Prosthodontics

In vivo color stability of resin composite veneers andacrylic resin teeth in removable partial dentnresMartin Rosentritt. MS*/Jacqueline Esch. DDS**/Michael Belir, DDS, MS***/Alexander Leibrock, DDS. MS i **/Gerhard Handel. DDS, MS.

Objective: The color stability of laboratory-made composite veneers was compared to tiiat of artificialresin teeth under in vivo conditions.Method and materials: Veneers and re.sin teeth of removable partial dentures were measured colorimet-rically with reflection spectrophotometiy: the color changes were characterized in the CommissionInternationale d'Eclairage L*a*?i* color space. The color wasßrst determined 24 hours afler manufac-ture and again after 6, 12. and IS months at incisai, cen'ical, and centrofaciat tooth positions. The den-ture teeth and veneers were measured, cleaned to eliminate the influence of surface discoloration, andmeasured again at every recall. The food consumption and tooth cleaning habits of the patients weretaken into account.

Results: In all groups the mcaimum color changes from tiie baseline measurement were at* -2.1, Aa*= 0.4. and Ab* = 1.8. The changes in the AE* values were between 1.0 and 2.5 units. Despite polishing,the AE'*' values increased by approximately 0.2 to 0.3 units in relation to the previous measurement withincreased wearing time. External discolorations were eliminated by polishing, depending on the type ofmaterial: the maximum color change because of polishing was between 0.8 and 2.0 units for AE*. Theresin teeth .showed no significant changes in the Af* values.

Conclusion: After a wearing period of 18 months, the discolorations of the tested materials were clini-cally acceptable. The artificial resin teeth showed statistically smaller color changes than did the veneer-ing materials. (Quintessence Int 1998;29:517-522)

Key words: artificial resin teeth, CIEL'*a*"b' measurement, color stability, resin composite veneer

Clinical relevance

Laboratory-made composite veneers and artificialresin teeth showed good color performance over aperiod of 18 months in vivo.

Resin composite veneers offer high security in tele--scopic dentures hecause of their high modulus of

•Engineer, Deparlmeni o I" Pros ihe lit Demislry, Universily Clinics,Universit)' of Regensburg, Regensburg, Germany

**Clinical Assistant, Deparlmeni of Proilhetie Dentislry, UniversityClinics, University of Regensburg, Regensburg, Germany.

*'*Assistant Professor, Department of Prostheiie Dentistry, UniversityClimes, University of Regensburg, Regensburg, Germany.

****PiDfes.sQr and Chairman, Deparlment of Prosthetie Dentistry, Uni-versity Clinics, University of Regensburg, Regensburg, Germany.

Reprint requests: Mr Martin Rosentritt, Department oT ProslheticDentistry, University of Regensbtirg, D-93042 Regensburg, Germany, E-maii: Martm,Rosentritt@'klinik,uni-regensbijrg,de

elasticity,' Resin composite veneers are easier to pro-cess and repair than porcelain veneers because of iheeasy handling. The color stahility of composite veneersis, however, lower than that of ceramic veneers'; com-posites even show colorimetric changes during the light-curing process.

Consequently, various attempts have been made tooptimize the polymer materials to achieve long-termcolor stahility. Visible color change, could be ascer-tained and characterized in tbe Commission Inter-nationale d'Eclairage (CÍE) L' a' b '' color system witbtbe belp of reflection spectropbolometry.-" Time-lapsedartificial agitig processes bave been used lo simulate tbealterations in color caused by, eg, ultraviolet ligbt, invitro,^''

The aim of this in vivo examination was to comparethe color performance of various laboratory-manufac-tured veneers and artificial acrylic resin teeth, Tbe in-fluence of the patient's tootb-cleaning habits and con-sumption behavior on tooth color should be taken intocon .si deration.

Quintessence inlernationai 517

Rosentritt et ai

Denture

Position ofmeasurement; /

incisai ¡Í

centrofacial \

cervical V

my—X V

\

O 1

^ ^ / Positioning/ ^ S template

JMeasurementdei/ice/

' ) ' ()

Fig 1 Design of measurement.

