Pisani Et Al-2012-Brazilian Dental Journal
Content
Braz Dent J (2012) 23(1): 15-21
Denture teeth and Ricinus communis solution
ISSN 0103-6440
15
Effect of Experimental Ricinus communis Solution
for Denture Cleaning on the Properties
of Acrylic Resin Teeth
Marina Xavier PISANI
Ana Paula MACEDO
Helena de Freitas Oliveira PARANHOS
Cláudia Helena Lovato da SILVA
Department of Dental Materials and Prosthodontics, Ribeirão Preto Dental School,
USP -University of São Paulo, Ribeirão Preto, SP, Brazil
This study evaluated Knoop hardness, surface roughness and color alteration of artificial teeth for dentures after immersion in water,
1% sodium hypochlorite and an experimental solution of 2% Riccinus communis (RC). Thirty specimens of Vipi, Biolux and Trilux
were analyzed. Tests of Knoop hardness, surface roughness and color alteration were conducted immediately after specimen preparation
(T0) and after two immersion protocols for 15 days (ΔT15) and 183 days (ΔT183). Data variation (ΔT) were subjected to ANOVA and
Tukey’s test (p<0.05). At ΔT15, Vipi presented hardness increase and Biolux presented the highest variation (p=0.01). RC caused the
highest increase in hardness (p=0) and the lowest increase (p=0.005) in roughness. Biolux presented the lowest color alteration (p
=0). At ΔT183, Trilux underwent the highest hardness variation (p=0). Biolux presented an increase in roughness (p=0). There was no
significant differences in color alteration among the artificial teeth (p=0.06) and among solutions (p=0.08) after 183 days of immersion.
All solutions (distilled water, 1% sodium hypochlorite and 2% RC) caused alterations on the analyzed properties. Both immersion
protocols caused alterations on the analyzed properties.
Key Words: denture cleanser, Ricinus communis, acrylic denture teeth.
INTRODUCTION
Denture cleansing is important to increase
denture longevity, maintain the health of oral mucosa
and improve patient’s quality of life. Chemical
disinfectants for immersion have been widely used as
denture cleansers. It is essential that these cleansers have
bactericidal and fungicidal properties and effectively
remove organic and inorganic matter from denture
surface (1). Another important consideration is that the
mechanical and physical properties of the acrylic resin
and artificial denture teeth should remain unaltered after
denture cleansing. However, it has been shown that some
disinfectant solutions cause alterations in physical and
mechanical properties of denture base resins (2,3) and
artificial teeth (4). Some components of these solutions
can penetrate into the material and not be completely
eliminated by rinsing (5).
New formulations of denture cleansers are
welcome because until now an ideal denture cleanser
is not available. The World Health Organization has
encouraged the search for substances and products
derived from animal, vegetal and mineral sources. Many
plants are known for their medical and antimicrobial
properties and the efforts have been directed towards
the search of alternative and low cost cleaning products
that could be safely used by the population. One of these
plants is Ricinus communis or castor plant (division
Magnoliophyta, class Magnoliopside, sub-class Rosidae,
order Euforbiales, family Euforbiaceae), which is a
vegetal typically found in tropical climate areas. Because
of its climatic characteristics, Brazil has one of the largest
areas cultivated with Ricinus communis in the world (6).
The oil extracted from the Ricinus communis
seeds is used in the production of a detergent. In
Endodontics, this detergent has been tested as an
Correspondence: Profa. Dra. Cláudia Helena Lovato da Silva, Departamento de Materiais Dentários e Prótese, Faculdade de Odontologia de Ribeirão
Preto, Universidade de São Paulo, Avenida do Café s/n, 14040-904 Ribeirão Preto, SP, Brasil. Tel: +55-16-3602-4006. email: [email protected]
Braz Dent J 23(1) 2012
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M.X. Pisani et al.
irrigating solution and has shown biocompatibility to
periapical tissues and antimicrobial, bactericidal and
antiinflammatory activity similar to sodium hypochlorite
(NaOCl) (7). The Ricinus communis detergent acts by
breaking sugar leakage of the cellular wall of pathogenic
microorganisms, consequently the loss of cytoplasmic
material leads to cell destruction (7,8). Based on this, an
experimental solution of 2% Ricinus communis has been
developed to be used as a denture cleanser. In addition to
its antimicrobial and cleaning potential, it is important to
analyze whether this solution can affect the properties of
denture components, such as the acrylic denture teeth.
Three important properties to be analyzed are
hardness, surface roughness and color change of acrylic
denture teeth. Hardness has been used as a measurement
to predict wear resistance (9), roughness is related to
biofilm adhesion (10) and color change is related to
aesthetics and is an indicative of the serviceability of
the material (11). Therefore, the aim of this study was
to evaluate the effect of 2% Ricinus communis solution
on Knoop hardness, surface roughness and color change
of three brands of acrylic resin denture teeth compared
with 1% NaOCl after two immersion protocols. The null
hypothesis tested is that 2% Ricinus communis has no
effect on the hardness, roughness and color change of
the acrylic resin denture teeth.
MATERIAL AND METHODS
Specimen Preparation and Groups
no difference existed between hardness of the surface
layer and the worn palatal surface (4). Moreover,
it is important to analyze the inner surface, as the
outer surface or enamel layer of denture teeth is often
removed due to many reasons, such as masticatory
wear, or mostly occlusal adjustments or alterations of
the occlusal scheme by the dentist (9). The color change
was measured on the buccal face instead of the palatal
face because aesthetics is important in this area.
