Evaluation of light-curing units in rural and urban areas

ObjectivesTo evaluate the distribution of light-curing units (LCU) used in an urban area (Riyadh) and a rural area (Kharj) of Saudi Arabia, and to compare their irradiance values.MethodsThe study involved three dental centers in urban areas and two in rural areas, all of which were parts of a single healthcare institution providing dental services. The light outputs (power mW) from 140 LCUs were measured by laboratory-grade spectrometry, and the irradiance (mW/cm²) was calculated from the tip area of each LCU. The minimum acceptable irradiance outputs for the quartz-tungsten-halogen (QTH) and light-emitting diode (LED) units were set at 300 and 600 mW/cm², respectively. The ages of these units and the protocol used to light-cure the resins were also determined.ResultsThe total number of LCUs was 140, 112 (78%) in urban areas, and 28 (22%) in rural areas. In rural areas, only 7 of the 22 (32%) QTH units delivered irradiances greater than 300 mW/cm² and were therefore considered clinically acceptable, whereas 4 of the 6 (66.7%) LED units delivered values greater than 600 mW/cm². In urban centers, 43 of 61 (70.5%) LED units and 25 of 61 (49%) QTH units were considered clinically acceptable. Irradiance values for both QTH (P < 0.01) and LED (P < 0.05) units were significantly better in urban than in rural areas.ConclusionsUrban areas had a greater distribution of LCUs than rural areas. Overall, irradiance values were significantly higher in urban areas.     

Correlation between the beam profile from a curing light and the microhardness of four resins

ObjectiveTo demonstrate the effect of localized irradiance and spectral distribution inhomogeneities of one LED-based dental light-curing unit (LCU) on the corresponding microhardness values at the top, and bottom surfaces of four dental resin-based composites (RBCs), which contained either camphorquinone (CQ) alone or a combination of CQ and monoacylphosphine oxide (TPO) as photoinitiators.MethodsLocalized irradiance beam profiles from a polywave LED-based LCU were recorded five times using a laser beam analyzer, without and with either a 400 nm or 460 nm narrow bandpass filter placed in front of the camera lens. Five specimens of each of the four RBCs (two containing CQ/TPO and two containing CQ-only) were exposed for 5-, 10-, or 30-s with the light guide directly on the top surface of the RBC. After 24 h, Knoop microhardness values were measured at 45 locations across the top and bottom surfaces of each specimen. Microhardness readings for each RBC surface and exposure time were correlated with localized patterns of the LCU beam profile, measured using the 400 nm and 460 nm bandpass filters. Spearman rank correlation was used to avoid relying on an assumption of a bivariate normal distribution for the KHN and irradiance.ResultsThe local irradiance and spectral emission values were not uniformly distributed across the light tip. There was a strong significant positive correlation with the irradiance beam profile values from the LCU taken through bandpass filters and the microhardness maps of the RBC surfaces exposed for 5 and 10 s. The strength of this correlation decreased with increasing exposure time for the RBCs containing CQ only, and increased for the RBCs containing both CQ and TPO.ConclusionsLocalized beam and spectral distributions across the tip end of the light guide strongly correlated with corresponding areas of microhardness in both the top and bottom surfaces among four RBCs with different photoinitiator contents.SignificanceA light-curing unit with a highly inhomogeneous light output can adversely affect localized microhardness of resin-based composites and this may be a contributing factor for premature failure of a restoration.     

Mathematical model for assessing true irradiance received by luting materials while curing through modern CAD/CAM resin composites

