j o u r n a l o f d e n t i s t r y 4 0 s ( 2 0 1 2 ) e 4 7 – e 5 4

Available online at www.sciencedirect.com

journal homepage: www.intl.elsevierhealth.com/journals/jden

Effects of ageing and staining on color of acrylic resindenture teeth

Wendy C. Gregorius a,*, Mathew T. Kattadiyil b, Charles J. Goodacre a,1,Clyde L. Roggenkamp a, John M. Powers c, Rade D. Paravina d

aDepartment of Restorative Dentistry, Loma Linda University School of Dentistry, 11092 Anderson Street, Loma Linda, California 92350,

United StatesbAdvanced Specialty Education Program in Prosthodontics, Department of Restorative Dentistry, Loma Linda University School of Dentistry,

11092 Anderson Street, Loma Linda, California 92350, United StatescOral Biomaterials, Department of Restorative Dentistry and Prosthodontics, The University of Texas School of Dentistry at Houston,

7500 Cambridge Street, Houston, Texas 77054, United StatesdHouston Center for Biomaterials and Biomimetics, Department of Restorative Dentistry and Prosthodontics, The University of Texas School of

Dentistry at Houston, 7500 Cambridge Drive, Houston, Texas 77054, United States

a r t i c l e i n f o

Article history:

Received 25 June 2012

Received in revised form

9 September 2012

Accepted 11 September 2012

Keywords:

Staining

Ageing

Color

Denture

Teeth

Acrylic

Coffee

Red wine

a b s t r a c t

Objectives: To assess the color stability of high-strength acrylic resin denture teeth after

exposure to red wine, coffee and artificial ageing.

Methods: Four different shades of acrylic resin denture teeth were selected from three

manufacturers. The teeth were evaluated in two phases: Phase I, upon staining for 7 days

in distilled water (control Group A), red wine (experimental Group B) and coffee (experi-

mental Group C), and Phase II, upon artificial ageing in a Weather-Ometer for a total

exposure of 150 kJ/m2 (control Group A; Phase I). Denture tooth positioning jigs were

fabricated and color data recorded by means of an intra-oral spectrophotometer and

expressed using the Commission Internationale d’Eclairage (CIE) L*a*b* color notation

system. Means and standard deviations were determined. The staining data were analysed

by three-way ANOVA, while the artificial ageing data were analysed by two-way ANOVA.

Fisher’s PLSD intervals were calculated at a significance level of P � 0.05.

Results: In the staining experiment, the main effects of stains and denture teeth and the

two-way and three-way interactions among stains, denture teeth and shades were signifi-

cant (P � 0.05). The same was true for the main effects of denture teeth and shades and their

interactions in the ageing experiment.

The smallest overall color change upon staining in red wine was recorded for Vita

Physiodens denture teeth (DE* = 0.9 � 0.4), followed by SR Vivodent PE 1.2 (0.6) and Portrait

IPN 2.4 (0.6). Corresponding values for staining in coffee were 2.0 (0.6), 1.7 (1.0) and 1.8 (0.8),

while ageing-dependent changes in color were 1.7 (0.4), 2.4 (0.8) and 1.1 (0.4) for Portrait IPN,

SR Vivodent PE and Vita Physiodens teeth, respectively.

Conclusion: Although the null hypothesis has been partially rejected, because some statisti-

cally significant changes

* Corresponding author. Tel.: +1 909 558 4640; fax: +1 909 558 0253.E-mail address: wgregorius@llu.edu (W.C. Gregorius).

1 Office of the Dean, Department of Restorative Dentistry, Loma LinLinda, California, 92350, United States.0300-5712/$ – see front matter # 2012 Elsevier Ltd. All rights reservedhttp://dx.doi.org/10.1016/j.jdent.2012.09.009

in color and color coordinates occurred upon staining and ageing,

da University School of Dentistry, 11092 Anderson Street, Loma

.

all evaluated denture teeth exhibited good color stability compared to the 50:50% acceptability

threshold used in data interpretation.

Clinical significance: Selection of a color stable and stain-resistant denture tooth can contribute

to denture longevity and overall patient satisfaction.

