Dental Restorative Composites Research Articles

DEAE-Dextran Coated AgNPs: A Highly Blendable Nanofiller Enhances Compressive Strength of Dental Resin Composites.

Micro-crack formation and resultant bacterial infiltration are major causes of secondary caries formation in dental resin-based composite restorations. Improving dental resin composites’ mechanical and biological properties using highly bendable nanoparticles (NPs) can resolve this issue. This study aims to develop novel Diethylaminoethyl (DEAE)-Dextran silver nanoparticles (AgNPs) and subsequently modify composite resins with these NPs to enhance their mechanical and antibacterial properties. DEAE-Dextran AgNPs were successfully synthesized using a chemical reduction method that was confirmed with the help of ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Zeta potential, and energy-dispersive X-ray spectroscopy (EDS). Antibacterial activity of a composite disc with DEAE-Dextran AgNPs was tested against Streptococcus mutans, Enterococcus faecalis, and oral microcosm. The composite discs prepared with DEAE-Dextran AgNPs exhibited excellent antibacterial activity compared with composite resin reinforced by simple AgNPs (p < 0.05). Mechanical properties were significantly enhanced by adding DEAE-Dextran into composite resin (p < 0.05). Moreover, unlike AgNPs, DEAE-Dextran AgNPs were found to be less hemolytic. The results establish strong ground applications for DEAE-Dextran-modified dental composite resins in restorative dental applications.

Dual-functional adhesive containing amorphous calcium phosphate nanoparticles and dimethylaminohexadecyl methacrylate promoted enamel remineralization in a biofilm-challenged environment

ObjectiveThe cariogenic biofilm on enamel, restoration, and bonding interface is closely related to dental caries and composite restoration failure. Enamel remineralization at adhesive interface is conducive to protecting bonding interface and inhibiting secondary caries. This study intended to assess the remineralization efficiency of adhesive with dimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP) on initial caries lesion of biofilm-coated enamel. MethodsArtificial initial carious lesion was created via 72-hour immersion in demineralization solution and cariogenic biofilm was formed after 24-hour culture of Streptococcus mutans (S. mutans). Specimens were then divided into 4 groups: enamel control, enamel treated with NACP, DMAHDM and NACP+DMAHDM respectively. Samples next underwent 7-day cycling, 4 h in BHIS (brain heart infusion broth containing 1 % sucrose) and 20 h in AS (artificial saliva) per day. The pH of BHIS was tested daily. So did the concentration of calcium and phosphate in BHIS and AS. Live/dead staining, colony-forming unit (CFU) count, and lactic acid production of biofilms were measured 7 days later. The enamel remineralization efficiency was evaluated by microhardness testing and transverse microradiography (TMR) quantitatively. ResultsEnamel of NACP+DMAHDM group demonstrated excellent remineralization effectiveness. And the NACP+DMAHDM adhesive released a great number of Ca2+ and PO43- ions, increased pH to 5.81 via acid neutralization, decreased production of lactic acid, and reduced CFU count of S. mutans (P < 0.05). SignificanceThe NACP+DMAHDM adhesive would be applicable to preventing secondary caries, strengthening enamel-adhesive interface, and extending the lifespan of composite restoration.

Clinical efficiency of the technique for restoring the contact surfaces of the posterior teeth considering the age features

BACKGROUND: Esthetic restoration methods of the posterior teeth using composite materials currently used in dentistry can only be used to create contact in a shape of a point, which does not correspond to the age characteristics of the teeth of adult patients.&#x0D; AIM: This study aimed to develop and introduce into the dental practice methods for creating and precise positioning of contact pads with size and location that correlated with the patients age.&#x0D; MATERIAL AND METHODS: The quality of restorations of the contact surfaces of the teeth and contact points were assessed considering age characteristics. A total of 289 direct composite restorations of class II (Black) defects that were performed during the treatment of dental caries in 178 patients aged 2059 years were conducted. The characteristics of 162 Black class II composite restorations performed with modeling contact pads/surfaces using contact formers were compared with the characteristics of 127 Black class II composite restorations performed using the traditional restoration technique.&#x0D; RESULTS: In the study groups (restorations created using contact formers) 7 days after treatment, restorations were completely in line with the clinical requirements (4 of 4 points) according to the criteria for assessing the quality of the contact surfaces of the teeth and contact pads: 98.3%1.02% of restorations; after 12 months, 92.5%2.07%; after 24 months, 74.8%3.41% of the investigated composite dental restorations. In the comparison groups, the values were as follows: 16.3%3.28% of restorations (p 0.005); after 12 months, 11.3%2.81% (p 0.005); and after 24 months, 9.8%2.64% (p 0.005).&#x0D; CONCLUSION: The clinical application of the developed technique of contact area modeling during posterior teeth caries treatment, taking into account the age characteristics and using the contact adapter of the original design, makes it possible to improve the quality of the restoration of the contact surfaces of the teeth, contact areas, interdental embrasures, and anatomy of the interdental spaces in general.

