Reduced Polymerization Shrinkage Research Articles

The evolution of adhesive dentistry: a review of materials and techniques

Adhesive dentistry has undergone remarkable advancements since its inception, fundamentally transforming restorative dental care. Initially marked by the development of early resins and etching techniques, adhesive dentistry has evolved to incorporate sophisticated materials and innovative techniques that significantly enhance clinical outcomes. The introduction of Bis-GMA resins in the 1960s improved mechanical properties and reduced polymerization shrinkage, paving the way for modern composite resins. These composites, enhanced by nanotechnology and advanced filler technology, provide superior strength, wear resistance, and esthetic qualities. Techniques such as selective enamel etching and multi-layering of adhesive systems have further improved bond strength and reduced technique sensitivity. The clinical applications of adhesive dentistry are extensive, ranging from direct and indirect restorations to cosmetic procedures and preventive measures. Direct composite restorations offer minimally invasive solutions with excellent esthetics, while indirect restorations such as inlays, onlays, and veneers benefit from strong, reliable bonds and improved durability. Cosmetic procedures, including veneers, achieve dramatic esthetic improvements with long-lasting results. Preventive applications, such as sealants, effectively protect against caries, especially in pediatric and high-caries-risk patients. The continuous refinement of materials and techniques has led to better clinical outcomes, increased patient satisfaction, and reduced need for invasive procedures. Advances in adhesive materials and methods have ensured that restorations not only mimic natural tooth structures but also maintain their integrity under functional forces. As research and development in adhesive dentistry continue to progress, the field is poised to offer even more innovative and effective solutions, further enhancing the quality of dental care. Overall, the evolution of adhesive dentistry underscores its pivotal role in modern dental practice, providing durable, esthetic, and reliable restorative options that meet the diverse needs of patients.

Impact of optical fiber-based photo-activation on dental composite polymerization

ObjectivesThe study aimed to introduce a novel two-step optical fiber-based photo-activation of dental resin-based composites (RBCs) for reducing polymerization shrinkage stress (PSS). MethodsProposed protocol design – in the first step, two flexible plastic optical fibers connected to a dental light curing unit (LCU), were used as light guides inserted into the filling to initiate low-irradiance polymerization from within; in the second step, fibers were extracted and remaining voids were filled with RBC, followed by conventional high-irradiance curing to finalize polymerization. Three bulk-fill RBCs were tested (Beautifil-Bulk Restorative, Filtek Bulk-fill Posterior, Tetric PowerFill) using tooth cavity models. Three non-invasive examination techniques were employed: Digital Holographic Interferometry, Infrared Thermography, and Raman spectroscopy for monitoring model deformation, RBC temperature change, and degree of conversion (DC), respectively. A control group (for each examined RBC) underwent conventional photo-activation. ResultsThe experimental protocol significantly reduced model deformation by 15 – 35 %, accompanied by an 18 – 54 % reduction in RBC temperature change, emphasizing the impact of thermal shrinkage on PSS. Real-time measurements of deformation and temperature provided indirect insights into reaction dynamics and illuminated potential mechanisms underlying PSS reduction. After a 24-hour dark-storage period, DC outcomes comparable to conventional curing were observed, affirming the clinical applicability of the method. ConclusionsProtocol involving the use of two 1.5 mm fibers in the first step (300 mW/cm2 x 10 s), followed by a second conventional curing step (1000 mW/cm2 x 10 s), is recommended to achieve the desired PSS reduction, while maintaining adequate DC and ensuring efficient clinical application. Clinical SignificanceObtained PSS reduction offers promise in potentially improving the performance of composite restorations. Additionally, leveraging the flexibility of optical fibers improves light guide approach for restorations on posterior teeth. Meanwhile, implementation in clinical practice is easily achievable by coupling the fibers with commercial dental LCUs using the provided plastic adapter.

