Dental Materials最新文献

Objectives: To evaluate the effect of different speed-sintering cooling rates on the phase composition, microstructure, optical and mechanical properties of monolithic zirconia.

Methods: Speed-sintered ZirCAD LT (Ivoclar) (LT_1200; 5 min at 1480 °C; oven-door opening and air-cooling: 1200 °C) and Katana STML (Kuraray Noritake) (STML_800; 30 min at 1560 °C; oven-door opening and air-cooling: 800 °C) were compared to speed-sintered ZirCAD LT and Katana STML with a steady cooling rate and oven-door opening at 300 °C (LT_300 and STML_300, respectively). Density was measured by Archimedes' principle; composition by XRF; phase by XRD; grain size by SEM; translucency parameter by spectrophotometry. Vickers hardness, indentation fracture toughness, and biaxial strength were also assessed.

Results: Regardless of the cooling rate, ZirCAD LT and Katana STML revealed similar density, chemical composition and grain size. Both 3Y-TZP ZirCAD LT_1200/300 zirconia had lower cubic ZrO₂-phase content, and lower Y₂O₃ content in the remaining tetragonal ZrO₂ phases compared to 5Y-PSZ Katana STML_800/300 zirconia. In contrast to 3Y-TZP, 5Y-PSZ contained a high amount of metastable t'-phase. TP of ZirCAD LT and Katana STML were not affected by the cooling rate. The hardness and fracture toughness of both 3Y-TZP and 5Y-PSZ were not influenced by cooling rate variations. Steady cooling significantly diminished flexural strength and mechanical reliability of Katana STML_300, while it did not have any effect on the ZirCAD LT zirconia grades.

Significance: Steady cooling during speed-sintering did not significantly influence the performance of 3Y-TZP but can negatively influence flexural strength and mechanical reliability of 5Y-PSZ zirconia ceramics.

Objectives: Photo-polymerizable resins can be used to print clear orthodontic aligners with several advantages compared to thermoformed ones. However, the safety of these new printed devices, their efficacy, and the impact of aging on safety and performance are still insufficiently known. This study aims to evaluate several 3D printing resins used in dentistry to produce clear gutters, regarding biocompatibility, leached compounds (release kinetics), surface state, and thermo-mechanical properties before and after simulated intra-oral aging. The impact of post-curing time on their behavior was also evaluated.

Methods: Three resins - NextDent Ortho Flex, Freeprint Ortho Detax, and Graphy TC-85DAC - were tested using a standardized approach that included the same printer and a standard post-polymerization process. Chemical modifications were analyzed by ATR-FTIR, surface morphology by SEM, thermal properties by TGA and DSC, and cytotoxicity by MTT tests. Mechanical properties were characterized through tensile tests, and substance release in a salivary simulant based on PBS was monitored by HPLC. Aging in simulated saliva was followed for 15 days, corresponding to the duration of use of one aligner.

Results: The results showed good biocompatibility for the printed materials, except for the insufficiently post-cured materials. In addition, significant differences in release kinetics and physical properties were observed as a function of the resin used and the post-polymerization time. Intra-oral aging impacts all the properties of the materials tested, particularly the thermo-mechanical (maximum force and T_g) and surface properties, and leads to a release of residual resin and degradation products into the simulant which increases cytotoxicity.

Significance: This study highlights the importance of strictly standardizing post-polymerization protocols to ensure the safety and performance of 3D-printed dental devices and underlines the risk of the cumulative effect of leached compounds for the patient's health, even if measured cell viability and photo-initiator exposure dose were within acceptable limits. Moreover, whatever the resin, aging leads to a decrease in thermo-mechanical properties that may affect the device's performance.

Objective: This randomized clinical trial investigated the 96-month clinical performance of a universal adhesive (Adhese Universal Vivapen, Ivoclar Vivadent) applied in etch-and-rinse (ER) and self-etch (SE) modes in Class II bulk-fill composite restorations.

Materials and methods: Thirty-five patients, each with at least two Class II carious lesions, were enrolled. Using a split-mouth design, cavities were randomly assigned to ER or SE adhesive application. All restorations were placed with a high-viscosity bulk-fill resin composite (Tetric EvoCeram Bulk Fill, Ivoclar Vivadent). In total, 84 restorations were evaluated at baseline and at 12, 24, 36, 48, 60, 72, 84 and 96 months by two calibrated, blinded examiners according to modified USPHS criteria. Statistical analyses were performed with Chi-square, Friedman, Cochran's Q, and McNemar tests (α=0.05).

