color stability of different denture teeth materials: an ... · color stability of different...
TRANSCRIPT
193
Journal of Oral Science, Vol. 43, No. 3, 193-205, 2001
Color stability of different denture teeth materials:
an in vitro study
Lamia Mutlu-Sagesen§, Gulfem Ergun§, Yalgln Ozkan† and Bulent Bek§
§Department of Prosthodontics, Faculty of Dentistry, Gazi University, Ankara, Turkey
†Department of Pharmaceutical Technology, Gulhane Military Medical Academy,
Ankara, Turkey
(Received l 3 March and accepted 6 September 2001)
Abstract: The aim of this in vitro study was to
compare the color stability of commercially available
porcelain, reinforced acrylic, and conventional acrylic
denture teeth materials used in removable prostheses.
Two brands of porcelain (Unilux-Enta Lactona-Holland
and Vivoperl-Ivoclar-Liechtenstein), 2 brands of
reinforced acrylic (Optodent-Bayer-Germany and
Ivolek-Ivoclar-Liechtenstein), and 2 brands of
conventional acrylic (Isodent-Guney Dis Deposu-Turkey
and Samed-Turkey), were made, for a total of 6 different
denture teeth groups. Denture teeth were subjected to
3 staining solutions (filtered coffee, tea, and cola) and
distilled water. From each group of denture teeth, 4 sets
of maxillary anterior denture teeth were immersed in
each of the 4 solutions. The color values of denture teeth
were measured colorimetrically with the Gardner XL
20 Tristimulus Colorimeter (Gardner Lab. Inc.,
Bethesda, Maryland, USA). Color changes were
characterized in the CIEL*a*b* color space. Color
change values were determined after 1 day, 1 week, 2
weeks, and 4 weeks. The color difference values were
calculated and then evaluated by two-way ANOVA
statistically. The filtered coffee solution was found to
be more chromogenic than the other 2 staining solutions,
while porcelain denture teeth materials were more
color stable. Assuming the color change of ĢE* < 1.0
as a discernible limit and ĢE* = 3.3 as an acceptable
value, the filtered coffee, tea, and cola had slight staining effects on all 6 groups of denture teeth. (J. Oral Sci. 43, 193-205, 2001)
Key words : color stability; acrylic denture teeth;
porcelain denture teeth.
Introduction
Increased demand for aesthetic dentistry has been coupled with a rapid rate of the development of new
denture materials. In partially or completely edentulous
patients, function, phonetics and aesthetics can be provided with removable dentures. These kind of dentures should
also improve the psychological state of edentulous patients
(1). In removable dentures, aesthetics is best obtained by
denture teeth, either porcelain or acrylic resin. While manufacturing a removable denture, the denture teeth can
be selected according to the demands and the financial state of the patient. Rapid development of the dental material
industry could represent many available denture teeth alternatives to dentists. These alternatives might be
porcelain, reinforced acrylic, conventional acrylic denture teeth or combinations of these 3 main groups (2).
Conventional acrylic teeth have been customarily employed as artificial denture teeth attached to a denture
base, because it is relatively easy to arrange such teeth and adjust their occlusion. Failure or success of any aesthetic
approach depends on the color stability of the material. Color stability, the property of a material to retain its color
over a period of time and in a specified environment, is an important physical property of many materials used in dentistry (3). Conventional acrylic teeth are more
Correspondence to Dr. Lamia Mutlu-Sagesen, 35. sokak 7/13 06500 Bahcelievler, Ankara, Turkey Tel: +90-312-215-08-68 E-mail address: [email protected]
This study was presented as an oral presentation at the TDA and FDI Joint Congress, Istanbul-Turkey, 21-26/6/1999.
194
susceptible to abrasion and pigments than porcelain teeth
and tend to become gradually discolored by pigments
contained in drinks with long-term use, causing an aesthetic
failure.
To overcome these aesthetic and abrasive shortcomings
of conventional acrylic denture teeth, reinforced acrylic
denture teeth and porcelain denture teeth have been
developed and are now widely employed clinically. Though
reinforced acrylic denture teeth constructed of hard plastic
are still susceptible to pigments, dentists have observed
the aesthetics of removable partial dentures made with such
acrylic teeth gradually become impaired in many patients.
