Soft-start Mode Research Articles

Influence of Exposure Distance on Light Irradiance of Dental Curing Lamps in Various Operating Modes

The efficiency of photopolymerisation significantly impacts achieving a high degree of conversion and, consequently, determines the success and strength of resin-based composite (RBC) restorations. The study aimed to measure the light irradiance of selected LED curing lamps, taking into account various exposure modes and the increased distance of the light source from the radiometer surface. The study material consisted of 21 LED polymerisation lamps of a single type (Woodpecker Medical Instrument Co., Guilin, China) with three exposure modes: standard, soft start, and pulse. During the measurement, the distance was increased from 0 mm to 8 mm, every 2 mm. Light irradiance measurements were made with a Bluephase Meter II photometer (Ivoclar Vivadent, Opfikon, Switzerland). Increasing the distance affected the soft mode the most, causing a significant drop in light irradiance on the photometer. Standard mode coped best with distance. Even at a distance of 0 mm, the soft start mode does not reach the power of the standard and pulse modes. The standard mode seems to be the most clinically effective, especially if it is planned to polymerise a material in a deep cavity. The soft start mode, as the least resistant to increasing distance, is recommended for use in front teeth or the cervical area.

Evaluation of pre-heated composite resins with soft-start polymerization and conventional composite restorations in class-I carious lesions – A randomized clinical trial

BackgroundBy increasing fluidity and conversion, pre-heated composites enhance adaptability and strength, while soft-start polymerization decreases internal stresses. AimOver a period of a year, this split-mouth design, randomized controlled clinical trial (RCT) compared pre-heated composites with soft-start polymerization to conventional composites in class-I lesions, with the goal of improving restoration outcomes. Methodsand Findings: Immediately following ethical approval and registration with CTRI, 37 patients with in-formed permission who met specified inclusion and exclusion criteria for class-I lesions were chosen for enrollment. Using a 1:1 ratio, teeth were randomly assigned to Group-A (pre-heated composite with soft-start polymerization) or Group-B (traditional composite restoration). At three-time intervals, the evaluation was blinded and calibrated using Modified United States Public Health Service (USPHS) criteria: baseline, six-month, and one-year marks. Statistical analysis was performed using SPSS 21.0 and the Mann-Whitney U test for inter-group comparisons and the Friedman test for intra-group comparisons. InterpretationPre-heated composites with soft-start polymerization performed better in terms of marginal adaptation with a statistically significant difference (p = 0.019) and in terms of color match they performed better clinically (p = 0.062) at 12 months. Other variables like marginal discolouration, sec-ondary caries, anatomic form, post-operative sensitivity, surface texture and retention showed no statistically significant difference (p < 0.05). Pre-heated composites with soft-start mode performed marginally better than nanofilled composites. However, both techniques can be used to successfully restore simple class-I carious lesions.

Effects of the conventional, soft start, and pulse delay modes produced by light-emitting diode device on metal brackets bond strength and enamel damage: An in vitro comparative study

This study aimed to compare the bond strength and enamel damage following debonding of metal brackets cured by different light-curing modes: conventional, soft start, and pulse delay modes. Sixty extracted upper premolars were randomly divided into three groups according to the used light-curing mode. Metal brackets were bonded with a light-emitting diode device employing different modes. Group 1: conventional mode (10s mesial+10 s distal); group 2: soft start mode (15s mesial+15s distal); group 3: pulse delay mode (3s mesial+3s distal, followed by 3min of no photoactivation, then 9s mesial+9s distal). Radiant exposure was the same in all study groups. Shear bond strengths of the brackets were tested with a universal testing machine. A stereomicroscope was used to determine the number and length of enamel microcracks. One-Way ANOVA and Kruskal-Wallis tests were used to detect significant differences in shear bond strength and microcracks number and length among groups. The soft start and pulse delay modes produced significantly greater shear bond strength than the conventional mode (19.46±4.90MPa; 20.47±4.97MPa; 12.14±3.79MPa, respectively, P<0.001). However, there was no significant difference between the soft start and pulse delay groups (P=0.768). The number and length of microcracks increased significantly after debonding in all study groups. The change in microcracks length was not different among study groups. The soft start and pulse delay modes produced greater bond strength than the conventional mode without predisposing enamel to higher risk of damage. Conservative methods for debonding are still required.

