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Effect of fabrication stages and cementation on the marginal fit of CAD-CAM monolithic zirconia crowns
RESEARCH AND EDUCATION
Effect of fabrication stages and cementation on the marginal fit of CAD-CAM monolithic zirconia crowns Ediz Kale, DDS, PhD,a Burak Yilmaz, DDS, PhD,b Emre Seker, DDS, PhD,c and Tuncer Burak Özcelik, DDS, PhDd The evolution of computerABSTRACT aided design and computerStatement of problem. Monolithic zirconia crowns fabricated using computer-aided design and aided manufacturing (CADcomputer-aided manufacturing (CAD-CAM) technology have recently become an alternative CAM) technology has rapidly dental prosthetic treatment. The marginal fit of monolithic zirconia crown may be affected by increased the use of zirconia different stages of the fabrication procedures in the laboratory and cementation. Information regarding the accuracy of fit of monolithic zirconia crowns at different stages of fabrication and ceramic restorations.1 With the cementation is limited. introduction of monolithic zirconia restorations, a major Purpose. The purpose of this in vitro study was to evaluate the effect of different stages of fabrication and cementation on the vertical marginal discrepancy (VMD) of CAD-CAM fabricated drawback related to the clinical monolithic zirconia crowns. use of traditional zirconia restorations has been eliminated, that Material and methods. Six ivorine right maxillary first molar typodont teeth with standardized is, the need to veneer the zircoanatomic preparations for complete coverage ceramic crowns were scanned with a 3-dimensional laboratory scanner. Crowns were designed using CAD software and milled from presintered nia framework with feldspathic monolithic zirconia blocks in a 5-axis dental milling machine. A cement space of 25 mm for the porcelain.2,3 Several studies4-9 margins and a 50-mm space starting 1 mm above the finish lines of the teeth were virtually set have reported fracture, chipin the CAD software. A total of 144 measurements were performed on 6 specimens with 8 ping, or delamination of the measurement locations in 3 different stages using stereoscopic zoom microscopy; after initial feldspathic porcelain layer over production of the crowns (post-sintering group), after glazing (post-glazing group), and after the zirconia framework. Slow cementation (post-cementation group). The VMD values were statistically analyzed with 1-way cooling and slow heating regirepeated measures ANOVA and the Holm-Sidak method (a=.05). mens have been integrated in Results. Different stages of fabrication and cementation significantly affected the VMD of tested the veneering process in an crowns (P=.003). The mean VMD was 38 mm for post-sintering group, 38 mm for post-glazing group, attempt to largely overcome the and 60 mm for post-cementation group, with statistical differences between the post-sintering problem.10 As a novel alternagroup, the post-cementation group (P<.002), and the post-glazing group and post-cementation group (P<.003); there were no statistical differences between the post-sintering group and the tive dental prosthetic treatment post-glazing group (P=.966). using monolithic zirconia, highstrength tooth- or implantConclusions. Within the limitations of this in vitro study, glazing did not significantly change the VMD of CAD-CAM monolithic zirconia crowns. Cementation significantly increased the VMD supported restorations can be values. (J Prosthet Dent 2017;-:---) fabricated with acceptable esthetic results in a reasonable occlusal forces20 in the posterior section of the mouth. Initial time and at a reasonable cost.3,11-18 Even after mechanical studies of the survival rate of monolithic zirconia crowns and thermal aging, monolithic zirconia crowns can endure have estimated fracture rates of between 0.2% and 0.7% for much higher fracture loads19 than the average maximal
a
Assistant Professor, Department of Prosthodontics, Faculty of Dentistry, Mustafa Kemal University, Hatay, Turkey. Associate Professor, Department of Restorative Science and Prosthodontics, The Ohio State University College of Dentistry, Columbus, Ohio. c Assistant Professor, Department of Prosthodontics, Faculty of Dentistry, Eskis¸ehir Osmangazi University, Eskisehir, Turkey. d Associate Professor, Department of Prosthodontics, Faculty of Dentistry, Bas¸kent University, Ankara, Turkey. b
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Clinical Implications Simulated cement space can be set at 50 mm for the clinically acceptable marginal fit of CAD-CAM monolithic zirconia crowns in the molar region when the tested cement is used for cementation.
