Translucency of ceramic material in different core-veneer combinations Pinar Kursoglu, DDS, PhD,a Pelin F. Karagoz Motro, DDS, MSc, PhD,b and Ender Kazazoglu, DDS, PhDc Faculty of Dentistry, Yeditepe University, Istanbul, Turkey Statement of problem. Understanding the translucency of ceramic materials is important to achieve good esthetics. Ceramic thickness is related to translucency; however, less information about core-veneer thickness in combination is available. Purpose. The purpose of this study was to investigate the translucency parameters of core-veneer thicknesses in 2 different ceramic materials. Material and Methods. A total of 56 ceramic disks of different thickness were fabricated as cores according to the manufacturer’s recommendations and divided into groups (n¼7). Each was veneered with its compatible veneer ceramic with a different thickness (0.2, 0.5, 0.7 mm). One group of each ceramic type was left without veneer. The groups were named according to core names (group IPS e.max Press [EP], group IPS Empress Esthetic [EE]), and numbers were given according to thickness combination: 1¼(1.00þ0.5); 2¼(0.8þ0.7); 3¼(1.00); 4¼(0.8þ0.2). All surfaces were measured by profilometry to ensure consistency within the groups. A glass disk (1.5 mm) positive control (group P) and a metal core (1.5 mm) negative control (group N) were prepared. The translucency parameter values were calculated by using spectrophotometry to calculate the color differences of the specimens over black and white backgrounds. Results. A 1-way ANOVA found significant differences among the translucency parameter values of the ceramic groups (P.05). Conclusions. Total ceramic thickness affected the translucency; higher combined ceramic thickness resulted in lower translucency parameter values. When total thickness decreases, the translucency of core material has more effect than that of veneer material on translucency parameter values. (J Prosthet Dent 2014;-:---)
Clinical Implications Different core-veneer combinations may have different translucencies. The most appropriate ceramic material can be decided based only on the specific clinical situation being faced. Ceramic restorations offer excellent optical characteristics to match tooth structure.1,2 Because enamel and dentin have natural translucency,3,4 reproduction of the optical properties of natural teeth should be considered when fabricating new restorations.5 Obtaining a translucency that gives a lifelike effect to the restoration is essential, in addition to matching the a
shape and the texture with the adjacent natural teeth. Ceramic systems involve core and veneer combinations with different translucency and thickness to obtain a natural appearance.5 The translucency of ceramics has been identified as an important factor for obtaining good esthetics and is significantly influenced by both material and thickness.1,6,7 In addition,
Associate Professor, Department of Prosthodontics. Doctoral student, Department of Prosthodontics. c Head of Department and Professor, Department of Prosthodontics. b
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translucency is affected by fabrication technique, material composition, and illuminants.8,9 The translucency parameter (TP)10,11 and contrast ratio (CR)12,13 are most frequently used to measure the translucency of dental materials,1,6,7,14 and either CR or TP can be used to evaluate the relative translucency of ceramic systems.15 Translucency is the relative
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Volume amount of light transmitted through a material,16 and TP is calculated directly from the color difference of specimens on a black-and-white background.11 The background substrate influences the definitive appearance of a ceramic specimen.17 Black and white backgrounds have been used in determining the influence of ceramic thickness on the definitive shade of ceramic restorations.18 In translucency studies, the edge loss phenomenon, which can result in loss of accuracy in color measurement,4,19,20 should be considered. To decrease the edge loss, the window size of the spectrophotometer can be increased.19 Because the window size is limited by the dimension and shape of the specimen, the observation port should be 2 or 3 times larger than the size of the light beam.19,21 Furthermore, optical contact of the specimen with the backing controls the edge loss.20,22,23 For this purpose, various solutions (such as a sucrose solution,20,22,23 optical fluid,14,24 immersion liquid,25 and water solution) have been offered.15 In recent years, the number of ceramic materials has increased, and several studies have evaluated their mechanical and physical properties.26,27 Because esthetics are increasingly important, optical properties, including the translucency of ceramic materials, have been the focus of many studies.1,6,7,9,14,28 The translucencies of ceramic materials have been studied,1,26,29 and the effects of ceramic
Table I. Group EP
thickness,7,29,30 shade alternatives,14 different fabrication techniques, ceramic composition,6 and surface texture31 have been reported; the influence of different illuminants14 has also been described. Although some studies have focused on the TPs of core and veneer systems and the color parameters of core and veneer combinations,29,30,32 no study to date has examined the effects of the thickness of core-veneer combinations on translucency. Therefore, in the present study, the TPs of various core thicknesses layered with several veneer thicknesses in 2 different ceramic materials were investigated. The null hypothesis was that the translucency of the ceramic would not be influenced by ceramic type or core and veneer thickness in combination.
