The development and testing of glaze materials for application to the fit surface of dental ceramic restorations

ObjectivesThe aims of the study were to develop and test overglaze materials for application to the fit surface of dental ceramic restorations, which could be etched and adhesively bonded and increase the flexural strength of the ceramic substrate.MethodsThree glaze materials were developed using commercial glass powders (P25 and P54, Pemco, Canada). P25 (90 wt%) was mixed with P54 (10 wt%) to produce (P25/P54). P54 (90 wt%) was mixed with P25 (10 wt%) to produce (P54/P25). P25 (90 wt%) was mixed with 10 wt% of an experimental glass powder (P25/frit). Eighty-two disc specimens (14 mm × 2 mm) were produced by heat pressing a leucite glass–ceramic and were sandblasted with 50 μm glass beads. Group 1 control specimens (10) were sandblasted. Groups 2–4 (10 per group) were coated using P25/frit (Group 2), P25/P54 (Group 3) and P54/P25 (Group 4) overglazes before sintering. Groups 1–4 were etched for 2 min using 9.5% HF (Gresco, USA). Composite cylinders (Marathon^® v, Den-Mat) were light cured and bonded to the glazed and prepared disc surfaces and groups water stored for 8 days. Groups were tested using shear bond strength (SBS) testing at 0.5 mm/min. Disc specimens (42) were tested using the biaxial flexural strength (BFS) test at a crosshead speed of 0.15 mm/min. Group 1 was tested as sandblasted (21) and Group 2 (21) after coating the tensile surface with P25/frit. Xrd, Eds and Sem analyzes were carried out.ResultsMean SBS (MPa ± S.D.) were: Group 1: 10.7 ± 2.1; Group 2: 9.8 ± 1.9; Group 3: 1.8 ± 1.0 and Group 4: 2.6 ± 1.7. Groups 1 and 2 were statistically different to Groups 3 and 4 (p < 0.001), but there was no difference between Groups 1 and 2 and 3 and 4 (p > 0.05). The mean BFS (MPa ± S.D.) of the overglazed Group 2 (200.2 ± 22.9) was statistically different (p < 0.001) to Group 1 (150.4 ± 14.3).SignificanceThe P25/frit overglaze significantly (p < 0.001) increased the biaxial flexural strength of the leucite glass–ceramic substrate and produced comparable shear bond strengths to an etched and bonded control. The application of etched overglaze materials to dental glass–ceramic and ceramic substrates may be useful in adhesive dentistry.     

Effect of sandblasting,etching and resin bonding on the flexural strength/bonding of novel glass-ceramics

Objectives

To process novel leucite glass-ceramics and test the effects of surface treatment and resin bonding on the biaxial flexural strength (BFS) and shear bond strength (SBS).

Crystallization of high-strength fine-sized leucite glass-ceramics

Manufacturing of leucite glass-ceramics often leads to materials with inhomogeneous microstructures. Crystal-glass thermal mismatches which produce microcracking around larger crystals-agglomerates are associated with reduced mechanical properties. The hypotheses were that fine (< 1 μm) crystal size and uniform microstructure in a thermally matched glass would increase the biaxial flexural strength (BFS). Glass was synthesized, attritor-milled, and heat-treated. Glasses and glass-ceramics were characterized by XRD, SEM, and Dilatometry. Experimental (A, M1A and M2A) and commercial glass-ceramics were tested by the BFS test. Experimental glass-ceramics showed an increased leucite crystal number and decreased crystal size with glass particle size reduction. Leucite glass-ceramics (< 1 μm) showed minimal matrix microcracking and BFS values of [mean (SD) MPa]: M1A = 253.8 (53.3); and M2A = 219.5 (54.1). Glass-ceramics M1A and M2A had higher mean BFS and characteristic strength than the IPS Empress Esthetic glass-ceramic (p < 0.05). Fine-grained, translucent leucite glass-ceramics were synthesized and produced high mean BFS.     

