Current classification of zirconia in dentistry: an updated review

Optical properties of repaired additively manufactured resin composites and zirconia and subtractively manufactured ceramics: a comparative study of composite resins

OBJECTIVE

This study aims to examine color properties of repairs made with various composites on restorations produced through additive-manufactured resin composites (AM-RC) and zirconia (AM-Z) or subtractive manufacturing (SM) after coffee thermocycling (CTC).

MATERIALS AND METHODS

Disk-shaped specimens (Ø10 × 2 mm; N = 120) were fabricated using six different material groups: additively manufactured resin composite (AM-RC) materials (Crowntec [C], NextDent [ND]), additively manufactured zirconia (AM-Z) materials (Lithoz [LI], INNI-Cera [IN]), and subtractively manufactured (SM) materials (CEREC Tessera [ALD], Vita Enamic [EN]). Subsequently, each group was further subdivided into two subgroups (n = 10) based on the type of repair using two different composites resins: Clearfil Majesty Posterior (CL) (n = 60) and Filtek Z350 (FZ) (n = 60). Specimens underwent thermal cycling (CTC), consisting of 10,000 cycles between 5 °C and 55 °C. Color measurements were performed both before and after thermal cycling for all materials. Color discrepancies (ΔE00) and relative translucency parameters (RTPs) were calculated. Statistical analyses were conducted at a significance level of α = 0.05.

RESULTS

A one-way ANOVA of ΔE00 values between CL and FZ revealed a significant difference (P = 0.007), with FZ exhibiting higher ΔE00 values. Significant differences in ΔE00 values were also observed among IN, C, and ND after CTC (P < 0.05). ALD demonstrated the lowest amount color change (P < 0.05). LI and EN colors showed no significant difference (P = 0.75). Following CTC, C, ND, and IN colors matched CL. In contrast, ALD, EN, and L colors exhibited significant differences (P ≤ 0.050). FZ showed a poor color match with all AM and SM materials. Furthermore, significant differences in RTP values were identified for all specimens (P < 0.001), with LI having the highest RTP and IN the lowest (P < 0.001).

CONCLUSION

The optical properties of composite and ceramic materials, as well as their stability over time, are crucial for their durability. ALD demonstrated the most consistent color stability. While the CL repair composites experienced some color changes, these changes remained within acceptable limits. Additionally, the LI (AM-Z) material exhibited the highest level of translucency.

Gingival Soft Tissue Integrative Zirconia Abutments with High Fracture Toughness and Low-Temperature Degradation Resistance

Low fracture toughness, low-temperature degradation (LTD) susceptibility, and inadequate soft tissue integration greatly limit the application of zirconia ceramic abutment. Integrating the "surface" of hard all-ceramic materials into the gingival soft tissue and simultaneously promoting the "inner" LTD resistance and fracture toughness is challenging. Composite ceramics are effective in improving the comprehensive properties of materials. In this study, we aim to develop a zirconia composite abutment with high "inner" structure stability and "surface" bioactivities simultaneously and to explore the mechanism of performance improvement. Therefore, elongated SrAl12O19 and equiaxed Al2O3 were introduced into the zirconia matrix by using the Pechini method. Reinforcements of different shapes can promote the density, reduce the grain size, and increase the phase stability of composite ceramics, which improves the fracture toughness and LTD susceptibility. In addition, the released strontium ions (Sr2+), without sacrificing the mechanical properties of the material, could activate the biological capacity of the zirconia surface by activating the M2 polarization of macrophages through the Sr2+/calcium-sensing receptor/SH3 domain-binding protein 5 axis, thereby promoting the collagen matrix synthesis of fibroblasts and the angiogenesis of vascular endothelial cells. This successful case proposes a novel strategy for the development of advanced high-strength and bioactive all-ceramic materials by introducing reinforcements containing biofunctional elements into the ceramic matrix. The approach paves the way for the widespread application of such all-ceramic materials in soft-tissue-related areas.

Biaxial Flexural Strength and Vickers Hardness of 3D-Printed and Milled 5Y Partially Stabilized Zirconia

This study compares the mechanical properties of 5-mol% yttria partially stabilized zirconia (5Y-PSZ) materials, designed for 3D printing or milling. Three 5Y-PSZ materials were investigated: printed zirconia (PZ) and two milled zirconia materials, VITA-YZ-XT (MZ-1) and Cercon xt (MZ-2). PZ samples were made from a novel ceramic suspension via digital light processing and divided into three subgroups: PZ-HN-ZD (horizontal nesting, printed with Zipro-D Dental), PZ-VN-Z (vertical nesting, printed with Zipro-D Dental) and PZ-VN-Z (vertical nesting, printed with Zipro Dental). Key outcomes included biaxial flexural strength (ISO 6872) and Vickers hardness (n ≥ 23 samples/subgroup). Microstructure and grain size were analyzed using light and scanning electron microscopy. Printed specimens exhibited biaxial flexural strengths of 1059 ± 178 MPa (PZ-HN-ZD), 797 ± 135 MPa (PZ-VN-ZD), and 793 ± 75 MPa (PZ-VN-Z). Milled samples showed strengths of 745 ± 96 MPa (MZ-1) and 928 ± 87 MPa (MZ-2). Significant differences (α = 0.05) were observed, except between vertically printed groups and MZ-1. Vickers hardness was highest for PZ-VN-Z (HV0.5 = 1590 ± 24), followed by MZ-1 (HV0.5 = 1577 ± 9) and MZ-2 (HV0.5 = 1524 ± 4), with significant differences, except between PZ and MZ-1. PZ samples had the smallest grain size (0.744 ± 0.024 µm) compared to MZ-1 (0.820 ± 0.042 µm) and MZ-2 (1.023 ± 0.081 µm). All materials met ISO 6872 standards for crowns and three-unit prostheses in posterior regions.

