Polymerization Shrinkage Research Articles

Antimicrobial dental composites with K18-methyl methacrylate and K18-filler

ObjectiveTo determine the effects of using K18-methyl methacrylate (K18-MMA) and K18-Filler on composite cure, esthetic, mechanical, polymerization shrinkage, and antimicrobial properties. MethodsK18-MMA (0–20% w/w) was used to replace TEGDMA in a 70:30 Bis-GMA:TEGDMA composite filled to 70% w/w with barium glass or K18-Filler. Composite degree of cure (Rockwell15T hardness and near Infrared FTIR), hydrophilicity (contact angle measurements), translucency (transparency parameter measurements, TP), mechanical (3-point bend test), polymerization shrinkage (volumetric shrinkage and shrinkage stress), and antimicrobial properties (colony counting assay) against Streptococcus mutans, Streptococcus sanguinis, and Candida albicans were determined. ResultsAll experimental groups had comparable degrees of cure (near Infrared FTIR and Rockwell15T Hardness), TP, moduli, polymerization volumetric shrinkages and shrinkage stresses to those of controls (Bonferroni corrected p > 0.0018). Only one group (15% K18-MMA+K18-Filler) had significantly different (lower) contact angles as compared to that of controls (Bonferroni corrected p < 0.0018). Most of the K18-Filler-containing composites had significantly lower ultimate transverse strengths (UTS) than controls (Bonferroni corrected p < 0.0018). Controls had significantly greater S mutans colony counts than 15% and 20% w/w K18-MMA+K18-Filler groups, and greater S sanguinis and C albicans colony counts than K18-containing groups. Of the composites with that provided significant antimicrobial properties against S. mutans, S. sanguinis, and C. albicans, only the 20% K18-MMA+K18-Filler group had significantly lower UTS than controls. SignificanceComposites with K18-MMA and K18-Filler with comparable physical properties to control composites and significant antimicrobial properties have been developed. K18-MMA and K18-Filler seem to be suitable for incorporation into commercial dental resins.

Novel low-shrinkage dental resin containing microcapsules with antibacterial and self-healing properties

Dental resin restorations commonly fail because of fractures and secondary caries. The aim of this research was to synthesize a novel low-shrinkage dental resin with antibacterial and self-healing properties. The low-shrinkage dental resin was obtained by incorporating a 20 wt% anti-shrinkage mixture of an expanding monomer 3,9-diethyl-3,9-dimethylol −1,5,7,11-tetraoxaspiro[5,5] undecane and an epoxy resin monomer diallyl bisphenol A diglycidyl ether (1:1, referred as “UE”) and different mass fractions of self-healing antibacterial microcapsules (0%, 2.5%, 5%, 7.5%, and 10%) were incorporated into the matrix to prepare multifunctional dental resin. Polymerization shrinkage, mechanical properties, antibacterial activity, self-healing ability, and cytotoxicity of this dental resin were evaluated. The polymerization volumetric shrinkage of resin containing 20 wt% UE and 7.5 wt% microcapsules was reduced by 30.12% (4.13% ± 0.42%) compared with control. Furthermore, it exhibited high antibacterial activity and a good self-healing efficiency of 71% without adversely affecting the mechanical property and cell viability. This novel multifunctional dental resin with low polymerization shrinkage and excellent antibacterial activity and self-healing capability has potential application as a dental resin material to decrease the incidence of fractures and secondary caries.

Luting laminate veneers: Do resin-composites produce less polymerization stress than resin cements?

