Influence of laser intensity and BaTiO3 content on the surface properties of 3YSZ

Zirconia-based dental implants are in direct contact with living tissues and any improvements in their bioactivity and adhesion to the tissues are highly welcome. In this study, different ratios of barium titanate (BT) were added to 3 mol% yttria-stabilized zirconia (3YSZ) through conventional sintering. The laser-texturing technique was also conducted to improve the biological performance of 3YSZ ceramics. The composition and the surface of the prepared composites were characterized by X-ray diffraction and scanning electron microscopy (SEM), respectively. The roughness and surface wettability of the composites were also measured. Furthermore, MC3T3-E1 pre-osteoblast cells were used for the in vitro experiments. Cell viability was evaluated using a commercial resazurin-based method. Morphology and cellular adhesion were observed using SEM. Based on the results, the laser texturing and the barium titanate content influenced the surface characteristics of the prepared composites. The laser-textured 3YSZ/7 mol% BT composites showed a lower water contact angle compared to the other samples, which indicated superior surface hydrophilicity. The cell viability and cell adhesion of 3YSZ/BT composites increased with the rise in the barium titanate content and laser power. An elongated cell morphology and apatite nucleation were also observed by the BT content. Overall, the laser-treated 3YSZ/5 and 7 mol% BT composites may be promising candidates in hard tissue repair due to their good cell response.

Enhanced human periodontal ligament stem cell viability and osteogenic differentiation on two implant materials: An experimental in vitro study

Background: Surface roughness of dental implants impacts the survival of adult periodontal stem cells and rate of differentiation. This research was conducted to test how human periodontal ligament stem cells behaved on yttria stabilized tetragonal zirconia polycrystals and polyetheretherketone (PEEK) discs with different surface topographies. Methods: Discs roughening was prepared by sandblasting. Stem cells were cultivated on zirconia discs with a polished surface, PEEK discs with a polished surface, sandblasted zirconia discs and sandblasted PEEK discs. Cells viability was assessed after 24, 48, 72 hours. Scanning electron microscopy was used to examine the adherence and attachment of cells. Osteoblastic differentiation capacity was studied by checking the mineralization clusters development through alizarin red S staining and alkaline phosphatase assay. ANOVA and the Tukey post hoc test were used for the statistical analysis. Results: Polished PEEK discs showed lower cell viability, whereas roughened sandblasted zirconia and PEEK discs showed the highest proliferation rates and cell viability percent. The osteogenic differentiation was enhanced for rough surfaces in comparison to polished surfaces. Sandblasted zirconia and PEEK discs showed a markedly increased mineralized nodule development and ALP enzyme activity compared to the polished surface and control. Conclusions: Micro- topographies creation on the PEEK implant surface enhances stem cell attachment, viability, and osteogenic differentiation.

High-Strength, Biomimetic Functional Chitosan-Based Hydrogels for Full-Thickness Osteochondral Defect Repair

Fabrication of a hydrogel scaffold for full-thickness osteochondral defect repair remains a grand challenge. Developing layered and multiphasic hydrogels to mimic the intrinsic hierarchical structure of the osteochondral unit is a promising strategy. Chitosan-based hydrogels are widely applied for biomedical applications. However, insufficient mechanical strength and lack of biological cues to restore damaged cartilage and subchondral tissue significantly hinder their application in osteochondral tissue engineering. In this study, a strong and tough, osteochondral-mimicking functional chitosan-based hydrogel (bilayer-gel) with an in situ mineralized, osteoconductive lower layer and a basic fibroblast growth factor (bFGF)-incorporated, chondrogenic inducing upper layer was developed. The obtained bilayer-gel showed a depth-dependent gradient pore structure and composition. The strong double crosslinked hydrogel network and the homogeneous deposition of hydroxyapatite nanoparticles (HAp) at the lower layer provided a compressive strength of up to 2.5 MPa and a compressive strain of up to 40%. In vitro study showed that the bilayer-gel facilitates both chondrogenic differentiation in the upper layer and osteogenic differentiation in the lower layer. In vivo implantation revealed that the bilayer-gel could simultaneously promote hyaline cartilage and subchondral bone formation, thus resulting in an improved osteochondral reconstruction outcome. The present bilayer-gel thus shows great potential for full-thickness osteochondral defect repair.

