Color stability of facial prostheses.pdf

7/30/2019 Color stability of facial prostheses.pdf

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C o l o r s t a b i l i t y o f f a c i a l p r o s t h e s e sJ a m e s C . L e m o n , D D S , a M a r k S . C h a m b e r s , D M D , bM i c h a e l L . J a c o b s e n , D D S , c a n d J o h n M . P o w e r s , P h D dThe U nivers i ty of Texas, M. D. And erson Can cer Cente r , Hous ton , Tex .

T h e l i m i t e d s e r v i c e o f f a ci a l p r o s t h e s e s i s t h e r e s u l t o f d e g ra d a t i o n o f t h e e l a s t o m e ra n d c o l o r i n s t ab i l i ty . D e t e r i o ra t i o n m a y b e c a u s e d b y m a n y f a c to r s, w h i c h i n c l u d ee n v i r o n m e n t a l e x p o s u r e a n d c h a n g e s i n h u m i d i t y . T h i s i n v e s t i g a t i o n a s s e s se d t h ee f f i c a c y o f a n a d d i t i v e , i n t r i n s i c , b r o a d - s p e c t r u m u l t r a v i o l e t l i g h t a b s o r b e r o n t h ec o l or s t a b i l i t y o f a p i g m e n t e d f a c i a l e l a s to m e r . S a m p l e s w e r e w e a t h e r e d a r t if i c ia l l ya n d o u t d o o r s a t e x p o s u r e l e v e l s o f r a d i a n t e n e r g y o f 1 50 t o 4 5 0 k J / m 2. T h e s a m p l e sc h a n g e d c o l o r s l i g h t l y b u t p e r c e p t i b l y . A r t i f i c ia l a g i n g c a u s e d a g r e a t e r c h a n g e t h a no u t d o o r a g i n g . T h e u l t r a v i o l e t l i g h t a b s o r b e r U V - 5 41 1 d i d n o t p r o t e c t t h e s a m p l e s f r o mcol or ch an ge s . (J PROSTHET DENT 1995;74:613-8 .)

M a x i l l o f a c i a l p r o s t h et i c t r e a t m e n t a ll o w s m a n yp a t i e n t s w i t h o r o f ac i a l d ef e c ts t o r e t u r n t o a n a c t i v e r o l e inp u b li c .1 T h e r e s u l t s o f p r o s t h e t i c t r e a t m e n t a r e i n f l u e n c e db y t h e n a t u r e o f t h e d e fe c t , th e s k il l o f t h e p r o s t h o d o n t i s t ,a n d t h e p r o p e r t i e s o f t h e m a t e r i a l s u s e d . T h e m o s t c ri t i ca lp r o p e r t i e s a r e e s t h e t i c s, d u r a b i l i ty , a n d a c c u r a c y o f p r o -c e s si n g . 2 P a t i e n t s a r e c o n c e r n e d w i t h t h e d u r a b i l i t y a n de s t h e t i c s o f t h e p r o s t h e s i s . A p r o s t h e s i s m u s t b e d u r a b l e ,e s t h e ti c , a n d c o l or st a b le , 3 a n d w i t h t h e a d v e n t o f i m p l a n t -r e t a i n e d f a c ia l p r o s t h e s e s , c o l o r s t a b i l i t y i s o f p a r t i c u l a rc o n c e r n .

T h e l i m i t e d s e r v ic e o f f a c ia l p r o s t h e s e s i s a r e s u l t o f t h er a p i d d e g r a d a t i o n o f t h e e l a s t o m e r a n d i t s c o l o r i n s t a b il i t y .T h e w e a r i n g t i m e f o r f a c ia l p r o s t h e s e s a v e r a g e s f r o m 3m o n t h s t o I y e a r. D e t e r i o r a t i o n i s m a i n l y c a u s e d b y e n v i-r o n m e n t a l e x p o s u r e t o u l t r a v i o l e t ( U V ) l ig h t , a i r p o l l u ti o n ,a n d c h a n g e s in h u m i d i t y a n d t e m p e r a t u r e . H a n d l i n g t h ep r o s t h e s i s d u r i n g c l e a n i n g a n d t h e a p p l i c a t i o n o f a d h e -s i v e s a n d c o s m e t i c a d d i t i v e s m a y a l s o a l t e r t h e p h y s i c a lp r o p e r t i e s a n d c o l o r s t a b i l i t y o f t h e m a t e r i a l . 3-6 S u r v e y sh a v e r e p o r t e d c o l o r f a d i n g a s t h e m o s t f r e q u e n t r e a s o n p a -t i e n t s g i v e f o r d i s l i k i n g t h e i r p r o s t h e s e s . O b j e c t i v e i n v e s -t i g a t i o n s o f c o l o r s t a b i l i ty i n f a c i a l e l a s t o m e r s h a v e u s e da r t if i c ia l l i g h t s o u r c e s , a rt i f ic i a l w e a t h e r i n g c h a m b e r s , a n dr e f l e c t i o n s p e c t r o p h o t o m e t r y . 2, 7-10

