cally significant difference was found in marginal adaptation between Dicor and metal ceramic crowns on the one hand and Renaissance crowns on the other hand. Dicor and metal ceramic crowns demonstrated a similar cement film thickness. An SEM examination was performed to evaluate the quality of the margin for each system. The advantages and indications of the three different designs for croWns were discussed: REFERENCES

1. PannoFV, VahidiF, GulkerI, GhaliliKM. Evaluationor the 45~degree labial bevel with a shoulder preparation. J PROSTHETDENT 1986; 56:655-61. 2. SorensenJA, Okamot0SK, MillerR, YaroveskyU. Marginalfidelityof four methods of Renaissancecrownfabrication[Abstract].J Dent Res 1987;66:283. 3. Eames WB, O'NealSJ, MonteiroJ, Miller C, Roan JD, Jr. CohenKS. Techniquesto improvethe seating of casting. J Am Dent Assoc 1978; 96:432-7. 4. GrajowerR, LewinsteinI. A mathematicaltreatise on the fit of crown castings. J PROSTHETDENT1983;49:663-74.

5. Kuwata M. GingNal margin design of abutments for ceramometal res~ toratlons. Quintessence Dent Technol 1979;10:19-23. 6. Holmes JR, Bayne S0, Sulik WD, Hiilland GA. Marginal fit of castable ceramic (Dicor) crowns [Abstract]. J Dent Res 1987;66:283. 7. Davis DR. Comparison of fit eftwo types of all-ceramic crowns. J PROSTHET DENT 1988;59:12-6. 8. Sorensen JA, Okamoto SK. Comparison of' marginal fit of all ceramic crown system [Abstract]. J Dent Res 1987;66:283. 9. Hung SH, Hung KS, Eick JD, Tira DE, Chappell RP. Marginal fit and microleakage of Dicor, Cerestore, and PFM crowns [Abstract]. J Dent Res 1988;67:377. i0. Schfirer P, Sato T, Wohlwend A. Marginal fit in the Ceraplation crown system. Quintessence Dent Technol 1987;1:11-25. 11. Schfirer P, Sat() T, Wohlwend A. A comparison of the marginal fit of three cast ceramic crown system. J PROSTHET DENT 1988;59:534-42. 12. Koerber KH, Ludwig K. Die faltenfreie Keraplatinfolie Ulite ~ Die Herstellungsfolge. Zahnaeztliche Wochen Rundscbau 1988;97:200-2. 13. Savitt ED, Malament KA, Socransky SS, Melcer AG, Backman KG. Effects on cokmization of oral microbiota by a cast glass ceramic restoration. J Periodont Rest Dent 1987;2:23-35.

Reprint requests to: DR. FARHADVAHIDI 265 EAST 64TH ST. NEW YORK, NY 10021

Film t h i c k n e s s of die c o a t i n g a g e n t s D. W. R i c h a r d s o n , D D S , a V. A. F l e t c h e r , D D S , b L. K. G a r d n e r , D D S , c a n d J. D. A l i e n , D D S d

Medical College of Georgia, School of Dentistry, Augusta, Ga., and University of Tennessee, School of Dentistry, Memphis, Tenn. Die coating agents are often used during the fabrication of porcelain m a r g i n s for c r o w n s and fixed partial dentures. T h e s e agents seal microscopic irregularities w i t h i n the stone die and resist abrasion. This i n v e s t i g a t i o n m e a s u r e d the film t h i c k n e s s of s e v e r a l die coating agents. A specific r e f e r e n c e point w a s used during the m e a s u r e m e n t process. The results indicate that there is no significant difference b e t w e e n the die coating agents e x a m i n e d under the conditions of the study. The film t h i c k n e s s m e a s u r e m e n t s ranged b e t w e e n 0.367 um for Duro s u p e r Glue Material and 2.3 #m for Zap CA material. (J PROSTHET DENT 1991;66:431-4.)