While a number of authors have reported on the color
changes and staining of acrylic denture teeth materials under
Table 1 Denture teeth used in this study
Table 2 Solutions used in this study
195
conditions of accelerated aging and exposure to oral fluids
(1,2,4,5), the literature contains few references to the color
stability of both acrylic and porcelain denture teeth materials
(2).
The purpose of this in vitro study was to analyze the
discoloration of commercially available porcelain,
reinforced and conventional acrylic denture teeth used in
removable dentures when exposed to common dietary
fluids using colorimetric techniques.
Materials and Methods
In this study, 2 brands of porcelain [Unilux (UL) and
Vivoperl (VP)], 2 brands of reinforced acrylic [Optodent
(OD) and Ivolek (IL)] , and 2 brands of acrylic denture teeth
[Isodent (ID) and Ultraplus (UP)] were selected. The trade
names, manufacturers, types, shades, forms, and codes of
the denture teeth used in this study are given in Table 1.
Denture teeth were subjected to 3 staining solutions
[filtered coffee (FC), tea (T), cola (C)], and distilled water
(DW) as detailed in Table 2.
From each brand of denture teeth, 4 sets of maxillary
anterior denture teeth were used in this study. Each denture
tooth was bonded on to the modelling pink wax plate
having dimensions of 15 mm •~ 15 mm from the palatinal
side. From each brand of denture teeth, a set of maxillary
anterior denture teeth was prepared for each of the 4
different solutions. Each specimen was suspended in the
solutions with dental floss, so that it did not contact the
container or other specimens. Before immersing each set
of denture teeth into the solutions, they were stored in
distilled water at 37 •} 1•Ž for 24 hours. Then, a set of
maxillary anterior denture teeth was immersed in each of
4 different solutions at 37•}1•Ž for a month in a dark room.
Color measurements were taken just prior to immersion
(Control) and after 1 day, 1 week, 2 weeks, and 4 weeks.
Solutions were freshened at the beginning of every week.
In addition, to reduce the precipitation of particles within
solutions, solutions were stirred twice a day.
Before each measurement, denture teeth were
ultrasonically cleaned(Ultrasonic Cleaner, HS Health-
Sonics CorPoration) in non-ionic multipurpose ultrasonic
solution(HS Health-Sonics Corporation)for 5 min, and
dried using a tissue paper. This cleaning procedure removed
the stains that were not strongly adhered to the samples'
surfaces. Thus, overall color change as a result of entire
matrix discoloration and stain adsorption on the samples'
surfaces was measured.
These denture teeth were tested by the XL-20 Tristimulus
Colorimeter(Gardner Lab. Inc., Bethesda, Maryland,
USA)immediately after removal from the distilled water.
The testing procedure was done with the evaluation of the
light directed and reflected from the tooth surface with a
constant angle. Using a tungsten-halogen lamp as a light
source, all measurements were done according to the CIE
standards(6), from incisal, middle, and cervical thirds of
these denture teeth. These 3 regions were measured in every
tooth.
Before each measurement session, the colorimeter was
calibrated according to the manufacturer's instructions by
using the supplied white calibration standard.
Values were recorded using the Commision
Internationale d'Eclairage(CIE)L*a*b*color system(6).
The CIEL*a*b*system is an approximately uniform color
space with coordinates for lightness, i.e.,white-black(L*),
redness-greenness(a*), and yellowness-blueness(b*)(Fig.
1).The L*, a*, and b*values of each sample(tooth)before
immersion(Control)and after immersion at each specified
time interval(1D,1W,2W, and 4W)were measured 3 times
from insizal, middle, and cervical thirds of these denture
teeth by the same person(5,7,8). The mean values ofΔL*,
Δa*,andΔb*after 3 measurements were automatically
calculated by the colorimeter and recorded.Color difference
(ΔE*)was calculated from the meanΔL*,Δa*, andΔb*
values for each tooth with the following formula(6),
where ĢL*, Ģa*, and Ģb* are the differences in L*, a*,
Fig. 1 Coordinates of the color space: L* (white-black), a* (red-green), and b* (yellow-blue).
