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Clinical evaluations of cast gold alloy, machinable zirconia, and semiprecious alloy crowns: A multicenter study
CLINICAL RESEARCH
Clinical evaluations of cast gold alloy, machinable zirconia, and semiprecious alloy crowns: A multicenter study Ji-Man Park, DDS, PhD,a Yong-Shin Hong, DDS,b Eun-Jin Park, DDS, PhD,c Seong-Joo Heo, DDS, PhD,d and Namsik Oh, DDS, PhDe Computer-aided design and ABSTRACT computer-aided manufacture Statement of problem. Few studies have compared the marginal and internal fits of crowns (CAD/CAM) technology, which fabricated from machinable palladium-silver-indium (Pd-Ag-In) semiprecious metal alloy. uses a computer to design and Purpose. The purpose of this clinical study was to evaluate and compare the marginal and internal precisely mill dental prostheses, fits of machined Pd-Ag-In alloy, zirconia, and cast gold crowns. has been applied to multiple Material and methods. A prospective clinical trial was performed on 35 participants and 52 areas of dentistry, including the abutment teeth at 2 centers. Individuals requiring prosthetic restorations were treated with gold design and fabrication of simple alloy or zirconia crowns (2 control groups) or Pd-Ag-In alloy crowns (experimental group). A replica inlays and crowns, complex technique was used to evaluate the marginal and internal fits. The buccolingual and mesiodistal fixed and removable dental cross-sections were measured, and a noninferiority comparison was conducted. prostheses, implants, and Results. The mean marginal gaps were 68.2 mm for the gold crowns, 75.4 mm for the zirconia cement- and screw-retained crowns, and 76.9 mm for the Pd-Ag-In alloy crowns. In the 5 cross-sections other than the distal implant-supported restoracross-section, the 2-sided 95% confidence limits for the differences between the Pd-Ag-In alloy tions.1-9 In addition, this techcrowns and the 2 control groups were not larger than the 25-mm noninferiority margin. The nology results in consistent control groups displayed smaller internal gaps in the line angle and occlusal spaces compared material properties by addresswith the Pd-Ag-In crown group. ing the deformation issues that Conclusion. The marginal gaps of machinable Pd-Ag-In alloy crowns did not meet the result from the casting and noninferiority criterion in the distal margin compared with zirconia and gold alloy crowns. sintering processes and by conNonetheless, all 3 crowns had clinically applicable precision. (J Prosthet Dent 2015;-:---) trolling the shapes and thicknesses of the prosthesis and the space for cement.10,11 with soldering, which makes it difficult to fabricate longThe increased cost of gold has resulted in the need for span fixed dental prostheses. a replacement material and the use of a precious metal To overcome the limitations of cast gold crowns and alloy that contains less gold. Zirconia, which is widely the disadvantages of zirconia, machinable metals have used clinically, has been shown to be robust, biocombeen developed.18 Titanium has been used as the main patible, esthetically pleasing, and applicable to the CAD/ machinable metal,19,20 but bonding to a ceramic veneer is CAM systems.12-17 Zirconia units cannot be connected difficult due to the thick oxide layer.21-23 Thus, instead of
This work was partially supported by the Medical Devices Comparative Clinical and Performance Evaluation Program of the Korea Medical Devices Industrial Cooperation Association (KMDICA) and the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Science, ICT, and Future Planning (NRF-2013R1A1A1076022). a Clinical Associate Professor, Department of Prosthodontics and Dental Research Institute, Seoul National University Gwanak Dental Hospital, Seoul, Korea. b Former resident, Department of Prosthodontics, School of Medicine, Ewha Womans University, Seoul, Korea. c Professor, Department of Prosthodontics, School of Medicine, Ewha Womans University, Seoul, Korea. d Professor, Department of Prosthodontics and Dental Research Institute, Seoul National University, Seoul, Korea. e Professor, Department of Dentistry, School of Medicine, Inha University, Incheon, Korea.
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Clinical Implications The marginal and internal fittings of machinable Pd-Ag-In alloy crowns were comparable to those of conventional cast and zirconia crowns.
titanium alloy, alloys of platinum group metals have been used for fixed prostheses and implant abutments. Although the platinum metal alloys have been used in conventional casting methods, their specific compositions differ from those of the conventional alloys if they are manufactured for precision milling.24-26 If the weight ratio of palladium (Pd) and indium (In) is adjusted, the alloy has a gold-like color, excellent physical properties, and adequate bond strength with ceramic. The machinable Pd-silver (Ag)-In alloy has a hardness of between 185 and 330 VHN, an elongation of 5%, a modulus of elasticity of 80 GPa, and a bond strength with ceramic of 38 MPa.27 Moreover, it displays resistance to corrosion and discoloration that is higher than the criteria for clinical use. For long-term success, prostheses made of a variety of materials require appropriate marginal and internal adaptation. Inappropriate margins may cause restoration failure due to the accumulation of plaque and secondary caries, and the excess or lack of space for the cement can result in fracture, detachment, or incomplete placement.28,29 Many in vitro and in vivo studies have been conducted on marginal and internal gaps.30-44 Although a consensus has not yet been reached, a marginal gap of 100 to 120 mm and an internal gap of 140 to 150 mm are recommended as the clinical upper limits for complete crowns.38-40 A representative method for identifying the in vivo marginal and internal fits is the replica technique, which was described by Molin et al in 1993.45 This technique, which duplicates the relationship of the inner space of a crown and an abutment on a model with the registration material, has a number of advantages. A crown does not need to be sectioned, and the number of measurement sites can be decided without restriction. In addition, repeated measurements are possible. Consequently, this method has been frequently used in in vitro and in vivo studies.4,46-54 Most studies of the marginal accuracy of crowns have examined CAD/CAM prostheses or compared cast alloy crowns and CAD/CAM crowns.55-59 Few comparative studies of the fits of Pd-Ag-In semiprecious metal crowns, CAD/CAM zirconia crowns, and/or cast gold alloy crowns have been conducted. Thus, in this study, prostheses fabricated with gold alloy, zirconia, and PdAg-In alloy were provided for study participants, and their marginal and internal fits were compared. The