Biomimetic Implant Surfaces and Their Role in Biological Integration—A Concise Review

Background: The increased use of dental implants in oral rehabilitation has been followed by the development of new biomaterials as well as improvements in the performance of biomaterials already in use. This triggers the need for appropriate analytical approaches to assess the biological and, ultimately, clinical benefits of these approaches. Aims: To address the role of physical, chemical, mechanical, and biological characteristics in order to determine the critical parameters to improve biological responses and the long-term effectiveness of dental implant surfaces. Data sources and methods: Web of Science, MEDLINE and Lilacs databases were searched for the last 30 years in English, Spanish and Portuguese idioms. Results: Chemical composition, wettability, roughness, and topography of dental implant surfaces have all been linked to biological regulation in cell interactions, osseointegration, bone tissue and peri-implant mucosa preservation. Conclusion: Techniques involving subtractive and additive methods, especially those involving laser treatment or embedding of bioactive nanoparticles, have demonstrated promising results. However, the literature is heterogeneous regarding study design and methodology, which limits comparisons between studies and the definition of the critical determinants of optimal cell response.

Osteoblast Attachment on Titanium Coated with Hydroxyapatite by Atomic Layer Deposition

Background: The increasing demand for bone implants with improved osseointegration properties has prompted researchers to develop various coating types for metal implants. Atomic layer deposition (ALD) is a method for producing nanoscale coatings conformally on complex three-dimensional surfaces. We have prepared hydroxyapatite (HA) coating on titanium (Ti) substrate with the ALD method and analyzed the biocompatibility of this coating in terms of cell adhesion and viability. Methods: HA coatings were prepared on Ti substrates by depositing CaCO₃ films by ALD and converting them to HA by wet treatment in dilute phosphate solution. MC3T3-E1 preosteoblasts were cultured on ALD-HA, glass slides and bovine bone slices. ALD-HA and glass slides were either coated or non-coated with fibronectin. After 48h culture, cells were imaged with scanning electron microscopy (SEM) and analyzed by vinculin antibody staining for focal adhesion localization. An 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) test was performed to study cell viability. Results: Vinculin staining revealed similar focal adhesion-like structures on ALD-HA as on glass slides and bone, albeit on ALD-HA and bone the structures were thinner compared to glass slides. This might be due to thin and broad focal adhesions on complex three-dimensional surfaces of ALD-HA and bone. The MTT test showed comparable cell viability on ALD-HA, glass slides and bone. Conclusion: ALD-HA coating was shown to be biocompatible in regard to cell adhesion and viability. This leads to new opportunities in developing improved implant coatings for better osseointegration and implant survival.

Surface modification of zirconia dental implants by laser texturing

The aim of this work was to perform an integrative literature review on the influence of laser irradiation on zirconia implants to enhance surface topographic aspects and the biological response for osseointegration. An electronic search was carried out on the PubMed database using the following search terms: "zirconia" AND "laser" AND "surface modification" OR "surface treatment" AND "dental implants" OR "bone" OR "osteoblast" OR "osseointegration." Of the identified articles, 12 studies were selected in this review. Results reported that the laser irradiation was capable of promoting changes on the zirconia surfaces regarding topographic aspects, roughness, and wettability. An increase in roughness was recorded at micro- and nano-scale and it resulted in an enhanced wettability and biological response. Also, adhesion, spreading, proliferation, and differentiation of osteogenic cells were also enhanced after laser irradiation mainly by using a femtosecond laser at 10nJ and 80 MHz. After 3 months of osseointegration, in vivo studies in dogs revealed a similar average percentage of bone-to-implant contact (BIC) on zirconia surfaces (around 47.9 ± 16%) when compared to standard titanium surfaces (61.73 ±16.27%), denoting that there is no significant difference between such different materials. The laser  approach revealed several parameters that can be used for zirconia surface modification such as irradiation intensity, time, and frequency. Laser irradiation parameters can be optimized and well-controlled to reach desirable surface morphologic aspects and biological response concerning the osseointegration process.