Fit accuracy and fracture resistance evaluation of advanced lithium disilicate crowns (in- vitro study)

BACKGROUND

Increasing demand for durable and aesthetically pleasing dental restorations, including laminates, inlays, onlays, and crowns, has led to advancements in all-ceramic systems, particularly with the development of advanced lithium disilicate materials. However, limited data on the fit accuracy and fracture resistance of these materials restricts their wider application in clinical restorative practices.

AIM OF THE STUDY

This in vitro study aims to compare the marginal and internal fit, assess the fracture resistance, and evaluate the failure modes of crowns fabricated from advanced and conventional lithium disilicate materials.

MATERIALS AND METHODS

Thirty two (n = 32) crowns were fabricated and categorized into two groups based on the material used: Group (CT), where crowns were milled from CEREC Tessera (n = 16), and Group (EM), where crowns were milled from IPS e.max CAD (n = 16) using a CAD/CAM system. The marginal and internal fit were assessed digitally via a triple scan protocol. All samples were subjected to a fracture resistance test with a universal testing machine, followed by an analysis of failure modes under a stereomicroscope.

RESULTS

In the evaluation of marginal, internal and total gaps, CEREC Tessera (CT) showed slightly better fit with lower gap values compared to e.max CAD (EM). However, an independent samples t-test indicated no statistically significant differences between the two groups (p = 0.141, p = 0.471). For fracture resistance (N), the CT group demonstrated higher values than the EM group; however, the independent samples t-test indicated no statistically significant difference (p = 0.053). Additionally, the Chi-squared test with Monte Carlo correction revealed no statistically significant differences in the modes of fracture between the two groups (p = 0.484).

CONCLUSION

Considering the limitations of this study, advanced lithium disilicate crowns demonstrated better results in terms of marginal fit, internal adaptation, and fracture resistance compared to traditional lithium disilicate crowns; however, the differences were not statistically significant. Both materials exhibited comparable fracture patterns.

Effect of different surface treatments on shear bond strength of zirconia with various yttria contents

BACKGROUND

Achieving a stable bond with zirconia requires mechanical and chemical bonding methods. Information regarding the optimal treatment method for zirconia with varying yttrium content is scarce. This study evaluated the effect of different surface treatments on the shear bond strength of zirconia with various yttria contents.

MATERIALS AND METHODS

A total of 168 disc-shaped zirconia specimens were classified into 12 groups based on the surface treatment method, including airborne-particle abrasion (APA), selective infiltration etching (SIE), hot etching (HE), and control group with no treatment; and yttria contents including Zolid Zi (4.5-5.6 wt% yttrium), Zolid HT White (6.7-7.2 wt% yttrium), and Ceramill Zolid FX (9.15-9.55 wt% yttrium). The surface roughness (Ra and Rz) of the specimens and the shear bond strength was measured (α = 0.05).

RESULTS

The results indicated that the mean bond strength of all specimens was higher after different surface treatments compared to the control group, of which the APA method resulted in higher bonding strength in all kinds of zirconia than other methods (P < 0.05). In all types of zirconia, a significant difference was observed in surface roughness (Ra and Rz) resulting from various surface treatment methods (P < 0.001). Interaction of surface treatment methods and zirconia type significantly affected shear bond strength and surface roughness (P < 0.05).

CONCLUSION

APA significantly enhanced shear bond strength and surface roughness across all zirconia types and yttria contents. The SIE and HE methods also showed promising results. Zolid Zi showed superior bond strength, whereas Zolid FX demonstrated reduced bond strength.

Bonding super translucent multilayered monolithic zirconia to different foundation materials: an invitro study

BACKGROUND

The objective of this study was to investigate the effect of bonded substrate, zirconia surface conditioning and the interaction between them on the shear bond strength of monolithic zirconia.

METHODS

Forty-eight monolithic zirconia discs were CAD-CAM fabricated and divided into two groups according to surface treatment either as milled and universal primer application (Monobond N, Ivoclar-Vivadent) (P) or sandblasting then universal primer application (Monobond N) (SP). Each main group was further divided into three test groups according to the bonded substrate: dentin (DSP, DP), composite (CSP, CP) or resin modified glass ionomer (RMGI) (GSP, GP). Adhesive resin cement (Multilinik automix, Ivoclar-Vivadent) was used for bonding. Specimens were stored in water bath for six months before thermal cycling for 10,000 cycles to mimic intra oral condition. All specimens underwent shear bond strength test (SBS) using a universal testing machine. Two and one-way ANOVA and Bonferroni Post Hoc tests were used for statistical analyses.

RESULTS

The means ± SD SBS of all test groups were recorded in (MPa). DSP group showed the highest mean SBS (22.65 ± 2.0) followed by DP group (18.61 ± 2.55). Meanwhile, GSP and GP groups showed the lowest mean SBS (4.77 ± 0.09, 4.57 ± 0.73 respectively).

