Advances in Ceramics for Dental Applications

Overview of Current Dental Ceramics

A wide range of ceramics is available for clinicians to select for each clinical scenario. Each type of ceramic has its own advantages, disadvantages, and clinical considerations. This article summarizes the different types of ceramics available for the fabrication of ceramic restorations and recent advances in these materials in terms of composition and fabrication methods. Recent systematic reviews and clinical evidence are also discussed.

Additive-manufactured ceramics for dental restorations: a systematic review on mechanical perspective

Background

Additive manufacturing (AM) is rapidly expanding as a substitute for conventional heat-pressing and milling techniques for ceramic restorations. However, experimental and clinical evidence on the mechanical properties and performance of the final ceramic products is yet insufficient. This systematic review aimed to update the latest advances in additive manufacturing of restorative ceramics with a focus on their mechanical properties.

Methods

This systematic review was structured using the 5-step methodology based on the research question: what are the mechanical properties of additive-manufactured restorative ceramics in comparison with subtractive manufacturing? The electronic literature search was performed independently by 2 authors in the following databases: PubMed/MEDLINE, Web of Science, and Scopus. Published articles from 2019 to 2023 were screened, analysed and the relevant papers were selected for inclusion in this review.

Results

A total of 40 studies were included. The available ceramics include zirconia, alumina and alumina-zirconia composites, lithium disilicate, porcelain and fluorapatite glass ceramic. The mechanical properties were summarized according to material and technique: density (15 studies), flexural strength (31 studies), fracture toughness (7 studies), Young's modulus (7 studies), hardness (11 studies) and performance (7 studies). Overall, the properties exhibited an upward trend toward the values of conventional techniques. Typical processing defects, including porosity, agglomerates, cracks, surface roughness, and other defects, were also analyzed.

Conclusions

With significant technological advancements, the mechanical properties of AM ceramics have come close to ceramics by conventional manufacturing, whereas their reliability, the influence of printing layer orientations, and long-term performance still need further investigation.

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.

Occlusion and Its Role in the Long-Term Success of Dental Restorations: A Literature Review

Occlusion plays a fundamental role in the long-term success of dental restorations by influencing both their functional stability and durability. This review explores the occlusal considerations for various restorative modalities, including fixed and removable prostheses, implant-supported restorations, and adhesive restorations. Special attention is given to the biomechanical principles involved, such as force distribution, stress management, and the role of occlusion in temporomandibular joint health. Diagnostic tools, including traditional and digital techniques such as T-Scan and OccluSense, are discussed to highlight their relevance in detecting occlusal disharmony. Additionally, the review examines the effects of parafunctional habits on restoration longevity and the influence of occlusal trauma on prosthetic outcomes. Despite advances in materials and technology, achieving functional occlusion remains essential in minimizing complications and ensuring patient comfort. This review underscores the need for proper occlusal analysis during treatment planning to enhance clinical outcomes and extend the lifespan of dental restorations.

In Vitro Aging and Fracture Tests on Differently Veneered Partially Stabilized Zirconia Anterior Crowns

Objectives: To evaluate the fracture resistance of veneered incisor crowns made from highly translucent zirconia frameworks. Materials and Methods: Ninety-six all-ceramic single crowns were based on either a coping with minimum wall thickness or a cutback framework fabricated from highly translucent zirconia (5Y-PSZ). Each one-third of the specimens was finalized with different veneering ceramics using standardizations and glaze firing. Crowns were luted to cobalt-chromium dies with MDP-containing composite cement. Half of the entire sample underwent artificial aging (chewing simulation and thermocycling) before fracture load tests were conducted using a 6 mm steel sphere applied in a 90° angle to the oral aspect of the crowns with 1.3 mm distance to the incisal edge. Besides descriptive presentation of recorded forces at first damage (F1d) and fracture (Fu), Kruskal Wallis and Mann-Whitney U tests were used to analyze data at α = 0.05. Results: Directly after manufacturing, incisor crowns of all test groups showed sufficient mean fracture resistances. After artificial aging, crack formation was observed in a high percentage for fully veneered crowns of all test groups, but only for one veneering ceramics with cutback crowns. Mean test forces of unaged crowns were F1d,mean ≥ 422 N | Fu,mean ≥ 749 N (fully veneered) and F1d,mean ≥ 644 N | Fu,mean ≥ 706 N (cutback) dropped significantly to F1d,mean ≥ 131 N | Fu,mean ≥ 223 N (fully veneered) and F1d,mean ≥ 324 N | Fu,mean ≥ 524 N (cutback) . Conclusions: Within the limitations of this laboratory study, 5Y-PSZ based anterior crowns can be a viable treatment option. Framework design, choice of the veneering ceramics and artificial aging show relevant effects on the fracture resistances. Concerted veneering ceramics should be used and partially veneering of the zirconia frameworks should be favored over full veneers.

