Postoperative Sensitivity of Composite Replacement of Amalgam Restoration: A Randomized Clinical Trial.

PURPOSE: This randomized clinical trial aimed to evaluate the postoperative sensitivity of different resin composite/adhesive materials, placed either by an incremental or bulk-fill technique in posterior resin composite replacement of amalgam restorations. METHODS AND MATERIALS: A total of 47 patients with good overall health and at least four class I or class II amalgam restorations to be replaced participated in this study. The characteristics of 188 cavities were registered and randomly restored using incremental (Z350XT, 3M) or bulk-fill (Filtek Bulk Fill, 3M; Sonic Fill, Kerr; and Opus Bulk Fill, FGM) technique. The postoperative sensitivity was assessed using a Visual Analog Scale (0-100) after 24 hours, 7 days, and 30 days. Pain scores were temporally analyzed using Friedman test followed by Dunn post hoc test (α=0.05). The frequency of tests was calculated according to the frequency and percentage of the McNemar test. RESULTS: The restorative technique and the bulk-fill system used did not affect the postoperative sensitivity, except for Filtek Bulk Fill group, which presented less postoperative sensitivity after 24 hours (p=0.037). Regardless of the restorative material, the postoperative sensitivity decreased after 24 hours, and no differences were found after 7 and 30 days. CONCLUSIONS: After 1 week, the filling technique and the bulk-fill system have no influence on the postoperative sensitivity.

Effect of Sandblasting with Fluorapatite Glass-ceramic Powder and Chemical Primers/Adhesives on Shear Bond Strength of Indirect Repairing Composite to Zirconia.

OBJECTIVE: To investigate the effect of sandblasting with fluorapatite glass-ceramic (FGC) powder on zirconia surface roughness, crystallinity, and shear bond strength (SBS) of indirect repairing composite to zirconia using different primers/adhesives. METHODS: Zirconia blocks were treated as follows: no treatment (control group), blasting with 30-µm silica-coated alumina (CoJet group), and blasting with FGC powder (FGC group). The surface topography, silica content, roughness, and crystallinity of treated zirconia surfaces were analyzed by a scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), an optical profilometer, and X-ray diffraction (XRD), respectively. Four primers/adhesives (Monobond Plus, Calibra Silane, Futurabond M+, and Scotchbond Universal) were compared to bond precured resin composite to zirconia groups using Multilink Automix resin cement. Bonded specimens were thermocycled for 10,000 cycles and tested in SBS and the modes of failure were recorded. The effect of different surface treatments and primers/adhesives on SBS results were statistically analyzed using two-way ANOVA and Bonferroni post-hoc tests (α=0.05). RESULTS: Both CoJet and FGC groups showed rough surfaces with a higher content of silica in FGC, but less monoclinic crystals, compared to the CoJet group. The highest mean SBS was found in the FGC group treated with Monobond Plus compared to CoJet and Control groups. Adhesive failure was predominant in control groups, while combined failure was found in the CoJet and FGC groups regardless of the primers/adhesives employed. CONCLUSION: Sandblasting zirconia with FGC powder increased SBS of resin composite to zirconia with lower monoclinic phase transformation compared to CoJet sand. Monobond Plus reported the highest means of SBS values compared to other primers/adhesives.

Graphene Nanocoating: High Quality and Stability upon Several Stressors.

Titanium implants present 2 major drawbacks-namely, the long time needed for osseointegration and the lack of inherent antimicrobial properties. Surface modifications and coatings to improve biomaterials can lose their integrity and biological potential when exposed to stressful microenvironments. Graphene nanocoating (GN) can be deposited onto actual-size dental and orthopedic implants. It has antiadhesive properties and can enhance bone formation in vivo. However, its ability to maintain structural integrity and quality when challenged by biologically relevant stresses remains largely unknown. GN was produced by chemical vapor deposition and transferred to titanium via a polymer-assisted transfer technique. GN has high inertness and did not increase expression of inflammatory markers by macrophages, even in the presence of lipopolysaccharides. It kept high coverage at the top tercile of tapered dental implant collars after installation and removal from bone substitute and pig maxilla. It also resisted microbiologically influenced corrosion, and it maintained very high coverage area and quality after prolonged exposure to biofilms and their removal by different techniques. Our findings show that GN is unresponsive to harsh and inflammatory environments and that it maintains a promising level of structural integrity on the top tercile of dental implant collars, which is the area highly affected by biofilms during the onset of implant diseases. Our findings open the avenues for the clinical studies required for the use of GN in the development of implants that have higher osteogenic potential and are less prone to implant diseases.