CONCLUSION

Sandblasting with priming is recommended as a monolithic zirconia surface treatment method. Dentin is the most reliable substrate followed by composite.

Effect of metal elements in coloring liquids used in the infiltration method on the physical properties of zirconia

OBJECTIVES

This study aimed to clarify the effect of metal elements in the coloring liquids used in the infiltration method on the physical properties of zirconia.

METHODS

Two types of zirconia discs 5Y-PSZ (SHOFU Disc ZR Lucent FA, SHOFU, Kyoto, Japan) were used: with monolayer shades from W2 to W3 (Pearl White) and 5Y-PSZ with multilayer shades from A3 to A4 (L). Five kinds of coloring liquid were used to infiltrate into semi-sintered Pearl White (T-glass [CT], A4 [CA], White-Opaque [CW], Gingiva 1 [CG], and Blue X [CB]). In addition, uncolored Pearl White set to as the control (C). These specimens were analyzed using a three-point bending test (3PBT), and the fracture surface after the test was analyzed by scanning electron microscopy, elemental analysis, and crystal structure analysis. In addition, from the polished surface part of the after the 3PBT specimens, the elemental composition was analyzed using X-ray fluorescence spectroscopy (XRF).

RESULTS

The flexural strength of CB and CG were lower than that of C (p < 0.05). XRF results showed that the Erbium (Er) content of CG was significantly greater than that of C (p < 0.05). CB exhibited a significantly higher Yttrium (Y) content compared with C (p < 0.05), and numerous pores were observed in the micrographs of the fracture surface of CG and CB.

SIGNIFICANCE

In zirconia, where the content of Y and Er was significantly increased by infiltration with a coloring liquid, pores were observed between the zirconia crystals, and the mechanical strength decreased.

Impact of zirconia-based oxide on endothelial cell dynamics and extracellular matrix remodeling

INTRODUCTION

Zirconia (ZrO2) is highly regarded in dental restoration due to its aesthetic compatibility and mechanical properties that align with biological tissues. This study explores the effects of stabilized ZrO2 on endothelial cell function and extracellular matrix (ECM) remodeling, processes critical to successful osseointegration in dental implants.

METHODOLOGY

Human Umbilical Vein Endothelial Cells (HUVECs) were cultured in ZrO2 -enriched medium under both static and shear stress conditions. Newly implemented techniques, including detailed zirconia surface characterization using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD), were used to verify material properties. Gene and protein expression related to cell adhesion, proliferation, and ECM remodeling were assessed through RT-qPCR and Western blotting. Zymography was used to evaluate the activity of matrix metalloproteinases (MMP2 and MMP9) involved in ECM remodeling.

RESULTS

Characterization data confirmed the stability and structural properties of ZrO2, revealing a tetragonal crystalline structure and rough surface morphology conducive to cell adhesion. ZrO2 exposure led to the downregulation of Src, a key regulator of cell adhesion, while upregulating cell cycle regulators p15, CDK2, and CDK4, indicating enhanced cell proliferation. Under shear stress, ZrO2 modulated TGF-β and MAPK signaling, affecting cell proliferation and angiogenesis. MMP2 and MMP9 activity increased in static conditions but decreased under shear stress, suggesting ZrO2 dynamic role in ECM remodeling.

CONCLUSION

This study shows that stabilized zirconia (ZrO2) modulates endothelial cell dynamics and ECM remodeling, key for osseointegration. ZrO2 downregulated Src expression and upregulated cell cycle regulators, enhancing endothelial proliferation. It also affected TGF-β and MAPK pathways, influencing angiogenesis, and differentially modulated MMP2 and MMP9 activity depending on mechanical conditions. These findings highlight ZrO2 has potential ability to enhance vascular and tissue integration in dental applications.

Streptococcus-mutans and Porphyromonas-gingivalis adhesion to glazed/polished surfaces of CAD/CAM restorations

Purpose

Dental restorations fabricated using CAD/CAM require modification/adjustment before cementation. Streptococcus mutans (S.mutans) and Porphyromonas gingivalis (P.gingivalis) are prevalent bacterial species that may adhere to these materials and can cause caries, gingivitis/periodontitis. The purpose of this in vitro study was to evaluate the bacterial adherence of S.mutans and P.gingivalis to five different kinds of modern CAD/CAM restorative materials with different compositions following chairside finishing/polishing and glazing.

Materials and methods

Specimens (N = 75) from five test materials (n = 15 each) "Tetric-CAD®; IPS-e.max-CAD®; IPS-e.max-ZirCAD®; CELTRA-Duo® and Vita-Enamic®" were prepared in disc shape (10 × 3 mm) using CAD/CAM. The specimens underwent glazing and finishing/polishing using established procedures. The surface roughness was measured in micrometers (μm) using a profilometer. Bacterial adherence to test materials' glazed and finished/polished surfaces was tested using bacterial culture growth over the test materials. Data obtained was tabulated and statistical analysis performed using Kruskal Wallis test, post-hoc Conover test, Mann-Whitney U test and Tukey post hoc test.