Effects of the conventional, soft start, and pulse delay modes produced by light-emitting diode device on microleakage beneath metal brackets: An in vitro comparative study

This study aimed to evaluate microleakage beneath metal brackets cured by different light curing modes. Sixty extracted human premolars were randomly divided into three groups according to the light curing mode. Metal brackets were bonded in all groups according to the manufacturer's recommendations with a light-emitting diode device. Light curing was applied as follows: group 1: conventional mode (10s mesial+10s distal); group 2: soft start mode (15s mesial+15s distal); group 3: pulse delay mode (3s mesial+3s distal, followed by 3min of no photoactivation, then 9s mesial+9s distal). Radiant exposure was the same in all study groups. After curing, the teeth were incubated at 37 degrees for 24hours, then thermocycled 500 times. Next, they were sealed with nail varnish, immersed in methylene blue 1% for 24hours, sectioned, and examined under a stereomicroscope. Microleakage was measured at both enamel-adhesive and bracket-adhesive interfaces, and the total microleakage for each tooth was computed. Statistical analyses were performed using Kruskal-Wallis and Welch test for comparing microleakage among groups. Wilcoxon signed ranks test was used for comparing microleakage between the bracket-adhesive and enamel-adhesive interfaces. There was no significant difference in microleakage at the bracket-adhesive interface among study groups. At the enamel-adhesive interface and total microleakage, the pulse delay group exhibited significantly lower microleakage than the conventional group. Whereas there was no significant difference between the soft start group and other study groups. In all study groups, microleakage at the enamel-adhesive interface was greater than that at the bracket-adhesive interface. The pulse delay mode caused lesser microleakage than the conventional mode. This supports the use of this mode in orthodontic bonding.

Effect of photo-polymerization mode on the degree of conversion of resin cement under different ceramic materials.

BACKGROUND This study evaluated the effect of different polymerization modes and duration on the degree of conversion (DC) of resin cement under different types of ceramics. METHODS Ceramic materials were divided into 3 groups (n=60): Group 1; CERASMART, Group 2; Vita Enamic and Group 3; Vita MARK II. Each group was then divided into three subgroups (n=20) according to the polymerization mode (A; low-intensity, B; high-intensity, and C; soft-start). Subgroups were then divided into two further groups according to the polymerization time (I; 10 s and II; 20 s). DC of light-cured resin cement beneath different kinds of ceramics was tested using FTIR spectroscopy. Results were compared to a control group cured without overlying ceramic. RESULTS While the type of ceramic and mode of polymerization showed a significant effect on the DC of resin cement, polymerization duration did not. Vita Mark II group showed significantly the highest DC of resin cement, followed by Vita Enamic and Cerasmart. High and low intensity polymerization modes did not show significant difference but both showed significantly lower DC when compared to soft start mode. CONCLUSIONS Type of ceramic and polymerization mode showed a direct effect on the DC of resin cement.

Microhardness of fiberglass – reinforced photocomposite material under different conditions of light polimerization

The aim : to study in laboratory conditions the microhardness of a glass-fiber-reinforced photocomposite under different modes of light exposure at different times. Materials and methods . The microhardness of the everX Posterior, GC glass-fiber-reinforced photocomposite was investigated on 60 samples using a PMT-3 microhardness meter on three sample surfaces within 1 hour, 1 day and 7 days after polymerization. Samples of a cylindrical shape with a height of 3 mm of group 1 were irradiated with the light flux of a photopolymerizer in the soft start mode, samples of group 2 were polymerized with light of constant high intensity 1400 mW/cm 2 . Research results . After 1 hour, the microhardness on the surface closest to the LED was 87.34±1.21 kgf/mm 2 in samples of group 1, 102.0±0.94 kgf/mm 2 (p<0.05) in group 2, and 70.98±1.23 kgf/mm 2 (the lowest indicator) and 90.65±1.12 kgf/mm 2 (p<0.05). After 1 day, on the nearest surface, the microhardness increased in the samples of group 1 to 97.03±1.25 kgf/mm 2 , group 2 – to 114.61±1.13 kgf/mm 2 (p<0.05), on the most distant - up to 75.95±1.11 kgf/mm 2 and 99.83±1.24 kgf/mm 2 (p<0.05), respectively. At 7 days, the indicators on the first surface in group 1 were 104.64±1.23 kgf/mm 2 , in 2 – 123.35±1.15 kgf/mm 2 (p<0.05), on the other surface – 80.25±1.48 kgf/mm 2 and 107.53±0.92 kgf/mm 2 (p<0.05). The growth of microhardness on these surfaces for the entire period was 16.5 % and 11.6 % in the samples of group 1, and 17.3 % and 15.7 % in group 2. Conclusions. The light flux of constant high intensity provides statistically significantly (p <0.05) higher microhardness indices of the glass-fiber reinforced photocomposite on all surfaces of the samples than the light exposure in the “soft start” mode. In the direct restoration of teeth, it is necessary to reduce the thickness of the photocomposite layer for soft start polymerization