Enhancing the Opacity of Glass Ceramics by Applying Opaque Stains to the Intaglio Surface

OBJECTIVE

The aim of this study was to assess the effect of opaque stain application to the intaglio surface of lithium disilicate glass ceramics on the masking ability of discolored substrates and bond strength to a resin-based luting agent (depending on etching time); the stain film-thickness was also assessed.

MATERIALS AND METHODS

Ceramic specimens were produced with CAD-CAM blocks of lithium disilicate (IPS e.max CAD). Two opaque stains were tested at ceramic intaglio surface: opaque glassy stain for titanium frameworks (OP-ti) and low-fusion glassy stain for ceramic characterization (LFG-iv). Non-stained ceramic specimens served as controls. For optical and colorimetric analyses, A2-shaded ceramics of medium and low-translucencies were tested, in thicknesses of 1.0- and 1.5-mm (n = 10), with two coupling agents (non-shaded-glycerin and A2-shaded try-in paste). CIEDE2000 formula was used for calculation of translucency parameter (TP00) and color differences (ΔE00). Whiteness index for dentistry (WID) was also reported. ΔE00 were assessed over discolored substrates (tooth-shaded A2-reference, A4, C3, and C4; coppery metal, silvery metal, white zirconia, and PEEK). Microshear bond strength of stained and non-stained ceramic specimens to a resin-based luting agent was evaluated. Film-thickness of stains was assessed by scanning electron microscopy.

RESULTS

The application of opaque stains to the intaglio surface of lithium disilicate ceramics resulted in significant reduction of TP00 (p < 0.001) and WID (p < 0.001) and differences in L*, C*, and ho color coordinates (especially with OP-ti) (p < 0.001). ΔE00 was significantly reduced in stained ceramic groups in comparison with the control, for all discolored substrates (p < 0.001). Acceptable color matching was obtained with stained ceramic specimens for all discolored substrates, depending on the type of stain, ceramic thickness, ceramic translucency, and coupling agent. The application of stains to the ceramic intaglio surface was not detrimental to bond strength to a resin-based luting agent, but depended on the time of hydrofluoric acid-etching (20 s for OP-ti and 60 s for LFG-iv) (p < 0.001). Film-thickness of stains presented mean values <70 μm.

CONCLUSION

The application of opaque stains to the intaglio surface of lithium disilicate glass ceramics was effective to mask severely discolored substrates, presenting adequate bond strength to the luting agent and thin film-thicknesses.

CLINICAL SIGNIFICANCE

For indirect restorations over severely discolored substrates, the application of opaque stain to the intaglio surface of lithium disilicate glass ceramic ensures acceptable color matching, with adequate bond strength to resin-based luting agents and clinically acceptable stain film-thickness.

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.

Fracture behavior of short fiber-reinforced CAD/CAM inlay restorations after cyclic fatigue aging

The aim of this study was to assess the fracture behavior of molar teeth restored with MOD inlays made of experimental short fiber-reinforced CAD/CAM composite block (SFRC CAD) before and after cyclic fatigue aging. Standardized MOD cavities were prepared on 60 intact mandibular molars. Three groups of CAD/CAM made inlay restorations (Cerasmart 270, Enamic, and SFRC CAD) were fabricated (n = 20/group). All restorations were luted with self-adhesive dual-cure resin cement (G-Cem One). Half of restored teeth per each group (n = 10) were quasi-statically loaded until fracture without aging. The other half underwent cyclic fatigue aging for 500,000 cycles (Fmax = 150 N) before being loaded quasi-statically until fracture. Then, the fracture type was visually inspected. The microstructure and elemental content of CAD/CAM materials were assessed using SEM and EDS. Two-way analysis of variance (ANOVA) was used to statistically examine the data, and it was followed by the Tukey HSD test (α = 0.05). ANOVA demonstrated that both material type and aging had a significant effect (p < 0.05) on the load-bearing capacity values of the restorations. Teeth restored with SFRC CAD showed significantly the highest (p < 0.05) load-bearing capacity (2535 ± 830 N) after fatigue aging among all groups. SEM images showed the ability of short fibers in SFRC CAD composite to redirect and hinder crack propagation. With regard to fracture mode, Enamic group revealed 85% of catastrophic failure (vs. 45% and 10% for Cerasmart 270 and SFRC CAD, respectively). Large MOD cavities on molar teeth were most favorably restored with SFRC CAD inlays, yielding the highest load-bearing capacity and more restorable failures.

Resin composite layering on discolored substrates ensures masking ability for monolithic ceramics

OBJECTIVE

the aim of this study was to evaluate the effect of resin composite layering on discolored substrates to obtain masking ability with monolithic ceramics.