Results

With the exception of IPS-e.max-ZirCAD®, which showed the contrary, the adherence of S.mutans & P.gingivalis was less on glazed surfaces compared to finished/polished surfaces for four test materials: "Tetric-CAD®, IPS-e.max-CAD®, CELTRA-Duo®, and Vita-Enamic®". On the glazed surfaces, the adhesiveness of S.mutans and P.gingivalis was not significant (p = 0.099; p = 0.660); however, on the finished/polished surfaces, it was significant (p = 0.002; p = 0.004). With the exception of 'IPS-e.max-ZirCAD®', which showed the reverse behavior, the adhesion of S.mutans & P.gingivalis to finished/polished surfaces was greater for each of the four ceramics under investigation "Tetric-CAD®, IPS-e.max-CAD®, CELTRA-Duo®, and Vita-Enamic®".

Conclusion

Glazed surfaces for majority of test materials demonstrated decreased adhesion from S.mutans & P.gingivalis, hence prior to final placement of restoration, it is advised to adhere to the minimal glazing criteria. Regardless of the chemical composition of the materials, the surface texture of the tested materials significantly influenced bacterial adhesion.

Effects of Er:YAG laser debonding on changes in the properties of dental zirconia

OBJECTIVES

To investigate changes in the optical and mechanical properties of novel zirconia ceramics applied in dentistry after Er:YAG laser debonding and to evaluate the feasibility and value of reusing zirconia restorations debonded by an Er:YAG laser.

METHODS

Four types of zirconia ceramics were investigated: self-glazed zirconia (SGZ), 3Y-TZP, 4Y-PSZ and 5Y-PSZ. Forty rectangular (25 mm*8 mm*1.5 mm) specimens were fabricated for each zirconia type, and a total of 160 specimens were manufactured. The zirconia specimens were divided into four subgroups according to the applied Er:YAG laser debonding process: the control group, 4 W laser group, 5 W laser group, and 6 W laser group. For each subgroup, 10 specimens were subjected to color tests (color difference (△E) and transparency parameter (TP) tests) and subsequent mechanical tests (flexural strength (FS), elastic modulus (EM), Vickers hardness (VH) and surface roughness (Ra) tests). The △E, TP, FS, EM, VH and Ra values were measured and calculated. One random sample from each subgroup was observed by SEM. Statistical analyses were performed by one-way ANOVA followed by post hoc comparisons (α = 0.05).

RESULTS

The △E and TP values after Er:YAG laser debonding were not significantly different among the subgroups (P > 0.05). However, the 6 W laser group had the highest △E and lowest TP. The ranges of changes in △E and TP were below the clinically detectable threshold (△E = 1.2, △TP = 1.33). In terms of the mechanical properties, there were no significant differences in the FS, EM, VH or Ra among the subgroups. No obvious microcracks were detected on the surfaces of the zirconia specimens during SEM.

CONCLUSIONS

Er:YAG laser debonding does not obviously affect the optical or mechanical properties of novel zirconia ceramics in dentistry. Moreover, it is potentially feasible and valuable to reuse zirconia restorations after Er:YAG laser debonding.

Impact of Speed Sintering on Translucency, Opalescence and Microstructure of Dental Zirconia with a Combination of 5 mol% and 3 mol% Yttria-Stabilized Zirconia

Optical characteristics and microstructure of multilayered zirconia with different yttria contents in each layer can be influenced differently with a layer after speed sintering. The layer-wise translucency and opalescence of dental zirconia (E.max, E.max ZirCAD prime; Cercon, Cercon ht ML) after conventional (control) and speed sintering were analyzed using a spectrophotometer (n = 5). Specimens were subjected to microstructural analyses (n = 2) using field-emission scanning electron microscopy (FE-SEM) and phase analyses (n = 1) using high-resolution X-ray diffraction (HRXRD) and Rietveld refinement. The translucency parameter (TP) and opalescence parameter (OP) were analyzed using a 3-way ANOVA, followed by Scheffé's post hoc test (α = 0.05). The average grain size was analyzed using the Welch's t-test and Kruskal-Wallis test, followed by the Bonferroni-Dunn post hoc test (α = 0.05). Changes to the TP and OP after speed sintering were only observed in the dentin layers. Although the TP of E.max increased (p < 0.05), the difference was below the 50:50% perceptibility threshold (ΔE00 = 0.8). The OP of E.max decreased slightly, whereas that of Cercon increased slightly (p < 0.05). The microstructure and phase fraction of both zirconia barely changed. Therefore, speed sintering is considered to have a negligible clinical impact on the optical characteristics and microstructure.

The Role of Porcelain Veneers in the Aesthetic Restoration of Discolored Endodontically Treated Teeth

BACKGROUND

The discoloration of endodontically treated anterior teeth poses a significant aesthetic concern for many individuals, impacting their confidence and self-image. Porcelain veneers have emerged as a popular solution for the aesthetic restoration of such teeth. This paper explores the role of porcelain veneers in addressing tooth discoloration, examining their efficacy, durability, and aesthetic outcomes via a clinical case.

CASE DESCRIPTION

In this clinical case, an aesthetic restoration of a discolored central incisor was performed using a ceramic veneer. Due to the high degree of discoloration, an internal bleaching of the tooth was carried out prior to the final restoration. Various factors influencing the selection of porcelain veneers as a treatment modality, including shade matching, preparation techniques, and adhesive bonding, are discussed.