at least 5 years of service in the molar region.16,18 In vitro investigations have shown that monolithic zirconia crowns with a minimal occlusal thickness of 0.7 mm for implantsupported21 and 0.5 mm for tooth-supported15,17 restorations can withstand the masticatory forces in the posterior segment in the long term. This makes them a viable alternative for restorations in patients with limited interarch distance,21 the need for preservation of tooth structure,3,19 and insufficient clinical crown length. Recent clinical evidence has presented the results of monolithic zirconia restorations as wear-friendly to opposing dental enamel in their polished state compared with glazed metal ceramic restorations placed in the premolar and molar regions.22 Additionally, the surface finishing state of monolithic zirconia crowns does not affect their fracture resistance, being significantly higher than conventional metal ceramic crowns, even after prolonged artificial aging conditions.23 In addition to improved physical properties and esthetics, appropriate marginal adaptation is fundamental for the long-term clinical success of ceramic restorations.2,11,24-27 Excessive marginal discrepancy may lead to unfavorable results for the supporting structure and its peripheral tissues (periodontal or periimplant).2,28-32 Although reports are not in agreement as to what should constitute clinically acceptable maximum marginal discrepancy, many33-35 studies agree that it should be less than 120 mm. Other researchers36,37 believe that the marginal discrepancy should not be more than 100 mm in the era of CAD-CAM technology. Given the importance of accurate marginal adaptation of restorations, there has been much debate in published articles.2,26 Studies have investigated the fitting precision of zirconia crown margins2,24-26,38-42 before or after veneering process. Veneering may have a significant influence on the marginal fit of zirconia restorations.43-45 However, as monolithic zirconia crowns are not veneered but characterized only with staining through glazing,46 how the marginal fit of the monolithic zirconia crowns is affected by the fabrication stages is important. Cementation may also affect the marginal fit of ceramic crowns.24,26,47 However, to the best of the authors’ knowledge, reports regarding the accuracy of fit for monolithic zirconia crowns at different stages of fabrication are limited.48,49 The purpose of this in vitro study was to evaluate the effect of different stages of fabrication and cementation
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on the vertical marginal discrepancy (VMD) of CADCAM monolithic zirconia crowns. The null hypothesis was that no differences would be found in VMD values obtained after different stages of fabrication, before and after glazing of the crown and after cementation. MATERIAL AND METHODS This study used 6 ivorine right maxillary first molar typodont teeth (1860P03FC EP-TPR-860 #3/CVC; Columbia Dentoform) with standard anatomic preparations supplied by the manufacturer (0.5-mm axial reduction, 360-degree chamfer margin) for complete coverage ceramic restorations.49,50 The teeth were scanned with a 3-dimensional (3D) laboratory scanner (D900; 3Shape), and CAD design software (Dental System; 3Shape) was used to design a crown with identical external contours for each tooth. The designed crown data were processed with CAM software (CORiTEC iCAM V5; iMES-iCORE), and CAD-CAM ceramic crowns were milled from presintered monolithic zirconia blocks (StarCeram Z-Nature; H.C. Starck) in a 5-axis computer numeric control dental milling machine (CORiTEC 550i; iMES-iCORE) and sintered (Sinterofen HT-S Speed; Mihm-Vogt) according to the manufacturer’s instructions. The crowns had a simulated cement space of 25 mm around the margins and 50 mm starting 1 mm above the finish lines of the teeth (Fig. 1). After they had been seated onto their corresponding teeth,51 the VMDs of the crowns were measured circumferentially at 8 consecutive locations (mesiopalatal, mesial, mesiobuccal, buccal, distobuccal, distal, distopalatal, and palatal), using ×3.5 to ×180 magnification zoom stereomicroscopy (SM-3TZZ-54S-10M; AmScope) equipped with a 10 megapixels digital camera (MU1000; AmScope) and light-emitting diode ring light (LED-54S; AmScope).38,49,52 The camera attached to the microscope was calibrated using a single calibration slide (MR100; AmScope) with a precision stage micrometer (0.01 mm).38,49,52 The specimens were aligned perpendicularly to the evaluation sight of the microscope and manually rotated to measure each point.38,49,52 To standardize the measurement locations, a castmetal ring guide with 8 horn-like projections, each indicating the locations to be measured, was fabricated to fit the cervix of the typodont teeth.49 The measurements were performed in real time on 3584×2748 resolution live-video stream computer image at ×100 to ×120 magnification by means of software (AmScope x86, v3.7.3980; AmScope), measuring the shortest distance between 2 parallel lines drawn at the crown margin and finish line of the teeth (Fig. 2).49 After measurement, the crowns were glazed, and the VMDs were measured again using the same sequence (Fig. 2A). The crowns were then cemented to their respective teeth with a polycarboxylate
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central fossa of the crown parallel to the vertical axis of the tooth was applied on each specimen for 5 minutes.17,53 The excess cement was removed, and after setting, the VMD was measured again in the same manner (Fig. 2B). All measurements and cementation procedures were done by a single operator (E.K.). A total of 144 measurements were performed on 6 specimens with 8 measurement locations in 3 different stages (post sintering, post glazing, and post cementation) of the restoration with monolithic zirconia crowns. The average value of the 8 measurement points was calculated for each specimen and considered the circumferential VMD value for the specimen at a certain stage of measurement. The means ±standard deviations (SD) were calculated for each stage of measurement and statistically analyzed for significant differences with 1-way repeated measures ANOVA and the Holm-Sidak method, using statistical software (IBM SPSS Statistics v21.0; IBM Corp) (a=.05). RESULTS The results of 1-way repeated measures ANOVA indicated that different stages of fabrication and cementation significantly affected the VMD of tested crowns (F=11.464; P=.003). The pairwise multiple comparison (Holm-Sidak) test revealed statistical differences between the post-sintering and post-cementation groups (P<.002) and between the post-glazing and post-cementation groups (P<.003), whereas no statistical differences were found between the post-sintering and post-glazing groups (P=.966). Table 1 shows the mean VMD, SD, standard error, and minimum-maximum range values for each group. None of the VMD values measured in any of the 8 measurement locations in the post-sintering and postglazing groups was above the clinically acceptable threshold of 120 mm, with only 1 value over 100 mm measured in the post-glazing group. The VMD values over 100 mm in post-cementation group were 6, measured in 4 different specimens. The largest VMD per measurement obtained in the post-cementation group was 149 mm, which was 1 of only 2 values that exceeded 120 mm (Fig. 3). Figure 1. A, Scanned typodont tooth on CAD software (detecting path of insertion). B, Simulated cement space on tooth image (50 mm). C, Virtual crown design (distal view on CAD software).
