Impact of light-curing distance on the effectiveness of cure of bulk-fill resin-based composites

ObjectiveTo investigate the effect of light-curing distance on the effectiveness of cure (EC) of bulk-fill resin-based composites (RBCs).Materials and methodsTwo bulk-fill RBCs (a Tetric N-Ceram Bulk Fill (TN) and a Filtek Bulk Fill (FK)) are evaluated. Specimens (4 mm high) are cured for 20 s at different distances (0 mm (D0), 2 mm (D2), 4 mm (D4), 6 mm (D6) and 8 mm (D8)) and stored for 24 h in 100% relative humidity at 37 °C. The top and bottom surface hardness (SH) (n = 12) are assessed using a Knoop microhardness tester and the EC is calculated. The EC is characterized by the hardness ratio (HR) (mean bottom: top SH). An HR of 0.8 is used as the benchmark for an effective/adequate cure. Data are analyzed using one-way analysis of variance and Tukey’s post hoc test (α = 0.05). Correlations between the top and bottom surfaces are examined using the Pearson correlation (α = 0.05).ResultsFor the TN, the HR at D8 is significantly lower than all other light-curing distances, while for the FK, it is significantly lower than D0 only.ConclusionThe effect of light-curing distance on the EC of bulk-fill RBCs is material dependent. Notwithstanding the light-curing distance, the EC of the FK and TN is below the threshold HR value of 0.8 when photopolymerized for 20 s in 4 mm increments in black opaque molds.     

Degree of conversion and microhardness of bulk-fill dental composites polymerized by LED and QTH light curing units

ObjectivesThe degree of monomer conversion is crucial in determining the mechanical and clinical performance of dental resin composites. This study investigated the polymerization adequacy of two bulk-fill resin composites polymerized by Quartz-Tungsten-Halogen (QTH) and Light Emitting Diode (LED) light curing units at different depths.MethodsTwo bulk-fill resin composites (X-tra Fil; Voco and Tetric N-Ceram Bulk-fill; Ivoclar-Vivadent) with diameters of 7 mm and thicknesses of 1–4 mm were prepared and light-cured by LED or QTH. Then, the degree of conversion (DC) and microhardness of the two bulk-fill composites were evaluated.ResultsThe microhardness of X-tra fill was significantly higher than that of Tetric N-Ceram polymerized by LED or QTH. The microhardness and DC of X-tra fil exhibited no significant difference among the increments regardless of type of light source. The DC, however, significantly decreased in deep increments for Tetric N-Ceram polymerized by QTH.ConclusionsThe polymerization efficacies of the two bulk-fill composites were different in terms of the depth of cure and type of light source. The DC and microhardness of the X-tra fill bulk-fill composite polymerized by either QTH or LED did not decrease up to a thickness of 4 mm. Thus, new generations of LED light sources are better options for polymerizing the bulk-fill resin composites than QTH.     

Spatio-temporal temperature fields generated coronally with bulk-fill resin composites: A thermography study

