Additively manufactured zirconia periodontal splint integrated prosthesis: A proof-of-concept

OBJECTIVES

To provide a digital workflow for designing custom zirconia periodontal splints using material jetting (MJ) technology to support and rehabilitate periodontally compromised anterior teeth.

METHODS

Initially, the maxillary and mandibular teeth were scanned using a Trios3 intraoral scanner (IOS). Subsequently, the periodontal splint was digitally designed using a computer-aided design software. Then, a zirconia periodontal splint was produced using MJ technology with a three-dimensional (3D) printer (Carmel 1400C). Additionally, the trueness of the periodontal splint was analyzed using 3D detection software (Geomagic Control X 2018). Finally, the periodontal splint was adhered using resin cement.

RESULTS

In terms of trueness, the intaglio surface and the prosthesis of the periodontal splint matched well, whereas the lingual surface showed some deviation areas. The trueness root mean square (RMS) value of the splint was 57.7 μm and the deviation remained within ± 200 μm. For clinical treatment, the periodontal splint was precisely bonded and achieved the effect of supporting and rehabilitating periodontally compromised anterior teeth. After six months of treatment, the follow-up results showed that the splint remained intact, with no further absorption of the alveolar bone.

CONCLUSIONS

Additively manufactured zirconia periodontal splints exhibit good trueness and aesthetics. Periodontal splints can achieve precise bonding and maintain long-term bonding stability, and can help stabilize loosened teeth and prevent further absorption by the alveolar bone.

CLINICAL SIGNIFICANCE

This proof-of-concept outlines a digital workflow for designing zirconia periodontal splints using MJ technology to improve outcomes of periodontitis treatments. Moreover, the adhesive stability and efficacy of periodontitis treatment using the periodontal splint were preliminarily verified.

Comprehensive review of polyetheretherketone use in dentistry

PURPOSE

This study aimed to comprehensively summarize the current state, shortcomings, and challenges regarding the use of polyetheretherketone (PEEK) in various fields of stomatology.

STUDY SELECTION

This study reviewed articles retrieved from PubMed, Google Scholar, Web of Science, and ScienceDirect databases. The main keywords used during the search included "polyetheretherketone (PEEK)," "dental materials," "orthodontics," "prosthodontics," "oral implantology," "oral and maxillofacial surgery," "periodontics" "osseointegration," and "surface modification."

RESULTS

Numerous studies have highlighted the properties of PEEK that contribute to its usefulness in dentistry, including its high biocompatibility, fracture resistance, aesthetics, radiolucency, and bone-like mechanical properties. Promising applications of PEEK in dentistry include orthodontic archwires, interceptive orthodontic appliances, fixed lingual retainers, crowns, post and cores, fixed partial dentures, removable partial dentures, maxillofacial prostheses, dental implants, implant abutments, alveolar bone scaffolds, jaw reconstruction, temporomandibular joint reconstruction, periodontal splints, and occlusal splints. In addition, many in vitro and in vivo experiments have demonstrated that the in vivo bone integration capability can be effectively improved using advanced surface modification technologies.

CONCLUSIONS

PEEK has been explored in several dentistry fields owing to its excellent properties. PEEK and its modifications are most frequently used in clinical dentistry. However, most of its applications are based on in vitro or short-term in vivo evaluations. Additional long-term clinical data are required to demonstrate the applicability and superiority of PEEK in dentistry.

Effect of different additive manufacturing technologies on the fracture load of 3-unit monolithic zirconia fixed partial dentures: In vitro mechanical evaluation and energy-dispersive spectroscopy analysis

STATEMENT OF PROBLEM

Studies examining the influence of different fabrication techniques on the fracture load (FL) of monolithic zirconia restorations are sparse.

PURPOSE

The purpose of this in vitro study was to compare the FL of monolithic zirconia restorations manufactured with different technologies.

MATERIAL AND METHODS

A typodont model with a missing left first molar was used and laboratory scanned (inEos X5; Dentsply Sirona). Data were transferred to a computer-aided design software program (InLab 16.1; Dentsply Sirona). The cement space for the 3-unit fixed partial dentures was set at 50 µm, and the connector area was specified as 9 ±0.2 mm2. The subtractive technique was designated as the control group (GC Initial Zirconia HT; GC Corp), while 3 experimental groups were created by using different additive techniques (GrSLA [3DMix Zirconia 3Y; 3D Ceram], GrDLP [Inni Cera; Aon], and GrLCM [LithaCon 3Y 210; Lithoz]) (n=8). In all groups, 3 mol% yttria-stabilized tetragonal zirconia polycrystalline was used. The FL test was conducted on models fabricated from glass-filled resin-based methacrylate and postpolymerized. After thermal cycling (5000 cycles, 5-55 °C), all specimens were loaded with a stainless-steel ball at a crosshead speed of 1 mm/minute until fracture in a precision universal testing device. The maximum loads at fracture were recorded in N. Weibull analysis was used to determine the characteristic strength and reliability. The fracture lines were analyzed by scanning electron microscopy at magnifications of ×50 and ×500. The elemental compositions were compared with energy dispersive spectroscopy. A 1-way ANOVA and Tukey post hoc test were used for statistical analysis (α=.05).

RESULTS

Significant differences in FL values were found among the groups (P<.001). GrDLP had the lowest FL (821 ±160 N), while the highest FL belonged to the control group, followed by GrLCM (1132 ±209 N). Weibull analysis showed GrDLP had the highest reliability. Failure analysis indicated that there were fractures and cracks in the pontic region in all groups.

CONCLUSIONS

Although the control group performed better, the FL values of monolithic zirconia restorations fabricated by using different additive manufacturing methods exceeded the clinically relevant threshold (790 N), demonstrating their suitability for posterior use.

Miscible chemical ordering in Ti-Cr-Mo quinary system by solid solution of Mo2Ti2AlC3 and Cr2.5Ti1.5AlC3 o-MAXs

Out-of-plane ordering is promising for separately adjusting the heterodesmic chemical bonding inside the MAX phase thus tuning their properties, while constructing the out-of-plane ordered-MAX (o-MAX) is still a challenge. In this work, a strategy towards o-MAX by solid solutions of two existing o-MAXs is verified, i.e., Cr2.5Ti1.5AlC3 and Mo2Ti2AlC3, with controllable stoichiometric ratios (1:2, 1:1, and 2:1). A miscible chemical ordering is observed in three Ti-Cr-Mo quinary MAXs, which inherits the out-of-plane ordering from both parental o-MAXs. Meanwhile, through density functional theory (DFT) calculations, the electronic structure and bonding states inside the quinary o-MAXs are analyzed. Based on the calculations, anisotropic and improved mechanical properties are predicted, which agree with the experimental observed high compressive strength and tunable capacity of energy dissipation. The present work proves a promising way for synthesizing multicomponent o-MAXs.

Influence of Pontic Length on the Structural Integrity of Zirconia Fixed Partial Dentures (FPDs)

OBJECTIVE

This study aims to evaluate the influence of pontic length and design on the fracture resistance of zirconia fixed dental prostheses (FDPs). By assessing different span lengths under controlled mechanical loading conditions, the research seeks to provide insights into optimizing the structural integrity of zirconia dental bridges.

MATERIALS AND METHODS

A total of 20 zirconia bridges were fabricated and tested in vitro. Ten bridges were designed to replace a single missing molar (tooth 46), with a pontic span of 11 mm, while the remaining ten were crafted for two missing teeth (35 and 36), featuring a longer pontic span of 17 mm. The zirconia frameworks were milled using the Wieland Zenotec® Select Hybrid system and cemented onto metal abutments with Voco Meron Plus QM resin-reinforced glass ionomer cement. The specimens were subjected to occlusal loading using a ZwickRoell ProLine Z005 testing machine at a crosshead speed of 1 mm/min until fracture occurred.

RESULTS

The mechanical testing revealed a significant correlation between pontic length and fracture resistance. The mean fracture resistance for three-unit bridges (single pontic) was 3703 N, whereas four-unit bridges (double pontic) exhibited a significantly lower resistance of 1713 N. These findings indicate that increased span length reduces the fracture resistance of zirconia restorations due to higher stress accumulation and reduced rigidity.

CONCLUSIONS

This study underscores the importance of pontic length and design in determining the fracture resistance of zirconia restorations. Shorter spans exhibit greater structural stability, reinforcing the need for careful treatment planning when designing multi-unit zirconia bridges. By optimizing bridge parameters, clinicians can improve clinical outcomes and extend the longevity of zirconia prostheses in restorative dentistry.

Effect of Cement Type on Marginal Microleakage of Zirconia Crowns with or without Cervical Margin Relocation: An In Vitro Study

This study evaluated the microleakage in zirconia crowns cemented with bioactive vs resin cements at two margin locations: cementum/dentin deep margin and composite-elevated margins. Standardized mesial box cavities were prepared in 30 molar teeth, with proximal cavosurface margins placed 1 mm below the cemento-enamel junction (CEJ) and restored with resin composite. The teeth were prepared for zirconia crowns, with mesial margins on the composite and distal margins on tooth structure 1 mm below the CEJ. Following digitization and zirconia crown fabrication, the specimens were randomly allocated into five groups based on the type of cement used: one multistep adhesive resin, one self-adhesive resin, one bioactive hybrid ionic resin, and two bioceramic cements. Microleakage was evaluated by measuring the percentage of dye penetration depth at the interfaces, with data analyzed using two-way ANOVA. The results revealed a significant interaction between cement type and margin location, with elevated margins exhibiting less leakage than deep ones across all cement types (p≤0.001). However, the effect of margin location on microleakage varied depending on the cement type, with variations in microleakage scores at each margin location ranging from statistically nonsignificant (p>0.05) to statistically significant (p≤0.05). Adhesive resin and hybrid bioactive cements significantly outperformed others in reducing microleakage at both margin interfaces.

