Dental Glass Research Articles

Effect of Thermal Mismatch on Fracture Characteristics of Porcelain Veneered Lithia-Based Disilicate Posterior Ceramic Crown

(1) Background: Dental glass–ceramics shrink during crystallization, complicating restoration manufacturing. Thermo-pressure molding was introduced to address this, with lithium disilicate crystals providing high strength. Residual tensile stresses can influence the chipping strength of single tooth crowns. (2) Methods: Insync dentine was layered onto three lithia-based disilicate core ceramics (Amber Press, IPS e.max Press) for microtensile bond strength tests. The Vickers test assessed the residual tensile stress and interfacial bonding. Porcelain-veneered posterior ceramic crowns were fabricated and subjected to axial loading, measuring fracture loads (three per group). (3) Results: A chemical bonding layer formed at the interface, which was thicker in the Insync-IPS e.max Press and increased with more firings. The ultimate tensile bond strength was 28.5 MPa for the four-times-fired Insync-Amber Press, similar to the twice-fired Insync-IPS e.max Press. No residual tensile stress was found in the Insync-Amber Press; the Insync-IPS e.max Press showed crack growth within 250 μm of the bonded interface. The average fracture resistance was twice as high for the Insync-Amber Press. (4) Conclusions: The Insync-Amber Press exhibited better thermal harmony with no crack growth, while the IPS e.max Press showed crack growth due to residual tensile stress. Insync-Amber Press posterior ceramic crowns had significantly greater fracture resistance than Insync-IPS e.max Press crowns.

Applications of bioactive glass: A review

The scope of research on dental materials has significantly increased throughout the last century. Bioactive glass has become an attractive option in biomaterials because of its unique qualities that promote advantageous biological responses. Compared to traditional dental glasses, bioactive glasses are innovative dental materials. As bioactive glass can form bonds with live tissues, mainly composed of calcium, phosphorus, and silicon, it is an excellent choice for many biomedical uses. At the vanguard of biomaterials, bioactive glass provides a unique blend of bioactivity, flexibility, and versatility. The bioactivity of bioactive glass is one of its primary characteristics. Bioactive glass generates a hydroxyapatite coating on its surface when it comes into contact with physiological fluids. The potential for introducing growth factors and bioactive substances to enhance the material's capacity to communicate with biological tissues has been studied. Various uses of bioactive glass have been discovered, including wound healing, bone grafts, dentin hypersensitivity, regeneration, implant devices, etc. Cement was used for dental applications, and the attachment of joint prostheses to bone was also made using bioactive glass. Bioactive glasses are present in the composition of several dental and oral hygiene products. Because of their many benefits—such as their capacity to maintain biological tissues' structural integrity, their usefulness as scaffolds, and their capacity to inhibit bacterial growth—bioactive glasses are becoming increasingly valuable in several dental specialties.

MODIFICATION OF GLASS IONOMER FILLING MATERIAL BY METAL NANOPARTICLES AND THEIR COMPOUNDS: EFFECT ON ANTI-MICROBIAL ACTIVITY

Background: Glass ionomer filling materials are widely used in stomatology, but do not have an antimicrobial effect that effectively prevents the development of secondary and recurrent dental caries. Researchers are attempting to modify these materials by introducing various biologically active additives into them. The aim of the study was to evaluate the antimicrobial properties of a dental ionomer filling material modified withadditives based on high–energy nanoparticles of silver, copper, titanium and their compounds. Material and methods: Colloidal aqueous and alcoholic solutions of metals and their oxides with stabilizers were obtained by the electroerosion method. Citric acid, cetylpyridinium chloride and Trilon B were used as stabilizers. The zeta potential and the distribution of particles of the dispersed phase in solutions were measured. Samples of dental glass ionomer cement "Cemion-Aqua" were impregnated with colloidal solutions of nanoparticles. The microbiological activity of glass ionomer fillings samples in relation to plaque was determined by disc diffusion and suspension methods. Results: The results showed that modification of glass ionomer cement samples with silver hydrosols in citric acid solutions with concentrations of 0.04% and 0.0025% increases the zone of radial lysis of microbial plaque colonies around the cement samples by 1.5 and 2.5 times compared with the control. By the suspension method, it was determined that silver hydrosols in a solution of citric acid and without it reduce the formation of colonies of microorganisms to several units up to 72 hours of exposure compared with the control. And copper hydrosols in solutions of cetylpyridinium chloride prevent an increase in the number of colonies of microorganisms after 24 hours of exposure compared with the control. Silver hydrosol in a solution of citric acid with a concentration of 0.0025% and silver alcohol sol reduce the number of colonies of microorganisms to several units after 3 hours of exposure.