TABLE 1 Veneering materials and artificial teeth

MaterialVisio-Gem (ESPE)

(iight-curing)

Dentacoior (Kulzer)(iight-curing)

Vitapan(VitaZahnfabriii)(acrylic resin teeth]

Vita Zeta(Vita Zahntabrik)(heat-curing]

Shades

A3, A3.5, A4,C2, C3, D4

A3, A3.5, B3,B4, C2, C3. D2

A3, A3.5. A4,B3, B4, C2,C3, D2. D3A3, A3.5

Composition of resins

Pastes: bisacrylates, calcium fiuoride.silanized siiicic acid, camphorquinone, aminephosphine oxides, stabilizers, pigments

Liquid: methyi methacryiate, bifunctionaiacrylate, capper cheiate, amine hydrochio-ride. phospliine oxide, copolymer

51% pyrcgenic siiicium dioxide48.5% muitifunctional methacrylic esters24% inorganic filier (oniy by shade modifiers)14% highiy-dispersed silicic acid85% poly(methyi methacrylate)1% inorganic shade pigmentsLlrethanedimethacryiate, dimethacryiate.

pciymethacryiate, silicic acid, peroxides.inorganic shade pigments, paste materiai(hydroquinone-free)

Method and materials

In 25 patients. 62 veneers (20 Visio-Gem, 6 VitaZeta, 36 Dentacoior) and 32 ncighhoring resin compos-ite teeth on removable dentures were coiorimetricaliymeasured. The materials were assigned randomly, eachpatient receiving only one type of material. Maxillaryand mandibular anterior teeth, from centrai incisors topremolars. were fitted for new dentures. The veneeringmaterials (Tabie I) were appiied and light cured ontothe doubie crowns of the removable partiai dentures ac-cording to each manufacturer's instructions at a com-mercial dental laboratory. The tested colors were A3,A3.5, A4, B3, B4, C2, C3, D2, and D4 according to theVita color scale (Vita Zahnfabrik).

Ail color measurements were made incisaliy, centro-

facially, and cervically with a spectral photometer(Castor, Nordmeditech) using a positioning tetnplate de-scribed by Leibrock et aF (Fig 1). Ten separate measure-ments were carried out on every position, and the meanvalue and standard deviations of the color coordinates,L*, a• and b" ', were calculated. The color tneasurementsallow evaluation of the coior changes in each sampie.The CTE L*a*b* system is defined as a color space withcoordinates for whiteness-blackness (L"=), redness-green-ness (a'"), and yellowness-hlueness (b ). Total color dif-ferences are expressed by the following fonimla:

AE ' jb = [(AL*)= + (Aa*)- + (Ab i')2]i'2

where AL"% Aa^S and Ab* are differences in the respec-tive L•^ a"-, and b''' values.

518 Voiume 29. Number g,

Rosen tritt et al

Visio-Gem Dentacolor Vi ta pan

Fig 2 AE' values from unpolished material after corresponding poiishing (median [blsok iine],25th percentiie [bottom of bar], and 75th perceniiie [top of bar]).

As dictated by the German Institute of Organizing6174." the color difference (AE*) and the color contri-bution (AC*) were calculated in relation to a controlmea.surement. Teeth and veneers were measured for thefirst time 24 hours after manufacture (control, measure-ment 0). Additional measurements were carried outafter a wearing period of 6 months (first measurement),12 months (third measurement), and 18 months (fifthmeasurement). The second, fourth, and sixth measure-ments represent the corresponding values after polish-ing (P3 Pohshing toothpaste. Polirapit). Measurementswere carried out on air-dried and disinfected specimens(Impresept, ESPE).

The patients were questioned about tbeir consump-tion behavior, such as tea or coffee drinking and smok-ing, and cleaning habits, such as their use of cleaningtahlets, toothpaste, or liquid for cleaning their dentures.A questionnaire was used to determine the amount andfrequency of the patients' habits. Median and the 25%and 75?i: percentiles were calculated for the color dif-ferences. AE ' and AC*. Statistical analysis was per-formed with the program SPSS for Windows (6.0.1)using the Mann-Whitney U test. The level of signifi-cance was set at a = .05.''"'