Is Deterioration of Surface Properties of Resin Composites Affected by Filler Size?

PURPOSE: To investigate the effect of filler size on surface gloss and roughness of resin composites using a glossmeter and 3D noncontact surface topography, respectively, before and after tooth-brushing abrasion. MATERIALS AND METHODS: Seven model resin composites and one commercial were tested in the study. All materials were first polished, and then the surface gloss and 2D and 3D roughness parameters were recorded. Materials are then subjected to abrasion in a tooth-brushing simulator. Roughness parameters were recorded after 10,000 cycles, and after 20,000 cycles, both roughness and gloss were recorded. One-way ANOVA and Bonferroni post hoc test (p < 0.05) were used to analyze data. CONCLUSION: Filler size is strongly correlated to gloss and surface roughness retention.

Academy of Dental Materials guidance-Resin composites: Part II-Technique sensitivity (handling, polymerization, dimensional changes).

OBJECTIVE: The objective of this work, commissioned by the Academy of Dental Materials, was to review and critically appraise test methods to characterize properties related to critical issues for dental resin composites, including technique sensitivity and handling, polymerization, and dimensional stability, in order to provide specific guidance to investigators planning studies of these properties. METHODS: The properties that relate to each of the main clinical issues identified were ranked in terms of their priority for testing, and the specific test methods within each property were ranked. An attempt was made to focus on the tests and methods likely to be the most useful, applicable, and supported by the literature, and where possible, those showing a correlation with clinical outcomes. Certain methods are only briefly mentioned to be all-inclusive. When a standard test method exists, whether from dentistry or another field, this test has been identified. Specific examples from the literature are included for each test method. RESULTS: The properties for evaluating resin composites were ranked in the priority of measurement as follows: (1) porosity, radiopacity, sensitivity to ambient light, degree of conversion, polymerization kinetics, depth of cure, polymerization shrinkage and rate, polymerization stress, and hygroscopic expansion; (2) stickiness, slump resistance, and viscosity; and (3) thermal expansion. SIGNIFICANCE: The following guidance is meant to aid the researcher in choosing the most appropriate test methods when planning studies designed to assess certain key properties and characteristics of dental resin composites, specifically technique sensitivity and handling during placement, polymerization, and dimensional stability.

Academy of Dental Materials guidance-Resin composites: Part I-Mechanical properties.

OBJECTIVE: The objective of this project, which was initiated from the Academy of Dental Materials, was to review and critically appraise methods to determine fracture, deformation and wear resistance of dental resin composites, in an attempt to provide guidance for investigators endeavoring to study these properties for these materials. METHODS: Test methods have been ranked in the priority of the specific property being tested, as well as of the specific test methods for evaluating that property. Focus was placed on the tests that are considered to be of the highest priority in terms of being the most useful, applicable, supported by the literature, and which show a correlation with clinical findings. Others are mentioned briefly for the purpose of being inclusive. When a standard test method exists, including those used in other fields, these have been identified in the beginning of each section. Also, some examples from the resin composite literature are included for each test method. RESULTS: The properties for evaluating resin composites were ranked in the priority of measurement as following: (1) Strength, Elastic Modulus, Fracture toughness, Fatigue, Indentation Hardness, Wear-abrasion (third body) and Wear-attrition (contact/two body), (2) Toughness, Edge strength (chipping) and (3) Wear determined by toothbrush. SIGNIFICANCE: The following guidance is meant to aid the researcher in choosing the proper method to assess key properties of dental resin composites with regard to their fracture, deformation and wear resistance.

