Chitosan and its application in dental implantology.

OBJECTIVE: The aim of this review was to evaluate the properties of chitosan for an application in dental implantology. METHODS: Electronic Databases: PubMed, Google Scholar, Scopus, were used to recherche the articles published from 2010 to 2021. The keywords used were: chitosan, biocompatible, antibacterial, osseointegration, implant, bioactive. After a carefully selection according to the above keywords 46 articles met the condition to be studied RESULTS: Chitosan is a biopolymer, that can be easy produced. Its antibacterial, anti-inflammatory, anti-fugal, hemostatic, analgesic, mucoadhesive, osseointegrative properties and its excellent film-forming ability make chitosan a material with a future in dental implantology and in other areas of dental applications. Titan implants coated with chitosan showed better bioactive properties than uncoated implants. The treatment of the implant surface played an important role on the stability of implants. The activity of osteoblasts increased when the surface was laser-treated followed by coating with chitosan. The subsequent coating with apatite improved the bioactivity of chitosan. CONCLUSION: Chitosan is a promising biocompatible and bioactive material in dental implantology. Its antibacterial properties can be enhanced by modification of its structure. Its bioactive properties can be improved when mixing with hydroxy apatite.

Properties of hot-pressed lithium silicate glass-ceramics.

OBJECTIVES: New lithium silicate/disilicate hot-pressed glass-ceramics are introduced into the dental market. It is known that the mechanical properties of this material depend on the microstructure, chemical composition, glass matrix, morphology of crystals, volume ratio crystal/glass, additive, and treatments. This contribution investigates how these factors affect the properties of the new generation of lithium silicate/disilicate hot-pressed glass-ceramics. METHODS: Three lithium silicate/disilicate hot-pressed glass-ceramics were investigated; IPS e.max Press (control group), Initial LiSi Press and Celtra Press. The specimens were prepared according to the manufacturers` instructions. Different methods; DTA, XRD, Raman, optical spectroscopy, SEM were used to characterize the properties of these materials before, after heat and etching treatments. The heat treatments (four firings) were performed according to the manufacturer's instructions (GC company) for veneering (initial LiSi) of LS2 glass-ceramics. The etching was performed according to the manufacturer's instruction. Vita ceramics etch gel (HF 5%) was used as an etching agent. The mechanical properties were investigated according to DIN EN ISO 6872:2015 and ASTM C 1327-08 instructions. RESULTS: DTA and XRD analysis revealed that the transformation of the lithium silicate (LS) phase to the LS2 phase was completed for IPS e.max and Initial LiSi Press ingots while for Celtra Press ingots it was not. After pressing, the rod-shaped crystals were aligned parallel to the extrusion direction, while the platelet-shaped crystals having an interlocking microstructure were not. The mechanical properties depend on the microstructure, the chemical composition, the crystals morphology, the volume crystal/glass ratio, and the treatments (heat and etching). ZrO2 did not improved the mechanical properties. Etching with HF gel decreased the flexural strength. After four heat treatments, the biaxial flexural strength, the KIC, the roughness and the optical properties were affected. According to the HT-XRD, IPS e.max Press ingots can be hot pressed up to 900 °C, the initial LiSi Press ingots up to 940 °C and Celtra Press ingots up to 880 °C. SIGNIFICANCE: The properties of LS2 glass-ceramics depend on the chemical composition, the microstructure, the morphology of the crystals, the properties of the residual glass matrix, the volume ratio of crystal/glass, and the treatments (heat and etching).

Effect of microstructure on the mechanical properties of lithium disilicate glass-ceramics.

The mechanical properties of lithium disilicate glass-ceramics depend on various factors, a prominent one being their microstructure. The aim of this review article is to elucidate the effect of processing parameters such as annealing temperature, holding time, number of heating stages and chemical composition and additives on the microstructure and physical properties of these glass-ceramics.

Effect of surface modifications on the bond strength of zirconia ceramic with resin cement resin.

