Degree of conversion of experimental resin composites containing bioactive glass 45S5: the effect of post-cure heating

The impact of inorganic fillers, organic content, and polymerization mode on the degree of conversion of monomers in resin-matrix cements for restorative dentistry: a scoping review

PURPOSE

The main aim of the present study was to carry out a scoping review on the differences in degree of conversion of monomers regarding several types resin cements, indirect restorative materials, and light-curing procedures used in dentistry.

METHOD

A bibliographic review was performed on PubMed using the following search items: "degree of conversion" OR "filler" AND "resin cement" OR "inorganic cement" AND "organic" OR "radiopacity" OR "refractive" OR "transmittance" OR "type" AND "resin composite." The search involved articles published in English language within the last thirteen years. A research question has been formulated following the PICO approach as follow: "How different is the degree of conversion of monomers comparing several types of resin-matrix cements?".

RESULTS

Within the 15 selected studies, 8 studies reported a high degree of conversion (DC) of the organic matrix ranging from 70 up to 90% while 7 studies showed lower DC values. Dual-cured resin-matrix cements revealed the highest mean values of DC, flexural strength, and hardness when compared with light- and self-polymerized ones. DC mean values of resin-matrix cements light-cured through a ceramic veneer with 0.4 mm thickness were higher (~ 83%) than those recorded for resin-matrix cements light-cured through a thicker ceramic layer of 1.5 mm (~ 77%).

CONCLUSIONS

The highest percentage of degree of conversion of monomers was reported for dual-cured resin-matrix cements and therefore both chemical and light-induced pathways promoted an enhanced polymerization of the material. Similar degree of conversion of the same resin-matrix cement were recorded when the prosthetic structure showed a low thickness. On thick prosthetic structures, translucent materials are required to allow the light transmission achieving the resin-matrix cement.

CLINICAL RELEVANCE

The chemical composition of resin-matrix cements and the light-curing mode can affect the polymerization of the organic matrix. Thus, physical properties of the materials can vary leading to early clinical failures at restorative interfaces. Thus, the analysis of the polymerization pathways of resin-matrix cements is significantly beneficial for the clinical performance of the restorative interfaces.

Marginal integrity of prototype bioactive glass-doped resin composites in class II cavities

OBJECTIVES

This in vitro study examined the marginal integrity of experimental composite materials doped with bioactive glass (BG).

MATERIALS AND METHODS

Class-II MOD cavities were prepared and restored with one of the following composite materials: a commercial composite material as a reference (Filtek Supreme XTE), an experimental composite doped with BG 45S5 (C-20), and an experimental composite doped with a fluoride-containing BG (F-20). Six experimental groups (n = 8) were used, as each of the three composites was applied with (+) or without (-) a universal adhesive (Adper Scotchbond Multipurpose). All specimens were subjected to thermocycling (10,000 x, 5-55 °C) and then additionally stored in artificial saliva for eight weeks. Scanning electron micrographs of the mesial and the distal box were taken at three time points (initial, after thermocycling, and after eight weeks of storage in artificial saliva). The margins were classified as "continuous" and "non-continuous" and the percentage of continuous margins (PCM) was statistically analyzed (α = 0.05).

RESULTS

In most experimental groups, thermocycling led to a significant decrease in PCM, while the additional 8-week aging had no significant effect. F-20 + performed significantly better (p = 0.005) after 8 weeks storage in artificial saliva than the reference material with adhesive, while no statistically significant differences were observed at the other two time points. C-20 + exhibited significantly better PCM than the reference material with adhesive after thermocycling (p = 0.026) and after 8 weeks (p = 0.003).

CONCLUSIONS

Overall, the experimental composites with BG showed at least as good marginal adaptation as the commercial reference, with an indication of possible re-sealing of marginal gaps.

CLINICAL RELEVANCE

Maintaining or improving the marginal integrity of composite restorations is important to prevent microleakage and its likely consequences such as pulp irritation and secondary caries.

POSS hybrid bioactive glass dental composite resin materials: Synthesis and analysis

INTRODUCTION

This study create a dental composite by hybirding polyhedral oligo-sesquioxide nano monomers and bioactive glass BG 45S5.

METHODS

Make an experimental composite resin material with a 60 % filler content overall by substituting 20 % of the filler with BG 45S5. The experimental resins are grouped and named P0, P2, P4, P6 and P8 based on the reactive nanomonomer methacrylic acid-based multifaceted oligomeric sesquisiloxane (POSS) added by 2 %-8 % in the resin matrix portion of each group. Utilize a universal testing machine to analyze and compare the mechanical properties of these, then perform Fourier infrared spectrum analysis, double bond conversion analysis, and scanning electron microscope analysis. Based on this, after soaking the experimental materials artificial saliva solution or lactic acid solution for a while, the pH changes of the solution, the release of Ca2+ and PO43- ions, and the precipitation of apatite on the resin material's surface were tested and analyzed. Cell viability tests were used to assess sample cell viability and quantify the cytotoxicity of biological cells. The independent sample t-test was used to examine the group comparisons, and a difference was considered statistically significant at P<0.05.

RESULTS

Outstanding mechanical and the double bond conversion are demonstrated by the nanocomposites when the POSS concentration hits 4 wt%. Agglomeration will cause the performance to deteriorate if the concentration beyond this threshold. In the P4 group, the double bond conversion, CS, and FS rose by a large margin, respectively, in comparison to the blank control group P0. Thankfully, the data demonstrate that adding POSS increases adhesive ability when compared to the blank group P0, however, there is no discernible difference between the other experimental groups. The acid neutralization capacity of the P4 group is essentially the same as that of the control group (P0). Ca2+ and PO43- ions are released in significant amounts following treatment with lactic acid solution, although this tendency is clearly less pronounced in artificial saliva. SEM and EDX data indicate that when the experimental resin is soaked in lactic acid solution and artificial saliva, apatite precipitation will happen on its surface. The results of the cell viability test indicated that there was no statistically significant difference between the experimental groups, and the viability of the cells increased after 24hours and 48 hours.

CONCLUSIONS

POSS was included into the composite resin along with 20% bioactive glass as a filler. When the proportion of POSS is less than 4%, the indices of composite resin materials rise in a dose-dependent way. When this value is surpassed, performance begins to deteriorate. The inclusion of POSS has no influence on the biological activity of the composites, which means that the hybrid composite resin is capable of acid neutralization, ion release, and apatite precipitation.

CLINICAL SIGNIFICANCE

The experimental composite resin can be used as an intelligent material in clinical treatment. It has the clinical application potential of preventing demineralization of tooth hard tissue, promoting remineralization, and improving edge sealing through apatite precipitation.

Influence of the Bracket Material on the Post-Cure Degree of Conversion of Resin-Based Orthodontic Adhesive Systems

The aim of this study was to examine the influence of the orthodontic bracket material on the short-term and long-term post-cure development of the degree of conversion (DC) of resin-based orthodontic adhesive systems. Five commercially available materials characterized by different compositions and curing modes (light-curable or dual-curable) were tested under three different light curing conditions: without brackets (control group, CO), and in the presence of metal brackets (MB group) or ceramic brackets (CB group). Fourier-transform infrared spectroscopy was used to determine the post-cure DC development, both after "short-term" periods (2, 6, and 10 min) and "long-term" periods (1, 7, and 28 days). The short-term DC values ranged from 43.9% to 76.1%, and the long-term DC values were higher and ranged from 54.3% to 85.3%. The MB group demonstrated significantly lower short-term DC values compared to the CO and the CB groups, while the CB group had statistically similar or slightly lower DC values compared to the CO group. Long-term DC values in the MB and the CB groups were statistically lower or similar compared to the CO group, which depended on the post-cure time. The results indicated that the post-cure DC development was highly material-dependent and affected by the presence of different types of bracket material.