Comparison of polymerization stresses of dental resin composites evaluated by two indentation fracture methods.

Polymerization stress is a major problem in dental resin composite restorations. Two indentation fracture methods can be applied to evaluate the stress, however, they often calculate different values. To compare polymerization stresses of dental composites determined by the two methods. Glass disks with a central hole were used. Two indentation fracture methods (Methods1 and2) were employed to determine the polymerization stresses of low-shrinkage and bulk-fill composites. Method1: Cracks were made in the glass surface at 300μm from the hole. The hole was filled with the composite. Polymerization stresses at 30min after filling were calculated from the lengths of crack extension. Method2: The hole was filled with the composite. Cracks were introduced in the glass at 1,000μm from the hole at 30min after the polymerization and the stresses were calculated from the crack lengths. Stresses at composite-glass bonded interface were calculated from the stress values obtained by the two methods. The bulk-fill composite generated the smallest interfacial stress, and Method1 revealed lower values than Method2. The composites yielded relatively small stresses. Method1 calculated smaller stress values, possibly affected by the lower threshold stress intensity factor.

Effects of the crosslinking of chitosan/DCPA particles in the antimicrobial and mechanical properties of dental restorative composites

The development of restorative materials containing antibacterial agents is an alternative to reduce the progression of caries lesions. Objectiveto compare the influence of the degree of crosslinking of chitosan particles loaded with dibasic calcium phosphate (DCPA) on the mechanical properties, degree of conversion (DC), and antimicrobial properties of experimental composites. MethodsChitosan/DCPA particles were synthesized by the electrospraying, crosslinked by 0, 8, or 16 h in glutaraldehyde, and characterized by zeta potential and minimum inhibitory concentration (MIC) against S. mutans. Experimental resin composites of Bis-GMA and TEGDMA and 59.5% of barium glass were synthesized, chitosan/DCPA particles were added at 0 or 0.5 wt% with the different crosslinking time. The materials were subject to DC analysis, three-point bending test at 24 h and 7 days, and antimicrobial assays. Data were submitted to one-way ANOVA and Tukey test (α = 0.05). ResultsThe particles with longer crosslinking time presented higher zeta potential and MIC, and the composite containing these particles showed significantly higher biofilm inhibition than the control group. The other two groups were similar to each other and the control. The composite containing particles with 88 h crosslinking time showed the lowest flexural strength at 7 days in water, and materials with non-crosslinked particles and longer crosslinking time presented flexural strength similar to control. The flexural modulus and DC showed no statistical difference among groups. Significancecomposite resin containing 0.5% chitosan/DCPA particles crosslinked by 16 h showed a reduction of biofilm formation without affecting the mechanical properties in relation to the control.

Influence of Practitioner-Related Placement Variables on the Compressive Properties of Bulk-Fill Composite Resins-An In Vitro Clinical Simulation Study.

Aims: To determine if restoration location and/or execution behavior force parameters have an influence on the mechanical properties of bulk-fill composite dental restorations. Methods: Pressure transducers were placed within each quadrant of dental mannequin jaws. Cylindrical molds were placed above the transducers and filled with two bulk-fill composite materials, Filtek and Tetric, by four experienced dentists. Each dentist prepared five specimens per quadrant and material. The total placement time, mean force, number of peak forces (above 25 N), and mean peak(s) force during placement were measured. Then, the stiffness and maximal compressive strength of the specimens were determined while loading the specimens up to failure using a universal loading machine. Results: Placement time was affected by jaw (p < 0.004) and side (p < 0.029), with the shortest time demonstrated for the left side of the mandible. Force exerted during restoration placement was not normally distributed without differences in location (jaw) or material. A higher application force was found on the right side (p < 0.01). The number of peak forces was affected by side (p < 0.03), with less peaks on the left side. No significant differences were found in compressive strength when correlated to restoration location, participant, or material (p = 0.431). The stiffness values of Filtek (3729 ± 228 N/mm) were found to be 15% higher than Tetric (3248 ± 227 N/mm) (p < 0.005). No correlations were found between the compressive strength or stiffness and the amount of force applied during placement. Conclusions: The individual restoration material placement parameters did influence practitioner performance; however, these differences did not affect the mechanical properties of the final restoration.

