Zirconia in dental implantology: A review

Potential of Graphene-Functionalized Polymer Surfaces for Dental Applications: A Systematic review

Graphene, a two-dimensional carbon nanomaterial, has garnered widespread attention across various fields due to its outstanding properties. In dental implantology, researchers are exploring the use of graphene-functionalized polymer surfaces to enhance both the osseointegration process and the long-term success of dental implants. This review consolidates evidence from in-vivo and in-vitro studies, highlighting graphene's capacity to improve bone-to-implant contact, exhibit antibacterial properties, and enhance mechanical strength. This research investigates the effects of incorporating graphene derivatives into polymer materials on tissue response and compatibility. Among 123 search results, 14 articles meeting the predefined criteria were analyzed. The study primarily focuses on assessing the impact of GO and rGO on cellular function and stability in implants. Results indicate promising improvements in cellular function and stability with the use of GO-coated or composited implants. However, it is noted that interactions between Graphene derivatives and polymers may alter the inherent properties of the materials. Therefore, further rigorous research is deemed imperative to fully elucidate their potential in human applications. Such comprehensive understanding is essential for unlocking the extensive benefits associated with the utilization of Graphene derivatives in biomedical contexts.

Gallium-doped zirconia coatings modulate microbiological outcomes in dental implant surfaces

Despite the significant recent advances in manufacturing materials supporting advanced dental therapies, peri-implantitis still represents a severe complication in dental implantology. Herein, a sol-gel process is proposed to easily deposit antibacterial zirconia coatings onto bulk zirconia, material, which is becoming very popular for the manufacturing of abutments. The coatings' physicochemical properties were analyzed through x-ray diffraction and scanning electron microscopy-energy-dispersive x-ray spectroscopy investigations, while their stability and wettability were assessed by microscratch testing and static contact angle measurements. Uniform gallium-doped tetragonal zirconia coatings were obtained, featuring optimal mechanical stability and a hydrophilic behavior. The biological investigations pointed out that gallium-doped zirconia coatings: (i) displayed full cytocompatibility toward human gingival fibroblasts; (ii) exhibited significant antimicrobial activity against the Aggregatibacter actinomycetemcomitans pathogen; (iii) were able to preserve the commensal Streptococcus salivarius. Furthermore, the proteomic analyses revealed that the presence of Ga did not impair the normal oral microbiota. Still, interestingly, it decreased by 17% the presence of Fusobacterium nucleatum, a gram-negative, strictly anaerobic bacteria that is naturally present in the gastrointestinal tract. Therefore, this work can provide a valuable starting point for the development of coatings aimed at easily improving zirconia dental implants' performance.

Advanced Antimicrobial and Anti-Infective Strategies to Manage Peri-Implant Infection: A Narrative Review

Despite reductions in bacterial infection and enhanced success rate, the widespread use of systemic antibiotic prophylaxis in implant dentistry is controversial. This use has contributed to the growing problem of antimicrobial resistance, along with creating significant health and economic burdens. The basic mechanisms that cause implant infection can be targeted by new prevention and treatment methods which can also lead to the reduction of systemic antibiotic exposure and its associated adverse effects. This review aims to summarize advanced biomaterial strategies applied to implant components based on anti-pathogenic mechanisms and immune balance mechanisms. It emphasizes that modifying the dental implant surface and regulating the early immune response are promising strategies, which may further prevent or slow the development of peri-implant infection, and subsequent failure.

Electrochemical behavior and surface stability of dental zirconia ceramics in acidic environments

Dental zirconia ceramics, widely employed in dentistry for their biocompatibility and mechanical properties, face challenges in long-term viability within the oral cavity. This study focuses on analyzing the electrochemical behavior of a commercial dental zirconia ceramic type in acidic environments. Through extensive electrochemical investigations, including Electrochemical Impedance Spectroscopy (EIS) and cyclic polarization resistance (Cpol), corrosion resistance was assessed. Despite indications of material dissolution, our results demonstrate significant corrosion resistance, as reflected in low corrosion current density (Icorr) values. Notably, the study reveals the development of a protective oxide layer at the ceramic-electrolyte interface, contributing to material stability. XRD analysis confirms the presence of stable crystallographic phases (t-ZrO2) even after exposure to acidic media. Surface characterizations utilizing scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) affirm minimal surface damage and maintained elemental composition. These findings illuminate the intricate electrochemical behavior of dental zirconia ceramics in challenging environments, underscoring their potential for durable dental restorations. This interdisciplinary research bridges dentistry and materials science, providing valuable insights for optimizing material properties and advancing dental materials and restorative techniques.

Antimicrobial Activity of Nanozirconium Oxide

The goal behind this work is to prepare, characterize, and study the antimicrobial behavior of zirconia (ZrO2) nanoparticles (NPs). Various techniques, such as X-ray diffraction (XRD), were used for studying the mineralogical structure and crystal size. The microstructure and chemical composition of the prepared particles were analyzed using a scanning electron microscope attached with an energy-dispersive X-ray analysis (EDAX) unit. The antagonistic ability against several Gram-negative and Gram-positive bacteria, including Salmonella paratyphi, Pseudomonas aeruginosa, Alcaligenes aquatilis, Escherichia coli, Streptococcus pneumoniae, and Staphylococcus aureus, was assessed using the well diffusion method. The results of XRD and scanning electron microscopy (SEM) analyses revealed that the prepared material exhibited the phase of zirconium nanoparticles with particle sizes ranging between 40 and 75 nm. The antimicrobial test results demonstrated that the inhibitory effect increased with the increase of concentration. The inhibitory effect was more pronounced against Gram-positive bacteria, as indicated by the larger size of the inhibitory zone. At a 9% dimethyl sulfoxide (DMSO) concentration, the inhibitory zone had a diameter of 3.50 mm for S. aureus compared to a diameter of 3.40 mm for S. pneumoniae. The use of zirconium oxide nanoparticles reduced the diameter of the inhibitory zone when tested against S. aureus at a 3% DMSO concentration (0.50 mm diameter) and against S. pneumoniae (0.40 mm diameter). Zirconia nanoparticles were also evaluated for their antifungal activity against several species, including Aspergillus niger, Aspergillus flavus, and Penicillium sp. The size of the inhibitory zone indicated the susceptibility of microorganisms to nanozirconium oxide, resulting in a stronger inhibition of Penicillium sp. at a 100% DMSO concentration (4.50 mm diameter) compared to A. niger and A. flavus (3.00 mm diameter). The results for Penicillium sp. at a 3% DMSO concentration showed a diameter of the inhibitory zone of 0.90 mm, while for A. niger and A. flavus, the diameter was 0.80 mm. Thus, our findings demonstrate that the zirconium oxide nanoparticles possess the capability to reduce the inhibition zone effectively for both bacterial and fungal activities.

