Polymerization Of Composite Resins Research Articles

BASE SURFACE TEMPERATURE OF BULK FILL RESIN COMPOSITE WITH DIFFERENT THICKNESS

Background: The material thickness is one factor that influences the polymerization of resin composites. Bulk fill resin composite is an efficient dental resin composite restoration material because it can be cured to a thickness of up to 4-5 mm. The thickness of the material can also affect the temperature rise, while maintaining the temperature is very important because a significant increase can damage the pulp. Purpose: This research aimed to analyze the base surface temperature of bulk fill resin composite with different thicknesses. Methods: Thirty bulk fill resin composite samples with a diameter of 5 mm were divided into three groups with different thicknesses, namely group I (3 mm), group II (4 mm), and group III (5 mm). Each group of samples was cured using an LED Light Curing Unit for 20 seconds, and carried out simultaneously with the measurement of the base surface temperature using a type-K digital thermocouple. Data analyzed using One Way ANOVA and LSD post hoc tests. Results: The mean and standard deviation of the base surface temperature of bulk fill resin composite in groups I, II, and III, respectively, is 37.56 ± 1.06oC, group II 36.89 ± 1.23oC, and group III 36.00 ± 1.2 oC. It showed significantly different between the groups (p<0,05). Conclusion: The thicker the bulk fill resin composite, the lower the base surface temperature.

Bulk-fill composite in challenging cavities: conversion rate, solubility, and water absorption analysis.

In a deep, curved cavity, polymerization of a bulk fill composite can be challenging. The aim of this study was to investigate the solubility, water absorption, and conversion rate of bulk-fill composite samples prepared using molds with various slope angles. Bulk-fill composite resin (Filtek One Bulk Fill) was placed into cylindrical Teflon molds with a depth of 4mm, angled at varying degrees (90°, 75°, 60°, 45°). Two different LED light-curing units (VALO Cordless, iLed Curing Light) were used to cure the samples. Polymerizations were performed at three different distances (0mm, 2mm, and 4mm). Five samples per group were used, resulting in a total of 24 groups. The Fourier Transform Infrared Spectrometer was utilized to evaluate the conversion levels of the samples. Water sorption and solubility values were determined by storing the composites in distilled water at 37°C for 21days. The VALO light-curing unit applied closest to samples inserted in a 90° angulation mold had the highest mean degree of conversion (41.55%), while iLED light-curing unit group that applied from 4mm to the samples inserted in a 45° angulation mold had the lowest mean conversion (8.97%). The angle of the cavity and the distance at which the light-curing unit is applied significantly affected bulk-fill composite resin conversion. In addition, the choice of light-curing unit impacted the conversion levels. However, with the tested conditions, the water sorption and solubility values of polymerized composite resin samples remain unaffected by these factors.

A Comparative Evaluation of the Shear Bond Strength of Three Different Hybrid Tooth-Colored Restorative Materials to Dentin: An In-Vitro Study.

Silver amalgam, glass ionomer, resin-modified glass ionomer, compomers, light polymerized hybrid composite resin, and hybrid glass ionomer are among the most frequent restorative materials used as cavity-based or post-endodontics. Thus, to meet the needs of both patients and dentists, Cention N reimagines the traditional filling by integrating bulk placement, ion release, and durability into a dual-curing, aesthetically pleasing solution. Hoewver, we do not have enough information from studies comparing this hybrid restorative material's shear bond strengths to dentin to draw any firm conclusions. Cention N, zirconomer, and Vitremer are three hybrid tooth-colored restorative materials that were evaluated for their shear bond strength to dentin. This research aimed to compare and evaluate these materials. The purpose of this research was to use a universal Instron machine to measure the shear bond stress of three distinct hybrid tooth-colored restorative materials in relation to dentin.The research samples consisted of 45 extracted lower first premolars from humans.The teeth were then assigned into three groups of 15 samples each according to different color acrylic resin blocks, namely, group A (pink acrylic blocks), which had Cention in cement; group B (white acrylic blocks), which has zirconomer cement; and group C (violet acrylic blocks), which had Vitremer cement. There was no statistically significant difference between the three groups and the normal distribution, as shown by the negligible values in the tests involving the three groups. Put simply, each of the three categories exhibits data that follows a normal distribution. This allows for further data analysis to be conducted using the parametric test of significance. The shear bond strength of hybrid glass ionomer restorative materials has to be further investigated in both laboratory and living organism settings.

