Polymerization Shrinkage Rate Research Articles

Real-time measurement of transmittance changes during photo-polymerization of conventional and bulk-fill composites.

This study investigated transmittance changes during photo-polymerization of composites in real-time. The transmittance changes of one conventional micro-hybrid, three conventional nano-hybrid, and four bulk-fill composites were measured before, during, and after photo-polymerization, and the maximum rate of transmittance change was compared with that of polymerization shrinkage. A significant difference in transmittance of composite between before and after photo-polymerization was observed. The transmittance of composites except for one bulk-fill composite increased during photo-polymerization. There was a correlation between the maximum rate of transmittance change and the maximum rate of polymerization shrinkage. The transmittance analysis of composites gives very important information to know for the final aesthetic restoration and allows to evaluate polymerization kinetics.

Polymerization Shrinkage of Short Fiber Reinforced Dental Composite Using a Confocal Laser Analysis.

The purpose of this study was to investigate the polymerization shrinkage of short fiber reinforced composite (SFRC) using a multicolor confocal displacement laser that can measure the polymerization shrinkage with high accuracy. The three types of SFRCs used in this study were XD (Ever X Flow Dentin), XB (Ever X Flow Bulk), and XP (EverX Posterior). In addition, CF (Clearfil majesty ES Flow) with hybrid type filler was used as a control. The measured values of the final polymerization shrinkage rate and amount of polymerization shrinkage rate when the polymerization shrinkage rate became constant (less than 0.1 µm/s) were approximated for all SFRCs. XP had a large aspect ratio of glass fiber filler and showed a significant difference from XD with a small aspect ratio (p < 0.05). There was no significant difference in the measured value of time when the polymerization contraction reached a constant speed (0.1 µm/s or less) for all SFRCs (p > 0.05). There was no significant difference in the measured values of polymerization shrinkage rate after the polymerization shrinkage reached a constant rate for all SFRCs (p > 0.05). These results show that glass fiber with large aspect ratio can alleviate polymerization shrinkage stress. The polymerization behavior of SFRC was found to be dependent on the amount of glass fiber filler, aspect ratio, and orientation.

Polymerization Shrinkage, Shrinkage Stress, and Degree of Conversion in Bulk-Fill Resin Composites After Different Photo-Activation Methods

Introduction: The aim of this study was to evaluate the effect of photo-activation methods on the shrinkage behavior of bulk-fill resin composites. Materials and Methods: Three bulk-fill resin composites (Tetric N-Ceram bulk-fill, Xtra fill, and Filtek flowable) were compared in terms of polymerization shrinkage, shrinkage stress, and degree of conversion (DC). Two curing methods were used: 1) conventional and 2) soft-start curing. Five disk-shaped specimens of each bulk-fill composite were fabricated. The deflection disk method and custom-made linear variable differential transformer (LVDT) device evaluated the dimensional changes during polymerization. Universal testing machine was used to measure shrinkage stress. To evaluate DC, the absorbance peaks were obtained using Fourier Transformation Infrared Spectroscopy (FTIR). Data were analyzed by one-way ANOVA and Tukey test. Results: Tetric N-Ceram bulk-fill (conventional mode) showed the highest polymerization shrinkage rate. Filtek flowable resin composite showed least amount of shrinkage stress and highest DC, while Xtra fill (with conventional curing) showed the highest shrinkage stress. Conclusion: Photo-activation method had no effect on decreasing the polymerization shrinkage except for Tetric N-Ceram; also, polymerization shrinkage stress in Filtek flowable composites with both curing methods was less than other groups. DC was product dependent.

Shrinkage characteristics of a novel lower contractile acrylic pattern resin.

Forming models and brazing parts, both of which require high accuracy, are greatly affected the polymerization shrinkage of pattern resin. In 2018, a lower-shrinkage autopolymerizing pattern resin (PRK) was introduced. In this work, we compared the rate of polymerization shrinkage between PRK with that of three autopolymerizing resins -GC Pattern Resin (GPR), Pi-Ku Plast (PIK), and Fixpeed (FIX)- as controls. The shrinkage percentages at 10 min were 7.26±0.88 for PRK, 10.78±2.28 for GPR, 8.03±1.08% for PIK, and 7.46±1.25 for FIX. The shrinkage of PRK was significantly lower than that of GPR. The lower-shrinkage autopolymerizing resin contains some multifunctional monomer and indicated that the amount of monomer was accordingly reduced from the result of polymer size and abundance ratio. Our results suggested that the monomer component and the polymer particle size were factors that contribute to reducing contraction of the resins.

