J Bagh College Dentistry Vol. 28(4), December 2016 Comparison of the Restorative Dentistry 28 Comparison of the Marginal Fitness of the Ceramic Crowns Fabricated with Different CAD/CAM Systems (An In Vitro Study) Akram M. Abdulkareem, B.D.S. (a) Adel F. Ibraheem, B.D.S., M.Sc. (b) ABSTRACT Background: The marginal fit is the most characteristic that closely related to the longevity or success of a restoration, which is absolutely affected by the fabrication technique. The objective of present in vitro study was to evaluate the effect of four different CAD/CAM systems on the marginal fit of lithiµm disilicate all ceramic crowns. Materials and Methods: Adentoform tooth of a right mandibular first molar was prepared to receive all ceramic crown restoration with deep chamfer finishing line (1mm) and axial reduction convergence angle of 6 degree, dentoform model duplicated to have Nickel-Chromiµm master die. Thirty two stone dies produce from master die and distributed randomly in to four groups (8 dies for each group) according to the type of CAD/CAM system that used: Group A: fabricated with CERAMILL motion2 (Amann Girrbach); Group B:fabricated with CEREC in lab MCXL (Sirona);Group C: fabricated with CORiTEC 250i (imes-icore); Group D: fabricated with ZIRKONZAHN M5 (Zirkonzahn). Marginal discrepancy was measured at four points at each tooth surface. Sixteen points per tooth were measured using digital stereomicroscope at (140X) magnification. Results: ANOVA and LSD post Hoc tests were used to identify and localize the source of difference among the groups. It was found that there is a highly significant difference in the marginal gap mean values between group C and group D, and highly significant differences between group A and group D. Conclusions: From the above result we can conclude that better marginal fit values were may be exhibited by CORiTEC 250i CAD/CAM system. Key words: marginal fitness, CAD/CAM system, ceramic crown. (J Bagh Coll Dentistry 2016; 28(4):28-33) INTRODUCTION Although marginal discrepancy alone does not directly correlate with microleakage, the accuracy of marginal adaptation is valued as one of the most important parameters for the clinical quality, success, and longevity of fixed dental restorations (1). The importance of precise marginal fit and the subsequent implications of marginal misfit, including microleakage, caries, and periodontal inflammation, have been confirmed in many studies (2). Generally, marginal fit proposed as clear terminology by Holmes et al. through the measuring the marginal gap or the absolute marginal discrepancy (3-5). The vertical distance from the finishing line of the preparation to the cervical margin of the restoration was obvious definition of the marginal gap (6). An overall review of the data collected for the vertical marginal gap presented that 94.9% of the values measured were less than or equal to120 µm, The widest marginal gap measured was 174 µm, and the smallest was 3.7 µm (7). All-ceramic restorations are vastly used in dental field to attain the superior esthetics demanded by patients. (a) M.Sc. student, Department of Conservative Dentistry, College of Dentistry, University of Baghdad. (b) Professor, Department of Conservative Dentistry, College of Dentistry, University of Baghdad. They show better light transmission than other restorative material, which improved reproduction of the color and translucency of natural teeth (8). Many commercially in office and laboratory CAD/CAM systems are available today (9,10). Marginal adaptation of CAD/CAM restorations is relying on different parameters that include finishing line configuration, die space, type of cement used, and the cementation technique (11,12). Studies were suggested that scanning, software, and milling process have a detrimental effect on the marginal adaptation of CAD/CAM restorations (13,14). Recent studies have reported average marginal discrepancies for CAD/CAM restoration that range from 24-110 µm (15), and clinical studies with scanning electron microscopy data have equivalent values about 35-71µm (16). Several studies have been investigated the effect of scanning and milling process of CAD/CAM and its related to the marginal adaptation (14,17,18). Following on from these studies, it was of interest to investigate whether or not the CAD/CAM system used could influence the marginal accuracy of the CAD/CAM crowns when fabricated with lithiµm disilicate glass ceramic material. It