Partially absorbable meshes for hernia repair offer advantages over nonabsorbable meshes

BACKGROUND: The aim of this study was to establish whether new prosthetic materials with absorbable components, designed to reduce the amount of foreign material in abdominal wall repair, offer advantages over the conventional polypropylene meshes. METHODS: Seven x 5 cm defects created in the anterior abdominal wall of New Zealand white rabbits were repaired by using a nonabsorbable polypropylene prosthesis (Surgipro; Tyco, Barcelona, Spain) or 1 of 2 partially absorbable prostheses available on the market (Vypro II and Ultrapro; Johnson & Johnson, St. Stevens-Woluwe, Belgium). At 14 and 90 days after surgery, tissue/prosthesis specimens were subjected to histological studies, biomechanical strength tests, and shrinkage evaluation. RESULTS: At 90 days, the absorbable filaments of Vypro II had been completely reabsorbed, whereas Ultrapro only showed signs of biodegradation in a few zones. Host tissue infiltration and collagen I deposition in the 3 reticular meshes was optimal. Macrophage counts, mesh shrinkage, and biomechanical resistance values were similar. CONCLUSIONS: Partially absorbable prostheses perform as well as the standard polypropylene mesh and have the benefit that less foreign material remains in the recipient, without compromising mechanical resistance.     

Role of filler and functional group conversion in the evolution of properties in polymeric dental restoratives

Objectives

To examine effects of shrinkage and modulus on the dynamic development of shrinkage stress as a function of methacrylate conversion and filler loading in a model photocurable dimethacrylate-based resin with a silanized barium glass filler.

Methods

BisGMA/TEGDMA samples with filler loading levels of 0–70 wt% were evaluated. Irradiation times and intensities were varied to achieve a wide range of conversion. Shrinkage stress measurements were accompanied with real-time conversion monitoring, while shrinkage and modulus measurements were made at different static conversion points.

Results

Shrinkage increased nearly linearly with respect to conversion, while for a given value of conversion, it decreased proportionally with increasing filler content. Modulus advanced in an exponential fashion with conversion and also increased incrementally with filler content; however, modulus values rose disproportionately rapidly for the highest filler loading. At either high or low filler loading levels, stress at limiting conversion, which was inversely proportional to the filler load, was high while at an intermediate filler content, a minimum in stress was observed due to the combined effects of filler based shrinkage reduction, restricted limiting conversion and only moderately enhanced modulus. The level of polymerization stress predicted from the conversion-indexed shrinkage and modulus measurements over-estimated the experimental stress states as modulus evolved due to system compliance that to some degree mimics the clinical situation presented by photocuring bonded composite restorations.Significance Measurement of monomer conversion provides a common basis by which different material properties can be rationally compared.     

Influence of composition on rate of polymerization contraction of light-curing resin composites

A slow contraction may result in reduced gap formation when a restorative resin polymerizes in a dental cavity. It was the aim in the present work to investigate the rate of contraction in relation to composition of experimental light-curing resin composites. The monomer of the resin composites consisted of mixtures of BisGMA, TEGDMA, and in one series HEMA. The resins contained varying amounts of initiators, co-initiators, and inhibitor, and were made composite by adding a silanized glass filler to a content of 74% by weight of the composite paste. The polymerization contraction up to 120 sec was determined by means of the bonded-disk method. Within the ranges studied, the concentration of initiator and co-initiator in the monomer mixture had only an insignificant influence on rate of polymerization. In comparison to camphorquinone, the initiators 1-phenyl-1,2-propanedione and benzil reduced the rate of polymerization without affecting the final contraction. In comparison to N,N-dimethyl- p -aminobenzoic acid ethyl ester, N,N-cyanoethyl methylaniline was as effective, while N,N-diethanol- p -toluidine was less effective as co-initiator. A relatively high content of the inhibitor methoxyhydroquinone reduced the initial rate but not the final polymerization contraction. The rate of polymerization increased with the level of HEMA and TEGDMA in the monomer mixture. It was concluded that intrinsic slow cure may be obtained with certain compositions of resin composites without impairing the final extent of polymerization.     

Changes on MRI in lumbar disc protrusions in two patients after intradiscal electrothermal therapy

We examined changes to the protruded lumbar disc after intradiscal electrothermal therapy (IDET) using magnetic resonance imaging (MRI) in two patients with chronic discogenic low back pain who underwent IDET. MRI was performed before and 6 months after the treatments. In the follow-up MRI studies, the protrusions were almost abolished and normalized in both patients. We thus confirmed shrinkage of the protruded disc by IDET on MRI images in two patients.     

定量阻力呼气与缩唇呼吸治疗Ⅱ型呼吸衰竭临床对比研究

目的：比较定量阻力呼气与缩唇呼吸治疗Ⅱ型呼吸衰竭的临床疗效。方法选取该院2013年1月—2014年5月收治的慢性阻塞性肺疾病（COPD）合并Ⅱ型呼吸衰竭患者72例,随机分为两组,每组各36例。 A组患者采用定量阻力呼气进行肺康复,B组患者采用缩唇呼吸进行肺康复。观察对比两组患者治疗5 d后的血气分析结果。结果两组的血气情况均较治疗前有显著改善,A组治疗后的PaO2指数明显高于治疗前(P<0.05),PaCO2指数明显低于治疗前(P<0.05);B组治疗后的PaO2指数显著高于治疗前(P<0.05),PaCO2指数较治疗前降低(P<0.05);两组治疗前后pH值变化差异无统计学意义（P>0.05）。结论定量阻力呼气与缩唇呼吸治疗Ⅱ型呼吸衰竭均有显著的临床疗效,可有效改善患者的缺氧和二氧化碳潴留症状。定量阻力呼气在控制PEEPe水平上精确性高于缩唇呼吸,减少呼气负荷过大和呼吸肌做功引发的风险。     

Polymerization shrinkage and polymerization shrinkage stress in polymer-based restoratives

Objectives: This paper is intended to contribute to the recognition and understanding of problems related to polymerization shrinkage.

