Reactivity and Bond Strength of Universal Dental Adhesives with Co-Cr Alloy and Zirconia

The aim of this study was to evaluate (a) the reactivity of six universal dental adhesives with polished cobalt-chrome (Co-Cr) alloy and zirconia (3Y-TZP) surfaces; and (b) to assess the shear bond strength (SBS) of a resin composite with polished and alumina-blasted surfaces as mediated by these adhesives. The products tested were Adhese Universal (AD), All-Bond Universal (AB), Clearfill Universal Bond (CB), G-Premio Bond (GP), Prelude One (PO) and Scotchbond Universal (SB). The reactivity on polished substrates was evaluated by reflection infrared microscopy (RFTIRM). The roughness parameters of polished and 50 μm alumina grit-blasted surfaces were assessed by optical profilometry. The SBS of the composite bonded to the substrates treated with each adhesive (n = 10/product) was evaluated after 1 week of storage (H₂O/37 °C) by Weibull statistics. Evidence of phosphate interaction with polished substrates was obtained by FTIRM, with higher peaks on the alloy. Alumina-blasting increased all roughness parameters with higher values on the alloy. AD, CB were the strongest (σ₀) treatments on alloy surfaces and AD, CB, AB, SB on zirconia. GP was the weakest on both substrates and the least reliable (β) on alloy. On polished alloy GP, PO performed better (σ₀), whereas on zirconia there were no significant differences. All adhesives showed more prominent reaction with the Co-Cr alloy than with 3Y-TZP.

Universal Adhesives: Setting Characteristics and Reactivity with Dentin

The aim of the study was to evaluate the performance of six commercially available universal dental adhesives: Adhese Universal (ADU), All-Bond Universal (ABU), Clearfil Universal Bond Quick (CBQ), G-Premio Bond (GPB), Prelude One (PRO) and Scotchbond Universal (SBU). The properties tested were: (a) degree of C=C conversion (DC%); (b) Vickers micro-hardness (VHN); (c) extent of oxygen inhibition (OI/μm), all related with the adhesive film properties; (d) extent of dentin demineralisation (DM%), insoluble salt formation (AS%); and (e) shear bond strength (SBS, self-etch mode) related to the adhesive-dentin interactions. Statistical analysis (α = 0.05) was performed by one-way ANOVA and Tukey's test (DC%, VHN, OI, DM% AS%) and Weibull analysis (SBS, σ_0-β). The DC ranged from 67.2-82.5% (all >GPB), OI from 5.6-18.6 μm (SBU > ADU, GPB, ABU > CBQ > PRO), microhardness from 1.1-6.6 VHN (SBU > ADU > ABU > CBQ > PRO > GPB: not measurable), DM from 69.3% (GPB) to 16-12.5% (CBQ, SBU, ADU) and 13.2-10.6% (ABU, ADU, PRO), in homogeneous groups and AS from 26-15.9% (ABU, CBQ > GPB, PRO, ADU, SBU). For SBS the σ₀ (characteristic life) ranged from 29.3-16.6 MPa (CBQ, ADU, ABU, SBU > PRO > GPB), the β (reliability) from 5.1-9.7 (p > 0.05). All failure modes were of mixed type (adhesive and composite cohesive). Although all these adhesives were based on the 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) adhesive monomer, the different co-monomers, solvents and catalysts led to variations in their film properties, reactivity and bonding capacity with dentin.

Viscoelastic properties of orthodontic adhesives used for lingual fixed retainer bonding

OBJECTIVE

To evaluate the viscoelastic properties of two experimental BPA-free and one BisGMA-based orthodontic resin composite adhesives for bonding fixed retainers.

METHODS

A commercially available BisGMA-based (TXA: Transbond LR) and two bisphenol A-free experimental adhesives (EXA and EXB) were included in the study. The viscoelastic behavior of the adhesives was evaluated under static and dynamic conditions at dry and wet states and at various temperatures (21, 37, 50°C). The parameters determined were shear modulus (G), Young's modulus (E) under static testing and storage modulus (G₁), loss tangent (tanδ) and dynamic viscosity (n*) under dynamic testing. Statistical analysis was performed by 2-way ANOVA and Bonferroni post-hoc tests (α=0.05).