ObjectiveThis study aimed to investigate the effects of (i) a high-irradiance (3s) light-curing protocol versus (ii) two standard-irradiance (10s) protocols on 2D temperature maps during intra-dental photo-irradiation within a molar cavity restored with either Ultra-Rapid Photo-Polymerized Bulk Fill (URPBF) composites or a pre-heated thermo-viscous bulk-fill composite, compared to a standard bulk-fill resin-based-composite (RBC). The specific objectives included visual assessment of the temperature maps and quantitative assessment of several temperature/time plots at four different locations.MethodsA caries-free lower first molar cavity served as a natural tooth mold. Resin composites were placed without intermediary adhesive. Two URPBF composites (PFill; PFlow) and one pre-heated thermo-viscous bulk-fill composite (Viscalor: VC) were compared to a contemporary bulk-fill composite (One Bulk Fill: OBF). Two LED-LCU devices were used: Bluephase PowerCure (PC) and Elipar S10 (S10), with three light-irradiation protocols (PC-3s, PC-10s and S10-10s). 2D temperature maps over the entire coronal area were recorded for 120 s during and after irradiation using a thermal imaging camera. Changes at four different levels were selected from the data sets: (0, 2 and 4 mm from the cavity top and at 1 mm below the dentin cavity floor). The maximum temperature attained (T_max), the mean temperature rise (ΔT), the time (s) to reach maximum temperature and the integrated areas (°C s) under the temperature/time (T/t) plots were identified. Data were analysed via three-way ANOVA, One-way ANOVA, independent t-tests and Tukey post-hoc tests (p < 0.05).ResultsAll RBCs showed qualitatively similar temperature-time profiles. PFlow reached T_max in the shortest time. PC-3s (3000 mW/cm²) generated comparable ΔT to S10-10s, except with PFill, where ΔT was greater. Despite the same irradiance (1200 mW/cm²), Elipar S10 led to higher T_max and ΔT compared to PC-10s. The highest T_max and ΔT were observed at the 2 mm level, and the lowest were at 1 mm depth into the underlying dentin.SignificanceCoronal 2D temperature maps showed rises largely confined within the bulk-fill RBC materials, with maxima at 2 mm rather than 4 mm depth indicating some extent of thermal insulation for the underlying dentin and pulp. RBCs polymerized via different irradiation protocols showed similar temperature changes. With the PC-3s protocol – also with pre-heated VC – minimal temperature rises at 1 mm within dentin suggest their clinical safety when sufficient remaining dentin thickness is present.     

New bulk-fill composite system with high irradiance light polymerization: Integrity and degree of conversion

ObjectiveThe study used optical coherence tomography (OCT) and micro Raman microscopy (mRM) to investigate internal defect (ID) and degree of conversion (DC) of two bulk-fill composite systems with high-irradiance or conventional light polymerization settings.MethodsThe ID and DC of the new bulk-fill composites; Tetric PowerFill (PwrPst) and Tetric PowerFlow (PwrFlw) were compared with the predecessor bulk-fill composites; Tetric EvoCeram Bulkfill (EvoPst) and Tetric EvoFlow Bulkfill (EvoFlw), using LED light curing unit in two settings; normal (LED-Nrm: 1000 mW/cm², 10-s) or PowerCure (LED-Pwr: 3000 mW/cm², 3-s). ID formation was observed in bonded cylindrical composite cavities (4-mm depth, 3-mm diameter) using Yoshida Dental OCT. From the vertically projected 2D image, ID area percentage (ID-A%) was calculated. DC at the top and bottom and bottom/top DC ratio (DC-R%) of 4-mm thick discs was calculated using mRM. All data were statistically analyzed at significance level of α = 0.05.ResultsFlowable composites in LED-Pwr showed smaller ID frequencies than other groups (PwrFlw: 0/8, EvoFlw: 2/8) (p < 0.05). Composite type significantly affected ID-A%, DC and DC-R% (p < 0.001), while light settings significantly affected ID-A% but not DC and DC-R% (p > 0.05). In both light settings, EvoPst showed the lowest DC-R% (<80%).SignificanceInternal defect and degree of conversion of bulk-fill composites were affected by their composition and light settings. There was a tendency for less defects and better polymerization for the flowable bulk-fills. The new flowable bulk-fill composite with 3-seconds high irradiance light curing showed no defect formation.     

Ability of short exposures from laser and quad-wave curing lights to photo-cure bulk-fill resin-based composites