cement (Adhesor Carbofine; SpofaDental) according to the manufacturer’s instructions. The crowns were seated with a rocking motion53 and maximum index finger pressure (180-degree distal pad press) of a young adult male (50 N)54 as in the clinical situation.48 During setting, a static standardized force (40 N) directed onto the Kale et al
DISCUSSION The results of the current study showed significant differences for VMD values in the post-glazing and postcementation groups and no differences between the post-sintering and post-glazing groups, thus, the null hypothesis was rejected. For the CAD-CAM-fabricated monolithic zirconia crowns investigated in this study, the smallest mean VMD value was observed in the postsintering group (38 mm). The mean VMD in the postglazing group (38 mm) was slightly higher with no THE JOURNAL OF PROSTHETIC DENTISTRY
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Figure 2. A, Vertical marginal discrepancy measurement after glazing (original magnification ×100 to 120). B, Vertical marginal discrepancy measurement after cementation (original magnification ×100 to 120). zc, zirconia crown; tt, typodont tooth; mrg, metal ring guide. *Cement material.
significant differences from those of the post-sintering group, and the post-cementation group (60 mm) had a significantly higher mean VMD than the other 2 groups. A cement space set at 50 mm has been suggested for the fabrication of clinically acceptable cast crown restorations.55 This recommendation is supported by the results of a recent in vitro study of the VMD of monolithic zirconia crowns with different virtual cement space settings.49 Kale et al49 reported 53 mm of mean VMD measured before cementation for glazed monolithic zirconia crowns fabricated with 50 mm of virtual cement space. Among the individually measured values per location, only 1 was reported to be on the edge of the clinically acceptable threshold of 120 mm, with another below that limit but still over 100 mm. In the current study, the mean VMD calculated for the crowns post glazing was 38 mm with only 1 individually measured value over 100 mm. The results of the current study are consistent with those in the study by Kale et al,49 taking into account the comparable study design in regard to CAD-CAM workflow, cement space settings, and restoration materials used. The differences in VMDs between these 2 studies may be attributed to the different sample size and calculated SDs. The glazing procedure did not significantly affect the VMD of monolithic zirconia crowns in the present study. Previous studies have reported that repeated firing cycles and various veneering techniques may negatively affect the marginal discrepancy of zirconia restorations by inducing a tendency for distortion in the zirconia framework.2,43-45 To the best of the authors’ knowledge, the effect of glazing on the marginal accuracy of monolithic zirconia crowns has not yet been investigated. Further research is needed to investigate the effect of glazing and repeated firing cycles on the marginal fitting accuracy of monolithic zirconia crowns with different restoration thicknesses. THE JOURNAL OF PROSTHETIC DENTISTRY
Table 1. Range of VMD measurements (mm) according to stage of restoration procedure Group
No. of Specimens Mean ±SD SE Minimum Maximum
Post-sintering
6
38 ±11a
4
19
60
Post-glazing
6
38 ±12a,b
5
26
52
Post-cementation
6
60 ±15c
6
36
74
VMD, vertical marginal discrepancy. Different superscript letters indicate significant difference between group pairs according to Holm-Sidak test (P<.05).
Several studies27,56,57 have reported VMD mean values between 75 mm and 120 mm for veneered zirconia crowns by measuring the thickness of low-viscosity silicone (the replica technique). Berrendero et al56 indicated that this method can simulate clinical cementation. Comparing the results of the current study with the 60 mm of the VMD post cementation, those of Park et al27 with 75 mm, Huang et al57 with 84 mm, and Berrendero et al56 with 107 mm to 120 mm of VMD for veneered zirconia crowns with a simulated cement space of at least 50 mm, it appears that monolithic zirconia crowns have improved VMD compared with veneered restorations. This improvement might be due to the absence of veneering in the monolithic zirconia crown fabrication stages.45 Ji et al48 recently reported VMD mean values of 92 mm and 119 mm after cementation for 2 different monolithic zirconia crown brands, using shoulder finish line preparations, and 85 mm and 109 mm for identical restorations with chamfer margins. The simulated cement space set during the CAD-CAM was 30 mm, and the type of luting agent was a resin cement, which may explain the unfavorable performance of those crowns compared with the crowns of the current study after cementation. Cement space may significantly influence the marginal accuracy of CAD-CAM fabricated monolithic zirconia crowns, and 30 mm of virtual cement thickness may significantly increase the VMD compared with those of 50 mm.49 Using luting agents with different Kale et al
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Vertical Marginal Discrepancy (µm)
160 148.88
140 120 100 80
85.51
60 40
43.21
20 0
9.79
Post-sintering
Post-glazing
Post-cementation
Specimen 1
Specimen 2
Specimen 3
Specimen 4
Specimen 5
Specimen 6
Figure 3. Box plot diagrams of individually measured VMD values for each group.
