IMPRESSION ADHESIVE:PARTI

prosthodontics. 2nd ed. Chicago: Quintessence Publishing Co, Inc, 1981. 8. de AraujoPA, Jorgsnsen KD. Effect of material bulk and undercuts on the accuracyof impressionmaterials. J PROSTHETDENT1985;54:791-4. 9. StackhouseJA. Dimensionalchange of custom acrylicimpressiontrays. J New Jersey Dent Assoc 1976;47:28-9. 10. Pagniano RP, Scheid RC, ClowsonRL, Daagefoerde RO, Zardiackas LD. Linear dimensional change of acylicresins used in fabrication of custom trays. J PROSTHETDENT1982;47:279-83. 11. GoldfogelM, HarveyWL, WinterD. Dimensionalchangeof acrylicresin tray materials. J PROSTHETDENT1985;54:284-6. 12. Eames WB, SiewekeJC. Seven acrylicresins for custom trays and five putty-wash systems compared. Oper Dent 1980;5:162-7. 13. FehiingAW, Hesby RA, Pelleu GB Jr. Dimensionalstability of autopolymerizing acrylic resin impression trays. J PEOSTHETDENT 1986; 55:592-7. 14. Collard EW, Caputo AA, Standlee JP, Trabert KC. Dynamicstresses encountered in impressionremoval.J PROSTHETDENT1973;29:498-506. 15. Samman JM, Fletcher AM. A study of impression tray adhesives. Quintessence Intl 1985;4:305-9. 16. Ellam AH, Smith DC. The relative effectiveness of adhesives for polysulphide impression materials. Br Dent J 1966;120:135-8.

17. Shigeto N, Kawazoe Y, Hamada T, Yamada S. Adhesion between copper-plated acrylictray resin and a polysulfiderubber impression material.J PROSTHET DF~r 1979;42:228-30. 18. Kawamura M. The bonding of rubber impression materials to tray mater/als.J Osaka Odontol Soc 1970;33:359. 19. Davis GB, Moser JB, Brinsden GI. The bonding propertiesof elastomer tray adhesives. J PROSTHET DENT 1976;36:278-87. 20. PhillipsRW. Elements of dental material. 4th ed. Philadelphia: W B Saunders, 1984:121. 21. Nicholson JW, Porter KH, Dolan T. Strength of tray adhesives for

elastomeric impression materials. Oper Dent 1985;10:12-6. 22. Grant BE, Tjan AHL.Tensileand peal bond strengths oftray adhesives. J PROSTHETDENT1988;59:165-8. 23. PhillipsRW. Skinner'sscienceof dental materials. 8th ed. Philadelphia: WB Saundars, 1982:150. Reprint requests to:

DR. JOHNNYY. CHAI DENTALSCHOOL NORTHWESTERN UNIVERSITY 240 E. HURON ST. CHICAGO, IL 60611

Effect of p o r c e l a i n c r o w n s u b s t r u c t u r e s on v i s u a l l y perceivable Value B. J. C r i s p i n , D D S , M S , a S. K. O k a m o t o , D D S , b a n d H. G l o b e c University of California, Los Angeles, School of Dentistry, Los Angeles, Calif. F a c t o r s t h a t will affect the p o t e n t i a l color of c e r a m i c r e s t o r a t i o n s m u s t be u n d e r stood to co n t r o l v a r i a b l e s t h a t exist. Clinical o b s e r v a t i o n s o f p o r c e l a i n r e s t o r a t i o n s l e a d to the h y p o t h e s i s t h a t c e r t a i n s u b s t r u c t u r e s tend to p r o d u c e c r o w n s w i t h a l o w e r t h a n e x p e c t e d V a l u e (brightness). This study w a s done to d e t e r m i n e w h e t h e r a v i s u a l l y p e r c e i v a b l e difference could be d e t e c t e d b e t w e e n g r o u p s of c e r a m i c c r o w n s w i t h different s u b s t r u c t u r e s . T w o t e s t g r o u p s of c r o w n t y p e s w i t h f o u r different p o r c e l a i n s u b s t r u c t u r e s w e r e c o m p a r e d . In the first group, m e t a l c e r a m i c c r o w n s m a d e w i t h e i t h e r G a l a x y o r R e x il l i u m I I I alloys w e r e co m p ar ed . In the second group, aluminous p o r c e l a i n j a c k e t c r o w n s w i t h and w i t h o u t a tin-plated, bonded p l a t i n u m foil i n t e r n a l l y w e r e c o m p a r e d . Visual a n a l y s i s s h o w e d t h a t (1) in the m e t a l c e r a m i c group, the c r o w n s with the Rex i l l i u m I I I s u b s t r u c t u r e w e r e s c o r e d as m o r e o f te n h a v i n g a l o w e r significant Value, and (2) in the aluminous p o r c e l a i n j a c k e t g r o u p t h e c r o w n s w i t h t h e tin-plated, bonded p l a t i n u m s u b s t r u c t u r e s w e r e s c o r e d as m o r e o f te n h a v i n g a l o w e r significant Value. (J PROSTHET DENT 1991;66:209-12.)