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primary null hypothesis was that the marginal fit of the semiprecious metal alloy crown was statistically noninferior to that of the zirconia and cast gold crowns. The secondary null hypothesis was that the internal fit of the Pd-Ag-In alloy crown did not differ statistically from those of the control groups. MATERIAL AND METHODS This study was approved by the Institutional Review Board of Inha University and Ewha Womans University Hospitals. The study participants were adults ranging from 20 to 81 years of age who voluntarily consented to enroll in this clinical trial. Individuals under the age of 20, pregnant women or women suspected of being pregnant, individuals with alcohol addiction or mental illness, and individuals with abnormal clinical findings that a study supervisor or investigator considered inappropriate for this study were excluded. Prosthesis materials were gold alloy (DeguDent LTG; DeguDent GmbH), zirconia (Lava; 3M ESPE), and blocktype Pd-Ag-In alloy (Innovium; Ceragem Biosys Co). The gold alloy and zirconia were fabricated as controls, and the Pd-Ag-In alloy was the experimental material. The crown that was selected among the 3 by the participant was cemented for the definitive prosthesis. To determine the necessary number of participants, differences in the marginal gaps of the matched pairs were set as the primary evaluation variable. When the actual differences and standard deviations of the differences in the marginal gaps of the Pd-Ag-In alloy crown compared with the gold alloy and zirconia crowns of the 2 control groups were set to 0 mm and 63.7 mm, respectively, the number of required participants was estimated to be 52 from a noninferiority test with a noninferiority margin of 25 mm, a 1-sided alpha level of .025 and a power of 80%.60,61 Fifty-two teeth (31 molars, 11 premolars, 2 canines, and 8 anterior teeth; 20 teeth in the maxilla and 32 in the mandible) in 35 participants (16 men and 19 women; average age, 46.7 years) who needed metal or ceramic complete crown restorations because of tooth damage such as dental caries or tooth fractures were enrolled. A definitive cast was produced for the tooth to be treated according to the conventional restoration process through tooth preparation and impression making. The preparation design was for a ceramic restoration with rounded line angles. The design of an equally placed gingival finish line was the chamfer for the most part and the deep chamfer for the esthetic areas. The definitive stone cast underwent the die process and was then scanned with a 3-dimensional model scanner (Dental Wings 7Series; Dental Wings Inc) to generate a virtual model. The gold alloy crown was fabricated by the conventional waxing, investment, wax elimination, and
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Figure 1. Fabrication process of 3 types of crowns under same conditions. A, After preparing tooth, impression was made with elastomeric impression material. B, Abutment tooth was scanned with desktop scanner after cast sectioning. C, Wax pattern was made by skilled technician and scanned to make shape of crowns identical. D, Crown was fabricated by superimposing wax pattern scan on abutment with double scan technique.
casting processes. For the fabrication of the zirconia and Pd-Ag-In alloy crowns, a double scanning method was used. The waxing that was made for the cast gold crown was scanned 3 dimensionally, and the scan was superimposed on the existing cast and applied as the contour and morphology of the Pd-Ag-In alloy crown.62,63 This method was used to exclude variables other than the marginal and internal fit. For crowns in the esthetic area, a veneering ceramic was applied on the labial surface with a conventional layering technique. The marginal and internal cement space parameters and the minimum core thickness of both the Lava and Innovium crowns were set in the CAD program at 35 mm, 70 mm, and 0.5 mm, respectively (Fig. 1). Based on the completed design, the Innovium alloy and Lava zirconia blocks were processed and finished with a milling machine (Dento Mc5AX; Digiworks), and the Lava zirconia blocks were processed with a Lava CNC 500 (3M). The replica technique was used to examine the marginal and internal fit.41 The 3 types of completed crowns were evaluated separately on the abutment tooth. The proximal contact, margin, and occlusion were evaluated. After an initial adjustment, the intaglio surface of the Park et al
crown was filled with a silicone registration material (Fit Checker II; GC Corp), and the crown was placed on the prepared tooth. The patient was instructed to clench their teeth on a gauze wrapped stick placed on the occlusal surface. After 2 minutes for polymerization, the crown was removed from the oral cavity, and the registration material was assessed for bubbles or tears. Subsequently, the intaglio was filled with a polyvinyl siloxane impression material (Examixfine; GC Corp), and the base was supplemented with a putty silicone (Exaflex; GC Corp) and stabilized, which yielded a replica (Fig. 2). Among the 3 types of complete crowns, the crown that was selected by the patient was delivered with resin-modified glass ionomer cement (FujiCEM; GC Corp). The molar was sectioned twice, and the premolar and canine were sectioned once from the center in the buccolingual direction to obtain cross-sections to visualize the gaps between the crown and the tooth. In the mesiodistal direction, all teeth were cut from the center. Four regions were selected as reference points for the measurements of the marginal and internal gaps. For the measurement of the gaps in each sectioned part, images were made with a stereoscopic microscope (SZX7; Olympus Corp) at ×30 THE JOURNAL OF PROSTHETIC DENTISTRY
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Figure 2. Replica technique procedure to measure internal fit of crowns. A, Internal gaps of crowns in 3 groups were made with silicone registration material under same condition. B, Replica was prepared by stabilizing volume of registration material with silicone material with different color.
magnification, and images were analyzed with image analysis software (ImageJ version 1.45 software; US National Institutes of Health). A laboratory technician, who did not participate in the clinical process, performed the measurement (Fig. 3). The dental laboratory processes were evaluated by comparing the fit on a cast, shape reproducibility, level of oxide layer formation, bubbles during the opaque application, properties and deformation level of the surface, deformation level after ceramic veneering, and satisfaction with ceramic shades relative to each material. Measurements from the replica specimen were analyzed with statistical software (SAS v9.2; SAS Institute, Inc). Comparisons of the noninferiority of the margins between the experimental group with crowns that were prepared by milling the Pd-Ag-In alloy block and the control groups of the cast and zirconia crowns were performed as the primary end point. If the upper limit of the 95% confidence interval (CI) of the gap difference between the 2 groups was less than the prespecified noninferiority margin of 25 mm, the Pd-Ag-In alloy group was considered noninferior to the gold or zirconia group at a 1-sided alpha level of .025. The same method and criteria were applied for the values of 6 sections from different locations. The results of the survey of the evaluations of the laboratory procedure were analyzed by obtaining the average ranking from the rankings for each of the respective items.
