In vitro study of fracture resistance and color stability of 3D-printed, milled hybrid ceramic, milled PMMA and prefabricated zirconia crowns for restoration of primary incisors

Background: The advancement of digital technology has expanded the options for pediatric dental restorations, offering more esthetic alternatives and optimizing tooth structure preservation. However, the mechanical properties of these emerging materials remain insufficiently investigated. This study evaluates the fracture resistance and color stability of 3D (Three-dimensional) - printed resin, milled hybrid ceramic, milled PMMA (Polymethyl Methacrylate) and prefabricated zirconia crowns in restoring primary incisors. Methods: An intact naturally exfoliated maxillary primary central incisor was collected and prepared for restoration. Digital impressions of the prepared incisor were taken, and resin dies were printed and used as supporting materials. Crowns were digitally fabricated using 3D-printed (RC), milled hybrid ceramic (HC), milled PMMA (PC) with thicknesses of 1 mm and prefabricated zirconia crowns (ZC) with the same thickness (n = 20 crowns/group) were prepared. After cementation using resin-modified glass ionomer cement, it was subjected to 1000 thermal cycles (5–55 ◦C). Fracture resistance was assessed using a universal testing machine with axial loading. Color stability was evaluated with a spectrophotometer after two weeks of immersion in orange juice and a carbonated beverage. Data were analyzed using one-way analysis of variance and post hoc tests (α = 0.05). Results: All crowns exhibited fracture resistance above 400 N. A statistically significant difference was found between RC and ZC (p = 0.0398). The lowest value is in the RC group (433.1 ± 61.9 N), and the highest is in the ZC group (511 ± 65.0 N). No significant differences were observed among the other groups. RC exhibited the highest color change (∆E = 5.4 ± 0.6), while HC, PC and ZC demonstrated better stability. Conclusions: 3D-printed resin, milled hybrid ceramic crowns and milled PMMA crowns demonstrated good fracture resistance and acceptable color stability for primary incisor restorations. These materials have potential clinical applications but require further in vivo studies to assess long-term effectiveness.

CAD/CAM; Crown; 3D printed resin; Hybrid ceramic; PMMA; Zirconia; Fracture resistance; Color stability

[1] Sasaki H, Ogawa T, Kawaguchi M, Sobue S, Ooshima T. Multiple fractures of primary molars caused by injuries to the chin: report of two cases. Endodontics and Dental Traumatology. 2000; 16: 43–46.

[2] Holsinger DM, Wells MH, Scarbecz M, Donaldson M. Clinical evaluation and parental satisfaction with pediatric zirconia anterior crowns. Pediatric Dentistry Journal. 2016; 38: 192–197.

[3] American Academy of Pediatric Dentistry. Clinical guideline on pediatric restorative dentistry. Pediatric Dentistry Journal. 2004; 26: 106–114.

[4] Chisini LA, Collares K, Cademartori MG, de Oliveira LJC, Conde MCM, Demarco FF, et al. Restorations in primary teeth: a systematic review on survival and reasons for failures. International Journal of Paediatric Dentistry. 2018; 28: 123–139.

[5] Waggoner WF. Restoring primary anterior teeth: updated for 2014. Pediatric Dentistry Journal. 2015; 37: 163–170.

[6] Clark L, Wells MH, Harris EF, Lou J. Comparison of amount of primary tooth reduction required for anterior and posterior zirconia and stainless steel crowns. Pediatric Dentistry Journal. 2016; 38: 42–46.

[7] van Noort R. The future of dental devices is digital. Dental Materials. 2012; 28: 3–12.

[8] Suganna M, Kausher H, Tarek Ahmed S, Sultan Alharbi H, Faraj Alsubaie B, Ds A, et al. Contemporary evidence of CAD-CAM in dentistry: a systematic review. Cureus. 2022; 14: e31687.

[9] Alabdullah JH, Daniel SJ. A systematic review on the validity of teledentistry. Telemedicine and e-Health. 2018; 24: 639–648.

[10] Beuer F, Schweiger J, Edelhoff D. Digital dentistry: an overview of recent developments for CAD/CAM generated restorations. British Dental Journal. 2008; 204: 505–511.

[11] Awada A, Nathanson D. Mechanical properties of resin-ceramic CAD/CAM restorative materials. The Journal of Prosthetic Dentistry. 2015; 114: 587–593.

[12] Mourouzis P, Arhakis A, Tolidis K. Computer-aided design and manufacturing crown on primary molars: an innovative case report. International Journal of Clinical Pediatric Dentistry. 2019; 12: 76–79.

