The impact of base design and restoration type on the resin consumption, trueness, and dimensional stability of dental casts additively manufactured from liquid crystal display 3D printers.

PURPOSE: To evaluate the effects of two base types and three restoration designs on the resin consumption and trueness of the 3D-printed dental casts. Additionally, the study explored the dimensional stability of these 3D-printed dental casts after 1 year of storage. MATERIALS AND METHODS: Various types of reference dental casts were specifically designed to represent three types of dental restoration fabrications, including full-arch (FA), long-span (LS), and single-unit (SU) prostheses. The reference casts were digitized with a dental laboratory scanner and used to create flat and hollow base designs (N = 18) for the 3D-printed study casts. The 3D-printed study casts were digitized and evaluated against their corresponding references immediately after 3D printing and again after 1 year of storage, with the trueness quantified using the root mean square error (RMSE) at both time points. Volumes of resin used were recorded to measure resin consumption, and the weights of the 3D-printed study casts were also measured. The data were analyzed using two-way ANOVA and a Tukey post hoc test, α = 0.05. RESULTS: Volumetric analysis showed the flat-base design had significantly higher resin consumption with weights for the FA group at 42.51 ± 0.16 g, the LS group at 31.64 ± 0.07 g, and the SU group at 27.67 ± 0.31 g, as opposed to 26.22 ± 1.01 g, 22.86 ± 0.93 g, and 20.10 ± 0.19 g for the hollow designs respectively (p < 0.001). Trueness, assessed through two-way ANOVA, revealed that the flat-base design had lower RMSE values indicating better trueness in the LS (54 ± 6 µm) and SU (59 ± 7 µm) groups compared to the hollow-base design (LS: 73 ± 5, SU: 99 ± 11 µm, both p < 0.001), with no significant difference in the FA group (flat-base: 50 ± 3, hollow: 47 ± 5 µm, p = 0.398). After 1 year, the flat-base design demonstrated superior dimensional stability in the LS (flat base: 56 ± 6 µm, hollow base: 149 ±45 µm, p < 0.001) and SU groups (flat base: 95 ± 8 µm, hollow base: 183 ±27 µm, p < 0.001), with the FA group showing no significant difference in the base design (flat base: 47 ± 9, hollow base: 62 ± 12 µm, p = 0.428). CONCLUSIONS: The hollow-base design group showed lower resin consumption than the flat-base design group. However, the flat-base designs exhibited superior trueness and less distortion after 1 year of storage. These findings indicate that despite the higher material usage, flat-base designs provide better initial accuracy and maintain their dimensional stability over time for most groups.

EFFECTIVENESS OF RESIN INFILTRATION IN CARIES INHIBITION AND AESTHETIC APPEARANCE IMPROVEMENT OF WHITE-SPOT LESIONS: AN UMBRELLA REVIEW.

OBJECTIVES: Resin infiltration technique is a minimal interventive approach to manage white-spot lesions. The present umbrella review aimed to comprehensively appraise the previously published systematic reviews on the effectiveness of resin infiltration in arresting caries progression and improving the aesthetic appearance of white-spot lesions. MATERIAL AND METHODS: Ten electronic databases were searched between January 1960 and May 2021. Only systematic reviews published in English on the use of resin infiltration in primary or permanent teeth were included. The degree of overlap across each review was calculated using the Corrected Covered Areas method and their evidence quality were assessed using A MeaSurement Tool to Assess systematic Reviews 2 assessment tool. Umbrella meta-analysis was carried out using a random-effects model. RESULTS: Thirteen systematic reviews were chosen, but only eight were eligible for an umbrella meta-analysis. The overall Corrected Covered Areas value was very high (19.8%), whereas only three studies were classified as 'High Quality'. Qualitative synthesis suggested that resin infiltration demonstrated acceptable aesthetic results, whereas quantitative analysis showed favourable outcomes in minimizing the risk of caries progression (RR: 0.32; 95% CI: 0.29-0.36). White-spot lesions treated with resin infiltrant in permanent teeth demonstrated a lower risk of caries progression (P < .001) than primary teeth. Overall, low data heterogeneity was observed (I2: 0%-20%). However, quantitative umbrella analysis on the aesthetic outcome was unable to perform due to limited data. CONCLUSION: Resin infiltration can be regarded as an effective treatment modality in minimizing the risk of caries progression and improving the aesthetic appearance of white-spot lesions. Future well-designed high-quality systematic reviews with long-term follow-up and more control of confounding variables are warranted.

