- Email: [email protected]
Comparative radiopacity of ceramics and metals with human and bovine dental tissues
Comparative radiopacity of ceramics and metals with human and bovine dental tissues Gurel Pekkan, DDS, PhD,a Keriman Pekkan, MSc, PhD,b Mujgan Gungor Hatipoglu, DDS, PhD,c and Suleyman Hakan Tuna, DDS, PhDd Faculty of Dentistry, Dumlupinar University, Kutahya, Turkey; Faculty of Dentistry, Suleyman Demirel University, Isparta, Turkey Statement of problem. Ceramics should be radiopaque enough to be seen on radiographs and to be distinguishable from tooth structures. Information on the radiopacity of different ceramics used in restorative dentistry is limited. Purpose. The purpose of this study was to investigate the radiopacity of ceramics in comparison with human and bovine dental hard tissues and metals. Material and methods. A total of 128 disk-shaped specimens, 6 x 1 mm (n=8), were prepared from dental ceramic materials and metals. The optical densities of each material, along with 2 tooth sections (canine and molar teeth), bovine dentin and enamel specimens, and 2 different aluminum step wedges, were measured from radiographic images using a transmission densitometer. The optical densities of the specimens were used to determine the equivalent aluminum thicknesses. The data were analyzed by nonparametric 1-way ANOVA (Kruskal-Wallis) and Student-Newman-Keuls multiple range tests for post hoc comparison (α=.05). Results. Among ceramic materials, Cercon Zirconia had the highest and the Cergo Pressable Ceramic had the lowest radiopacity values. Cergo Pressable Ceramic, Noritake Super Porcelain EX3 dentin, IPS Empress e.max Press, Cercon Kiss dentin, IPS Empress 2, Cercon Ceram dentin, bovine dentin, human canine, and molar tooth dentin radiopacity measurements were not significantly different. The radiopacity measurements of In-Ceram Alumina, In-Ceram Spinell, Celay Alumina, Titanium alloy (Ti-6Al-4V), Celay Zirconia, In-Ceram Zirconia, NiCr alloy, Wieland Zirconia, Cercon Zirconia, and 22-carat gold were significantly higher than that of bovine enamel (P<.05). Conclusions. Significant differences in radiopacity were found among ceramic materials, when compared to metals, bovine enamel and human and bovine dentin. Cercon and Wieland Zirconia had high radiopacity values, which were similar to metals. (J Prosthet Dent 2011;106:109-117)
Clinical Implications
Adequate radiopacity of ceramics assists in the radiological assessment and diagnosis of caries, cement failure, voids between restoration and tooth structure, marginal gaps, and the overall condition of existing restorations. Clinicians should be aware of the radiopacity of the ceramic system(s) they use. Among ceramic materials and metals tested, In-Ceram Alumina, In-Ceram Spinell, Celay Alumina, Titanium alloy (Ti-6Al-4V), Celay Zirconia and In-Ceram Zirconia had adequate radiopacity values. Supported in part by the Dumlupinar University Research Fund (Grant no. 2007-8). Assistant Professor, Faculty of Dentistry, Dumlupinar University. Assistant Professor, Faculty of Dentistry, Dumlupinar University. c Assistant Professor, Faculty of Dentistry, Dumlupinar University. d Assistant Professor, Department of Prosthodontics, Faculty of Dentistry, Suleyman Demirel University. a
b
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Volume 106 Issue 2 Ceramic systems were developed to improve the esthetics and biological compatibility of fixed dental prostheses.1-3 Ceramic restorations are frequently used instead of metal ceramic restorations, depending on the indication.2-4 Ceramic systems are generally categorized as castable glass ceramics, ceramics obtained through the refractory die technique, ceramics produced with computer-aided manufacturing (CAM) or computeraided design (CAD)/CAM systems, and heat-pressed ceramics.4-7 Ceramic restorations are capable of reflecting light, which produces an appearance and color similar to that of natural teeth. Such restorations possess thermal expansion coefficients and thermal conductivity that are similar to natural teeth.8 Their compressive strength is high and they are chemically inert.9,10 These restorations do not cause unusual tastes.8 They are used in the fabrication of crowns, fixed partial dental prostheses, inlays, onlays, and laminate veneers.1-7 Such restorations, however, have some negative characteristics, such as brittleness and low flexural strength.4,8-11 Due to such weaknesses in ceramic structure, the development of reinforcement techniques has been considered a necessity12-14 to prevent the formation and propagation of microcracks.2-4 To this end, crystalline additives (leucite, alumina, magnesia, magnesium aluminate, lithium disilicate, zirconia, sanidine) and ceramic matrix composites (zirconia whiskers) have been added.4,8-10,13-17 In glass ceramic systems, an attempt has been made to improve durability by adding small amounts of such nucleating agents as tetrasilisic fluormica, oxy-apatite (CaP2O5SiO5) and β-spodumene into molten glass.1,8,18,19 Due to these reinforcing additives or reinforcement procedures, ceramics possess different radiopacities.8,20,21 Most ceramic systems ensure radiographic diagnosis of caries; however, only a few authors evaluated the radiopacity of these materials.8,20,21 It is recognized that ceramic inlay
materials should be more radiopaque than enamel to allow the detection of recurrent caries.20,21 An in vitro study of ceramic inlay materials found that Cerec Vita did not possess sufficient radiopacity to permit detection of recurrent caries.20 According to the author, inaccurate interpretation of radiographs of Cerec inlays resulted in the unnecessary replacement of restorations.21 Radiopacity is widely acknowledged as a desirable property of all intraoral materials, including directrestorative materials,22-31 cavity liners,27,30 denture base materials,32 elastomeric impression materials,33 endodontic sealers,34 posts and retrograde materials,35,36 core foundation materials,28,36 luting agents,24,25,30,37-40 and adhesive systems.40-44 The radiopacity of these materials aids localization following the accidental swallowing of fixed or removable dental prostheses and interim crowns.42 Due to the radiopacity of restorative materials, it is possible to radiologically detect the form,45 contour, and deficiencies of restorations, as well as localize the dental pulp.22-26 Furthermore, the radiopacity of restorative materials facilitates the detection of secondary caries under the restoration and enables the observation of periodontal effects of the overhangs in the restoration.23,38 Previous radiopacity studies have been performed using dental materials with the same thickness as the enamel and dentin, and using aluminum (Al) step wedges and radiographs with specific standards.26,34-36,38,46,47 Ideally, restorative materials should have radiopacity values equivalent to or greater than that of enamel.37-40 Radiopacity is generally defined by equivalent Al thickness.35 The International Organization for Standardization (ISO) published a radiopacity protocol and guidelines for polymerbased restorative and luting materials.43 These materials should have radiopacity equal to or greater than that of Al.43,44 Nevertheless, neither the ISO nor the American National
The Journal of Prosthetic Dentistry
Standards Institute/American Dental Association (ANSI/ADA) has issued radiopacity guidelines for dental ceramic restorative materials. However, methods for determining the radiopacity of materials used in dentistry (ISO/New Work Item Proposal (NP) 13116) are under development. The purpose of this study was to compare the radiopacity of different ceramics to human dentin and bovine enamel-dentin and metals by referring to Al step wedges. The hypotheses were that the: (1) radiopacity levels of dental ceramic systems would be different from each other; (2) radiopacity levels of dental ceramics would be higher than that of enamel; (3) radiopacity levels of dental ceramics would be higher than that of dentin.