RESULTS

For static testing, a significant difference was found within material and storage condition variables and a significant interaction between the two independent variables (p<0.001 for G and E). EXA demonstrated the highest G and E values at 21°C/dry group. Dry specimens showed the highest G and E values, but with no significant difference from 21°C/wet specimens, except EXA in G. Wet storage at higher temperatures (37°C and 50°C) adversely affected all the materials to a degree ranging from 40 to 60% (p<0.001). For dynamic testing, a significant difference was also found in material and testing condition groups, with a significant interaction between the two independent variables (p<0.001 for G₁ and n*, p<0.01 for tanδ). Reduction in G₁, and n* values, and increase in tanδ values were encountered at increased water temperatures.

SIGNIFICANCE

The apparent detrimental effect of high temperature on the reduction of properties of adhesives may contribute to the loss of stiffness of the fixed retainer configuration under ordinary clinical conditions with unfavorable effects on tooth position and stability of the orthodontic treatment result.

Losartan Reduces Left Ventricular Hypertrophy Proportionally to Blood Pressure Reduction in Hypertensives, but Does Not Affect Diastolic Cardiac Function

In contrast to the well-recognized salutary effects of angiotensin-converting enzyme inhibition, the value of angiotensin II type I (ATl)-receptor blockade on left ventricular hypertrophy (LVH) is controversial. In addition, the data on the influence of this therapy on cardiac diastolic function are scarce. Thirty-nine patients with moderate primary hypertension, LVH, and normal systolic function received losartan, 50 to 100 mg daily. Transthoracic echocardiography was performed at baseline and after 6 months of treatment. Thirty-one patients completed and were included in the study (16 males, 61.1 ±1.0 years). The patients were divided into responders if mean blood pressure (BP) decreased >5 mm Hg at the end of the study (20 patients) and non-responders (mean BP decrease ≤5 mm Hg, 11 patients). The BP and the LVH were significantly reduced (systolic BP by 10.0%, diastolic BP 6.5%, mean BP 8.2%, left ventricular mass index [LVMI] 6.2%, interventricular septum 5.8%, posterior wall 3.0%) (p≤0.02), attributed to the reduction of BP and LVH in responders; the LVH in non-responders did not alter with treatment. A significant correlation was noted between changes in BP and LVMI ( r =0.60, p<0.001). The systolic cardiac function remained normal. The Doppler parameters usually used to assess the diastolic function of the LV (early diastolic filling velocity [E wave], late diastolic filling velocity [A wave], ratio of E/A waves, isovolumic relaxation time), which were abnormal at baseline, did not change with treatment. The size of the left atrium increased (p<0.05) at the end of the study. In conclusion, a 6-month course with losartan decreased BP and LVH. However, the LVH regression was rather associated with the reduction of the hemodynamic stimulus per se, than any trophic effect of the drug in the myocardium. The diastolic cardiac function remained abnormal with treatment.

Mechanical viscoelastic behavior of dental adhesives

OBJECTIVES

The purpose of the study was to evaluate the mechanical properties of dental adhesive materials at different testing temperatures after dry and wet storage.

METHODS

Specimens (d=1 mm, l=18 mm) from six materials were tested: Silorane Adhesive System (SL), Heliobond (HE), One-Step Plus (OS), Optibond Solo Plus (OP), cmf Adhesive System (CF) and Protobond (PR). Static and creep testing was performed by applying a constant torque below the proportional limit of the materials, while dynamic testing consisted of dynamic torsional loading. Experiments were performed after 24h of dry and wet storage under temperatures from 21°C to 50°C and various viscoelastic parameters were calculated.

RESULTS

Shear modulus ranged from 0.19 to 1.99 GPa, while flexural modulus from 0.67 to 5.69 GPa. Most of the materials were affected by the presence of water and increase of temperature. OP showed the highest recovery after creep, while SL exhibited the highest permanent deformation.

SIGNIFICANCE

Contact with water after polymerization and increase of temperature resulted in a decline of the mechanical properties, especially for the HEMA-containing adhesives.

The effect of temperature on viscoelastic properties of glass ionomer cements and compomers