Synthesis and Characterization of Novel Quaternary Ammonium Urethane-Dimethacrylate Monomers-A Pilot Study.

Six novel urethane-dimethacrylate analogues (QAUDMAs) were synthesized and characterized. They consisted of the 2,4,4,-trimethylhexamethylene diisocyanate (TMDI) core and two methacrylate-terminated wings containing quaternary ammonium groups substituted with alkyl chains of 8, 10, 12, 14, 16, or 18 carbon atoms. QAUDMAs, due to the presence of quaternary ammonium groups, may have possible antibacterial effects. Since they showed satisfactory physicochemical properties, they will be subjected to further research towards the development of dental composites with a capacity to reduce secondary caries. The synthesis of QAUDMAs included three stages: (i) transesterification of methyl methacrylate (MMA) with N-methyldiethanolamine (MDEA), (ii) N-alkylation of the tertiary amino group with alkyl bromide, and (iii) addition of TMDI to the intermediate achieved in the second stage. The formation of QAUDMAs was confirmed by 1H and 13C NMR. They were characterized for density (dm), viscosity (η), refractive index (RI), glass transition temperature (Tg), polymerization shrinkage (S), and degree of conversion (DC). QAUDMAs were yellow, viscous resins (the η values ranged from 1.28 × 103 to 1.39 × 104 Pa·s, at 50 °C). Their RI ranged from 1.50 to 1.52, Tg from -31 to -15 °C, DC from 53 to 78%, and S from 1.24 to 2.99%, which is appropriate for dental applications.

Fluorescence of natural teeth and restorative materials, methods for analysis and quantification: A literature review.

OBJECTIVE: This review integrates published scientific information about the fluorescence of natural teeth, dental resins and ceramics, and the main methods of analysis and quantification presented in the literature. OVERVIEW: Fluorescence is an emission of light (photons) by a substance that has absorbed light of higher energy. In natural teeth, it is more intense in the dentin than in the enamel and presents a bluish-white color. In dental resins and ceramics, fluorescence is obtained by the incorporation of materials that contain rare-earth luminescence centers (more precisely lanthanide luminescence centers), which allows these artificial materials to simulate natural teeth in a more beautiful and vital-looking way. However, the lack of knowledge about this optical phenomenon on the part of professionals indicates the need for more scientific studies and dissemination on this topic. CONCLUSIONS: Aesthetic materials have variable spectral compositions and fluorescence intensities, which are not always compatible with natural teeth. The fluorescence of teeth and restorative materials can be influenced by several factors, such as aging, temperature, and bleaching. Several devices for fluorescence evaluation and quantification are used in studies under different methodologies, but the small number of studies on the subject make it difficult to compare their results. CLINICAL SIGNIFICANCE: Fluorescence is a fundamental optical property for aesthetic rehabilitations since its presence and intensity in the restorative materials allows achieving an aesthetic result much closer to reality. However, the fluorescent behavior of natural teeth and aesthetic restorative materials is not yet fully understood by researchers and clinicians. Greater understanding of this phenomenon will contribute to the selection, indication, and clinical use of these materials.

Evaluation of pre-heated composite resins with soft-start polymerization and conventional composite restorations in class-I carious lesions - A randomized clinical trial.