Metallic Dental Implants Wear Mechanisms, Materials, and Manufacturing Processes: A Literature Review

OBJECTIVES

From the treatment of damaged teeth to replacing missing teeth, dental biomaterials cover the scientific interest of many fields. Dental biomaterials are one of the implants whose effective life depends vastly on their material and manufacturing techniques. The purpose of this review is to summarize the important aspects for metallic dental implants from biomedical, mechanical and materials science perspectives. The review article will focus on five major aspects as mentioned below. Tooth anatomy: Maximizing the implant performance depends on proper understanding of human tooth anatomy and the failure behavior of the implants. Major parts from tooth anatomy including saliva characteristics are explored in this section. Wear mechanisms: The prominent wear mechanisms having a high impact on dental wear are abrasive, adhesive, fatigue and corrosion wear. To imitate the physiological working condition of dental implants, reports on the broad range of mastication force and various composition of artificial saliva have been included in this section, which can affect the tribo-corrosion behavior of dental implants. Dental implants classifications: The review paper includes a dedicated discussion on major dental implants types and their details for better understanding their applicability and characteristics. Implant materials: As of today, the most established dental implant materials are SS316L, cobalt chrome alloy and titanium. Detailed discussion on their material properties, microstructures, phase transformations and chemical compositions have been discussed here. Manufacturing techniques: In terms of different production methods, the lost wax casting method as traditional manufacturing is considered. Selective Laser Melting (SLM) and Directed Energy Deposition (DED) as additive manufacturing techniques (AM) have been discussed. For AM, the relationships between process-property-performance details have been explored briefly. The effectiveness of different manufacturing techniques was compared based on porosity distribution, mechanical and biomechanical properties.

SUMMARY

Despite having substantial research available on dental implants, there is a lack of systematic reviews to present a holistic viewpoint combining state-of-the-art from biomedical, mechanical, materials science and manufacturing perspectives. This review article attempts to combine a wide variety of analyzing approaches from those interdisciplinary fields to deliver deeper insights to researchers both in academia and industry to develop next-generation dental implants.

Development of a novel hybrid Ti6Al4V-ZrO2 surface with high wear resistance by laser and hot pressing techniques for dental implants

The development of implant metal-free surfaces has gained attention since non-benefic results have been reported related to the metallic ions released from metal implants to the human body. Ceramic coatings have been proposed as a possible solution however, the detachment of these coatings, during implantation or even in function, can compromise its function. In order to overcome this problem, this work proposes a novel hybrid Ti6Al4V-ZrO2 surface, starting with laser texturing of the Ti6Al4V substrate by Laser Nd:YV04, followed by the allocation of the zirconia (ZrO2) powder and its subsequent sintering by hot pressing process. Results revealed that zirconia strongly adheres to titanium textured surfaces since no detachment was found under tribological and adhesion scratch tests. Moreover, the tribological results showed that the incorporation of zirconia into textured titanium surface reduces significantly the wear rate of titanium (≈93%), which is a good indicator of low metallic particles/ions released to the body. These results suggest that this novel surface with good aesthetic properties and improved wear resistance (given by zirconia) and mechanical resistance (from titanium) can be a promising solution for dental implants, especially for implant/abutment or abutment/ceramic contact zones, and thus have a huge impact on the long-term performance of implants.

Epithelial cell attachment and adhesion protein expression on novel in sol TiO2 coated zirconia and titanium alloy surfaces

An adequate mucosal attachment is important when it comes to preventing peri-implant inflammation. The aim of this study was to compare epithelial cell adhesion and adhesion protein expression on in sol TiO₂ -coated and non-coated zirconia and titanium alloy surfaces. Fifty-six zirconia and titanium discs were cut, and half of them were coated with bioactive TiO₂ -coating. To study the epithelial cell attachment, human gingival keratinocytes were cultivated on discs for 1, 3, 6, and 24 h. The cell proliferation was detected by cultivating cells for 1, 3, and 7 days. In addition, the levels of adhesion proteins laminin y2, integrin α6, β4, vinculin, and paxillin were detected with Western Blot method. Furthermore, high-resolution imaging of the actin cytoskeleton and focal adhesion proteins was established. Longer-term cell culture (1-7 days) revealed higher cell numbers on the coated zirconia and titanium discs compared to non-coated discs. The difference was statistically significant (p < .05) after 24 h on coated zirconia and after 3 and 7 days on coated titanium discs compared to non-coated discs. Clear induction in the protein levels of laminin y2 and integrin α6 were detected on both coated samples, meanwhile integrin β4 were clearly induced on coated titanium alloy. The microscope evaluation showed significantly increased cell spreading on the coated discs. According to this study, the in sol induced TiO₂ -coating increases keratinocyte attachment and the expression of adhesion proteins on coated zirconia and titanium in vitro. Consequently, the coating has potential to enhance the mucosal attachment on implant surfaces.

The Main Bacterial Communities Identified in the Sites Affected by Periimplantitis: A Systematic Review

(1) Background: Periimplantitis is an infectious condition that affects the periimplant tissue and is of bacterial etiology. However, to date, the exact bacterial flora involved in its occurrence is not known. The aim of this literature review was to summarize the articles published on this topic and to identify the main bacterial species isolated in periimplantitis. (2) Methods: The articles published in three databases were researched: Pubmed, Embase and Web of Science using Prisma guides and combinations of MeSH terms. We selected 25 items from the 980 found by applying the inclusion and exclusion criteria. (3) Results: We quantified the results of the 25 studies included in this review. In general, the most commonly identified bacterial species were Gram-negative anaerobic species, as Prevotella, Streptococcus, Fusobacterium and Treponema. (4) Conclusion: The most frequent bacteria in the periimplantitis sites identified in this review are Gram-negative anaerobic species, also involved in the pathogenesis of the periodontal disease.

Structural Characterization and Osseointegrative Properties of Pulsed Laser-Deposited Fluorinated Hydroxyapatite Films on Nano-Zirconia for Implant Applications

Standard zirconia implants used in restoration still present problems related to inertness and long-term stability. Various physicochemical approaches have been used to modify the implant surfaces to improve early and late bone-to-implant integration; however, no ideal surface modification has been reported. This study used pulsed laser deposition to deposit a fluorinated hydroxyapatite (FHA) film on a zirconia implant to create a biologically active surface. The film prepared was uniform, dense, and crack-free, and exhibited granular surface droplets; it also presented excellent mechanical strength and favorable biological behavior. The FHA-coated implant was implanted on the femur of Sprague-Dawley rats, and various tests and analyses were performed. Results show that the in vitro initial cell activity on the FHA-coated samples was enhanced. In addition, higher alkaline phosphatase activity and cell mineralization were detected in cells cultured on the FHA-coated groups. Further, the newly formed bone volume of the FHA-coated group was higher than that of the bare micro-adjusted composite nano-zirconia (NANOZR) group. Therefore, the FHA film facilitated osseointegration and may improve the long-term survival rates of dental implants, and could become part of a new treatment technology for implant surfaces, promoting further optimization of NANOZR implant materials.