OBJECTIVES: Purpose of this in vitro study was to evaluate the effect of surface modifications on the tensile bond strength between zirconia ceramic and resin. METHODS: Zirconia ceramic surfaces were treated with 150-µm abrasive alumina particles, 150-µm abrasive zirconia particles, argon-ion bombardment, gas plasma, and piranha solution (H2SO4:H2O2=3:1). In addition, slip casting surfaces were examined. Untreated surfaces were used as the control group. Tensile bond strengths (TBS) were measured after water storage for 3 days or 150 days with additional 37,500 thermal cycling for artificial aging. Statistical analyses were performed with 1-way and 3-way ANOVA, followed by comparison of means with the Tukey HSD test. RESULTS: After storage in distilled water for three days at 37 °C, the highest mean tensile bond strengths (TBS) were observed for zirconia ceramic surfaces abraded with 150-µm abrasive alumina particles (TBS(AAP)=37.3 MPa, TBS(CAAP)=40.4 MPa), and 150-µm abrasive zirconia particles (TBS(AZP)=34.8 MPa, TBS(CAZP)=35.8 MPa). Also a high TBS was observed for specimens treated with argon-ion bombardment (TBS(BAI)=37.8 MPa). After 150 days of storage, specimens abraded with 150-µm abrasive alumina particles and 150-µm abrasive zirconia particles revealed high TBS (TBS(AAP)=37.6 MPa, TBS(CAAP)=33.0 MPa, TBS(AZP)=22.1 MPa and TBS(CAZP)=22.8 MPa). A high TBS was observed also for specimens prepared with slip casting (TBS(SC)=30.0 MPa). A decrease of TBS was observed for control specimens (TBS(UNT)=12.5 MPa, TBS(CUNT)=9.0 MPa), specimens treated with argon-ion bombardment (TBS(BAI)=10.3 MPa) and gas plasma (TBS(GP)=11.0 MPa). A decrease of TBS was observed also for specimens treated with piranha solution (TBS(PS)=3.9 MPa, TBS(CPS)=4.1 MPa). A significant difference in TBS after three days storage was observed for specimens treated with different methods (p<0.001). Thermal cycling significantly reduced TBS for all groups (p<0.001) excluding groups: AAP(p>0.05), CAAP(p>0.05) and SC(p>0.05). However, the failure patterns of debonded specimens prepared with 150-µm abrasive zirconia particles were 96.7% cohesive. CONCLUSION: Treatment of zirconia ceramic surfaces with abrasive zirconia particles is a promising method to increase the tensile bond strength without significant damage of the ceramic surface itself. An alternative promising method is slip casting.

Effect of surface treatments on the properties and morphological change of dental zirconia.

STATEMENT OF PROBLEM: Creating a rough surface for bonding with airborne-particle abrasion with alumina may damage the surface of zirconia. Other treatment methods for creating a bonding surface without causing damage require investigation. PURPOSE: The purpose of this in vitro study was to find ways of treating the zirconia surface without causing flaws, debris, pits, microcracks, or tetragonal to monoclinic phase transformation. MATERIAL AND METHODS: Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic surfaces were treated with gas plasma, argon-ion bombardment, 150-µm abrasive zirconia particles, and abrasive 150-µm alumina particles; untreated surfaces were used as the control group. X-ray diffraction (XRD) and confocal Raman spectroscopy were used to study the phase transformation. The roughness of specimens was measured with a confocal 3D laser scanning microscope. Modification of surface topography was analyzed with field emission scanning electron microscopy (FESEM), and the flexural strength was measured with a universal testing machine. Statistical analyses were performed with 1-way ANOVA, followed by comparison of means with the Tukey honest significant difference test. The standard deviation was calculated with descriptive statistics. RESULTS: The sintered Y-TZP ceramic used in this study showed 2 phases, tetragonal and cubic. Specimens abraded with 150-µm alumina particles showed a higher monoclinic volume fraction (VmXRD=8.68%) and roughness (Ra=0.91µm) than specimens abraded with 150-µm zirconia particles (VmXRD=1.22%, Ra=0.08µm). One-way ANOVA indicated a significance difference in roughness among groups (P<.01). No phase transformation was observed in specimens treated with argon-ion bombardment or plasma. According to the Raman results, the volume fraction of the monoclinic phase for the specimens treated with airborne-particle abrasion depended on the distance from the ceramic surfaces and decreased with the increase in this distance. A slightly higher flexural strength was observed for untreated specimens (1009 MPa), followed by specimens treated with gas plasma (1000 MPa) and those airborne-particle abraded with 150-µm zirconia particles (967 MPa). The flexural strength of other specimens was lower (940 MPa for specimens abraded with 150-µm alumina particles and 916 MPa for specimens subjected to argon-ion bombardment). One-way ANOVA analysis indicated no significant difference in flexural strengths among all groups (P>.2). FESEM measurements showed that airborne-particle abrading Y-TZP surfaces with 150-µm alumina particles caused more damage to this area than the other methods. CONCLUSIONS: Y-TZP ceramic surfaces treated with zirconia particles, argon-ion bombardment, and gas plasma were damaged less in comparison with surfaces abraded with alumina particles.

