1http://dx.doi.org/10.20396/bjos.v20i00.8664873 Volume 20 2021 e214873 Original Article ¹ Department of Prosthodontics and Periodontology, University of Campinas - Piracicaba Dental School, Piracicaba, SP, Brazil. 2 Department of Periodontology and Oral Implantology, Dental Research Division, Univeritas – University of Guarulhos, Guarulhos, SP, Brazil. 3 Department of Prosthodontics and Periodontology, University of São Paulo - Bauru Dental School, Bauru, SP, Brazil. 4 Department of Prosthodontics, Faculty of Technology and Sciences (UniFTC), Salvador, BA, Brazil. Corresponding author: Dr. Raissa Micaella Marcello Machado Department of Prosthodontics and Periodontology University of Campinas - Piracicaba Dental School Limeira avenue, 901 – Piracicaba, SP, Brazil. E-mail address: raissammm@ gmail.com Editor: Dr Altair A. Del Bel Cury Received: March 5, 2021 Accepted: March 29, 2021 Marginal misfit of heat-pressed milled wax-pattern and CAD/CAM crowns and its effect on stress distribution in implant-supported rehabilitations Michele Costa de Oliveira Ribeiro¹ , Raissa Micaella Marcello-Machado1,* , Dimorvan Bordin2 , Edmara T. P. Bergamo3 , Rafael Soares Gomes4 Aim: To compare the marginal fit of lithium disilicate CAD/CAM crowns and heat-pressed crowns fabricated using milled wax patterns, and evaluate its effect on stress distribution in implant- supported rehabilitation. Methods: A CAD model of a mandibular first molar was designed, and 16 lithium disilicate crowns (8/group) were obtained. The crown-prosthetic abutment set was evaluated in a scanning electron microscopy. The mean misfit for each group was recorded and evaluated using Student’s t-test. For in silico analysis, a virtual cement thickness was designed for the two misfit values found previously, and the CAD model was assembled on an implant-abutment set. A load of 100 N was applied at 30° on the central fossa, and the equivalent stress was calculated for the crown, titanium components, bone, and resin cement layer. Results: The CAD/CAM group presented a significantly (p=0.0068) higher misfit (64.99±18.73 µm) than the heat-pressed group (37.64±15.66 µm). In silico results showed that the heat-pressed group presented a decrease in stress concentration of 61% in the crown and 21% in the cement. In addition, a decrease of 14.5% and an increase of 7.8% in the stress for the prosthetic abutment and implant, respectively, was recorded. For the cortical and cancellous bone, a slight increase in stress occurred with an increase in the cement layer thickness of 5.9% and 5.7%, respectively. Conclusion: The milling of wax patterns for subsequent inclusion and obtaining heat-pressed crowns is an option to obtain restorations with an excellent marginal fit and better stress distribution throughout the implant-abutment set. Keywords: Dental materials. Dental marginal adaptation. Dental prosthesis, implant-supported. Microscopy, electron, scanning. Finite element analysis. https://orcid.org/0000-0001-7679-0502 https://orcid.org/0000-0001-7661-703X https://orcid.org/0000-0002-8466-9558 https://orcid.org/0000-0002-5006-2184 https://orcid.org/0000-0002-7989-0098 2 Ribeiro et al. Introduction The marginal misfit of dental restorations has been associated with clinical failures. It is commonly related to microleakage, caries, margin staining, debonding, and resto- ration fracture1-3. In addition, the misfit between the crown and implant-abutment set can lead to biofilm and food accumulation, which could result in peri-implant compli- cations4. Some studies have reported that marginal misfit can influence the stress distribution around restorations, where a thick cement layer increases the stress in itself and is harmful to the longevity of the restoration1,2. A 120 µm misfit was con- sidered as a minimum clinically acceptable value in the past, and the current studies still consider this value as a reference even with the higher accuracy of the current techniques and devices3,5,6. Technology devices such as computer-aided design/computer-aided manufac- turing (CAD/CAM) systems have been successfully used to improve restorative procedures in the dental field. This technology offers faster and more practical procedures to obtain ceramic restorations compared