Effect of cooling protocol on mechanical properties and microstructure of dental veneering ceramics

ObjectivesUnderstand how cooling protocols control the microstructure and mechanical properties of veneering porcelains.MethodsTwo porcelain powders were selected, one used to veneer metallic frameworks (VM13) and one for zirconia frameworks (VM9). After the last firing cycle, the monolithic specimens were subjected to two cooling protocols: slow and fast. Flexural strength (FS) was evaluated by three-point beam bending and fracture toughness (K_IC) was evaluated by the single-edge V-notch beam (SEVNB) method. Scanning electron microscopy (SEM) was performed to determine the leucite crystal volume fraction (%), particle size, and matrix microcrack density. The results were compared by analysis of variances (ANOVA) and Tukey’s multiple comparison test.ResultsThe mechanical properties were significantly (p < 0.05) higher for the VM13 porcelain (FS = 111.0 MPa, K_IC = 1.01 MPa.√m) compared to VM9 (FS = 79.6 MPa, K_IC =0.87 MPa.√m) regardless of cooling protocol due to ∼250% higher volume fraction of leucite crystals. The slow cooled VM13 and fast cooled VM9 resulted in the highest and lowest mechanical properties, respectively, while the VM9 slow cooled properties were similar to the VM13 fast cooled. The SEM revealed that the slow cooling significantly increased the volume fraction of leucite crystals by 33–41 %. Across both porcelains, a significant linear correlation between both mechanical properties (strength and toughness) and leucite crystal content was found. Slow cooling was also associated with increased crystal growth resulting in more matrix microcracking.SignificanceControlled crystallization using slow cooling can be applied as a means of strengthening dental porcelains. However, the benefits of slow cooling may be partially offset by increasing the microcrack density in the glass matrix. To achieve the maximum benefit of slow cooling, it is recommending to develop heat treatments to produce porcelain with fine-grained and homogenously dispersed leucite crystals to achieve minimal glass matrix microcracking.     

Manufacture,characterisation and properties of novel fluorcanasite glass–ceramics

ObjectiveThe aim of this study was to investigate the manufacture and characterisation of different compositions of fluorcanasite glass–ceramics with reduced fluorine content and to assess their mechanical and physical properties.MethodsThree compositional variations (S80, S81 and S82) of a fluorcanasite glass were investigated. Differential thermal analysis (DTA) and X-ray diffraction (XRD) identified crystallisation temperatures and phases. X-ray fluorescence (XRF) determined the element composition in the glass–ceramics. Different heat treatments [2 h nucleation and either 2 or 4 h crystallisation] were used for the glasses. Scanning electron microscopy (SEM) examined the microstructure of the cerammed glass. The chemical solubility, biaxial flexural strength, fracture toughness, hardness and brittleness index of S81 and S82 fluorcanasite were investigated with lithium disilicate (e.max CAD, Ivoclar Vivadent) as a commercial comparison. Statistical analysis was performed using one-way ANOVA with Tukey's multiple comparison tests (P < 0.05). Weibull analysis was employed to examine the reliability of the strength data.ResultsAll compositions successfully produced glasses. XRD analysis confirmed fluorcanasite formation with the S81 and S82 compositions, with the S82 (2 + 2 h) showing the most prominent crystal structure. The chemical solubility of the glass–ceramics was significantly different, varying from 2565 ± 507 μg/cm² for the S81 (2 + 2 h) to 722 ± 177 μg/cm² for the S82 (2 + 2 h) to 37.4 ± 25.2 μg/cm² for the lithium disilicate. BFS values were highest for the S82 (2 + 2 h) composition (250 ± 26 MPa) and lithium disilicate (266 ± 37 MPa) glass–ceramics. The fracture toughness was higher for the S82 compositions, with the S82 (2 + 2 h) attaining the highest value of 4.2 ± 0.3 MPa m^1/2(P = 0.01). The S82 (2 + 2 h) fluorcanasite glass–ceramic had the lowest brittleness index.ConclusionThe S82 (2 + 2 h) fluorcanasite glass–ceramic has acceptable chemical solubility, high biaxial flexural strength, fracture toughness and hardness.Clinical significanceA novel glass–ceramic has been developed with potential as a restorative material. The S82 (2 + 2 h) has mechanical and physical properties that would allow the glass–ceramic to be used as a machinable core material for veneered resin-bonded ceramic restorations.     