Background: By increasing fluidity and conversion, pre-heated composites enhance adaptability and strength, while soft-start polymerization decreases internal stresses. Aim: Over a period of a year, this split-mouth design, randomized controlled clinical trial (RCT) compared pre-heated composites with soft-start polymerization to conventional composites in class-I lesions, with the goal of improving restoration outcomes. Methods: and Findings: Immediately following ethical approval and registration with CTRI, 37 patients with in-formed permission who met specified inclusion and exclusion criteria for class-I lesions were chosen for enrollment. Using a 1:1 ratio, teeth were randomly assigned to Group-A (pre-heated composite with soft-start polymerization) or Group-B (traditional composite restoration). At three-time intervals, the evaluation was blinded and calibrated using Modified United States Public Health Service (USPHS) criteria: baseline, six-month, and one-year marks. Statistical analysis was performed using SPSS 21.0 and the Mann-Whitney U test for inter-group comparisons and the Friedman test for intra-group comparisons. Interpretation: Pre-heated composites with soft-start polymerization performed better in terms of marginal adaptation with a statistically significant difference (p = 0.019) and in terms of color match they performed better clinically (p = 0.062) at 12 months. Other variables like marginal discolouration, sec-ondary caries, anatomic form, post-operative sensitivity, surface texture and retention showed no statistically significant difference (p < 0.05). Pre-heated composites with soft-start mode performed marginally better than nanofilled composites. However, both techniques can be used to successfully restore simple class-I carious lesions.

Mechanical and Antimicrobial Properties of Boron Nitride/Methacrylic Acid Quaternary Ammonium Composites Reinforced Dental Flowable Resins.

Dental resin composites (DRCs) are commonly used to restore teeth affected by dental caries or defects. These materials must possess excellent properties to withstand the complex oral environment. The objective of this study was to prepare and characterize Boron nitride nanosheets (BNN)/ dimethyl amino hexadecyl methacrylate (DMAHDM) composites (BNN/DMA), and to evaluate them as functional fillers to enhance the mechanical and antimicrobial properties of dental resins. The BNN/DMA composites were successfully prepared under the theoretical guidance of molecular dynamics (MD), and then the physicochemical and morphological characterization of the BNN/DMA composites were carried out by using various test methods, such as FT-IR, XRD, UV-vis spectroscopy, SEM, TEM, and AFM. It was doped into the dental flowable resin in a certain proportion, and the results showed that the flexural strength (FS), elastic modulus (EM), compressive strength (CS), and microhardness (MH) of the modified resin composites were increased by 53.29, 47.8, 97.59, and 37.1%, respectively, with the addition of 0.8 wt % of BNN/DMA composite fillers. It has a good inhibition effect on Streptococcus mutans, with an inhibition rate as high as 90.43%. Furthermore, this effect persists even after one month of aging. In conclusion, the modification of flowable resins with low-concentration BNN/DMA composites favorably integrates the mechanical properties and long-term antimicrobial activity of dental resins. At the same time, they have good biocompatibility and do not affect the aesthetics. The BNN/DMA composite modified flowable resin has the potential to become a new type of antimicrobial dental restorative material.

Analysis of Gingival Fibroblasts Behaviour in the Presence of 3D-Printed versus Milled Methacrylate-Based Dental Resins-Do We Have a Winner?

Computer-aided design and computer-aided manufacturing (CAD/CAM) techniques are based on either subtractive (milling prefabricated blocks) or additive (3D printing) methods, and both are used for obtaining dentistry materials. Our in vitro study aimed to investigate the behavior of human gingival fibroblasts exposed to methacrylate (MA)-based CAD/CAM milled samples in comparison with that of MA-based 3D-printed samples to better elucidate the mechanisms of cell adaptability and survival. The proliferation of human gingival fibroblasts was measured after 2 and 24 h of incubation in the presence of these samples using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and the membrane integrity was assessed through the lactate dehydrogenase release. The level of reactive oxygen species, expression of autophagy-related protein LC3B-I, and detection of GSH and caspase 3/7 were evaluated by fluorescence staining. The MMP-2 levels were measured using a Milliplex MAP kit. The incubation with MA-based 3D-printed samples significantly reduced the viability, by 16% and 28% from control after 2 and 24 h, respectively. There was a 25% and 55% decrease in the GSH level from control after 24 h of incubation with the CAD/CAM milled and 3D-printed samples, respectively. In addition, higher levels of LC3B-I and MMP-2 were obtained after 24 h of incubation with the MA-based 3D samples compared to the CAD/CAM milled ones. Therefore, our results outline that the MA-CAD/CAM milled samples displayed good biocompatibility during 24-h exposure, while MA-3D resins are proper for short-term utilization (less than 24 h).