ObjectiveThis study investigated the ability of a laser, and a ‘quad-wave’ LCU, to photo-cure paste and flowable bulk-fill resin-based composites (RBCs).MethodsFive LCUs and nine exposure conditions were used. The laser LCU (Monet) used for 1 s and 3 s, the quad-wave LCU (PinkWave) used for 3 s in the Boost and 20 s in the Standard modes, the the multi-peak LCU (Valo X) used for 5 s in the Xtra and 20 s in the Standard modes, were compared to the polywave PowerCure used in the 3 s mode and for 20 s in the Standard mode, and to the mono-peak SmartLite Pro used for 20 s. Two paste consistency bulk-fill RBCs: Filtek One Bulk Fill Shade A2 (3 M), Tetric PowerFill Shade IVA (Ivoclar Vivadent), and two flowable RBCs: Filtek Bulk Fill Flowable Shade A2 (3 M), Tetric PowerFlow Shade IVA (Ivoclar Vivadent) were photo-cured in 4-mm deep x 4-mm diameter metal molds. The light received by these specimens was measured using a spectrometer (Flame-T, Ocean Insight), and the radiant exposure delivered to the top surface of the RBCs was mapped. The immediate degree of conversion (DC) at the bottom, and the 24-hour Vickers Hardness (VH) at the top and bottom of the RBCs were measured and compared.ResultsThe irradiance received by the 4-mm diameter specimens ranged from 1035 mW/cm² (SmartLite Pro) to 5303 mW/cm² (Monet). The radiant exposures between 350 and 500 nm delivered to the top surface of the RBCs ranged from 5.3 J/cm² (Monet in 1 s) to 26.4 J/cm² (Valo X), although the PinkWave delivered 32.1 J/cm² in 20 s 350 to 900 nm. All four RBCs achieved their maximum DC and VH values at the bottom when photo-cured for 20 s. The Monet used for 1 s and the PinkWave used for 3 s on the Boost setting delivered the lowest radiant exposures between 420 and 500 nm (5.3 J/cm² and 3.5 J/cm² respectively), and they produced the lowest DC and VH values.ConclusionsDespite delivering a high irradiance, the short 1 or 3-s exposures delivered less energy to the RBC than 20-s exposures from LCUs that deliver> 1000 mW/cm². There was an excellent linear correlation (r > 0.98) between the DC and the VH at the bottom. There was a logarithmic relationship between the DC and the radiant exposure (Pearson's r = 0.87-97) and between the VH and the radiant exposure (Pearson's r = 0.92–0.96) delivered in the 420-500 nm range.     

Effect of exposure time and pre-heating on the conversion degree of conventional,bulk-fill,fiber reinforced and polyacid-modified resin composites

Objective

To determine the degree of conversion (DC) of different type of resin-based composites (RBC) in eight-millimeter-deep clinically relevant molds, and investigate the influence of exposure time and pre-heating on DC.

Curing characteristics of flowable and sculptable bulk-fill composites

Objectives

The aim of this study was to determine and correlate the degree of conversion (DC) with Vickers hardness (VH) and translucency parameter (TP) with the depth of cure (DoC) of five bulk-fill composites.

Materials and methods

Six specimens per group, consisting of Tetric EvoCeram Bulk Fill (“TEC Bulk,” Ivoclar Vivadent), SonicFill (Kerr), SDR Smart Dentin Replacement (“SDR,” Dentsply), Xenius base (“Xenius,” StickTech; commercialized as EverX Posterior, GC), Filtek Bulk Fill flowable (“Filtek Bulk,” 3M ESPE), and Tetric EvoCeram (“TEC,” control), were prepared for DC and VH: two 2-mm-thick layers, each light-cured for 10 s; one 4-mm bulk-fill, light-cured for 10 or 20 s; and one 6-mm bulk-fill, cured for 20 s. DC was measured using a Fourier-transform infrared spectrometer, VH using a Vickers hardness tester. DoC and TP were measured using an acetone-shaking test and a spectrophotometer, respectively. Data were analyzed using ANOVA and Pearson’s correlation (α = 0.05).

Results

DC and VH ranged between 40–70 % and 30–80 VHN, respectively. TEC Bulk, Xenius, and SonicFill, bulk-filled as 4-mm-thick specimens, showed bottom-to-top hardness ratios above 80 % after 20 s curing. A positive linear correlation was found for bottom DC and VH. An average DC ratio of 0.9 corresponded to a bottom-to-top VH ratio of 0.8.

Conclusions

Sculptable bulk-fills require 20 s, whereas 10 s curing time was sufficient for flowable bulk-fills using a high-intensity LED unit.

Clinical relevance

Clinicians should be aware that longer curing times may be required for sculptable than flowable bulk-fill composites in order to achieve optimal curing characteristics.