Influence of internal angle and shape of the lining on residual stress of Class II molar restorations

Polymerization shrinkage is a major side effect of resin composite materials that affects the success and longevity of caries restorations. This study was to analyze the effect of the internal angle and shape of the lining on the shrinkage residual stress of dental restorations in Class II mesio-occlusal-distal (MOD) cavities through finite element analysis (FEA). A 3D reconstructed model of a human mandibular first molar was created from micro-CT images, and then the tooth was prepared as a Class II MOD cavity. 3D models of four regular internal corner shapes of Class II MOD cavities with different internal angles of lining and one 90° filleted corner model were created. The thermal expansion technique was applied to approximate the shrinkage impact of composite resin polymerization in the FE software ABAQUS. Von Mises stress was taken as a metric. The results showed that the level of residual stresses in the Class II MOD cavities was greatly dependent on the internal angle of the lining. The maximum von Mises stress in tooth tissue decreased as the internal angle of the lining increased. The internal shapes of the lining had no obvious effect on the stress, and the filleted corner model had less stress. This lining strategy is appropriate for Class II MOD cavities with serious loss of tooth tissue.

Clinical Evaluation of Two Different Nanohybrid Composite Restorations Using FDI Criteria – A Randomized Clinical Trial

Background: Several approaches were introduced in placing the composite resin into the prepared cavity. Some researchers recommend using an incremental technique. The material is gradually placed in 2 mm or less thick layers, resulting in better curing by adequate light penetration and better composite resin polymerization. However, disadvantages like voids and the time taken to complete the procedure are lengthier due to the time consumption in placement and polymerization of each increment. Time-saving restorative materials are an ongoing demand for posterior restorations. A newer resin-based composite, bulk-fill composites, have been introduced to speed up the restoration process by enabling up to 4–5 mm thick increments to be cured in one step, thus skipping the time-consuming layering process. Materials and Methods: The randomized clinical trial was conducted on 40 patients with 80 restorations. Randomization was followed by using a random number table. Patients with at least two class I or class II restorations were selected. One tooth is restored with bulk-fill followed by capping with ceram x, and the other with bulk-fill followed by Filtek Z250. All the patients were recalled after 6 months and 12 months. Two examiners evaluated restorations using Federation Dentaire International (FDI) criteria at baseline, 3, 6, and 12 months. Results: The collected data from the participants were analyzed using SPSS software. There was no statistically significant difference observed between the two restorations placed with two nanohybrid composites (ceram x and Filtek Z250). Conclusion: The study concludes that bulk-fill resin composites capped with nanohybrid composites show excellent clinical performance equal to conventional composites and are beneficial to the clinician in reducing the time. Smart dentin replacement has a self-leveling capacity, showing better marginal adaptation and thus helping reduce secondary caries.

Light-curing units for composite resin polymerization

Light-curing units for light polymerization of composite resins are important instruments of dental practice, and their proper use has a direct impact on the physical characteristics of the material being illuminated, its biocompatibility, as well as on the overall clinical success and durability of dental composites. Irradiance represents the power of radiation per unit of irradiated surface and should be distinguished from irradiance measured directly at the lamp head, which is called output irradiance or emittance. Also, different areas on the surface of the material can be exposed to different radiation powers, which sometimes significantly deviate from the given average value. The reason for this is the inhomogeneity of the radiation beam. The 3D profile of the light beam gives the most precise information about the quality of radiation to which the material will be exposed. Due to the existence of different photoinitiator systems, the use of devices with a wider emission spectrum that covers a larger range of light wavelengths is often recommended today. An important characteristic of the light-curing unit is its power, but the use of lamps of higher power does not mean a proportional reduction in polymerization time. The quality and maintenance of light sources are certainly one of the important factors that influence the success of restorations.

