The aim of this study was to perform a narrative review to identify the modifications applied to the chemical structure of third- and fourth-generation zirconia ceramics and to determine the influence of these changes on the mechanical and optical properties. A bibliographical search using relevant keywords was conducted in the PubMed^® and EBSCO databases. The abstracts and full texts of the resulting articles were reviewed for final inclusion. Fifty-four articles were included in this review. The analyzed topics were: (1) the composition of first- and second-generation zirconia materials (Y-TZP), (2) the behavior of the studied generations in relation to mechanical and optical properties, and (3) the modifications that were carried out on third-generation (5Y-TZP) and fourth-generation (4Y-TZP) zirconia materials. However, studies focusing on these specific characteristics in third- and fourth-generation zirconia materials are scarce. The review shows that there is a lack of sufficient knowledge about the chemical modifications of zirconia in the new generations.

Bioactive materials have emerged as a promising alternative to conventional restorative materials as part of more conservative dentistry. The aim of this study was to evaluate and compare the shear bond strength (SBS) and microleakage of a new bioactive restorative material, two bulk-fill restorative composites, and a conventional composite at 24 h, 4 weeks, and 8 weeks. Three hundred and sixty molars and premolars were divided into four groups: ACTIVA™ BioACTIVE Restorative™, Filtek™ Bulk-Fill Restorative Composite, Tetric^® N-Ceram Bulk-Fill Composite, and G-aenial^® Composite. The normality of the data was determined with the Kolmogorov-Smirnov test, then the two-way ANOVA and Fisher’s test were used for analyzing SBS data, and the Kruskal-Wallis and DSCF tests were conducted to analyze the microleakage. In the SBS test, there were no statistically significant differences between materials (p = 0.587), and the relation between material and time (p = 0.467), time points showed statistically significant differences (p = 0.016). As for the microleakage, statistically significant differences were found for all three time periods (p < 0.05), showing the conventional composite to have the lowest microleakage, followed by the bioactive material, and lastly the two bulk-fill composites. In conclusion, the new bioactive material has similar evaluated properties to bulk-fill composites (bond strength) and conventional composites (bond strength and microleakage) and can be used as an alternative restorative material.

Biodentine^® is a bioactive dentin coating widely used for dental restoration; however, its adhesion to the substrate could limit its clinical success. The aim of this study was to evaluate the shear bond strength (SBS) between Biodentine^® and a composite resin, using different types of adhesive. In total, 120 acrylic blocks with a central hole were prepared. They were fully filled with Biodentine^®, and divided into two time groups: 12 min (n = 60) and 24 h (n = 60); each group was subdivided into four groups according to the adhesive: three-step etch and rinse (3-E&R) (n = 15), two-step etch and rinse (n = 15), and a universal adhesive subdivided into two groups, two-step etch and rinse (n = 15) and one-step self-etch adhesive system (n = 15). After adhesive application, the composite was applied and stored at 100% humidity, at 37 °C, for 24 h, before the SBS test. Data were analyzed with one-way ANOVA, Fisher post hoc test, and Kolmogorov–Smirnov test. The 12-min group showed statistically significant differences (p = 0.009), with the highest values of adhesion for 3-E&R. No statistically significant differences were observed for the 24-h group (p = 0.813) and between adhesive systems (p = 0.071) regardless of adhesion time. Higher adhesion values were found at 24 h. It is essential to consider the longest setting time for Biodentine^®. In terms of adhesive, 3-E&R had the highest adhesion values.

The color stability of interim computer-aided design and computer-assisted manufacturing (CAD/CAM) materials has not been exhaustively investigated. The aim of this study was to compare the translucency (TP) and contrast ratio (CR) of CAD/CAM blocks and conventional interim materials, as well as the effects of varnish application and tooth-brushing on color stability after immersion in different staining solutions. Four hundred and eighty specimens were fabricated with four different interim materials (n = 120) and were divided into three experimental, and one control group (n = 30). The color measurements were taken at the initial time (T0), 24 h (T1), 7 days (T2), and 30 days (T3) after immersion in different solutions. CIEDE2000 (ΔE₀₀) values were analyzed with ANOVA and Fischer’s LSD test with a 95% confidence interval. The relationship between TP and CR was analyzed with a Pearson correlation. All interim materials showed a significant difference (p < 0.05) in color change after 30 days. Results showed that polyethyl methacrylate resins (PEMA) had the highest stability over time. The TP and CR were statistically significant (p < 0.05). It was observed that brushing improved the color stability but the ΔE₀₀ were the highest when the varnish alone or varnish and brushing were used, except in the bis-acryl group, in which varnish and brushing decreased the color stainability.

Objectives: Printed dental materials have emerged to overcome the limitations associated with the subtractive CAD/CAM technologies. The aim of the present study was to evaluate the optimal adhesive strategy for Permanent Crown Resin, a printed hybrid material. Material and Methods: Eighteen specimens of Permanent Crown Resin were divided into three groups of six blocks each, measuring 30 × 30 × 10 mm. A specific surface pretreatment was performed, involving two groups undergoing hydrofluoric acid etching (60 s) and sandblasting (20 s), whereas the third group remained devoid of any pretreatment. Comprehensive surface characterization was achieved using a scanning electron microscope (SEM) at magnifications of 500× and 1000×. Each of the main groups was further divided into three subgroups, each containing two blocks. The paired blocks within each subgroup were then cemented to each other using different cementation protocols: a dual‐cure self‐adhesive resin cement RelyX ^TM Unicem 2, a dual‐cure adhesive ExciTE® F DSC, followed by dual‐cure resin cement Variolink® Esthetic DC, and a light‐cure universal adhesive Scotchbond ^TM Universal in combination with preheated composite Filtek ^TM Supreme XTE. Subsequently, the specimens were sectioned, and 20 sound micro‐bars were obtained from each specimen ( n = 180). Each micro‐bar was subjected to microtensile bond strength (μTBS) testing at a crosshead speed of 0.5 mm/min. Results: SEM analysis revealed a smooth surface in the control group, whereas the HF group showed numerous micropores. The sandblasting group showed the roughest surface. Statistical analysis was performed using two‐way ANOVA, and a p ‐value of ≤ 0.05 was considered statistically significant. Regarding the μTBS test, sandblasting pretreatment combined with RelyX ^TM Unicem 2 demonstrated higher bond strength than the other groups (60.23 MPa). The predominant mode of failure across all groups was adhesive. Conclusions: Within the limitations of this study, sandblasting in conjunction with RelyX ^TM Unicem 2 provided the highest bond strength for Permanent Crown Resin.