Valorization of crop by-products into bio-based dental materials: advancements and prospects

The objective of this review is to deepen understanding and emphasize scientific and technological progress in the transformation of crop by-products into bio-based dental materials. Amid heightened environmental sustainability consciousness, various sectors including dentistry have achieved novel advancements by utilizing bio-based materials from crop by-products for dental restorations. This paper provides a thorough review of the extraction, processing, and application of natural polymers, biopolymers, and bio-based mixtures at both the macroscopic and nanoscopic scales, with a focus on their contextualization within dental practices. The performance and efficacy of bio-resins, bio-sourced monomers, and biopolymers derived from these resources were scrutinized and compared with traditional petroleum-based counterparts. This study addresses the recycling and industrial valorization of bio-based dental materials, emphasizing their potential to foster a circular economy in dentistry.

In vitro Analysis of DSPP and BSP Expression: Comparing the Odontogenic Influence of Bio-C Repair and Biodentine in hDPSCs

OBJECTIVES

 This study compared the ability of BIO-C Repair (BC) and Biodentine (BD) in relation to odontogenic differentiation by evaluating the dentin sialophosphoprotein (DSPP) and bone sialoprotein (BSP) expression and mineral deposition of human dental pulp stem cells (hDPSCs).

MATERIALS AND METHODS

 BC and BD were pulverized and sterilized (ISO 10993-5:2009). The hDPSCs were the result of primary cultures that were 80% confluent (having gone through the stem cell marker tests CD90 98%, CD105 99.7%, CD73 94%, and LinNeg 0.5%) and reached P2-3 by means of serum starvation for 24 hours. This study involved seven groups, in which the hDPSCs were cultured on osteogenic media with the addition of either BD (Septodont, United States) at concentrations of 1:1, 1:2, or 1:5; BC (Angelus, Brazil) at concentrations of 1:1, 1:2, or 1:5; or the negative control (Dulbecco's modified eagle medium + osteogenic media). The hDPSC differentiation was determined via enzyme-linked immunosorbent assays of DSPP and BSP expression performed on days 7 and 14 and alizarin red staining performed on day 21.

STATISTICAL ANALYSIS

 The data were analyzed using a one-way analysis of variance, followed by Tamhane's post hoc test, to compare the differences between groups. The t-test dependent was also used to identify differences between groups.

RESULTS

 BC and BD at 1:1 concentration, there was a statistically significant difference in DSPP and BSP expression. However, at concentrations of 1:2 and 1:5, there was no significant difference observed in either duration of observation (p > 0.05). The highest DSPP and BSP concentrations after 7 and 14 days of observation were observed with BD and BC at 1:5 concentration (6.6-6.71 and 13.20-13.47 ng/mL).

CONCLUSION

 The study shows that BC is as effective as BD in enhancing DSPP and BSP expression and mineral deposition in hDPSCs. The 1:5 concentration of BC showed the highest levels of DSPP and BSP expression and mineral deposition.

Retrospective Long-Term Survival Rate and Clinical Performance of Zirconium Oxide Restorations over the Past 5 Years: A Comparative Study Between Single Crowns and Fixed Dental Prostheses

Background and Objectives: This five-year retrospective study evaluated the survival and clinical performance of 1143 zirconium oxide restorations, including both monolithic (144) and layered (999) restorations. Materials and Methods: The analysis included clinical records and follow-up data of patients treated with zirconium oxide restorations. Failures in layered restorations were examined, particularly focusing on chipping caused by unsupported feldspathic ceramic exceeding 1.5 mm. Monolithic restorations were used as a benchmark for durability. Results: The results demonstrated a high overall survival rate of 96.3%, with monolithic restorations achieving a perfect survival rate of 100%, while layered restorations had a survival rate of 95.8%. Failures in the layered restorations were primarily associated with chipping, especially when the unsupported feldspathic ceramic exceeded 1.5 mm. Conclusions: This finding highlights the importance of maintaining adequate support for the ceramic layer to prevent such complications. Monolithic restorations, in contrast, showed superior durability, with no failures reported, making them a more reliable option for long-term success. These findings emphasize the need for the careful selection of zirconium oxide restoration types based on the clinical context, particularly in cases where durability is critical.

Mechanical Behavior of PEEK and PMMA Graphene and Ti6Al4V Implant-Supported Frameworks: In Silico Study

A comparative analysis has been carried out between three different dental materials suitable for the prostheses manufacturing. The analysis performed is based on the finite elements method (FEM) and was made to evaluate their performance under three different loading conditions. Three different materials were modeled with 3D CAD geometry, all of them suitable to be simulated by means of a linear elastic model. The materials employed were graphene polymethyl methacrylate (G-PMMA) with 0.25% of graphene, polyether ether ketone (PEEK), and Ti6Al4V. Three loading conditions have been defined: distal, medial, and central. In all cases under study, the load was applied progressively, 5 N by 5 N until a previously fixed threshold of 25 N was reached, which always ensures that work is carried out in the elastic zone. The behavior of G-PMMA and PEEK in the tests performed is similar. Regarding maximum deformations in the model, it has been found that deformations are higher in the G-PMMA models when compared to those made of PEEK. The highest values of maximum stress according to the von Mises criteria are achieved in models made of Ti6Al4V, followed by G-PMMA and PEEK. G-PMMA is more prone to plastic deformations compared to Ti6Al4V. However, due to its relatively higher stiffness compared to other common polymers, G-PMMA is able to withstand moderate stress levels before significant deformation occurs, placing it in the intermediate position between Ti6Al4V and PEEK in terms of stress capacity. It should be noted that there is also a difference in the results obtained depending on the applied load, whether distal, medial, or central, proving that, in all simulations, it is the distal test that offers the worst results in terms of presenting a higher value for both displacement and tension. The results obtained allow us to identify the advantages and limitations of each material in terms of structural strength, mechanical behavior, and adaptability to loading conditions that simulate realistic scenarios.

Impact of surface pre-treatment on bond strength between cement and zirconia: A systematic review and network meta-analysis

STATEMENT OF PROBLEM

The optimal zirconia pretreatment, contingent upon the type of cement used, warrants further research.

PURPOSE

The purpose of this investigation was to evaluate the influence of various surface pretreatments on the bonding efficacy of cement to zirconia.

MATERIAL AND METHODS

A comprehensive search was conducted across the PubMed, Embase, Scopus, and Web of Science databases for in vitro studies related to bonding with zirconia up to April 2024, supplemented by a manual search. A network meta-analysis was executed to compare different types of cement.

RESULTS

Of the 6118 articles screened, 21 were selected for inclusion in this review. These studies examined various surface pretreatment techniques, primers, resin cements, aging protocols, and bond strength testing methods. The highest bond strengths were observed with 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-based cements. The network meta-analysis indicated that mechanical and mechano-chemical pretreatments yielded superior results across all cement types.

CONCLUSIONS

The existing evidence indicates that both surface pretreatments and the specific type of cement should be considered when interpreting the findings of in vitro studies for their application in clinical practice.

Single-cell analysis of peri-implant gingival tissue to assess implant biocompatibility and immune response

PURPOSE

The innate immune response, particularly the reaction of polymorphonuclear neutrophils (PMNs), is crucial in shaping the outcomes of chronic inflammation, fibrosis, or osseointegration following biomaterial implantation. Peri-implantitis or peri-implant mucositis, inflammatory conditions linked to dental implants, pose a significant threat to implant success. We developed a single-cell analysis approach using a murine model to assess the immune response to implant materials, offering a practical screening tool for potential dental implants.

METHODS

We performed bioinformatics analysis and established a peri-implant inflammation model by inserting two titanium implants into the maxillary region, to examine the immune response.

RESULTS

Bioinformatics analysis revealed that titanium implants triggered a host immune response, primarily mediated by PMNs. In the in vivo experiments, we observed a rapid PMN-mediated response, with increased infiltration around the implants and on the implant surface by day 3. Remarkably, PMN attachment to the implants persisted for 7 days, resembling the immune profiles seen in human implant-mediated inflammation.

CONCLUSIONS

Our findings indicate that persistent attachment of the short-living PMNs to titanium implants can serve as an indicator or traits of peri-implant inflammation. Therefore, analyzing gingival tissue at the single-cell level could be a useful tool for evaluating the biocompatibility of candidate dental implants.

Nonthermal Atmospheric Plasma Promotes Bonding Between Adhesive Monomers and Zirconia

OBJECTIVE

To investigate whether nonthermal atmospheric plasma (NTAP) can promote bonding between commonly used adhesive monomers and zirconia.

