RESEARCH AND EDUCATION
Evaluation of marginal and internal fit of ceramic and metallic crown copings using x-ray microtomography (micro-CT) technology Manuel Antonio Pimenta, PhD,a Luis Carlos Frasca, PhD,b Ricardo Lopes, PhD,c and Elken Rivaldo, PhDd Ceramic crowns fabricated by ABSTRACT a variety of systems, whether Statement of problem. Prosthetic crown fit to the walls of the tooth preparation may vary mechanized or manual, can depending on the material used for crown fabrication. be used throughout the dental Purpose. The purpose of this study was to compare the marginal and internal fit of crown copings arch to obtain natural esthetics fabricated from 3 different materials. and biocompatibility.1 In addMaterial and methods. The selected materials were zirconia (ZirkonZahn system, group Y-TZP), ition to esthetic and functional lithium disilicate (IPS e.max Press system, group LSZ), and nickel-chromium alloy (lost-wax casting, outcomes, longevity is another group NiCr). Five specimens of each material were seated on standard dies. An x-ray determinant of their success. microtomography (micro-CT) device was used to obtain volumetric reconstructions of each Longevity, whether from a specimen. Points for fit measurement were located in Adobe Photoshop, and measurements mechanical or a biologic were obtained in the CTAn SkyScan software environment. Marginal fit was measured at 4 standpoint, is directly associpoints and internal fit at 9 points in each coping. Mean measurements from the 3 groups were compared by analysis of variance (ANOVA) at the 5% significance level, and between-group ated with the quality of mardifferences were assessed with the Tukey range test. ginal and internal fit.2,3 In metal ceramic crowns, Results. The nickel-chromium alloy exhibited the best marginal fit overall, comparable with zirconia widely studied and accepted and significantly different from lithium disilicate. Lithium disilicate exhibited the lowest mean values for internal fit, similar to zirconia and significantly different from the nickel-chrome alloy. for their longevity and clinical success rates, most instances Conclusions. The marginal and internal fit parameters of the 3 tested materials were within clinof failure are attributable to ically acceptable range. (J Prosthet Dent 2015;-:---) secondary caries and only rarely to structural failure.4,5 Inadequate marginal fit researchers seeking to assess marginal and internal fit. Of (>120 mm)6 may lead to plaque buildup, dissolution of the various methods used to evaluate the fit of prosthetic the cementing agent, caries, pulp inflammation, and restorations, x-ray microtomography (micro-CT)12-14 is periodontal disease.7 Likewise, internal gaps greater than nondestructive and able to reproduce these measure122 mm at the axial walls may reduce the fracture ments repeatedly at the same sites or at different sites strength of ceramic restorations.8-10 with micrometer-level precision.15-19 Despite its importance, the concept of restoration fit Of the systems currently used to fabricate ceramic has been poorly defined, and the term has often been crowns, computer-aided design/computer-aided manused for different measurements and sites. Holmes et al11 ufacturing (CAD/CAM) is least dependent on the skills of standardized the terminology and measurement sites for the laboratory technician,20 unlike the widely used
a
Professor, Professor, c Professor, d Professor, b
Department of Prosthodontics, Federal University of Santa Maria, Santa Maria, RS, Brazil. Department of Prosthodontics, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil. Department of Nuclear Engineering, Federal University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil. Postgraduate Program in Dentistry, Lutheran University of Brazil, Canoas, RS, Brazil.
THE JOURNAL OF PROSTHETIC DENTISTRY
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Table 1. Material, fabrication method, and composition of specimens from each experimental group
Clinical Implications Crown fit to the walls of the tooth preparation must be precise to ensure a thin cement line, thus enhancing the mechanical and biologic performance of the crown. The assessment of gap dimensions is essential to determine the different techniques and materials available for crown fabrication.