Irradiance of Different Curing Modes of Common Light Cure Devices: An In Vitro Study.

ABSTRACTAim:The aim of this study was to test the irradiance values of different curing modes of commonly available light cure devices (LCDs).Materials and Methods:An in vitro investigation was carried out to compare the irradiance output of 10 brands of LCDs available in Saudi Arabia measured using a digital radiometer. Values were recorded for three time points when applicable (0, 10, and 20s). This technique was repeated five times for each LCD. Normal, high-intensity, and soft-start modes were evaluated for all brands with the features available. Irradiance values between brands were analyzed using one-way analysis of variance followed by Bonferroni method. Changes in irradiance between different time points were analyzed using one sample t test for normal and high-intensity modes and using paired t test for soft-start mode. All comparisons were carried out at 0.05 significance level.Results:The highest values were reported for Ortholux Luminous, Elipar DeepCure-S, Elipar DeepCure, and KaVo mini-LED with values above 1000 mW/cm2. All LCDs showed values above 600 mW/cm2. Three LCDs had high-intensity mode and only one device had soft-start mode. Changes over the different time points were not statistically significant exept for soft-start mode.Conclusion:All tested LCDs had irradiance values sufficient for adequate polymerization of resin composite. Only four of these are capable of curing bulk-fill composites.

Thermal rise during photopolymerization and degree of conversion of bulk fill and conventional resin composites

Light curing of resin composite is associated with a thermal rise that may have harmful effect on the health of the vital pulp. In addition, desirable polymerization is important to achieve mechanical properties and clinical function. The purpose of this in-vitro study was to compare the thermal rise under normal dentin during photopolymerization and degree of conversion (DC) of bulk fill and conventional resin composite using continuous high- and soft-start mode. In this in-vitro study, Cl I cavities with a dimension of 4 mm × 4 mm × 4 mm and remaining dentin thickness of 1 mm were prepared on 56 extracted human molars. The temperature rise during the light curing of conventional resin composite (Tetric N Ceram, Ivoclar Vivadent) by incremental filling technique and bulk-fill resin composite (Tetric N Ceram Bulk Fill, Ivoclar Vivadent) by bulk-filling technique were measured with a K-type thermocouple wire. DC of both resin composites was measured using Fourier-transform infrared spectroscopy. Data were analyzed using one-way ANOVA, Tamhane and Duncan post hoc, two-way ANOVA at the significance level of α = 0.05. Photopolymerization temperature rise due to soft start mode and the first layer of conventional composite was higher than continuous high mode and bulk-filling technique, respectively (P < 0.001). DC of conventional resin composite was higher than bulk-fill composite (P < 0.001). Soft-start mode produced higher thermal rise than continuous high mode and conventional resin composite showed higher DC than bulk-fill composite.

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 &amp;lt;0.05). There was a statistically significant difference according to the thickness (p &amp;lt;0.05). There was no statistically significant difference according to polymerization procedures (p &amp;gt;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.

Wplyw warunkow fotopolimeryzacji na wybrane wlasciwosci mechaniczne kompozytow stomatologicznychl

The paper presents the results of an investigation of the effect of photopolymerization conditions on the selected mechanical properties of dental composites based on dimethacrylate resin with an inorganic phase content ranging from 22 wt % to 65 wt %. The continuous and intermittent lighting was used with uniform and variable light intensity. It was found that the Shore hardness, maximum shear force value and adhesion of the composite to the metal substrate are strongly dependent on the radiation intensity and exposure time. The tribological properties (friction coefficient and wear resistance) of dental composites were also determined using a pin-on-disc station. The highest values of Shore A hardness were measured for the composites exposed to light using SOFT-START mode, while the lowest hardness value was observed for the composite irradiated in uniform continuous mode. It was found that the highest force values were generated when the composite was exposed to light in the PULSE DELAY mode.

