Polymerization Shrinkage Kinetics Research Articles

Polymerization shrinkage kinetics and degree of conversion of commercial and experimental resin modified glass ionomer luting cements (RMGICs)

ObjectivesTetrahydrofurfuryl-methacrylate (THFM) and hydroxypropyl-methacrylate (HPM) were used to partially or fully replace HEMA in experimental RMGICs. The experimental materials were compared with home and commercial products in terms of degree of conversion, polymerization shrinkage and exotherm. MethodsTwo commercial RMGICs used were Fuji-Plus (FP, GC, Japan) and RelyX-Luting (RX, 3M-ESPE, USA). Two additional in-house liquids were prepared based on the commercial materials liquids. Eight experimental liquid compositions (F1, F2, F3 and F4 based on Fuji-Plus; R1, R2, R3 and R4 based on RelyX-Luting) were prepared replacing 100% HEMA with HPM in F1 and R1 or 70%/30% HPM/THFM in F2 and R2. 50% HEMA was replaced with THFM in F3 and R3 compared to 30% in F4 and R4. All liquids were mixed with the corresponding commercial powder. Degree of conversion was determined using Fourier-transform infrared spectroscopy (FT-IR). Polymerization shrinkage and exotherm were measured using the bonded-disk method. ResultsCompositions containing HPM (F1 and R1) showed lower degree of conversion compared to experimental compositions containing THFM, home and commercial materials (p<0.0001). FP-commercial showed significantly higher polymerization shrinkage and exotherm compared to all other materials in both groups (p<0.0001). FP-commercial showed higher degree of polymerization shrinkage and exotherm at 5min compared to all materials due to the incorporation of an additional cross-linker (glycerol-dimethacrylate). In general, compositions containing THFM, presented polymerization shrinkage and degree of conversion values similar to their corresponding commercial products. SignificanceTHFM monomer showed promising results and could be potentially useful in the development of new RMGICs with improved properties.

Polymerization shrinkage kinetics and degree of conversion of resin composites.

This study compared shrinkage strain, polymerization shrinkage kinetics, and degree of conversion (DC) of a set of resin composites and investigated their influencing factors. Ten commercial resin composites were assessed, and 5 specimens (n = 5) were developed for material and subjected to light curing using light emitting diode light at 650 mW/cm2 for 40 s. The laser triangulation method was adopted to assess the shrinkage strain, and Fourier transform infrared spectroscopy was used to measure DC. The shrinkage strain was monitored for 5 min in real time and its data were subjected to differential calculations to get the shrinkage strain rate curve with respect to time, obtaining the maximum shrinkage strain rate (Rmax) and gel time. The values of shrinkage strain varied from 1.28% to 2.10%. The Rmax values were between 5.17 μm/s and 21.83 μm/s. Gel time values varied from 3.08 s to 4.32 s. The DC yielded values ranging from 53.62% to 87.01%. The values of polymerization shrinkage and DC were dependent on the composition of materials, including the monomer matrix and filler system. Compared to the micro-filler materials, the nano-filler resin composites had higher values of DC. Some resin composites are suitable for clinical applications because of their superior polymerization shrinkage properties and DC.

Polymerization shrinkage kinetics and shrinkage-stress in dental resin-composites

ObjectivesTo investigate a set of resin-composites and the effect of their composition on polymerization shrinkage strain and strain kinetics, shrinkage stress and the apparent elastic modulus. MethodsEighteen commercially available resin-composites were investigated. Three specimens (n=3) were made per material and light-cured with an LED unit (1200mW/cm2) for 20s. The bonded-disk method was used to measure the shrinkage strain and Bioman shrinkage stress instrument was used to measure shrinkage stress. The shrinkage strain kinetics at 23°C was monitored for 60min. Maximum strain and stress was evaluated at 60min. The shrinkage strain rate was calculated using numerical differentiation. ResultsThe shrinkage strain values ranged from 1.83 (0.09) % for Tetric Evoceram (TEC) to 4.68 (0.04) % for Beautifil flow plus (BFP). The shrinkage strain rate ranged from 0.11 (0.01%s−1) for Gaenial posterior (GA-P) to 0.59 (0.07) %s−1 for BFP. Shrinkage stress values ranged from 3.94 (0.40)MPa for TET to 10.45 (0.41)MPa for BFP. The apparent elastic modulus ranged from 153.56 (18.7)MPa for Ever X posterior (EVX) to 277.34 (25.5) MPa for Grandio SO heavy flow (GSO). SignificanceThe nature of the monomer system determines the amount of the bulk contraction that occurs during polymerization and the resultant stress. Higher values of shrinkage strain and stress were demonstrated by the investigated flowable materials. The bulk-fill materials showed comparable result when compared to the traditional resin-composites.