W

h

i

l

e

the esthetic demands of patients have never been greater, factors affecting the color of ceramic restorations must be understood to control the variables t h a t exist. 1"7 Clinical observations of porcelain restorations made at the University of California, Los Angeles (UCLA), School of Dentistry with various substructures indicated t h a t certain trends existed. When esthetically demanding single-unit all-ceramic restorations were made by use of the

aAssociate Professor, Director, Center for Esthetic Dentistry. bAdjunct Professor, Section of Removable Prosthodontics. CResearch Associate; Certified Dental Technician. 10/1/14819 THE JOURNALOF PROSTHETICDENTISTRY

twin foil technique (tin-plated, platinum-bonded aluminous porcelain jacket), they appeared lower in Value than aluminous porcelain jacket crowns made without the bonded platinum foil. In addition, follow-up of a population treated with etched-metal bonded fixed partial dentures made with a nickle-chrome alloy indicated t h a t the pontics were routinely lower in Value t h a n conventional fixed partial dentures made with a gold-palladium alloy. Hue and Chroma discrepancies in a ceramic restoration appear less significant and are easier to modify than increasing the Value when it is too low. 1 Any factor t h a t may reduce the Value of a ceramic restoration must be understood in order to be controlled. This preliminary study visually compared two groups of 209

C R I S P I N , OKAMOTO, AND GLOBE

Fig. 1. One set of five metal ceramic crowns (Galaxy). Fig. 2. Two aluminous porcelain crowns. Crown on right contains bonded platinum foil substructure. Fig. 3. T y p o d o n t test model with maxillary central incisors prepared. Fig. 4. One pair of crowns in position on test model for testing.

crowns made with different substructures for differences in percei~ed Value. MATERIAL

AND METHODS

Two test groups of crown types with four different porcelain substructures were compared in this study. The first group compared five pairs of metal ceramic crowns made with either Galaxy (APM-Sterngold, Attelboro, Mass.) (Au ~1.~. ,~.~ Pd 37,9 ~, In 7.5~7) or Rexillium III (Jeneric Industries, Wallington, Conn.) (Ni 74% - 7 8 ~ , Cr 12% 2.4 %, Be 1.8[:i, Mo 5~i - 9%) substructures (Fig. 1). The second group compared five pairs of aluminous porcelain jacket crowns made with tin-plated, bonded platinum foil internally (twin foil technique) to crowns with no bonded platinum substructure (Fig. 2). Five crowns were made with each type of substructure on a typodont with the ~naxillary central incisors prepared for full esthetic crowns i Fig. 3). For each pair, the different crown types in each group were made on contralateral central incisors so they could be seated in a simulated oral environment for eval-

~:~

uation {Fig. 4). Comparison of actual crowns might be more realistic than comparing coupons or disks in a nonoral environment.