MATERIALS AND METHODS

The zirconia surface and monomers (HEMA, BisGMA, TEGDMA, and MDP) were treated with different NTAP approaches (10 w, 30 s), and the surface characteristics and chemical structures between the zirconia surface and monomers were verified by the contact angle, scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared (ATR/FT-IR) spectroscopy, and x-ray photoelectron spectroscopy (XPS). Scotchbond Universal adhesive with two different resin cements, RelyX Ultimate and RelyX Unicem 2, was applied, followed by NTAP-aided clinical procedures, and then microtensile bond strength test (μTBS) and failure mode evaluation were tested for preliminary mechanical properties assessment. One-way ANOVA was employed for the statistical analysis.

RESULTS

The contact angle analysis, SEM, and ATR-FTIR confirmed that NTAP can promote the polymerization of BisGMA, TEGDMA, and MDP on the zirconia surface, while XPS confirmed that NTAP can induce a chemical reaction between MDP and zirconia.

CONCLUSIONS

Nonthermal atmospheric plasma can increase the affinity between selected monomers and zirconia and promote the chemical bonding strength between phosphate monomers and zirconia; besides, it can enhance the bonding strength of two different adhesive systems.

CLINICAL SIGNIFICANCE

The mechanism of how NTAP improved common adhesive monomers interacting with zirconia surfaces was revealed in this study. NTAP, as a relatively high energy-boosting method, could not only improve the surface affinity of zirconia and chemical bonding in-between monomers and zirconia but also enhance the polymerization of different monomers onto zirconia, resulting in improved bonding properties. Thus, further exploration of versatile bonding materials and/or onto different dental substrates could take this into account.

Preparation and antibacterial evaluation of silver-doped zirconia for enhanced dental restoration performance

Because of its superior strength, esthetic properties, and excellent biocompatibility, zirconia is preferred for dental prosthetic such as crowns and bridges. However, zirconia crowns and bridges are susceptible to secondary caries owing to margin leakage. Silver is a well-known antibacterial agent, making it a desirable additive to zirconia crowns and bridges for secondary caries prevention. This study focuses on imparting zirconia composite with antibacterial properties to enhance its protective capacity in dental restorations. We used the sol-gel method to dope Ag into zirconia. Silver-doped zirconia powders were prepared at Zr:Ag molar ratios of 100:0,100:0.1, 100:0.5, 100:1, 100:3, and 100:5 (respective samples denoted as Ag-0, Ag-0.1, Ag-0.5, Ag-1, Ag-3, and Ag-5) and were subjected to firing at various temperatures (400 °C-1000 °C). We performed x-ray diffraction to investigate the crystal phase of these powders and x-ray fluorescence and field emission scanning electron microscopy to analyze their elemental composition and surface morphology, respectively. Moreover, we performed spectrophotometry to determine theL*a*b* color values, conducted dissolution tests, and quantified the Ag content through inductively coupled plasma optical emission spectroscopy. In addition, we studied the antibacterial activity of the samples. Analyses of the samples fired at ⩽600 °C revealed a predominantly white to grayish-white coloration and a tetragonal crystal phase. Firing at ⩾700 °C resulted in gray or dark gray coloration and a monoclinic crystal phase. The Ag content decreased after firing at 900 °C or 1000 °C. Ag-0.5 and above exhibited antibacterial activity against bothEscherichia coliandStaphylococcus aureus. Therefore, the minimum effective silver-doped zirconia sample was found to be Ag-0.5. This study allows the exploration of the antimicrobial potential of silver-doped zirconia materials in dental applications such as prosthdontical lining materials, promoting the development of innovative restorations with protective capacity against secondary caries.

The physical-mechanical properties of 3D-printed versus conventional milled zirconia for dental clinical applications: A systematic review with meta-analysis

AIM OF STUDY

This systematic review aimed to compare the physical-mechanical properties of 3D-printed (additively manufactured (AM)) zirconia compared to conventionally milled (subtractive manufactured: SM) zirconia specimens.

MATERIALS AND METHODS

A thorough search of Internet databases was conducted up to September 2023. The search retrieved studies that evaluated AM zirconia specimens and restorations regarding the physical-mechanical properties and mechanical behavior of zirconia. The main topic focused on 3Y-TZP. However, records of 4YSZ and 5YSZ were also included to gather more comprehensive evidence on additively manufactured zirconia ceramic. The quality of studies was assessed using the ROB2 tool, Newcastle Ottawa scale, and the Modified Consort Statement. Of 1736 records, 57 were assessed for eligibility, and 38 records were included in this review, only two clinical trials meet the inclusion criteria and 36 records were laboratory studies. There were no signs of mechanical complications and wear to antagonists with short-term clinical observation. SM thin specimens ≤1.5 mm showed statistically significant higher flexural strength than AM zirconia (p ≤ 0.01), while thicker specimens showed comparable outcomes (p > 0.5). The fracture resistance of dental restorations was dependent on the aging protocol, restoration type, and thickness. The bond strength of veneering ceramic to zirconia core was comparable.

CONCLUSIONS

The results pooled from two short-term clinical trials showed no signs of mechanical or biological complications of additively manufactured 3Y-TZP zirconia crowns. The flexural strength might depend on the specimens' thickness, but it showed promising results to be used in clinical applications, taking into account the printing technique and orientation, material composition (yttria content), solid loading, and sintering parameters. 3D-printed restorations fracture resistance improved when adhered to human teeth. The veneering ceramic bond was comparable to milled zirconia specimens. Long-term RCTs are recommended to confirm the mechanical behavior of 3D-printed restorations.

Synergetic impact of MgO on PMMA-ZrO2 hybrid composites: Evaluation of structural, morphological and improved mechanical behavior for dental applications

This work aims to demonstrate the effect of ZrO2 and MgO inclusion into the Poly(methyl methacrylate) (PMMA). To fabricate novel hybrid composites via heat cure method, various composites (PZM2, PZM4 and PZM6) were synthesized in the system [(95-x) PMMA + 5 ZrO2 + x MgO] (x = 2, 4, and 6) respectively. Density of the prepared composites were determined and varying between 1.035-1.152 g/cm3. X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) followed by EDAX and mechanical testing were performed to evaluate the fabricated composite properties. Moreover, to explore the structure of the fabricated composites the 13 C CP-MAS SSNMR and 1 H-13 C Phase-Modulated Lee Goldberg (PMLG) HETCOR Spectrum were recorded which clarify chemical shifting and motional dynamics of the composites. Mechanical tests were performed by UTM and the obtained parameters such as compressive strength, Young's modulus, fracture toughness, brittleness coefficient, flexural strength and flexural modulus are found to be in the range of 91-100 MPa, 0.48-0.51 GPa, 9.122-9.705 MPa.m1/2, 0.66-0.815, 51.03-42.78 MPa and 499-663 MPa respectively. Some more mechanical parameters such as proportional limit, elastic limit, failure strength, modulus of resilience and modulus of toughness were also calculated. Furthermore, tribological properties were also determined and the coefficient of friction (COF) was decreased by 17.4 % and 38 % for composite PZM6 at 20 N and 40 N as compared to the composite PZM2 and the lowest wear volume of 1.55 mm3 was observed for PZM2, whereas the maximum volume loss of 5.64 mm3 is observed for composite PZM6. To check out the biocompatibility, cytotoxicity and genotoxicity of the fabricated composites the Trypan-blue assay was also performed for PZM2 and PZM6 composites. Dissection on the gut of larvae was also performed on the both composites followed by DAPI and DCFH-DA staining. Therefore, these synthesized samples can be used for the fabrication of denture materials.

Advances in zirconia-based dental materials: Properties, classification, applications, and future prospects

OBJECTIVES

Zirconia (ZrO2) ceramics are widely used in dental restorations due to their superior mechanical properties, durability, and ever-improving translucency. This review aims to explore the properties, classification, applications, and recent advancements of zirconia-based dental materials, highlighting their potential to revolutionize dental restoration techniques.

STUDY SELECTION, DATA AND SOURCES

The most recent literature available in scientific databases (PubMed and Web of Science) reporting advances of zirconia-based materials within the dental field is thoroughly examined and summarized, covering the major keywords "dental zirconia, classification, aesthetic, LTD, applications, manufacturing, surface treatments".

CONCLUSIONS

An exhaustive overview of the properties, classifications, and applications of dental zirconia was presented, alongside an exploration of future prospects and potential advances. This review highlighted the importance of addressing challenges such as low-temperature degradation resistance and optimizing the balance between mechanical strength and translucency. Also, innovative approaches to improve the performances of zirconia as dental material was discussed.

CLINICAL SIGNIFICANCE

This review provides a better understanding of zirconia-based dental biomaterials for dentists, helping them to make better choice when choosing a specific material to fabricate the restorations or to place the implant. Moreover, new generations of zirconia are still expected to make progress on key issues such as the long-term applications in dental materials while maintaining both damage resistance and aesthetic appeal, defining the directions for future research.

Advances in ceramics for tooth repair: From bench to chairside

OBJECTIVES

To give a comprehensive review of advancement in dental ceramics, fabrication methods, and the challenges associated with clinical application.

DATA, SOURCES AND STUDY SELECTION

Researches on chemical composition, biomechanical behaviors, optical properties, bonding strategies and fabrication methods were included. The search of articles was independently conducted by two authors in the PubMed, Scopus, Medline and Web of Science.