Statement of problemMeasurement of irradiance passing through a dental restoration for properly curing a dual- or light-polymerized luting composite is imprecise due to surface reflection.ObjectiveTo provide a mathematical correction of measured transmitted irradiance for predicting true transmitted light intensity through CAD/CAM restorations.MethodsA total of 432 specimens were fabricated. Seven modern CAD/CAM resin-based composites (RBCs) and one CAD/CAM glass-ceramic (control group) were sectioned and polished into specimens of 0.5–5 mm thickness (in 0.5 mm steps, n = 6). Irradiance of a violet-blue LED light curing unit (LCU) (power modes: Standard, High and Plasma) was measured after passing through each specimen with a spectrometer. Data was compared based on 95% confidence intervals and using univariate ANOVA followed by Tukey HSD (α = 0.05).ResultsThe measured transmitted irradiance passing through the specimens decreased exponentially. Significantly highest values of transmitted irradiance were measured for 0.5 mm thick specimens for all materials (p < 0.05). The decadic absorption coefficient for CAD/CAM-RBCs ranged from 0.292 mm⁻¹ to 0.387 mm⁻¹ while the control group (glass-ceramic) reached a significantly lower value of 0.283 mm⁻¹. The reflection ratio for all materials ranged from 12.6% to 18.5%.SignificanceA correction can be implemented to predict the true transmitted irradiance after passing through a dental restoration as function of initial irradiance, specimen thickness and material specific parameters. For a practitioner, this model may be applied depending on the specific treatment conditions, the individual LCU's radiant emittance and restoration thickness for the tested materials.     

Characterization of heat emission of light-curing units

ObjectivesThis study was designed to analyze the heat emissions produced by light-curing units (LCUs) of different intensities during their operation. The null hypothesis was that the tested LCUs would show no differences in their temperature rises.MethodsFive commercially available LCUs were tested: a “Flipo” plasma arc, “Cromalux 100” quartz–tungsten–halogen, “L.E. Demetron 1” second-generation light-emitting diode (LED), and “Blue Phase C5” and “UltraLume 5” third-generation LED LCUs. The intensity of each LCU was measured with two radiometers. The temperature rise due to illumination was registered with a type-K thermocouple, which was connected to a computer-based data acquisition system. Temperature changes were recorded in continues 10 and 20 s intervals up to 300 s.ResultsThe Flipo (ARC) light source revealed the highest mean heat emission while the L.E. Demetron 1 LED showing the lowest mean value at 10 and 20 s exposure times. Moreover, Cromalux (QTH) recorded the second highest value for all intervals (12.71, 14.63, 14.60) of heat emission than Blue Phase C5 (LED) (12.25, 13.87, 13.69), interestingly at 20 s illumination for all intervals the highest results (18.15, 19.27, 20.31) were also recorded with Flipo (PAC) LCU, and the lowest (6.71, 5.97, 5.55) with L.E. Demetron 1 LED, while Blue Phase C5 (LED) recorded the second highest value at the 1st and 2nd 20 s intervals (14.12, 11.84, 10.18) of heat emission than Cromalux (QTH) (12.26, 11.43, 10.26). The speed of temperature or heat rise during the 10 and 20 s depends on light intensity of emitted light. However, the QTH LCU was investigated resulted in a higher temperature rise than LED curing units of the same power density.ConclusionThe PAC curing unit induced a significantly higher heat emission and temperature increase in all periods, and data were statistically different than the other tested groups (p < .05). LED (Blue Phase C5) was not statistically significant (p < .05) (at 10 s) than QTH units, also LED (Blue Phase C5, UltraLume 5) generates obvious heat emission and temperature rises than QTH units (at 20 s) except for those which have lower power density of LED curing units (first generation). Thus, the null hypothesis was rejected.     

Effect of delivering light in specific narrow bandwidths from 394 to 515 nm on the micro-hardness of resin composites

ObjectivesThis study investigated the wavelength-dependent photosensitivity of eleven resin composites (Admira A2, Heliomolar A2, Herculite XRV A2, Pyramid Dentin A2, Solitaire 2 A2, Z250 A2, Ælite LS A2, Vit-l-escence A2, Tetric Ceram Bleach XL, Tetric Ceram A2, Pyramid Enamel Neutral).MethodsResin composites 1.6 mm thick were exposed to narrow bandwidths of light at the following peak wavelengths: 394, 400, 405, 410, 415, 420, 430, 436, 442, 450, 455, 458, 467, 470, 480, 486, 493, 500, 505, and 515 ± 5 nm. A spectroradiometer was used to ensure that the same irradiance (mW/cm²) and total energy density (J/cm²) was delivered through each filter. For each resin composite, three specimens were exposed through each filter. The Knoop micro-hardness at the top and bottom of the composites was then measured. The wavelength-dependent photosensitivity of each resin composite was analyzed by plotting the mean hardness achieved at each wavelength.ResultsThe composites responded variably when they received light through the narrow bandpass filters. Six resin composites had a single peak of wavelength-dependent photosensitivity at ～470 nm. Four resin composites had two peaks of wavelength-dependent photosensitivity at ～470 and ～405 nm. One resin composite had a single peak of wavelength-dependent photosensitivity at ～405 nm and was only sensitive to light below 436 nm.SignificanceUsing light delivered through narrow bandpass filters is a convenient method to determine the wavelength-dependent photosensitivity of resins and can be used to predict the performance of dental curing lights.     