Influence of silane coupling agent on the mechanical performance of flowable fibre-reinforced dental composites

ObjectivesThis experimental investigation explored the optimisation of silane treatment of surface-modified S-2 Glass fibres in restorative dental composites for improved mechanical performance. The influence of optimum amount of silane to improve the interfacial adhesion at the fibre-matrix interfaces and its effect on the mechanical properties of the restorative composites were explored. MethodsS-2 Glass fibres of 5 μm diameter and 250 μm length were surface modified using the acid etching technique. The etched fibres were then treated with either 3-methacryloxypropyltrimethoxysilane (3-MPS), 3-Glycidoxipropyltrimethoxysilane (3-GPS) or 8-methacryloxyoctyltrimethoxysilane (8-MOTS) at varying molar % / wt% concentrations. Fibres that were not silanised with any silane coupling agents were used as the control sample. The silanol content of each mixed silane was observed using Fourier transform infrared (FT-IR) spectroscopy analysis. Fibres (5 wt%) with optimised molar% / wt% silane coupling concentration were added to UDMA/TEGDMA dental resin. Mechanical properties such as flexural strength, flexural modulus, and the breaking energy of the materials were evaluated using a comprehensive experimental programme. ResultsFTIR spectrum of glass fibre silanised with each silane coupling agent revealed many peaks from 3800 to 1400 cm−1, indicative of -CH3, -CH2, and CO bonding, suggesting the proper silanization of the fibre. The contact angle test revealed that optimum wt% concentration of 3-MPS, 3-GPS and 8-MOTS were 0.5%, 0.8% and 1.4% respectively. The flexural strength of the fibre-reinforced with optimum concentration of 3-MPS (DC-3-MPS_0.5%) increased by 7.0% compared to those of the 2 wt% concentration of 3-MPS fibre-reinforced composite (DC-3-MPS_2.0%). While the flexural strength of optimum concentration 8-MOTS grafted dental resin composites (DC-8-MOTS_1.4%) were 9.9% higher than that of 2 wt% concentration 8-MOTS grafted dental resin composite (DC-8-MOTS_2.0%) and the flexural strength of optimum concentration of 3-GPS (DC-3-GPS_0.8%) was 7.5% higher when compared to that of 2 wt% concentration 3-GPS grafted dental resin composites (DC-3-GPS_2.0%). A concurrent trend was found while investigating the fracture behaviour of the dental composite with optimum wt% concentration of each silane coupling agent against its corresponding higher wt% concentrations. The ANOVA results showed that the optimum fibre-reinforced dental composites grafted with 8-MOTS showed better mechanical behaviour when compared to 3-GPS and 3-MPS. SignificanceThe interfacial adhesion between the fibre and the resin due to silane coupling agents has helped to improve the mechanical properties of the fibre-reinforced dental composite. This is the first experimental study to provide a thorough investigation into the significance of the optimal use of silane coupling agents to treat the S-2 Glass fibres and subsequently the influence on the mechanical performance of the fibre-reinforced flowable dental composites.

A Retrospective Study of 23 Cases: Are Lichenoid Lesions of the Labial Mucosa Induced?