CONCLUSIONS

Dental ceramics have shown significant advancements in terms of esthetics and function. However, improving fracture toughness without compromising optical properties remains a challenge. Repairing fractured zirconia or glass-matrix ceramic prostheses with the same material is difficult due to the sintering process. Developing innovative bonding techniques that provide strong and long-lasting bonding strength between ceramics and tooth structures poses a recurring obstacle.

CLINICAL SIGNIFICANCE

Despite the emergence of dental ceramics and fabrication techniques, certain limitations such as susceptibility to brittleness and fracture still exist. Therefore, the current review provided valuable information around the advanced dental ceramics in tooth repair. The laboratory test data and the clinical outcome are also presented in details, aiming to guide clinicians in making informed decisions regarding ceramic restorations.

Color stability of precolored and extrinsically colored monolithic multilayered polychromatic zirconia: Effects of surface finishing and aging

PURPOSE

To explore the impact of zirconia types, coloring methods, and surface finishing on the color stability of monolithic multilayered polychromatic zirconia after artificial aging, including thermocycling and simulated toothbrushing.

MATERIALS AND METHODS

Eighty square-shaped zirconia samples were divided into 2 types (M3Y-TZP and M6Y-PSZ), further categorized based on coloring methods (precolored and extrinsically colored) and surface finishing techniques (mechanical polishing or glazing). The color stability was assessed using the CIEDE2000 formula. Artificial aging was simulated via thermocycling and toothbrushing. All samples were analyzed with a spectrophotometer to determine the post-aging color changes (ΔE00). The ΔE00 were interpreted and classified using the 50:50% perceptibility threshold (PT) and the 50:50% acceptability threshold (AT). Comparisons between groups for ΔE00 differences were performed using three-way ANOVA, with pairwise comparisons facilitated by Fisher's protected least significant difference test, α = 0.05.

RESULTS

The study results indicated significant impacts of zirconia type, coloring method, and surface finishing on color stability. The M6Y groups experienced significantly greater color changes (6.61 ± 1.63) compared to the M3Y groups (3.40 ± 2.24), p < 0.0001. For both types of zirconia, extrinsically colored samples exhibited significantly higher ΔE00 when mechanically polished (p = 0.004). However, surface finishing had no significant effect on ΔE00 in precolored samples of either zirconia material (p = 1.000). The evaluation and categorization of ΔE00 variations indicated that nearly all color changes in the M6Y groups, regardless of being precolored, extrinsically colored, polished, or glazed, were deemed extremely unacceptable (Grade 1). In contrast, the M3Y groups showed more acceptable results, with the majority of color changes classified as moderately unacceptable (Grade 3).

CONCLUSIONS

The color stability of multilayered polychromatic zirconia is influenced by the type of material, extrinsic coloring, and the chosen surface treatment post-artificial aging. The translucent 6Y-PSZ exhibited lower color stability, especially with only mechanical polishing. For the fabrication of M3Y-TZP and 6Y-PSZ monolithic multilayered polychromatic zirconia restorations, extrinsic coloring should be paired with glazing to maintain color stability. Conversely, in the absence of extrinsic coloring, both glazing and mechanical polishing are effective in preserving color stability.

Biocompatibility and acid resistance of preformed crowns in children: an in vitro study

PURPOSE

To investigate the in vitro biocompatibility of human gingival fibroblasts with preformed paediatric crowns and resistance to acid exposure at levels that simulate the oral environment.

METHODS

This laboratory study investigated primary HGFs viability, metabolic activity, cytotoxicity, and apoptotic events on preformed metal crown discs, composite resin-coated wells, and monolithic zirconia fragments at 24, 48, and 72 h using the ApoTox-Glo Triplex assay. The PPCs were also immersed in 0.1% lactic acid, 0.2% phosphoric acid, or 10% citric acid for 7 days at 37 °C to reproduce conditions associated with dietary intake or gastric reflux. Samples were then subject to inductively coupled plasma optical emission spectrometry to quantitate the release of ions.

RESULTS

The viability of HGFs on stainless steel and CR significantly declined at 48 and 72 h, representing potential cytotoxicity (p < 0.05). Cytotoxicity of HGFs was also higher for stainless steel and ZR compared to control (p < 0.05). PMCs and ZR crowns gave minimal ion release. Meanwhile, significant quantities of metallic ions, including copper (Cu), iron (Fe), nickel (Ni), and zinc (Zn), were present in eluates from veneered-preformed metal crowns.

CONCLUSION

As PPCs can be exposed to highly acidic environments for many years, thus the release of metallic ions from V-PMCs should form the further investigation in future studies.

Comprehensive Evaluation of Titanium, Zirconia, and Ceramic Dental Implant Materials: A Comparative Analysis of Mechanical and Esthetic Properties

BACKGROUND

Dental implant materials play a pivotal role in the success of restorative dentistry. This study comprehensively compares the mechanical and esthetic properties of three commonly used dental implant materials: titanium, zirconia, and ceramic.

OBJECTIVE

This study aimed to provide insights into the suitability of titanium, zirconia, and ceramic for various clinical applications within implant dentistry.

METHODS

Ninety dental implants, 30 for each material, were selected based on their well-established usage in dental implantology. Mechanical properties, including tensile strength, modulus of elasticity, and fatigue resistance, were assessed using state-of-the-art testing machines. Esthetic properties, such as color stability and translucency, were scrutinized through immersion in staining solutions and spectrophotometer measurements. Fracture properties and biocompatibility were also evaluated.

RESULTS

Mechanical testing revealed that titanium exhibited the highest tensile strength (810 ± 55 MPa), while zirconia demonstrated the highest modulus of elasticity (208 ± 8 GPa). Titanium also displayed the greatest fatigue resistance (1,010,000 ± 95,000 cycles), whereas zirconia had the highest hardness (1190 ± 45 Vickers hardness number (VHN)). Esthetically, zirconia showed superior color stability (ΔE: 1.7 ± 0.2), while ceramic exhibited the highest translucency (TP%: 15.3 ± 1.7). Zirconia presented the lowest surface roughness (0.28 ± 0.04 μm).

CONCLUSION

This study provides insights into potential dental implant material performance, with zirconia emerging as a promising alternative. Future research should validate these findings in clinical settings, considering a broader array of variables and long-term outcomes.

Zirconia Hybrid Dental Implants Influence the Biological Properties of Neural Crest-Derived Mesenchymal Stromal Cells

Dental implants are regularly employed in tooth replacement, the good clinical outcome of which is strictly correlated to the choice of an appropriate implant biomaterial. Titanium-based implants are considered the gold standard for rehabilitation of edentulous spaces. However, the insurgence of allergic reactions, cellular sensitization and low integration with dental and gingival tissues lead to poor osseointegration, affecting the implant stability in the bone and favoring infections and inflammatory processes in the peri-implant space. These failures pave the way to develop and improve new biocompatible implant materials. CERID dental implants are made of a titanium core embedded in a zirconium dioxide ceramic layer, ensuring absence of corrosion, a higher biological compatibility and a better bone deposition compared to titanium ones. We investigated hDPSCs' biological behavior, i.e., cell adhesion, proliferation, morphology and osteogenic potential, when seeded on both CERID and titanium implants, before and after cleansing with two different procedures. SEM and AFM analysis of the surfaces showed that while CERID disks were not significantly affected by the cleansing system, titanium ones exhibited well-visible modifications after brush treatment, altering cell morphology. The proliferation rate of DPSCs was increased for titanium, while it remained unaltered for CERID. Both materials hold an intrinsic potential to promote osteogenic commitment of neuro-ectomesenchymal stromal cells. Interestingly, the CERID surface mitigated the immune response by inducing an upregulation of anti-inflammatory cytokine IL-10 on activated PBMCs when a pro-inflammatory microenvironment was established. Our in vitro results pave the way to further investigations aiming to corroborate the potential of CERID implants as suitable biomaterials for dental implant applications.

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.

Bio-inspired nacre-like zirconia/PMMA composites for chairside CAD/CAM dental restorations

OBJECTIVES

To introduce a versatile fabrication process to fabricate zirconia/PMMA composites for chairside CAD/CAM dental restorations. These zirconia composites have nacre-like lamellar microstructures, competent and tooth-matched mechanical properties, as well as crack resistance behaviours.

METHODS

Bi-directional freeze casting was used to fabricate ceramic green bodies with highly aligned lamellar structure. Pressure was then applied to control the ceramic volume fraction. PMMA was infiltrated into the ceramic scaffold. Mechanical tests including 3-point bending, Vickers hardness, and fracture toughness were performed on the composites. The machinability of the composites was also characterised.

RESULTS

Two types of nacre-like zirconia/PMMA composites, i.e., 3Y-YZP/PMMA and 5Y-PSZ/PMMA composites were fabricated. The microstructure created was similar to the 'brick and mortar' structure of nacre. Excellent flexural strength (up to 400 MPa and 290 MPa for 3Y-TZP/PMMA and 5Y-PSZ/PMMA composite, respectively), tuneable hardness and elastic modulus within the range similar to enamel, along with improved crack-resistance behaviour were demonstrated on both zirconia composites. In addition, both zirconia/PMMA composites showed acceptable machinability, being easy to mill, as would be required to produce a dental crown.