The influence of various light curing units on the cytotoxicity of dental adhesives

ObjectivesThe objective of this study was to test the hypothesis that various light curing units (LCUs) have an influence on the cytotoxic action of adhesive systems.MethodsSamples of the dental adhesives (Syntac^®, iBondTM, Clearfil? Protect Bond, Prime & Bond? NT, Adper? Prompt? L-Pop?) were prepared in microwell plates, making use of the LCUs Voco Polofil Lux (VPL), EMS Swiss Master Light^® (SML) and the LED prototype developed by the IMT of Jena University. To obtain extracts, the samples were topped with cell culture medium, which was changed daily on the 1st to 7th days and then on the 14th, 21st and 28th day, and stored for further use at ?20 °C. Human gingival fibroblasts (HGFs) were cultivated in the extract-containing medium for 48 h. The viability of the HGFs was determined by the neutral red (NR) uptake test. The statistical test was performed by one-way ANOVA according to Bonferroni.ResultsDuring the first few days, reduction of the viability rates of the HGFs by 85–90% were observed in all adhesives. A rise up to a plateau phase was observed at different times depending on the materials. The influence of the LCUs on the cytotoxic action of the dental adhesives was clearly evident for the adhesives Syntac^® and Clearfil? Protect Bond. In case of the Syntac^® extracts, cytotoxicity after polymerization with the VPL was statistically significant reduced compared to the other LCUs used (p < 0.001). A comparison between all the adhesives used proved that Adper? Prompt? L-Pop? and Prime & Bond NT^® had the lowest overall cytotoxicities.SignificanceIn practice, one should use combinations of dental adhesive and LCU in which the material has the least toxic influences.     

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 time on the post-irradiation curing of six resin-based composites

ObjectivesTo evaluate the effect of time on the Vickers microhardness (VH) at the top and bottom surfaces of six conventional resin-based composites (RBCs) up to twelve weeks after light curing.MethodsFive specimens of Filtek Supreme Ultra, Herculite Ultra, Mosaic Ultra, Tetric EvoCeram, TPH Spectra HV, and Venus Pearl were packed into opaque molds that were 2.3 mm in diameter and 2.5 mm deep. The uncured RBC specimens were covered by a polyester strip and photo-cured with an Elipar DeepCure-S light-curing unit (LCU) according to the manufacturer's instructions. After irradiation, the polyester strip was removed, and the Vickers microhardness was measured immediately at top and bottom surfaces. The hardness measurements were repeated after 30 min, 1 h, 2 h, 4 h, 24 h, 1 week, 4 weeks, and 12 weeks. In between, the specimens were stored in dry and dark conditions at 37 °C. Two-way ANOVA (α = 0.05) followed by Tukey–Kramer post hoc multiple comparison tests were used to determine where statistically significant differences existed.ResultsThe micro-hardness values at the top surface always exceeded those at the bottom surface. A significant logarithmic increase of the micro-hardness due to post-irradiation curing took place between 30 min and 24 h (p < 0.05). There was no significant increase in the VH after 24 h. Depending on the RBC, compared to the immediate values the hardness 24 h post-irradiation had increased by 11–27% at the top surface and by 21–58% at the bottom.SignificanceEven after 12 weeks, the bottom hardness values never reached the top microhardness values. The results of studies that wait 24 h or longer before measuring the properties of RBC specimens will be significantly enhanced by the impact of post-irradiation curing. Especially within the first 4 h, the time when specimens are measured is critical information and should be reported.     

