Clinical applications of glass-ceramics in dentistry

Quantitative examination of factors influencing the colour reproduction ability of lithium disilicate glass-ceramics

BACKGROUND

Effects of ceramic translucency, layer thickness, and substrate colour on the shade of lithium disilicate glass-ceramic restorations proved to be significant in several studies, however, quantitative, numerical results on the relationship between the colour difference and these parameters are still lacking. The purpose of this in vitro study was to quantitatively determine how the colour reproduction ability of a lithium disilicate glass-ceramic is affected by its translucency, layer thickness, and substrate colour.

METHODS

Ceramic samples were prepared from A2 shade IPS e.max CAD blocks with high and low translucencies (HT and LT) in a thickness range of 0.5-2.5 mm (+/- 0.05 mm). Layered samples were acquired utilizing composite substrates in 9 shades; transparent try-in paste was used. The spectral reflectance of the specimens was assessed under D65 standard illumination with a Konica Minolta CM-3720d spectrophotometer. The CIEDE2000 colour difference (ΔE00) between two samples was analysed using perceptibility and acceptability thresholds set at 50:50%. Statistical analysis involved linear regression analysis and the Kruskal-Wallis test.

RESULTS

An increase in the thickness of 0.5 mm reduced the ΔE00 of the HT samples to 72.8%, and that of the T samples to 71.1% (p < 0.0001). 7 substrates with HT and LT specimens had significantly different results from the mean (p < 0.05). A thickness of 0.5 mm is not sufficient to achieve an acceptable result at any level of translucency, while the low translucency ceramic at a thickness of 1.5 mm gave acceptable results, except for severely discoloured substrates (ND8 and ND9).

CONCLUSIONS

The colour reproduction ability of lithium disilicate glass-ceramics is significantly affected by their translucency, layer thickness, and 7 substrates out of 9 substrates examined.

Novel biocompatible denture material incorporating type I collagen with improved functional properties for oral health

The use of collagen is the recent development in various medical fields. Huge quantities of hide and skin trimmings are generated during the leather processing are wasted or underutilized. Trimmings contain collagen which can be beneficially extracted and utilized for high value products. Poly methyl methacrylate based denture materials exhibit serious concerns such as high porosity, presence of residual monomer, shrinkage, distortion and high rate of deterioration of the materials. This study aims to incorporate extracted Type I collagen with polymer to obtain denture base and investigate its chemical and mechanical properties. The present research methodology also reduces the quantity of monomer and acrylic resin usage. The collagen was extracted from animal skin and hide trimmings which are otherwise disposed as wastes. This study investigated the effect of visco-elastic characteristics of resulted specimens and their transition temperature, mechanical properties, decomposition temperature and leachability. The collagen-based specimens have better tensile strength with high decomposition temperature compared to control specimens. Scanning Electron Microscopy analysis revealed that the experimental specimens was cohesive and homogeneous which explained the higher tensile and decomposition values. The study suggests that collagen cross-linked acrylic denture base exhibit better mechanical and thermal resistance properties when compared to control specimens. The study indicates that biomaterials are emerging as smart products of value in human health.

Recent advances in glass-ceramics: Performance and toughening mechanisms in restorative dentistry

The use of glass-ceramics in the medical field has grown significantly since the 1980s. With excellent aesthetic properties, semi-translucency, outstanding mechanical properties, corrosion resistance, wear resistance and great biocompatibility and workability glass-ceramics is one of the most commonly used materials in restorative dentistry and is widely used in veneers, inlays, onlays, all-ceramic crowns, and implant abutments. This review provides an overview of the research progress of glass-ceramics in restorative dentistry, focusing on the classification, performance requirements, toughening mechanisms and their association with clinical performance, as well as the manufacturing and fabrication of glass-ceramics in restorative dentistry. Finally, the developments and prospects of glass-ceramics in restorative dentistry are summarized and discussed.

Dental Materials Applied to 3D and 4D Printing Technologies: A Review

As computer-aided design and computer-aided manufacturing (CAD/CAM) technologies have matured, three-dimensional (3D) printing materials suitable for dentistry have attracted considerable research interest, owing to their high efficiency and low cost for clinical treatment. Three-dimensional printing technology, also known as additive manufacturing, has developed rapidly over the last forty years, with gradual application in various fields from industry to dental sciences. Four-dimensional (4D) printing, defined as the fabrication of complex spontaneous structures that change over time in response to external stimuli in expected ways, includes the increasingly popular bioprinting. Existing 3D printing materials have varied characteristics and scopes of application; therefore, categorization is required. This review aims to classify, summarize, and discuss dental materials for 3D printing and 4D printing from a clinical perspective. Based on these, this review describes four major materials, i.e., polymers, metals, ceramics, and biomaterials. The manufacturing process of 3D printing and 4D printing materials, their characteristics, applicable printing technologies, and clinical application scope are described in detail. Furthermore, the development of composite materials for 3D printing is the main focus of future research, as combining multiple materials can improve the materials' properties. Updates in material sciences play important roles in dentistry; hence, the emergence of newer materials are expected to promote further innovations in dentistry.

