Incorporating Aminated Nanodiamonds to Improve the Mechanical Properties of 3D-Printed Resin-Based Biomedical Appliances

Enhancing 3D-printed denture base resins: A review of material innovations

The limited physical and mechanical properties of polymethyl methacrylate (PMMA), the current gold standard, necessitates exploring improved denture base materials. While three-dimensional (3D) printing offers accuracy, efficiency, and patient comfort advantages, achieving superior mechanics in 3D-printed denture resins remains challenging despite good biocompatibility and esthetics. This review investigates the potential of innovative materials to address the limitations of 3D-printed denture base materials. Thus, this article is organized to provide a comprehensive overview of recent efforts to enhance 3D-printed denture base materials, highlighting advancements. It critically examines the impact of incorporating various nanoparticles (zirconia, titania, etc.) on these materials' physical and mechanical properties. Additionally, it delves into recent strategies for nanofiller surface treatment and biocompatibility evaluation and explores potential future directions for polymeric composites in denture applications. The review finds that adding nanoparticles significantly improves performance compared to unmodified resins, and properties can be extensively enhanced through specific modifications, particularly silanized nanoparticles. Optimizing 3D-printed denture acrylics requires a multifaceted approach, with future research prioritizing novel nanomaterials and surface modification techniques for a novel generation of superior performance, esthetically pleasing, and long-lasting dentures.

Tritium-Labeled Nanodiamonds as an Instrument to Analyze Bioprosthetic Valve Coatings: A Case of Using a Nanodiamond Containing Coating on a Pork Aorta

Coatings with xenogenic materials, made of detonation nanodiamonds, provide additional strength and increase elasticity. A functionally developed surface of nanodiamonds makes it possible to apply antibiotics. Previous experiments show the stability of such coatings; however, studies on stability in the bloodstream and calcification of the material in natural conditions have yet to be conducted. Tritium-labeled nanodiamonds (negative and positive) were obtained by the tritium activation method and used to develop coatings for a pork aorta to analyze their stability in a pig's bloodstream using a radiotracer technique. A chitosan layer was applied from a solution of carbonic acid under high-pressure conditions to prevent calcification. The obtained materials were used to prepare a porcine conduit, which was surgically stitched inside the pig's aorta for four months. The aorta samples, including nanodiamond-coated and control samples, were analyzed for nanodiamond content and calcium, using the radiotracer and ICP-AES methods. A histological analysis of the materials was also performed. The obtained coatings illustrate a high in vivo stability and low levels of calcification for all types of nanodiamonds. Even though we did not use additional antibiotics in this case, the development of infection was not observed for negatively charged nanodiamonds, opening up prospects for their use in developing coatings.

The Impact of Technology Teaching in the Dental Predoctoral Curriculum on Students' Perception of Digital Dentistry

The goal was to assess dental students' perception of digital technologies after participating in a CAD/CAM exercise for scanning, designing, and manufacturing computer-aided provisional fixed dental restorations. A survey was conducted among second- (pre-D2 and post-D2), first- (D1, negative control), third-, and fourth-year dental students (D3 and D4, positive controls). Only OSU College of Dentistry students who completed the activity and completed the surveys were included. Seven questions were rated, which evaluated changes in knowledge, skill, interest, the importance of technology availability in an office, patients' perception of technology, the importance of having the technology, and the expected frequency of clinics utilizing the technology. Statistical analysis was performed with a significance level of 0.05. A total of 74 pre-D2 and 77 post-D2 questionnaires were completed. Additionally, 63 D1, 43 D3, and 39 D4 participants responded to the survey. Significant differences were found for "knowledge" and "skill" between the pre-D2 and post-D2 and pre-D2 and control groups (p < 0.001). There was a significant difference between the post-D2 participants and all the controls in terms of "interest" (p = 0.0127) and preference for in-practice technology availability (p < 0.05). There were significant results between the post-D2 participants and all the controls regarding the importance of technology availability in an office (p < 0.001) and the expected frequency of clinics utilizing the technology (p = 0.01). No significance was found for "value of technology to patients" and "the importance of having the technology". The presence of technology in practice and in educational academic environments significantly improved students' interest and perception of their knowledge and skill.