An overview of dental glass–ceramics: From material design to the manufacturing process

AbstractAs a subserie of the dental ceramic material family, glass–ceramics are favored for their excellent aesthetic properties. The feasibility of current commercially available dental glass–ceramics applications has been proven, while the assurance and development of more functional properties for them are still being explored. Effective utilization of various modification mechanisms by adjusting the chemical composition and microstructure is essential to improve the mechanical properties, aesthetic properties, and other properties such as biocompatibility of dental restorative materials. Among them, the mechanical properties of restorations should take into account the mechanical properties of glass ceramics and the final restoration (restoration and tooth set) in the mechanical behavior. This paper provides an overview of the chemical composition design, classification of microstructure, property requirements, and strengthening methods applied to dental glass–ceramics, including ion exchange, chain effects, heat treatment modulation, and strengthening mechanisms. In addition, research on traditional hot pressing, subtractive manufacturing, and newly developed additive manufacturing in glass–ceramics are systematically presented. Finally, the tendency of dental glass–ceramics was forecasted by analyzing the relationship between glass–ceramic composition, process, and mechanical properties.

BIOCHEMICAL PARAMETERS OF BLOOD OF LABORATORY ANIMALS IN CASE OF PROLONGED CONTACT WITH THE RESEARCH MATERIAL

The purpose of this study was to determine the biochemical parameters of blood of laboratory animals in prolonged contact with the experimental material
 Materials and methods. An experimental study was conducted in the laboratories and vivarium of the State Institution "Institute of Spine and Joint Pathology named after Prof. M.I. Sitenko" on 28 white laboratory rats aged 6 months with a body weight of 200 to 250 grams. The animals were randomly divided into two groups: a control group (14 rats) and an experimental group (14 rats), which were exposed to dental glass ionomer cement at a dose of 1.0 mg/kg. Toxic effects were evaluated for 1 month. The blood sampling procedure included tail vein dilation, disinfection, tail fixation, and blood collection. The study was conducted in special conditions with full feeding.
 Results. The study found no significant negative effects of prolonged use of dental glass ionomer cement (GIC) on kidney function. Analysis of diuresis, urea and creatinine levels in urine and blood serum showed no statistically significant differences between males and females. No sugar, ketones, or protein were detected in the animals' urine. Serum creatinine levels were (65.47±4.6) μmol/l in males and (63.38±7.1) μmol/l in females, while serum urea levels were (4.84±0.47) μmol/l in males and (4.67±0.42) μmol/l in females. Urinary urea levels were (374.35±20.7) mmol/l in males and (371.15±22.3) mmol/l in females.
 Conclusions. The obtained results of the study indicate statistically significant deviations in the studied indicators of the functional state of the kidneys both in males and females after prolonged use of dental glass-inomer cement based on polyacrylate carboxylate. The presence of sugar, ketones and protein was not detected in the urine of the animals. The analysis of serum creatinine levels showed no statistically significant differences between the conditions, and serum urea levels did not differ between them either. Thus, it can be concluded that the use of glass-inomer cement has no negative effect on the functional state of the kidneys in the studied animals.