Toward optimizing dental implant performance: Surface characterization of Ti and TiZr implant materials.

OBJECTIVE: Targeting understanding enhanced osseointegration kinetics, the goal of this study was to characterize the surface morphology and composition of Ti and TiZr dental implant substrates subjected to one of two surface treatments developed by Straumann. These two treatments are typically known as SLA and SLActive, with the latter resulting in more rapid osseointegration. METHODS: A range of techniques was applied to characterize four different substrate/surface treatment combinations (TiSLA, TiSLActive, TiZrSLA, and TiZrSLActive). Contact angle measurements established their hydrophilic/hydrophobic nature. Surface morphology was probed with scanning electron microscopy. X-ray diffraction, Raman µ-spectroscopy, and X-ray photoelectron spectroscopy were used to elucidate the composition of the near-surface region. RESULTS: Consistent with previous work, surface morphology was found to differ only at the nanoscale, with both SLActive substrates displaying nano-protrusions. Spectroscopic data indicate that all substrates exhibit surface films of titanium oxide displaying near TiO2 stoichiometry. Raman µ-spectroscopy reveals that amorphous TiO2 is most likely the only phase present on TiSLA, whilst rutile-TiO2 is also evidenced on TiSLActive, TiZrSLA, and TiZrSLActive. For TiZr alloy substrates, there is no evidence of discrete phases of oxidized Zr. X-ray photoelectron spectra demonstrate that all samples are terminated by adventitious carbon, with it being somewhat thicker (∼1nm) on TiSLA and TiZrSLA. SIGNIFICANCE: Given previous in vivo studies, acquired data suggest that both nanoscale protrusions, and a thinner layer of adventitious carbon contribute to the more rapid osseointegration of SLActive dental implants. Composition of the surface oxide layer is apparently less important in determining osseointegration kinetics.

Viscoelastic properties of orthodontic adhesives used for lingual fixed retainer bonding.

OBJECTIVE: To evaluate the viscoelastic properties of two experimental BPA-free and one BisGMA-based orthodontic resin composite adhesives for bonding fixed retainers. METHODS: A commercially available BisGMA-based (TXA: Transbond LR) and two bisphenol A-free experimental adhesives (EXA and EXB) were included in the study. The viscoelastic behavior of the adhesives was evaluated under static and dynamic conditions at dry and wet states and at various temperatures (21, 37, 50°C). The parameters determined were shear modulus (G), Young's modulus (E) under static testing and storage modulus (G1), loss tangent (tanδ) and dynamic viscosity (n*) under dynamic testing. Statistical analysis was performed by 2-way ANOVA and Bonferroni post-hoc tests (α=0.05). RESULTS: For static testing, a significant difference was found within material and storage condition variables and a significant interaction between the two independent variables (p<0.001 for G and E). EXA demonstrated the highest G and E values at 21°C/dry group. Dry specimens showed the highest G and E values, but with no significant difference from 21°C/wet specimens, except EXA in G. Wet storage at higher temperatures (37°C and 50°C) adversely affected all the materials to a degree ranging from 40 to 60% (p<0.001). For dynamic testing, a significant difference was also found in material and testing condition groups, with a significant interaction between the two independent variables (p<0.001 for G1 and n*, p<0.01 for tanδ). Reduction in G1, and n* values, and increase in tanδ values were encountered at increased water temperatures. SIGNIFICANCE: The apparent detrimental effect of high temperature on the reduction of properties of adhesives may contribute to the loss of stiffness of the fixed retainer configuration under ordinary clinical conditions with unfavorable effects on tooth position and stability of the orthodontic treatment result.

Water sorption and solubility of core build-up materials.