Results: At 96 months, 74 restorations in 33 participants were examined. No loss of retention/fractures occurred. Seven restorations were replaced (six due to secondary caries-ER: 1, SE: 5 and one due to unacceptable marginal adaptation-SE), yielding crude cumulative replacement rates of 2.4 % (ER) and 14.3 % (SE). Kaplan-Meier analysis showed significantly higher survival for ER than SE (97.4 % vs 85.2 %, p = 0.049). Marginal discoloration was consistently higher with SE from 36 months onward (p < 0.05), whereas marginal adaptation showed no differences between groups at any recall. Other criteria were comparable, and no postoperative sensitivity was recorded.

Conclusions: Despite a statistically higher incidence of marginal discoloration in the SE approach, both strategies demonstrated comparable long-term outcomes, with no retention loss after 96 months. The ER showed a higher cumulative survival. These findings confirm the clinical acceptability of universal adhesives in Class II bulk-fill composite restorations over extended service periods.

Clinical significance: Universal adhesives demonstrated durable adhesion and predictable performance in posterior bulk-fill restorations with both strategies, while the ER approach provided additional benefits in marginal discoloration and lower cumulative replacement needs over the long term.

Objectives: Even though improvements in CAD/CAM technology have allowed the milling protocol to be modified according to specific treatment requirements, it remains unclear how different protocols affect the surface quality and mechanical properties of the final restoration. This study aims to evaluate the effect of the CAD/CAM milling protocol on the topography, flexural strength, and reliability of 3 mol% yttria partially stabilized zirconia (3Y-PSZ).

Methods: Disc-shaped specimens (∅12 mm×1.2 mm) were fabricated using three different CAD/CAM dry-milling protocols (n = 20): slow (S), normal (N), and fast (F). Control polished specimens were fabricated by cutting pre-sintered CAD/CAM blocks using a cutting machine and polishing with silicon carbide papers, in wet (P_wet) and dry (P_dry) conditions (n = 20). Surface topography was evaluated using an optical profilometer (n = 3). Specimens were subjected to a piston-on-three-balls flexural strength test using a universal testing machine. Fractographic analysis was performed using optical and scanning electron microscopes. The characteristic flexural strength (σ₀), Weibull modulus (m), and the 90 % confidence intervals (90 % CI) were estimated. XRD was used to identify the tetragonal, cubic, and monoclinic phases.

Results: Distinct topographies were observed for polished and CAD/CAM-milled specimens. Surface roughness parameters (Sa and Sz) followed a decreasing order: F > N > S > P (P_wet and P_dry) There was no difference for σ₀ and m values among the three CAD/CAM milling protocols. P_dry had similar σ₀ and m to CAD/CAM-milled groups, while P_wet resulted in lower values.

Significance: Distinct CAM-milling protocols produce apparent differences in the topography of 3Y-PSZ while preserving flexural strength and reliability.

Objective: To evaluate the long-term effect of ammonia- and water-based silver fluoride treatments on the degradation of the dentin collagen matrix.

Methods: Dentin beams (0.3x3x7mm) were demineralized (10 % H₃PO₄), rinsed and randomly distributed into six groups. Groups (n = 10 beams/group) were treated with (1) ammonia-based silver fluoride = SDF; (2) SDF + potassium iodide = KI (3) water-based silver fluoride = SF (4) SF + KI (5) KI (6) untreated demineralized dentin beams served as control. Following treatments, dry mass, modulus of elasticity and enzymatic activity were assessed. Dentin beams were incubated in calcium- and zinc-containing artificial saliva up to 6 months. After different incubation periods (1 week, 1 month, 3 months or 6 months), dry mass, modulus of elasticity and enzymatic activity were reevaluated. The aliquots of incubation media were analyzed to determine the solubilized telopeptides of collagen (ICTP and CTX immunoassays), hydroxyproline release and total extractable protein (Bradford assay). Scanning electron microscopy imaging and in situ zymography analyses were conducted. Data were statistically analyzed with ANOVA followed by Tukey test (α=0.05).

Results: Silver fluoride treatments reduced the total enzymatic activity, but increased the solubilized telopeptides of collagen throughout incubation periods (p < 0.05). The addition of KI exacerbated the loss of dry mass, modulus of elasticity, hydroxyproline release and total protein loss (p < 0.05).

Significance: Ammonia- and water-based silver fluoride treatments may reduce long-term degradation of dentin collagen. However, potassium iodide can further increase endogenous protease activity and compromise the structural integrity of dentin's organic matrix.

Objective: Monomer leaching from resin-based restorations is a concern due to possible adverse effects on the oral environment. This study evaluated a validated artificial saliva model and a multi-instrument analytical workflow to characterize two liquid resins for 3D-printing, compare findings with manufacturers' SDSs, and determine leachable profiles from test specimens incubated in artificial saliva.