SIGNIFICANCE

Nacre-like zirconia/PMMA composites therefore exhibit the potential for use in the production of chairside CAD/CAM dental restorations.

The possibility of clinical bonding between metal/ceramic brackets to zirconia: in vitro study

Objective: The present study aimed to assess the bond strength and durability of six bonding agents concerning their application to metal or ceramic brackets and zirconia. Materials and Methods: Six resin cement bonding agents (XT, XTS, RSBU, RGBU, SBPM, and GMP) were chosen for this investigation. Specimens were either stored in distilled water at 37°C for 24 h or subjected to 5,000 thermocycles before conducting a Shear Bond Strength (SBS) test. Statistical analysis of the SBS data was performed using three-way ANOVA and Games-Howell tests (α = 0.05). The Adhesive Remnant Index was examined, and the debonding surface details on brackets and zirconia were observed. Results: For metal brackets, all groups demonstrated clinically acceptable bond strength, irrespective of storage conditions, except for the XT group. Regarding ceramic brackets, all groups displayed acceptable bond strength after 24 h of water storage. However, following thermocycling, a significant decrease in SBS was noted across all groups (p < 0.05), with SBPM exhibiting a higher bond strength. Three-way ANOVA analysis indicated that SBS values were notably influenced by each factor, and an interaction among the three independent variables was observed (p = 0.000). Conclusion: The reliable bond strength between ceramic brackets and zirconia was significantly lower after thermocycling compared to that of metal brackets and zirconia. SBPM exhibited consistent and robust bond strength between ceramic/metal brackets and zirconia across various storage conditions. Furthermore, the HEMA-free adhesive demonstrated a potentially more consistent bonding performance compared to the HEMA-containing adhesive employed in this study.

Zirconia Ceramics

Zirconia ceramics have become popular among other dental ceramics thanks to their biological, mechanical, optical, and aesthetic properties. CAD/CAM (computer-aided design/ computer-aided manufacturing) technology improvement has played a vital role in the increased popularity of zirconia ceramics; easy computer manipulation significantly expanded the possibility of using different types of restorations. Zirconia ceramics have a broad spectrum of indications in prosthetic dentistry, from simple restorations to complex structures supported by dental implants. A good orientation in the classification, features, and manipulation of zirconia ceramics is the main key to success.

Hydroxyapatite-Based Coatings on Silicon Wafers and Printed Zirconia

Dental surgery needs a biocompatible implant design that can ensure both osseointegration and soft tissue integration. This study aims to investigate the behavior of a hydroxyapatite-based coating, specifically designed to be deposited onto a zirconia substrate that was intentionally made porous through additive manufacturing for the purpose of reducing the cost of material. Layers were made via sol-gel dip coating by immersing the porous substrates into solutions of hydroxyapatite that were mixed with polyethyleneimine to improve the adhesion of hydroxyapatite to the substrate. The microstructure was determined by using X-ray diffraction, which showed the adhesion of hydroxyapatite; and atomic force microscopy was used to highlight the homogeneity of the coating repartition. Thermogravimetric analysis, differential scanning calorimetry, and Fourier transform infrared spectroscopy showed successful, selective removal of the polymer and a preserved hydroxyapatite coating. Finally, scanning electron microscopy pictures of the printed zirconia ceramics, which were obtained through the digital light processing additive manufacturing method, revealed that the mixed coating leads to a thicker, more uniform layer in comparison with a pure hydroxyapatite coating. Therefore, homogeneous coatings can be added to porous zirconia by combining polyethyleneimine with hydroxyapatite. This result has implications for improving global access to dental care.

Biomaterials Adapted to Vat Photopolymerization in 3D Printing: Characteristics and Medical Applications

Along with the rapid and extensive advancements in the 3D printing field, a diverse range of uses for 3D printing have appeared in the spectrum of medical applications. Vat photopolymerization (VPP) stands out as one of the most extensively researched methods of 3D printing, with its main advantages being a high printing speed and the ability to produce high-resolution structures. A major challenge in using VPP 3D-printed materials in medicine is the general incompatibility of standard VPP resin mixtures with the requirements of biocompatibility and biofunctionality. Instead of developing completely new materials, an alternate approach to solving this problem involves adapting existing biomaterials. These materials are incompatible with VPP 3D printing in their pure form but can be adapted to the VPP chemistry and general process through the use of innovative mixtures and the addition of specific pre- and post-printing steps. This review's primary objective is to highlight biofunctional and biocompatible materials that have been adapted to VPP. We present and compare the suitability of these adapted materials to different medical applications and propose other biomaterials that could be further adapted to the VPP 3D printing process in order to fulfill patient-specific medical requirements.

Vertical Marginal Discrepancy of a Monolithic Zirconia Crown with Different Cement Spaces

The long-term clinical success of indirect restorations highly depends on their marginal integrity. The cement space is an element that might affect the marginal integrity, but it can be altered during the configuring of the computer-assisted designing/computer-aided manufacturing (CAD-CAM) restoration. However, there is controversy in the literature regarding the effect of the cement space on the precision of zirconia crown marginal adaptation. The aim of this study was to measure the vertical marginal discrepancies between different cement thickness settings for CAD-CAM monolithic zirconia restorations. Material and Methods. An artificial mandibular right molar tooth mounted on a typodont was prepared for a zirconia crown using the standard method. The study sample consisted of 30 zirconia crowns (Zenostar Zr Translucent Zirconia, Weiland Dental, Germany) milled using an (iMes-iCore) milling machine. Each group of 10 crowns was designed with 30-50 and 70 μm spacer thicknesses. The vertical marginal adaptation at the center of the four different planes (mesial, distal, buccal, and palatal) was measured under a microscope at 40x magnification. A one-way analysis of variance test was used for statistical analysis. Results. The mean of Group 30 was 27.45; of Group 50 was 22.22; and of Group 70 was 22.90. There was no statistically significant difference between the groups (p ≥ 0.5). Conclusions. The increase in the cement space up to 70 μm did not influence the vertical marginal adaptation of the monolithic zirconia crowns.

Evaluation of mechanical properties of dental zirconia in different milling conditions and sintering temperatures

STATEMENT OF PROBLEM

The dry processing of zirconia has the disadvantage of dust dispersal during milling; thus, wet milling may be preferable. However, research on the mechanical properties of dental zirconia milled under different conditions and sintered at different temperatures is lacking.

PURPOSE

The purpose of this in vitro study was to evaluate changes in the mechanical properties of zirconia specimens after milling under dry and wet conditions at different sintering temperatures.

MATERIAL AND METHODS

Four hundred Ø20.0×1.5-mm presintered zirconia specimens were prepared by using a computer-aided design and computer-aided manufacturing (CAD-CAM) system and divided into 8 groups (n=50) based on the sintering (1230, 1330, 1430, and 1530 °C) and milling conditions (dry or wet). The mechanical properties (Vickers hardness, biaxial flexural strength, and fracture toughness) and physical properties (linear shrinkage and density) were examined. The microstructures of the specimens were observed with a scanning electron microscope. The crystal phases of the sintered green bodies were analyzed by using an X-ray diffractometer. The data were analyzed with descriptive statistics and 1-way and 2-way analyses of variance with Tukey HSD tests (α=.05).

RESULTS

The mechanical properties of all specimens increased with increasing sintering temperature, except for 1530 °C and the dry milling condition. The mechanical properties of the groups fabricated under wet milling conditions were better than those of the groups fabricated under dry milling conditions. Microscopic examination of the structure showed that the porosity decreased with increasing sintering temperature regardless of the milling conditions.

CONCLUSIONS

Higher sintering temperatures increased the mechanical properties (biaxial flexural strength, Vickers hardness, fracture toughness). However, phase transformation from tetragonal to cubic was observed for dry milled specimens sintered at 1530 °C, with decreased mechanical properties. Specimens fabricated by wet milling exhibited better mechanical properties than those fabricated by dry milling.

Corrosion of Fixed Orthodontic Appliances: Causes, Concerns, and Mitigation Strategies

The orthodontic supply market is a prosperous billion-dollar industry, driven by an increasing demand for orthodontic appliances. The supremacy of metallic first-generation biomaterials is evident for manufacturing brackets, archwires, bands, and other components due to their well-recognized chemical inertness, spontaneous passivation, biocompatibility, and favorable mechanical properties combination. However, the oral cavity is the ultimate corrosion-promoting environment for any metallic material. In this work, the general picture of the intraoral degradation of fixed orthodontic appliances is first addressed, from the causes to the harmful effects and their oral clinical implications. Current mitigation strategies are also pointed out, including the alloys’ bulk composition adjustment combined with new and advanced manufacturing processes and/or their surface treatment or coating deposition. The versatile use of thin films and coatings stands out with different deposition technologies: Many in vivo and in vitro efforts have been devoted to oral aging, from monolithic to composite architectures and micro- to nano-scale materials, to meet the best and safest oral practice demands. Unfortunately, literature data suggest that even the existing commercially available protective coatings have drawbacks and are fallible. Further multidisciplinary research is still required to effectively mitigate the corrosion behavior of fixed orthodontic appliances.