The thickness in the cervical, middle and incisal
areas was 4 mm, 3.3 mm and 2 mm, respectively, as
confirmed with an electronic caliper (CD-6” CSX-B;
Mitutoyo South American Ltda., Suzano, SP, Brazil).
Ninety specimens, 30 of each brand, were
randomly assigned to 3 groups of immersion in 200
mL of the solutions: Negative control group (distilled
water at 37oC); positive control group (1% NaOCl;
Asfer Chemistry Ind. Ltda, São Paulo, SP, Brazil) and
experimental group (2% Ricinus Communis solution,
Chemistry Institute, University, São Carlos, SP, Brazil).
Experimental Period
The hardness, roughness and color were assessed
immediately after specimen preparation (baseline)
and after different immersion periods. The specimens
were immersed in each of the three solutions for 15
consecutive days to simulate 3 years following a denture
cleansing regimen of 20 min daily (∆T15) (2). After this
period, new tests of color, hardness and roughness were
conducted. The specimens were then immersed for 183
consecutive days (∆T183) to simulate 1.5 year of use
following a regimen of 8 h (overnight) daily (2). After
this period, new tests were performed. The immersion
solutions were changed once a day for both protocols.
Three commercially available brands of acrylic
resin denture teeth were used; their names and bath
numbers are presented in Table 1. The maxillary central
incisor of largest size of each brand was selected to
establish a standard for comparison and
because these teeth are located in an esthetic
Table 1. Acrylic resin denture teeth.
region of the mouth.
The artificial teeth had their palatal face
Commercial
Model
Manufacturer
brand
flattened with a sequence of 180-, 220-, 360and 400-grit silicon carbide papers (Norton
28
Dental Vipi Ltda,
- Saint-Gobain Abrasivos Ltda., Guarulhos,
VipiDent Plus
Pirassununga, SP, Brazil
Color: 66
SP, Brazil). The buccal face was not altered.
Surface roughness and Knoop hardness tests
V17
Dental Vipi Ltda,
needed a flat surface because the indentor
Biolux
Pirassununga, SP, Brazil
Color: 66
tip for both tests must be perpendicular to
the surface to be analyzed. According to the
E5
Ruthinium Group Badia
manufacturers, the denture teeth tested have
Trilux
Polesine, Rovigo Italy
Color: 66
a uniform composition. It was assumed that
Braz Dent J 23(1) 2012
Batch
number
6501
6907
6600
Denture teeth and Ricinus communis solution
17
Analysis of Knoop Hardness and Surface Roughness
Knoop Hardness
Knoop hardness was measured with a Shimadzu
microhardness tester (model HMV-2; Shimadzu
Corporation, Kyoto, Japan) with a load of 25 g for 5 s.
The roughness test was performed using roughness tester
(SJ-201P; Mitutoyo Corp, Kawasaki, Japan).
For both tests, teeth were fixed on a #9 wax
plate (Lysanda Inc., Presidente Prudente, SP, Brazil).
The palatal face was stable and perpendicular to the
Knoop and roughness indentor tip. The surface of each
specimen was divided into three equal parts and three
measurements were made in each part to obtain the mean.
For ∆T15, statistically significant difference
was found among the teeth (p=0.01) and among the
solutions (p=0), but not for interactions (p=0.41).
Only Vipi presented hardness increase; Biolux and
Trilux presented hardness decrease and there were no
statistically significant difference among them. Ricinus
communis solution caused hardness increase; distilled
water and NaOCl caused hardness decrease (Fig. 1).
For ∆T183, there was statistically significant
difference among teeth (p=0) and among the solutions
(p=0.01), but not for interactions (p=0.15). All tooth
brands underwent hardness decrease. Trilux differed
significantly from Vipi and Biolux, and presented the
highest hardness variation. All solutions caused hardness
decrease. Ricinus communis solution was significantly
different from distilled water and NaOCl, and caused
the smallest hardness variation (Fig. 1).
Analysis of Color Change
For color measurements of acrylic resin teeth,
a reference mark was used for placing the measuring
port of the instrument on the same location on the
specimen for repeated measures, and a silicone device
was developed (Zetalabor Zhermack, Rovigo, Italy) for
inserting the specimen insertion in the spectrocolorimeter
opening. The spectrocolorimeter (BYK-Gardner
GmbH - 07/2002, Geretsried, Germany) was calibrated
according to the manufacturer’s instructions before
each measurement period using the white calibration
cap supplied by the manufacturer. Color change (ΔE)
were calculated by measuring tristimulus values using
the CIE L*a*b* Color Scale.
Data Analysis
Statistical analysis of hardness, roughness and
color change was carried out SPSS statistical software
(SPSS Inc., Chicago, IL, USA).
Variation of hardness and roughness data at
both evaluation periods was calculated by subtracting
the values obtained after immersion for 15 days (∆T15)
and 183 days (∆T183), respectively, from those obtained
at baseline. Therefore, negative values represented a
reduction and positive values an increase of the variable.
A two-way ANOVA was performed using materials and
immersion solutions as independent factors. Multiple
comparisons were done by Tukey’s test (α=0.05).
RESULTS
Comparisons among means and the respective
standard deviations (SD) are presented in Figures 1-3.
Surface Roughness
For ∆T15, statistically significant difference was
found only among the solutions (p=0.005). Ricinus
communis solution caused roughness increase. Distilled
water and NaOCl caused roughness decrease and were
statistically similar (Fig. 2).
