Gastric acid challenge of lithium disilicate-reinforced glass-ceramics and zirconia-reinforced lithium silicate glass-ceramic after polishing and glazing-impact on surface properties.

OBJECTIVES: To investigate the impact of simulated gastric acid on the surface properties of lithium disilicate-reinforced glass-ceramics and zirconia-reinforced lithium silicate glass-ceramic after certain polishing and glazing procedures. MATERIALS AND METHODS: Four different types of square-shaped specimens (10 × 10 × 2 mm3, n = 13) were manufactured: lithium disilicate-reinforced glass-ceramic milled and polished (LDS-P); milled, polished, and glazed (LDS-PG); milled, glazed, and no polishing (LDS-G); and milled and polished zirconia-reinforced lithium silicate glass-ceramic (ZR-LS). Specimens were immersed in hydrochloride acid (HCl 0.06 M, pH 1.2) to simulate gastric acid irritation and stored in the acid for 96 h in 37 °C. Specimen weight, surface gloss, Vickers surface microhardness and surface roughness (Ra, Rq, with optical profilometer), and surface roughness on nanometer level (Sq, Sal, Sq/Sal, Sdr, Sds with atomic force microscope) were measured before and after the acid immersion. RESULTS: ZR-LS specimens lost significantly more weight after acid immersion (p = 0.001), also surface microhardness of ZR-LS was significantly reduced (p = 0.001). LDS-G and LDS-PG showed significantly lower surface roughness (Sa, Sq) values compared to LDS-P before (p ≤ 0.99) and after (p ≤ 0.99) acid immersion and ZR-LS after acid immersion (p ≤ 0.99). CONCLUSIONS: Gastric acid challenge affects the surface properties of lithium disilicate-reinforced glass-ceramic and zirconia-reinforced lithium silicate glass-ceramic. Glazing layer provides lower surface roughness, and the glazed surface tends to smoothen after the gastric acid challenge. CLINICAL RELEVANCE: Surface finish of lithium disilicate-reinforced glass-ceramic and zirconia-reinforced lithium silicate glass-ceramic has a clear impact on material's surface properties. Gastric acidic challenge changes surface properties but glazing seems to function as a protective barrier. Nevertheless, also glazing tends to smoothen after heavy gastric acid challenge. Glazing can be highly recommended to all glass-ceramic restorations but especially in patients with gastroesophageal reflux disease (GERD) and eating disorders like bulimia nervosa.

Influence of Surface Characteristics of TiO2 Coatings on the Response of Gingival Cells: A Systematic Review of In Vitro Studies.

The soft tissue-implant interface requires the formation of epithelium and connective tissue seal to hinder microbial infiltration and prevent epithelial down growth. Nanoporous titanium dioxide (TiO2) surface coatings have shown good potential for promoting soft tissue attachment to implant surfaces. However, the impact of their surface properties on the biological response of gingival cells needs further investigation. This systematic review aimed to investigate the cellular behavior of gingival cells on TiO2-implant abutment coatings based on in vitro studies. The review was performed to answer the question: "How does the surface characteristic of TiO2 coatings influence the gingival cell response in in vitro studies?". A search in MEDLINE/PubMed and the web of science databases from 1990 to 2022 was performed using keywords. A quality assessment of the studies selected was performed using the SciRAP method. A total of 11 publications were selected from the 289 studies that fulfilled the inclusion criteria. The mean reporting and methodologic quality SciRAP scores were 82.7 ± 6.4/100 and 87 ± 4.2/100, respectively. Within the limitations of this in vitro systematic review, it can be concluded that the TiO2 coatings with smooth nano-structured surface topography and good wettability improve gingival cell response compared to non-coated surfaces.

Enhancement of Gingival Tissue Adherence of Zirconia Implant Posts: In Vitro Study.