to the conventional manual method3,7 because it allows a chairside digital workflow without the need for physi- cal models8. A clinical study9 assessing implant-supported single crowns in the pos- terior region showed that the use of the CAD/CAM technique produced crowns with excellent adaptation in relation to interproximal and occlusal contacts, without the need for adjustments. Another option for fabricating dental restorations is the heat-press technique (HPT)3,7,10,11, where a tooth is waxed-up, invested in refractory material, and heated in an oven3,7,12. The space created by wax elimination is filled with a ceramic ingot that is heat-pressed to obtain the restoration12,13. The waxing-up procedure can be handmade (conventional method), or computer-aided designed and milled in wax blocks10-12. Mill- ing restoration directly from ceramic blocks decreases one step compared to milling those in wax blocks, which needs to be invested and heat-pressed. However, some studies report that the latter procedure is related to the production of a better fit than the former7,10,14,15. Furthermore, when several restorations are made, the milling pro- cess directly from single ceramic blocks could be slow to obtain a large number of restorations because of its hardness15. In contrast, milling from a wax block is faster, and the investment of the restorations for pressing can be made with several resto- rations at the same time16. CAD/CAM restorations have the advantage of good accuracy and a computer-con- trolled process that can provide well-defined and fitted margins17. In practice, the milled edges of thin crowns on hard materials can produce defects in their margins which worsens their fit and produce stresses in that region, which could lead to resto- ration of failure14,18. A possible solution would be a combination of CAD/CAM and HPT. From a digital design, a crown can be milled in a wax block10,12. Since wax presents a soft surface with low hardness, it is an easy material to be milled and consequently to produce high margin accuracy restorations18,19. This wax crown can be invested to create a ceramic restoration by HPT afterwards16,20. 3 Ribeiro et al. Different commercial presentations of the same material are available some- times21. One of these materials is lithium disilicate, a glass-ceramic material that has been well studied; however, it is still controversial whether the material pro- vides better edge stability and marginal fit7,22. Currently, this material is available in blocks for CAD/CAM or ingots for HPT to furnish all market demand3,7. Although many studies have compared the marginal fit of lithium disilicate CAD/CAM crowns to those made by HPT, the wax patterns of the HPT are often produced manually by dental technician7,12. As all manual labor, reproducibility is a factor that can compromise the comparison between such techniques7. However, this problem can be solved by a controlled milling process23. Additionally, the stress distribution in lithium disilicate implant-supported single crowns manufactured by the two techniques remains unclear, and its influence on the implant components and bone is still unclear. The objective of the present study was to compare the marginal fit of lithium disilicate CAD/CAM crowns and heat-pressed crowns fab- ricated using milled wax patterns and evaluate its effect on stress distribution in implant-supported rehabilitation. Material and Methods In vitro analysis Using a CAD software (Ceramill Mind; Amann Girrbach, Koblach, Vorarlberg, Austria) a mandibular first molar (height, 10.6 mm; buccal-lingual width, 10.8 mm; mesio-distal width, 11.4 mm) was designed over a universal prosthetic abutment (4.5 diameter, 6 mm height, 2.5 mm collar height). The relief adopted followed the standard of the software used, which is 0.05 mm. From this CAD, sixteen crowns were milled, eight from lithium disilicate blocks (IPS E.max CAD; Ivoclar), and eight from a wax block (Odontofix; Ribeirão Preto, São Paulo, Brazil). The crowns were milled under irrigation using a 5-axis milling unit (Cera- mill Motion 2 5X; Amann Girrbach, Koblach, Vorarlberg, Austria) using a new bur for each group. For the heat-pressed group, the wax-up was invested with a phosphate-bonded universal