196
and b* values before and after immersion at each time
interval.
The mean ĢE* value calculated from the 3 measurements
of each tooth were obtained for each solution and each
group of denture teeth.
Average color changes after 1 day, 1 week, 2 weeks, and
4 weeks were also determined. The mean and the standard
deviation values were calculated for each set of teeth and
each solution.
The color system employed in this analysis was L*, a*,
and b* of CIE1986L*a*b* color difference (ĢE*) between
the value at each observation point and the control value
(2). The value of color difference was multiplied by 0.92
in order to get the value of the National Bureau of Standards
(NBS) (2,9,10). Based on the NBS rating system (2,10), which is the way a color change is evaluated by the human eye (Table 3), color changes of the 6 artificial tooth types in the 4 different solutions were determined.
According to the design of the experiment, the most
appropriate statistical analysis is a repeated-measure analysis of variance (ANOVA), with 2 between-units factors (6 materials and 4 solutions) and 1 within-units
factor (5 measurement times). The null hypothesis was that the main effects of the factors involved (solution, material,
and time) as well as possible interactions between them, were equal to zero. Further analyses were carried out at
particular times and for particular materials and solutions. Two-way ANOVA at each immersion time (1 day, 1 week, 2 weeks, and 4 weeks) was used to test the significance
of the factors involved (denture teeth and solutions). These
analyses were performed with the program SPSS for Windows (7.5.1).
Results Table 4 shows the color conditions of 6 denture tooth
groups observed before immersion.
Table 3 NBS Rating
Table 4 Color of denture teeth before immersion
197
Table 5 Color of denture teeth after immersion in filtered coffee
Table 6 Color of denture teeth after immersion in tea
Table 7 Color of denture teeth after immersion in cola
198
The coloring conditions of 6 denture tooth groups after
1 day, 1 week, 2 weeks, and 4 weeks immersed in the
filtered coffee, tea, cola, and distilled water are shown in
Tables 5, 6, 7, and 8 and also in Figs. 2, 3, 4, and 5,
respectively. The values of color difference (ĢE*) and
their corresponding NBS values for all 6 groups of denture teeth in 4 solutions are given in Table 9.
The results of the repeated-measure ANOVA indicated that the effects of all 3 factors, as well as all of the possible
interactions between them, were statistically significant (P
Table 8 Color of denture teeth after immersion in distilled water
Fig. 2 Color of denture teeth immersed in filtered coffee.
Fig. 3 Color of denture teeth immersed in tea.
199
Fig. 4 Color of denture teeth immersed in cola.
Fig. 5 Color of denture teeth immersed in distilled water.
Table 9 Color differences of denture teeth
200
<0.0001).Material-solution interaction was also significant
(P<0.0001).Further analyses were carried out at particular
times and for particular materials and solutions. Two-way
ANOVA revealed that denture teeth material and staining
solutions are factors that significantly(P<0.0001)affect
the staining resistance at each immersion period.The
interaction of these factors was also significant(P<
0.0001)at each time period. Table g shows the meanΔE*
values and standard deviations of denture teeth after the
staining procedure at each immersion period.
At the 1-day immersion period, the two-way ANOVA
indicated that UP material Showed the highest ΔE*value
in the filtered coffee solution, and OD material had the
lowest ΔE* value in the distilled water solution(P<
0.0001).Regarding the staining capacity of the solutions
used, the filtered coffee and the cola solutions seem to
provoke greater color changes respectively in UP and ID
materials compared to the tea or the distilled water solutions
(Fig.6).
At the second immersion period(1 week), UP material-
filtered coffee solution combination had the highest ĢE*
value (1.045) compared to the other combinations (P <
0.0001) (Fig. 7).
At the third immersion period (2 weeks), the UP material
combined with 2 staining solutions (filtered coffee and cola)
exhibited a significant color difference (P < 0.0001). This
difference was more than double that of the analogous
combinations of the UL, VP, and OD materials. In the tea
and the distilled water solutions, almost all of the materials
showed similar behavior (Fig. 8).