Pre-cementation treatment of glass-ceramics with vacuum impregnated resin coatings

ObjectiveThe study aimed to investigate the effectiveness of a vacuum impregnation process to eliminate the porosity at the ceramic-resin interface to optimize the reinforcement of a glass-ceramic by resin cementation.Methods100 leucite glass-ceramic disks (1.0 ± 0.1 mm thickness) were air-abraded, etched with 9.6 % HF acid, and silanated. Specimens were randomly allocated to 5 groups (n = 20). Group A received no further treatment (uncoated control). Groups B and D were resin-coated under atmospheric pressure, whereas groups C and E were resin-coated using vacuum impregnation. The polymerized resin-coating surfaces of specimens in groups B and C were polished to achieve a resin thickness of 100 ± 10 µm, while in groups D and E no resin-coating modification was performed prior to bi-axial flexure strength (BFS) determination. Optical microscopy was undertaken on the fracture fragments to identify the failure mode and origin. Comparisons of BFS group means were made by a one-way analysis of variance (ANOVA) and post-hoc Tukey test at α = 0.05.ResultsAll resin-coated sample groups (B–E) showed a statistically significant increase in mean BFS compared with the uncoated control (p < 0.01). There was a significant difference in BFS between the ambient and vacuum impregnated unpolished groups (D and E) (p < 0.01), with the greatest strengthening achieved using a vacuum impregnation technique.SignificanceResults highlight the opportunity to further develop processes to apply thin conformal resin coatings, applied as a pre-cementation step to strengthen dental glass-ceramics.     

The mechanical properties of nanofilled resin-based composites: The impact of dry and wet cyclic pre-loading on bi-axial flexure strength

ObjectivesTo determine the influence of nano-sized filler particles and agglomerates of nanoparticles (‘nanoclusters’) in resin-based composite (RBC) materials on the bi-axial flexure strength (BFS) following cyclic pre-loading and storage in a ‘dry’ or ‘wet’ environment.MethodSeven commercially available RBC restoratives, Heliomolar (Ivoclar Vivadent, Schaan, Liechtenstein), Z100 MP Restorative, Filtek? Z250, Filtek? Supreme (3M ESPE, St. Paul, MN, USA) in Body (FSB) and Translucent (FST) shades, Grandio and Grandio Flow (VOCO, Cuxhaven, Germany), containing differing filler particle types and morphologies were investigated. Specimens were pre-loaded at 20, 50 or 100 N for 2000 cycles and stored in a ‘dry’ or ‘wet’ environment prior to BFS testing.ResultsA general linear model analysis of variance highlighted a reduction in the BFS following pre-loading, however, individual RBC materials responded differently. The RBCs containing agglomerated nano-sized particles or ‘nanoclusters’ (Filtek? Supreme) demonstrated distinctive and unique patterns of response to pre-loading. Cyclic pre-loading at 20 and 50 N significantly increased the Weibull modulus of both FSB (8.53 ± 1.91 and 10.23 ± 2.29) and FST (16.89 ± 3.78 and 10.91 ± 2.45) compared with FSB and FST control (no pre-cyclic load) specimens (5.98 ± 1.34 and 7.99 ± 1.78, respectively). BFS of FSB and FST was maintained or significantly increased compared with the other materials following 20 and 50 N cyclic pre-load (P < 0.05).SignificanceThe ‘nanoclusters’ provided a distinct reinforcing mechanism compared with the microhybrid, microfill or nanohybrid RBC systems resulting in significant improvements to the strength and reliability, irrespective of the environmental storage and testing conditions. Silane infiltration within interstices of the nanoclusters may modify the response to pre-loading induced stress, thereby enhancing damage tolerance and providing the potential for improved clinical performance.     

Crystallization and flexural strength optimization of fine-grained leucite glass-ceramics for dentistry

Objectives

Leucite glass-ceramics with fine-grained leucite crystals promote improved mechanical strength and increased translucency. The objectives of the study were to optimize the microstructure of a fine-grained leucite glass-ceramic in order to increase its flexural strength and reliability as measured by its Weibull modulus.

Methods

Glass was prepared by a melt-derived method and ground into a powder (M1A). The glass crystallization kinetics were investigated using high temperature XRD and DSC. A series of two-step heat treatments with different nucleation/crystal growth temperatures and holds were carried out to establish the optimized crystallization heat treatment. Glass-ceramics were characterized using XRD, SEM and dilatometry. The glass-ceramic heat treated at the optimized crystallization parameters (M1A_opt) was both sintered (SM1A_opt) and heat extruded (EM1A_opt) into discs and tested using the biaxial flexural strength (BFS) test.