Characterisation of mechanical and surface properties of novel biomimetic interpenetrating alumina-polycarbonate composite materials

ObjectiveTo determine the mechanical and surface characteristics of two novel biomimetic interpenetrating phase alumina-polycarbonate (Al₂O₃-PC) composite materials, comprising aligned honeycomb-like porous ceramic preforms infiltrated with polycarbonate polymer.MethodTwo composite materials were produced and characterised. Each comprised a porous structure with a ceramic-rich (polymer-poor) top layer, graduated through to a more porous ceramic-poor (polymer-rich) bottom layer. In addition, pure polycarbonate and dense alumina specimens were subjected to the same characterisation namely: density, compression, three-point bend, hardness, surface loss and surface roughness testing. Scanning electron microscopy and micro computerised tomography were employed for structural examination.ResultsThree-dimensional aligned honeycomb-like ceramic structures were produced and full interpenetration of the polymer phase was observed using MicroCT. Depending on the ceramic volume in the initial aqueous ceramic suspension, the density of the final interpenetrating composites ranged from 2.64 to 3.01 g/cm³, compressive strength ranged from 192.43 to 274.91 MPa, flexural strength from 105.54 to 148.47 MPa, fracture toughness from 2.17 to 3.11 MPa.m^½, hardness from 0.82 to 1.52 GPa, surface loss from 0.71 to 1.40 μm and surface roughness, following tooth brushing, from 0.70 to 0.99 μm. Composite specimens showed characteristic properties part way between enamel and polycarbonate.SignificanceThere was a correlation between the initial solid ceramic loading in the aqueous suspension, used to produce the porous ceramic scaffolds, and the subsequent characteristic properties of the composite materials. These novel composites show potential as aesthetic orthodontic bracket materials, as their properties fit part way between those of ceramic, enamel and polycarbonate.     

Pre-heating time and exposure duration: Effects on post-irradiation properties of a thermo-viscous resin-composite

ObjectiveTo evaluate the effects of pre-heating time and exposure duration on the degree of conversion (DC), maximum rate of polymerization (RP_max), polymerization shrinkage strain (PS) and surface micro-hardness (VHN) of Viscalor.MethodsViscalor syringes were pre-heated using a Caps Warmer (VOCO, Germany) in T3 mode (at 68 °C) for 30 s (T3-30s) and 3 min (T3-3min) and then the composite paste was extruded into appropriately sized molds. Light irradiation was applied at zero distance from the upper surface with a LED-LCU of mean irradiance 1200 mW/cm² for either 20 or 40 s. The real-time polymerization kinetics and DC at 5 min and 24 h post-irradiation (DC_5min and DC_24h) were measured using ATR-FTIR (n = 3). PS was obtained with the bonded-disk technique (n = 3). Top and bottom Vickers micro-hardness (VHN_top and VHN_bottom) were measured at 5 min post-irradiation and after 24 h dry storage (n = 5). Data were analysed using one-way ANOVA, two-way ANOVA, independent t-test and Tukey post hoc tests (p < 0.05).ResultsPolymerization kinetic curves of Viscalor from 0 to 15 min were similar for different pre-heating times and exposure durations. Pre-heated Viscalor (T3-30s and T3-3min) with 40 s exposure had greater VHN_top and VHN_bottom than for Viscalor (no heat) (p < 0.05). Exposure duration did not significantly affect DC, RP_max and PS (p > 0.05). After 24 h storage, DC and VHN increased. Pre-heating did not increase the DC_24h, relative to no pre-heating (p > 0.05). Two-way ANOVA showed that there was no significant interaction between pre-heating time and exposure duration (p > 0.05).SignificanceIncreasing irradiation time from 20 to 40 s did not affect DC, RP_max or PS, but increased VHN_top. Composite pre-heating had no adverse effect through any premature polymerization. For Viscalor, 3 min pre-heating and 20 s irradiation were sufficient to provide adequate hardness, without increasing PS or compromising polymerization kinetics.     

Effect of high-intensity curing lights on the polymerization of bulk-fill composites

Objectives

The purpose of this study was to investigate the effect of high-irradiance light-curing-units (LCUs) on the depth-of-cure (DoC) and degree-of-polymerization (DoP) of bulk-fill composites (BFCs).