Effect of differences in coefficient of thermal expansion of veneer and Y-TZP ceramics on interface phase transformation.

STATEMENT OF PROBLEM: The stability of veneering ceramics requires further investigation. PURPOSE: The purpose of this study was to investigate, with Raman spectroscopy, the occurrence and extent of the tetragonal to monoclinic phase transformation in yttria partially stabilized tetragonal polycrystalline zirconia (Y-TZP) ceramic at the veneer-framework interface. MATERIALS AND METHODS: Three different Y-TZP blanks Cercon base, ZENO TEC, and Zerion were used. The specimens were sintered according to the recommendations of the manufacturers (1350°C Cercon base, 1450°C ZENO TEC, and 1500°C Zerion for 2 hours). Three veneer ceramics with different coefficients of thermal expansion, Cercon ceram kiss, Zirox, and VITA VM9 were used to veneer the Y-TZP frameworks. For the investigation of the temperature gradient on the phase transformation of Y-TZP ceramic, some specimens were fractured, with a universal testing machine along the long axis of the coping. RESULTS: No evidence was found for the presence of the tetragonal to monoclinic phase transformation for nonabraded and nonveneered specimens. The tetragonal to monoclinic phase transformation was observed at the veneer-framework interface for all veneered specimens and was dependent on the sintering temperature of the framework. The highest volume fractions of the monoclinic phase at the veneer-framework interface amounted to 0.57 (Cercon base), 0.69 (ZENO TEC), and 0.72 for the Zerion framework. The tetragonal to monoclinic phase transformation was not homogenous along the veneer-framework interface and depended on the distance from the cross section of the veneer-framework interface. The greatest tetragonal to monoclinic transformation was observed at the interface and disappeared with increasing distance from it. For the veneered Cercon base specimens, the volume fraction of the monoclinic phase decreased from 0.53 to 0.13 over a distance of 20 µm. No phase transformation was observed at a distance that exceeded 20 µm from the cross section of the veneer-framework interface. CONCLUSION: This study demonstrated that the firing process of veneer ceramic and the difference in the coefficients of thermal expansion between the ceramic framework and the veneer ceramic significantly influenced the stability of the tetragonal phase of Y-TZP ceramic at the veneer-framework interface.

The effect of zirconia sintering temperature on flexural strength, grain size, and contrast ratio.

OBJECTIVE: This study investigated the effect of sintering temperatures on flexural strength, contrast ratio, and grain size of zirconia. MATERIALS AND METHODS: Zirconia specimens (Ceramill ZI, Amann Girrbach) were prepared in partially sintered state. Subsequently, the specimens were randomly divided into nine groups and sintered with different final sintering temperatures: 1,300°C, 1,350°C, 1,400°C, 1,450°C, 1,500°C, 1,550°C, 1,600°C, 1,650°C, or 1,700°C with 120 min holding time. Three-point flexural strength (N = 198; n = 22 per group) was measured according to ISO 6872: 2008. The contrast ratio (N = 90; n = 10 per group) was measured according to ISO 2471: 2008. Grain sizes and microstructure of different groups were investigated (N = 9, n = 1 per group) with scanning electron microscope. Data were analyzed using one-way ANOVA with Scheffé test and Weibull statistics (p < 0.05). Pearson correlation coefficient was calculated between either flexural strength or contrast ratio and sintering temperatures. RESULTS: The highest flexural strength was observed in groups sintered between 1,400°C and 1,550°C. The highest Weibull moduli were obtained for zirconia sintered at 1,400°C and the lowest at 1,700°C. The contrast ratio and the grain size were higher with the higher sintering temperature. The microstructure of the specimens sintered above 1,650°C exhibited defects. Sintering temperatures showed a significant negative correlation with both the flexural strength (r = -0.313, p < 0.001) and the contrast ratio values (r = -0.96, p < 0.001). CONCLUSIONS: The results of this study showed that the increase in sintering temperature increased the contrast ratio, but led to a negative impact on the flexural strength. CLINICAL RELEVANCE: Considering the flexural strength values and Weibull moduli, the sintering temperature for the zirconia tested in this study should not exceed 1,550°C.