Pd-Ag-In alloy crowns and the 2 control groups did not exceed the noninferiority margin of 25 mm. However, in the distal section, the marginal gap was larger in the PdAg-In alloy group (84.5 mm) than those in the gold group (67.9 mm, P=.002) and the zirconia group (69.8 mm, P=.01). The difference in the marginal gap between the experimental group and the gold group was 16.6 mm (95% confidence limits [CL]: 6.3, 26.9 mm) and that between the experimental group and the zirconia group was 14.7 mm (95% CL: 3.4, 26 mm). Thus, the criterion for noninferiority was not met in the distal sections (Fig. 4). At the axial wall, the gap difference between the gold alloy and the Pd-Ag-In alloy crowns was 11.9 mm (95% CL: −2.4, 26.2 mm). At the mesiobuccal section, the gap differences were 26 mm (95% CL: 10.2, 41.7 mm) between the gold and Pd-Ag-In crowns and 18.8 mm (95% CL: 1.9, 35.7 mm) between the zirconia and Pd-Ag-In alloy crowns. These differences did not meet the noninferiority criteria. However, in the remaining 4 sections, the upper limit of the CL did not exceed the noninferiority margin (Fig. 5). For the line angle and occlusal space, the size of the internal gaps of the experimental group did not meet the noninferiority criteria in comparison with the gold alloy and zirconia crowns in all of the sections (Figs. 6-8). In the evaluations of the fabrication procedures of the crowns in the dental laboratory, the zirconia crown displayed the best overall results for all of the items, including the model fit and bubble formation during the opaque application (Table 2).
RESULTS The average marginal gap measured on the silicone replica of the cast gold crowns was 68.2 m m, 75.4 mm for the zirconia crowns, and 76.9 mm for the Pd-Ag-In alloy crowns. The average internal gaps at the margin, axial wall, line angle, and occlusal space are shown in Table 1. In the 5 sections other than the distal section of the margin, the differences in the gaps between the THE JOURNAL OF PROSTHETIC DENTISTRY
DISCUSSION In an in vitro study that compared the fit of different crowns fabricated with the CAD/CAM system under the same conditions, Gonzalo et al35 reported that, in 3-unit partial fixed dental prostheses made of Lava, Procera zirconia, InCeram zirconia, and metal ceramic, the first 3 groups showed smaller marginal gaps than metal ceramic. Park et al
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Figure 4. Two-sided 95% CI of gap differences at margin. Blue dotted line denotes noninferiority margin (25 mm). MP, machined group of PdAg-In alloy; MZ, machined group of zirconia.
In addition, Baig et al55 reported that the marginal gaps were 66.4 mm for the Cercon system and 36.6 mm for the IPS Empress II system, both made with the CAD/CAM method, and 37.1 mm for a cast complete metal crown. In an in vivo study that was conducted on 19 participants, Park et al
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Figure 3. Cross-section view of each area to measure marginal and internal gaps in silicone replica after mesiodistal and buccolingual sectioning (×30 magnification). A, Margin. B, Axial wall. C, Line angle. D, Occlusal space.
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Figure 5. Two-sided 95% CI of gap differences at axial wall.
Reich et al50 reported that the marginal gaps of the Lava and Cerec systems were both approximately 65 mm, which was not significantly different from the 54 mm for the metal ceramic crown. Wettstein et al51 reported that, when the Cercon zirconia framework and conventional metal ceramic framework were selectively fabricated for 25 participants, the internal fits of the zirconia framework were cervical, 189.6 mm; axial, 140.5 mm; occlusal cusp tip, 121.3 THE JOURNAL OF PROSTHETIC DENTISTRY
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Figure 6. Two-sided 95% CI of gap differences at line angles.
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Figure 7. Two-sided 95% CI of gap differences at occlusal spaces.
mm, and centro-occlusal, 192.0 mm; these values were significantly greater than those of the metal ceramic framework, which were 118.6 mm, 95.7 mm, 122.5 mm, and 153.1 mm. Thus, in most studies, the crowns fabricated with the CAD/CAM method were comparable with metal ceramic or complete-metal crowns that were made by casting and had marginal and internal fits that were within the clinically acceptable range.21,38,44,52 In addition, Tan et al59 compared the vertical margin openings of titanium crowns that were designed by CAD software, milled titanium crowns that were waxed followed by double scanning with a 3-dimensional scanner, and cast high noble crowns. The marginal discrepancies were 79 mm, 73 mm, and 24 mm, respectively. In addition, the CAD/CAM method with and without double scanning did not show significantly different marginal gaps. In this in vivo study, the first null hypothesis was rejected because the crown that was fabricated by milling the Pd-Ag-In alloy block showed a marginal fit on the distal cross-section of the crown that was inferior to that of the cast crowns and zirconia crowns. However, the marginal gap of the Pd-Ag-In alloy crown was not statistically inferior to those of the control groups on all of the cross-sections except for the distal section. The average marginal gaps of the cast crowns (68.2 mm), zirconia crowns (75.4 mm), and Pd-Ag-In alloy crowns (76.9 mm) were generally greater compared with the results of previous in vivo studies.55-58 In contrast, other in vivo studies have reported larger marginal gaps than those found in our study.50,51 In addition, the marginal gap (84.5 mm) of the distal section was statistically inferior to the 120 mm that was proposed as the clinically acceptable gap by Hung et al,38 indicating that the Pd-Ag-In alloy crown had a clinically applicable fit. The differences in the internal gaps at the axial wall between the Pd-Ag-In group and the control groups exceeded the noninferiority margin at the mesial section (100.8 mm) and mesiobuccal section (103.1 mm). THE JOURNAL OF PROSTHETIC DENTISTRY