Biocompatibility of 3D-Printed Dental Resins: A Systematic Review.

BACKGROUND: The biocompatibility of 3D-printed dental resins has become a critical concern in modern dentistry due to the increasing utilization of additive manufacturing (AM) techniques in dental applications. These resins serve as essential materials for fabricating dental prostheses, orthodontic devices, and various dental components. As the clinical adoption of 3D printing in dentistry grows, it is imperative to comprehensively assess the biocompatibility of these materials to ensure patient safety and dental treatment efficacy. This systematic review aimed to evaluate the existing body of literature on the biocompatibility of 3D-printed dental resins, thereby providing valuable insights into the potential biological risks associated with their use. METHODS: The search strategy to identify relevant papers was implemented across PubMed/MEDLINE, Scopus, Web of Science, Embase, Cochrane Library, CINAHL, and Google Scholar to identify relevant studies. Study selection was not limited to any particular timeframe of publishing. The revised CONSORT criteria were used to ascertain the authenticity and dependability of the review's outcomes. Comprehensive screening and eligibility assessment processes were conducted to select studies meeting predefined criteria. Biocompatibility-related parameters, including toxicity, mechanical properties, cell viability, and other relevant outcomes, were analyzed across selected studies using a standardized variable extraction protocol. RESULTS: A total of 9 studies were included in the systematic review. The findings encompassed various aspects of biocompatibility assessment, including material composition, mechanical properties, cell viability, and cytotoxicity. Some studies revealed significant improvements in flexural strength and cell viability with specific resin formulations, demonstrating their potential for enhanced clinical utility. Conversely, certain resins exhibited cytotoxicity, while others displayed promising biocompatibility profiles. CONCLUSION: As per the assessed findings, material composition, post-processing techniques, and manufacturing methods emerged as critical factors influencing biocompatibility outcomes. While some resins exhibited favorable biocompatibility profiles, others raised concerns due to cytotoxicity. These findings emphasize the need for careful consideration when selecting and implementing 3D-printed dental resins, with a focus on materials engineering and comprehensive biocompatibility testing. Further research is warranted to elucidate the long-term biocompatibility and clinical implications of these materials.

Molecular Simulations of Low-Shrinkage Dental Resins Containing Methacryl-Based Polyhedral Oligomeric Silsesquioxane (POSS).

Nanocomposites of methacrylate-based polyhedral oligomeric silsesquioxane (POSS) are used as resins in dentistry to fill dental cavities. In this article, molecular dynamics simulations (MDS) are used to study and understand the interactions of monofunctional and multifunctional methacrylate groups on hybrid resins containing POSS additives for dental applications. These interactions are further related to the structural properties of the nanocomposites, which in turn affect their macro-properties that are important, especially when used for specific uses such as dental resins. For monofunctional methacrylate, nanocomposite of methacryl isobutyl POSS (MIPOSS) and for multifunctional methacrylate, methacryl POSS (MAPOSS) are used in this study. Molecular dynamic simulations (MDS) are performed on both MIPOSS and MAPOSS systems by varying the amount of POSS. On a weight percent basis, 1%, 3%, 5%, and 10% POSS are added to the resin. Density calculations, stress-strain, and powder diffraction simulations are used to evaluate the macro-properties of these nanocomposites and compare them with the experimental findings reported in the literature. The observations from the simulation results when compared to the experimental results show that MDS can be efficiently used to design, analyze, and simulate new nanocomposites of POSS.

Monitoring the Calibration of In-Office 3D Printers.