investment (IPS PressVest Premium; Ivoclar Viva- dent) and after heat pressing with a lithium disilicate ingot (IPS E.max Press; Ivoclar Vivadent) in a furnace (Programat P310, Ivoclar Vivadent) according to the manufacturer’s instructions. The crowns were sputter-coated with gold for evaluation using a scanning electron microscope (SEM) (JSM-5600LV, Jeol, Bos- ton, Massachusetts, USA)24. The crown was fixed with carbon adhesive tape from the occlusal surface to the base of the prosthetic abutment and positioned perpendicular to the stub. To avoid bias, the crowns were evaluated exactly in the way they were manufactured, without any kind of adjustment. The measurement was standardized on the center of the buccal, lingual, mesial, and distal faces with a zoom of 550x24,25. Four measures were made in each face with a distance of approximately 50 µm between them, and a mean of misfit was obtained for each crown (Figure 1). 4 Ribeiro et al. Normal data distribution was confirmed by the Shapiro-Wilk test and homogeneity by Lev- ene’s test. The mean misfit between the CAD/CAM and heat-pressed groups was evalu- ated by Student’s t-test. Statistical analysis was performed using the SAS system release 9.3 (SAS Institute Inc., Cary, NC, USA), and a significance level of 5% (α=0.05) was adopted. In silico analysis The same mandibular first molar CAD model used for milling the crowns was exported to SolidWorks software (SolidWorks 2013; Dassault Systèmes Solidworks Corp). The crown was assembled in a universal prosthetic abutment (4.5 mm width × 2.5 mm collar height × 6 mm height), which was screwed in a 4 mm width x 11 mm height morse taper implant (Intraoss, Itaquaquecetuba, São Paulo, Brazil). Both universal prosthetic abutment and implant CADs were supplied by the manufacturer (Intraoss). The implant was inserted into a jaw segment with cortical and cancellous bones. A virtual cement thickness was designed for the two values found previously in the marginal fit evaluation to form the two experimental models (Figure 2). The two models were exported to the Ansys Workbench software for mathematical analysis (Ansys Workbench 15.0; Canonsburg, PA, USA). A 0.6 mm tetrahedral mesh was generated after 5% convergence analysis. The elastic mod- ulus and Poisson’s ratio of each material were used in the simulations (Table 1). A load of 100 N was applied at 30° to the central fossa. The maximum principal stress (σmax) was calculated for the prosthetic crown, von Mises stress (σvM) for titanium com- Figure 1. Measurement of the gap existing between the crown and the prosthetic abutment. 15 kV x550 20 µm 46.5 µm 47.6 µm46.9 µm 48.4 µm Table 1. Material properties used in finite element models. Material Elastic modulus (GPa) (E) Poisson’s ratio (δ) Lithium disilicate26 95 0.20 Resin cement27 18.3 0.33 Titanium28 110 0.35 Cortical Bone28 13.6 0.26 Cancellous bone28 1.36 0.31 5 Ribeiro et al. ponents (implant and prosthetic abutment), and maximum shear stress (τmax) for bone (cancellous and cortical) and resin cement layer26,28. The results were evaluated qualita- tively by the stress distribution and quantitatively by the peak stress (MPa) generated in each model. All models were assumed to be homogeneous, isotropic, and linearly elastic. Results The mean misfit for the heat-press group was 37.64 ± 15.66 µm, statistically different (p = 0.0068) from the CAD/CAM group, which presented a mean of 64.99 ± 18.73 µm. These values were used to simulate the cement thickness in the finite element analy- sis (FEA) (Figure 2). The FEA results (Table 2) revealed an important influence of the cement thickness on the stress distribution in the two studied models. The most substantial difference occurred in the crown and cement layer, where the model restored with the lowest cement thickness (heat-press group) presented a decrease of 61% in the σmax of the crown and 21% in the τmax of the cement, both compared to the CAD/CAM group, restored with the highest cement thickness layer (Figure 3). Figure 2. Occlusal and sectional schematic view showing the crown dimensions and cement thickness used in the CAD/CAM (A) and heat-pressed milled wax-pattern (B) groups. 