∆T183, significant differences were found only
among the teeth (p=0). Vipi and Trilux presented decrease
of roughness. Biolux was statistically different from Vipi
and Trilux, and presented increase of roughness (Fig. 2).
Color Change
For ∆T15, significant differences were found
only among the teeth (p=0), where Biolux presented
the smallest color change. For ∆T183, there were no
statistically significant differences among the teeth
(p=0.06), solutions (p=0.08) or significant interactions
(p=0.16) (Fig. 3).
DISCUSSION
The present study evaluated the effect of 2%
Ricinus communis solution on hardness, roughness and
color change of three brands of acrylic resin denture
teeth in comparison with 1% NaOCl and distilled water
as a control group. The null hypothesis was rejected as
all solutions caused some alteration on the physical and
Braz Dent J 23(1) 2012
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M.X. Pisani et al.
mechanical properties analyzed.
The acrylic denture teeth used in this study are
composed of PMMA (polymethyl metracrylate) and
EDMA (dimethacrylate of polymerized ethylene glycol),
which is a cross-linking agent. An optimal amount of
cross-linking can improve the mechanical properties
of acrylic resin denture teeth, reducing the tendency to
craze (form pre-cracks) under stress and the solubility to
organic solvents (12). Trilux artificial teeth have triple
press (incisal, cervical and dentin), are made of acrylic
resin of high molecular weight combined with the use
of double cross-linking (DCL) system and have organic
modified ceramics (Ormocer®). Biolux teeth have double
press (body and enamel) and are made of polymer of
high molecular weight combined with the use of DCL.
Vipi teeth have double press (body and enamel) and a
Figure 1. Comparison of means (SD) of Knoop hardness for ∆T15 and ∆T183. Different letters indicate statistically significant difference
at 0.05. SH= sodium hypochlorite; RC= Ricinus communis.
Figure 2. Comparison of means (SD) of roughness for ∆T15 (solutions) and ∆T183 (teeth). Different letters indicate statistically significant
difference at 0.05. SH= sodium hypochlorite; RC= Ricinus communis.
Figure 3. Comparison of means (SD) of color alteration (∆E) of the artificial teeth for ∆T15. Different letters indicate statistically
significant difference at 0.05.
Braz Dent J 23(1) 2012
Denture teeth and Ricinus communis solution
linear and not interpenetrate polymer chain.
There are in the literature few studies analyzing
the effects of denture cleansers in artificial denture teeth
(4,13). The effects of 2% Ricinus communis solution in
mechanical and physical properties of denture acrylic
resin (2) and denture liners (14) have already been
investigated using the same cleansing protocols of the
present study. In acrylic resins, the Ricinus communis
solution caused alterations on the properties and was
not superior to 1% NaOCl (2). However, the Ricinus
communis solution had less effect on the properties of
silicone-based denture liners compared to 1% NaOCl
(14). The observation of the effect of denture cleaners
after long period of use (3 years and 1.5 year) is also
important because patients rarely change their prosthesis
before this period. The regimens used were 15 min
daily immersion and overnight daily immersion; both
recommended procedures by the dentists to their patients
(2,14).
The results regarding Knoop hardness showed for
∆T15 (Fig. 1) that Biolux and Trilux underwent hardness
decrease, while Vipi underwent hardness increase and
Ricinus communis solution was the main responsible for
the hardness increase in comparison with the baseline
values. The hardness increase for Vipi can be explained,
perhaps, by the fact that they are less resistant to the
loss of plasticizers and do not have DCL chains, which
reduce their resistance.
After simulation of 1.5 year of overnight
immersion (∆T183), all tooth brands presented a decrease
in hardness (Fig. 1); Trilux underwent the highest
reduction, followed by Biolux and Vipi. These results
are in accordance with those of Campanha et al. (4)
who also worn the occlusal teeth surface and found
a reduction in hardness of Trilux after immersion for
7 days in 1% NaOCl The Ricinus communis solution
caused the lowest hardness reduction after this period
of immersion (Fig. 1). Pavarina et al. (13) found that
the immersion in distilled water decreased hardness
of the acrylic denture teeth tested. The absorption of
water and aqueous cleansers such as NaOCl and Ricinus
communis caused reduction in hardness due to the fact
that these solutions could act as plasticizers. Similar to
what happens with acrylic resin, in denture teeth basically
composed of the same material, small molecules of water
diffuse into the polymer mass and cause the relaxation
of polymer chains, consequently reducing the hardness
of artificial teeth (15). Probably, microcracks formed
during the wear of the palatal face could have facilitated
19
the infiltration of solutions, accelerating the process of
PMMA plasticizing (16).
Teeth composed by double cross-linked agents
should promote, in theory, a decrease in fluid diffusion
to the polymer because of their inseparable chains and
higher resistance. However, Trilux teeth showed the
highest reduction in hardness for ∆T183 (Fig. 1), perhaps
due to some intrinsic factor related to their composition
or their triple press. For polymer based materials, there
may be also several other factors that may influence
the hardness values including time and speed of elastic
recovery (12).
For ∆T15, there was no roughness difference
among the tooth brands, only among the solutions.
(Fig. 2). The 2% Ricinus communis solution caused an
increase in roughness (Fig. 2), while distilled water and
NaOCl caused reduction in this property. Pisani et al.