Most desktop 3D printers lack features that allow manual calibration of printer parameters. It is crucial to assess the accuracy of printing to minimize the margin of error and variance between each print. Therefore, this study aimed to develop a method for monitoring the calibration of in-office 3D printers. A calibration coupon was designed to have a tolerance and dimensions that define nominal geometry and allow the measurement of variances occurring in X−Y axes and curvature. Ten printing cycles were run on two stereolithography (SLA) 3D printers with two different resins. Additionally, the coupons were positioned in five positions on the build platform to assess errors caused by differences in positioning. Measurements were made on the X and Y axes. No statistical difference was noted between the coupons being printed in different positions on the build platform and between the two resins at both X and Y axes of measurement (p > 0.05). Desktop 3D printers currently lack a standardized calibration protocol, which provides a closed loop for design and manufacturing of printed parts. The coupon in this study will allow monitoring the calibration of desktop 3D printers to ensure high-quality printing.

The Influence of Polishing and Artificial Aging on BioMed Amber® Resin's Mechanical Properties.

Currently, 3D print is becoming more common in all branches of medicine, including dentistry. Some novel resins, such as BioMed Amber (Formlabs), are used and incorporated to more advanced techniques. The aims of the study were to check whether or not polishing and/or artificial aging influences the properties of the 3D-printed resin. A total of 240 specimens of BioMed Resin were printed. Two shapes (rectangular and dumbbell) were prepared. Of each shape, 120 specimens were divided into four groups each (with no influence, after polishing only, after artificial aging only, and after both polishing and artificial aging). Artificial aging took place in water at the temperature of 37 °C for 90 days. For testing, the universal testing machine (Z10-X700, AML Instruments, Lincoln, UK) was used. The axial compression was performed with the speed of 1mm/min. The tensile modulus was measured with the constant speed of 5 mm/min. The highest resistance to compression and tensile test were observed in the specimens that were neither polished nor aged (0.88 ± 0.03 and 2.88 ± 0.26, respectively). The lowest resistance to compression was observed in the specimens that were not polished, but aged (0.70 ± 0.02). The lowest results of the tensile test were observed when specimens were both polished and aged (2.05 ± 0.28). Both polishing and artificial aging weakened the mechanical properties of the BioMed Amber resin. The compressive modulus changed much with or without polishing. The tensile modulus differed in specimens that were either polished or aged. The application of both did not change the properties when compared to the polished or aged probes only.

The Clinical Potential of 3D-Printed Crowns Reinforced with Zirconia and Glass Silica Microfillers.

The development of 3D-printed crown resin materials with improved mechanical and physical properties is an area of growing interest in dentistry. This study aimed to develop a 3D-printed crown resin material modified with zirconia glass (ZG) and glass silica (GS) microfillers to enhance overall mechanical and physical properties. A total of 125 specimens were created and divided into five groups: control unmodified resin, 5% either ZG or GS reinforced 3D-printed resin, and 10% either ZG or GS reinforced 3D-printed resin. The fracture resistance, surface roughness, and translucency parameter were measured, and fractured crowns were studied under a scanning electron microscope. The results showed that 3D-printed parts that were strengthened with ZG and GS microfillers demonstrated comparable mechanical performance to unmodified crown resin but resulted in greater surface roughness, and only the group that contained 5% ZG showed an increase in translucency. However, it should be noted that increased surface roughness may impact the aesthetics of the crowns, and further optimisation of microfillers concentrations may be necessary. These findings suggest that the newly developed dental-based resins that incorporate microfillers could be suitable for clinical applications, but further studies are necessary to optimise the nanoparticle concentrations and investigate their long-term clinical outcomes.

Fracture Strength of Composite Rest Seats: An In Vitro Comparative Study of Different Composite versus Amalgam Restorations.