A study of polymerization shrinkage kinetics using digital image correlation

ObjectiveTo investigate the polymerization shrinkage kinetics of dental resin composites by measuring in real time the full-field shrinkage strain using a novel technique based on digital image correlation (DIC). MethodsPolymerization shrinkage in resin composite specimens (Filtek LS and Z100) was measured as a function of time and position. The main experimental setup included a CCD camera and an external shutter inversely synchronized to that of the camera. The specimens (2mm×4mm×5mm) were irradiated for 40s at 1200mW/cm2, while alternating image acquisition and obstruction of the curing light occurred at 15fps. The acquired images were processed using proprietary software to obtain the full-field strain maps as a function of time. ResultsZ100 showed a higher final shrinkage value and rate of development than LS. The final volumetric shrinkage for Z100 and LS were 1.99% and 1.19%, respectively. The shrinkage behavior followed an established shrinkage strain kinetics model. The corresponding characteristic time and reaction order exponent for LS and Z100 were calculated to be approximately 23s and 0.84, and 14s and 0.7, respectively, at a distance of 1.0mm from the irradiated surface, the position where maximum shrinkage strain occurred. Thermal expansion from the exothermic reaction could have affected the accuracy of these parameters. SignificanceThe new DIC method using an inversely synchronized shutter provided realtime, full-field results that could aid in assessing the shrinkage strain kinetics of dental resin composites as a function of specimen depth. It could also help determine the optimal curing modes for dental resin composites.

Effect of initiator and inhibitor concentration on the polymerization shrinkage kinetics of experimental dental composites

Effect of initiator and inhibitor concentration on the polymerization shrinkage kinetics of experimental dental composites

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.

A new method to measure the polymerization shrinkage kinetics of composites using a particle tracking method with computer vision

Objectives The aim of this study was to develop a new method to measure the polymerization shrinkage of light cured composites and to evaluate the overall utility and significance of the technique. Methods An optical instrument to measure the linear polymerization shrinkage of composites without directly contacting the specimen was developed using a particle tracking method with computer vision. The measurement system consisted of a CCD color video camera, a lens, an image storage device, and image processing and analysis software. The shrinkage kinetics of a commercial silorane-based composite (P90) and two conventional methacrylate-based composites (Z250 and a flowable Z350) were investigated and compared with the data measured using the “bonded disc method”. Results The linear shrinkage of the composites was 0.33–1.41%. The shrinkage value was lowest for the silorane-based (P90) composite and highest for the flowable Z350 composite. The estimated volume shrinkages of the materials were comparable to the axial shrinkages measured with the bonded disc method. Significance The new instrument was able to measure the true linear shrinkage of composites without sensitivity to the specimen geometry and the viscosity of the material. Therefore, this instrument can be used to characterize the shrinkage kinetics for a wide range of commercial and experimental visible-light-cure materials in relation to the composition and chemistry.

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).

Polymerization shrinkage kinetics of dimethacrylate resin-cements

Objectives To determine polymerization shrinkage-strain ( S Y) and shrinkage-stress ( S Z) of six resin-cements and to compare their performance with the aid of degree of conversion (DC) data. Methods Variolink 2 (VL2), Multilink Automix (MA), Multilink Sprint (MS, all Ivoclar-Vivadent), Nexus 2 (NX2), Maxcem (MX, both Kerr) and RelyX Unicem (RX, 3M-Espe) were investigated. MS, MX and RX were self-adhesive; others require a bonding-agent. All measurements were conducted at 23 °C for 60 min ( n = 5), except 80 min for RX, with materials self-cured only (sc) and dual-cured (dc); NX2 and VL2 were additionally light-cured only (lc). S Y was measured by the bonded-disk method [Watts DC, Cash AJ. Determination of polymerization shrinkage kinetics in visible-light-cured materials: methods development. Dent Mater 1991;7(4):281–7; Watts DC, Marouf AS. Optimal specimen geometry in bonded-disk shrinkage-strain measurements on light-cured biomaterials. Dent Mater 2000;16(6):447–51]; S Z by the Bioman instrument [Watts DC, Satterthwaite JD. Axial shrinkage-stress depends upon both C-factor and composite mass. Dent Mater 2008;24(1):1–8 [Epub October 24, 2007]; Watts DC, Marouf AS, Al-Hindi AM. Photo-polymerization shrinkage-stress kinetics in resin-composites: methods development. Dent Mater 2003;19(1):1–11]. Light-cure was achieved by QTH at 500 mW/cm 2. The respective DCs were measured under the same conditions by FTIR–ATR spectroscopy. Data were analyzed by One-Way ANOVA plus Bonferroni test, and by t-test, at p < 0.05. Results DC by self-curing was less than the DC by dual-curing, for all cements. Shrinkage-strain ranged from 1.77 to 5.29% and shrinkage-stress from 3.36 to 10.37 MPa. NX2 and VL2 were not significantly different, when light-cured only. Except for RX, sc and dc shrinkage-strain varied maximally by 0.4%. MX showed the highest S Y, RX the lowest. When sc, RX initially expanded by <0.5% ( t ∼ 5 min). For most materials, S Y correlated with their filler loading. The highest stress with sc was exerted by MX, and when dc by MS, which was not statistically different from MX. Significance Shrinkage data of resin-cements are of intrinsic clinical importance. Self-cure, despite a lower DC, did not necessarily result in a lower S Y compared to dual-cure. S Y-rate and S Z development depend upon cure mode and S Y upon filler fraction.