Fracture Resistance of Zirconia Abutments with or without a Titanium Base: An In Vitro Study for Tapered Conical Connection Implants

Dental implants with tapered conical connections are often combined with zirconia abutments for esthetics; however, the effect of the titanium base on the implant components remains unclear. This study evaluated the effects of a titanium base on the fracture resistance of zirconia abutments and damage to the tapered conical connection implants. Zirconia (Z) and titanium base zirconia (ZT) abutments were fastened to Nobel Biocare (NB) implants and Straumann (ST) implants and subjected to static load testing according to ISO 14801:2016. The experiments were performed with 3 mm of the platform exposed (P3) and no platform exposed (P0). The fracture loads were statistically greater in the titanium base abutments than the zirconia abutments for the NB and ST specimens in the P0 condition. In the P3 condition of the ST specimens, the deformation volume of the ZT group was significantly greater than the Z group. The titanium base increased the fracture resistance of the zirconia abutments. Additionally, the titanium base caused more deformation in the P3 condition. The implant joint design may also affect the amount of damage to the implants when under a load. The mechanical properties of the abutment should be considered when selecting a clinical design.

Intranuclear cell uptake and toxicity of titanium dioxide and zirconia particles as well as bacterial adhesion on dental titanium- and zirconia-implants

OBJECTIVE

Previous studies have shown that particles can be released from dental titanium (Ti)- and zirconia (ZrO₂)-implants. Titanium dioxide (TiO₂)- and ZrO₂-particles were compared regarding their toxicity and intranuclear cell uptake as well as the adhesion of various anaerobic bacteria on Ti- and ZrO₂-implants.

METHODS

Cyto- and genotoxicity of TiO₂-microparticles (TiO₂-MPs) and TiO₂-nanoparticles (TiO₂-NPs) in periodontal ligament (PDL)-hTERT cells were determined with XTT test and DNA damage with comet assay. Particle sizes of TiO₂- and ZrO₂-particles were measured with scanning electron microscope. Intranuclear uptake in PDL-hTERT cells was determined with laser scanning confocal microscopy. Adhesions of relevant anaerobic mouth bacteria Porphyromonas gingivalis, Prevotella intermedia and Aggregatibacter actinomycetemcomitans on Ti- and ZrO₂-implants were investigated by cultivation and counting bacterial colonies.

RESULTS

Particle size measurements revealed that 99% of the TiO₂-NPs had a size below 100 nm and 88% of the TiO₂-MPs sizes were between 50 and 200 nm. Following EC₅₀ values were found for particles (mg/l): 92 (TiO₂-MPs) and 15 (TiO₂-NPs). A significant increase in olive tail moment (OTM) was found for TiO₂-NPs at a concentration of 1/10 EC₅₀. TiO₂- and ZrO₂-NPs had a higher intranuclear cell uptake efficiency, compared to corresponding TiO₂- and ZrO₂-MPs. All investigated particles could be detected in cell nucleus. Adhesion of all investigated bacterial species was significantly higher on Ti-implants, compared to ZrO₂-implants.

CONCLUSION

Ti usually develops an oxide layer (TiO₂). Particles released from Ti-implants should be TiO₂-particles or Ti-particles coated with a TiO₂-layer. Toxicity of released Ti-particles depends on their oxidation state and on their size (NP or MP). Particularly, NPs were more cyto- and genotoxic compared to the corresponding MPs. TiO₂- and ZrO₂-NPs showed a significant increase in the intranuclear cell uptake ratio at higher exposure concentration, compared to lower concentrations and consequently might lead to a higher potential of DNA damage. Adhesion of bacteria to ZrO₂-implants is reduced, compared to Ti-implants. Therefore, ZrO₂-implants might contribute to reduced biological complications (e.g. periimplantitis).

Influence of TiO2 and ZrO2 Nanoparticles on Adhesive Bond Strength and Viscosity of Dentin Polymer: A Physical and Chemical Evaluation

The present study aimed to formulate an experimental adhesive (EA) and reinforce it with 5 wt.% titanium dioxide (TiO₂) or zirconium oxide (ZrO₂) to yield 5% TiO₂ and 5% ZrO₂ adhesives, respectively, and then analyze the impact of this reinforcement on various mechanical properties of the adhesives. The EA contained a blend of monomers such as bisphenol A glycol dimethacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA), 2-hydroxyethyl methacrylate (HEMA), and ethyl 4-dimethylamino benzoate and camphorquinone. The EA included ethyl 4-dimethylamino benzoate and camphorquinone photo-initiators, and diphenyliodonium hexafluorophosphate (DPIHP) was also included to act as an electron initiator. The TiO₂ and ZrO₂ nanoparticles were incorporated into the EA post-synthesis. To characterize the filler nanoparticles, scanning electron microscopy (SEM) and line-energy dispersive X-ray (EDX) spectroscopy were performed. The adhesives were characterized by analyzing their rheological properties, shear-bond strength (SBS), and interfacial failure types. Further, the resin-dentin interface was also analyzed via SEM. The TiO₂ nanoparticles were spherically shaped on the SEM micrographs, while the ZrO₂ nanoparticles were seen as non-uniformly shaped agglomerates. The EDX mapping demonstrated the presence of Ti and oxygen for TiO₂ and Zr and oxygen for the ZrO₂ nanoparticles. Both 5% TiO₂ and 5% ZrO₂ adhesives revealed decreased viscosity as compared with the EA. The 5% TiO₂ adhesive demonstrated higher SBS values for both non-thermocycled (NTC) and thermocycled samples (NTC: 25.35 ± 1.53, TC: 23.89 ± 1.95 MPa), followed by the 5% ZrO₂ adhesive group (NTC: 23.10 ± 2.22, TC: 20.72 ± 1.32 MPa). The bulk of the failures (>70%) were of adhesive type in all groups. The SEM analysis of the resin-dentin interface revealed the development of a hybrid layer and resin tags (of variable depth) for the EA and 5% TiO₂ groups. However, for the 5% ZrO₂ group, the hybrid layer and resin tag establishment appeared compromised. Reinforcement of the EA with TiO₂ or ZrO₂ caused an increase in the adhesive's SBS (with the 5% TiO₂ group demonstrating the highest values) in comparison with the EA (without nanoparticles). However, both nanoparticle-containing adhesives revealed decreased viscosity compared with the EA (without nanoparticles). Further studies investigating the impact of diverse filler concentrations on the properties of adhesives are suggested.

Impact of physical decontamination methods on zirconia implant surface and subsequent bacterial adhesion: An in-vitro study

Objective

To evaluate the effect of routinely used physical decontamination methods on the surface characteristics of zirconia implants and subsequent ability of bacteria to adhere in vitro.

Background

Physical decontamination methods commonly used in peri‐implantitis therapy and routine implant maintenance can potentially alter zirconia implant surfaces.

Methods

Acid‐etched zirconia discs were instrumented with titanium curette (TC), plastic curette, air abrasive device, ultrasonic scaler (US) with stainless steel tip. Following instrumentation, surface topography, and surface elemental composition was analyzed using 3D‐laser scanning microscopy and energy‐dispersive X‐ray spectroscopy, respectively. Subsequently, plaque biofilm was cultured on zirconia discs for 48 h and bacterial adhesion assessed using a turbidity test and scanning electron microscopy.