(2) also found roughness increase in acrylic resins after
immersion in Ricinus communis and attributed this result
to a tick and sticky film formed on specimen surface. In
Endodontics, the use of Ricinus communis solution as
an as irrigant increased root canal dentin permeability
due to its low superficial tension and the moisturizing
capacity, which increases the contact of the solution
with tooth surface (6,7). Although this consideration
is not related to acrylic denture teeth, it is necessary to
investigate the action of this solution on the permeability
and degradation of organic matrix present in artificial
teeth, which could represent an increase in roughness.
Additional studies concerning the mechanism of action
of Ricinus communis solution should be developed in
the future.
For ∆T183 (Fig. 2), only Biolux presented
roughness increase, regardless the solution. After
immersion in solutions, Biolux teeth were less resistant
to the action of solvents, which may have allowed the
loss of components such as plasticizers and exposure
of the layers polished with smaller grain sandpapers,
creating porosities in the polymer mass, which could
be representative of an increase in roughness.
For ∆T15 (Fig. 3), Biolux showed smaller color
change compared with Vipi and Trilux. There was no
significant difference among distilled water, NaOCl
and 2% Ricinus communis solution. Color change
can occur due to extrinsic or intrinsic factors (11,17).
Extrinsic factors, such as absorption and adsorption,
can cause discoloration (11). According to Anil et al.
(17), other factors are also related to color change, such
as stain dehydration, water absorption, leakage, rough
Braz Dent J 23(1) 2012
20
M.X. Pisani et al.
surfaces, chemical and aging degradation, oxidation
during the double reaction of carbon-producing peroxide
composites, and permanent formation of pigments
following product degradation. The intrinsic factors
are related to the chemical stability of the material and
oxidation of the polymer matrices (17).
Having more discoloration in one substance
than in another is due to the various pigmentations
present in the characterization of teeth and absorption
and adsorption of solutions. Hydrophilic components,
such as HEMA, generally exhibit a greater color change
than hydrophobic materials (9,12). Acrylic resin teeth
composed by PMMA have a high conversion rate and
a low quantity of additional reagents, such as dibenzoyl
peroxide, that remain after the reaction and may cause
color instability (12). Biolux teeth presented less color
change. These teeth are probably fabricated with a
more hydrophobic monomer liquid, which absorb less
amount of solution are thus esthetically favorable. The
low susceptibility to staining is related to low solution
sorption (11,12). Therefore, Vipi and Trilux teeth may
present lower solubility than the others, resulting in
higher values than Biolux for ΔT15.
For ΔT183, there was no significant difference
among the solutions or among the teeth, so the presence
of cross-linked agents may have prevented changes due
to the resistance to solvents (12). ΔE value above 3.3
is clinically perceptible and unacceptable (18). In the
present study, all color changes observed in the denture
teeth were below this value, representing lack of visible
color change.
According to Robinson et al. (19), the different
layers of acrylic resin artificial teeth are affected in
different degrees of intensity for solutions and there is
a modification of the interstitial matrix. Surface clarity
and color of the object may influence color determination
(20). Thickness and smoothness of the specimen surface
can also influence color evaluation (20). Kanie et al. (20)
observed that the luminosity of acrylic resin decreases
as the material thickness increases.
One of the limitations of this study is that there are
some methodological problems for the detection of color
change in artificial teeth once that the oral environment is
hardly reproduced and spectrocolorimeter can spread the
light in different directions because the buccal face is not
flat. Moreover, few reports were found in the literature
using acrylic denture teeth (4,13) and Ricinus communis
(2,14) for comparison of results. Also, to overcome the
limitations of in vitro tests, the color change of acrylic
Braz Dent J 23(1) 2012
resin denture teeth should be evaluated intraorally. It
is important to point out that alterations did occur, but
the mean values were within the acceptable limits for
roughness, hardness and color change.
In conclusion, the solutions (distilled water,
1% NaOCl and Ricinus communis) and the protocols
of immersion (ΔT15 and ΔT183) caused alterations on
the hardness, roughness and color of the acrylic resin
denture teeth.
RESUMO
Este estudo avaliou a dureza Knoop, rugosidade e alteração de cor
de dentes artificiais após imersão em água, hipoclorito de sódio
1% e solução de Ricinus communis 2% (RC). Trinta espécimes
de dentes das marcas Vipi, Biolux e Trilux foram analisados. Os
testes de dureza, rugosidade e alteração de cor foram realizados
após a obtenção dos espécimes (T0) e após dois protocolos
de imersão nas soluções por 15 dias (Δ15) e 183 dias (Δ183). A
variação dos dados (ΔT) foi submetida à ANOVA e teste de
Tukey (p<0,05). Em ΔT15, Vipi apresentou aumento da dureza e
Biolux, a maior variação (p =0,01). RC causou o maior aumento
na dureza (p=0). RC causou o menor aumento na rugosidade
(p=0,005). Biolux apresentou a menor alteração de cor (p=0).
Em ΔT183, Trilux apresentou a maior variação na dureza. (p=0).
Biolux apresentou aumento na rugosidade (p=0). Não houve
diferença significante na alteração de cor entre dentes (p=0,06)
e entre soluções (p=0,08) após 183 dias de imersão. Todas as
soluções (água destilada, hipoclorito de sódio 1% e RC) causaram
alterações nas propriedades analisadas. Ambos os protocolos de
imersão causaram alterações nas propriedades analisadas.
ACKNOWLEDGEMENTS
The authors wish to thank Dr. Gilberto Chiérese for providing
the Ricinus communis solution.
