Light irradiance through novel CAD-CAM block materials and degree of conversion of composite cements.

OBJECTIVE: To assess light irradiance (LI) delivered by two light-curing units (LCU's) and to measure the degree of conversion (DC) of three composite cements, when cured through different thicknesses of two novel CAD-CAM block materials. METHODS: 100-µm-thick films of a dual-curable composite cement (G-CEM LinkAce, GC), a light-curable flowable resin-based composite (RBC) (G-ænial Universal Flo, GC) and a micro-hybrid RBC (G-ænial Posterior, GC) were investigated as luting agents. Two 'polymer-ceramic' CAD-CAM blocks (Cerasmart, GC; Enamic, Vita Zahnfabrik) were sectioned in slabs with different thicknesses (1, 3 and 5mm). LI at the bottom of the specimens was measured using a calibrated spectrometer, while being light-cured through the CAD-CAM block slabs for 40s with a low- (±500mW/cm2) or high- (±1,600mW/cm2) irradiance LCU (n=5). After light-curing, micro-Raman spectra of the composite films were acquired to determine DC at 5min, 10min, 1h and 24h. LI data were statistically analyzed by Kruskal-Wallis followed by post-hoc comparisons, while a linear mixed-effect model was applied for the DC analysis. In addition, the CAD-CAM blocks ultrastructure was characterized upon argon-ion slicing using scanning transmission electron microscopy (STEM). Finally, light transmission (LT) through each CAD-CAM block material was assessed using a spectrophotometer. RESULTS: Curing-light attenuation and DC were significantly influenced by thickness and type of the overlying material. LCU only had a significant effect on DC of the micro-hybrid RBC. DC significantly increased over time for all composite cements. CAD-CAM block structural analysis revealed a relatively small and homogenous filler configuration (mean filler size of 0.2-0.5µm) for Cerasmart, while Enamic contained ceramic grains varying in shape and size (1-10µm), which were interconnected by the polymer-based network. LT was much higher at a wavelength range of 300-800nm for Cerasmart than for Enamic. SIGNIFICANCE: Light-curable composite cements can be cured through a restoration up to 2.7-mm thickness, depending on the kind of CAD-CAM material. A high-irradiance LCU only has a limited effect on the maximum thickness of the polymer-ceramic CAD-CAM material that can be cured through.

Bulk-Fill Composites: A Review of the Current Literature.

PURPOSE: The aim of this article was to provide an overview of the literature on the currently available bulk-fill composites, and to describe the common trends as well as the wide variations. The findings may help the clinician to select the proper material with regard to its applicability in various clinical situations. METHODS: The literature up to October 2016 was reviewed based on a PubMed search (keywords: "bulk-fill OR bulkfill OR bulk fill" AND "composite OR composites"). RESULTS: This review revealed that bulk-fill composites differ most from conventional composites in their increased depth of cure, which could mainly be attributed to an increase in translucency. However, the literature is inconsistent regarding the determination of the depth of cure. Flowable "base" bulk-fill composites seem most suitable for narrow cavities deeper than 4 mm, in particular when a higher adaptation potential thanks to better flowability in less accessible cavity configurations is desirable. In more extensive cavities, "full-body" bulk-fill composites with a high filler load are preferable. Then, resistance against wear and fracture becomes increasingly important, while a thicker consistency might also help in obtaining a good contact point. Tests related to shrinkage stress induced by bulk-filling seem inconsistent and their clinical relevance is unclear. CONCLUSION: More clinical studies that specifically focus on bulk-filling deep and large restorations are definitely required to fully explore the clinical benefits of bulk-fill composites.

Strain development in bulk-filled cavities of different depths characterized using a non-destructive acoustic emission approach.