CONCLUSIONS

The advancements in materials and techniques have enhanced the versatility and aesthetic appeal of porcelain veneers, making them a valuable option for achieving natural-looking and durable aesthetic restorations in individuals with discolored endodontically treated anterior teeth.

In Vitro Evaluation of Speed Sintering and Glazing Effects on the Flexural Strength and Microstructure of Highly Translucent Multilayered 5 mol% Yttria-Stabilized Zirconia

This study aimed to investigate the impact of speed sintering and glazing on the flexural strength and microstructure of multilayered 5 mol% yttria-stabilized (5Y-) zirconia, which remains unknown. Bar-shaped specimens (N = 600) were fabricated from 5Y-zirconia (FX; Ceramill Zolid FX ML, ST; Katana STML) by cutting, polishing, sintering (conventional and speed sintering), and then glazing. A flexural strength test (n = 30/group), field emission scanning electron microscopy (FE-SEM) observation (n = 2/group), and an X-ray diffraction (XRD) study with Rietveld refinement (n = 1/group) were performed. The flexural strength was analyzed using three-way ANOVA and a post hoc Scheffé test. The grain size was analyzed using the Kruskal-Wallis H test and Bonferroni-Dunn post hoc test. Flexural strength slightly decreased in the nonglazed FX after speed sintering (p < 0.05). Glazing with and without glazing paste did not affect flexural strength at both sintering speeds (p > 0.05). Speed sintering and glazing minimally changed the Weibull modulus and phase fraction, and did not affect grain size (p > 0.05). ST had a larger grain size and lower tetragonal phase content than FX and had a lower flexural strength than FX in most groups (p < 0.05). Overall, the multilayered 5Y-zirconia is considered suitable for dental application using speed sintering and glazing.

Cytokines profile in gingival crevicular fluid of subjects wearing fixed dental prostheses: a systematic review and meta-analysis

BACKGROUND

Fixed dental prostheses (FDP) can affect the production of inflammatory cytokines causing damage to periodontal tissues. A systematic review and meta-analysis was carried out with the following two objectives: (1) to determine the prevalence and function of the different inflammatory cytokines present in gingival crevicular fluid (GCF) of teeth with metal-ceramic (M/C) and all-ceramic (A-Cs) prostheses, and (2) to analyze and compare the levels of inflammatory cytokines in GCF of teeth with M/C and A-Cs prostheses.

METHODS

The protocol followed PRISMA and Cochrane guidelines and was registered in the OSF:10.17605/OSF.IO/RBHJU. A digital search was conducted in the databases PubMed/MEDLINE, Cochrane Library, Dentistry & Oral Sciences Source, Scopus, Web of Science, ScienceDirect, and Google Scholar, from July 15th, 2000 to March 1st, 2024. Study quality was assessed using the JBI tool for cross-sectional and longitudinal studies. A meta-analysis was performed using a random-effects model to evaluate the concentration of IL-1β in GCF of teeth with FDP of M/C and A-Cs.

RESULTS

The search strategy provided a total of 8,172 articles, of which 14 investigations met the inclusion criteria. The total number of patients studied was 468 of whom 53% were women and the rest (47%) were men. The ages of the patients ranged from 19 to 73 years, with a mean age ± standard deviation (SD) of 38,5 ± 12,8 years. A total of 843 fixed dental prostheses were studied, of which 407 (48,27%) were M/C prostheses and 410 (48,63%) were A-Cs prostheses. We found that the levels of IL-1β, IL-1α, PGE2, NKA, CGRP, and CX3CL1 were increased in teeth with M/C prostheses compared to teeth with A-Cs prostheses. Meta-analysis revealed that there are no significant differences between IL-1β levels in GCF in teeth with M/C prostheses compared to teeth with A-Cs prostheses (SMD = 13.89 pg/ml (CI = -14.29-42.08), p =  > 0.05).

CONCLUSIONS

A trend toward increased levels of inflammatory cytokines was found in GCF of teeth with M/C prostheses compared to teeth with A-Cs prostheses.

Zirconia Dental Implant Designs and Surface Modifications: A Narrative Review

Titanium currently has a well-established position as the gold standard for manufacturing dental implants; however, it is not free of flaws. Mentions of possible soft-tissue discoloration, corrosion, and possible allergic reactions have led to the development of zirconia dental implants. Various techniques for the surface modification of titanium have been applied to increase titanium implants' ability to osseointegrate. Similarly, to achieve the best possible results, zirconia dental implants have also had their surface modified to promote proper healing and satisfactory long-term results. Despite zirconium oxide being a ceramic material, not simply a metal, there have been mentions of it being susceptible to corrosion too. In this article, we aim to review the literature available on zirconia implants, the available techniques for the surface modification of zirconia, and the effects of these techniques on zirconia's biological properties. Zirconia's biocompatibility and ability to osseointegrate appears unquestionably good. Despite some of its mechanical properties being, factually, inferior to those of titanium, the benefits seem to outweigh the drawbacks. Zirconia implants show very good success rates in clinical research. This is partially due to available methods of surface treatment, including nanotopography alterations, which allow for improved wettability, bone-to-implant contact, and osteointegration in general.