After 4 weeks of immersion in staining solutions, the
UP material in the filtered coffee and the ID material in
the cola reached the highest AE* value of this period (-
0.950). The tea solution also had almost the same high
staining effect on all of the materials. Ranging the values
from 0.180 (ID material) to 0.295 (OD material), the
distilled water solution had the lowest AE* values of this
period (Fig. 9).
The cumulative results of this in vitro study are
summarized in Fig. 10. After a period of 4 weeks, the most
Fig. 6 Color differences of denture teeth immersed in solutions
after 1 day.
Fig. 7 Color differences of denture teeth immersed in solutions
after 1 week.
Fig. 8 Color differences of denture teeth immersed in solutions
after 2 weeks.
Fig. 9 Color differences of denture teeth immersed in solutions
after 4 weeks.
201
staining solution was filtered coffee while the least staining
one was, as expected, distilled water (P < 0.0001).
Discussion The physical properties of porcelain denture teeth may
be best shown when they are compared with the properties
of plastic denture teeth and, when possible, with those of natural teeth. These properties, however, often are so
radically different that they cannot be measured with the same equipment or compared quantitatively (11).
Methodology problems are inherent to the evaluation of color change in vitro, because it is not easy to reproduce the exact conditions of the oral environment in the
laboratory (12). Dentists often come face to face with a
problem of tooth discoloration and because of this phenomenon, filtered coffee, tea and cola were chosen as test agents for they had shown to have greater staining ability on restorations and natural tooth structure (13-16).
Clinical discoloration of aesthetic materials may be
caused by intrinsic and extrinsic factors (17,18). Intrinsic factors are related to the material's chemical stability and
oxidation of polymer matrices. The intrinsic color can be
altered as a result of accelerated aging conditions, mimicking sunlight and water effects, such as ultraviolet
irradiation, temperature, and humidity changes (18-20). Extrinsic factors producing discoloration include staining
by adsorption or absorption of stains or colorants
(15,17,21,22). Colored solutions, coffee, tea, beverages, chlorhexidine, cola and nicotine, are known to cause
staining of oral tissues and dental restorations. Among these, coffee, tea and cola are known to cause heavy staining of
dental restorations and appliances (1,12-6,21-27). Discoloration from staining solutions is found to be
considerably more intensive in terms of coloring than by ultraviolet light or distilled water alone (20,28).
To detect color differences, "evaluation by observation" and "evaluation by color analysis instruments" methods have been used (4,5,15,16,20,22,29,30). In this study, the
latter method was preferred because it is a sensitive and objective method for investigating color change (21,22).
This method achieves a reproducible means for determining when change in color occurs below visual perception levels (7,31). Investigators (7,32) have evaluated the
performance of devices used for color analysis. These authors concluded that all the instruments were able to
assess color with precision, although the measurements varied somewhat depending on the instrument used and the type of material surface being measured. It was shown
that a photometric tristimulus colorimeter had the best overall performance for determining color even on porcelain
surfaces (32). In dentistry, a discoloration that is more than
perceptible (ĢE* < 1.0) will be refered to as acceptable up
to value ĢE* = 3.3 which is considered to be the upper limit
of acceptability in subjective visual evaluations. Color
changes above this level will be refered to as unacceptable
(22).So, none of these denture teeth tested in this study
have shown an unacceptable color change(1.058≧ΔE*
≧0.112),i.e. greater than 3.3.
It is known that obtaining conditions of the oral
environment in vitro is not easy. To simulate in vivo
conditions in this study,3 different coloring solution
(filtered coffee, tea, cola)and the distilled water were
used at a constant temperature of 37±1℃ (14-17,
23,24,27,33-37).Many investigators who evaluated the
coloration effect of tea, coffee, nicotine, erythrosine and
other drinks(8,12-17,21-25,27,28,33-38)and of time-
lapsed artificial aging methods(17-20,28,31,39)either
on natural teeth or on aesthetic dental materials. However,
few investigators compared the color stability of restorative
dental materials and denture tooth materials under in vivo
conditions in their studies(5,7,40).