Surface Modifications for Zirconia Dental Implants: A Review

Zirconia-based bioceramic is a potential material for dental implants developed and introduced in dentistry 30 years ago. However, some limitations still exist for zirconia implants caused by several factors, such as manufacturing difficulties, low-temperature degradation (LTD), long-term stability, and clinical experience. Several studies validated that some subtle changes on the zirconia surface might significantly impact its mechanical properties and osseointegration. Thus, attention was paid to the effect of surface modification of zirconia implants. This review generally summarizes the surface modifications of zirconia implants to date classified as physical treatment, chemical treatment, and surface coating, aiming to give an overall perspective based on the current situation. In conclusion, surface modification is an effective and essential method for zirconia implant application. However, before clinical use, we need more knowledge about these modification methods.

Effects of ytterbium laser surface treatment on the bonding of two resin cements to zirconia

Monolithic zirconia crowns bonded to zirconia abutments have become more commonly used in the construction of cement-retained implant superstructures. The present study aimed to examine the effects of laser surface treatments on the bond strength of two resin cements to zirconia. Three types of surfaces were examined: untreated, alumina blasted, and ytterbium laser treated; and two types of resin cements: 4-META/MMA-TBB resin cement and composite resin cement. Half of the specimens were subjected to a thermocycling process. Subsequently, a shear bond test was carried out. In addition, surface roughness was measured for each surface type. The results showed that laser treatment increased zirconia surface roughness and that laser treatment significantly increased shear bond strength after the thermocycling of both cement types compared to no treatment. Our experimental results suggested that ytterbium laser surface treatment of zirconia increased the bond strength of resin cements.

Comparative evaluation of surface-modified zirconia for the growth of bone cells and early osseointegration

STATEMENT OF PROBLEM

Rapid osseointegration between implant and bone tissue for early loading of a prosthesis with sufficient primary stability depends on the surface characteristics of the implant. The development and characterization of suitable surface coatings on dental implants is a major challenge.

PURPOSE

The purpose of this in vitro study was to evaluate and compare the osteogenic potential and cytotoxicity of unmodified zirconia, acid-etched zirconia, bioactive glass-coated zirconia, and tamarind kernel polysaccharide with hydrophilic acrylic acid (TKP-AA) hydrogel-coated zirconia.

MATERIAL AND METHODS

Thirty-six disks each of unmodified zirconia, acid-etched, 45S5 bioactive glass-coated, and TKP-AA hydrogel-coated zirconia were evaluated for osteogenic potential and cytotoxic effect by using human osteoblast Saos-2 cells. The surface topography of the disks and the morphology of the cells grown on these surfaces were examined by scanning electron microscopy (n=3). The cell attachment was evaluated by confocal imaging (n=3). The cytotoxic effect was evaluated by cell viability assay (n=9). Osteoblast maturation was assessed by alkaline phosphatase assay (n=9) and cell mineralization by alizarin red staining (n=9). ANOVA and Bonferroni multiple comparison post hoc tests were used to evaluate the statistical significance of the intergroup differences in these characteristics (α=.05).

RESULTS

The surface modifications resulted in distinct changes in the surface morphology of zirconia disks and the growth of Saos-2 cells. Zirconia disks coated with TKP-AA promoted higher proliferation of osteoblasts compared with unmodified disks (P<.001). Similarly, the surface modifications significantly increased the differentiation of mesenchymal stem cells to osteoblasts as compared with uncoated zirconia (P<.001). However, the rate of differentiation to osteoblasts was similar among the surface modifications. Acid-etched and TKP-AA-coated disks promoted mineralization of osteoblasts to the same extent, except bioactive glass coating, which significantly increased the rate of mineralization (P<.001).