Prevention of bacterial inflammation around dental implants (peri-implantitis) is one of the keys to success of the implantation and can be achieved by securing the gingival tissue-abutment interface preventing penetration of bacteria. Modern dental practice has adopted zirconia abutments in place of titanium, but the adhesion of gingival tissue to zirconia is inferior to titanium. The aim of this study was to assess and improve the adhesion of mucosal tissues to zirconia posts using sol-gel derived TiO2 coating following dynamic mechanical testing. The posts were cultivated with porcine bone-gingival tissue specimens in vitro for 7 and 14 days and then subjected to dynamic mechanical analysis simulating physiological loading at 1 Hz up to 50 µm amplitude. In parallel in silico analysis of stresses and strains have been made simulating "the worst case" when the fixture fails in osseointegration while the abutment still holds. Results show treatment of zirconia can lead to double interface stiffness (static shear stiffness values from 5-10 to 17-23 kPa and dynamic from 20-50 to 60-125 kPa), invariant viscostiffness (from 5-35 to 45-90 kPa·sα) and material memory values (increased from 0.06-0.10 to 0.17-0.25), which is beneficial in preventing bacterial contamination in dental implants. This suggests TiO2-coated zirconia abutments may have a significant clinical benefit for prevention of the bacterial contamination.

Zirconia implants with improved attachment to the gingival tissue.

BACKGROUND: Gingival tissue attachment is known to be important for long-term prognosis of implants. This in vitro study evaluated the gingival attachment to zirconia implants and zirconia implants modified with sol-gel derived TiO2 coatings. METHODS: Zirconia endodontic posts (n = 23) were used to function as implants that were inserted into the center of full-thickness porcine gingival explants (n = 31). The tissue/implant specimens were then individually placed at an air/liquid interface on a stainless-steel grid in cell culture wells containing a nutrient solution. The tissue cultures were incubated at 37°C in a 5% CO2 environment and at days 7 and 14, the specimens were harvested and analyzed by dynamic mechanical analysis (DMA) measurements under dynamic loading conditions mimicking natural mastication. Specimens were also analyzed by immunohistochemical staining identifying the laminin (Ln) γ2 chain specific for Ln-332, which is known to be a crucial molecule for the proper attachment of epithelium to tooth/implant surface. RESULTS: Tissue attachment to TiO2 -coated zirconia demonstrated higher dynamic modulus of elasticity and higher creep modulus, meaning that the attachment is stronger and more resistant to damage during function over time. Laminin γ2 was identified in the attachment of epithelium to TiO2 -coated zirconia. CONCLUSIONS: Both DMA and histological analysis support each other, so the gingival tissue is more strongly attached to sol-gel derived TiO2 -coated zirconia than uncoated zirconia. Immunohistochemical staining showed that TiO2 coating may enhance the synthesis and deposition of Ln-332 in the epithelial attachment to the implant surface.

TiO2 Coating and UV Photofunctionalization Enhance Blood Coagulation on Zirconia Surfaces.

This in vitro study was designed to evaluate the effect of sol-gel derived TiO2 coating on blood coagulation, blood protein adsorption, and platelet response on zirconia surfaces. Square-shaped zirconia (n=96) (10x10x2 mm) was cut, ground, sintered, and finally cleansed ultrasonically in each of acetone and ethanol for 5 minutes. Three experimental groups (n=32) were fabricated: (a) zirconia coated with sol-gel derived TiO2, (b) zirconia coated with sol-gel derived TiO2 and treated with ultraviolet (UV) irradiation for 1 hour, and (c) non-coated zirconia as control. The coatings were prepared from tetraisopropyl orthotitanate solution by dip-coating. The thrombogenicity of the specimens was evaluated using a whole blood kinetic clotting time method where the extent of blood clotting was evaluated at 10, 20, 30, 40, 50, and 60 minutes (n=4/time point, total n=24/group). Scanning electron microscope images were taken to observe platelet morphologies after 1-hour incubation with platelet-rich plasma (PRP) (n=5/group). Surface characteristics were visualized using atomic force microscopy (n=1/group). Adsorption of plasma proteins and fibronectin on each surface was studied by gel electrophoresis (n=2/group). Significant differences were observed in blood coagulation between the test groups at 20-, 30-, 40-, and 50-minute time points (p<0.005). UV treated TiO2 coated specimens showed fastest blood coagulation followed by TiO2 coated and non-coated specimens. Furthermore, platelets appeared at a higher activation state on coated specimens. Gel electrophoresis revealed no difference in protein adsorption among the experimental groups. In summary, TiO2 coatings promoted blood coagulation, and it was further enhanced by UV treatment, which has the potential to hasten the wound healing process in vivo.

TiO2-Modified Zirconia Surface Improves Epithelial Cell Attachment.