ObjectivesRegular composites could produce less polymerization stress than resin cements when luting laminate veneers but there is no proper evidence to support this theory. The current study aimed to determine the degree of conversion, volumetric shrinkage, polymerization stress and the resultant elastic moduli of materials currently used for adhesive cementation and to determine possible correlations. MethodsThe study considered (i) regular resin composites (Admira Fusion, Gradia, Grandioso, Palfique, Sirius Z, Viscalor and Z100) at room and pre-warmed (PW) at 69ºC, (ii) flowable composites (Sigma Flow and Grandioso Flow); (iii) solely light-activated cements (AllCem Veneer, Variolink Esthetic and RelyX Veneer); and (iv) one dual-activated resin cement (SpeedCEM). Degree of conversion (DC, n = 3) was accessed with FTIR 1 h after irradiation. Bonded-disk and Bioman II instruments were used to access polymerization shrinkage strain and shrinkage stress, respectively, for 60 min at 23 ± 1◦C (n = 3). The elastic modulus was determined by 3-point bending flexural test (n = 6). The results were submitted to analyse s of variance, Tukey’s, and correlation tests. ResultsFor regular composites, the pre-warming did not affect DC, shrinkage and modulus but significantly increased the stress magnitude. Correlation tests indicated a significant relationship only between stress and polymerization shrinkage (r = 0.811343). SignificanceRegular composites can produce less polymerization stress than resin cements when luting laminate veneers. Polymerization stress was dependent on the shrinkage magnitude, but not on the degree of conversion nor the elastic modulus.

The effect of different enamel surface preparations on microleakage under orthodontic brackets

Microleakage is caused by many factors, including polymerization shrinkage of the resin, thermal expansion differences between the enamel and the adhesive, and inadequate adherence. This study aims to assess the microleakage value under orthodontic brackets after three distinct enamel surface preparations and compare the results to the traditional procedure. Fifty-four intact upper premolars were randomly distributed into three groups. First group 18 teeth etched with 36% phosphoric acid Dentsply. Second group 18 teeth etched with %1.23 acidulated phosphate fluoride (APF) incorporated phosphoric acid 25%APF 75%phosphoric acid Dentsply. Third group 18 teeth etched with Trans Bond TM Plus Self-Etching prime 3M Unitek, Monrovia, USA. Then, according to the manufacturer's instructions, all groups bonded to stainless steel brackets RAZOR, IOS, USA, using light-cured composite 3M Unitek/ Monrovia, USA. Then, each subgroup was divided into 3 subgroups, 6 teeth each. The first subgroup thermocycled 500 cycles between 5 C and 55 UC in deionized water and tested after 24 hours of water storage. The second subgroup was also thermocycled and tested after 2 months of water storage. The third subgroup was subjected to cyclic acid attack for 2 months by an acidic solution pH=2.5. Microleakage was evaluated using a dye penetration technique. All samples are sectioned and evaluated under a stereomicroscope. For statistical analysis, the Kruskal-Wallis test was employed. P=0.05 was the level of significance. A significant difference was between etching groups following a thermocycler and a twenty-four-hour water storage, no significant difference after thermocycling and two months of water storage, and significant difference at the occlusal side and between overall means of compared etching groups. This study revealed that the highest microleakage values were in the SEP self-etch prime group, then EF 1.23% APF incorporated phosphoric acid group and the ER 36% phosphoric acid group. The gingival side had more microleakage than the occlusal side. Adding around 20-25 percent of 1.23 percent of phosphoric acid for enamel preparation before orthodontic bonding increases microleakage values, but SEP remains the highest. Keywords: Microleakage, Self-etch prime, Acidulated phosphate fluoride, Stainless steel brackets

Effect of preheating of bulk-fill resin dental composite on polymerization shrinkage strain

Effect of preheating of bulk-fill resin dental composite on polymerization shrinkage strain

Deterioration and mitigation of efflorescence of alkali-activated phosphorus slag