However, similar to the marginal gap, all of the internal gaps obtained in this study showed values less than 140 to 150 mm. For the line angle and occlusal space, the second null hypothesis was rejected because the Pd-Ag-In alloy crown showed larger internal gaps in all of the cross sections compared with the control groups. Both the PdAg-In alloy and zirconia crowns had significantly greater internal gaps in the occlusal space compared with the cast crowns. This was likely a result of the characteristics of the CAD/CAM fabrication method, such as the limited size of the milling tool and tool compensation.64 In addition, some crowns have their internal spacer parameters set to be bigger in the CAD system to avoid early contact on the sharp edge of a preparation and to reduce the marginal gap. Therefore, the gap might become larger in the CAD process compared with a cast restoration.56,65 The larger gap in the line angle and the occlusal space of the Pd-Ag-In alloy crown compared with the zirconia crown from the same CAD/CAM method was thought to result from differences in the gaps that might have occurred as a result of the parameters set during milling because of the difference between zirconia, which has volume reduction during the sintering process, and the Pd-Ag-In alloy, which has no volume change. For the general procedures for crowns in the dental laboratory evaluations, the zirconia crowns appeared to be the easiest to fabricate. However, this was thought to be because of skill differences, and the fabrication and placement of the gold or Pd-Ag-In alloy crowns was not exceptionally difficult. The methods that are used to evaluate the fit of a crown include direct visualization under a microscope, visualization by the attachment of the crown to a die that is followed by sectioning, evaluation after impression making, and evaluation with an explorer and the naked eye.66,67 This in vivo study used the replica technique Park et al
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A deep chamfer finish line was prepared for the labial or buccal side of the incisors, canines, and premolars, while a conventional chamfer margin was prepared for the remaining margin. Syu et al68 suggested that the type of finish line does not affect the marginal gap. In addition, the preparation design may not result in significant differences between the fit of the cast crowns and CAD/ CAM crowns.69,70 The analysis in this clinical study indicated that the marginal and internal fits of the crowns fabricated by milling machining Pd-Ag-In semiprecious metal alloys were comparable with those of the conventionally used cast crowns and zirconia crowns. Although the Pd-Ag-In crowns did not meet the noninferiority criterion compared with the existing materials for the line angle and occlusal space, their values were within the clinically acceptable range. Furthermore, most areas of the marginal and axial locations met the noninferiority criterion. However, because this study had a small sample size and a short period for crown placement, long-term clinical studies that involve a larger sample are required. In addition, studies on possible events in the oral cavity, such as antagonistic tooth wear or fracture, chipping of the ceramic veneer, and methods of fabricating more precise crowns through improvements of the CAD/CAM technique are necessary. CONCLUSIONS Within the limitations of this in vivo study, the following conclusions may be drawn. 1. The average ±standard deviation marginal gaps were 68.2 ±24.8 mm for the cast gold crowns, 75.4 ±28.8 mm for the zirconia crowns, and 76.9 ±27.0 mm for the Pd-Ag-In alloy crowns. The Pd-Ag-In alloy crowns met the noninferiority criterion in all the areas, except for the distal cross-section, compared with the control groups. 2. For the line angle and occlusal space, the Pd-Ag-In alloy crowns were inferior to the control groups for the internal gaps. Figure 8. Representative silicone replicas of internal gaps of crowns evaluated. A, Gold alloy group. B, Zirconia group. C, Pd-Ag-In alloy group. (×30 magnification).
which duplicated the state of the abutment because directly cutting the patient’s tooth was not possible.45 No significant differences have been reported between the die sectioning method and replica technique, and these results were not affected by the type of silicone registration material.53,54 Although the replica was prepared using the maximum clenching force of a patient, the replica may not have reflected the precise positions, possibly increasing the standard deviation of the occlusal space. Park et al
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43. Walton JN, Gardner FM, Agar JR. A survey of crown and fixed partial denture failures: length of service and reasons for replacement. J Prosthet Dent 1986;56:416-21. 44. Christensen GJ. Marginal fit of gold inlay castings. J Prosthet Dent 1966;16: 297-305. 45. Molin M, Karlsson S. The fit of gold inlays and three ceramic inlay systems. A clinical and in vitro study. Acta Odontol Scand 1993;51:201-6. 46. Boening KW, Wolf BH, Schmidt AE, Kastner K, Walter MH. Clinical fit of Procera AllCeram crowns. J Prosthet Dent 2000;84:419-24. 47. Coli P, Karlsson S. Fit of a new pressure-sintered zirconium dioxide coping. Int J Prosthodont 2004;17:59-64. 48. Kohorst P, Brinkmann H, Dittmer MP, Borchers L, Stiesch M. Influence of the veneering process on the marginal fit of zirconia fixed dental prostheses. J Oral Rehabil 2010;37:283-91. 49. Reich S, Kappe K, Teschner H, Schmitt J. Clinical fit of four-unit zirconia posterior fixed dental prostheses. Eur J Oral Sci 2008;116:579-84. 50. Reich S, Wichmann M, Nkenke E, Proeschel P. Clinical fit of all-ceramic three-unit fixed partial dentures, generated with three different CAD/CAM systems. Eur J Oral Sci 2005;113:174-9. 51. Wettstein F, Sailer I, Roos M, Hammerle CH. Clinical study of the internal gaps of zirconia and metal frameworks for fixed partial dentures. Eur J Oral Sci 2008;116:272-9. 52. Fransson B, Oilo G, Gjeitanger R. The fit of metal-ceramic crowns, a clinical study. Dent Mater 1985;1:197-9. 53. Rahme HY, Tehini GE, Adib SM, Ardo AS, Rifai KT. In vitro evaluation of the “replica technique” in the measurement of the fit of Procera crowns. J Contemp Dent Pract 2008;9:25-32. 54. Laurent M, Scheer P, Dejou J, Laborde G. Clinical evaluation of the marginal fit of cast crownsevalidation of the silicone replica method. J Oral Rehabil 2008;35:116-22. 55. Baig MR, Tan KB, Nicholls JI. Evaluation of the marginal fit of a zirconia ceramic computer-aided machined (CAM) crown system. J Prosthet Dent 2010;104:216-27. 56. Bindl A, Mormann WH. Marginal and internal fit of all-ceramic CAD/CAM crown-copings on chamfer preparations. J Oral Rehabil 2005;32:441-7. 