Effect of inert glass on the physical and mechanical properties of zirconia dental ceramics fabricated by digital light processing

AbstractZirconia dental ceramics incorporated with inert dental glass (IDG) were fabricated by digital light processing (DLP). The effects of the amount of added IDG on the physical properties and microstructure of sintered samples were investigated. Highly dense zirconia dental ceramic samples with a relative density of 98.9% were obtained by adding different amounts of IDG sintered at 1500°C. With the addition of 1 wt% IDG, the Vickers hardness, fracture toughness, and wear resistance increased to 13.03 GPa, 6.33 MPa m1/2, and 0.03 mg/(mm2 min), respectively. However, with the incremental addition of IDG at 3 and 5 wt%, a slight reduction in Vickers hardness, fracture toughness, and wear resistance was observed. The values recorded were 12.68 GPa, 5.90 MPa m1/2, and 0.05 mg/(mm2 min) for the former, and 11.86 GPa, 5.48 MPa m1/2, and 0.06 mg/(mm2 min) for the latter. Scanning electron microscopy observation suggested that 1 wt% IDG incorporated into zirconia dental ceramic samples resulted in an optimal microstructure, with IDG existing at triple junctions of zirconia grains to form a discrete secondary phase. The broken surface revealed transgranular fracture features. This investigation indicates that adding a proper amount of IDG is an effective method to enhance the properties of DLP‐fabricated zirconia dental ceramics.

Effect of Bombyx Mori Silk Fiber Volumetric on Water Sorption of Fiber-reinforced Composite

Background: Dental resin is frequently reinforced with synthetic dental fibers like glass fiber. Dental glass fiber can be challenging to find and costly in Indonesia. Bombyx mori silk fiber is a robust, convenient, and reasonably priced natural fiber substitute. Bombyx mori silk fiber is commonly used in medicinal applications as a post-surgical suture. Aim: The aim of this study was to assess the volumetric effect of Bombyx mori silk fiber on the water sorption of fiber-reinforced composite (FRC). Material and Methods: This study was an experimental laboratory. The materials used in this study were Bombyx mori silk fiber and flowable composite. Four groups of FRC samples were made using volumetric fibers at 0%, 5%, 10%, and 15% (n = 4). The test of water sorption was standardized (ISO 4049). The results were analyzed using one-way ANOVA (p<0.05). Results: The mean of water sorption of Bombyx mori silk fiber FRC for volumetric 0%, 5%, 10%, and 15% were: 0.475±0.030%; 0.681±0.033%; 0.889±0.008%; 1.318±0.039%, respectively. The present study showed that Bombyx mori silk fiber volumetric influenced the water sorption of FRC (p<0.05). Conclusion: The increased Bombyx mori silk fiber volumetric significantly increased the water sorption of FRC. The presence of a small gap caused by the weak interfacial bonds of the dental resin and fiber leads to water penetration.

The impact of non dental glass fiber addition against tensile strength pre-polymerized fiber reinforced composite

Background: Composite resin is one of the most used materials in dentistry because of the simplicity and high aesthetic value. One of the varieties of composite resin is prepolymerized composite resin. Some research show that prepolymerized composite resin has relatively low mechanical strength. Therefore fiber needs to be added in prepolymerized composite resin. The aim of this research is to find out the effect of adding non dental glass fiber into tensile strength fiber reinforced composite. 
 
 Method: This research used true experimental method with post test only control group design, there are two groups, the first one is prepolymerized composite resin with additional non dental glass fiber. The data has been tested with parametric independent T-test.
 
 Result: The result showed the average flexural strength of prepolymerized composite resin without additional non dental glass fiber was 10.6625 Mpa, while the prepolymerized composite resin + non dental glass fiber was also 18.2263 Mpa. Independent T-test showed the p value = 0.000
 
 Conclusion: The conclusion of this research is that prepolymerized resin + non dental glass fiber has higher tensile strength than composite resin without additional non dental glass fiber, thus it can be used as alternative choice applied in dentistry.

Effect of Dental Glass Fiber Posts on Root Stresses and Fracture Behavior of Endodontically Treated Maxillary Central Incisors: A Finite Element Analysis Study.