The objective of this study was to determine the viscoelastic properties of different types of glass ionomer cements (GICs) and compomers under varying temperature conditions found in the mouth. The materials tested were a conventional GIC (Aqua Ionofil U), a resin modified GIC (Fuji II LC), a highly viscous GIC (Voco Ionofil Molar), and two polyacid modified composite resins/compomers (Glasiosite and Dyract Flow). Six groups of four specimens were prepared from each material. One group was stored dry for 24 h and was subsequently tested dry at 21 degrees C. Each of the remaining five groups was stored for 24 h in distilled water at the temperatures 21, 30.5, 37, 43.5, and 50 degrees C, respectively, and was subsequently tested at that temperature. Shear storage modulus and loss tangent were determined by conducting dynamic torsional loading. Static shear moduli were determined by applying a constant torque (below the proportional limit of the materials) for 10 s and recording the angular deformation of the specimens. Data were analyzed by ANOVA and Duncan's test (alpha= 0.05). It was found that the viscoelastic properties varied significantly (p < 0.05) across the different materials. The compomer Glasiosite, with the highest filler content, and the highly viscous GIC Voco Ionofil Molar exhibited the highest elastic moduli and lowest loss tangents. Viscoelastic properties varied also significantly (p < 0.05) with temperature levels, but changes in the tested region were not indicative of a glass transition. Dynamic shear storage moduli were highly correlated to the static ones. Storage in water lowered the values of elastic moduli.

Spatial QRS-T angle: association with diabetes and left ventricular performance

The spatial QRS-T angle obtained by vectorcardiography is a combined measurement of the electrical activity of the heart and predicts cardiovascular morbidity and mortality. Disturbances in repolarization and depolarization are common in diabetes. No data, however, exist on the effect of diabetes on QRS-T angle. In this study we examined differences in QRS-T angle between type 2 diabetic and non-diabetic subjects; in addition, the potential relationship between QRS-T angle and left ventricular performance as well as glycaemic control were also examined. A total of 74 subjects with type 2 diabetes and 74 non-diabetic individuals, matched for age and sex with the diabetic subjects were examined. All subjects were free of clinically apparent macrovascular complications. Spatial vectorcardiogaphic descriptors of ventricular depolarization and repolarization were reconstructed from the 12-electrocardiographic leads using a computer-based electrocardiogram. Left ventricular mass and performance were measured using M-mode and Doppler echocardiography. QRS-T angle values were higher (by almost 2-fold) in the diabetic in comparison with the non-diabetic subjects (P < 0.001). After multivariate adjustment, QRS-T angle was independently associated with age (P = 0.01), HbA(1c) (P = 0.003), and low-density lipoprotein cholesterol levels (P = 0.04) in the non-diabetic, and with HbA(1c) (P = 0.03) as well as Tei index (P = 0.003) in the diabetic subjects. The spatial QRS-T angle is high in subjects with type 2 diabetes and is associated with glycaemic control and left ventricular performance. The prognostic importance of the higher spQRS-T angle values in subjects with diabetes remains to be evaluated in prospective studies.

Fatigue of packable dental composites

OBJECTIVE

The purpose of the study was to measure the fatigue properties of four dental resin composites using a dynamic mechanical analysis and to relate the results with viscoelastic properties.

METHODS

Dynamic torsional loading was conducted at resonance at 30-50Hz. Specimens were thoroughly cured and tested dry at 21 degrees C.

RESULTS

All of the specimens showed a loss of strength following repeated stress, due to material fatigue. The material with the highest shear modulus had the lowest damping and the highest fatigue strength.

SIGNIFICANCE

Dental composites exhibit a modest loss of strength due to fatigue. Since mastication involves many cycles of stress during the life of a restoration, fatigue properties should be taken into account in restoration design.

Losartan controlled blood pressure and reduced left ventricular hypertrophy but did not alter arrhythmias in hypertensive men with preserved systolic function

The effect of antihypertensive therapy on arrhythmias is controversial. An initial study in patients with chronic heart failure indicated that losartan, an angiotensin II receptor antagonist, may possess antiarrhythmic properties. However, the effect of AT1 receptor antagonists on arrhythmias of subjects with good systolic function has never been evaluated. Thirty-nine men with primary hypertension (18 without left ventricular hypertrophy [LVH], and 21 with LVH, aged 48.2 +/-8.6 and 50.5 +/-6.0 years, respectively), 15 healthy normotensive subjects (47.9 +/-8.5 years), and 14 highly trained athletes (34.1 +/-1.6 years) were studied. Transthoracic echocardiography and 24-hour Holter ambulatory monitoring were performed at baseline (without treatment). Hypertensive patients underwent the same examinations after 8 months of losartan administration. The prevalence and complexity of ventricular arrhythmias, and the frequency of supraventricular arrhythmias were increased in hypertensive patients with LVH compared to normotensive controls and athletes, at baseline. A similar significant reduction of blood pressure (BP) was noted in both groups of patients (p < 0.001). The LVH was reduced in hypertensives with LVH (the left ventricular mass index by 12%, the interventricular septum by 8.1%, the posterior wall by 7%, all p < 0.01). However, the arrhythmias did not change in either group of patients, even if all hypertensives were considered as 1 group. In conclusion, an 8-month course with losartan was effective in lowering BP and reducing LVH. However, the increased arrhythmias, which were registered in hypertensive patients with LVH at baseline, did not change.