57. Hertlein GHS, Frank S, Suttor D. Marginal fit of CAD/CAM manufactured all ceramic prosthesis. J Dent Res 2001;80:42-4. 58. May KB, Russell MM, Razzoog ME, Lang BR. Precision of fit: the Procera AllCeram crown. J Prosthet Dent 1998;80:394-404. 59. Tan PL, Gratton DG, Diaz-Arnold AM, Holmes DC. An in vitro comparison of vertical marginal gaps of CAD/CAM titanium and conventional cast restorations. J Prosthodont 2008;17:378-83. 60. Kokubo Y, Tsumita M, Kano T, Sakurai S, Fukushima S. Clinical marginal and internal gaps of zirconia all-ceramic crowns. J Prosthodont Res 2011;55:40-3. 61. Chow SC, Shao J, Wang H. Sample size calculations in clinical research. 2nd ed. Boca Raton, FL: Chapman and Hall/CRC; 2007. 62. Beuer F, Stimmelmayr M, Gueth JF, Edelhoff D, Naumann M. In vitro performance of full-contour zirconia single crowns. Dent Mater 2012;28:449-56. 63. Kollar A, Huber S, Mericske E, Mericske-Stern R. Zirconia for teeth and implants: a case series. Int J Periodontics Restorative Dent 2008;28:479-87. 64. Sturdevant JR, Bayne SC, Heymann HO. Margin gap size of ceramic inlays using second-generation CAD/CAM equipment. J Esthet Dent 1999;11: 206-14. 65. Bornemann G, Lemelson S, Luthardt R. Innovative method for the analysis of the internal 3D fitting accuracy of Cerec-3 crowns. Int J Comput Dent 2002;5:177-82. 66. Sorensen JA. A standardized method for determination of crown margin fidelity. J Prosthet Dent 1990;64:18-24. 67. Holmes JR, Bayne SC, Holland GA, Sulik WD. Considerations in measurement of marginal fit. J Prosthet Dent 1989;62:405-8. 68. Syu JZ, Byrne G, Laub LW, Land MF. Influence of finish-line geometry on the fit of crowns. Int J Prosthodont 1993;6:25-30. 69. Tsitrou EA, Northeast SE, van Noort R. Evaluation of the marginal fit of three margin designs of resin composite crowns using CAD/CAM. J Dent 2007;35: 68-73. 70. Ayad MF. Effect of the crown preparation margin and die type on the marginal accuracy of fiber-reinforced composite crowns. J Contemp Dent Pract 2008;9:9-16. Corresponding author: Dr Namsik Oh Inha University, 7-206 #3 Shinhung-dong, Jung-gu Incheon, 400-711 REPUBLIC OF KOREA Email: [email protected] Acknowledgments The authors thank Dr Kyoung-Ae Kong for performing statistical analyses in this study. Copyright © 2015 by the Editorial Council for The Journal of Prosthetic Dentistry.
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Clinical evaluations of cast gold alloy, machinable zirconia, and semiprecious alloy crowns: A multicenter study Ji-Man Park, DDS, PhD,a Yong-Shin Hong, DDS,b Eun-Jin Park, DDS, PhD,c Seong-Joo Heo, DDS, PhD,d and Namsik Oh, DDS, PhDe Computer-aided design and ABSTRACT computer-aided manufacture Statement of problem. Few studies have compared the marginal and internal fits of crowns (CAD/CAM) technology, which fabricated from machinable palladium-silver-indium (Pd-Ag-In) semiprecious metal alloy. uses a computer to design and Purpose. The purpose of this clinical study was to evaluate and compare the marginal and internal precisely mill dental prostheses, fits of machined Pd-Ag-In alloy, zirconia, and cast gold crowns. has been applied to multiple Material and methods. A prospective clinical trial was performed on 35 participants and 52 areas of dentistry, including the abutment teeth at 2 centers. Individuals requiring prosthetic restorations were treated with gold design and fabrication of simple alloy or zirconia crowns (2 control groups) or Pd-Ag-In alloy crowns (experimental group). A replica inlays and crowns, complex technique was used to evaluate the marginal and internal fits. The buccolingual and mesiodistal fixed and removable dental cross-sections were measured, and a noninferiority comparison was conducted. prostheses, implants, and Results. The mean marginal gaps were 68.2 mm for the gold crowns, 75.4 mm for the zirconia cement- and screw-retained crowns, and 76.9 mm for the Pd-Ag-In alloy crowns. In the 5 cross-sections other than the distal implant-supported restoracross-section, the 2-sided 95% confidence limits for the differences between the Pd-Ag-In alloy tions.1-9 In addition, this techcrowns and the 2 control groups were not larger than the 25-mm noninferiority margin. The nology results in consistent control groups displayed smaller internal gaps in the line angle and occlusal spaces compared material properties by addresswith the Pd-Ag-In crown group. ing the deformation issues that Conclusion. The marginal gaps of machinable Pd-Ag-In alloy crowns did not meet the result from the casting and noninferiority criterion in the distal margin compared with zirconia and gold alloy crowns. sintering processes and by conNonetheless, all 3 crowns had clinically applicable precision. (J Prosthet Dent 2015;-:---) trolling the shapes and thicknesses of the prosthesis and the space for cement.10,11 with soldering, which makes it difficult to fabricate longThe increased cost of gold has resulted in the need for span fixed dental prostheses. a replacement material and the use of a precious metal To overcome the limitations of cast gold crowns and alloy that contains less gold. Zirconia, which is widely the disadvantages of zirconia, machinable metals have used clinically, has been shown to be robust, biocombeen developed.18 Titanium has been used as the main patible, esthetically pleasing, and applicable to the CAD/ machinable metal,19,20 but bonding to a ceramic veneer is CAM systems.12-17 Zirconia units cannot be connected difficult due to the thick oxide layer.21-23 Thus, instead of
This work was partially supported by the Medical Devices Comparative Clinical and Performance Evaluation Program of the Korea Medical Devices Industrial Cooperation Association (KMDICA) and the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Science, ICT, and Future Planning (NRF-2013R1A1A1076022). a Clinical Associate Professor, Department of Prosthodontics and Dental Research Institute, Seoul National University Gwanak Dental Hospital, Seoul, Korea. b Former resident, Department of Prosthodontics, School of Medicine, Ewha Womans University, Seoul, Korea. c Professor, Department of Prosthodontics, School of Medicine, Ewha Womans University, Seoul, Korea. d Professor, Department of Prosthodontics and Dental Research Institute, Seoul National University, Seoul, Korea. e Professor, Department of Dentistry, School of Medicine, Inha University, Incheon, Korea.