Color Stability of Provisional Restorative Materials - A Tabular Review

Temporary prosthodontic materials used for temporization for crown and bridges to protect the vital tooth or teeth from hypersensitivity. Most commonly used temporization materials are Polymethylmethacrylate (PMMA), Bis-acryl composite resin, Light polymerized composite resin, and CAD/CAM provisional restorative material. In this review we have made an attempt to discuss the advantages and disadvantages of temporary prosthetic materials in a tabular format.

In vitro comparative study between adhesion forces obtained on zirconia ceramic micromechanically treated with femtosecond laser (1027nm), carbon dioxide laser (10,600nm), and aluminum-oxide particles.

Conventional surface roughening treatments used for silica-based ceramics in order to improve subsequent adhesion become unreliable for zirconia ceramics. Laser conditioning can be a good alternative. The purpose of this in vitro study was to compare conventional (macro) shear bond strength (SBS) values obtained between resin composite and zirconium oxide ceramic samples grouped according to different micromechanical treatments received, and examine differences in surface roughness. One-hundred and fifty disks of sintered zirconia were randomly divided into 5 groups and roughened as follows: (1) Group NOT, no surface treatment; (2) Group APA, abraded with 50-μm aluminum-oxide (Al2O3) particles; (3) Group TBS, abraded with 30-μm aluminum-oxide particles covered with silica; (4) Group CO2, irradiated with a CO2 laser which emitted in continuous wave mode at 3 W of power; and (5) Group FEM, irradiated with a pulsed femtosecond laser, with an incident energy of 10μJ, a frequency of 1000Hz, and a fluence of 1.3kJ/cm2. All surfaces were treated with a MDP-containing adhesive/silane coupling agent mixture upon which were prepared and light polymerized composite resin cylinders. Shear bond strength was measured and samples were observed by scanning electron microscopy (SEM). Statistically significant differences (p < 0.05) were found among all groups, except between CO2 and FEM, which showed the highest adhesion values (15.12 ± 2.35MPa and 16.03 ± 2.73MPa). SEM revealed differences in surface patterns. CO2 laser irradiation can be an alternative to sandblasting, although it could also weaken the ceramic. Suitable surface patterns on zirconia ceramics can be obtained with ultrashort pulsed radiation emitted by a pulsed femtosecond laser.

Degree of conversion of light-polymerized composite resin in implant prosthesis screw access opening.

The mechanical and physical properties of implant screw access opening deteriorate if composite resin is not polymerized properly. Therefore, this study aimed to analyze the effect of using composite resin in implant access opening on the degree of conversion (DC). Two prosthetic materials (Co-Cr and zirconia), two types of composite resin (low and high viscosity), two light-cured resin depths (2 and 3mm), and two polymerization methods (max-mode 10s and mid-mode 20s: 16 and 22J/cm2 , respectively) were considered (n=192). The DC of the polymerized composite resin was measured through Fourier-transform infrared spectroscopy. The top and bottom surfaces of the polymerized composite resin body were observed through scanning electron microscopy. Multiple linear regression analysis and analysis of variance were used to identify significant differences in DC (α=0.05). The DC was lower when the low-viscosity composite resin (β=-0.431), light-polymerized resin depth of 2mm (β=-0.430), zirconia prosthesis (β=-0.191), and mid-mode polymerization method (β=-0.164) were used. The resin type, depth of resin to be light-cured, prosthesis material, and polymerization method had an effect on the DC. Low-viscosity composite resin should be polymerized at a low irradiance and long polymerization time (such that the light-cured resin depth does not exceed 2mm) to ensure proper composite resin polymerization in implant screw access opening.