15,21
ceramic injection and lost-wax casting techniques. The initial results of CAD/CAM systems provided poor fit,22 and despite advances in this fabrication technique, few comparisons are available between it and other methods, in that most studies have compared different CAD/CAM systems among themselves.16,23-31 Further comparisons with other technologies are warranted. The present study sought to compare the quality of the marginal and internal fit of ceramic crown copings fabricated from 3 different materials: zirconia (ZirkonZahn system); lithium disilicate (IPS e.max Press system); and a nickel-chromium alloy (lost-wax casting technique). MATERIAL AND METHODS The specimen comprised the experimental groups and materials described in Table 1. A heat-polymerized acrylic resin model of a left maxillary canine was prepared for a complete crown with the following characteristics: facial, palatal, and proximal walls tapered 6 degrees; 2-mm incisal reduction; 1.2-mm facial reduction; rounded angles; and a 120-degree chamfer finish line.32-34 The prepared tooth was scanned and reproduced in zirconia to create a master model. To fabricate the specimen copings, 15 impressions of the master model were made with polyether impression material (Impregum Penta; 3M ESPE). After setting, 15 model dies were produced with a die stone (Fujirock; GC). In group Y-TZP (zirconia, ZirkonZahn, CAD/CAM), the stone model dies were scanned (ZirkonZahn S600 Scanner; VITA Zahnfabrik), and 5 copings were designed in the ZirkonZahn software environment and fabricated in a milling unit (M3, ZirkonZahn). The copings were stored in a temperature-controlled environment for 3.5 hours as a predrying procedure and then sintered for 7 hours at 1600 C in a furnace (inFire HTC Speed; Sirona). After cooling, airborne-particle abrasion was performed with 125-mm aluminum oxide (Basic Master; Renfert GmbH). In group LSZ (lithium disilicate, IPS e.max Press, ceramic injection molding), copings were fabricated through the lost-wax investment casting technique, with a thickness of 0.6 mm and by using Gilvest HS THE JOURNAL OF PROSTHETIC DENTISTRY
-
Material/Fabrication Method
Composition
Group
Zirconia (ZirkonZahn CAD-CAM, VITA Zahnfabrik)
Yttrium oxide partially stabilized tetragonal zirconia polycrystal
Y-TZP
Lithium disilicate (IPS e.max Press, Ivoclar Vivadent), ceramic injection
Lithium disilicate
LSZ
Tilite, induction casting (Talladium Inc)
Nickel-chrome metal alloy
NiCr
investment. After heating in a microprocessor-controlled furnace (Kota Knebel) at 850 C, lithium disilicate ingots were injected using a press furnace (Programat EP3000; Ivoclar Vivadent), and the resulting copings underwent airborne-particle abrasion (Basic Master; Renfert GmbH). These copings were clear, in that they consisted of glass ceramic containing lithium disilicate and lithium orthophosphate crystals, with a crystal content of approximately 60% by volume. In group NiCr (nickel-chromium alloy; Tilite), copings were fabricated by induction casting through the lostwax technique to a final thickness of 0.6 mm. The waxed dies were invested (Micro-Fine; Talladium Inc) and fired in a furnace (Ney Vulcan 3-130; Dentsply Intl) at a starting temperature of 400 C and a final temperature of 800 C. Induction casting was carried out in a benchtop casting machine (Fornax T; Bego). After cleaning, the copings were airborne-particle abraded (Basic Master; Renfert GmbH). Correction or adjustment of copings was not performed in any of the groups.15,25 Micro-CT measurements of marginal and internal fit were performed by x-ray microtomography. The master model was attached to an acrylic resin base, and the specimens (copings) were seated individually and scanned in a SkyScan 1173 micro-CT scanner (Bruker). Images were acquired using 130 kV maximum voltage, 61 mA current, and a 1-mm-thick aluminum filter with a pixel size of 9.91 mm. A detector size of 2240×2240 pixels was chosen. The specimens were scanned over 360 degrees (1 complete rotation) at 5 frames per rotation step of 0.38 degree. The average scanning time of each specimen was approximately 90 minutes. After scanning, the