BackgroundLichen planus (LP) is a pathology that affects the skin and the mucosa. The lips are rarely involved but represent a diagnostic challenge in those cases. Oral lichenoid lesions (OLL) are defined as lesions that resemble oral lichen planus (OLP) but do not fully meet the clinical and/or histologic criteria for OLP. This study aimed to present our case series and to study the correlation between the location of the lesion and the dental factor (resin composite, amalgams, crowns, abrasive teeth, and mandibular crossbite) that could cause the lesion.MethodsWe conducted a retrospective observational study of 23 patients with LP/OLL of the lips treated in the Department of Oral Mucosal Pathology of the Department of Stomatology and Maxillofacial Surgery of the Pitié-Salpêtrière Hospital in Paris between January 2017 and February 2021. We noted the location of the lesion (upper, lower, or both lips), medical history, treatments, smoking habits, and the aspect of the teeth facing the lesion. Patients received a local corticoid treatment and were monitored via follow-up.ResultsSixteen patients had lesions on the upper lip, two on the lower lip, and five on both lips, and most patients (n = 14, 60.1%) had a dental factor facing the lesion (e.g., abrasive teeth, resin composites, dental crowns, and mandibular crossbite). Six patients received clobetasol propionate, and 15 patients received a preparation combining betamethasone and benzocaine (Orabase, ConvaTec, Deeside, UK). Fourteen patients returned for post-treatment follow-up consultations approximately two months after treatment. Seven patients saw clinical improvement, five had partial improvement, and two had no improvement.ConclusionsLesions of the labial mucosa appear to be a rare condition in LP/OLL. The difference between LP and OLL can be difficult, even with histological analysis. Its pathogenesis remains unknown, although some studies found evidence of lichenoid reactions of the lips in contact with dental composite restorations. In our study, 14 of our patients had a dental factor facing the lesions. However, our study failed to show a correlation between the presence of an inducing factor and the lesion. In a future study, the potential effect of dental inducing factor removal could be studied. This topic requires further investigations, particularly regarding the inducing factor and the optimal therapeutic approach.

Influence of thermal and thermomechanical stimuli on a molar tooth treated with resin-based restorative dental composites

ObjectivesIn-vivo experimental techniques to understand the biomechanical behavior of a restored tooth, under varying oral conditions, is very limited because of the invasive nature of the study and complex tooth geometry structure. Therefore, 3D-Finite element analyses are used to understand the behavior of a restored tooth under varying oral conditions. In this study, the distribution of maximum principal stress (MaxPS) and the location of MaxPS on a restored tooth using six different commercially available dental resin composites under the influence of thermal and thermomechanical stimuli are performed. MethodsAn intact tooth was scanned using µ-CT and segmented to obtain separate geometric models of the tooth, including enamel and dentine. Then, a class II mesial-occlusal-distal (MOD) cavity was constructed for the tooth model. The restored tooth model was further meshed and imported to the commercial Finite Element (FE) software ANSYS. Thermal hot and cold stimuli at 50 °C and 2 °C, respectively, were applied on the occlusal and lingual surface of the tooth model with the tooth’s ambient temperature set at 37 °C. A uniform loading of 400 N was applied on the occlusal surface of the tooth to imitate the masticatory forces during the cyclic thermal stimuli. ResultsThe results of this study showed that the restorative materials with higher thermal conductivity showed a lower temperature gradient between the restoration and enamel, during the application of thermal stimuli, leading to a higher value of MaxPS on the restoration. Moreover, on applying thermal stimuli, the location of MaxPS at the restoration-enamel junction (REJ) changes based on the value of the coefficient of thermal expansion (CTE). The MaxPS distribution on the application of simultaneous thermal and mechanical stimuli was not only dependent on the elastic modulus of restorative materials but also their thermal properties such as the CTE and thermal conductivity. The weakest part of the restoration was at the REJ, as it experienced the peak stress level during the application of thermomechanical stimuli. SignificanceThe findings from this study suggest that restorative materials with lower values of elastic modulus, lower coefficient of thermal expansion and higher values of thermal conductivity result in lower stresses on the restoration. The outcomes from this study also suggest that the thermal and mechanical properties of a restorative material can have a considerable effect on the selection of restorative materials by dental clinicians over conventional restorative materials.