Measurement of the full-field polymerization shrinkage and depth of cure of dental composites using digital image correlation

ObjectivesThe aim of this study was to measure the full-field polymerization shrinkage of dental composites using optical image correlation method.MethodsBar specimens of cross-section 4 mm × 2 mm and length 10 mm approximately were light cured with two irradiances, 450 mW/cm² and 180 mW/cm², respectively. The curing light was generated with Optilux 501 (Kerr) and the two different irradiances were achieved by adjusting the distance between the light tip and the specimen. A single-camera 2D measuring system was used to record the deformation of the composite specimen for 30 min at a frequency of 0.1 Hz. The specimen surface under observation was sprayed with paint to produce sufficient contrast to allow tracking of individual points on the surface. The curing light was applied to one end of the specimen for 40 s during which the painted surface was fully covered. After curing, the cover was removed immediately so that deformation of the painted surface could be recorded by the camera. The images were then analyzed with specialist software and the volumetric shrinkage determined along the beam length.ResultsA typical shrinkage strain field obtained on a specimen surface was highly non-uniform, even at positions of constant distance from the irradiation surface, indicating possible heterogeneity in material composition and shrinkage behavior in the composite. The maximum volumetric shrinkage strain of ～1.5% occurred at a subsurface distance of about 1 mm, instead of at the irradiation surface. After reaching its peak value, the shrinkage strain then gradually decreased with increasing distance along the beam length, before leveling off to a value of approximately 0.2% at a distance of 4–5 mm. The maximum volumetric shrinkage obtained agreed well with the value of 1.6% reported by the manufacturer for the composite examined in this work. Using irradiance of 180 mW/cm² resulted in only slightly less polymerization shrinkage than using irradiance of 450 mW/cm².SignificanceCompared to the other measurement methods, the image correlation method is capable of producing full-field information about the polymerization shrinkage behavior of dental composites.     

Thermal shrinkage reveals the feasibility of pulse-delay photocuring technique

ObjectivesTo resolve the feasibility of the pulse-delay photocuring technique as a clinical strategy for reducing the detrimental polymerization stress induced in dental composites during the photocuring process.MethodsModel dental composites with high and low-filler contents were cured with the pulse-delay photocuring technique using different combinations of photocuring variables (irradiance, exposure time, and delay time). Irradiance used ranged from 0.1 W/cm² to 4 W/cm². The exposure time of the first pulse varied from 0.2 s to 27.2 s and the delay times ranged from 10 s to 120 s. The radiant exposure was varied from 4 J/cm² to 20 J/cm². A cantilever-beam based instrument (NIST Standards Reference Instrument 6005) was used to implement the photocuring technique for the measurement of the polymerization properties (the degree of monomer conversion, polymerization stress induced due to shrinkage, and temperature change due to the reaction exotherm and curing light absorbance) simultaneously in real-time. These properties were compared with those obtained using the conventional photocuring technique (i.e., using a constant irradiance for a fixed exposure time, a uniform exposure).ResultsThere exists a minimum radiant exposure, such that a reduction in the polymerization stress can be achieved without sacrificing the degree of monomer conversion by using the pulse-delay over the conventional photocuring technique. More specifically, stress reductions of up to 19% and 32% was observed with the pulse-delay when compared with the conventional photocuring technique at an irradiance of 0.5 W/cm² and 4 W/cm², respectively. The reduction occurred when the exposure time of the first pulse was greater than, but closer to, the gelation time (i.e., lower than the vitrification time) of the composite, regardless of the delay time used. Lower thermal shrinkage (contraction) during the post-curing time, rather than the stress relaxation during the delay time or lower degree of monomer conversion as claimed in the literature, is the cause of the reduction in the polymerization stress.SignificanceThe study clarifies a long-standing confusion and controversy on the applicability of the pulse-delay photocuring technique for reducing the polymerization stress and promotes its potential clinical success for dental restorative composites.     