3D printed denture base material: The effect of incorporating TiO2 nanoparticles and artificial ageing on the physical and mechanical properties

OBJECTIVES

To evaluate the physical and mechanical properties of three-dimensional (3D) printed denture base resin incorporating TiO2 nanoparticles (NPs), subjected to a physical ageing process.

METHODS

Acrylic denture base samples were prepared by a Stereolithography (SLA) 3D printing technique reinforced with different concentrations (0.10, 0.25, 0.50, and 0.75) of silanated TiO2 NPs. The resulting nanocomposite materials were characterized in terms of degree of conversion (DC), and sorption/solubility flexural strength, impact strength, Vickers hardness and Martens hardness and compared with unmodified resin and conventional heat-cured (HC) material. The nanocomposites were reassessed after subjecting them to ageing in artificial saliva. A fractured surface was studied under a scanning electron microscope (SEM).

RESULTS

The addition of TiO2 NPs into 3D-printed resin significantly improved flexural strength/modulus, impact strength, Vickers hardness, and DC, while also slightly enhancing Martens hardness compared to the unmodified resin. Sorption values did not show any improvements, while solubility was reduced significantly. The addition of 0.10 wt% NPs provided the highest performance amongst the other concentrations, and 0.75 wt% NPs showed the lowest. Although ageing degraded the materials' performance to a certain extent, the trends remained the same. SEM images showed a homogenous distribution of the NPs at lower concentrations (0.10 and 0.25 wt%) but revealed agglomeration of the NPs with the higher concentrations (0.50 and 0.75 wt%).

SIGNIFICANCE

The outcomes of this study suggested that the incorporation of TiO2 NPs (0.10 wt%) into 3D-printed denture base material showed superior performance compared to the unmodified 3D-printed resin even after ageing in artificial saliva. The nanocomposite has the potential to extend service life of denture bases in future clinical use.

Cerium oxide nanozymes confer a cytoprotective and bio-friendly surface micro-environment to methacrylate based oro-facial prostheses

Poly-(methyl methacrylate) (PMMA) is the preferred biomaterial for orofacial prostheses used for the rehabilitation of naso-palatal defects. However, conventional PMMA has limitations determined by the complexity of the local microbiota and the friability of oral mucosa adjacent to these defects. Our purpose was to develop a new type of PMMA, i-PMMA, with good biocompatibility and better biological effects such as higher resistance to microbial adhesion of multiple species and enhanced antioxidant effect. The addition of cerium oxide nanoparticles to PMMA using a mesoporous nano-silica carrier and polybetaine conditioning, resulted in an increased release of cerium ions and enzyme mimetic activity, without tangible loss of mechanical properties. Ex vivo experiments confirmed these observations. In stressed human gingival fibroblasts, i-PMMA reduced the levels of reactive oxygen species and increased the expression of homeostasis-related proteins (PPARg, ATG5, LCI/III). Furthermore, i-PMMA increased the levels of expression of superoxide dismutase and mitogen-activated protein kinases (ERK and Akt), and cellular migration. Lastly, we demonstrated the biosafety of i-PMMA using two in vivo models: skin sensitization assay and oral mucosa irritation test, respectively. Therefore, i-PMMA offers a cytoprotective interface that prevents microbial adhesion and attenuates oxidative stress, thus supporting physiological recovery of the oral mucosa.

Changes in mechanical and bacterial properties of denture base resin following nanoceria incorporation with and without SBA-15 carriers