Development of Novel Antimicrobial Dental Composite Resin with Nano Cerium Oxide Fillers

Objectives To assess the antibacterial efficacy of experimental dental composite resin with cerium oxide nanoparticles as fillers. Methods The cerium oxide nanoparticles were prepared by the coprecipitation procedure. Synthesized 3wt% CeO2 nanoparticles were added to the composite resin as antibacterial filler. Experimental composite resin was manually prepared by adding ingredients. The resin matrix consisted of two mixed monomers, bisphenol A-glycidyl methacrylate and triethylene glycol dimethacrylate, diketone as the photo initiator, and N, N-dimethylaminoethyl methacrylate as a coinitiator. The antibacterial efficacy against Streptococcus mutans, Streptococcus mitis, Streptococcus aureus, and Lactobacillus spp. bacterial strains was tested using the microdilution method keeping commercially available 3M Filtek Z250 restorative composite as control. Results The experimental dental composite demonstrated 99.503% efficacy against Streptococcus mutans, 99.441% efficacy against Streptococcus mitis, 99.416% efficacy against Streptococcus aureus, and 99.233% efficacy against Lactobacillus spp. Conclusion Integrating cerium oxide nanoparticles as fillers into dental composite resin can be promising in terms of antibacterial activity, provided furthermore study has to be conducted to examine other properties. Clinical Significance. Previous studies attempted adding CeO2 nanoparticles into acrylic resins that showed improvement in mechanical properties, but literature is nil on the dental composite resin and cerium oxide nanoparticles. This study demonstrates the development of an experimental antibacterial dental composite resin that can resolve most of the problems related to secondary caries around dental composite restorations.

Effect of aluminium oxide, titanium oxide, hydroxyapatite filled dental restorative composite materials on physico-mechanical properties

The effects of nano-hydroxyapatite in micro-aluminum oxide and titanium oxide on the physical, chemical, and mechanical characteristics of dental resin composite series (DHA and DHT) were investigated in this work. For each series, five distinct formulations were created by combining weight percentages (0, 2, 4, 6, and 8 wt%) of nano-hydroxyapatite. For each dental formulation, the amount of aluminium oxide and titanium oxide remained consistent (20 wt%). A statistical analysis was used for result analysis and the significance level was 0.05. The DOC of hybrid Al2O3-nHA dental composites was 77, 72, 66, 64, and 61%, while 74, 70, 63, 61, and 60% for hybrid TiO2-nHA dental restorative composites. The highest water sorption was found in DHT8 (28.83 μg/mm3). The diminishing tendency was recorded in polymerization shrinkage and depth of cure. The higher compressive strength (201 MPa), flexural strength (92 MPa), and Vickers hardness (45 Hv) were found in the DHA8 dental composite. Superior results were observed in DHA than DHT dental composites.

Staining susceptibility of dental composite resins with various nano-filler technologies

Background: Discoloration of dental composite restoration is a common problem that usually results in refurbishing or replacement or even removal of the restoration. Objective: The purpose of this study was to evaluate the color stability of polished composite resin material with different filler technologies. Methodology: Three composites were studied; Filtek™ Z350 XT (3M, ESPE, St. Paul, USA) [Group-I] that has nano-cluster filler particles, Brilliant EverGlow™ (Coltene/Whaledent® AG, Altstatten, Switzerland) [Group-II] which consists of submicron barium glass fillers and pre-polymerized fillers and Ceram.X® Sphere TEC™ (Dentsply, Konstanz, Germany) [Group-III] with advanced granulated filler technology composite. Twenty standardized composite discs were prepared with each composite resin, and it was polished with Sof-Lex disks (3M, ESPE, St. Paul, USA). The baseline color was then recorded using a spectrophotometer (X-Rite PANTONE® iPro-2, Michigan). Eight samples from each group were then subdivided and immersed into freshly prepared solutions of turmeric, coffee, and four samples into distilled water for a total period of 3 hours/day for 30 days. Following this, the color was again recorded. Statistical analysis: The change in color (ΔE) was calculated, and the data obtained were subjected to Kruskal Wallis and Mann Whitney test. Results: A significant difference was seen between the staining characteristics of Group-III and Group-I (p&amp;lt;0.05). The mean color change in the values was highest in Ceram.X that was clinically unacceptable (ΔE&amp;gt;3.3). Conclusion: Though all composites revealed color changes after their immersion into the staining solutions, the amount of stain varied based on their constituents and filler characteristics.