Assessment of physical/mechanical properties and cytotoxicity of dual-cured resin cements containing Sr-bioactive glass nanoparticles and calcium phosphate

The aim was to develop dual-cured resin cements containing Sr-bioactive glass nanoparticles (Sr-BGNPs; 5 or 10 wt%) and monocalcium phosphate monohydrate (MCPM; 3 or 6 wt%). Effects of additives on degree of monomer conversion (DC), biaxial flexural strength/modulus, shear bond strength (SBS), mass/volume change, color stability, ion release, and cytotoxicity were examined. Controls included material without reactive fillers and Panavia SA Plus (PV). Experimental cements showed higher DC than PV regardless of light activation (p<0.05). Mean SBS and color stability were comparable between experimental cements and PV. Cell viability upon the exposure to sample extracts of experimental cements was 80%-92%. High additive concentrations led to lower strength and modulus than PV (p<0.05). The additives increased mass change, reduced color stability, and promoted ion release. The experimental resin cements demonstrated acceptable mechanical/chemical properties and cytotoxicity. The additives reduced the strength but provided ion release, a desirable action to prevent recurrent caries.

Physical-Chemical and Microhardness Properties of Model Dental Composites Containing 1,2-Bismethacrylate-3-eugenyl Propane Monomer

A new eugenyl dimethacrylated monomer (symbolled BisMEP) has recently been synthesized. It showed promising viscosity and polymerizability as resin for dental composite. As a new monomer, BisMEP must be assessed further; thus, various physical, chemical, and mechanical properties have to be investigated. In this work, the aim was to investigate the potential use of BisMEP in place of the BisGMA matrix of resin-based composites (RBCs), totally or partially. Therefore, a list of model composites (CEa0, CEa25, CEa50, and CEa100) were prepared, which made up of 66 wt% synthesized silica fillers and 34 wt% organic matrices (BisGMA and TEGDMA; 1:1 wt/wt), while the novel BisMEP monomer has replaced the BisGMA content as 0.0, 25, 50, and 100 wt%, respectively. The RBCs were analyzed for their degree of conversion (DC)-based depth of cure at 1 and 2 mm thickness (DC1 and DC2), Vickers hardness (HV), water uptake (WSP), and water solubility (WSL) properties. Data were statistically analyzed using IBM SPSS v21, and the significance level was taken as p < 0.05. The results revealed no significant differences (p > 0.05) in the DC at 1 and 2 mm depth for the same composite. No significant differences in the DC between CEa0, CEa25, and CEa50; however, the difference becomes substantial (p < 0.05) with CEa100, suggesting possible incorporation of BisMEP at low dosage. Furthermore, DC1 for CEa0-CEa50 and DC2 for CEa0-CEa25 were found to be above the proposed minimum limit DC of 55%. Statistical analysis of the HV data showed no significant difference between CEa0, CEa25, and CEa50, while the difference became statistically significant after totally replacing BisGMA with BisMEP (CEa100). Notably, no significant differences in the WSP of various composites were detected. Likewise, WSL tests revealed no significant differences between such composites. These results suggest the possible usage of BisMEP in a mixture with BisGMA with no significant adverse effect on the DC, HV, WSP, and degradation (WSL).

Synergistic effect of ion-releasing fillers on the remineralization and mechanical properties of resin-dentin bonding interfaces

In modern restorative dentistry, adhesive resin materials are vital for achieving minimally invasive, esthetic, and tooth-preserving restorations. However, exposed collagen fibers are found in the hybrid layer of the resin-dentin bonding interface due to incomplete resin penetration. As a result, the hybrid layer is susceptible to attack by internal and external factors such as hydrolysis and enzymatic degradation, and the durability of dentin bonding remains limited. Therefore, efforts have been made to improve the stability of the resin-dentin interface and achieve long-term clinical success. New ion-releasing adhesive resin materials are synthesized by introducing remineralizing ions such as calcium and phosphorus, which continuously release mineral ions into the bonding interface in resin-bonded restorations to achieve dentin biomimetic remineralization and improve bond durability. As an adhesive resin material capable of biomimetic mineralization, maintaining excellent bond strength and restoring the mechanical properties of demineralized dentin is the key to its function. This paper reviews whether ion-releasing dental adhesive materials can maintain the mechanical properties of the resin-dentin bonding interface by supplementing the various active ingredients required for dentin remineralization from three aspects: phosphate, silicate, and bioactive glass.

Water-Induced Changes in Experimental Resin Composites Functionalized with Conventional (45S5) and Customized Bioactive Glass

The aim of the study was to evaluate microhardness, mass changes during 1-year water immersion, water sorption/solubility, and calcium phosphate precipitation of experimental composites functionalized with 5-40 wt% of two types of bioactive glass (BG): 45S5 or a customized low-sodium fluoride-containing formulation. Vickers microhardness was evaluated after simulated aging (water storage and thermocycling), water sorption and solubility were tested according to ISO 4049, and calcium phosphate precipitation was studied by scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy. For the composites containing BG 45S5, a significant reduction in microhardness was observed with increasing BG amount. In contrast, 5 wt% of the customized BG resulted in statistically similar microhardness to the control material, while higher BG amounts (20 and 40 wt%) resulted in a significant improvement in microhardness. Water sorption was more pronounced for composites containing BG 45S5, increasing 7-fold compared to the control material, while the corresponding increase for the customized BG was only 2-fold. Solubility increased with higher amounts of BG, with an abrupt increase at 20 and 40 wt% of BG 45S5. Calcium phosphate was precipitated by all composites with BG amounts of 10 wt% or more. The improved properties of the composites functionalized with the customized BG indicate better mechanical, chemical, and dimensional stability without compromising the potential for calcium phosphate precipitation.

Effect of monodisperse mesoporous bioactive glass spheres (MBGs) on the mechanical properties and bioactivity of dental composites

Secondary caries is one of the main reasons for the failure of dental resin composites, and adding bioactive fillers such as bioactive glass and amorphous calcium phosphate to the resin composites has been proved to be an effective solution for this problem. In the present study, we investigated the effect of monodisperse mesoporous bioactive glass spheres (MBGs) we prepared on the mechanical properties and bioactivity of dental resins. The results revealed that compared with traditional bioactive glass (BG), MBGs fillers significantly enhanced the mechanical properties of the dental resin composites, whether they were added alone or as functional fillers together with nonporous silica particles. The dental resins filled with bimodal fillers (mass ratio of MBGs: nonporous silica = 10:50, total filler loading 60 wt%) exhibited the best mechanical performance. Their flexural strength was 37.66% higher than the samples with BG at the same filling proportion. Furthermore, the prepared MBGs possessed excellent monodispersity and sufficient apatite formation performance, and the biocompatibility of the composites were also improved by MBGs fillers. These suggest the potential use of the prepared MBGs as multifunctional fillers for the improvement of the performance of dental resins.