[13] Alp G, Murat S, Yilmaz B. Comparison of flexural strength of different CAD/CAM PMMA-based polymers. Journal of Prosthodontics. 2019; 28: e491–e495.

[14] Díez-Pascual AM. PMMA-based nanocomposites for odontology applications: a state-of-the-art. International Journal of Molecular Sciences. 2022; 23: 10288.

[15] Zafar MS. Prosthodontic applications of polymethyl methacrylate (PMMA): an update. Polymers. 2020; 12: 2299.

[16] Kihara H, Sugawara S, Yokota J, Takafuji K, Fukazawa S, Tamada A, et al. Applications of three-dimensional printers in prosthetic dentistry. Journal of Oral Science. 2021; 63: 212–216.

[17] Atria PJ, Bordin D, Marti F, Nayak VV, Conejo J, Benalcázar Jalkh E, et al. 3D-printed resins for provisional dental restorations: comparison of mechanical and biological properties. Journal of Esthetic and Restorative Dentistry. 2022; 34: 804–815.

[18] Al-Halabi MN, Bshara N, Nassar JA, Comisi JC, Rizk CK. Clinical performance of two types of primary molar indirect crowns fabricated by 3D printer and CAD/CAM for rehabilitation of large carious primary molars. European Journal of Dentistry. 2021; 15: 463–468.

[19] Gresnigt MM, Özcan M, van den Houten ML, Schipper L, Cune MS. Fracture strength, failure type and Weibull characteristics of lithium disilicate and multiphase resin composite endocrowns under axial and lateral forces. Dental Materials. 2016; 32: 607–614.

[20] Lehmann F, Eickemeyer G, Rammelsberg P. Fracture resistance of metal-free composite crowns-effects of fiber reinforcement, thermal cycling, and cementation technique. The Journal of Prosthetic Dentistry. 2004; 92: 258–264.

[21] de Oliveira CB, Maia LG, Santos-Pinto A, Gandini Junior LG. In vitro study of color stability of polycrystalline and monocrystalline ceramic brackets. Dental Press Journal of Orthodontics. 2014; 19: 114–121.

[22] Douglas RD, Brewer JD. Acceptability of shade differences in metal ceramic crowns. The Journal of Prosthetic Dentistry. 1998; 79: 254–260.

[23] Cho L, Song H, Koak J, Heo S. Marginal accuracy and fracture strength of ceromer/fiber-reinforced composite crowns: effect of variations in preparation design. The Journal of Prosthetic Dentistry. 2002; 88: 388–395.

[24] Denry I, Kelly JR. State of the art of zirconia for dental applications. Dental Materials. 2008; 24: 299–307.

[25] Aldegheishem A, AlDeeb M, Al-Ahdal K, Helmi M, Alsagob EI. Influence of reinforcing agents on the mechanical properties of denture base resin: a systematic review. Polymers. 2021; 13: 3083.

[26] Alharbi N, Osman R, Wismeijer D. Effects of build direction on the mechanical properties of 3D-printed complete coverage interim dental restorations. The Journal of Prosthetic Dentistry. 2016; 115: 760–767.

[27] Jain S, Sayed ME, Shetty M, Alqahtani SM, Al Wadei MHD, Gupta SG, et al. Physical and mechanical properties of 3D-printed provisional crowns and fixed dental prosthesis resins compared to CAD/CAM milled and conventional provisional resins: a systematic review and meta-analysis. Polymers. 2022; 14: 2691.

[28] Owais AI, Shaweesh M, Abu Alhaija ES. Maximum occusal bite force for children in different dentition stages. European Journal of Orthodontics. 2013; 35: 427–433.

[29] Zhang Y, Lawn BR. Evaluating dental zirconia. Dental Materials. 2019; 35: 15–23.

[30] Sulaiman TA. Materials in digital dentistry—a review. Journal of Esthetic and Restorative Dentistry. 2020; 32: 171–181.

[31] Barizon KT, Bergeron C, Vargas MA, Qian F, Cobb DS, Gratton DG, et al. Ceramic materials for porcelain veneers: part II. Effect of material, shade, and thickness on translucency. The Journal of Prosthetic Dentistry. 2014; 112: 864–870.

[32] Revilla-León M, Özcan M. Additive manufacturing technologies used for processing polymers: current status and potential application in prosthetic dentistry. Journal of Prosthodontics. 2019; 28: 146–158.