Results

All veneers showed similar color differences afterwearing periods of 6, 12. and 18 months. The AE''' andAC* values increased, and the veneers became darkerand more yellow. Only Visio-Gem and Vitapan showeda smaller increase in AC* values after 18 months incomparison to the values after 12 months. No color

changes could be determined for all six samples of VitaZeta after 18 months becau.se that patient failed to ap-pear for follow-up. All values on the red-green axischanged slightly (Aa* < 0.4). The resin teeth showed thesmallest color changes. The maximum color change,AE*, was 2.7 units for Vita Zeta, followed hy Visio-Gem (2.2 units), Dentacolor (1.8 units), and Vitapan( 1.4 units). Regarding the color behavior of the differentshades, only shade C2 (measurement 4) and C3 (mea-surements 5 and 6) showed significantly higher AE*values.

Polishing of the materials caused an inerease inbrightness of AL* (0.1 unit); the Ah* values of all mate-rials decreased ahout 0.1 to 1.2 units, and the Aa* val-ues hardly changed at all (Aa* < 0.2). The maximumcolor difference, AE*, hetween polished and unpolishedmaterials was achieved by Visio-Gem (AE* = 2.0). Theresin teeth showed the smallest color difierence (AE*between 0.8 and 1.3 units). The polishing achieved anaverage change of 1.65 units in AE* values (Fig 2).

The position of the measurement point only showeda significant influence (P - .04 and /• = .01) on the in-cisal area for the enamel materials of Visio-Gem and ofVita Zeta.

No significant infiuence of the consumption hehaviorand the cleaning habits on the AE* values could be es-tabli.shed. All color changes are shown in Fig 3; the cor-responding significances are listed in Tahle 2.

Discussion

The National Bureau of Standards (NBS) estab-lished a sophisticated ciassificafion to describe color

Quintessence International 519

Rosentriit et ai

Visio-G em Dentacolor Vi tapan

QAt ter 6 months(1. measurement)

After polishing(2. measurement)

1 ^ After 12 months(3. rnea sûrement)

^ A f t e r polishing(4. measurement)

M After 18 mcnths(5. measurement)

B Alter pciishing(6. measurement)

Fig 3 AE" values after 6,12. and 18 mcnths of wear and atter corresponding polishing (median[black line], 251h percentiie (bcttom of bar], and 751h percentile [lop of bar]).

TABLE 2 Statistical analysis (Mann-Whitney Utesta = .05)

Visio-Gem

AE'5AE*6

DenlacolorAE*2AE*gAE*4AE*5AE-6

VitapanAE*2AE;3

AE*6

Vita Zeta

AE*^

NS = not significant

AE-1

„

NS*NS

NSNSNS

NS

NSNSNSNSNS

NSNS

AE-2

•

NS

NSNS

NS

NSNSNSNS

.

NS

* = significant; —

AE-3

NSNS

NS

NS

NSNSNS

-

AE

NS

NSNS

NSNS

-

- missing values.

AE-5

NS

NS

NS

differences hy NBS units. Assuming that color changesof AE '' < 1.0= 'I are a discernible limit and AE* -3.3'-"'"'is an acceptable valiie, ihe tested color changeswere in the visible ranges, but still acceptable. As men-tioned by Setz and Engel' and described hy Leihrock

et al,' the deviation of the measured values was im-proved by using a positioning template for the measur-ing head.

The artificial resin teeth showed statistically smallercolor changes than did the veneering materials. After an18-montli period of intraoral service, no significantcolor change could be determined for the resin tooihmaterial. The different color performances of the ve-neering materials and the resin teeth can be attributed toprocessing and composition of the materials. The re.sinteeth, based on polylmethyl methacrylate), have a highconversion rate (according to the manufacturer) and alow content of additional reagents, such as dihenzoyiperoxide, for example, that remain after the reaction andmay spoil the color stability. Seher and Vi o hi "• descrihedthat polydiiethyl methacrylate) and diurethane di-methacrylate had hetter color stabihty than did experi-mental resins.

