Photopolymerization shrinkage-stress reduction in polymer-based dental restoratives by surface modification of fillers

ObjectivesThis research explores the use of polymer brushes for surface treatment of fillers used in polymer-based dental restoratives with focus on shrinkage stress reduction. The influence of interfacial reactive groups on shrinkage stress is explored.MethodsOligomers of varying lengths and with varying number of reactive groups along the length were synthesized by modifying commercial oligomers. Surface of silica fillers (OX50) was treated with methylaminopropyltrimethoxysilane and this was further reacted with the synthesized oligomers to obtain a series of polymer brushes on the surface. Fillers modified with γ-methacryloxypropyltrimethoxysilane were used as a control. Filler surface treatment was confirmed using diffuse reflectance spectroscopy and thermogravimetric analysis. Fillers were added at 30 wt % to a resin made of BisGMA/TEGDMA and polymerization kinetics, shrinkage stress, volumetric shrinkage, flexural strength and modulus, viscosity were measured.ResultsComposites with polymer brush functionalized fillers showed up to a 30 % reduction in shrinkage stress as compared to the control, with no reduction in flexural strength and modulus. Shrinkage stress reduced with increasing length of the polymer brush and increased with increase in number of reactive groups along the length of the polymer brush.SignificanceThe interface between inorganic fillers and an organic polymer matrix has been utilized to reduce shrinkage stress in a composite with no compromise in mechanical properties. This study gives insights into the stress development mechanism at the interface.     

Bis(4-methyl phenyl)iodonium as an alternative component to diphenyliodonium in camphorquinone-based ternary initiating systems

ObjectiveTo evaluate the influence of different co-initiators (diphenyliodonium hexafluorophosphate - DPI - and bis(4-methyl phenyl)iodonium hexafluorophosphate – BPI) on chemical and mechanical properties of resins.MethodsNine experimental resins (50% Bis-GMA and 50% TEGDMA, w/w) with 60 wt% filler particles were formulated. The initiating system used was camphorquinone (CQ-1 mol%) and ethyl dimethylaminobenzoate (EDAB-2 mol%). Experimental groups were established according to DPI and BPI quantities (0.25, 0.5, 0.75, and 1 mol%). The control group was a resin containing only CQ-EDAB. Light transmission through the resin during polymerisation was analysed with a UV–vis spectrophotometer. Real-time polymerisation of the systems was evaluated using an FTIR spectrometer. Real-time polymerisation shrinkage strain was evaluated, and the flexural strength and modulus of materials were obtained by 3-point bending. Experimental groups were statistically analysed by Analysis of Variance and Tukey’s test (α = 0.05). Dunnett’s test was applied to compare experimental groups with control.ResultsLight transmission rapidly increased initially for resins containing DPI or BPI. After 30 s cure, the irradiance on the lower surface of resin specimens was similar for all groups. After 10 s of light irradiation, groups containing DPI and BPI had higher conversion than the control. However, conversion after 120 s post-irradiation was similar for all groups. The rate of polymerisation, shrinkage strain, and the maximum strain rate were higher for groups containing DPI/BPI. The use of iodonium salts increased the flexural strength and flexural moduli of resins.SignificanceDPI and BPI increased resin reactivity similarly. Increased rate of polymerization influenced light transmission through the resin in the first seconds of polymerisation and increased resin shrinkage and rate of shrinkage, as well as flexural strength and moduli.     

