Effect of artificial aging on fracture toughness and hardness of 3D-printed and milled 3Y-TZP zirconia.

PURPOSE: This study aimed to evaluate the impact of artificial aging on the fracture toughness and hardness of three-dimensional (3D)-printed and computer-aided design and computer-aided manufacturing (CAD-CAM) milled 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP). MATERIALS AND METHODS: Forty bar-shaped specimens (45 × 4 × 3 mm) were prepared using two manufacturing technologies: 3D printing (LithaCon 3Y 210, Lithoz GmbH, Vienna, Austria; n = 20) and milling (Initial Zirconia ST, GC, Japan; n = 20) of 3Y-TZP. The chevron-notch beam method was used to assess the fracture toughness according to ISO 24370. Specimens from each 3Y-TZP group were divided into two subgroups (n = 10) based on the artificial aging process (autoclaving): nonaged and aged. Nonaged specimens were stored at room temperature, while aged specimens underwent autoclave aging at 134°C under 2 bar-pressure for 5 h. Subsequently, the specimens were immersed in absolute 99% ethanol using an ultrasonic cleaner for 5 min. Each specimen was preloaded by subjecting it to a 4-point loading test, with a force of up to 200 N applied for three cycles. Further 4-point loading was conducted at a rate of 0.5 mm/min under controlled temperature and humidity conditions until fracture occurred. The maximum force (Fmax) was recorded and the chevron notch was examined at 30 × magnification under an optical microscope for measurements before the fracture toughness (KIc) was calculated. Microhardness testing was also performed to measure the Vickers hardness number (VHN). A scanning electron microscope (SEM) coupled with an energy dispersive X-ray unit (EDX) was used to examine surface topography and chemical composition. X-ray diffraction (XRD) was conducted to identify crystalline structure. Data were statistically analyzed using two-way ANOVA and Student's t-test with a significance level of 0.05. RESULTS: The nonaged 3D-printed 3Y-TZP group exhibited a significantly higher fracture toughness value (6.07 MPa m1/2) than the milled 3Y-TZP groups (p < 0.001). After autoclave aging, the 3D-printed 3Y-TZP group maintained significantly higher fracture toughness (p < 0.001) compared to the milled 3Y-TZP group. However, no significant differences in hardness values (p = 0.096) were observed between the aged and nonaged groups within each manufacturing process (3D-printed and milled) independently. CONCLUSION: The findings revealed that the new 3D-printed 3Y-TZP produced by the lithography-based ceramic manufacturing (LCM) technology exhibited superior fracture toughness after autoclave aging compared to the milled 3Y-TZP. While no significant differences in hardness were observed between the aged groups, the 3D-printed material demonstrated greater resistance to fracture, indicating enhanced mechanical stability.

Effects of two dentifrices on the surface properties and staining susceptibility of polymer-based materials.

PURPOSE: This study examined the effect of whitening and abrasive regular dentifrices on the surface characteristics and stain susceptibility of polymer-based CAD-CAM blocks subjected to artificial toothbrushing abrasion (TB). MATERIALS AND METHODS: Two resin composite blocks [CeraSmart (CS) and Grandio Blocs (GB)], one polymer-infiltrated ceramic [Vita Enamic (VE)], and one direct resin composite [GrandioSO (RC)] were used to produce 60 specimens. The baseline mass, gloss, roughness, Vickers hardness (Hv), and color were measured after 7 days of water storage. The specimens were then separated into three TB treatment groups (n = 5): water control (C), regular daily dentifrice (R), and whitening dentifrice (W). Measurements were repeated post-TB (20,000 cycles). All specimens were immersed in coffee, and the CIE ΔE00 was measured after 1, 7, and 14 days. Two-way, one-way ANOVA, and Tukey's post hoc tests were performed to determine any significant differences between the materials and TB groups. To determine the stain resistance, repeated measures of ANOVA, one-way ANOVA, and Tukey's post hoc tests were used (α = 0.05). RESULTS: The R and W mass changes were minimal (-3.77 to 3.16 g%). W reduced the gloss of all the materials by 12.6%-65%. All materials in W were slightly rougher (Ra, 0.107-0.144 µm) than those in R (Ra, 0.049-0.072 µm). The ΔE00 ranged from 0.6 to 1.6 in W and 0.4 to 1.4 in R. VE was the hardest material at baseline (Hv = 362), whereas brushing and staining lowered Hv in all TB groups (282.8-300.6). After brushing in W, VE, and RC were more susceptible to coffee stains than were CS and GB. CONCLUSIONS: The whitening dentifrice roughened CAD-CAM specimens, reducing gloss, yet lightened some materials. Polymer-infiltrated ceramic and direct resin composite specimens brushed with abrasive regular or whitening dentifrice resulted in more intense staining than the CAD-CAM resin composites.

Effect of CAD/CAM aesthetic material thickness and translucency on the polymerisation of light- and dual-cured resin cements.