Results

A significant difference in surface roughness was observed between the US and control group (p < 0.05). The US and TC caused gray surface discolouration on zirconia discs due to deposition of metallic residue as confirmed by X‐ray spectroscopy. No significant difference in bacterial adhesion was noted among all treatment groups (p > 0.05).

Conclusion

TC and US with stainless steel tips should be used with caution due to deposition of metallic residue on the surface. Air abrasive devices and plastic curettes caused minimal surface alterations and are, therefore, safer for zirconia implant decontamination.

The effects of physical decontamination methods on zirconia implant surfaces: a systematic review

PURPOSE

Peri-implantitis therapy and implant maintenance are fundamental practices to enhance the longevity of zirconia implants. However, the use of physical decontamination methods, including hand instruments, polishing devices, ultrasonic scalers, and laser systems, might damage the implant surfaces. The aim of this systematic review was to evaluate the effects of physical decontamination methods on zirconia implant surfaces.

METHODS

A systematic search was conducted using 5 electronic databases: Ovid MEDLINE, PubMed, Scopus, Web of Science, and Cochrane. Hand searching of the OpenGrey database, reference lists, and 6 selected dental journals was also performed to identify relevant studies satisfying the eligibility criteria.

RESULTS

Overall, 1049 unique studies were identified, of which 11 studies were deemed suitable for final review. Air-abrasive devices with glycine powder, prophylaxis cups, and ultrasonic scalers with non-metal tips were found to cause minimal to no damage to implant-grade zirconia surfaces. However, hand instruments and ultrasonic scalers with metal tips have the potential to cause major damage to zirconia surfaces. In terms of laser systems, diode lasers appear to be the most promising, as no surface alterations were reported following their use.

CONCLUSION

Air-abrasive devices and prophylaxis cups are safe for zirconia implant decontamination due to preservation of the implant surface integrity. In contrast, hand instruments and ultrasonic scalers with metal tips should be used with caution. Recommendations for the use of laser systems could not be fully established due to significant heterogeneity among included studies, but diode lasers may be the best-suited system. Further research-specifically, randomised controlled trials-would further confirm the effects of physical decontamination methods in a clinical setting.

Silica@zirconia Core@shell Nanoparticles for Nucleic Acid Building Block Sorption

The development of delivery systems for the immobilization of nucleic acid cargo molecules is of prime importance due to the need for safe administration of DNA or RNA type of antigens and adjuvants in vaccines. Nanoparticles (NP) in the size range of 20-200 nm have attractive properties as vaccine carriers because they achieve passive targeting of immune cells and can enhance the immune response of a weakly immunogenic antigen via their size. We prepared high capacity 50 nm diameter silica@zirconia NPs with monoclinic/cubic zirconia shell by a green, cheap and up-scalable sol-gel method. We studied the behavior of the particles upon water dialysis and found that the ageing of the zirconia shell is a major determinant of the colloidal stability after transfer into the water due to physisorption of the zirconia starting material on the surface. We determined the optimum conditions for adsorption of DNA building blocks, deoxynucleoside monophosphates (dNMP), the colloidal stability of the resulting NPs and its time dependence. The ligand adsorption was favored by acidic pH, while colloidal stability required neutral-alkaline pH; thus, the optimal pH for the preparation of nucleic acid-modified particles is between 7.0-7.5. The developed silica@zirconia NPs bind as high as 207 mg dNMPs on 1 g of nanocarrier at neutral-physiological pH while maintaining good colloidal stability. We studied the influence of biological buffers and found that while phosphate buffers decrease the loading dramatically, other commonly used buffers, such as HEPES, are compatible with the nanoplatform. We propose the prepared silica@zirconia NPs as promising carriers for nucleic acid-type drug cargos.

Full Zirconia Implant-Born Prosthetic Rehabilitation with CAD/CAM Technology after Accurate Digital Planning. A Case Report

CAD/CAM technology can enhance the dentistry application of ceramic materials that meet the more relevant biocompatibility and aesthetics demands. In implant-borne prosthesis rehabilitation, yttria-stabilized zirconia appeared to be a valid alternative to metal-alloys and titanium, with comparable mechanical properties and even better interaction with bone and soft tissues. The improvement of monolithic CAD/CAM manufacturing allows for a reliable, predictable, and rapid workflow that can correspond to a holistic treatment philosophy associated with zirconia fixtures. This reported clinical case highlights the advantages of this approach in resolving particularly functionally and aesthetically complex situations. A 40-year-old patient with permanent canine impaction and the persistence of a deciduous tooth compromised by caries was successfully rehabilitated with the surgical removal of the enclosed tooth, the seating of a mono-phase zirconia implant after the deciduous extraction and its loading with a zirconia single crown, without any clinical or radiographical alteration up to seven years follow-up.

Will Zirconia Implants Replace Titanium Implants?

This review aims to discuss the advantages and disadvantages of zirconia implants compared with titanium implants. Moreover, it intends to review the relevant available long-term literature of these two materials regarding osteointegration, soft-tissue, microbiota, and peri-implantitis, focusing on clinical results. Briefly, titanium implants are a reliable alternative for missing teeth; however, they are not incapable of failure. In an attempt to provide an alternative implant material, implants made from ceramic-derivate products were developed. Owing to its optimal osseointegration competence, biocompatibility, and esthetic proprieties, zirconium dioxide (ZrO2), also known as zirconia, has gained popularity among researchers and clinicians, being a metal-free alternative for titanium implants with its main use in the anterior esthetic zones. This type of implant may present similar osseointegration as those noted on titanium implants with a greater soft-tissue response. Furthermore, this material does not show corrosion as its titanium analog, and it is less susceptible to bacterial adhesion. Lastly, even presenting a similar inflammatory response to titanium, zirconia implants offer less biofilm formation, suggesting less susceptibility to peri-implantitis. However, it is a relatively new material that has been commercially available for a decade; consequently, the literature still lacks studies with long follow-up periods.

Core-shell structured SiO2@ZrO2@SiO2 filler for radiopacity and ultra-low shrinkage dental composite resins

To overcome the interfacial problem between X-ray radiopaque ZrO₂ fillers and polymer resin in dental composites, monodispersed SiO₂@ZrO₂@SiO₂ (SZS) microspheres with narrow size distribution were prepared by a controlled sol-gel method. In the presence of SiO₂ coating layer over SiO₂@ZrO₂ (SZ) microspheres, they were easily silanized same as SiO₂ microspheres. Ethoxylated bisphenol A dimethacrylate (EBPADMA) with a higher molecular weight and a lower viscosity was used as base resin monomer mixed with a low amount of diluent triethylene glycol dimethacrylate (TEGDMA). Additionally, the addition of a small amount of pore agent acetone dicarboxylic acid (ADCA) produced some voids, thereby effectively reducing the polymerization shrinkage of the resin. The prepared dental composites combining 52 wt% monodispersed silica microsphere, 20 wt% SZS microspheres, exhibited significantly enhanced capacity in radiopacity (higher than tooth enamel) and very low shrinkage (<0.1%). It also has better mechanical properties than resin composites filled with SiO₂ microspheres, and its strength can meet practical applications. The properties of the radiopaque dental composite were to be further tuned by varying the amount of SZS microspheres contents, and the radiopaque resin has an advantage over the commercial one in that it is clinically nondestructive.