Results

High temperature XRD suggested leucite and sanidine crystallization at different temperatures. Optimized crystallization resulted in an even distribution of fine leucite crystals (0.15 (0.09) μm²) in the glassy matrix, with no signs of microcracking. Glass-ceramic M1A_opt showed BFS values of [mean (SD), MPa]: SM1A_opt = 252.4 (38.7); and EM1A_opt = 245.0 (24.3). Weibull results were: SM1A_opt; m = 8.7 (C.I. = 7.5-10.1) and EM1A_opt; m = 11.9 (C.I. = 9.3-15.1). Both experimental groups had a significantly higher BFS and characteristic strength than the IPS Empress Esthetic glass-ceramic, with a higher m value for the EM1A_opt material (p < 0.05).

Significance

A processable fine-grained leucite glass-ceramic with high flexural strength and improved reliability was the outcome of this study.     

High-translucent yttria-stabilized zirconia ceramics are wear-resistant and antagonist-friendly

ObjectivesTo evaluate two-body wear of three zirconia ceramics stabilized with 3, 4 and 5 mol% yttria and to compare their wear behavior with that of a lithium-disilicate glass-ceramic.MethodsSixteen rectangular-shaped specimens made from three grades of zirconia ceramics and a lithium-disilicate glass-ceramic were polished and dynamically loaded in a chewing simulator (2 kg vertical load, 2.1 Hz) under water at 90 °C for 1.2 × 10⁶ cycles (about 7 days) in the ball-on-plate mode against steatite antagonists. Surface roughness was measured before and after wear testing. Wear tracks were scanned with a non-contact 3D profilometer and super-impositions were used to determine wear loss of the antagonists. Wear surfaces were imaged by SEM. XRD and micro-Raman spectroscopy were used to characterize phase transformation and stress status in the worn and unworn areas of the zirconia ceramics.ResultsIndependent of fracture toughness, strength and aging-susceptibility, the three zirconia ceramics showed a similar and limited amount of wear (∼10 μm in depth) and were more wear-resistant than the lithium-disilicate glass-ceramic (∼880 μm in depth). Abrasive wear without obvious cracks was observed for all investigated zirconias, whereas the glass-ceramic with a lower fatigue threshold and high susceptibility to surface dissolution exhibited significant abrasion, fatigue and corrosion wear. All three zirconia ceramics yielded a lower antagonist wear than the glass-ceramic and no significant differences were found between the zirconia ceramics.SignificanceIn the context of this study, high-translucent zirconia ceramics stabilized with a higher yttria content, recently introduced in the dental field, were as wear-resistant and antagonist-friendly as conventional high-strength zirconia and suitable for monolithic restorations.     

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.     

Calcium and phosphate ion releasing composite: Effect of pH on release and mechanical properties

ObjectivesSecondary caries and restoration fracture are the two main challenges facing tooth cavity restorations. The objective of this study was to develop a composite using tetracalcium phosphate (TTCP) fillers and whiskers to be stress-bearing, and to be “smart” to increase the calcium (Ca) and phosphate (PO₄) ion release at cariogenic pH.MethodsTTCP was ball-milled to obtain four different particle sizes: 16.2, 2.4, 1.3, and 0.97 μm. Whiskers fused with nano-sized silica were combined with TTCP as fillers in a resin. Filler level mass fractions varied from 0 to 75%. Ca and PO₄ ion releases were measured vs. time at pH of 7.4, 6, and 4. Composite mechanical properties were measured via three-point flexure before and after immersion in solutions at the three pH.ResultsTTCP composite without whiskers had flexural strength similar to a resin-modified glass ionomer (Vitremer) and previous Ca–PO₄ composites. With whiskers, the TTCP composite had a flexural strength (mean ± S.D.; n = 5) of (116 ± 9) MPa, similar to (112 ± 14) MPa of a stress-bearing, non-releasing hybrid composite (TPH) (p > 0.1). The Ca release was (1.22 ± 0.16) mmol/L at pH of 4, higher than (0.54 ± 0.09) at pH of 6, and (0.22 ± 0.06) at pH of 7.4 (p < 0.05). PO₄ release was also dramatically increased at acidic pH. After immersion, the TTCP–whisker composite matched the strength of TPH at all three pH (p > 0.1); both TTCP–whisker composite and TPH had strengths about threefold that of a releasing control.SignificanceThe new TTCP–whisker composite was “smart” and increased the Ca and PO₄ release dramatically when the pH was reduced from neutral to a cariogenic pH of 4, when these ions are most needed to inhibit caries. Its strength was two- to threefold higher than previously known Ca–PO₄ composites and resin-modified glass ionomer. This composite may have the potential to provide the necessary combination of load-bearing and caries-inhibiting capabilities.     