In this work, the influence of glass fiber posts with different designs on the root stress that had endodontic treatment was examined using the finite element method. Using two distinct materials (metal and glass fiber) and two different prototypes (tapered and parallel-sided), four three-dimensional (3D) finite element models of an upper central incisor were made and studied. Each 3D model received an oblique loading of 100 N. All forces were dispatched as distributed pressure to the aforementioned region. There were no considerations made for potential stresses when performing the endodontic procedure. The endodontic treatment was conducted without taking into account any potential stressors. The root stresses were then recorded. The largest tensile stress is often focused at the apical third of the post and post/cement contact, as well as at the coronal third of the root on both the labial and palatal sides of the root, independent of the post's design and material. Restoration of endodontically treated maxillary central incisors with glass fiber posts has been shown to have less stress concentration than titanium posts. Regardless of the post materials employed, the tapered post design generated a higher tensile stress distribution than the parallel side design. Prefabricated fiber posts used in model restoration resulted in more evenly distributed stress and less concentrated stress on the root. Reduction in modulus of elasticity of post materials used generally shows less stress concentration.

Effect of Biosilicate® Addition on Physical–Mechanical and Biological Properties of Dental Glass Ionomer Cements

This study investigated the influence of incorporating Biosilicate® on the physico-mechanical and biological properties of glass ionomer cement (GIC). This bioactive glass ceramic (23.75% Na2O, 23.75% CaO, 48.5% SiO2, and 4% P2O5) was incorporated by weight (5%, 10%, or 15%) into commercially available GICs (Maxxion R and Fuji IX GP). Surface characterization was made by SEM (n = 3), EDS (n = 3), and FTIR (n = 1). The setting and working (S/W time) times (n = 3) and compressive strength (CS) were analyzed (n = 10) according to ISO 9917-1:2007. The ion release (n = 6) was determined and quantified by ICP OES and by UV-Vis for Ca, Na, Al, Si, P, and F. To verify cell cytotoxicity, stem cells from the apical papilla (SCAP) were exposed to eluates (n = 3, at a ratio of 1.8 cm2/mL) and analyzed 24 h post-exposure. Antimicrobial activity against Streptococcus mutans (ATCC 25175, NCTC 10449) was analyzed by direct contact for 2 h (n = 5). The data were submitted for normality and lognormality testing. One-way ANOVA and Tukey’s test were applied for the working and setting time, compressive strength, and ion release data. Data from cytotoxicity and antimicrobial activity were submitted for Kruskal–Wallis’ testing and Dunn’s post hoc test (α = 0.05). Among all experimental groups, only those with 5% (wt) of Biosilicate® showed better surface quality. Only M5% showed a comparable W/S time to the original material (p = 0.7254 and p = 0.5912). CS was maintained for all Maxxion R groups (p > 0.0001) and declined for Fuji IX experimental groups (p < 0.0001). The Na, Si, P, and F ions released were significantly increased for all Maxxion R and Fuji IX groups (p < 0.0001). Cytotoxicity was increased only for Maxxion R with 5% and 10% of Biosilicate®. A higher inhibition of S. mutans growth was observed for Maxxion R with 5% of Biosilicate® (less than 100 CFU/mL), followed by Maxxion R with 10% of Biosilicate® (p = 0.0053) and Maxxion R without the glass ceramic (p = 0.0093). Maxxion R and Fuji IX presented different behaviors regarding Biosilicate® incorporation. The impacts on physico-mechanical and biological properties were different depending on the GIC, but therapeutic ion release was increased for both materials.