Video-controlled characterization of polymerization shrinkage in light-cured dental composites

This study investigated a procedure to measure the intrinsic polymerization contraction of dental resin-based materials. A CCD-camera interfaced with a computer through video-interface hardware measured the coordinates of the centers of gravity of two dot markers stuck on a resin composite cylinder before and after the irradiation. The distances of the centers of gravity, and hence the linear percentage shrinkage, were calculated. The values obtained were compared with those measured by the deflecting disk technique [D.C. Watts, A.J. Cash, Determination of polymerization shrinkage kinetics in visible-light-cured materials: methods development, Dent. Mater. 7 (1991) 281–287.], which assessed polymerization shrinkage through deflection of a glass disk measured by an linear vertical displacement transducer (LVDT). Three resin composites, light-cured for 40 s at 800 mW cm −2, were tested: Solitaire 2 [SOL2], Tetric Ceram [TECE] and Z100 [Z100]. The data were subjected to the Kruskal–Wallis test ( p < 0.05). Whatever the experimental procedure, the three resin composites did not present statistically different polymerization shrinkage, and data obtained with the video-controlled technique were statistically higher than with the deflecting disk method.

Influence of ceramic thickness and curing mode on the polymerization shrinkage kinetics of dual-cured resin cements

Objectives The purpose of this study was to assess how ceramic disc thickness and curing mode (light or chemical) affects the polymerization shrinkage of dual-cured resin cements and to evaluate the effect of the ceramic discs on the curing speed of the cements during light exposure. Methods Six commercial resin cements, RelyX ARC, Bistite II, Duolink, Panavia F, Variolink II and Choice were used. Filler weight contents were determined by the ash method. Four ceramic discs with thicknesses of 0.5, 1, 2 and 4 mm, respectively, were made. The attenuation of light intensity due to the ceramic discs was measured using a radiometer. The polymerization shrinkage kinetics of the resin cements by chemical or light cure through the different ceramic discs was measured using a bonded-disc method. Results There were differences in filler content among brands of resin cement. The polymerization shrinkage without ceramic disc was 2.61–4.59% by chemical cure and 2.93–4.66% by light cure. The polymerization shrinkage of RelyX ARC and Panavia F by chemical cure was statistically lower than by light cure ( p < 0.05). Polymerization shrinkage and filler weight were inversely related ( R = −0.965). Both the transmitted light intensity and polymerization shrinkage decreased with increasing thickness of ceramic discs ( p < 0.05). The time to reach the maximum shrinkage rate of the resin cements increased with increasing ceramic thickness. The cure speed by light cure was 15–322 times faster than by chemical cure. Significance The polymerization shrinkage kinetics of dual-cured resin cements significantly differed between brands under various curing conditions. Clinicians should be aware of the setting characteristics of the cements, so they can choose the optimal materials for different clinical situations.

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.

Polymerization shrinkage-strain kinetics of temporary crown and bridge materials

Objective. The purpose of this study was to measure the polymerization shrinkage kinetics of four commercially available polymer-based temporary crown and bridge materials, including the effect of ambient temperature. Methods. Three dimethacrylate-based materials and one monomethacrylate-based material were investigated. The polymerization shrinkage-strains were measured by using the Bonded-disk method with initial specimen temperature at both 23 and 37 °C, with values particularly noted at 5, 10, and 120 min after mixing. Five recordings were taken for each material. The progress of the setting reaction and its temperature-dependence were evaluated by the kinetic curves, and net shrinkage and total shrinkage (inclusive of expansion magnitude) of each material were compared by independent sample t-test and one-way ANOVA. Results. Most shrinkage occurred in the first 10 min after mixing although there was an early expansion especially with the monomethacylate in the first 5 min. At 120 min, the net shrinkage-strain at 23 and 37 °C of the materials used in this test ranged from 3.54 to 4.13%. The fastest setting dimethacrylate-based material and the monomethacrylate-based material showed higher shrinkage-strain than other materials. No significant differences of net shrinkage-strain were found between 23 and 37 °C, but higher shrinkage rates were measured at 37 °C than at 23 °C. Significance. The Bonded-disk method is a suitable method for measuring temperature-dependence of shrinkage-strain of polymer-based temporary materials. The dimethacrylate-based materials are preferable to monomethacrylates for temporary restoration as judged by the magnitude of polymerization shrinkage-strain, the majority of which is apparent within 10 min from the start of mixing and may affect the clinical outcome.