# 2012 Elsevier Ltd. All rights reserved.

j o u r n a l o f d e n t i s t r y 4 0 s ( 2 0 1 2 ) e 4 7 – e 5 4e48

1. Introduction

Manufacturers have been striving to improve the stain

resistance and mechanical properties of denture teeth for

decades. Dentsply Trubyte (York, PA) introduced denture teeth

to reduce the potential for discolorations and delamination

between layerscausedbytooth wear or laboratoryalterations in

the 1970s.1 The material reportedly was made of poly(methyl

methacrylate), or PMMA, with an inter-penetrating polymer

network (IPN) and a double cross-linked material layering. Ten

years later, denture teeth made of sustained life material (SLM)

that combined IPN technology with ultra-high molecular

weight polyethylene, which reportedly increased wear resis-

tance by 25%, were introduced.1 Ivoclar Vivadent (Amherst, NY)

introduced denture teeth made of a synthetic polymer based on

PMMA with a double cross-linked (DCL) polymer and matrix,

which reportedly is solvent resistant (SR) and provides shade

stability and resistance to mechanical wear.2 Anterior teeth

with a pearly effect (PE) have a blue iridescence and reportedly

give a denture the vital appearance of healthy teeth.2 Vident, A

VITA Company (Brea, CA) distributes Vita Physiodens denture

teeth. Vita MRP (microfiller reinforced polyacrylic) material,

developed and used in the fabrication of Vita Physiodens, is

comprised of a triple cross-linked PMMA, a cross-linked

monomer, and inorganic microparticle filler that are poly-

merised into a polymer network. The manufacturer claims that

this tooth is a hard, homogenous structure that is abrasion and

craze resistant with a lifelike surface anatomy.3

In the United States, the population of 65 year olds and

older is increasing in number as the average life expectancy

increases. Currently, the annual estimate of resident popula-

tion for both sexes over the age of 65 years is 38.8 million,

which is approaching 13% of the total population.4 In 2050, the

number of Americans aged 65 and older is projected to be 88.5

million, more than double its projected population of 40.2

million in 2010.4

The importance of stain and wear resistant denture teeth

becomes clear when considering the number of patients who

will need prosthodontic treatment. While there will be a

decrease in the percentage of the population that is complete-

ly edentulous, there will be a steady to increasing need for

complete dentures until 2020 due to patients living longer.5 A

surveillance study conducted by the National Health and

Nutrition Examination Survey, authorised by the Centres for

Disease Control, during the periods of 1988–1994 and 1999–

2002, showed that edentulism was<1% among adults aged 20–

39 years, 4.9% among those aged 40–59 years, and 24.9%

among those aged >60 years. The mean number of teeth

present in the individuals surveyed was shown to correlate

inversely with age. Approximately 8% of adults>20 years were

completely edentulous.6

Many studies draw attention to the notion that the

psychological impact of aesthetic dentistry to patients is

positive.7–11 Studies also suggest that the ageing population

tend to focus on the whiteness and color of their teeth.12,13

Studies evaluating patient satisfaction with their dental

appearance and tooth color show different outcomes in terms

of age-related perceptions, but invariably agree with the

conclusion that aesthetics and tooth color remain important

to patients in all age groups. In a study to evaluate a range of

aesthetic factors, fifty-three percent of patients placed priority

on shade selection and teeth whitening.14 The results of

another study showed no difference in patient satisfaction

with tooth color based on age, moreover, tooth color was

found to be independent of age suggesting a broad-based

application of aesthetic dentistry.15

The importance of aesthetics in restorative dentistry is

linked to the selection of durable and color stable biomaterials.

With the introduction of a newer generation of denture teeth,

evaluation of the long-term effects of ageing and staining are

needed. Few reports in the literature have tested the color

stability and staining of acrylic resin denture teeth. They

maintain that high-strength acrylic resin denture teeth

remain susceptible to staining by pigments.16–18 With an

increase in aesthetic demands and patient expectations of

removable prostheses, the resistance of denture teeth to color

changes plays a significant role in the selection of denture

teeth.

The ability of denture teeth to remain color stable through

wear and time is critical and a measure by which the longevity

and patient acceptance of a removable prosthesis may be

evaluated. The aetiology of artificial tooth discoloration is

multifactorial. Wear, lack of patient maintenance, the effect of

compositional characteristics, exposure to stains, and time

are factors that contribute to intrinsic and extrinsic staining.