11.4 mm 10.6 mm 65 µm 38 µm A B 10.8 mm Table 2. Peak stress (MPa) and difference between groups after load. Component CAD/CAM Heat-press % stress Crown (σmax) 132 51 *61% Cement layer (τmax) 21.2 16.7 *21% Prosthetic abutment (σvM) 302 258 *14.5% Implant (σvM) 152 165 #7.8% Cortical bone (τmax) 29.9 31.8 #5.9% Cancellous bone (τmax) 11.4 12.1 #5.7% (*) Stress decrease. (#) Stress increase. 6 Ribeiro et al. The 38-µm cemented thickness model presented a decrease of 14.5% and an increase of 7.8% in the σvM for the prosthetic abutment and implant, respectively, compared to the 65-µm cemented thickness model (Figure 4). For the cortical and cancellous bone, a slight increase in τmax occurred with a decrease in the cement layer thickness of 5.9% and 5.7%, respectively (Figure 5). A C B D 132 Max 120 107 95.3 83.2 71 58.9 46.7 34.6 22.4 10.2 -1.92 -14.1 26.2 -38.4 Min 21.2 Max 19.7 18.2 16.7 15.3 13.8 12.3 10.8 9.34 7.86 6.39 4.91 3.43 1.95 -0.47 Min 132 Max 121 110 99 88 76.9 65.9 21,2 19,6 51 Max 16,7 Max 32.9 21.9 10.9 -0.125 -11.1 -22.1 Min 14,8 13,3 11,7 10,1 8,5 6,91 5,32 3,74 2,15 0,562 Min Figure 3. Stress distribution in the crown (σmax) and cement layer (τmax). Cervical view of the crown restored with a 65 µm (A) and 38 µm (B) cement layer showing the stress peak on the inner face. Isometric view of the cement layer with 65 µm (C) showing the stress peak on the occlusal face, and 38 µm (D) with the stress peak on the axial face. 7 Ribeiro et al. Figure 4. Stress distribution in the prosthetic abutment and implant (σvM). Vestibular view of the prosthetic abutment of the model restored with a 65 µm (A) and 38 µm (B) cement layer showing the stress peak on the prosthetic abutment collar. Isometric view of the implant of the model restored with a 65 µm (C) and 38 µm (D) cement layer showing the stress peak on the corresponding abutment collar level. A C B D 302 Max 280 259 237 216 194 173 151 130 108 86.7 65.2 43.7 22.2 0.666 Min 165 152 Max 130 118 107 94.8 83 71.2 59.4 47.7 35.9 24.1 12.3 0.541 Min 165 Max 154 142 130 118 107 94.8 83 71.2 59.4 47.6 35.8 24 12.2 0.452 Min 302 280 -22.1 Min 237 216 194 173 151 130 108 86,6 65,1 43,6 22 0,488 Min 8 Ribeiro et al. Discussion The concerns related to the study of restoration marginal fit have been addressed for many years29. Whenever a new material or technique arises, some studies resort to this methodology18. The concern about poorly fitting restorations is justifiable. Sev- eral studies have shown that a poor fit can cause many problems in the restoration such as cement dissolution, microleakage, and lower fracture strength7,18,23,30. Clini- cally acceptable values of 120 µm were established many years ago, regardless of the material and technique that are likely capable of generating better adjustment values than those reported in the past as acceptable5,23. Thus, this study evaluated, through in vitro and in silico analysis, the marginal fit and stress distribution of implant-sup- ported rehabilitations restored with lithium disilicate crowns manufactured by CAD/CAM and the heat-pressed technique. Regardless of the technique used for crown manufacture, the present study found values lower than 120 µm for both groups. This finding is supported by most studies related to the marginal fit of this material7,13,18,31. However, the result of a better fit Figure 5. Stress distribution in the cortical and cancellous bone (τmax). Exterior view of the cortical bone of the model restored with a 65 µm (A) and 38 µm (B) cement layer showing τmax in the cervical inferior area at the buccal portion. Exterior view of the cancellous bone of the model restored with a 65 µm (C) and 38 µm (D) cement layer showing τmax at buccal region. A C B D 29.9 Max 27.3 25 22.7 20.4 18.2 15.9 13.6 11.4 9.09 6.82 4.55 2.28 0.0112 Min 11.4 Max 10.3 9.43 8.58 7.72 6.86 5.15 4.3 3.44 2.58 1.73 0.872 0.0165 Min 12.1 Max 11.2 10.4 9.49 8.63 7.77 6.91 6.04 5.18 4.32 3.46 2.6 1.74 0.878 0.0166 Min 31.8 Max 29.9 27.2 25 22.7 20.4 18.2 15.9 13.6 11.4 9.08 6.82 4.55 2.28 0.0117 Min 31.8 12 9 Ribeiro et al. to the heat-pressed group in this study is controversial12. Some others consider that the CAD/CAM process, owing to its high accuracy, produces the best values for the marginal fit of the restorations12,13,30. However, these studies do not consider chipping that may