Machine learning-based scoring system to predict in-hospital outcomes in patients hospitalized with COVID-19

BackgroundThe evolution of patients hospitalized with coronavirus disease 2019 (COVID-19) is still hard to predict, even after several months of dealing with the pandemic.AimsTo develop and validate a score to predict outcomes in patients hospitalized with COVID-19.MethodsAll consecutive adults hospitalized for COVID-19 from February to April 2020 were included in a nationwide observational study. Primary composite outcome was transfer to an intensive care unit from an emergency department or conventional ward, or in-hospital death. A score that estimates the risk of experiencing the primary outcome was constructed from a derivation cohort using stacked LASSO (Least Absolute Shrinkage and Selection Operator), and was tested in a validation cohort.ResultsAmong 2873 patients analysed (57.9% men; 66.6 ± 17.0 years), the primary outcome occurred in 838 (29.2%) patients: 551 (19.2%) were transferred to an intensive care unit; and 287 (10.0%) died in-hospital without transfer to an intensive care unit. Using stacked LASSO, we identified 11 variables independently associated with the primary outcome in multivariable analysis in the derivation cohort (n = 2313), including demographics (sex), triage vitals (body temperature, dyspnoea, respiratory rate, fraction of inspired oxygen, blood oxygen saturation) and biological variables (pH, platelets, C-reactive protein, aspartate aminotransferase, estimated glomerular filtration rate). The Critical COVID-19 France (CCF) risk score was then developed, and displayed accurate calibration and discrimination in the derivation cohort, with C-statistics of 0.78 (95% confidence interval 0.75–0.80). The CCF risk score performed significantly better (i.e. higher C-statistics) than the usual critical care risk scores.ConclusionsThe CCF risk score was built using data collected routinely at hospital admission to predict outcomes in patients with COVID-19. This score holds promise to improve early triage of patients and allocation of healthcare resources.     

Property evolution during vitrification of dimethacrylate photopolymer networks

Objectives

This study seeks to correlate the interrelated properties of conversion, shrinkage, modulus and stress as dimethacrylate networks transition from rubbery to glassy states during photopolymerization.

Methods

An unfilled BisGMA/TEGDMA resin was photocured for various irradiation intervals (7–600 s) to provide controlled levels of immediate conversion, which was monitored continuously for 10 min. Fiber optic near-infrared spectroscopy permitted coupling of real-time conversion measurement with dynamic polymerization shrinkage (linometer), modulus (dynamic mechanical analyzer) and stress (tensometer) development profiles.

Results

The varied irradiation conditions produced final conversion ranging from 6% to more than 60%. Post-irradiation conversion (dark cure) was quite limited when photopolymerization was interrupted either at very low or very high levels of conversion while significant dark cure contributions were possible for photocuring reactions suspended within the post-gel, rubbery regime. Analysis of conversion-based property evolution during and subsequent to photocuring demonstrated that the shrinkage rate increased significantly at about 40% conversion followed by late-stage suppression in the conversion-dependent shrinkage rate that begins at about 45–50% conversion. The gradual vitrification process over this conversion range is evident based on the broad but well-defined inflection in the modulus versus conversion data. As limiting conversion is approached, modulus and, to a somewhat lesser extent, stress rise precipitously as a result of vitrification with the stress profile showing little if any late-stage suppression as seen with shrinkage.

Significance

Near the limiting conversion for this model resin, the volumetric polymerization shrinkage rate slows while an exponential rise in modulus promotes the vitrification process that appears to largely dictate stress development.     

Dimethacrylate network formation and polymer property evolution as determined by the selection of monomers and curing conditions

Objectives

This overview is intended to highlight connections between monomer structure and the development of highly crosslinked photopolymer networks including the conversion dependent properties of shrinkage, modulus and stress.

Methods

A review is provided that combines the polymer science and dental materials literature along with examples of relevant experimental results, which include measurements of reaction kinetics, photorheology as well as polymerization shrinkage and stress.

Results

While new monomers are continually under development for dental materials applications, mixtures of dimethacrylate monomers persist as the most common form of dental resins used on composite restorative materials. Monomer viscosity and reaction potential is derived from molecular structure and by employing real-time near-infrared spectroscopic techniques, the development of macromolecular networks is linked to the evolution of polymerization shrinkage (measured by linometer), modulus (measured by photorheometer), and stress (measured by tensometer). Relationships between the respective polymer properties are examined.