In general, the results of this in vitro study are in
agreement with earlier works(16,35,38), but it has to be
taken into consideration that the type and the geometry of
materials, the types of solutions and the systematic
techniques of colorimetric instruments were different.
In previous in vitro studies, many investigators(12,22,26)
compared the staining effect of coffee and tea, and on the
contrary to our findings, they reported that the tea had a
superior discoloration effect on polymeric dental materials
than the coffee. Um and Ruyter(22)reported that the tea
produced a yellow-brown stain while coffee stain was
yellowish. The discoloration from the tea was probably due
to adsorption of polar colorant from the tea at the surface
of composite resin materials. However, in the present
Fig. 10 Color differences of denture teeth immersed in
solutions after 4 weeks in general.
202
study and other studies (16,21,23,24,37) the coffee was found to be a more chromogenic material than the tea. The
preparation and concentration of the coffee and the tea may change the results. The solutions used in the present study were prepared closer to "real" drinks. The discoloration
from the coffee was due to both surface adsorption and absorption of colorants. The less polar colorants from the coffee had penetrated into the materials, probably because
the colorants were compatible with the polymer matrices of the composite resin materials. The reason color
differences of acrylic denture teeth, either conventional or reinforced, were higher than the porcelain denture teeth
in the filtered coffee is considered to be the result of relatively large water sorption value for the former group.
In in vitro color stability studies, a period of 4 weeks immersion may be considered to be too long. However,
to reach the cumulative staining results of these solutions,
it was decided to continue testing until the end of a period
of 4 weeks (2,18). The color difference values of this in vitro study were
converted into NBS units in order to be able to make a
comparison in the clinics. Based on the NBS rating system
(Table 9), UL, VP, and OD denture teeth showed extremely slight changes and IL, ID, and UP materials which showed
only slight changes in color after 4 weeks in the filtered coffee. Thus, the color change of porcelain (UL and VP) and one of the reinforced acrylic (OD) denture teeth in the
filtered coffee were less than that of the reinforced acrylic denture teeth (IL), and conventional acrylic denture teeth
(ID and UP). Moreover, the UL, VP, OD, and IL denture teeth showed extremely slight changes after 1 day, 1 week, 2 weeks, and slight changes after 4 weeks in the tea solution. The ID denture teeth revealed extremely slight
changes after 1 day and 4 weeks, and slight changes after 1 and 2 weeks, whereas the UP denture teeth exhibited slight
changes after 1 day and 1 week and extremely slight changes after 2 weeks and 4 weeks in the tea solution. Thus,
the color change of the porcelain (UL and VP) and the reinforced acrylic (OD and IL) denture teeth in tea were less than that of the conventional acrylic (ID and UP)
denture teeth. When denture teeth after the filtered coffee immersion were compared with those after the tea
immersion, the filtered coffee had a greater tendency to color acrylic denture teeth than the tea, and the tea had a
greater tendency to color porcelain denture teeth than the filtered coffee.
According to the NBS rating system (Table 9),
conventional acrylic denture tooth (ID and UP) specimens revealed color difference values greater than reinforced
acrylic and porcelain denture tooth specimens in the cola solution. The color changes of ID specimens after 1 day
and 4 weeks and those of UP specimens after 1 week and 2 weeks in the cola were considered as slight changes.
Finally, as expected, all of the denture tooth specimens exhibited extremely slight color changes in the distilled
water. As seen in Fig. 10, for one of the reinforced acrylic
denture teeth (IL material) and one of the conventional
acrylic denture teeth (UP material), the filtered coffee
produced the highest staining effect; while for the other conventional acrylic denture teeth (ID material) it was the cola and for porcelain denture teeth (UL and VP
materials) and the other reinforced acrylic denture teeth
(OD material), it was the tea. For all 6 groups of denture teeth materials the distilled water, as expected, exhibited the least color difference means.
