Soft-start Technique Research Articles

Evaluation of the Polymerization Depth of Bulk Fill Resin Composites Polymerized by Different Procedures: An In-Vitro Study

Objective: The aim of this study is to investigate the depth of cure (DOC) of the bulk fill composite samples prepared in different thicknesses with two different modes of light curing device with Vickers hardness tester.Methods: Five different bulk-fill composite materials were used in the present study. 20 sample of 2 mm and 20 sample of 4 mm thick samples were prepared, 10 samples from each group were polymerized for 20 seconds with the standard mode (Mode 1) of the light curing device and 10 samples polymerized with soft-start mode (Mode 2) for 25 seconds (n=10). Hardness measurements were made from the upper and lower surfaces of each sample and the hardness ratio was calculated. The statistical analysis was performed using three-way analysis of variance (ANOVA) and Tukey multiple comparisons (p = 0.05).Results: The hardness ratios of all composites were determined to be over 80%, which is clinically acceptable. There was a statistically significant difference between the DOC levels according to the composites (p <0.05). There was a statistically significant difference according to the thickness (p <0.05). There was no statistically significant difference according to polymerization procedures (p >0.05).Conclusions: The surface hardness ratios of all groups were determined to be over 80%, which is clinically acceptable. The polymerization with soft start technique may not different from the standard-mode for polymerization depth.

EVALUATION OF GINGIVAL MICROLEAKAGE IN CLASS II COMPOSITE RESTORATIONS: AN IN VITRO STUDY

Introduction: Evaluation of microleakage is important for assessing the success of new restorative materials and methods. The aim of this study was to assess the microleakage of class II restorations with different flowable composites as liners and two different polymerization techniques classic and soft start. Materials and Methods: 40 extracted human premolars teeth with class II cavity preparation medial and distal (80 cavities) were divided into four groups: 1.Vertise Flow (VF)+micro hybrid composite Herculite 2.Surefil SDR Flow (SDRF)+micro-hybrid composite Herculite 3.Tetric Flow (TF)+micro-hybrid composite Herculite 4.control group micro-hybrid composite Herculite. Mesial cavities are polymerized with classic and distal cavity with soft start technique of polymerization. After that, the samples were immersed in 0.5% AgNO3 solution and sectioned into the mesiodistal direction. Using a stereomicroscope (Nikon - Japan), with a magnification of 40x, the gingival microleakage of cavities was examined. Data were analyzed using Fisher's and Student's tests. Results: After using the classical polymerization technique, all three used flowable composites VF+Herculite, SDRF+Herculite, TF+Herculite showed less gingival microleakage than the control group. This difference was statistically significant. After the application of the soft-start technique of polymerization, VF+Herculite and SDRF+Hercules showed a statistically significant reduction in gingival microleakage, while TF+Herculite showed a comparable result with control group, without a statistically significant difference. There was no statistically significant difference between classical and soft start polymerization techniques. Conclusion: Flowable composites in this study have reduced gingival microleakage and can be used as liners in the restoration of II class cavities.

A High Speed On-Chip Soft-Start Technique With High Start-Up Stability for Current-Mode DC-DC Converter

In high efficiency and high-frequency applications, the soft-start methods for DC-DC converter with fast output voltage settling speed have attracted widespread attention. A novel soft-start circuit with controllable start-up time, high start-up speed, high stability, and no off-chip capacitor for a current mode DC-DC is proposed in this paper. The proposed soft-start circuit introduces a current-limiting feedback technique so that the inductor current during soft-start is controllable. The stability of the soft-start technique is verified theoretically in this paper. A Boost converter using this novel soft-start technique is fabricated in 0.35 μm BCD process. The soft-start time of the Boost converter is only 380 μs at the conditions of 45 V output voltage, 20 μF load capacitance, and 500 mA load current.

Design and Experimental Measurement of EMI Reduction Techniques for Integrated Switching DC/DC Converters

This paper presents the design and verification of electromagnetic interference (EMI) reduction techniques for switching dc/dc converters. A 48-V dc/dc converter for electric/hybrid cars is considered as an application case study. An EMI filter with a very low inductor value is designed to reduce the overvoltage issues. The proposed design procedure takes into account the converter impedance and the cable model in order to avoid the state-of-the-art tendency of oversizing the filter components. Thus, the filter implementation is simplified and its EMI reduction capability is kept unaltered. Measurements of near EM field in anechoic room show that, using a low switching frequency for the dc/dc converter, the EMI problem is shifted from radiated to conducted emissions. A SKIP-mode modulation technique is implemented to control the converter output and also to reduce the conducted EMI, as shown by CAD simulations and experimental measurements. In addition, a soft-start technique, which reduces by three times the currents' spikes, is integrated into the dc/dc converter to minimize the EMI at the car's starting.