High-performance new photoinitiators for the preparation of functional photocurable polymer composites

Obtaining dental composites with the desirable physical, mechanical and visual properties that polymerise according to an environmentally friendly cationic mechanism is a significant challenge. This is due to the lack of high-performance initiators for this type of material. This is because there are dental composites on the market that have, among other things, toxic monomers such as BisGMA. This paper presents five high-performance, completely new iodonium derivatives of biphenyl-based iodonium salts differentiated by push–pull structure of chromophores determined by positions of methoxy and trisilyl groups in the biphenyl rings. The influence of the methoxy grouping in the biphenyl ring on the push–pull effect was explained, and their spectroscopic and electrochemical properties were determined. For the first time, the possibility of using these compounds as high-performance initiators of cationic and radical polymerization was presented and described. New two-component initiator systems composed of iodonium salts and thiadiazole derivatives for preparing new-generation dental composites have also been proposed. The thiadiazole derivative was an very effective alternative to camphorquinone, commonly used in the dental industry. Completely new organic matrix compositions and a new curing mechanism have also been proposed by introducing monomers that polymerize according to radical and cationic mechanisms. As a result, dental composites with significantly reduced polymerization shrinkage compared to commercially available materials were obtained. Finally, a new photoinitiating system we have developed, makes it possible to obtain new composites that are an exciting alternative to materials currently used in dentistry.

Use of fiber-containing materials in restorative dentistry

It is aimed at providing chewing function in restorative treatment in dentistry, to protect the tooth structure based on the minimally invasive approach and to meet the aesthetic expectations of the patient. Studies including application techniques are carried out to improve the mechanical and physical properties of composite resins and to reduce polymerization shrinkage. The success of composite restorations has increased with the use of fibers and fiber-reinforced composite resin materials, and the indications of composite resins as direct restoration material have expanded thanks to the production of newly developed fiber-reinforced composite resin materials and their use with the biomimetic restoration technique. In this review, information about the properties and types of fiber structures, advantages, disadvantages, and application areas is explained.

Yttrium aluminum garnet-based filler resin composites used as clear aligner attachments.

The objective of this study was to develop a novel resin composite containing yttrium aluminum garnet (Y3Al5O12, YAG) nanoparticles for clear aligner attachments. After the silanization of YAG, their Fourier-transform infrared (FT-IR) and thermogravimetric (TGA) analyses were performed. By conducting flexural and compressive strength measurements, the optimal YAG concentration was selected for the subsequent experiments. Next, Vickers microhardness values, fluidities, attachment volumes, conversion degrees, and volumetric shrinkages of the resin were determined. The obtained FT-IR and TG results revealed that γ-methacryloxypropy ltrimethoxysilane coupling agent was successfully grafted onto the surface of YAG, which enabled their use as inorganic fillers. Furthermore, adding 9 wt% YAG in the resin can increase Vickers hardness and fluidity, reduce polymerization shrinkage, and enhance the restoration of the clear aligner attachment shape on the premise of guarantee proper flexural and compressive strength of the resin, which can help control tooth movement and increase orthodontic efficiency.

Novel antibacterial low-shrinkage-stress resin-based cement

ObjectiveA low-shrinkage-stress resin-based cement with antibacterial properties could be beneficial to create a cement with lower stress at the tooth-restoration interface, which could help to enhance the longevity of the fixed dental restoration by reducing microleakage and recurrent caries. To date, there has been no report on the development of a low-shrinkage-stress and bio-interactive cement. Therefore, the objectives of this study were to develop a novel low-shrinkage-stress resin-based cement containing dimethylaminohexadecyl methacrylate (DMAHDM) and investigate the mechanical and antibacterial properties for the first time. MethodsThe monomers urethane dimethacrylate (UDMA) and triethylene glycol divinylbenzyl ether (TEG-DVBE) were combined and denoted as UV resin. Three cements were fabricated: (1) UV+ 0%DMAHDM (experimental control); (2) UV+ 3%DMAHDM, (3) UV+ %5DMAHDM. RelyX Ultimate cement was used as commercial control. Mechanical properties and Streptococcus mutans (S. mutans) biofilms growth on cement were evaluated. ResultsThe novel bio-interactive cement demonstrated excellent antibacterial and mechanical properties. Compared to commercial and experimental controls, adding DMAHDM into the UV cement significantly reduced colony forming unit (CFU) counts by approximately 7 orders of magnitude, metabolic activities from 0.29 ± 0.03 A540/cm2 to 0.01 ± 0.01 A540/cm2, and lactic acid production from 22.3 ± 0.74 mmol/L to 1.2 ± 0.27 mmol/L (n = 6) (p < 0.05). The low-shrinkage-stress cement demonstrated a high degree of conversion of around 70 %, while reducing the shrinkage stress by approximately 60%, compared to a commercial control (p < 0.05). ConclusionsThe new antibacterial low-shrinkage-stress resin-based cement provides strong antibacterial action and maintains excellent mechanical properties with reduced polymerization shrinkage stress. Clinical significanceA low-shrinkage-stress resin-based cement containing DMAHDM was developed with potent antibacterial effects and promising mechanical properties. This cement may potentially enhance the longevity of fixed dental restoration such as a dental crown, inlay, onlay, and veneers through its excellent mechanical properties, low shrinkage stress, and strong antibacterial properties.