The predisposing factors for staining of aesthetic dental
materials are: contamination of materials, porosity
depending on the technique, insufficient oral hygiene, dietary habits, surface failures, and polishibility of the
materials (1,13,14,20,22,28,41). Comparing the conventional acrylic denture teeth group
with the other 2 groups, color change of the former group was greater than those of the latter in all 3 staining solutions
(filtered coffee, tea, and cola). Rough surfaces mechanically retain surface stains more than smooth surfaces. To achieve less color change, special attention should be paid to
obtain a perfect surface finish. Roughening of the surface caused by wear and chemical degradation can also increase extrinsic staining (17).
Although dental porcelain is thought to be a color-stable aesthetic material, in previous studies (31,34) and also in
the present study, surprisingly, porcelain material was found to be stained by the coloring solutions. It is well-known that the integrity of the glaze of a dental porcelain
restoration decreases the roughness of the porcelain surface and thus minimizes staining. However, occlusal wear or
the omission of a proper porcelain adjustment protocol may leave an unglazed porcelain surface that encourages staining. Studies have shown that an unglazed porcelain
surface was affected more than a glazed porcelain surface from staining (41). A nonglazed surface provides for the
seepage of staining materials through the porosities and surface defects of the porcelain. Although the staining medium used (methylene blue) can be considered rather
aggressive in such studies, clinical equivalents could be stains of coffee, tea, or cigarette tar. These substances
could cause possible discoloration of porcelain materials if adjustments are performed without polishing and glazing.
It is therefore suggested that clinical corrections warrant
glazing of the porcelain prior to cementation to decrease the possibility of staining such restorations (41). From this
203
point of view, it can be said that color variation of denture
teeth made of acrylic resin material may be due to the
absorption and adsorption of colorants by the teeth, whereas
color variation of porcelain denture teeth may be due to
only the adsorption of colorants. The variation in
discoloration is directly proportional to ĢE* (28,42).
For all groups of denture teeth used in this study, the
filtered coffee (with a mean AE* value of 0.999) was the
most staining agent, followed by the tea and the cola, and
the distilled water was the least intense staining agent for
all types of denture teeth.
Water bleaching and sunlight, to some extent, have no
effect on porcelain, but repeated cycles of drying and
water immersion may cause whitening and loss of color
both in acrylic and porcelain denture teeth. Continued
exposure to ultraviolet light may also cause a slight
yellowing (11). This phenomenon could explain why the
b* values of porcelain denture teeth were slightly changed
in this present study. Porcelain is resistant to the action of
solvents, with only hydrofluoric acid being known to have
any significant effect on it. The cross-linked plastics are
relatively craze resistant and are immune to reasonable
amounts of ordinary solvents. They may, however, be
softened to some extent by a number of organic solvents.
When plastic is softened by solvents, organic dyes penetrate
the outer layer and cause discoloration (11).
According to the results of this in vitro study, while
selecting a denture teeth material in construction of a
removable prosthesis, from the point of color stability, a
reinforced acrylic or a porcelain denture teeth material may
be recommended.
It can be concluded that this kind of in vitro experiments
should be supported by planned in vivo observations.
Conclusions
Six commercially available denture teeth materials were
evaluated after 1 day, 1 week, 2 weeks, and 4 weeks of
immersion in various staining solutions. Within the
limitations of this in vitro study, these conclusions can be
drawn:
1. Clinical discoloration is affected by many parameters,
including the type of denture tooth, dietary habits, and
oral hygiene of patients. Clinical discoloration in denture
teeth is also because of extrinsic staining.
2. Among the denture teeth materials investigated in this
study, the UP denture teeth material had the highest color
difference values. At the 1 day, 1 week and 4 weeks
measurements in the filtered coffee and at the 2 weeks
measurements in the cola, the UP material revealed the
highest color difference values.
3. Although the most staining solution was the filtered
coffee, the highest color difference mean was obtained
in the cola at the 2 weeks measurement of UP material. However, when the results were evaluated in general,
the filtered coffee was found to be the most staining solution and UP material was found to have the highest discoloration value.
Acknowledgments The authors wish to thank Dr. Arife Dogan (Department
of Prosthodontics of Faculty of Dentistry of Gazi University) for her constructive criticism of this manuscript,
Mr. Mustafa Semiz (MSc) (Department of Statistics of Faculty of Arts and Sciences of Gazi University) for his
statistical evaluations, the Guney Di§ Deposu Company and Mr. Atakan Orhon for kindly supplying materials
used in this study.