OBJECTIVES: This study investigated potential variations in polymerisation of light- and dual-cured (LC and DC) resin cements photoactivated through four CAD/CAM restorative materials as a function of substrate thickness. METHODS: Four CAD/CAM materials [two resin composites CeraSmart (CS) and Grandio Blocs (GB); a polymer infiltrated ceramic Vita Enamic (VE) and a feldspathic ceramic Vita Mark II (VM)], with five thicknesses (0.5, 1, 1.5, 2, and 2.5 mm) were prepared and their optical characteristics measured. 1 mm discs of LC and DC resin cement (Variolink® Esthetic, Ivoclar AG) were photoactivated through each specimen thickness. After 1 h post-cure, polymerisation efficiency was determined by degree of conversion (DC%) and Martens hardness (HM). Interactions between materials, thicknesses and properties were analysed by linear regressions, two-way ANOVA and one-way ANOVA followed by post hoc multiple comparisons (α = 0.05). RESULTS: All substrates of 0.5- and 1.0-mm thickness transmitted sufficiently high peak irradiances at around 455 nm: (It = 588-819 mW/cm2) with translucency parameter TP = 21.14 - 10.7; ranked: CS> GB = VM> VE. However, increasing the substrate thickness (1.5-2.5 mm) reduced energy delivery to the luting cements (4 - 2.8 J/cm2). Consequently, as their thicknesses increased beyond 1.5 mm, HM of the cement discs differed significantly between the substrates. But there were only slight reduction of DC% in LC cements and DC cement discs were not affected. SIGNIFICANCE: Photoactivating light-cured Ivocerin™ containing cement through feldspathic ceramics and polymer-infiltrated ceramics achieved greater early hardness results than dual-cured type, irrespective of substrate thickness (0.5 - 2.5 mm). However, only 0.5 and 1 mm-thick resin composites showed similar outcome (LC>DC). Therefore, for cases requiring early hardness development, appropriate cement selection for each substrate material is recommended.

Mechanical behaviour of prosthodontic CAD/CAM polymer composites aged in three food-simulating liquids.

OBJECTIVES: This study investigated the effect of ageing in three food-simulating liquids (FSLs) on mechanical properties of three prosthodontic CAD/CAM polymer composites intended for construction of implant-supported frameworks. METHODS: Materials investigated were: (i) a carbon fibre-reinforced composite (CarboCAD 3D dream frame; CC), (ii) a glass fibre-reinforced composite (TRINIA; TR), and (iii) a reinforced PEEK (DentoKeep; PK). Filler contents and microstructural arrangements were determined by thermo-gravimetry and tomography (µ-CT), respectively. Flexural properties (FS and Ef) were measured by 3-point bending (3PB) of 1 mm and 2 mm thick beam specimens. Fracture toughness (KIC) was measured by single-edge-notched-bending (SENB). All measurements were made at baseline (dry) and after 1-day and 7-day storage at 37 â„ƒ in either water, 70 % ethanol/water (70 % E/W) or methyl ethyl ketone (MEK). Failed specimens were examined microscopically. Statistical analyses included four-way ANOVA, two-way ANOVA and multiple Tukey comparison tests (α = 0.05). Multiple independent t-tests were performed regarding thickness effects on FS and Ef (α = 0.05). RESULTS: At baseline, the mechanical properties increased in the sequence: PK< TR< CC (p < 0.001). FS ranged from 192.9 to 501.5 MPa; Ef from 4.2 to 18.1 GPa; and KIC from 4.9-12.4 MPa.m0.5. Fibre-reinforced composites (CC and TR) were significantly stronger than PK. However, all properties of CC and TR reduced after 1 d storage in 70 % E/W and MEK with FS ranging from 58.6 to 408 MPa; Ef from 1 to 15.4 GPa; KIC from 6.87 to 10.17 MPa.m0.5. Greater reductions occurred after 7 d storage. MEK was more detrimental than 70 % E/W and water on fibre-reinforced composites. SIGNIFICANCE: Mechanical properties of each CAD/CAM composite were strongly dependent upon media and ageing. Although the mechanical properties of PK were initially inferior, it was relatively stable in all FSLs. All three materials exhibited sufficient mechanical properties at 1 mm thickness, but thicker specimens were more tolerant to ageing.

Is the radiopacity of CAD/CAM aesthetic materials sufficient?