occur at the margin of the thin restorations during the milling process, which could lead to higher misfit values18,19. One of the most accepted theories for the best fit of the heat-pressed group is pre- cisely the fact that it was made based on a milled wax pattern, which combined the high accuracy of the CAD/CAM system with the easy milling from wax, causing less occurrence of cervical defects on them12,18,19. Usually, the inaccuracies of the resto- ration fit occur in techniques where the manual skill of the technician is indispens- able, as in the conventional lost-wax method, to fabricate porcelain fused to metal crowns12. Although marginal fit problems are minimized with CAD/CAM restorations, when compared to manual techniques, the final fit quality of restoration will further depend on the type of material milled18,19. The ease of how a material is milled depends directly on its hardness, which together with fracture toughness will be responsible for the final restorations edge quality19. The greater the hardness and the lower the mate- rial fracture toughness, the greater will be the difficulty of milling and achieving a good quality margin18,19. The difference between the two cement layers, although statistically significant, could not be clinically relevant because such a small difference found could not pres- ent different behaviors in the clinical environment. However, FEA seems to show a relevant influence of the cement layer on the stress behavior through rehabilitation, mainly for the crown and the cement itself. This stress distribution difference, over time, could lead to different fatigue behaviors with different failure load32. It is pos- sible that the lower cement thickness in the heat-pressed group, as it presented the lowest stress value, would take longer to fail, which could decrease the chance of failure due to crown debonding when compared to the CAD/CAM group. It can also be seen that when a thicker cement layer is used, the stress peak in the crown is 2.5 times higher. This suggests that thinner cement layers favor the stress distribution throughout the crown ad cement layer and at the same time do not compromise in a relevant way the adjacent structures, such as the prosthetic abutment, implant, and bone, as the heat-pressed group showed only slightly higher values of stress for that component. Moreover, it is better for rehabilitation that the highest stress concen- tration is in the titanium components; ceramic restorations, due to their brittleness index, are more vulnerable to chipping33 than prosthetic abutments and implants that are ductile and therefore withstand a certain level of plastic deformation before fail- ure34. Hence, the higher stress in the ceramic crown could increase the possibility of crown chipping/fracture over time1,35 and increase the risk of infiltration and solubility of the cement layer. Although the heat-pressed group showed better results in both evaluations, this study had some limitations. This includes the absence of a mechanical test that allows the identification of the failure modes of the rehabilitation tested in the FEA, as it is numer- ical theoretical analysis. In addition, the lack of evaluation of the axial and occlusal discrepancies, since it is not possible to visualize the interior of the crown-prosthetic abutment set using the SEM, as the assessment restricted only to the margin of the 10 Ribeiro et al. restoration. Hence, further in vitro studies in this regard are needed to validate the results of the FEA, and to assess the internal misfit of the crowns. Despite these limitations, it is worth remembering that although one technique has excelled the other, even the worst result can be considered as a good performance, being approximately half of what is considered clinically acceptable5. Therefore, it is up to each dentist and prosthetic technician to consider which procedure would work better in the workflow of their office or laboratory15. In conclusion, both methods achieved marginal misfit values within the clinically acceptable limits. The milling of wax patterns for subsequent inclusion and obtaining heat-pressed crowns is an option to obtain restorations with an excellent marginal fit and better stress distribution