MATERIAL AND METHODS A total of 56 disks (IPS e.maxPress, IPS Empress Esthetic; Ivoclar Vivadent), 15 mm in diameter with different thicknesses (0.80 mm, 1.00 mm), were fabricated as core materials with the lost wax and heat-press techniques, according to the manufacturer’s recommendations. They were divided into groups (n¼7), the size of which was determined by power analysis (D¼0.2; power¼0.80; a¼.05). Each core material was veneered with its compatible veneer ceramic (IPS e.max Ceram, IPS Empress Esthetic Veneer; Ivoclar Vivadent) at different thicknesses (0.2 mm, 0.5 mm, 0.7 mm) according to the manufacturer’s
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recommendations. One group each of IPS e.max Press and IPS Empress Esthetic was left without veneer. The groups were named according to their core materials (group IPS e.max Press [EP], group IPS Empress Esthetic [EE]), and numbers were given according to thickness combination: 1¼(1.00þ0.5); 2¼(0.8þ0.7); 3¼(1.00); 4¼(0.8þ0.2) (Table I; Fig. 1). Veneered materials were fired 3 times to compensate for ceramic shrinkage during the firing procedure, according to the manufacturer’s instructions. The thickness of each core specimen was measured 3 times with an electronic caliper (Absolute Digimatic Caliper; Mitutoyo), and the averages were calculated to ensure consistency within the groups. All core specimens were veneered with their compatible veneer materials. After veneering, the thickness of all specimens was measured 3 times, and the average was calculated again with a digital caliper to provide the same thickness within the groups. A 1-sample t test was performed to ensure consistency within the groups (P>.05). The specimens were wet ground on a device (Phoenix Beta; Buehler) with 240-, 400-, 600-, 800-, and 1200-grit silicon carbide paper (English Abrasives & Chemicals Ltd) to provide a high shine. The application was performed for 15 seconds with finger pressure, and during the abrasion procedure, the specimens were frequently measured with electronic calipers (Absolute Digimatic Caliper; Mitutoyo) to avoid
Core and veneer materials: types and properties
Material
Type
Technique
Color
Lithium disilicate glass ceramic
Press
MO1 Ivoclar Vivadent
Veneer IPS e.max Ceram
Nanofluorapatite glass ceramic
Layer
A1/TI1
Leucite reinforced glass ceramic
Press
HT01
Ivoclar Vivadent
Core IPS Empress Esthetic
Manufacturer Ivoclar Vivadent
Core IPS e.max press
EE
-
Ivoclar Vivadent
Veneer IPS Empress Esthetic Veneer
The Journal of Prosthetic Dentistry
Feldspathic porcelain
Layer
ETC0
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3 0.5 mm 1.00 mm
EP Group
EP1 Core IPS e.max Press
0.5 mm 1.00 mm
EE Group
EE1 Core IPS Empress Esthetic
0.7 mm 0.8 mm
1.00 mm
0.2 mm 0.8 mm
EP2
EP3
EP4
0.7 mm 0.8 mm
1.00 mm
0.2 mm 0.8 mm
EE2
EE3
EE4
Veneer IPS e.max Ceram
Veneer IPS Empress Esthetic Veneer