OBJECTIVES: To investigate the variation in water sorption and solubility across a range of different core build-up materials. METHODS: Five materials were tested, four of which are resin-based materials (Grandio Core, Core.X Flow, Bright Flow Core, Speedee) and one resin-modified glass ionomer (Fuji II LC). All specimens (n=10) were immersed in 10ml distilled water in individual glass containers and weighed at one week, 14 and 28 days. After a total immersion time of 28 days, 7 specimens were dried to a constant mass, in a desiccator for 28 days. Three samples of each material were not dried, but were left in distilled water for 1 year, to determine the long-term water sorption properties. Specimens were weighed at monthly intervals until 6 months and then at the 9th and 12th months. Each specimen was measured using a digital electronic caliper (Mitutoyo Corporation, Japan). RESULTS: After 28 days immersion, the change in water sorption and solubility of the materials ranged from 12.9 to 67.1µg/mm(3) (P<0.001) and 0.9-6.4µg/mm(3) respectively (P<0.001). Except for Fuji II LC, an independent T-test showed significantly higher water sorption and solubility for the other materials after 1-year total immersion in water compared to 1 month (P<0.05). Using repeated measures ANOVA, all materials showed mass changes over time (1 month) (P<0.001). SIGNIFICANCE: Grandio Core had the lowest water sorption and solubility among the tested materials. According to the ISO 4049 standards, all the tested materials showed acceptable water sorption and solubility, apart from the water sorption behavior of Fuji II LC.

Post-cure depth of cure of bulk fill dental resin-composites.

OBJECTIVES: To determine the post-cure depth of cure of bulk fill resin composites through using Vickers hardness profiles (VHN). METHODS: Five bulk fill composite materials were examined: Tetric EvoCeram(®) Bulk Fill, X-tra base, Venus(®) Bulk Fill, Filtek™ Bulk Fill, SonicFill™. Three specimens of each material type were prepared in stainless steel molds which contained a slot of dimensions (15 mm × 4 mm × 2 mm), and a top plate. The molds were irradiated from one end. All specimens were stored at 37°C for 24h, before measurement. The Vickers hardness was measured as a function of depth of material, at 0.3mm intervals. Data were analysed by one-way ANOVA using Tukey post hoc tests (α=0.05). RESULTS: The maximum VHN ranged from 37.8 to 77.4, whilst the VHN at 80% of max.VHN ranged from 30.4 to 61.9. The depth corresponding to 80% of max.VHN, ranged from 4.14 to 5.03 mm. One-way ANOVA showed statistically significant differences between materials for all parameters tested. SonicFill exhibited the highest VHN (p<0.001) while Venus Bulk Fill the lowest (p≤0.001). SonicFill and Tetric EvoCeram Bulk Fill had the greatest depth of cure (5.03 and 4.47 mm, respectively) and was significant's different from X-tra base, Venus Bulk Fill and Filtek Bulk Fill (p≤0.016). Linear regression confirmed a positive regression between max.VHN and filler loading (r(2)=0.94). SIGNIFICANCE: Bulk fill resin composites can be cured to an acceptable post-cure depth, according to the manufacturers' claims. SonicFill and Tetric EvoCeram Bulk Fill had the greatest depth of cure among the composites examined.

Hygroscopic expansion kinetics of dental resin-composites.

OBJECTIVE: To evaluate the extent and rate of hygroscopic expansion of resin composites at 37°C. METHODS: Eight resin composites were examined: 1 micro-hybrid (Bright Light(®)), 5 nano-hybrids (Experimental Vertise™; Nanoceram-Bright(®); Tetric EvoCeram(®); Grandio(®) SO; Ceram X™ duo) and 2 flowables (X-tra base; Venus(®) Diamond Flow). Five disks (15 mm×2 mm) of each material were prepared. The mean change in specimen diameter was recorded by a custom-built non-contact laser micrometer. Specimens were initially measured dry and then at fixed time intervals, over 150 days, after storage in distilled water at 37±1°C. Data were re-expressed in volumetric terms and analysed by repeated measures ANOVA, one-way ANOVA and Tukey's post hoc test (α=0.05). RESULTS: The volumetric hygroscopic expansion ranged from 0.58 to 2.26 and can be considered in three bands. First, Experimental Vertise had the highest expansion (p<0.001). Venus Diamond Flow, Tetric EvoCeram and Ceram X duo were the second band. The third band, with still lower expansion, consisted of Bright light, Grandio So, Nanoceram-Bright and X-tra base, with no significant difference between them. CONCLUSION: For the size (2mm thickness) and shape of specimen measured, equilibrium was attained in all cases by 60 days. Within this set of resin-composites the equilibrium expansion varied by almost 400% of the lowest material.