aAssociate Professor , Section of Oncologic De ntist ry an d Pro stho-donticsbMaxillofacial Prosthodo ntist, S ection o f Oncologic De ntistr y andPros thodont ic .CMaxillofac ia l Pros thodont is t , Pr iva te Prac t ice , Kan sas City , Kan-sas.dprofessor, D epa rtm ent of Basic Sciences, and D irector , Biomate-r i a ls Re s e a r c h Ce n te r, Un iv e r s i ty o f Te x a s - Ho u s to n He a l thSc ience Cente r , Denta l Branch .Co p y r ig h t 9 1995 by the Edito rial Council of THE JOURNALOFPROSTHETIC DENTISTRY.0022-3913/95 /$5.00 + 0. 10/1/67769

I n v e s t i g a t i o n s i n t o w h e t h e r a n a d d i t i v e U V l i g h t a b -s o r b e r w o u l d i m p r o v e c o lo r st a b i l i t y o f fa c i al e l a s t o m e r sa r e l im i t e d . A d d i n g a n o v e r - t h e - c o u n t e r s u n s c r e e n p r o d u c tt o a f a c ia l e l a s t o m e r m a y i n t e r f e r e w i t h t h e p o l y m e r i z a t i o na n d p r o p e r t i e s o f t h e e l a s t o m e r b e c a u s e o f t h e p r e s e n c e o fp r o p y l e n e , g l y c er y l , s t e a r a t e s , a n d m i n e r a l o i ls in t h e s u n -s c r e e n t h a t m a y i n h i b i t t o t a l c u r i n g . 6, 11 N e v e r t h e l e s s , C h ua n d F i s c h e r TMe v a l u a t e d t h e e f fi c ie n c y o f a d d i t i v e U V l i g h ta b s o r b e r s a n d a n t i o x i d a n t s i n p o l y u r e t h a n e e l a s t o m e r s b ye x p o s i n g 1 1 t y p e s o f U V l i g h t a b s o r b e r s c o u p l e d w i t h o n ea n t i o x i d a n t t o U V li g h t i n a n a g i n g c h a m b e r . T h e y fo u n dt h a t y e l l o w i n g w a s s i g n i f i c a n t l y l e s s e n e d a n d t h a t U V l i g h ta b s o r b e r s m a d e f r o m b e n z o t r i a z o l e o r a m i n e g r o u p s w e r et h e m o s t e f f e c ti v e c o m p o u n d s .T h e p l a s t i c s a n d c o s m e t i c s i n d u s t r i e s h a v e a d d r e s s e dp r o b l e m s o f c o l or s t a b i l i t y b y u s i n g c h e m i c a l a d d i t i v e s i nf o r m u l a t i o n s . S p e c t r a - s o r b U V - 5 4 1 1 ( A m e r i c a n C y a n a m i dC o . , W a y n e , N . J .) , a n o f f - w h i t e fr e e - f l o w i n g p o w d e r , i s ab e n z o t r i a z o l e c o m p o u n d w i t h d u r a b i l i ty , b r o a d - r a n g e ( 2 60t o 3 9 0 n m ) U V - a b s o r p t i o n p r o p e r t i e s, l o w c o lo r , g o o d c om -p a t i b i l i t y , a v i r t u a l l y u n l i m i t e d s h e l f l if e , a n d r e a s o n a b l ec o s t . N o r m a l c o n c e n t r a t i o n s i n i n d u s t r i a l u s e r a n g e f r o m0 . 5 % t o 1 . 0 % b y w e i g h t . I t i s r e l a t i v e l y n o n t o x i c , a se v i d e n c e d b y l a c k o f s k i n i r r i t a t i o n o r a l l er g i c s e n s i t i z a t i o ni n 1 0 0 h u m a n s u b j e c t s t e s t e d w i t h t h e M o d i f i e d D r a i z e -S h e l a n s k i I n s u l t P a t c h T e s t. 13T h i s i n v e s t i g a t i o n a s s e s s e d t h e e f f i c ac y o f a U V l i g h t a b -s o r b e r o n t h e c o l o r s t a b i l i t y o f a f a c i a l e l a s t o m e r . C o l o r w a se v a l u a t e d b e f o r e a n d a f t e r a r t i fi c i al w e a t h e r i n g a n d d i r e c to u t d o o r e x p o s u r e . S p e c t r o p h o t o m e t r i c a n a l y s i s w a s p e r -f o r m e d t o a s s e s s c o l o r c h a n g e s a n d t o d e t e r m i n e t h e e f f ec t so f a r t if i c ia l w e a t h e r i n g a n d o u t d o o r w e a t h e r i n g o n c o l o rs t a b i l i t y .M E T H O D S A N D M A T E R I A L