Polymerization behavior of bulk-fill and hybrid-type resin composites using different light curing mode

Purpose: This study aimed to investigate if the hardness ratio of the bulk-fill-type resin composite is higher than that of the hybrid-type resin composite, to determine when the radiant exposure was the same, and to investigate if the polymerization of resin composites at the top and bottom surfaces and the hardness ratio is affected by differences in irradiance light sources. Methods: The light-curing unit used was the LED G-Light Prima-II Plus (blue + violet LED) light-curing unit. The light-cured resin composites were hybrid-type Clearfil AP-X and bulk-fill flowable-type Gracefil BulkFlo. Composite specimens with 2-mm-thick were polymerized in Teflon molds using radiant exposure of 24 J/cm2. The light-curing methods were 1,100 mW/cm2 for 22 s and 600 mW/cm2 for 40 s. Just after light-curing, the Knoop hardness was measured at the top and bottom surfaces of each specimen using a hardness tester, and the hardness ratio was calculated. Results: The bulk-fill flowable type resin composite, Gracefil BulkFlo, showed a lower hardness ratio than the hybrid-type resin composite, Clearfil AP-X. When radiant exposure was the same, 600 mW/cm2 irradiance light created more uniform polymerization of the resin composite than 1,100 mW/cm2 irradiance light for both bulk-fill and hybrid-type resin composites.Conclusion: It was suggested that curing with an irradiance of 600 mW/cm2 for 40 s created more uniform polymerization for both materials.

Color Stability of Provisional Restorative Materials in Different Mouthwash Solutions

Purpose. This study is a comparison of the effects of temporary restorative materials (PRMs) on the color change that occurs due to the use of different mouthwash solutions in two time periods. Material and Methods. One hundred fifty disc-shaped specimens (10 mm × 2 mm) were fabricated with three PRMs chemically polymerized PMMA (Imident-I), chemically polymerized bisacrylic composite resin (Acrytemp-A), and CAD/CAM PMMA-based polymer (TelioCAD-T) according to manufacturers’ instruction and using a CAD/CAM milling system (n = 10). CIE L ∗ a ∗ b ∗ values of specimens were recorded before immersion. Samples were immersed in solutions (Distilled water-DW, Kloroben-CHX, Listerine Advanced White-LAW, Listerine Total Care-TC, and Listerine Zero-TCZ) in two time periods (t1, t2). Color measurements of the samples were made with the help of a spectrophotometer before and after they were removed in mouthwashes (VITA Easyshade V). Results. According to the statistical analysis results, significant differences were observed between the results obtained in our study. The highest roughness values in ΔE1 were seen in A-LAW (1.83) and the lowest in T-DW (0.61). In ΔE2, the highest roughness values were observed in I-LAW (2.70), and the lowest in T-DW (1.05). ΔE values of all obtained groups were found within clinically acceptable limits (ΔE &lt; 3.7). Conclusions. The content of temporary restorative materials, the production technique, the type of mouthwash, and the immersion time of the restoration affect the color stability. Mouthwash with a whitening effect caused the most discoloration. Among the temporary restorative materials, it was the CAD/CAM material that best preserved its color stability.

Effect of different polymerization times on color change, translucency parameter, and surface hardness of bulk-fill resin composites.

Polymerization plays an important role in the optical and mechanical properties resin composite materials. The current study aimed to evaluate the effect of different polymerization times on the color change, translucency parameter (TP), and surface hardness of resin composites after thermocycling. Microhybrid resin composite (Filtek Z250; used in the control group) and bulk-fill resin composites (Filtek One Bulk-Fill Restorative, Tetric EvoCeram Bulk-Fill, and Tetric N-Ceram Bulk-Fill) were used. Each bulk-fill composite was placed as a single layer. Polymerization of the bulk-fill composites in the first group was completed in 20 s, and that in the second group was completed in 40 s (n = 10). Filtek Z250's polymerization was completed with 2 mm (20 s) + 2 mm (20 s). The color change (ΔE00) and translucency parameter (TP00) were calculated using the CIEDE2000 formula. Before and after thermocycling, the TP and surface hardness values were measured. The data were analyzed using one- and two-way analysis of variance, paired-samples t-test, and Tukey's test (P < 0.05). After thermocycling, the ΔE00 values of the resin composite samples were 1.66-2.56. Compared to the control group, the Filtek One Bulk-Fill 20 s group exhibited the lowest color change values. The Filtek Z250 group exhibited lower TP and significantly higher microhardness values than the other bulk-fill resin groups before and after thermocycling (P < 0.05). There were no observed differences in the Tetric N-Ceram and Tetric EvoCeram groups before and after thermocycling. Under the conditions of 10,000 thermal cycles, different curing times did not affect the color change and hardness values of the bulk-fill materials. However, differences were observed among the composite materials. After thermocycling, the surface hardness and TP values decreased in all the resin composites. Depending on the material content, effective results can be obtained from the 20 s polymerization of bulk-fill resin composites.