CONCLUSIONS

Surface modification of zirconia by acid etching and coating with Bioglass or TKP-AA hydrogel resulted in the improved growth and differentiation of osteoblasts. TKP-AA hydrogel coating promoted the proliferation of osteoblasts, whereas Bioglass coating showed better mineralization. TKP-AA hydrogel coating is a promising candidate for improving the osseointegration of dental implants that warrants further investigation.

Peptidic biofunctionalization of laser patterned dental zirconia: A biochemical-topographical approach

A dual approach employing peptidic biofunctionalization and laser micro-patterns on dental zirconia was explored, with the aim of providing a flexible tool to improve tissue integration of restorations. Direct laser interference patterning with a femtosecond Ti:Sapphire laser was employed, and two periodic grooved patterns were produced with a periodicity of 3 and 10 μm. A platform containing the cell-adhesive RGD and the osteogenic DWIVA peptides was used to functionalize the grooved surfaces. Topography and surface damage were characterized by confocal laser scanning (CLSM), scanning electron and scanning transmission electron microscopy techniques. The surface patterns exhibited a high homogeneity and subsurface damage was found in the form of nano-cracks and nano-pores, at the bottom of the valleys. Accelerated tests in water steam were carried out to assess hydrothermal degradation resistance, which slightly decreased after the laser treatment. Interestingly, the detrimental effects of the laser modification were reverted by a post-laser thermal treatment. The attachment of the molecule was verified trough fluorescence CLSM and X-ray photoelectron spectroscopy. Finally, the biological properties of the surfaces were studied in human mesenchymal stem cells. Cell adhesion, morphology, migration and differentiation were investigated. Cells on grooved surfaces displayed an elongated morphology and aligned along the patterns. On these surfaces, migration was greatly enhanced along the grooves, but also highly restricted in the perpendicular direction as compared to flat specimens. After biofunctionalization, cell number and cell area increased and well-developed cell cytoskeletons were observed. However, no effects on cell migration were found for the peptidic platform. Although some osteogenic potential was found in specimens grooved with a periodicity of 10 μm, the largest effects were observed from the biomolecule, which favored upregulation of several genes related to osteoblastic differentiation in all the surfaces.

The Impact of Dental Implant Surface Modifications on Osseointegration and Biofilm Formation

Implant surface design has evolved to meet oral rehabilitation challenges in both healthy and compromised bone. For example, to conquer the most common dental implant-related complications, peri-implantitis, and subsequent implant loss, implant surfaces have been modified to introduce desired properties to a dental implant and thus increase the implant success rate and expand their indications. Until now, a diversity of implant surface modifications, including different physical, chemical, and biological techniques, have been applied to a broad range of materials, such as titanium, zirconia, and polyether ether ketone, to achieve these goals. Ideal modifications enhance the interaction between the implant's surface and its surrounding bone which will facilitate osseointegration while minimizing the bacterial colonization to reduce the risk of biofilm formation. This review article aims to comprehensively discuss currently available implant surface modifications commonly used in implantology in terms of their impact on osseointegration and biofilm formation, which is critical for clinicians to choose the most suitable materials to improve the success and survival of implantation.