Marginal seal of direct composite veneers

Introduction. Advance in new nano-composite materials and adhesive systems has provided stronger bond with hard dental tissue as well as possibility for minimal cavity preparation. The aim of this study was to evaluate, using dye method, marginal seal of direct composite veneers placed on intact and abraded anterior teeth and polymerized with classical and soft start light curing technique. Material and Methods. The study was conducted on 40 extracted human anterior teeth. They were extracted for periodontal reasons and divided into two groups: intact teeth (20) and abraded teeth (20). 10 teeth in each group were polymerized with classical and soft start technique. Dye penetration was measured using stereo loupes with micrometer scale and six times magnification. Results. Linear dye penetration on the gingival wall when direct composite veneers were placed in intact teeth and polymerized with classical technique was 2.50 ?m, while on the incisal wall it was 0.5 ?m. Linear dye penetration on the gingival wall in intact teeth polymerized with soft start technique was 2.25 ?m, while on the incisal wall it was 2.0 ?m. Average dye penetration of direct composite veneers in abraded teeth polymerized with classical technique on the gingival wall was 3.0 ?m while on the incisal wall it was 1.25 ?m. Linear dye penetration in abraded teeth polymerized with soft start technique was greater on the gingival wall (3.50 ?m) than on the incisal wall (3.25 ?m). Conclusion. Smaller microcrack was observed on the incisal wall than on the gingival wall in all teeth regardless of the technique of polymerization used. The least dye penetration was observed in the group of intact teeth polymerized with classical technique of polymerization.

Influence of different restorative techniques on marginal seal of class II composite restorations

ObjectiveTo evaluate the gingival marginal seal in class II composite restorations using different restorative techniques.Material and MethodsClass II box cavities were prepared in both proximal faces of 32 sound human third molars with gingival margins located in either enamel or dentin/cementum. Restorations were performed as follows: G1 (control): composite, conventional light curing technique; G2: composite, soft-start technique; G3: amalgam/composite association (amalcomp); and G4: resin-modified glass ionomer cement/ composite, open sandwich technique. The restored specimens were thermocycled. Epoxy resin replicas were made and coated for scanning electron microscopy examination. For microleakage evaluation, teeth were coated with nail polish and immersed in dye solution. Teeth were cut in 3 slices and dye penetration was recorded (mm), digitized and analyzed with Image Tool software. Microleakage data were analyzed statistically by non-parametric Kruskal-Wallis and Mann-Whitney tests.ResultsLeakage in enamel was lower than in dentin (p<0.001). G2 exhibited the lowest leakage values (p<0.05) in enamel margins, with no differences between the other groups. In dentin margins, groups G1 and G2 had similar behavior and both showed less leakage (p<0.05) than groups G3 and G4. SEM micrographs revealed different marginal adaptation patterns for the different techniques and for the different substrates.ConclusionThe soft-start technique showed no leakage in enamel margins and produced similar values to those of the conventional (control) technique for dentin margins.

Influence of light-curing unit systems on shear bond strength and marginal microleakage of composite resin restorations

The aim of the present study was to evaluate the influence of different photopolymerization (halogen, halogen soft-start and LED) systems on shear bond strength (SBS) and marginal microleakage of composite resin restorations. Forty Class V cavities (enamel and dentin margins) were prepared for microleakage assessment, and 160 enamel and dentin fragments were prepared for the SBS test, and divided into 4 groups. Kruskal-Wallis and Wilcoxon tests showed statistically significant difference in microleakage between the margins (p 0.05) neither between substrates nor among groups. It was concluded that Soft-Start technique with high intensity end-light influenced negatively the cervical marginal sealing, but the light-curing systems did not influence adhesion.