MATERIAL AND METHODS The radiopacity levels of 13 different dental ceramics, titanium alloy (Ti), NiCr alloy (NiCr), and 22-carat gold (G) were evaluated. The materials used, the manufacturers and the composition for the materials are listed in Table I. Human canine dentin (Can) and molar dentin (Mol), bovine dentin (BD) and bovine enamel (BE), and 2 Al step wedges were used as controls. Eight specimens were fabricated for all test groups. No power analysis was performed to determine adequate sample size. For fabricating ceramic specimens, auto-polymerizing acrylic resin (Pattern Resin; GC Corp, Tokyo, Japan) disk-shaped specimens were prepared using stainless steel molds (6.0 x 1.0 mm). IPS Empress 2 (E2) IPS Empress e-max Press (IPSE), and Cergo Pressable Ceramic (CPC) were invested and (IPS Empress 2 Special Investment Material; Ivoclar Vivadent, Schaan, Liechtenstein, and Cergo Fit Investment Material; Degussa AG, Hanau, Germany) were eliminated to obtain molds for heat pressing according to the manufacturers’ instructions. E2, IPSE, and CPC specimens were fabricated by heat-pressing them into molds. Noritake super porce-
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Table I. Materials evaluated. Composition information provided by manufacturers. Materials
Manufacturer
IPS Empress 2 (E2)
Ivoclar Vivadent
SiO2, Li2O, K2O, P2O5, ZnO, MgO, La2O3, Al2O3
Cergo Pressable Ceramic (CPC)
Degudent GmbH
SiO2, Al2O3, K2O, Na2O, CaO
In-Ceram Spinell (SP)
Vita Zahnfabrik
MgAl2O4
In-Ceram Alumina (ICA)
Vita Zahnfabrik
In-Ceram Alumina powder: Al2O3 100%; Glass powder: SiO2 14-17%, Al2O3 14-17%,B2O3 12-15%,TiO2 3-5%, La2O3 39-48%, CeO2 2-5%, CaO 2-4%, coloring oxides < 2%
In-Ceram Zirconia (ICZ)
Vita Zahnfabrik
In-Ceram Zirconia Powder: Al2O3 67%, ZrO2 33%; Glass powder: Al2O3 14-18%, SiO2 14-18%, B2O3 11-15%, TiO2 2-7%, La2O3 25-30%, CeO2 6-10%, CaO 4-8%, ZrO2 1-4%, Y2O3 2-6%
IPS Empress e-max Press (IPSE)
Ivoclar Vivadent
SiO2, Li2O, K2O, P2O5, ZnO, ZrO2, other oxides and pigments
Noritake super porcelain EX-3 dentin (Nor)
Noritake Dental Supply Co, Ltd, Aichi, Japan
SiO2, Al2O3, K2O, Na2O, Ba2O, CaO, other oxides and pigments
Celay Alumina (CA)
Vita Zahnfabrik
Celay Alumina blank: Al2O3 100%; Glass powder: SiO2 14-17%, Al2O3 14-17%,B2O3 12-15%, TiO2 3-5%, La2O3 39-48%, CeO2 2-5%, CaO 2-4%, coloring oxides < 2%
Celay Zirconia (CZ)
Vita Zahnfabrik
Celay Zirconia blank: Al2O3 67%, ZrO2 33%; Glass powder: Al2O3 14-18%, SiO2 14-18%, B2O3 11-15%, TiO2 2-7%, La2O3 25-30%, CeO2 6-10, CaO 4-8%, ZrO2 1-4%, Y2O3 2-6%
Cercon Zirconia (CerZ)
Degudent GmbH
ZrO2 > 92%, Y2O3 5%, HfO2 < 2%, Al2O3 and SiO2 < 1%
Cercon Kiss dentin (CK)
Degudent GmbH
SiO2, Al2O3, K2O, Na2O, Ba2O, CaO, other oxides and pigments
Cercon Ceram dentin (CCD)
Degudent GmbH
SiO2, Al2O3, K2O, Na2O, Ba2O, CaO, other oxides and pigments
Wieland Zirconia (WZ)
Wieland Dental
ZrO2 and HfO2 94%,Y2O3 5%, Al2O3 < 1%
Titanium alloy (Ti-6Al-4V) (Ti)
Arcam AB
Gold-22-carat (G)
Merkür Ltd, Istanbul, Turkey
Nickel-Chromium alloy (NiCr)
Eisenbacher Dentalwaren GmbH
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Composition
Al 6%, V 4%, O 0.15%, Fe 0.1%, N 0.01%, C 0.03%, H 0.003%, Ti balance Au 91.6%, and Pd, Ir and other elements 8.4% Ni 63%, Cr 25%, Mo 11%, Si 1.5%, Mn< 0.1%, C< 0.1%
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Volume 106 Issue 2 lain EX-3 dentin (Nor), Cercon Kiss dentin (CK), Cercon Ceram dentin (CCD) specimens, acrylic resin (Pattern resin; GC Corp) specimens were embedded in the investment material of each system according to the manufacturers’ instructions. After the acrylic resin (Pattern resin; GC Corp) specimens were eliminated, ceramic specimens were fabricated using a refractory die technique. In-Ceram Alumina (ICA), In-Ceram Zirconia (ICZ), and In-Ceram Spinell (SP) specimens were fabricated by a slip-casting technique after preparing molds from Vita In-Ceram Special Plaster (Vita Zahnfabrik, Bad Sackingen, Germany) using acrylic resin (Pattern resin; GC Corp). Thereafter, ICA, ICZ, and SP specimens were glass infiltrated to strengthen the slip-cast core, as described by the manufacturers of these ceramics. Specimens of Celay Alumina (CA) and Celay Zirconia (CZ) were prepared from Vita Celay alumina AC12 and zirconia ZC-12 blanks (Vita ZahnFabrik) by cutting them with a saw (Isomet 4000; Buehler, Lake Bluff, Ill). Afterwards, the CA and CZ specimens were glass infiltrated as ICA and ICZ specimens. Cercon Zirconia (CerZ), yttria-stabilied tetragonal zirconia polycrystal (Y-TZP) ceramic, specimens were prepared from a base (Cercon; Degudent GmbH, Hanau, Germany) for crowns. The prepared acrylic resin patterns were scanned, and the digitized framework was enlarged. Then, the specimens were milled from a prefabricated homogeneous porous blank of zirconia (Cercon; Degudent GmbH). The zirconia specimens were then sintered to full density for 8 hours at 1350°C to achieve the final form. Wieland Zirconia (WZ) specimens were milled from a Wieland Zeno zirconia disk (Wieland Dental + Technik GmbH and Co, KG, Pforzheim, Germany) in the same manner as the CerZ specimens were fabricated and sintered according to the manufacturer’s instructions. In total, 104 (n=8) ceramic specimens were obtained. Additionally, 8 specimens were prepared from ti-
tanium (Arcam AB, Mölndal, Sweden) and NiCr (Kera N; Eisenbacher Dentalwaren ED GmbH, Wörth, Germany) alloys by slicing ingots 1 mm in thickness with a precision saw (Isomet 4000; Buehler). The metal specimens were then ground to 6 mm in diameter. After eliminating the acrylic resin (Pattern resin; GC Corp), specimens (6 x 1 mm) that were embedded in gypsum-bonded investment material (Deguvest California; Degudent GmbH) and 22-carat gold (Merkür Ltd, Istanbul, Turkey) specimens were obtained by casting them into these prepared molds. All specimens were ground through 400-grit silicon carbide paper (SiC) (Struers GmbH, Willich, Germany) to create a flat surface and measured with a digital calliper (Youfound Precision Co, Ltd, Zhejiang, China) after fabrication to verify the critical tolerance of 1.0 ±0.01 mm. All specimens were ultrasonically cleaned in distilled water for 5 minutes using an ultrasonic bath (Eurosonic 4D; Euronda SPA, Vicenza, Italy). Eight bovine enamel and dentin disk specimens were prepared from bovine mandibular incisor teeth (6 x 1 mm). Bovine dentin and enamel specimens were obtained by longitudinal sectioning of the buccal side of teeth after separating the roots. Longitudinal sections of human permanent molar and canine teeth were also prepared to the same thickness using a micro-slicing device (Accutom; Struers A/S, Ballerup, Denmark) (n=8 for each). Two different step wedges, Al-1 (Alu-Keil; PEHA Med Geräte GmbH, Sulzbach, Germany) and Al-2 were prepared. Al-2 step wedge had lesser amounts of Al in its composition so that it was harder and more machinable than Al-1. The step wedges’ maximum thickness was 14 mm; each step had a thickness of 1 mm, a length of 4 mm, and width of 14 mm. All specimens were soaked in distilled water using a water bath (NB9; Nüve Temel Laboratuar Cihazları, Ankara, Turkey) at 37°C for 24 hours. One specimen of each material, bovine dentin and enamel, 2 tooth (ca-
The Journal of Prosthetic Dentistry
nine and molar) sections and Al step wedges were positioned side by side on occlusal D speed radiographic film (Kodak Ultra-speed; Eastman Kodak Company, Rochester, NY). A special holder was mounted to ensure a fixed focus/film distance. The film was exposed for 0.38 seconds with a dental radiographic system (Trophy Radiologie, Vincennes, France) at 70 kV and 8 mA; the object-to-film distance was 30 cm. All films were processed immediately in an automatic processor (Velopex Extra-X; Medivance Instruments Ltd, Harlesden, UK) using fresh developer and fixing solutions (Velopex Ready Mixed Developer and Fixer; Hexagon International (GB) Ltd, Berkhamsted, UK). The optical density of the radiographic images was measured with a transmission densitometer (Denso-Dent Densitometer; PEHA Med Geräte GmbH) (mean of at least 3 readings per specimen) with an aperture size of 3 mm (DIN 6868/55). All measurements were completed by one individual and the densitometer was calibrated after reading each radiograph. Following the method of El-Mowafy and Benmergui,40 the optical density data for the Al steps were entered into a computer, and the best possible exponential fit was used for curves of Al optical density. Two graphs were plotted to illustrate the relationship between step wedge thickness and optical density values (ODVs) with the following equations: y=-0.5077Ln(x) + 1.8817, and y=-0.4798Ln(x) + 1.6626 (Fig. 1) From these graphs, ODVs of the specimens were used to determine the equivalent Al thickness (eq Al) values. One-way analysis of variance (ANOVA), Kruskal-Wallis, and StudentNewman-Keuls (SNK) multiple range tests were conducted to statistically analyze the ODVs and eq Al values of the materials (α=.05). Pearson correlation analysis was used to evaluate correlations of the step wedges’ density measurements and the eq Al values. Statistical software (SPSS 13.0 for Windows; SPSS Inc, Chicago, Ill)
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Optical Density Values
2.0 Al-2 step wedge Al-1 step wedge Log. (Al-2 step wedge) Log. (Al-1 step wedge)
y=–0.4798Ln(x) + 1.6626 R2=0.9901
1.5
1.0 y=–0.5077Ln(x) + 1.8817 R2=0.9942
0.5
0
0
3
6
12
9
15
Aluminum Step Wedge Thickness (mm) 1 Optical density calibration curves for Al-1 and Al-2 step wedges.