Evaluation of the physical properties of dental resin composites using optical fiber sensing technology

ObjectivesThe characterization of the physical properties of dental resin composites is fraught with difficulties relating to significant intra and inter test parameter variabilities and is relatively time consuming and expensive. The main aim of this study was to evaluate whether optical fiber Bragg grating (FBG) sensing system may become a viable tool to study dental material characteristics. Of particular focus was the potential for the system to demonstrate a multi parameter all-in-one feature. MethodsA miniature FBG was embedded in six different dental resin composites and employed as a sensor to evaluate linear polymerization shrinkage, thermal expansion and water sorption. Six commercially available dental composites with different filler types and volume are evaluated. The tests are repeated with three sets of samples. The curing characteristics and residual strain gradient exhibited by the cured dental composites were also observed and commented. ResultsAmong the studied samples, SDR shows lowest polymerization shrinkage, while Beautifil FO3 shows the highest. The results also show clear distinction between particle filler type and fiber reinforcement based composites in their polymerization shrinkage properties. The agreement of the results with existing literatures show that FBG based system provides accurate results. Polymerization shrinkage rate of the samples are also obtained. Thermal expansion of the composites are measured using the FBG sensing method for the first time and is correlated with resin type, volume, filler type and glass transition temperature. The water sorption characteristics of the dental composite are also successfully measured using the FBG sensing method. The high level of repeatability and the low standard deviations shown in the results indicate good reliability with the use of FBG sensors. SignificanceThis study demonstrates how optical fiber technology can provide simple and reliable methods of measuring the critical physical properties of dental composites. In addition due to the embedding and preservation of the sensor within the samples multiple parameters can be tested for with the same sample. These features are expected to greatly assist material science researchers in dentistry as well as other biomedical fields. Of some interest the phenomenon of stress relaxation of dental composite at higher temperature was observed.

Property evolution during vitrification of dimethacrylate photopolymer networks

ObjectivesThis study seeks to correlate the interrelated properties of conversion, shrinkage, modulus and stress as dimethacrylate networks transition from rubbery to glassy states during photopolymerization. MethodsAn unfilled BisGMA/TEGDMA resin was photocured for various irradiation intervals (7–600s) to provide controlled levels of immediate conversion, which was monitored continuously for 10min. Fiber optic near-infrared spectroscopy permitted coupling of real-time conversion measurement with dynamic polymerization shrinkage (linometer), modulus (dynamic mechanical analyzer) and stress (tensometer) development profiles. ResultsThe varied irradiation conditions produced final conversion ranging from 6% to more than 60%. Post-irradiation conversion (dark cure) was quite limited when photopolymerization was interrupted either at very low or very high levels of conversion while significant dark cure contributions were possible for photocuring reactions suspended within the post-gel, rubbery regime. Analysis of conversion-based property evolution during and subsequent to photocuring demonstrated that the shrinkage rate increased significantly at about 40% conversion followed by late-stage suppression in the conversion-dependent shrinkage rate that begins at about 45–50% conversion. The gradual vitrification process over this conversion range is evident based on the broad but well-defined inflection in the modulus versus conversion data. As limiting conversion is approached, modulus and, to a somewhat lesser extent, stress rise precipitously as a result of vitrification with the stress profile showing little if any late-stage suppression as seen with shrinkage. SignificanceNear the limiting conversion for this model resin, the volumetric polymerization shrinkage rate slows while an exponential rise in modulus promotes the vitrification process that appears to largely dictate stress development.

Silorane-기질 치아 수복용 복합레진의 중합수축과 중합수축응력

본 연구의 목적은 silorane 기질의 치아 수복용 복합레진의 중합수축과 수축응력의 동력학을 평가하고 전통적인 methacrylate 기질의 복합레진과 비교하기 위함이다. 두 종의 methacrylate 기질의 복합레진(Z250, Z350 flowable)과 silorane 기질 복합레진(P90)이 사용되었다. 아르키메데스 원리를 응용해 자체 제작한 중합수축 측정 장치를 사용하여 광중합 중 일어나는 복합레진의 체적 중합수축을 측정하였고 스트레인게이지로 중합수축응력을 측정하였다. Silorane 기질 복합레진인 P90의 중합수축과 최대 중합수축률이 가장 낮았고 methacrylate 기질 복합레진인 Z350 flowable이 가장 높았다. Methacrylate 기질의 복합레진과 비교하여 silorane 기질의 복합레진 P90이 최대 수축률에 이른 시간은 더 길었고 중합수축응력은 낮았다. The purpose of this study was to measure the volumetric polymerization shrinkage kinetics and stress of a silorane-based dental restorative composite and compare it with those of conventional methacrylate-based dental composites. Two methacrylate-based composites (Z250, Z350 flowable) and one silorane-based composite (P90) were investigated. The volumetric polymerization shrinkage of the composites during light curing was measured using a laboratory-made volume shrinkage measurement instrument based on the Archimedes' principle, and the polymerization stress was also determined with the strain gage method. The shrinkage of silorane-based composites (P90) was the lowest, and that of Z350 flowable was the highest. Peak polymerization shrinkage rate was the lowest in P90 and the highest in Z350 flowable. The time to reach peak shrinkage rate of P90 was longer than those of the methacrylate-based composites. The polymerization shrinkage stress of P90 was lower than those of the methacrylate-based composites.