OBJECTIVES: This study was designed to investigate CAD/CAM restorative blocks and other resin-based materials by (i) determining their chemical composition, (ii) comparing their radiopacity and (iii) correlating their radiopacity with specimen thickness. METHODS: Disk specimens, of 1and 2 mm thickness (n = 3), were prepared from five CAD/CAM and six resin-based composites (RBCs). The CAD/CAM resin-composites included aesthetic types: CeraSmart (CS), Grandio Blocs (GB), Lava Ultimate (LU), plus a polymer infiltrated ceramic Vita Enamic (VE), and a feldspathic ceramic Vita Mark II (VM II). The six RBCs were for different clinical applications: direct filling, flowable, bulk fill, base and two luting cements. The specimens were radiographed alongside an aluminium step wedge and a tooth section. Digital images were analysed, and the radiopacity of each specimen was determined according to ISO 1311/2014. Statistical analyses of radiopacity, expressed as mm Al (n = 15), were carried out using the Kruskal-Wallis test followed by pairwise comparisons (α = 0.05). RESULTS: Radiopacities of CAD/CAM materials were, in ascending order, VE, VM II, CS, LU, and GB. At 1 mm thickness, the radiopacities of all CAD/CAM specimens were matching or slightly lower than enamel. At 2-mm thickness, the resin composite blocks were significantly more radiopaque than the ceramics VE and VM II (p < 0.0001). No statistically significant differences in radiopacity were detected between the 1-mm thick infiltrated ceramic, enamel, dentin and various resin composites except for filling and bulk fill types. The radiopacity of polymer-infiltrated ceramics was low despite the presence of radiopacifying elements and high filler content. SIGNIFICANCE: Identifying thin restorations in standard radiographs is necessary with the development and expanded application of 'digital' dental materials in restorative treatment. This study confirmed the joint influence of composition and thickness on radiopacity. CAD/CAM restorative materials showed thickness-dependant radiopacity. But polymer-infiltrated ceramics were fairly radiolucent. There is a need to revisit radiopacity requirements for CAD/CAM restorative materials.

Effects of three food-simulating liquids on the roughness and hardness of CAD/CAM polymer composites.

OBJECTIVE: Implant-supported frameworks constructed from high-performance polymer CAD/CAM composites are exposed to liquids from the oral environment and routine care maintenance. Therefore, this study investigated the effect of food-simulating liquids (FSLs) on surface properties of three CAD/CAM polymer composite blocks. METHODS: The composites investigated were (i) a carbon fibre-reinforced composite (CarboCAD 3D dream frame; CC), (ii) a glass fibre-reinforced composite (TRINIA; TR), and (iii) a reinforced PEEK (DentoKeep; PK). The filler contents were determined by thermo-gravimetry. The surface properties were roughness, Vickers hardness (HV), properties measured by Martens force/depth indentation, namely: hardness (HM), modulus (EIT) and creep (CIT). Property measurements were made at baseline on polished specimens and then, where possible, after 1- and 7-days storage at 37 â„ƒ in three different media: water, 70% ethanol/water and MEK (methyl ethyl ketone). Specimens were selected for light and scanning electron microscopy. Statistical analysis was performed by two-way repeated measures ANOVA, one-way ANOVA, and multiple comparison tests (α = 0.05). RESULTS: The baseline roughness and hardness (HV, HM) and modulus (EIT) correlated approximately with filler content (wt%), with the fibre-reinforced composites being rougher, harder and stiffer than PK. At baseline, roughness (Sa) ranged from 0.202 to 0.268 µm; HV from 23.1 to 36.9; HM from 224.5 to 330.6 N/mm2; EIT: from 6 to 9.8 GPa. After ageing in 70% ethanol and MEK, more pronounced roughness and hardness changes were observed than in water. MEK caused greater deterioration for the FRC than 70% ethanol, while PK specimens showed slight changes in 70% ethanol. SIGNIFICANCE: Storage media adversely affected the surface and mechanical properties of each CAD/CAM composite. However, during ageing, the reinforced PEEK showed greater relative stability in these properties. Nevertheless, the deterioration may indicate the need for full protection by a veneer material on each surface of an implant-supported framework.

Do dentists practice what they know? A cross-sectional study on the agreement between dentists' knowledge and practice in restoring endodontically treated teeth.

BACKGROUND: There are very few studies comparing dentists' knowledge in relation to their clinical approach despite the existence of a possible gap between what they know and what they do. AIM: To measure the agreement between knowledge and practice methods related to a selected clinical scenario involving the placement of an indirect post in endodontically treated teeth (ETT) among different types of practitioners. METHODS: An electronic questionnaire was emailed to members of the Saudi Dental Society. The questionnaire presented a clinical scenario of restoring a posterior ETT with an indirect post, core unit, and crown, followed by specific questions regarding knowledge and practice related to ten different treatment aspects such as who prepares the post space, technique, isolation, time, gap between gutta-percha, and time to cementation of the crown. Each question was presented twice for each aspect, once asking about their practice method and then what they thought was the correct practice (knowledge). The relationship between the participants' responses and their specialty and the agreement between the responses of knowledge and practice for each participant were analyzed by Pearson's chi-square test and Kappa. RESULTS: 203 completed questionnaires were analyzed. Most participants were 30 years old or younger (62.6%), and general dental practitioners (59%). When comparing the knowledge to the practice methods of each participant, nine out of ten aspects were of a "weak" level agreement or below (kappa < 0.59, p < 0.001). Only one aspect demonstrated a "strong" level of agreement (Kappa = 0.804), which was related to the duration of time between obturation and post space preparation in the presence of a periapical lesion. However, this strong agreement in the responses was not aligned with current evidence. There was also a significant difference among the responses of endodontists, restorative dentists and general practitioners in most of the aspects. CONCLUSION: Overall, there was a weak agreement between what practitioners know and do in most aspects of a selected clinical scenario involving the placement of an indirect post in posterior ETT. Moreover, the participant's specialty influenced their responses regarding both knowledge and clinical practice.