To achieve the efficient application of alkali-activated phosphorus slag (AAPS), this study revealed the efflorescence mechanisms and found a feasible way to mitigate the efflorescence deterioration. The efflorescence formations were mainly constituted of Na2CO3·H2O, Na3H(CO3)2·2H2O and NaHCO3. The order of the efflorescence ability of Na species was Naf (free Na in unreacted alkali activator) > Naw (weakly bonded Na in calcium-sodium aluminosilicate hydrate (CNASH)) > Nas (strongly bonded Na in CNASH). CNASH with lower Na/Si ratios and higher polymerization degrees was harder to form efflorescence. The accelerated efflorescence not only caused the dealkalization, dealumination and polymerization shrinkage of CNASH, but also deteriorated the homogeneity of CNASH distribution in pastes, due to the uneven carbonization of the upper and lower parts of pastes. The growth of efflorescence formation and the polymerization shrinkage of CNASH caused the upper parts of pastes to crack, which deteriorated the integrity of pastes. The accelerated efflorescence deteriorated the homogeneity and integrity of pastes. An effective strategy to mitigate the efflorescence and crack of pastes resulted from the addition of aggregates, which assisted in the development of compressive strength. AAPS mortars with low Na2O doses or moderate silicate moduli had better resistance to efflorescence.

Anti-cracking coating with wrinkled morphology for enhancing oxidation resistance of carbon-based fiber aerogel

In our previous work, ceramic precursor coating with wrinkled morphology was obtained by cross-linking gradient generated from ultraviolet and cross-linking agent to improve the anti-cracking of the coating in the pyrolysis. However, the cross-linking gradient was difficult to control with ultraviolet and cross-linking agent. Herein, a simple method was proposed to form the wrinkled morphology of the coating by the steady-state temperature gradient field generated from constant temperature pre-treatment. Composite aerogels were prepared by pyrolysis at high temperature. The thermal insulation and oxidation resistance of the composite aerogels were explored. The heat transfer behavior within the composite aerogels was analyzed by simulation. The results showed that the stored strain of wrinkled morphology counteracted the shrinkage of ceramic precursor polymer during the pyrolysis, which prevented the cracking of the coating. Compared with the aerogels of our previous work, the composite aerogels of this work demonstrated improved thermal insulation and oxidation resistance.

Evaluation of physical/mechanical properties of an experimental dental composite modified with a zirconium-based metal-organic framework (MOF) as an innovative dental filler.

This study aimed to modify an experimental dental composite using a synthesized nano-structured methacrylated zirconium-based MOF to enhance physical/mechanical properties. The previously known Uio-66-NH2 MOF was first synthesized and post-modified with Glycidyl Methacrylate (GMA). Fourier Transform Infrared (FTIR) Spectroscopy and CHNS analysis confirmed the post-modification reaction. The prepared filler was investigated by XRD, BET, SEM-EDS, and TEM. The experimental composite was prepared by mixing 60% wt. of resin matrix with 40% wt. of fillers, including silanized silica (SS) or Uio-66-NH-Me (UM). The experimental composites' depth of cure (DPC) was investigated in five groups (G1=40% SS, G2=30%SS+10%UM, G3=20%SS+20%UM, G4=10%SS+30%UM, G5=40%UM). Then flexural strength(FS), Elastic Modulus(EM), solubility(S), water sorption(WS), degree of conversion(DC), polymerization shrinkage(PS), and polymerization stress(PSR) of the groups with DPC of more than 1mm were investigated. Finally, the cytotoxicity of composites was studied. The groups with more than 20% wt. UM, filler (G4, G5) had lesser than 1mm DPC. Therefore, we investigated three groups' physical and mechanical properties with lower than 20% UM filler (G1-G3). Within these groups, G3 has a higher FS, EM (P<0.05), and lower WS and S (P<0.05). DC dropped in G2 and G3 compared to G1 (p<0.05), but there was no significant difference between G2 and G3 (P=0.594). This new filler is an innovative coupling-agent free filler and can be part of dental filler technology itself. It can also introduce a new group of dental fillers based on MOFs, but it still needs a complete investigation to be widely used.

Comparison of a Nanofiber-Reinforced Composite with Different Types of Composite Resins.