References
1. Denli, N., Uludag, B., Kilicarslan, M.A. and Ozkan, Y. (1996) Resistance of artificial acrylic resin teeth
to staining. Turkiye Klin. Dishek. Bil. Derg. 2, 38-42
2. Satoh, Y., Nagai, E., Azaki, M., Morikawa, M., Ohyama, T., Toyoma, H., Itoh, S., Sakurai, H., Iwasawa, A., Ohwa, M., Ohki, K., Nishiyama, M.
and Ohta, H. (1993) Study on high-strength plastic teeth. Tooth discoloration. J. Nihon Univ. Sch. Dent.
35, 192-199 3. Council on Dental Materials, Instruments and
Equipment (1984) Dental Terminology. ANSI/ADA
Specification No. 33. American Dental Association, Chicago, 14
4. Liberman, R., Combe, E.C., Piddock, V. and Watts, D.C. (1996) Color changes in acrylic teeth-comparison of an objective and subjective method.
J. Oral Rehabil. 23, 464-469 5. Rosentritt, M., Esch, J., Behr, M., Leibrock, A. and
Handel, G. (1998) In vivo color stability of resin composite veneers and acrylic resin teeth in removable partial dentures. Quintessence Int. 29,
517- 522 6. Central Bureau of the International Commision on
Illumination, Austria (1986) Colorimetry. 2nd ed., CIE Publication No. 15.2, Vienna, 30
7. Douglas, R.D. (1997) Precision of in vivo colorimetric assessments of teeth. J. Prosthet. Dent. 77, 464-470
8. Ergun, G., Dogan, O.M., Ozkan, Y. Demirel, E. and Dogan, A. (2000) Color stability of denture base materials after soaked in different aging solutions.
Balk. J. Stom. 4, 93-97
204
9. Yaman, P., Razzoog, M. and Brandau, H.E. (1989)
In vitro color stability of provisional restorations. Am. J. Dent. 2, 48-50
10. Razzoog, M.E., Lang, B.R., Russell, M.M. and May, K.B. (1994) A comparison of the color stability
of conventional and titanium dental porcelain. J. Prosthet. Dent. 72, 453-456
11. Craig, R.G. and Ward, M.L. (1997) Restorative dental materials. 10th ed., Mosby, St. Louis, 479-
483 12. Khokhar, Z.A., Razzoog, M.E. and Yaman, P. (1991)
Color stability of restorative resins. Quintessence Int.
22, 733-737 13. Alacam, A. and Burgaz Y. (1989) The effect of
various polishing techniques on restorative resin discoloration. A.U. Dis Hek. Fak. Derg. 16, 123-
127 (in Turkish) 14. Burgaz, Y., Bek, B. and Demirkoprulu, H. (1987)
Color stability of crown and bridge acrylic resins. G.U. Dishek. Fak. Der. 4, 93-104 (in Turkish)
15. Cooley, R.L., Barkmeier, W.W., Matis, B.A. and Siok, J.F. (1987) Staining of posterior resin
restorative materials. Quitessence Int. 18, 823-827 16. Luce, M.S. and Campbell, C.E. (1988) Stain potential
of four microfilled composites. J. Prosthet. Dent. 60, 151-154
17. Iazetti, G, Burgess, J.0., Gardiner, D. and Ripps, A.
(2000) Color stability of fluoride-containing restorative materials. Oper. Dent. 25, 520-525
18. Inokoshi, S., Burrow, M.F., Kataumi, M., Yamada,
T. and Takatsu, T. (1996) Opacity and color changes of tooth-colored restorative materials. Oper. Dent. 21, 73-80
19. Asmussen, E. (1983) Factors affecting the color stability of restorative resins. Acta Odontol. Scand.
41, 11-18 20. Burrow, M.F. and Makinson, O.F. (1991) Color
change in light-cured resins exposed to daylight.
Quintessence Int. 22, 447-452 21. Gokay, O., Yilmaz, B., Akin, S. and Mujdeci, A.
(1998) Evaluation of different finishing techniques on color stability of a hybrid composite resin. A.U.