PURPOSE: Good cell adhesion is an important prerequisite for soft tissue attachment on implant abutment or crown surfaces. The aim of this study was to evaluate the adhesion and proliferation of human epithelial cells on sol-gel-derived TiO2-coated and noncoated zirconia. MATERIALS AND METHODS: Altogether, 56 zirconia disks (Z-CAD, Metoxit) were fabricated for this study. Half of the disks were coated with a sol-gel-derived TiO2 coating (MetAlive, ID Creations). The rest of the disks were noncoated and formed the control group. Surface properties of the disks were characterized by contact angle measurements and surface free energy (SFE) calculation. The cell adhesion was tested by cultivating epithelial cells (20,000 cells/cm2) on the experimental disks for 1, 3, 6, and 24 hours, after which the fluorescence of the samples was measured (BioTek synergy HT). The amount of cells was detected by comparing the fluorescence value to the standard curve. In addition, the proliferation was studied by growing epithelial cells (25,000 cells/cm2) for 1, 3, and 7 days. The number of cells was calculated by defining the absorbance of the samples (Multiskan EX, Thermo Labsystems), followed by a comparison with the standard curve. Finally, the samples were processed for light microscopy. RESULTS: TiO2-coated disks were significantly more hydrophilic with higher total SFE than noncoated disks (P < .05). The amount of epithelial cells was greater on TiO2-coated disks than on controls after 24 hours (P < .05). Regarding cell proliferation, the difference was statistically significant (P < .05) on days 3 and 7. Light microscope evaluation confirmed viable cells, which were in immediate close contact with both substrate surfaces. The cell layers on the coated disks appeared to be more uniform and cell rich than the layers on noncoated disks. CONCLUSION: This study indicated that TiO2 coating improves epithelial cell attachment and proliferation on zirconia surfaces. This has good potential to enhance formation of the epithelial junction to the coated zirconia surfaces.

Effect of different treatments on the flexural strength of fully versus partially stabilized monolithic zirconia.

STATEMENT OF PROBLEM: Recent monolithic zirconia materials used for indirect restorations are predominantly fully stabilized zirconia with claims of enhanced optical properties. These restorations may behave differently from the conventional partially stabilized zirconia restorations, which may negatively affect some of the core properties required for restoration success. PURPOSE: The purpose of this in vitro study was to evaluate and compare the effects of staining, airborne-particle abrasion, and artificial aging on the flexural strength of fully and partially stabilized zirconia material. MATERIAL AND METHODS: Each partially stabilized monolithic zirconia (PSZ) and fully stabilized zirconia (FSZ) material and a zirconia core material (control) were prepared as bar-shaped specimens (2×2×25 mm) and divided into 6 groups (n=8/subgroup): regular sintering, vacuum sintering, stained, airborne-particle abrasion, artificially aged regular sintering, and artificially aged vacuum sintering. Critical load to fracture was determined for all groups by using monotonic uniaxial loading in accordance with International Organization for Standardization standard 6872. Data were analyzed using univariate analysis of variance, followed by the Tukey honest significant difference post hoc test (α=.05). RESULTS: The control and PSZ (1034 and 1008 MPa) displayed a significantly higher (P<.05) flexural strength than FSZ (582 MPa). Airborne-particle abrasion significantly (P<.05) enhanced the strength of the control and PSZ (1413 and 1227 MPa) but significantly (P<.05) reduced the flexural strength of the FSZ (442 MPa). Staining, artificial aging, and vacuum sintering had no significant effects on any of the groups. CONCLUSIONS: Fully stabilized zirconia may behave differently from conventional PSZ, especially with regard to airborne-particle abrasion, which may weaken the FSZ. The strength of PSZ is approximately double the strength of FSZ. Both of the zirconia materials showed resistance to artificial aging.

The effect of rubber dam on atmospheric bacterial aerosols during restorative dentistry.