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Received May 25, 2011
Accepted November 17, 2011
Braz Dent J 23(1) 2012
Denture teeth and Ricinus communis solution
ISSN 0103-6440
15
Effect of Experimental Ricinus communis Solution
for Denture Cleaning on the Properties
of Acrylic Resin Teeth
Marina Xavier PISANI
Ana Paula MACEDO
Helena de Freitas Oliveira PARANHOS
Cláudia Helena Lovato da SILVA
Department of Dental Materials and Prosthodontics, Ribeirão Preto Dental School,
USP -University of São Paulo, Ribeirão Preto, SP, Brazil
This study evaluated Knoop hardness, surface roughness and color alteration of artificial teeth for dentures after immersion in water,
1% sodium hypochlorite and an experimental solution of 2% Riccinus communis (RC). Thirty specimens of Vipi, Biolux and Trilux
were analyzed. Tests of Knoop hardness, surface roughness and color alteration were conducted immediately after specimen preparation
(T0) and after two immersion protocols for 15 days (ΔT15) and 183 days (ΔT183). Data variation (ΔT) were subjected to ANOVA and
Tukey’s test (p<0.05). At ΔT15, Vipi presented hardness increase and Biolux presented the highest variation (p=0.01). RC caused the
highest increase in hardness (p=0) and the lowest increase (p=0.005) in roughness. Biolux presented the lowest color alteration (p
=0). At ΔT183, Trilux underwent the highest hardness variation (p=0). Biolux presented an increase in roughness (p=0). There was no
significant differences in color alteration among the artificial teeth (p=0.06) and among solutions (p=0.08) after 183 days of immersion.
All solutions (distilled water, 1% sodium hypochlorite and 2% RC) caused alterations on the analyzed properties. Both immersion
protocols caused alterations on the analyzed properties.
Key Words: denture cleanser, Ricinus communis, acrylic denture teeth.
INTRODUCTION
Denture cleansing is important to increase
denture longevity, maintain the health of oral mucosa
and improve patient’s quality of life. Chemical
disinfectants for immersion have been widely used as
denture cleansers. It is essential that these cleansers have
bactericidal and fungicidal properties and effectively
remove organic and inorganic matter from denture
surface (1). Another important consideration is that the
mechanical and physical properties of the acrylic resin
and artificial denture teeth should remain unaltered after
denture cleansing. However, it has been shown that some
disinfectant solutions cause alterations in physical and
mechanical properties of denture base resins (2,3) and
artificial teeth (4). Some components of these solutions
can penetrate into the material and not be completely
eliminated by rinsing (5).
New formulations of denture cleansers are
welcome because until now an ideal denture cleanser
is not available. The World Health Organization has
encouraged the search for substances and products
derived from animal, vegetal and mineral sources. Many
plants are known for their medical and antimicrobial
properties and the efforts have been directed towards
the search of alternative and low cost cleaning products
that could be safely used by the population. One of these
plants is Ricinus communis or castor plant (division
Magnoliophyta, class Magnoliopside, sub-class Rosidae,
order Euforbiales, family Euforbiaceae), which is a
vegetal typically found in tropical climate areas. Because
of its climatic characteristics, Brazil has one of the largest
areas cultivated with Ricinus communis in the world (6).
The oil extracted from the Ricinus communis
seeds is used in the production of a detergent. In
Endodontics, this detergent has been tested as an
Correspondence: Profa. Dra. Cláudia Helena Lovato da Silva, Departamento de Materiais Dentários e Prótese, Faculdade de Odontologia de Ribeirão
Preto, Universidade de São Paulo, Avenida do Café s/n, 14040-904 Ribeirão Preto, SP, Brasil. Tel: +55-16-3602-4006. email: [email protected]
Braz Dent J 23(1) 2012
16
M.X. Pisani et al.
irrigating solution and has shown biocompatibility to
periapical tissues and antimicrobial, bactericidal and
antiinflammatory activity similar to sodium hypochlorite
(NaOCl) (7). The Ricinus communis detergent acts by
breaking sugar leakage of the cellular wall of pathogenic
microorganisms, consequently the loss of cytoplasmic
material leads to cell destruction (7,8). Based on this, an
experimental solution of 2% Ricinus communis has been
developed to be used as a denture cleanser. In addition to
its antimicrobial and cleaning potential, it is important to
analyze whether this solution can affect the properties of
denture components, such as the acrylic denture teeth.
Three important properties to be analyzed are
hardness, surface roughness and color change of acrylic
denture teeth. Hardness has been used as a measurement
to predict wear resistance (9), roughness is related to
biofilm adhesion (10) and color change is related to
aesthetics and is an indicative of the serviceability of
the material (11). Therefore, the aim of this study was
to evaluate the effect of 2% Ricinus communis solution
on Knoop hardness, surface roughness and color change
of three brands of acrylic resin denture teeth compared
with 1% NaOCl after two immersion protocols. The null
hypothesis tested is that 2% Ricinus communis has no
effect on the hardness, roughness and color change of
the acrylic resin denture teeth.
MATERIAL AND METHODS
Specimen Preparation and Groups
no difference existed between hardness of the surface
layer and the worn palatal surface (4). Moreover,
it is important to analyze the inner surface, as the
outer surface or enamel layer of denture teeth is often
removed due to many reasons, such as masticatory
wear, or mostly occlusal adjustments or alterations of
the occlusal scheme by the dentist (9). The color change
was measured on the buccal face instead of the palatal
face because aesthetics is important in this area.