     

The effect of high-irradiance rapid polymerization on degree of conversion,monomer elution,polymerization shrinkage and porosity of bulk-fill resin composites

ObjectiveThe purpose was to compare the degree of conversion (DC), monomer elution (ME), polymerization shrinkage (PS) and porosity of two addition-fragmentation chain transfer (AFCT) modified resin-based composites (RBC) light-cured with rapid- (RP), turbo- (TP) or conventional polymerization (CP) settings.MethodsCylindrical samples (6-mm wide, 4-mm thick) were prepared from Tetric PowerFill (TPF) and Filtek One Bulk (FOB). Four groups were established according to the polymerization settings: 3s-RP, 5s-TP, 10s-CP and 20s-CP. Samples in 1 mm thickness with 20s-CP settings served as controls. The DC at the top and bottom surfaces was measured with micro-Raman spectroscopy. ME was detected with high-performance liquid chromatography. PS and porosity were analyzed by micro-computed tomography. ANOVA and Tukey’s post-hoc test, multivariate analysis and partial eta-squared statistics were used to analyze the data (p < 0.05).ResultsFOB showed higher DC values (61.5–77.5 %) at the top compared to TPF (43.5–67.8 %). At the bottom TPF samples achieved higher DCs (39.9–58.5 %) than FOB (18.21–66.18 %). Extending the curing time increased DC (except the top of FOB) and decreased ME. BisGMA release was the highest among the detected monomers from both RBCs. The amount was three-fold more from TPF. The factor Material and Exposure significantly influenced DC and ME. PS (1.8–2.5 %) did not differ among the groups and RBCs except for the lowest value of TPF cured with the 3s_RP setting (p = 0.03). FOB showed 4.5-fold lower porosity (p < 0.001). Significantly higher pore volume was detected after polymerization in 3s_RP (p < 0.001).SignificanceHigh-irradiance rapid 3-s curing of AFCT modified RBCs resulted in inferior results for some important material properties. A longer exposure time is recommended in a clinical situation.     

Influence of resin matrix on the rheology,translucency, and curing potential of experimental flowable composites for bulk-fill applications

ObjectiveTo propose monomer formulations that show an optimal degree of conversion as a function of depth for bulk-fill applications.MethodsFour resin blends were formulated with methacrylate-based monomers: BisGMA + TEGDMA (control); BisEMA + BisGMA + TEGDMA (BisEMA-based); UDMA + BisGMA + TEGDMA (UDMA-based) and BisEMA + UDMA + BisGMA + TEGDMA (BisEMA + UDMA-based). For each material, a photoinitiating system and silanized filler particles were added. The rheological analyses were performed with a rotational rheometer using the cone/plate geometry. CIELab coordinates were assessed over black and white backgrounds using a bench spectrophotometer (SP60, X-Rite) to calculate the translucency parameter (TP) for samples with 0.5, 4, and 6 mm thickness. The degree of CC conversion (DC) was determined by infrared spectroscopy (FTIR/ATR) at 0.05 mm (top), 4, and 6 mm depths (bottom), and the bottom-to-top ratio was considered. A broad spectrum–based LED was used for light activation. Analysis of variance and Tukey’s test (95%) were performed on the results.ResultsThe materials tested showed pseudoplastic and thixotropic behavior and a predominance of viscous effects over elastics. The control resin yielded the lowest viscosity for the entire shear rate investigated, followed by the BisEMA-based, BisEMA + UDMA-based, and UDMA-based group, which had the highest viscosity. The UDMA-based material showed the lowest TP as a function of thickness. Both the materials’ formulations and depths significantly influenced the DC. The UDMA-based group promoted the highest DC ??on the top (71 ± 1%) and 4 mm depth (68 ± 1%) but exhibited lower bottom-to-top DC ratio. The BisEMA + UDMA-based material promoted the highest bottom-to-top DC ratio at 4 mm (99%) and 6 mm (97%).SignificanceThe resin matrix interferes in the rheological behavior, translucency parameter, and polymerization capacity as a function of depth. The material formulated with the addition of UDMA and BisEMA demonstrated the highest curing potential as a function of depth and can be useful for bulk-fill applications.     