Enhancing the zircon yield through the addition of calcium phosphates into ZrO2-SiO2 binary systems: synthesis and structural, morphological, mechanical and in vitro analysis

The crystallization of ZrSiO4 is generally accomplished by the addition of mineralizers into ZrO2-SiO2 binary oxides. The current investigation aimed to investigate the effect of adding calcium phosphates into ZrO2-SiO2 binary oxides on the yield of ZrSiO4. The concentration of calcium phosphate additions were varied to obtain ZrSiO4 that fetches improved mechanical and biological properties for application in hard tissue replacements. The findings highlight the significant role of Ca2+ and P5+ in triggering the ZrSiO4 formation via their accommodation at the Zr4+ and Si4+ sites. Especially, calcium phosphate additions trigger the t- → m-ZrO2 transition beyond 1000 °C, which consequently reacts with SiO2 to promote ZrSiO4 formation. Calcium phosphates are accommodated at the lattice sites of ZrSiO4 with a maximum limit of 20 mol%, beyond which the crystallization of β-Ca3(PO4)2 is noticed. The optimum amount of 20 mol% of calcium phosphates displayed a better strength than that of all the investigated specimens. More than 80% of cell viability in MG-63 cells was invariably determined in all the calcium phosphate-added ZrSiO4 systems.

Clinical performance of full-arch implant-supported fixed restorations made of monolithic zirconia luted to a titanium bar: A retrospective study with a mean follow-up of 16 months

OBJECTIVES

This retrospective case series aimed to evaluate the short-term clinical advantages and limitations of full-arch implant-supported restorations made of monolithic zirconia suprastructures passively luted to titanium bar infrastructures and to report the rate of complications within a minimum of 1-year follow-up.

MATERIALS AND METHODS

This study included 31 patients (19 men and 12 women) requiring full-arch implant-supported prostheses in the upper or lower jaw. The patients were treated using an entirely digital approach from implant planning and guided implant placement to prosthetic construction planning, design, and fabrication. Full-arch implant-supported monolithic zirconia suprastructures luted to prism-shaped titanium bars were used in all the cases. All the restorations were evaluated for biological and technical complications during fixed control appointments.

RESULTS

No implant failures or serviceable prosthetic complications were reported, and the prosthetic survival rate was 100%, with a follow-up duration ranging from 12 months to 20 months. In two cases, a fracture line was observed in the zirconia suprastructures, although it did not require any intervention.

CONCLUSIONS

After a 16-month mean follow-up period, the monolithic zirconia implant-supported full-arch fixed dental prostheses demonstrated no biological or technical complications. Further clinical studies with long-term results are required to confirm these reported outcomes.

CLINICAL SIGNIFICANCE

CAD-/CAM-milled monolithic zirconia structures passively luted to titanium bar infrastructures are a viable treatment option for full-arch restorations over implants, demonstrating 100% survival and success rates in the present study. The outcomes of this short-term retrospective study indicated high success in function, aesthetics, phonetics, and the ability to maintain flawless hygiene. However, the long-term results of restorations produced using the proposed technique should be considered before recommending this approach for routine clinical use.

Zirconia Facts and Perspectives for Biomaterials in Dental Implantology

Dental implantology has witnessed remarkable advancements in recent years, and zirconia has emerged as a prominent biomaterial for dental implant applications. This review explores the multifaceted aspects of zirconia, focusing on its properties, processing methods, biocompatibility, mechanical performance, and clinical applications. Over the past few decades, the most popular choice of material for dental implantology has been titanium which has been found to have the highest success rate of implant treatment. However, recently, it has been observed that zirconia might replace titanium and eventually emerge as one of the gold-standard materials of dental implants. Analysis of biomechanical sciences and biomaterial sciences provides an opportunity for the refinement of design and material notions for surgical implants. However, the most important aspect and prime concern is how tissue at the implant site responds to biomechanical disturbances caused by foreign materials. The literature revealed that zirconia has certain characteristics that make it an excellent material for implants, including biocompatibility and osseointegration which depicts positive soft tissue response with low plaque affinity as well as aesthetics owing to light transmission and color. Additionally, this review discusses the current challenges and prospects of zirconia in dental implantology as well as aims to provide dental professionals and researchers with a comprehensive understanding of zirconia's potential as a biomaterial in dental implantology. The present overview of available literature intends to highlight and explore the biological characteristics of zirconia for applications in dental implantology. However, research is urgently required to fill in gaps over time for clinical assessments of all zirconia implants, consequently, the implementation of hybrid systems (a titanium screw with a zirconia collar) has recently been suggested.

Enhanced bioactivity and hydrothermal aging resistance of Y-TZP ceramics for dental implant

Although yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) ceramics have been widely used as restorative materials due to their high mechanical strength, unique esthetic effect, and good biocompatibility, their general application to implant materials is still limited by their biological inertness and hydrothermal aging phenomenon. Existing studies have attempted to investigate how to enhance the bioactivity or hydrothermal aging resistance of Y-TZP. Still, more studies need to be done on the modification that combines these two aspects. In this study, Y-TZP was prepared by 77S bioactive glass (BG) sol and akermanite (AKT) sol infiltration and microwave sintering, which provided Y-TZP with high bioactivity while maintaining resistance to hydrothermal aging. Results of phase composition evaluation, microstructural characteristics, and mechanical property tests showed that modified Y-TZP specimens exhibited little or no tetragonal-to-monoclinic (t → m) transformation and maintained relatively high mechanical properties after accelerated hydrothermal aging treatment. The in vitro biological behaviors showed that the introduction of 77S BG and AKT significantly promoted cell adhesion, spreading, viability, and proliferation on the surface of modified Y-TZP ceramics. Therefore, this modification could effectively enhance the bioactivity and hydrothermal aging resistance of Y-TZP ceramics for its application in dental implant materials.

The Shear Bond Strength of Resin-Based Luting Cement to Zirconia Ceramics after Different Surface Treatments

Due to its unique properties, zirconia is increasingly being used in dentistry, but surface preparation for bonding is difficult because of its polycrystalline structure. This study aimed to determine the effect of a new etching technique (Zircos-E) on Ceramill Zi (Amann Girrbach). The effect of etching and the use of primers (Monobond Plus and MKZ Primer) on the bond strength of zirconia with resin cement (NX3) was assessed. Shear bond strength was evaluated after storage in water for 24 h and after thermal aging (5000 thermocycling at 5 °C/55 °C). A scanning electron microscope (Hitachi S-4700) was used to evaluate the surface structure before and after the Zircos-E system. The roughness parameters were assessed using an SJ-410 profilometer. The etched zirconia surface is more homogeneous over the entire surface, but some localized forms of erosion exist. The etching of zirconia ceramics caused changes in the surface structure of zirconia and a significant increase in the shear bond strength between zirconia and resin cement. The use of primers positively affects the adhesion between resin cement and zirconia. Aging with thermocycler significantly reduced the shear bond strength, with one exception-sandblasted samples with MKZ Primer. Standard ceramic surface preparation, involving only alumina sandblasting, does not provide a satisfactory bond. The use of etching with the Zircos-E system and primers had a positive effect on the strength of the zirconium-resin cement connection.

Ultrashort pulse laser patterning of zirconia (3Y-TZP) for enhanced adhesion to resin-matrix cements used in dentistry: An integrative review

Surface modification of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) using lasers for adhesion enhancement with resin-matrix cement has been increasingly explored. However, Y-TZP is chemically inert and non-reactive, demanding surface modification using alternative approaches to enhance its bond strength to resin-matrix cements. The main aim of this study was to conduct an integrative review on the influence of ultrashort pulse laser patterning of zirconia (3Y-TZP) for enhanced bonding to resin-matrix cements. An electronic search was performed on web of science, SCOPUS, Pubmed/Medline, Google Scholar and EMBASE using a combination of the following search items: zirconia, 3Y-TZP, surface modification, laser surface treatment, AND laser, ultrashortpulse laser, bonding, adhesion, and resin cement. Articles published in the English language, up to January 2022, were included regarding the influence of surface patterning on bond strength of Y-TZP to resin-matrix cements. Out of the 12 studies selected for the present review 10 studies assessed femtosecond lasers while 2 studies assessed picosecond lasers. Ultrashort pulsed laser surface patterning successfully produced different surface morphological aspects without damaging the bulk properties of zirconia. Contrarily, defects such as micro-cracks occurs after surface modification using traditional methods such as grit-blasting or long-pulsed laser patterning. Ultrashort pulsed laser surface patterning increase bond strength of zirconia to resin-matrix cements and therefore such alternative physical method should be considered in dentistry. Also, surface defects were avoided using ultrashort pulsed laser surface patterning, which become the major advantage when compared with traditional physical methods or long pulse laser patterning.