Microhardness of resin composite materials light-cured through fiber reinforced composite

ObjectivesTo compare polymerization efficiency of resin composite basing materials when light-cured through resin composite and fiber reinforced composite (FRC) by testing microhardness.MethodsSimulated indirect restorations were prepared by application of resin composite (Clearfil AP-X) or FRC (EverStick) to nylon rings with 1.5 mm thickness and 8 mm diameter, followed by light-curing. Resin composite basing material (Clearfil Majesty Flow or Clearfil AP-X) was applied to identical rings and light-cured through the simulated indirect restorations with exposure times of 20, 40, or 60 s. Light-curing though a ring without resin material (=no indirect restoration) served as control. For each combination of basing material and indirect restoration 10 specimens were prepared for each exposure time. Top and bottom surface Vickers microhardness numbers (VHNs) of basing materials were recorded after 24 h.ResultsAfter 60 s exposure time, VHNs with indirect FRC were not different from control VHNs, while VHNs with indirect resin composite were significantly lower (p < 0.001). Linear regression analysis revealed that resin composite basing material used had the greatest effect on top and bottom VHNs (p < 0.001). The presence of an indirect restoration resulted in decreased VHNs (p < 0.001), with resin composite resulting in lower VHNs when compared to FRC. Moreover, a longer exposure time resulted in increased VHNs (p < 0.001).SignificanceResults suggest that polymerization of resin composite basing materials is more effective when light-curing through an FRC than through a resin composite indirect restoration. Prolonging of exposure time, however, is necessary when compared to light-curing without presence of indirect restoration material.     

Conversion kinetics of rapid photo-polymerized resin composites

ObjectiveTo measure the degrees of conversion (DC), conversion kinetics, and the effect of post-irradiation time on rapid photo-polymerized bulk-fill resin composites under conditions equivalent to clinical depths of 1 and 4 mm.Methods36 specimens (n = 3), based on two resin composites incorporating PowerCure rapid-polymerization technology in two consistencies (PFill; PFlow) and two comparators with matching consistencies (Eceram; EFlow), were investigated from the same manufacturer (Ivoclar AG, Liechtenstein). Specimens were prepared within 4 mm diameter cylindrical molds, of either 1 mm or 4 mm depths respectively, to simulate near-surface and deep locations in a bulk-fill restoration. The independent variables in this study were: materials, thickness and time. Two high irradiance polymerization protocols were utilized for PowerCure materials: 2000 and 3050 mW/cm² for 5 and 3 s, respectively. A standard (1200 mW/cm²) polymerization protocol was used with control materials. FTIR was utilized to measure DC in real-time for 24 h post-irradiation. The data were analyzed using Welch’s-ANOVA, Games-Howell post-hoc test, kinetic dual-exponential sum function and independent sample t-tests (p = 0.05).ResultsThe DC of the materials ranged between 44.7–59.0 % after 5 min, which increased after 24 h reaching 55.7–71.0 % (p < 0.05). Specimen thickness did not influence the overall DC. At 5 min, the highest DC was shown in EFlow. But PFlow, irradiated for 3 s and 5 s exhibited comparable results (p > 0.05). PFill composite irradiated with the 3 s and 5 s protocols did not differ from ECeram (p > 0.05). Specimen thickness and material viscosity affected polymerization kinetics and rate of polymerization (RP_max). Faster polymerization occurred in 1 mm specimens (except PFill-5 s and ECeram). PFill and PFlow exhibited faster conversion than the controls. RP_max varied across the specimen groups between 4.3–8.8 %/s with corresponding DC _RPmax between 22.2–45.3 %.SignificancePolymerization kinetics and RP_max were influenced by specimen thickness and material viscosity. PFill and PFlow materials produced an overall comparable conversion at 5 min and 24 h post-irradiation, despite the ultra-short irradiation times, throughout the 4 mm specimen thickness.     

Nano-structured hydroxyapatite and titanium dioxide enriching PENTA /UDMA adhesive as aesthetic coating for tooth enamel

ObjectivesThe aim of this study was to investigate the effect of the nanostructured hydroxyapatite (NHAp) and titanium dioxide nanoparticles (NTiO₂) on dispersion in an adhesive containing monomers of Dipenta erythritol penta-acrylate monophosphate (PENTA) and Urethane dimethacrylate (UDMA), as well as evaluating the structural, optical and mechanical behavior of the composite material for dental aesthetic application.MethodsThe NHAp powders were synthesized through the wet chemical methods of hydrothermal and ultrasound-assisted precipitation. The microstructure, morphology and composition analysis of the powder of NHAp and NTiO₂ were performed by scanning and transmission electron microscopy. The optical microscopic identification of the different colors was obtained due to varying the amounts of NHAp and NTiO₂ in the adhesive. On the other hand, the diffuse reflectance spectra of the coatings were evaluated every 2 nm with the wavelength from 400 to 800 nm for combined specular and diffuse reflectance. The nanomechanical properties of the aesthetic coating such as (H), elastic modulus (E) and nanoscratching were evaluated by nanoindentation. The roughness of the composite coatings were evaluated by AFM.ResultsFrom different powders combinations, NHAP 75%Wt-NTiO₂ %25 Wt, at (10Wt %) into a dental adhesive, the resulting mixture manifested the optimum aesthetic white appearance. The scanning and transmission electron microscopy images confirmed that the HAp nanorods and TiO₂ nanoparticles sized were 55 nm and 20 nm respectively prepared by the high-energy ball mixed process. The values of nanomechanical properties of the optimum aesthetic coating were hardness, H = 3.2 ± 0.3 GPa, elastic modulus, E = 78 ± 3 GPa, Yield point, Y = 107 MPa ± 2 and scratching, maximum wear track deformation 3.7 ± 0.12 μm². The percentage of reflectance to optimum aesthetic white appearance was of 46.83% at 423 nm of wavelength.ConclusionsThe nanocomposite PENTA/UDMA with mixtures of Nanohydroxyapatite and titanium dioxide may be considerate as a mechanical toughened, also an option to modify shade qualities for dental aesthetic applications.     

Hardness and fracture toughness of resin-composite materials with and without fibers

ObjectiveTo investigate the surface micro-hardness (VHN) and fracture toughness (K_IC) of resin-composites, with and without incorporated short fibers, after solvent storage.MethodsThree resin-composites incorporating fibers, additional to particle reinforcement, were examined: everX™, NovoPro Fill™ and NovoPro Flow™. Four composites were used as controls, with only particle reinforcement: Filtek bulk Fill™, Filtek bulk one™, Filtek XTE™, and Filtek Flow XTE™. For hardness measurement, materials were cured in 2 mm thick molds for 20 s by a LED source of average irradiance 1.2 W/cm². Specimens (n = 6/group) were stored dry for 1 h and then in either water or 75% ethanol/water for 1 h, 1 day and 30 days at 37 ± 1 °C. Vickers hardness was measured under a load of 300 g for 15 s. For fracture toughness (K_IC) measurements, single-edge-notched specimens (n = 6/group) were prepared: (32 × 6 × 3 mm) for 3-point bending and stored for 1 and 7 days in water at 37 °C. Fractured surfaces of fiber-reinforced composite were examined by scanning electron microscopy (SEM). VHN data were analyzed using three-way ANOVA, one-way ANOVA and the Tukey post hoc test (p ≤ 0.05). K_IC data were analyzed by two-way ANOVA and one-way ANOVA and the Tukey post hoc test (p ≤ 0.05). An independent t-test was used to detect differences (α = 0.05) in K_IC between stored groups for each material.ResultsVHN decreased for all composites with storage time in both solvents, but more appreciably in 75% ethanol/water (an average of 20%). K_IC ranged from 2.14 (everX Posterior) to 0.96 NovoPro Flow) MPa. m^0.5. The longer storage period (7 days) had no significant effect on this property relative to 1 day storage.SignificanceReinforcement with short fibers, and possibly matrix compositional differences, significantly enhanced the fracture toughness of EVX. However, for nano-fiber containing composites, there were no evident beneficial effects upon either their fracture toughness or hardness compared to a range of control composites. Water storage for 7 days of all these resin-composites produced no significant change in their K_IC values, relative to 1 day storage.     

Hydrogen peroxide induces cell proliferation and apoptosis in pulp of rats after dental bleaching in vivo: Effects of the dental bleaching in pulp

ObjectiveThis study provides an in vivo evaluation of the inflammatory response, levels of cell proliferation and apoptosis, and the presence of necrosis after dental bleaching with two concentrations of hydrogen peroxide (H₂O₂).DesignWistar rats were divided into Control (placebo gel), BLUE (20% H₂O₂, 1 × 50 min), and MAXX (35% H₂O₂, 3 × 15 min) groups. At 2 and 30 days, the rats were killed (n = 10). The jaws were processed for histology analysis and PCNA and Caspase-3-cleaved immunohistochemistry, and data were submitted to the Mann-Whitney or ANOVA test (P < 0.05).ResultsAt 2 days, the MAXX group showed necrosis and the BLUE group revealed moderate inflammation on the occlusal third of the crown (P < 0.05). At 30 days, tertiary dentin had formed and there was an absence of inflammation. The level of cell proliferation was higher in the middle third of the BLUE group (P < 0.05), and cervical of MAXX at 2 days (P < 0.05), decreasing at 30 days. The apoptosis was present at 2 days, particularly in the cervical third of the crown in the bleached groups (P < 0.05), with a decrease only at 30 days in the BLUE group (P < 0.05).ConclusionsThe concentration of H₂O₂ influences effects on the pulp tissue, where a higher concentration of H₂O₂ can cause necrosis in the pulp and a prolonged effect within the apoptotic process; lower concentrations of H₂O₂ provide moderate inflammation, cell proliferation and apoptosis with a reduction of these processes over time.     

Influence of photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites

ObjectiveTo establish the relationship between photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites.MethodsModel composites based on BisGMA/TEGDMA (60:40 mol%) were loaded with 40 wt% of 7 nm or 16 nm-sized filler particles. One of the following photoinitiator systems was added: camphorquinone (CQ) associated with an amine (EDMAB), monoacylphosphine oxide (TPO), or bysacylphosphine oxide (BAPO). The optical properties of disk-shaped specimens were measured 24 h after curing and repeated after storage in water for 90 days and coffee for 15 days. A large spectrum LED unit (Bluephase G2, Ivoclar Vivadent) was used for photoactivation. CIE L*a*b* parameters, color difference (ΔE), and translucency parameter (TP) were calculated. Knoop hardness readings were taken at top and bottom composite surfaces. Cure efficiency was determined by bottom/top hardness ratio. Data were statistically analyzed at α = 0.05 significance level.ResultsComposites formulated with 16 nm particles had higher CIE L* than those with 7 nm particles in all storage conditions. BAPO-based composites generally had lower CIE a* than the other composites. The group TPO + 16 nm before storage and all groups with 16 nm-sized particles after storage had lower CIE b* (i.e. lower degree of yellowing) than the other groups. TPO-based materials had higher color stability. The cure efficiency was not significantly affected by photoinitiator system or particle size. CQ + 7 nm had the lowest and BAPO + 16 nm the highest hardness values.SignificanceCombination of photoinitiator system and filler particle size might affect the optical properties of composites, with low influence on cure efficiency.     

Effect of interocclusal appliance on bite force,sleep quality,salivary cortisol levels and signs and symptoms of temporomandibular dysfunction in adults with sleep bruxism

ObjectiveThe purpose was to evaluate the effect interocclusal appliance therapy on bite force (BF), sleep quality and salivary cortisol levels in adults with SB diagnosed by polysomnography. As a secondary aim, signs and symptoms of temporomandibular dysfunction (TMD) were evaluated.DesignForty-three adults (19–30 y/o) were divided into two groups: experimental group (G_SB), composed of 28 subjects with SB, and control group (G_C), without SB and TMD (n = 15). G_SB was treated with stabilization interocclusal splint and evaluated at time intervals: before (baseline), one month (T1) and two months (T2) after therapy began, to collect data related to BF, sleep quality (Pittsburgh Sleep Quality Index), salivary cortisol levels and TMD. G_C was also examined three times and received no therapy. Data were analysed by means of normality tests, t-test/Mann-Whitney and One-way ANOVA repeated measures (Tukey post-test). Two-way ANOVA test for repeated measures was applied to verify the effect time*group interaction on the variance of each dependent variable (α = 0.05).ResultsG_SB showed an increase in BF and a positive effect on muscular symptomatology, range of mandibular movements and sleep quality; in G_C these parameters did not differ. Cortisol concentration decreased between baseline and T1 in G_SB (F_(1,31) = 4.46; test power = 62%; p = 0.017). The variance observed for BF, TMD and sleep quality among time points was dependent on the group (moderate effect size: partial Eta square >0.16; test power >80%).ConclusionsThe results suggested that short-term interocclusal appliance therapy had a positive effect on BF, temporomandibular symptomatology, sleep quality and salivary cortisol levels in adults with SB.