Crown fabrication All of the crowns were made with A-1 body porcelain only. No incisal porcelain was used. 6 The five pairs of porcelain-fused-to-metal substructures were cast in either Rexillium III or Galaxy alloys according to the manufacturers' recommendation. They were finished to a uniform facial and interproximal thickness or 0.3 to 0.35 mm. No facial metal was left uncovered by porcelain whereas approximately a third of the lingual surface had exposed metal (Fig. 1). The substructures were air abraded with 25 t~m aluminous oxide and cleaned ultrasonically in distilled water before oxidization. Three opaque thermal cycles were used to produce a uniform thickness of 0.2 m m (VMK 68 No. 510, Vident, Baldwin Park, Calif.). Body porcelain was applied by using three thermal cycles to bring the crowns to full contour (VMK 68 No. 540). The manufac-

At)GUST 1991

VOLUME 66

NUMBER 2

PORCELAIN CROWN SUBSTRUCTURES

Mesial

Facial

Facial

Distal

Incisal

8 3 7 6

21

2

12 11

D

10

22

'

23

Fig. 5. Measurement points for aluminous porcelain core substructure.

,o',}

17~ 1 ~ 1 J 2 1 3 21

'+

13

22

Fig. 6. Measurement points for completed aluminous porcelain crowns. turer's recommendations were followed for all steps. The contralateral crown types were measured with an H-A dial caliper (Health-Aids, Hayward, Calif.) with an accuracy of 0.05 mm to maintain consistency for each pair and for each layer. The total midfacial thickness of the crowns ranged from 1 mm to 1.3 mm as measured from the gingival to the incisal end of the metal coping. The metal ceramic crowns were all made by the same individual (H.G.). The five pairs of aluminous porcelain jacket crowns, with and without tin-plated bonded platinum, were made by use of the Vita P T and Vitadur N techniques respectively with the corresponding substructure material (Vita-PT No. 400 and Vitadur N No. 337N). The tin-plated platinum foil was plated and oxidized before substructure fabrication. The aluminous porcelain substructures for each pair were made by the use of three bakes to a uniform facial thickness of 0.3 mm _+ 0.05 mm as measured at 23 points with the H-A dial caliper (Fig. 5). The crowns were built to full contour with Vitadur N body porcelain shade A-1 (Vitadur-N No. 351) without incisal porcelain. The thickness of contralateral crowns was standardized by measuring at 26 points (Fig. 6). The total midfacial crown thickness ranged from 1 to 1.6 m m as measured from the gingival margin to the incisal end of the coping. The porcelain jacket crowns were all made by the same individual (S.K.O.).

Crown evaluation All of the crowns in this study were air abraded with 25 #m aluminous oxide to provide a consistant surface texture during the evaluation. A thin layer of Vita-chrome L staining liquid (Vident) was applied to the exterior surfaces of the crowns in the typodont to give a consistant glazed appearance (Fig. 7). Comparison of the crowns in each group was done by placing one crown of each type in the typodont by use of a random pairing method. The crowns were glazed as described and placed in an environment with color-corrected artificial lights, north facing natural light, and a mediumblue background. Each examiner was asked whether the

THE J O U R N A L OF PROSTI-IETIC D E N T I S T R Y

Fig. 7. Test crowns with staining liquid on surface providing consistent glazed appearance.

crowns in each group looked the same or different in color. If the response was different, the examiner was further asked to select the crown with the lower Value. The examination population consisted of two faculty members from each of the Sections of Fixed Prosthodontics, Removable Prosthodontics, and Operative Dentistry. In addition, two ceramists and five dental students formed a total examining population of 13. For each of the two crown test groupings a total of 65 random comparisons were made. Each group had five crowns of each type times 13 examiners. Two statistical techniques were used for data analysis. McNeman's chisquare tested the equality of the crowns in each pair. Exact binomial 95 % confidence intervals were estimated for the portion of time that the two crown types in each pair were judged not equal. Statistical significance was verified by less than 0.05 p values.

RESULTS M e t a l c e r a m i c group The crowns in this group were judged different 75% of the time or in 49 of 65 comparisons. The evaluators scored

211

CRISPIN, OKAMOTO, AND GLOBE

Table L V~ue ~ r e s : ~ u m i,

,

Same Faculty Students Total

11 5 16

versus Galexy

, Rexlllium lower 25* 15" 40*

Table II. Value scores: Aluminous versus platinum

i i

Galaxy lower 4 5 9

*Statistically significant for portion of responses judged not same.

bonded aluminous

Faculty Students Total

Aluminous lower

Bonded

Same 9 2 11

30* 18" 48*

1 5 6

lower

*Statistically significant for portion of responses judged not same.

the Rexillium alloy crowns as having the lower Value 40 times compared with only nine times for the Galaxy alloy crowns (Table I). These figures were found statistically significant (p < 0.05}.