The veneering materials contain ultraviolet stabiliz-ers, which could be obstructed in their activity by unfin-ished polymerization processes or through aging result-ing from moisture, warmth, or massive ultravioletrays." Raecke"* demonstrated in in vitro tests that ultra-violet light-curing composites show, comparatively, thehighest discoloration. Differences in the amount of inor-ganic niler, eg, for Visio-Gem and Dentacolor, have noeffects on the color stahility of the materials.^ '

In contrast to the results of similar in vitro tests byRuyter et al,'= the heat-curing material (Vita Zeta)showed worse results than the light-curing materials(Visio-Gem, Dentacolor). A number of variables mavhave affected the color stability, eg, chemical differ-ences among the resin components, both filler type and

520 Voiume 29, Numbers, 1998

Rosentritt el al

coticentration.i-' and irnprecise observance of the pre-scribed polymerization time during the processing ofthe heat-curing material.

The position of the measurement point had a signifi-cant influence on the color changes of Visio-Gem (in-cisal) and Vita Zeta (incisai). The location of the mea-surement positions (cervical, centrofaciai, incisai),which take into account the differences between enameland dentinal material or the oral situation, had onlysmall influence on the level of discoloration of the ve-neers. The differences in ihe color hehavior of thevarious color shades—only C2 and C3 showed anysignificant AE^ values (measurement 5)—indicated asmall influence of color pigments or the composition ofthe differently colored materials. Because the layeringtechnique and the shades cannot be .standardized, thedifferent color shades could mutually affect eachother.-

The polishing of the veneers Increased their hright-ness and reduced their yellowness; exogenous discol-oration can be reduced by polishing the surface of thematerial."-' Despite repeated polishing, an increasingcolor change was detected, which indicated that internalreactions affect the discoloration. Um and Ruyter"demonstrated in vitro that the discoloration is caused bydistinct pigments that penetrate the structure of theresin. Assuming coior changes of 6 units in a 3-yearwearing period' and that the first signs of poor appear-ance could clinically be detected after 3 to 4 years,-^ thepolishing of the dentures would contribute to an ex-tended life span.

After 18 months, an increase in AE''- values could bedetermined; however, a significant correlation to foodconsumption habits could not be established. This is re-lated to the fact that the superficial di.scoloration was re-moved at 6, 12, and 18 months, so exogenous discol-oration could not accumulate.

Results by Khokhar et al,-' .showing that discol-oration can be removed from Dentacolor and Visio-Gemif the patient practices adequate oral hygiene could notbe confirmed because of the test design. According toPlacek,--" color changes on resin composites seem not todepend on the amount of plaque or on smoking and cof-fee or tea drinking. Seher and Viohl.'" however, showedin vitro that staining has a greater effect on discol-oration than ultraviolet irradiation.

Some variables in clinical color testing could beavoided, for example, by using a positioning template, alevel and even measurement area, the same test person,and standardized conditions in roughness, dampness,and shine. By observing the individual habits and fac-tors, the sample size of the individual groups is greatlyreduced, and the statistical expressiveness suffers

greatly. Both patient dropout and patient education, incombination with the changed cleaning behavior duringthe examination, may affect the results.

Conclusion

Successful assessment of color stability cannot heachieved by absolute color measurements but rather bymeasuring relative—before and after—color changes.Overall, the tested materials showed a good color perfor-mance over a wearing period of 18 months. The methodused for colorimetric examination of resin veneers invivo proved to he good for relative color measurement.

References

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2. Mnrxkors R, Meiners H. Kunitsto live rb lend ungen. Abrasion undZahtipflcgc. Indikation [n: Taschenbuch der ïahnarztliehenWerkstoffe, ed 3. Munich: Hanser, 1988:154-156.

3. Seghi RR. Gritz MD, Kim J. Colorimetric changes in compositesresulting from visible-light-initiated polymerization. Dent Mater1990;6:133-137.

4. DIN EN 27491: Zahnärztliche Werkstoffe, Bestitiimting derFiirbbeständigkeit bei zahnärztlichen Kunststoffen. Berlin:Beuth. 1991.

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6. Lang R. Rosentriu M, Leibrock A, Behr M, Handel G. Color sta-bility of provisional crown and bridge restoration maierials.Presented at the 34th CED/IADR Session, Madrid, 1997.

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