Data sources: Scientific publications of relevance with regard to this subject were critically reviewed.

Study selection: The dimensional changes which develop during the curing of resin composites and glass polyalkenoate cements are studied, with special reference to methods of determining shrinkage, shrinkage stress and stress relief.

Conclusions: As no method for handling the adhesive restorative materials has yet been described which guarantees a leakproof restoration, the practitioner has to accept the problem of polymerization shrinkage and destructive shrinkage stress. Only a proper understanding of the mechanisms that cause these problems and the techniques that may reduce their effects will enable the practitioner to derive maximum benefit from the application of resin composites and glass polyalkenoate cements in restorative dentistry.     

Development of an oxirane/acrylate interpenetrating polymer network (IPN) resin system

Objective

Develop a hydrophobic, degradation-resistant dental restorative based on an Oxirane-Acrylate IPN System (OASys) with low shrinkage-stress to substantially extend clinical lifetime.

Shrinkage stress and cuspal deflection in MOD restorations: analytical solutions and design guidelines

ObjectiveThis paper aimed to derive analytical solutions for the shrinkage stress and cuspal deflection in model Class-II mesial-occlusal-distal (MOD) resin-composite restorations to better understand their dependence on geometrical and material parameters. Based on the stress solutions, it was shown how design curves could be obtained to guide the selection of dimensions and materials for the preparation and restoration of this class of cavities.MethodsThe cavity wall was considered as a cantilevered beam while the resin composite was modeled as Winkler’s elastic foundation with closely-spaced linear springs. Further, a mathematical model that took into account the combined effect of material properties, sample geometry and compliance of the surrounding constraint was employed to relate the shrinkage stress at the “tooth-composite” interface to the local compliance of the cavity wall. Exact analytical solutions were obtained for cuspal deflection and shrinkage stress along the cavity wall by solving the resulting differential equation, which had the same form as that for a beam on elastic foundation with a distributed load. To quantify the shrinkage stress at the cavity floor, the resin composite was assumed to be a beam, fixed at both ends and loaded with a uniformly distributed load that approximated the shrinkage stress. The analytical solutions thus obtained were compared with results from finite element analysis (FEA).ResultsThe analytical solution for cuspal deflection contains a dimensionless parameter, γ, which represents the stiffness of the cavity wall relative to that of the cured resin composite. For the same shrinkage strain, cuspal deflection increases with reducing γ, i.e. reducing stiffness of the cavity wall or increasing stiffness of the composite. For the same γ, cuspal deflection increases proportionally with shrinkage strain. Shrinkage stress along the cavity wall is maximum at the cavity corner and reduces towards the occlusal surface; the maximum value depends only on Young’s modulus and the shrinkage strain of the resin composite. For low values of γ, the interfacial stress at the occlusal surface can become compressive. The interfacial stress at the cavity floor can be much higher than that along the cavity wall, increasing exponentially with the resin composite’s thickness. The analytical solutions agree well with FEA predictions.SignificanceWhen validated, the analytical solutions and design curves presented in this study can provide useful guidelines for choosing appropriate dimensions of cavity preparations and resin composite materials with suitable mechanical properties for Class-II MOD restorations to help avoid tooth fracture and interfacial debonding caused by polymerization shrinkage.     

Adhesive class I restorations in sound molar teeth incorporating combined resin-composite and glass ionomer materials: CAD-FE modeling and analysis

ObjectivesTo investigate the influence of different resin composite and glass ionomer cement material combinations in a “bi-layer” versus a “single-layer” adhesive technique for class I cavity restorations in molars using numerical finite element analysis (FEA).Materials and MethodsThree virtual restored lower molar models with class I cavities 4 mm deep were created from a sound molar CAD model. A combination of an adhesive and flowable composite with bulk fill composite (model A), of a glass ionomer cement with bulk fill composite (model B) and of an adhesive with bulk fill composite (model C), were considered. Starting from CAD models, 3D-finite element (FE) models were created and analyzed. Solid food was modeled on the occlusal surface and slide-type contact elements were used between tooth surface and food. Polymerization shrinkage was simulated for the composite materials. Physiological masticatory loads were applied to these systems combined with shrinkage. Static linear analyses were carried out. The maximum normal stress criterion was adopted as a measure of potential damage.ResultsAll models exhibited high stresses principally located along the tooth tissues–restoration interfaces. All models showed a similar stress trend along enamel–restoration interface, where stresses up to 22 MPa and 19 MPa was recorded in the enamel and restoration, respectively. A and C models showed a similar stress trend along the dentin-restoration interface with a lower stress level in model A, where stresses up to 11.5 MPa and 7.5 MPa were recorded in the dentin and restoration, respectively, whereas stresses of 17 MPa and 9 MPa were detected for model C. In contrast to A and C models, the model B showed a reduced stress level in dentin, in the lower restoration layer and no stress on the cavity floor.SignificanceFE analysis supported the positive effect of a “bi-layer” restorative technique in a 4 mm deep class I cavities in lower molars versus “single-layer” bulk fill composite technique.