Effect of heat application on the mechanical behaviour of glass ionomer cements

Objectives

The aim of this study was to examine the long-term effect of heat on the mechanical behaviour of conventional highly viscous glass ionomer cements. Besides, the effect of storage time was evaluated.

Materials and methods

Five cements (ChemFil Rock, Riva Self Cure, Fuji IX GP Fast, Equia and Ketac Molar Aplicap) were evaluated using three different preparation methods: no heat application, application of heat by means of a LED curing unit for 20 and 60 s. Four hundred fifty bar-shaped specimens were produced, maintained in distilled water at 37 °C and tested after 1 week, 1 month and 3 months (n?=?10). The Vickers hardness, indentation modulus and creep were measured. In addition, the amount and size of the glass fillers and voids were examined using a light and a scanning electron microscope.

Results

Fuji IX GP Fast showed the highest Vickers hardness, Ketac Molar Aplicap showed the highest indentation modulus and the best value of creep was measured for Riva Self Cure. Vickers hardness, modulus of elasticity and creep resistance increased most for ChemFil Rock and Equia up to 1-month storage.

Conclusions

Heat application showed no effect on the mechanical behaviour of ChemFil Rock, Fuji IX GP Fast and Equia at all ageing time. The impact of storage duration was low.

Clinical relevance

Considering the measured mechanical properties, there is no need of using heat when restoring teeth with glass ionomer cements.     

Polymerization kinetic calculations in dental composites: a method comparison analysis

Objectives

This study aimed to describe the polymerization process and to quantify the parameters of influence in two bulk-fill resin-based composites by comparing two real-time methods: the Fourier transform infrared (FTIR) spectroscopy and the visible light transmission spectrometry.

Materials and methods

The degree of conversion (DC) was recorded in real time for 5 min using the attenuated total reflectance FTIR spectroscopy (n?=?6) on the lower surface of 2, 4, and 6 mm thick samples irradiated for 20 s. The variation in irradiance was recorded during material irradiation at the bottom of the samples (n?=?5). Results were statistically analyzed using one-way and multiple-way ANOVAs with Tukey HSD post hoc test (α?=?0.05), partial eta-squared statistics, and Pearson correlation.

Results

No significant difference was found in DC in any materials as a function of incremental thickness, whereas the irradiance passing the specimens differed consistently within both analyzed increments and materials. These data could be described by the superposition of two exponential functions, the first being attributed to the gel phase and the second to the glass phase, resulting in an exponential sum function. DC data were able to calculate the end of the gel phase and the beginning of the glass phase, whereas irradiance measurements were able to detect only the last phase. The polymerization kinetics in the glass phase was less material-dependent as in the gel phase.

Conclusions

The irradiance measurements were more sensitive to variation in thickness, meaning that translucency is continuing to change as a function of thickness at a higher extent than DC.

Clinical relevance

Knowing the impact of the modulation factors describing the calculated sum exponential function allows the manipulation of the polymerization process at different stages to tailor material properties.     

Effect of sonic-activated resin composites on the repair of aged substrates: an in vitro investigation

Objectives

This study aimed to evaluate whether sonic-activated resin-based composites (RBCs) used as repair materials might improve the repair bond strength of aged RBC substrates.

Materials and methods

Five RBCs were repaired by themselves and by all other materials. The repair was applied with and without sonic activation, resulting in 50 material application technique combinations (n?=?15) and 750 specimens. The cohesive strength of the five materials was used as control (n?=?15). Substrates were aged for 8 weeks in distilled water at 37 °C, roughened, cleaned with phosphoric acid, and repaired by using a silane primer and an adhesive as intermediate agents. The repair bond strength was assessed in a shear test. The modulus of elasticity (E) of the five RBCs was additionally evaluated in a three-point bending test.

