1 Volume 22 2023 e237338 Original Article Braz J Oral Sci. 2023;22:e237338http://dx.doi.org/10.20396/bjos.v22i00.8667338 1 Graduate Program in Dentistry, Department of Restorative Dentistry, Federal University of Pelotas, Pelotas, RS, Brazil. ORCID 2 Graduate Program in Dentistry, São Leopoldo Mandic College, São Paulo, SP, Brazil. Corresponding author: catarinacumerlato@hotmail.com Federal University of Pelotas, Graduate Program in Dentistry Rua Gonçalves Chaves 457. 96015-560, Pelotas-RS, Brazil Tel./Fax: +55-53-3222.6690 Editor: Dr. Altair A. Del Bel Cury Received: October 21, 2021 Accepted: May 5, 2022 Fracture strength and failure load of CAD/CAM fabricated endocrowns performed with different designs Fernanda Angeloni de Souza1 , Catarina Borges da Fonseca Cumerlato1,* , Pedro Paulo Feltrin2 , Ricardo Tatsuo Inoue2 , Raquel Virginia Zanetti2 Aim: Endocrown restorations are commonly used to rehabilitate endodontically treated posterior teeth and their use is well- founded in these cases. However, to date, there is little scientific evidence of their behavior in anterior teeth. The aim of this in vitro study was to evaluate the compressive strength of upper central incisors teeth, restored with glass-ceramic total crowns by the conventional anatomical core technique, and compare them to teeth restored with endocrowns with and without the presence of ferrule. Methods: Thirty teeth were randomly distributed into three groups: GE2 - endocrown group with 2 mm ferrule, GE0 - endocrown group without a ferrule, and GC - conventional crown with intraradicular post group. Crowns were cemented and teeth submitted to the 45o compression test until the fracture happened. Fractured specimens were analyzed to determine the fracture pattern. Descriptive analysis of the variables was performed and one-way analysis of variance was utilized to analyze the data for significant differences at p < 0.05. Results: The results of the control group (284.5 ± 201.05N) showed the highest fracture resistance value, followed by the 2mm group (274.54 ± 199.43N) and by the 0mm group (263.81 ± 80.05N). There was no statistically significant difference between all the groups (p = 0.964). Conclusions: The absence of a cervical enamel necklace favored a debonding of the pieces and endodontically treated anterior teeth could be restored with endocrown, which could be considered a conservative and viable treatment option. Keywords: Endodontics. Computer-aided design. Crowns. Flexural strength. https://orcid.org/0000-0001-5591-2507 https://orcid.org/0000-0001-5943-6958 https://orcid.org/0000-0001-8570-3773 https://orcid.org/0000-0001-7960-3995 https://orcid.org/0000-0003-3823-856X 2 Souza et al. Braz J Oral Sci. 2023;22:e237338 Introduction Restoration of endodontically treated teeth (ETT) is often a clinical challenge because the ETT are frequently fragile and more susceptible to fracture than vital teeth due to loss of structural integrity, as a result of caries, trauma, previous restorations, and endodontic treatment1-3. With the development of adhesion methods, endocrowns can be used to restore supragingival structure of posterior demaged teeth. The advantages of using these restorations include fewer dental structures preparation compared with post and cores, as well as reduced intervention in the root canals4,5. This is an important advan- tage since it is know that the higher the ferrule of tooth, the higher the fracture resis- tance6. Moreover, compared to traditional methods they need less time to be made and fewer interfaces between each part of the restorations and the teeth. Five-year clinical observations reveal that 87.1% of endocrowns in posterior teeth functioned well, without fracture or debonding7,8. Considering all of these critical factors, endocrowns restorations are commonly used for restoring endodontically treated teeth9-11. Besides that, an