Effects and underlying mechanism of micro-nano-structured zirconia surfaces on biological behaviors of human gingival fibroblasts under inflammatory conditions

Zirconia is one of the most commonly used materials for abutments of dental implants, especially in the anterior region. Soft tissue integration to the zirconia abutment surface remains a challenge. Peri-implant soft tissue integration serves as a physiological barrier, attenuating pathogen penetration and preventing peri‑implant disease. The surface microstructure of zirconia has significant effects on the biological behaviors of human gingival fibroblasts (HGFs), but the effects under inflammatory conditions are still unclear. In this study, we established two micro-nano structures on zirconia surfaces using a femtosecond laser, including microgrooves with widths of 30 µm (G3) and 60 µm (G6) and depths of 5 µm, and nanoparticles inside the microgrooves. Polished surfaces were used as controls. HGFs were seeded onto the three groups of zirconia specimens and stimulated with lipopolysaccharide. The HGFs on micro-nano-structured zirconia surfaces exhibited lower inflammatory responses and higher cell adhesion, proliferation, and migration under inflammatory conditions compared with the polished surfaces. Additionally, the G3 group exhibited lower inflammatory responses and higher cell adhesion and migration than the G6 group. The micro-nano-structured zirconia surface exhibited decreased neutrophil infiltration and increased M2-type macrophage polarization in vivo. To explore the molecular mechanism, RNA sequencing and gene silencing were utilized, which revealed two critical target genes regulated by the G3 group. Overall, we proposed an innovative micro-nano-structured zirconia surface that reduced the in vitro and in vivo inflammatory responses and promoted HGF adhesion, migration, and proliferation under inflammatory conditions, in which TRAFD1 and NLRC5 were the underlying key genes. STATEMENT OF SIGNIFICANCE: Zirconia is one of the most commonly used materials for abutments, especially in the anterior region. The surface microstructure of zirconia has significant effects on the biological behaviors of human gingival fibroblasts (HGFs), but few studies have investigated these effects under inflammatory conditions, and the mechanism remains unclear. In this study, we developed an innovative micro-nano-structured zirconia surface using a femtosecond laser, which reduces the in vitro and in vivo pro-inflammatory responses and promotes HGFs adhesion, migration, and proliferation under inflammatory conditions compared with the polished zirconia surface. The potential underlying mechanism was also investigated. This work has provided some theoretical basis for the micro-nano-structured zirconia surface in potentially reducing the inflammation and enhancing peri‑implant soft-tissue integration under inflammatory conditions.

Fracture Resistance of Zirconia Surveyed Crowns With Digitally Designed and Hand-Modified Occlusal Rest Seats

Background In light of the trend of using zirconia crowns, clinicians will likely face abutment included in removable partial dentures (RPD) designs with existing zirconia. However, the decision to replace the existing crown with a surveyed crown or modify the existing crown to accept the RPD is unclear. To the best of our knowledge, there is a lack of literature on the effect of preparing a rest seat on the existing monolithic zirconia crown in the patient's mouth on the fracture resistance of the crown. Therefore, in this study, we aimed to evaluate the fracture resistance of computer-aided design/computer-aided manufacturing (CAD/CAM) zirconia surveyed crowns with digitally designed rest seats and hand-modified rest seats. Methods Thirty CAD/CAM zirconia surveyed crowns were digitally designed and fabricated and divided into groups (n=10 per group) as follows: Group 1 comprised surveyed crowns with no occlusal rest seat; Group 2 comprised surveyed crowns with a digitally designed mesial rest seat; and Group 3 comprised surveyed crowns with a hand-modified mesial rest seat. Then, with all the crowns cemented to metal dies, the specimens were subjected to a fracture resistance test using a universal testing machine (Model 8501 Instron, Norwood, MA, USA). Results Surveyed crowns without any rest seat and those with digitally created and hand-modified rest seats displayed different fracture resistances: crowns with no rest seat offered the highest fracture resistance (5831 ± 895.15 N), followed by those with a digitally designed and milled rest seat (5280 ± 1673.33 N). Crowns with a hand-modified rest seat provided the lowest fracture resistance (4976 ± 322.5 N). Based on our results, surveyed crowns without a rest seat displayed higher fracture resistance than those with a rest seat. Conclusion The fracture resistance of crowns with a digitally designed and milled rest seat was statistically similar to that of control crowns with no rest seat, whereas hand-modified rest seats significantly reduced the fracture resistance of surveyed zirconia crowns.

Comparison of the fracture strengths of single-unit metal-ceramic and monolithic zirconium restorations in the molar region: a systematic review and meta-analysis

Despite the success of monolithic zirconia restorations (MZ), metal-ceramic restorations (MC) are still considered the gold standard for fixed prosthetics in the posterior region. This systematic review and meta-analysis aimed to compare the fracture strengths of single-unit MC and MZ in the molar region. This review was based on the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA, 2020) statement. All articles were searched from the PubMed and Web of Science databases until November 18, 2022. All in vitro studies evaluating the fracture strengths of MC and MZ were also included. Statistical analysis was performed with the Comprehensive Meta-Analysis program, with a significance level of 0.05. Out of 753 studies, five were selected. The fracture strengths of MZ and MC did not show any statistically significant difference for both tooth (95% CI - 1.589: 2.118, p = 0.779, z = 0.280) and implant (95% CI - 2.215: 2.191, p = 0.992 z = - 0.010) supported restorations. However, different abutment materials (p < 0.001) and aging treatments (p < 0.001) in tooth-supported restorations displayed a significant statistical difference. Additionally, a significant difference was also observed in subgroup analysis considering different cements (p = 0.001) and load speeds (p = 0.001) in implant-supported restorations. Fracture strengths of MZ and MC did not show a significant statistical difference in implant or tooth-supported single-unit posterior restorations. MZ may be a suitable alternative to MC in single-unit posterior restorations. The results should be interpreted with caution, as the included studies were in vitro.