Effect of Light Curing Modes of High-Powered LEDs on Temperature Rise under Primary Teeth Dentin (An In Vitro Study)

Background: Temperature rise in the pulp chamber is a severe stress that can cause irreversible damage to the pulp. This study aimed to evaluate the effect of three curing modes of a high-powered LED and two remining dentin thicknesses on the temperature rise under primary teeth dentin. Methods: One dentin disc of 1 mm thickness were prepared from human primary molar. The dentin disc was exposed to curing light using a high-powered LED for 10 s to simulate bonding agent polymerization (stage 1 curing). Five specimens of resin composite were cured for 20 s. The different modes tested were standard, ramp, and pulse mode (n=5). After that the dentin disc was grinded to 0.5 mm thick and the experiments were repeated. Temperature change data were subjected to analysis of variance (ANOVA) and Tukey's test. Results: The highest temperature rise was observed under the 0.5-mm-thick dentin disc with standard mode (7.6±0.234; 4.78±0.4207), whereas the lowest values were recorded with pulse mode under 1-mm-thick dentin (4.8±0.458; 3.16±0.829) during stage 1 curing and resin composite polymerization, respectively. Pulse mode produced a significantly lower values compared to standard mode in all conditions (P&lt;0.05). An inverse proportion was found between the mean temperature rise values and the dentin thickness. Conclusions: High-powered LEDs should not be used to cure bonding agents in deep cavities. The maximum temperature rise induced by a high-powered LED during resin composite polymerization was not critical for pulpal health. Temperature rise related to dentin thickness and curing modes.

Application of Reactive Oxygen Species in Dental Treatment.

Reactive oxygen species (ROS) and free radicals, which have been implicated in inflammation, pain, carcinogenesis, and aging, are actually used in dental treatments such as tooth bleaching and composite resin polymerization. Recently, numerous studies have investigated the application of ROS in the medical and dental fields. In previous studies, ROS were generated intentionally through pathways such as photolysis, photocatalytic methods, and photodynamic therapy, which are used in the medical field to target cancer. In the field of dentistry, generated ROS are applied mainly for periodontal treatment and sterilization of the root canal, and its effectiveness as an antibacterial photodynamic therapy has been widely reported.. Given this background, the present article aimed to review the basic effects of ROS in dental medicine, especially endodontic therapy, and to discuss future applications of ROS.

Evaluation of Temperature Changes in the Pulp Chamber During Bulk-Fill Composite Polymerization: An In-Vitro Study

Aim: To investigate the temperature changes occurring in the pulp chamber during the polymerization of bulk-fill resin materials cured with different light sources by using a pulpal microcirculation simulation device in vitro. Materials and Methods: Class I cavities of width 2 × 3 mm were prepared on 120 permanent noncarious teeth. All samples were adjusted to maintain 2 mm dentin thickness within the pulp chamber and the cavity base. Venus Bulk Fill, Tetric Evo Ceram Bulk Fill, Filtek Bulk Fill, and Filtek Z250 were used as restorative materials. Materials were polymerized with Valo Light Emitting Diode (LED), Elipar S10, and Elipar Deepcure-S devices. A j-type thermocouple with microcirculation assemblies was used for measuring the temperature increments inside the pulp chamber during the polymerization of bulk-fill composite resins. The obtained data were recorded. Results: Statistically significant difference was found between the light sources and the temperature changes occurring during the polymerization ( P &lt;.05). The difference in temperature increases was found to be significant ( P &lt;.05) between restorative materials. The highest temperature rise values were obtained from Venus Bulk Fill. Conclusion: All light devices used in the study caused an increase in temperature in the pulp chamber in all groups. For all resin materials used, it was observed that the temperature values arising during the polymerization via used light sources did not exceed 5.5°C, which is the critical value for pulp.