While denture teeth have been modified to address some

of these factors, there is a need for research relating to the

various brands of artificial teeth and their color stability

compared to other restorative materials. Many studies have

investigated the effects of staining pigments on ceramics,

composite resins, provisional acrylic resins and denture

base materials. However, few studies have assessed the

extent to which reinforced acrylic resin denture teeth resist

color changes when aged and exposed to staining pig-

ments.16–18

The purpose of this study was to assess the color stability of

high-strength acrylic resin denture teeth from three manu-

facturers when compared to the control by evaluating in vitro

staining after exposure to red wine and coffee and artificial

ageing-dependent color changes. The null hypothesis was that

no significant color changes would occur upon staining and

ageing.

j o u r n a l o f d e n t i s t r y 4 0 s ( 2 0 1 2 ) e 4 7 – e 5 4 e49

2. Materials and methods

Maxillary right central incisor denture teeth in Vita shades

B1, A2, A3, and A4 were selected from three different

manufacturers: Portrait IPN (DENTSPLY Trubyte, York, PA),

SR Vivodent PE (Ivoclar Vivadent, Amherst, NY), and Vita

Physiodens (Vident, A VITA Company, Brea, CA) (Fig. 2). Using

manufacturer mould comparison charts, tooth moulds of

similar size and shape having a near-flat facial surface were

selected: 21J Portrait IPN, A17 SR Vivodent PE, and T9L VITA

Physiodens.

Five maxillary central incisor denture teeth in four shades

(n = 20) from each of the three manufacturers (n = 3 � 20 = 60)

were tested in a control group (Group A) and equal numbers

of teeth in two experimental groups (Groups B and C). Groups

A–C represented Phase I. Group A teeth, serving as the

control, were tested in distilled water for 7 days. The teeth in

Group B were tested in red wine for 7 days separately from

Group C teeth, which were tested in coffee for 7 days. The red

wine and coffee solutions were replaced every 12 h during

the 7-day testing period. The total sample size of teeth for

Groups A–C for Phase I were 180 denture teeth. Phase II

included only the teeth from the control Group A

(n = 3 � 20 = 60) and were subjected to artificial ageing in a

Weather-Ometer.

A positioning jig (Fig. 1) was made for each of the three

tooth moulds to consistently direct the placement of the 5 mm

diameter probe of the intra-oral spectrophotometer (VITA

Easyshade, Vident, A VITA Company, Brea, CA) against the

facial surface of each denture tooth for measurements. The

three jigs were made from acrylic blocks, which were milled so

that a concavity on one surface was larger in depth and

diameter than each acrylic resin denture tooth being mea-

sured. Four cylindrical indices were placed on the tooth-

positioning surface of the block and at the midpoint between

the four sides of the block and the central tooth concavity, for

repositioning of the top portion of the jig. Poly(vinyl siloxane)

(PVS) material was expressed into the concavity in the acrylic

block and one denture tooth was placed into the PVS material

during polymerisation, so that the near-flat facial surface of

[(Fig._1)TD$FIG]

Fig. 1 – Custom positioning Jig: (A) view of the acrylic block with

the jig and measuring probe; (B) view of the relationship betwee

portion of the jig and probe; (C) assembled jig with measuring

the tooth was horizontal and facing upward with the ridge lap

portion of the tooth stabilised in PVS material within the

concavity. The facial portion of the tooth was elevated above

the block. An acrylic rod, measuring the same diameter as the

Easyshade measuring probe and 5 mm in height, was attached

to the central portion of the tooth surface, and PVS material

was expressed surrounding the acrylic rod, over exposed

portions of the tooth, along the surface of the block and into

the indices for a stable repositioning jig for the tooth and

Easyshade measuring probe. The two larger components of

the jig, PVS repositioning portion and acrylic block, were

detachable and replaceable, due to the repositioning indices,

which allowed each denture tooth from the same manufac-

turer to be placed within the jig and measured with

repeatability.

The color data were recorded by one operator. Color was

measured at baseline and after 7 days of total immersion in red

wine (2009 Robert Mondavi Cabernet Sauvignon) and coffee

(ground, drip brewed, caffeinated, dark roast, Starbucks Caffe

Verona Bold) for Groups B and C (experimental groups, n = 10).

The color of teeth in Group A (control group, n = 5) also was

measured at baseline and after 7 days of total immersion in the

distilled water. As significant color changes of the control

group were not anticipated, in Phase II, the control group

teeth were used to evaluate color before (baseline) and

after artificial ageing by exposure to 150 kJ/m2 in a Weather-

Ometer (Atlas Ci35A Xenon Weather-Ometer, Atlas Material

Testing Technology LLC, Chicago, IL, USA). A Weather-Ometer

is an artificial ageing machine, in which an object may be

exposed to light and darkness and intermittent exposure to

water spray that simulates direct exposure with additional

short wavelength energy.19 The denture teeth were exposed to

a controlled irradiance xenon arc filtered through borate

borosilicate glass. Color coordinates were determined by

one operator using the Easyshade intra-oral spectrophotom-

eter and results expressed using Commission Internationale

d’Eclairage (CIE) L*a*b* color notation system (CIELAB). Color

differences (DE*) were determined using the following

equation20:

DE� ¼ ½ðDL�Þ2 þ ðDa�Þ2 þ ðDb�Þ2�1=2

tooth positioned in the central concavity with top portion of

n the four cylindrical indices of the acrylic block to the top

probe.