Effect of application technique and mode of curing on nano-leakage of universal adhesive system

This study was carried out to Investigate the effect of application technique (total etch &self etch) and curing mode (regular & soft start) on nanoleakage of universal adhesive system in coronal and root dentine. A total number of 80 freshly extracted lower molars were used. The teeth were divided into two groups (40 teeth each) according to the application technique of the adhesive (either total or self-etch mode). Each group was subdivided into two subgroups (20 teeth each) according to the mode of curing that was used either regular or soft start mode. Each subgroup was further divided into two divisions (10 teeth each) according to the surface to which the adhesive will be applied either coronal or root dentin. The roots of all teeth were cut off at the cemento-enamel junction. The occlusal enamel of the coronal portion was removed to the depth of the central fossa to expose dentine. For the root portion, the cervical 1/3 of the buccal surface was flattened by wet grinding on a bench grinder machine. The adhesive was applied according to manufacturer instructions. Resin composite was incrementally packed and light cured either in the regular continuous mode for 20 s or cured in the ramp soft-start mode. The specimens were sectioned into beams of 1 mm thick. The beams were immersed in ammonical silver nitrate for 24 h, rinsed with distilled water, and immersed in a photo-developing solution for 8 h. Nanoleakage patterns were detected using an environmental scanning electron microscope (ESEM), and the amount of silver nitrate penetration (Wt%) was analyzed using the EDAX. The results revealed that, regardless the mode of curing in coronal or root dentine, self-etch application technique showed statistically significantly higher nanoleakage mean values compared to total-etch in all the groups. In all the groups regular curing mode showed statistically significantly higher nanoleakage mean values than soft start mode, except in coronal dentine with the self-etch application technique there was no statistically significant difference between nanoleakage mean values of the two curing modes. Regardless the curing mode with self-etch application technique, there was no statistically significant difference between nanoleakage mean value of coronal and root dentin, while for total etch technique with regular curing mode, root dentin showed statistically significantly higher nanoleakage % mean value than coronal dentin. It could be concluded that, Nanoleakage varied with technique of application of the universal adhesive system being greater with the self-etch technique. Total etch technique using soft start curing mode in coronal and root dentine presented the lowest nanoleakage between the groups.

An in -vitro study to evaluate the dentin bond strength and color change of bulk fill resin composites with different incremental thickness using two curing modes

This study was directed to evaluate the dentin bond strength and color change of bulk fill resin composites with different incremental thickness using two curing modes. Extracted human molars teeth were used to prepare one hundred and twenty specimens. For shear bond strength, the specimens were divided into two main groups according to types of composite (Tetric N Ceram, Quixfil). Each main group was divided into two groups according to thickness of composite (2& 4 mm). Each group was divided into two sub-groups according to curing mode (Continuous and soft start mode). Then, each group was divided into three classes according to storage time (one day, three months, and six months). Fr color change, one hundred and twenty discs of resin composite were used in this study. The discs were divided into two main groups according to types of composites (Tetric N Ceram, Quixfil). Each main group was divided into two groups according to thickness of composite (2 mm, 4 mm). Each group was divided into two sub groups according to curing modes (Continuous and soft start mode). Then, each sub-group was divided into three classes according to immersions media (Acidic ph, alkaline ph solution. Neutral ph). Finally, each class was divided into three sub classes according to storage time (one day, three months, and six months). The shear bond strength was evaluated using universal testing machine at a crosshead speed of 0.5 mm/min until failure occurred. Data were recorded, tabulated and statistically analysed.The specimen’s colors were measured using a Reflective spectrophotometer. The result showed the highest bond strength was recorded by (Quixfill, 4 mm, soft start at one day). For color change the (Quixfil, 4 mm, soft start, and acidic solution recorded the highest color change.