Effect of dental headlights spectrum on the polymerization and working time of light-cured resin composites.

BackgroundThe use of dental headlights is a common practice to better illuminate the operatory field and achieve excellence in restorative dentistry. However, visible light-cured dental materials can have reduced working time under headlight illumination. The aim of this study was to evaluate the influence of the spectral irradiance power of two dental headlights on the degree of polymerization and working time of light-curable dental composites. Material and MethodsTwo headlights, StarLight Nano 3 (StarMed) (SN) and Zeon Endevour XL (Orascoptic) (ZE) were characterized using a spectrophotometer coupled to an integrating sphere (MARC® Light Collector, BlueLight Analytics). The degree of conversion of the two composites, Filtek Supreme (3M) and Tetric Prime (Ivoclar Vivadent), was evaluated using an FTIR spectroscope (NicoletTM iS20, Thermo Fisher). ResultsBoth headlights emitted a significant amount of blue light. The Zeon headlamp without filter emitted a broader spectrum with lower blue intensity and higher CRI than the White LED of the Nano 3. The Zeon headlamp with the blue blocking filter emitted a broader spectrum than the Orange LED of the Nano 3. There were no differences in the degree of conversion and working time of the Filtek Supreme and Tetric Prime composites when illuminated by the different headlamps. Both Zeon and the White LED of the Nano 3 were capable to cure the composites within only 5-10 minutes of irradiation. There were no changes in the degree of conversion of the composites when the Orange LED of the Nano 3 or the blue blocking filter of the Zeon were used. ConclusionsBoth headlights reduced the working time of light-cured materials. The use of orange filters prevented the composite polymerization and maintained the working time. Key words:Surgical Headlight, degree of conversion, working time, light-curing.

Influence of Monowave and Polywave LED Unites on G-Aenial Resin Composites’ Polymerization: An In Vitro Study

Objectives: Trimethylbenzoyldiphenylphosphine oxide and phenylpropanedione photoinitiator components in resin composites have been used widely due to their white color. However, it seems that there are some limitations in the required polymerization initiator wavelength. This study aimed to evaluate the polywave and monowave light-activating devices (LEDs) on polymerization and shrinkage strain of two dental composites with different photoinitiator systems. Methods: In this experimental study, 24 samples were prepared in two groups, including G-Aenial A2 and bleach composites. Each group was divided into two subgroups: one cured by monowave LED unit and the other by polywave device. Then shrinkage strain of samples was evaluated using bonded disk technique. Results: Results showed the shrinkage strain of A2 and bleach composites using PW device was significantly greater than MW device. In addition, the A2 composite shrinkage action polymerized with MW device was significantly lower than shrinkage action of A2 and bleach composite using PW machine. Conclusion: The findings of this study revealed that polywave LEDs were more beneficial for the polymerization of resin composites.

Spectrophotometric evaluation of staining of different types of light-cure composite resins after exposure with different light-cure intensities: An in vitro study.

Relation between the adequate intensity output of curing lights on color stability of composite resin is well accepted. To investigate the effect of different light-curing intensities and its relation to color stability of different polymerized composite resin materials using the spectophotometric analysis. Comparative in vitro study done on composite resin discs. A total of 180 discs comprising sixty discs prepared from three different composite resins, namely microhybrid composite resin (Filtek Z100,3M ESPE), nanohybrid composite resin (Filtek Z250 XT, 3M ESPE), and nanofilled composite resin (Filtek Z350 XT,3M ESPE) using three different light curing intensities, viz., 325-425 mW/cm2, 750-850 mW/cm2, and 1000-1100 mW/cm2. Later these discs were stained with 2% methylene blue followed by re-absorption in absolute alcohol for supernatant solution preparation which is used for the spectrophotometric analysis. Spectrophotometric absorption values were analyzed using the one-way ANOVA test for intergroup analysis. Mean stain absorption was the highest with nanofilled composite resin (Filtek Z350 XT,3M ESPE) after exposure with light-curing intensity of 325-425 mW/cm2 and least with microhybrid composite resin (Filtek Z100, 3M ESPE) after exposure with light-curing intensity of 750-850 mW/cm2 and this difference found was highly significant statistically (P < 0.001). Microhybrid composite resin (Filtek Z100, 3M ESPE) cured with intensity of 750-850 mW/cm2 showed least stain absorption indication most color stability and esthetic function.