The aim of this study was a comprehensive evaluation and comparison of the physical and mechanical properties of a newly developed nano-sized hydroxyapatite fiber-reinforced composite with other fiber-reinforced and particle-filled composites. Commercially available eight composite resins (3 fiber-reinforced and 5 particle-filled) were used: Fiber-reinforced composites: (1) NovaPro Fill (Nanova): newly developed nano-sized hydroxyapatite fiber-reinforced composite (nHAFC-NF); (2) Alert (Pentron): micrometer-scale glass fiber-reinforced composite (µmGFC-AL); (3) Ever X Posterior (GC Corp): millimeter-scale glass fiber-reinforced composite (mmGFC-EX); Particle-filled composites: (4) SDR Plus (Dentsply) low-viscosity bulk-fill (LVBF-SDR); (5) Estelite Bulk Fill (Tokuyama Corp.) low-viscosity bulk-fill (LVBF-EBF); (6) Filtek Bulk Fill Flow (3M ESPE) low-viscosity bulk-fill (LVBF-FBFF); (7) Filtek Bulk Fill (3M ESPE) high-viscosity bulk-fill (HVBF-FBF); and (8) Filtek Z250 (3M ESPE): microhybrid composite (µH-FZ). For Vickers microhardness, cylindrical-shaped specimens (diameter: 4 mm, height: 2 mm) were fabricated (n = 10). For the three-point bending test, bar-shaped (2 × 2 × 25 mm) specimens were fabricated (n = 10). Flexural strength and modulus elasticity were calculated. AcuVol, a video image device, was used for volumetric polymerization shrinkage (VPS) evaluations (n = 6). The polymerization degree of conversion (DC) was measured on the top and bottom surfaces with Fourier Transform Near-Infrared Spectroscopy (FTIR; n = 5). The data were statistically analyzed using one-way ANOVA, Tukey HSD, Welsch ANOVA, and Games-Howell tests (p < 0.05). Pearson coefficient correlation was used to determine the linear correlation. Group µH-FZ displayed the highest microhardness, flexural strength, and modulus elasticity, while Group HVBF-FBF exhibited significantly lower VPS than other composites. When comparing the fiber-reinforced composites, Group mmGFC-EX showed significantly higher microhardness, flexural strength, modulus elasticity, and lower VPS than Group nHAFC-NF but similar DC. A strong correlation was determined between microhardness, VPS and inorganic filler by wt% and vol% (r = 0.572-0.877). Fiber type and length could affect the physical and mechanical properties of fibers containing composite resins.

Comparative Evaluation of Microleakage of G-Aenial, Bis-GMA Nanohybrid and Bis- GMA Microhybrid Flowable Composites in Class I Cavities – An in Vitro Study.

The most vulnerable area while restoring a tooth surface lies at the interphase between the restoration and the tooth margins.This area is the weakest junction in a tooth and serves as a potential pathway for microorganisms to invade into the tooth. This leads tofailures in existing restorations paving way for the initiation of secondary caries progression. An advanced restorative material bridges thisgap and seals off the weak interphasic junctions. Flowable composites having adequate strength and lesser polymerisation shrinkage werechosen. The aim of this study was to find a material having lesser microleakage deemed suitable for restorative purposes. Three types offlowable composites were chosen, which had the objective of being tested as a flowable material for evaluation of microleakage amongstthe three tested groups. Dye penetration test was carried out to evaluate the amount of microleakage occurring under flowable resinswhich were then evaluated under a light reflecting digital compound microscope. A total of 45 extracted human premolars were selectedfor the study; scoring of specimens was done with the help of an Ordinal scale to detect microleakage. The results obtained from thestudy was that G-aenial Universal Flo, performed superior than Tetric N flow which was then followed by Kulzer Charisma Flo whichshowed highest dye penetration. The amount of dye penetration reflects directly the microleakage occuring at the interphases ofrestoration. The novelty of this study lies in the fact that this is one of its kind of study evaluating the amount of microleakage occurringbetween three different flowable composites. It was concluded that G-aenial Universal Flo, showed the least amount of microleakagewhen compared against two similar flowable composites to provide an adequate marginal seal.Keywords: , , , , ,

