Effect of Thermocycling on Surface Topography and Fracture Toughness of Milled and Additively Manufactured Denture Base Materials: An In-vitro Study PDF

Abdul-Monem and Hanno BMC Oral Health (2024) 24:267 BMC Oral Health https://doi.org/10.1186/s12903-024-03991-7 RESEARCH...

Abdul-Monem and Hanno BMC Oral Health (2024) 24:267 BMC Oral Health https://doi.org/10.1186/s12903-024-03991-7 RESEARCH Open Access Effect of thermocycling on surface topography and fracture toughness of milled and additively manufactured denture base materials: an in-vitro study Mohamed M. Abdul-Monem1,2 and Kenda I. Hanno3* Abstract Background Studies investigating thermocycling effect on surface topography and fracture toughness of resins used in digitally manufactured denture bases are few. The study aimed to assess the impact of thermocycling on surface topography and fracture toughness of materials used for digitally manufactured denture bases. Methods Water sorption, solubility, hardness, surface roughness, and fracture toughness of both three-dimensional (3D)-printed and computer-aided design, computer-aided manufacturing (CAD-CAM) milled specimens (n = 50) were assessed both prior to and following 2000 thermocycles, simulating 2 years of clinical aging. Surface hardness (n = 10) was measured using a Vickers hardness testing machine, surface roughness (n = 10) was determined by a contact profilometer, and fracture toughness (n = 20) was measured using the 3-point bend test, then studying the fractured surfaces was done via a scanning electron microscope (SEM). Prior to and following thermocycling, water sorption and solubility (n = 10) were assessed. Normally distributed data was tested using two-way repeated ANOVA and two- way ANOVA, while Mann Whitney U test and the Wilcoxon signed ranks test were used to analyze data that was not normally distributed (α < 0.05). Results Following thermocycling, Vickers hardness and fracture toughness of both groups declined, with a significant reduction in values of the 3D-printed resin (P <.001). The 3D-printed denture base resins had a rougher surface following thermocycling with a significant difference (P <.001). The sorption and solubility of water of both materials were not affected by thermocycling. Conclusions Before and after thermocycling, milled specimens had lower surface roughness and a greater degree of hardness and fracture toughness than 3D-printed specimens. Thermocycling lowered hardness and fracture toughness, and increased surface roughness in both groups, but had no effect on water sorption and solubility. The manuscript is original research work and is not derived from any dissertations or theses. *Correspondence: Kenda I. Hanno [email protected] Full list of author information is available at the end of the article © The Author(s) 2024. 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The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Abdul-Monem and Hanno BMC Oral Health (2024) 24:267 Page 2 of 11 Keywords CAD-CAM, Milled, 3D-printed, Thermocycling, Surface roughness, Fracture toughness, Hardness, Sorption, Solubility Background on average A recognized technique for subjecting Complete dentures (CDs) have been made using the tra- dental materials to water baths with varying temperatures ditional compression mold or the flask-pack-press for and simulating intraoral temperature changes is thermal more than 50 years. Polymethylmethacrylate (PMMA) cycling at 5° to 55 °C for 30 s [30, 33]. The surfaces of den- resin and heat polymerization have been used to produce tures may degrade as a result of thermal stresses brought CDs. on by these temperature variations [32, 34]. The advancement of CAD-CAM processes for CDs, Research has shown that CAD-CAM milled resins have however, has caused a notable revolution in this protocol improved properties compared with 3D-printed resins in recent years. In contrast to conventional methods, such as higher fracture toughness, lower water sorption CAD-CAM dentures may be constructed without the [35–37], and higher flexural modulus , while another need for time-consuming labor-intensive processes [3– study showed higher fracture toughness for 3D-printed 6]. Digital methods have the advantage of faster denture resins. Additional research [40–43] focused on the fabrication and fewer stages in the