 5 samples per
group were pooled. Variations within each
group were very small and typically the
standard deviations were less than 6% of the
mean. Image analysis was performed in a
blinded fashion using coded images to
obviate any concerns regarding bias
regarding particular products. Statistical
analysis employed the two-tailed unpaired
Student’s t test with Welch correction for
unequal standard deviations, using the soft-
ware package GraphPad Instat version 3.01.
Changes in pH over time
A temperature-corrected digital pH meter
(Dick Smith Electronics) was calibrated
using a pH 7.0 standard. One sachet of
Cal-Dent powder was added to 250 mL of
hot (50 degree Celsius) tap water and the
pH recorded (to an accuracy of 0.01 pH
units) using a digital pH meter at time
zero, at 30 seconds and 60 seconds, and
then at each minute up to 10 minutes. The
same method was used with Steradent (1
tablet added to 250 mL).
Corrosion assessment
Five identical partial acrylic dentures were
constructed from a master cast. Each denture
had a wrought stainless steel circumferential
clasp and an occlusal rest. Two dentures were
immersed in either Cal-Dent or Steradent
solution (freshly prepared as described
above), and the remaining denture used as a
control. The dentures were removed and
photographed using a macro lens after 10, 20
or 30 minutes (Figures 8 and 9).
Results
Staining: Qualitative results
Because the greatest intensity of staining
was achieved using wine (Figures 4 and
5), detailed digital analysis of the images
was undertaken for the wine samples only.
Lesser staining occurred with tea,
coffee and chlorhexidine and in each of
these three sub-groups, the combination
of soaking and gentle brushing gave com-
plete stain removal when assessed
visually. Cal-Dent visibly gave more
effective stain removal from soaking alone
than Steradent, and thus was confirmed
subsequently by digital image analysis.
With wine, a visibly noticeable difference
was that intense staining of teeth and gingival
margin regions was not removed completely
with either cleaning agent, with Steradent
performing much worse in this regard.
Staining: Quantitative results
Luminosity data for wine staining are pre-
sented in Figures 10 and 11. The main
points can be stated as follows:
1. There was no difference in the groups at
baseline. As expected, the groups are
comparable before stain removal was
undertaken.
2. With both products, there was a signifi-
cant increase in luminosity with either
soaking alone, or soaking followed by
brushing (P<0.001 in all cases).
3. With both products, soaking followed
by brushing gave better stain removal
than soaking alone. Nevertheless, a sig-
nificant benefit was gained by soaking
alone, thus confirming the concept of
“chemical cleaning” of appliances.
128 Australasian Dental Practice November/December 2007
clinical | EXCELLENCE
Figure 8. Small areas of surface corrosion on clasp from 20
minutes in Steradent (arrows).
Figure 9. Sample kept for 30 minutes in Cal-Dent does not
show corrosion.
4. Comparing the two products, for the
oral surface of dentures, Cal-Dent gave
greater stain removal (higher lumi-
nosity) both with soaking alone, and
with soaking followed by brushing.
5. For the fitting (tissue) surface of den-
tures, there was a clear trend for better
stain removal by soaking alone, how-
ever this did not reach statistical
significance. Cal-Dent gave greater
stain removal than Steradent for the
combination of soaking and brushing.
Changes in pH
Following mixing, effervescence was
noted immediately with both Cal-Dent
and Steradent. In both cases, no further
effervescence was seen after approxi-
mately 60 seconds. Both products were
highly acidic when dissolved; there was a
rapid drop in pH during the first minute,
and this drop was more pronounced with
Cal-Dent, which maintained a lower pH
by more than 1 pH unit across the period
of measurement (Figure 12).
Corrosion assessment
When the five partial acrylic dentures
were examined, the following observa-
tions were made. After 10, 20 or 30
minutes, no corrosion could be seen when
the metal components of dentures soaked
in Cal-Dent were examined (Figure 9).
With Steradent, no visible corrosion was
seen at 10 minutes, however after 20 min-
utes of immersion, subtle brown coloured
surface reaction products were seen on the
clasp surface (Figure 8). These were
easily removed by gentle brushing, and no
visible surface pitting was seen.
Conclusions
1. Chemical cleaning (removal of external
stains) from oral appliances can be
effective with common types of stains.
2. Staining from red wine is more difficult
to remove by chemical cleaning.
3. With common stains (tea, coffee and
chlorhexidine), both commercial prod-
ucts assessed achieved complete stain
removal when dentures were soaked
and then brushed gently.
4. Brushing using a wet toothbrush
(without any paste) facilitated stain
removal by dislodging material loos-
ened by the denture cleaning solutions.
5. For more difficult and resistant stains
(i.e. red wine), Cal-Dent (for 30 min-
utes) gave better stain removal than
Steradent (for 10 minutes).
6. Cal-Dent was more acidic (lower pH)
than Steradent.
7. Cal-Dent did not cause visible corro-
sion of wrought stainless steel clasps
when used for 30 minutes. Mild corro-
sion occurred with Steradent.
About the author
Professor Laurence J. Walsh is the tech-
nology editor of Australasian Dental
Practice magazine. He is also a noted
commentator on and user of new technolo-
gies and is the Head of The University of
Queensland School of Dentistry.
130 Australasian Dental Practice November/December 2007
Figure 12. Changes in pH over time.
clinical | EXCELLENCE
Figure 10. Luminosity data for the fitting surface for the wine
group. The higher the luminosity, the better the stain removal and
the brighter the surface.
Figure 11. Luminosity data for the polished oral (palatal) surface
for the wine group.
CPD POINTS AVAILABLE
Continuing Education credits are 
available on this article for subscribers
by answering the questionnaire at
www.dentalpractice.com.au


Chemical cleaning of oral appliances

http://espace.library.uq.edu.au/view/UQ:137307/Chemclean.pdf

Chemical cleaning of oral appliances

Abstract

Similar works

Full text

Available Versions

University of Queensland eSpace