Preparation and characterization of lithium disilicate-fluorcanasite glass-ceramics for dental applications

The purpose of this research is to discuss the preparation, characterization, and characteristics of lithium disilicate-fluorcanasite (LF) glass-ceramics in order to develop new dental glass-ceramics. A typical melt quenching method was used to produce the lithium disilicate (LD) and fluorcanasite (FC) types of glass. Following that, the LD and FC glass frits were combined and remelted in the following LD:FC ratios of 100:0, 0:100, 75:25, and 50:50 wt%, represented by S1, S2, S3, and S4, respectively. Based on the thermal analysis data, the glass-ceramic samples were fabricated through the heat treatment method. XRD and SEM were used to characterize the phase formation and microstructures of the prepared glass-ceramics. Archimedes' principle, three-point bending, and chemical solubility tests were used to determine density, flexural strength, and chemical solubility, respectively. The elastic modulus and fracture toughness of the selected samples were also evaluated using a Vickers hardness test. It was found that the S3 glass-ceramic sample (S3-789) has a longer LD crystalline phase than that of the S4 glass-ceramic sample (S4-788), resulting in a higher density and hardness. Furthermore, the S3-789 sample had by far the greatest Vickers hardness, elastic modulus, fracture toughness, and flexural strength, so it was chosen for future study to assess its bioactivity in SBF due to its superior mechanical properties and good machinability. The SBF bioactivity test validated the S3-789 sample's high bioactive performance. As a result, the S3-789 sample may be a good option for use as a novel material in dental applications.

Ceramics overview

Ceramic materials have rapidly become the material of choice for indirect restorations. There are a variety of material types available for use such as feldspathic ceramics, glass ceramics and many types of zirconia. Advances in digital dentistry led to a rapid switch from porcelain fused to metal restorations to all-ceramic restorations. Variations in composition, microstructure and processing affect mechanical properties and use of these materials. Having a better understanding of their differences is important for proper clinical selection. Ceramic materials may be classified several ways including by composition, microstructure, processing technique and clinical application. This article reviews the various types of ceramics based on structure and properties that relate to clinical selection. After reading this article, the reader should be able to: explain the types of ceramics in use in dentistry; understand clinical selection based on properties; and discuss the differences in zirconia-based ceramics.

Sol-gel preparation of ZrO2-Li2Si2O5 ceramics and their sintering properties

Despite zirconia (ZrO₂) ceramics and lithium disilicate (Li₂Si₂O₅) glass-ceramics have been widely applied on the market for dental restorations, composites that can combine the advantages of both are still demanded. Here we introduced a ZrO₂-Li₂Si₂O₅ ceramic with minimized glass phases that fabricated through a sol-gel method and subsequent pressureless sintering. ZrO₂-Li₂Si₂O₅ powders were obtained after the gel precursors were heat treated under 800 °C. The gel-derived powders were molded and pressureless sintered under 900-1000 °C to investigate their sintering properties. From the microstructures of the sintered samples, we knew that the densification process was dominated by the growth of Li₂Si₂O₅ grains instead of the growth of ZrO₂ grains. Increasing in Li₂Si₂O₅ content can promote ceramic densification. Interestingly, reactions between ZrO₂ and Li₂Si₂O₅ were observed with sintering temperature higher than 916 °C, which can increase the porosity of the ceramics. Therefore, both the content of Li₂Si₂O₅ and sintering temperature should be well adjusted to achieve samples with desired properties. Finally, ceramics with flexural strength of 226 MPa and porosity of 0.4% were achieved from powders with moderate Li₂Si₂O₅ content after sintering at 1000 °C.

Marginal and internal adaptation of lithium disilicate partial restorations: A systematic review and meta-analysis

Aim:

The aim of this meta analysis was to evaluate the influence of the processing method on the marginal and internal gaps of lithium disilicate inlays/onlays.

Settings and Design:

A systematic literature review was conducted using the PubMed/Medline, Embase, Scopus, and Cochrane Library databases. This review was registered on the PROSPERO platform.

Materials and Methods:

The studies were selected according to the marginal and internal gaps of two different fabrication methods for lithium disilicate (milled and pressed).

Statistical Analysis Used:

The meta analysis was performed based on the Mantel–Haenszel and inverse variance methods, using the random effects model and a 95% confidence interval.

Results:

From all databases, 127 studies were identified. Four in vitro studies were included in the qualitative analysis and three in the meta analysis. Moreover, 197 restorations were evaluated (103 pressed and 94 milled). During the evaluation of only the internal gap, there was a statistically significant difference favoring the pressed technique (P = 0.002). There was no statistically significant difference in the analyses of the marginal gap (P = 0.530) and the total gap (P = 0.450).

Conclusion:

Both the techniques provided acceptable marginal and total gaps, although the pressed technique revealed a more favorable internal adaptation than the milled onlays/inlays.