was also of interest to evaluate whether the use of a different CAD/CAM system would produce a different marginal integrity of the ceramic restoration. J Bagh College Dentistry Vol. 28(4), December 2016 Comparison of the Restorative Dentistry 29 MATERIALS AND METHODS Preparation of Master Die: A dentoform tooth of a mandibular right first molar (Dentoform, Nissin, Kyoto, Japan) was prepared to receive all-ceramic crown restoration with following preparation properties: deep chamfer finish line (1mm), flat occlusal reduction to the depth of central occlusal pit, 1 to 1.5 mm of axial reduction with 6 degree convergence angle (Fig.1) (19,20).The prepared dentoform tooth was used as a pattern for the construction of the metal master die (Fig. 2). The dentoform tooth was sprued, invested, burn out and casting using non- precious-dental cast alloy for ceramics on nickel base, type 3, hard. Figure 1: A dentoform tooth prepared with deep chamfer finish line Figure 2: Master Metal die fixed to acrylic base Impression procedures A special tray was fabricated to be used during impression procedure. prior to fabrication of special tray, A two layer of modeling wax were adapted all around the metal die, this will provide a space about (2-2.5mm) for the impression material, the traditional method was followed to fabricate the special tray using translucent cold cure acrylic resin (21). To ensure that there is a single path of insertion and removal of the impressions, a dental surveyor was used during impression procedure. In order for the special tray to be attached on the dental surveyor, some modifications were carried out; one end of the analysis rod was fixed to the most upper part of special tray while the other end connected to the vertical suspending arm of surveyor. In addition, the lower part of the special tray that opposing the horizontal surface of the acrylic base of master die was designed so that it contained three pines to engage three holes on the acrylic base, this will serve as a guide and stopper for the special tray during impression procedure (22,23). A thin layer of tray adhesive was brushed onto the tray 24 hours after the tray fabrication. Two- step impression technique was selected as technique for impression making. Auto mix heavy and light viscosity polyvinylesiloxanes (PVS) (Ivoclar vivadent AG, Liechtenstein, Italy) was used as impression materials (Fig. 3). This procedure was continued thirty two times to get thirty two impression. Impressions were then poured using type IV dental die stone; all the procedure was done with manufacturer's instructions. Figure 3: Impression making with dental surveyor. Crown Construction Using CAD/CAM System Thirty two stone dies were used to produce 32 crowns by using 4 different CAD/CAM systems. To ensure standardization the same CAD programs parameters was detected for all CAD/CAM system, so the parameters were selected as follows: Full anatomical tooth 46#; Wet milling; Spacer, 50µm; Marginal adhesive gap, 0; Starting or begin, 50µm; proximal contact, Non; Minimal thickness (Radial), No; Minimal thickness (occlusal), No; Margin thickness, 0; Consider instrument Geometry, No; Remove undercuts, yes (18). In addition, one type of lithiµm disilicate J Bagh College Dentistry Vol. 28(4), December 2016 Comparison of the Restorative Dentistry 30 glass ceramics material blocks, IPS e.max–CAD (Ivoclar Vivadent, Schaan, Liechtenstein), for CEREC and Inlab, LT A2, C14were used for the fabrication of the all-crowns and new set of milling burs were used for each group. CERAMILL motion 2 CERAMILL Map 400 scanner and CeramillR mind software (Amann Girrbach GMbH, Durrenweg 40, Pforzheim, Germany) were used for scanning and designing of the group A restorations. Data were sent to the Ceramill Motion 2 milling engine, 5-axis milling device, Wet grinding, three steps milling with diamond burs: 2.5mm, 1.0mm and 0.6mm (Fig :4). Figure 4: Final crown design before milling CEREC in Lab MCXL InEos Blue scanner and In Lab 4.2 software (Sirona Dental Systems GmbH, Bensheim, Germany) were used for scanning and designing of the group B restorations. CEREC In Lab MCXL milling engine, 4-axis milling device, Wetgrinding, Two step milling with diamond burs: Step bur 12S (1.2 mm) and Step bur 12 (1.0 mm) has been used to produce eight glass ceramic crowns by milling the IPS emax CAD blocks. CORiTEC 250i I3D scan scanner and the exocad software were used for the scanning and designing of the