Development of a gum recession model in an experiment

Background: The article presents experimental studies conducted on Wistar rats in the amount of 50 individuals. An artificial gum recession defect was created.Aim: to evaluate the effectiveness of creating a gum recession model in the proposed way.Material and methods: Experimental animals at the beginning of the study had an intact oral mucosa: pale pink color, without pathological changes. An experimental model of gum recession was created by excision of V-shaped periodontal tissues from the vestibular surface in the area of the lower jaw incisors of a rat, then a DispodentPak No. 000 retraction thread was applied in the area of the lower central incisors in the circular ligament of the tooth to a depth of 1.5 mm, and Vitrebond dental glass ionomer cement was applied to the vestibular surface of the neck of the tooth of the lower incisors, with at the same time, prednisone is administered intramuscularly at the rate of 12 mg / kg of animal weight on the 1st, 3rd and 5th day. For the experiment, female white rats in the amount of 50 individuals were used as a model. All animals were divided into 2 groups depending on the method of creating a gum recession defect. In the control group of rats, the defect was created according to the standard procedure by conducting a V-shaped incision.Results: When creating the proposed model of experimental gum recession, the clinical and pathomorphological picture is achieved under the influence of local factors: V-shaped gum incision, retraction thread, dental glass ionomer cement. To suppress the processes of self-regeneration of the gums, the optimal dose of prednisone is administered.Conclusions: On the 3rd day of the experiment, a V-shaped defect was observed in animals. On the 10th day, clinical signs of gum recession are determined: a defect with a depth of 2 mm. The average depth of recession in animals was (2 ± 1.7 mm). A relatively short process of modeling a gum recession (no more than a month). In this case, a local lesion of the gum is created, not burdened by any other pathology in the animal, and having both local and general (stress) pathogenetic factors, against the background of changes in the reactivity of the organism, which corresponds to the modern theory of the occurrence of recession as a polyethological disease in humans.

A one-step facile process for extraction of cellulose from rice husk and its use for mechanical reinforcement of dental glass ionomer cement

The extraction of cellulose was optimized using only hypochlorite and characterized and then utilized as a filler in glass ionomer cement where its strength and elasticity were studied.

ИСЛЕДОВАНИЕ КОМПОЗИЦИОННЫХ МАТЕРИАЛОВ НА ОСНОВЕ АЛЮМОФТОРСИЛИКАТНОГО СТЕКЛА

The results of a comparative analysis of dental glass ionomer cements are compared: "AHfil +" (AHL, United Kingdom), "Ketac Molar Easymix" (3M ESPE, USA), "Fuji IX GP" (GC, Japan), "ProGlass Nine" (Silmet , Israel), "Polyacrylin" (TechnoDent, Russia), "Cemion" (VladMiVa, Russia), "Kemfil" (StomaDent, Russia) and "Glassin Rest" (Omega-Dent, Russia) in terms of working time, hardening time, strength compression, radiopacity, microstructure and chemical composition. It is shown that the main component of the powders of these GICs is crushed calcium ("Kemfil"), strontium ("AHfil +", "Cemion" and "Fuji IX GP"), calcium-strontium ("ProGlass Nine", "Polyacrylin" and "Glassin Rest") and lanthanum-calcium aluminofluorosilicate glass ("Ketac Molar Easymix"). All of them contain phosphorus. Differences in powder granulometric composition indicate a difference in the technology of glass grinding during their production. The working time of the studied GICs is from 1 to 3.5 minutes. The requirements of GOST 31578-2012 and ISO 9917-1:2007 do not correspond to "ProGlass Nine" (36 ± 3 MPa), "Kemfil" (68±6 MPa) and "Glassin Rest" in terms of strength, and "ProGlass Nine" in hardening time. "Fuji IX GP" has the highest strength (201 ± 33 MPa), the rest of the GIC - 142-169 MPa. All studied GICs, with the exception of the non-radiopacity "ProGlass Nine", have a radiopacity corresponding to 1 mm of aluminum. According to the results of the tests, "AHfil +", "Ketac Molar Easymix", "Fuji IX GP", "Polyacrylin" and "Cemion" are recommended for clinical use by dentists