Poly (methyl methacrylate) (PMMA) is a commonly used material for the fabrication of biomedical appliances. Although PMMA has several advantages, it is susceptible to microbial insults with practical use. Therefore, different bioactive nanomaterials, such as nanoceria (CeN), have been proposed to enhance the properties of PMMA. In this study, we investigated the effect of the incorporation of CeN into PMMA with and without the use of mesoporous silica nanoparticle (SBA-15) carriers. The unmodified PMMA specimens (control, CTRL) were compared to groups containing SBA-15, CeN, and the synthesized SBA-15 impregnated with CeN (SBA-15@CeN) at different loading percentages. The mechanical and physical properties of the different SBA-15@CeN groups and their effects on cell viability were investigated, and the optimal CeN concentration was identified accordingly. Our results revealed that flexural strength was significantly (P < 0.01) reduced in the SBA-15@CeN_3× group (containing 3-fold the CeN wt. %). Although the surface microhardness increased with the increase in the wt. % of SBA-15@CeN, cell viability was significantly reduced (P < 0.001). The SBA-15@CeN_1× group had the optimal concentration and displayed significant resistance to single-and multispecies microbial colonization. Finally, the enzymatic activity of CeN was significantly high in the SBA-15@CeN_1× group. The proinflammatory markers (IL-6, IL-1β, TNF-α, CD80, and CD86) showed a significant (P < 0.001) multifold reduction in lipopolysaccharide-induced RAW cells treated with a 5-day eluate of the SBA-15@CeN_1× group. These results indicate that the addition of SBA-15@CeN at 1.5 wt % improves the biological response of PMMA without compromising its mechanical properties.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and amino-functionalized nanodiamond bionanocomposites for bone tissue defect repair

Injection-molded nanocomposites of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) with 6 % of 3-hydroxyvalerate (HV) and amino-nanodiamonds (nD-A) were produced and characterized to investigate the effect of functionalized nanodiamonds on mechanical and biological behavior to bone replacement application. To prepare mixtures of PHBHV and nD-A in different concentrations, nD-A was dispersed in chloroform by sonication with 40 % of amplitude. Three specimens were characterized by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (DRX), differential scanning calorimetry (DSC), 3-point flexural tests, dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). FTIR and TGA evidenced the existence of interactions between the nD-A and PHBHV. The crystallinity degree of PHBHV slightly reduced (~9 %) in nanocomposites and the morphology of the crystals changed. Nanocomposites achieved satisfactory dispersion and distribution of nD-A for low concentrations. Elastic modulus (E) increased from 1.96 ± 0.20 (PHBHV) to 2.59 ± 0.19 GPa (PHBHV/1.0%nD-A) (30 %). Despite the relatively limited dispersion, PHBHV/2.0 % nD-A had the best combination of E, strength, and maximum deformation. It had the highest glass transition temperature (43.1 vs 40.3 °C of PHBHV) and the best adhesion coefficient and reinforcement effectiveness. PHBHV-nD-A did not induce toxicity in 7 days and allowed cell fixation and expansion. These bionanocomposites should be considered for supplementary studies for bone tissue engineering.

3D-Printable Denture Base Resin Containing SiO2 Nanoparticles: An In Vitro Analysis of Mechanical and Surface Properties

PURPOSE

To evaluate the flexural strength (FS), impact strength (IS), surface roughness (Ra), and hardness of 3D-printed resin incorporating silicon dioxide nanoparticles (SNPs).

MATERIALS AND METHODS

A total of 320 acrylic specimens were fabricated with different dimensions according to test specifications and divided into a control group of heat denture base resin, and 3 test groups (80/test (n = 10) of unmodified, 0.25 wt%, and 0.5 wt% SNPs modified 3D-printed resin. 10,000 thermal cycles were performed to half of the fabricated specimens. FS, IS (Charpy impact), Ra, and hardness were evaluated and the collected data was analyzed with ANOVA followed by Tukey's post hoc test (α = 0.05).

RESULTS

Incorporating SNPs into 3D-printed resin significantly increased the FS, IS (at 0.5%) and hardness compared to unmodified 3D-printed resin (p < 0.001). However, the FS of pure 3D-printed and 3D/SNP-0.50% resin and IS of all 3D-printed resin groups were significantly lower than the control group (p < 0.0001). Hardness of 3D/SNP-0.25% and 3D/SNP-0.50% was significantly higher than control and unmodified 3D-printed resin (p < 0.0001), with insignificant differences between them. The Ra of all 3D-printed resin groups were significantly higher than control group (p < 0.001), while insignificant difference was found between 3D-printed groups. Thermal cycling significantly reduced FS and hardness for all tested groups, while for IS the reduction was significant only in the control and 3D/SNP-0.50% groups. Thermal cycling significantly increased Ra of the control group and unmodified 3D-printed resin (p < 0.001).