group C restoration, which was milled with CORITEC 250i milling engine (Imes-Icore GmbH, Leibozgraben, Germany) , 5-axis milling device, Wet grinding, Three steps milling with diamond grinding pins: 2.5/6.0 mm, 1.0/6.0 mm and 0.6/6.0 mm. ZIRKONZAHN M5 S600 ARTI Scanner and ZirkonZahn software package were used for the scanning and designing of the group D restoration. IPS emax CAD block has been milled with M5 milling engine (ZirkonZahn GMbH, Italy), 5+1 axis milling device, Wet grinding, Three steps milling with diamond burs: 2.5 mm for rough milling, 1.0 mm for precise milling and 0.6 mm for very precise milling. This procedure was repeated for each die stone with his group following the manufacturer's instructions. After the completion of the glass ceramic crowns construction for all groups, all crowns were glazed and fired using IPS e-max CAD crystal/glaze (Ivoclar Vivadent, Italy) and fired with digital porcelain Furnace (Programat EP3000), (Ivoclar Vivadent AG, Schaan, Liechtenstein), IPS emax glazing program. Measurement of the marginal gap The marginal fit of the crown was calculated by measuring the vertical gap between the margin of the master die and that of the ceramic crown, all crowns were seated on master die to ensure standardization of study. Four indentations on the margin at the midpoint of mesial, distal, buccal and palatal surfaces of the master die were done. Four points in each surface were selected for vertical marginal gap measurement by using a stereo-microscope (17,22,24). A screw loaded holding device (Essentials, china) was used during all measurement steps in order to maintain a seating pressure of(50 N) between all-ceramic crown and the master die (19, 25-27).To apply a uniform static load on the tested crown, a loading cell sensor (SF-400, china) was fixed to the metal die base during measurement procedure. The measurement were performed on four points on each surface (two on each side of the indentation), first point was determined on the edge of the indentation whereas the second one was (1mm) away from the first point (28). This was achieved by using a stereo microscope with a digital camera in the eye lens connected with the computer. The digital images were captured and measurements were done using IMAGE J software (Image J 1.32, U.S. NIH, Bethesda, MA, USA) which calculated the values in pixels, mark by drawing a line between the finishing line on the die and the crown margin line (29) (Fig. 5). Figure 5: Two points for marginal gap measurement with Image J J Bagh College Dentistry Vol. 28(4), December 2016 Comparison of the Restorative Dentistry 31 The images were observed and captured at 140X magnification and calibrated using a photograph of a (1mm) increment taken at the same focal length and input into (IMAGE J) by the option of set scale, which converted all the calculated reading from pixels to (µm) (24). Sixteen measurements were obtained from all the four surfaces (mesial, distal, palatal and buccal) of each sample. All measurements were done by the same investigator (17,28). Statistical analyses Data were collected and analyzed using SPSS (statistical package of social science) software version 15 for windows 8.1 Chicago, USA. The following statistics were used: A- Descriptive statistic: including mean, standard deviation, statistical tables and graphical presentation by bar charts. B- Inferential statistics 1- One way analysis of variance test (ANOVA) was used to see if there were any significant differences among the means of groups. 2-LSD (least significant difference) test was carried out to examine the source of differences among the four groups. RESULTS Total of (512) measurements of vertical marginal gap from four groups were recorded, with 16 measurements for each crown. Table (1) showed that the highest mean of vertical marginal gap was recorded in group D (39.12 µm ± 3.969) (manufactured with ZirkonZhan CAD/CAM system).While the lowest mean marginal gap was recorded in group C (29.00 µm ±4.761) (Manufactured with Imes- Icore CAD/CAM system). Table (2) showed that there is a highly significant difference in vertical marginal gap among the four groups. Table 1: Descriptive statistics of vertical marginal gap for the four groups in (µm) Source of variation N Mean S.D. Min Max Group A Amann Girrbach system 8 29.3984 ±5.569 21.63 37.75 Group B Sirona system 8 33.6484 ±5.409 28.88 43.63 Group C Imes-Icore 8 29.0000 ±4.761 22.63 35.94 Group D Zirkonzhan system 