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.

In vitro and in vivo antibacterial performance of Zr & O PIII magnesium alloys with high concentration of oxygen vacancies

The effects of dual Zr and O plasma immersion ion implantation (Zr & O PIII) on antibacterial properties of ZK60 Mg alloys are systematically investigated. The results show that a hydrophobic, smooth, and ZrO₂-containing graded film is formed. Electrochemical assessment shows that the corrosion rate of the plasma-treated Mg alloy decreases and the decreased degradation rate is attributed to the protection rendered by the surface oxide. In vitro and in vivo antibacterial tests reveal Zr & O PIII ZK60 presents higher antibacterial rate compared to Zr PIII ZK60 and untreated control. The hydrophobic and smooth surface suppresses bacterial adhesion. High concentration of oxygen vacancies in the surface films are determined by X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra (UV–vis DRS) and electron paramagnetic resonance (EPR) and involved in the production of reactive oxygen species (ROS). The higher level of ROS expression inhibits biofilm formation by down-regulating the expression of icaADBC genes but up-regulating the expression of icaR gene. In addition, Zr & O PIII improves cell viability and initial cell adhesion confirming good cytocompatibility. Dual Zr & O PIII is a simple and practical means to expedite clinical acceptance of biodegradable magnesium alloys.

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A ZrO₂-containing graded film with high concentration of oxygen vacancies was formed via PIII.

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S. aureus adhesion was suppressed due to enhanced hydrophobicity and decreased roughness.

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High concentration of oxygen vacancies lead to the upregulation of ROS expression.

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ROS mediates biofilm-associated genes expression to inhibit biofilm formation in vitro and in vivo.

Atomic layer deposition on dental materials: Processing conditions and surface functionalization to improve physical, chemical, and clinical properties - A review

Surface functionalization is an effective approach to improve and enhance the properties of dental materials. A review of atomic layer deposition (ALD) in the field of dental materials is presented. ALD is a well-established thin film deposition technique. It is being used for surface functionalization in different technologies and biological related applications. With film thickness control down to Ångström length scale and uniform conformal thin films even on complex 3D substrates, high quality thin films and their reproducibility are noteworthy advantages of ALD over other thin film deposition methods. Low temperature ALD allows temperature sensitive substrates to be functionalized with high quality ultra-thin films too. In the current work, ALD is elaborated as a promising method for surface modification of dental materials. Different aspects of conventional dental materials that can be enhanced using ALD are discussed. Also, the influence of different ALD thin films and their microstructure on the surface properties, corrosion-resistance, antibacterial activity, biofilm formation, and osteoblast compatibility are addressed. Depending on the stage of advancement for the studied materials reported in the literature, these studies are then categorized into four stages: fabrication & characterization, in vitro studies, in vivo studies, and human tests. Materials coated with ALD thin films with potential dental applications are also presented here and they are categorized as stage 1. The purpose of this review is to organize and present the up to date ALD research on dental materials. The current study can serve as a guide for future work on using ALD for surface functionalization and resulting property tuning of materials in real world dental applications.

Laser Surface Texturing for Biomedical Applications: A Review

For generating a texture or pattern on a work surface, one of the emerging processes is laser surface texturing (LST). It is an effective method for producing texture on a work surface. Literature shows that various lasers have been applied to generate textures on the surface of work materials. Recently, LST has shown tremendous potential in the field of biomedical applications. Applying the LST process, the efficacy of the biomaterial has been drastically improved. This paper presents an in-depth review of laser surface texturing for biomedical applications. The effect of LST on important biomaterial has been thoroughly studied; it was found that LST has extreme potential for surface modification of biomaterial and can be utilized for biomedical applications.

Piezoelectric Direct Discharge: Devices and Applications

The piezoelectric direct discharge (PDD) is a comparatively new type of atmospheric pressure gaseous discharge for production of cold plasma. The generation of such discharge is possible using the piezoelectric cold plasma generator (PCPG) which comprises the resonant piezoelectric transformer (RPT) with voltage transformation ratio of more than 1000, allowing for reaching the output voltage >10 kV at low input voltage, typically below 25 V. As ionization gas for the PDD, either air or various gas mixtures are used. Despite some similarities with corona discharge and dielectric barrier discharge, the ignition of micro-discharges directly at the ceramic surface makes PDD unique in its physics and application potential. The PDD is used directly, in open discharge structures, mainly for treatment of electrically nonconducting surfaces. It is also applied as a plasma bridge to bias different excitation electrodes, applicable for a broad range of substrate materials. In this review, the most important architectures of the PDD based discharges are presented. The operation principle, the main operational characteristics and the example applications, exploiting the specific properties of the discharge configurations, are discussed. Due to the moderate power achievable by PCPG, of typically less than 10 W, the focus of this review is on applications involving thermally sensitive materials, including food, organic tissues, and liquids.

The Advances of Ceria Nanoparticles for Biomedical Applications in Orthopaedics

The ongoing biomedical nanotechnology has intrigued increasingly intense interests in cerium oxide nanoparticles, ceria nanoparticles or nano-ceria (CeO2-NPs). Their remarkable vacancy-oxygen defect (VO) facilitates the redox process and catalytic activity. The verification has illustrated that CeO2-NPs, a nanozyme based on inorganic nanoparticles, can achieve the anti-inflammatory effect, cancer resistance, and angiogenesis. Also, they can well complement other materials in tissue engineering (TE). Pertinent to the properties of CeO2-NPs and the pragmatic biosynthesis methods, this review will emphasize the recent application of CeO2-NPs to orthopedic biomedicine, in particular, the bone tissue engineering (BTE). The presentation, assessment, and outlook of the orthopedic potential and shortcomings of CeO2-NPs in this review expect to provide reference values for the future research and development of therapeutic agents based on CeO2-NPs.

Retentive Force of Glass-Ceramic Soldered Customized Zirconia Abutment Copings with Prefabricated Titanium Bases

Two-piece abutments consisting of customized zirconia abutment copings and prefabricated titanium bases are popular due to their biological and esthetic advantages. Glass-ceramic solder (GS) is an alternative biocompatible connective agent. This in vitro study evaluated the retentive force of GS in comparison to classical resin composite cements (RC) after artificial aging and autoclaving. Ninety specimens consisting of prefabricated titanium bases and zirconia abutment copings were fabricated. The two parts of each specimen were fixed either by RC (n = 30) or GS with a luting space of either 30 µm (n = 30) or 100 µm (n = 30). Ten specimens of each group underwent autoclaving before artificial aging (water storage, thermocycling). Twenty specimens (including the 10 autoclaved specimens) of each group were exposed to a mechanical load. The retentive force between the zirconia and titanium in all specimens was determined. A fractographic analysis was performed to analyze the fracture surfaces of the GS specimens. The RC- and GS-connected two-piece abutments showed no relevant differences, independent of the luting space. RC appears to be more vulnerable to the thermal and mechanical loads than GS. Thus, GS may be an appropriate alternative to RC for two-piece abutments, especially for patients with enhanced biocompatibility requirements.