Novel 1,2-Bismethacrylate-3-Eugenyl Propane for Resin Composites: Synthesis, Characterization, Rheological, and Degree of Conversion

This work aimed to synthesize a novel dimethacrylated-derivative of eugenol (Eg) (termed EgGAA) as potential biomaterial for certain applications such as dental fillings and adhesives. EgGAA was synthesized through a two-step reaction: (i) a mono methacrylated-eugenol (EgGMA) was produced via a ring-opening etherification of glycidyl methacrylate (GMA) with Eg; (ii) EgGMA was condensed with methacryloyl chloride into EgGAA. EgGAA was further incorporated in matrices containing BisGMA and TEGDMA (50:50 wt%) (TBEa), in which EgGAA replaced BisGMA as 0–100 wt% to get a series of unfilled resin composites (TBEa0–TBEa100), and by addition of reinforcing silica (66 wt%), a series of filled resins were also obtained (F-TBEa0–F-TBEa100). Synthesized monomers were analyzed for their structural, spectral, and thermal properties using FTIR, 1H- and 13C-NMR, mass spectrometry, TGA, and DSC. Composites rheological and DC were analyzed. The viscosity (η, Pa·s) of EgGAA (0.379) was 1533 times lower than BisGMA (581.0) and 125 times higher than TEGDMA (0.003). Rheology of unfilled resins (TBEa) indicated Newtonian fluids, with viscosity decreased from 0.164 Pa·s (TBEa0) to 0.010 Pa·s (TBEa100) when EgGAA totally replaced BisGMA. However, composites showed non-Newtonian and shear-thinning behavior, with complex viscosity (η*) being shear-independent at high angular frequencies (10–100 rad/s). The loss factor crossover points were at 45.6, 20.3, 20.4, and 25.6 rad/s, indicating a higher elastic portion for EgGAA-free composite. The DC was insignificantly decreased from 61.22% for the control to 59.85% and 59.50% for F-TBEa25 and F-TBEa50, respectively, while the difference became significant when EgGAA totally replaced BisGMA (F-TBEa100, DC = 52.54%). Accordingly, these properties could encourage further investigation of Eg-containing resin-based composite as filling materials in terms of their physicochemical, mechanical, and biological potentiality as dental material.

Influence of Eugenol and Its Novel Methacrylated Derivative on the Polymerization Degree of Resin-Based Composites

The aim of this work was to assess the limiting rate of eugenol (Eg) and eugenyl-glycidyl methacrylate (EgGMA) at which the ideal degree of conversion (DC) of resin composites is achieved. For this, two series of experimental composites, containing, besides reinforcing silica and a photo-initiator system, either EgGMA or Eg molecules at 0-6.8 wt% per resin matrix, principally consisting of urethane dimethacrylate (50 wt% per composite), were prepared and denoted as UGx and UEx, where x refers to the EgGMA or Eg wt% in the composite, respectively. Disc-shaped specimens (5 × 1 mm) were fabricated, photocured for 60 s, and analyzed for their Fourier transform infrared spectra before and after curing. The results revealed concentration-dependent DC, increased from 56.70% (control; UG0 = UE0) to 63.87% and 65.06% for UG3.4 and UE0.4, respectively, then dramatically decreased with the concentration increase. The insufficiency in DC due to EgGMA and Eg incorporation, i.e., DC below the suggested clinical limit (>55%), was observed beyond UG3.4 and UE0.8. The mechanism behind such inhibition is still not fully determined; however, radicals generated by Eg may drive its free radical polymerization inhibitory activity, while the steric hindrance and reactivity of EgGMA express its traced effect at high percentages. Therefore, while Eg is a severe inhibitor for radical polymerization, EgGMA is safer and can be used to benefit resin-based composites when used at a low percentage per resin.

Influence of Ionizing Radiation on Fluoride-Releasing Dental Restorative Materials

This study aimed to investigate the effects of radiotherapy on the mechanical, chemical, and surface properties of two recently introduced restorative dental materials (a glass hybrid and an alkasite), while two conventional restorative materials served as references. Material specimens of the experimental groups (irradiated) were compared to the specimens of the control groups that underwent the same preparation procedure but without irradiation. The experimental groups of restorative material specimens were irradiated with a total of 70 Gy over 35 days (2 Gy/day × 35 days), while the control groups received no treatment. The following properties were evaluated: surface microhardness (Vickers), surface roughness, color change, flexural strength, flexural modulus, material reliability, and infrared spectra. For the experimental groups, measurements were performed 24 h after specimen preparation, i.e., before radiotherapy and after the completion of the irradiation protocol. For the control groups, measurements were performed after the corresponding periods of no treatment. A statistically significant increase in microhardness (p = 0.001-0.004) and surface roughness (p = 0.013) was observed as a result of material aging/maturation in both the control and experimental groups. However, the only statistically significant difference between the control and experimental groups was observed in the discoloration of the conventional reference material (p < 0.001). In conclusion, no statistically significant negative effects of a therapeutic dose of radiotherapy on any of the tested properties of the alkasite and glass hybrid materials were observed, whereas only a minor negative effect of radiotherapy in terms of discoloration was found for a conventional resin composite that was used as a reference material.

Design and tribological performance of short S-Glass fibre reinforced biocomposites on the influence of fibre length and concentration

Fibre-reinforced biocomposites usage has gained prominence over the past decade. Although higher fracture toughness was observed when fibres were added to biocomposites, material degradation could occur due to filler and fibre content intolerance in the biocomposite matrix. Optimisation of resin-fibre-filler ratios helps in increasing the tribological performance of high load-bearing applications. However, the tribological performance is less understood due to limited in-vitro studies on the effect of fibre microstructures. A comprehensive investigation of the reciprocating and rotary wear behaviour of different compositions was carried out by varying fibre (0%, 5%, 10% and 15%) to particulate filler (40%, 45%, 50%, and 55%) weight fractions. The investigation aimed to identify the optimal composition of fibre-reinforced biocomposites based on the in-vitro ball-on-disc reciprocating and rotary wear tests in the presence of modified Fusayama solution. The cross-sectional areas of wear tracks were analysed using laser microscopy and scanning electron microscopy techniques to assess the surface morphology and subsurface damage of the wear tracks on biocomposites and the antagonist. The numerical results were statistically analysed using two-way ANOVA followed by a posthoc Tukey's test (p = 0.05). The results showed a combination of adhesive, abrasive and fatigue wear for all the tested Groups. The friction coefficient had a longer transient period for the 5 wt% and 10 wt% Groups. Based on the surface roughness, coefficient of friction, SEMs, specific wear rate, and ease of manufacturing, the threshold limit for fibre loading was found to be 10 wt%. The rotary test had a considerably lower specific wear rate compared to the reciprocating test. Fibre weight fraction was found to be the influencing factor of the abrasive wear behaviour compared to fibre length for the tested Groups.