Occlusal rest provides support for removable partial dentures (RPD). Rest seats are ideally prepared in enamel, but the abutment teeth might be restored or need restorations. This study compared the fracture strength of abutments restored with composite to amalgam restorations after rest seat preparation. Disto-occlusal cavities were prepared in 30 extracted human maxillary premolars. The specimens were allocated in three groups (n = 10) based on the type of restoration. All the specimens were exposed to thermomechanical aging followed by cycling loading. Fracture strength was tested using a universal testing machine, and then, the fracture mode was recorded. The data were analyzed using Kruskal-Wallis test with a significance level set at 0.05. The fracture mode was recorded as catastrophic or non-catastrophic. The fracture strength between all tested groups showed no significant difference. The highest and lowest fracture strength were recorded on amalgam and Tetric N-Ceram groups, respectively. Composite Tetric N-Ceram showed equal distribution of fracture sites on the restorative materials and teeth, it also displayed the highest number of non-catastrophic fractures unlike other groups where the fracture occurred more within the restorations. The fracture strength of composite was comparable to that of amalgam restorations with prepared rest seats.

Exploring the use of a Ruthenium complex incorporated into a methacrylate-based dental material for antimicrobial photodynamic therapy.

OBJECTIVES: To evaluate the effects of a blue light photosensitizer (PS), Ruthenium II complex (Ru), on the chemical, physical, mechanical, and antimicrobial properties of experimental dental resin blends. METHODS: The experimental resin (BisEMA, TEEGDMA, HPMA, ethanol, and photoinitiator) was loaded with Ru at 0.00%, 0.07%, 0.14%, 0.28%, 0.56%, 1.12%, 1.2%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% w/w. Samples were evaluated for the degree of conversion (DC) after 30 and 60 s curing-time (n = 6). Selected formulations (0.00%, 0.28%, 0.56%, 1.12%) were further tested for shear bond strength (SBS) (n = 15); flexural strength (FS) (n = 12); and antimicrobial properties (CFUs), in dark and light conditions. These latter tests were performed on specimens stored for 24-h or 2-month in 37°C water. Water sorption (WS) and solubility (SL) tests were also performed (n = 12). Data were analyzed either by a one- or two-factor general linear model (α = 0.05). RESULTS: Overall, Ru concentration above 1.2% resulted in reduced DC. In SBS results, only the 1.12%Ru resin blend samples had statistically lower values compared to the 0.00%Ru resin blend at 24-h storage (p = 0.004). In addition, no differences in SBS were detected among the experimental groups after 2-month storage in water. Meanwhile, FS increased for all experimental groups under similar aging conditions (p < 0.001). Antimicrobial properties were improved upon inclusion of Ru and application of light (p < 0.001 for both) at 24-h and 2-month storage. Lastly, no detectable changes in WS or SL were observed for the Ru-added resins compared to the 0.00%Ru resin blend. However, the 0.28% Ru blend presented significantly higher WS compared to the 0.56% Ru blend (p = 0.007). CONCLUSIONS: Stable SBS, improved FS, and sustained antimicrobial properties after aging gives significant credence to our approach of adding the Ruthenium II complex into dental adhesive resin blends intended for an aPDT approach.

[Light-curing effectiveness using led lamps: a review]. / Efectividad de fotopolimerización usando lámparas led: una revisión.

Introduction: LED lamps have a new light-curing technology which can be monowave or polywave, which allows it to reach more initiators such as camphorquinone, Lucirin TPO and Propanodione, which have a wide variety of advantages and disadvantages. These lamps have evolved over time, as have different ergonomics, longevity, systems and quality standards. Objective: The objective of this literature review is to improve the clinician on the proper use of different LED lamps and how they influence the efficiency of resin photopolymerization. Material and methods: Extensive research has been carried out in the existing literature on this topic. From the beginning of this information until April 18, 2022, the bibliographic search carried out includes 86 articles published in the Medline database through PubMed, LILACS, Science Direct and SciELO, and there is no language restriction. Results: The photopolymerization effects of Polywave and Monowave LED lamps present significant differences between the compressive strength of the light-cured resin, with single-wave and polyvalent LED lamps where the types of light and lamp directly influence the compressive strength of the resin. composite resins. Conclusion: The type of light and lamp directly affects the efficiency of the photopolymerization of the composite resin, so it is concluded that LED lamps with single wave technology (Monowave) produce a greater depth of photopolymerization than those with multiple wave technology (Polywave).