OBJECTIVES: (1) To evaluate the effect of cavity depth and composite type on the interfacial debonding in bulk-filled cavities. (2) To correlate the theoretical shrinkage stress and the level of interfacial debonding determined by acoustic emission (AE). METHODS: 80 sound molars were divided in two groups to receive a Class-I cavity (3.5×3.5mm) with 2.5- or 4.0-mm depth. The cavities were restored with either a conventional paste-like (Filtek Z100, 3M ESPE), a conventional flowable (G-ænial Universal Flo, GC), a bulk-fill paste-like (Tetric EvoCeram Bulk Fill, Ivoclar Vivadent) or a bulk-fill flowable (SDR, Dentsply) composite (n=10). AE signals were recorded from the start of curing for 20min. The cumulative number of AE events was correlated with the theoretical maximum shrinkage stress induced by each composite. Two samples from each group were scanned using micro-computed tomography (µCT) and qualitatively evaluated. RESULTS: Both composite type and cavity depth had a significant influence on the number of AE. The conventional paste-like composite generated significantly more AE than the other composites. The AE number increased sigmoidally in function of time, with a more rapid increase after a few seconds for the conventional composites than for the bulk-fill composites. A strong linear correlation was found between the predicted shrinkage stress values and the total number of AE events for both cavities depth. Representative µCT images showed larger de-bonding areas for 4.0-mm cavities and for conventional composites. SIGNIFICANCE: Premature interfacial or cohesive cracks can already develop during placement/curing of the composite. This might compromise the restoration integrity and in turn affect its survival in the long term. The amount AE events increased linearly with the theoretical maximum shrinkage stress of the composites.

Short fibre-reinforced composite for extensive direct restorations: a laboratory and computational assessment.

OBJECTIVES: The objective of the study was to evaluate the effectiveness of a short fibre-reinforced composite (FRC) applied in combination with a conventional filler composite (CFC) on the fatigue resistance, fracture strength, failure mode and stress distribution, for restorations of premolars under two loading angles. MATERIAL AND METHODS: Thirty-two inferior premolars received extensive cavities with removal of the lingual cusp. Teeth were restored directly using 'FRC (EverX Posterior, GC) + CFC (G-aenial, GC)' or 'CFC only' and received two fatigue/fracture loadings at two different angles (0°/45°) (n = 8). Data were submitted to two-way ANOVA (α = 5 %) and Tukey test. Failure mode was analysed using SEM. Four 3D finite element (FE) models were constructed and static, linear and elastic analyses were performed. Maximum principal and von Mises stresses were evaluated. RESULTS: All specimens survived the mechanical fatigue simulation. No statistical difference in fracture resistance was recorded between FRC + CFC and CFC only, considering both loading angles (p = 0.115). However, the 0° loading showed a statistical significant higher strength than the 45° loading (p = 0.000). Failure mode analysis revealed more repairable fractures upon 0° loading, versus more root fractures (unrepairable) upon 45° loading. FE revealed a higher amount of stress upon 45° loading, with tensile stress being imposed to the lingual cervical area. CONCLUSION: The fracture strength was not increased using the FRC. Loading at a 45° decreased significantly the fracture resistance. CLINICAL RELEVANCE: The restoration of extensive cavities in posterior tooth is a challenge for the clinicians and the choice of the material that increases the fracture strength of tooth-restoration complex is required.

Influence of reused dental burs on bond strength to dentin

AIM: this study evaluated the bond strength of an adhesive system to human dentin prepared with reused diamond burs. MATERIAL AND METHODS: five molars (G1) were prepared in a standardized way with five diamond burs. Flat deep dentin surfaces were etched, received adhesive and received composite build-ups. The same burs were cleaned and reused on another five teeth groups (G2 until G8). After 24-hours storage and thermocycling, 50 dentin-resin sticks per group were obtained and subjected to microtensile bond strength test (µTBS). RESULTS: analysis of variance (ANOVA) and Tukey test were applied to identify differences between groups (p<0.05). The reuse of a diamond bur for more than two preparations resulted in significantly lower µTBS values (G1 = G2 > G3 = G4 = G5 = G6 = G7 = G8). CONCLUSION: Reuse of diamond burs interfered on adhesion between dentin and resin.