Effects of thermal cycling on mechanical and antibacterial durability of bioactive low-shrinkage-stress nanocomposite

ObjectivesRecent studies developed low-shrinkage-stress composite with remineralizing and antibacterial properties to combat secondary caries and increase restoration longevity. However, their long-term durability in thermal cycling is unclear. The objectives of this study were to develop an antibacterial, remineralizing and low-shrinkage-stress composite, and to investigate its durability in thermal cycling for 20,000 cycles, equivalent to two years of clinical life. MethodsThe resin consisted of urethane dimethacrylate (UDMA) and triethylene glycol divinylbenzyl ether (TEG-DVBE). Composites were made with 5% dimethylaminohexadecyl methacrylate (DMAHDM) and 20% of nanoparticles of amorphous calcium phosphate (NACP). Composites were thermal cycled at 5°C and 55°C for 20,000 cycles. A human salivary biofilm model was used to evaluate antibiofilm activity before and after thermal cycling. ResultsAfter 20,000 cycles, the flexural strength of bioactive low-shrinkage-stress composite matched commercial control with no antibacterial activity (p > 0.05). Surface roughness was clinically acceptable at less than 0.2 μm. UV+NACP+DMAHDM composite reduced the total microorganisms, total streptococci, and mutans streptococci by 2-5 logs, compared to commercial composite. Biofilm lactic acid production was reduced by 11 folds. The antibacterial performance was maintained after thermal cycling, with no decrease after 20,000 cycles. ConclusionsBioactive low-shrinkage-stress composite possessed good mechanical properties that matched commercial composite both before and after thermal cycling. The new composite had potent antibacterial activity, which was maintained and did not decrease after thermal cycling. Clinical significanceThe new bioactive low-shrinkage-stress composite could reduce polymerization shrinkage stress and release calcium and phosphate ions, with good mechanical properties and strong antibacterial function that were durable after thermal cycling. These properties indicate great potential for inhibiting recurrent caries and increasing the restoration longevity.

Low-Shrinkage Resin Matrices in Restorative Dentistry-Narrative Review.

Dimethacrylate-based resin composites restorations have become widely-used intraoral materials in daily dental practice. The increasing use of composites has greatly enhanced modern preventive and conservative dentistry. They have many superior features, especially esthetic properties, bondability, and elimination of mercury and galvanic currents. However, polymeric materials are highly susceptible to polymerization shrinkage and stresses that lead to microleakage, biofilm formation, secondary caries, and restoration loss. Several techniques have been investigated to minimize the side effects of these shrinkage stresses. The primary approach is through fabrications and modification of the resin matrices. Therefore, this review article focuses on the methods for testing the shrinkage, as well as formulations of resinous matrices available to reduce polymerization shrinkage and its associated stress. Furthermore, this article reviews recent cutting-edge developments on bioactive low-shrinkage-stress nanocomposites to effectively inhibit the growth and activities of cariogenic pathogens and enhance the remineralization process.

A low-shrinkage, hydrophobic, degradation-resistant, antimicrobial dental composite using a fluorinated acrylate and an oxirane.