Er,Cr:YSGG Laser in the Debonding of Feldspathic Porcelain Veneers: An In Vitro Study of Two Different Fluences

Background: New applications in laser technology in aesthetic restorative dentistry merit further research. This study compares the debonding strength and failure mode of feldspathic ceramic veneers using either Er,Cr:YSGG (erbium,chromium:ytrrium-scandium-gallium-garnet) laser at two levels of fluency or no laser (control group). Methods: An in vitro comparative study was carried out using bovine teeth that were randomly distributed into 3 groups of 21 specimens each: (a) experimental group 1 (EG1): irradiated with Er,Cr:YSGG (Waterlase iPlus®; Biolase, Irvine) at an energy density per pulse of 4 J/cm2, using a handpiece (Turbo; Biolase) with a sapphire tip (MX7) and applying the beam perpendicular to the specimen at a distance of 4 mm for 60 sec; (b) experimental group 2 (EG2): irradiated as in EG1, but at 2.7 J/cm2; and (c) control group (CG): debonding without laser irradiation. Results: The stress required for veneer debonding was 8.19 MPa in CG, 0.91 MPa in EG1, and 0.48 MPa in EG2. The difference between the control and both experimental groups was statistically significant (p < 0.001). The percentages of adhesive failure were 40%, 61.9%, and 96%, respectively. Conclusions: Using the Er,Cr:YSGG laser at 4 or 2.7 J/cm2 requires significantly less force to debond ceramic veneers. The percentage of adhesive failures in the two experimental protocols was higher than in the control group. Application of the Er,Cr:YSGG laser using the parameters in this study may be useful in removing feldspathic ceramic veneers, avoiding damaging them and protecting the enamel.

In-vitro polishing of CAD/CAM ceramic restorations: An evaluation with SEM and confocal profilometry

AIM

The objective of this In-vitro investigation was to analyze and compare the surface after polishing of 63 all-ceramic restorations fabricated out of monolithic zirconium dioxide (ZIR), lithium disilicate (LS) or feldspathic ceramic (FC) under standardized laboratory conditions with different protocols. The primary outcome was defined as the roughness (R_a/S_a) of different ceramic surfaces after distinctive polishing procedures.

MATERIAL AND METHODS

The study set-up consisted of three main groups: ZIR, LS, FC (20 crowns each), every group divided into two sub-groups (10 crowns each) depending on the polishing method. The untouched glazed surface of one crown per material served as a control. Every crown displayed a defined supra-contact at the palatal cusp which was removed with a fine grain (38-45 μm) diamond bur. Surface polishing was carried out with either a two-step system (one kit for zirconium dioxide (ZIR₂), another kit for lithium disilicate (LS₂) and feldspatic ceramic (FC₂)), or a three-step system (ZIR₃, LS₃, FC₃) under standardized conditions. Roughness parameters (R_a and S_a) were measured by means of confocal profilometry. Specimens were also visually inspected with scanning electron microscopy (SEM). Statistical analyses were performed using SPSS Statistics software.

RESULTS

Visual examination of the specimens using SEM showed several inhomogeneities on the glazed surface of the control samples, i.e. pores and particles. On every test sample, the grinding curves of the diamond bur were still recognizable. Polishing revealed similar median R_a 0.491 μm (ZIR₂) and 0.434 μm (LS₂) after two-step polishing (p = 0.754), and 0.311 μm (ZIR₃) and 0.208 μm (LS₃) after three-step polishing (p = 0.917). Surface roughness in group FC measured 0.889 μm (FC₂) after the two-step polishing process and 0.903 μm (FC₃) following three-step surface refinement. No significant difference was detectable between surface roughness of glazed controls compared to either polished surfaces with two-step or three-step treatment within one material. ZIR and LS presented significantly lower median roughness R_a after two-step and three-step procedures than test samples of FC, measured subsequent to either of the polishing methods (p = 0.016, p = 0.009).

CONCLUSION

The surface roughness of ZIR, LS and FC crowns after the use of chairside polishing kits was comparable with the roughness measured before occlusal adjustment. A two-step procedure showed as good results as a three-step process. A smoother surface was obtained for ZIR and LS compared to FC with both polishing protocols.

The impact of restorative material and ceramic thickness on CAD\CAM endocrowns

Background

Endocrown restorations as a conservative approach to restore endodontically treated teeth still need in vitro investigation under fatigue and made in different materials. This study evaluated the effect of restorative material and restoration thickness on the maximum fracture load of endocrowns subjected to cyclic loading.

Material and Methods

Sixty (60) third molar teeth received an endocrown preparation with three different heights of remaining dental tissue (1.5, 3.0 or 4.5 mm). A leucite-based ceramic (LEU) and a lithium disilicate (LD) based ceramic were selected to manufacture the CAD/CAM endocrown restorations, totaling 6 groups (n=10). The specimens were subjected to fatigue loading (200N, 2 x 106 cycles, water) and then to the single load to failure test (1 mm/min crosshead speed). Data were analyzed by using two-way ANOVA and Tukey tests (p< 0.05).

Results

All endocrowns survived the fatigue test. The thickness did not influence the restoration’s fracture load (p=0.548) instead the restorative material (p=0.003). LD showed higher mean values (1714.43 N)A than LEU (1313.47 N)B.

Conclusions

Endocrowns manufactured with CAD/CAM lithium disilicate blocks showed superior fracture load than the leucite-based blocks after mechanical fatigue. Nevertheless, both materials presented acceptable survival and fracture load as long as the material’s minimum thickness and the enamel adhesion are respected.

