Clinical Marginal and Internal Fit of Crowns Fabricated Using Different CAD/CAM Technologies Zhuoli Huang, DDS, Lu Zhang, DDS, Jingwei Zhu, DDS, Yiwei Zhao, DDS, & Xiuyin Zhang, DDS, PhD Department of Prosthodontics, 9th People’s Hospital, Shanghai Jiao Tong University, School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, P. R. China

Keywords Fit; crown; selective laser melting; CAD/CAM grinding technology. Correspondence Xiuyin Zhang, 639# Zhi Zao Ju Road, Shanghai 200011 P. R. China. E-mail: [email protected] The authors acknowledge the support of the Natural Science Foundation of China (81070857) for this study. The authors deny any conflicts of interest. Accepted April 2, 2014 doi: 10.1111/jopr.12209

Abstract Purpose: The aims of this in vivo investigation were to compare the marginal and internal fit of single-unit crowns fabricated using a selective laser melting (SLM) procedure with two CAD/CAM grinding procedures, and to evaluate the influence of tooth type on the parameters measured. Materials and Methods: A total of 270 crowns were evaluated, including 90 SLM metal-ceramic crowns (group B), 90 zirconium-oxide-based ceramic crowns (group L), and 90 lithium disilicate ceramic crowns (group C). The marginal and internal gaps of the crowns were recorded using a replica technique with a silicone indicator paste stabilized with a light-body silicone. The gap replica specimen were sectioned buccolingually and mesiodistally and then examined using a stereomicroscope at 30× magnification. Ten reference points were measured on each anterior and premolar specimen, and 20 reference points were measured on each molar specimen. Two-way ANOVA was performed to identify the significant differences between the groups. Results: The mean marginal fit of group B was significantly better than those of group C and group L (p < 0.005), but a significant difference was not found between group C and group L (p > 0.05). The mean axial gap of group B was significantly smaller than those of group C and group L (p < 0.01), while group C was not different from group L (p > 0.05). The mean occlusal gap of group B was significantly higher than those of group C and group L (p < 0.05), and no difference was found between group C and group L (p > 0.05). The marginal and internal gaps of crowns varying according to tooth type were not significantly different (p > 0.05). Conclusion: The SLM system demonstrated better marginal and internal fit compared to the two CAD/CAM grinding systems examined. Tooth type did not significantly influence the marginal or internal fit.

Numerous CAD/CAM systems are available for processing CAD/CAM dental restorations in dental clinics, dental laboratories, and machining centers.1-3 Various materials from metal to glass ceramics and high-performance ceramics have been developed and introduced to fabricate CAD/CAM restorations.4,5 CAD/CAM grinding systems use a scanning, design, and milling process to custom shape copings from prefabricated material blocks.6 However, waste of raw materials and the risk of microscopic cracks are disadvantages of the grinding technology.7 In recent years, a “generative manufacturing technique” has been introduced as a CAD/CAM procedure.8 Selective laser melting (SLM), a novel technology, has attracted great attention because of its high productivity and low cost.8.9 It works by adding material layer by layer to build up a 3D component, thus avoiding the deficiencies associated with grinding

techniques.7,8 A new cobalt-chromium (Co-Cr) alloy powder has recently been used to produce SLM crown and fixed partial denture (FPD) copings.10 However, other materials based on SLM technology are still in development. Marginal and internal fit are the key criteria for the clinical success of dental restorations11,12 Poor marginal adaptation can increase microleakage and plaque accumulation, leading to cement dissolution, secondary caries, and periodontal disease.13,14 Excellent internal fit will facilitate crown seating without compromising retention and resistance forms.15,16 Unfortunately, there are no clear guidelines for clinically acceptable marginal and internal fit. Christensen17 considered 39 µm the least acceptable marginal discrepancy, according to the linear regression prediction formula; however, McLean and von Fraunhofer18 conducted a clinical study evaluating the marginal fit of crowns for 5 years, and reported that marginal