Fabrication, characterization, and optimization selection of ceramic particulate reinforced dental restorative composite materials

The objective of the article is to explore the fabrication of dental restorative composite materials and the ranking order using the preference selection index (PSI) as a multi criteria decision making (MCDM) technique under a set of conflict performance defining criteria (PDCs). The polymer matrix of the dental restorative composite was prepared using bisphenol a-glycidyl methacrylate (55 wt.%), triethylene glycol dimethacrylate (44 wt.%), camphorquinone (0.3 wt.%), and ethyl 4-(dimethylamino) benzoate (0.7 wt.%). Five different dental restorative composite material compositions were fabricated using hybrid nSiO2-TiO2 particulates with a variation of nSiO2 (0, 2, 4, 6, 8 wt.%) while TiO2 is constant (15 wt.%). The results revealed that an increasing trend has been found in compressive strength, flexural strength, Vickers hardness, etc., while a decreasing trend has been shown in depth of cure, polymerization shrinkage, degree of conversion etc. The performance analysis of five dental composite formulations via the PSI method shows the following ranking order: nS4 &gt; nS6 &gt; nS2 &gt; nS0 &gt; nS8. The obtained experimental results are associated with the ranking order of the different sets of dental composite formulations. Hence, the preference selection index approach is one of the best techniques among MCDM techniques for ranking under different PDCs.

Comparative evaluation of three nanofilled resin-based dental composites: Cytotoxicity, surface roughness, and flexural properties

The clinical performance of dental composite restoration and its overall success are the result of physical, mechanical, and biological properties of the filling materials. The present study aimed to evaluate surface roughness, flexural properties, and cytotoxicity of two nanohybrids, namely, MI Gracefil and Herculite Ultra, and one nanoceramic dental resin composite DiamondLite. The surface roughness was assessed in two different grinding conditions. Flexural properties were measured by, the three-point bending test and the specimens’ fractured surface was analyzed by scanning electron microscopy. Weibull analysis was performed on the flexural strength data to determine the composites’ reliability. The cytotoxicity test was conducted on MC3T3-E1 cells by the MTS assay. The results showed that grinding conditions had a significant effect on all nanocomposites' surface roughness ( p &lt; .05). Herculite Ultra had a significantly higher flexural strength (125.8 MPa) and flexural modulus (9.8 GPa) as compared to other two nanocomposites ( p &lt; .05). Further, cytotoxicity results indicated that DiamondLite had the lowest cell viability during the incubation period ( p &lt; .05). The current study, therefore, concluded that the evaluated nanocomposites showed satisfactory surface roughness. Herculite Ultra flexural properties and Weibull modulus results make it a reliable choice for direct restorations. The cell viability results also showed that all three nanocomposites had moderate cytotoxicity, making them acceptable for direct application in the mouth.

Effects of Light-Curing Techniques on Dental Resins - A Cross-Sectional Study

Background: Commonly used dental resin composites are used as dental filling materials with the help of light induced polymerization reaction. The purpose of this cross-sectional research was to compare the results of different light intensities on the hardness of different dental composites. Following light treatment units were used.&#x0D; &#x0D; QTH also called Quartz Tungsten Halogen&#x0D; LED also called Light Emitting Diodes&#x0D; &#x0D; Methods: This one-month cross-sectional, in-vitro study was carried out in the Dental Materials Laboratory in Saudi Arabia. Using non-probability, convenient sampling, a single trained operator prepared 60 dental restorative composites (DRC) samples in steel molds with a diameter of 10mm and each mold was 2mm thick. During the polymerization of DRCs, the effects of light intensities, sorption and solubility, and microhardness were all measured. SPSS was used for statistical analysis and a p-value of &lt;0.05 was declared striking.&#x0D; Results: When QTH and LED lamps were used, the average micro hardness of DRC was estimated to be 15.480.46 and 18.260.53, respectively. The mean light intensity of QTH was 434 mW/cm2 and for LED lights it was 925mW/cm2. There was no notable difference in DRC sorption and solubility capability (p=0.001) during the polymerization reaction (p=0.128).&#x0D; Conclusion: When it came to increasing the surface micro hardness of DRC, LED light was found to be more effective than QTH light.