Mechanisms and differences between sodium and magnesium sulfate attacks on alkali-activated phosphorus slag

To promote the application of alkali-activated phosphorus slag (AAPS), a new type of alkali-activated cement (AAC), this study revealed the mechanisms and differences between Na2SO4 and MgSO4 attacks. During Na2SO4 exposure, the deterioration of AAPS was caused by the expansion of calcium-sodium aluminosilicate hydrate (C-N-A-S-H). The dealkalization of C-N-A-S-H was accelerated by the formation of (NaOH)0, which promoted the polymerization shrinkage of C-N-A-S-H and improved the volume stability of AAPS. During MgSO4 exposure, the deterioration of AAPS was caused by C-N-A-S-H deterioration and Mg(OH)2 expansion, but the Mg(OH)2 layer protected the AAPS from MgSO4 attack. The dealkalization, decalcification and dealumination of C-N-A-S-H was accelerated by the formation of Mg(OH)2 and (NaSO4)−, transforming C-N-A-S-H into magnesium-sodium aluminosilicate hydrate (M-N-A-S-H). The resistance of AAPS to Na2SO4 was excellent, but its resistance to MgSO4 was poorer. These differences were caused by the different binding capacities of Mg2+ and Na+ with OH− and the different degrees of forward movement of the dissolution equilibrium of C-N-A-S-H caused by Na2SO4 and MgSO4.

Measuring polymerization shrinkage of dental composite by using PhS-OCT

A method based on phase-sensitive optical coherence tomography (PhS-OCT) was developed to investigate the depth-resolved polymerization shrinkage of dental composites. The method uses optical coherence tomography (OCT) system to acquire the interference spectra during dental composite polymerization and then estimate the refractive index variation and shrinkage strain from the phase variations of the acquired spectrum. Since OCT is a tomographic imaging technique, PhS-OCT is also available for imaging full-field polymerization behavior inside dental composites. For validation, the polymerization processes of three dental composites, FiltekTM Z350, FiltekTM Z250 and FiltekTM P60, were monitored with PhS-OCT. The strain results agree with the reference values and the relative errors are less than 10%. In addition, the vitrification-point delayed curves were measured, revealing the vitrification-point retardation phenomenon. Finally, the flowable dental composite that polymerized inside the human artificial tooth was also measured, successfully demonstrating the depth-resolved full-field polymerization behavior inside the dental composite.

Comparative Evaluation of Marginal Microleakage of a Bioactive Composite Resin Using Three Different Bonding Agents in Non-Carious Cervical Lesions– An In Vitro Study

Background and objectives: Increasing prevalence of non-carious cervical lesions makes it imperative to overcome challenges in tooth preparation, isolation and restoration. Bio-active restorative materials are relatively new concepts in dentistry having the potential to prevent secondary caries, a major cause of failure of restorations. Composite resins have the disadvantage of polymerization shrinkage leading to marginal gap formation. This study evaluated the marginal microleakage properties of Activa bio-active composite resin using three different adhesives in non- carious cervical lesions. Materials and method: Forty extracted maxillary &amp; mandibular premolars for the study were collected. The specimens were divided into groups (n= 10). Box type class V cavities, 2mm inciso-gingivally, 3mm mesio-distally &amp; 2mm in depth was prepared on the buccal surfaces. Group 1: Activa bio-active resin +No bonding agent, Group 2: Activa bio-active resin +Tetric N-bond, Group 3: Activa bio-active resin +Single bond Universal, Group 4: Activa bio-active resin + G Premio bond. Restorations were done and samples subjected to thermocycling. They were immersed in Rhodamine B dye solution for 24 hours. The samples were longitudinally sectioned in a bucco-lingual direction with diamond discs, examined under a stereo-microscope with 30x magnification and depth of penetration analyzed. The statistical analysis for microleakage was performed using the Kruskal Wallis test followed by the Mann Whitney U-tests with the Wilcoxon correction for pair-wise comparisons at a significance level of p &lt; 0.05. Results: Activa bio-active resin + G Premio bond showed lesser micro-leakage compared to other groups and the difference was statistically significant. Conclusion: Activa bioactive resin with G Premio bond, 8th generation bonding agent showed lesser micro-leakage when compared with 5th and 7th generation bonding agents.