Influence of various irradiation processes on the mechanical properties and polymerisation kinetics of bulk-fill resin based composites

ObjectivesTo assess the effect of irradiation time and distance of the light tip on the micro-mechanical properties and polymerisation kinetics of two bulk-fill resin-based composites at simulated clinically relevant filling depth.MethodsMicro-mechanical properties (Vickers hardness (HV), depth of cure (DOC) and indentation modulus (E)) and polymerisation kinetics (real-time increase of degree of cure (DC)) of two bulk-fill resin-based composites (Tetric EvoCeram^® Bulk Fill, Ivoclar Vivadent and x-tra base, Voco) were assessed at varying depth (0.1–6 mm in 100 μm steps for E and HV and 0.1, 2, 4 and 6 mm for DC), irradiation time (10, 20 or 40 s, Elipar Freelight2) and distances from the light tip (0 and 7 mm). Curing unit's irradiance was monitored in 1 mm steps at distances up to 10 mm away from the light tip on a laboratory-grade spectrometer.ResultsMultivariate analysis (α = 0.05), Student's t-test and Pearson correlation analysis were considered. The influence of material on the measured mechanical properties was significant (η² = 0.080 for E and 0.256 for HV), while the parameters irradiation time, distance from the light tip and depth emphasise a stronger influence on Tetric EvoCeram^® Bulk Fill. The polymerisation kinetics could be described by an exponential sum function, distinguishing between the gel and the glass phase. The above mentioned parameters strongly influenced the start of polymerisation (gel phase), and were of less importance for the glass phase.ConclusionsBoth materials enable at least 4 mm thick increments to be cured in one step under clinically relevant curing conditions.Clinical significanceThe susceptibility to variation in irradiance was material dependent, thus properties measured under clinically simulated curing conditions might vary to a different extent from those measured under ideal curing conditions.     

Different depth-related polymerization kinetics of dual-cure,bulk-fill composites

ObjectiveThe aim of this study was to evaluate the polymerization kinetics qualitatively and quantitatively for dual-cure bulk-fill composites in comparison with light-cure bulk-fill and traditional incremental composites at two clinically relevant depths.MethodsFive commercial dental composites were evaluated, including three dual-cure bulk-fill composites (BulkEZ, HyperFIL and Injectafil), one light-cure bulk-fill composite Filtek Bulk Fill Flowable (FBF) and one traditional incremental composite Filtek Z250 (Z250) as controls. Specimens were prepared in two different depths (0.5 mm and 5 mm) for 20 s light irradiation. Self-cure was also evaluated for the three dual-cure composites. The polymerization kinetics were measured continuously in real-time for at least 10 min using a Fourier-transform infrared spectroscopy (FTIR) with an attenuated total reflectance (ATR) accessory. The experimental kinetic data were fitted using two mathematical models — a sigmoidal function and a superposition of two exponential functions characterizing the gel phase and glass phase. The degree of conversion (DC) and the rate of polymerization were calculated for all test conditions.ResultsBoth experimental FTIR measurements and mathematical modeling revealed distinct depth-related polymerization kinetics for BulkEZ compared to the other two dual-cure composites. Specifically, BulkEZ exhibited moderately-paced polymerization kinetics at both depths while HyperFIL and Injectafil exhibited faster polymerization at 0.5 mm and slower polymerization at 5 mm. The bulk-fill FBF and incremental Z250 exhibited relatively fast polymerization at both depths, a characteristic for light-cure. The DC values at the two depths were not significantly different for BulkEZ, but significantly higher at 0.5 mm than at 5 mm for the other four composites (α = 0.05).SignificancePolymerization kinetics and their depth variation for dual-cure bulk-fill composites are material dependent. The distinct depth-related polymerization kinetics revealed for BulkEZ compared to other composites may affect their contraction stress and clinical performance.     

Light transmittance and micro-mechanical properties of bulk fill vs. conventional resin based composites

Objectives

The aim of this study was to quantify the blue light that passes through different incremental thicknesses of bulk fill in comparison to conventional resin-based composites (RBCs) and to relate it to the induced mechanical properties.

Materials and methods

Seven bulk fill, five nanohybrid and two flowable RBCs were analysed. Specimens (n?=?5) of three incremental thicknesses (2, 4 and 6 mm) were cured from the top for 20 s, while at the bottom, a spectrometer monitored in real time the transmitted irradiance. Micro-mechanical properties (Vickers hardness, HV, and indentation modulus, E) were measured at the top and bottom after 24 h of storage in distilled water at 37 °C. Electron microscope images were taken for assessing the filler distribution and size.