in vitro study has investigated the fracture resistance of restorations from endodontically treated anterior teeth and promising results for endocrowns were found12. However, there is limited evidence about the endocrown’s behaviour with and without ferrule com- ponent, compared to conventional crown technique. In addition, it is not possible to find, in the available literature, accurate information on the use of endocrowns for the rehabilitation of incisors. In this sense, this study aimed to evaluate the fracture strength of teeth restored with glass-ceramic total crowns by the conventional anatomical core technique and compare them to teeth restored with endocrowns with and without the presence of ferrule. Material and Methods Ethical Issues All stages of this study were approved by the Human Research Ethics Committee of the School of Dentistry and Dental Research, São Leopoldo Mandic (Process Number 2.604.244/18). Specimen Preparation Thirty maxillary central incisors with complete root formation were collected from the Tooth Bank of the School of Dentistry at the Health Science Center/Federal University of São Paulo. Teeth were examined under ×4 magnification and cleaned to remove all tissues and debris. Then, specimens were randomly distributed into three groups (10 specimens for each): endocrown group with 2mm ferrule (GE2), endocrown group without ferrule (GE0) and conventional crown with intraradicular post group (GC) (Figure 1). 3 Souza et al. Braz J Oral Sci. 2023;22:e237338 GC GE2 GE0 Fiber Post Remaining of gutta percha Remaining of gutta percha Height of crown 10mm Height of crown 2mm Composite Crown Composite Endorown Figure 1. Image of the section type according to the amount of wear. GC - Control group; GE2 – endocrown with 2 mm ferrule group; GE0 – endocrown with 0 mm ferrule group. All teeth received conventional endodontic treatment, where root canals were pre- pared up to no. 60 K file using manual instrumentation (Dentsply Sirona, Bensheim, Germany) and irrigation with 2% chlorhexidine. Each canal was then obturated using lateral condensation of the gutta-percha (Dentsply Sirona, Bensheim, Germany), and sealed with sealing cement (AH26, Dentsply Sirona, Bensheim, Germany). The ana- tomic crowns were reduced according to the predetermined height for the experimen- tal groups. The cement enamel junction (CEJ) served as the circumferential reference for the linear measurement of the remaining coronal heights for each specimen. Endocrown Preparation and Conventional Crown Preparation Preparations for endocrowns were performed using a standardization device adapted from an optical microscope. Entrances and undercuts were made 2mm from the cervical margin, limited by the canal anatomy, and then, protected using an adhe- sive system (Ambar Universal, FGM, Joinville, Brazil) and a flowable resin (Opallis Flow, FGM, Joinville, Brazil). Roots from Group GC received glass fiber post #1 (White Post, FGM, Joinvile, SC, Brazil) with was anatomized with composite resin (Vitra APS, FGM, Joinville, Brazil) and cemented using an adhesive system (Ambar Universal; FGM, Joinville, Brazil) and dual cure resin cement (Allcem Core – FGM, Joinville, Brazil). To standardize the core height a transparent addition silicone mold (Transil, Ivoclar-Vivadent AG, Schaan, Switzerland), was filled and with the mold sitting on the tooth was light activated for 60 seconds. It resulted in final margins with width of 1.7 mm. Small adjustments were also performed in cases in which the core exceeded the height of 7 mm. Laboratory Phase Specimens were scanned using a desktop scanner (Ceramil Mind, Amann Girrbach, Koblach, Austria), and the virtual planning of the standardized crowns was started using the CAD system from the software Total Ceramil Mind. And then, crowns were 4 Souza et al. Braz J Oral Sci. 2023;22:e237338 milled on a 3D printer (Amann Girrbach DNA Motion 2, Koblach, Austria) using blocks of glass-ceramic resin (BRAVA BLOCK, FGM, Joinville, Brazil). Marginal adaptation was checked with the aid of a 4x magnifying glass (EyeMag Smart, Zeiss, Jena, Ger- many) and samples that showed mismatch were excluded and a new crown milled. Cimentation Aluminum oxide blasting (CoeJet, 3M ESPE, Minnesota, USA) was carried out with a pressure of about 3 bar in the internal surface of the crown until it became matte, and then was rinsed for 180 seconds. Subsequently, the adhesive system was applied, waiting for 20 seconds, and a light jet of air was applied for 5 seconds. The remaining coronary structure was cleaned with pumice and water prophylaxis and washed for 30 seconds to remove debris. Acid conditioning was performed on the enamel for 30 seconds and on the dentin for 15 seconds, and then ilhe struc- ture was rinsed and blot-dried (Ultra-Etch Indispense 35% - Ultradent). Afterwards an adhesive system was applied actively for 20 seconds, and dried for 5 seconds. The cementation of the glass-ceramic pieces was carried out with dual cure resin cement (Allcem Core, FGM, Joinville, Brazil). After reconstruction, the teeth were fixed in cylinders of a self-curing resin having a height of 30mm and 22mm in diameter and taken to the universal testing machine, model DL 2000 (EMIC, São José dos Pinhais, Brazil). Fracture Strength Test To perform the fracture strength test, each specimen in a fixation device was placed obliquely on the base of a universal testing machine (EMIC, São José dos Pinhais, Brazil). A compressive load was applied at a 135-degrees angle to the long axis of the tooth, on the internal and central face of the lingual cuspid of all ceramic crowns5. This was done by means of a metal rod 6 mm in diameter at a speed of 1.0 mm/min until failures occurred, represented by fracturing and/or debonding of the tooth and/or crown. The amount of force required to cause failure was recorded for each specimen in Newton (N)5 (Figure 2). 135.4° 135° 45° 45° Figure 2. Schematic drawing of test specimens subjected to load at 45° in a universal testing machine. Pressure from the rod tip was applied at a crosshead speed of 1 mm/min (3 mm below the incisal edge) on the palatal surface of the crown. 5 Souza et al. Braz J Oral Sci. 2023;22:e237338 Data analysis Statistical analysis was conducted with SPSS 23.0 (SPSS INC., Chicago, USA). Descriptive analysis was performed, presenting the maximum, minimum, means and standard deviations of the variables. One-way analysis of variance (ANOVA) was uti- lized to analyze the data for significant differences at p < 0.05. Results Fracture resistance Table 1 shows the descriptive analysis of the samples from each group tested. The results of the control group (284.5 ± 201.05N) showed the highest fracture resis- tance value, followed by the 2mm group (274.54 ± 199.43N) and by the 0mm group (263.81 ± 80.05N). The analysis of variance (ANOVA) showed no statistically significant difference among the tested groups (p = 0.964). Table 1. Descriptive analysis of the sample including the maximum, minimum, mean values of load failure with standard deviation for each tested group (Newton). Group N Max. Min. Mean ± SD P value 0.964 GE0 10 763.77 93.2 263.81±80.05 GE2 10 374.07 80.05 274.54±199.43 GC 10 664.89 131.02 284.50±201.05 Failure mode Types of fractures were classified according to the position of the failure and the dam- age to the prosthetic crown and the dental remnant. The classification was developed by us based on the observation of flaws presented (Figure 3). Type I Type II Type III Figure 3. Failure pattern of the specimens according to the type of fracture (I- Catastrophic fracture of the crown and/or remnant (below CEJ); II- Fracture of the crown with remnant above or at CEJ; III- Debonding of the glass-ceramic crown). 