In vitro biocompatibility testing of 3D printing and conventional resins for occlusal devices.

OBJECTIVE: To assess and compare the in vitro biocompatibility of new resins (Keysplint Soft (Keystone Industries), NextDent Ortho Rigid (3D System), and Freeprint Splint (Detax)) and traditional resins (Orthocryl (Dentaurum)) used for dental splints. METHODS: Standardized discs (n = 40) and 1:1, 1:2, and 1:4 extracts of the tested materials were prepared. Human gingival fibroblasts (hGFs) were isolated from gingival tissues. Different biological tests were carried out, including MTT assays to assess cell metabolic activity, cell migration assays, cell cytoskeleton staining, cell apoptosis, generation of intracellular reactive oxygen species (ROS), and scanning electron microscopy (SEM). Statistical analyses were performed using one-way ANOVA and Tukey's post hoc test (p<0.05). RESULTS: MTT experiments showed that Freeprint Splint significantly reduces the hGF metabolic activity (***p<0.001), whereas SEM analysis showed almost no cells adhered on its surface. Cell migration was significantly lower after exposure to undiluted extracts of Freeprint Splint at 48 and 72 h (***p<0.001). Cell cytoskeleton staining assays showed fewer attached cells in 1:1 and 1:2 dilutions of Freeprint Splint. Annexin-V and 7-AAD staining assays showed that only cells exposed to Keysplint Soft extracts displayed similar cell viability to the control group. Finally, ROS levels detected in undiluted extracts of all resins were significantly enhanced compared to the control group (***p<0.001). CONCLUSIONS: The 3D-printed resins and the conventional dental resin showed a similar biocompatibility, except for Freeprint Splint, which was the most cytotoxic on hGFs. CLINICAL SIGNIFICANCE: 3D printing has been on the rise in recent years and its use in daily clinical practice is expanding over time. Two of the three 3D-printed resins tested in this study performed as well in the cytotoxicity tests as the conventional one, supporting their use, but caution and further testing are required.

Identification of chemicals leaching from dental resin-based materials after in vitro chemical and salivary degradation.

OBJECTIVES: Only little is known about degradation of methacrylate monomers. Therefore, using in vitro chemical and saliva degradation this study aimed to identify the degradation products of organic compounds present in resin-based dental materials. METHODS: Ten dental monomers and nine polymerized dental resin-based materials were immersed for 24 h in chemical media (0.1 M HCl, 0.1 M NaOH) and human pooled saliva in order to identify leached monomers and degradation products from chemical and saliva degradation. Samples were analyzed using liquid chromatography coupled to high-resolution mass spectrometry to identify previously unknown degradation products. RESULTS: During in vitro chemical degradation, uncured monomers were rapidly hydrolyzed into mono- and demethacrylated degradation products. During chemical degradation in alkaline conditions of polymerized materials, considered the worst-case scenario, only degradation products could be detected. In acidic conditions, monomers and their degradation products were detected. In addition, different additives such as EDMAB, DMPA and HMBP were present in acidic degradation samples. Degradation in human pooled saliva for 24 h to mimic the in vivo situation, resulted in the identification of both monomers and their degradation products. CLINICAL SIGNIFICANCE: Using state-of-the-art high-resolution mass spectrometry previously unknown degradation products of commonly used monomers were identified for the first time. Results show that patients may be exposed to monomers and their degradation products in the first 24 h after restorative procedures. The results provide a base for further research on the degradation of resin-based dental composites in order to assess their safety using elution and toxicity studies.

Novel nanoparticle-modified multifunctional microcapsules with self-healing and antibacterial activities for dental applications.