[(Fig._2)TD$FIG]

Fig. 2 – Denture teeth and Vita (or Vita equivalent) shades

B1, A2–A4 from left to right: (A) Portrait IPN, shades B1, A2–

A4; (B) SR Vivodent PE denture teeth shades 110/01, 130/

2A, 210/2B, 340/3E; (C) Vita Physiodens denture teeth

shades 1M1, A2–A4.

j o u r n a l o f d e n t i s t r y 4 0 s ( 2 0 1 2 ) e 4 7 – e 5 4e50

where L* is lightness, a* is green-red coordinate, and b* is blue-

yellow coordinate. Chroma, C*, and hue angle, h8, were calcu-

lated from a* and b* coordinate values.

Previous visual judgement thresholds were used in the

interpretation of results. A DE* = 1.8 was considered as the

50:50% perceptibility threshold, while a DE* = 3.5 was consid-

ered to be a 50:50% acceptability threshold.21

Means and standard deviations for comparisons among

three stains, three denture teeth and four shades were

determined. The staining data were analysed by three-way

analysis of variance (ANOVA) with factors of denture tooth,

shade, and staining solution with interactions. The artificial

ageing data were analysed by two-way ANOVA with factors of

denture tooth and shade with interactions. Fisher’s PLSD

Table 1 – Differences in color (DE*): staining (7 days minus bas

Denture teeth* Shade Distilled water

Portrait IPN (21J) P11 0.9 (0.3)

P2 0.7 (0.3)

P3 0.6 (0.2)

P4 1.3 (0.8)

SR Vivodent PE (A17) 110 0.5 (0.3)

130 1.0 (0.5)

210 1.1 (1.2)

340 1.0 (0.4)

Vita Physiodens (T9L) 1M1 0.9 (0.5)

A2 0.7 (0.3)

A3 0.5 (0.1)

A4 0.6 (0.5)

* Fisher’s PLSD intervals at the 0.05 level of significance were 0.2, 0.2 and

and four shades.y Fisher’s PLSD intervals at the 0.05 level of significance were 0.4 and 0.4

intervals for comparison of means were calculated at the 0.05

level of significance.

3. Results

3.1. Color difference

Since the mean color difference upon storage in distilled

water was below DE* = 1, it will not be listed by manufacturer

and for individual color coordinates. The mean color

differences upon staining in red wine were 2.4 (0.6), 1.2

(0.6) and 0.9 (0.4) for Portrait IPN, SR Vivodent PE and Vita

Physiodens teeth, respectively. Corresponding values for

staining in coffee were 2.0 (0.6), 1.7 (1.0) and 1.8 (0.8), while

ageing-dependent changes in color were 1.7 (0.4), 2.4 (0.8) and

1.1 (0.4) for Portrait IPN, SR Vivodent PE and Vita Physiodens

teeth, respectively (Table 1).

In the staining experiment, the main effects of stains and

denture teeth and the two-way interactions among teeth and

stain and three-way interactions among stains, denture teeth

and shades were significant at the 0.05 level. With SR Vivodent

PE and Vita Physiodens teeth, coffee caused larger changes in

DE* than distilled water and red wine. With Portrait IPN teeth,

both coffee and red wine caused larger changes in DE* than

distilled water.

In the ageing experiment, the main effects of denture teeth

and shades and their interactions were significant at the 0.05

level. Ageing caused the largest changes in DE* for SR Vivodent

PE teeth. In general, the less chromatic shades had larger

changes in DE*.

3.2. Lightness difference

The mean lightness differences upon staining in red wine

were �1.8 (0.6), �0.5 (0.6) and 0.3 (0.3) for Portrait IPN, SR

Vivodent PE and Vita Physiodens teeth, respectively. Corre-

sponding values for staining in coffee were�1.5 (0.8),�0.2 (0.6)

and �1.0 (0.6), while ageing-dependent changes in lightness

eline) and ageing (150 kJ/m2 minus baseline).