8 39.1250 ±3.969 34.25 46.00 Total 32 32.7930 6.28571 21.63 46.00 Table 2: One way-ANOVA test among the four groups Significant at P≤ 0.05 DISCUSSION Results obtained from the current study showed that the marginal gap of the 4 tested groups was within the clinically acceptable range and with acceptable range of the CAD/CAM fabricated restoration marginal gap, because the mean marginal gap with the range of 100 μm have been proposed as being clinically acceptable with regard to the longevity of restorations(30). Furthermore, recent studies have reported that vertical marginal gap for CAD/CAM fabricated all ceramic restorations range from 24 to 110 µm (6,15,27). This study revealed different values of vertical marginal gap among the four groups, which indicated that the type of the CAD/CAM system may affected the marginal adaptation of the all ceramic crown fabricated with CAD/CAM technology, these results were in agreement with other study reported the same result (14,17,18,31,32). In present study there is a highly significant difference was reported between group D (Zirkonzhan M5) with group A (Ceramill motion 2) and C (CORiTECH 250i) respectively, in addition to the significant differences between group D and group B (CEREC in lab MCXL), the explanation that the various result for different CAD/CAM systems has been resulted during different steps in CAD/CAM processing, scanning, design and milling step. The first three systems (Ceramill motion 2, CEREC in lab MCXL, CORiTEC 250i) used the blue-light scanning technology, which use short wavelength that lead to high level of scanning accuracy as compared to the S600 ARTI scanner of zirkonzhan system which used the red laser ANOVA Sµm of Squares d.f. Mean Square F-test Sig. Between Groups 533.887 3 177.962 7.212 .001 (HS) Within Groups 690.929 28 24.676 Total 1224.816 31 J Bagh College Dentistry Vol. 28(4), December 2016 Comparison of the Restorative Dentistry 32 technology to capture image from multiple angles for scanning, but with the higher wavelength of red laser, the accuracy of scanner may reduce, this findings were in agreement with that reported by Neves et al. (33). But disagree with another opinion that the variability of cutting tool was another explanation of these differences. An additional to the problem that may associate with scanning device during ceramic restorations constructed with CAD/CAM, the design of the cutting tools may affect the marginal accuracy of all ceramic restoration because it may be larger in diameter than some small parts of the tooth preparation, such as the inner surface of the finish line causing misfits, resulting in inferior marginal adaptation, this will coincided with that reported by Reich et al. (34). In current study, CEREC in lab MCXL system (group B) may provide less marginal fit as compared with group A and group C, these differences may attributed to that CEREC in lab MCXL system was used a 4-axis milling device, while the CORiTEC 250i and Ceramill motion 2 systems were used a 5-axis milling machine. The Five-axis milling machine have been found to improve accuracy and precision of the ceramic restorations by using the machines additional axes; these 2 additional orientation axes allow the machining and processing of complex parts, which cannot be machined with 3-axis and 4-axis orientation machines. The 5-axis machinery has superior cutting conditions to those of the 3-axis type or 4-axis type, which improves the efficiency of the milling by creating efficient tool paths and movement directions which improve the dimensional accuracy, texture, and surface finish of the milled products. This may explain the more accurate fit of restoration that fabricated with 5- axis milling machine (13,35).These findings were coincided with different studies reported that the 5-axis milling device of CAD/CAM system provided better marginal adaptation than 4-axis milling device (14,17,18). However conflicted with another opinion that the quality or marginal accuracy of the ceramic restoration does not necessarily improve as the number of milling device axes increases, which reported with a study that done by Beuer et al. (36). In this study, the result was revealed that the CORiTEC 250i (group C) may demonstrated smaller marginal gaps than the Ceramill motion 2 (group A) group. In spite of that the both CAD/CAM systems are similar to each other in fabricating steps of lithium disilicate restorations and the milling device