THE EFFECT OF NON-DENTAL GLASS FIBER COMBINATION ON FLEXURAL STRENGTH OF PREPOLYMERIZED FIBER-REINFORCED COMPOSITE

Background: Fiber reinforced composite is a combination of composite resin and fiber. Fiber in FRC serves as a reinforcement to be resistant to fractures. One of the fibers used in FRC is dental glass fiber because it can increase mechanical strength. Dental glass fiber is very limited and expensive while glass fiber which available in the market is non dental glass. This material has mechanical properties almost same as dental e-glass fiber used in dentistry, so it can be used as an alternative material FRC. The aim of this study was to identify the effect of flexural strength of non dental glass fiber to prepolymerized fiber reinforced composites. Method: This study used true experimental design with 16 samples. The samples were divided into two groups according to prepolymerized composite resin groups without fiber and prepolymerized composite resins with the addition of non dental glass fiber. Data analysis in this study used the normality test with the Sapiro-Wilk test, levene test and independent t-test. Result: The results were statistically analyzed, the average flexural strength of prepolymerized composite resin without fiber is 36.60 MPa and prepolymerized composite resin with the addition of non dental glass fiber which is 54.26 MPa. Based on the normality test and the levene test values (p> 0.05) and independent t-test values (p <0.05) were obtained. Conclusion: The conclusion obtained that there is an effect of the addition of non dental glass fiber to the flexural strength of prepolymerized fiber reinforced composite.

Effect of aqueous environment on wear resistance of dental glass\u2013ceramics

BackgroundWear resistance affects dental ceramics longevity and the functions of the opposing teeth. However, data for the effect of aqueous environment on wear resistance of dental ceramics are lacking. This study evaluated the effect of aqueous environment on wear resistance of typical dental glass–ceramics.MethodsDisk specimens were prepared from lithium disilicate glass–ceramics (LD) and leucite reinforced glass–ceramics (LEU). The disk specimens paired with steatite antagonists were tested in a pin-on-disk tribometer under both wet and dry conditions with 10 N up to 500,000 wear cycles. The wear analysis of glass–ceramics was performed using a 3D profilometer after 100,000, 300,000 and 500,000 wear cycles. Wear morphologies were analyzed by employing scanning electron microscopy (SEM). The crystalline compositions of specimens stored in a dry environment and subsequently immersed in distilled water for 40 h were separately determined using X-ray diffraction (XRD). The chemical states of the wear surfaces for LD were analyzed by X-ray photoelectron spectroscopy (XPS). The data analysis and multiple pair-wise comparisons of means were performed by using one-way analysis of variance (ANOVA) and Tukey’s post-hoc test.ResultsLEU in a wet environment exhibited less wear volume loss than that in a dry environment (p < 0.05). The volume loss of LD in a wet environment was higher than that in a dry environment (p < 0.05). The wear volumes of steatite antagonists paired with two glass–ceramics under dry conditions were higher than under wet conditions.ConclusionsXPS spectra of LD under wet conditions indicated that high wear loss might result from the effect of stress corrosion by water and reaction of water with the ionic-covalent bonds at the crack tip. XPS spectra and SEM images of LD under dry conditions showed a possible formation of tribofilm. Within the limitations of this in vitro study, water was wear-friendly to LEU and all opposing steatites but aggravated wear for LD.

Comparison of capsule-mixed versus hand-mixed glass ionomer cements Part II: Porosity

Glass ionomer restorative cements (GIC) are routinely used in dental practice. During mixing, air incorporation may lead to higher porosity with subsequent weakening of the cement. The degree of porosity will determine whether capsule-mixed or hand-mixed GIC are mechanically stronger for clinical use. To compare the porosity of four commercially available dental glass ionomer cements, supplied in both hand mix and capsule-mix formulations, by evaluating number of voids (%), total volume of voids (mm3 ) and volume percentage of voids (%). Eighty samples were manufactured from hand-mixed GIC: Riva Self Cure; Fuji IX GP ; Ketac Universal, Ketac Molar Easymix, and equivalent capsule-mixed GIC: Riva Self Cure; Fuji IX GP ; Ketac Universal Aplicap and Ketac Molar Aplicap. Micro-CT scanning was used to evaluate porosity. The number of voids (mm3 ), total volume of voids (mm3 ) and the volume percentage of voids (%) were calculated.