A Narrative Review of Bioactive Glass-Loaded Dental Resin Composites

This review aims to provide a comprehensive analysis of the characterizations of bioactive glass (BAG)-loaded dental resin-based composite materials. Online databases (Web of Science, PubMed, and Science Direct) were used to collect data published from January 2011 to January 2022. Only BAG-containing resin adhesive and resin restorative composites are discussed in this narrative review. BAG-loaded resin composites exhibit excellent mineralization ability reflecting enhanced ion release, pH elevation, and apatite formation, especially regarding high BAG loading. This aids the anti-demineralization and remineralization of teeth. Furthermore, BAG-loaded resin composites demonstrated in vitro biocompatibility and antibacterial performance. It has been suggested that BAG fillers with small particle sizes and no more than 20 wt% in terms of loading amount should be used to guarantee the appropriate mechanical properties of resin composites. However, most of these studies focused on one or some aspects using different resin systems, BAG types, and BAG amounts. As such, this makes the comparison difficult, and it is essential to find an optimal balance between different properties. BAG-loaded resin composites can be regarded as bioactive materials, which present major benefits in dentistry, especially their capability in the bacterial inhibition, cell biocompatibility, anti-demineralization, and remineralization of teeth.

Improved Flexural Properties of Experimental Resin Composites Functionalized with a Customized Low-Sodium Bioactive Glass

This study evaluated the flexural properties of an experimental composite series functionalized with 5-40 wt% of a low-Na F-containing bioactive glass (F-series) and compared it to another experimental composite series containing the same amounts of the conventional bioactive glass 45S5 (C-series). Flexural strength and modulus were evaluated using a three-point bending test. Degree of conversion was measured using Fourier-transform infrared spectroscopy. Weibull analysis was performed to evaluate material reliability. The control material with 0 wt% of bioactive glass demonstrated flexural strength values of 105.1-126.8 MPa). In the C-series, flexural strength ranged between 17.1 and 121.5 MPa and was considerably more diminished by the increasing amounts of bioactive glass than flexural strength in the F-series (83.8-130.2 MPa). Analogously, flexural modulus in the C-series (0.56-6.66 GPa) was more reduced by the increase in bioactive glass amount than in the F-series (5.24-7.56 GPa). The ISO-recommended "minimum acceptable" flexural strength for restorative resin composites of 80 MPa was achieved for all materials in the F-series, while in the C-series, the materials with higher bioactive glass amounts (20 and 40 wt%) failed to meet the requirement of 80 MPa. The degree of conversion in the F-series was statistically similar or higher compared to that of the control composite with no bioactive glass, while the C-series showed a declining degree of conversion with increasing bioactive glass amounts. In summary, the negative effect of the addition of bioactive glass on mechanical properties was notably less pronounced for the customized bioactive glass than for the bioactive glass 45S5; additionally, mechanical properties of the composites functionalized with the customized bioactive glass were significantly less diminished by artificial aging. Hence, the customized bioactive glass investigated in the present study represents a promising candidate for functionalizing ion-releasing resin composites.

Post-Cure Development of the Degree of Conversion and Mechanical Properties of Dual-Curing Resin Cements

This study investigated the effect of different curing conditions on the degree of conversion and mechanical properties of contemporary dual-curing resin cements. The material specimens were either light-cured directly, light-cured through a 1-mm lithium disilicate glass-ceramic layer, or self-cured. The degree of conversion was measured in 0.1-mm films using Fourier-transform infrared spectroscopy 1 day, 7 days, and 28 days post-cure. Specimens used to study the flexural strength and modulus were prepared according to the ISO 4049 protocol, stored for 28 days post-cure, and subjected to accelerated aging by absolute ethanol immersion. The degree of conversion values ranged between 44.3–77.8%. Flexural strength varied between 11.4–111.1 MPa, while flexural modulus amounted to 0.7–5.5 GPa. The degree of conversion was significantly affected by material type, curing conditions, and post-cure time; however, variations in curing conditions were the least influential factor. A statistically significant effect of curing conditions on the degree of conversion was identified for only one of the five materials tested, whereas the flexural strength and modulus of all tested materials were significantly reduced in the experimental groups that were light-cured through a ceramic layer or self-cured. The effect size analysis showed that mechanical properties were most affected by the material type, while the differences in curing conditions were less influential. A comparison of the degree of conversion and mechanical properties indicated that different curing conditions may lead to significantly different flexural strength and modulus, which are not necessarily accompanied by identifiable variations in the degree of conversion.

Photoinitiator Selection and Concentration in Photopolymer Formulations towards Large-Format Additive Manufacturing

Photopolymers are an attractive option for large-format additive manufacturing (LFAM), because they can be formulated from structural thermosets and cure rapidly in ambient conditions under low-energy ultraviolet light-emitting diode (UV LED) lamps. Photopolymer cure is strongly influenced by the depth penetration of UV light, which can be limited in the 2–4 mm layer thicknesses typical of LFAM. Photoinitiator (PI) systems that exhibit photobleaching have proven useful in thick-section cure applications, because they generate a photoinitiation wavefront, but this effect is time-dependent. This study investigates the light transmission and through-thickness cure behavior in (meth)acrylate photopolymer formulations with the photobleaching initiator bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (BAPO). Utilizing an optical model developed by Kenning et al., lower concentrations (0.1 wt% to 0.5 wt%) of BAPO were predicted to yield rapid onset of photoinitiation. In situ cure measurements under continuous UV LED irradiation of 380 mW/cm² showed that a 0.1 wt% concentration of BAPO achieved peak polymerization rate within 2.5 s at a 3-mm depth. With only 1 s of irradiation at 1.7 W/cm² intensity, the 0.1 wt% BAPO formulation also achieved the highest level of cure of the formulas tested. For an irradiation dose of 5.5 J/cm² at a duration of 3.7 s, cured polymer specimens achieved a flexural strength of 108 MPa and a flexural modulus of 3.1 GPa. This study demonstrates the utility of optical modeling as a potential screening tool for new photopolymer formulations, primarily in identifying an upper limit to PI concentration for the desired cure depth. The results also show that photobleaching provides only a limited benefit for LFAM applications with short (1.0 s to 3.7 s) UV irradiation times and indicate that excess PI concentration can inhibit light transmission even under extended irradiation times up to 60 s.

Effects of Sr/F-Bioactive Glass Nanoparticles and Calcium Phosphate on Monomer Conversion, Biaxial Flexural Strength, Surface Microhardness, Mass/Volume Changes, and Color Stability of Dual-Cured Dental Composites for Core Build-Up Materials

This study prepared composites for core build-up containing Sr/F bioactive glass nanoparticles (Sr/F-BGNPs) and monocalcium phosphate monohydrate (MCPM) to prevent dental caries. The effect of the additives on the physical/mechanical properties of the materials was examined. Dual-cured resin composites were prepared using dimethacrylate monomers with added Sr/F-BGNPs (5 or 10 wt%) and MCPM (3 or 6 wt%). The additives reduced the light-activated monomer conversion by ~10%, but their effect on the conversion upon self-curing was negligible. The conversions of light-curing or self-curing polymerization of the experimental materials were greater than that of the commercial material. The additives reduced biaxial flexural strength (191 to 155 MPa), modulus (4.4 to 3.3), and surface microhardness (53 to 45 VHN). These values were comparable to that of the commercial material or within the acceptable range of the standard. The changes in the experimental composites’ mass and volume (~1%) were similar to that of the commercial comparison. The color change of the commercial material (1.0) was lower than that of the experimental composites (1.5–5.8). The addition of Sr/F-BGNPs and MCPM negatively affected the physical/mechanical properties of the composites, but the results were satisfactory except for color stability.