movement axes, there is apriority for the CORiTEC system in the result obtained with each systems. These priority may attributed to the efficiency of CAD software and the constant quality of scanners, which may make the restoration fabricated with the CORiTEC 250i system more precise in marginal fit. These results were in agreement with that reported by Agarwal and Ram (37) that the type of the CAD/CAM scanner have been affected the marginal adaptation of the ceramic restoration. Also, software limitations in restorations design, could produce errors in the CAD/CAM technique especially during manual tracing of the finish line, this fact was coincided with other studies (38,39), But disagree with another studies that reported, the shape of the cutting instrument is various and these differences may affect the final result of ceramic restoration (18,33). For example, significant enlargement in internal gap would result when the internal cutting bur that used in milling device larger than small parts of the tooth preparation considering manufacturing techniques and tools, this will agree and parallel with that reported by Abduo et al. (40). It can be concluded that better marginal fit values were exhibited by CORiTEC 250i CAD/CAM system. The present study was supported the good performance of CAD/CAM milling process of single- unite lithiµme disilicate FDP while also highlighting the possible effect of different CAD/CAM scanner and software on FDP fabrication. REFERENCES 1. White SN, Ingles S, Kipnis V. Influence of marginal opening on microleakage of cemented artificial crowns. J Prosthet Dent 1994; 71(3): 257-64. 2. Beuer F, Naµmann M, Gernet W, Sorensen JA. Precision of fit: zirconia three-unit fixed dental prostheses. Clin Oral Investig 2009; 13: 343-49. 3. Holmes JR, Bayne SC, Holland GA, Sulik WD. Considerations in measurement of marginal fit. J Prosthet Dent 1989; 62: 405-8. 4. Suarez MJ, Gonzalez de Villaµmbrosia P, Pradies G, Lozano JF. Comparison of the marginal fit of Procera AllCeram crowns with two finish lines. Int J Prosthodont 2003; 16: 229-32. 5. Pelekanos S, Koµmanou M, Koutayas SO, Zinelis S, Eliades G. Micro-CT evaluation of the marginal fit of different In-Ceram alµmina copings. Eur J Esthet Dent 2009; 4: 278-92. 6. Euán R, Figueras-Álvarez O, Cabratosa- Termes J, Brufau-de Barbera M, Gomes- Azevedo S. Comparison of the marginal adaptation of zirconiµm dioxide crowns in preparations with two different finish lines. J Prosthodont 2012; 21: 291-5. 7. Contrepois M, Soenen A, Bartala M, Laviole O. Marginal adaptation of ceramic crowns: A systematic review. J Prosthet Dent 2013; 110: 447-54. 8. Christensen GJ. Esthetic dentistry-2008. Alpha Omegan 2008; 101: 69-70. 9. Mörmann WH, Bindl A. All-ceramic, chair-side computer-aided design/computer-aided machining restorations. Dent Clin North Am 2002; 46(2): 405-26. http://www.ncbi.nlm.nih.gov/pubmed/12014040 J Bagh College Dentistry Vol. 28(4), December 2016 Comparison of the Restorative Dentistry 33 10. 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. 11. Gu XH, Kern M Gu XH, Kern M. Marginal discrepancies and leakage of all-ceramic crowns: influence of luting agents and aging conditions. Int J Prosthodont 2003; 16: 109-16. 12. Grenade C, Mainjot: comparison between various manufacturing processes. J Prosthet Dent 2011; 105: 249-55. 13. Delong R, Heinzen M, Hodges JS, Ko CC, Douglas WH. Accuracy of a system for creating 3D computer models. J Dent Res 2003; 82: 438-42. 14. Giannetopoulos S, van Noort R, Tsitrou E. Evaluation of the marginal integrity of ceramic copings with different marginal angles using two different CAD/CAM systems. J Dent 2010; 38(12): 980-6. 15. Karatasli Ö, Kurso_glu P, Çapa N, Kazazo_glu E. Comparison of the marginal fit of different coping materials and designs produced by computer aided manufacturing systems. Dent Mater J 2011; 30: 97- 102. 16. Biscaro L, Bonfiglioli R, Soattin M, Vigolo P. An in vivo evaluation of fit of zirconiµm-oxide based ceramic single crowns, generated with two CAD/CAM systems, in comparison to metal ceramic single crowns. J Prosthodont 2013; 22: 36-41. 17. Hamza TA, Ezzat HA, El-Hossary MMK, Katamish HAE, Shokry TE, Rosenstiel SF. Accuracy of ceramic restorations made with two CAD/CAM systems. J Prosthet Dent 2013; 109: 83-87. 18. Bosch G, Ender A, Mehl A. A 3-dimensional accuracy analysis of chairside CAD/CAM milling processes. J Prosthet Dent 2014; 112: 1425-31. 