Red wine Coffee A. ageingy

2.4 (0.8) 2.9 (0.8) 1.8 (0.4)

1.9 (0.2) 2.0 (0.8) 1.6 (0.1)

2.8 (0.6) 1.9 (0.4) 1.3 (0.3)

2.5 (0.7) 1.3 (0.4) 2.0 (0.7)

1.3 (0.9) 1.7 (0.8) 2.7 (0.4)

1.0 (0.2) 1.3 (0.7) 1.8 (0.8)

1.4 (0.5) 1.1 (0.7) 3.2 (1.3)

1.1 (0.7) 2.8 (1.4) 1.9 (0.5)

0.7 (0.3) 2.0 (0.5) 1.9 (0.2)

1.1 (0.6) 1.5 (0.6) 1.1 (0.3)

0.8 (0.2) 1.9 (0.9) 0.6 (0.2)

0.8 (0.5) 1.8 (1.0) 0.8 (0.7)

0.3 for comparisons of DE* among three stains, three denture teeth

for comparisons of DE* among three denture teeth and four shades.

Table 2 – Differences in lightness (DL*): staining (7 days minus baseline) and ageing (150 kJ/m2 minus baseline).

Denture teeth* Shade Distilled water Red wine Coffee A. ageingy

Portrait IPN (21J) P11 �0.1 (0.7) �1.8 (0.7) �2.4 (0.6) �1.4 (0.4)

P2 �0.4 (0.2) �1.4 (0.2) �1.4 (0.6) �1.3 (0.3)

P3 �0.2 (0.3) �2.4 (0.5) �1.0 (0.6) �1.1 (0.3)

P4 0.4 (0.1) �1.7 (0.6) �0.9 (0.5) �1.3 (0.4)

SR Vivodent PE (A17) 110 0.0 (0.5) �0.5 (0.9) 0.0 (0.6) �1.6 (0.3)

130 �0.3 (0.3) �0.1 (0.6) �0.1 (0.7) �0.8 (0.8)

210 �0.2 (0.2) �0.6 (0.3) �0.2 (0.5) �1.4 (0.4)

340 �0.4 (0.2) �0.6 (0.4) �0.5 (0.5) �0.7 (0.2)

Vita Physiodens (T9L) 1M1 0.8 (0.6) 0.3 (0.5) �0.7 (0.7) �1.5 (0.3)

A2 0.2 (0.3) 0.4 (0.4) �1.2 (0.5) �0.5 (0.4)

A3 �0.1 (0.5) 0.3 (0.2) �1.2 (0.7) �0.3 (0.3)

A4 0.0 (0.3) 0.2 (0.3) �1.1 (0.5) �0.2 (0.3)

* Fisher’s PLSD intervals at the 0.05 level of significance were 0.2, 0.2 and 0.2 for comparisons of DL* among three stains, three denture teeth

and four shades.y Fisher’s PLSD intervals at the 0.05 level of significance were 0.2 and 0.2 for comparisons of DL* among three denture teeth and four shades.

j o u r n a l o f d e n t i s t r y 4 0 s ( 2 0 1 2 ) e 4 7 – e 5 4 e51

were �1.3 (0.4), �1.1 (0.5) and �0.6 (0.6) for Portrait IPN, SR

Vivodent PE and Vita Physiodens teeth, respectively (Table 2).

In the staining experiment, the main effects of stains and

denture teeth and the two- and three-way interactions among

stains, denture teeth and shades were significant at the 0.05

level. With Portrait IPN teeth, red wine and coffee caused

larger changes in DL* than distilled water. With Vita

Physiodens teeth, coffee caused larger changes in DL* than

distilled water and red wine.

In the ageing experiment, the main effects of denture teeth

and shades and their interactions were significant at the 0.05

level. Ageing caused larger changes in DL for Portrait IPN teeth.

In general, the less chromatic shades had larger changes in DL*.

3.3. Chroma difference

The mean chroma differences upon staining in red wine were

1.2 (0.6), �0.1 (1.0) and 0.4 (0.7) for Portrait IPN, SR Vivodent PE

and Vita Physiodens teeth, respectively. Corresponding values

for staining in coffee were 1.2 (0.7), 1.0 (1.7) and 1.3 (0.8), while

ageing-dependent changes in chroma were �0.1 (1.0), �1.6

Table 3 – Differences in chroma (DC*): staining (7 days minus

Denture teeth* Shade Distilled water

Portrait IPN (21J) P11 �0.6 (0.4)

P2 �0.5 (0.4)

P3 �0.4 (0.3)

P4 �1.1 (0.9)

SR Vivodent PE (A17) 110 �0.1 (0.4)

130 �0.3 (1.1)

210 �0.8 (1.5)

340 �0.5 (0.9)

Vita Physiodens (T9L) 1M1 0.2 (0.3)

A2 0.3 (0.6)

A3 0.2 (0.3)

A4 0.4 (0.6)

* Fisher’s PLSD intervals at the 0.05 level of significance were 0.3, 0.3 and

and four shades.y Fisher’s PLSD intervals at the 0.05 level of significance were 0.5 and 0.6

(1.1) and �0.3 (0.8) for Portrait IPN, SR Vivodent PE and Vita

Physiodens teeth, respectively (Table 3).