Aluminous porcelain group The crowns in this group were judged different 83 % of the time or in54 of 65 comparisons. The evaluations scored the tin-plated platinum bonded crowns lower in Value 48 times compared with six times for the aluminous porcelain jackets with no bonded platinum (Table II). Again these figures were verified to be statistically significant (p < 0.05).

DISCUSSION Even though this simulated clinical evaluation is limited in scope, it reempbasizes the difficulty of interpreting and applying laboratory data to a clinical environment. The metal ceramic results appear to differ from Brewer et al.'s study. 6 which showed no differences for the metal types. This difference, in part, may be due to the difficulties in standardizing the opaque thickness in clinical patients compared with a fiat laboratory test coupon. It may also be speculated that the opaque layers should be varied in thickness dependent on the substructure to which it is fused, to ensure consistant clinical results. Moreover, in clinical crowns the thickness of the dentin porcelain varies considerably, The need for a standardized, repeatable approach for porcelain color testing seems obvious. For the group of aluminous porcelain jacket crowns no other studies were found for comparison. This study suggesr~ that when the platinum-bonded technique is used, the Value of the resultant crown may be lower than that of nonplatinum bonded crowns. This finding is of more significance with the lighter shades that may have a low Value and need modification. This study further exemplifies the persistant problem of inadequate shade-matching systems and the need to customize the approach to the materials being used in crown fabrication

cieved Value. Metal ceramic crowns with Rexillium III alloy (Ni-Cr) and Galaxy alloy (Au-Pd) substructures were compared. &luminous porcelain jacket crowns with and without tin-plated, platinum bonded internally were also compared and both groupings were visually analyzed by a group of 13 examiners for differences in Value. The results of this study were statistically analyzed and showed that (1) in the metal ceramic group, the crowns with the Rexillium HI alloy substructure were scored as having a lower Value significantly more often than those with the Galaxy alloy substructure, (2) in the aluminous porcelain jacket group of crowns, the crowns with the tin-plated, bonded platinum foil substructure were scored as having a lower Value significantly more often than those with no bonded platinum foil, and (3) further investigation into the esthetic effects that porcelain substructures have on the color of porcelain crowns is necessary to better control the variables involved in achieving optimal esthetic results. We thank Dr. Jim Baker for his help during the evaluation process, Irene Petravicius in the preparation of this manuscript, and the UCLA Word Processing Center.

REFERENCES 1. Barghi N, Goldberg J. Porcelain shade stabilityafterrepeated firing.J PROSTHET DENT 1977;37:173-5. 2. Barghi N, Richardson JT. A study of various factors influencing shade of bonded porcelain. J PROSTHETDENT 1978;39:282-4. 3. Barghi N. Color and glaze: effects of repeated firings. J PROSTHETDENT 1982;47:393-5. 4. Jorgenson MW, Goodkind RJ. Spectrophotometric study of five porcelain shades relative to the dimensions of color, porcelain thickness, and repeated firings. J PROSTHET DENT 1979;42:96-105. 5. Obregon A, Goodkind RJ, Schwabacher WB. Effects of opaque and porcelain texture on the color of ceramometal restorations. J PROSTHET DENT 1981;46:330-40. 6. Brewer JD, Akers CK, Garlapo DA, Sorensen SE. Spectrometric analysis of the influence on metal-ceramic restorations. J Dent Res 1985; 64:74-7. 7. Jaeobs SH, Goodacre CJ, Moore BK, Dykema RW. Effect of porcelain thickness and type of metal-ceramic alloy on color. J PROSTHETDENT 1987;57:138-45. Reprint requests to:

SUMMARY

AND CONCLUSIONS

This study compared two groupings of ceramic crowns made with different substructures for differences in per-

~I~

DR. BRUCE J. CRISPIN SCHOOLOF DENTISTRY UNIVERSITYOF CALIFORNIA LOS ANGELES,CA 90024

AUGUST 1991 VOLUME66 NUMBER 2