1 Study design and definition of groups. reducing the thickness of the specimens excessively. All specimens were cleaned with steam (Triton SLA Steam Cleaner; Bego) under 0.3 MPa pressure and then placed in an ultrasonic cleaner (CD4800 Digital Ultrasonic Cleaner; Jeken) for 180 seconds to remove remnants. All surfaces were measured by profilometry to ensure consistency within the groups, and values were compared between groups. To ensure consistency within groups, a 1-way ANOVA was performed (P>.05). A glass disk (1.5 mm) was included as a positive control, and a metal core (1.5 mm) was included as a negative control. The International Commission on Illumination (CIE) L*a*b* values of each specimen were measured on a black background (L*¼1.05, a*¼0.16, and b*¼0.08) and on a white background (L*¼99.41, a*¼0.07, and b*¼0.20) with a spectrophotometer. The dimension of the window (measuring area) was 3 mm in diameter to control the edge loss.19 The TP values were calculated with spectrophotometry (CM-2600d; Konica Minolta Sensing Inc) by calculating the color difference of specimens against a black and white background from the following equation10: TP¼([Lb* Lw*]2 þ [ab* aw*]2 þ [bb* bw*]2)½, where b refers to the color coordinates over the black background and w to those over the white. The light source illumination corresponded to average daylight (D65). The illuminating
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and viewing configuration was CIE diffuse/10-degree geometry. A 1-sample t test was performed to determine the consistency of thickness, and a 1-way analysis was performed to ensure the consistency of surface roughness within the groups (P>.05). A 1-way ANOVA was used to identify significantly different TP values within the groups. The Tukey multiplecomparison test was used to determine which groups differed. All statistical tests were performed at the 95% confidence level (a¼.05).
RESULTS The 1-way ANOVA found no significant difference in specimen surface roughness (Ra values) among the ceramic groups (F¼0.859; P¼.545), and the mean Ra values were as follows: EP1, 0.082 0.02; EP2, 0.075 0.02; EP3, 0.078 0.04; EP4, 0.099 0.01; EE1, 0.067 0.02; EE2, 0.065 0.05; EE3, 0.067 0.03; and EE4, 0.078 0.04. These values confirmed the consistency of surface roughness within groups. Therefore, the surface texture of the specimens did not relate to the results of the study. The mean values of thickness, SDs, and P values of the groups for the core materials were as follows: EP1, 1.009 0.042 (P¼.594); EP2, 0.800 0.008 (P¼.993); EP3, 0.998 0.015 (P¼.813); EP4, 0.804 0.011 (P¼.429); EE1, 0.998 0.008 (P¼.640); EE2,
0.797 0.006 (P¼.284); EE3, 1.022 0.079 (P¼.486); and EE4, 0.799 0.009 (P¼.781). The mean values of thickness, SDs, and P values for the layered groups were as follows: EP1, 1.501 0.009 (P¼.687); EP2, 1.494 0.009 (P¼.133); EP4, 1.008 0.030 (P¼.514); EE1, 1.498 0.013 (P¼.770); EE2, 1.496 0.011 (P¼.349); EE4, 1.010 0.029 (P¼.407). No significant difference was found between the thickness values of both the core and veneered materials and the tested values according to the 1-sample t test (P>.05). The mean TP values ranged from 1.39 to 65.26 and were 1.39 0 (SD) for group N, 13.764 0.42 for group EP2, 14.477 2.46 for group EP1, 15.076 0.43 for group EE2, 15.280 0.31 for group EE1, 20.026 0.35 for group EP3, 20.884 0.66 for group EP4, 23.003 0.65 for group EE3, 24.744 1.23 for group EE4, and 65.26 0 for group P. A 1-way ANOVA found significant differences among the TP values of the ceramic groups (F¼2188.489; P¼.001) (P