Effect of Soft-start Curing Mode on Postoperative Hypersensitivity of Class I Posterior Composites Restorations

Objectives: To evaluate the occurrence of postoperative hypersensitivity (POH) in Class I posterior composite restorations comparing the soft-start with the constant light curing modes. Materials and Methods: Seventy patients with each having contra lateral class I occlusal caries lesions in premolars and molars teeth were participated. 140 class I cavity preparations were restored with Adper™ Single Bond 2 adhesive and Filtek™ Z250 XT resin composite (3M-ESPE). For each patient, one restoration was cured with soft-start mode and the contralateral restoration was cured with constant curing modes using Light Emitting Diode (LED) curing light. POH to various stimuli was evaluated at week 1, 4, and 13 post-treatment using Visual Analog Scale (VAS). Data were collected and analyzed by Chi-Square and Fischer Exact tests.&#x0D; Results: No statistical significant differences were observed between the two curing modes (soft-start or constant) in occurrence of postoperative hypersensitivity (P&gt;0.05). Out of 140 restorations that were placed, only two (1.4 %) restorations reported POH to cold stimuli at week 1 post-treatment, being in mild; VAS=3 for soft-start and moderate; VAS=5 for constant light curing mode. No POH was reported at week 4 and 13 for soft-start or constant curing modes.&#x0D; Conclusion: Soft-start curing mode did not show any difference in occurrence of POH in class I posterior composite restorations when compared with constant curing mode.

Effects of light curing modes and ethanol-wet bonding on dentin bonding properties

This study explored the effects of different light curing modes and ethanol-wet bonding on dentin bonding strength and durability. A total of 54 molars were randomly divided into three groups: Single Bond 2, Gluma Comfort Bond, and N-Bond. Based on the three light-curing modes and presence or absence of ethanol pretreatment, the samples were assigned to six subgroups: high-light mode, ethanol pretreatment+high-light mode, soft-start mode, ethanol pretreatment+soft-start mode, standard mode, and ethanol pretreatment+standard mode. All samples were bonded with resin based on the experimental groups. After 24 h and 6 months of water storage, a universal testing machine was used to measure microtensile bond strength. Scanning electron microscopy (SEM) was applied to observe mixed layer morphology. The 24-h and 6-month microtensile bond strengths of the ethanol pretreatment groups were significantly higher than those of the non-ethanol pretreatment groups at the same light modes (P<0.05). With or without ethanol pretreatment, the microtensile bond strengths of the high-light modes were significantly lower than those of the soft-start modes and standard modes (P<0.05). The microtensile bond strengths of samples from the 6-month water storage group significantly decreased compared with those of samples from the 24-h water storage group (P<0.05). The soft-start groups and standard groups formed better mixed layers than the high-light mode groups, whereas the ethanol pretreatment groups formed more uniform mixed layers than those without ethanol pretreatment. Ethanol-wet bonding technique, soft-start, and standard modes could improve dentin bonding properties.

Analysis and Research of Soft-Start Mode Applied to Large Capacity and Long-Distance Belt Conveyor

Through the research on the structure and properties of different soft start device applied to long distance and large capacity belt conveyor. Analysis and comparison of technical characteristics of some used soft start of this kind of belt conveyor, and then get the reasonable way of soft start. In order to provide optimization scheme of application of belt conveyor in long distance and large capacity in the actual production for enterprise.

Soft-Starting Method Analysis of Belt Conveyor

This paper introduces several methods of soft start of belt conveyor, Through the analysis of all kinds of soft start mode, the prospects of development of soft start device of belt conveyor, and through the comparison of several commonly used start speed curve, the reasonable start speed curve, pointed out the direction for the research of soft start device of belt conveyor.

Comparative Evaluation of the Effects of Light Intensities and Curing Cycles of QTH, and LED Lights on Microleakage of Class V Composite Restorations.

The purpose of this study was to evaluate the effects of light intensity and curing cycles of QTH and LED lights on the microleakage of Class V composite restorations. Eighty freshly extracted human maxillary premolars were used for this study. Standardized Class V cavities were prepared and they were restored with microhybrid resin composite. According to the curing protocol, the teeth were then divided into 4 groups (n=20): QTH curing (standard and soft start modes), and LED (standard and soft start modes) irradiations. Microleakage was evaluated by immersion of the samples in 50% silver nitrate solution. The samples were then sectioned, evaluated under a stereomicroscope, and scored for microleakage. The results of the present in-vitro study showed mean dye leakage scores of 1.9, 1.2, 1.45 and 0.90 for Group I (QTH-Standard mode), Group II (QTH-Soft Start mode), Group III (LED-Standard mode) and Group IV (LED-Soft Start mode) respectively. It was thus concluded that the soft start polymerization showed a highly significant difference as compared to the standard curing modes of QTH and LED lights, respectively.