The thickness in the cervical, middle and incisal
areas was 4 mm, 3.3 mm and 2 mm, respectively, as
confirmed with an electronic caliper (CD-6” CSX-B;
Mitutoyo South American Ltda., Suzano, SP, Brazil).
Ninety specimens, 30 of each brand, were
randomly assigned to 3 groups of immersion in 200
mL of the solutions: Negative control group (distilled
water at 37oC); positive control group (1% NaOCl;
Asfer Chemistry Ind. Ltda, São Paulo, SP, Brazil) and
experimental group (2% Ricinus Communis solution,
Chemistry Institute, University, São Carlos, SP, Brazil).
Experimental Period
The hardness, roughness and color were assessed
immediately after specimen preparation (baseline)
and after different immersion periods. The specimens
were immersed in each of the three solutions for 15
consecutive days to simulate 3 years following a denture
cleansing regimen of 20 min daily (∆T15) (2). After this
period, new tests of color, hardness and roughness were
conducted. The specimens were then immersed for 183
consecutive days (∆T183) to simulate 1.5 year of use
following a regimen of 8 h (overnight) daily (2). After
this period, new tests were performed. The immersion
solutions were changed once a day for both protocols.
Three commercially available brands of acrylic
resin denture teeth were used; their names and bath
numbers are presented in Table 1. The maxillary central
incisor of largest size of each brand was selected to
establish a standard for comparison and
because these teeth are located in an esthetic
Table 1. Acrylic resin denture teeth.
region of the mouth.
The artificial teeth had their palatal face
Commercial
Model
Manufacturer
brand
flattened with a sequence of 180-, 220-, 360and 400-grit silicon carbide papers (Norton
28
Dental Vipi Ltda,
- Saint-Gobain Abrasivos Ltda., Guarulhos,
VipiDent Plus
Pirassununga, SP, Brazil
Color: 66
SP, Brazil). The buccal face was not altered.
Surface roughness and Knoop hardness tests
V17
Dental Vipi Ltda,
needed a flat surface because the indentor
Biolux
Pirassununga, SP, Brazil
Color: 66
tip for both tests must be perpendicular to
the surface to be analyzed. According to the
E5
Ruthinium Group Badia
manufacturers, the denture teeth tested have
Trilux
Polesine, Rovigo Italy
Color: 66
a uniform composition. It was assumed that
Braz Dent J 23(1) 2012
Batch
number
6501
6907
6600
Denture teeth and Ricinus communis solution
17
Analysis of Knoop Hardness and Surface Roughness
Knoop Hardness
Knoop hardness was measured with a Shimadzu
microhardness tester (model HMV-2; Shimadzu
Corporation, Kyoto, Japan) with a load of 25 g for 5 s.
The roughness test was performed using roughness tester
(SJ-201P; Mitutoyo Corp, Kawasaki, Japan).
For both tests, teeth were fixed on a #9 wax
plate (Lysanda Inc., Presidente Prudente, SP, Brazil).
The palatal face was stable and perpendicular to the
Knoop and roughness indentor tip. The surface of each
specimen was divided into three equal parts and three
measurements were made in each part to obtain the mean.
For ∆T15, statistically significant difference
was found among the teeth (p=0.01) and among the
solutions (p=0), but not for interactions (p=0.41).
Only Vipi presented hardness increase; Biolux and
Trilux presented hardness decrease and there were no
statistically significant difference among them. Ricinus
communis solution caused hardness increase; distilled
water and NaOCl caused hardness decrease (Fig. 1).
For ∆T183, there was statistically significant
difference among teeth (p=0) and among the solutions
(p=0.01), but not for interactions (p=0.15). All tooth
brands underwent hardness decrease. Trilux differed
significantly from Vipi and Biolux, and presented the
highest hardness variation. All solutions caused hardness
decrease. Ricinus communis solution was significantly
different from distilled water and NaOCl, and caused
the smallest hardness variation (Fig. 1).
Analysis of Color Change
For color measurements of acrylic resin teeth,
a reference mark was used for placing the measuring
port of the instrument on the same location on the
specimen for repeated measures, and a silicone device
was developed (Zetalabor Zhermack, Rovigo, Italy) for
inserting the specimen insertion in the spectrocolorimeter
opening. The spectrocolorimeter (BYK-Gardner
GmbH - 07/2002, Geretsried, Germany) was calibrated
according to the manufacturer’s instructions before
each measurement period using the white calibration
cap supplied by the manufacturer. Color change (ΔE)
were calculated by measuring tristimulus values using
the CIE L*a*b* Color Scale.
Data Analysis
Statistical analysis of hardness, roughness and
color change was carried out SPSS statistical software
(SPSS Inc., Chicago, IL, USA).
Variation of hardness and roughness data at
both evaluation periods was calculated by subtracting
the values obtained after immersion for 15 days (∆T15)
and 183 days (∆T183), respectively, from those obtained
at baseline. Therefore, negative values represented a
reduction and positive values an increase of the variable.
A two-way ANOVA was performed using materials and
immersion solutions as independent factors. Multiple
comparisons were done by Tukey’s test (α=0.05).
RESULTS
Comparisons among means and the respective
standard deviations (SD) are presented in Figures 1-3.
Surface Roughness
For ∆T15, statistically significant difference was
found only among the solutions (p=0.005). Ricinus
communis solution caused roughness increase. Distilled
water and NaOCl caused roughness decrease and were
statistically similar (Fig. 2).
