RICHARDSON ET AL
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
434
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
AND
METHODS
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
OCTOBER 1991
VOLUME 66
NUMBER 4
SPECTRAL TRANSMITTANCE OF LIGHT
I
•
SPECTRORADIOMETER
SAMPLE STAGE [ HEAT GLASS
I
•
SOURCE
F i g . 1. Schematic illustration of apparatus for measuring spectral transmission.
Table I. Mean percent transmittance (_+ SEM) at 460, 470, and 480 nm for samples with thicknesses of I m m (A), 0.75 mm (B), and 0.50 m m (C): Percent transmittance is given for three opacities: 100%, 75%, and 25% % T r a n s m i t t a n c e [ M e a n (± SEM)] Opacity
No.
460
nm
470
nm
480
nm
A 1ram
100% 75% 25% B 0.75 mm 100% 75% 25 % C 0.50 mm 100% 75% 25%
5 5 5
1.49 (_+0.03) 1.14 (-+0.06) 1.50 (-+0.11)
1.63 (-+0.03) 1.28 (-+0.06) 1.63 (-+0.11)
1.76 (-+0.03) 1.39 (_+0.06) 1.75 (-+0.11)
5 5 5
1.96 (_+0.08) 2.05 (_+0.09) 2.26 ( _+0.08)
2.10 (_+0.07) 2.21 (-+0.10) 2.40 ( -+0.07)
2.21 (-+0.07) 2.31 (_+0.09) 2.52 ( -+0.07)
5 5 5
2.87 (_+0.09) 2.75 (_+0.14) 3.03 (-+0.13)
3.02 (-+0.09) 2.87 (-+0.13) 3.16 (_+0.12)
3.08 (-+0.09) 2.95 (-+0.14) 3.19 (-+0.12)
the 0.75 m m and 0.50 m m thickness prepared with opacities of 100%, 75%, and 25%. All of the samples were the same shade, Vita B2 (Vita Zahnfabrik, Bad Sackingen, Germany), and were made according to the porcelain manufacturer's (Ceramco II veneer porcelain kit, Ceramco Inc., Johnson and Johnson, East Windsor, N. J.) specifications for mixing, handling, and glazing. The three thicknesses of 0.5, 0.75, and 1 m m are representative of the thickness of clinical porcelain veneers and were prepared with a machined metal mold to ensure uniformity of the thickness and diameter. The three opacities were mixed according to the manufacturer's instructions for three levels of opacity t h a t are selected by the dentist depending on specific tooth discoloration. Measurements of spectral transmittance were recorded at 10 nm intervals, from 430 nm to 600 nm, with a Pritchard spectroradiometer (Model No. 1980 B, Photo Research,
THE JOURNAL OF PROSTHETIC DENTISTRY
Chatsworth, Calif.) having a half bandwidth of 10 nm. These wavelengths were chosen because the effective wavelengths for curing composite resins were within this range. The a p p a r a t u s for measuring the transmittance is illustrated in Fig. 1. A 150 W heat-filtered tungsten halogen lamp (GE 77, General Electric Co., Cleveland, Ohio) was used to irradiate the samples t h a t were centered on a 6.3 m m diameter aperture located on a horizontal stage above the light source. Light passing through the aperture irradiated a diffusely reflecting surface oriented at 45 degrees to both the axis of illumination and the axis of measurement. Radiance (Lx) on this surface was measured with the sample (L'x) in the light p a t h and with the sample (L"x) out of the light path. The ratio of these two radiances is the transmittance of the sample at each wavelength: L ' x / L"~ = transmittance. Three measures of transmittance were determined at
435
O'KEEFE,PEASE,ANDHERRIN (a)
1.0 n~n Thick
3.6
o
S P E C U L A R T R A N SMYvr A N CE
25%
3.2
2 2.4 20 1.6 12 08
.
8 LJ
SAMPLE
(b) DIFFUSETRANSMTI'TANCE
Wav~,en~ O. 75 mm Thick
4°I .~,~
3.6
*
75% 26%
SOURCE~
,
32 2.B
~ 2.4 20 1.6
DETECTOR Fig. 3. Distinction between specular and diffuse transmittance. Measurement of specular transmittance is accomplished (a) when transmitted rays (RT) reach the detector but scattered rays (Rs) do not, while measurement of diffuse transmittance is (b) accomplished when all Rs and RT reach the detector after integration.
Wavelength
0 . 5 0 mm Thick
~ 2.0~ 1.6 1.2 0.8
-460
4.80
500 520 Wavele~h
540
560
580
600
Fig. 2. Mean percent transmittance for I mm thick samples for three opacities (top panel), same for 0.75 mm thick samples (middle panel), and same for 0.50 mm thick samples ( b o t t o m panel). [% 100% opacity; +, 75% opacity; 0, 25 % opacity.
each wavelength at intervals of I0 nm (430 to 600 nm) and the mean was used to calculate the spectral transmittance of the 45 samples. The repeatability of the measurements was assessed for one sample at one wavelength. The standard deviation of 10 measures of transmittance was + 0.03 %.