6 Souza et al. Braz J Oral Sci. 2023;22:e237338 The delimited groups were: I - Catastrophic fracture of the crown and/or remnant (below CEJ); II - Fracture of the crown with remnant above or at CEJ; III - Debonding of the glass-ceramic crown. In relation to the failure pattern, endocrowns with no ferrule (Group 0mm) obtained the highest rates of debonding without fracture of the part and/or dental remnant in 50% of the total sample (Type III), followed by catastrophic fracture of the den- tal remnant in 30% (Type I). And only 20% of the sample obtained a favorable fracture (Type II). The endocrown group with 2mm of ferrule showed a catastrophic failure pattern (Type I) in 60% of the sample followed by 30% of the crown fracture with the dental remnant at gingival level (Type II). Control group showed a higher fracture rate (50%) of the glass-ceramic piece without compromising the post or the dental remnant (Type II), followed by a fracture pattern involving the post and/or root remnant (Type I - 40%). Discussion The decision to restore a non-vital tooth with loss of coronary structure can be com- plex so aspects such as planning, selection of the restorative system and adequate cavity preparation must be carefully considered13. The classic alternative to rehabili- tate endodontically treated teeth is through the use of intraradicular posts as retain- ers of total crowns4,14. However, with the placement of post and cores, there is a risk of root perforation and thinning of the canal walls due to excessive preparation15. The advantages of endocrown restorations include less preparation of den- tal structures compared to posts and cores, as well as reduced intervention in the root canals. Compared to traditional methods, they need less laboratory and clinical time for the treatment to be completed16-18. In addition, the masticatory stresses and forces received to the tooth are better dissipated when endocrows are placed19. Nevertheless, some studies show that the full crown is still more reliable than endocrown4,20. From the results of this study, we could observe that the group with no ferrule effect showed greater resistance to compression. However, when it was compared to the group with 2mm of ferrule, the group with no ferrule exhibited a higher rate of debond- ing. This may be attributed to the fact that the surface available for the adhesive joint is reduced, the cementation is only in dentin substrate and there is no ferrule for a better distribution of force, corroborating with another studies2-5,7,10,11,18. On the other hand, the group with 2mm of ferrule, showed lower rates of fracture resistance, and the worst results when assessing the fracture pattern of the pieces, since 60% of the samples had catastrophic fractures (Type I) corroborating with the findings from recent studies8,21. In contrast, some studies observed that the presence of ferrule increased fracture resistance2,6. Extrapolating to the clinical 7 Souza et al. Braz J Oral Sci. 2023;22:e237338 environment, this type of fracture are critically and normally irreparable leading to tooth extraction. The control group has shown a higher fracture rate (50%) of the glass-ceramic piece without compromising the fiber post or the remnant (Type II), agreeing with several authors4,18-23. In relation to failure mode, it has been reported in literature a maximum incisal forces of almost always below 200N for restorations in anterior teeth24,25. Our research demonstrated the need of a greater force for fracturing the central incisors than the normal values of oblique loads described in the literature, corroborating with some recent studies10,19,22,23. Moreover, it is worth mentioning that this study applied only a static dynamic load, being a limitation that should be considered. In conclusion, endodontically treated anterior teeth with a ferrule effect of at least 2 mm can be restored with endocrown, as well as using a glass fiber post with an adhe- sive crown/endocrown. No statistically significant difference was found in fracture resistance and failure mode in upper central incisors cemented with glass-ceramic resin comparing total crown with glass fiber post and endocrown with 0mm and 2mm of a template. In this sense, crowns and endocrowns fabricated from machin- able glass-ceramic resin blocks are a viable alternative to the restoration of anterior endodontically treated teeth. Acknowledgments The authors declare no potential conflicts of interest. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. Author Contribution Conceptualization: Zanetti RV. Data curation: de Souza FA and Cumerlato CBF. For- mal analysis: de Souza FA and Zanetti RV. Investigation: de Souza FA. Methodology: Feltrin PP, Inoue RT. Project administration: Zanetti RV. Resources: Souza FA and Zanetti RV. Software: de Souza FA. Supervision: Zanetti RV. Validation: de Souza FA. Visualization: Cumerlato CBF, Feltrin PP, Inoue RT. Writing - original draft: de Souza FA and Cumerlato CBF. Writing - review & editing: Zanetti RV, Feltrin PP, Inoue RT. All authors actively participated in the discussion of the manuscript’s findings, revised, and approved the final version of the manuscript. References 1. Skupien JA, Opdam NJ, Winnen R, Bronkhorst EM, Kreulen CM, Pereira-Cenci T, et al. Survival of restored endodontically treated teeth in relation to periodontal status. Braz Dent J. 2016 Jan-Feb;27(1):37-40. doi: 10.1590/0103-6440201600495.  2. Santos Pantaleón D, Morrow BR, Cagna DR, Pameijer CH, Garcia-Godoy F. Influence of remaining coronal tooth structure on fracture resistance and failure mode of restored endodontically treated maxillary incisors. J Prosthet Dent. 2018 Mar;119(3):390-6. doi: 10.1016/j.prosdent.2017.05.007. 8 Souza et al. Braz J Oral Sci. 2023;22:e237338 3. Gulec L, Ulusoy N. Effect of endocrown restorations with different CAD/CAM materials: 3D finite element and weibull analyses. Biomed Res Int. 2017;2017:5638683. doi: 10.1155/2017/5638683. 4. Dejak B, Mlotkowski A. Strength comparison of anterior teeth restored with ceramic endocrowns vs custom-made post and core. J Prosthet Dent. 2018 Apr;62(2):171-6. doi: 10.1016/j.jpor.2017.08.005. 5. Kanat-Ertürk B, Saridağ S, Köseler E, Helvacioğlu-Yiğit D, Avcu E, Yildiran-Avcu Y. Fracture strengths of endocrown restorations fabricated with different preparation depths and CAD/CAM materials. Dent Mater J. 2018 Mar;37(2):256-65. doi: 10.4012/dmj.2017-035. 6. Pereira JR, de Ornelas F, Conti PCR, do Valle AL. Effect of a crown ferrule on the fracture resistance of endodontically treated teeth restored with prefabricated posts. J Prosthet Dent. 2006 Jan;95(1):50-4. doi: 10.1016/j.prosdent.2005.10.019. 7. Bindl A, Richter B, Mörmann WH. Survival of ceramic computer-aided design/manufacturing crowns bonded to preparations with reduced macroretention geometry. Int J Prosthodont. 2005 May-Jun;18(3):219-24. doi: 10.1016/j.prosdent.2005.09.002. 8. Salameh Z, Sorrentino R, Ounsi HF, Sadig W, Atiyeh F, Ferrari M. The effect of different full- coverage crown systems on fracture resistance and failure pattern of endodontically treated maxillary incisors restored with and without glass fiber posts. J Endod. 2008 Jul;34(7):842-6. doi: 10.1016/j.joen.2008.03.025. 9. Zarone F, Sorrentino R, Apicella D, Valentino B, Ferrari M, Aversa R, et al. Evaluation of the biomechanical behavior of maxillary central incisors restored by means of endocrowns compared to a natural tooth: A 3D static linear finite elements analysis. Dent Mat. 2006 Nov;22(11):1035-44. doi: 10.1016/j.dental.2005.11.034. 10. El-Badawy AA, El Aziz MH, Omar EA. Failure load of maxillary central incisor restored with CAD/CAM endocrown using different designs. Int J Dent Sci Res. 2019;7(1):5-9. doi: 10.12691/ijdsr-7-1-2. 