Table II. Means and standard deviations (SD) of optical density and equivalent aluminum thickness values of materials and the statistical category according to SNK multiple range tests
Material Code
Optical Density Mean Values ± SD
Equivalent Al-1 Step Wedge Mean Values ± SD
Equivalent Al-2 Step Wedge Mean Values ± SD
Statistical Category
CPC Nor Can IPSE Mol CK E2 BD CCD BE ICA SP CA Ti CZ ICZ NiCr WZ CerZ G
1.88 ± 0.08 1.86 ± 0.08 1.86 ± 0.08 1.85 ± 0.07 1.84 ± 0.05 1.82 ± 0.09 1.81 ± 0.08 1.81 ± 0.07 1.79 ± 0.08 1.62 ± 0.07 1.46 ± 0.08 1.43 ± 0.06 1.40 ± 0.06 0.90 ± 0.03 0.79 ± 0.05 0.76 ± 0.05 0.44 ± 0.02 0.43 ± 0.02 0.42 ± 0.02 0.38 ± 0.01
1.00 ± 0.11 1.05 ± 0.17 1.06 ± 0.17 1.07 ± 0.15 1.09 ± 0.11 1.15 ± 0.19 1.15 ± 0.16 1.16 ± 0.15 1.22 ± 0.18 1.70 ± 0.23 2.31 ± 0.34 2.46 ± 0.31 2.61 ± 0.31 6.93 ± 0.42 8.62 ± 0.79 9.23 ± 0.81 17.25 ± 0.66 17.63 ± 0.56 17.90 ± 0.76 19.17 ± 0.53
0.64 ± 0.10 0.67 ± 0.11 0.67 ± 0.12 0.68 ± 0.10 0.70 ± 0.08 0.73 ± 0.13 0.74 ± 0.11 0.74 ± 0.10 0.78 ± 0.12 1.11 ± 0.16 1.53 ± 0.24 1.64 ± 0.22 1.75 ± 0.22 4.91 ± 0.32 6.19 ± 0.60 6.66 ± 0.62 12.89 ± 0.52 13.19 ± 0.44 13.41 ± 0.60 14.41 ± 0.42
A A A A A A A A A B C C C D E E F F F F
Different uppercase letters demonstrate significant difference by SNK multiple range test (P<.05).
was used for the analyses. The Al compositions of the step wedges were examined using scanning electron microscopy and an energy dispersive X-ray micro-analyzer (SEM/ EDX, Zeiss Supra 50 VP; Carl Zeiss SMT AG, Oberkochen, Germany).
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RESULTS Table II demonstrates the means and standard deviations of ODVs and eq Al values for all tested materials. The Kruskal-Wallis test indicated significant differences between the
ODVs and eq Al values of the materials (P<.001) (Table II). The SNK multiple range test revealed G to have an ODV (0.38 ±0.01) significantly lower than other materials, except CerZ, NiCr and WZ. CPC had the highest ODV (1.88 ±0.08), which was significantly higher
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Volume 106 Issue 2 Al Al
Cu Ca Ca 0
Cu O 0.5
C
Si 1
1.5
2
2.5
3
keV
A
0
Mg
Cu 1
2
3
4
5
6
keV
Mg
Al
Cu
Si
Ca
Al-1
–
98.30
–
1.14
0.56
Al-2
1.44
93.99
4.57
–
–
7
B
C
2 SEM/EDX surface analyses of (A) Al-1, (B) Al-2 step wedges and (C) elemental analyses.
than the other materials (P<.05), except Nor, Can, IPSE, Mol, CK, E2, BD, and CCD. Lower values represent greater radiopacity. The radiopacity values of all materials were similar to or greater than human and bovine dentin. However, the radiopacity values of CCD, E2, CK, IPSE, Nor, CPC were significantly lower than bovine enamel (P<.05). The Kruskal-Wallis test revealed significant differences between the ODVs of the 2 step wedges (P<.001). Nevertheless, the density measurements of the 2 step wedges and the eq Al values of the materials calculated using each step wedge demonstrated strong positive correlations (r=0.99). SNK multiple range tests showed G to have the highest equivalent Al-1 and Al-2 step wedge values (19.17 ±0.53 and 14.42 ±0.42 mm eq Al, respectively), whereas CPC had the lowest equivalent Al-1 and Al-2 step wedge values (1.00 ±0.11 and 0.64 ±0.10 mm eq Al, respectively). ICA, SP, CA, Ti, CZ, ICZ, NiCr, WZ, CerZ, and G were found to have eq Al values that were significantly higher than BE. The SEM/EDX analysis revealed that Al-1 and Al-2 were composed of approximately 98% and 94% Al, respectively (Fig. 2A-C).
DISCUSSION It is undesirable for the radiopacity of restorative materials to be lower than that of the replaced dental hard tissues. Therefore, it is important that dental ceramics, which are used to replace enamel tissue, are more radiopaque than human dental enamel.8,45 Thus, the marginal integrity and contours of the restoration could be detected.20,21 In this study, the radiopacity of ceramic materials commonly used in clinical practice, and the radiopacity of materials to which they are likely to be compared in the clinical setting, were evaluated radiographically. The results support the first hypothesis that the radiopacity measurements of ceramic materials differ from each other. The radiopacity of alumina-containing ICA and CA was similar to magnesium aluminate-containing ceramic material SP. The radiopacity values of CZ and ICZ were also similar to each other, as expected. Zirconia ceramics, such as WZ and CerZ, had radiopacity values similar to NiCr and G. The authors believe that the high radiopacity of WZ and CerZ ceramics, which is similar to that of metals, is a disadvantage. These
The Journal of Prosthetic Dentistry
materials, when used in the clinical practice, may mask cement dissolutions and caries, which could occur under the crown. The radiopacity values of CCD, E2, CK, IPSE, Nor, and CPC were significantly lower than that of BE (Table II). Therefore, the second hypothesis that the radiopacity of dental ceramics is higher than that of enamel was not accepted. Nevertheless, similar to CCD, CK and Nor are generally used for fabricating metal ceramic restorations. However, E2, IPSE and CPC are ceramic systems, which are commonly used in clinical applications, and, according to this study, the radiopacity of these materials is low. The radiopacity of ceramics was higher than that of human and bovine dentin, except CPC, Nor, IPSE, CK, E2, and CCD (Table II). No significant differences were identified between CPC, Nor, IPSE, CK, E2, CCD, and human and bovine dentin. The third hypothesis that the radiopacity of ceramics is higher than that of dentin was not accepted. The radiopacity of Ti was significantly lower than that of ceramics that contain zirconia, NiCr and G. According to these results, it is suggest-
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August 2011 ed that cement dissolution and caries could be detected by radiographical evaluation when Ti alloys are used as a restorative material. Akerboom et al24 suggested using human teeth as a standard, and reported that variations in the radiopacity of specimens may cause discrepancies between studies. However, ISO standards require that the minimum radiopacity of restorative materials be equal to or greater than that of an equivalent thickness of Al.43 Although the radiopacity of dentin and enamel specimens varies, pure Al provides a constant reference value. To make comparisons between different studies, an Al step wedge was chosen as a standard for measuring radiopacity, because its linear absorption coefficient is on the same order as dental enamel.46 The radiopacity values of human dentin, obtained from this study using an Al-1 step wedge (1.06 ±0.17 mm Al/1 mm dentin for canine teeth and 1.09 ±0.11 mm Al/1 mm dentin for molar teeth), were found to be comparable to those reported by Turgut et al31 (1.13 mm Al/1 mm dentin), El-Mowafy et al20 (1.16 mm Al/1 mm dentin), Williams and Billington29 (1 mm Al/1 mm dentin), and Stanford et al22 (0.79 mm Al/1 mm dentin). According to some studies, when bovine teeth are compared to human teeth, they have similar morphological and histological characteristics.41,47 In this study, bovine teeth were used because the test device required large specimens. The measurement device used in this study measures the radiopacity of a space with an approximate area of 7 mm2. This area is equivalent to a circle with a diameter of 3 mm. In this study, disks with a diameter of 6 mm and a thickness of 1 mm were obtained from the enamel of bovine mandibular incisors. It is not possible to prepare a specimen of human dental enamel with these dimensions. In previous radiopacity studies,26,31 the aperture sizes of the device probes were not generally stated. Among the studies in which aperture size was stated, O’Rourke et
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al26 used an optical densitometer with an operating aperture of 2 mm, Sabbagh et al35 used a 1 mm aperture, and Gürdal and Akdeniz36 used a digital transmission densitometer with a 0.1 mm aperture. In the authors’ opinion, aperture size differences may affect radiopacity measurements in materials with non-homogenous compositions. Devices with small aperture diameters may yield artificially high or low radiopacity values in nonhomogenous materials. Researchers should use the largest aperture possible without exceeding the size of the image area. In the current study, the effect of using step wedges with different Al contents on the evaluation of radiopacity was analyzed by using 2 types of step wedges concurrently. SEM/ EDX analysis revealed that the Al-2 step wedge was comprised of approximately 94% Al, whereas Al-1 step wedge consisted of approximately 98% Al (Fig. 2). Watts and McCabe44 stated that the content of Al step wedges used in studies is important, and the proportion of Al should not be lower than 98%. However, Al of this level of purity is relatively soft and difficult to manufacture into step wedge geometry. In the current study, the most important reason for testing an Al-2 step wedge is that it is difficult to process Al-1 step wedges with a high percentage of Al. An Al-2 step wedge could be processed more easily. Although an Al-2 step wedge with a smaller proportion of Al demonstrated lower optic density values, a high correlation was found between the ODVs of both step wedges (r=0.99). It was concluded that both step wedges could be used to evaluate radiopacity, despite the difference in their Al content. Further studies are needed to clarify this issue. It was reported that the variability in radiopacity measurements of the same restorative materials among different studies depends on a number of factors, including speed of the radiographic film, exposure time, voltage used and the age of the de-