Chronophysiological features of the normal mineral composition of human saliva

BackgroundThe high rate of changes in the composition of saliva can be used for the monitoring of various biorhythms in order to study the physiological characteristics of the human body.Research objectiveThe study of the dynamics of the near-24-h mineral composition of saliva in men and women.MethodsThe study involved 20 men and 20 women, age 23.1 ± 0.9 years. Saliva samples were collected every 3 h during the day within 10 min. The mineral composition of saliva was defined by the capillary electrophoresis technique. The cross-group differences were evaluated using the non-parametric criterion.ResultsIt was shown that the maximum values of the mineralizing capacity fall to 7–8 a.m. and 18–19p.m., which is due to the change in the rate of saliva secretion. The near-24-h dynamics of the saliva pH practically coincides with the dynamics of the Ca/P ratio; there are evident maxima at 9:00 am and 15–18p.m. The values of the Na/K ratio are out of phase with the Ca/P ratio. There is one maximum, corresponding to 3 am in the night, and one minimum at 12–13p.m., which is due to a decreased level of sodium and increased potassium concentration. Statistically valid differences between men and women in pH (p < 0.001), concentrations of inorganic phosphorus (p < 0.001), as well as Ca/P coefficient (p = 0.011) were identified.ConclusionThe dynamics of the studied parameters during 24 h is characterized by pronounced intervals.     

An in situ and ex situ study of the microstructural evolution of a novel lithium silicate glass-ceramic during crystallization firing

ObjectiveTo elucidate the compositional and microstructural developments of a novel lithium silicate glass-ceramic during its crystallization cycle.MethodsBlocks of a lithium silicate glass-ceramic (Obsidian®, Glidewell Laboratories) were cut into 1 mm thick plates and polished to 1 μm finish. Some of them were crystallized prior to polishing. Firstly, ex situ compositional and microstructural characterizations of both the pre- and post-crystallized samples were performed by wavelength dispersive X-ray fluorescence, field-emission scanning electron microscopy, and X-ray diffractometry. Secondly, the pre-crystallized samples were subjected to in situ compositional and microstructural characterizations under non-isothermal heating by simultaneous thermogravimetry/differential scanning calorimetry, X-ray thermo-diffractometry, and field-emission scanning electron thermo-microscopy.ResultsThe microstructure of pre-crystallized Obsidian® consists of an abundant population of perlitic-like/dendritic lithium silicate (Li₂SiO₃) nanocrystals in a glass matrix. Upon heating, the residual glassy matrix does not crystallize into any form of SiO₂; elemental oxides do not precipitate unless over-heated above 820 °C; and the Li₂SiO₃ nanocrystals do not react with the glassy matrix to form typical lithium disilicate (Li₂Si₂O₅) crystals. Nonetheless, the Li₂SiO₃ nanocrystals grow and spheroidize through the solution-reprecipitation process in the softened glass, and new lithium orthophosphate (Li₃PO₄) nanocrystals precipitate from the glass matrix.SignificanceThe identification of compositional and microstructural developments of Obsidian® indicates that, by controlling the firing conditions, it is possible to tailor its microstructure, which in turn could affect its mechanical and optical properties, and ultimately its clinical performance.     

Crystallization of high-strength nano-scale leucite glass-ceramics

Objectives

Fine-grained, high strength, translucent leucite dental glass-ceramics are synthesized via controlled crystallization of finely milled glass powders. The objectives of this study were to utilize high speed planetary milling of an aluminosilicate glass for controlled surface crystallization of nano-scale leucite glass-ceramics and to test the biaxial flexural strength.