Key words:Endocrown, CAD/CAM, Endodontically treated teeth, Failure load, Minimal intervention dentistry.

Evaluation of fracture strength for single crowns made of the different types of lithium disilicate glass-ceramics

Lithium disilicate glass-ceramics with high mechanical strength are being widely used as ingots for heat-pressing technique and blocks for CAD/CAM processing in clinical dentistry as aesthetic prosthetic materials. The purpose of this study was to evaluate the fracture strength of single crowns made of the different types of lithium disilicate glass-ceramics. Single crowns for mandibular second premolar with thickness of 1.5 mm were manufactured. IPS e.max Press and Amber Press crowns were produced by heat-pressing, and IPS e.max CAD and Rosetta SM crowns was produced by milling. Amber Lisi-POZ crown was produced by heat-pressing on the zirconia frame. Fracture strength test was performed at 10 degrees of inclination toward the load after bonding crown on metal abutment using dual-curing resin cement. Statistical analysis of fracture strength was conducted through Weibull statistics (n = 15 per group). The mean fracture strength (2087.4 N) of Amber Lisi-POZ group produced by heat-pressing on the zirconia frame was significantly higher than that (1479.8 N) of Rosetta SM group produced by milling. Weibull coefficients for IPS e.max CAD and Rosetta SM groups were, respectively, 14.44 and 9.39, and those for IPS e.max Press, Amber Press, and Amber Lisi-POZ groups produced by heat-pressing were in the range between 4.72 and 5.16. In conclusion, the fracture strength of Amber Lisi-POZ crown with zirconia framework was the highest, and the buccal cusps fractured from the central groove of the all crowns. Weibull modulus of crowns produced by milling was higher than those of crowns produced by heat-pressing.

Evaluation of Wear Resistance of Dental Chairside CAD/CAM Glass Ceramics Reinforced by Different Crystalline Phases

The mechanical properties of crystalline phase of glass ceramics are critical. This study aimed to evaluate wear resistance of different crystalline-reinforced dental chairside computer-aided design/computer-aided manufacturing (CAD/CAM) glass ceramics. Materials of feldspar (Vita Mark II, VM), leucite (IPS Empress CAD, EC), lithium disilicate (IPS e.max CAD, EX), lithium disilicate enriched with zirconia (Vita Suprinity, VS), and enamel were embedded, grounded, and polished, respectively. Samples were indented with a Vickers hardness tester to test the fracture resistance (KIC). Two-body wear tests were performed in a reciprocal ball-on-flat configuration under artificial saliva. The parameters of load force (50 N), reciprocating amplitude (500 μm), frequency (2 Hz), and the test cycle (10,000 cycles) were selected. Specimen microstructure, indentation morphology, and wear scars were observed by scanning electron microscope (SEM), optical microscopy, and three-dimensional profile microscopy. EX, VS, and EC demonstrated significantly higher KIC values than the enamel, while ceramic materials showed smaller wear depth results. Cracks, massive delamination, and shallow plow were seen on the enamel worn scar. Long deep plow, delamination, and brittle cracks are more common for VM and EC, and short shallow plow and smooth subsurface are the characteristics of EX and VS. Greater fracture toughness values indicated higher wear resistances of the materials for the test glass ceramics. The CAD/CAM glass ceramics performed greater wear resistance than enamel. Feldspar- and leucite-reinforced glass ceramics illustrated better wear resistance similar to enamel than lithium disilicate glass ceramics, providing amicable matching with the opposite teeth.

Microstructural development during heat treatment of a commercially available dental-grade lithium disilicate glass-ceramic

OBJECTIVE

To elucidate the microstructural evolution of a commercial dental-grade lithium disilicate glass-ceramic using a wide battery of in-situ and ex-situ characterization techniques.

METHODS

In-situ X-ray thermo-diffractometry experiments were conducted on a commercially available dental-grade lithium disilicate glass-ceramic under both non-isothermal and isothermal heat treatments in air. These analyses were complemented by experiments of ex-situ X-ray diffractometry, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, differential scanning calorimetry, and field-emission scanning electron thermo-microscopy.

RESULTS

It was found that the non-fired blue block consists of ∼40 vol % crystals embedded in a glass matrix. The crystals are mainly lithium metasilicate (Li₂SiO₃) along with small amounts of lithium orthophosphate (Li₃PO₄) and lithium disilicate (Li₂Si₂O₅). Upon heating, the glassy matrix in the as-received block first crystallizes partially as SiO₂ (i.e., cristobalite) at ∼660 °C. Then, the SiO₂ crystals react with the original Li₂SiO₃ crystals at ∼735 °C, forming the desired Li₂Si₂O₅ crystals by a solid-state reaction in equimolar concentration (SiO₂ + Li₂SiO₃ → Li₂Si₂O₅). Precipitation of added colourant Ce ions in the form of CeO₂ appears at ∼775 °C. These events result in a glass-ceramic material with the aesthetic quality and mechanical integrity required for dental restorations. It also has a microstructure consisting essentially of elongated Li₂Si₂O₅ grains in a glassy matrix plus small cubic CeO₂ grains at the outermost part of the surface.