Monomer Release from Dental Resins: The Current Status on Study Setup, Detection and Quantification for In Vitro Testing

Improvements in mechanical properties and a shift of focus towards esthetic dentistry led to the application of dental resins in various areas of dentistry. However, dental resins are not inert in the oral environment and may release monomers and other substances such as Bisphenol-A (BPA) due to incomplete polymerization and intraoral degradation. Current research shows that various monomers present cytotoxic, genotoxic, proinflammatory, and even mutagenic effects. Of these eluting substances, the elution of BPA in the oral environment is of particular interest due to its role as an endocrine disruptor. For this reason, the release of residual monomers and especially BPA from dental resins has been a cause for public concern. The assessment of patient exposure and potential health risks of dental monomers require a reliable experimental and analytical setup. However, the heterogeneous study design applied in current research hinders biocompatibility testing by impeding comparative analysis of different studies and transfer to the clinical situation. Therefore, this review aims to provide information on each step of a robust experimental and analytical in vitro setup that allows the collection of clinically relevant data and future meta-analytical evaluations.

A Bioactive Enamel Sealer Can Protect Enamel during Orthodontic Treatment: An In Vitro Study

Background: This study aimed to evaluate the effectiveness of an experimental bioactive enamel resin sealer in protecting the enamel adjacent to orthodontic brackets against erosion. Methods: Orthodontic brackets (n = 50) were bonded to freshly extracted, sound maxillary premolars using Transbond™ XT Primer (3M Unitek, Monrovia, CA, USA) and Transbond Plus Color Change adhesive (3M Unitek, USA). Five experimental groups (n = 10) had the following treatments applied: a resin bioactive sealer with 45S5 bioglass, 35% by weight; a resin sealer without bioactive glass; fluoride; the orthodontic sealer, Opal Seal (Opal-Orthodontics, South Jordan, UT, USA); and, in the control group, an untreated surface. All the specimens were stored for 18 min in 1% citric acid. All the specimens were examined by SEM and electron dispersive spectroscopy (EDS). The Wilcoxon signed-rank test was used to compare the enamel surfaces covered by the sealers before and after the acid challenge. Attenuated total reflectance Fourier transform infrared spectroscopy detected the degree of the experimental resins’ conversion to verify their suitability for clinical use. Results: The percentage of the bioactive resin sealer and Opal Seal groups’ protection against enamel erosion was 100%, which was significantly more than the other groups, p < 0.05. The degree of conversion for the bioactive and unfilled resins was 42.4% ± 3.6% and 48.57% ± 5%, respectively. Conclusion: The bioactive resin sealer and the Opal Seal both protected the enamel from erosion.

Raman Spectroscopy: A Potential Diagnostic Tool for Oral Diseases

Oral diseases impose a major health burden worldwide and have a profound effect on general health. Dental caries, periodontal diseases, and oral cancers are the most common oral health conditions. Their occurrence and development are related to oral microbes, and effective measures for their prevention and the promotion of oral health are urgently needed. Raman spectroscopy detects molecular vibration information by collecting inelastic scattering light, allowing a “fingerprint” of a sample to be acquired. It provides the advantages of rapid, sensitive, accurate, and minimally invasive detection as well as minimal interference from water in the “fingerprint region.” Owing to these characteristics, Raman spectroscopy has been used in medical detection in various fields to assist diagnosis and evaluate prognosis, such as detecting and differentiating between bacteria or between neoplastic and normal brain tissues. Many oral diseases are related to oral microbial dysbiosis, and their lesions differ from normal tissues in essential components. The colonization of keystone pathogens, such as Porphyromonas gingivalis, resulting in microbial dysbiosis in subgingival plaque, is the main cause of periodontitis. Moreover, the components in gingival crevicular fluid, such as infiltrating inflammatory cells and tissue degradation products, are markedly different between individuals with and without periodontitis. Regarding dental caries, the compositions of decayed teeth are transformed, accompanied by an increase in acid-producing bacteria. In oral cancers, the compositions and structures of lesions and normal tissues are different. Thus, the changes in bacteria and the components of saliva and tissue can be used in examinations as special markers for these oral diseases, and Raman spectroscopy has been acknowledged as a promising measure for detecting these markers. This review summarizes and discusses key research and remaining problems in this area. Based on this, suggestions for further study are proposed.

Polymerization kinetics of experimental resin composites functionalized with conventional (45S5) and a customized low-sodium fluoride-containing bioactive glass

This study aimed to investigate polymerization kinetics and curing light transmittance of two series of experimental dental resin composites filled with 0–40 wt% of either 45S5 bioactive glass (BG) or a customized low-Na F-containing BG. Polymerization kinetics in 0.1-mm and 2-mm thick layers were investigated through real-time degree of conversion measurements using a Fourier transform infrared (FTIR) spectrometer. FTIR spectra were continuously collected at a rate of 2 s⁻¹ during light-curing (1340 mW/cm²). Light transmittance through 2-mm thick composite specimens was measured using a UV–Vis spectrometer at a rate of 20 s⁻¹. Unlike BG 45S5, which led to a dose-dependent reduction in the rate and extent of polymerization, the customized low-Na F-containing BG showed a negligible influence on polymerization. The reduction in light transmittance of experimental composites due to the addition of the low-Na F-containing BG did not translate into impaired polymerization kinetics. Additionally, the comparison of polymerization kinetics between 0.1-mm and 2-mm thick layers revealed that polymerization inhibition identified for BG 45S5 was not mediated by an impaired light transmittance, indicating a direct effect of BG 45S5 on polymerization reaction. A customized low-Na F-containing BG showed favourable behaviour for being used as a functional filler in light-curing dental resin composites.

A modified TEGDMA-based resin infiltrant using polyurethane acrylate oligomer and remineralising nano-fillers with improved physical properties and remineralisation potential

OBJECTIVES

This study aimed to modify an experimental triethylene glycol dimethacrylate (TEGDMA) based resin infiltrant using PUA oligomer and two remineralising fillers, including fluorohydroxyapatite (FHA) and fluoride-doped bioactive glass (FD-BG), to improve the mechanical and physical properties and induce remineralising potential.

MATERIALS AND METHODS

The polyurethane acrylate oligomer (PUA) was synthesised and characterised. Experimental resin infiltrant was prepared by mixing 10% of synthesised PUA with 88% TEGDMA. Water contact angle, penetration coefficient, and penetration depth were then measured. The FHA and FD-BG fillers were synthesised and characterised. To prepare nano-filled resin infiltrant, 5% of each powder was mixed with the prepared resin infiltrant. The prepared resin infiltrants were characterised to evaluate their degree of conversion, mechanical properties, water sorption, and solubility. The ion release of filled resin was also assessed. The non-infiltrated and infiltrated enamel specimens underwent fourteen days of pH-cycling, and a surface microhardness was done to assess the resistance to demineralisation.

RESULTS

The results showed that the addition of PUA to TEGDMA increased the mechanical properties and decreased water sorption and solubility. The addition of synthesised FD-BG fillers to resin infiltrant significantly improved the resistance to demineralisation of enamel samples compared with other groups (p ≤ 0.001). The FHA fillers also improved the resistance to demineralisation; however, the produced changes were not statistically meaningful (p > 0.05).

CONCLUSIONS

Based on the results, the PUA+TEGDMA+ FD-BG/FHA composite can be used as an alternative material for pure TEGDMA in enamel infiltration approaches owing to its better mechanical properties, lower water sorption and solubility, and also remineralisation potential.