MATERIALS AND METHODS

Four groups (n = 8) of computer-aided design/computer aided manufacturing (CAD/CAM) monolithic ceramics, shade A1, with thicknesses of 1.0 and 1.5 mm, were tested: feldspathic (FC), leucite-reinforced (LC), lithium disilicate-reinforced (LD), and translucent zirconia (5YSZ). Five substrates were used: A1 (used as reference), A3.5, C4, and coppery and silvery metals. The substrates were separated as non-layered or layered (with flowable opaque resin composite (FL), white opaque restorative resin composite (WD), and A1-shaded opaque restorative resin composite (A1D)). Resin composite layers of 0.5 and 1.0 mm were tested. The try-in paste, shade A1, was used as a luting agent. Translucency parameter (TP00 ) was assessed for the ceramics. Color differences (∆E00 ) were assessed for the restorative ceramics and resin composite layers over discolored substrates with the CIEDE2000 formula. The results were compared statistically, and descriptively with acceptability (AT, 1.77) and perceptibility (PT, 0.81) thresholds.

RESULTS

Feldspathic showed the highest TP00 (for both ceramic thicknesses) and LD the lowest (for 1.5 mm of ceramic thickness) (P < 0.001). For substrate A3.5, layering with 1.0 mm of A1D or WD ensured ∆E00 below PT for all ceramics tested (P < 0.001). The use of 0.5 mm of FL or 1.0 mm of A1D associated with ceramics LC, LD, and 5YSZ ensured ∆E00 below AT for substrates C4 and coppery metal (P < 0.001). Silvery background layered with 0.5 mm of FL presented ∆E00 below AT for all ceramics and ∆E00 below PT for lithium disilicate of 1.0 mm of thickness (∆E00  = 0.72).

CONCLUSIONS

Layering severely discolored substrates with selected opaque resin composites ensures masking ability for restoration with CAD/CAM monolithic ceramics.

CLINICAL SIGNIFICANCE

Severely discolored substrates are predictably restored with monolithic CAD/CAM ceramics by performing a previous layering of the substrate with opaque resin composite.

Fatigue performance analysis of strength-graded zirconia polycrystals for monolithic three-unit implant-supported prostheses

The aim of this study was to evaluate the fatigue behavior of strength-graded zirconia polycrystals used as monolithic three-unit implant-supported prosthesis; complementarily, crystalline phase and micromorphology were also assessed. Fixed prostheses with 3 elements supported by 2 implants were confectioned, as follows: Group 3Y/5Y - monolithic structures of a graded 3Y-TZP/5Y-TZP zirconia (IPS e.max® ZirCAD PRIME); Group 4Y/5Y - monolithic structures of a graded 4Y-TZP/5Y-TZP zirconia (IPS e.max® ZirCAD MT Multi); Group Bilayer - framework of a 3Y-TZP zirconia (Zenostar T) veneered with porcelain (IPS e.max Ceram). The samples were tested for fatigue performance with step-stress analysis. The fatigue failure load (FFL), the number of cycles required until failure (CFF), and the survival rates in each cycle were recorded. The Weibull module was calculated and the fractography analyzed. The crystalline structural content via Micro-Raman spectroscopy and the crystalline grain size via Scanning Electron microscopy were also assessed for graded structures. Group 3Y/5Y showed the highest FFL, CFF, probability of survival, and reliability (based on Weibull modulus). Group 4Y/5Y showed significantly superior FFL and probability of survival than group bilayer. Fractographic analysis revealed catastrophic flaws in the monolithic structure and cohesive fracture of porcelain in bilayer prostheses, all originating from the occlusal contact point. The graded zirconia presented small grain size (≤0.61 μm), with the smallest values at the cervical region. The main composition of graded zirconia was of grains at tetragonal phase. The strength-graded monolithic zirconia, especially the 3Y-TZP/5Y-TZP, showed to be promising for use as monolithic three-unit implant-supported prosthesis.

Ceramic Materials for Biomedical Applications: An Overview on Properties and Fabrication Processes

A growing interest in creating advanced biomaterials with specific physical and chemical properties is currently being observed. These high-standard materials must be capable to integrate into biological environments such as the oral cavity or other anatomical regions in the human body. Given these requirements, ceramic biomaterials offer a feasible solution in terms of mechanical strength, biological functionality, and biocompatibility. In this review, the fundamental physical, chemical, and mechanical properties of the main ceramic biomaterials and ceramic nanocomposites are drawn, along with some primary related applications in biomedical fields, such as orthopedics, dentistry, and regenerative medicine. Furthermore, an in-depth focus on bone-tissue engineering and biomimetic ceramic scaffold design and fabrication is presented.