Khalil Shahramian

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.

Titanium dioxide (TiO₂) nanotubes are emerging as a provocative target for oral implant research. The aim of this study was to evaluate the effect of UV on the wettability behavior, bacterial colonization, and fibroblast proliferation rate of TiO₂ nanotube surfaces prepared using different anodization voltages and aimed for use as implant abutment materials. Four different experimental materials were prepared: (1) TiO₂ nanotube 10 V; (2) TiO₂ nanotube 15 V; (3) TiO₂ nanotube 20 V; and (4) commercial pure titanium as a control group. TiO₂ nanotube arrays were prepared in an aqueous electrolyte solution of hydrofluoric acid (HF, 0.5 vol.%). Different anodization voltages were used to modify the morphology of the TiO₂ nanotubes. Equilibrium contact angles were measured using the sessile drop method with a contact angle meter. The investigated surfaces (n = 3) were incubated at 37 °C in a suspension of Streptococcus mutans (S. mutans) for 30 min for bacterial adhesion and 3 days for biofilm formation. Human gingival fibroblasts were plated and cultured on the experimental substrates for up to 7 days and the cell proliferation rate was assessed using the AlamarBlue assay^TM (BioSource International, Camarillo, CA, USA). The data were analyzed using one-way ANOVA followed by Tukey’s post-hoc test. Water contact angle measurements on the TiO₂ after UV treatment showed an overall hydrophilic behavior regardless of the anodization voltage. The ranking of the UV-treated surfaces of experimental groups from lowest to highest for bacterial adhesion was: TiO₂ nanotube 20 V < Ti and TiO₂ nanotube 15 V < TiO₂ nanotube 10 V (p < 0.05), and for bacterial biofilm formation was: TiO₂ nanotube 20 V-TiO₂ nanotube 10 V < Ti-TiO₂ nanotube 15 V (p < 0.05). Fibroblast cell proliferation was lower on TiO₂ nanotube surfaces throughout the incubation period and UV light treatment showed no enhancement in cellular response. UV treatment enhances the wettability behavior of TiO₂ nanotube surfaces and could result in lower bacterial adhesion and biofilm formation.

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·s^α) 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.

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.

This in vitro study was designed to evaluate the effect of sol-gel derived TiO₂coating 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 TiO₂and 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 (p2coated specimens showed fastest blood coagulation followed by TiO₂coated 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, TiO₂coatings promoted blood coagulation, and it was further enhanced by UV treatment, which has the potential to hasten the wound healing process in vivo.

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. 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. 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. 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.

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.