CLINICAL SIGNIFICANCE

A resin infiltrant with remineralisation potential, lower water sorption and solubility and higher mechanical properties may enhance the management of early caries lesions.

The Effect of Incorporating Different Concentrations of Octenidine Dihydrochloride on the Degree of Conversion of an Experimental Flowable Resin Composite

BACKGROUND: One of the important parameters in assessing the definitive physical, mechanical, and biological characteristics of resin composites is the degree of conversion (DC), as composite qualities have been proven to improve with increasing the DC after photo-polymerization. Besides, fracture or secondary caries are the most common causes of composite resin failure. Accordingly, this reflects the need of formulating dental restorative materials possessing antibacterial activity. AIM: This study was designed to incorporate different concentrations of a new antibacterial agent (Octenidine dihydrochloride [OCT]) into an experimentally formulated flowable resin composite and evaluate its DC. MATERIALS AND METHODS: Four groups were tested in this study; group I was used as the control group, it’s a commercially available flowable composite “Herculite Ultra Flowable”. Group II was an experimental flowable composite with no antibacterial agent. During the preparation of the experimental flowable resin composite material, OCT antibacterial agent was added to the filler in special dark containers at a concentration of 1% wt. and 1.5% wt. respectively, in groups III and IV. The DC was measured and compared to the commercially available resin composite using the Fourier Transform Infrared spectroscopy method. RESULTS: Results of the current study showed that the mean values of DC ranged between (70.37 and 48.7), where Group1 showed the highest mean value, followed by Group 2 than Group 3, Group 4 specimens had the lowest mean value. The data showed that there is a statistically significant difference between all the tested groups. However, the DC was still within the accepted ranges for dental use. CONCLUSION: Based on the results obtained within the experimental conditions of this study it may be stated that the inclusion of the antibacterial OCT 1% and 1.5% wt., into the flowable resin composite showed satisfactory results for the DC as it met the ADA requirements for clinical use.

Short- and Long-Term Dentin Bond Strength of Bioactive Glass-Modified Dental Adhesives

This study investigated the short- and long-term effects of dental adhesives doped with nano-sized bioactive glass 45S5 (BAG) on the resin-dentin interfacial bond strength. Two etch-and-rinse adhesives (Adper Scotchbond Multi-Purpose (ASB) and Solobond Plus (SB)) and one self-etch adhesive (Clearfil SE Bond (CF)) were doped with different concentrations of BAG (5, 10, and 20 wt%). The unmodified (0 wt% BAG) commercial adhesives served as control groups. Dentin of 120 molars (n = 10 per group) was treated with the different adhesives, followed by buildups with a conventional composite restorative material. From each tooth, 14 sticks were prepared for micro-tensile bond strength (µTBS) testing. The sticks were stored in simulated body fluid at 37 °C and tested after 24 h or six months for µTBS and failure mode. Data were analyzed using Kruskal-Wallis tests in combination with post-hoc Conover-tests and Wilcoxon signed-rank tests at a level of significance of α = 0.05. After 24 h and six months, both etch-and-rinse adhesives with a low BAG content (up to 10 wt% for ASB and 5 wt% for SB) showed similar µTBSs as their respective control groups (0 wt% BAG). CF showed a significant decrease in µTBS even after addition of 5 wt% BAG. At a high concentration of added BAG (20 wt%), all three adhesives showed a significant decrease in µTBS compared to the unmodified controls. The CF control group showed significantly lower µTBS after 6 months of storage than after 24 h. In contrast, the µTBS of all CF groups modified with BAG was unaffected by aging. In conclusion, the tested etch-and-rinse adhesives can be modified with up to 5 wt% (SB), or 10 wt% (ASB) of BAG without reducing their short- and long-term dentin bond strength. Moreover, the addition of nano-sized BAG may prevent long-term bond strength deterioration of a self-etch adhesive.

Anti-Microbial and Remineralizing Properties of Self-Adhesive Orthodontic Resin Containing Mesoporous Bioactive Glass

Self-adhesive resins (SARs) contain adhesives, which simplify the procedures of resin application, and primers, which provide sufficient bonding ability. In this study, mesoporous bioactive glass nanoparticles (MBN) were added to a SAR to easily improve the physical properties and remineralization ability. The experimental resins comprised 1%, 3%, and 5% MBN mixed in Ortho Connect Flow (GC Corp, Tokyo, Japan). As the MBN content in the SAR increased, the microhardness increased, and a statistically significant difference was observed between the cases of 1% and 5% MBN addition. Shear bond strength increased for 1% and 3% MBN samples and decreased for 5% MBN. The addition of MBN indicated a statistically significant antibacterial effect on both gram-negative and gram-positive bacteria. The anti-demineralization experiment showed that the remineralization length increased with the MBN content of the sample. Through the above results, we found that SAR containing MBN has antibacterial and remineralization effects. Thus, by adding MBN to the SAR, we investigated the possibility of orthodontic resin development, wherein the strength is enhanced and the drawbacks of the conventional SAR addressed.

Anti-demineralizing protective effects on enamel identified in experimental and commercial restorative materials with functional fillers

The aim of this study was to investigate whether experimental and commercial dental restorative materials with functional fillers can exert a protective anti-demineralizing effect on enamel that is not immediately adjacent to the restoration. Four experimental resin composites with bioactive glass and three commercial restorative materials were investigated. Enamel blocks were incubated in a lactic acid solution (pH = 4.0) at a standardized distance (5 mm) from cured specimens of restorative materials. The lactic acid solution was replenished every 4 days up to a total of 32 days. Surfaces of enamel blocks were periodically evaluated by Knoop microhardness measurements and scanning electron microscopy. The protective effect of restorative materials against acid was identified as enamel microhardness remaining unchanged for a certain number of 4-day acid addition cycles. Additionally, the pH of the immersion medium was measured. While enamel microhardness in the control group was maintained for 1 acid addition cycle (4 days), restorative materials postponed enamel softening for 2–5 cycles (8–20 days). The materials capable of exerting a stronger alkalizing effect provided longer-lasting enamel protection. The protective and alkalizing effects of experimental composites improved with higher amounts of bioactive glass and were better for conventional bioactive glass 45S5 compared to a fluoride-containing bioactive glass. Scanning electron micrographs evidenced the protective effect of restorative materials by showing a delayed appearance of an etching pattern on the enamel surface. A remotely-acting anti-demineralizing protective effect on enamel was identified in experimental composites functionalized with two types of bioactive glass, as well as in three commercial ion-releasing restorative materials.

Novel Bioactive Glass-Modified Hybrid Composite Resin: Mechanical Properties, Biocompatibility, and Antibacterial and Remineralizing Activity

Secondary caries seriously limits the lifetime of composite resin. However, integrating all desirable properties (i.e., mechanical, antibacterial, bioactivity, and biocompatibility) into one composite resin is still challenging. Herein, a novel bioactive glass (BAG)-modified hybrid composite resin has been successfully developed to simultaneously achieve excellent mechanical properties, good biocompatibility, and antibacterial and remineralizing capabilities. When the mass fractions of BAG particles were added from 8 to 23 wt %, the original mechanical properties of the composite resin, including flexural strength and compressive strength, were not obviously affected without compromising the degree of conversion. Although the BAG incorporation of mass fractions of 16 wt % to 23 wt % in composite resins reduced cell viability, the viability could be recovered to normal by adjusting the pH value. Moreover, the BAG-modified composite resins that were obtained showed good antibacterial effects against Streptococcus mutans and enhanced remineralizing activity on demineralized dentin surfaces with increasing incorporation of BAG particles. The possible mechanisms for antibacterial and remineralizing activity might be closely related to the release of bioactive ions (Ca²⁺, Si⁴⁺), suggesting that its antibacterial and biological properties can be controlled by modulating the amounts of bioactive ions. The capability to balance the mechanical properties, cytotoxicity, antibacterial activity, and bioactivity makes the BAG-modified composite resin a promising prospect for clinical application. Our findings provide insight into better design and intelligent fabrication of bioactive composite resins.