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Clinical Implications The marginal and internal fittings of machinable Pd-Ag-In alloy crowns were comparable to those of conventional cast and zirconia crowns.
titanium alloy, alloys of platinum group metals have been used for fixed prostheses and implant abutments. Although the platinum metal alloys have been used in conventional casting methods, their specific compositions differ from those of the conventional alloys if they are manufactured for precision milling.24-26 If the weight ratio of palladium (Pd) and indium (In) is adjusted, the alloy has a gold-like color, excellent physical properties, and adequate bond strength with ceramic. The machinable Pd-silver (Ag)-In alloy has a hardness of between 185 and 330 VHN, an elongation of 5%, a modulus of elasticity of 80 GPa, and a bond strength with ceramic of 38 MPa.27 Moreover, it displays resistance to corrosion and discoloration that is higher than the criteria for clinical use. For long-term success, prostheses made of a variety of materials require appropriate marginal and internal adaptation. Inappropriate margins may cause restoration failure due to the accumulation of plaque and secondary caries, and the excess or lack of space for the cement can result in fracture, detachment, or incomplete placement.28,29 Many in vitro and in vivo studies have been conducted on marginal and internal gaps.30-44 Although a consensus has not yet been reached, a marginal gap of 100 to 120 mm and an internal gap of 140 to 150 mm are recommended as the clinical upper limits for complete crowns.38-40 A representative method for identifying the in vivo marginal and internal fits is the replica technique, which was described by Molin et al in 1993.45 This technique, which duplicates the relationship of the inner space of a crown and an abutment on a model with the registration material, has a number of advantages. A crown does not need to be sectioned, and the number of measurement sites can be decided without restriction. In addition, repeated measurements are possible. Consequently, this method has been frequently used in in vitro and in vivo studies.4,46-54 Most studies of the marginal accuracy of crowns have examined CAD/CAM prostheses or compared cast alloy crowns and CAD/CAM crowns.55-59 Few comparative studies of the fits of Pd-Ag-In semiprecious metal crowns, CAD/CAM zirconia crowns, and/or cast gold alloy crowns have been conducted. Thus, in this study, prostheses fabricated with gold alloy, zirconia, and PdAg-In alloy were provided for study participants, and their marginal and internal fits were compared. The
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primary null hypothesis was that the marginal fit of the semiprecious metal alloy crown was statistically noninferior to that of the zirconia and cast gold crowns. The secondary null hypothesis was that the internal fit of the Pd-Ag-In alloy crown did not differ statistically from those of the control groups. MATERIAL AND METHODS This study was approved by the Institutional Review Board of Inha University and Ewha Womans University Hospitals. The study participants were adults ranging from 20 to 81 years of age who voluntarily consented to enroll in this clinical trial. Individuals under the age of 20, pregnant women or women suspected of being pregnant, individuals with alcohol addiction or mental illness, and individuals with abnormal clinical findings that a study supervisor or investigator considered inappropriate for this study were excluded. Prosthesis materials were gold alloy (DeguDent LTG; DeguDent GmbH), zirconia (Lava; 3M ESPE), and blocktype Pd-Ag-In alloy (Innovium; Ceragem Biosys Co). The gold alloy and zirconia were fabricated as controls, and the Pd-Ag-In alloy was the experimental material. The crown that was selected among the 3 by the participant was cemented for the definitive prosthesis. To determine the necessary number of participants, differences in the marginal gaps of the matched pairs were set as the primary evaluation variable. When the actual differences and standard deviations of the differences in the marginal gaps of the Pd-Ag-In alloy crown compared with the gold alloy and zirconia crowns of the 2 control groups were set to 0 mm and 63.7 mm, respectively, the number of required participants was estimated to be 52 from a noninferiority test with a noninferiority margin of 25 mm, a 1-sided alpha level of .025 and a power of 80%.60,61 Fifty-two teeth (31 molars, 11 premolars, 2 canines, and 8 anterior teeth; 20 teeth in the maxilla and 32 in the mandible) in 35 participants (16 men and 19 women; average age, 46.7 years) who needed metal or ceramic complete crown restorations because of tooth damage such as dental caries or tooth fractures were enrolled. A definitive cast was produced for the tooth to be treated according to the conventional restoration process through tooth preparation and impression making. The preparation design was for a ceramic restoration with rounded line angles. The design of an equally placed gingival finish line was the chamfer for the most part and the deep chamfer for the esthetic areas. The definitive stone cast underwent the die process and was then scanned with a 3-dimensional model scanner (Dental Wings 7Series; Dental Wings Inc) to generate a virtual model. The gold alloy crown was fabricated by the conventional waxing, investment, wax elimination, and
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Figure 1. Fabrication process of 3 types of crowns under same conditions. A, After preparing tooth, impression was made with elastomeric impression material. B, Abutment tooth was scanned with desktop scanner after cast sectioning. C, Wax pattern was made by skilled technician and scanned to make shape of crowns identical. D, Crown was fabricated by superimposing wax pattern scan on abutment with double scan technique.