Laser Nd:YAG patterning enhance human osteoblast behavior on zirconia implants

Zirconia has been regarded as a promising material for dental implants, and Nd:YAG laser treatment has been proposed as a potential strategy to improve its bioactivity. The main aim of the present study was to evaluate the in vitro behavior of human fetal osteoblasts in contact with laser-textured zirconia implant surfaces assessing the effect of different texture patterns, spacing between laser passes and number of laser passes. Zirconia discs were produced and treated with Nd:YAG laser according to test group variables: texture (microgrooves and micropillar array), distance between surface features (25 μm, 30 μm and 35 μm), and laser passes [1, 2, 4, and 8]. Untextured sandblasted and acid-etched zirconia discs (SBAE) were used as controls. Human osteoblasts (hFOB 1.19) were cultured for 14 days on test and control samples. Morphology and cellular adhesion were observed using scanning electron microscopy (SEM). Cell viability and proliferation were evaluated at 1, 3, 7, and 14 days using a commercial resazurin-based method. Collagen type I was evaluated at 3 days using ELISA. Alkaline phosphatase (ALP) activity was evaluated at 7 days using a colorimetric enzymatic technique. Group comparisons were tested using ANOVA or Mann-Whitney test (Tukey's post hoc) using statistical software, and significance was set at p < 0.05. Cell viability and proliferation increased over time for all groups with statistically higher values for laser-textured groups when compared with control at 7 and 14 days in culture (p < 0.05). Collagen type I levels were higher for study groups (p < 0.05) when compared with control group. No statistically differences were detected for ALP activity levels between texture and control groups (p > 0.05). The results suggest that laser-machined zirconia implant surfaces may benefit biological osteoblast response. However, the type of texture, spacing at the range of 25-35 μm, and number of laser passes did not seem to be relevant variables.

An introduction of biological performance of zirconia with different surface characteristics: A review

Zirconia (ZrO₂) ceramic is widely used in dentistry as a clinical dental biomaterial. In this review, we are focusing on and summarizing the biological performance of zirconia under different surface characteristics. We have included an initial tissue cell attachment study on zirconia and bacterial adhesion on zirconia. Our results suggest that surface modifications applied on zirconia may change the interfacial surface characteristics e.g. surface roughness, surface free energy, and chemistry of zirconia. The modifications also result in advanced biological performance of zirconia, including enhanced tissue cell attachment and reduction of bacterial adhesion. The recent laboratory research has provided many interesting modification methods and showed clinically interesting and promising outcomes. A few of the outcomes are validated and have been applied in clinical dentistry.

Surrounding Tissue Response to Surface-Treated Zirconia Implants

Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP), which are partially stabilized zirconia, have been used for fabricating dental implants. This study investigated the soft tissue attachment, the collagen fiber orientation to zirconia at different surface conditions, and the bone response using implantation experiments in animals. The zirconia implant surfaces were treated with ultraviolet irradiation (UV), a combination of large-grit sandblasting and hydrofluoric acid etching (blastedHF), and a combination of blastedHF and UV (blastedHF+UV). The surface treated with blastedHF and blastedHF+UV appeared rough and hydrophilic. The surface treated with blastedHF+UV appeared to be superhydrophilic. Subsequently, tapered cylindrical zirconia implants were placed in the alveolar sockets of the maxillary molars of rats. The bone-to-implant contact ratio of blastedHF and blastedHF+UV implants was significantly higher than that of the non-treated controls and UV-treated implants. The four different surface-treated zirconia implants demonstrated tight soft tissue attachments. Perpendicularly oriented collagen fibers towards zirconia implants were more prominent in blastedHF and blastedHF+UV implants compared to the controls and UV-treated implants. The area of the soft tissue attachment was the greatest with the perpendicularly oriented collagen fibers of blastedHF+UV-treated implants. In conclusion, blastedHF+UV treatment could be beneficial for ensuring greater soft-tissue attachment for zirconia implants.

Enhanced chondrogenic differentiation of equine bone marrow-derived mesenchymal stem cells in zirconia microwell substrata