Clinical Evaluation of the Soft-Start (Pulse-delay) Polymerization Technique in Class I and II Composite Restorations

The polymerization shrinkage of resin composites may affect restoration quality. A double blind, randomized clinical trial was carried out to compare two curing techniques-Soft-Start (SS) and the plasma arc curing light (PAC). The hypothesis that, delaying the gel point (with SS) improves marginal seal, was tested at alpha = 0.05. Also, this report includes two-week, three-month, one-year and two-year results for post-op sensitivity. Twenty informed participants, each needing two Class II and/or complex Class I restorations, gave written consent. All the teeth were trans-illuminated to rule out pre-op crack lines before restoration placement. Fifty Z100-Single Bond restorations (25/SS and 25/PAC) were placed under rubber dam. Protocols: PAC (Control)-incremental curing < 2.0 mm, 2000 mW/cm2 for 10 seconds for all layers, SS (Treatment)-incremental curing <2.0 mm, 600 mW/cm2 for 20 seconds, except the final layer or enamel replacement increment, which was cured as follows-(mW/cm2/time) 200/3 seconds, wait 3 minutes; 200/3 seconds, wait 5 minutes; 600/20 seconds from multiple angles. Sensitivity to a standardized cold stimulus was performed preoperatively at 2 weeks and at 3, 12 and 24 months. Patients rated their sensitivity after stimulus by means of a Visual Analog Scale (VAS). In addition, two independent, calibrated investigators evaluated the restorations clinically at each appointment. There were no significant differences in VAS scores between the two groups at any appointment period (two-way ANOVA; p > 0.05). Several conditions were defined as indicating marginal stress before the start of the trial. At 24 months, there was no significant difference between the SS and PAC groups. Within the limitations of this study, Class I and II restorations placed with a SS technique did not show significant changes in post-op sensitivity or decreased signs of marginal stress.

Effect of Stepped Exposure on Quantitative In Vitro Marginal Microleakage

The aim of this in vitro study was to evaluate the effect of a soft-start curing mode on microleakage Standardized Class V cavities were prepared within all the margins in the buccal enamel or dentin surface of sound, freshly extracted inferior bovine incisors. Forty preparations were filled with a restorative system (Single Bond and Filtek Z250, 3M ESPE, St. Paul, MN, USA). Ten restorations of each group were made on both types of substrates and polymerized with a conventional curing technique (600 mW/cm2/40 s) or with a soft-start technique (150 mW/cm2/10 s + 600 mW/cm2/30 s). All specimens were thermocycled 3000 times and then immersed in methylene blue 2% for 12 hours. The specimen microleakage was quantitatively determined in a spectrophotometer. The soft-start technique resulted in statistically significant less microleakage for each substrate (p < .05). The conventional groups exhibited 6.1 (dentin) to 15.4% (enamel) more leakage compared with the soft-start groups. When compared with the enamel margins, the dentin margins demonstrated greater microleakage: from 15.5% greater with the conventional light-curing mode to 25.6% greater with the soft-start light-curing mode. The polymerization technique using a very low initial intensity (150 mW/cm2/10 s) decreased the microleakage of composite resin restorations. A soft-start light-curing approach to resin composite polymerization resulted in less microleakage at enamel and dentin margins in Class V cavities compared with resin composite restorations polymerized using a conventional light-curing approach.

Mechanical properties and microleakage of composite resin materials cured by variable light intensities

Mechanical properties and microleakage of two composites [conventional hybrid type DenFil (VERICOM Co., Anyang, Korea) / micro matrix hybrid type Esthet X (Dentsply Caulk, Milford, DE, U.S.A.)] were evaluated to assess whether variable light intensity curing is better than conventional curing technique. Curing was done for 40 seconds in two ways of 2 step soft-start technique and 5 step ramping technique. Three kinds of light intensities of 50, 100, 200 mW/cm2 were initially used for 10, 20, 30 seconds each and the maximum intensity of 600 mW/cm 2 was used for the rest of curing time in a soft-start curing technique. In a ramping technique, curing was done with the same initial intensities and the light intensity was increased 5 times with the same rate to the maximum intensity of 600 mW/cm2 . After determining conditions that showed no different mechanical properties with conventional technique, Esthet X composite was filled in a class V cavity, which dimension was 4×3×1.5 mm and cured under those conditions. Microleakage was evaluated in two ways of dye penetration and maximum gap estimation through SEM observation. ANOVA and Spearman's rho test were used to confirm any statistical significance among