T h e s t u d y c o n s i s t e d o f t h r e e g r o u p s o f 1 2 s a m p l e s e a c ht h a t r e p r e s e n t e d t h r e e d i f f e r e n t f o r m u l a t i o n s . T h e b a s ee l a s t o m e r m a t e r i a l t e s t e d w a s a m i x t u r e o f R T V s i l ic o n e s

DECEMBER 1995 613


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THE JOURNAL OF PROSTHETIC DENTISTRY LEMON ET AL

Table I. Parameters in experimental designAging conditions Artificial aging

Outdoor weatheringFormulations (% of 0.0

UV-5411) 0.10.25

Exposure energy 150(kJ/m2) 300450Repetitions 6 samples for each formulation

and aging conditionMeasurement Color (CIE L*a*b* and AE*) by

ASTM D22442~ using areflectance spectrophotometer

Table II. Eval uati on of weath erin g by test specificationSAE J196014Light source

Irradiance level

Test cycle

Black paneltemperatureDry bulb temperature

Relative humidity (%)

Controlled-irradiance xenonarc filtered through highborate borosilicate innerand outer glass filters.

0.55 W/m2/nm at 340 nm fortest intervals of 150, 300,and 450 kJ /m 2

40 minute s light only20 minutes light plus front

spray60 minutes light only60 minutes dark plus back

spray70 3 ~ C light/38 + 3 ~ C

dark47 2 ~ C light/38 _+ 4 ~ Cdark

50 5 light/95 _+ 5 dark

(MDX4-4210 and type A medical adhesive, Dow Coming,Midland, Mich.), oil-base pigments, and kaolin (Factor II,Georgia Silica, Lakeside, Ariz.). A UV light absorber UV-5411 (Spectra-sorb UV-5411; American Cyanamid Co.)was added in the formul ations of the three grou ps (0.0%,control; 0.1% and 0.25% by weight) of 12 samples each. Sixsamples from each group were subjected to artificial aging,and six were exposed to outdoor weathering. The experi-mental design is summa rized in Table I.S a m p l e p r e p a r a t i o n a n d m a t e r i a l sm a n i p u l a t i o n

The samp les, 2.4 mm x 6 cm x 4.5 cm sheets, were mad eby invest ing wo layers ofbaseplate wax (Truwax, DentsplyInte rnat ion al, York, Pa.) in a polyvinyl chloride flask withvacuum-mixed stone (Die-Keen; Miles Inc. Dental Prod-ucts, So uth Bend, Ind.). A tinfoil substitu te was used to fa-cilitate separation of the flasks. The wax was boiled out,

and t he flasks were allowed to cool. Eigh tee n flasks yieldeda total of 18 samples.

A 3:1 ratio of type A medi cal adhe sive to MDX4-4210elastomer by volume was used to prepare 54 samples. Thekaolin was added at 10% by volume. The UV light absorberUV-5411 was also added at 0.0%, 0.1%, and 0.25% byweight . Prel i minary mixing trials determin ed that 240 ccof mate rial was needed for each of 18 samples. Thus a180-cc mix of MDX4-4210, pigm ents, a nd kaolin was firstmade to ensur e consistency of samples. A tubercul insyrin ge was us ed to add 0.05 cc of yellow ochre, cadm iumred, and bu rn t sienn a oil-base pigmen ts (M. Grumbacher,Inc., Cranb ury, N. J.) to each sample an d produced a com-mon Caucasian base color. The mixture was then appor-tioned into three 60 cc parts, each weighing 74 gm. To each60 cc (74 gm) part, 24 cc (13 gin) of kao lin was added. Ty peA adhesive was t hen combined with each pigznented por-tion up to 240 cc (total weight 290 gm). Finally, UV-5411was in corporated into two of the m ixtures at 0.1% (0.29 gin)and 0.25% (0.73 gm), respectively.Individual mixtures were spatulated by hand u nti l thecolors were evenly distributed. T hen m ixtur es were pouredinto the flask with no sepa ratin g medium. The flasks wereplaced into a standar d, tigh tened flask press. The mater ialwas allowed to set at room tem pera ture for 24 hours. After24 hours the flasks were placed in circulating hot air at 80 ~C for 30 minutes. The samples were remov ed and placedinto an oven for 30 minut es to ensur e complete curing. Thesamples were inspected for voids, bubbles, and contami-nants, and the 12 best samples in each 18-sample groupwere selected for a total of 36 samples.S a m p l e e x p o s u r e s a n d e v a l u a t i o n o f co l or