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discrepancies ranging up to 120 µm were acceptable. Several authors consider marginal discrepancies between 100 and 150 µm clinically acceptable.19-21 The marginal and internal fit of restorations fabricated with different CAD/CAM grinding systems have been studied extensively. Bindl and M¨ormann3 evaluated the fit of CAD/CAM crown-copings prepared using different CAD/CAM systems (CEREC inLab, DCS, Decim, and Procera) in vitro and showed marginal gaps in a range of 17 to 43 µm and internal gaps in a range of 110 to 136 µm. In another in vitro study, a mean marginal gap of 82 to 83 µm was found for zirconium-oxidebased crowns fabricated using Digident and Lava CAD/CAM systems.22 Reich et al23 also investigated the marginal and internal fit of three-unit FPDs fabricated using Digident, Vita In-Ceram, and Lava CAD/CAM systems; the clinical study showed marginal gaps ranging from 67 to 92 µm and internal gaps ranging from 105 to 383 µm. A clinical study showed that single crowns made by a chairside CAD/CAM system demonstrated marginal gaps of 100 µm and internal gaps of 148 to 284 µm.24 Some studies have focused on the fit of restorations fabricated using generative manufacturing techniques and have reported an acceptable marginal and internal fit.25,26 However, research on comparing the fit of restorations fabricated using different CAD/CAM technologies remains scarce. The aim of this study was to compare the marginal and internal fit of single-unit crowns fabricated with an SLM procedure and two CAD/CAM grinding procedures in vivo and to evaluate the influence of tooth type on the parameters measured. The null hypothesis was that: (1) the marginal and internal fit of crowns fabricated with SLM and grinding procedures were similar and (2) the marginal and internal fit of crowns would be similar among the anterior, premolar, and molar teeth.

Materials and methods A total of 270 single-unit crowns were provided to 246 patients between July 2011 and June 2013 at Ninth People’s Hospital, Shanghai Jiao Tong University. According to the manufacturing procedure, all crowns were divided into three groups: group B—90 SLM Co-Cr metal-ceramic crowns (BEGO Medifacturing System; BEGO Medical, Bremen, Germany); group C— 90 lithium disilicate ceramic crowns (Chairside CEREC 3D; Sirona Dental Systems GmbH, Bensheim, Germany); group L—90 zirconinum-oxide-based crowns (LavaTM All-Ceramic; 3M ESPE, St. Paul, MN). All patients chose the CAD/CAM techniques and restoration materials because of esthetics, time, and financial considerations. The distribution of abutment teeth of the crowns generated by the three CAD/CAM systems is listed in Table 1. The study protocol was approved by the Ethics Committee of Shanghai Jiao Tong University. Tooth preparation

All teeth were prepared with a circumferential chamfer finishing line design. The circumferential reduction of tooth substance was between 1.2 and 1.5 mm, depending on the remaining hard tissue. Occlusal reduction was approximately 2 mm. The complete angle of convergence was aimed to be 5° to 6°. All internal edges were rounded and smoothed out. The entire 2

treatment for the crowns was carried out by one dentist with over 20 years of experience with FPDs. Manufacturing of the crowns

The impressions of the prepared teeth from groups B and L were made using polyvinyl siloxane material (Zenith/DMG, Englewood, NJ, USA) and reproduced in type V dental stone (Heraeus Kulzer, Hanau, Germany) to obtain the master casts. All casts were sent to one dental laboratory. Each master cast from group B was scanned using strip-light projection (BEGO Medifacturing System). The metal copings were designed with the CAD software, and the cement spacers were set at 70 µm. Using the laser melting technology (BEGO Medifacturing System), all copings were made with Co-Cr alloy (Wirobond C+; BEGO Medical). The copings were tried in for fit checks. If some points contacted tightly, they were removed. Then, the metal copings were veneered (IPS d.Sign; Ivoclar Vivadent, Schaan, Liechtenstein) in the same dental laboratory. Before glazing, the veneered copings were tried in to check both the proximal contacts and the static and dynamic occlusion. The casts from group L were digitized using an optical 3D scanning instrument (Lava Scan; 3M ESPE). All of the copings were designed (Lava CAD; 3M ESPE) with the preset cement space at 50 µm and were then milled from semisintered zirconia by a three-axis milling machine (Lava Form; 3M ESPE). After the fit check, all copings were sintered to full density in a sintering furnace (Lava Therm; 3M ESPE) for 8 hours and were veneered using the specified layering ceramics (Lava Ceram; 3M ESPE). The definitive crowns were tried in on their respective casts and glazed before sending back to the clinic. The prepared teeth from group C were scanned directly with an intraoral camera (Chairside CEREC 3D; Sirona Dental Systems GmbH) instead of making impressions. The copings were designed by an experienced dental technician with cement space settings at 30 µm and were milled from IPS e.max CAD blocks (Ivoclar Vivadent). Before sintering and glazing, the copings were tried in to adjust proximal contacts and occlusion. Production of the replicas and microscopic evaluation