Time-lapse submicrometer particle motion reveals residual strain evolution and damaging stress relaxation in clinical resin composites sealing human root canals

Polymer based composites are widely used for treatment, for example as biofilm resistant seals of root canal fillings. Such clinical use, however, fails more frequently than other dental composite restorations, due to stress-related misfits. The reason for this is that the biomaterials used are inserted as viscous masses that may bond to the substrate, yet shrinkage stresses arising during setting of the cross-linking polymer, work against durable adhesion. Here we combine phase contrast enhanced time-lapse radiography (radioscopy), digital image correlation (DIC) and submicrometer resolution phase-contrast enhanced microtomography (PCE-CT), to reveal the spatial and temporal dynamics of composite polymerization and strain evolution. Radioscopy of cavities located in the upper part of human root canals demonstrates how the composite post-gelation “densification” is dominated by viscous flow with quantifiable motion of both particles and entrapped voids. Thereafter, these composites enter a “stress-relaxation” stage and exhibit several structural adaptations, induced by residual shrinkage stresses. Consequently critical alterations to the final biomaterial geometry emerge: (i) entrapped bubbles expand; (ii) microscopic root filling pull-out occurs; (iii) the cavity walls deform inwards, and (iv) occasionally delamination ensues, propagating out from the root canal filling along buried restoration-substrate interfaces. Our findings shed new light on the interactions between confined spaces and biomedical composites that cross-link in situ, highlighting the crucial role of geometry in channeling residual stresses. They further provide new insights into the emergence of structural flaws, calling attention to the need to find new treatment options. Statement of significanceThis work quantifies recurring spatial and temporal material redistribution in composites used clinically to fill internal spaces in teeth. This knowledge is important for both promoting biomaterial resistance against potentially pathologic biofilms and for improving structural capacity to endure years of mechanical function. Our study demonstrates the significant role of geometry and the need for improved control over stress raisers to develop better treatment protocols and new space filling materials. The use of high-brilliance X-rays for time-lapse imaging at submicrometer resolution provides dynamic information about the damaging effects of stress relaxation due to polymerization shrinkage.

Novel low-shrinkage-stress bioactive nanocomposite with anti-biofilm and remineralization capabilities to inhibit caries

Background/purposeA common reason for dental composite restoration failure is recurrent caries at the margins. Our objectives were to: (1) develop a novel low-shrinkage-stress, antibacterial and remineralizing resin composite; (2) evaluate the effects of dimethylaminohexadecyl methacrylate (DMAHDM) on mechanical properties, biofilm inhibition, calcium (Ca) and phosphate (P) ion release, degree of conversion, and shrinkage stress on the new low-shrinkage-stress resin composite for the first time.Material and methodsThe resin consisted of urethane dimethacrylate (UDMA) and triethylene glycol divinylbenzyl ether (TEG-DVBE) with high resistance to salivary hydrolytic degradation. Composites were made with 0%–8% of DMAHDM for antibacterial activity, and 20% of nanoparticles of amorphous calcium phosphate (NACP) for remineralization. Mechanical properties and Streptococcus mutans biofilm growth on composites were assessed. Ca and P ion releases, degree of conversion and shrinkage stress were evaluated.ResultsAdding 2–5% DMAHDM and 20% NACP into the low-shrinkage-stress composite did not compromise the mechanical properties (p > 0.05). The incorporation of DMAHDM greatly reduced S. mutans biofilm colony-forming units by 2–5 log and lactic acid production by 7 folds, compared to a commercial composite (p < 0.05). Adding 5% DMAHDM did not compromise the Ca and P ion release. The low-shrinkage-stress composite maintained a high degree of conversion of approximately 70%, while reducing the shrinkage stress by 37%, compared to a commercial control (p < 0.05).ConclusionThe bioactive low-shrinkage-stress composite reduced the polymerization shrinkage stress, without compromising other properties. Increasing the DMAHDM content increased the antibacterial effect in a dose-dependent manner.