Two groups of 18 samp les were exposed to two differentconditions, artificial aging an d direct outdoor weathering.Specification SAEJ 1960 was used for the artificial agingparam eters. 14 Samples were placed in an aging chambe r(Ci35 Weather-Ometer, Atlas Electronics, Chicago, Ill.)and subjected to light exposure, water spray, te mperatu re,and humidity (Table II). Light from the xenon arc lightsource was filtered thro ugh high borate borosilicate inn erand o uter filters to better simulate the spectral power dis-tribu tion of sunlight. 15 The test w as ru n at a n irra diancelevel of 0.55 W/m2/nm at 340 nm for increm ents of 150,300,and 450 kJ/m 2 of total rad ian t energy. 16

The outdoor samples were mounted on an untreated,plywood-backed exposure rack (ASTM G7) and were ex-posed according to the ASTM E782 v ariable angle sched-

17 18ule. ' Duri ng the outdoor exposure the samples were leftuncovered and exposed to the enviro nmen t. The exposurerack was adjusted to an angle close to perpendicu lar to thedirect beam of solar radiati on to maximize the a mou nt ofsunlight on the samples. Peak radiation levels in Floridaduring the summe r month s can reach 1.0 W/m2/nm at 340nm.15

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L E M O N E T A L T H E J O U R N A L O F P R O S T H E T I C D E N T I S T R Y

Table III. The effect of artificial aging on CIE color par ame ter sU V - a b s o r b e r c o n c e n t r a t i o n

E n e r g y( k J i m 2 ) P a r a m e t e r 0 . 0 % 0 . 1 % 0 . 25%0 L* 74.33 (0.24)* 74.64 (0.10) 73.67 (0.20)

a* 10.16 (0.05) 9.30 (0.10) 9.39 (0.11)b* 16.31 (0.21) 16.04 (0.21) 15.63 (0.11)150 L* 74.82 (0.17) 75.50 (0.08) 74.75 (0.15)a* 9.25 (0.06) 8.56 (0.10) 8.80 (0.12)b 16.59 (0.10) 16.81 (0.15) 16.63 (0.12)AE* 1.08 (0.08) 1.37 (0.10) 1.58 (0.09)

300 L* 74.48 (0.19) 75.26 (0.08) 74.49 (0.12)a* 9.13 (0.06) 8.36 (0.11) 8.51 (0.10)b* 16.93 (0.10) 17.32 (0.13) 17.10 (0.16)AE* 1.21 (0.07) 1.70 (0.15) 1.90 (0.10)

450 L* 74.40 (0.18) 75.21 (0.06) 74.28 (0.23)a* 8.94 (0.08) 8.20 (0.12) 8.34 (0.14)b* 16.96 (0.08) 17.49 (0.12) 17.23 (0.23)hE* 1.39 (0.07) 1.91 (0.12) 2.01 (0.16)

* M e a n w i t h s t a n d a r d d e v i a t i o n i n p a r e n t h e s e s . T h e T u k e y - K r a m e r i n t e rv a l f o r c o m p a r i s o n s o f m e a n s o f A E * a m o n g c o n c e n t r a t i o n s a t t h e 0 . 0 5 si g n i f ic a n c el e ve l w a s 0 . 1 5 . D i f f e re n c e s b e t w e e n m e a n s g r e a t e r t h a n t h e T u k e y - K r a m e r i n t e r v a l w e r e c o n s i d e r e d s t a t is t i c a l ly s i g n if i c an t .