Methods

An aluminosilicate glass was synthesized, attritor or planetary milled and heat-treated. Glasses and glass-ceramics were characterized using particle size analysis, X-ray diffraction and scanning electron microscopy. Experimental (fine and nanoscale) and commercial (Ceramco-3, IPS Empress Esthetic) leucite glass-ceramics were tested using the biaxial flexural strength (BFS) test. Gaussian and Weibull statistics were applied.

Results

Experimental planetary milled glass-ceramics showed an increased leucite crystal number and nano-scale median crystal sizes (0.048–0.055 μm²) as a result of glass particle size reduction and heat treatments. Experimental materials had significantly (p < 0.05) higher mean BFS and characteristic strength values than the commercial materials. Attritor milled and planetary milled (2 h) materials showed no significant (p > 0.05) strength difference. All other groups’ mean BFS and characteristic strengths were found to be significantly different (p < 0.05) to each other. The mean (SD) MPa strengths measured were: Attritor milled: 252.4 (38.7), Planetary milled: 225.4 (41.8) [4 h milling] 255.0 (35.0) [2 h milling], Ceramco-3: 75.7 (6.8) and IPS Empress: 165.5 (30.6).

Significance

Planetary milling enabled synthesis of nano-scale leucite glass-ceramics with high flexural strength. These materials may help to reduce problems associated with brittle fracture of all-ceramic restorations and give reduced enamel wear.     

Salivary levels of calcium,phosphorus, potassium,albumin and correlation with serum biomarkers in hemodialysis patients

ObjectivesEvidences suggest that hemodialysis patients have reduced salivary flow and changes in the composition of salivary secretion. These changes may reflect local and systemic disorders. The objectives of this study were to compare the salivary levels of calcium (Ca), phosphorus (P), potassium (K) and albumin in hemodialysis patients and healthy subjects, and to investigate a possible correlation between their serum and salivary levels.DesignA case–control study was conducted with 60 hemodialysis patients (HD group) and 37 systemically healthy individuals (control group). Stimulated saliva samples were collected for biochemical analysis (Ca, P, K and albumin). Serum data were collected in the HD group. Statistical analysis included t-test, Pearson correlation and simple linear regression.ResultsThe HD group exhibited higher salivary levels of Ca, P, and albumin (p < 0.05). There was a significant positive correlation between serum PTH and salivary phosphorus (r = 0.342, p = 0.009), and between serum PTH and salivary potassium (r = 0.306, p = 0.020). An increase of 100 pg/dL in serum PTH was associated with an elevation of salivary P levels (0.34 mg/dL, p = 0.009), and salivary K levels (0.20 mmol/dL, p = 0.02), in the HD group.ConclusionsThe findings suggest that HD patients present increased levels of salivary components (Ca, P, and albumin), and changes commonly observed in HD patients, such as hyperparathyroidism, appear to have an influence on salivary composition.     

Cell migration,viability and tissue reaction of calcium hypochlorite based-solutions irrigants: An in vitro and in vivo study

ObjectiveThis study aimed to analyze in vitro cytotoxicity to cultured 3T3 fibroblasts and in vivo inflammatory reaction in rats by calcium hypochlorite (Ca(OCl)₂) solutions compared with sodium hypochlorite (NaOCl) solutions.DesignCultured 3T3 fibroblasts were exposed to different concentrations of (Ca(OCl)₂) and NaOCl solutions, and a scratch assay was performed. The viability rate was analyzed with trypan blue assay. Both solutions of 1% and 2.5% concentrations were injected into the subcutaneous tissue of 18 male Wistar rats aged 18 weeks. The inflammatory tissue reaction was evaluated at 2 h, 24 h, and 14 days after the injections. The samples were qualitatively analyzed using a light microscope. Statistical analysis was performed with ANOVA and Tukey post hoc tests for in vitro assays and Kruskal–Wallis and Dunn post hoc tests for in vivo assays (α = 0.05).ResultsIn the scratch assay, Ca(OCl)₂ showed no significant difference compared with the control group (culture medium) at 24 h (p < 0.05). Solutions of 0.0075% and 0.005% NaOCl and Ca(OCl)₂ concentrations presented similar results compared with those in the positive control group (hydrogen peroxide) (p > 0.05) in the trypan blue assay. In the in vivo assay, 1% Ca(OCl)₂ group showed a significant decrease in neutrophils at 2 h and 24 h (p = 0.041) and 2 h and 14 days (p = 0.017). There was no statistically significant difference for lymphocyte/plasmocyte and macrophage counts among the different concentration groups.ConclusionsCa(OCl)₂ showed favorable results of viability and induced a low-level inflammatory response. Ca(OCl)₂ presented acceptable cytotoxicity and biocompatibility as an irrigant solution.     