images were reconstructed in software (SkyScan NRecon 1.6.9.4 and InstaRecon 1.3.9.2), which uses a Feldkamp-based algorithm. This reconstruction software enables preprocessing and the selection of several parameters so as to generate a higher quality image. The reconstruction settings used were level 14 ring artifact correction, 40% beam hardening artifact correction, and level 4 smoothing. The SkyScan DataViewer 1.5.0 software can generate 3 views: coronal (x-z plane), sagittal (y-z plane), and transaxial (x-y plane). These views were used to locate the mesiodistal and buccolingual positions of the crown. Pimenta et al
-
2015
3
Table 2. Means and 95% confidence intervals of marginal fit on sagittal and coronal micro-CT in each experimental group (mm) Marginal Fit Y-TZP
LSZ
NiCr
P .111
Sagittal Left
60.95A
113.80A
48.44A
95% CI
0-123
40.14-187.45
23.82-80.40
Right
44.01A
53.22A
64.03A
35.57-53.71
0-110.38
21.66-102.76
52.48A
83.51A
56.24A
26.86-82.87
50.35-119.43
30.01-72.42
Left
20.55A
80.47B
2.08A
95% CI
0-63.28
31.92-129.03
0-7.88
Right
16.55A
57.26B
21.64A
95% CI
0-34.94
39.38-75.14
0-49.10
95% CI Mean 95% CI
.620 .176
Coronal
Figure 1. Scanned tooth (image generated by SkyScan 1173 Micro-CT scanner; Bruker) showing sites of marginal fit (MF), chamfer area (CA), axial wall (AW), axio-occlusal angle (AOA), occlusal area (OA), and center (CE) measurement.
Mean
18.55A
68.86B
11.86A
95% CI
0-42.43
50.41-87.32
0-27.88
35.5A
76.19B
10.85-60.18
52.71-99.66
95% CI
RESULTS Tables 2 and 3 show the mean marginal and internal fit values obtained from micro-CT measurements. As seen in Table 2, regarding marginal fit, the smallest mean values were found for the nickel-chromium alloy and were statistically similar to those of the zirconia system. Both were statistically different from the IPS e.max Press lithium disilicate system. Table 3 lists the measurements of internal fit at each point. At CA, the smallest mean score was obtained with the nickel-chromium alloy. This value was significantly Pimenta et al
.010
Evaluation of marginal and internal fit of ceramic and metallic crown copings using x-ray microtomography (micro-CT) technology Manuel Antonio Pimenta, PhD,a Luis Carlos Frasca, PhD,b Ricardo Lopes, PhD,c and Elken Rivaldo, PhDd Ceramic crowns fabricated by ABSTRACT a variety of systems, whether Statement of problem. Prosthetic crown fit to the walls of the tooth preparation may vary mechanized or manual, can depending on the material used for crown fabrication. be used throughout the dental Purpose. The purpose of this study was to compare the marginal and internal fit of crown copings arch to obtain natural esthetics fabricated from 3 different materials. and biocompatibility.1 In addMaterial and methods. The selected materials were zirconia (ZirkonZahn system, group Y-TZP), ition to esthetic and functional lithium disilicate (IPS e.max Press system, group LSZ), and nickel-chromium alloy (lost-wax casting, outcomes, longevity is another group NiCr). Five specimens of each material were seated on standard dies. An x-ray determinant of their success. microtomography (micro-CT) device was used to obtain volumetric reconstructions of each Longevity, whether from a specimen. Points for fit measurement were located in Adobe Photoshop, and measurements mechanical or a biologic were obtained in the CTAn SkyScan software environment. Marginal fit was measured at 4 standpoint, is directly associpoints and internal fit at 9 points in each coping. Mean measurements from the 3 groups were compared by analysis of variance (ANOVA) at the 5% significance level, and between-group ated with the quality of mardifferences were assessed with the Tukey range test. ginal and internal fit.2,3 In metal ceramic crowns, Results. The nickel-chromium alloy exhibited the best marginal fit overall, comparable with zirconia widely studied and accepted and significantly different from lithium disilicate. Lithium disilicate exhibited the lowest mean values for internal fit, similar to zirconia and significantly different from the nickel-chrome alloy. for their longevity and clinical success rates, most instances Conclusions. The