Dis Hek. Fak. Derg. 25, 211-220 (in Turkish) 22. Um, C.M. and Ruyter, I.E. (1991) Staining of resin-
based veneering materials with coffee and tea.
Quintessence Int. 22, 377-386 23. Chan, K.C., Fuller, J.L. and Hormati, A.A. (1980)
The ability of foods to stain two composite resins. J. Prosthet. Dent. 43, 542-545
24. Chan, K.C., Hormati, A.A. and Kerber, P.E. (1981)
Staining calcified dental tissues with food. J. Prosthet.
Dent. 46, 175-178 25. Kesim, B. and Belli, E. (1994) Effect of tea, coffee,
and cola on color stability of aesthetic materials. S.U. Dishek. Fak. Derg. 4, 90-94 (in Turkish)
26. Polyzois, G.L., Yannikakis, S.A. and Zissis, A.J.
(1999) Color stability of visible light-cured, hard direct denture reliners: an in vitro investigation. Int.
J. Prosthodont. 12, 140-146 27. Ulusoy, M., Uludag, B. and Kilicarslan, M.A. (1998)
In-vitro comparison of staining properties of resin-based veneering materials. Balk. J. Stom. 2, 32-36
28. Seher, J. and Viohl, J. (1992) In-vitro-Verfarbungen von Kunststoffen durch Farbstoffe and UV-Strahlung. Dtsch. Zahnarztl. Z. 47, 634-636 (in
German) 29. Craig, R.G. and Ward, M.L. (1997) Restorative
dental materials. 10th ed., Mosby, St. Louis, 30-32
30. Johnston, W.M. and Kao, E.C. (1989) Assessment of appearance match by visual observation and clinical colorimetry. J. Dent. Res. 68, 819-822
31. Douglas, R.D. (2000) Color stability of new-
generation indirect resins for prosthodontic application. J. Prosthet. Dent. 83, 166-170
32. Seghi, R.R., Johnston, W.M. and O'Brien, W.J.
(1989) Performance assessment of colorimetric devices on dental porcelains. J. Dent. Res. 68, 1755-1759
33. Fay, R.M., Servos, T. and Powers, J.M. (1999) Color of restorative materials after staining and bleaching. Oper. Dent. 24, 292-296
34. Belli, S., Tanriverdi, F.F. and Belli, E. (1997) Color stability of three aesthetic laminate materials against
to different staining agents. J. Marmara Univ. Dent. Fac. 2, 643-648
35. Dietschi, D., Campanile, G., Holz, J. and Meyer, J.-
M. (1994) Comparison of the color stability of ten new-generation composites: an in vitro study. Dent.
Mater. 10, 353-362 36. Hasanreisoglu, U., Kahpolar, B. and Karaagachoglu,
L. (1988) Evaluation of color stability in some
veneering materials. A.U. Di§ Hek. Fak. Derg. 15, 289-294 (in Turkish)
37. Scotti, R., Mascellani, S.C. and Forniti, F. (1997) The in vitro color stability of acrylic resins for
provisional restorations. Int. J. Prosthodont. 10, 164-168
38. Seghi, R.R. (1990) Effects of instrument-measuring
geometry on colorimetric assessments of dental porcelains. J. Dent. Res. 69, 1180-1183
39. Lang, R., Rosentritt, M., Leibrock, A., Behr, M. and Handel, G. (1998) Color stability of provisional
205
crown and bridge restoration materials. Br. Dent. J. 185, 468-471
40. Gladys, S., Van Meerbeek, B., Lambrechts, P. and Vanherle, G. (1999) Evaluation of aesthetic
parameters of resin-modified glass-ionomer materials and a polyacid-modified resin composite in Class V cervical lesions. Quintessence Int. 30, 607-614
41. Esquivel, J.F., Chai, J. and Wozniak, W.T. (1995) Color stability of low-fusing porcelains for titanium.
Int. J. Prosthodont. 8, 479-485 42. Izgii, E. and Baykara, T. (1981) The solid state
stability of oral rehydration salts. J. Clin. Hosp. Pharm. 6, 135-144