veloping and fixing solutions.20,25,40 Furthermore, source-film distance, intensifying screens and grids are also factors that affect measurements of radiopacity. While some authors have stated that radiopacity is not a requirement for anterior restorations,23,31 others have indicated that excessive radiopacity in restorative materials may have some disadvantages.29,39 It was reported that the higher radiopacity of amalgam restorations may result in under- and over-scoring of secondary caries and marginal defects, compared to composite resin restorations.39 It was concluded that caries and marginal defects may be over-diagnosed with highly radiopaque restorations. Moreover, Rasimick et al34 stated that a radiopaque core foundation material allows a clinician to radiographically inspect the core material for voids. However, in that study, the authors tested metal-reinforced glass ionomer core foundation materials that were extremely radiopaque. Therefore, the authors suggested that excessively radiopaque core materials could hinder a clinician’s ability to identify voids or marginal defects. Highly radiopaque restorative materials may mask caries near the buccal or lingual margin of a Class II restoration. This phenomenon may result from the angulation of the radiographic beam superimposing high radiopaque restorations over carious tooth structure.30 Moderate radiopacity may be more favorable and could facilitate the detection of caries.39 Many authors have used different techniques to study the radiopacity of restorative materials. Measurements derived from radiographical images, using a transmission or photographic densitometer, were most common. Recently, digital imaging systems have been used to measure radiopacity.34 Sabbagh et al35 stated that, despite the numerous benefits offered by the digital imaging system (low radiation dose, instant image, image manipulation), the conventional radiographic film technique is more accurate for
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Volume 106 Issue 2 measuring radiopacity. However, digitizing radiographs and importing the images to a software program is another method to measure radiopacity.27,34 Radiopacity measurements were expressed in optical density for conventional films and in pixels and grey shades for digital systems. Studies have claimed that the difference in a material’s measured radiopacity, as determined by a digital sensor compared to conventional film, is greater than 10%.34,35 A limitation of this study may be the thickness of the specimens that might have affected the radiopacity values.44 Some core ceramics investigated are almost never used clinically in 1 mm thickness. When core materials such as CerZ, and WZ are used, their thickness range could be 0.3 to 0.7 mm depending on the abutment tooth and interocclusal distance. Also, no power analysis was performed to determine adequate sample size. Also, there was no assessment of intrareader variability for the reader of the densitometer. Adequate radiopacity of ceramics assists in the radiological assessment and diagnosis of caries, cement failure, voids between restoration and tooth structure, marginal gaps, and the overall condition of existing restorations. Adequate radiopacity must, therefore, be accepted as a factor when evaluating the clinical success of ceramic restorations. For a patient with a high incidence of caries, ceramic systems with optimum radiopacity should be used. Furthermore, studies are needed to compare the radiopacity of adhesive cements that are used with the ceramic systems.
CONCLUSIONS All dental ceramic materials used in this study were found to have radiopacity values similar to or greater than human and bovine dentin. CPC, Nor, IPSE, CK, E2, and CCD had radiopacity values significantly lower than bovine enamel. ICA, SP, CA, Ti, CZ, and ICZ had moderate radiopac-
ity values that were statistically higher than bovine enamel. CerZ and WZ had high radiopacity values, which are similar to G and NiCr.
REFERENCES 1. Grossman DG. Cast glass Cceramics. Dent Clin N Am 1985;29:725-39. 2. Kelly JR, Nishimura I, Campbell SD. Ceramics in dentistry: historical roots and current perspectives. J Prosthet Dent 1996;75:18-32. 3. Mclean JW. Evolution of dental ceramics in the twentieth century. J Prosthet Dent 2001;85:61-6. 4. Tinschert J, Zwez D, Marx R, Anusavice KJ. Structural reliability of alumina-, feldspar-, leucite-, mica- and zirconia-based ceramics. J Dent 2000;28:529-35. 5. Mörmann WH, Bindl A. All-ceramic, chairside computer-aided design/computer-aided machining restorations. Dent Clin North Am 2002;46:405-26. 6. Raigrodski AJ. Contemporary materials and technologies for all-ceramic fixed partial dentures: a review of the literature. J Prosthet Dent 2004;92:557-62. 7. Pekkan G, Hekimoglu C. Evaluation of shear and tensile bond strength between dentin and ceramics using dual-polymerizing resin cements. J Prosthet Dent 2009;102:242-52. 8. O’Brien WJ. Dental Materials and Their Selection. 3rd ed., Quintessence Publishing Co, Inc, Hanover Park, Illinois, 2002, p. 210-221. 9. Höland W, Schweiger M, Frank M, Rheinberger V. A Comparison of the Microstructure and Properties of the IPS Empress 2 and the IPS Empress Glass-Ceramics. J Biomed Mater Res 2000;53:297-303. 10.Guazzato M, Albakry M, Swain MV, Ironside J. Mechanical Properties of In-Ceram Alumina and In-Ceram Zirconia. Int J Prosthodont 2002;15:339-46. 11. Strub JR, Beschnidt SM. Fracture strength of 5 different all-ceramic crown systems. Int J Prosthodont 1998;11:602-9. 12.Zeng K, Odén A, Rowcliffe D. Flexure tests on dental ceramics. Int J Prosthodont 1996;9:434-9. 13.Guazzato M, Proos K, Quach L, Swain MV. Strength, reliability and mode of fracture of bilayered porcelain/zirconia (Y-TZP) dental ceramics. Biomaterials 2004;25:5045-52. 14.Sundh A, Sjögren G. Fracture resistance of all-ceramic zirconia bridges with differing phase stabilizers and quality of sintering. Dent Mater 2006;22:778–84. 15.Callister WD. Materials Science and Engineering. 4th ed., John Willey & Sons Inc, New York, 1997, p. 372-433. 16.Manicone PF, Rossi Iommetti P, Raffaelli L. An overview of zirconia ceramics: basic properties and clinical applications. J Dent 2007;35:819-26. 17.Kollar A, Huber S, Mericske E, MericskeStern R. Zirconia for teeth and implants: a case series. Int J Periodontics Restorative Dent 2008;28:479-87.
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18.Sjögren G, Lantto R, Tillberg A. Clinical evaluation of all-ceramic crowns (Dicor) in general practice. J Prosthet Dent 1999;81:277-84. 19.Malament KA, Socransky SS. Survival of Dicor glass-ceramic dental restorations over 16 years. Part III: effect of luting agent and tooth or tooth-substitute core structure. J Prosthet Dent 2001;86:511-9. 20.el-Mowafy OM, Brown JW, McComb D. Radiopacity of direct ceramic inlay restoratives. J Dent 1991;19:366-8. 21.Hars E. CEREC in X-ray. In: Mörmann WH, ed. CAD/CAM in aesthetic dentistry. CEREC 10 Year Anniversary Symposium. Berlin: Quintessence, 1996, p. 653-7. 22.Stanford CM, Fan PL, Shoenfeld CM, Knoeppel R, Stanford JW. Radiopacity of lightcured posterior composite resins. J Am Dent Assoc 1987;115:722-4. 23.Curtis PM Jr, Von Fraunhofer JA, Farman AG. The radiographic density of composite restorative resins. Oral Surg Oral Med Oral Pathol 1990;70:226-30. 24.Akerboom HB, Kreulen CM, Van Amerongen WE, Mol A. Radiopacity of posterior composite resins, composite resin luting cements, and glass ionomer lining cements. J Prosthet Dent 1993;70:351-5. 25.Langland OE, Langlais R, Preece J. Principles of Dental Imaging. Lippincott Williams and Wilkins, Baltimore, 1997, p. 49-65. 26.O’Rourke B, Walls AW, Wassell RW. Radiographic detection of overhangs formed by resin composite luting agents. J Dent 1995;23:353-7. 27.Tanomaru-Filho M, Jorge EG, Tanomaru JM, Gonçalves M. Evaluation of the radiopacity of calcium hydroxide- and glass-ionomer-based root canal sealers. Int Endod J 2008;41:50-3. 28.Bouschlicher MR, Cobb DS, Boyer DB. Radiopacity of compomers, flowable and conventional resin composites for posterior restorations. Oper Dent 1999;24:20-5. 29.Williams JA, Billington RW. The radiopacity of glass ionomer dental materials. J Oral Rehabil 1990;17:245-8. 30.Goshima T, Goshima Y. Radiographic detection of recurrent carious lesions associated with composite restorations. Oral Surg Oral Med Oral Pathol 1990;70:236-9. 31.Turgut MD, Attar N, Onen A. Radiopacity of direct esthetic restorative materials. Oper Dent 2003;28:508-14. 32.Bloodworth KE, Render PJ. Dental acrylic resin radiopacity: literature review and survey of practitioners’ attitudes. J Prosthet Dent 1992;67:121-3. 33.Parissis N, Iakovidis D, Chirakis S, Tsirlis A. Radiopacity of elastomeric impression materials. Aust Dent J 1994;39:184-7. 34.Rasimick BJ, Gu S, Deutsch AS, Musikant BL. Measuring the radiopacity of luting cements, dowels, and core build-up materials with a digital radiography system using CCD sensor. J Prosthodont 2007;16:357-64. 35.Sabbagh J, Vreven J, Leloup G. Radiopacity of resin-based materials measured in film radiographs and storage phosphor plate (Digora). Oper Dent 2004;29:677-84.
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August 2011 36.Gürdal P, Akdeniz BG, Comparison of two methods for radiometric evaluation of resin-based restorative materials. Dentomaxillofac Radiol 1998;27:236-9. 37.Prévost AP, Forest D, Tanguay R, DeGrandmont P. Radiopacity of glass ionomer dental materials. Oral Surg Oral Med Oral Pathol 1990;70:231-5. 38.Attar N, Tam LE, McComb D. Mechanical and physical properties of contemprorary dental luting agents. J Prosthet Dent 2003;89:127-34. 39.Tveit AB, Espelid I. Radiographic diagnosis of caries and marginal defects in connection with radiopaque composite fillings. Dent Mater 1986;2:159-62. 40.el-Mowafy OM, Benmergui C. Radiopacity of resin-based inlay luting cements. Oper Dent 1994;19:11-5. 41.Soares CJ, Mitsui FH, Neto FH, Marchi GM, Martins LR. Radiodensity evaluation of seven root post systems. Am J Dent 2005;18:57-60.
42.Price C. A method of determining the radiopacity of dental materials and foreign bodies. Oral Surg Oral Med Oral Pathol 1986;62:710-8. 43.International Standards Organization. ISO 4049. Dentistry--polymer-based filling, restorative and luting materials. 3rd ed. 2000. 44.Watts DC, McCabe JF. Aluminium radiopacity standards for dentistry: an international survey. J Dent 1999;27:73-8. 45.Manicone PF, Rossi Iommetti P, Raffaelli L. An overview of zirconia ceramics: basic properties and clinical applications. J Dent 2007;35:819-26. 46.Cook WD. An investigation of the radiopacity of composite restorative materials. Aust Dent J 1981;26:105-12. 47.Fonseca RB, Haiter-Neto F, Fernandes-Neto AJ, Barbosa GA, Soares CJ. Radiodensity of enamel and dentin of human, bovine and swine teeth. Arch Oral Biol 2004;49:919-22.
Corresponding author: Dr Gurel Pekkan Dumlupinar University Faculty of Dentistry Merkez Kampus, Tavsanli Yolu 10. Km. Kutahya TURKEY Fax: +90-274-2652277 E-mail: [email protected] Acknowledgments The authors thank Dr Huseyin Kayadibi for the statistical analyses. Copyright © 2011 by the Editorial Council for The Journal of Prosthetic Dentistry.
Noteworthy Abstracts of the Current Literature Five-year follow-up of implant-supported Y-TZP and ZTA fixed dental prostheses. A randomized, prospective clinical trial comparing two different material systems Larsson C, Vult von Steyern P. Int J Prosthodont. 2010 Nov-Dec;23(6):555-61. Purpose. The aim of this study was to evaluate the clinical performance of two- to five-unit implant-supported all-ceramic restorations and to compare the results of two different all-ceramic systems, Denzir (DZ) and In-Ceram Zirconia (InZ). Materials and Methods. Eighteen patients were treated with a total of 25 two- to five-unit implant-supported fixed dental prostheses. Nine patients were given DZ system restorations and 9 were given InZ system restorations. The restorations were cemented with zinc phosphate cement onto customized titanium abutments and were evaluated after 1, 3, and 5 years. Results. At the 5-year follow-up, all restorations were in function; none had fractured. However, superficial cohesive (chip-off ) fractures were observed in 9 of 18 patients (11 of 25 restorations). Sixteen units in the DZ group (9 of 13 restorations) and 3 in the InZ group (2 of 12 restorations) had chip-off fractures. The difference between the two groups regarding frequency of chip-off fractures was statistically significant (P < .05 at the FDP level and P < .001 at the unit level). Conclusion. The results suggest that all-ceramic implant-supported fixed dental prostheses of two to five units may be considered a treatment alternative. The DZ system, however, exhibited an unacceptable amount of veneering porcelain fractures and thus cannot be recommended for the type of treatment evaluated in this trial. Poor compatibility or problems with the bond mechanisms between the veneer and framework could not explain the chip-off fractures. Stress distribution, as well as other factors concerning the veneering porcelain, need to be evaluated further. Reprinted with permission of Quintessence Publishing.
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Clinical Implications
Adequate radiopacity of ceramics assists in the radiological assessment and diagnosis of caries, cement failure, voids between restoration and tooth structure, marginal gaps, and the overall condition of existing restorations. Clinicians should be aware of the radiopacity of the ceramic system(s) they use. Among ceramic materials and metals tested, In-Ceram Alumina, In-Ceram Spinell, Celay Alumina, Titanium alloy (Ti-6Al-4V), Celay Zirconia and In-Ceram Zirconia had adequate radiopacity values. Supported in part by the Dumlupinar University Research Fund (Grant no. 2007-8). Assistant Professor, Faculty of Dentistry, Dumlupinar University. Assistant Professor, Faculty of Dentistry, Dumlupinar University. c Assistant Professor, Faculty of Dentistry, Dumlupinar University. d Assistant Professor, Department of Prosthodontics, Faculty of Dentistry, Suleyman Demirel University. a
b
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Volume 106 Issue 2 Ceramic systems were developed to improve the esthetics and biological compatibility of fixed dental prostheses.1-3 Ceramic restorations are frequently used instead of metal ceramic restorations, depending on the indication.2-4 Ceramic systems are generally categorized as castable glass ceramics, ceramics obtained through the refractory die technique, ceramics produced with computer-aided manufacturing (CAM) or computeraided design (CAD)/CAM systems, and heat-pressed ceramics.4-7 Ceramic restorations are capable of reflecting light, which produces an appearance and color similar to that of natural teeth. Such restorations possess thermal expansion coefficients and thermal conductivity that are similar to natural teeth.8 Their compressive strength is high and they are chemically inert.9,10 These restorations do not cause unusual tastes.8 They are used in the fabrication of crowns, fixed partial dental prostheses, inlays, onlays, and laminate veneers.1-7 Such restorations, however, have some negative characteristics, such as brittleness and low flexural strength.4,8-11 Due to such weaknesses in ceramic structure, the development of reinforcement techniques has been considered a necessity12-14 to prevent the formation and propagation of microcracks.2-4 To this end, crystalline additives (leucite, alumina, magnesia, magnesium aluminate, lithium disilicate, zirconia, sanidine) and ceramic matrix composites (zirconia whiskers) have been added.4,8-10,13-17 In glass ceramic systems, an attempt has been made to improve durability by adding small amounts of such nucleating agents as tetrasilisic fluormica, oxy-apatite (CaP2O5SiO5) and β-spodumene into molten glass.1,8,18,19 Due to these reinforcing additives or reinforcement procedures, ceramics possess different radiopacities.8,20,21 Most ceramic systems ensure radiographic diagnosis of caries; however, only a few authors evaluated the radiopacity of these materials.8,20,21 It is recognized that ceramic inlay
materials should be more radiopaque than enamel to allow the detection of recurrent caries.20,21 An in vitro study of ceramic inlay materials found that Cerec Vita did not possess sufficient radiopacity to permit detection of recurrent caries.20 According to the author, inaccurate interpretation of radiographs of Cerec inlays resulted in the unnecessary replacement of restorations.21 Radiopacity is widely acknowledged as a desirable property of all intraoral materials, including directrestorative materials,22-31 cavity liners,27,30 denture base materials,32 elastomeric impression materials,33 endodontic sealers,34 posts and retrograde materials,35,36 core foundation materials,28,36 luting agents,24,25,30,37-40 and adhesive systems.40-44 The radiopacity of these materials aids localization following the accidental swallowing of fixed or removable dental prostheses and interim crowns.42 Due to the radiopacity of restorative materials, it is possible to radiologically detect the form,45 contour, and deficiencies of restorations, as well as localize the dental pulp.22-26 Furthermore, the radiopacity of restorative materials facilitates the detection of secondary caries under the restoration and enables the observation of periodontal effects of the overhangs in the restoration.23,38 Previous radiopacity studies have been performed using dental materials with the same thickness as the enamel and dentin, and using aluminum (Al) step wedges and radiographs with specific standards.26,34-36,38,46,47 Ideally, restorative materials should have radiopacity values equivalent to or greater than that of enamel.37-40 Radiopacity is generally defined by equivalent Al thickness.35 The International Organization for Standardization (ISO) published a radiopacity protocol and guidelines for polymerbased restorative and luting materials.43 These materials should have radiopacity equal to or greater than that of Al.43,44 Nevertheless, neither the ISO nor the American National
The Journal of Prosthetic Dentistry
Standards Institute/American Dental Association (ANSI/ADA) has issued radiopacity guidelines for dental ceramic restorative materials. However, methods for determining the radiopacity of materials used in dentistry (ISO/New Work Item Proposal (NP) 13116) are under development. The purpose of this study was to compare the radiopacity of different ceramics to human dentin and bovine enamel-dentin and metals by referring to Al step wedges. The hypotheses were that the: (1) radiopacity levels of dental ceramic systems would be different from each other; (2) radiopacity levels of dental ceramics would be higher than that of enamel; (3) radiopacity levels of dental ceramics would be higher than that of dentin.