CONCLUSION

The addition of SNPs to 3D-printed denture base resin improved its mechanical properties while Ra was not significantly altered. Thermal cycling adversely affected tested properties, except IS of unmodified 3D-printed resin and 3D/SNP-0.25%, and Ra of modified 3D-printed resin.

Evaluation of the color stability of 3D printed resin according to the oxygen inhibition effect and temperature difference in the post-polymerization process

The aim of this study was to determine the color stability of 3D printed resin according to the post-curing conditions (polymerization conditions and temperature). Specimens were post-polymerized under different conditions of oxygen inhibition, such as on glycerin immersion (GLY), medium-low vacuum environment (VA), and oxygen contact (CON, the control group), and temperature (35 °C, 60 °C, and 80 °C). The degree of conversion (DC), water sorption (Wsp) and solubility (Wsl), surface roughness (Ra) were measured. Additionally, surface free energy (SFE), pH values of colorants were measured. Grape juice (grape), coffee, and curry were used as the colorants, and distilled water (DW) was used as a control. And the color value was measured before and after immersion using a spectrophotometer. Then, Calculated the color change. For statistical methods, The Shapiro-Wilk test performed to check for normality revealed that the data presented a normal distribution (p>0.05). ΔE values were analyzed using three-way ANOVA. DC, Wsp, Wsl, SFE, and Ra were analyzed using two-way ANOVA. To confirm the linear correlation, Pearson's correlation coefficient was determined. The threshold for significance (p) was set at 0.05 (95% confidence interval) for all tests. DC was the highest at 80 °C in the GLY group (95.08 ± 4.88%). And Wsl decreased with increasing temperature, and was lowest at 80 °C in the GLY group (0.46 ± 0.30 um/mm3). After the colorants were immersed for 30 days, as the temperature increased, ΔE decreased in the GLY group but not in the VA and CON groups, and was the lowest at 80 °C in the GLY group: (DW, 0.95 ± 0.45 [mean± SD]; grape, 6.45± 0.69; coffee, 4.50± 0.56; curry, 9.37± 1.40). There was also a significant inverse relation between DC and ΔE. A significant inverse relation was found between Wsl and DC, and a significant positive correlation was found between Wsl and ΔE. Wsp, SFE, and Ra did not affect color stability. In the post-polymerization process, increasing the temperature and GLY were effective in reducing ΔE, which was lowest at 80 °C in the GLY group. It was also observed that a complex mechanism between the DC, Wsl of 3D printed resin affects ΔE of the resin.

Tailoring of Optical Properties of Methacrylate Resins Enriched by HPHT Microdiamond Particles

Diamond particles have great potential to enhance the mechanical, optical, and thermal properties of diamond–polymer composites. However, the improved properties of diamond–polymer composites depend on the size, dispersibility, and concentration of diamond particles. In the present study, diamond–polymer composites were prepared by adding the microdiamond particles (MDPs) with different concentrations (0.2–1 wt.%) into polymers (acrylate resins) and then subjected to a photocuring process. The surface morphology and topography of the MDPs–polymer composites demonstrated a uniform high-density distribution of MDPs for one wt.% MPDs. Thermogravimetric analysis was employed to investigate the thermal stability of the MDPs–polymer composites. The addition of MDPs has significantly influenced the polymers’ thermal degradation. Absorption and emission spectra of thin layers were recorded through UV/Vis spectrophotometry and spectrofluorimetry. The obtained results revealed a significant increase in the fluorescence intensity of MDPs–polymer composites (at 1 wt.% of MDPs, a 1.5×, 2×, and 5× increase in fluorescence was observed for MDPs–green, MDPs–amber daylight, and MDPs–red resin, respectively) compared with the reference polymer resins. The obtained results of this work show the new pathways in producing effective and active 3D-printed optical elements.