Analyses of Experimental Dental Adhesives Based on Zirconia/Silver Phosphate Nanoparticles

This study aimed to evaluate the incorporation of zirconia/silver phosphate nanoparticles to develop experimental dental adhesives and to measure their physical and mechanical properties. The nanoparticles were synthesized by the sonication method, and the phase purity, morphological pattern, and antibacterial properties with Staphylococcus aureus and Pseudomonas aeruginosa were assessed. The silanized nanoparticles were incorporated (0, 0.15, 0.25, and 0.5 wt.%) into the photoactivated dimethacrylate resins. The degree of conversion (DC) was assessed, followed by the micro-hardness and flexural strength/modulus test. Long-term color stability was investigated. The bond strength with the dentin surface was conducted on days 1 and 30. The transmission electron microscopy and X-ray diffractogram confirmed the nano-structure and phase purity of the particles. The nanoparticles showed antibacterial activities against both strains and inhibited biofilm formation. The DC range of the experimental groups was 55-66%. The micro-hardness and flexural strength increased with the concentration of nanoparticles in the resin. The 0.5 wt.% group showed significantly high micro-hardness values, whereas a non-significant difference was observed between the experimental groups for flexural strength. The bond strength was higher on day 1 than on day 30, and a significant difference was observed between the two periods. At day 30, the 0.5 wt.% showed significantly higher values compared to other groups. Long-term color stability was observed for all the samples. The experimental adhesives showed promising results and potential to be used for clinical applications. However, further investigations such as antibacterial, penetration depth, and cytocompatibility are required.

A Fully Implantable and Programmable Epidural Spinal Cord Stimulation System for Rats With Spinal Cord Injury

Epidural spinal cord stimulation (ESCS) is a potential treatment for the recovery of the motor function in spinal cord injury (SCI) patients. Since the mechanism of ESCS remains unclear, it is necessary to study the neurophysiological principles in animal experiments and standardize the clinical treatment. In this paper, an ESCS system is proposed for animal experimental study. The proposed system provides a fully implantable and programmable stimulating system for complete SCI rat model, along with a wireless charging power solution. The system is composed of an implantable pulse generator (IPG), a stimulating electrode, an external charging module and an Android application (APP) via a smartphone. The IPG has an area of ${25} \times {25}$ mm2 and can output 8 channels of stimulating currents. Stimulating parameters, including amplitude, frequency, pulse width and sequence, can be programmed through the APP. The IPG was encapsulated with a zirconia ceramic shell and two-month implantable experiments were carried out in 5 rats with SCI. The main focus of the animal experiment was to show that the ESCS system could work stably in SCI rats. The IPG implanted in vivo can be charged through the external charging module in vitro without anesthetizing the rats. The stimulating electrode was implanted according to the distribution of ESCS motor function regions of rats and fixed on the vertebrae. The lower limb muscles of SCI rats can be activated effectively. The two-month SCI rats needed greater stimulating current intensity than the one-month SCI rats The results indicated that the stimulating system provides an effective and simplified tool for studying the ESCS application in motor function recovery for untethered animals.

Effect of thermocycling on the mechanical properties, inorganic particle release and low temperature degradation of glazed high translucent monolithic 3Y-TZP dental restorations

The influence of thermocycling on the surface deterioration of glazed monolithic high translucent 3Y-TZP dental restorations is still unclear. The purpose of this study therefore was to evaluate low temperature degradation (LTD), elemental release and surface degradation pattern after five years of simulated clinical time. A total of 123 specimens were prepared from second-generation high translucent 3Y-TZP as per ISO 6872:2015 standards (3 mm × 4 mm × 30 mm). They were classified as per glazing and thermocycling protocol; group CPT, DGT and IGT. Glaze materials were applied on one surface of the specimen and subjected to a thermocycling in artificial saliva, four-point bending test, inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and x-ray diffraction (XRD). Flexural strength, characteristic strength and Weibull modulus values were derived from four-point bending test. Descriptive fractographic analysis of surfaces was conducted to observe the surface degradation characteristics and point of failure. Control/no glaze with thermocycling (CPT = 621.5, 1σ = 117.0 MPa) presented higher flexural strength values compared to glaze I with thermocycling (442.4, 1σ = 45.4 MPa) and glaze II with thermocycling (534.3, 1σ = 46.3 MPa). Characteristic strength from Weibull analysis also observed higher values (669.2 MPa) for the control specimens. XRD analysis showed that monoclinic volume fraction (Vm = 11.0, 1σ = 0.7%) was highest in control specimens. Fractographic analysis suggested that there was no correlation between the point of failure initiation and mean flexural strength values. Glazing protected the high translucent 3Y-TZP surface against LTD during thermocycling but negatively impacted on the flexural strength.

The Effect of Multiple Applications of Phosphate-Containing Primer on Shear Bond Strength between Zirconia and Resin Composite

Occasional chipping can still occur with zirconia material despite its high strength. Emergency repairs can be accomplished using zirconia primer, adhesive agent, and resin composite when the fracture of zirconia exposes the zirconia framework. Phosphate-containing primers play an important role in zirconia surface treatment. The objective of this investigation was to evaluate the effect of multiple applications of phosphate-containing primer on shear bond strength between zirconia and resin composite. In this case, 78 zirconia discs were sandblasted by alumina particles; the zirconia was then randomized into six groups for single application and multiple applications of phosphate-containing primer according follows; group 1: no application, group 2: one application, group 3: two applications, group 4: three applications, group 5: four applications, and group 6: five applications. Adhesive was applied on the zirconia surface and the resin composite was bonded. Shear bond strength was assessed using a universal testing machine. The de-bonded surface was examined using a stereomicroscope. The shear bond strengths were statistically analyzed with one-way ANOVA and Bonferroni. Group 1 had the lowest shear bond strength with a significant difference compared to groups 2–6, whereas group 4 had the highest shear bond strength, with no significant difference compared to groups 5–6. The failure mode revealed 100% adhesive failure in all groups. In conclusion, to maximize shear bond strength at zirconia and resin composite interfaces, sandblasted zirconia surfaces should be treated with three applications of phosphate-containing primer prior to the adhesive agent.

3D-Printed Polymer-Infiltrated Ceramic Network with Antibacterial Biobased Silver Nanoparticles

This work aimed at the antimicrobial functionalization of 3D-printed polymer-infiltrated biomimetic ceramic networks (PICN). The antimicrobial properties of the polymer-ceramic composites were achieved by coating them with human- and environmentally safe silver nanoparticles trapped in a phenolated lignin matrix (Ag@PL NPs). Lignin was enzymatically phenolated and used as a biobased reducing agent to obtain stable Ag@PL NPs, which were then formulated in a silane (γ-MPS) solution and deposited to the PICN surface. The presence of the NPs and their proper attachment to the surface were analyzed with spectroscopic methods (FTIR and Raman) and X-ray photoelectron spectroscopy (XPS). Homogeneous distribution of 13.4 ± 3.2 nm NPs was observed in the transmission electron microscopy (TEM) images. The functionalized samples were tested against Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) bacteria, validating their antimicrobial efficiency in 24 h. The bacterial reduction of S. aureus was 90% in comparison with the pristine surface of PICN. To confirm that the Ag-functionalized PICN scaffold is a safe material to be used in the biomedical field, its biocompatibility was demonstrated with human fibroblast (BJ-5ta) and keratinocyte (HaCaT) cells, which was higher than 80% in both cell lines.

Effect of surface treatments on biaxial flexural strength, fatigue resistance, and fracture toughness of high versus low translucency zirconia

BACKGROUND

Mechanical surface treatments can deteriorate the mechanical properties of zirconia. This study evaluated and compared the biaxial flexural strength, fracture toughness, and fatigue resistance of high translucency (HT) to low translucency (LT) zirconia after various mechanical surface treatments.

METHODS

Four hundred eighty zirconia discs were prepared by milling and sintering two HT (Katana and BruxZir) and LT (Cercon and Lava) zirconia blocks at targeted dimensions of 12 mm diameter × 1.2 mm thickness. Sintered zirconia discs received one of the following surface treatments: low-pressure airborne particle abrasion (APA) using 50 µm alumina particles, grinding using 400 grit silicon carbide paper, while as-sintered specimens served as control. Internal structure and surface roughness were evaluated by scanning electron microscope (SEM) and a non-contact laser profilometer, respectively. Half of the discs were tested for initial biaxial flexural strength, while the rest was subjected to 10⁶ cyclic fatigue loadings, followed by measuring the residual biaxial flexural strength. Fractured surfaces were examined for critical size defects (c) using SEM to calculate the fracture toughness (K_IC). The effect of surface treatments, zirconia type, and cyclic fatigue on the biaxial flexural strength was statistically analyzed using three-way analysis of variance (ANOVA) and Tukey HSD post hoc tests (α = 0.05). Weibull analysis was done to evaluate the reliability of the flexural strength for different materials.

RESULTS

The initial biaxial flexural strength of LT zirconia was significantly higher (p < 0.001) than that of HT zirconia in all groups. While low APA significantly increased the biaxial flexural strength of LT zirconia, no significant change was observed for HT zirconia except for Katana. Surface grinding and cyclic fatigue significantly reduced the flexural strength of all groups. High translucency zirconia reported higher fracture toughness, yet with lower Weibull moduli, compared to LT zirconia.

CONCLUSION

LT zirconia has higher biaxial flexural strength, yet with lower fracture toughness and fatigue resistance, compared to HT zirconia. Low-pressure APA has significantly increased the biaxial flexural strength in all zirconia groups except BruxZir. Grinding was deteriorating to biaxial flexural strength and fracture toughness in all zirconia types. Cyclic fatigue has significantly decreased the biaxial flexural strength and reliability of HT and LT zirconia.