∆T183, significant differences were found only
among the teeth (p=0). Vipi and Trilux presented decrease
of roughness. Biolux was statistically different from Vipi
and Trilux, and presented increase of roughness (Fig. 2).
Color Change
For ∆T15, significant differences were found
only among the teeth (p=0), where Biolux presented
the smallest color change. For ∆T183, there were no
statistically significant differences among the teeth
(p=0.06), solutions (p=0.08) or significant interactions
(p=0.16) (Fig. 3).
DISCUSSION
The present study evaluated the effect of 2%
Ricinus communis solution on hardness, roughness and
color change of three brands of acrylic resin denture
teeth in comparison with 1% NaOCl and distilled water
as a control group. The null hypothesis was rejected as
all solutions caused some alteration on the physical and
Braz Dent J 23(1) 2012
18
M.X. Pisani et al.
mechanical properties analyzed.
The acrylic denture teeth used in this study are
composed of PMMA (polymethyl metracrylate) and
EDMA (dimethacrylate of polymerized ethylene glycol),
which is a cross-linking agent. An optimal amount of
cross-linking can improve the mechanical properties
of acrylic resin denture teeth, reducing the tendency to
craze (form pre-cracks) under stress and the solubility to
organic solvents (12). Trilux artificial teeth have triple
press (incisal, cervical and dentin), are made of acrylic
resin of high molecular weight combined with the use
of double cross-linking (DCL) system and have organic
modified ceramics (Ormocer®). Biolux teeth have double
press (body and enamel) and are made of polymer of
high molecular weight combined with the use of DCL.
Vipi teeth have double press (body and enamel) and a
Figure 1. Comparison of means (SD) of Knoop hardness for ∆T15 and ∆T183. Different letters indicate statistically significant difference
at 0.05. SH= sodium hypochlorite; RC= Ricinus communis.
Figure 2. Comparison of means (SD) of roughness for ∆T15 (solutions) and ∆T183 (teeth). Different letters indicate statistically significant
difference at 0.05. SH= sodium hypochlorite; RC= Ricinus communis.
Figure 3. Comparison of means (SD) of color alteration (∆E) of the artificial teeth for ∆T15. Different letters indicate statistically
significant difference at 0.05.
Braz Dent J 23(1) 2012
Denture teeth and Ricinus communis solution
linear and not interpenetrate polymer chain.
There are in the literature few studies analyzing
the effects of denture cleansers in artificial denture teeth
(4,13). The effects of 2% Ricinus communis solution in
mechanical and physical properties of denture acrylic
resin (2) and denture liners (14) have already been
investigated using the same cleansing protocols of the
present study. In acrylic resins, the Ricinus communis
solution caused alterations on the properties and was
not superior to 1% NaOCl (2). However, the Ricinus
communis solution had less effect on the properties of
silicone-based denture liners compared to 1% NaOCl
(14). The observation of the effect of denture cleaners
after long period of use (3 years and 1.5 year) is also
important because patients rarely change their prosthesis
before this period. The regimens used were 15 min
daily immersion and overnight daily immersion; both
recommended procedures by the dentists to their patients
(2,14).
The results regarding Knoop hardness showed for
∆T15 (Fig. 1) that Biolux and Trilux underwent hardness
decrease, while Vipi underwent hardness increase and
Ricinus communis solution was the main responsible for
the hardness increase in comparison with the baseline
values. The hardness increase for Vipi can be explained,
perhaps, by the fact that they are less resistant to the
loss of plasticizers and do not have DCL chains, which
reduce their resistance.
After simulation of 1.5 year of overnight
immersion (∆T183), all tooth brands presented a decrease
in hardness (Fig. 1); Trilux underwent the highest
reduction, followed by Biolux and Vipi. These results
are in accordance with those of Campanha et al. (4)
who also worn the occlusal teeth surface and found
a reduction in hardness of Trilux after immersion for
7 days in 1% NaOCl The Ricinus communis solution
caused the lowest hardness reduction after this period
of immersion (Fig. 1). Pavarina et al. (13) found that
the immersion in distilled water decreased hardness
of the acrylic denture teeth tested. The absorption of
water and aqueous cleansers such as NaOCl and Ricinus
communis caused reduction in hardness due to the fact
that these solutions could act as plasticizers. Similar to
what happens with acrylic resin, in denture teeth basically
composed of the same material, small molecules of water
diffuse into the polymer mass and cause the relaxation
of polymer chains, consequently reducing the hardness
of artificial teeth (15). Probably, microcracks formed
during the wear of the palatal face could have facilitated
19
the infiltration of solutions, accelerating the process of
PMMA plasticizing (16).
Teeth composed by double cross-linked agents
should promote, in theory, a decrease in fluid diffusion
to the polymer because of their inseparable chains and
higher resistance. However, Trilux teeth showed the
highest reduction in hardness for ∆T183 (Fig. 1), perhaps
due to some intrinsic factor related to their composition
or their triple press. For polymer based materials, there
may be also several other factors that may influence
the hardness values including time and speed of elastic
recovery (12).
For ∆T15, there was no roughness difference
among the tooth brands, only among the solutions.
(Fig. 2). The 2% Ricinus communis solution caused an
increase in roughness (Fig. 2), while distilled water and
NaOCl caused reduction in this property. Pisani et al.