Chlorhexidine-impregnated PEM/THFM polymer exhibits superior activity to fluconazole-impregnated polymer against Candida albicans biofilm formation.

Biofilm-associated infections represent a major challenge for biomaterials. Methods to alter the chemical characteristics of biomaterials offer an attractive solution for enhanced microbial control. The aim of this study was to investigate the efficacy of a poly(ethyl methacrylate)/tetrahydrofurfuryl methacrylate (PEM/THFM) acrylic model impregnated with fluconazole (FLU) or chlorhexidine (CHX) in preventing Candida biofilm formation in vitro. PEM/THFM disks impregnated with CHX (n=50) or FLU (n=50) and drug-free control disks (n=50) were infected with Candida albicans ATCC 90028. Disks were incubated for 2, 7, 14, 21 or 28 days at 37 °C and the biofilm biomass and metabolic activity was quantified at each time point using crystal violet staining and XTT [2,3-bis(2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide] reduction assay. FLU disks exhibited poor overall biofilm inhibitory characteristics, with mean metabolic and biomass inhibition of 12.6% and 8.8%, respectively. Conversely, CHX disks were highly effective, significantly inhibiting biofilm development by 75% (P ≤ 0.001) and its metabolism by 84% (P ≤ 0.001) for all time points tested. The notable efficacy of CHX against C. albicans biofilms is a promising outcome to overcome the side effects and poor relative activity of conventional antifungal agents against Candida biofilms. These findings indicate that impregnation of PEM/THFM with antimicrobials has potential as a treatment modality for denture stomatitis.

Candidacidal effect of fluconazole and chlorhexidine released from acrylic polymer.

OBJECTIVES: To investigate the efficacy and rate of killing of a fluconazole- or chlorhexidine-impregnated polymeric delivery system against fluconazole-susceptible and -resistant Candida albicans and fluconazole-resistant Candida glabrata. METHODS: Poly(ethyl methacrylate)/tetrahydrofurfuryl methacrylate (PEM/THFM) discs impregnated with chlorhexidine, pure fluconazole (FLCp) or fluconazole from capsules (FLCc) were prepared by substituting a portion of PEM powder with an equivalent amount of each drug. Discs were incubated in sterile water for 1, 3, 7, 14, 21 and 28 days. The amounts of drugs in the leachates were measured spectrophotometrically and their antifungal activity against fluconazole-susceptible (n=1) and fluconazole-resistant (n=2) candidal isolates was determined using a time-kill method and by comparing the released concentrations with the corresponding MICs. RESULTS: Fluconazole and chlorhexidine leached from PEM/THFM polymer for up to 28 days and the released concentrations were fungicidal against all three Candida isolates for at least the first 7 days. Chlorhexidine leachates killed all Candida isolates more rapidly than the two fluconazole formulation leachates throughout the study period. FLCc leachates required longer incubation for 100% killing than FLCp leachates. The proportion of viable C. glabrata dropped more slowly than that of C. albicans with the same MIC. CONCLUSIONS: The concentrations of chlorhexidine and fluconazole leached from the PEM/THFM polymer were fungicidal against all Candida isolates, including those resistant to fluconazole, for the first 7 days. Chlorhexidine leachates showed a rapid fungicidal activity for up to 4 weeks, which can be of use in cases with poor response to conventional antifungals.

Temperature-dependence of creep behaviour of dental resin-composites.