SIGNIFICANCE

It was found that by judiciously controlling the heat treatment parameters, it is possible to tailor the microstructure of the resulting glass-ceramics and thus optimizing their performance and lifespan as dental restorations.

Retrospective clinical evaluation of ceramic onlays placed by dental students

STATEMENT OF PROBLEM

Indirect restorations with partial or complete occlusal surface coverage have been recommended to restore teeth with weakened walls in order to prevent cusp fracture. The success of these restorations when performed by dental students is unknown.

PURPOSE

The purpose of this retrospective study was to evaluate the clinical performance of adhesively bonded ceramic onlay restorations placed by third- and fourth-year dental students.

MATERIAL AND METHODS

Sixty-five ceramic onlays were placed in patients between 2009 and 2015. The onlays were laboratory or chairside fabricated with a computer-aided design and computer-aided manufacturing (CAD-CAM) system, using either IPS e.max Press or IPS e.max CAD. An adhesive technique and luting composite resin agent were used to cement the restorations. Thirty-seven onlays were evaluated clinically using the modified United States Public Health Service (USPHS) criteria. Data were statistically analyzed using the Cox proportional hazards model to compare tooth type and failures and the Fisher exact and McNemar tests to compare the USPHS criteria for significant differences (α=.05). Survival probability was calculated using the Kaplan-Meier algorithm.

RESULTS

Five onlays were considered to be failures and needed replacement. According to the Kaplan-Meier analysis, the estimated survival rate was 96.3% after 2 years and 91.5% at 4 years. All 5 of the failures occurred on molars (13.5%) and none on premolars (P=.025). A statistically significant difference was found for marginal discoloration between onlays placed within 0 to 3 years and 3 to 6 years (P<.05) but no differences between any other criteria.

CONCLUSIONS

Ceramic onlays placed by dental students demonstrated acceptable long-term clinical performance.

Dental ceramics: a review of new materials and processing methods

The evolution of computerized systems for the production of dental restorations associated to the development of novel microstructures for ceramic materials has caused an important change in the clinical workflow for dentists and technicians, as well as in the treatment options offered to patients. New microstructures have also been developed by the industry in order to offer ceramic and composite materials with optimized properties, i.e., good mechanical properties, appropriate wear behavior and acceptable aesthetic characteristics. The objective of this literature review is to discuss the main advantages and disadvantages of the new ceramic systems and processing methods. The manuscript is divided in five parts: I) monolithic zirconia restorations; II) multilayered dental prostheses; III) new glass-ceramics; IV) polymer infiltrated ceramics; and V) novel processing technologies. Dental ceramics and processing technologies have evolved significantly in the past ten years, with most of the evolution being related to new microstructures and CAD-CAM methods. In addition, a trend towards the use of monolithic restorations has changed the way clinicians produce all-ceramic dental prostheses, since the more aesthetic multilayered restorations unfortunately are more prone to chipping or delamination. Composite materials processed via CAD-CAM have become an interesting option, as they have intermediate properties between ceramics and polymers and are more easily milled and polished.

Bioactive-glass ceramic with two crystalline phases (BioS-2P) for bone tissue engineering

We aimed to evaluate the in vitro osteogenic and osteoinductive potentials of BioS-2P and its ability to promote in vivo bone repair. To investigate osteogenic potential, UMR-106 osteoblastic cells were cultured on BioS-2P and Bioglass 45S5 discs in osteogenic medium. The osteoinductive potential was evaluated using mesenchymal stem cells (MSCs) cultured on BioS-2P, Bioglass 45S5 and polystyrene in non-osteogenic medium. Rat bone calvarial defects were implanted with BioS-2P scaffolds alone or seeded with MSCs. UMR-106 proliferation was similar for both materials, while alkaline phosphatase (ALP) activity and mineralization were higher for BioS-2P. Bone sialoprotein (BSP), RUNX2 and osteopontin (OPN) gene expression and BSP, OPN, ALP and RUNX2 protein expression were higher on BioS-2P. For MSCs, ALP activity was higher on Bioglass 45S5 than on BioS-2P and was lower on polystyrene. All genes were highly expressed on bioactive glasses compared to polystyrene. BioS-2P scaffolds promoted in vivo bone formation without differences in the morphometric parameters at 4, 8 and 12 weeks. After 8 weeks, the combination of BioS-2P with MSCs did not increase the quantity of new bone compared to the BioS-2P alone. To stimulate osteoblast activity, drive MSC differentiation and promote bone formation, BioS-2P is a good choice as a scaffold for bone tissue engineering.