A Comparative in vitro Investigation on the Impact of Fiber Insertion on Cuspal Deflection of Maxillary Premolars Restored with Various Types of Bulk Fill Direct Composite Restorations

Background: Polymerization shrinkage remains a significant disadvantage that makes the use of direct composite restorations difficult. Objective: To evaluate how well a fiber insert and multiple bulk-fill direct restorations worked on the cuspal deflection of MOD cavities in premolar teeth using a Dino-Lite digital microscope and computer software. Methods: In sixty fresh maxillary first premolars, large MOD cavities were created. Teeth were randomly divided into six groups of ten based on restorative materials. SonicFill®, Beautifil Bulk®, and Filtek® Bulk Fill posterior restoratives were used in groups A1, B1, and C1, whereas groups A2, B2, and C2 used the same bulk composite with E-glass fiber (UFM, Dentapreg). Under a digital microscope, the intercuspal distance between two reference points on the cusp tips was measured before preparation, after preparation, 15 minutes after finishing restorations, and one month following incubation. Results: There was a significant difference between the groups after 15 minutes of restoration, but no significant differences following cavity preparation or one month of incubation. CD values were considerably higher after 15 minutes of restoration in groups restored with bulk fill only. Beautifil Bulk Fill restorative resulted in greater cuspal deflection than the other groups. The CD values in each group were significantly higher 15 minutes after restoration compared to cavity preparation and a month of incubation. Conclusion: Using inserts, cuspal deflection in MOD cavities can be significantly minimized, and stress release usually occurs after water incubation.

Preparation of an experimental dental composite with different Bis-GMA/UDMA proportions

ABSTRACT Three types of matrix with constant amount of TEGDMA (30 wt.%), and Bis-EMA (10 wt.%) and variable values of Bis-GMA (10, 5, or 0 wt.%) and UDMA (50, 55, or 60 wt.%) were prepared. Composites were filled with 45 wt.% of silanized silica. Both matrices and composites were tested for flexural strength (FS), diametral tensile strength (DTS), hardness (HV) and polymerization shrinkage stress. There were no significant differences for the DTS test. All materials meet the FS requirements for type 2 dental composites. A significant decrease in HV was observed for matrix non-containing Bis-GMA. The highest value of shrinkage stress had material without Bis-GMA and it amounted 16,6 ± 1.0 MPa (filled) or 13.6 ± 0.8 MPa (unfilled). It was also shown that increasing the amount of UDMA while simultaneously reducing Bis-GMA in the studied materials increases polymerization shrinkage stress, which could be unfavorable for dental materials.

Effect of Attenuated Light Through Translucent Zirconia on the Interfacial Adaptation and Polymerization of Resin Cements.

The first objective was to determine if dual-curing of resin cement with reduced light could affect interfacial adaptations of zirconia restoration. The second objective was to examine whether cement type and pretreatment method of universal adhesive affected interfacial adaptation. The final objective was to compare the polymerization degree of cement under different reduced-light conditions. Inlay cavities were prepared on extracted third molars. Translucent zirconia restorations were milled using Katana UTML (Kuraray Noritake) in three groups with restoration thicknesses of 1, 2, and 3 mm, respectively. Each group had three subgroups using different cementation methods. For subgroup 1, restorations were cemented with self-adhesive cement. For subgroup 2, universal adhesive was applied and light cured. After the restoration was seated with conventional resin cement, light curing was performed. For subgroup 3, after adhesive was applied, the restoration was seated with conventional resin cement. Light curing was performed for the adhesive and cement simultaneously. After thermocycling, interfacial adaptation at the restoration-tooth interface was investigated using swept-source optical coherence tomography imaging. Finally, polymerization shrinkage of the cement was measured using a linometer and compared under the conditions of different zirconia thicknesses and light-curing durations. Interfacial adaptation varied signficantly depending on the zirconia thickness, pretreatment, polymerization mode and cements used (p < 0.05). The effects of the adhesive and polymerization shrinkage differed signficantly, depending on the reduced light under the zirconia (p < 0.05). Lower curing-light irradiance may lead to inferior adaptation and lower polymerization of the cement. Polymerization of resin cement can differ depending on the light irradiance and exposure duration.