The effect of LED curing mode on microleakage of Class V cavity restored by silorane-based composite

Objective. This in vitro study evaluated the effect of soft-start curing mode by LED unit on the marginal microleakage of silorane composite restoration. Materials and methods. Class V cavities were prepared on the buccal surfaces of 80 extracted molars at the cementoenamel junction and randomly divided into eight groups. In groups 1–4, four adhesive/composite combinations (silorane/silorane, silorane/Z250, Adper Single Bond/Z250, Clearfil SE Bond/Clearfil AP-X) were applied and the composites were cured under standard mode at 1500 mW/cm2 for 20 s. In the other four groups, after applying the same adhesive/composite combinations, the composites were cured at 550 mW/cm2 for 10 s followed at 1500 mW/cm2 for 15 s. After 24 h of water storage and thermocycling, the specimens were placed in 1% methylene blue solution. The dye penetration was assessed under a stereomicroscope. The data were analysed using non-parametric tests. Results. There were no significant differences among four groups for two curing modes at the occlusal and gingival margins (p > 0.05). The soft-start curing had a positive effect on the gingival marginal sealing of group 1 (p < 0.05), but not for the other three groups (p > 0.05). Conclusion. The beneficial effect of relatively high soft-start curing on marginal sealing of Class V restoration depends on a combination of the adhesive and composite types, having a positive effect on silorane adhesive/silorane-based composite at the gingival margin.

Effects of different photo-polymerization protocols on resin–dentine μTBS, mechanical properties and cross-link density of a nano-filled resin composite

ObjectivesTo evaluate the effects of four different light-curing protocols on the microtensile bond strength (μTBS), ultimate tensile strength (UTS), Knoop micro-hardness (KH) and cross-link density (CLD) of a nano-filled resin composite. MethodsFiltek Supreme XT (3M-ESPE) was used for the entire experiments following four light-curing approaches: ST, standard irradiance; HI, high irradiance; PD, pulse delay; SS, soft start. The specimens were submitted to different storage periods (24h or 6 months), cut into match-sticks and subsequently submitted to μTBS testing. Hourglass specimens were also prepared for UTS and KH. Cylindrical specimens were prepared for the CLD evaluation after absolute ethanol challenge. The results were statistically analyzed with a two-way ANOVA and Tukey's test (α=0.05). ResultsFor UTS and KH, continuous irradiance (PD and SS) induced statistically higher results (p<0.05) both after 24h and 6 months of water storage compared to ST and HI groups. However, a drop in UTS and KH was obtained after 6 months in all groups. The μTBS was not affected by the different light-curing approaches and, no statistical differences (p>0.05) were observed between 24h and 6 months storage. The CLD evaluation showed a statistical drop in KH after 24h of ethanol storage for PD and SS (step-curing protocols) compared to those attained in continuous mode (ST and HI). ConclusionThe soft-start mode may improve the UTS and KH of nano-filled resin composites without compromising the resin–dentine μTBS. However, both the step-curing protocols may reduce the cross-link density of the composite polymeric network. Clinical significanceHigh irradiances photo-polymerization may be adequate for direct aesthetic restorations such as veneers and onlays. Meanwhile, the soft start protocol would seem more appropriate for the photo-polymerization of high c-factors class I and II restorations.

Kinetic parameters and monomeric conversion of different dental composites using standard and soft-start photoactivation modes

This paper evaluates the photopolymerization kinetics and degree of conversion of different commercial dental composites when photoactivated by a LED curing unit using two different modes (standard and soft-start mode). The investigation was performed on with RelyX ARC (dual-cured), Filtek Z-350 (Nanocomposite), Filtek Z-250 (Hybrid), and Filtek Z-350flow (Flowable) resin composites. The analysis used was attenuated total reflection with a Fourier transform infrared (ATR-FTIR). The RelyX ARC resin demonstrated the highest degree of conversion with both LED photoactivation modes. For this resin a 28% decrease in maximum rate was observed and the time to reach its highest rate was almost 2.3 times higher than when the soft-start photoactivation light curing was used. Z-350flow resin recorder a higher maximum rate using the soft-start mode rather than the standard mode. In contrast, the Z-250 showed a higher value using the standard mode. Although Z-250 and Z-350 showed a higher total degree of conversion effectiveness using the soft-start mode, RelyX and Z-350flow achieved a higher value using the standard mode.