Fracture, roughness and phase transformation in CAD/CAM milling and subsequent surface treatments of lithium metasilicate/disilicate glass-ceramics

This paper studied surface fracture, roughness and morphology, phase transformations, and material removal mechanisms of lithium metasilicate/disilicate glass ceramics (LMGC/LDGC) in CAD/CAM-milling and subsequent surface treatments. LMGC (IPS e.max CAD) blocks were milled using a chairside dental CAD/CAM milling unit and then treated in sintering, polishing and glazing processes. X-ray diffraction was performed on all processed surfaces. Scanning electron microscopy (SEM) was applied to analyse surface fracture and morphology. Surface roughness was quantitatively characterized by the arithmetic average surface roughness R_a and the maximum roughness R_z using desktop SEM-assisted morphology analytical software. The CAD/CAM milling induced extensive brittle cracks and crystal pulverization on LMGC surfaces, which indicate that the dominant removal mechanism was the fracture mode. Polishing and sintering of the milled LMGC lowered the surface roughness (ANOVA, p < 0.05), respectively, while sintering also fully transformed the weak LMGC to the strong LDGC. However, polishing and glazing of LDGC did not significantly improve the roughness (ANOVA, p > 0.05). In comparison of all applied fabrication process routes, it is found that CAD/CAM milling followed by polishing and sintering produced the smoothest surface with R_a = 0.12 ± 0.08µm and R_z = 0.89 ± 0.26µm. Thus_, it is proposed as the optimized process route for LMGC/LDGC in dental restorations. This route enables to manufacture LMGC/LDGC restorations with cost effectiveness, time efficiency, and improved surface quality for better occlusal functions and reduced bacterial plaque accumulation.

Changes in actin and tubulin expression in osteogenic cells cultured on bioactive glass-based surfaces

The present study evaluated whether the changes in the labeling pattern of cytoskeletal proteins in osteogenic cells cultured on bioactive glass-based materials are due to altered mRNA and protein levels. Primary rat-derived osteogenic cells were plated on Bioglass® 45S5, Biosilicate®, and borosilicate (bioinert control). The following parameters were assayed: (i) qualitative epifluorescence analysis of actin and tubulin; (ii) quantitative mRNA and protein expression for actin and tubulin by real-time PCR and ELISA, respectively, and (iii) qualitative analysis of cell morphology by scanning electron microscopy (SEM). At days 3 and 7, the cells grown on borosilicate showed typical actin and tubulin labeling patterns, whereas those on the bioactive materials showed roundish areas devoid of fluorescence signals. The cultures grown on bioactive materials showed significant changes in actin and tubulin mRNA expression that were not reflected in the corresponding protein levels. A positive correlation between the mRNA and protein as well as an association between epifluorescence imaging and quantitative data were only detected for the borosilicate. SEM imaging of the cultures on the bioactive surfaces revealed cells partly or totally coated with material aggregates, whose characteristics resembled the substrate topography. The culturing of osteogenic cells on Bioglass® 45S5 and Biosilicate® affect actin and tubulin mRNA expression but not the corresponding protein levels. Changes in the labeling pattern of these proteins should then be attributed, at least in part, to the presence of a physical barrier on the cell surface as a result of the material surface reactions, thus limiting fluorescence signals.

Impact Behavior of Three Notched All-Ceramic Restorations after Soaking in Artificial Saliva

Biomechanics play a critical role in influencing the clinical applications of all-ceramic dental restorations. The restorative biomaterials have to demonstrate mechanical durability in the oral environment because they are always exposed to a variety of oral environments. This study was designed to evaluate the effect of soaking time, notch and saliva pH values on the impact energy of three commonly used all-ceramic materials for CAD/CAM. The leucite-reinforced glass ceramic (ProCAD), lithium disilicate glass ceramic (IPS e.max CAD) and zirconia-based ceramic materials (IPS e.max ZirCAD) were used. The experimental results indicated that the impact energy of ProCAD decreased with an increase in soaking time, but not for IPS e.max CAD and IPS e.max ZirCAD. The impact energy of the zirconia system was higher than leucite-reinforced and lithium disilicate-based ceramic systems. When subjected to preformed 0.5 mm U-shape notch on the bar specimen of 3 mm thick, the impact energy of the all-ceramic restorations revealed a markedly reduction of about 80%–90%, almost irrespective of dental compositions, which indicated the effect of flaw to a great degree. No statistically significant influence (p > 0.05) of pH values (4, 7 and 9) on impact energy was found for each group. It is concluded that the no matter which all-ceramic materials were used, it was appreciably sensitive to the presence of notches. The ceramic composition and microstructure have been shown to affect mechanical durability.

Effect of heat-pressing temperature and holding time on the microstructure and flexural strength of lithium disilicate glass-ceramics

The present study aimed to evaluate the influence of various heat-pressing procedures (different holding time and heat pressing temperature) on the microstructure and flexural strength of lithium disilicate glass ceramic. An experimental lithium silicate glass ceramic (ELDC) was prepared from the SiO2-Li2O-K2O-Al2O3-ZrO2-P2O5 system and heat-pressed following different procedures by varying temperature and holding time. The flexural strength was tested and microstructure was analyzed. The relationships between the microstructure, mechanical properties and heat-pressing procedures were discussed in-depth. Results verified the feasibility of the application of dental heat-pressing technique in processing the experimental lithium disilicate glass ceramic. Different heat-pressing procedures showed significant influence on microstructure and flexural strength. ELDC heat-pressed at 950℃ with holding time of 15 min achieved an almost pore-free microstructure and the highest flexural strength, which was suitable for dental restorative application.