High-performance photoinitiating systems for new generation dental fillings.

To obtain new generation dental composites with improved performance properties compared to currently available dental fillings on the market and to determine the influence of new initiating systems on final product parameters such as degree of cure, hardness, color, and shrinkage. In order to verify the effectiveness of the developed initiating systems, typical spectroscopic, electrochemical, and kinetic studies using the real-time FT-IR method were shown. Moreover, paste dental fillings were prepared, the compositions were irradiated with the dental lamp, and the degrees of cross-linking were measured by Raman spectroscopy. The polymerization shrinkage was also determined using the rheometer. In addition, their hardness was examined on the Shore scale. Finally, the color analysis of the composites in the L*a*b*color space was compared with the VITA CLASSIC colorant. It was shown that, due to their excellent spectroscopic and electrochemical properties, new quinazolin-2-one can act as co-initiators in cationic and radical photopolymerization. It was demonstrated that the most effective composite containing the initiator system in the form of 3-SCH3Ph-Q, IOD, MDEA, and an inorganic filler as nanometric silica and a bonding agent is cured more than 90% after just 1 cycle of dental lamp exposure (30s), the hardness of the composite after curing on the Shor Scale is 82±4, and the polymerization shrinkage is less than 2.8%. The article demonstrates effective new initiator systems as an alternative to CQ/amine for obtaining new-generation dental composites. The developed dental composites are a big competition to the currently used dental fillings on the market.

Synthesis and Characterization of Dental Nanocomposite Resins Reinforced with Dual Organomodified Silica/Clay Nanofiller Systems.

Quaternary ammonium (QA) compounds have been widely studied as potential disinfectants in dental restorative materials. The present work investigates whether the gradual displacement of nanosilica by QA-clay nanoparticles may have an impact on the physicochemical and mechanical properties of dental nanocomposite resins. For this purpose, Bis-GMA/TEGDMA-based composite resins were initially synthesized by incorporating 3-(trimethoxysilyl)propyl methacrylate (γ-MPS)-modified nanosilica/QA-clay nanoparticles at 60/0, 55/5, 50/10, 40/20, and 30/30 wt% filler loadings. Their structural characterization was performed by means of scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). The degree of double bond conversion (DC) over time and the polymerization shrinkage were determined with Fourier transform infrared spectroscopy (FTIR) and a linear variable displacement transducer (LVDT), respectively. Mechanical properties as well as water sorption and solubility parameters were also evaluated after storage of nanocomposites in water for 7 days at 37 °C. Spectral data revealed intercalated clay configurations along with areas characterized by silica-clay clusters for clay loadings up to 30 wt%. Furthermore, the insertion of 10 wt% QA-clay enhanced the auto-acceleration effect also sustaining the ultimate (DC), reduced the setting contraction and solubility, and, finally, yielded flexural modulus and strength very close to those of the control nanocomposite resin. The acquired results could herald the advanced design of dental restorative materials appropriate for contemporary clinical applications.

Effect of elastomeric urethane monomer on physicochemical properties and shrinkage stress of resin composites.