To develop a low shrinkage, hydrophobic, degradation-resistant, antimicrobial dental composite using a fluorinated acrylate, and a difunctional oxirane. The effects of a fluorinated acrylate (2-(perfluorooctyl)ethyl acrylate; PFOEA), a difunctional oxirane (EPALLOY™ 5001; EP5001), and a three-component initiator system (camphorquinone/ethyl 4-dimethylaminobenzoate/4-Isopropyl-4'-methyldiphenyl iodonium Tetrakis (pentafluorophenyl) borate; CQ/EDMAB/Borate) on bisphenol A glycidyl dimethacrylate: triethylene glycol dimethacrylate (BisGMA:TEGDMA) composite surface hardness, degree of monomer-to-polymer conversion, hydrophobicity, translucency, mechanical properties, polymerization shrinkage and shrinkage stress, degradation, water imbibition, and antimicrobial properties were determined. Overall the experimental composites had comparable mechanical properties and lower volumetric polymerization shrinkage and shrinkage stress as compared to BisGMA:TEGDMA controls. Addition of PFOEA increased composite hydrophobicity, but it decreased degree of cure, ultimate transverse strength, and translucency. It also decreased polymerization shrinkage and shrinkage stress. The use of the CQ/EDMAB/Borate initiator system was beneficial for the cure and mechanical properties of the 30% w/w PFOEA group. However, it decreased the hydrophobicity and translucency of those composites. The addition of EP5001, at the low concentration used in this work, did not contribute to reduced polymerization volumetric shrinkage or antimicrobial properties, but it did reduce shrinkage stress. A mechanically viable hydrophobic composite system with reduced polymerization shrinkage and shrinkage stress has been developed by adding PFOEA and EP5001. However, the addition of EP5001 did not render the composite antimicrobial due to the low concentration used. Further research is needed to determine the lowest concentration at which EP5001 provides antimicrobial activity. The composites developed here have the potential to improve longevity of traditional BisGMA:TEGDMA composite systems.

Comparative Evaluation of Microleakage in Premolars after Placement of Microhybrid and Nanohybrid Composite Using Snow Plow Technique

Background: Microleakage is the significant reason for composite restoration failure. The type of composite material utilized should reduce polymerization shrinkage and hence avoid micro-leakage.&#x0D; Objectives:&#x0D; &#x0D; To evaluate microleakage in Class I cavity using microhybrid composite in snow plow placement technique.&#x0D; To evaluate microleakage in Class I cavity using nanohybrid composite in snow plow placement technique&#x0D; To compare microleakage in Class I cavity with microhybrid composite and nanohybrid composite using snow plow placement technique.&#x0D; &#x0D; Methodology: Prepared Class I cavities in 22 human premolars will be divided randomly into 2 groups based on the restorative material used. These cavity preparations will be restored using the snow plow technique. All the specimens will be thermocycled and stained with 50% silver nitrate solution. We will wash the specimens in the distilled water, store them in the developing solution and for 24 hours exposed to sunlight. The samples will be sectioned longitudinally from the middle of cavity into two parts and will be then evaluated for microleakage on the basis of silver nitrate penetration under stereomicroscope (20X). To compare the microleakage, data will be subjected to statistical analysis.&#x0D; Expected Results: Nanohybrid composite placement using snow plow technique is expected to have less micro-leakage than microhybrid composite placement using the same technique.&#x0D; Conclusion: If this study proves correct, this would be helpful for the clinicians to choose the most efficient restorative material with the best technique and minimal microleakage which will aid in the success of the root canal treatment.

Enhancing Toughness and Reducing Volumetric Shrinkage for Bis-GMA/TEGDMA Resin Systems by Using Hyperbranched Thiol Oligomer HMDI-6SH.