OBJECTIVES: To determine the effect of temperature, over a clinically relevant range, on the creep behaviour of a set of conventional and flowable resin-composites including two subgroups having the same resin matrix and varied filler loading. METHODS: Eight dental resin-composites: four flowable and four conventional were investigated. Stainless steel split moulds (4 mm × 6 mm) were used to prepare cylindrical specimens for creep examination. Specimens were irradiated in the moulds in layers of 2mm thickness (40s each), as well as from the radial direction after removal from the moulds, using a light-curing unit with irradiance of 650 mW/cm(2). A total of 15 specimens from each material were prepared and divided into three groups (n=5) according to the temperature; Group I: (23°C), Group II: (37°C) and Group III: (45°C). Each specimen was loaded (20 MPa) for 2h and unloaded for 2h. Creep was measured continuously over the loading and unloading periods. RESULTS: At higher temperatures greater creep and permanent set were recorded. The lowest mean creep occurred with GS and GH resin-composites. Percentage of creep recovery decreased at higher temperatures. At 23°C, the materials exhibited comparable creep. At 37°C and 45°C, however, there was a greater variation between materials. For all resin-composites, there was a strong linear correlation with temperature for both creep and permanent set. CONCLUSIONS: Creep parameters of resin-composites are sensitive to temperature increase from 23 to 45°C, as can occur intra-orally. For a given resin matrix, creep decreased with higher filler loading.

Chlorhexidine is a highly effective topical broad-spectrum agent against Candida spp.

The objective of this study was to compare the in vitro antifungal activities of chlorhexidine (CHX) and fluconazole (FLZ) against Candida isolates comprising eight different species associated with oral candidosis. A broth microdilution method as described in Clinical and Laboratory Standards Institute (CLSI) protocol M27-A3 was used to determine susceptibility. A total of 79 clinical isolates and reference strains belonging to eight different Candida spp. was tested. The minimum inhibitory concentration (MIC) was the lowest drug concentration that reduced growth by 50% for FLZ at 48 h and by 80% for CHX at 24h and 48 h. The geometric mean MIC (and MIC range) at 48 h for CHX was 3.03 mg/L (0.78-6.25mg/L) and for FLZ was 19.12 mg/L (≤0.125-256 mg/L). Of the 79 isolates, 14 (18%) were resistant to FLZ (MIC≥64 mg/L). All isolates were effectively inhibited by ≤6.25mg/L CHX, and Candida CHX MICs are below the CHX levels found in saliva following normal dosing. No cross-resistance between CHX and FLZ was detected (r(s)=0.039, P=0.733). CLSI M27-A3 methodology proved to provide reproducible results with clear endpoints for CHX. In conclusion, the findings showed that CHX has excellent broad-spectrum antifungal activity in vitro. It was effective at concentrations detected in saliva when using standard dosing regimens. Moreover, no cross-resistance was detected between CHX and FLZ, even among Candida spp. highly resistant to FLZ.

Nanomechanical properties of dental resin-composites.

OBJECTIVE: To determine by nanoindentation the hardness and elastic modulus of resin-composites, including a series with systematically varied filler loading, plus other representative materials that fall into the categories of flowable, bulk-fill and conventional nano-hybrid types. METHODS: Ten dental resin-composites: three flowable, three bulk-fill and four conventional were investigated using nanoindentation. Disc specimens (15mm×2mm) were prepared from each material using a metallic mold. Specimens were irradiated in the mold at top and bottom surfaces in multiple overlapping points (40s each) with light curing unit at 650mW/cm(2). Specimens were then mounted in 3cm diameter phenolic ring forms and embedded in a self-curing polystyrene resin. After grinding and polishing, specimens were stored in distilled water at 37°C for 7 days. Specimens were investigated using an Agilent Technologies XP nanoindenter equipped with a Berkovich diamond tip (100nm radius). Each specimen was loaded at one loading rate and three different unloading rates (at room temperature) with thirty indentations, per unloading rate. The maximum load applied by the nanoindenter to examine the specimens was 10mN. RESULTS: Dependent on the type of the resin-composite material, the mean values ranged from 0.73GPa to 1.60GPa for nanohardness and from 14.44GPa to 24.07GPa for elastic modulus. There was a significant positive non-linear correlation between elastic modulus and nanohardness (r(2)=0.88). Nonlinear regression revealed a significant positive correlation (r(2)=0.62) between elastic moduli and filler loading and a non-significant correlation (r(2)=0.50) between nanohardness and filler loading of the studied materials. Varying the unloading rates showed no consistent effect on the elastic modulus and nanohardness of the studied materials. SIGNIFICANCE: For a specific resin matrix, both elastic moduli and nanohardness correlated positively with filler loading. For the resin-composites investigated, the group-average elastic moduli and nanohardnesses for bulk-fill and flowable materials were lower than those for conventional nano-hybrid composites.