marginal and internal fit parameters of the 3 tested materials were within clinof failure are attributable to ically acceptable range. (J Prosthet Dent 2015;-:---) secondary caries and only rarely to structural failure.4,5 Inadequate marginal fit researchers seeking to assess marginal and internal fit. Of (>120 mm)6 may lead to plaque buildup, dissolution of the various methods used to evaluate the fit of prosthetic the cementing agent, caries, pulp inflammation, and restorations, x-ray microtomography (micro-CT)12-14 is periodontal disease.7 Likewise, internal gaps greater than nondestructive and able to reproduce these measure122 mm at the axial walls may reduce the fracture ments repeatedly at the same sites or at different sites strength of ceramic restorations.8-10 with micrometer-level precision.15-19 Despite its importance, the concept of restoration fit Of the systems currently used to fabricate ceramic has been poorly defined, and the term has often been crowns, computer-aided design/computer-aided manused for different measurements and sites. Holmes et al11 ufacturing (CAD/CAM) is least dependent on the skills of standardized the terminology and measurement sites for the laboratory technician,20 unlike the widely used
a
Professor, Professor, c Professor, d Professor, b
Department of Prosthodontics, Federal University of Santa Maria, Santa Maria, RS, Brazil. Department of Prosthodontics, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil. Department of Nuclear Engineering, Federal University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil. Postgraduate Program in Dentistry, Lutheran University of Brazil, Canoas, RS, Brazil.
THE JOURNAL OF PROSTHETIC DENTISTRY
1
2
Volume
Issue
-
Table 1. Material, fabrication method, and composition of specimens from each experimental group
Clinical Implications Crown fit to the walls of the tooth preparation must be precise to ensure a thin cement line, thus enhancing the mechanical and biologic performance of the crown. The assessment of gap dimensions is essential to determine the different techniques and materials available for crown fabrication.
15,21
ceramic injection and lost-wax casting techniques. The initial results of CAD/CAM systems provided poor fit,22 and despite advances in this fabrication technique, few comparisons are available between it and other methods, in that most studies have compared different CAD/CAM systems among themselves.16,23-31 Further comparisons with other technologies are warranted. The present study sought to compare the quality of the marginal and internal fit of ceramic crown copings fabricated from 3 different materials: zirconia (ZirkonZahn system); lithium disilicate (IPS e.max Press system); and a nickel-chromium alloy (lost-wax casting technique). MATERIAL AND METHODS The specimen comprised the experimental groups and materials described in Table 1. A heat-polymerized acrylic resin model of a left maxillary canine was prepared for a complete crown with the following characteristics: facial, palatal, and proximal walls tapered 6 degrees; 2-mm incisal reduction; 1.2-mm facial reduction; rounded angles; and a 120-degree chamfer finish line.32-34 The prepared tooth was scanned and reproduced in zirconia to create a master model. To fabricate the specimen copings, 15 impressions of the master model were made with polyether impression material (Impregum Penta; 3M ESPE). After setting, 15 model dies were produced with a die stone (Fujirock; GC). In group Y-TZP (zirconia, ZirkonZahn, CAD/CAM), the stone model dies were scanned (ZirkonZahn S600 Scanner; VITA Zahnfabrik), and 5 copings were designed in the ZirkonZahn software environment and fabricated in a milling unit (M3, ZirkonZahn). The copings were stored in a temperature-controlled environment for 3.5 hours as a predrying procedure and then sintered for 7 hours at 1600 C in a furnace (inFire HTC Speed; Sirona). After cooling, airborne-particle abrasion was performed with 125-mm aluminum oxide (Basic Master; Renfert GmbH). In group LSZ (lithium disilicate, IPS e.max Press, ceramic injection molding), copings were fabricated through the lost-wax investment casting technique, with a thickness of 0.6 mm and by using Gilvest HS THE JOURNAL OF PROSTHETIC DENTISTRY