Impact of air-abrasion on fracture load and failure type of veneered anterior Y-TZP crowns before and after chewing simulation.

The purpose of this study was to determine the fracture load and failure types of veneered zirconia crowns that were air-abraded on either the veneering or cementation surface. Fracture loads were determined before and after chewing simulation. Standardized Y-TZP frameworks (n = 360) for canines were fabricated and divided into one control group (n = 72) and 12 test groups (n = 24). The test groups were air-abraded using alumina powder (10 s, 2 bar, distance: 10 mm) with particle size of 50 µm resp. 110 µm and veneered with one of the veneering ceramics: Triceram, Zirox, or VITA VM9. The crowns were cemented on their corresponding CoCr abutment. The initial fracture load was measured in one half of each group (n = 12), and the other half (n = 12) was subjected to chewing cycling. The data were analyzed using three-way and one-way ANOVA, a post-hoc Scheffé test, two sample Student's t-test, and Weibull statistics (p < 0.05). Thus, nonaged, air-abraded groups of two veneering ceramics (Triceram, VITA VM9) showed higher mean fracture load compared to control groups. After chewing simulation, air-abraded groups showed lower mean fracture load compared to control groups. Aging decreased the Weibull modulus of all tested groups, and air-abraded groups showed lower Weibull moduli compared to control groups.

Surface characterization of dental Y-TZP ceramic after air abrasion treatment.

OBJECTIVE: The aim of this study was to characterize the surface of Y-TZP after abrasion with various airborne particles. METHODS: The Y-TZP blanks were cut into 44 discs and sintered according to the manufacturer's instructions. The specimens were treated as follows: (a) control specimens, (b) abraded with 50µm alumina, (c) abraded with 110µm alumina, (d) abraded with 30µm silica-coated alumina, (e) abraded with 110µm silica-coated alumina, (f) abraded with 110µm alumina followed by 110µm silica-coated alumina particles. Airborne abrasion was performed at a pressure of 2.5bar for 15s/cm(2). The Y-TZP was characterized using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and X-ray diffraction analysis (XRD). RESULTS: Surface morphology of Y-TZP ceramic was changed after the airborne abrasion process compared to the control specimens. The grain boundaries disappeared and part of the airborne particles are embedded and/or rested on the ceramic surfaces. The elemental composition of the Y-TZP surface after the airborne abrasion process depended on the type and size of these particles. The concentration of Si resulted higher after the airborne abrasion process with 110µm alumina followed by 110µm silica-coated alumina particles in comparison to the specimens abraded with 110µm silica-coated alumina particles. The ratio of elements normalized by yttrium for these specimens was: [Zr]/[Y]/[Al]/[Si]=15.2/1.0/26.0/73.6, respectively. CONCLUSION: The change of grain topography occurred during each impact process. Silica nano-particles covered not only loosely the abraded ceramic surface after abrasion process, but the release of kinetic energy in form of thermal energy resulted in melting of the ceramic surface and in the formation of zirconium silicate.

The influence of grain size on low-temperature degradation of dental zirconia.

UNLABELLED: The purpose of this study was to evaluate the influence of grain size and air abrasion on low-temperature degradation (LTD) of yttria stabilized tetragonal zirconia polycrystalline (Y-TZP). Disc-shaped specimens were sintered at 1350, 1450, and 1600°C. Air abrasion was performed with different abrasive particles. The specimens were stored for 2 h at 134°C under 2.3 bar water vapor pressure. All specimens were characterized by X-ray powder diffraction analysis (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM). Y-TZP sintered at a temperature of 1350°C did not undergo the t-m phase transformation during accelerated aging. The diffusion-controlled t-m phase transformation initiated with the specimens sintered at 1450°C. This transformation was remarkable for the specimens sintered at 1600°C. X-ray photoelectron spectroscopy (XPS) measurements did not confirm the generation of Zr-OH and Y-OH bonds. No increase of yttrium concentration on the grain boundaries of Y-TZP was detected, which could be responsible for the destabilization of dental zirconia ceramics. A slight increase of diffusion-controlled t-m phase transformations was observed for all abraded specimens sintered at 1350 and 1450°C. The size of abrasive particles did not play a crucial role on LTD of Y-TZP. The retardation of diffusion-controlled t-m phase transformation was evident for all abraded specimens sintered at 1600°C by comparison to non-abraded specimens. CONCLUSION: The LTD of Y-TZP can be suppressed when the sintering temperature is set between 1350 and 1450°C.