film thicknesses might have resulted in different post cementation marginal discrepancies,24 as studies have shown that a significant difference in film thickness may occur between resin-based and water-based luting agents as used in the present study.58 The cementation process had a significant effect on the VMD of CAD-CAM fabricated monolithic zirconia crowns in the present study. This result is in agreement with those of previous studies investigating the marginal discrepancy of ceramic crowns before and after cementation.24 Evidence shows that an increase in VMD should be expected as the consequence of forming film thickness of luting agent or any other medium for definitive or interim fixation of the crowns on their respective abutments.24,58 The results of the present study revealed an increase in VMD mean values of approximately 22 mm after cementation, which is in agreement with previously published studies58 and within the standards currently set by the International Organization for Standardization that require a film thickness that does not exceed the limit of 25 mm at the time of seating for water-based luting cements.59 In the current study, the mean VMD values calculated for the tested stages of restoration with CAD-CAM fabricated monolithic zirconia crowns were all within the threshold of clinically acceptable value, 120 mm. Among the individually measured values, only 2 exceeded that limit but were still under 150 mm as measured post cementation. Reporting the peak values for each measurement location to avoid misleading conclusions regarding studies evaluating the marginal discrepancy of crown restorations has already been emphasized.36,49 Matta et al36 have also calculated mean VMD values below 100 mm for zirconia copings cemented with a Kale et al
water-based luting agent under in vitro conditions, drawing attention to the priority of detailed reporting of the measurement results. They reported 12% of individually measured values over 100 mm and 5% over 150 mm of VMD in a group of 5 specimens. In the present study, individually measured values over 100 mm post cementation were 12.5% for 6 specimens, correlating with the results of previous publications.36 The results of this study should be interpreted considering that only 1 type of zirconia brand and cement were tested using 1 CAD-CAM system. These results should be corroborated with those of other clinical studies. CONCLUSIONS Within the limitations of this in vitro study, the following conclusions were drawn: 1. The glazing procedure had no significant effect on the VMD of CAD-CAM monolithic zirconia crowns. 2. The cementation process significantly affected the VMD of CAD-CAM monolithic zirconia crowns. 3. The mean VMD values were within the clinically acceptable limits for all tested stages of fabrication and cementation (<120 mm). REFERENCES 1. Tinschert J, Natt G, Hassenpflug S, Spiekermann H. Status of current CAD/ CAM technology in dental medicine. Int J Comput Dent 2004;7:25-45. 2. Abduo J, Lyons K, Swain M. Fit of zirconia fixed partial denture: a systematic review. J Oral Rehabil 2010;37:866-76. 3. Øilo M, Kvam K, Gjerdet NR. Load at fracture of monolithic and bilayered zirconia crowns with and without a cervical zirconia collar. J Prosthet Dent 2016;115:630-6. 4. Al-Amleh B, Lyons K, Swain M. Clinical trials in zirconia: a systematic review. J Oral Rehabil 2010;37:641-52. 5. Bachhav VC, Aras MA. Zirconia-based fixed partial dentures: a clinical review. Quintessence Int 2011;42:173-82. 6. Raigrodski AJ, Yu A, Chiche GJ, Hochstedler JL, Mancl LA, Mohamed SE. Clinical efficacy of veneered zirconium dioxide-based posterior partial fixed dental prostheses: five-year results. J Prosthet Dent 2012;108:214-22. 7. Schmitter M, Mussotter K, Rammelsberg P, Gabbert O, Ohlmann B. Clinical performance of long-span zirconia frameworks for fixed dental prostheses: 5-year results. J Oral Rehabil 2012;39:552-7. 8. Raigrodski AJ, Hillstead MB, Meng GK, Chung KH. Survival and complications of zirconia-based fixed dental prostheses: a systematic review. J Prosthet Dent 2012;107:170-7. 9. Pang Z, Chughtai A, Sailer I, Zhang Y. A fractographic study of clinically retrieved zirconia-ceramic and metal-ceramic fixed dental prostheses. Dent Mater 2015;31:1198-206. 10. Tan JP, Sederstrom D, Polansky JR, McLaren EA, White SN. The use of slow heating and slow cooling regimens to strengthen porcelain fused to zirconia. J Prosthet Dent 2012;107:163-9. 11. Batson ER, Cooper LF, Duqum I, Mendonça G. Clinical outcomes of three different crown systems with CAD/CAM technology. J Prosthet Dent 2014;112:770-7. 12. Zesewitz TF, Knauber AW, Northdurft FP. Fracture resistance of a selection of full-contour all-ceramic crowns: an in vitro study. Int J Prosthodont 2014;27:264-6. 13. 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. 14. de Kok P, Kleverlaan CJ, de Jager N, Kuijs R, Feilzer AJ. Mechanical performance of implant-supported posterior crowns. J Prosthet Dent 2015;114: 59-66. 15. Nakamura K, Harada A, Inagaki R, Kanno T, Niwano Y, Milleding P, et al. Fracture resistance of monolithic zirconia molar crowns with reduced thickness. Acta Odontol Scand 2015;73:602-8.
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40. Rinke S, Fornefett D, Gersdorff N, Lange K, Roediger M. Multifactorial analysis of the impact of different manufacturing processes on the marginal fit of zirconia copings. Dent Mater J 2012;31:601-9. 41. An S, Kim S, Choi H, Lee JH, Moon HS. Evaluating the marginal fit of zirconia copings with digital impressions with an intraoral digital scanner. J Prosthet Dent 2014;112:1171-5. 42. Gonzalo E, Suarez MJ, Serrano B, Lozano JF. Marginal fit of Zirconia posterior fixed partial dentures. Int J Prosthodont 2008;21:398-9. 43. 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. 44. Pak HS, Han JS, Lee JB, Kim SH, Yang JH. Influence of porcelain veneering on the marginal fit of Digident and Lava CAD/CAM zirconia ceramic crowns. J Adv Prosthodont 2010;2:33-8. 45. Torabi K, Vojdani M, Giti R, Taghva M, Pardis S. The effect of various veneering techniques on the marginal fit of zirconia copings. J Adv Prosthodont 2015;7:233-9. 46. Kim HK, Kim SH, Lee JB, Ha SR. Effects of surface treatments on the translucency, opalescence, and surface texture of dental monolithic zirconia ceramics. J Prosthet Dent 2016;115:773-9. 47. 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. 48. Ji MK, Park JH, Park SW, Yun KD, Oh GJ, Lim HP. Evaluation of marginal fit of 2 CAD-CAM anatomic contour zirconia crown systems and lithium disilicate glass-ceramic crown. J Adv Prosthodont 2015;7:271-7. 