Significance

Through a better understanding of the polymer network formation and property development processes using conventional dimethacrylate monomer formulations, the rational design of improved materials is facilitated with the ultimate goal of achieving dental polymers that deliver enhanced clinical outcomes.     

Reduced polymerization stress of MAPO-containing resin composites with increased curing speed,degree of conversion and mechanical properties

Objectives

The degree and rate of photopolymerization in resin-based dental composites will significantly affect polymer network formation and resultant material properties that may determine their clinical success. This study investigates the mechanical properties, the generation of stress from polymerization, tooth cusp deflection and marginal integrity of experimental resin composites that contain different photoinitiators.

Methods

Experimental light-activated resin composites (60 vol% particulate filled in 50/50 mass% bis-GMA/TEGDMA) were formulated using a monoacylphosphine oxide (MAPO) photoinitiator and compared with a conventional camphoroquinone (CQ)-based system. Similar radiant exposure was used (18 J cm⁻²) for polymerization of each material although the curing protocol was varied (400 mW cm⁻² for 45 s, 1500 mW cm⁻² for 12 s and 3000 mW cm⁻² for 6 s). Degree and rate of polymerization was calculated in real-time by near infrared spectroscopy and the generation of stress throughout polymerization measured using a cantilever beam method. Flexural strength and modulus were acquired by three-point bend tests. Standardized cavities in extract pre-molar teeth were restored with each material, the total cuspal deflection measured and post-placement marginal integrity between the tooth and restoration recorded.

Results

Generally, MAPO- exhibited a significantly higher degree of conversion (72 ± 0.8 to 82 ± 0.5%) compared with CQ-based materials (39 ± 0.7 to 65 ± 1.6%) regardless of curing protocol (p < 0.05) and MAPO-based materials exhibited less difference in conversion between curing protocols. CQ-based materials exhibited between ∼85 and 95% of the maximum rate of polymerization at <15% conversion, whereas MAPO-based RBCs did not approach the maximum rate until >50% conversion. Higher irradiance polymerization had a significant deleterious effect on the mechanical properties of CQ-based materials (p < 0.05) whereas MAPO-based materials exhibited increased strength and modulus and were less affected by the curing method. Total cuspal deflection in restored extracted teeth was higher for CQ- compared with MAPO-based materials cured at the lowest irradiance curing protocol (12.9 ± 4.0 and 8.3 ± 1.5 μm) and similar at 3000 mW cm⁻¹ for 6 s (10.1 ± 3.5 and 9.0 ± 1.5 μm). A significant decrease in marginal integrity was observed for CQ-based RBCs cured at high irradiance for short exposure time compared with that of the MAPO-based RBC cured using a similar protocol (p = 0.037).

Significance

Polymer network formation dictates the final properties of the set composite and the use MAPO photoinitiators may provide an effective restorative material that exhibits higher curing speeds, increased degree of conversion, strength and modulus without compromise in terms of polymerization stress and marginal integrity between tooth and restoration.     

Fibroid embolization

The most common surgical treatment for fibroids is hysterectomy and approximately 30,000 are carried out annually in the UK for this condition. The operation, however, carries a significant complication rate. Since the first case was carried out in 1989 there has been increasing interest in the interventional radiological procedure called fibroid embolization where angiographic techniques are used to occlude the vascular supply of fibroids. This article is a review of the world experience of fibroid embolization, its development, techniques, indications, results and complications. So far evidence indicates very promising mid-term results but more long-term comprehensive data is needed from large trials.     