In human cartilage tissue engineering, three-dimensional zirconia substrata have the potential advantage of producing many uniform cell clusters of controlled size without xenobiotic material, allowing easy clinical application. The objective of this study was to evaluate the possibility of using zirconia porous three-dimensional microwell substrata for chondrogenic differentiation of equine bone marrow-derived mesenchymal stem cells (BMMSCs) in vitro. In regular medium, 8 × 10⁵, 2 × 10⁶, and 5 × 10⁶ equine BMMSCs from five thoroughbred horses were cultured on zirconia microwell substrata for 4 days to allow formation of clusters. The medium was replaced by chondrogenic culture medium. After chondrogenic culture for 7, 14 and 21 days, analysis of collagen type II alpha 1 gene (COL2A1) gene expression and observation of chondrogenic aggregates by scanning electron microscopy (SEM) were performed. SEM showed size-controlled cell clusters and increasing extracellular matrix over time when using 5 × 10⁶ cells. The expression of COL2A1 on day 7 and 14 with 5 × 10⁶ cells was significantly higher than that of conventional pellet culture with 2 × 10⁶ cells. Histological evaluation by immunohistochemical staining for type II collagen (ColII) was performed after chondrogenic culture for 7 days. The clusters showed wide distribution of ColII. The results suggest that the zirconia substrata have the potential to enhance the chondrogenic differentiation of equine BMMSCs, allowing effective equine cartilage tissue engineering without xenobiotic materials.

Analysis of osteogenic potential on 3mol% yttria-stabilized tetragonal zirconia polycrystals and two different niobium oxide containing zirconia ceramics

PURPOSE

This study was performed to evaluate the osteogenic potential of 3mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) and niobium oxide containing Y-TZPs with specific ratios, new (Y,Nb)-TZPs, namely YN4533 and YN4533/Al20 discs.

MATERIALS AND METHODS

3Y-TZP, YN4533 and YN4533/Al20 discs (15 mm diameter and 1 mm thickness) were prepared and their average surface roughness (R_a) and surface topography were analyzed using 3-D confocal laser microscope (CLSM) and scanning electron microscope (SEM). Mouse pre-osteoblast MC3T3-E1 cells were seeded onto all zirconia discs and evaluated with regard to cell attachment and morphology by (CLSM), cell proliferation by PicoGreen assay, and cell differentiation by Reverse-Transcription PCR and Quantitative Real-Time PCR, and alkaline phosphatase (Alp) staining.

RESULTS

The cellular morphology of MC3T3-E1 pre-osteoblasts was more stretched on a smooth surface than on a rough surface, regardless of the material. Cellular proliferation was higher on smooth surfaces, but there were no significant differences between 3Y-TZP, YN4533, and YN4533/Al20. Osteoblast differentiation patterns on YN4533 and YN4533/Al20 were similar to or slightly higher than seen in 3Y-TZP. Although there were no significant differences in bone marker gene expression (alkaline phosphatase and osteocalcin), Alp staining indicated better osteoblast differentiation on YN4533 and YN4533/Al20 compared to 3Y-TZP.

CONCLUSION

Based on these results, niobium oxide containing Y-TZPs have comparable osteogenic potential to 3Y-TZP and are expected to be suitable alternative ceramics dental implant materials to titanium for aesthetically important areas.

Behavior of human periodontal ligament cells on dentin surfaces ablated with an ultra-short pulsed laser

This study aimed to evaluate the effects of an ultrashort pulsed laser (USPL) (1064 nm, 20 ps, 100 kHz) with different laser fluences (F, 4, 6, 8 J/cm²) and pulse overlaps (PO, 0, 50%) on human periodontal ligament cells (hPDLs) behavior. Dentin samples were ablated with USPL with different combinations of fluences and pulse overlaps; some samples were ablated with an Er:YAG laser (2940 nm, 150 µs, 100 mJ/pulse, 5 J/cm²) and some samples were ground with a carbide bur. Then hPDLs were grown on the samples after different treatments. Dentin morphology and cell adhesion were observed with SEM and gene expressions were measured by RT-PCR. The results showed dentin surfaces ablated with USPL when F = 4 J/cm², PO = 0, and F = 6 J/cm², PO = 0 were partially intact with obvious ridges and valleys and cells on these surfaces grew mostly along the valleys. USPL ablated surfaces in other groups were entirely ablated and cell cluster formation was observed. The RT-PCR results showed an upregulation of osteocalcin of cells grown on the dentin after some laser treatment. It can be concluded that USPL could improve the attachment and differentiation of hPDLs and thus potentially promote periodontal tissue regeneration.