process, which can color stability and roughness of the surface of denture lower the likelihood of errors [7, 8]. base resins. There is insufficient data on how thermal The process of creating digital dentures was first estab- stresses affect the surface characteristics and fracture lished as a subtractive technique in which the dentures toughness of digitally manufactured resins used for den- were manufactured from pre-polymerized resin blocks. ture bases, thus it is important to test the effect of ther- Research has concluded that milled resins exhibit higher mal stresses to have a better prediction of which type will surface and mechanical properties [4, 9–12], reduced have a greater resistance to thermal changes and is better microbial colonization [13, 14], a decreased leach rate of suited for long term prostheses clinically. residual monomer , and comparable color stability The aim of our study is to evaluate the effect of ther- [16–18], in comparison to compression molded resins, mal cycling on Vickers hardness, surface roughness, because controlled conditions and high pressure were fracture toughness, sorption of water, and solubility of used during manufacturing of pre-polymerized blocks. denture base materials that have been CAD-CAM milled Later, the additive approach was introduced, in which and 3D-printed. The null hypothesis was that ther- digital technology was used to manufacture dentures mocycling would have no effect on the tested proper- layer by layer utilizing 3D printing technology and liquid ties of 3D-printed and CAD-CAM milled denture base resins polymerized using ultraviolet light. Dentistry materials. has made use of a variety of 3D printers and materials, such as fused deposition modeling (FDM), thermal inkjet Methods (TIJ), and selective laser sintering (SLS). This method The Committee of Research Ethics in Alexandria Univer- is more cost-effective because it allows for the simulta- sity, Faculty of Dentistry (IORG 0008839) has approved neous production of several products and eliminates the the research prior to any research-related activities. need for rotary tool wear and raw material waste [21, 22]. Two groups (n = 50) were investigated in this study, It is crucial to evaluate the surface qualities and 3D-printed resin (Denture base LP; Formlabs) and pre- mechanical characteristics of CAD-CAM materials to polymerized blanks (M-PM; Merz Dental GmbH), guarantee their success [23–27]. The wettability, hard- (Table 1). The estimated sample size was 100 specimens, ness, and surface properties of acrylic resins may have based upon the assumptions of a 95% level of confidence an impact on plaque buildup [28, 29]. Dentures are con- and an 80% study power [32, 44]. A computer program stantly exposed to temperature fluctuations brought on (G*power 3.0.10; Heinrich Heine University Düsseldorf ) by food and beverages [30, 31]. The characteristics of and Rosner technique was used to calculate the dental materials may be negatively impacted by these sample size. temperature fluctuations, especially if they are experi- For each material, Vickers hardness (n = 10), surface enced frequently. As a result, it is critical to evaluate roughness (n = 10), fracture toughness(n = 20), solubil- denture base material performance in settings that mimic ity, and sorption (n = 10) were evaluated before and after the intraoral environment. thermocycling. The specimens were created using a soft- Due to temperature variations brought on by ingested ware program (Autodesk Meshmixer; Autodesk Inc.) and foods and beverages, the intraoral environment is a ther- stored as standard tessellation language (STL) files. mally dynamic medium. The oral cavity’s tempera- ture fluctuates 20 to 50 times a day, or 10,000 times a year Abdul-Monem and Hanno BMC Oral Health (2024) 24:267 Page 3 of 11 Table 1 Composition of 3D printing resin and prepolymerized blanks for CAD-CAM milling Material Brand Name Composition 3D printing resin Denture Base Resin LP Formlabs 55–75% w/w urethane dimethacrylate Inc., MA, USA 15–25% w/w methacrylate monomers < 0.9% w/w phenyl bis (2,4,6- trimethylbenzoyl)-phosphine oxide Prepolymerized blanks for CAD-CAM milling M-PM, Merz Dental GmbH, Lütjenburg, Germany Pre-polymerized PMMA: >98% Methyl 2-methylprop-2-enoate Methyl2-methylpropenoate Methyl methacrylate: