Efficacy of Modern Light Curing Units in Polymerizing Peripheral Zones in Simulated Large Bulk-fill Resin-composite Fillings

Comparison of restorative materials and surface alterations after prebiotic and probiotic beverages: A nanoindentation and SEM study

The purpose was to investigate the surface characteristics of various resin-based materials by immersing in probiotic beverages. A total of 420 disc-shaped samples (5 mm × 2 mm) were prepared from resin-based composites. Samples were divided into four groups and immersed for 10 min/day for 1 month in either a probiotic sachet, kefir, kombucha, or artificial saliva (control). Surface roughness was measured at baseline and 1 month. One sample of each of the tested materials was examined under nanoindentation to evaluate the reduced elasticity modulus and nanohardness scores. Scanning electron microscopy (SEM) was used to compare surface differences. Data were analyzed statistically using one-way ANOVA test and the significance was set at p < .05. The lowest roughness scores were observed in Z250, Estelite Bulk Fill, and HRi ENA in most of the test groups. Among conventional composites, Z250 group had the highest nanohardness and elasticity modulus scores. Among bulk-fill composites, Estelite Bulk Fill Flow had the lowest surface roughness after immersion in probiotic beverages and the highest nanohardness values. Reveal HD, as a bulk-fill group showed higher surface roughness and considerably lower nanohardness and elasticity modulus scores. Maximum height levels of samples were recorded. SEM images revealed voids and microcracks on the surfaces of test materials. Dentists may prefer Z250 as microhybrid and Estelite Bulk Fill Flow as bulk-fill composites for the restorations of patients who consume gut-friendly drinks regularly. When there are various types of materials, nanoindentation is a useful method for evaluating surface alterations and sensible comparisons.

Estimation of the tolerance threshold for the irradiance of modern LED curing units when simulating clinically relevant polymerization conditions

The study aims to characterize various LED light curing units (LED-LCU) in order to determine the tolerance threshold for varying the polymerization conditions. Two violet-blue and two blue LED-LCUs were analyzed by using a laboratory-grade spectrophotometer system. Fifty-five curing conditions were simulated in each LED-LCU by varying the position (centered and with an offset of 3-mm to the left, right, lower and upper direction) and the exposure distance (0 mm to 10 mm in 1-mm steps). Irradiance decreased with increasing exposure distance, while the effect of the LCU position was significant and LCU-specific. Only one LED-LCU enables the irradiance threshold of 1,000 mW/cm² to be achieved in all positions up to an exposure distance of 4 mm. LCUs with a more homogeneous light beam profile more easily tolerate deviations from the ideal curing conditions. The study enables dentists to identify the limits of modern LED-LCUs and to estimate potential deviations from ideal curing conditions for clinically relevant situations.

Evaluation of intensity standards of tungsten-halogen and led curing units

Current evidence indicates that the minimum light intensity of photo curing units required to polymerize in a reliable way a composite resin, in increments of 2mm, is 300mW/cm2. The recent introduction of new generations of composite resin materials for large volume increments, partially contrasts with ISO 4049 (2009), calling for the use of light intensity of 1,000mW/cm2. Therefore, it is considered relevant to carry out periodic measurements of the emission intensity of light-curing units of clinical use. The aim of this study was to test the intensity [mW/cm2] of a representative sample of tungsten-halogen and LED photopolymerization units used in private and public health service in different areas of the Valparaíso Region in Chile. This was achieved through the use of dental radiometers, without considering the variables of intensity modification over time (either spontaneously, by undesirable inherent characteristics of the device, or by programs of intensity modification in time), or the density of accumulated power needed. This in vitro diagnostic test, evaluated a sample of 507 units, 107 halogen and 400 LED, for a period of around one month, using two radiometers as measuring instruments. For LED units the Bluephase Meter® radiometer, from Ivoclar-VivadentTM was used, and for halogen units we used the Coltolux® from ColténeTM. As a result, 85% of the LED and halogen units achieved the minimum requirements of intensity needed for the polymerization of conventional dental biomaterials. However, only 25% from the tested units achieved a power density of 1,000mW/cm2.

Sufficiency of curing in high-viscosity bulk-fill resin composites with enhanced opacity

OBJECTIVES

The study aims analyzing if improved opacity in modern high-viscosity bulk-fill resin composites (BF-RBC) contradicts with the sufficiency of curing and to assess material's tolerance to less ideal curing conditions.

MATERIALS AND METHODS

Simulated large cavities (10 × 6) mm were filled in one increment with three BF-RBCs (Filtek One, FO; Tetric Evo Ceram Bulk Fill, TEC-BF; SonicFill2, SF2). One central and two peripheral (4 mm apart from the center) micromechanical property line-profiles (HV, Vickers hardness; Y_HU, indentation modulus) were measured in 0.2-mm steps at 24 h post-polymerization (n = 6). Depth of cure (DOC) was calculated from the HV variation in depth. A scratch test (DOC_{scratch test}) estimated the tolerance in polymerization when simulating clinically relevant curing conditions (exposure distance up to 7 mm; centered and with a 3-mm offset placement of the LCU). Irradiance and spectral distribution of the used light curing unit (LCU) were assessed at various curing conditions.

RESULTS

DOC varied among 3.6 mm (SF2, peripheral) and 5.7 mm (FO, central). The BF-RBC influences DOC stronger (p < 0.001, ηP² = 0.616) than the width (p < 0.001, ηP² = 0.398). Significant lower DOC (t test) was measured peripheral compared to center in all materials. Y_HU was more sensitive to the varied parameters as HV. DOC_{scratch test} varied among 2.4 mm (SF2, 3-mm offset, exposure distance 7 mm) and 3.9 mm (FO, center, 0 mm).

CONCLUSIONS

Whether opacity competes with DOC is material dependent. BF-RBCs tolerate small variations in LCU's centricity better than variations in exposure distance.

CLINICAL RELEVANCE

The upper incremental thickness threshold of 4 or 5 mm was not reached in all BF-RBCs under simulated clinically relevant curing conditions.