This study aimed to evaluate the effect of an elastomeric urethane monomer (Exothane-24) in different concentrations on physicochemical properties, gap formation, and polymerization shrinkage stress of experimental resin composites. All experimental composites were prepared with 50 wt.% of Bis-GMA and 50 wt.% of TEGDMA, to which 0 wt.% (control), 10 wt.%, 20 wt.%, 30 wt.%, and 40 wt.% of Exothane-24 were added. Filler particles (65 wt.%) were then added to these resin matrixes. Ultimate tensile strength (UTS: n = 10), flexural strength (FS: n = 10), flexural modulus (FM: n = 10), hardness (H: n = 10), hardness reduction (HR: n = 10), degree of conversion (DC: n = 5), gap width (GW: n = 10), and polymerization shrinkage stress in Class I (SS-I: n = 10) and Class II (SS-II: n = 10) simulated configuration. All test data were analyzed using one-way ANOVA and Tukey's test (α = 0.05;  = 0.2). Exothane-24 in all concentrations decreased the H, HR, DC, GW, SS-I, and SS-II (p < 0.05) without affecting the UTS, and FS (p > 0.05). Reduction in FM was observed only in the Exothane 40% and 30% groups compared to the control (p < 0.05). Exothane-24 at concentrations 20% and 30% seems suitable since it reduced GW and polymerization SS without affecting the properties of the composite resins tested, except for H.

Trueness of 3-dimensionally printed complete arch implant analog casts

Statement of problemAlthough a completely digital workflow has numerous advantages, a physical definitive cast may be especially helpful for the accurate assembly of components of complex complete arch-fixed prostheses, the evaluation of esthetic and occlusion features, or prosthesis fabrication. Research on the accuracy of additive complete arch casts with implants positioned with a large anterior-posterior (A-P) spread is sparse. PurposeThe purpose of this in vitro study was to evaluate the trueness of complete arch 4-implant analog casts with a large A-P distribution fabricated with different 3-dimensional (3D) printers. Material and methodsTen systems were evaluated representing currently available printing technologies and materials for the additive fabrication of complete arch 4-implant analog casts and compared for deviations in the X-, Y-, and Z-axes from the master model scan (MMS), recorded in standard tessellation language (STL). The MMS was provided to the laboratory selected by the manufacturer, permitting them to create their specific cast with computer-aided design and computer-aided manufacture specific to a particular system, including analog receptacle offset settings. Laboratories fabricated N=10 casts and affixed analogs. A conventional splinted impression and stone cast (CON) was fabricated as a control. The casts were scanned with a precision laboratory scanner (D2000; 3Shape A/S), and files were imported into the Convince metrology software program (3Shape A/S) for comparison with the MMS for mean deviations in the X-, Y-, and Z- axes. A 2-way ANOVA and the Tukey HSD comparison tests were performed between system groups and the 4 implant locations (α=.05). Comparative color maps were used to determine dimensional changes of the edentulous ridges. ResultsFor 2-dimensional deviations from the MMS in each of the 3 axes, the printer type, implant location, and interaction between those 2 variables were found to be statistically significant (P<.05). Comparisons among printers showed the smallest deviations for Asiga Pro 4K (ASG) and Stratasys Origin One (ORI) printers in both the X- and Y-axes and for CON in the Z-axis. For 3D deviations, comparison among printers indicated that ORI, SprintRay Pro55 S (SPR), and Ackuretta SOL (ACK) had the largest deviations, whereas CON and ASG showed the smallest deviations. Comparison color mapping demonstrates a disparity between printed model dimensional changes and implant analog positioning since the color maps of the casts’ ridge crests were not in concordance with the results of the implant analog deviations. ConclusionsASG, 3D Systems ProJet MJP 2500 Plus (MJP), 3D Systems NextDent 5100 (NEX), Stratasys J5 DentaJet (PJ5), Ivoclar PrograPrint PR5 (PR5), and Prodways ProMaker LD20 (PWY) were similar in terms of 3D deviations to the conventional stone cast control. Comparative color mapping showed the direction and quantity of the dimensional changes of the ridge crest frequently did not correlate with the 3D deviations of implant analog positioning. Implant analog insertion errors were predominantly responsible for analog position 3D deviations rather than the polymerization shrinkage of additive photopolymers.