Table IV. Analysis of varian ce of the effects of energy levels of artificial aging a nd UV absorb er conc entration on colorchange (AE*)

S o u r c e d f S u m o f s q u a r e s M e a n s q u a r e F v a l u e p V a l u eConcentration 2 3.470 1.735 57.8 0.0001Sample 15 0.450 0.030Energy 2 1.631 0.815 347 0.0001Energy*conc. 4 0.107 0.027 11.4 0.0001Energy*sample 30 0.070 0.002

Color was determined from spectral reflectance mea-surements in the visible range of 400 to 700 nm with adouble-beam, UV-visible spectrophotometer a nd integrat-ing sphere (MacBeth Color Eye 7000, Newburgh, N.Y.)with specular reflectance component included. The spec-trophoto meter was calibrated with a zero cone and a pri-mary w hite porcelain stan dar d of kno wn absolute reflec-tance value.

Reflectance measurements were made for each sampleat the interv als of interest. Before the samples were mea-sured, they were cleaned by wiping with gauze soaked i ndistilled water. The position of the samples was th e samefor each data-recording interval. CIELAB L*a*b* colordata were computed (Version 1.2KA, MacBeth Optiview,Newburgh , N. Y.) based on the CIE chrom aticity diagr am1931 and source A. 19 The v alue s of L*, a*, an d b* wer e en-tered on a spreadsheet program (Microsoft Excel, Red-mond , Wash.) for calculat ion of AE* as follows.

AE* = [(AL*)2 + (Aa*) 2 + (Ab*)2]1/2, wh ere AL*, ha* , an dhb* are changes in L*, a*, and b* between the int erval ofintere st an d b aseline, and hE* is the color difference. 2~L*,a*, b*, and AE* are dimensionless.

Means and standard deviations of L*, a*, b*, and AE*were calculated. A two-way analy sis of vari ance (ANOVA)with r epeated -measur es (SuperANOVA, Abacus Concepts,Berkeley, Calif.) was performed for the color difference(AE*) with the factors of exposure energy (repeated mea-sure at 150,300, or 450 kJ/ m 2) and concentr ation of the UVabso rber (0.0%, 0.1%, or 0.25%). In the second exper imen ta two-wa y ANOVA of AE* was u sed w ith factors of condi-tion (artificial or outdoor exposure) and concentration(0.0%, 0.1%, or 0.25%) of the UV abso rber. Means w erecompared by Tuk ey-K rame r intervals (SuperANOVA) cal-culated a t the 0.05 significance level. Differences betweenmeans greater than the Tukey-K ramer interval were con-sidered stati stica lly significant. Valu es of L*, a*, and b* arereported but were not analyzed statistically.R E S U L T SE f f e c t s o f a r t i f i c i a l a g i n g

The samples were examin ed initially for color unifor mityand were assessed to be uniform. A sample from each UV-5411 concentratio n group was tested in 10 different orien-tations on the spectrophotometer. The means and stan-

D E C E M B E R 1 9 95 6 1 5


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T H E J O U R N A L O F P R O S T H E T I C D E N T IS T R Y L E M O N E T A L

T a b l e V . E f f e c t s of a r t i f ic i a l v e r s u s o u t d o o r a g i n g a n d U V - a b s o r b e r c o n c e n t r a t i o n o n A E *U V - a b s o r b e r C o n c e n t r a t i o n

M o d e o f E n e r g ye x p o s u r e ( k J i m 2) P a r a m e t e r 0 . 0 % 0 . 1 % 0.25%A rtific ial 0 L* 73.33 (0.24)* 74.64 (0.10) 73.67 (0.20)

a* 10.16 (0.05) 9.30 (0.10) 9.39 (0.11)b* 16.31 (0.21) 16.04 (0.21) 15.63 (0.11)150 L* 74.82 (0.17) 75.50 (0.08) 74.75 (0.15)a* 9.25 (0.06) 8.56 (0.10) 8.80 (0.12)b* 16.59 (0.10) 16.81 (0.15) 16.63 (0.12)AE* 1.08 (0.08) 1.37 (0.10) 1.58 (0.09)

Ou tdo or 0 L* 74.30 (0.15) 74.37 (0.14) 73.57 (0.18)a* 10.16 (0.09) 9.33 (0.06) 9.27 (0.12)b* 16.28 (0.22) 15.97 (0.10) 15.57 (0.25)

150 L* 73.77 (0.16) 74.23 (0.16) 73.59 (0.13)a* 9.65 (0.11) 8.76 (0.30) 9.07 (0.08)b* 16.50 (0.19) 16.78 (0.28) 16.55 (0.25)hE * 0.78 (0.09) 1.04 (0.38) 1.01 (0.14)

* M e a n w i t h s t a n d a r d d e v i a t i o n i n p a r e n t h e s e s . T u k e y - K r a m e r in t e r v a l s f o r c o m p a r i s o n s o f m e a n s o f h E * b e t w e e n a g i n g c o n d i t i o n s a n d a m o n g c o n c e n t r a t i o n sa t t h e 0 . 0 5 s i g n if i c a n c e l e v el w e r e 0 . 1 2 a n d 0 . 18 . D i ff e r e n c e s b e t w e e n m e a n s g r e a t e r t h a n t h e a p p r o p r i a t e T u k e y - K r a m e r i n t e r v a l w e r e c o n s i d e r e d s ta t i s ti c a l l ys i g n i f i c a n t .