49. Kale E, Seker E, Yilmaz B, Ozcelik TB. Effect of cement space on the marginal fit of CAD/CAM-fabricated monolithic zirconia crowns. J Prosthet Dent 2016;116:890-5. 50. Rosenstiel SF, Land MF, Fujimoto J. Contemporary fixed prosthodontics. 5th ed. St. Louis: Elsevier; 2016. p. 264-77. 51. Witkowski S, Komine F, Gerds T. Marginal accuracy of titanium copings fabricated by casting and CAD/CAM techniques. J Prosthet Dent 2006;96: 47-52. 52. Seker E, Ozcelik TB, Rathi N, Yilmaz B. Evaluation of marginal fit of CAD/ CAM restorations fabricated through cone beam computerized tomography and laboratory scanner data. J Prosthet Dent 2016;115:47-51. 53. Hoang LN, Thompson GA, Cho SH, Berzins DW, Ahn KW. Die spacer thickness reproduction for central incisor crown fabrication with combined computer-aided design and 3D printing technology: an in vitro study. J Prosthet Dent 2015;113:398-404. 54. Didomenico A, Nussbaum M. Measurement and prediction of single and multi-digit finger strength. Ergonomics 2003;46:1531-48. 55. Grajower R, Lewinstein I. A mathematical treatise on the fit of crown castings. J Prosthet Dent 1993;49:663-74. 56. Berrendero S, Salido MP, Valverde A, Ferreiroa A, Pradíes G. Influence of conventional and digital intraoral impressions on the fit of CAD/CAMfabricated all-ceramic crowns. Clin Oral Investig 2016;20:2403-10. 57. Huang Z, Zhang L, Zhu J, Zhao Y, Zhang X. Clinical marginal and internal fit of crowns fabricated using different CAD/CAM technologies. J Prosthodont 2015;24:291-5. 58. Osman SA, McCabe JF, Walls AW. Film thickness and rheological properties of luting agents for crown cementation. Eur J Prosthodont Restor Dent 2006;14:23-7. 59. International Organization for Standardization. ISO 9917-1. Water-based cements. Part 1: powder/liquid acid-base cements. Geneva: ISO; 2007. Available at: http://www.iso.org/webstore.htm. Accessed September 1, 2016. Corresponding author: Dr Ediz Kale Mustafa Kemal University Faculty of Dentistry Department of Prosthodontics 31040 Antakya-Hatay TURKEY Email: [email protected] Copyright © 2017 by the Editorial Council for The Journal of Prosthetic Dentistry.
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Effect of fabrication stages and cementation on the marginal fit of CAD-CAM monolithic zirconia crowns Ediz Kale, DDS, PhD,a Burak Yilmaz, DDS, PhD,b Emre Seker, DDS, PhD,c and Tuncer Burak Özcelik, DDS, PhDd The evolution of computerABSTRACT aided design and computerStatement of problem. Monolithic zirconia crowns fabricated using computer-aided design and aided manufacturing (CADcomputer-aided manufacturing (CAD-CAM) technology have recently become an alternative CAM) technology has rapidly dental prosthetic treatment. The marginal fit of monolithic zirconia crown may be affected by increased the use of zirconia different stages of the fabrication procedures in the laboratory and cementation. Information regarding the accuracy of fit of monolithic zirconia crowns at different stages of fabrication and ceramic restorations.1 With the cementation is limited. introduction of monolithic zirconia restorations, a major Purpose. The purpose of this in vitro study was to evaluate the effect of different stages of fabrication and cementation on the vertical marginal discrepancy (VMD) of CAD-CAM fabricated drawback related to the clinical monolithic zirconia crowns. use of traditional zirconia restorations has been eliminated, that Material and methods. Six ivorine right maxillary first molar typodont teeth with standardized is, the need to veneer the zircoanatomic preparations for complete coverage ceramic crowns were scanned with a 3-dimensional laboratory scanner. Crowns were designed using CAD software and milled from presintered nia framework with feldspathic monolithic zirconia blocks in a 5-axis dental milling machine. A cement space of 25 mm for the porcelain.2,3 Several studies4-9 margins and a 50-mm space starting 1 mm above the finish lines of the teeth were virtually set have reported fracture, chipin the CAD software. A total of 144 measurements were performed on 6 specimens with 8 ping, or delamination of the measurement locations in 3 different stages using stereoscopic zoom microscopy; after initial feldspathic porcelain layer over production of the crowns (post-sintering group), after glazing (post-glazing group), and after the zirconia framework. Slow cementation (post-cementation group). The VMD values were statistically analyzed with 1-way cooling and slow heating regirepeated measures ANOVA and the Holm-Sidak method (a=.05). mens have been integrated in Results. Different stages of fabrication and cementation significantly affected the VMD of tested the veneering process in an crowns (P=.003). The mean VMD was 38 mm for post-sintering group, 38 mm for post-glazing group, attempt to largely overcome the and 60 mm for post-cementation group, with statistical differences between the post-sintering problem.10 As a novel alternagroup, the post-cementation group (P<.002), and the post-glazing group and post-cementation group (P<.003); there were no statistical differences between the post-sintering group and the tive dental prosthetic treatment post-glazing group (P=.966). using monolithic zirconia, highstrength tooth- or implantConclusions. Within the limitations of this in vitro study, glazing did not significantly change the VMD of CAD-CAM monolithic zirconia crowns. Cementation significantly increased the VMD supported restorations can be values. (J Prosthet Dent 2017;-:---) fabricated with acceptable esthetic results in a reasonable occlusal forces20 in the posterior section of the mouth. Initial time and at a reasonable cost.3,11-18 Even after mechanical studies of the survival rate of monolithic zirconia crowns and thermal aging, monolithic zirconia crowns can endure have estimated fracture rates of between 0.2% and 0.7% for much higher fracture loads19 than the average maximal
a
Assistant Professor, Department of Prosthodontics, Faculty of Dentistry, Mustafa Kemal University, Hatay, Turkey. Associate Professor, Department of Restorative Science and Prosthodontics, The Ohio State University College of Dentistry, Columbus, Ohio. c Assistant Professor, Department of Prosthodontics, Faculty of Dentistry, Eskis¸ehir Osmangazi University, Eskisehir, Turkey. d Associate Professor, Department of Prosthodontics, Faculty of Dentistry, Bas¸kent University, Ankara, Turkey. b
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Clinical Implications Simulated cement space can be set at 50 mm for the clinically acceptable marginal fit of CAD-CAM monolithic zirconia crowns in the molar region when the tested cement is used for cementation.