Cyanoacrylate–POSS nanocomposites: Novel adhesives with improved properties for dental applications

ObjectivesThis study evaluates the effect of incorporation of an acrylate polyhedral oligomeric silsesquioxane nanostructure (APOSS) on the physical and mechanical properties and hydrolytic stability of octyl cyanoacrylate (CA) adhesives. Materials and methodsCA was photopolymerized under irradiation of visible light using 1-phenyle-1,2-propandione (PPD), and 2,3-botanedione (BD) as photoinitiators. Following the polymerization shrinkage kinetics of the adhesives, the initiator concentration was optimized. Mechanical properties of the bulk CA–APOSS nanocomposites, including flexural strength and modulus, were investigated. Miroshear bond strength of dental composite bonded to human dentin applying the CA–APOSS adhesives was also determined. The effect of APOSS on the stability of CA adhesive against hydrolysis studied performing solubility, water uptake, and aging tests. ResultsThe results revealed higher efficiency of BD in comparison to PPD. A 3% (mol/mol) of BD was obtained as the optimum photoinitiator concentration. The incorporation of APOSS increased the polymerization shrinkage rate of the CA adhesives. The flexural strength of CA adhesive was significantly improved incorporating less than 20wt.% APOSS while an increasing trend was observed in the flexural modulus with the nanostructures loading. The microshear bond strength to dentin was also enhanced using 10wt.% APOSS as reinforcing/crosslinking nanofillers. A decrease in the solubility and water sorption was the result of incorporation of APOSS in CA adhesives. Degradation due to the hydrolysis in water was diminished in the specimens containing APOSS nanostructures, revealed after aging in water at 37°C. SignificanceCA adhesives are good soft tissue adhesives which their low mechanical properties and lack of hydrolytic stability has made them less interesting in the applications deal with hard tissues. The study shows that the incorporation of POSS nanostructures into CA could reduce the drawbacks.

Polymerization shrinkage kinetics of silorane-based composites

Dental composites have improved significantly in physical properties over the past few decades. However, polymerization shrinkage and stress is still the major drawback of composites, limiting its use to selected cases. Much effort has been made to make low shrinking composites to overcome this issue and silorane-based composites have recently been introduced into the market. The aim of this study was to measure the volumetric polymerization shrinkage kinetics of a silorane-based composite and compare it with conventional methacrylate-based composites in order to evaluate its effectiveness in reducing polymerization shrinkage. Five commercial methacrylate-based (Beautifil, Z100, Z250, Z350 and Gradia X) and a silorane-based (P90) composites were investigated. The volumetric change of the composites during light polymerization was detected continuously as buoyancy change in distilled water by means of Archemedes' principle, using a newly made volume shrinkage measurement instrument. The null hypothesis was that there were no differences in polymerization shrinkage, peak polymerization shrinkage rate and peak shrinkage time between the silorane-based composite and methacrylate-based composites. The results were as follows: 1. The shrinkage of silorane-based (P90) composites was the lowest (1.48%), and that of Beautifil composite was the highest (2.80%). There were also significant differences between brands among the methacrylate-based composites. 2. Peak polymerization shrinkage rate was the lowest in P90 (0.13%/s) and the highest in Z100 (0.34%/s). 3. The time to reach peak shrinkage rate of the silorane-based composite (P90) was longer (6.7 s) than those of the methacrylate-based composites (2.4-3.1 s). 4. Peak shrinkage rate showed a strong positive correlation with the product of polymerization shrinkage and the inverse of peak shrinkage time (R = 0.95).