T a b l e V I . A n a l y s i s o f v a r i a n c e o f ef fe c ts o f a g i n g c o n d i t i o n a n d U V a b s o r b e r c o n c e n t r a t i o n o n c o l o r c h a n g e ( h E * )S o u r c e d f S t u n o f s q u a r e s M e a n s q u a r e F v a l u e p V a l u e

Co ndi tion 1 1.480 1.480 45.6 0.0001Co ncen t ra t ion 2 0 .876 0 .438 13.5 0 .0001Cond.*co nc. 2 0.135 0.067 2.07 0.14Re sidu al 30 0 .974 0 .032

d a r d d e v i a t i o n s w e r e v e r y s i m i l a r , a n d t h e c o e f fi c ie n t s o fv a r i a t i o n w e r e l ow .T h e m e a n s a n d s t a n d a r d d e v i a t i o n s fo r v a l u e s o f L * , a * ,

b * , a n d A E * o f t h e a r t i f i c i a l l y a g e d s a m p l e s a r e p r e s e n t e di n T a b l e I I I . T h e a n a l y s i s o f v a r i a n c e o f A E * ( T a b l e I V ) r e -v e a l e d t h a t s i g n i f i c a n t d i f f er e n c e s w e r e f o u n d , b e c a u s e e n -e r g y h a d a g r e a t e r i n f l u e n c e o n A E * t h a n d i d U V - a b s o r b e rc o n c e n t r a t i o n . T h e i n t e r a c t i o n o f e n e r g y a n d c o n c e n t r a t i o nw a s s i g n i f i c a n t b u t h a d l e s s o f a n e f fe c t t h a n t h e m a i n f a c -t o rs . T h e T u k e y - K r a m e r i n t e r v a l fo r c o m p a r is o n s o f m e a n so f A E * a m o n g c o n c e n t r a t i o n s a t t h e 0 .0 5 s i g n i f ic a n c e l e v e lw a s 0 . 1 5 .

V a l u e s o f L * fo r t h e 0 . 0 a n d 0 .2 5 c o n c e n t r a t i o n s i n -c r e a s e d a t 1 5 0 k J / m 2, t h e n d e c r e a s e d w i t h i n c r e a s i n g e n -e r g y . F o r a l l c o n c e n t r a t i o n s t e s t e d a * d e c r e a s e d , w h e r e a sb * i n c r e a s e d w i t h i n c r e a s i n g e n e r g y . V a l u e s o f A E * i n-c r e a s e d w i t h i n c r e a s i n g e n e r g y f o r a l l c o n c e n t r a t i o n s .E f f e c t s o f a r t i f i c ia l v e r s u s o u t d o o r a g i n g

T h e m e a n s a n d s t a n d a r d d e v i a ti o n s fo r A E * of t h e s a m -p l e s a g e d a r t i f i c i a l l y a n d o u t d o o r s a r e p r e s e n t e d i n T a b l eV . T h e A N O V A ( T a b l e V I ) r e v e a l e d s i g n i f i c a n t d i f f er e n c e sb e t w e e n c o n d i t i o n o f e x p o s u r e a n d U V a b s o r b e r c o n c e n -

t r a t i o n ( p < 0 .0 5 ). T u k e y - K r a m e r i n t e r v a l s a t t h e 0 . 0 5 s i g-n i f i c a n c e l e v e l w e r e 0 . 1 2 f o r c o n d i t i o n o f e x p o s u r e a n d 0 . 18f o r c o n c e n t r a t i o n .