Nanoparticles of Bioactive Glass Enhance Biodentine Bioactivity on Dental Pulp Stem Cells

This study aimed to investigate the cytotoxicity and bioactivity of a novel nanocomposite containing nanoparticles of bioactive glass (nBGs) on human dental pulp stem cells (hDPSCs). nBGs were synthesized by the sol–gel method. Biodentine (BD) nanocomposites (nBG/BD) were prepared with 2 and 5% wt of nBG content; unmodified BD and glass ionomer cement were used as references. Cell viability and attachment were evaluated after 3, 7 and 14 days. Odontogenic differentiation was assessed with alkaline phosphatase (ALP) activity after 7 and 14 days of exposure. Cells successfully adhered and proliferated on nBG/BD nanocomposites, cell viability of nanocomposites was comparable with unmodified BD and higher than GIC. nBG/BD nanocomposites were, particularly, more active to promote odontogenic differentiation, expressed as higher ALP activity of hDPSCs after 7 days of exposure, than neat BD or GIC. This novel nanocomposite biomaterial, nBG/BD, allowed hDPSC attachment and proliferation and increased the expression of ALP, upregulated in mineral-producing cells. These findings open opportunities to use nBG/BD in vital pulp therapies.

Vertical Bite Rehabilitation of Severely Worn Dentitions with Direct Composite Restorations: Clinical Performance up to 11 Years

Our aim was to evaluate the clinical performance of direct composite restorations placed in patients with severely worn dentitions at an increased vertical dimension of occlusion, after up to 11 years. One hundred and sixty-four teeth in 13 patients with severely worn dentitions had been reconstructed with either microhybrid (first cohort; n = 59) or nanofilled (second cohort; n = 105) composite restorations at increased vertical dimension of occlusion using a wax-up-based template-aided placement technique. From the dental records, information about repair and replacement of restorations was obtained. Patients were clinically examined after a mean follow-up time of 10.7 years (first cohort) or 5.2 years (second cohort) using United States Public Health Service (USPHS) criteria. Subjective patient satisfaction was also recorded using visual analogue scales (VAS). The overall quality of the restorations was good with predominantly 'Alpha' and 'Bravo' scores, respectively. Nanofilled composite showed less surface degradation and better margin qualities than microhybrid composite. Of the 59 restored teeth in the first cohort, 13 restorations showed unfavorable events after 10.7 years, of which ten could be repaired. In the second cohort, 23 of 105 restorations showed unfavorable events, which could all be repaired. VAS scores revealed high patient satisfaction with the treatment approach. In conclusion, direct composite restorations placed at an increased vertical dimension of occlusion show good clinical long-term performance in patients with severe tooth wear.

Effect of Varying Working Distances between Sandblasting Device and Composite Substrate Surface on the Repair Bond Strength

This study investigates the effect of defined working distances between the tip of a sandblasting device and a resin composite surface on the composite–composite repair bond strength. Resin composite specimens (Ceram.x Spectra ST (HV); Dentsply Sirona, Konstanz, Germany) were aged by thermal cycling (5000 cycles, 5–55 °C) and one week of water storage. Mechanical surface conditioning of the substrate surfaces was performed by sandblasting with aluminum oxide particles (50 µm, 3 bar, 10 s) from varying working distances of 1, 5, 10, and 15 mm. Specimens were then silanized and restored by application of an adhesive system and repair composite material (Ceram.x Spectra ST (HV)). In the negative control group, no mechanical surface pretreatment or silanization was performed. Directly applied inherent increments served as the positive control group (n = 8). After thermal cycling of all groups, microtensile repair bond strength was assessed, and surfaces were additionally characterized using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The negative control group reached the significantly lowest microtensile bond strength of all groups. No significant differences in repair bond strength were observed within the groups with varying sandblasting distances. Composite surfaces sandblasted from a distance of 1 mm or 5 mm showed no difference in repair bond strength compared to the positive control group, whereas distances of 10 or 15 mm revealed significantly higher repair bond strengths than the inherent incremental bond strength (positive control group). In conclusion, all sandblasted test groups achieved similar or higher repair bond strength than the inherent incremental bond strength, indicating that irrespective of the employed working distance between the sandblasting device and the composite substrate surface, repair restorations can be successfully performed.

Influence of polymerization pressure and post-cure treatment on conversion degree and viscoelastic properties of polymer infiltrated ceramic network

This study aimed at determining an optimum polymerization pressure for Polymer Infiltrated Ceramic Network (PICN) blocks by characterizing the conversion degree (DC) and the viscoelastic properties of experimental PICN blocks polymerized at 90 °C under various high pressures followed or not by post-cure treatment (PC). Near infrared analysis and dynamic mechanical analysis were used to characterize DC and viscoelastic properties of sixteen PICN: one control (thermo-cured) and fifteen experimental groups (one thermo-cured followed by PC and fourteen high pressure polymerized PICN, in the range of 50-350 MPa without and with PC). Conversion degree of high pressure polymerized PICN blocks without post curing displays an optimum between 100 and 150 MPa resulting in an improved E' and T_g. Post curing induces a higher DC with a controversial effect on thermomechanical properties. The results suggested that 100-150 MPa without PC is an optimum polymerization parameter, resulting in PICN blocks with significantly better DC, T_g, E'.

Development of a Bioactive Flowable Resin Composite Containing a Zinc-Doped Phosphate-Based Glass

Flowable resins used for dental restoration are subject to biofilm formation. Zinc has antibacterial properties. Thus, we prepared a zinc-doped phosphate-based glass (Zn-PBG) to dope a flowable resin and evaluated the antibacterial activity of the composite against Streptococcus mutans (S. mutans) to extrapolate the preventative effect toward secondary caries. The composites were prepared having 0 (control), 1.9, 3.8, and 5.4 wt.% Zn-PBG. The flexural strength, elastic modulus, microhardness, depth of cure, ion release, inhibition zone size, and number of colony-forming units were evaluated and analyzed using ANOVA. The flexural strength of the control was significantly higher than those of Zn-PBG samples (p < 0.05). However, all samples meet the International Standard, ISO 4049. The microhardness was not significantly different for the control group and 1.9 and 3.8 wt.% groups, but the 5.4 wt.% Zn-PBG group had a significantly lower microhardness (p < 0.05). Further, the composite resins increasingly released P, Ca, Na, and Zn ions with an increase in Zn-PBG content (p < 0.05). The colony-forming unit count revealed a significant reduction in S. mutans viability (p < 0.05) with increase in Zn-PBG content. Therefore, the addition of Zn-PBG to flowable composite resins enhances antibacterial activity and could aid the prevention of secondary caries.

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.