3D-Printed Nanocomposite Denture-Base Resins: Effect of ZrO2 Nanoparticles on the Mechanical and Surface Properties In Vitro

Due to the low mechanical performances of 3D-printed denture base resins, ZrO2 nanoparticles (ZrO2NPs) were incorporated into different 3D-printed resins and their effects on the flexure strength, elastic modulus, impact strength, hardness, and surface roughness were evaluated. A total of 286 specimens were fabricated in dimensions per respective test and divided according to materials into three groups: heat-polymerized as a control group and two 3D-printed resins (NextDent and ASIGA) which were modified with 0.5 wt.%, 1 wt.%, 3 wt.%, and 5 wt.% ZrO2NPs. The flexure strength and elastic modulus, impact strength, hardness, and surface roughness (µm) were measured using the three-point bending test, Charpy’s impact test, Vickers hardness test, and a profilometer, respectively. The data were analyzed by ANOVA and Tukey’s post hoc test (α = 0.05). The results showed that, in comparison to heat-polymerized resin, the unmodified 3D-printed resins showed a significant decrease in all tested properties (p < 0.001) except surface roughness (p = 0.11). In between 3D-printed resins, the addition of ZrO2NPs to 3D-printed resins showed a significant increase in flexure strength, impact strength, and hardness (p < 0.05) while showing no significant differences in surface roughness and elastic modulus (p > 0.05). Our study demonstrated that the unmodified 3D-printed resins showed inferior mechanical behavior when compared with heat-polymerized acrylic resin while the addition of ZrO2NPs improved the properties of 3D-printed resins. Therefore, the introduced 3D-printable nanocomposite denture-base resins are suitable for clinical use.

3D Printed Customized Facemask for Maxillary Protraction in the Early Treatment of a Class III Malocclusion: Proof-of-Concept Clinical Case

In order to improve fit and comfort, a maxillary protraction facemask customized to the patient’s anatomy was produced by means of 3D face scanning, digital design and additive manufacturing. An 8-year-old patient in need of early treatment for the Class III malocclusion received a rapid palatal expander and a Petit-type facemask, whose components were digitally designed on a 3D scan of the patient’s face. For face scanning, the iPad Pro 2018 tablet (Apple, Cupertino, CA, USA) with the Bellus3D DentalPro application (Bellus3D, Campbell, CA, USA) was used. Facemask components were modelled with 3D Blender software. The rests were 3D printed in BioMed Clear biocompatible resin (Formlabs, Somerville, MA, USA), and the bar in stainless steel. For greater comfort, the internal surface of the rests was lined with a polymer gel pad (Silipos, Niagara Falls, NY, USA). The manufacturing procedure of the customized facemask is patented. The patient wore the facemask at night for a period of 9 months. The patient’s experience was evaluated with a questionnaire at 1 week, 3, 6, and 10 months of treatment. The customized facemask was well accepted by the patient and obtained the expected treatment outcome. Furthermore, 3D face scanning, 3D modelling and 3D printing allow for the manufacturing of customized facemasks with improved fit and comfort, favoring patient compliance and treatment success.

Modified Nanodiamonds as a Means of Polymer Surface Functionalization. From Fouling Suppression to Biosensor Design

The development of different methods for tuning surface properties is currently of great interest. The presented work is devoted to the use of modified nanodiamonds to control the wetting and biological fouling of polymers using optical sensors as an example. We have shown that, depending on the type of modification and the amount of nanodiamonds, the surface of the same fluorinated polymer can have both bactericidal properties and, on the contrary, good adhesion to the biomaterial. The precise control of wetting and biofouling properties of the surface was achieved by the optimization of the modified nanodiamonds thermal anchoring conditions. In vitro and in vivo tests have shown that the fixation of amine functional groups leads to inhibition of biological activity, while the presence of a large number of polar groups of mixed composition (amide and acid chloride) promotes adhesion of the biomaterial and allows one to create a biosensor on-site. A comprehensive study made it possible to establish that in the first 5 days the observed biosensor response is provided by cells adhered to the surface due to the cell wall interaction. On the 7th day, the cells are fixed by means of the polysaccharide matrix, which provides much better retention on the surface and a noticeably greater response to substrate injections. Nevertheless, it is important to note that even 1.5 h of incubation is sufficient for the formation of the reliable bioreceptor on the surface with the modified nanodiamonds. The approach demonstrated in this work makes it possible to easily and quickly isolate the microbiome on the surface of the sensor and perform the necessary studies of its substrate specificity or resistance to toxic effects.