11. El-Damanhoury HM, Haj-Ali RN, Platt JA, Fracture resistance and microleakage of endocrowns utilizing three CAD-CAM blocks. Oper Dent. 2015 Mar-Apr;40(2):201-10. doi: 10.2341/13-143-L. 12. Ramírez-Sebastià A, Bortolotto T, Cattani-Lorente M, Giner L, Roig M, Krejci I. Adhesive restoration of anterior endodontically treated teeth: influence of post length on fracture strength. Clin Oral Invest. 2014;18(2):545-54. doi: 10.1007/s00784-013-0978-3. 13. Ploumaki A, Bilkhair A, Tuna T, Stampf S, Strub JR. Sucess rates of prosthetic restorations on endodontically treated teeth: a systematic review after 6 years. J Oral Rehabil. 2013 Aug;40(8):618-30. doi: 10.1111/joor.12058. 14. Mannocci F, Bertelli E, Sherriff M, Watson TF, Pitt Ford TR. Three-year comparison of survival of endodontically teeth restores with full case coverage or with direct composite restoration. J Prosthet Dent. 2002 Sep;88(3):297-301. doi: 10.1067/mpr.2002.128492. 15. Clavijo VGR, Souza NC de, Kabbach W, Calixto LR, Andrade MF de, Susin AH. [Endocrown restorations: an approach for non-vital posterior teeth]. Clin Inter J Braz Dent. 2007;3(3):246-52. Portuguese. 16. Shin Y, Park S, Park JW, Kim KM, Park YB, Roh BD. Evaluation of the marginal and internal discrepancies of CAD-CAM endocrowns with different cavity depths: an in vitro study. J Prosthet Dent. 2017 Jan;117(1):109-15. doi: 10.1016/j.prosdent.2016.03.025. 17. Helal MA, Wang Z. Biomechanical assessment of restored mandibular molar by endocrown in comparison to a glass fiber post-retained conventional crown: 3d finite element analysis. J Prosthodont. 2019 Dec;28(9):988-96. doi: 10.1111/jopr.12690. 18. Bankoglu Gungor M, Turhan Bal B, Yilmaz H, Aydin C, Karakoca Nemli S. Fracture strength of CAD/CAM fabricated lithum disilicate and resin nano ceramic restorations used for endodocntically treated teeth. Dent Mat J. 2017 Mar;36(2):135-41. doi: 10.4012/dmj.2016-017. 9 Souza et al. Braz J Oral Sci. 2023;22:e237338 19. Chang CY, Kuo JS, Lin YS, Chang YH. Fracture resistance and failure modes of CEREC endo-crowns and conventional post and core-supported CEREC crowns. J Dental Sci. 2009 Sep;4(3):110-7. doi: 10.1016/S1991-7902(09)60016-7. 20. Silva-Sousa AC, Moris ICM, Simões Barbosa AF, Corrêa Silva-Sousa YT, Sousa-Neto MD, Ferreira Pires CR, et al. Effect of restorative treatment with endocrown and ferrule on the mechanical behavior of anterior endodontically treated teeth: An in vitro analysis. J Mech Behav Biomed Mat. 2020 Dec;112:104019. doi: 10.1016/j.jmbbm.2020.104019. 21. Clausson C, Schroeder CC, Goloni PV, Farias FAR, Passos L, Zanetti RV. Fracture resistance of CAD/CAM lithium disilicate of endodontically treated mandibular damaged molars based on different preparation designs. Int J Biomater. 2019 May;2019:2475297. doi: 10.1155/2019/2475297. 22. Casagrande DDA. [Analysis of the compressive strength at 45° of full lithium disilicate crowns cemented in endodontically treated maxillary central incisors with 2mm and 4mm reconstruction (Buildup) with composite resin] [dissertation]. Campinas: São Leopoldo Mandic College; 2019. Portuguese. 23. Gresnigt MMM, Özcan M, van den Houten MLA, Schipper L, Cune MS. Fracture strength, failure type and Weibull characteristics of lithium disilicate and multiphase resin composite endocrowns under axial and lateral forces. Dent Mater. 2016 May;32(5):607-14. doi: 10.1016/j.dental.2016.01.004. 24. Qing H, Zhu Z, Chao Y, Zhang W. In vitro evaluation of the fracture resistance of anterior endodontically treated teeth restored with glass fiber and zircon posts. J Prosthet Dent. 2007 Feb;97(2):93-8. doi: 10.1016/j.prosdent.2006.12.008. 25. Tan PL, Aquilino SA, Gratton DG, Stanford CM, Tan SC, Johnson WT, et al. In vitro fracture resistance of endodontically treated central incisors with varying ferrule heights and configurations. J Prosthet Dent. 2005 Apr;93(4):331-6. doi: 10.1016/j.prosdent.2005.01.013.