Dimensional change measurements of conventional and flowable composite resins using a laser displacement sensor

The polymerization shrinkage values of commercial flowable and conventional composites were measured with a newly developed laser displacement sensor. Compressive strength and filler content were also measured. Compared to conventional composites, the flowable composites required a longer time - not exceeding 4 minutes - to reach a constant polymerization shrinkage rate. In terms of shrinkage ratio, it was less than 1.5% for conventional composites at 90 minutes, which was lower than that of flowable composites, i.e. more than 2.0%. The compressive strength of conventional composites was higher than that of flowable composites. A highly significant correlation between filler content and polymerization shrinkage at 90 minutes was observed, and polymerization shrinkage tended to decrease as filler content increased. In light of the results obtained in this study, the newly developed displacement meter with a laser displacement sensor proved to be effective for in-depth investigation of the polymerization shrinkage of dental composites.

Effect of intermittent polymerization on the rate of polymerization shrinkage and cuspal deflection in composite resin

This study investigated the effect of intermittent polymerization on the rate of polymerization shrinkage and cuspal deflection in composite resins. The linear polymerization shrinkage of each composite was measured using the custom-made linometer along with the light shutter specially devised to block the light at the previously determined interval. Samples were divided into 4 groups by light curing method; Group 1) continuous light (60s with light on); Group 2) intermittent light (cycles of 3s with 2s light on & 1s with light off for 90s): Group 3) intermittent light (cycles of 2s with 1s light on & 1s with light off for 120s); Group 4) intermittent light (cycles of 3s with 1s light on & 2s with light off for 180s). The amount of linear polymerization shrinkage was measured and its maximum rate (Rmax) and peak time (PT) in the first 15 seconds were calculated. For the measurement of cuspal deflection of teeth, MOD cavities were prepared in 10 extracted maxillary premolars. Reduction in the intercuspal distance was measured by the custom-made cuspal deflection measuring machine. ANOVA analysis was used for the comparison of the light curing groups and t-test was used to determine significant difference between the composite resins. Pyramid showed the greater amount of polymerization shrinkage than Heliomolar (p

Effects of Water Pressure during Polymerization on Mechanical Properties of Autopolymerized Resins

Purpose: This study evaluated the effects of water pressure on the mechanical properties and tensile bond strength of autopolymerized resins during polymerization at room temperature using a dental pressure pot with chair-side ease of handling.Methods: Four different autopolymerized resins (Unifast II, Unifast III, Provinice, and Miky Plus) were used. Specimens were fabricated by the brush-on technique. In the pressure group, specimens were polymerized in a dental pressure pot under 0.2 MPa water pressure at room temperature. In the non-pressure group, specimens were polymerized on bench. The 2 groups were compared for dimensional accuracy, 3-point bending, and tensile bond strength. Data were statistically analyzed by two-way analysis of variance (ANOVA) with Tukey’s multiple comparison test at a significance level of α=0.05.Results: Two-way ANOVA indicated that both resin and pressure had significant effects on the polymerization shrinkage rate (PSR). Interaction between resin and pressure was also significant. The PSR was lower in the pressure group than in the non-pressure group. The PSRs of Unifast II and Miky Plus were greatly improved by pressure polymerization. Significant differences in flexural strength were observed between the 2 groups. The flexural strength significantly increased under pressure. No significant differences in tensile bond strength were observed between the 2 groups.Conclusion: The dimensional accuracy and flexural strength of autopolymerized resins were significantly improved by the application of water pressure during polymerization. No significant changes in tensile bond strength were observed following pressure application at room temperature.

Dynamics of composite polymerization mediates the development of cuspal strain

Objectives In the current study, we used electronic speckle pattern interferometry (ESPI) to measure tooth deformation in response to polymerization of five resin composites with a range of polymerization shrinkage. Our hypothesis was that composites with higher polymerization shrinkage should cause more cuspal strain as measured by ESPI. Methods Standardized MOD cavities were prepared and placed into the ESPI apparatus before the cavities were filled with composites ( n = 10). The ESPI apparatus was constructed to measure the out-of-plane displacement of the lingual cusps of the teeth during the polymerization of the restorative material. A thermocouple was attached to the specimen to monitor thermal changes throughout the polymerization process. Results Experiments with empty preparations demonstrated that the ESPI technique was temporally responsive and sensitive to dimensional changes. However, the correlation between polymerization shrinkage of composite resins and ESPI-measured tooth deformation was not straightforward. In particular, a flowable material did not deform the tooth significantly more that a conventional hybrid. Further, an experimental silorane material (with the lowest axial shrinkage) induced the least tooth deformation. Significance We concluded that ESPI is a viable method for assessing cuspal strain induced by shrinkage of bonded composite restorations, but that polymerization shrinkage data may overestimate shrinkage-induced tooth deformation. The rate of polymerization shrinkage appeared to mediate the development of cuspal strain.