Determination of the toxicity glass ionomer cements for permanent fixa-tion of non-removable constructions of dentures

The experiment was carried out on groups of laboratory rats with a detailed study of the injected material, hematological, biochemical parameters of blood, behavioral reactions of animals and kidney function of experimental animals. The aim of the study was to determine the toxic effect of the new glass ionomer cement for permanent fixation of fixed structures of dentures on organs and tissues of laboratory animals. The keeping of animals and experiments were carried out in accordance with the "European Convention for the Protection of Vertebrate Animals used for Experimental and Other Scientific Purposes" (Strasbourg, 1986), Law of Ukraine No. 3447-IV on 21 Feb 2006 "On protection of animals from cruel treatment". Observations of the state and behavior of the animals showed that they tolerate daily contact with glass ionomer cement for one month satisfactorily. Indicators of liver weight in females (5.135±0.233) g and in males (6.234±0.342) g. In the experimental groups in contact with glass ionomer material, there were no significant differences in the number of erythrocytes [females – (4.86±0.26)·1012/l and in males – (4.53±0.14)·1012/l], hemoglobin [in females – (79.62±2.37) g/l, in males – (81.21±5.48) g/l], leukocytes [in males – (10.27±0.94)·109, in females – (9.81±0.68)·109/l]. The data obtained indicate the absence of toxic the effect of dental glass ionomer cement on peripheral blood. So the studied glass ionomer cement had no cytolyses effect on the liver. Changes in the composition of total protein [in males – (69.79±2.36) mmol/l, while in females – (67.35±2.47) mmol/l], albumin [in males – (28.56±1.87) mmol/l, in females – (28.49±2.36) mmol/l] in blood serum correspond to disorders of protein synthesis associated with damage to the liver parenchyma. The obtained results indicate that glass ionomer cement for permanent fixation of non-removable orthopedic prostheses did not have a toxic effect on the organs and tissues of experimental animals with prolonged use. Keywords: glass ionomer cement, permanent fixation, fixed structures of dentures, toxicity, experiment.

Experimental analysis and machine learning modeling of optical properties of lithium disilicate glass–ceramics comprising lithium tantalate as a secondary phase

AbstractColor is an important property of lithium disilicate (LD) glass–ceramics for a variety of applications. For example, the color of dental glass–ceramics needs to be tuned to match the color of natural teeth. The present study examines the optical properties of LD glass–ceramics containing lithium tantalate as a secondary phase via ultraviolet–visible spectroscopy. A large data set is analyzed to investigate the relationship between heat treatments and optical properties, specifically the L*a*b* color coordinates. The color coordinates are dependent on the heat treatment following previously acquired phase data. The data are used to train a two‐step machine learning model to predict what heat treatment is needed to obtain a given set of color coordinates.

10 - Functionalization of Restorative Dental Glass-Ceramics with Bactericidal Properties