Margin Integrity of Bulk-Fill Composite Restorations in Primary Teeth

This in vitro study examined the margin integrity of sculptable and flowable bulk-fill resin composites in Class II cavities of primary molars. Standardized Class II cavities were prepared in human primary molars and restored with the following resin composite materials after application of a universal adhesive: a sculptable bulk-fill composite (Tetric EvoCeram Bulk Fill (TEC) or Admira Fusion x-tra (AFX)), a flowable bulk-fill composite (Venus Bulk Fill (VBF) or SDR), or a conventional composite (Filtek Supreme XTE (FS)). The bulk-fill materials were applied in 4 mm layers, while the conventional composite was applied in either 2 mm (FS2, positive control) or 4 mm layers (FS4, negative control). The specimens were exposed to thermo-mechanical loading (TML) in a computer-controlled masticator. A quantitative margin analysis was performed both before and after TML using scanning electron microscopy, and the percentage of continuous margins (margin integrity) was statistically analyzed (α = 0.05). All composites showed a significant decline in margin integrity after TML. AFX exhibited the significantly highest margin integrity of all materials after TML (97.5 ± 2.3%), followed by FS2 (79.2 ± 10.8%), TEC (73.0 ± 9.1%), and FS4 (71.3 ± 14.6%). SDR (43.6 ± 22.3%) and VBF (25.0 ± 8.5%) revealed the lowest margin integrity. In conclusion, the tested sculptable bulk-fill materials show similar or better margin integrity in primary molars than the conventional resin composite placed in 2 mm increments.

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

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

The effect of rapid high-intensity light-curing on micromechanical properties of bulk-fill and conventional resin composites

Rapid high-intensity light-curing of dental resin composites is attractive from a clinical standpoint due to the prospect of time-savings. This study compared the effect of high-intensity (3 s with 3,440 mW/cm²) and conventional (10 s with 1,340 mW/cm²) light-curing on micromechanical properties of conventional and bulk-fill resin composites, including two composites specifically designed for high-intensity curing. Composite specimens were prepared in clinically realistic layer thicknesses. Microhardness (MH) was measured on the top and bottom surfaces of composite specimens 24 h after light-curing (initial MH), and after subsequent immersion for 24 h in absolute ethanol (ethanol MH). Bottom/top ratio for initial MH was calculated as a measure of depth-dependent curing effectiveness, whereas ethanol/initial MH ratio was calculated as a measure of crosslinking density. High-intensity light-curing showed a complex material-dependent effect on micromechanical properties. Most of the sculptable composites showed no effect of the curing protocol on initial MH, whereas flowable composites showed 11–48% lower initial MH for high-intensity curing. Ethanol/initial MH ratios were improved by high-intensity curing in flowable composites (up to 30%) but diminished in sculptable composites (up to 15%). Due to its mixed effect on MH and crosslinking density in flowable composites, high-intensity curing should be used with caution in clinical work.

A New Customized Bioactive Glass Filler to Functionalize Resin Composites: Acid-Neutralizing Capability, Degree of Conversion, and Apatite Precipitation

This study introduced an experimental bioactive glass (BG) with a lower Na₂O content than conventional BG 45S5 (10.5 wt% vs. 24.5 wt%), additionally containing CaF₂ (12 wt%) and a network connectivity similar to that of BG 45S5. A series of experimental composites functionalized with 5-40 wt% of the novel BG was prepared and compared to a corresponding series of experimental composites functionalized with 5-40 wt% of BG 45S5. Commercial acidneutralizing materials (alkasite, giomer, and glass ionomer) were used as references. The capabilities of the materials to neutralize hydrochloric acid (pH = 2.6) and lactic acid (pH = 4.5) were evaluated by real-time pH measurements over 1 h. The degree of conversion and precipitation of calcium phosphate were also investigated. Data were analyzed using one-way and Welch ANOVA at an overall level of significance of 0.05. The acid-neutralizing potential of the experimental BG incorporated into resin composites was generally comparable to that of BG 45S5, and better than that of a giomer and glass ionomer. Fluorine was identified in the precipitate that developed on the composites functionalized with the experimental BG, suggesting a capability of forming fluorapatite. Unlike the 45S5 composition, the experimental BG did not impair the degree of conversion of resin composites. The novel BG filler is therefore an interesting candidate for future investigations of caries-preventive resin composites, and their potential clinical applicability for restorative, preventive, and orthodontic purposes.

Bioactivity and Physico-Chemical Properties of Dental Composites Functionalized with Nano- vs. Micro-Sized Bioactive Glass

Bioactive resin composites can contribute to the prevention of secondary caries, which is one of the main reasons for failure of contemporary dental restorations. This study investigated the effect of particle size of bioactive glass 45S5 on chemical and physical composite properties. Four experimental composites were prepared by admixing the following fillers into a commercial flowable composite: (1) 15 wt% of micro-sized bioactive glass, (2) 15 wt% of nano-sized bioactive glass, (3) a combination of micro- (7.5 wt%) and nano-sized (7.5 wt%) bioactive glass, and (4) 15 wt% of micro-sized inert barium glass. Hydroxyapatite precipitation and pH rise in phosphate-buffered saline were evaluated during 28 days. Degree of conversion and Knoop microhardness were measured 24 h after specimen preparation and after 28 days of phosphate-buffered saline immersion. Data were analyzed using non-parametric statistics (Kruskal-Wallis and Wilcoxon tests) at an overall level of significance of 5%. Downsizing the bioactive glass particles from micro- to nano-size considerably improved their capability to increase pH. The effect of nano-sized bioactive glass on degree of conversion and Knoop microhardness was similar to that of micro-sized bioactive glass. Composites containing nano-sized bioactive glass formed a more uniform hydroxyapatite layer after phosphate-buffered saline immersion than composites containing exclusively micro-sized particles. Partial replacement of nano- by micro-sized bioactive glass in the hybrid composite did not impair its reactivity, degree of conversion (p > 0.05), and Knoop microhardness (p > 0.05). It is concluded that downsizing bioactive glass particles to nano-size improves the alkalizing potential of experimental composites with no negative effects on their fundamental properties.

Light Transmittance and Polymerization of Bulk-Fill Composite Materials Doped with Bioactive Micro-Fillers

This study investigated the effect of bioactive micro-fillers on the light transmittance and polymerization of three commercially available bulk-fill resin composites. These were mixed with 20 wt% bioactive glass 45S5, Portland cement, inert dental barium glass, or nothing (controls). Composites were photo-activated and light transmittance through 4 mm thick specimens was measured in real time. Moreover, degree of conversion (DC) and Knoop hardness (KHN) were assessed. Light transmittance of all bulk-fill composites significantly decreased (p < 0.05) with addition of 20 wt% bioactive glass 45S5 but not when inert barium glass was added. For bulk-fill composites modified with Portland cement, light irradiance dropped below the detection limit at 4 mm depth. The DC at the top surface of the specimens was not affected by addition of bioactive or inert micro-fillers. The bottom-to-top ratio of both DC and KHN surpassed 80% for bulk-fill composites modified with 20 wt% bioactive or inert glass fillers but fell below 20% when the composites were modified with Portland cement. In contrast to Portland cement, the addition of 20 wt% bioactive glass maintains adequate polymerization of bulk-fill composites placed at 4 mm thickness, despite a decrease in light transmittance compared to the unmodified materials.