-
Material/Fabrication Method
Composition
Group
Zirconia (ZirkonZahn CAD-CAM, VITA Zahnfabrik)
Yttrium oxide partially stabilized tetragonal zirconia polycrystal
Y-TZP
Lithium disilicate (IPS e.max Press, Ivoclar Vivadent), ceramic injection
Lithium disilicate
LSZ
Tilite, induction casting (Talladium Inc)
Nickel-chrome metal alloy
NiCr
investment. After heating in a microprocessor-controlled furnace (Kota Knebel) at 850 C, lithium disilicate ingots were injected using a press furnace (Programat EP3000; Ivoclar Vivadent), and the resulting copings underwent airborne-particle abrasion (Basic Master; Renfert GmbH). These copings were clear, in that they consisted of glass ceramic containing lithium disilicate and lithium orthophosphate crystals, with a crystal content of approximately 60% by volume. In group NiCr (nickel-chromium alloy; Tilite), copings were fabricated by induction casting through the lostwax technique to a final thickness of 0.6 mm. The waxed dies were invested (Micro-Fine; Talladium Inc) and fired in a furnace (Ney Vulcan 3-130; Dentsply Intl) at a starting temperature of 400 C and a final temperature of 800 C. Induction casting was carried out in a benchtop casting machine (Fornax T; Bego). After cleaning, the copings were airborne-particle abraded (Basic Master; Renfert GmbH). Correction or adjustment of copings was not performed in any of the groups.15,25 Micro-CT measurements of marginal and internal fit were performed by x-ray microtomography. The master model was attached to an acrylic resin base, and the specimens (copings) were seated individually and scanned in a SkyScan 1173 micro-CT scanner (Bruker). Images were acquired using 130 kV maximum voltage, 61 mA current, and a 1-mm-thick aluminum filter with a pixel size of 9.91 mm. A detector size of 2240×2240 pixels was chosen. The specimens were scanned over 360 degrees (1 complete rotation) at 5 frames per rotation step of 0.38 degree. The average scanning time of each specimen was approximately 90 minutes. After scanning, the images were reconstructed in software (SkyScan NRecon 1.6.9.4 and InstaRecon 1.3.9.2), which uses a Feldkamp-based algorithm. This reconstruction software enables preprocessing and the selection of several parameters so as to generate a higher quality image. The reconstruction settings used were level 14 ring artifact correction, 40% beam hardening artifact correction, and level 4 smoothing. The SkyScan DataViewer 1.5.0 software can generate 3 views: coronal (x-z plane), sagittal (y-z plane), and transaxial (x-y plane). These views were used to locate the mesiodistal and buccolingual positions of the crown. Pimenta et al
-
2015
3
Table 2. Means and 95% confidence intervals of marginal fit on sagittal and coronal micro-CT in each experimental group (mm) Marginal Fit Y-TZP
LSZ
NiCr
P .111
Sagittal Left
60.95A
113.80A
48.44A
95% CI
0-123
40.14-187.45
23.82-80.40
Right
44.01A
53.22A
64.03A
35.57-53.71
0-110.38
21.66-102.76
52.48A
83.51A
56.24A
26.86-82.87
50.35-119.43
30.01-72.42
Left
20.55A
80.47B
2.08A
95% CI
0-63.28
31.92-129.03
0-7.88
Right
16.55A
57.26B
21.64A
95% CI
0-34.94
39.38-75.14
0-49.10
95% CI Mean 95% CI
.620 .176
Coronal
Figure 1. Scanned tooth (image generated by SkyScan 1173 Micro-CT scanner; Bruker) showing sites of marginal fit (MF), chamfer area (CA), axial wall (AW), axio-occlusal angle (AOA), occlusal area (OA), and center (CE) measurement.
Mean
18.55A
68.86B
11.86A
95% CI
0-42.43
50.41-87.32
0-27.88
35.5A
76.19B
10.85-60.18
52.71-99.66
95% CI
RESULTS Tables 2 and 3 show the mean marginal and internal fit values obtained from micro-CT measurements. As seen in Table 2, regarding marginal fit, the smallest mean values were found for the nickel-chromium alloy and were statistically similar to those of the zirconia system. Both were statistically different from the IPS e.max Press lithium disilicate system. Table 3 lists the measurements of internal fit at each point. At CA, the smallest mean score was obtained with the nickel-chromium alloy. This value was significantly Pimenta et al
.010