In order to improve the toughness and reduce polymerization shrinkage of traditional bisphenol A-glycidyl methacrylate (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) based dental resin system, a hyperbranched thiol oligomer (HMDI-6SH) was synthesized via thiol-isocyanate click reaction using pentaerythritol tetra(3-mercaptopropionate (PETA) and dicyclohexylmethane 4,4′-diisocyanate (HMDI) as raw materials. Then HMDI-6SH was mixed with 1,3,5-Triallyl-1,3,5-Triazine-2,4,6(1H,3H,5H)-Trione (TTT) to prepare thiol-ene monomer systems, which were added into Bis-GMA/TEGDMA resins with different mass ratio from 10 wt% to 40 wt% to serve as anti-shrinking and toughening agent. The physicochemical properties of these thiol-ene-methacrylate ternary resins including functional groups conversion, volumetric shrinkage, flexural properties, water sorption, and water solubility were evaluated. The results showed that the incorporation of HMDI/TTT monomer systems into Bis-GMA/TEGDMA based resin could improve C=C double bond conversion from 62.1% to 82.8% and reduced volumetric shrinkage from 8.53% to 4.92%. When the mass fraction of HMDI/TTT monomer systems in the resins was no more than 20 wt%, the flexural strength of the resin was higher or comparable to Bis-GMA/TEGDMA based resins (p > 0.05). The toughness (it was measured from the stress–strain curves of three-point bending test) of the resins was improved. Water sorption and water solubility tests showed that the hydrophobicity of resin was enhanced with increasing the content of thioester moiety in resin.

Marginal Adaptation and Micropermeability of Class II Cavities Restored with Three Different Types of Resin Composites—A Comparative Ten-Month In Vitro Study

The development of composite materials is subject to the desire to overcome polymerization shrinkage and generated polymerization stress. An indicator characterizing the properties of restorative materials, with specific importance for preventing secondary caries, is the integrity and durability of marginal sealing. It is a reflection of the effects of polymerization shrinkage and generated stress. The present study aimed to evaluate and correlate marginal integrity and micropermeability in second-class cavities restored with three different types of composites, representing different strategies to reduce polymerization shrinkage and stress: nanocomposite, silorane, and bulk-fill composite after a ten-month ageing period. Thirty standardized class ΙΙ cavities were prepared on extracted human molars. Gingival margins were 1 mm apical to the cementoenamel junction. Cavities were randomly divided into three groups, based on the composites used: FiltekUltimate-nanocomposite; Filtek Silorane LS-silorane; SonicFill-bulk-fill composite. All specimens were subjected to thermal cycles after that, dipped in saline for 10-mounds. After ageing, samples were immersed in a 2% methylene blue. Thus prepared, they were covered directly with gold and analyzed on SEM for assessment of marginal seal. When the SEM analysis was completed, the teeth were included into epoxy blocks and cut longitudinally on three slices for each cavity. An assessment of microleakage on stereomicroscope followed. Results were statistically analyzed. For marginal seal evaluation: F.Ultimate and F.Silorane differ statistically with more excellent results than SonicFill for marginal adaptation to the gingival margin, located entirely in the dentin. For microleakage evaluation: F.Ultimate and F.Silorane differ statistically with less microleakage than SonicFill. Based on the results obtained: a strong correlation is found between excellent results for marginal adaptation to the marginal gingival ridge and micropermeability at the direction to the axial wall. We observe a more significant influence of time at the gingival margin of the cavities. There is a significant increase in the presence of marginal fissures (p = 0.001). A significant impact of time (p < 0.000) and of the material (p < 0.000) was found in the analysis of the microleakage.

Does overlay preparation design affect polymerization shrinkage stress distribution? A 3D FEA study

This study evaluated the polymerization shrinkage stress of three tooth preparation designs for indirect ceramic overlay by finite element analysis: isthmus preparation (IST); without isthmus preparation (wIST); and non-retentive preparation (nRET). The models were created based in prepared dental typodonts and were digitally impressed with an intraoral scanner. The interfaces in all models were considered perfectly bonded and all materials were considered homogeneous, linear, and isotropic. The polymerization shrinkage of the cement layer (100 µm) was simulated and evaluated by maximum principal stress criteria. The stress peaks followed this sequence: restoration = IST (13.4 MPa) > wIST (9.3 MPa) > nRET (9 MPa); cement layer = IST (16.9 MPa) > wIST (12.6 MPa) > nRET (10-7.5 MPa); and teeth = IST (10.7 MPa) > wIST (10.5 MPa) > (9 MPa). For the cement layer, the non-retentive preparation (nRET) had the lowest shrinkage stress from all the groups, obtaining a more homogeneous stress distribution on the cement surface. Regarding the abutment teeth, the IST generated a higher shrinkage stress area on the dental structure, concentrating higher stress magnitude at the axiopulpar and axiogingival angles. Non-retentive preparation seems to reduce polymerization shrinkage stress.