Methods: Liquid resins (Saremco print CROWNTEC, SCT; FREEPRINT® temp, FPT) were analyzed by UHPLC-HRMS and GC-MS. Disc-shaped specimens were 3D-printed and, as control, milled from Temp Premium Flexible (TPF) (n = 6). Samples were immersed in artificial saliva (surface area-to-volume ratio 1.2 cm²/mL, 37 °C). Aliquots were analyzed for methacrylate monomers and photoinitiators after 1 h, 24 h, 1 week, and 3 months using quantitative LC-MS/MS. Specimens incubated for 24 h and 3 months were further examined by untargeted UHPLC-HRMS.

Results: SDSs identified BisEMA as the main methacrylate in both resins, confirmed by UHPLC-HRMS. FPT also contained nondisclosed UDMA. Targeted analysis showed significantly higher concentrations of leachables (P < 0.05) from FPT than SCT or TPF at all time points. Untargeted analysis supported this, revealing the greatest number of leachables in FPT incubations, with at least 67 putative compounds.

Significance: Most residual methacrylate monomers elute within 24 h after 3D-printing. However, untargeted results suggest different leaching dynamics for other substances, highlighting the importance of broader analytical approaches in assessing biocompatibility.

Objectives: This study aimed to evaluate the biomechanical effects of deep margin elevation (DME) and restorative material selection for overlays in maxillary molars with mesio-occluso-distal (MOD) subgingival defects via in vitro deformation analysis, fracture resistance tests, and 3D finite element analysis (FEA).

Methods: Three MOD overlay models (Model 1, Model 2, and Model 3) were created for maxillary molars by positioning the mesial and distal margins 1 mm above, at, and 1 mm below the cementoenamel junction (CEJ), respectively. Model 3 underwent DME modification, generating Models 4 (1 mm supragingival) and 5 (CEJ). The five models were restored with two materials (E: IPS e.max CAD; L: Lava Ultimate), yielding 10 test groups (E1-E5/L1-L5). The CEJ deformation, load resistance, and restoration failure modes were evaluated using deformation analysis and fracture resistance tests. 3D FE modeling was used to quantify the von Mises stress (VMS) distributions in the restorations, bonding, and DME layers, which were validated by cross-method correlation with experimental data.

Results: Deformation analysis revealed consistent mesial microstrains greater than distal microstrains, with E-groups having lower values than L-groups. Fracture resistance tests revealed that Model 3 (subgingival margin) was the weakest, with higher catastrophic failure rates than the supragingival designs. Compared with the non-DME group, the L4 (2-mm DME) group presented the best biomechanical performance with a greater load capacity. FE analysis demonstrated that E1 and L1 achieved optimal stress dispersion and that E3/L3 developed critical stress increases. The post-DME groups (E4/E5/L4/L5) exhibited homogeneous VMS distributions compared with the E3/L3 stress increases. DME layers concentrated VMS mesially, and FEA-in vitro correlation showed strong method concordance across all parameters.

Significance: As the subgingival defect depth increases, restorations progressively degrade. For sub-CEJ defects, the use of the 2-mm DME method to increase margins to 1 mm supragingival along with Lava Ultimate resulted in optimized stress distributions and improved biomechanical performance, resulting in greater longevity than non-DME methods. Thus, this protocol is recommended.

Objective: Although the accuracy of scanning technologies has been extensively explored, a research gap still exists concerning the scanning results of dental impression materials, particularly regarding their color and gloss characteristics. This study aims to evaluate and compare the scanning capabilities of blue-light scanners for various dental impression materials characterized by different colors and gloss levels.

Methods: Blue (B), green (G), red (R), and yellow (Y) dental impression materials were selected for this study. Colorimetric analyses were conducted using a spectrophotometer. The gloss levels of the samples were quantified using a gloss meter. The accuracy and surface detail reproduction of a blue-light scanner were analyzed by scanning impression materials in four different colors. The four-unit crown-bridge model for accuracy analysis was based on International Standardization Organization (ISO) standard 12836. The data measured by the coordinate measuring machine (CMM) served as the gold standard and were used for parameter comparison (height, angle, and distance) and 3D fitting with the scanned files.

Results: Surface detail reproduction analyses revealed significant differences among the various groups. Notably, Group B consistently demonstrated superior scanning accuracy across all measurements, indicating its effectiveness as a dental impression material in blue-light scanning applications. Significant differences were observed in the rate of surface detail, angle parameters, and corner height across the various groups (p < 0.05). Additionally, the root-mean-square error values pertaining to trueness exhibited significant disparities in all the specimens (p < 0.05).

Significance: The absence of significant gloss differences across all color variations indicates that color should be evaluated alongside other critical factors when employing blue-light scanners for measurement accuracy.