In the staining experiment, the main effects of stains and

denture teeth and the two- and three-way interactions among

stains, denture teeth and shades were significant at the 0.05

level. With Portrait IPN teeth, red wine caused large negative

changes in DC*, whereas coffee caused large positive increases

in DC*. With SR Vivodent PE and Vita Physiodens teeth, coffee

caused the most significant changes in DC* when compared to

red wine and the control.

In the ageing experiment, the main effects of denture teeth

were significant at the 0.05 level.

Ageing caused larger changes in DC* for Vita Physiodens

teeth. In general, the more chromatic shades had larger

changes in DC*.

3.4. Hue difference

The mean hue differences upon staining in red wine were�2.1

(1.2), �0.7 (0.5) and �1.2 (1.2) for Portrait IPN, SR Vivodent PE

and Vita Physiodens teeth, respectively. Corresponding values

baseline) and ageing (150 kJ/m2 minus baseline).

Red wine Coffee A. ageingy

�1.0 (0.5) 1.6 (0.6) 0.6 (0.7)

�0.9 (0.6) 1.2 (0.9) 0.4 (0.5)

�1.3 (0.4) 1.5 (0.4) 0.0 (0.6)

�1.5 (0.9) 0.6 (0.8) �1.3 (0.8)

�0.4 (1.2) 1.0 (1.6) �1.8 (0.5)

0.2 (0.7) 1.3 (0.6) �0.9 (1.1)

0.6 (1.2) �0.8 (1.0) �2.2 (1.7)

�0.7 (0.8) 2.7 (1.4) �1.3 (0.7)

�0.1 (0.3) 2.0 (0.5) 0.9 (0.3)

0.7 (1.0) 0.8 (0.6) 0.7 (0.6)

0.6 (0.3) 1.3 (0.7) �0.1 (0.4)

0.5 (0.7) 1.3 (1.1) �0.3 (0.9)

0.3 for comparisons of DC* among three stains, three denture teeth

for comparisons of DC* among three denture teeth and four shades.

Table 4 – Differences in hue (Dh8): staining (7 days minus baseline) and ageing (150 kJ/m2 minus baseline).

Denture teeth* Shade Distilled water Red wine Coffee A. ageingy

Portrait IPN (21J) P11 0.3 (0.2) �3.8 (1.2) �1.0 (0.5) 2.7 (0.4)

P2 �0.3 (0.2) �1.9 (0.7) �0.7 (0.3) 2.1 (0.3)

P3 �0.2 (0.1) �1.5 (0.4) �0.6 (0.1) 1.4 (0.3)

P4 �0.2 (0.2) �1.3 (0.3) �0.4 (0.2) 1.3 (0.4)

SR Vivodent PE (A17) 110 �0.3 (0.3) �0.4 (0.8) �0.5 (0.4) 4.0 (0.4)

130 0.0 (0.3) �1.0 (0.4) �0.5 (0.4) 2.9 (0.5)

210 0.0 (0.3) �0.9 (0.4) 0.5 (0.2) 2.9 (0.7)

340 �0.1 (0.3) �0.5 (0.2) �0.5 (0.4) 2.0 (0.2)

Vita Physiodens (T9L) 1M1 �0.4 (0.3) �3.1 (0.9) �1.1 (0.4) 2.8 (0.3)

A2 �0.3 (0.2) �0.5 (0.3) �0.9 (0.2) 1.0 (0.2)

A3 �0.2 (0.1) �0.5 (0.1) �0.9 (0.4) 0.8 (0.2)

A4 �0.2 (0.1) �0.5 (0.2) �0.5 (0.2) 0.8 (0.2)

* Fisher’s PLSD intervals at the 0.05 level of significance were 0.2, 0.2 and 0.2 for comparisons of Dh8 among three stains, three denture teeth

and four shades.y Fisher’s PLSD intervals at the 0.05 level of significance were 0.2 and 0.3 for comparisons of Dh8 among three denture teeth and four shades.

j o u r n a l o f d e n t i s t r y 4 0 s ( 2 0 1 2 ) e 4 7 – e 5 4e52

for staining in coffee were �0.7 (0.3), �0.3 (0.6) and �0.9 (0.4),

while ageing-dependent changes in hue were 1.9 (0.7), 3.0 (0.9)

and 1.3 (0.9) for Portrait IPN, SR Vivodent PE and Vita

Physiodens teeth, respectively (Table 4).