casting processes. For the fabrication of the zirconia and Pd-Ag-In alloy crowns, a double scanning method was used. The waxing that was made for the cast gold crown was scanned 3 dimensionally, and the scan was superimposed on the existing cast and applied as the contour and morphology of the Pd-Ag-In alloy crown.62,63 This method was used to exclude variables other than the marginal and internal fit. For crowns in the esthetic area, a veneering ceramic was applied on the labial surface with a conventional layering technique. The marginal and internal cement space parameters and the minimum core thickness of both the Lava and Innovium crowns were set in the CAD program at 35 mm, 70 mm, and 0.5 mm, respectively (Fig. 1). Based on the completed design, the Innovium alloy and Lava zirconia blocks were processed and finished with a milling machine (Dento Mc5AX; Digiworks), and the Lava zirconia blocks were processed with a Lava CNC 500 (3M). The replica technique was used to examine the marginal and internal fit.41 The 3 types of completed crowns were evaluated separately on the abutment tooth. The proximal contact, margin, and occlusion were evaluated. After an initial adjustment, the intaglio surface of the Park et al
crown was filled with a silicone registration material (Fit Checker II; GC Corp), and the crown was placed on the prepared tooth. The patient was instructed to clench their teeth on a gauze wrapped stick placed on the occlusal surface. After 2 minutes for polymerization, the crown was removed from the oral cavity, and the registration material was assessed for bubbles or tears. Subsequently, the intaglio was filled with a polyvinyl siloxane impression material (Examixfine; GC Corp), and the base was supplemented with a putty silicone (Exaflex; GC Corp) and stabilized, which yielded a replica (Fig. 2). Among the 3 types of complete crowns, the crown that was selected by the patient was delivered with resin-modified glass ionomer cement (FujiCEM; GC Corp). The molar was sectioned twice, and the premolar and canine were sectioned once from the center in the buccolingual direction to obtain cross-sections to visualize the gaps between the crown and the tooth. In the mesiodistal direction, all teeth were cut from the center. Four regions were selected as reference points for the measurements of the marginal and internal gaps. For the measurement of the gaps in each sectioned part, images were made with a stereoscopic microscope (SZX7; Olympus Corp) at ×30 THE JOURNAL OF PROSTHETIC DENTISTRY
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Figure 2. Replica technique procedure to measure internal fit of crowns. A, Internal gaps of crowns in 3 groups were made with silicone registration material under same condition. B, Replica was prepared by stabilizing volume of registration material with silicone material with different color.
magnification, and images were analyzed with image analysis software (ImageJ version 1.45 software; US National Institutes of Health). A laboratory technician, who did not participate in the clinical process, performed the measurement (Fig. 3). The dental laboratory processes were evaluated by comparing the fit on a cast, shape reproducibility, level of oxide layer formation, bubbles during the opaque application, properties and deformation level of the surface, deformation level after ceramic veneering, and satisfaction with ceramic shades relative to each material. Measurements from the replica specimen were analyzed with statistical software (SAS v9.2; SAS Institute, Inc). Comparisons of the noninferiority of the margins between the experimental group with crowns that were prepared by milling the Pd-Ag-In alloy block and the control groups of the cast and zirconia crowns were performed as the primary end point. If the upper limit of the 95% confidence interval (CI) of the gap difference between the 2 groups was less than the prespecified noninferiority margin of 25 mm, the Pd-Ag-In alloy group was considered noninferior to the gold or zirconia group at a 1-sided alpha level of .025. The same method and criteria were applied for the values of 6 sections from different locations. The results of the survey of the evaluations of the laboratory procedure were analyzed by obtaining the average ranking from the rankings for each of the respective items.
Pd-Ag-In alloy crowns and the 2 control groups did not exceed the noninferiority margin of 25 mm. However, in the distal section, the marginal gap was larger in the PdAg-In alloy group (84.5 mm) than those in the gold group (67.9 mm, P=.002) and the zirconia group (69.8 mm, P=.01). The difference in the marginal gap between the experimental group and the gold group was 16.6 mm (95% confidence limits [CL]: 6.3, 26.9 mm) and that between the experimental group and the zirconia group was 14.7 mm (95% CL: 3.4, 26 mm). Thus, the criterion for noninferiority was not met in the distal sections (Fig. 4). At the axial wall, the gap difference between the gold alloy and the Pd-Ag-In alloy crowns was 11.9 mm (95% CL: −2.4, 26.2 mm). At the mesiobuccal section, the gap differences were 26 mm (95% CL: 10.2, 41.7 mm) between the gold and Pd-Ag-In crowns and 18.8 mm (95% CL: 1.9, 35.7 mm) between the zirconia and Pd-Ag-In alloy crowns. These differences did not meet the noninferiority criteria. However, in the remaining 4 sections, the upper limit of the CL did not exceed the noninferiority margin (Fig. 5). For the line angle and occlusal space, the size of the internal gaps of the experimental group did not meet the noninferiority criteria in comparison with the gold alloy and zirconia crowns in all of the sections (Figs. 6-8). In the evaluations of the fabrication procedures of the crowns in the dental laboratory, the zirconia crown displayed the best overall results for all of the items, including the model fit and bubble formation during the opaque application (Table 2).
RESULTS The average marginal gap measured on the silicone replica of the cast gold crowns was 68.2 m m, 75.4 mm for the zirconia crowns, and 76.9 mm for the Pd-Ag-In alloy crowns. The average internal gaps at the margin, axial wall, line angle, and occlusal space are shown in Table 1. In the 5 sections other than the distal section of the margin, the differences in the gaps between the THE JOURNAL OF PROSTHETIC DENTISTRY
DISCUSSION In an in vitro study that compared the fit of different crowns fabricated with the CAD/CAM system under the same conditions, Gonzalo et al35 reported that, in 3-unit partial fixed dental prostheses made of Lava, Procera zirconia, InCeram zirconia, and metal ceramic, the first 3 groups showed smaller marginal gaps than metal ceramic. Park et al
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Figure 4. Two-sided 95% CI of gap differences at margin. Blue dotted line denotes noninferiority margin (25 mm). MP, machined group of PdAg-In alloy; MZ, machined group of zirconia.
In addition, Baig et al55 reported that the marginal gaps were 66.4 mm for the Cercon system and 36.6 mm for the IPS Empress II system, both made with the CAD/CAM method, and 37.1 mm for a cast complete metal crown. In an in vivo study that was conducted on 19 participants, Park et al
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Figure 3. Cross-section view of each area to measure marginal and internal gaps in silicone replica after mesiodistal and buccolingual sectioning (×30 magnification). A, Margin. B, Axial wall. C, Line angle. D, Occlusal space.
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Figure 5. Two-sided 95% CI of gap differences at axial wall.