Graded structures for damage resistant and aesthetic all-ceramic restorations

ObjectivesClinical studies revealed several performance deficiencies with alumina- and zirconia-based all-ceramic restorations: fracture; poor aesthetic properties of ceramic cores (particularly zirconia cores); and difficulty in achieving a strong ceramic–resin-based cement bond. We aim to address these issues by developing a functionally graded glass/zirconia/glass (G/Z/G) structure with improved damage resistance, aesthetics, and cementation properties.MethodsUsing a glass powder composition developed in our laboratory and a commercial fine zirconia powder, we have successfully fabricated functionally graded G/Z/G structures. The microstructures of G/Z/G were examined utilizing a scanning electron microscopy (SEM). The crystalline phases present in G/Z/G were identified by X-ray diffraction (XRD). Young's modulus and hardness of G/Z/G were derived from nanoindentations. Critical loads for cementation radial fracture in G/Z/G plates (20 mm × 20 mm, 1.5 or 0.4 mm thick) bonded to polycarbonate substrates were determined by loading with a spherical indenter. Parallel studies were conducted on homogeneous yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) controls.ResultsThe G/Z/G structure consists of an outer surface aesthetic glass layer, a graded glass–Y-TZP layer, and a dense Y-TZP interior. The Young's modulus and hardness increase from surface to interior following power-law relations. For G/Z/G plates of 1.5 and 0.4 mm thick, critical loads for cementation radial fracture were 1990 ± 107 N (mean ± S.D., n = 6) and 227 ± 20 N (mean ± S.D., n = 6), respectively, which were ～30 and 50% higher than those for their monolithic Y-TZP counterparts (1388 ± 90 N for 1.5 mm and 113 ± 10 N for 0.4 mm thick; mean ± S.D., n = 6 for each thickness). A 1-sample t-test revealed significant difference (p < 0.001) in critical loads for radial fracture of G/Z/G and homogeneous Y-TZP for both specimen thicknesses.SignificanceOur results indicate that functionally graded G/Z/G structures exhibit improved damage resistance, aesthetics, and potentially cementation properties compared to homogeneous Y-TZP.     

Effects of ZnO/TiO2 nanoparticle and TiO2 nanotube additions to dense polycrystalline hydroxyapatite bioceramic from bovine bones

ObjectivesA bovine dense hydroxyapatite ceramic (HA) was produced as new biomaterial, however, the production of a material with consistently high flexural strength remains challenging. The objective of this study was to evaluate the effects of ZnO nanoparticles, TiO₂ nanoparticles, and TiO₂ nanotubes (1%, 2%, and 5% by weight) on the microstructure and flexural strength of a bovine dense hydroxyapatite ceramic (HA).MethodsDiscs (Ø = 12.5 mm; thickness = 1.3 mm) were prepared and subjected to X-ray diffraction (XRD), and observation with a field emission scanning electron microscope (FE-SEM), biaxial flexural strength (BFS) testing, and Vickers hardness (VH) testing. The BFS and VH data were subjected to ANOVA and Tukey post-hoc tests (α = 0.05) and Weibull analysis.ResultsThe XRD showed that the addition of nanomaterials caused the formation of a secondary phase when 5% of the ZnO nanoparticles was used, or when all percentages of the TiO₂ nanoparticles/nanotubes were used, and the HA crystallographic planes were maintained. Differences were not observed between the higher BFS values obtained with pure HA and those obtained with the 5% addition of TiO₂ nanoparticles. However, the results were different compared with the other groups (α = 0.05). The results obtained by Weibull analysis revealed that the 1%, 2%, and 5% addition of TiO₂ nanotubes, and the 1% and 2% addition of TiO₂ nanoparticles decreased the HA characteristic strength (σ₀), while the Weibull modulus (m) increased when 5% of TiO₂ nanoparticles, 1% and 2% of ZnO nanoparticles, and 2% of TiO₂ nanoparticles were added, but with no statistical difference from the pure HA. The 5% addition of ZnO₂ nanoparticles decreased the σ₀ without changing m. Moreover, the 5% addition of TiO₂ nanoparticles resulted in an m closest to that of pure HA. Regarding the VH results, the blend of HA with 1% and 2% addition of TiO₂ nanoparticles exhibited the higher values, which were similar between the different addition ratios (p = 0.102). Moreover, the addition of 5% TiO₂ nanoparticles resulted in higher value compared with pure HA.SignificanceThis study demonstrated that the HA blend with 5% of TiO₂ nanoparticles has the greatest potential as a bovine HA dense bioceramic reinforcement.     