Nanoindentation creep versus bulk compressive creep of dental resin-composites.

OBJECTIVES: To evaluate nanoindentation as an experimental tool for characterizing the viscoelastic time-dependent creep of resin-composites and to compare the resulting parameters with those obtained by bulk compressive creep. METHODS: Ten dental resin-composites: five conventional, three bulk-fill and two flowable were investigated using both nanoindentation creep and bulk compressive creep methods. For nano creep, disc specimens (15mm×2mm) were prepared from each material by first injecting the resin-composite paste into metallic molds. Specimens were irradiated from top and bottom surfaces in multiple overlapping points to ensure optimal polymerization using a visible light curing unit with output irradiance of 650mW/cm(2). Specimens then were mounted in 3cm diameter phenolic ring forms and embedded in a self-curing polystyrene resin. Following grinding and polishing, specimens were stored in distilled water at 37°C for 24h. Using an Agilent Technologies XP nanoindenter equipped with a Berkovich diamond tip (100nm radius), the nano creep was measured at a maximum load of 10mN and the creep recovery was determined when each specimen was unloaded to 1mN. For bulk compressive creep, stainless steel split molds (4mm×6mm) were used to prepare cylindrical specimens which were thoroughly irradiated at 650mW/cm(2) from multiple directions and stored in distilled water at 37°C for 24h. Specimens were loaded (20MPa) for 2h and unloaded for 2h. One-way ANOVA, Levene's test for homogeneity of variance and the Bonferroni post hoc test (all at p≤0.05), plus regression plots, were used for statistical analysis. RESULTS: Dependent on the type of resin-composite material and the loading/unloading parameters, nanoindentation creep ranged from 29.58nm to 90.99nm and permanent set ranged from 8.96nm to 30.65nm. Bulk compressive creep ranged from 0.47% to 1.24% and permanent set ranged from 0.09% to 0.38%. There was a significant (p=0.001) strong positive non-linear correlation (r(2)=0.97) between bulk creep and nano creep that could also be expressed via a simple fractional-power function. A significant (p=0.003) positive linear correlation (r(2)=0.69) existed between nano creep recovery and bulk creep recovery. With both methods of examination, except for Venus Bulk Fill™ (VB), the flowable and bulk-fill resin-composites exhibited creep within the range exhibited by the conventional resin-composites. SIGNIFICANCE: Despite the differences in loading and unloading conditions, in both methods of examination the correlation observed between the creep and recovery responses for a set of resin-composites was high. Both nano creep and recovery positively correlated with loading and unloading rates, respectively.

Creep deformation of restorative resin-composites intended for bulk-fill placement.