Wear behavior of pressable lithium disilicate glass ceramic

This article reports effects of surface preparation and contact loads on abrasive wear properties of highly aesthetic and high-strength pressable lithium disilicate glass-ceramics (LDGC). Abrasive wear testing was performed using a pin-on-disk device in which LDGC disks prepared with different surface finishes were against alumina pins at different contact loads. Coefficients of friction and wear volumes were measured as functions of initial surface finishes and contact loads. Wear-induced surface morphology changes in both LDGC disks and alumina pins were characterized using three-dimensional laser scanning microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The results show that initial surface finishes of LDGC specimens and contact loads significantly affected the friction coefficients, wear volumes and wear-induced surface roughness changes of the material. Both wear volumes and friction coefficients of LDGC increased as the load increased while surface roughness effects were complicated. For rough LDGC surfaces, three-body wear was dominant while for fine LDGC surfaces, two-body abrasive wear played a key role. Delamination, plastic deformation, and brittle fracture were observed on worn LDGC surfaces. The adhesion of LDGC matrix materials to alumina pins was also discovered. This research has advanced our understanding of the abrasive wear behavior of LDGC and will provide guidelines for better utilization and preparation of the material for long-term success in dental restorations. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 968-978, 2016.

Fatigue of dental ceramics

OBJECTIVES

Clinical data on survival rates reveal that all-ceramic dental prostheses are susceptible to fracture from repetitive occlusal loading. The objective of this review is to examine the underlying mechanisms of fatigue in current and future dental ceramics.

DATA/SOURCES

The nature of various fatigue modes is elucidated using fracture test data on ceramic layer specimens from the dental and biomechanics literature.

CONCLUSIONS

Failure modes can change over a lifetime, depending on restoration geometry, loading conditions and material properties. Modes that operate in single-cycle loading may be dominated by alternative modes in multi-cycle loading. While post-mortem examination of failed prostheses can determine the sources of certain fractures, the evolution of these fractures en route to failure remains poorly understood. Whereas it is commonly held that loss of load-bearing capacity of dental ceramics in repetitive loading is attributable to chemically assisted 'slow crack growth' in the presence of water, we demonstrate the existence of more deleterious fatigue mechanisms, mechanical rather than chemical in nature. Neglecting to account for mechanical fatigue can lead to gross overestimates in predicted survival rates.

CLINICAL SIGNIFICANCE

Strategies for prolonging the clinical lifetimes of ceramic restorations are proposed based on a crack-containment philosophy.

Saliva and tongue coating pH before and after use of mouthwashes and relationship with parameters of halitosis

OBJECTIVES

The aim of this work was to evaluate saliva and tongue coating pH in oral healthy patients with morning bad breath before and after use of different oral mouthrinses.

MATERIAL AND METHODS

Saliva and tongue coating pH of 50 patients allocated in 5 groups were measured respectively by a digital pHmeter and color pH indicators, before, immediately after and 30 min after rinsing 5 different mouthrinses: cetilpiridine chloride associated with sodium chloride, triclosan, enzymatic solution, essential oil and distilled water.

RESULTS

Only triclosan and essential oil increased salivary pH immediately after rising. The enzymatic solution decreased salivary and tongue coating pH immediately after rinsing.

CONCLUSIONS

Salivary pH tended to be acidic while tongue coating pH tended to be alkaline, even after rising. Triclosan and essential oil mouthrinses increased salivary pH immediately after rinsing. Enzymatic solution decreased saliva and tongue coating pH immediately after rising.

Flexural strength of fluorapatite-leucite and fluorapatite porcelains exposed to erosive agents in cyclic immersion

Objective

The aim of this study was to evaluate the flexural strength of two porcelain materials (IPS d.SIGN and IPS e.max Ceram) exposed to erosive agents

Material and Methods

One hundred and twenty bar-shaped specimens were made from each of fluorapatite-leucite porcelain (IPS d.SIGN) and fluorapatite porcelain (IPS e.max Ceram) and divided into 8 groups of 15 specimens each. Six groups were alternately immersed in the following storage agents for 30 min: deionized water (control), citrate buffer solution, pineapple juice, green mango juice, cola soft drink and 4% acetic acid. Then, they were immersed for 5 min in deionized water at 37°C. Seven cycles were completed, totalizing 245 min. A 7^th group was continuously immersed in 4% acetic acid at 80°C for 16 h. The final, 8^th, group was stored dry at 37°C for 245 min. Three-point bending tests were performed in a universal testing machine. The data were analyzed statistically by 2-way ANOVA, Tukey’s HSD test and t-test at significance level of 0.05.

Results

The flexural strengths of all groups of each porcelain after exposure to erosive agents in cyclic immersion did not differ significantly (p>0.05). For both types of porcelain, dry storage at 37°C yielded the highest flexural strength, though without significant difference from the other groups (p>0.05). The flexural strengths of all groups of fluorapatite porcelains were significantly higher (p<0.05) than those of the fluorapatite-leucite porcelains.

Conclusions

This study demonstrated that the erosive agents evaluated did not affect the flexural strength of the tested dental porcelains.