MATERIAL AND METHODS The radiopacity levels of 13 different dental ceramics, titanium alloy (Ti), NiCr alloy (NiCr), and 22-carat gold (G) were evaluated. The materials used, the manufacturers and the composition for the materials are listed in Table I. Human canine dentin (Can) and molar dentin (Mol), bovine dentin (BD) and bovine enamel (BE), and 2 Al step wedges were used as controls. Eight specimens were fabricated for all test groups. No power analysis was performed to determine adequate sample size. For fabricating ceramic specimens, auto-polymerizing acrylic resin (Pattern Resin; GC Corp, Tokyo, Japan) disk-shaped specimens were prepared using stainless steel molds (6.0 x 1.0 mm). IPS Empress 2 (E2) IPS Empress e-max Press (IPSE), and Cergo Pressable Ceramic (CPC) were invested and (IPS Empress 2 Special Investment Material; Ivoclar Vivadent, Schaan, Liechtenstein, and Cergo Fit Investment Material; Degussa AG, Hanau, Germany) were eliminated to obtain molds for heat pressing according to the manufacturers’ instructions. E2, IPSE, and CPC specimens were fabricated by heat-pressing them into molds. Noritake super porce-
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Table I. Materials evaluated. Composition information provided by manufacturers. Materials
Manufacturer
IPS Empress 2 (E2)
Ivoclar Vivadent
SiO2, Li2O, K2O, P2O5, ZnO, MgO, La2O3, Al2O3
Cergo Pressable Ceramic (CPC)
Degudent GmbH
SiO2, Al2O3, K2O, Na2O, CaO
In-Ceram Spinell (SP)
Vita Zahnfabrik
MgAl2O4
In-Ceram Alumina (ICA)
Vita Zahnfabrik
In-Ceram Alumina powder: Al2O3 100%; Glass powder: SiO2 14-17%, Al2O3 14-17%,B2O3 12-15%,TiO2 3-5%, La2O3 39-48%, CeO2 2-5%, CaO 2-4%, coloring oxides < 2%
In-Ceram Zirconia (ICZ)
Vita Zahnfabrik
In-Ceram Zirconia Powder: Al2O3 67%, ZrO2 33%; Glass powder: Al2O3 14-18%, SiO2 14-18%, B2O3 11-15%, TiO2 2-7%, La2O3 25-30%, CeO2 6-10%, CaO 4-8%, ZrO2 1-4%, Y2O3 2-6%
IPS Empress e-max Press (IPSE)
Ivoclar Vivadent
SiO2, Li2O, K2O, P2O5, ZnO, ZrO2, other oxides and pigments
Noritake super porcelain EX-3 dentin (Nor)
Noritake Dental Supply Co, Ltd, Aichi, Japan
SiO2, Al2O3, K2O, Na2O, Ba2O, CaO, other oxides and pigments
Celay Alumina (CA)
Vita Zahnfabrik
Celay Alumina blank: Al2O3 100%; Glass powder: SiO2 14-17%, Al2O3 14-17%,B2O3 12-15%, TiO2 3-5%, La2O3 39-48%, CeO2 2-5%, CaO 2-4%, coloring oxides < 2%
Celay Zirconia (CZ)
Vita Zahnfabrik
Celay Zirconia blank: Al2O3 67%, ZrO2 33%; Glass powder: Al2O3 14-18%, SiO2 14-18%, B2O3 11-15%, TiO2 2-7%, La2O3 25-30%, CeO2 6-10, CaO 4-8%, ZrO2 1-4%, Y2O3 2-6%
Cercon Zirconia (CerZ)
Degudent GmbH
ZrO2 > 92%, Y2O3 5%, HfO2 < 2%, Al2O3 and SiO2 < 1%
Cercon Kiss dentin (CK)
Degudent GmbH
SiO2, Al2O3, K2O, Na2O, Ba2O, CaO, other oxides and pigments
Cercon Ceram dentin (CCD)
Degudent GmbH
SiO2, Al2O3, K2O, Na2O, Ba2O, CaO, other oxides and pigments
Wieland Zirconia (WZ)
Wieland Dental
ZrO2 and HfO2 94%,Y2O3 5%, Al2O3 < 1%
Titanium alloy (Ti-6Al-4V) (Ti)
Arcam AB
Gold-22-carat (G)
Merkür Ltd, Istanbul, Turkey
Nickel-Chromium alloy (NiCr)
Eisenbacher Dentalwaren GmbH
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Composition
Al 6%, V 4%, O 0.15%, Fe 0.1%, N 0.01%, C 0.03%, H 0.003%, Ti balance Au 91.6%, and Pd, Ir and other elements 8.4% Ni 63%, Cr 25%, Mo 11%, Si 1.5%, Mn< 0.1%, C< 0.1%
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Volume 106 Issue 2 lain EX-3 dentin (Nor), Cercon Kiss dentin (CK), Cercon Ceram dentin (CCD) specimens, acrylic resin (Pattern resin; GC Corp) specimens were embedded in the investment material of each system according to the manufacturers’ instructions. After the acrylic resin (Pattern resin; GC Corp) specimens were eliminated, ceramic specimens were fabricated using a refractory die technique. In-Ceram Alumina (ICA), In-Ceram Zirconia (ICZ), and In-Ceram Spinell (SP) specimens were fabricated by a slip-casting technique after preparing molds from Vita In-Ceram Special Plaster (Vita Zahnfabrik, Bad Sackingen, Germany) using acrylic resin (Pattern resin; GC Corp). Thereafter, ICA, ICZ, and SP specimens were glass infiltrated to strengthen the slip-cast core, as described by the manufacturers of these ceramics. Specimens of Celay Alumina (CA) and Celay Zirconia (CZ) were prepared from Vita Celay alumina AC12 and zirconia ZC-12 blanks (Vita ZahnFabrik) by cutting them with a saw (Isomet 4000; Buehler, Lake Bluff, Ill). Afterwards, the CA and CZ specimens were glass infiltrated as ICA and ICZ specimens. Cercon Zirconia (CerZ), yttria-stabilied tetragonal zirconia polycrystal (Y-TZP) ceramic, specimens were prepared from a base (Cercon; Degudent GmbH, Hanau, Germany) for crowns. The prepared acrylic resin patterns were scanned, and the digitized framework was enlarged. Then, the specimens were milled from a prefabricated homogeneous porous blank of zirconia (Cercon; Degudent GmbH). The zirconia specimens were then sintered to full density for 8 hours at 1350°C to achieve the final form. Wieland Zirconia (WZ) specimens were milled from a Wieland Zeno zirconia disk (Wieland Dental + Technik GmbH and Co, KG, Pforzheim, Germany) in the same manner as the CerZ specimens were fabricated and sintered according to the manufacturer’s instructions. In total, 104 (n=8) ceramic specimens were obtained. Additionally, 8 specimens were prepared from ti-
tanium (Arcam AB, Mölndal, Sweden) and NiCr (Kera N; Eisenbacher Dentalwaren ED GmbH, Wörth, Germany) alloys by slicing ingots 1 mm in thickness with a precision saw (Isomet 4000; Buehler). The metal specimens were then ground to 6 mm in diameter. After eliminating the acrylic resin (Pattern resin; GC Corp), specimens (6 x 1 mm) that were embedded in gypsum-bonded investment material (Deguvest California; Degudent GmbH) and 22-carat gold (Merkür Ltd, Istanbul, Turkey) specimens were obtained by casting them into these prepared molds. All specimens were ground through 400-grit silicon carbide paper (SiC) (Struers GmbH, Willich, Germany) to create a flat surface and measured with a digital calliper (Youfound Precision Co, Ltd, Zhejiang, China) after fabrication to verify the critical tolerance of 1.0 ±0.01 mm. All specimens were ultrasonically cleaned in distilled water for 5 minutes using an ultrasonic bath (Eurosonic 4D; Euronda SPA, Vicenza, Italy). Eight bovine enamel and dentin disk specimens were prepared from bovine mandibular incisor teeth (6 x 1 mm). Bovine dentin and enamel specimens were obtained by longitudinal sectioning of the buccal side of teeth after separating the roots. Longitudinal sections of human permanent molar and canine teeth were also prepared to the same thickness using a micro-slicing device (Accutom; Struers A/S, Ballerup, Denmark) (n=8 for each). Two different step wedges, Al-1 (Alu-Keil; PEHA Med Geräte GmbH, Sulzbach, Germany) and Al-2 were prepared. Al-2 step wedge had lesser amounts of Al in its composition so that it was harder and more machinable than Al-1. The step wedges’ maximum thickness was 14 mm; each step had a thickness of 1 mm, a length of 4 mm, and width of 14 mm. All specimens were soaked in distilled water using a water bath (NB9; Nüve Temel Laboratuar Cihazları, Ankara, Turkey) at 37°C for 24 hours. One specimen of each material, bovine dentin and enamel, 2 tooth (ca-