RESULTS The mean spectral transmittance for the five samples in each group is presented in Fig. 2. All of the samples, regardless of the thickness and opacity, are characterized by having continuous spectral transmission curves that are 436
essentially parallel. Table I summarizes the results for the wavelengths 460 nm through 480 nm. Analysis of variance (ANOVA) was computed to assess significant differences in mean transmittance at three wavelengths: 460,470, and 480 nm. The results of ANOVA are shown in Table II, and of the three variables in the table, thickness is clearly the main factor determining transmittance. The ANOVA identiffed significant differences (p < 0.05) in mean transmittance between the samples of each thickness (1, 0.75, and 0.50 ram). For the i mm thick samples, there were small but significant differences between the samples with 100 % and 75% opacities, 75% and 25% opacities, but not between the samples having opacities of 100% and 25%. The only significant difference in the mean transmittance for the 0.75 mm thick samples was between the samples having opacities of 100% and 25%. There was no significant difference in transmittance for the three opacities at the 0.5 mm thickness. This analysis (ANOVA) confirmed what is apparent in Fig. 2: there were greater variations in transmittance for different thicknesses than there were for the same thickness but varying opacities. DISCUSSION The thickness, opacity, and shade of composite resin materials can reduce the available light energy to polymerize light-cured resin systems32' 13 The effect of thickness and opacity of a porcelain veneer on transmitted light energy were evaluated in this study. The thickness of the veneers had a substantial effect on the light energy passing through the veneers, as shown in Table II, while the
OCTOBER1991 VOLUME66 NUMBER4
SPECTRAL TRANSMITTANCE OF LIGHT
T a b l e II. Analysis of variance results Source of variation
DF
SS
MS
F
p Value
Thickness (A) Opacity (B) Wavelength (C) Ax B AXC BxC Ax B x C Error Total
2 2 2 4 4 4 8 108 134
49.54 1.74 1.25 0.81 0.03 0.00 0.00 4.58 57.95
24.77 0.87 0.62 0.20 0.00 0.00 0.00 0.04
583.91 20.51 14.69 4.77 0.15 0.00 0.01
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
434
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
AND
METHODS
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
OCTOBER 1991
VOLUME 66
NUMBER 4
SPECTRAL TRANSMITTANCE OF LIGHT
I
•
SPECTRORADIOMETER
SAMPLE STAGE [ HEAT GLASS
I
•
SOURCE
F i g . 1. Schematic illustration of apparatus for measuring spectral transmission.
Table I. Mean percent transmittance (_+ SEM) at 460, 470, and 480 nm for samples with thicknesses of I m m (A), 0.75 mm (B), and 0.50 m m (C): Percent transmittance is given for three opacities: 100%, 75%, and 25% % T r a n s m i t t a n c e [ M e a n (± SEM)] Opacity
No.
460
nm
470
nm
480
nm
A 1ram
100% 75% 25% B 0.75 mm 100% 75% 25 % C 0.50 mm 100% 75% 25%
5 5 5
1.49 (_+0.03) 1.14 (-+0.06) 1.50 (-+0.11)
1.63 (-+0.03) 1.28 (-+0.06) 1.63 (-+0.11)
1.76 (-+0.03) 1.39 (_+0.06) 1.75 (-+0.11)
5 5 5
1.96 (_+0.08) 2.05 (_+0.09) 2.26 ( _+0.08)
2.10 (_+0.07) 2.21 (-+0.10) 2.40 ( -+0.07)
2.21 (-+0.07) 2.31 (_+0.09) 2.52 ( -+0.07)
5 5 5
2.87 (_+0.09) 2.75 (_+0.14) 3.03 (-+0.13)
3.02 (-+0.09) 2.87 (-+0.13) 3.16 (_+0.12)
3.08 (-+0.09) 2.95 (-+0.14) 3.19 (-+0.12)
the 0.75 m m and 0.50 m m thickness prepared with opacities of 100%, 75%, and 25%. All of the samples were the same shade, Vita B2 (Vita Zahnfabrik, Bad Sackingen, Germany), and were made according to the porcelain manufacturer's (Ceramco II veneer porcelain kit, Ceramco Inc., Johnson and Johnson, East Windsor, N. J.) specifications for mixing, handling, and glazing. The three thicknesses of 0.5, 0.75, and 1 m m are representative of the thickness of clinical porcelain veneers and were prepared with a machined metal mold to ensure uniformity of the thickness and diameter. The three opacities were mixed according to the manufacturer's instructions for three levels of opacity t h a t are selected by the dentist depending on specific tooth discoloration. Measurements of spectral transmittance were recorded at 10 nm intervals, from 430 nm to 600 nm, with a Pritchard spectroradiometer (Model No. 1980 B, Photo Research,
THE JOURNAL OF PROSTHETIC DENTISTRY
Chatsworth, Calif.) having a half bandwidth of 10 nm. These wavelengths were chosen because the effective wavelengths for curing composite resins were within this range. The a p p a r a t u s for measuring the transmittance is illustrated in Fig. 1. A 150 W heat-filtered tungsten halogen lamp (GE 77, General Electric Co., Cleveland, Ohio) was used to irradiate the samples t h a t were centered on a 6.3 m m diameter aperture located on a horizontal stage above the light source. Light passing through the aperture irradiated a diffusely reflecting surface oriented at 45 degrees to both the axis of illumination and the axis of measurement. Radiance (Lx) on this surface was measured with the sample (L'x) in the light p a t h and with the sample (L"x) out of the light path. The ratio of these two radiances is the transmittance of the sample at each wavelength: L ' x / L"~ = transmittance. Three measures of transmittance were determined at
435
O'KEEFE,PEASE,ANDHERRIN (a)
1.0 n~n Thick
3.6
o
S P E C U L A R T R A N SMYvr A N CE
25%
3.2
2 2.4 20 1.6 12 08
.