at least 5 years of service in the molar region.16,18 In vitro investigations have shown that monolithic zirconia crowns with a minimal occlusal thickness of 0.7 mm for implantsupported21 and 0.5 mm for tooth-supported15,17 restorations can withstand the masticatory forces in the posterior segment in the long term. This makes them a viable alternative for restorations in patients with limited interarch distance,21 the need for preservation of tooth structure,3,19 and insufficient clinical crown length. Recent clinical evidence has presented the results of monolithic zirconia restorations as wear-friendly to opposing dental enamel in their polished state compared with glazed metal ceramic restorations placed in the premolar and molar regions.22 Additionally, the surface finishing state of monolithic zirconia crowns does not affect their fracture resistance, being significantly higher than conventional metal ceramic crowns, even after prolonged artificial aging conditions.23 In addition to improved physical properties and esthetics, appropriate marginal adaptation is fundamental for the long-term clinical success of ceramic restorations.2,11,24-27 Excessive marginal discrepancy may lead to unfavorable results for the supporting structure and its peripheral tissues (periodontal or periimplant).2,28-32 Although reports are not in agreement as to what should constitute clinically acceptable maximum marginal discrepancy, many33-35 studies agree that it should be less than 120 mm. Other researchers36,37 believe that the marginal discrepancy should not be more than 100 mm in the era of CAD-CAM technology. Given the importance of accurate marginal adaptation of restorations, there has been much debate in published articles.2,26 Studies have investigated the fitting precision of zirconia crown margins2,24-26,38-42 before or after veneering process. Veneering may have a significant influence on the marginal fit of zirconia restorations.43-45 However, as monolithic zirconia crowns are not veneered but characterized only with staining through glazing,46 how the marginal fit of the monolithic zirconia crowns is affected by the fabrication stages is important. Cementation may also affect the marginal fit of ceramic crowns.24,26,47 However, to the best of the authors’ knowledge, reports regarding the accuracy of fit for monolithic zirconia crowns at different stages of fabrication are limited.48,49 The purpose of this in vitro study was to evaluate the effect of different stages of fabrication and cementation
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on the vertical marginal discrepancy (VMD) of CADCAM monolithic zirconia crowns. The null hypothesis was that no differences would be found in VMD values obtained after different stages of fabrication, before and after glazing of the crown and after cementation. MATERIAL AND METHODS This study used 6 ivorine right maxillary first molar typodont teeth (1860P03FC EP-TPR-860 #3/CVC; Columbia Dentoform) with standard anatomic preparations supplied by the manufacturer (0.5-mm axial reduction, 360-degree chamfer margin) for complete coverage ceramic restorations.49,50 The teeth were scanned with a 3-dimensional (3D) laboratory scanner (D900; 3Shape), and CAD design software (Dental System; 3Shape) was used to design a crown with identical external contours for each tooth. The designed crown data were processed with CAM software (CORiTEC iCAM V5; iMES-iCORE), and CAD-CAM ceramic crowns were milled from presintered monolithic zirconia blocks (StarCeram Z-Nature; H.C. Starck) in a 5-axis computer numeric control dental milling machine (CORiTEC 550i; iMES-iCORE) and sintered (Sinterofen HT-S Speed; Mihm-Vogt) according to the manufacturer’s instructions. The crowns had a simulated cement space of 25 mm around the margins and 50 mm starting 1 mm above the finish lines of the teeth (Fig. 1). After they had been seated onto their corresponding teeth,51 the VMDs of the crowns were measured circumferentially at 8 consecutive locations (mesiopalatal, mesial, mesiobuccal, buccal, distobuccal, distal, distopalatal, and palatal), using ×3.5 to ×180 magnification zoom stereomicroscopy (SM-3TZZ-54S-10M; AmScope) equipped with a 10 megapixels digital camera (MU1000; AmScope) and light-emitting diode ring light (LED-54S; AmScope).38,49,52 The camera attached to the microscope was calibrated using a single calibration slide (MR100; AmScope) with a precision stage micrometer (0.01 mm).38,49,52 The specimens were aligned perpendicularly to the evaluation sight of the microscope and manually rotated to measure each point.38,49,52 To standardize the measurement locations, a castmetal ring guide with 8 horn-like projections, each indicating the locations to be measured, was fabricated to fit the cervix of the typodont teeth.49 The measurements were performed in real time on 3584×2748 resolution live-video stream computer image at ×100 to ×120 magnification by means of software (AmScope x86, v3.7.3980; AmScope), measuring the shortest distance between 2 parallel lines drawn at the crown margin and finish line of the teeth (Fig. 2).49 After measurement, the crowns were glazed, and the VMDs were measured again using the same sequence (Fig. 2A). The crowns were then cemented to their respective teeth with a polycarboxylate
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central fossa of the crown parallel to the vertical axis of the tooth was applied on each specimen for 5 minutes.17,53 The excess cement was removed, and after setting, the VMD was measured again in the same manner (Fig. 2B). All measurements and cementation procedures were done by a single operator (E.K.). A total of 144 measurements were performed on 6 specimens with 8 measurement locations in 3 different stages (post sintering, post glazing, and post cementation) of the restoration with monolithic zirconia crowns. The average value of the 8 measurement points was calculated for each specimen and considered the circumferential VMD value for the specimen at a certain stage of measurement. The means ±standard deviations (SD) were calculated for each stage of measurement and statistically analyzed for significant differences with 1-way repeated measures ANOVA and the Holm-Sidak method, using statistical software (IBM SPSS Statistics v21.0; IBM Corp) (a=.05). RESULTS The results of 1-way repeated measures ANOVA indicated that different stages of fabrication and cementation significantly affected the VMD of tested crowns (F=11.464; P=.003). The pairwise multiple comparison (Holm-Sidak) test revealed statistical differences between the post-sintering and post-cementation groups (P<.002) and between the post-glazing and post-cementation groups (P<.003), whereas no statistical differences were found between the post-sintering and post-glazing groups (P=.966). Table 1 shows the mean VMD, SD, standard error, and minimum-maximum range values for each group. None of the VMD values measured in any of the 8 measurement locations in the post-sintering and postglazing groups was above the clinically acceptable threshold of 120 mm, with only 1 value over 100 mm measured in the post-glazing group. The VMD values over 100 mm in post-cementation group were 6, measured in 4 different specimens. The largest VMD per measurement obtained in the post-cementation group was 149 mm, which was 1 of only 2 values that exceeded 120 mm (Fig. 3). Figure 1. A, Scanned typodont tooth on CAD software (detecting path of insertion). B, Simulated cement space on tooth image (50 mm). C, Virtual crown design (distal view on CAD software).