Customized Therapeutic Surface Coatings for Dental Implants

Dental implants are frequently used to support fixed or removable dental prostheses to replace missing teeth. The clinical success of titanium dental implants is owed to the exceptional biocompatibility and osseointegration with the bone. Therefore, the enhanced therapeutic effectiveness of dental implants had always been preferred. Several concepts for implant coating and local drug delivery had been developed during the last decades. A drug is generally released by diffusion-controlled, solvent-controlled, and chemical controlled methods. Although a range of surface modifications and coatings (antimicrobial, bioactive, therapeutic drugs) have been explored for dental implants, it is still a long way from designing sophisticated therapeutic implant surfaces to achieve the specific needs of dental patients. The present article reviews various interdisciplinary aspects of surface coatings on dental implants from the perspectives of biomaterials, coatings, drug release, and related therapeutic effects. Additionally, the various types of implant coatings, localized drug release from coatings, and how released agents influence the bone–implant surface interface characteristics are discussed. This paper also highlights several strategies for local drug delivery and their limitations in dental implant coatings as some of these concepts are yet to be applied in clinical settings due to the specific requirements of individual patients.

Prolonged UV-C Irradiation is a Double-Edged Sword on the Zirconia Surface

Zirconia has become an excellent choice of dental implants because of its excellent mechanical strength, aesthetic, and biocompatibility. Although some studies have shown ultraviolet (UV) irradiation is effective to photofunctionalize dental zirconia that can improve osteoblastic function, the scattered information has not identified the most effective exposure time and wavelength of UV. Herein, this study has investigated the effects of UV irradiation on zirconia after UV-A (365 nm) or UV-C (243 nm) photofunctionalization for different times (15 min, 3 and 24 h). After irradiation, the zirconia surface was analyzed by color spectrophotometry, scanned electron microscopy (SEM), energy-dispersive X-ray spectrometry, water contact angle (WCA) with goniometer, and X-ray diffraction. Osteoblastic (MC3T3-E1) cells were cultured on zirconia discs and evaluated with a CCK-8 test kit for cell proliferation (3 h and 1 day) and with alkaline phosphatase (ALP) activity (14 days). Significant color change (ΔE) was observed by irradiating with UV-C for 15 min (1.99), 3 h (1.92), and 24 h (3.35), whereas only minute changes were observed with UV-A (respectively, ΔE: 0.18, 0.14, 0.57). No surface textural changes were observed nor a monoclinic phase was detected on both the UV-A and UV-C irradiated samples. UV-C significantly decreased the C/Zr ratios and WCA, with irradiating for 24 h presenting the lowest values, and it was the only condition to give significantly higher ALP activity at 14 days (p < 0.05) and CCK-8 values for 1 day culture (p < 0.05). It is concluded that UV-C (but not UV-A) irradiation can significantly change the aesthetic in color, and only prolonged 24 h UV-C irradiation can enhance MC3T3-E1 cell adhesion on zirconia by photofunctionalization.

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.

Effect of reduced airborne-particle abrasion pressure on the retention of zirconia copings resin bonded to titanium abutments

STATEMENT OF PROBLEM

The optimal conditioning of zirconia is essential for a durable bond between zirconia copings and titanium inserts in 2-piece dental implant abutments. Low-pressure activation of the zirconia surface may be adequate for retention.

PURPOSE

The purpose of this in vitro study was to evaluate the influence of airborne-particle abrasion (APA) of the zirconia surface with different pressures on the retention of zirconia copings bonded to titanium abutments. In addition, 2 luting systems were compared.

MATERIAL AND METHODS

Computer-aided design and computer-aided manufacturing (CAD-CAM) zirconia copings were divided into 3 groups (n=32): 0.1 MPa, 0.25 MPa, and not airborne-particle abraded surfaces with 50-μm alumina (Al₂O₃) particles. Compatible titanium abutments were airborne-particle abraded at a pressure of 0.25 MPa. All specimens were ultrasonically cleaned before bonding. Each group was divided into 2 subgroups (n=16) with different luting composite resins. A 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) containing self-adhesive luting composite resin (Panavia SA Cement Plus) and a conventional luting composite resin (Multilink Hybrid Abutment) in combination with a 10-MDP-containing universal primer (Monobond Plus) was compared. Two storage conditions were tested: in water (37 °C) for 3 days or 150 days with 37 500 thermocycles between 5 °C and 55 °C. After artificial aging, retention was measured in tension, and the failure modes were analyzed by using a light microscope and a scanning electron microscope. Statistical analysis was performed with 1-way ANOVA and the Games-Howell test for post hoc analysis (α=.05).

RESULTS

The mean retention of the airborne-particle abraded groups ranged from 576.0 N to 1049.3 N after 150 days of water storage and 37 500 thermocycles. No significant difference in bond strength was found between the 2 luting composite resin groups with airborne-particle abraded zirconia surfaces after 150 days (P<.05). Both bonding systems provided durable bond strength after 3 and 150 days. Failure mode was mainly cohesive at the titanium surfaces and predominantly adhesive at the zirconia surfaces. The retention was significantly higher if APA was used versus no APA (P<.05), while the APA pressure used made no significant difference.

CONCLUSIONS

The APA of zirconia copings at a pressure of 0.1 MPa in combination with 10-MDP-containing luting composite resins and primers is adequate for the durable bonding of zirconia copings to titanium inserts.

Clinical performance of zirconia implants: A meta-review

STATEMENT OF PROBLEM

The clinical effectiveness of zirconia implants as an alternative to titanium implants is still controversial.

PURPOSE

The purpose of this analysis was to identify and evaluate systematic reviews reporting on the clinical outcomes of zirconia implants for oral rehabilitation.

MATERIAL AND METHODS

An electronic search was undertaken on MEDLINE, Embase, and the Cochrane Oral Health Reviews databases up to December 24, 2018, without language restriction. Eligible reviews were screened and assessed. The eligibility criteria were systematic reviews or meta-analyses, implant survival rate, implant success, marginal bone loss, peri-implant soft tissue status, and biologic and functional complications of zirconia implants. Two review authors independently evaluated the quality assessment of the secondary studies by applying the Assessing the Methodological Quality of Systematic Reviews (AMSTAR) tool.

RESULTS

Nine reviews fulfilled the inclusion criteria and were evaluated. Seven reviews were classified as moderate and 2 as high quality. The overall AMSTAR's quality of these reports was moderate. In the primary studies contained in these reviews, zirconia implant clinical outcomes were found to be similar or inferior to those for titanium implants. The few primary clinical studies contained in these reviews were not homogeneous among each other, presented poor methodology, and only offered promising short-term outcomes due to the lack of long-term follow-ups.

CONCLUSIONS

Based on this meta-review, in spite of short-term promising results of zirconia implants, evidence with long term is lacking.