Results

Bulk fill RBCs (except SonicFill) were more translucent than conventional RBCs. Low-viscosity bulk fill materials showed the lowest mechanical properties. HV depends highly on the following parameters: material (η_p ²?=?0.952), incremental thickness (0.826), filler volume (0.747), filler weight (0.746) and transmitted irradiance (0.491). The bottom-to-top HV ratio (HV_bt) was higher than 80 % in all materials in 2- and 4-mm increments (except for Premise), whereas in 6-mm increments, this is valid only in four bulk fill materials (Venus Bulk Fill, SDR, x-tra fil, Tetric EvoCeram Bulk Fill).

Conclusions

The depth of cure is dependent on the RBC’s translucency. Low-viscosity bulk fill RBCs have lower mechanical properties than all other types of analysed materials. All bulk fill RBCs (except SonicFill) are more translucent for blue light than conventional RBCs.

Significance

Although bulk fill RBCs are generally more translucent, the practitioner has to follow the manufacturer’s recommendations on curing technique and maximum incremental thickness.     

A randomized controlled three year evaluation of “bulk-filled” posterior resin restorations based on stress decreasing resin technology

ObjectiveThe objective of this randomized controlled prospective clinical trial was to evaluate the efficacy of a flowable resin composite (SDR) bulk fill technique in posterior restorations and to compare it intraindividually with a conventional 2 mm resin composite curing technique in a 3-year follow up.Materials and methodsThirty-eight pairs Class II and 15 pairs Class I restorations were placed in 38 patients with a mean age of 55.3 years (range 32–87). Each patient received at random at least two, as similar as possible, Class II or Class I restorations of two restorative techniques. In all cavities a single step self-etch adhesive (Xeno V) was applied. In one of the cavities of each pair, a flowable resin composite (SDR) was placed, in bulk increments up to 4 mm as needed to fill the cavity 2 mm short of the occlusal cavosurface. The occlusal part was completed with a nano-hybrid resin composite (Ceram X mono) layer. In the second cavity, the hybrid resin composite was placed in 2 mm increments. The restorations were evaluated using slightly modified USPHS criteria at baseline and then yearly during 3 years. Caries risk and parafunctional habits of the participants were estimated.ResultsAfter three years, 76 Class II and 28 Class I restorations could be observed. One molar resin composite-only tooth showed post-operative sensitivity during 3 weeks for temperature changes and occlusal forces. Two failed Class II molar restorations in the resin composite-only group were observed during the first year, one cusp fracture and one resin composite fracture. An annual failure rate of 1.3% was found for the resin composite only restorations and of 0% in the bulk-filled restorations (n.s.). Ten participants were estimated as having high caries risk and eleven showed active bruxing habits.SignificanceThe 4 mm bulk-fill technique with the flowable resin composite SDR showed highly clinical effectiveness, which was comparable during the 3-year follow-up with the 2 mm resin composite layering technique.     

Degree of conversion of nano-hybrid resin-based composites with novel and conventional matrix formulation

Objectives

This study aimed to determine the degree of conversion (DC) of two nano-hybrid resin-based composites (RBCs) with novel monomer composition based on dimer acid derivates (hydrogenated dimer acid) and tricyclodecane–urethane structure compared to three nano-hybrid materials containing conventional matrices. DC was evaluated at 0.1, 2, and 6 mm depth at varying irradiation times (10, 20, and 40 s) and layering techniques (bulk and incremental).

Materials and methods

DC was measured in real time by a Fourier transform infrared spectroscopy (FTIR) spectrometer with attenuated total reflectance accessory. The FTIR spectra were recorded on the bottom of the samples in real time for 5 min from photoinitiation. Results were compared using one- and multiple-way ANOVA, Tukey's HSD post hoc test (α?=?0.05), and partial eta-squared statistic.

Results

After 5 min of measurement, DC showed no significant difference by varying cure time for specimens of 0.1 mm thickness. At 2 mm depth, the DC significantly increased after a cure time of 20 s compared to 10 s, remaining equal after 40 s of irradiation. At 6 mm depth, bulk curing showed significantly lower DC compared to incremental curing for all polymerization times. Specimen geometry revealed a strong effect on DC (η ²?=?0.90) followed by curing time (η ²?=?0.39).