Fabrication of translucent graded dental crown using zirconia-yttrium multi-slurry tape casting 3D printer

This paper aims to fabricate functionally graded dental crown using a multi-slurry tape casting additive manufacturing technology. The different luminescence of the dental crown was obtained with different composition of zirconia and yttria. Zirconia with tunable mechanical properties and translucency are obtained by adding 3, 3.5, 4, 4.5, and 5 mol% of yttrium oxide to zirconia powder. After obtaining the printable slurry with maximum solid loading, the green bodies are prepared using the in-house built high-speed multi-ceramic tape casting technology. They are later sintered with two-stage sintering method. After the successful fabrication, the mechanical properties and translucency of the specimens were evaluated with Vickers hardness, three-point bending and translucency parameter tests. Finally, an FGM tooth crown with five photocurable slurries is proposed to demonstrate the translucent gradient effect of sintered part. The solid loading of 80% zirconia and 20% resin delivered samples without any surface cracks. The shrinkage ratio analysis showed that the sintered sample dimension was reduced by 20%, 20%, and 23% along X, Y, and Z directions. The samples fabricated with 3% yttrium oxide to zirconia delivered excellent hardness (1687 HV) and flexural strength (650.6 MPa). However, the relative luminescence increased with increasing the yttrium oxide for 3-5 mol%. With the optimized process parameters, the proposed dental crown is fabricated and analyzed for their shrinkage ratio, mechanical, and translucency properties. The study proposes the potential of fabricating customized dental crown with gradient translucent appearance.

Dental zirconia microwave-sintering followed by rapid cooling protocol

OBJECTIVES

This study aimed to evaluate the effect of microwave sintering temperature and cooling rate (MS) on 3Y-TZP ceramics and its influence on the ceramic microstructure and mechanical properties. Specifically, to optimize the sintering process, reducing the total sintering time compared to conventional sintering.

MATERIALS AND METHODS

Eighty-four pre-sintered Y-TZP discs (Vipi block Zirconn, VIPI) (ISO 6872) were divided into seven groups (n = 12) according to the sintering conditions: conventional sintering (CS) at 1530 °C for 120 min and microwave sintering at 1400 °C (MS1400) and 1450 °C (MS1450) for 15 min followed by different cooling conditions: rapid cooling (RC), cooling at 400 °C (C400) and 25 °C (C25). The specimens were submitted to apparent density measurements, X-ray diffraction analysis (XRD), scanning electron microscopy, and biaxial flexural strength test. Data was statistically analyzed through two-way ANOVA, Tukey, Sidak, Dunnett and Weibull (α = 0.05).

RESULTS

All MS1400 groups presented lower density values than the CS and MS1450 groups. Two-way ANOVA revealed that the MS temperature and cooling rate affected the biaxial flexural strength of the Y-TZP (p < 0.01). Group MS1400RC presented lower biaxial flexural strength values (681.9 MPa) than MS1450RC (824.7 MPa). The cooling rate did not statistically decrease the biaxial strength among the groups submitted to microwave sintering at 1450 °C. XRD analysis showed that the sintering and cooling temperature did not induce tetragonal to monoclinic phase transformation.

CONCLUSIONS

Microwave sintering at 1450 °C for 15 min followed by rapid cooling can be a viable fast alternative protocol for Y-TZP sintering, compared with the conventional sintering, reducing the total sintering time by 75% and reducing the energy used for the sintering process without affecting the Y-TZP biaxial flexural strength and relative density compared to the conventional sintering. Moreover, the microwave technique promoted smaller grains and did not induce monoclinic phase formation.

Use of Biomaterials in 3D Printing as a Solution to Microbial Infections in Arthroplasty and Osseous Reconstruction

The incidence of microbial infections in orthopedic prosthetic surgeries is a perennial problem that increases morbidity and mortality, representing one of the major complications of such medical interventions. The emergence of novel technologies, especially 3D printing, represents a promising avenue of development for reducing the risk of such eventualities. There are already a host of biomaterials, suitable for 3D printing, that are being tested for antimicrobial properties when they are coated with bioactive compounds, such as antibiotics, or combined with hydrogels with antimicrobial and antioxidant properties, such as chitosan and metal nanoparticles, among others. The materials discussed in the context of this paper comprise beta-tricalcium phosphate (β-TCP), biphasic calcium phosphate (BCP), hydroxyapatite, lithium disilicate glass, polyetheretherketone (PEEK), poly(propylene fumarate) (PPF), poly(trimethylene carbonate) (PTMC), and zirconia. While the recent research results are promising, further development is required to address the increasing antibiotic resistance exhibited by several common pathogens, the potential for fungal infections, and the potential toxicity of some metal nanoparticles. Other solutions, like the incorporation of phytochemicals, should also be explored. Incorporating artificial intelligence (AI) in the development of certain orthopedic implants and the potential use of AI against bacterial infections might represent viable solutions to these problems. Finally, there are some legal considerations associated with the use of biomaterials and the widespread use of 3D printing, which must be taken into account.

