Biomedical subjects

Nicoleta Ilie

Publications and source records attributed to Nicoleta Ilie.

6 recordsLinked to original sources

PubMed2006

The influence of curing times and light curing methods on the polymerization shrinkage stress of a shrinkage-optimized composite with hybrid-type prepolymer fillers.

OBJECTIVES: The aim of the study was to determine the influence of different light curing units (LCU) and regimes on the polymerization shrinkage stress (PSS) and the mechanical properties of a nano-hybrid composite. MATERIAL AND METHODS: The polymerization shrinkage force (PSF) was measured continuously with compliance compensation for 300s after photo-initiating the composite, Tetric EvoCeram (Ivoclar Vivadent, Schaan, FL, Shade A3) in a Stress-Strain Analyser. Astralis 10, Bluephase and MiniL.E.D LCU with exposure times 10, 20 and 40s were used (C-factor=0.33, n=8 per group). Immediately after the PSF measurements, mechanical properties of the samples were measured at the top and the bottom using a Fischerscope H100C (Helmut Fischer GmbH, Sindelfingen, Germany). Statistical analyses were done using one-way ANOVA (p<0.05) and Tukey post hoc test. RESULTS: Significant differences in the PSS for 10, 20 and 40s polymerization using Astralis 10 were found. The MiniL.E.D recorded low stress values. Modulus of elasticity is high after curing the composite with Astralis 10 at 10, 20 and 40s and for Bluephase 40s. Low moduli of elasticity were recorded for the MiniL.E.D and for the Bluephase 20 and 10s. The hardness values (HV) followed the same pattern as the modulus of elasticity. The Ramping mode of the MiniL.E.D had prolonged gel point. CONCLUSIONS: High intensity LCU produce not just high HV but also high shrinkage, making it important to balance both the effects by choosing the appropriate curing time. Soft-start regimes have no paramount benefit in a LED regarding stresses in the clinical situation.

Analysis of Variance↗

PubMed2006

Investigation of shear-peel bond strength of orthodontic brackets on enamel after using Pro Seal.

AIM: The aim of this investigation was to ascertain whether the use of a fluoride-releasing, light-curing sealant (Pro Seal, Reliance Orthodontic Products, Itasca, IL, USA) results in differences in shear-peel bond strength when teeth are etched via the conventional acid-etching method and with self-etching primers (SEP), respectively. We also examined whether Pro Seal functions as a substitute for the bonding agents recommended by the manufacturers. MATERIAL AND METHODS: To carry out this study, we randomly allocated 300 extracted molars (ISO 11405) into twelve groups (n=25). The brackets used (Victory Series, Twin UBi 0T/0A .022, 3M Unitek, Seefeld, Germany) were bonded using the same layer thickness of adhesive. The teeth were then stored for 24 h in de-ionized water (37 degrees C) and subsequently thermocycled. The brackets were debonded using a universal testing machine with a crosshead speed of 0.5 mm/min. For statistical evaluation we used the one-way analysis of variance (ANOVA [alpha = 0.05]) and the post hoc Tukey test and Weibull analysis. RESULTS: We could establish that the use of Pro Seal does not have a negative influence on shear-peel bond strength. When the compomer Assure was used, Pro Seal even led to an increase in shear-peel bond strength, especially when it was applied using the bonding agent recommended by the manufacturer. The highest Weibull modulus (m) was found for the self-etching primer IDEAL 1 without using Pro Seal (m=6.5) and the lowest for First Step SEP when using Pro Seal (m=2.2). There were also clear differences in characteristic shear-peel bond strength (sigma(0)) within some of the groups investigated. CONCLUSIONS: Although the statistical evaluation showed no significant negative influence on the shear-peel bond strength either when Pro Seal was used in addition, or when that fluoride-releasing, light-curing sealant was substituted for the bonding agent recommended by the manufacturer, the Weibull analysis showed that the use of Pro Seal in combination with SEP resulted in bond strength values that were less reliably reproducible.

Orthodontic Brackets↗

PubMed2006

Silorane-based dental composite: behavior and abilities.

The purpose of this study was to examine the characteristics of an innovative composite material for dental restorations based on silorane--a monomer with a new chemical composition, and thereby compare the examined characteristics against those of well-known methacrylate-based composites. Degree of conversion at 2-mm and 6-mm depths as well as hardness, modulus of elasticity, and creep resistance through the middle of 6-mm high samples were measured. It was observed that up to 20 minutes after curing, curing time--and not irradiance--played the determinant role for a high degree of cure. No differences were registered between the two categories of material in terms of hardness. However, modulus of elasticity of the silorane-based material was slightly lower and the creep resistance higher than a methacrylate composite (Tetric EvoCeram). In conclusion, siloranes exhibited good mechanical properties comparable to those of clinically successful methacrylate-based composite materials.

Acrylic Resins↗

PubMed2005

Evaluation of micro-tensile bond strengths of composite materials in comparison to their polymerization shrinkage.