Evaluation of Class II Restoration Microleakage with Various Restorative Materials: A Comparative In vitro Study.

Background and Objectives:The quest for a suitable esthetic material for tooth restoration has resulted in significant advancements in both material properties and application technique. Composites and acid-etch procedures are two significant advancements in esthetic restorative dentistry. Further research has strengthened composites' overall wear resistance and strength, but the problem of polymerization shrinkage has persisted. To reduce polymerization shrinkage and microleakage, a variety of techniques and material modifications have been suggested. The marginal leakage of amalgam, packable composite, flowable composite with packable composite, and high-viscosity traditional glass ionomer cement (GIC) was compared in this analysis to test the mentioned hypothesis.Materials and Methods:We chose 60 freshly extracted teeth and divided them into four classes of 15 teeth each. Class II cavities were prepared in a standardized manner. Group I was treated with amalgam, Group II with packable composite (GC G-aenial Posterior), Group III with flowable composite (G-aenial Universal Flo) as a liner and then restored with packable composite (GC G-aenial Posterior), and Group IV with high-viscosity traditional GIC (EQUI FORTE FILL). After that, the restorations were put through a thermocycling process. The specimens were soaked in 0.5% methylene blue dye before being cut into mesiodistal sections to assess microleakage at the gingival margin. After that, the parts were examined under a stereomicroscope. The degree of dye penetration was used to determine the score.Results:There was no microleakage in the control group, and the gap between the control and experimental groups was statistically significant (P = 0.017).Conclusion:The glass hybrid restorative device had less gingival microleakage than the resin-based restorative material, indicating that it has a better sealing capacity. Clinical acceptability of glass hybrid restorative systems, on the other hand, must be confirmed with a larger sample size and in vivo trials.

Comparison of strength characteristics of direct and indirect dental restorations under uniaxial compression

An urgent task in modern restorative therapeutic dentistry is to make a decision in each specific clinical case, which is justified not only from the esthetic and medical, but also from the economic, as well as the biomechanical and ergonomic points of view. According to many authors, the key to the successful restorative treatment of hard tissue defects of any genesis is to understand the etiological causes and conditions of their occurrence, as well as to assess the size of the defect and the level of material and technical base of modern dentistry.Long-term results of esthetic restoration of teeth using the direct method with various composite materials indicated the admission of multiple errors and complications, such as inconsistency in the color and transparency of the filling; violation of the marginal adherence; and the appearance of marginal staining along the border of the composite material with the tooth tissues, both during and in various terms after treatment.In contrast to the direct method of restoration, the ceramic inlay is made indirectly. This allows reducing polymerization shrinkage, which in turn improves marginal adherence and reduces the frequency of caries recurrence.

Influence of an Alkoxylation Grade of Acrylates on Shrinkage of UV-Curable Compositions.

Commercially available UV curable restorative materials are composed of inorganic filler hydroxyapatite, multifunctional methacrylate, photoinitiator and alkoxylated acrylate. Especially, the application of alkoxylated monomers with different alkoxylation grade allows the reduction of polymerization shrinkage which plays the major role by application of low shrinkage composites as high quality restorative dental materials or other adhesive materials in the form of UV-polymerized self-adhesive acrylics layers (films). There are several ways to reduce polymerization shrinkage of restorative compositions, for example, by adjusting different alkoxylated acrylic monomers, which are integral part of investigated UV curable restorative composites. This article is focused on the studies of contraction-stress measured as shrinkage during UV-initiated curing of restorative composites containing various commercially available alkoxylated acrylates. Moreover, studies with experimental restorative materials and recent developments typical for UV curing technology using special photoreactive monomers are described.

A new method for predicting the maximum filler loading of dental resin composites based on DEM simulations and experiments

ObjectiveThe inorganic fillers in dental resin composites can enhance their mechanical properties and reduce polymerization shrinkage. When the usage amount of inorganic fillers is closed to maximum filler loading (MFL), the composites will usually achieve optimal performances. This study aims to develop a method that can predict the MFL of dental resin composites for the optimization of filler formulations. MethodsA method based on discrete element method (DEM) simulations and experiments was firstly developed to predict the MFL of spherical silica particles for single-level and multi-level filling. ResultsThe results indicate that the presence of modifier can increase the MFL, and the MFL increment can be exponentially changed with the content of the modifier. Compared with the single-level filling, the addition of secondary fillers is beneficial to increase the MFL, and the increment can be affected by the particle size and size ratio. The prediction results show a good agreement with the experiment results. SignificanceThe accuracy of prediction results indicates a great potential of DEM simulations as a numerical experimental method in studying the MFL, and provides an effective method for the optimization of filler formulations.