Influence of the colloidal crystal-like arrangement of polymethylmethacrylate bonded aerosil particles on the polymerization shrinkage of composite resins

Determination of the roles on the polymerization shrinkage during light-curing of composite resins of (i) the filler structuring effect of methylmethacrylate polymer adsorbed on fractal silica particles and (ii) of the crystal-like arrangement of the filler within the matrix. Firstly, the domain of major efficiency of polymer in the aerosil agglomeration was determined. Secondly, the monomer system was changed in order to implement the spontaneous concentration of the filler within in a crystal-like arrangement. Finally, the rate of the polymerization shrinkage during light-curing of the resin was determined on the sediment recovered after centrifugation and on the colloidal crystal. Micro-modifications to the size of the samples were determined with the aid of the CCD Line Scan Sensor (H.-D. Rudolph GmbH, Germany). The composite micro-structure and the rate of polymerization shrinkage during light-curing of the resin are correlated with the amount of polymer initially supplied to the system that controls the degree of filler agglomeration. Different types of matrix/filler systems with typical shrinkage characteristics were sampled from the sediment containing amorphous and organized phases. The colloidal crystal-like system was determined to concentrate the filler within the matrix, and to give rise to the smallest shrinkage. This study suggests that the silica particles embedded in a micro-structured polymer network (the filler scaffold) slowly develop spontaneously towards a colloidal crystal-like arrangement, and opens up new processes to reduce polymerization shrinkage.

A new method to measure the polymerization shrinkage kinetics of light cured composites

This study was undertaken to develop a new measurement method to determine the initial dynamic volumetric shrinkage of composite resins during polymerization, and to investigate the effect of curing light intensity on the polymerization shrinkage kinetics. The instrument was basically an electromagnetic balance that was constructed with a force transducer using a position sensitive photo detector (PSPD) and a negative feedback servo amplifier. The volumetric change of composites during polymerization was detected continuously as a buoyancy change in distilled water by means of the Archimedes' principle. Using this new instrument, the dynamic patterns of the polymerization shrinkage of seven commercial composite resins were measured. The polymerization shrinkage of the composites was 1.92 approximately 4.05 volume %. The shrinkage of a packable composite was the lowest, and that of a flowable composite was the highest. The maximum rate of polymerization shrinkage increased with increasing light intensity but the peak shrinkage rate time decreased with increasing light intensity. A strong positive relationship was observed between the square root of the light intensity and the maximum shrinkage rate. The shrinkage rate per unit time, dVol%/dt, showed that the instrument can be a valuable research method for investigating the polymerization reaction kinetics. This new shrinkage-measuring instrument has some advantages that it was insensitive to temperature changes and could measure the dynamic volumetric shrinkage in real time without complicated processes. Therefore, it can be used to characterize the shrinkage kinetics in a wide range of commercial and experimental visible-light-cure materials in relation to their composition and chemistry.

Effect of light intensity on the polymerization rate of composite resin using real-time measurement of volumetric change

Objectives : The aim of this study is to evaluate the effect of light intensity variation on the polymerization rate of composite resin using IB system (the experimental equipment designed by Dr. IB Lee) by which real-time volumetric change of composite can be measured. Methods : Three commercial composite resins [Z100(Z1), AeliteFil(AF), SureFil(SF)] were photopolymerized with Variable Intensity Polymerizer unit (Bisco, U.S.A.) under the variable light intensity (75/150/225/300/375/450mW) during 20 sec. Polymerization shrinkage of samples was detected continuously by IB system during 110 sec and the rate of polymerization shrinkage was obtained by its shrinkage data. Peak time(P.T.) showing the maximum rate of polymerization shrinkage was used to compare the polymerization rate. Results : Peak time decreased with increasing light intensity(p

Basic study on visible light activated dental composite resins - Polymerization and curing properties in argon ion laser irradiation.

Light-activated dental composite resins undergo polymerization and curing by free-radical initiation like auto-cured resins. We studied the polymerization and curing properties of some commercially available light activated composites by using argon-ion laser.Results are summarized as: (1) The volume of a cured resion is dependent on the wavelength, and the maximum volume is obtained at 466 and 477 nm; (2) The volume of the cured resin increases with increasing irradiation power and time; (3) The rate of polymerization shrinkage gradually increases, before the saturation and (4) A correlation was observed between light transmittance and polymerization shrinkage for the composites of hybrid and traditional types which are relatively highly filled, but not for MFR type resins containing less micro-filler.