cement (Adhesor Carbofine; SpofaDental) according to the manufacturer’s instructions. The crowns were seated with a rocking motion53 and maximum index finger pressure (180-degree distal pad press) of a young adult male (50 N)54 as in the clinical situation.48 During setting, a static standardized force (40 N) directed onto the Kale et al
DISCUSSION The results of the current study showed significant differences for VMD values in the post-glazing and postcementation groups and no differences between the post-sintering and post-glazing groups, thus, the null hypothesis was rejected. For the CAD-CAM-fabricated monolithic zirconia crowns investigated in this study, the smallest mean VMD value was observed in the postsintering group (38 mm). The mean VMD in the postglazing group (38 mm) was slightly higher with no THE JOURNAL OF PROSTHETIC DENTISTRY
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Figure 2. A, Vertical marginal discrepancy measurement after glazing (original magnification ×100 to 120). B, Vertical marginal discrepancy measurement after cementation (original magnification ×100 to 120). zc, zirconia crown; tt, typodont tooth; mrg, metal ring guide. *Cement material.
significant differences from those of the post-sintering group, and the post-cementation group (60 mm) had a significantly higher mean VMD than the other 2 groups. A cement space set at 50 mm has been suggested for the fabrication of clinically acceptable cast crown restorations.55 This recommendation is supported by the results of a recent in vitro study of the VMD of monolithic zirconia crowns with different virtual cement space settings.49 Kale et al49 reported 53 mm of mean VMD measured before cementation for glazed monolithic zirconia crowns fabricated with 50 mm of virtual cement space. Among the individually measured values per location, only 1 was reported to be on the edge of the clinically acceptable threshold of 120 mm, with another below that limit but still over 100 mm. In the current study, the mean VMD calculated for the crowns post glazing was 38 mm with only 1 individually measured value over 100 mm. The results of the current study are consistent with those in the study by Kale et al,49 taking into account the comparable study design in regard to CAD-CAM workflow, cement space settings, and restoration materials used. The differences in VMDs between these 2 studies may be attributed to the different sample size and calculated SDs. The glazing procedure did not significantly affect the VMD of monolithic zirconia crowns in the present study. Previous studies have reported that repeated firing cycles and various veneering techniques may negatively affect the marginal discrepancy of zirconia restorations by inducing a tendency for distortion in the zirconia framework.2,43-45 To the best of the authors’ knowledge, the effect of glazing on the marginal accuracy of monolithic zirconia crowns has not yet been investigated. Further research is needed to investigate the effect of glazing and repeated firing cycles on the marginal fitting accuracy of monolithic zirconia crowns with different restoration thicknesses. THE JOURNAL OF PROSTHETIC DENTISTRY
Table 1. Range of VMD measurements (mm) according to stage of restoration procedure Group
No. of Specimens Mean ±SD SE Minimum Maximum
Post-sintering
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38 ±11a
4
19
60
Post-glazing
6
38 ±12a,b
5
26
52
Post-cementation
6
60 ±15c
6
36
74
VMD, vertical marginal discrepancy. Different superscript letters indicate significant difference between group pairs according to Holm-Sidak test (P<.05).
Several studies27,56,57 have reported VMD mean values between 75 mm and 120 mm for veneered zirconia crowns by measuring the thickness of low-viscosity silicone (the replica technique). Berrendero et al56 indicated that this method can simulate clinical cementation. Comparing the results of the current study with the 60 mm of the VMD post cementation, those of Park et al27 with 75 mm, Huang et al57 with 84 mm, and Berrendero et al56 with 107 mm to 120 mm of VMD for veneered zirconia crowns with a simulated cement space of at least 50 mm, it appears that monolithic zirconia crowns have improved VMD compared with veneered restorations. This improvement might be due to the absence of veneering in the monolithic zirconia crown fabrication stages.45 Ji et al48 recently reported VMD mean values of 92 mm and 119 mm after cementation for 2 different monolithic zirconia crown brands, using shoulder finish line preparations, and 85 mm and 109 mm for identical restorations with chamfer margins. The simulated cement space set during the CAD-CAM was 30 mm, and the type of luting agent was a resin cement, which may explain the unfavorable performance of those crowns compared with the crowns of the current study after cementation. Cement space may significantly influence the marginal accuracy of CAD-CAM fabricated monolithic zirconia crowns, and 30 mm of virtual cement thickness may significantly increase the VMD compared with those of 50 mm.49 Using luting agents with different Kale et al
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Vertical Marginal Discrepancy (µm)
160 148.88
140 120 100 80
85.51
60 40
43.21
20 0
9.79
Post-sintering
Post-glazing
Post-cementation
Specimen 1
Specimen 2
Specimen 3
Specimen 4
Specimen 5
Specimen 6
Figure 3. Box plot diagrams of individually measured VMD values for each group.