OBJECTIVE: The present study determined the influence of polymerization shrinkage of eight commercially available hybrid, micro-filled and nano composites (Z100 and Filtek Supreme, 3M-ESPE; Charisma and Durafill, Heraeus Kulzer; Tetric and InTen-S, Ivoclar Vivadent; Enamel plus HFO, GDF; Palfique Estelite Low Flow, Tokuyama) placed in large class 1 cavities on the bond strength to dentin. METHODS: Polymerization shrinkage was recorded for 300 s at room temperature with a Stress-Strain-Analyzer (C(FACTOR)=0.3). The maximum contraction stresses after 300 s, the time until gelation (t(0.5 N)) and the coefficient of near linear fit of contraction force/time (gradient) were analysed. For the evaluation of the micro-tensile-bond-strength (micro-TBS), hourglass shape samples obtained from a total of 32 no carious extracted human third and second molars, randomly divided into 8 groups, were used. Micro tensile bond strengths were determined by computing the ratio of maximum load by the adhesion area of the hourglass shape. In order to analyze the quality of the polymerization within fillings, hardness profiles of a surface cut thought the middle of the restored tooth and along the tooth axis were made. Further, the modulus of elasticity, determined in a three-point-bending test, as well as the variation of the modulus of elasticity and of the hardness within a filling were considered. The statistical analyses were conducted by ANOVA (alpha=0.05) and post-hoc Tukey's test. RESULTS: A significant correlation between polymerization shrinkage and micro-TBS was found (Pearson; -0.44). The correlation between modulus of elasticity in bending test and shrinkage stress (Pearson; 0.77), coefficient of near linear fit m (Pearson; 0.72), time until gelation (Pearson; -0.52) and micro-tensile-bond-strength (Pearson; -0.45) was also significant. A high polymerization tension and modulus of elasticity negatively affected the adhesion of the composite to the tooth hard substance. Further, the number of samples lost during the slice cutting and the hourglass shape preparation was found to correlate highly significantly with the shrinkage stress (Pearson; 0.97), coefficient of near linear fit m (Pearson; 0.94) and modulus of elasticity (Pearson; 0.82). All materials showed sufficient polymerization within the filling in comparison to the filling surface, the hardness at the bottom of the filling was greater than 80% of the maximum hardness value. The modulus of elasticity was not considerably reduced within the filling. SIGNIFICANCE: High contraction stress and modulus of elasticity, fast development of contraction force and an early start of stress build-up of materials placed in restrictive cavities cause tension in the material with a possible subsequent distortion of the bond to the tooth structure. A low modulus of elasticity is not necessarily associated with high bond strength. However, it causes a more uniform stress distribution at the restorative composite-tooth interface. This is also evident in a reduced sample loss during the different stages of sample preparation.

Analysis of Variance↗

PubMed2005

Shrinkage behavior of a resin-based composite irradiated with modern curing units.

OBJECTIVE: The present study determined the influence of different light curing regimes (four light-emitting diode (LED) units (Freelight 1 and 2, 3M-ESPE; e-light, GC; Bluephase (prototype), Ivoclar Vivadent), two quartz-tungsten-halogen (QTH) lights (Astralis 10, Ivoclar Vivadent; Swiss Master Light, EMS) and one plasma-light curing unit (Easy Cure, DMDS)) on the curing behavior of a resin-based composite material (InTen-S, Ivoclar Vivadent). METHODS: Polymerization shrinkage was induced by light curing the tested material with 14 different regimes of the curing units mentioned above. The contraction stress was recorded for 300 s at room temperature with a Stress-Strain-Analyzer (c(FACTOR)=0.3). The maximum contraction stresses after 300 s, the time until gelation (t(0.5N)), and the coefficient of near linear fit of contraction force/time (gradient) were analyzed. The statistical analysis was conducted using ANOVA (alpha=0.05) and Tukey's post hoc test. RESULTS: The five tested regimes of the LED unit e-light revealed the lowest statistically significantly maximum contraction stress followed by the low intensity LED unit Freelight 1 and the plasma curing unit Easy Cure. The high intensity LED unit Freelight 2 exhibited a significantly higher contraction stress compared to Freelight 1. No significant differences between the standard and exponential modes within these curing units were found. No significant differences were found between the LED unit Freelight 2 and the pulse program of the halogen light curing unit Astralis 10. The highest polymerization stresses were observed for the high energy curing units, either QTH (Swiss Master Light and Astralis 10) or LED (Bluephase). SIGNIFICANCE: Fast contraction force development, high contraction stress and an early start of stress build-up cause tension in the material with possible subsequent distortion of the bond to the tooth structure. The lowest polymerization stress was observed for the low energy LED lamps, while the plasma unit and the high energy QTH and LED curing units produced two to three times higher stress.

Analysis of Variance↗

PubMed2005

Curing behavior of a nanocomposite as a function of polymerization procedure.

The purpose of this study was to analyze the curing behavior of a nanocomposite by assessing in real time the degree of cure at depths of 2 mm and 6 mm. The variation of hardness with depth, shrinkage stress, and curing time until gelation with 16 curing regimes was further investigated using one halogen and three LED curing units. In the present study, it was shown that the soft-start polymerization concept is still valid, even with high-power LED curing units. A soft cure polymerization resulted in reduced shrinkage stress while simultaneously keeping the degree of cure and mechanical properties constant. For all tested curing unit types, a short polymerization duration (10 seconds) was insufficient to cure the nanocomposite in deeper layers--since the variation of hardness with depth showed a discontinuity between the layers, thus accounting for a decreased hardness of up to 30%.

Analysis of Variance↗