Polymerization shrinkage behaviour of resin composites functionalized with unsilanized bioactive glass fillers

Previous work has shown that partial replacement of reinforcing fillers with unsilanized silica particles can diminish polymerization shrinkage stress of dental resin composites. The aim of the present study was to investigate whether such an effect can be attained by using unsilanized bioactive glass (BG). Incorporating BG fillers into resin composites is interesting due to their potential for exerting caries-preventive effects. Experimental light-curable composites with a total filler load of 77 wt% were prepared. Reinforcing fillers were partially replaced with 0–60 wt% of BG 45S5 and an experimental low-sodium fluoride-containing BG. The following properties were investigated: linear shrinkage, degree of conversion, shrinkage stress, maximum shrinkage stress rate, and time to achieve maximum shrinkage stress rate. The diminishing effect of BG 45S5 on shrinkage stress was mediated by a decrease in degree of conversion caused by this BG type. In contrast, as the degree of conversion remained unaffected by the experimental BG, the resulting shrinkage behaviour was governed by the effect of varying amounts of silanized and unsilanized fillers on material’s viscoelastic properties. The replacement of silanized reinforcing fillers with unsilanized BG did not reduce polymerization shrinkage stress unless the reduction was attained indirectly through a diminished degree of conversion.

Factors influencing clinical application of bulk-fill composite resin

Bulk-fill composite resin are simple to operate, and they reduce polymerization shrinkage and microleakage compare to traditional resin-based composites. However, their clinical application could be affected by numerous factors, such as the material itself, light curing, placement techniques, storage condition, and preheating. This review aimed to summarize the definitions, classifications, indications, clinical properties, and influencing factors of the clinical application of bulk-fill resin-based composites and discuss the ways to improve their clinical effectiveness.

Physicochemical properties of dimethacrylate resin composites with comonomer of Hexa/Tri-ethylene glycol bis(carbamate-isoproply-α-methylstyrene)

New photocurable “Phene” like monomers Hexaethylene glycol bis(carbamate-isoproply-α-methylstyrene) (HE-Phene) and Triethylene glycol bis(carbamate-isoproply-α-methylstyrene) (TE-Phene) were synthesized and incorporated into Bis-GMA/TEGDMA with the aim of reducing polymerization shrinkage without detriment to the physical and handling properties of the resin composites. Phene like monomers (HE/TE-Phene) were synthesized through a one-step reaction route, and their structures were confirmed by FT-IR and 1H-NMR spectra. HE/TE-Phene were incorporated into Bis-GMA/TEGDMA (50/50,wt/wt) with a series of mass fraction (from 0 wt.% to 40 wt.%). Experimental resin composites were prepared by mixing 29 wt.% of resin matrix to 71 wt.% of particulate-fillers. Degree of conversion (DC) was determined by FT-IR analysis. The volumetric shrinkage (VS) was calculated as a buoyancy change in distilled water by means of the Archimedes principle. Polymerization shrinkage-stress (SS) was measured using the tensilometer technique. The flexural strength (FS), modulus (FM), and fracture toughness (FT) were measured using a three-point bending setup. Viscosity was analyzed with a rotating disk rheometer. Water sorption and solubility were also measured. ANOVA analysis showed that DC (after 40 s), VS, and SS were in a trend of decreasing with the increasing of HE/TE-Phene concentration. In general, the experimental resin composites had comparable FT, FS and FM (p > 0.05) when the mass fraction of HE/TE-Phene in resin matrix was not more than 30 wt.%. The overall tested properties prove that including HE/TE-Phene up to 30 wt.% into Bis-GMA/TEGDMA resin could be potentially useful in the formulation of low-shrinkage resin composites.