Evaluation of the biological behaviour of various dental implant abutment materials on attachment and viability of human gingival fibroblasts

OBJECTIVE

This study aimed to investigate the biological effects of yttria-stabilized zirconia (Y-TZP) compared to other dental implant abutment materials, i.e. lithium disilicate (LS2) and titanium alloy (Ti), as well as the effects of aging of Y-TZP on viability/proliferation and attachment properties of Human Gingival Fibroblasts (HGFs).

METHODS

Cylindrical specimens of each material were prepared as per manufacturer's instructions. Y-TZP specimens were divided into three groups: 1. no aging (Zr0), 2. aging for 5 h, 134 °C, 2 bars, 100% humidity (Zr5), 3. aging for 10 h under the same conditions (Zr10). Surface roughness was evaluated by optical profilometry; cell metabolic activity/viability by MTT assay, morphological changes by Scanning Electron Microscopy (SEM) and ratio of live/dead cells by confocal microscopy.

RESULTS

Results showed statistically significant reduction of HGF metabolic activity/viability in contact with Y-TZP after aging. Nevertheless, non-aged zirconia showed no significant differences compared with LS2, Ti and control cultures. In contrast, significant stimulation of cell metabolic activity/viability was observed in HGFs exposed to LS2 eluates. Differential morphological patterns were observed for HGF in contact with different materials/treatments, with obviously increased number of dead cells and sparser distribution of HGFs cultured on Zr10 specimens. These effects were not correlated with surface topography, since Y-TZP aging did not alter surface micro-roughness.

SIGNIFICANCE

These findings indicate that Y-TZP shows comparable biological properties to Ti and LS2 as implant abutment material. Nevertheless, Y-TZP aging might influence gingival cell attachment and proliferation properties, providing an alert to a potentially negative effect on the long-term maintenance of gingival architecture.

Improvement of mechanical properties of Y-TZP by thermal annealing with monoclinic zirconia nanoparticle coating

OBJECTIVE

To assess whether a thermal annealing with a monoclinic zirconia (mZrO₂) nanoparticle coating can improve the reliability of sandblasted yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) and maintain its mechanical strength.

METHODS

Commercially available Y-TZP (Lava Frame, 3M Dental Products) disks were sintered and surface-treated as follows: AS (as sintered, with no treatment); SB (sandblasting); SB-TA (sandblasting followed by thermal annealing at 1000 °C); and SB-mZr-TA (sandblasting followed by thermal annealing at 1000 °C with the mZrO₂ nanoparticle coating). The mZrO₂ nanoparticles of 21 nm in size were prepared by a hydrothermal method, and coated onto Y-TZP sintered disks as a 5 g/L ethanol dispersion. Biaxial flexural strength (S) was measured using the piston-on-three-ball test, and reliability was evaluated by the Weibull modulus (m).

RESULTS

Biaxial flexural tests showed a significant increase in the strength of Group SB (S_SB = 1445 ± 191 MPa) compared with Group AS (S_AS = 1071 ± 112 MPa). The thermal annealing improved the reliabilities of the sandblasted Y-TZP (m_SB-TA = 20.14 and m_SB-mZr-TA = 21.33), as compared with Group SB (m_SB = 7.77). However, the conventional thermal annealing without the mZrO₂ coating caused a significant decrease in the strength of sandblasted Y-TZP (S_SB-TA = 1273 ± 65 MPa). Importantly, the mZrO₂ coating prevented the decrease in the strength caused by conventional thermal annealing (S_SB-mZr-TA = 1379 ± 65 MPa).

SIGNIFICANCE

The thermal annealing with the mZrO₂ nanoparticle coating can improve the reliability of sandblasted Y-TZP and maintain its mechanical strength, which would otherwise be decreased by the conventional annealing process.

Influence of contact configuration and lubricating conditions on the microtriboactivity of the zirconia-Ti6Al4V pair used in dental applications

Loosening and fracture of implanted dental crowns is a consequence of relative micromovements between the zirconia abutment and the titanium alloy of the implant, in a biochemical aggressive environment. Thus, it is important to establish the in vitro tribological testing conditions that better mimics such environment. The present work aims to evaluate the effect of ball-on-plate tests configuration on the tribological behavior of ZrO2/Ti6Al4V pair in dry and lubricated conditions, using different lubricants: water, artificial saliva solution and human saliva. Ceramic balls sliding on metallic plates (TiPlate) and metallic balls sliding on ceramic plates (TiBall) were tested and the coefficient of friction (CoF) and wear response was monitored trough nanotribological tests. Open circuit potential was also measured during the tests carried out in saline solution (artificial saliva) to access the tribochemical response. The wear mechanisms were evaluated by scanning electron microscopy and atomic force microscopy analysis. Relevant differences were found between the two configurations, with and without the presence of human saliva: TiPlate presented always a higher CoF than TiBall, which may have resulted from differences in the degradation and regeneration processes of the titanium passive film during sliding. TiBall demonstrated to be the best choice to reproduce the in vivo conditions, since the metallic surface contacts permanently with zirconia, impairing the titanium repassivation. Regarding the effect of the lubricants, it was observed that human saliva had a protective action of the surfaces, leading to the lowest CoF among the lubricants used (0.19 ± 0.05 for TiBall and 0.35 ± 0.08 for TiPlate) and neglectable wear.

Biological characterization of surface-treated dental implant materials in contact with mammalian host and bacterial cells: titanium versus zirconia

Early-colonizing oral bacterial adhesion and mammal cell proliferation were similar on surface-treated titanium and zirconia.

Effects of different sterilization methods on surface characteristics and biofilm formation on zirconia in vitro

OBJECTIVE

The current laboratory study was to investigate the effect of different sterilization treatments on surface characteristics of zirconia, and biofilm formation on zirconia surface after exposure to these sterilization treatments.

METHODS

Commercially available zirconia discs (Cerconbase, Degu-Dent, Hanau, Germany) were prepared and polished to the same value of surface roughness. The discs were treated with one of the following sterilization methods steam autoclave sterilization, dry heat sterilization, ultraviolet C (UVC) irradiation, and gamma (γ) ray irradiation. The characteristics of zirconia surfaces were evaluated by scanning electron microscopy (SEM), surface roughness, surface free energy (SFE), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) measurements. Then, Staphylococcus aureus (S.a.) and Porphyromonas gingivalis (P.g.) bacteria were used and cultured on the respective sterilized zirconia surfaces. The amount of biofilm formation on zirconia surface was quantified by colony forming unit (CFU) counts.

RESULTS

Significant modifications were detected on the colour and SFE of zirconia. The colour of zirconia samples after UVC irradiation became light yellow whilst dark brown colour was observed after gamma ray irradiation. Moreover, UVC and gamma ray irradiation increased the hydrophilicity of zirconia surface. Overall, dry heat sterilized samples showed the significantly lowest amount of bacteria growth on zirconia, while UVC and gamma ray irradiation resulted in the highest.

SIGNIFICANCE

It is evident that various sterilization methods could change the surface which contribute to different biofilm formation and colour on zirconia.