throughout the rehabilitation. Conflicts Of Interest The authors state no conflicts of interest. Funding This study was supported by the São Paulo Research Foundation (FAPESP) (grant nº. 2014/23358-0), National Council for Scientific and Technological Development (CNPq) (grant nº. 308141/2006-7), and Coordination for the Improvement of Higher Education Personnel - Brazil (CAPES) – (grant nº. 001) Acknowledgements The authors are grateful to Intraoss for its support with the implant system CADs used in this study. References 1. Rojpaibool T, Leevailoj C. Fracture resistance of lithium disilicate ceramics bonded to enamel or dentin using different resin cement types and film thicknesses. J Prosthodont. 2017 Feb;26(2):141-9. doi: 10.1111/jopr.12372. 2. Tuntiprawon M, Wilson PR. The effect of cement thickness on the fracture strength of all-ceramic crowns. Aust Dent J. 1995 Feb;40(1):17-21. doi: 10.1111/j.1834-7819.1995.tb05607.x. 3. Dolev E, Bitterman Y, Meirowitz A. Comparison of marginal fit between CAD-CAM and hot- press lithium disilicate crowns. J Prosthet Dent. 2019 Jan;121(1):124-8. doi: 10.1016/j. prosdent.2018.03.035. 4. Vargas SP, Neves ACC, Vitti R, Amaral M, Henrique MN, Silva-Concílio LR. Influence of Different Ceramic Systems on Marginal Misfit. Eur J Prosthodont Restor Dent. 2017 Sep;25(3):127-30. doi: 10.1922/EJPRD_01702Vargas04. 5. McLean JW, von Fraunhofer JA. The estimation of cement film thickness by an in vivo technique. Br Dent J. 1971 Aug;131(3):107-11. doi: 10.1038/sj.bdj.4802708. 6. Daou EE, Baba NZ. Evaluation of Marginal and Internal Fit of Presintered Co-Cr and Zirconia Three-Unit Fixed Dental Prosthesis Compared to Cast Co-Cr. J Prosthodont. 2020 Dec;29(9):792-9. doi: 10.1111/jopr.13183. 11 Ribeiro et al. 7. Azar B, Eckert S, Kunkela J, Ingr T, Mounajjed R. The marginal fit of lithium disilicate crowns: Press vs. CAD/CAM. Braz Oral Res. 2018;32:e001. doi: 10.1590/1807-3107/2018.vol32.0001. 8. Joda T, Zarone F, Ferrari M. The complete digital workflow in fixed prosthodontics : a systematic review. BMC Oral Health. 2017 Sep;17(1):124. doi: 10.1186/s12903-017-0415-0. 9. Joda T, Brägger U. Time-efficiency analysis of the treatment with monolithic implant crowns in a digital workflow: a randomized controlled trial. Clin Oral Implants Res. 2016 Nov;27(11):1401-6. doi: 10.1111/clr.12753. 10. Homsy F, Bottin M, Özcan M, Majzoub Z. Fit accuracy of pressed and milled lithium disilicate inlays fabricated from conventional impressions or a laboratory-based digital workflow. Eur J Prosthodont Restor Dent. 2019 Feb;27(1):18-25. doi: 10.1922/EJPRD_01828Homsy08. 11. Schestatsky R, Zucuni CP, Dapieve KS, Burgo TAL, Spazzin AO, Bacchi A, et al. Microstructure, topography, surface roughness, fractal dimension, internal and marginal adaptation of pressed and milled lithium-disilicate monolithic restorations. J Prosthodont Res. 2020 Jan;64(1):12-9. doi: 10.1016/j.jpor.2019.05.004. 12. Shamseddine L, Mortada R, Rifai K, Chidiac JJ. Marginal and internal fit of pressed ceramic crowns made from conventional and computer-aided design and computer-aided manufacturing wax patterns: An in vitro comparison. J Prosthet Dent. 2016 Aug;116(2):242-8. doi: 10.1016/j.prosdent.2015.12.005. 13. Sadid-Zadeh R, Li R, Miller LM, Simon M. Effect of fabrication technique on the marginal discrepancy and resistance of lithium disilicate crowns: an in vitro study. J Prosthodont. 2019 Dec;28(9):1005-10. doi: 10.1111/jopr.13014. 14. Reich S, Gozdowski S, Trentzsch L, Frankenberger R, Lohbauer U. Marginal fit of heat-pressed vs. CAD/CAM processed all-ceramic onlays using a milling unit prototype. Oper Dent. 2008;33(6):644-50. doi: 10.2341/07-162. 15. Zeltner M, Sailer I, Mühlemann S, Özcan M, Hämmerle CHF, Benic GI. Randomized controlled within-subject evaluation of digital and conventional workflows for the fabrication of lithium disilicate single crowns. Part III: marginal and internal fit. J Prosthet Dent. 2017 Mar;117(3):354-62. doi: 10.1016/j.prosdent.2016.04.028. 16. Santos MJMC, Costa MD, Rubo JH, Pegoraro LF, Santos GC. Current all-ceramic systems in dentistry: a review. Compend Contin Educ Dent. 2015 Jan;36(1):31-7; quiz 38, 40. 17. Steinmassl O, Dumfahrt H, Grunert I, Steinmassl P-A. CAD/CAM produces dentures with improved fit. Clin Oral Investig. 