Durable Oral Biofilm Resistance of 3D-Printed Dental Base Polymers Containing Zwitterionic Materials

Poly(methyl methacralyate) (PMMA) has long been used in dentistry as a base polymer for dentures, and it is recently being used for the 3D printing of dental materials. Despite its many advantages, its susceptibility to microbial colonization remains to be overcome. In this study, the interface between 3D-printed PMMA specimens and oral salivary biofilm was studied following the addition of zwitterionic materials, 2-methacryloyloxyethyl phosphorylcholine (MPC) or sulfobetaine methacrylate (SB). A significant reduction in bacterial and biofilm adhesions was observed following the addition of MPC or SB, owing to their protein-repellent properties, and there were no significant differences between the two test materials. Although the mechanical properties of the tested materials were degraded, the statistical value of the reduction was minimal and all the properties fulfilled the requirements set by the International Standard, ISO 20795-2. Additionally, both the test materials maintained their resistance to biofilm when subjected to hydrothermal fatigue, with no further deterioration of the mechanical properties. Thus, novel 3D-printable PMMA incorporated with MPC or SB shows durable oral salivary biofilm resistance with maintenance of the physical and mechanical properties.

Resin-Based Sealant with Bioactive Glass and Zwitterionic Material for Remineralisation and Multi-Species Biofilm Inhibition

Since pits and fissures are the areas most commonly affected by caries due to their structural irregularity, bioactive resin-based sealant (RBS) may contribute to the prevention of secondary caries. This study aims to investigate the mechanical, physical, ion-release, enamel remineralisation, and antibacterial capabilities of the novel RBS with bioactive glass (BAG) and 2-methacryloyloxyethyl phosphorylcholine (MPC). For the synthesis, 12.5 wt% BAG and 3 wt% MPC were incorporated into RBS. The contact angle, flexural strength, water sorption, solubility, and viscosity were investigated. The release of multiple ions relating to enamel remineralisation was investigated. Further, the attachments of bovine serum albumin, brain heart infusion broth, and Streptococcus mutans on RBS were studied. Finally, the thickness and biomass of a human saliva-derived microsm biofilm model were analysed before aging, with static immersion aging and with thermocycling aging. In comparison to commercial RBS, BAG+MPC increased the wettability, water sorption, solubility, viscosity, and release of multiple ions, while the flexural strength did not significantly differ. Furthermore, RBS with MPC and BAG+MPC significantly reduced protein and bacteria adhesion and suppressed multi-species biofilm attachment regardless of the existence of aging and its type. The novel RBS has great potential to facilitate enamel remineralisation and suppress biofilm adhesion, which could prevent secondary dental caries.

Changes in tribological and antibacterial properties of poly(methyl methacrylate)-based 3D-printed intra-oral appliances by incorporating nanodiamonds

It is essential for 3D-printed intra-oral appliances to be able to withstand the mechanical and microbial insult existent in the harsh environment of the oral cavity. Poly(methyl methacrylate) (PMMA)-based appliances are widely used in dentistry. Hence, the present study aimed to evaluate the role of nanodiamonds (NDs) as fillers to enhance the resistance to friction and wear. Using a solution-based mixing technique, 0.1 wt% ND was incorporated into the PMMA, and specimens were 3D-printed for tribological and bacterial analysis. The control specimens without ND fillers were tested against specimens with both amine-functionalized NDs (A-ND) and pure non-functionalized NDs (ND). The surface hardness test revealed a statistically significant increase in the Vickers micro-hardness (p < 0.001) in the nanocomposite groups. There was a significant reduction in the coefficient of friction (COF) (p < 0.01) in both the ND and A-ND nanocomposites compared to the stainless steel (SS) counter surfaces. However, for titanium (Ti)-based specimens, the COF of the control group was similar to that of A-ND but lower than that of ND. The wear resistance evaluation revealed that both the ND and A-ND groups displayed enhanced resistance to surface loss in comparison to the controls for both SS and Ti counter-surfaces (p < 0.001). Furthermore, both A-ND and ND exhibited significantly enhanced resistance to the formation of Streptococcus mutans biofilms after 48 h (p < 0.01) compared to the control group. Hence, we concluded that the addition of 0.1 wt% ND in the PMMA-based resin for 3D printing resulted in significant improvement in properties such as COF, wear resistance, and resistance to S. mutans, without any notable impact associated with the functionalization of the NDs.