To evaluate and compare the gap dimensions between the crowns and the prepared teeth, replicas of the internal gaps of the crowns were made by the replica technique described by Boening et al27 and Reich et al.23 They were fabricated by repositioning the crowns on the prepared teeth with a white silicone indicator paste (Fit Checker; GC, Tokyo, Japan) coated on the inner surfaces. Excess silicone material was removed with a cotton pellet. During hardening of the silicone layers, the crowns were seated on the prepared teeth with finger pressure. Then, a light silicone material (Exafine Injection; GC) was injected to the inner spaces of the white silicone layer of each crown to stabilize the white silicone films. After setting, the crowns and the two layers of silicone materials were separated. The information for the replica specimens, including the manufacturing techniques and materials, was recorded by an assistant, and all the specimens were given a unique consecutive number according to the order of production. Then, the

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Table 1 Distribution of abutment teeth in each group Group

Anterior

Premolar

Molar

Total

B C L Total

30 34 31 95

30 30 31 91

30 26 28 84

90 90 90 270

Figure 1 Sectioning method for the internal gap replica (A) anterior and premolar replica (B) molar replica.

the replicas was digitally photographed using a stereomicroscope (Carl Zeiss AG, Jena, Germany) at 30× magnification. A corresponding image manager was used for measurement. Statistical analysis

The marginal and internal gaps of the three groups were evaluated statistically using two-way ANOVA with SPSS 19.0 (SPSS Inc., Chicago, IL) to determine the effects of the two main factors: the manufacturing system and the tooth type.

Results

Figure 2 The predefined measuring points on each slice of the internal gap replica. PM: marginal gap; PA: midpoint at the axial gap; PO: occlusal gap.

replica specimens were sent to the evaluator for microscopic evaluation. The evaluator was blinded to the information about the specimens except for their numbers. The replicas were sectioned by the evaluator with a razor blade. Anterior and premolar replicas were cut once in the buccolingual and once in the mesiodistal direction; molars were cut twice in the buccolingual and twice in the mesiodistal direction (Fig 1). The gaps of the white silicone layers were then measured at predefined points (Fig 2). For marginal gap measurement, four points were defined for the anterior teeth and premolars, and eight points were defined for the molars. For internal gap measurement, four (eight) points on the middle of the axial walls and two (four) on the center of the occlusal walls were defined on the anterior and premolar (molar) replicas. Each slice of

Table 2 shows the means and standard deviations of the marginal and internal gaps of the crowns for each group (B, C, L). The mean marginal gap of group B was 69.89 ± 28.14 µm and was significantly smaller than those of group C (89.93 ± 40.34 µm) and group L (87.41 ± 32.84 µm) (p < 0.005). A significant difference was not found between group C and group L (p > 0.05). At the midpoint of the axial walls, the mean gap width of group B was 125.59 ± 44.05 µm, which was significantly smaller than those of the two grinding groups (p < 0.01). The mean axial gap width of group C was not significantly different from that of group L (p > 0.05), 150.29 ± 55.30 and 147.35 ± 48.43 µm, respectively. When the different cement spacer thicknesses were taken into account and extracted from the measured gaps of all groups, group B (55.59 ± 28.51 µm) still showed a remarkably significant difference from group C (120.29 ± 55.30 µm) and group L (97.34 ± 48.43 µm) (p < 0.001), while group L showed a significant difference from group C (p < 0.01). The mean occlusal gap width of group B was 314.43 ± 111.41 µm, which was significantly higher than those of group C (276.74 ± 101.71 µm) and group L (266.87 ± 109.83 µm) (p < 0.05). Group C was not significantly different from group L in occlusal fit (p > 0.05); however, no significant difference

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Table 2 Mean marginal and internal gap for each group (µm) Gap Marginal Axial Occlusal

Group B

Group C

Group L

69.89 (28.14) 125.59 (44.05) 314.43 (111.41)

89.93 (40.34) 150.29 (55.30) 276.74 (101.71)

87.41 (32.84) 147.35 (48.43) 266.87 (109.83)

The gap widths are shown without consideration of the different preset cement spaces. The preset cement spaces were 70 µm for group B, 30 µm for group C, and 50 µm for group L. Table 3 Mean marginal and internal gaps for anterior, premolar, and molar crowns (µm) Gap

Anterior

Premolar

Molar

Marginal Axial Occlusal

82.69 (35.72) 146.44 (52.63) 264.47 (111.27)

81.58 (37.17) 129.62 (48.47) 302.19 (113.01)

82.86 (32.34) 144.99 (47.75) 303.29 (96.30)

was found among the three groups when the predetermined cement space was extracted from each group (p > 0.05). The mean marginal and internal gap widths of anterior, premolar, and molar crowns fabricated from the three systems are shown in Table 3. No significant differences were found among the anterior, premolar, and molar groups in either marginal or internal (axial and occlusal) fit (p > 0.05).