Conclusions

The RBCs containing the dimer acid and tricyclodecane–urethane structure showed a relatively low decrease of DC with increasing incremental thickness compared to the conventionally formulated materials. The former reached the highest DC among the tested materials.

Clinical relevance

For the tested RBCs, increments of 2 mm and irradiation time of at least 20 s may be recommended for clinical practice. The two materials containing novel monomer composition might be applied for enlarged increments because of the low decrease of DC they demonstrated for 6-mm increments.     

In vitro comparison of mechanical properties and degree of cure of bulk fill composites

Objectives

The aim of our study was to measure and compare degree of conversion (DC) as well as micro- (indentation modulus, E; Vickers hardness, HV) and macromechanical properties (flexural strength, σ; flexural modulus, E _flexural) of two recently launched bulk fill resin-based composites (RBCs): Surefil® SDR? flow (SF) and Venus® bulk fill (VB).

Materials and methods

DC (n?=?6) was investigated by Fourier transform infrared spectroscopy (FTIR) in clinical relevant filling depths (0.1, 2, and 4 mm; 6 mm bulk, 6 mm incremental) and irradiation times (10, 20, 40 s). Micro- (n?=?6) and macromechanical (n?=?20) properties were measured by an automatic microhardness indenter and a three-point bending test device after storing the specimens in distilled water for 24 h at 37°C. Furthermore, on the 6-mm bulk samples, the depth of cure was determined. A field emission scanning electron microscope was used to assess filler size. Results were evaluated using one-way analysis of variance, Tukey’s honest significance test post hoc test, a multivariate analysis (α?=?0.05) and an independent t test. Weibull analysis was used to assess σ.

Results

VB showed, in all depth, significant higher DC (VB, 62.4–67.4 %; SF, 57.1–61.9 %), but significant lower macro- (VB, E _flexural?=?3.6 GPa; σ?=?122.7 MPa; SF, E _flexural?=?5.0 GPa; σ?=?131.8 MPa) and micromechanical properties (VB, E?=?7.3–8.8 GPa, HV?=?40.7–46.5 N/mm²; SF, E?=?10.6–12.2 GPa, HV?=?55.1–61.1 N/mm²). Both RBCs showed high reliability (VB, m?=?21.6; SF, m?=?26.7) and a depth of cure of at least 6 mm at all polymerization times. The factor “RBC” showed the strongest influence on the measured properties (η ²?=?0.35–0.80) followed by “measuring depth” (η ²?=?0.10–0.46) and “polymerization time” (η ²?=?0.03–0.12).

Conclusions

Significant differences between both RBCs were found for DC, E, σ, and E _flexural at all irradiation times and measuring depths.

Clinical relevance

Curing the RBCs in 4-mm bulks for 20 s can be recommended.     

大块充填树脂的研究进展

目前大块充填树脂已经越来越广泛应用于临床。一次4-6mm的固化深度是大块充填树脂最突出的优点,便于临床操作。树脂的聚合收缩和边缘微渗漏及性能的长期稳定性与材料的临床应用效果密切相关。如何保证树脂具有较高的固化深度,较低的聚合收缩和边缘微渗漏,以及临床效果评价是大块充填树脂的研究热点,本文将对上述方面的研究进展进行综述。     

Cuspal deflection and microleakage in premolar teeth restored with bulk-fill flowable resin-based composite base materials

ObjectivesTo assess the cuspal deflection and cervical microleakage of standardised Class II cavities incrementally filled with a dimethacrylate RBC or bulk-fill flowable RBC bases.MethodsTwenty-four sound upper premolar teeth with Class II cavities were allocated to three groups (n = 8). Restoration of the teeth involved the placement of an RBC (GrandioSO) in eight oblique increments (Group A) or Groups B and C were restored to within 2 mm of the palatal cusp in a single increment with bulk-fill flowable RBC bases (SDR and x-tra base) before the two occlusal cavity increments were placed with GrandioSO. Buccal and palatal cusp deflections were recorded postirradiation using a twin channel deflection measuring gauge. Following restoration, the teeth were thermocycled, immersed in 0.2% basic fuchsin dye for 24 h, sectioned and examined for cervical microleakage.ResultsThe mean total cuspal deflection for the oblique incremental restoration technique was 11.26 (2.56) μm (Group A) and 4.63 (1.19) μm (Group B) and 4.73 (0.99) μm (Group C) for the bulk-fill flowable RBC bases. A significant increase in the mean total cuspal deflection for the incrementally filled GrandioSO compared with the SDR (P = 0.007) and x-tra base (P = 0.005) restored teeth was evident. No significant difference in the cervical microleakage scores was recorded between groups AC (P > 0.05).ConclusionsThe bulk-fill flowable RBC bases significantly reduced cuspal deflection compared with a conventional RBC restored in an oblique incremental filling technique with no associated change in cervical microleakage recorded.     