Thermal shrinkage reveals the feasibility of pulse-delay photocuring technique

ObjectivesTo resolve the feasibility of the pulse-delay photocuring technique as a clinical strategy for reducing the detrimental polymerization stress induced in dental composites during the photocuring process. MethodsModel dental composites with high and low-filler contents were cured with the pulse-delay photocuring technique using different combinations of photocuring variables (irradiance, exposure time, and delay time). Irradiance used ranged from 0.1W/cm2 to 4W/cm2. The exposure time of the first pulse varied from 0.2s to 27.2s and the delay times ranged from 10s to 120s. The radiant exposure was varied from 4J/cm2 to 20J/cm2. A cantilever-beam based instrument (NIST Standards Reference Instrument 6005) was used to implement the photocuring technique for the measurement of the polymerization properties (the degree of monomer conversion, polymerization stress induced due to shrinkage, and temperature change due to the reaction exotherm and curing light absorbance) simultaneously in real-time. These properties were compared with those obtained using the conventional photocuring technique (i.e., using a constant irradiance for a fixed exposure time, a uniform exposure). ResultsThere exists a minimum radiant exposure, such that a reduction in the polymerization stress can be achieved without sacrificing the degree of monomer conversion by using the pulse-delay over the conventional photocuring technique. More specifically, stress reductions of up to 19% and 32% was observed with the pulse-delay when compared with the conventional photocuring technique at an irradiance of 0.5W/cm2 and 4W/cm2, respectively. The reduction occurred when the exposure time of the first pulse was greater than, but closer to, the gelation time (i.e., lower than the vitrification time) of the composite, regardless of the delay time used. Lower thermal shrinkage (contraction) during the post-curing time, rather than the stress relaxation during the delay time or lower degree of monomer conversion as claimed in the literature, is the cause of the reduction in the polymerization stress. SignificanceThe study clarifies a long-standing confusion and controversy on the applicability of the pulse-delay photocuring technique for reducing the polymerization stress and promotes its potential clinical success for dental restorative composites.

Mechanical properties of resin composites containing bioactive glass and experimental nano zinc-silica complex

Aim: Secondary caries is an important problem in dental composite restoration, and nanoparticles are commonly added to the structures of resin composites to improve their antimicrobial properties. The aim of this study is to evaluate the mechanical properties of composite materials containing bioactive glass (BAG) and an experimental nano zinc-silica (NZS) complex.&#x0D; Methodology: An experimental resin composite containing 70 wt% filler was produced and used as a control sample. This experimental resin composite was then modified by adding different amounts of BAG (10%), NZS (10%), and both BAG and NZS (10% + 10%). NZS was synthesized in situ by milling zinc and silica to nanoscale level. Compressive strength and flexural strength were investigated using a universal testing machine. Data were analyzed using one-way ANOVA and the Tukey post-hoc test.&#x0D; Results: There were no statistically significant differences in compressive strength caused by the filler amount, but statistically significant changes were found in flexural strength. Although the addition of antimicrobial agents to resin composites reduces their physical properties, this is not a clinically unacceptable limit.&#x0D; Conclusion: NZS exhibits better mechanical properties than does BAG, but both materials can be used safely in restorative materials.&#x0D; &#x0D; How to cite this article: Tunçdemir MT, Demirel MG. Mechanical properties of resin composites containing bioactive glass and experimental nano zinc-silica complex. Int Dent Res 2021;11(Suppl.1):137-42. https://doi.org/10.5577/intdentres.2021.vol11.suppl1.21&#x0D; &#x0D; Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.&#x0D;

Multifunctional Dental Composite with Piezoelectric Nanofillers for Combined Antibacterial and Mineralization Effects.

After nearly seven decades of development, dental composite restorations continue to show limited clinical service. The triggering point for restoration failure is the degradation of the bond at the tooth-biomaterial interface from chemical, biological, and mechanical sources. Oral biofilms form at the bonded interfaces, producing enzymes and acids that demineralize hard tissues and damage the composite. Removing bacteria from bonded interfaces and remineralizing marginal gaps will increase restorations' clinical service. To address this need, we propose for the first time the use of piezoelectric nanoparticles of barium titanate (BaTiO3) as a multifunctional bioactive filler in dental resin composites, offering combined antibacterial and (re)mineralization effects. In this work, we developed and characterized the properties of dental piezoelectric resin composites, including the degree of conversion and mechanical and physical properties, for restorative applications. Moreover, we evaluated the antibacterial and mineralization responses of piezoelectric composites in vitro. We observed a significant reduction in biofilm growth (up to 90%) and the formation of thick and dense layers of calcium phosphate minerals in piezoelectric composites compared to control groups. The antibacterial mechanism was also revealed. Additionally, we developed a unique approach evaluating the bond strength of dentin-adhesive-composite interfaces subjected to simultaneous attacks from bacteria and cyclic mechanical loading operating in synergy. Our innovative bioactive multifunctional composite provides an ideal technology for restorative applications using a single filler with combined long-lasting nonrechargeable antibacterial/remineralization effects.