Setting characteristics and cavity adaptation of low-shrinking resin composites

ObjectivesThe aim of this study was to evaluate the setting characteristics of low-shrinking resin composites and examine the possible interactions with curing efficiency and marginal adaptation in dentin cavities.MethodsThe materials tested were Ceram X Mono/CM, Premise/PR, Clearfil Majesty/CM, ELS/EL, and Filtek Silorane/FS. Polymerization shrinkage strain (%S), strain rate (%S_r) and time at maximum strain rate (t_max) were measured using the bonded disk method. Curing efficiency was measured on the top and bottom surfaces of composites with ATR-FTIR spectroscopy. Marginal adaptation was measured in unbonded (%VVF) and bonded (%XVF) specimens by computerized X-ray microtomography (micro-XCT). The % linear length of the interfacial gaps along the cavity margins (%LD) and the maximum gap width (WD_max) were calculated under optical microscopy on sectioned specimens. Statistical analysis was performed with one- and two-way ANOVA, Bonferroni's post hoc test and Pearson's correlation coefficient.ResultsThe %S values ranged from 1.34% (FS) to 2.29% (CX), while %S_r ranged from 0.06%s^?1 (FS) to 0.15%s^?1 (CX). %VVF values extended from 1.9% (FS) to 5.3% (CX) and for %XVF from 1.98% (FS) to 3.35% (CX). The values for %LD ranged from 36.52% (FS) to 81.28% (CX). Linear regression showed strong positive correlation for %S_r and t_max with %VVF (r² = 0.884 and r² = 0.927) and also for %S_r and t_max with %LD (r² = 0.823 and r² = 0.869).Significance%S_r and t_max are more representative than %S in determining the setting pattern of the materials and are strongly correlated to marginal adaptation. The silorane material showed better behavior than the dimethacrylate materials in setting shrinkage and marginal adaptation.     

Computed tomographic measurements of mesh shrinkage after laparoscopic ventral incisional hernia repair with an expanded polytetrafluoroethylene mesh

Background  The potential for shrinkage of intraperitoneally implanted meshes for laparoscopic repair of ventral and incisional hernia (LRVIH) remains a concern. Numerous experimental studies on this issue reported very inconsistent results. Expanded polytetrafluoroethylene (ePTFE) mesh has the unique property of being revealed by computed tomography (CT). We therefore conducted an analysis of CT findings in patients who had previously undergone LRVIH with an ePTFE mesh (DualMesh, WL Gore, Flagstaff, AZ, USA) in order to evaluate the shrinkage of implanted meshes. Patients and methods  Of 656 LRVIH patients with DualMesh, all patients who subsequently underwent CT scanning were identified and only those with precisely known transverse diameter of implanted mesh and with CT scans made more than 3 months postoperatively were selected (n = 40). Two radiologists who were blinded to the size of the implanted mesh measured in consensus the maximal transverse diameter of the meshes by using the AquariusNET program (TeraRecon Inc., San Mateo, CA, USA). Mesh shrinkage was defined as the relative loss of transverse diameter as compared with the original transverse diameter of the mesh. Results  The mean time from LRVIH to CT scan was 17.9 months (range 3–59 months). The mean shrinkage of the mesh was 7.5% (range 0–23.7%). For 11 patients (28%) there was no shrinkage at all. Shrinkage of 1–10% was found in 16 patients (40%), of 10–20% in 10 patients (25%), and of 20–24% in 3 patients (7.5%). No correlation was found regarding the elapsed time between LRVIH and CT, and shrinkage. There were two recurrences, one possibly related to shrinkage. Conclusion  Our observations indicate that shrinkage of DualMesh is remarkably lower than has been reported in experimental studies (8–51%). This study is the first to address the problem of shrinkage after intraperitoneal implantation of synthetic mesh in a clinical material.     

GI—I型粉浆涂塑铝瓷核冠材料线收缩率测试

测试了ＧＩ－Ｉ型粉浆涂塑铝瓷核冠代型和铝瓷底层在不同烧烤时间、烧烤温度时的线收缩率。结果表明：代型和铝瓷底层在烧烤至１２０℃时，都有０．０２％的线膨胀；烧结烧烤完成后，代型的线收缩率为１３．２８％；铝瓷的线收缩率为０．２１％；代型的收缩主要发生在１２０～１１２０℃保持２ｈ的过程中，而铝瓷的收缩主要发生在１１２０℃保持２ｈ的过程中。