V a l u e s o f L * a t a l l U V a b s o r b e r c o n c e n t r a t i o n s i n c r e a s e dw i t h a r t i f ic i a l a g i n g b u t d e c r e a s e d w i t h o u t d o o r e x p o s u r e .F o r b o t h a g i n g c o n d i t i o n s a* d e c r e a s e d , w h e r e a s b * i n -c r e a s e d w i t h i n c r e a s i n g e n e r g y f o r a l l c o n c e n t r a t i o n . A te a c h c o n c e n t r a t i o n v a l u e s o f h E * w e r e g r e a t e r f o r a r ti f i c ia la g i n g t h a n f o r o u t d o o r e x p o s u r e .D I S C U S S I O N

T h e C I E L A B s y s t e m u s e s t h r e e p a r a m e t e r s ( L * , a * , b * )t o d e f i n e c o l o r ( F i g . 1). L * i s l i g h t n e s s , w h e r e a s a * a n d b *a r e c h r o m a t i c c o m p o n e n t s . R e d h a s a p o s i t iv e a* v a l u e ,w h e r e a s g r e e n h a s a n e g a t i v e a * v a lu e . Y e ll o w h a s a p o s -i t iv e b* v a l u e , w h e r e a s b l u e h a s a n e g a t i v e b * v a lu e . T w oo b j e ct s w i t h a A E * o f a p p r o x i m a t e l y o n e u n i t w e r e j u d g e dt o b e a c o lo r m a t c h 5 0 % o f t h e t i m e b y h u m a n o b s e r v e rs . 2 ~

A l l a r ti f i c i a l l y a g e d s a m p l e s a t 0 . 0 % a n d 0 .2 5 % c o n c e n -t r a t i o n s o f U V a b s o r b e r b e c a m e l i g h t e r w h e n e x p o s e d t o1 50 k J / m 2 o f e n e r g y , a n d t h e n t h e y g r a d u a l l y d a r k e n e d a se x p o s u r e i n c r e a s e d t o 4 5 0 k J / m 2 o f en e r g y . T h e o u t d o o r -a g e d s a m p l e s b e c a m e d a r k e r w h e n e x p o s ed t o 1 50 k J / m 2.

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L *

e f t

+ar e c b *

I l o w

ClELAB and Munse l l Co lor Space Ar rangementFig. 1. CIE L*a*b* and Munsell color arran gement s (adapted from Seghi RR, Johns tonWM, O'Brien WJ. Spect rophotomet ric analysi s of color differences between porcelain sys-tems. J PROSTHET DENT 1986;56:35-40).

The increase in L* for the artificially aged samples mayhave result ed from fading of the surface. The dar kening ofL* in the outdoor-aged samples is attributed to theimpregnation of dirt into the porous surface of the elas-tomer.

The decrease in a* for both modes of exposure relate s tothe f ading of red in the samples, which was more pro-nounced with artificial aging. The negative change in a*suggests a change in the red (cadmium red) and reddishbrown (burnt sienna) off-base pigments.

The b* value increased for both the artificially and out-door-aged samples, and t he samples became yellower. Thisprocess may ha ve occurred as a result of the fading of thered pigments with the emerging dominance of the yellow(yellow ochre) oil-base pigments. Another cause could bethe yellowing of the linseed oil within the base pigment.The change in b* became greater wi th the addition of theUV light absorber. The initial decrease in b* with the ad-dition of the UV light absorber may be due to its off-whitecolor. The UV light a bsorber also ma.y have blocked the re-flection of red in favor of yellow and thus may hav e madethe samples appear yellower.

The artificially aged samples showed an increase in theAE* values at each ag ing level for all UV absorber concen-trations. These va lues o f AE*, which ranged f rom 1.08 to

2.01, were considered minor changes, a lthough they werevisually perceptible. The changes in AE* were greater forthe artificially aged than for the outdoor-aged samples.The aging chamber is an intense, accelerated source ofmany weat hering factors. The addition of the UV light ab-sorber did not protect the samples from change.

The int ent of exposing samples to artificial and outdoorweather ing was to assess the color stability of a pigmented,silicone elastomer with and without a UV light absorber.The combination of pigments yielded a common base shadefor white people. The samples were made 2.4 mm thick toapproximate the usual thickness of a prosthesis. The effectof thickness on the wavelength sensitivity of a materialdemonstr ated that the screening requirements of a UVlight absorber for a thin sample or for the surface layers ofa thicker sample are different from those for the bulk of hematerial . 21

The conditions and energy of exposure along with thepresence of a UV light absorber affected the color stabilityof the elastomer and allowed the effectiveness of the UVlight absorber to be observed. Although this study waslimited to one UVlight absorber, future studies should dealwith several different types of UV light absorbers to deter-mine whether a suitable product exists.