D u r i n g the fabrication of a porcelain margin for fixed partial dentures, cyanoacrylate resin is recommended to coat the die margins. 14 The coating aids in sealing microscopic irregularities in the stone surface as well as increasing abrasion resistance) The film thickness of cyanoacrylate resins on a flat die

aAssistant Professor, Department of Prosthodontics, Medical College of Georgia, School of Dentistry: bAssistant Professor, Department of Prosthodontics, University of Tennessee, School of Dentistry. CAssociate Professor, Department of Prosthodontics, Medical College of Georgia, School of Dentistry. dAssistant Professor, Department of Occlusion, Medical College of Georgia, School of Dentistry. 10/1/27925 THE JOURNAL OF PROSTHETIC DENTISTRY

stone surface was measured by Fukui et al. 5 In that study, die stone blocks were separated into 12 equal sections. Three cyanoacrylate resins were placed on sections of a stone block and were then either (1) blotted with a tissue, (2) subjected to a blast of compressed air, or (3) simply shaken off. Their study found no significant difference between the cyanoacrylate resins tested when the resins were either blotted with a tissue or were air blasted. The range of thickness was 0.97 to 1,5 #m. In the study by Fukui et al., 5 the surface of the die stone blocks on which the coating agents were placed was made by pouring stone into a smooth plastic mold. When measurements were made, these investigations assumed that the die stone surface was exactly the same height in all areas of the stone block. In an effort to improve the experimental method, a single point on the stone block should 43~


Fig. 2. Mikrokator 509-4 thickness gauge.

Table IL Mean film thickness and standard deviation

Fig. 1. Mitutoyo 17-131 traveling microstage and stand with affixed resin block.




Std. dev.

Duro Super Glue Krazy glue Permabond 910 Zap CA Krylon acrylic spray

10 10 10 10 10

0.367 0.674 0.924 2.279 0.905

0.562 0.669 1.245 4.444 0.873

Table I. Materials tested MATERIAL Duro S u p e r Glue

(Woodhill Chemical Co., Cleveland, Ohio) Krazy glue (Toa Gosei Kagoku Industries Co., Ltd., Tokyo, Japan) Permabond 910 (National Starch and Chemical Corp., Englewood, N.J.) Zap/eA (Pacer Technology, Campbell, Calif.) Krylon acrylic spray (Borden, Inc., Dept. HPPG-Krylon, Columbus, Ohio)

No. 5



5 5

first be measured. Then the thickness of the coating agent at that precise point could be measured, This investigation measured the film thickness of several cyanoacrylate resin cements that are commonly used when one is making porcelain margins. A single point of reference was used for the measurements.




A mixture of Silky-Rock die stone (Whip Mix Corp., Louisville, Ky.) was mixed with deionized water at a ratio of 70 gm/16 ml. The die stone was hand spatulated into the water for 15 seconds. The mixture was then vacuum spatulated for 45 seconds at low speed in a Vac-U-Mixer (Whip Mix Corp.) instrument. The mixture was vibrated into a plastic mold and then inverted on a clean dry microscope slide. 5 Once the die stone had set for 2 hours, the plastic mold and glass microscope slide were removed. The die stone block then set for at least 2 additional hours. The block was affixed to a Mitutoyo 17-131 traveling microstage (Mitutoyo Mfg. Co., Ltd., Tokyo, Japan) (Fig. 1). A reference point was marked on the die stone block with a sharp Bard-Parker blade (Becton, Dickinson and Co., Rutherford, N.J.). A control measurement of height was made at the reference point on the untreated die stone block. A Mikrokator 509-4 thickness gauge (Aktiebolaget, D.E. Johansson, Eskilstuna, Sweden), accurate to _+1 ttm, was used as the measuring device (Fig. 2). A drop of a cy-







c~ I

-V 6





F i g . 3. Glue film thickness.

anoacrylate resin (Table I) was placed at the reference point on the stone block and was then immediately blasted with compressed air for 5 seconds. The acrylic resin (Krylon, Borden, Inc., Columbus, Ohio) was sprayed on the stone block for 2 seconds and was then allowed to dry for 30 minutes. A second measurement was then made for all coating agents at the reference point to assess film thickness. Five blocks were treated with each of the materials (Table I). Each point on the die stone sections were measured three times. The mean, s t a n d a r d deviation, and standard error of the mean were calculated using a one-factor analysis of variance (ANOVA). Significant differences among the means were calculated. RESULTS Table II lists the mean film thickness and standard deviation for each of the materials. Film thickness was calcu-


lated by the formula: [(preagent measurement) - (postagent measurement)]. The absolute value of the calculation is the film thickness. The results of a one-factor ANOVA of the film thickness d a t a indicate t h a t there were no significant differences (p = 0.3327) among means of the groups (Fig. 3).