OBJECTIVE: Although microcapsules (MCs) have been used for dental resins to achieve self-healing capabilities, the fragile organic shell and single healing event functions during the service period limit their use. Herein, a novel nanoparticle-modified MC with a nano-antibacterial inorganic filler (NIF) containing a quaternary ammonium salt was synthesized to address these issues. METHODS: MCs with 0 %-30 % NIFs were prepared via an in situ polymerization method and characterized their morphology, chemical composition, thermal stability, roughness, mechanical properties, and antibacterial effect. Subsequently, M-10 MCs were mixed into the resin matrix at a mass fraction of 7.5 %. The self-healing capability and cytotoxicity were evaluated. RESULTS: The introduction of nanomaterials enhances the shell of the MCs and endows them with an antibacterial effect. With the addition of NIFs, the roughness, modulus, and hardness values of MCs all increased (p < 0.05). The presence of M-10 MCs reduced the CFU by 2-3 orders of magnitude compared to the control group. The dental resin containing 7.5 % M-10 MCs obtained almost 69 % self-healing efficiency, without significantly compromising cell viability (p < 0.05). SIGNIFICANCE: Self-healing MCs with NIFs were prepared for the first time with strong antibacterial properties, a substantial self-healing capability, and low toxicity. This multifunctional MC is a promising candidate for use in dental resins to extend the service life and resolve the problem of bulk fracture and secondary caries.

The Influence of Low-Molecular-Weight Monomers (TEGDMA, HDDMA, HEMA) on the Properties of Selected Matrices and Composites Based on Bis-GMA and UDMA.

Bisphenol A-glycidyl methacrylate (bis-GMA) and urethane dimethacrylate (UDMA) are usually combined with low-viscosity monomers to obtain more desirable viscosity, handling characteristics and general properties. The present study determined the flexural strength (FS), flexural modulus (FM), diametral tensile strength (DTS), and hardness (HV) of five matrices and composites based on these resins. The polymerization shrinkage stress (PSS) was also studied for the composites. The polymer matrices were formed using bis-GMA and UDMA. TEGDMA, HEMA and HDDMA acted as co-monomers. The composites had 45 wt.% of filler content. The highest FS and FM were obtained from the UDMA/bis-GMA/TEGDMA/HEMA matrix and the composite (matrix + filler). The best DTS values were obtained from the UDMA/bis-GMA/HEMA matrix and the composite. One of the lowest values of FS, FM, and DTS was obtained from the UDMA/bis-GMA/HDDMA matrix and the composite. All the composites demonstrated similar hardness values. The lowest polymerization shrinkage stress was observed for the UDMA/bis-GMA/TEGDMA/HEMA composite, and the highest PSS was observed for the UDMA/bis-GMA/TEGDMA/HDDMA composite. The addition of HEMA had a positive effect on the properties of the tested materials, which may be related to the improved mobility of the bis-GMA and UDMA monomers.

Optimal resin monomer ratios for light-cured dental resins.

Monomer ratios play a crucial role on the performances of dental resins, the optimal monomer ratios for dental resins are determined by combining the degree of conversion (DC), rate of polymerization (Rp), and mechanical properties, based on commonly-used Bis-GMA (bisphenol A-glycidyl methacrylate), UDMA (urethane dimethacrylate), and TEGDMA (triethyleneglycol dimethacrylate) resins. The DC and mechanical properties of the dental resins are examined by NIR (Near Infrared Ray) spectroscopy and nanoindentation tests, respectively. The results indicate that the Rp increases while the DC decreases with the loading content of Bis-GMA or UDMA in dental resins (i.e., Bis-GMA/TEGDMA and UDMA/TEGDMA). Meanwhile, both elastic modulus and hardness also present a tendency to increase. Various different monomers maybe create a strong polymer matrix in proper proportions, comprehensively comparing the performances of dental resins in different monomer ratios, the cured resins containing Bis-GMA (15-35 wt%), UDMA (37-60 wt%) and TEGDMA (20-35 wt%) show better material properties. The present study offers a quantitative analysis for Bis-GMA/UDMA/TEGDMA dental resins as well as provides guidance for the research of dental resins.