Repair protocols for indirect monolithic restorations: a literature review

Despite the advancements in indirect monolithic restorations, technical complications may occur during function. To overcome this issues, intraoral repair using resin composite is a practical and low-cost procedure, being able to increase the restoration's longevity. This review aimed to evaluate the need for repair and suggest a standardized repair protocol to the main indirect restorative materials. For this, studies were surveyed from PubMed with no language or date restriction, to investigate the scientific evidence of indirect monolithic restoration repair with direct resin composite. A classification to guide clinical decisions was made based on the FDI World Dental Federation criteria about defective indirect restorations considering esthetic and functional standards, along with the patient's view, to decide when polishing, repairing or replacing a defective restoration. Based on 38 surveyed studies, different resin composite intraoral repair protocols, that included mechanical and chemical aspects, were defined depending on the substrate considering resin-based, glass-ceramic or zirconia restorations. The presented criteria and protocols were developed to guide the clinician's decision-making process regarding defective indirect monolithic restorations, prolonging longevity and increasing clinical success.

Fracture Resistance of Posterior Tooth-Supported Cantilever Fixed Dental Prostheses of Different Zirconia Generations and Framework Thicknesses: An In Vitro Study

The rehabilitation of free-end situations is a frequent indication in prosthetic dentistry. Cantilever fixed dental prostheses (cFDPs) made of 1st and 2nd generation zirconia are one treatment option. Due to a unique gradient technology, combinations of different zirconium dioxide generations are thus feasible in one restoration. However, data about these materials are rare. The purpose of this study was therefore to investigate the fracture resistance and fracture modes of tooth-supported cFDPs fabricated from different zirconia materials (gradient technology) and different framework thicknesses. A total of 40 cFDPs were fabricated using the CAD/CAM approach and belonged to five test groups. The different groups differed in the yttria content, the proportion of the tetragonal/cubic phases, or in wall thickness (0.7 mm or 1 mm). After completion, the cFDPs were subjected to thermal cycling and chewing simulation (1.2 × 106 load cycles, 108 N load). Afterwards, cFDPs were statically loaded until fracture in a universal testing machine. A non-parametric ANOVA was compiled to determine the possible effects of group membership on fracture resistance. In addition, post-hoc Tukey tests were used for bivariate comparisons. The mean fracture loads under axial load application ranged from 288 to 577 N. ANOVA detected a significant impact of the used material on the fracture resistances (p < 0.001). Therefore, the use of cFDPs fabricated by gradient technology zirconia may not be unreservedly recommended for clinical use, whereas cFPDs made from 3Y-TZP exhibit fracture resistance above possible masticatory loads in the posterior region.

Criteria for choosing prosthetic biomaterials according to their physicochemical properties for anterior and posterior sectors. a comprehensive review

Objective

To describe the existing knowledge about metal-free prosthetic biomaterials according to their physicochemical properties and based on this, define criteria for their placement in both the anterior and posterior sectors.

Materials and methods

A digital search was carried out in the databases: PubMed/Medline, Scopus, Web of Science and Google Scholar of the literature published in the English language without time restrictions and included original articles such as case reports, retrospective and prospective studies, narrative, comprehensive, systematic reviews and meta-analysis. Meanwhile, short communications, editorials and articles in a language other than English were excluded.

Results

40 articles were evaluated, published between 2000 and 2023. The main characteristics and physicochemical properties of ceramic biomaterials such as zirconia, feldspathic based ceramics, lithium disilicate and alumina, among others, were analyzed and summarized. In addition, certain criteria were defined based on the available scientific evidence on the use of different ceramic systems both in the anterior sector and in the posterior sector for patients who need some type of prosthetic restoration.

Conclusions

Among the different metal-free materials used for the construction of fixed dental prostheses, zirconia has been shown to have better aesthetic, biomechanical and biocompatibility properties, which makes it a candidate material for the rehabilitation of partially edentulous patients.

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.

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.

Translucent Zirconia in Fixed Prosthodontics-An Integrative Overview

Over the past two decades, dental ceramics have experienced rapid advances in science and technology, becoming the fastest-growing field of dental materials. This review emphasizes the significant impact of translucent zirconia in fixed prosthodontics, merging aesthetics with strength, and highlights its versatility from single crowns to complex bridgework facilitated by digital manufacturing advancements. The unique light-conducting properties of translucent zirconia offer a natural dental appearance, though with considerations regarding strength trade-offs compared to its traditional, opaque counterpart. The analysis extends to the mechanical attributes of the material, noting its commendable fracture resistance and durability, even under simulated physiological conditions. Various zirconia types (3Y-TZP, 4Y-TZP, 5Y-TZP) display a range of strengths influenced by factors like yttria content and manufacturing processes. The study also explores adhesive strategies, underlining the importance of surface treatments and modern adhesives in achieving long-lasting bonds. In the realm of implant-supported restorations, translucent zirconia stands out for its precision, reliability, and aesthetic adaptability, proving suitable for comprehensive dental restorations. Despite its established benefits, the review calls for ongoing research to further refine the material's properties and adhesive protocols and to solidify its applicability through long-term clinical evaluations, ensuring its sustainable future in dental restorative applications.