Effect of LEDs with Different Wavelengths on the Microhardness and Nanohardness of Nanohybrid Composite Resins

The aim of this study is to compare the effectiveness of polymerization of nanohybrid composite resins with different colors and thicknesses, photocured by units of different wavelengths through Knoop microhardness (KHN) and Berkovich nanohardness (DUH). One hundred twenty specimens of Tetric N-Ceram (Ivoclar/Vivadent) were divided into groups (n = 5) according to the experimental test, the color of the composite resin (A2 and Bleach-M/BM), the light source: monowave (Elipar™ FreeLight DeepCure-3M/ESPE), dental products-1200 mW/cm2/15 seconds (FL); or polywave (Bluephase-Ivoclar/Vivadent 1200 mW/cm2/15 and 30 seconds (BP), and thickness (irradiated surface,1, 2, and 3 mm). The specimens were stored dry for 24 hours at 37°C and received five indentations on the top and button surfaces. Analysis of variance (ANOVA), Tukey, and Pearson correlation (p < 0.01%) tests were used. A direct correlation was found between KHN and DUH. The higher values of KHN and DUH were observed with Elipar™ FreeLight DeepCure unit in irradiated surface and 1-mm-thick specimens at A2 color. That Elipar™ FreeLight DeepCure unit showed better effectiveness in curing nanohybrid composite resins, used in this work, in different colors and depths as compared to Bluephase in both experimental tests, and that DUH can substitute KHN test when comparing the effectiveness of polymerization. The evaluation of the mechanical properties of composite resins is essential to verify their possible clinical performance.

Effects of application method on shrinkage vectors and volumetric shrinkage of bulk-fill composites in class-II restorations

ObjectivesUpon initial proximal wall construction, the favorable C-factor of class-II cavities may become unfavorable. This study investigated the application method on bulk-fill resin composite polymerization shrinkage. MethodsOccluso-proximal class-II cavities were prepared in 40 molars and bonded with a self-etch adhesive (Adhese Universal). The study groups varied according to the resin composite application: group-1: bulk application, Tetric EvoCeram Bulk Fill (TBF); group-2: proximal wall construction (TBF) and occlusal cavity filling (TBF); group-3: thin flowable liner layer, Tetric EvoFlow Bulk Fill (TEF) and bulk filling (TBF); group-4: flowable liner (TEF), proximal wall (TBF), occlusal cavity (TBF); and group-5: bulk application, SDR (3 mm) and capping layer (TBF, 1 mm). Each resin composite increment was scanned twice using micro-CT (uncured, cured 40 s) at a resolution of 16 µm. Shrinkage vectors and volumetric polymerization shrinkage were evaluated and statistically analyzed (one-way ANOVA). SEM images were used to investigate the tooth-restoration interface. ResultsShrinkage vectors differed significantly among the groups and were greatest in gp5-fl/SDR (47.6 µm), followed by gp1-TBF (23.8 µm) and least in gp5-fl/SDR+TBF (11.1 µm). Volumetric shrinkage varied significantly with the use of SDR (gp5-fl/SDR: 2.6%) and TEF (gp4-fl/TEF: 2.5%) to TBF (gp4-fl/TEF+wl/TBF: 0.6%) in the incremental application. SignificanceBuilding a proximal resin composite wall yielded smaller shrinkage vectors than the bulk application. Applying a thin flowable liner decreased the shrinkage vectors, even more when building a proximal wall. A thin flowable liner is recommended when building a proximal resin composite wall.