In the staining experiment, the main effects of stains,

denture teeth and shades and the two-way and three-way

interactions among stains, denture teeth and shades were

significant at the 0.05 level. With Portrait IPN teeth, red wine

caused the largest changes in Dh8 with higher changes with

lighter shades (higher values). With Vita Physiodens teeth,

coffee caused larger changes in Dh8 than distilled water and

red wine.

In the ageing experiment, the main effects of denture teeth

and denture teeth and shade interactions were significant at

the 0.05 level. Ageing caused larger changes in Dh8 for SR

Vivodent PE teeth. In general, the less chromatic shades had

larger changes in Dh8.

4. Discussion

The null hypothesis has been partially rejected, because some

statistically significant changes in color and color coordinates

occurred upon staining and ageing. However, all staining and

ageing dependent differences in color were below the 50:50%

acceptability threshold of DE* = 3.5, thus indicating satisfactory

color stability of evaluated denture teeth.

A method for measuring color differences was employed

using an intra-oral spectrophotometer and custom reposition-

ing jig (Fig. 1) for repeatability of the probe in relationship to

the denture tooth surface. The custom positioning device

fabricated in this study was a modified version based on a jig

that was first introduced in an in vivo study in 2009. This

method addressed the problem of controlling probe angula-

tion and repositioning against a tooth.22

The changes in color and color coordinates likely would

have been greater if the teeth had been immersed in staining

solution for more than 7 days and aged for more than 150 kJ/

m2. However, a 7-day staining period was chosen based on the

assumption that exposure to coffee and red wine is on average

5–10 min a day. The 7-day exposure to a single solution,

therefore, corresponds to 34–67 months of its consumption of

staining.

When it comes to ageing, it has been reported that it is more

appropriate to express ageing in kJ/m2 than in lighting hours.23

However, it is more complex to determine the real-life

equivalent to the artificial ageing exposure utilised in this

study than in the case of staining. Also, one has to be aware of

the potential simultaneous effects of staining, ageing, oral

hygiene, and other habits in the patient’s lifestyle.

Recent evaluation of visual judgments of dental ceramics,21

used in result interpretation in this study, found that a 50:50%

CIELAB perceptibility threshold (DE* = 1.8) was statistically

different than corresponding 50:50% acceptability threshold

(DE* = 3.5). Another study reported significant differences in

50:50% acceptability thresholds for lightness, chroma and hue

differences for dental ceramics.24 Frequently referenced

earlier findings reported a DE* = 1.0 as the 50:50% perceptibility

threshold,25 whereas DE* = 2.726 and 3.327 were reported as the

50:50% perceptibility thresholds. The only study on visual

judgments performed on denture teeth reported DE* = 2.6 and

as the 50:50% perceptibility and DE* = 5.5 as the 50:50%

acceptability threshold.28 Significantly higher thresholds

compared to previous studies might have occurred due to

difference in areas compared visually and instrumentally,

sub-optimal color matching conditions and a ‘‘freestyle’’

shade matching method.29

In this study, all mean color differences by manufacturer

were below the 50:50% acceptability threshold of DE* = 3.5.

Actually, the color differences were above the 50:50%

perceptibility threshold only for Portrait IPN and SR Vivodent

PE denture teeth upon ageing. Color differences for Vita

Physiodens teeth upon staining in red wine and coffee, and

ageing were at or below the 50:50% perceptibility threshold.

Color changes by shade and differences in color coordinates

(Tables 1–4) can be easily interpreted using the threshold

values. Basically, all evaluated products and shades exhibited

good color stability and can be presented in the following

decreasing order: Vita Physiodens (most stable) > SR Vivodent

PE > Portrait IPN.

High-strength plastic denture teeth maintain resistance to

discoloration by pigments when compared to conventional

j o u r n a l o f d e n t i s t r y 4 0 s ( 2 0 1 2 ) e 4 7 – e 5 4 e53

denture teeth. The color stability was evaluated for two types

of high-strength plastic teeth and compared to two types of

conventional plastic teeth and one type of porcelain tooth in a

study that used food dye, coffee, and turmeric as coloring

liquids. High-strength denture teeth were significantly more

susceptible to pigments than porcelain teeth. The turmeric

coloring liquid had the greatest staining potential for all five

denture teeth, and color changes over time were significant.16

The high-strength plastic denture teeth used in this study

were susceptible to time-dependent color changes from coffee

and red wine that were found to be significant and clinically

perceptible.