OBJECTIVES: To determine the creep deformation of several "bulk-fill" resin-composite formulations in comparison with some other types. METHODS: Six resin-composites; four bulk-fill and two conventional were investigated. Stainless steel split molds (4 mm × 6 mm) were used to prepare cylindrical specimens for creep testing. Specimens were thoroughly irradiated with 650 mW cm(-2). A total of 10 specimens for each material were divided into two groups (n = 5) according to the storage condition; Group A stored dry at 37 °C for 24h and Group B stored in distilled water at 37 °C in an incubator for 24h. Each specimen was loaded (20 MPa) for 2h and unloaded for 2h. The strain deformation was recorded continuously for 4h. Statistical analysis was performed using a two-way ANOVA followed by one-way ANOVA and the Bonferroni post hoc test at a significance level of a = 0.05. RESULTS: The maximum creep strain % ranged from 0.72% up to 1.55% for Group A and the range for Group B increased from 0.79% up to 1.80% due to water sorption. Also, the permanent set ranged from 0.14% up to 0.47% for Group A and from 0.20% up to 0.59% for Group B. Dependent on the material and storage condition, the percentage of creep strain recovery ranged between 64% and 81%. Increased filler loading in the bulk-fill materials decreased the creep strain magnitude. SIGNIFICANCE: Creep deformation of all studied resin-composites increased with wet storage. The "bulk-fill" composites exhibited an acceptable creep deformation and within the range exhibited by other resin-composites.

A laboratory evaluation of the physical and mechanical properties of selected root canal sealers.

AIM: To evaluate and compare the porosity, degree of conversion (DC) and hardness of two resin-based sealers; RealSeal and EndoRez, and a silicon-based sealer; GuttaFlow to that of a traditional zinc oxide-based sealer; TubliSeal. METHODOLOGY: For porosity, four samples from each sealer were prepared and scanned using a SkyScan 1072 Micro-CT. Porosity was then calculated using specialized software. For DC, 10 samples from each sealer were prepared and placed onto a Fourier transform infrared spectroscopy spectrometer. Spectra readings were carried out before and after curing of the sealers, and the DC for each sealer was calculated. For hardness, 10 samples from each sealer were prepared and then tested using a Wallace hardness tester. SPSS software was used for statistical analysis of the data using one-way anova and independent t-tests. RESULTS: TubliSeal had the highest percentage porosity (3.52%), whilst RealSeal had the lowest percentage porosity (0.41%). Statistically significant differences (P = 0.01) in porosity were present between all groups except between RealSeal and EndoRez groups. RealSeal exhibited a significantly higher DC% than EndoRez (P = 0.01), whereas EndoRez had the highest hardness number [28.54 Vickers hardness number (VHN)] whilst TubliSeal showed the lowest (13.57 VHN). Statistically significant differences in hardness were found between all groups (P = 0.01) except between RealSeal and EndoRez groups. CONCLUSIONS: Resin-based sealers had less porosity, greater hardness and a high DC.

Surface characterization of zirconia dental implants.

OBJECTIVES: The aim of the study was to characterize the chemical composition, microstructure and roughness of two commercially available zirconia dental implants (WhiteSky and Zit-Z). METHODS: The chemical composition of the cervical collar and threaded root parts of the implants (n=2) were studied by XPS and HV-EDX. LV-SEM was used for morphological assessment, Raman microanalysis for microstructural characterization and optical profilometry for surface roughness measurements. XRD, HV-EDX and Raman microanalysis of bulk regions (longitudinal sections) were used as reference. RESULTS: XPS showed the presence of C, O, Zr and Y (collar) plus Al (root) at implant surfaces. More C (10-26at%) and a lower Al/Zr ratio were found in WhiteSky (1.05 vs 1.26 in Zit-Z). Zr, Y and Al were detected in single, fully oxidized states. The same elements, plus Hf, were identified by HV-EDX at bulk and surface regions, with a Al/Zr ratio higher in WhiteSky (0.17 vs 0.09 in Zit-Z). Na, K and Cl contaminants were traced at implant root parts by both methods. XRD analysis of cross-sectioned specimens revealed the presence of monoclinic and tetragonal zirconia along with cubic yttria phases. Raman microanalysis showed that the monoclinic zirconia volume fraction was higher at root surfaces than the collar. No monoclinic phase was found at bulk regions. Significantly higher Sa and Sq values were recorded in WhiteSky than Zit-Z, whereas Zit-Z showed higher Rt value. SIGNIFICANCE: The differences found between the implants in the extent of carbon contamination, residual alumina content, tetragonal to monoclinic ZrO(2) phase transformation and 3D-roughness parameters may contribute to a substantial differentiation in the cellular and tissue response.