Clinically, the periodontitis is related with the dental plaque, a biofilm of microorganisms, growth on the gum line and on the tooth interface. Therefore, a strategy to minimize this condition is the functionalization of the dental prosthesis, usually in contact with the gum, with antibacterial properties. The purpose of this study was to investigate the bactericidal potential of some commercial restorative glass-ceramic materials and to functionalize a commercial dental porcelain with antibacterial properties. Commercially available restorative glass-ceramics in powder (IPS d.SIGN), or as monolithic (IPS E.max Press e GC Initial LiSi Press) were used as control samples, and characterized by X-ray diffraction (XRD), Rietveld refinement, differential thermal analysis and particle size distribution. The IPS d.SIGN glass-ceramic was selected for functionalization with nanostructured β-AgVO 3 that was synthetized by a hydrothermal route, using AgNO 3 and NH 4 VO 3 as precursors, and characterized by XRD and Scanning Electron Microscopy (SEM). The glass-ceramic material was mixed with different percentages (1%, 2%, 4% or 6%wt) of β-AgVO 3 , uniaxially pressed at 50 MPa, and thermally treated at 900 C for 5 min, as indicated by the manufacturer. The functionalized glass-ceramics was characterized by XRD, Rietveld refinement, SEM, Vickers Hardness and Vickers indentation fracture toughness. The three commercial glass-ceramics, IPS d.SIGN, IPS E.max Press and GC Initial LiSi Press as well as the functionalized samples were evaluated for its bactericidal potential against model bacteria (Escherichia coli and Staphylococcus aureus). The as-received control samples presented leucite (KAlSi 2 O 6 ) as the only detectable crystalline phase, 62%wt of amorphous phase and a median particle size (D50) of 25.5 m in IPS d.SIGN. The product of the hydrothermal synthesis was characterized as pure needle like shaped β-AgVO 3 crystals. The heat-treated control samples still presented KAlSi 2 O 6 as the only detectable crystalline phase. However, a secondary feldspar (KAlSi 3 O 8 ) phase could be detected in the functionalized samples, which turns to be the main crystalline phase as a function of the increase in the β-AgVO 3 concentration. None of the commercially available samples showed antibacterial activity, but the IPS d.SIGN samples functionalized with 2%wt or more of β-AgVO 3 presented a clear inhibition halo, from 12, 70, 3 mm to 15, 50, 1 mm, suggesting bactericidal activity against both model bacteria. Preliminary, in vitro results indicated that the analyzed commercial dental glass ceramics demonstrated no antibacterial activity. Nevertheless, the functionalization of a commercially available veneering glass-ceramic with at least 2%wt of β-AgVO 3 can induce bactericidal activity against gram-positive and gram-negative bacteria.

5 - Effect of Roughness on Flexural Strength of Dental Lithium-Disilicate

A common process in dental clinics is to perform small fitting adjustments of dentures after testing in the patient's mouth using the micro-grinding tool. This procedure promotes a local roughness increase and can lead to the formation of microcracks on the prosthesis surface. The aim of this work was to investigate the benefits of a post-finishing heat treatment on the surface roughness smoothing and crack healing of lithium disilicate dental glass ceramics, and its effect on the flexural strength. Commercially available lithium metasilicate, Li 2 SiO 3 (IPS e-maxCAD), samples were heat treated at 840C-7min. The material was characterized by X-ray diffraction, Scanning Electron Microscopy, Vickers hardness, Youngs modulus and fracture toughness. One of the surfaces of the samples was machined, aiming to simulate the fitting procedure of dentures in the dentist's laboratory, generating a rough surface. Half of the samples were tested by biaxial flexural testing (3B-P) and the other half were submitted to a rapid heat treatment (840C-3min) and later tested by biaxial strength, with statistical analysis by Weibull. The Roughness parameters (Ra, PV and Rz) were measured using Zygo New View 7100 Optical Profiler. After the crystallization heat-treatment protocol suggested by the manufacturer, the formation of elongated lithium disilicate crystals, Li 2 Si 2 O 5 , with 36% residual amorphous phase was observed. In addition, the Vickers hardness of 6.1±0.3 GPa, fracture toughness of 1.90± 0.2 MPa.m1/2 and modulus of elasticity values of 91 ±2 GPa were obtained. The samples from the group without rapid heat-treatment showed bending strength of 203.5 ±33 MPa, with roughness values of Ra=0.6 ±0.2 μm, Rz=22 ±6 μm and PV=28 ±7 μm. After the rapid heat treatment, the roughness parameters Ra, Rz and PV were 0.3 ±0.2 μm, 9 ±6 μm and 5 ±4 μm, respectively. With this reduction in roughness, the flexural strength increased by 65%, with mean values of 336.6 ±32 MPa. Weibull modulus values were in the order of 5 for both groups. In the need for finishing machining of lithium disilicate-based glass-ceramic dental prostheses, the use of a rapid heat treatment at 840 C allows considerable gains in flexural strength. Increasing the service life of the prosthesis, due to a reduction on the surface roughness, promoted by the softening of the remaining amorphous phase in the glass-ceramic.