3D Printing of Bioinert Oxide Ceramics for Medical Applications

Three-dimensionally printed metals and polymers have been widely used and studied in medical applications, yet ceramics also require attention. Ceramics are versatile materials thanks to their excellent properties including high mechanical properties and hardness, good thermal and chemical behavior, and appropriate, electrical, and magnetic properties, as well as good biocompatibility. Manufacturing complex ceramic structures employing conventional methods, such as ceramic injection molding, die pressing or machining is extremely challenging. Thus, 3D printing breaks in as an appropriate solution for complex shapes. Amongst the different ceramics, bioinert ceramics appear to be promising because of their physical properties, which, for example, are similar to those of a replaced tissue, with minimal toxic response. In this way, this review focuses on the different medical applications that can be achieved by 3D printing of bioinert ceramics, as well as on the latest advances in the 3D printing of bioinert ceramics. Moreover, an in-depth comparison of the different AM technologies used in ceramics is presented to help choose the appropriate methods depending on the part geometry.

Zirconia fixed dental prostheses fabricated by 3D gel deposition show higher fracture strength than conventionally milled counterparts

Zirconia restorations, which are fabricated by additive 3D gel deposition and do not require glazing like conventional restorations, were introduced as "self-glazed" zirconia restorations into dentistry. This in vitro investigation characterized the surface layer, microstructure and the fracture and aging behavior of "self-glazed" zirconia (Y-TZP_SG) three-unit fixed dental prostheses (FDP) and compared them to conventionally CAD/CAM milled and glazed controls (Y-TZP_C-FDPs). For this purpose, the FDPs were analyzed by (focused ion beam) scanning electron microscopy, laserscanning microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and a dynamic and static loading test. For the latter, half of the samples of each material group (n = 16) was subjected to 5 million cycles of thermocyclic loading (98N) in an aqueous environment in a chewing simulator. Afterwards, all FDPs were loaded to fracture. Y-TZP_SG-FDPs demonstrated a comparable elemental composition but higher surface microstructural homogeneity and fracture strength compared to Y-TZP_C-FDPs. Microstructural flaws within the FDPs' surfaces were identified as fracture origins. The high fracture strength of the Y-TZP_SG-FDPs was attributed to a finer-grained microstructure with fewer surface flaws compared to the Y-TZP_C-FDPs which showed numerous flaws in the glaze overlayer. A decrease in fracture strength after dynamic loading from 5165N to 4507N was observed for the Y-TZP_SG-FDPs, however, fracture strength remained statistically significantly above the one measured for Y-TZP_C-FDPs (before chewing simulation: 1923N; after: 2041N). Within the limits of this investigation, it can therefore be concluded that Y-TZP_SG appears to be stable for clinical application suggesting further investigations to prove clinical applicability.

Toxicity of Silver Nanoparticles Supported by Surface-Modified Zirconium Dioxide with Dihydroquercetin

The antibacterial performance and cytotoxic examination of in situ prepared silver nanoparticles (Ag NPs), on inorganic-organic hybrid nanopowder consisting of zirconium dioxide nanoparticles (ZrO₂ NPs) and dihydroquercetin (DHQ), was performed against Gram (-) bacteria Escherichia coli and Gram (+) bacteria Staphylococcus aureus, as well as against human cervical cancer cells HeLa and healthy MRC-5 human cells. The surface modification of ZrO₂ NPs, synthesized by the sol-gel method, with DHQ leads to the interfacial charge transfer (ICT) complex formation indicated by the appearance of absorption in the visible spectral range. The prepared samples were thoroughly characterized (TEM, XRD, reflection spectroscopy), and, in addition, the spectroscopic observations are supported by the density functional theory (DFT) calculations using a cluster model. The concentration- and time-dependent antibacterial tests indicated a complete reduction of bacterial species, E. coli and S. aureus, for all investigated concentrations of silver (0.10, 0.25, and 0.50 mg/mL) after 24 h of contact. On the other side, the functionalized ZrO₂ NPs with DHQ, before and after deposition of Ag NPs, do not display a significant decrease in the viability of HeLa MRC-5 cells in any of the used concentrations compared to the control.

Model-free digital workflow and immediate functional loading of implant-supported monolithic glass-ceramic crowns: A case series

OBJECTIVES

The aim of this study is to evaluate surgical and prosthetic outcomes of immediate functional loading of implants with glass-ceramic screw-retained single crowns.

METHODS

A total of 22 implants were placed. Within 24 hours, functional full-contour glass ceramic crowns were delivered to patients. The amount of attached gingiva, Simplified Oral Hygiene Index Score, bleeding on probing, time after extraction, bone type, implant size, soft tissue thickness, primary stability, a general fit of the restoration, occlusal and proximal contacts were recorded. Restorations were followed-up at 1, 3, and 6 months tracking marginal bone loss (MBL), noting changes in occlusal and interproximal contacts, checking other possible complications.

RESULTS

One implant failed and was removed after 4 weeks (95.5 % survival rate). The rest of the implants and crowns functioned with no complications during the follow-up period of 6 months. Factors such as time after extraction, bone type, implant size, soft tissue thickness, and primary stability recorded in Ncm and implant stability quotient (ISQ) values, were not associated with MBL (p<0.05). Mean MBL was found to be 0.3 mm (standard deviation = 0.42) mesially and 0.4 mm (standard deviation = 0.66) distally. One distal and one mesial proximal contact were found to be missing at the 6-month check-up appointment.

CONCLUSIONS

Within the limits of this study, fully digital workflow without a 3D printed model could be successfully employed for immediate functional loading with single-unit implant-supported crowns. Further studies are needed to obtain long-term results with a larger sample of patients.

CLINICAL SIGNIFICANCE

Model-free digital workflow and immediate functional loading of implant-supported monolithic glass-ceramic crown might be viable option to restore a single tooth defect.

Enhanced osteogenic activity of titania-modified zirconia implant by ultraviolet irradiation

Zirconia is a superior implant material owing to its high mechanical strength, durable corrosion resistance, superior aesthetic effect and excellent biocompatibility. However, the bioactivity of zirconia surfaces remains a great challenge for implant osseointegration. A titania (TiO₂) coating was innovatively synthesized on the surface of zirconia by infiltration in a suspension of zirconium oxychloride and titania for dense sintering. Subsequently, the coating was subjected to ultraviolet (UV) light to enhance the biological inertness of zirconia. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and contact angle analysis were conducted to confirm the surface characteristics. Afterwards, in vitro assessments of cell adhesion, proliferation and osteogenic differentiation of MC3T3-E1 cells were performed. Zirconia samples were implanted into rat femurs to assess biocompatibility and host tissue response in vivo. Micro-CT evaluation and histological testing were conducted. After UV irradiation, the content of hydroxyl groups and hydrophilicity of TiO₂-modified zirconia were significantly increased. The results of in vitro experiments showed that TiO₂-modified zirconia subjected to UV light could promote cell proliferation and spreading, enhance ALP activity and the degree of mineralization, and upregulate osteogenesis-related genes. Furthermore, in vivo assessments confirmed that UV-irradiated TiO₂-modified zirconia implants maximized the promotion of osseointegration. TiO₂-modified zirconia after UV treatment will have broad clinical application prospects in improving the osseointegration of zirconia implants.

The Effect of Yttria Content on Microstructure, Strength, and Fracture Behavior of Yttria-Stabilized Zirconia

Yttria-stabilized zirconia (YSZ) is well-known as a material with perfect mechanical, thermal, and electrical properties. It is used for manufacturing various high-temperature components for aerospace and energy generation, as well as wear- and corrosion-resistant devices in medicine. This work investigated the effect of a Y2O3 addition to ZrO2 on the microstructure and mechanical properties of YSZ ceramics produced by one sintering schedule. ZrO2 ceramics doped with 3, 4, 5, 6, 7, and 8 mol% Y2O3 (designated 3YSZ through to 8YSZ) were prepared by using conventional sintering at 1550 °C for 2 h in argon. The effect of yttria content was analyzed with respect to grain size, morphology of the microstructural features, phase composition, parameters of fracture surface, and flexural strength. The 7YSZ ceramics sintered at 1550 °C for 2 h showed the highest level of flexural strength due to the formation of the fine-grained microstructure containing mainly the monoclinic and tetragonal zirconia phases. The fracture micromechanism in the studied YSZ ceramics is discussed.

Mechanical properties and electronic structure of Cu-doped tin: a first-principle study

Metal doping is an effective method for improving the toughness of ceramic materials and reducing coating fractures. In this study, first-principle calculations based on density functional theory were performed to study the formation energy, elastic constant, and electronic structure of Cu-doped TiN. The results reveal that Cu tends to replace the Ti sites in TiN crystal cells; with an increase in Cu concentration, the formation energy of the Cu-doped TiN system decreases. This indicates that the structural stability of Cu-doped TiN decreases. From the calculated elastic constant and the Voigt-Reuss-Hill approximation, it is evident that the bulk modulus B and shear modulus G decrease as the Cu concentration increases. However, G decreases more rapidly, thus increasing the B/G ratio. According to Paugh's ratio, the increase in B/G indicates an increase in the ductility of TiN. The results of the band structure, density of states, charge density, and Mulliken bond population analysis reveal that Cu doping reduces the covalent bond strength of TiN, enhances metallicity, and reduces the structural stability of the system, enhancing the toughness of TiN. The results of this study will provide theoretical and experimental guidance for improving the toughness of TiN coatings.