The influence of plasma arc vs. halogen standard or soft-start irradiation on polymerization shrinkage kinetics of polymer matrix composites

Objectives. To determine polymerization shrinkage kinetics and hardness of photo-activated polymer matrix composites (PMC) after plasma arc vs. halogen standard or soft-start irradiation. Methods. Polymerization shrinkage was measured using the ‘deflecting disk technique’, and Knoop hardness was measured at the bottom of 1.5 mm thick specimens stored for 24 h at 37 °C. The materials comprised one micro-filled (Silux Plus) and four fine hybrid PMC (Definite, Herculite XRV, Solitaire 2 and Z250). The irradiation protocols included halogen standard irradiation at three intensities (TriLight, ESPE), ramp curing (dito), step curing (HiLight, ESPE), pulse polymerization (VIP Light, BISCO) and plasma curing (Apollo 95E, DMDS; PAC Light, ADT). Results. Standard halogen irradiation at reduced intensity delayed the start and slowed down the progression of shrinkage strain, but (except for Z250) as well produced lower hardness. Soft-start halogen curing produced similar kinetics but maintained hardness. Plasma arc irradiation resulted in an immediate start and a rapid progression of polymerization contraction, but produced low hardness values in Definite (cured by the ADT unit) and in Solitaire 2 (both units). Z250 featured the highest, Silux Plus the lowest maximum rate of contraction. Despite soft-start irradiation, contraction of Z250 progressed faster than that of Silux Plus with halogen standard irradiation at high intensity. Conclusions. Soft-start halogen irradiation protocols provide better chances for compensation of shrinkage stress by flow within PMC without compromising hardness and may contribute to a better marginal integrity of the restorations. Irradiation protocols should be individually adjusted to compensate for the different curing characteristics of PMC.

Determination of polymerization shrinkage kinetics in visible-light-cured materials: methods development

An instrument for the reproducible measurement of polymerization shrinkage kinetics is described, constructed around a disc-shaped specimen sandwiched between two glass plates. Test specimens of light-sensitive dental restorative materials were irradiated through the lower, rigid plate. The upper, non-rigid plate was readily deflected by an increase of the adhesive stress from the polymerizing and shrinking sample. Deflection was measured by an LVDT transducer and computer-recorded. Dimensional changes were confined to the specimen disc-thickness dimension, such that the fractional linear shrinkage approximated the volumetric shrinkage. Shrinkage data are reported for representative materials: unfilled and resin composites, base-lining materials, and an impression material. Equilibrium shrinkage magnitudes ranged from 0.65%, for the impression material, to 7.9% for the unfilled resin. The kinetic behavior was approximately characterized by an overall time constant, ranging from 12.5 to 280 s, associated with an exponential growth curve, although the initial shrinkage was near-linear in time, for many, materials, due to non-steady-state concentrations of polymer free-radicals. The test-specimen geometry facilitates rapid and essentially uniform cure and hence the determination of minimum possible time-constants at each ambient temperature and incident light-intensity. Study of hybrid glass-ionomer materials, without spurious dehydration effects, was also achieved.

Kinetic measurements of photo-polymerization contraction in resins and composites

An instrument for the reproducible measurement of polymerization shrinkage kinetics is described, constructed around a disc-shaped specimen sandwiched between two glass plates. Test specimens of light-activated resins were irradiated through the lower, rigid plate. The physical response of this measurement system, in relation to the characteristics of photo-polymerized materials, has been subject to an original detailed analysis and validation. The upper non-rigid plate was readily deflected by an increase of the adhesive stress from the polymerizing and shrinking sample. Deflection was measured by a LVDT transducer and computer recorded. Dimensional changes were confined to the specimen disc-thickness dimension, such that the fractional linear shrinkage approximated the volumetric shrinkage. Shrinkage data are reported for representative unfilled and composite resins. Equilibrium shrinkage magnitudes ranged from 1.3 to 7.9%. The kinetic behaviour was approximately characterized by an overall time constant, ranging from 12.5-27 s, associated with an exponential growth curve, although the initial shrinkage was nearly linear in time, for many materials, due to non-steady-state concentrations of polymer free radicals.