Results

Results were compared using one- and multiple-way analyses of variance and Tukey’s honestly significant difference post hoc test (α?=?0.05), partial eta-square statistics, Pearson’s correlation, and Weibull’s analysis. No significant effect of sonic activation on the repair material was found in any material combination. The repair strength was 35.4–90.9 % of the cohesive strength of the original composites. E varied between 4.1 GPa (CLEARFIL MAJESTY Esthetic) and 9.7 GPa (CLEARFIL MAJESTY Posterior). The strongest influence on the shear bond strength was performed by E _repair (η ² _P?=?0.167), whereas the effect of E _substrate was significant but low (η ² _P?=?0.098). None of these parameters influenced the reliability of the repaired specimens (the Weibull parameter, m). The fracture pattern was mainly cohesive (93.3 %) in the control group and predominantly adhesive (89.2 %) in the repaired specimens.

Conclusions

Except for the material with the highest modulus of elasticity used as a substrate material, it was not detrimental to combine different RBCs in terms of repair.

Clinical relevance

If a substrate material is unknown, the recommendation for repairing would be in favor of a material with a high modulus of elasticity.     

Light transmittance and micro-mechanical properties of bulk fill vs. conventional resin based composites

Objectives

The aim of this study was to quantify the blue light that passes through different incremental thicknesses of bulk fill in comparison to conventional resin-based composites (RBCs) and to relate it to the induced mechanical properties.

Materials and methods

Seven bulk fill, five nanohybrid and two flowable RBCs were analysed. Specimens (n?=?5) of three incremental thicknesses (2, 4 and 6 mm) were cured from the top for 20 s, while at the bottom, a spectrometer monitored in real time the transmitted irradiance. Micro-mechanical properties (Vickers hardness, HV, and indentation modulus, E) were measured at the top and bottom after 24 h of storage in distilled water at 37 °C. Electron microscope images were taken for assessing the filler distribution and size.

Results

Bulk fill RBCs (except SonicFill) were more translucent than conventional RBCs. Low-viscosity bulk fill materials showed the lowest mechanical properties. HV depends highly on the following parameters: material (η_p ²?=?0.952), incremental thickness (0.826), filler volume (0.747), filler weight (0.746) and transmitted irradiance (0.491). The bottom-to-top HV ratio (HV_bt) was higher than 80 % in all materials in 2- and 4-mm increments (except for Premise), whereas in 6-mm increments, this is valid only in four bulk fill materials (Venus Bulk Fill, SDR, x-tra fil, Tetric EvoCeram Bulk Fill).

Conclusions

The depth of cure is dependent on the RBC’s translucency. Low-viscosity bulk fill RBCs have lower mechanical properties than all other types of analysed materials. All bulk fill RBCs (except SonicFill) are more translucent for blue light than conventional RBCs.

Significance

Although bulk fill RBCs are generally more translucent, the practitioner has to follow the manufacturer’s recommendations on curing technique and maximum incremental thickness.     

One-year evaluation of two hybrid composites placed in a randomized-controlled clinical trial

Objective

The aim of this prospective randomized-controlled clinical trial is to assess the long-term performance of two direct composite resins in posterior teeth. This study provides a survey of the one-year results.

Materials and methods

A total of 1805 restorations were placed by students in stress-bearing Class I/II cavities (including cuspal-coverage) in molars and premolars in 456 patients. Clinical evaluation was performed at baseline and after one year using modified USPHS criteria. The restorations in each patient were performed either with Ceram X/Prime&Bond NT or Tetric Ceram/Optibond Solo Plus.

Results

After one year 528 fillings with Ceram X and 580 with Tetric Ceram were available for evaluation of substance loss, contact point, color match, marginal staining, marginal adaptation, secondary caries and radiographic examination (if necessary). This represents a recall rate of 61.18% (279 patients). The failure rate per material was 5.3% in the Ceram X group and 6.1% in the Tetric Ceram group. Most of the failures were associated with marginal adaptation/integrity of the filling. A significant influence on the occurrence of a failure was observed for the number of treated teeth per patient, the age of the patient, the mesio-distal extension of the restoration and the tooth position. Gender, material, a previous root canal treatment, the bucco-lingual extension of the filling or cuspal-coverage did not significantly influence the failure rate. Patients attending the first recall were significantly older and had more fillings than patients not attending.

Conclusions

In a group of Class I/II restorations (including cuspal-coverage), there was no significant difference in failure rates between ormocer-based and bis-GMA-based restorative systems after one year. A previous root canal treatment had no negative influence on the failure rate. A longer observation period is indicated to get clear evidence of the long-term performance of these composite resin systems.     