2018 Nov;22(8):2829-35. doi: 10.1007/s00784-018-2369-2. 18. Gomes RS, Souza CMC de, Bergamo ETP, Bordin D, Del Bel Cury AA. Misfit and fracture load of implant-supported monolithic crowns in zirconia-reinforced lithium silicate. J Appl Oral Sci. 2017;25(3):282-9. doi: 10.1590/1678-7757-2016-0233. 19. Tsitrou EA, Northeast SE, van Noort R. Brittleness index of machinable dental materials and its relation to the marginal chipping factor. J Dent. 2007 Dec;35(12):897-902. doi: 10.1016/j.jdent.2007.07.002. 20. Sailer I, Benic GI, Fehmer V, Hämmerle CHF, Mühlemann S. Randomized controlled within-subject evaluation of digital and conventional workflows for the fabrication of lithium disilicate single crowns. Part II: CAD-CAM versus conventional laboratory procedures. J Prosthet Dent. 2017 Jul;118(1):43-8. doi: 10.1016/j.prosdent.2016.09.031.. 21. Guess PC, Schultheis S, Bonfante EA, Coelho PG, Ferencz JL, Silva NRFA. All-ceramic systems: laboratory and clinical performance. Dent Clin North Am. 2011 Apr;55(2):333-52, ix. doi: 10.1016/j.cden.2011.01.005. 22. Kim J-H, Jeong J-H, Lee J-H, Cho H-W. Fit of lithium disilicate crowns fabricated from conventional and digital impressions assessed with micro-CT. J Prosthet Dent. 2016 Oct;116(4):551-7. doi: 10.1016/j.prosdent.2016.03.028. 12 Ribeiro et al. 23. Boitelle P, Mawussi B, Tapie L, Fromentin O. A systematic review of CAD/CAM fit restoration evaluations. J Oral Rehabil. 2014 Nov;41(11):853-74. doi: 10.1111/joor.12205. 24. Castillo-Oyagüe R, Lynch CD, Turrión AS, López-Lozano JF, Torres-Lagares D, Suárez-García M-J. Misfit and microleakage of implant-supported crown copings obtained by laser sintering and casting techniques, luted with glass-ionomer, resin cements and acrylic/urethane-based agents. J Dent. 2013 Jan;41(1):90-6. doi: 10.1016/j.jdent.2012.09.014. 25. Barbosa Jr SA, Bacchi A, Barão VAR, Silva-Sousa YTC, Bruniera JF, Caldas RA, et al. Implant volume loss, misfit, screw loosening, and stress in custom titanium and zirconia abutments. Braz Dent J. 2020 Sep;31(4):374-9. doi: 10.1590/0103-6440202003643. 26. Schmitter M, Schweiger M, Mueller D, Rues S. Effect on in vitro fracture resistance of the technique used to attach lithium disilicate ceramic veneer to zirconia frameworks. Dent Mater. 2014 Feb;30(2):122-30. doi: 10.1016/j.dental.2013.10.008. 27. Lü L-W, Meng G-W, Liu Z-H. Finite element analysis of multi-piece post-crown restoration using different types of adhesives. Int J Oral Sci. 2013 Sep;5(3):162-6. doi: 10.1038/ijos.2013.50. 28. Cruz M, Wassall T, Toledo EM, da Silva Barra LP, Cruz S. Finite element stress analysis of dental prostheses supported by straight and angled implants. Int J Oral Maxillofac Implants. 2009 May-Jun;24(3):391-403. 29. Holmes JR, Bayne SC, Holland GA, Sulik WD. Considerations in measurement of marginal fit. J Prosthet Dent. 1989 Oct;62(4):405-8. doi: 10.1016/0022-3913(89)90170-4. 30. Mostafa NZ, Ruse ND, Ford NL, Carvalho RM, Wyatt CCL. Marginal fit of lithium disilicate crowns fabricated using conventional and digital methodology: a three-dimensional analysis. J Prosthodont. 2018 Feb;27(2):145-52. doi: 10.1111/jopr.12656. 31. Toniollo MB, Macedo AP, Silveira Rodrigues RC, Ribeiro RF, de Mattos MG. A three-dimensional finite element analysis of the stress distribution generated by splinted and nonsplinted prostheses in the rehabilitation of various bony ridges with regular or short morse taper implants. Int J Oral Maxillofac Implants. 2017;32(2):372-6. doi: 10.11607/jomi.4696. 32. Bonfante EA, Coelho PG. A critical perspective on mechanical testing of implants and prostheses. 2016 Mar;28(1):18-27. doi: 10.1177/0022034515624445. 33. Flask JD, Thompson GA, Singh M, Berzins DW. Edge chipping of translucent zirconia. J Prosthet Dent. 2021 Feb 11;S0022-3913(20)30801-5. doi: 10.1016/j.prosdent.2020.12.009. 34. Yamaguchi H, Takahashi M, Sasaki K, Takada Y. Mechanical properties and microstructures of cast dental Ti-Fe alloys. Dent Mater J. 2021 Jan;40(1):61-7. doi: 10.4012/dmj.2019-254. 35. Rezende CEE, Borges AFS, Gonzaga CC, Duan Y, Rubo JH, Griggs JA. Effect of cement space on stress distribution in Y-TZP based crowns. Dent Mater. 2017 Feb;33(2):144-51. doi: 10.1016/j.dental.2016.11.006.