Reich et al50 reported that the marginal gaps of the Lava and Cerec systems were both approximately 65 mm, which was not significantly different from the 54 mm for the metal ceramic crown. Wettstein et al51 reported that, when the Cercon zirconia framework and conventional metal ceramic framework were selectively fabricated for 25 participants, the internal fits of the zirconia framework were cervical, 189.6 mm; axial, 140.5 mm; occlusal cusp tip, 121.3 THE JOURNAL OF PROSTHETIC DENTISTRY
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Figure 7. Two-sided 95% CI of gap differences at occlusal spaces.
mm, and centro-occlusal, 192.0 mm; these values were significantly greater than those of the metal ceramic framework, which were 118.6 mm, 95.7 mm, 122.5 mm, and 153.1 mm. Thus, in most studies, the crowns fabricated with the CAD/CAM method were comparable with metal ceramic or complete-metal crowns that were made by casting and had marginal and internal fits that were within the clinically acceptable range.21,38,44,52 In addition, Tan et al59 compared the vertical margin openings of titanium crowns that were designed by CAD software, milled titanium crowns that were waxed followed by double scanning with a 3-dimensional scanner, and cast high noble crowns. The marginal discrepancies were 79 mm, 73 mm, and 24 mm, respectively. In addition, the CAD/CAM method with and without double scanning did not show significantly different marginal gaps. In this in vivo study, the first null hypothesis was rejected because the crown that was fabricated by milling the Pd-Ag-In alloy block showed a marginal fit on the distal cross-section of the crown that was inferior to that of the cast crowns and zirconia crowns. However, the marginal gap of the Pd-Ag-In alloy crown was not statistically inferior to those of the control groups on all of the cross-sections except for the distal section. The average marginal gaps of the cast crowns (68.2 mm), zirconia crowns (75.4 mm), and Pd-Ag-In alloy crowns (76.9 mm) were generally greater compared with the results of previous in vivo studies.55-58 In contrast, other in vivo studies have reported larger marginal gaps than those found in our study.50,51 In addition, the marginal gap (84.5 mm) of the distal section was statistically inferior to the 120 mm that was proposed as the clinically acceptable gap by Hung et al,38 indicating that the Pd-Ag-In alloy crown had a clinically applicable fit. The differences in the internal gaps at the axial wall between the Pd-Ag-In group and the control groups exceeded the noninferiority margin at the mesial section (100.8 mm) and mesiobuccal section (103.1 mm). THE JOURNAL OF PROSTHETIC DENTISTRY
However, similar to the marginal gap, all of the internal gaps obtained in this study showed values less than 140 to 150 mm. For the line angle and occlusal space, the second null hypothesis was rejected because the Pd-Ag-In alloy crown showed larger internal gaps in all of the cross sections compared with the control groups. Both the PdAg-In alloy and zirconia crowns had significantly greater internal gaps in the occlusal space compared with the cast crowns. This was likely a result of the characteristics of the CAD/CAM fabrication method, such as the limited size of the milling tool and tool compensation.64 In addition, some crowns have their internal spacer parameters set to be bigger in the CAD system to avoid early contact on the sharp edge of a preparation and to reduce the marginal gap. Therefore, the gap might become larger in the CAD process compared with a cast restoration.56,65 The larger gap in the line angle and the occlusal space of the Pd-Ag-In alloy crown compared with the zirconia crown from the same CAD/CAM method was thought to result from differences in the gaps that might have occurred as a result of the parameters set during milling because of the difference between zirconia, which has volume reduction during the sintering process, and the Pd-Ag-In alloy, which has no volume change. For the general procedures for crowns in the dental laboratory evaluations, the zirconia crowns appeared to be the easiest to fabricate. However, this was thought to be because of skill differences, and the fabrication and placement of the gold or Pd-Ag-In alloy crowns was not exceptionally difficult. The methods that are used to evaluate the fit of a crown include direct visualization under a microscope, visualization by the attachment of the crown to a die that is followed by sectioning, evaluation after impression making, and evaluation with an explorer and the naked eye.66,67 This in vivo study used the replica technique Park et al
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A deep chamfer finish line was prepared for the labial or buccal side of the incisors, canines, and premolars, while a conventional chamfer margin was prepared for the remaining margin. Syu et al68 suggested that the type of finish line does not affect the marginal gap. In addition, the preparation design may not result in significant differences between the fit of the cast crowns and CAD/ CAM crowns.69,70 The analysis in this clinical study indicated that the marginal and internal fits of the crowns fabricated by milling machining Pd-Ag-In semiprecious metal alloys were comparable with those of the conventionally used cast crowns and zirconia crowns. Although the Pd-Ag-In crowns did not meet the noninferiority criterion compared with the existing materials for the line angle and occlusal space, their values were within the clinically acceptable range. Furthermore, most areas of the marginal and axial locations met the noninferiority criterion. However, because this study had a small sample size and a short period for crown placement, long-term clinical studies that involve a larger sample are required. In addition, studies on possible events in the oral cavity, such as antagonistic tooth wear or fracture, chipping of the ceramic veneer, and methods of fabricating more precise crowns through improvements of the CAD/CAM technique are necessary. CONCLUSIONS Within the limitations of this in vivo study, the following conclusions may be drawn. 1. The average ±standard deviation marginal gaps were 68.2 ±24.8 mm for the cast gold crowns, 75.4 ±28.8 mm for the zirconia crowns, and 76.9 ±27.0 mm for the Pd-Ag-In alloy crowns. The Pd-Ag-In alloy crowns met the noninferiority criterion in all the areas, except for the distal cross-section, compared with the control groups. 2. For the line angle and occlusal space, the Pd-Ag-In alloy crowns were inferior to the control groups for the internal gaps. Figure 8. Representative silicone replicas of internal gaps of crowns evaluated. A, Gold alloy group. B, Zirconia group. C, Pd-Ag-In alloy group. (×30 magnification).
which duplicated the state of the abutment because directly cutting the patient’s tooth was not possible.45 No significant differences have been reported between the die sectioning method and replica technique, and these results were not affected by the type of silicone registration material.53,54 Although the replica was prepared using the maximum clenching force of a patient, the replica may not have reflected the precise positions, possibly increasing the standard deviation of the occlusal space. Park et al
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