Sufficiency of curing in high-viscosity bulk-fill resin composites with enhanced opacity

Clinical Oral Investigations - The study aims analyzing if improved opacity in modern high-viscosity bulk-fill resin composites (BF-RBC) contradicts with the sufficiency of curing and to assess...     

Early Repolarization Syndrome: Electrocardiographic Signs and Clinical Implications

Early repolarization syndrome (ERS) was previously considered as a benign variant, but it has recently emerged as a risk marker for idiopathic ventricular fibrillation (VF) and sudden death. As measured by electrocardiogram (ECG), early repolarization is characterized by an elevation of the J point and/or ST segment from the baseline by at least 0.1 mV in at least two adjoining leads. In particular, early repolarization detected by inferior ECG leads was found to be associated with idiopathic VF and has been termed as ERS. This condition is mainly observed in young men, athletes, and blacks. Also, it has become evident that electrocardiographic territory, degree of J‐point elevation, and ST‐segment morphology are associated with different levels of risk for subsequent ventricular arrhythmia. However, it is unclear whether J waves are more strongly associated with a depolarization abnormality rather than a repolarization abnormality. Several clinical entities can cause ST‐segment elevation. Therefore, clinical and ECG data are essential for differential diagnosis. At present, the data set is insufficient to allow risk stratification in asymptomatic individuals. ERS, idiopathic VF, and Brugada syndrome (known as J‐wave syndromes) are three clinical conditions that share many common ECG features; however, their clinical consequences are remarkably different. This review summarizes the current electrocardiographic data concerning ERS with clinical implications.     

Low-shrinkage composite for dental application

In modern research, development of monomers that reduce shrinkage of composite materials remains an ongoing quest and perennial challenge. The purpose of this study, therefore, was to analyze the shrinkage behaviour of an innovative composite material for dental restorations based on a monomer with a new chemical formulation, known as silorane. To this end, shrinkage stress development during curing, gel point, and coefficient of near linear fit of contraction stress/time were evaluated after polymerizing the material with 10 different curing regimes. Shrinkage stress varied between 1.4 MPa after a 10-second curing in a pulsed regime to 4.4 MPa after curing for 40 seconds with a high energy curing unit, Bluephase. Pearson correlation analysis showed that with respect to the tested curing units, shrinkage stress correlated significantly with energy density (0.89), irradiance (0.70), curing time (0.51), coefficient of near linear fit of contraction (0.70), and gel point (-0.60). Silorane exhibited low shrinkage stress values in comparison to regular methacrylate composites. Nevertheless, stress due to thermal contraction when the light exposure ended was not negligible-but could be reduced by applying the appropriate curing strategy.     

Dysfunction of human subcutaneous fat arterioles in obesity alone or obesity associated with Type 2 diabetes

The aim of the present study was to examine the effects of obesity alone and obesity associated with Type 2 diabetes on the structure, vascular reactivity and response to insulin of isolated human subcutaneous fat arterioles; these effects were correlated with the expression of insulin signalling proteins. Periumbilical subcutaneous adipose tissue was explanted during surgery, small arterioles (internal diameter 220 ± 40 μm) were dissected out and investigated by electron microscopy, myography and immunoblotting. Compared with the subcutaneous arterioles of lean subjects, obesity activated the endothelium, enhanced the accumulation of collagen within vascular wall and increased the sensitivity of adrenergic response; obesity also diminished eNOS (endothelial NO synthase) protein expression, NO production, and endothelium-dependent and insulin-induced vasodilatation, as well as the protein expression of both IRS (insulin receptor substrates)-1 and IRS-2 and of the downstream molecules in the insulin signalling pathway, such as PI3K (phosphoinositide 3-kinase), phospho-Akt and Akt. When obesity was associated with Type 2 diabetes, these changes were significantly augmented. In conclusion, obesity alone or obesity associated with Type 2 diabetes alters human periumbilical adipose tissue arterioles in terms of structure, function and biochemsitry, including diminished eNOS expression and reduced levels of IRS-1, IRS-2, PI3K and Akt in the insulin signalling pathway.