Dynamic and static elastic moduli of packable and flowable composite resins and their development after initial photo curing

OBJECTIVE

The purpose of this study was to evaluate the dynamic (storage) shear modulus and the static shear modulus of elasticity of packable and flowable composite resins and to investigate their development after initial photo-curing.

METHODS

Three pairs of a packable versus a flowable composite and a microfill composite resin were tested (Alert/Flow It, Filtek P60/Filtek Flow, Admira/Admira Flow, A 110). Cylindrical specimens (0.85 mm x 18 mm) were made for each material. All specimens were conditioned and tested dry at 21 degrees C. The specimens were tested at 30 min, 24h and 1 week after the end of photo curing. Storage shear modulus and loss tangent were determined by conducting dynamic torsional loading in the frequency range from 1 to 150 Hz. Static shear modulus measurements were made by applying a constant load (below the proportional limit of the materials) for 10s and recording the angular deformation of the specimens. Data were analyzed by ANOVA and Duncan's Post hoc test (alpha=0.05).

RESULTS

Storage shear moduli (at 1 week measurement) ranged from 3.39 to 9.67 GPa, and loss tangents from 0.0735 to 0.0235; static shear moduli ranged between 2.66 and 9.80 GPa. High values of elastic moduli and low tandelta values were obtained with packable composites, while low moduli values were obtained with flowable composites. Statistically significant (alpha=0.05) differences were recorded between materials of the same category. Storage time, 24h and 1 week after initial polymerization, resulted in significant increases in both moduli of elasticity. Dynamic shear storage moduli were highly correlated to the static ones (r(2)=0.92; P<0.05).

SIGNIFICANCE

The results of the aging studies showed that the rigidity of these materials increases significantly even 1 week after the clinician turns off the curing unit.

Corrected QT interval in relation to the severity of diabetic autonomic neuropathy

The aim of this study was to investigate to what extent the existence of objective signs of diabetic autonomic neuropathy affects the corrected QT interval (QTc) in diabetic subjects. A total of 105 diabetic subjects (type 1, n = 53; type 2, n = 52) as well as 40 matched (by age and sex) control subjects were studied. All subjects underwent the battery of five Ewing tests. Autonomic neuropathy was diagnosed if two of the five tests were abnormal. In addition, the result of each test was considered as normal (grade = 0), borderline (grade = 1) or abnormal (grade = 2), and on the basis of the sum of the scores we calculated a total score for autonomic neuropathy. The QTc interval was measured at rest, and a value > 440 ms was considered abnormal. The QTc interval was significantly more prolonged in diabetic persons with autonomic neuropathy than in those without neutopathy and in control subjects: 408.4 +/- 24.2 ms vs. 394.6 +/- 27.9 ms and 393.6 +/- 25.5 ms respectively (P = 0.001). Furthermore, multivariate analysis controlling for age, sex, systolic and diastolic blood pressure, body mass index (BMI), waist-hip ratio (WHR), smoking, type and duration of diabetes, type of treatment, HBA1c and total score of autonomic neuropathy eliminated the role of all these factors as potential confounders except for the total score of autonomic neuropathy, which was found to affect QTc interval independently and significantly (P = 0.012). In summary, the present study confirmed the well-known relation between autonomic neuropathy and QTc interval; in addition, it showed that QTc prolongation is associated with major degrees of autonomic neuropathy.

Intraerythrocytic 2,3-diphosphoglycerate concentration in hypertensive subjects before and following control by anti hypertensive treatment

METHODS

We measured the 2,3-diphosphoglycerate inraerythrocytic concentration in 24 normal controls and in 24 hypertensives before and following drug therapy.

RESULTS

In hypertensives the 2,3-diphosphoglycerate concentration was higher than that of the controls (14.96 mumol/g Hb vs 13.26 mumol/g Hb respectively); the difference is statistically significant (p < 0.001). Following control of the hypertension by drug therapy, the 2,3 DPG levels in the patients studied do not seem to differ statistically from those of the controls.

CONCLUSIONS

This may be a consequence of lower cardiac output in hypertension which results to a lower tissue perfusion, leading to an increased concentration of deoxygenated haemoglobin in the vein blood. Measurement of 2,3-diphosphoglucerate may prove of value in estimating tissue perfusion in hypertension.