Rotatory dental instruments generate atmospheric aerosols that settle on various surfaces, including the dentist's head. The aim of this study was to quantitatively assess bacterial contamination of the dentist's head and to evaluate whether it is affected by using a rubber dam. Senior dental students (n=52) were asked to wear autoclaved headscarves as collection media while performing restorative dental treatment with and without a rubber dam. Four points from each headscarf were swabbed for bacterial culture after 30min of operative work. Bacterial contamination was quantified by counting the colony-forming units. Regardless of the collection point, using a rubber dam was associated with more bacterial colony-forming units than not using a rubber dam (P=0.009). Despite its clinical value, the rubber dam seems to result in significantly higher aerosol levels on various areas of the dentist's head, requiring that dentists cover their heads with suitable protective wear.

Sol-gel derived bioactive coating on zirconia: Effect on flexural strength and cell proliferation.

The purpose of this study was to evaluate the effect of sol-gel derived bioactive coatings on the biaxial flexural strength and fibroblast proliferation of zirconia, aimed to be used as an implant abutment material. Yttrium stabilized zirconia disc-shaped specimens were cut, ground, sintered, and finally cleansed ultrasonically in each of acetone and ethanol for 5 minutes. Three experimental groups (n = 15) were fabricated, zirconia with sol-gel derived titania (TiO2 ) coating, zirconia with sol-gel derived zirconia (ZrO2 ) coating, and non-coated zirconia as a control. The surfaces of the specimens were analyzed through images taken using a scanning electron microscope (SEM), and a non-contact tapping mode atomic force microscope (AFM) was used to record the surface topography and roughness of the coated specimens. Biaxial flexural strength values were determined using the piston-on-three ball technique. Human gingival fibroblast proliferation on the surface of the specimens was evaluated using AlamarBlue assay™. Data were analyzed using a one-way analysis of variance (ANOVA) followed by Tukey's post-hoc test. Additionally, the biaxial flexural strength data was also statistically analyzed with the Weibull distribution. The biaxial flexural strength of zirconia specimens was unaffected (p > 0.05). Weibull modulus of TiO2 coated and ZrO2 coated groups (5.7 and 5.4, respectively) were lower than the control (8.0). Specimens coated with ZrO2 showed significantly lower fibroblast proliferation compared to other groups (p < 0.05). In conclusion, sol-gel derived coatings have no influence on the flexural strength of zirconia. ZrO2 coated specimens showed significantly lower cell proliferation after 12 days than TiO2 coated or non-coated control. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2401-2407, 2017.

Impact of gastric acidic challenge on surface topography and optical properties of monolithic zirconia.

OBJECTIVE: To evaluate the surface topography and optical properties of monolithic zirconia after immersion in simulated gastric acid. MATERIALS AND METHODS: Four partially stabilized (PSZ) and one fully stabilized (FSZ) zirconia materials were selected for the study: Prettau (PRT, Zirkonzahn), Zenostar (ZEN, Ivoclar), Bruxzir (BRX, Glidewell), Katana (KAT, Noritake) and FSZ Prettau Anterior (PRTA, Zirkonzahn). IPS e.max (Ivoclar) was used as a control. The specimens (10×10×1.2mm, n=5 per material) were cut, sintered, polished and cleaned before immersed in 5ml of simulated gastric acid solution (Hydrochloric acid (HCl) 0.06M, 0.113% solution in deionized distal water, pH 1.2) for 96h in a 37°C incubator. Specimens were weighed and examined for morphological changes under scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). Surface roughness was evaluated by a confocal microscope. Surface gloss and translucency parameter (TP) values were determined by a reflection spectrophotometer before and after acid immersion. The data was analyzed by one-way ANOVA followed by Tukey's HSD post hoc test (p<0.05). RESULTS: PRTA displayed the most weight loss (1.40%) among the zirconia specimens. IPS e.max showed about three times more weight loss (3.05%) than zirconia specimens as an average. SEM examination indicated areas of degradation, bead-like shapes and smoothening of the polishing scratches after acid immersion. EDX displayed ion interactions and possible ion leaching from all specimens. Sa and Sq values for PRTA, ZEN and IPS e.max were significantly lower (p<0.05) after acid immersion. TP values increased significantly for PRT, ZEN and IPS e.max (p<0.05), while the surface gloss of ZEN, PRTA and IPS e.max increased (p<0.05). SIGNIFICANCE: Monolithic zirconia materials show some surface alterations in an acidic environment with minimum effect on their optical properties. Whether a smoother surface is in fact a sign of true corrosion resistance or is purely the result of an evenly progressive corrosive process is yet to be confirmed by further research.