Conclusions

Discussion From the results of this study, the first null hypothesis was rejected. The marginal and internal fit of the SLM crowns was better than that of the CAD/CAM-fabricated crowns. The second null hypothesis was accepted: the marginal and internal fit of the crowns were not influenced by tooth type. Cement space thickness is an important factor for the accuracy of restoration margins16 and has a significant impact on ceramic flexural failure load.28 In this study, the cement spacer thickness of the CEREC system was set at 30 µm, in accordance with the report of Nakamura et al.29 Rekow et al30 suggested that a cement spacer thickness of 80 µm was suitable for zirconium-oxide-based crowns; however, Gonzalo et al31 found that a predetermined cement space of 50 µm would be sufficient to obtain a satisfactory marginal fit of the restorations in the Lava system. From the results of this study, the SLM crowns fabricated using the BEGO system exhibited better accuracy of fit, indicating that 70 µm may be an appropriate cement space thickness for the BEGO system. The influence of the abutment tooth type on the fit of a restoration is controversial.32 In this study, no differences of fit were found among anterior, premolar, and molar crowns. This finding is in accord with those of Kokubo et al.33 However, another study reported a different influence of the abutment tooth type on the fit of the restorations.34 This study was a clinical evaluation, and the results could be closer to reality than an in vitro study; however, there were some limitations, as follows: (1) the gap dimensions were measured using a replica technique, and as a result, the accuracy was measured at only 10 or 20 predefined points on each crown, 4

which might not represent the complete fit; (2) during the clinical try-in, only finger pressure was used, which might result in different thicknesses of the silicone layers; and (3) only one SLM system and two CAD/CAM grinding systems were evaluated, and more milling systems should be studied in the future to compare the fit of crowns fabricated using the two techniques.

Within the limitations of this clinical study, the following conclusions can be drawn: 1. The SLM crowns fabricated using the BEGO system demonstrated a better accuracy of fit when compared to CAD/CAM crowns fabricated using either the Lava system or the CEREC 3D system. 2. All of the crowns fabricated using the three systems were within an acceptable range. 3. The tooth type did not significantly influence the marginal and internal fit.

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22. Pak HS, Han JS, Lee JB, et al: Influence of porcelain veneering on the marginal fit of Digident and Lava CAD/CAM zirconia ceramic crowns. J Adv Prosthodont 2010;2:33-38 23. Reich S, Wichmann M, Nkenke E, et al: Clinical fit of all-ceramic three-unit fixed partial dentures, generated with three different CAD/CAM systems. Eur J Oral Sci 2005;113:174-179 24. Reich S, Uhlen S, Gozdowski S, et al: Measurement of cement thickness under lithium disilicate crowns using an impression material technique. Clin Oral Investig 2010;15:521-526 25. Ucar Y, Akova T, Akyil MS, et al: Internal fit evaluation of crowns prepared using a new dental crown fabrication technique: laser-sintered Co-Cr crowns. J Prosthet Dent 2009;102: 253-259 26. Quante K, Ludwig K, Kern M: Marginal and internal fit of metal-ceramic crowns fabricated with a new laser melting technology. Dent Mater 2008;24:1311-1315 27. Boening KW, Wolf BH, Schmidt AE, et al: Clinical fit of Procera AllCeram crowns. J Prosthet Dent 2000;84:419-424 28. Kim JH, Miranda P, Kim DK, et al: Effect of an adhesive interlayer on the fracture of a brittle coating on a supporting substrate. J Mater Res 2003;18:222-227 29. Nakamura T, Dei N, Kojima T, et al: Marginal and internal fit of Cerec 3 CAD/CAM all-ceramic crowns. Int J Prosthodont 2003;16:244-248 30. Rekow ED, Harsono M, Janal M, et al: Factorial analysis of variables influencing stress in all-ceramic crowns. Dent Mater 2006;22:125-132 31. Gonzalo E, Su´arez MJ, Serrano B, et al: A comparison of the marginal vertical discrepancies of zirconium and metal ceramic posterior fixed dental prostheses before and after cementation. J Prosthet Dent 2009;102:378-384 32. Wettstein F, Sailer I, Roos M, et al: Clinical study of the internal gaps of zirconia and metal frameworks for fixed partial dentures. Eur J Oral Sci 2008;116:272-279 33. Kokubo Y, Ohkubo C, Tsumita M, et al: Clinical marginal and internal gaps of Procera AllCeram crowns. J Oral Rehabil 2005;32:526-530 34. Nakamura T, Nonaka M, Maruyama T: In vitro fitting accuracy of copy-milled alumina cores and all-ceramic crowns. Int J Prosthodont 2000;13:189-193

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CAM Technologies.

The aims of this in vivo investigation were to compare the marginal and internal fit of single-unit crowns fabricated using a selective laser melting ...
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