Synthesis of novel tricalcium phosphate-bioactive glass composite and functionalization with rhBMP-2

A functionalization is required for calcium phosphate-based bone substitute materials to achieve an entire bone remodeling. In this study it was hypothesized that a tailored composite of tricalcium phosphate and a bioactive glass can be loaded sufficiently with rhBMP-2 for functionalization. A composite of 40 wt% tricalcium phosphate and 60 wt% bioactive glass resulted in two crystalline phases, wollastonite and rhenanite after sintering. SEM analysis of the composite's surface revealed a spongious bone-like morphology after treatment with different acids. RhBMP-2 was immobilized non-covalently by treating with chrome sulfuric acid (CSA) and 3-aminopropyltriethoxysilane (APS) and covalently by treating with CSA/APS, and additionally with 1,1'-carbonyldiimidazole. It was proved that samples containing non-covalently immobilized rhBMP-2 on the surface exhibit significant biological activity in contrast to the samples with covalently bound protein on the surface. We conclude that a tailored composite of tricalcium phosphate and bioactive glass can be loaded sufficiently with BMP-2.

Comparison of MTT assay, flow cytometry, and RT-PCR in the evaluation of cytotoxicity of five prosthodontic materials

In the present study, the cytotoxic effects of five prosthodontic materials on the L929 cell line were assessed by flow cytometry (FCM), reverse transcription PCR (RT-PCR), and MTT (3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazoli-umbromide) assay. The cells were treated with eluates resin (RE), pressable ceramics (PC), Co-Cr alloy-porcelain (CC), Ni-Cr alloy-porcelain (NC), and diatomite ceramics (DC). The cytotoxicity of all the materials tested by the MTT assay was grade 1. By FCM analysis, apoptosis rates of DC and PC were low, with no significant difference from the control (p > 0.05). The rest of the groups induced much higher apoptosis rates (p < 0.05), with the highest in the RE group. The necrotic cell levels of RE was also significantly increased (p < 0.05). Bcl-2 and Bax mRNA expression were determined by RT-PCR, and the Bax/Bcl-2 ratio in the DC and PC groups were not significantly different from the control (p > 0.05), whereas CC, NC, and RE groups showed significant differences (p < 0.05). Taken together, the results suggest that FCM and RT-PCR analyses can supplement the traditional MTT assay in evaluating the cytotoxicity of prosthodontic materials for selecting highly biocompatible materials.

Novel glass-ceramics for dental restorations

BACKGROUND

There are many different ceramic systems available on the market for dental restorations. Glass-ceramics are a popular choice due to their excellent esthetics and ability to bond to tooth structure allowing a more conservative approach. However, at present, these materials have insufficient strength to be used reliably in posterior regions of the mouth.

PURPOSE

The aim of this review article is to discuss the types of novel glass-ceramic currently be investigated including composition, microstructure and properties.

CONCLUSION

Current research in glass-ceramics focuses on the quest for a highly esthetic material along with sufficient strength to enable crowns and bridgework to be reliably placed in these areas.

CLINICAL SIGNIFICANCE

There is a gap in the market for a machinable resin bonded glass-ceramic with sufficient strength as well as excellent esthetics.

Ceramics as biomaterials for dental restoration

Sintered ceramics and glass-ceramics are widely used as biomaterials for dental restoration, especially as dental inlays, onlays, veneers, crowns or bridges. Biomaterials were developed either to veneer metal frameworks or to produce metal-free dental restorations. Different types of glass-ceramics and ceramics are available and necessary today to fulfill customers' needs (patients, dentists and dental technicians) regarding the properties of the biomaterials and the processing of the products. All of these different types of biomaterials already cover the entire range of indications of dental restorations. Today, patients are increasingly interested in metal-free restoration. Glass-ceramics are particularly suitable for fabricating inlays, crowns and small bridges, as these materials achieve very strong, esthetic results. High-strength ceramics are preferred in situations where the material is exposed to high masticatory forces.

In vitro cytotoxic response to lithium disilicate dental ceramics

OBJECTIVES

The use of lithium disilicate dental ceramics is increasing in dentistry and previous reports have suggested that they may have greater biological risks than previously thought. We tested a hypothesis that composition and processing influence the biological properties of these ceramics.

METHODS

The cytotoxicity of two machined and three pressed lithium disilicate materials (n=6) were tested in vitro using mouse fibroblasts in direct contact with the materials for 72h. Cellular response was estimated by mitochondrial succinate dehydrogenase activity (MTT method). Mitochondrial activity was expressed as a percentage of Teflon controls, then compared to Teflon using 2-sided t-tests (alpha=0.05). Polished materials were aged in artificial saliva and tested for cytotoxicity periodically over 6 weeks, then were repolished (320grit SiC paper), aged and tested again for 4 weeks.

RESULTS

All materials significantly (50-70%) suppressed cellular mitochondrial activity in the initial week, but suppression decreased by 25-30% over the next 2 weeks. In weeks 4 and 6 some materials exhibited a cytotoxic 'relapse' of 10-20%. The cytotoxic response was no different for machined or pressed materials, but the presence of ZnO had at least an association with longer-term cytotoxicity and relapse. Repolishing to 320grit did not increase cytotoxicity significantly.

SIGNIFICANCE

Our results suggest that lithium disilicates are not biologically inert, and that many have a similar cytotoxicity dynamic regardless of small differences in composition or processing.