The Journal of Prosthetic Dentistry
nine and molar) sections and Al step wedges were positioned side by side on occlusal D speed radiographic film (Kodak Ultra-speed; Eastman Kodak Company, Rochester, NY). A special holder was mounted to ensure a fixed focus/film distance. The film was exposed for 0.38 seconds with a dental radiographic system (Trophy Radiologie, Vincennes, France) at 70 kV and 8 mA; the object-to-film distance was 30 cm. All films were processed immediately in an automatic processor (Velopex Extra-X; Medivance Instruments Ltd, Harlesden, UK) using fresh developer and fixing solutions (Velopex Ready Mixed Developer and Fixer; Hexagon International (GB) Ltd, Berkhamsted, UK). The optical density of the radiographic images was measured with a transmission densitometer (Denso-Dent Densitometer; PEHA Med Geräte GmbH) (mean of at least 3 readings per specimen) with an aperture size of 3 mm (DIN 6868/55). All measurements were completed by one individual and the densitometer was calibrated after reading each radiograph. Following the method of El-Mowafy and Benmergui,40 the optical density data for the Al steps were entered into a computer, and the best possible exponential fit was used for curves of Al optical density. Two graphs were plotted to illustrate the relationship between step wedge thickness and optical density values (ODVs) with the following equations: y=-0.5077Ln(x) + 1.8817, and y=-0.4798Ln(x) + 1.6626 (Fig. 1) From these graphs, ODVs of the specimens were used to determine the equivalent Al thickness (eq Al) values. One-way analysis of variance (ANOVA), Kruskal-Wallis, and StudentNewman-Keuls (SNK) multiple range tests were conducted to statistically analyze the ODVs and eq Al values of the materials (α=.05). Pearson correlation analysis was used to evaluate correlations of the step wedges’ density measurements and the eq Al values. Statistical software (SPSS 13.0 for Windows; SPSS Inc, Chicago, Ill)
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Optical Density Values
2.0 Al-2 step wedge Al-1 step wedge Log. (Al-2 step wedge) Log. (Al-1 step wedge)
y=–0.4798Ln(x) + 1.6626 R2=0.9901
1.5
1.0 y=–0.5077Ln(x) + 1.8817 R2=0.9942
0.5
0
0
3
6
12
9
15
Aluminum Step Wedge Thickness (mm) 1 Optical density calibration curves for Al-1 and Al-2 step wedges.
Table II. Means and standard deviations (SD) of optical density and equivalent aluminum thickness values of materials and the statistical category according to SNK multiple range tests
Material Code
Optical Density Mean Values ± SD
Equivalent Al-1 Step Wedge Mean Values ± SD
Equivalent Al-2 Step Wedge Mean Values ± SD
Statistical Category
CPC Nor Can IPSE Mol CK E2 BD CCD BE ICA SP CA Ti CZ ICZ NiCr WZ CerZ G
1.88 ± 0.08 1.86 ± 0.08 1.86 ± 0.08 1.85 ± 0.07 1.84 ± 0.05 1.82 ± 0.09 1.81 ± 0.08 1.81 ± 0.07 1.79 ± 0.08 1.62 ± 0.07 1.46 ± 0.08 1.43 ± 0.06 1.40 ± 0.06 0.90 ± 0.03 0.79 ± 0.05 0.76 ± 0.05 0.44 ± 0.02 0.43 ± 0.02 0.42 ± 0.02 0.38 ± 0.01
1.00 ± 0.11 1.05 ± 0.17 1.06 ± 0.17 1.07 ± 0.15 1.09 ± 0.11 1.15 ± 0.19 1.15 ± 0.16 1.16 ± 0.15 1.22 ± 0.18 1.70 ± 0.23 2.31 ± 0.34 2.46 ± 0.31 2.61 ± 0.31 6.93 ± 0.42 8.62 ± 0.79 9.23 ± 0.81 17.25 ± 0.66 17.63 ± 0.56 17.90 ± 0.76 19.17 ± 0.53
0.64 ± 0.10 0.67 ± 0.11 0.67 ± 0.12 0.68 ± 0.10 0.70 ± 0.08 0.73 ± 0.13 0.74 ± 0.11 0.74 ± 0.10 0.78 ± 0.12 1.11 ± 0.16 1.53 ± 0.24 1.64 ± 0.22 1.75 ± 0.22 4.91 ± 0.32 6.19 ± 0.60 6.66 ± 0.62 12.89 ± 0.52 13.19 ± 0.44 13.41 ± 0.60 14.41 ± 0.42
A A A A A A A A A B C C C D E E F F F F
Different uppercase letters demonstrate significant difference by SNK multiple range test (P<.05).
was used for the analyses. The Al compositions of the step wedges were examined using scanning electron microscopy and an energy dispersive X-ray micro-analyzer (SEM/ EDX, Zeiss Supra 50 VP; Carl Zeiss SMT AG, Oberkochen, Germany).
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RESULTS Table II demonstrates the means and standard deviations of ODVs and eq Al values for all tested materials. The Kruskal-Wallis test indicated significant differences between the
ODVs and eq Al values of the materials (P<.001) (Table II). The SNK multiple range test revealed G to have an ODV (0.38 ±0.01) significantly lower than other materials, except CerZ, NiCr and WZ. CPC had the highest ODV (1.88 ±0.08), which was significantly higher
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Volume 106 Issue 2 Al Al
Cu Ca Ca 0
Cu O 0.5
C
Si 1
1.5
2
2.5
3
keV
A
0
Mg
Cu 1
2
3
4
5
6
keV
Mg
Al
Cu
Si
Ca
Al-1
–
98.30
–
1.14
0.56
Al-2
1.44
93.99
4.57
–
–
7
B
C
2 SEM/EDX surface analyses of (A) Al-1, (B) Al-2 step wedges and (C) elemental analyses.
than the other materials (P<.05), except Nor, Can, IPSE, Mol, CK, E2, BD, and CCD. Lower values represent greater radiopacity. The radiopacity values of all materials were similar to or greater than human and bovine dentin. However, the radiopacity values of CCD, E2, CK, IPSE, Nor, CPC were significantly lower than bovine enamel (P<.05). The Kruskal-Wallis test revealed significant differences between the ODVs of the 2 step wedges (P<.001). Nevertheless, the density measurements of the 2 step wedges and the eq Al values of the materials calculated using each step wedge demonstrated strong positive correlations (r=0.99). SNK multiple range tests showed G to have the highest equivalent Al-1 and Al-2 step wedge values (19.17 ±0.53 and 14.42 ±0.42 mm eq Al, respectively), whereas CPC had the lowest equivalent Al-1 and Al-2 step wedge values (1.00 ±0.11 and 0.64 ±0.10 mm eq Al, respectively). ICA, SP, CA, Ti, CZ, ICZ, NiCr, WZ, CerZ, and G were found to have eq Al values that were significantly higher than BE. The SEM/EDX analysis revealed that Al-1 and Al-2 were composed of approximately 98% and 94% Al, respectively (Fig. 2A-C).