(2) also found roughness increase in acrylic resins after
immersion in Ricinus communis and attributed this result
to a tick and sticky film formed on specimen surface. In
Endodontics, the use of Ricinus communis solution as
an as irrigant increased root canal dentin permeability
due to its low superficial tension and the moisturizing
capacity, which increases the contact of the solution
with tooth surface (6,7). Although this consideration
is not related to acrylic denture teeth, it is necessary to
investigate the action of this solution on the permeability
and degradation of organic matrix present in artificial
teeth, which could represent an increase in roughness.
Additional studies concerning the mechanism of action
of Ricinus communis solution should be developed in
the future.
For ∆T183 (Fig. 2), only Biolux presented
roughness increase, regardless the solution. After
immersion in solutions, Biolux teeth were less resistant
to the action of solvents, which may have allowed the
loss of components such as plasticizers and exposure
of the layers polished with smaller grain sandpapers,
creating porosities in the polymer mass, which could
be representative of an increase in roughness.
For ∆T15 (Fig. 3), Biolux showed smaller color
change compared with Vipi and Trilux. There was no
significant difference among distilled water, NaOCl
and 2% Ricinus communis solution. Color change
can occur due to extrinsic or intrinsic factors (11,17).
Extrinsic factors, such as absorption and adsorption,
can cause discoloration (11). According to Anil et al.
(17), other factors are also related to color change, such
as stain dehydration, water absorption, leakage, rough
Braz Dent J 23(1) 2012
20
M.X. Pisani et al.
surfaces, chemical and aging degradation, oxidation
during the double reaction of carbon-producing peroxide
composites, and permanent formation of pigments
following product degradation. The intrinsic factors
are related to the chemical stability of the material and
oxidation of the polymer matrices (17).
Having more discoloration in one substance
than in another is due to the various pigmentations
present in the characterization of teeth and absorption
and adsorption of solutions. Hydrophilic components,
such as HEMA, generally exhibit a greater color change
than hydrophobic materials (9,12). Acrylic resin teeth
composed by PMMA have a high conversion rate and
a low quantity of additional reagents, such as dibenzoyl
peroxide, that remain after the reaction and may cause
color instability (12). Biolux teeth presented less color
change. These teeth are probably fabricated with a
more hydrophobic monomer liquid, which absorb less
amount of solution are thus esthetically favorable. The
low susceptibility to staining is related to low solution
sorption (11,12). Therefore, Vipi and Trilux teeth may
present lower solubility than the others, resulting in
higher values than Biolux for ΔT15.
For ΔT183, there was no significant difference
among the solutions or among the teeth, so the presence
of cross-linked agents may have prevented changes due
to the resistance to solvents (12). ΔE value above 3.3
is clinically perceptible and unacceptable (18). In the
present study, all color changes observed in the denture
teeth were below this value, representing lack of visible
color change.
According to Robinson et al. (19), the different
layers of acrylic resin artificial teeth are affected in
different degrees of intensity for solutions and there is
a modification of the interstitial matrix. Surface clarity
and color of the object may influence color determination
(20). Thickness and smoothness of the specimen surface
can also influence color evaluation (20). Kanie et al. (20)
observed that the luminosity of acrylic resin decreases
as the material thickness increases.
One of the limitations of this study is that there are
some methodological problems for the detection of color
change in artificial teeth once that the oral environment is
hardly reproduced and spectrocolorimeter can spread the
light in different directions because the buccal face is not
flat. Moreover, few reports were found in the literature
using acrylic denture teeth (4,13) and Ricinus communis
(2,14) for comparison of results. Also, to overcome the
limitations of in vitro tests, the color change of acrylic
Braz Dent J 23(1) 2012
resin denture teeth should be evaluated intraorally. It
is important to point out that alterations did occur, but
the mean values were within the acceptable limits for
roughness, hardness and color change.
In conclusion, the solutions (distilled water,
1% NaOCl and Ricinus communis) and the protocols
of immersion (ΔT15 and ΔT183) caused alterations on
the hardness, roughness and color of the acrylic resin
denture teeth.
RESUMO
Este estudo avaliou a dureza Knoop, rugosidade e alteração de cor
de dentes artificiais após imersão em água, hipoclorito de sódio
1% e solução de Ricinus communis 2% (RC). Trinta espécimes
de dentes das marcas Vipi, Biolux e Trilux foram analisados. Os
testes de dureza, rugosidade e alteração de cor foram realizados
após a obtenção dos espécimes (T0) e após dois protocolos
de imersão nas soluções por 15 dias (Δ15) e 183 dias (Δ183). A
variação dos dados (ΔT) foi submetida à ANOVA e teste de
Tukey (p<0,05). Em ΔT15, Vipi apresentou aumento da dureza e
Biolux, a maior variação (p =0,01). RC causou o maior aumento
na dureza (p=0). RC causou o menor aumento na rugosidade
(p=0,005). Biolux apresentou a menor alteração de cor (p=0).
Em ΔT183, Trilux apresentou a maior variação na dureza. (p=0).
Biolux apresentou aumento na rugosidade (p=0). Não houve
diferença significante na alteração de cor entre dentes (p=0,06)
e entre soluções (p=0,08) após 183 dias de imersão. Todas as
soluções (água destilada, hipoclorito de sódio 1% e RC) causaram
alterações nas propriedades analisadas. Ambos os protocolos de
imersão causaram alterações nas propriedades analisadas.
ACKNOWLEDGEMENTS
The authors wish to thank Dr. Gilberto Chiérese for providing
the Ricinus communis solution.
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Received May 25, 2011
Accepted November 17, 2011
Braz Dent J 23(1) 2012