19. Quintas AF, Oliveira F, Bottino MA. Vertical marginal discrepancy of ceramic copings with different ceramic materials, finish lines, and luting agents: an in vitro evaluation. J Prosthet Dent 2004; 92: 250-7. 20. Renne W, McGill ST, Forshee KV, Mennito AS. Predicting marginal fit of CAD/CAM crowns based on the presence or absence of common preparation errors. J Prosthet Dent 2012; 108: 310-5. 21. Jonathan NG, Dorin R, Chris W. A comparison of the marginal fit of the crowns fabricated with digital and conventional methods. J Prosthetic Dent 2014; 112: 555-60. 22. Hmedat SJ, Ibraheem AF. A comparison of Vertical Marginal Fit of three different types of All-ceramic crown restoration. J Bagh Coll Dentistry 2013; 25(1):43. 23. Schaefer O, Kuepper H, Sigusch BW, Thompson GA, Hefti AF, Guentsch A. Three-dimensional fit of lithiµm disilicate partial crowns in vitro. J of dentistry, 2013, 42: 271-277. 24. Holden J E, Goldstein G R, Hittelman E L, Clark E A. Comparison of the marginal fit of pressable ceramic to metal ceramic restorations J Prosthodont 2009; 18 645-8. 25. Thiab SS, Zakaria MR. The evaluation of vertical marginal discrepancy induced by using as cast and as received base metal alloys with different mixing ratios for the construction of porcelain fused to metal copings. Al- Rafidain Dent J 2004; 4(1): 10-19. 26. 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. 27. Beuer F, Neµmeier P, Naµmann M. Marginal fit of 14-unit zirconia fixeddental prosthesis retainers. J Oral Rehabil 2009; 36: 142-9. 28. Lombardas P, Carbunaru A, McAlarney ME, Toothaker RW. Dimensional accuracy of castings produced with ringless and metal ring investment systems. J Prosthet Dent 2000; 84(1): 27-31. 29. Tan PL, Gratton DG, Diaz-Arnold AM, Holmes DC. An in vitro comparison of vertical marginal gaps of CAD/CAM titaniµm and conventional cast restorations. J Prosthodont 2008; 17(5): 378-83. 30. Gassino G, Barone Monfrin S, Scanu M, Spina G, Preti G. Marginal adaptation of fixed prosthodontics: A new in vitro 360- degree external examination procedure. Int J Prosthodont 2004; 17: 218-23. 31. Vigolo P, Mutinelli S. Evaluation of zirconiµm-oxide- based ceramic single-unit posterior fixed dental prostheses FDPs generated with two CAD/CAM systems compared to porcelain-fused-to-metal single- unit posterior FDPs: A 5-Year clinical prospective study. J Prosthodont 2012; 21: 265-9. 32. Song TJ, Kwon TK, Yang JH, Han JS, Lee JB, Kim SH, Yeo IS. Marginal fit of anterior 3-unit fixed partial zirconia restorations using different CAD/CAM systems. J Adv Prosthodont 2013; 5(3): 219–25. 33. Neves FD, Prado CJ, Prudente MS, Carneiro TAPN, Zancopé K, Davi LR, Mendonça G, Cooper LF, Soares CJ. Micro-computed tomography evaluation of marginal fit of lithium disilicate crowns fabricated by using chairside CAD/CAM systems or the heat- pressing technique. J Prosthet Dent 2014; 112(5): 1134-40. 34. 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: 174–83. 35. Cho HD, Jun YT, Yung MY. Five axis CNC milling for effective machining of sculptured surfaces. Int J Prod Res 1993; 31: 2559-73. 36. Beuer F, Schweiger J, Edelhoff D. Digital dentistry: An overview of recent developments for CAD/CAM generated restorations. Br Dent J 2008; 204(9): 505- 11. 37. Agarwal N, Ram S. A comparative evaluation of marginal fit of crowns fabricated by three all ceramic CAD/CAM systems using their respective scanners- An in vitro study. J Contemporary Dent 2012; 2(1): 10-9. 38. Aboushelib MN, Elmahy WA, Ghazy MH. Internal adaptation, marginal accuracy and microleakage of a pressable versus a machinable ceramic laminate veneers. J Dent 2012; 40: 670-7. 39. Kollmuss M, Kist S, Goeke JE, Hickel R, Huth KC. Comparison of chairside and laboratory CAD/CAM to conventional produced all-ceramic crowns regarding morphology, occlusion, and aesthetics. (Internet), Springer Berlin Heidelberg, 07 Aug 2015, available from: www.springer/link/com . 40. Abduo J, Lyons K, Swain M. Fit of zirconia fixed partial denture: a systematic review. J Oral Rehabil 2010; 37: 866–76. http://www.ncbi.nlm.nih.gov/pubmed/?term=Song%20TJ%5Bauth%5D http://www.ncbi.nlm.nih.gov/pubmed/?term=Kwon%20TK%5Bauth%5D http://www.ncbi.nlm.nih.gov/pubmed/?term=Yang%20JH%5Bauth%5D http://www.ncbi.nlm.nih.gov/pubmed/?term=Han%20JS%5Bauth%5D http://www.ncbi.nlm.nih.gov/pubmed/?term=Lee%20JB%5Bauth%5D http://www.ncbi.nlm.nih.gov/pubmed/?term=Kim%20SH%5Bauth%5D http://www.ncbi.nlm.nih.gov/pubmed/?term=Yeo%20IS%5Bauth%5D http://www.springer/link/com