DISCUSSION It is undesirable for the radiopacity of restorative materials to be lower than that of the replaced dental hard tissues. Therefore, it is important that dental ceramics, which are used to replace enamel tissue, are more radiopaque than human dental enamel.8,45 Thus, the marginal integrity and contours of the restoration could be detected.20,21 In this study, the radiopacity of ceramic materials commonly used in clinical practice, and the radiopacity of materials to which they are likely to be compared in the clinical setting, were evaluated radiographically. The results support the first hypothesis that the radiopacity measurements of ceramic materials differ from each other. The radiopacity of alumina-containing ICA and CA was similar to magnesium aluminate-containing ceramic material SP. The radiopacity values of CZ and ICZ were also similar to each other, as expected. Zirconia ceramics, such as WZ and CerZ, had radiopacity values similar to NiCr and G. The authors believe that the high radiopacity of WZ and CerZ ceramics, which is similar to that of metals, is a disadvantage. These
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materials, when used in the clinical practice, may mask cement dissolutions and caries, which could occur under the crown. The radiopacity values of CCD, E2, CK, IPSE, Nor, and CPC were significantly lower than that of BE (Table II). Therefore, the second hypothesis that the radiopacity of dental ceramics is higher than that of enamel was not accepted. Nevertheless, similar to CCD, CK and Nor are generally used for fabricating metal ceramic restorations. However, E2, IPSE and CPC are ceramic systems, which are commonly used in clinical applications, and, according to this study, the radiopacity of these materials is low. The radiopacity of ceramics was higher than that of human and bovine dentin, except CPC, Nor, IPSE, CK, E2, and CCD (Table II). No significant differences were identified between CPC, Nor, IPSE, CK, E2, CCD, and human and bovine dentin. The third hypothesis that the radiopacity of ceramics is higher than that of dentin was not accepted. The radiopacity of Ti was significantly lower than that of ceramics that contain zirconia, NiCr and G. According to these results, it is suggest-
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August 2011 ed that cement dissolution and caries could be detected by radiographical evaluation when Ti alloys are used as a restorative material. Akerboom et al24 suggested using human teeth as a standard, and reported that variations in the radiopacity of specimens may cause discrepancies between studies. However, ISO standards require that the minimum radiopacity of restorative materials be equal to or greater than that of an equivalent thickness of Al.43 Although the radiopacity of dentin and enamel specimens varies, pure Al provides a constant reference value. To make comparisons between different studies, an Al step wedge was chosen as a standard for measuring radiopacity, because its linear absorption coefficient is on the same order as dental enamel.46 The radiopacity values of human dentin, obtained from this study using an Al-1 step wedge (1.06 ±0.17 mm Al/1 mm dentin for canine teeth and 1.09 ±0.11 mm Al/1 mm dentin for molar teeth), were found to be comparable to those reported by Turgut et al31 (1.13 mm Al/1 mm dentin), El-Mowafy et al20 (1.16 mm Al/1 mm dentin), Williams and Billington29 (1 mm Al/1 mm dentin), and Stanford et al22 (0.79 mm Al/1 mm dentin). According to some studies, when bovine teeth are compared to human teeth, they have similar morphological and histological characteristics.41,47 In this study, bovine teeth were used because the test device required large specimens. The measurement device used in this study measures the radiopacity of a space with an approximate area of 7 mm2. This area is equivalent to a circle with a diameter of 3 mm. In this study, disks with a diameter of 6 mm and a thickness of 1 mm were obtained from the enamel of bovine mandibular incisors. It is not possible to prepare a specimen of human dental enamel with these dimensions. In previous radiopacity studies,26,31 the aperture sizes of the device probes were not generally stated. Among the studies in which aperture size was stated, O’Rourke et
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al26 used an optical densitometer with an operating aperture of 2 mm, Sabbagh et al35 used a 1 mm aperture, and Gürdal and Akdeniz36 used a digital transmission densitometer with a 0.1 mm aperture. In the authors’ opinion, aperture size differences may affect radiopacity measurements in materials with non-homogenous compositions. Devices with small aperture diameters may yield artificially high or low radiopacity values in nonhomogenous materials. Researchers should use the largest aperture possible without exceeding the size of the image area. In the current study, the effect of using step wedges with different Al contents on the evaluation of radiopacity was analyzed by using 2 types of step wedges concurrently. SEM/ EDX analysis revealed that the Al-2 step wedge was comprised of approximately 94% Al, whereas Al-1 step wedge consisted of approximately 98% Al (Fig. 2). Watts and McCabe44 stated that the content of Al step wedges used in studies is important, and the proportion of Al should not be lower than 98%. However, Al of this level of purity is relatively soft and difficult to manufacture into step wedge geometry. In the current study, the most important reason for testing an Al-2 step wedge is that it is difficult to process Al-1 step wedges with a high percentage of Al. An Al-2 step wedge could be processed more easily. Although an Al-2 step wedge with a smaller proportion of Al demonstrated lower optic density values, a high correlation was found between the ODVs of both step wedges (r=0.99). It was concluded that both step wedges could be used to evaluate radiopacity, despite the difference in their Al content. Further studies are needed to clarify this issue. It was reported that the variability in radiopacity measurements of the same restorative materials among different studies depends on a number of factors, including speed of the radiographic film, exposure time, voltage used and the age of the de-
veloping and fixing solutions.20,25,40 Furthermore, source-film distance, intensifying screens and grids are also factors that affect measurements of radiopacity. While some authors have stated that radiopacity is not a requirement for anterior restorations,23,31 others have indicated that excessive radiopacity in restorative materials may have some disadvantages.29,39 It was reported that the higher radiopacity of amalgam restorations may result in under- and over-scoring of secondary caries and marginal defects, compared to composite resin restorations.39 It was concluded that caries and marginal defects may be over-diagnosed with highly radiopaque restorations. Moreover, Rasimick et al34 stated that a radiopaque core foundation material allows a clinician to radiographically inspect the core material for voids. However, in that study, the authors tested metal-reinforced glass ionomer core foundation materials that were extremely radiopaque. Therefore, the authors suggested that excessively radiopaque core materials could hinder a clinician’s ability to identify voids or marginal defects. Highly radiopaque restorative materials may mask caries near the buccal or lingual margin of a Class II restoration. This phenomenon may result from the angulation of the radiographic beam superimposing high radiopaque restorations over carious tooth structure.30 Moderate radiopacity may be more favorable and could facilitate the detection of caries.39 Many authors have used different techniques to study the radiopacity of restorative materials. Measurements derived from radiographical images, using a transmission or photographic densitometer, were most common. Recently, digital imaging systems have been used to measure radiopacity.34 Sabbagh et al35 stated that, despite the numerous benefits offered by the digital imaging system (low radiation dose, instant image, image manipulation), the conventional radiographic film technique is more accurate for
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Volume 106 Issue 2 measuring radiopacity. However, digitizing radiographs and importing the images to a software program is another method to measure radiopacity.27,34 Radiopacity measurements were expressed in optical density for conventional films and in pixels and grey shades for digital systems. Studies have claimed that the difference in a material’s measured radiopacity, as determined by a digital sensor compared to conventional film, is greater than 10%.34,35 A limitation of this study may be the thickness of the specimens that might have affected the radiopacity values.44 Some core ceramics investigated are almost never used clinically in 1 mm thickness. When core materials such as CerZ, and WZ are used, their thickness range could be 0.3 to 0.7 mm depending on the abutment tooth and interocclusal distance. Also, no power analysis was performed to determine adequate sample size. Also, there was no assessment of intrareader variability for the reader of the densitometer. Adequate radiopacity of ceramics assists in the radiological assessment and diagnosis of caries, cement failure, voids between restoration and tooth structure, marginal gaps, and the overall condition of existing restorations. Adequate radiopacity must, therefore, be accepted as a factor when evaluating the clinical success of ceramic restorations. For a patient with a high incidence of caries, ceramic systems with optimum radiopacity should be used. Furthermore, studies are needed to compare the radiopacity of adhesive cements that are used with the ceramic systems.
CONCLUSIONS All dental ceramic materials used in this study were found to have radiopacity values similar to or greater than human and bovine dentin. CPC, Nor, IPSE, CK, E2, and CCD had radiopacity values significantly lower than bovine enamel. ICA, SP, CA, Ti, CZ, and ICZ had moderate radiopac-
ity values that were statistically higher than bovine enamel. CerZ and WZ had high radiopacity values, which are similar to G and NiCr.
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Corresponding author: Dr Gurel Pekkan Dumlupinar University Faculty of Dentistry Merkez Kampus, Tavsanli Yolu 10. Km. Kutahya TURKEY Fax: +90-274-2652277 E-mail: [email protected] Acknowledgments The authors thank Dr Huseyin Kayadibi for the statistical analyses. Copyright © 2011 by the Editorial Council for The Journal of Prosthetic Dentistry.
Noteworthy Abstracts of the Current Literature Five-year follow-up of implant-supported Y-TZP and ZTA fixed dental prostheses. A randomized, prospective clinical trial comparing two different material systems Larsson C, Vult von Steyern P. Int J Prosthodont. 2010 Nov-Dec;23(6):555-61. Purpose. The aim of this study was to evaluate the clinical performance of two- to five-unit implant-supported all-ceramic restorations and to compare the results of two different all-ceramic systems, Denzir (DZ) and In-Ceram Zirconia (InZ). Materials and Methods. Eighteen patients were treated with a total of 25 two- to five-unit implant-supported fixed dental prostheses. Nine patients were given DZ system restorations and 9 were given InZ system restorations. The restorations were cemented with zinc phosphate cement onto customized titanium abutments and were evaluated after 1, 3, and 5 years. Results. At the 5-year follow-up, all restorations were in function; none had fractured. However, superficial cohesive (chip-off ) fractures were observed in 9 of 18 patients (11 of 25 restorations). Sixteen units in the DZ group (9 of 13 restorations) and 3 in the InZ group (2 of 12 restorations) had chip-off fractures. The difference between the two groups regarding frequency of chip-off fractures was statistically significant (P < .05 at the FDP level and P < .001 at the unit level). Conclusion. The results suggest that all-ceramic implant-supported fixed dental prostheses of two to five units may be considered a treatment alternative. The DZ system, however, exhibited an unacceptable amount of veneering porcelain fractures and thus cannot be recommended for the type of treatment evaluated in this trial. Poor compatibility or problems with the bond mechanisms between the veneer and framework could not explain the chip-off fractures. Stress distribution, as well as other factors concerning the veneering porcelain, need to be evaluated further. Reprinted with permission of Quintessence Publishing.
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