Another study reported on color changes of three types of

reinforced acrylic denture teeth, and two types of porcelain

teeth after exposure to coffee, tea, and cola with distilled water

as the control. The research concluded that coffee was the

most chromogenic staining solution and discoloration was

time dependent.18 The present study confirms these findings,

as denture teeth became yellower and more chromatic due to

the effects of coffee.

The type of denture tooth, extrinsic staining, oral hygiene,

and diet affect the clinical discoloration of denture teeth. In a

study testing the discoloration of two types of porcelain,

conventional acrylic and reinforced acrylic denture teeth,

color evaluation for each group of teeth was done after

suspension in distilled water and immersion into solutions

of filtered coffee, tea, and cola. The greatest staining effect

for reinforced acrylic and conventional acrylic denture

teeth was seen with filtered coffee. However, cola had the

highest discoloration value for conventional acrylic denture

teeth.17

Microhybrid composite restorative materials exhibited less

pronounced color changes than nanohybrid composites when

exposed to discoloration media. Surface roughness, surface

integrity, and polishing technique affect stainability. The

superficial layer of composite resins adsorbs staining agents

leading to discoloration of composite resin restorations. A

study evaluated the discoloration of two nanohybrids, two

microhybrids, and a posterior composite resin material after

exposure to tea, cola, coffee, red wine, and water. Evaluation of

color was measured before and after immersion in each. A

significant change in color was found, and red wine held the

highest value for color change. The study concluded that all

composite restorations underwent clinically unacceptable

color changes, but that triethyleneglycol-dimethacrylate

(TEGDMA) may be responsible for high discoloration rates

due to its hydrophilic nature.30

A study to assess discoloration of acrylic resin denture

teeth following thermal cycling and polymerisation methods

was done using different denture teeth manufacturers. The

teeth were subjected to simulated microwave polymerisation

and simulated conventional polymerisation in a water bath

followed by thermal cycling in a simulation machine.

Significant color differences were found between Biotone

IPN and SR Vivodent PE teeth irrespective of the method of

polymerisation. However, DE* values were <3.5 overall and,

therefore, no clinically significant color changes were found.

No significant differences were found between color changes

following microwave polymerisation and conventional poly-

merisation.31

Cross-linking agents and fillers are added to acrylic teeth

to provide discoloration resistance, improve strength and

prevent crazing, and to increase resistance to wear.32 When

four experimental composite resin teeth were fabricated with

three types of fillers, it is interesting to note that color stability

was not influenced by the presence of a polished tooth

surface. Filler exposure and not surface roughness was

considered to be due to the effects of polishing. The study

showed that discoloration occurs in the matrix resin, filler,

and at the interface. Silanisation of the filler prevented gaps

that could form at the interface due to matrix resin swelling

by water uptake. Polishing was not a strong factor in

discoloration, if the surfaces were polished and the fillers

were silanised.33

5. Conclusions

Although the null hypothesis has been partially rejected,

because some statistically significant changes in color and

color coordinates occurred upon staining and ageing, all

evaluated denture teeth exhibited good color stability com-

pared to the 50:50% acceptability threshold used in data

interpretation.

The smallest overall color shift upon staining and ageing

was recorded for Vita Physiodens (most color stable), followed

by SR Vivodent PE and Portrait IPN denture teeth. The most

pronounced changes in lightness, chroma and hue were

recorded for Portrait IPN, Vita Physiodens and SR Vivodent PE

denture teeth, respectively. In general, the denture teeth

became darker, more chromatic, and redder, due to the effects

of red wine and coffee, but with varied degrees of staining

amongst them.

Conflict of interest statement

Dr. Paravina is a paid consultant for Vita Zahnfabrik. He

participates or has participated in projects funded by

Dentsply, Ivoclar Vivadent and Vita Zahnfabrik; however, no

significant financial contributions or funding to this work were

made by these manufacturers.

Acknowledgments

The authors thank Dr. W. Patrick Naylor, scientific advisor;

Dr. Judith M. Strutz and Dr. Warren S. Yow, critical reviewers;

Dr. Udochukwu E. Oyoyo, assistance with data analysis; Dr. R.

Steven Kurti, Mr. Miroljub Ilich, Mr. Ronald D. Moran, and Mr.

Daryl L. Osborne, technical advisors. Denture teeth for the

study were donated by Ivoclar Vivadent, Amherst, NY, Vident,

A Vita Company, Brea, CA and Dentsply Trubyte, York, PA.

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