DISCUSSION AND CONCLUSIONS During the fabrication of porcelain margins for fixed partial dentures, a coating agent is often used to protect the stone die. To make restorations with minimal marginal opening, a die coating agent with the minimal film thickness is recommended. The results of this study show t h a t the film thickness of the agents tested are not significantly different from each other when the material is blasted with forced air after initial application. All of the mean film thicknesses were less than 2.3 ttm. The range of the film thicknesses was from 0.367 ~m for



Duro Super Glue material to 2.3 t~m for Zap CA material. The least acceptable visually accessible marginal opening for gold inlays has been computed to be 39 #m. 6 Therefore 2.3 t~m or less seems to be a reasonable film thickness for die coating agents. REFERENCES 1. Toogood GD, Archibald JF. Technique for establishing porcelain margins. J PROSTHETDENT 1978;40:464-6. 2. Vryonis P. A simplified approach to the complete porcelain margin. J PROSTHET DENT 1979;42:592-3.

3. Prince J, Donovan T. The esthetic metal-ceramic margin: comparison of techniques. J PROSTHET DENT 1983;50:185-92. 4. Jarvis RH. The collarless ceramo-metal restoration--a presentation of three techniques. Oral Health 1984;74:23-5. 5. Fukui H, Lacy AM, Jendresen M. Effectiveness of hardening films of die stone. J PROSTHETDENT 1980;44:57-63. 6. Christensen G. Marginal fit of gold inlay castings. J PROSTHET DENT 1966;16:297-305. Reprint requests to: DR. DAVIDW. RICHARDSON SCHOOLOF DENTISTRY MEDICAL COLLEGEOF GEORGIA AUGUSTA,GA 30912

Variables affecting the spectral transmittance of light through porcelain v e n e e r samples K. L. O ' K e e f e , D D S , a P. L. P e a s e , O D , P h D , b a n d H. K. H e r r i n , D D S c University of Texas Health Science Center, Dental Branch, and University of Houston, College of Optometry, Houston, Texas The spectral t r a n s m i t t a n c e of porcelain l a m i n a t e v e n e e r s w a s m e a s u r e d at three different t h i c k n e s s e s (0.50, 0.75, and 1 ram) and three different opacities {25%, 75%, and 100%). The results indicated that the t h i c k n e s s of the porcelain Veneer w a s the primary factor affecting light t r a n s m i s s i o n and not the opacity. The m e a s u r e d Values of t r a n s m i t t a n c e w e r e then used to e s t i m a t e the setting time for light-cured luting a g e n t s of a porcelain veneer. (J PROSTHET DENT 1991;66:434-8.)

P o r c e l a i n laminate veneers are becoming increasingly popular for the esthetics of anterior teeth. Their strength, 1"~ wear resistance, ~ stain resistance, 5 and ease of placement 6 make porcelain laminates a viable alternative when one is selecting a tooth veneer. These restorations are mechanically bonded to the tooth with an enamel acid etching technique and one of the new low-viscosity composite resin luting agents. 7 T h e dentist has an expansive selection of luting composite resins; some are light cured while other, newer luting composite resins are dual cured with either chemical or visible light polymerization, s While polymerization of light-cured composite resins continues for some time after irradiation, a certain minimal cure is required. Therefore it is i m p o r t a n t to ensure t h a t adequate light energy reaches the luting agents to complete the

aAssistant Professor, Department of Occlusion and Fixed Prosthodontics, University of Texas Health Science Center. Dental Branch. bAssociate Professor. University of Houston, College of Optometry. CAssociate Professor, Department of Operative Dentistry, University of Texas Health Science Center, Dental Branch. 10/1/28259


polymerization, because early failure of the bond to enamel has been a t t r i b u t e d to incomplete curing of the luting agent. 9 Porcelain veneers can be made in various thicknesses and opacities selected by the dentist to disguise the discoloration of the tooth. These two variables, either individually or in combination, can affect the light energy reaching the composite resin luting agent, and it has also been shown t h a t light intensity affects the hardness and setting time of composite resins. 1°, i1 This study determined the effect of veneer thickness and opacity on the light energy t r a n s m i t t e d through veneers. The d a t a from this study, in conjunction with the established setting times for light-cured resins, can be used to estimate the light exposure time for curing resins of porcelain veneers with different thicknesses and opacities. MATERIAL



Nine groups of veneer samples were made consisting of three thicknesses (1, 0.75, and 0.50 mm) and three opacities {100%, 75%, and 25% ), and each group contained five specimens, for a total of 45 samples. Five 1 m m samples were made with a 100 % opacity, five with 75 % opacity, and five with 25 % opacity; similarly, there were five samples of




Film thickness of die coating agents.

Die coating agents are often used during the fabrication of porcelain margins for crowns and fixed partial dentures. These agents seal microscopic irr...
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