8 LJ
SAMPLE
(b) DIFFUSETRANSMTI'TANCE
Wav~,en~ O. 75 mm Thick
4°I .~,~
3.6
*
75% 26%
SOURCE~
,
32 2.B
~ 2.4 20 1.6
DETECTOR Fig. 3. Distinction between specular and diffuse transmittance. Measurement of specular transmittance is accomplished (a) when transmitted rays (RT) reach the detector but scattered rays (Rs) do not, while measurement of diffuse transmittance is (b) accomplished when all Rs and RT reach the detector after integration.
Wavelength
0 . 5 0 mm Thick
~ 2.0~ 1.6 1.2 0.8
-460
4.80
500 520 Wavele~h
540
560
580
600
Fig. 2. Mean percent transmittance for I mm thick samples for three opacities (top panel), same for 0.75 mm thick samples (middle panel), and same for 0.50 mm thick samples ( b o t t o m panel). [% 100% opacity; +, 75% opacity; 0, 25 % opacity.
each wavelength at intervals of I0 nm (430 to 600 nm) and the mean was used to calculate the spectral transmittance of the 45 samples. The repeatability of the measurements was assessed for one sample at one wavelength. The standard deviation of 10 measures of transmittance was + 0.03 %.
RESULTS The mean spectral transmittance for the five samples in each group is presented in Fig. 2. All of the samples, regardless of the thickness and opacity, are characterized by having continuous spectral transmission curves that are 436
essentially parallel. Table I summarizes the results for the wavelengths 460 nm through 480 nm. Analysis of variance (ANOVA) was computed to assess significant differences in mean transmittance at three wavelengths: 460,470, and 480 nm. The results of ANOVA are shown in Table II, and of the three variables in the table, thickness is clearly the main factor determining transmittance. The ANOVA identiffed significant differences (p < 0.05) in mean transmittance between the samples of each thickness (1, 0.75, and 0.50 ram). For the i mm thick samples, there were small but significant differences between the samples with 100 % and 75% opacities, 75% and 25% opacities, but not between the samples having opacities of 100% and 25%. The only significant difference in the mean transmittance for the 0.75 mm thick samples was between the samples having opacities of 100% and 25%. There was no significant difference in transmittance for the three opacities at the 0.5 mm thickness. This analysis (ANOVA) confirmed what is apparent in Fig. 2: there were greater variations in transmittance for different thicknesses than there were for the same thickness but varying opacities. DISCUSSION The thickness, opacity, and shade of composite resin materials can reduce the available light energy to polymerize light-cured resin systems32' 13 The effect of thickness and opacity of a porcelain veneer on transmitted light energy were evaluated in this study. The thickness of the veneers had a substantial effect on the light energy passing through the veneers, as shown in Table II, while the
OCTOBER1991 VOLUME66 NUMBER4
SPECTRAL TRANSMITTANCE OF LIGHT
T a b l e II. Analysis of variance results Source of variation
DF
SS
MS
F
p Value
Thickness (A) Opacity (B) Wavelength (C) Ax B AXC BxC Ax B x C Error Total
2 2 2 4 4 4 8 108 134
49.54 1.74 1.25 0.81 0.03 0.00 0.00 4.58 57.95
24.77 0.87 0.62 0.20 0.00 0.00 0.00 0.04
583.91 20.51 14.69 4.77 0.15 0.00 0.01