Osseointegration of zirconia and titanium implants in a rabbit tibiae model evaluated by microtomography, histomorphometry and fluorochrome labeling analyses

OBJECTIVES

This study compares the osseointegration of machined-zirconia implants containing yttria (M-Y-TZP) with machined (M-Ti) and resorbable blast media (RBM-Ti) titanium implants.

MATERIAL AND METHODS

M-Y-TZP, M-Ti and RBM-Ti implants were randomly placed in rabbit tibiae. Fluorochrome bone labels (tetracycline, alizarin and calcein) were administered at different time periods. After 8 weeks, osseointegration was evaluated in terms of bone-to-implant contact (BIC), new bone area (nBA), remaining cortical bone area (rBA) and temporal quantification of fluorochromes, using micro-CT and histomorphometric analyses.

RESULTS

RBM-Ti implants showed higher resorption of the remaining cortical bone and bone formation (rBA = 36.9% and nBA = 38.8%) than M-Y-TZP implants (rBA = 48% and nBA = 26.5%). The BIC values showed no differences among the groups in the cortical region (mean = 52.2%) but in the medullary region, they were 0.45-fold higher in the RBM-Ti group (51.2%) than in the M-Y-TZP group (35.2%). In all groups, high incorporation of tetracycline was observed (2nd to 4th weeks), followed by alizarin (4th to 6th weeks) and calcein (6th to 8th weeks). In the cortical region, incorporation of tetracycline was similar between RBM-Ti (49.8%) and M-Y-TZP (35.9%) implants, but higher than M-Ti (28.2%) implants. Subsequently, alizarin and calcein were 1.1-fold higher in RBM-Ti implants than in the other implants. In the medullary region, no significant differences were observed for all fluorochromes.

CONCLUSION

All implants favored bone formation and consequently promoted primary stability. Bone formation around the threads was faster in RBM-Ti and M-Y-TZP implants than in M-Ti implants, but limited bone remodeling with M-Y-TZP implants over time can have significant effects on secondary stability, suggesting caution for its use as an alternative substitute for titanium implants.

Protein Adsorption to Titanium and Zirconia Using a Quartz Crystal Microbalance Method

Protein adsorption onto titanium (Ti) or zirconia (ZrO₂) was evaluated using a 27 MHz quartz crystal microbalance (QCM). As proteins, fibronectin (Fn), a cell adhesive protein, and albumin (Alb), a cell adhesion-inhibiting protein, were evaluated. The Ti and ZrO₂ sensors for QCM were characterized by atomic force microscopy and electron probe microanalysis observation, measurement of contact angle against water, and surface roughness. The amounts of Fn and Alb adsorbed onto the Ti and ZrO₂ sensors and apparent reaction rate were obtained using QCM measurements. Ti sensor showed greater adsorption of Fn and Alb than the ZrO₂ sensor. In addition, amount of Fn adsorbed onto the Ti or ZrO₂ sensors was higher than that of Alb. The surface roughness and hydrophilicity of Ti or ZrO₂ may influence the adsorption of Fn or Alb. With regard to the adsorption rate, Alb adsorbed more rapidly than Fn onto Ti. Comparing Ti and ZrO₂, Alb adsorption rate to Ti was faster than that to ZrO₂. Fn adsorption will be effective for cell activities, but Alb adsorption will not. QCM method could simulate in vivo Fn and Alb adsorption to Ti or ZrO₂.

In vitro performance of one- and two-piece zirconia implant systems for anterior application

OBJECTIVES

To investigate the long-term in vitro performance and fracture resistance of one-piece and bonded two-piece zirconia implant systems for anterior application.

METHODS

Two groups of bonded two-piece zirconia (ZZB), four groups of one-piece zirconia (Z), and two groups of two-piece titanium (TTS, reference) implant systems were restored with identical monolithic zirconia crowns (n=10/group). Eight specimens per group were mounted at an angle of 135° in the chewing simulator and subjected to thermal cycling (TC:18,000 cycles; 5°/55°) and mechanical loading (ML:3.6×10(6) cycles; 100N) simulating an anterior situation. Fracture resistance and maximum bending stress were determined for specimens that survived aging and for two references per group after 24h water storage. SEM pictures were used for failure analysis. Data were statistically analysed (one-way-ANOVA, post-hoc Bonferroni, Kaplan-Meier-Log-Rank, α=0.05).

RESULTS

A one-piece zirconia and a two-piece titanium implant system survived TCML without failures. Both bonded two-piece zirconia implant systems and a one-piece zirconia implant system totally failed (fractures of abutment or implant). Failure numbers of the other systems varied between 1× (1 group) and 5× (2 groups). Significantly different survival rates were found (Log-Rank-test: p=0.000). Maximum fracture forces/bending stresses varied significantly (

ANOVA

p=0.000) between 188.00±44.80N/381.02±80.15N/mm(2) and 508.67±107.00N/751.45±36.73N/mm(2). Mean fracture values after 24h water storage and TCML were not significantly different.

CONCLUSION

Zirconia implant systems partly showed material defects or connection insufficiencies. Bonded two-piece systems had higher failure rates and lower fracture resistance than one-piece implants.

CLINICAL SIGNIFICANCE

Individual zirconia implant systems may be applied in anterior regions with limitations.

In vitro performance of two-piece zirconia implant systems for anterior application

OBJECTIVES

To investigate the influence of the implant-abutment connection on the long-term in vitro performance and fracture resistance of two-piece zirconia implant systems for anterior application.

METHODS

Six groups of two-piece zirconia implant systems (n=10/group) with screw-retained (5×) or bonded (1×) connections were restored with full-contour zirconia crowns. A two-piece screw-retained titanium system served as reference. For simulating anterior loading the specimens (n=8/group) were mounted at an angle of 135° in the chewing simulator, and subjected to thermal cycling (TC: 2×9000×5°/55°C) and mechanical loading (ML: 3.6×10(6)×100N). Failed restorations were examined (scanning electron microscopy). Fracture resistance and maximum bending stress of surviving restorations were determined. 2 specimens per group were loaded to fracture after 24h water storage without TCML. Data were statistically analyzed (ANOVA; Bonferroni; Kaplan-Meier-Log-Rank; α=0.05).

RESULTS

The bonded zirconia system and the titanium reference survived TCML without any failures. Screw-retained zirconia systems showed fractures of abutments and/or implants, partly combined with screw fracture/loosening. Failure frequency (F) varied between the groups (F=8×: 3 groups, F=3×: 1 group, F=1×: 1 group). The Log-Rank-test showed significant (p=0.000) differences. Fracture forces and maximum bending stresses (mean±standard deviation) differed significantly (

ANOVA

p=0.000) between 233.4±31.4N/317.1±42.6N/mm(2) and 404.3±15.1N/549.2±20.5N/mm(2). Fracture forces after TCML were similar to 24h fracture forces.

SIGNIFICANCE

Screw-retained two-piece zirconia implant systems showed higher failure rates and lower fracture resistance than a screw-retained titanium system, and may be appropriate for clinical anterior requirements with limitations. Failures involved the abutment/implant region around the screw, indicating that the connecting design is crucial for clinical success.