film thicknesses might have resulted in different post cementation marginal discrepancies,24 as studies have shown that a significant difference in film thickness may occur between resin-based and water-based luting agents as used in the present study.58 The cementation process had a significant effect on the VMD of CAD-CAM fabricated monolithic zirconia crowns in the present study. This result is in agreement with those of previous studies investigating the marginal discrepancy of ceramic crowns before and after cementation.24 Evidence shows that an increase in VMD should be expected as the consequence of forming film thickness of luting agent or any other medium for definitive or interim fixation of the crowns on their respective abutments.24,58 The results of the present study revealed an increase in VMD mean values of approximately 22 mm after cementation, which is in agreement with previously published studies58 and within the standards currently set by the International Organization for Standardization that require a film thickness that does not exceed the limit of 25 mm at the time of seating for water-based luting cements.59 In the current study, the mean VMD values calculated for the tested stages of restoration with CAD-CAM fabricated monolithic zirconia crowns were all within the threshold of clinically acceptable value, 120 mm. Among the individually measured values, only 2 exceeded that limit but were still under 150 mm as measured post cementation. Reporting the peak values for each measurement location to avoid misleading conclusions regarding studies evaluating the marginal discrepancy of crown restorations has already been emphasized.36,49 Matta et al36 have also calculated mean VMD values below 100 mm for zirconia copings cemented with a Kale et al
water-based luting agent under in vitro conditions, drawing attention to the priority of detailed reporting of the measurement results. They reported 12% of individually measured values over 100 mm and 5% over 150 mm of VMD in a group of 5 specimens. In the present study, individually measured values over 100 mm post cementation were 12.5% for 6 specimens, correlating with the results of previous publications.36 The results of this study should be interpreted considering that only 1 type of zirconia brand and cement were tested using 1 CAD-CAM system. These results should be corroborated with those of other clinical studies. CONCLUSIONS Within the limitations of this in vitro study, the following conclusions were drawn: 1. The glazing procedure had no significant effect on the VMD of CAD-CAM monolithic zirconia crowns. 2. The cementation process significantly affected the VMD of CAD-CAM monolithic zirconia crowns. 3. The mean VMD values were within the clinically acceptable limits for all tested stages of fabrication and cementation (<120 mm). REFERENCES 1. Tinschert J, Natt G, Hassenpflug S, Spiekermann H. Status of current CAD/ CAM technology in dental medicine. Int J Comput Dent 2004;7:25-45. 2. Abduo J, Lyons K, Swain M. Fit of zirconia fixed partial denture: a systematic review. J Oral Rehabil 2010;37:866-76. 3. Øilo M, Kvam K, Gjerdet NR. Load at fracture of monolithic and bilayered zirconia crowns with and without a cervical zirconia collar. J Prosthet Dent 2016;115:630-6. 4. Al-Amleh B, Lyons K, Swain M. Clinical trials in zirconia: a systematic review. J Oral Rehabil 2010;37:641-52. 5. Bachhav VC, Aras MA. Zirconia-based fixed partial dentures: a clinical review. Quintessence Int 2011;42:173-82. 6. Raigrodski AJ, Yu A, Chiche GJ, Hochstedler JL, Mancl LA, Mohamed SE. Clinical efficacy of veneered zirconium dioxide-based posterior partial fixed dental prostheses: five-year results. J Prosthet Dent 2012;108:214-22. 7. Schmitter M, Mussotter K, Rammelsberg P, Gabbert O, Ohlmann B. Clinical performance of long-span zirconia frameworks for fixed dental prostheses: 5-year results. J Oral Rehabil 2012;39:552-7. 8. Raigrodski AJ, Hillstead MB, Meng GK, Chung KH. Survival and complications of zirconia-based fixed dental prostheses: a systematic review. J Prosthet Dent 2012;107:170-7. 9. Pang Z, Chughtai A, Sailer I, Zhang Y. A fractographic study of clinically retrieved zirconia-ceramic and metal-ceramic fixed dental prostheses. Dent Mater 2015;31:1198-206. 10. Tan JP, Sederstrom D, Polansky JR, McLaren EA, White SN. The use of slow heating and slow cooling regimens to strengthen porcelain fused to zirconia. J Prosthet Dent 2012;107:163-9. 11. Batson ER, Cooper LF, Duqum I, Mendonça G. Clinical outcomes of three different crown systems with CAD/CAM technology. J Prosthet Dent 2014;112:770-7. 12. Zesewitz TF, Knauber AW, Northdurft FP. Fracture resistance of a selection of full-contour all-ceramic crowns: an in vitro study. Int J Prosthodont 2014;27:264-6. 13. 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. 14. de Kok P, Kleverlaan CJ, de Jager N, Kuijs R, Feilzer AJ. Mechanical performance of implant-supported posterior crowns. J Prosthet Dent 2015;114: 59-66. 15. Nakamura K, Harada A, Inagaki R, Kanno T, Niwano Y, Milleding P, et al. Fracture resistance of monolithic zirconia molar crowns with reduced thickness. Acta Odontol Scand 2015;73:602-8.
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