The test samples changed color as dete rmined by spec-

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trophotometric analysis. Although the changes were per-ceptible, they did not represent the level of color degrada-tion that is observed clinically. The major changes in ap-pearance of maxillofacial prostheses result from stainingthat is caused by environmental factors such as stains,fungal accumulation, handling, body oil accumulation, orcosmetics applied by the patient.C O N C L U S I O N S

The effect of a UV light absorber on the color stability ofa facial elastomer was evaluated by using reflection spec-trophotometry. The samples were weathered artificiallyand outdoors at exposure levels of 150 kJ/m 2 up to 450kJ/m 2 radia nt energy. Color changes were evalua ted wit hthe CIELAB system. Changes occurred in the color of thesamples, with artificial aging causing a greater changetha n outdoor aging. The UV light absorber UV-5411 didnot protect t he samples from color changes.

We appreciate t he ass istance of Mr. Jude Richard for his edito-rial expertise and continued support to our department.REFERENCES

1. Craig RG, Koran A, Yu R, Spencer J. Color stability of elastomers formaxillofacial appliances. J Den t Res 1978;57:866-71.2. Canto r R, Webber R, Straud L, Ryge G. Methods for evaluat ing pros-theti c facial materials. J PROSTHET DENT 1969;21:324-32.3. Chen MS, Udagama A, Drane JB. Evaluation of faciai prostheses forhead and neck cancer pat ients. J PROSTHET DENT 1981;46:538-54.4. Fine L, Robinson JE, Bar nha rt GW, Karl L. New method for coloringfacial prostheses . J PROSTHET DENT 1978;39:643-9.5. Jani RM, Schaaf NG. An evaluation of facial prostheses . J PROSTHETDENT 1978;39:546-50.6. Hanson MD, Shipman B, Blomfield JV, Janus CE. Commercialcosmetics and thei r role in the coloring of facial prostheses . J PROSTHETDENT 1983;50:818-20.7. Sweeney WT, Fische r TE, Castlebe rry DJ, Cowperthwaite GF. Evalu-ation of mproved maxillofacial prosthe tic materials. J PROSTHET DENT1972;27:297-305.

8. Goldberg AJ, Craig RG, Fillisko FE. Ultraviolet light stability of exter-nal maxillofacial p rostheti c materia ls [Abstract]. Inter nati onal Associ-ation for Dental Research Pr ogram and Abstracts of Papers. 1976;55:B138.9. Koran A, Yu R, Powers JM, Craig RG. Color stabili ty of a pigmentedela stomer for maxillofacial appliances. J Den t Res 1979;58:1450-4.10. Weins JP. A comparative study of selected el astomers subjected to ar-tificial and outdoor weathering . Masters the sis. Unive rsity of Minne-sota, 1980.

11. Lewis DH, Castleberry DJ. An assess ment of recen t advances in exter-nal maxillofacial mater ials. J PROSTHET DENT 1980;43:426-32.12. Chu CC, Fischer TE. Evaluation of sunlight stability of polyurethaneelastomers for maxillofacial use. I. J Biomed Mater Res 1978;12:347-59.13. Spectra-sorb UV 5411 ultraviolet li ght absorber , specification and tox-icity summary, Wayne, New Jersey: American Cyanamid Co, 1991.14. Society of Automotive Enginee rs. Accelerated exposure of automotiveexterior material s using a controlled irradiance water-cooled xenon arcapparatus. Specification SAEJ 1960, June 1989.15. Crewsdon L. Correlation of outdoor and labora tory accelerated weath-ering tests at currently used and hig her irradiance levels. Pa rt I. AtlasSun Spots 1991:21.16. Lane S. A guide to product durability testing and research. Miami,Florida, South Florida Tes t Service, 1989.17. Standar d practice for atmospheric environmental exposure testing ofnon-metallic mater ials (ASTM G7-83). In Annual Book of ASTM Stan-dards 1989:2740-8.18. Standar d practice for: exposure of cover mater ials for solar collectorsto natur al weat hering under conditions simulating operational mode(ASTM E782-81). Annual Book of ASTM Stan dards 1989:4264-70.19. Judd DB, Wyszecki G. Color in business, science, and industry. NewYork: Wiley and Sons, Inc, 1975:533.20. Standar d method for calculation of color differences from instrumen-tally measured color coordinates (ASTM D2244-85). Annual Book ofASTM Standards 1989:213-8.Searle NZ. Analytical photochemist ry and photochemical analysis ofsolids, solutions, and polymers. In: Fitzgerald JM, editor. MarcelDekker, Inc, 1971.

Reprint requests to:DR. MARK S. CHAMBERSSECTION OF ONCOLOGICDENTISTRYANDPROSTHODONTICS, BOX 69THE UNnrERSI~ OF TEXASM. D. ANDERSON CANCER CENTER1515 HOLCOMBE BLVD.HOUSTON, TX 77030

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