Osseointegration of fiber-reinforced composite implants: Histological and ultrastructural observations

ObjectivesThe aim of this study was to evaluate the bone tissue response to fiber-reinforced composite (FRC) in comparison with titanium (Ti) implants after 12 weeks of implantation in cancellous bone using histomorphometric and ultrastructural analysis.Materials and methodsThirty grit-blasted cylindrical FRC implants with BisGMA–TEGDMA polymer matrix were fabricated and divided into three groups: (1) 60 s light-cured FRC (FRC-L group), (2) 24 h polymerized FRC (FRC group), and (3) bioactive glass FRC (FRC–BAG group). Titanium implants were used as a control group. The surface analyses were performed with scanning electron microscopy and 3D SEM. The bone–implant contact (BIC) and bone area (BA) were determined using histomorphometry and SEM. Transmission electron microscopy (TEM) was performed on Focused Ion Beam prepared samples of the intact bone–implant interface.ResultsThe FRC, FRC–BAG and Ti implants were integrated into host bone. In contrast, FRC-L implants had a consistent fibrous capsule around the circumference of the entire implant separating the implant from direct bone contact. The highest values of BIC were obtained with FRC–BAG (58 ± 11%) and Ti implants (54 ± 13%), followed by FRC implants (48 ± 10%), but no significant differences in BIC or BA were observed (p = 0.07, p = 0.06, respectively). TEM images showed a direct contact between nanocrystalline hydroxyapatite of bone and both FRC and FRC–BAG surfaces.ConclusionFiber-reinforced composite implants are capable of establishing a close bone contact comparable with the osseointegration of titanium implants having similar surface roughness.     

Optimization of calcium concentration of saliva with phosphoryl oligosaccharides of calcium (POs-Ca) for enamel remineralization in vitro

ObjectivePhosphoryl oligosaccharides of calcium (POs-Ca) are highly soluble calcium source made from potato starch. The aim of this study was to investigate the optimal concentrations of POs-Ca for the remineralization of subsurface enamel lesions in vitro.DesignDemineralized bovine enamel slabs (n = 5) were remineralized in vitro for 24 h at 37 °C with artificial saliva (AS) containing 0–0.74% POs-Ca to adjust the Ca/P ratio to 0.4–3.0, then sectioned and analysed by transversal microradiography (TMR). The data were analysed by Scheffe's post hoc test. The Ca/P ratio with most remineralization was used to investigate the effect of calcium on enamel remineralization (n = 11). The demineralized slabs were treated with AS with calcium-chloride- (CaCl₂-) or POs-Ca with an identical calcium content, and sectioned for TMR and wide-angle X-ray diffraction (WAXRD) analyses to evaluate the local changes in hydroxyapatite (HAp) crystal content. The data were analysed using the Mann–Whitney U-test.ResultsThe highest mineral recovery rate resulted from addition of POs-Ca to adjust the Ca/P to 1.67. At this ratio, the mineral recovery rate for AS containing POs-Ca (24.2 ± 7.4%) was significantly higher than that for AS containing CaCl₂ (12.5 ± 11.3%) (mean ± SD, p < 0.05). The recovery rate of HAp crystallites for AS containing POs-Ca (35.7 ± 10.9%) was also significantly higher than that for AS containing CaCl₂ (23.1 ± 13.5%) (p < 0.05). The restored crystallites were oriented in the same directions as in sound enamel.ConclusionsPOs-Ca effectively enhances enamel remineralization with ordered HAp at a Ca/P ratio of 1.67.