In vivo temperature rise and acute inflammatory response in anesthetized human pulp tissue of premolars having Class V preparations after exposure to Polywave® LED light curing units

ObjectiveTo evaluate the influence of light emitted from two Polywave®, LED light-curing units (LCU) on in vivo pulp temperature (PT) rise and signs of acute inflammatory response in pulps of human premolar having deep Class V preparations.MethodsSixty intact, first premolars from 15 volunteers requiring extraction received infiltrative anesthesia. A sterile thermocouple probe was inserted within the pulp tissue through a minute occlusal pulp exposure in only 45 teeth (n = 9) to continuously monitor PT (°C). A deep buccal Class V preparation was created, and the surface was exposed to light from a commercial Polywave LCU (Bluephase 20i (20i), Ivoclar Vivadent) or from an experimental LCU (Exp) using the exposure modes (EM): 1s/Exp and 2s/Exp, 10s/20i, 20s/20i, and 60s/20i. Peak PT and PT rise values above baseline (ΔT) data were evaluated using a one-way ANOVA followed by Tukey’s post-hoc test (α = 5%). Teeth used for histological and immunohistochemical analyses (n = 3) were extracted approximately 2 h after exposure to the LCU.ResultsNo significant difference in peak PT and ΔT values was noted between 2s/Exp and 20s/20i groups, which both exhibited higher values than 1s/Exp and 10s/20i groups (p < 0.001). Dilated and congested blood vessels were seen after exposure to 1s/Exp, 2s/Exp, or 60s/20i EMs. The expression of IL-1β and TNF-α tended to be more intense when higher irradiance was delivered.SignificanceAlthough higher irradiance delivered over a short exposure caused lower PT rise than 5.5 °C, such EMs should be used with caution, as they have more potential to harm the pulp tissue.     

Long-term clinical evaluation of direct resin composite restorations in vital vs. endodontically treated posterior teeth — Retrospective study up to 13 years

ObjectivesThis retrospective study evaluated and compared the survival rate of Class II posterior direct resin based composite (RBC) restorations made in vital teeth (VT) and endodontically treated teeth (ETT). The influence of risk factors on the long-term performance of restorations was also investigated.MethodsPatients (n = 245) receiving RBC posterior restorations between 2004 and 2012 were selected. A total of 597 restorations (485 in VT, 112 in ETT) with minimum 2.5–3 mm remaining cusp thickness, made with the same brand of RBC and adhesive, were evaluated using the USPHS criteria. Data were analyzed with Mann–Whitney, Chi-square and Fisher’s Exact Test, Extended Cox-regression and Kaplan–Meier analysis (p < 0.05). Relative risk ratio was estimated for each evaluated parameter.ResultsThe mean observation period was 8.6 ± 2.3 years. An annual failure rate in VT and ETT of 0.08% and 1.78%, respectively, was detected. The reasons of failures included restoration fracture, secondary caries in VT; vertical root fracture, cusp fracture, restoration fracture, secondary caries and loss of adhesion in ETT. Significantly better performance was observed in RBCs of VT for each evaluated parameter. Among the evaluated risk factors only occlusal stress affected negatively the survival of RBC in ETT (Hazard Ratio 37.1; CI_95% 8.4–163.7).SignificanceAlthough, there is significant difference in the success rate of RBCs in VT (98.97%) and ETT (76.8%), the long-term (6–13 years) durability of Class II RBCs with 2.5–3 mm cusp thickness in ETT is also clinically acceptable. The presence of occlusal stress decreases the survival of RBCs in ETT.