Evaluation of custom posts and cores fabricated by two digital technologies in core and post space dimensions.

PURPOSE: To evaluate the adaptability between posts and post spaces and the rationality of cores fabricated by two digital custom post-and-core processes. MATERIALS AND METHODS: Titanium post-and-cores were fabricated by digital scanning impression technology or digital scanning wax-pattern technology on tooth defect molds of incisors, premolars, and molars, with traditional lost-wax casts of these teeth as the controls. Micro-CT and a laboratory scanner were used to determine intervals between post wall and root canal wall of the root apex, middle, and cervix of each sample in cross-, sagittal, and coronal sections; intervals between the end of post and tooth; diameters of cervical, middle, and incisal part at cross-, sagittal, and coronal sections of each sample, as well as shoulder widths. RESULTS: The three fabrication processes showed significant differences in intervals between post-and-core prostheses and root canal walls, diameters of all parts of cores, and shoulder widths. Scanning impressions showed significant advantages in the main part of post-and-cores in incisors and premolars, while the scanning wax-pattern process showed obvious inferiorities in premolars and molars. As to core spatial size, values of measured sites in the scanning impression process were closer to the standard than those of the traditional process, while differences between the measured value of the scanning wax-pattern process were much more obvious than in the traditional process. CONCLUSIONS: The use of digital custom post-and-core scanning impressions improved the rationality and precision of post-and-core dimensions compared with two other processes.

Mechanical properties of bulk-fill resin composites with single increment up to 4 mm: A novel mechanical strength test.

PURPOSE: To evaluate the mechanical properties of two brands of bulk-fill resin composites placed in a single increment up to 4 mm thickness via a novel mechanical strength test and provide related explanations. METHODS: Light transmission (LT), translucency parameter (TP), color difference (ΔE), Vickers hardness (HV) of two bulk-fill resin composites (Filtek Bulk Fill Posterior, Tetric N-Ceram Bulk Fill) and two conventional resin composites (Z100, Spectrum TPH) were evaluated. A novel flexural strength (FS) test method was applied for bulk-fill resin composite to determine the FS value of the bottom composites at depths of 1, 2, 3, and 4 mm after 24 hours of aging treatment (3 months water storage and 15,000 thermal cycles). The conventional resin composites were also tested for FS and all the FS results were subjected to Weibull analysis. Degree of conversion (DC) in the bulk-fill resin composites, light-cured at depths of 1, 2, 3, and 4 mm and conventional resin composites at depths of 2 and 4 mm, were assessed by FTIR. RESULTS: Both bulk-fill resin composites showed higher light transmission and translucency than that of conventional ones at each of the same thicknesses (1, 2, 3, 4 mm), wherein their flexural strength was not affected by depth. The Weibull analysis suggested both bulk-fill resin composites achieved good reliability and structural integrity under each curing thickness. Vickers hardness was affected by the material type and thickness. Bulk-fill resin composites showed a decrease in degree of conversion between 1 mm and 4 mm, but both were over 55%. CLINICAL SIGNIFICANCE: Filtek Bulk Fill Posterior, Tetric N-Ceram Bulk Fill achieved acceptable mechanical properties when cured at depths of up to 4 mm, which was beneficial from their optical and polymerized properties.

Evaluation of a half-digital technique for fabricating customized post-cores: A pilot study.

Objectives: The current half-digital post-core fabrication technique can replace the conventional methods; however, it does not consider the impact occlusion has on the digital design. This study proposed a half-digital workflow that integrated intracanal impression with dentition scanning, and evaluated the accuracy of the post-cores fabricated by it. Methods: Standard models with three extracted teeth (a central incisor, a premolar, and a molar) were prepared. Eight post-cores were fabricated for each tooth by the half-digital technique and eight by the conventional technique as controls. Scanning was performed with a microcomputed tomography system. The volume of the overall space (VOS) between the post and canal wall, the space areas in three standardized sections (A, B, and C), and the apical gap (AG) were calculated and statistically analyzed using two-way analysis of variance. Statistical significance was set at p < 0.05. Results: The two techniques differed significantly in the VOS (p < 0.05), section B (p < 0.05), and AG (p < 0.05) of all three teeth but not for sections A (p = 0.099) and C (p = 0.636). Conclusions: The half-digital technique investigated in this study could produce better-fitting customized post-cores than the conventional technique.

Effect of APTES- or MPTS-Conditioned Nanozirconia Fillers on Mechanical Properties of Bis-GMA-Based Resin Composites.

To investigate the effects of 3-aminopropyltriethoxysilane (APTES)- or (3-mercaptopropyl)trimethoxysilane (MPTS)-conditioned nanozirconia fillers on the mechanical properties of Bis-GMA-based resin composites. The conditioned fillers were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermodynamic calculations. They were then used to prepare Bis-GMA-based resin composites, whose flexural strength and elastic modulus were evaluated. The Cell Counting Kit-8 (CCK-8) assessed the composites' cytotoxicity. The FTIR spectra of the conditioned fillers showed new absorption bands at 1569 and 1100 cm-1, indicating successful grafting of APTES or MPTS onto nanozirconia. XPS confirmed the Zr-O-Si bonds in the APTES- or MPTS-conditioned fillers at contents of 2.02 and 6.98%, respectively. Thermodynamic calculations reaffirmed the chemical binding between the two silanes and nanozirconia fillers. Composites containing the conditioned nanozirconia fillers had significantly greater flexural strengths (APTES, 121.02 ± 8.31 MPa; MPTS, 132.80 ± 15.80 MPa; control, 94.84 ± 9.28 MPa) and elastic moduli (8.76 ± 0.52, 9.24 ± 0.60, and 7.44 ± 0.83 GPa, respectively) than a control with untreated fillers. The cytotoxicity assay identified no significant cytotoxicity by composites containing the conditioned fillers. Silanes were previously considered to be unable to chemically condition zirconia to bond with resin. Inclusion of APTES- or MPTS-conditioned nanozirconia fillers can improve the mechanical properties of Bis-GMA-based resin composites without obvious cytotoxicity in this study.

Glycerol Phosphate Dimethacrylate: An Alternative Functional Phosphate Ester Monomer to 10-Methacryloyloxydecyl Dihydrogen Phosphate for Enamel Bonding.

The bonding performance of a glycerol phosphate dimethacrylate (GPDM)-based, two-step, self-etch (SE) adhesive was experimentally compared to that of 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-based universal adhesives in different application modes for enamel bonding. Microtensile bond strength (µTBS) for adhesives bonded to enamel was measured initially (24 h water storage) and after 10 000 thermocycles plus water storage for 30 days. A GPDM-based, two-bottle, two-step, self-etch adhesive (Optibond Versa, OV) and three one-bottle MDP-based universal adhesives, one self-etching (Tetric N Bond Universal, TNBU) and two with etch-and-rinse (E&R) processing (Single Bond Universal (SBU); Clearfil Universal Bond Quick (CUBQ)), were tested. Scanning electron microscopy (SEM) evaluated nanoleakage at the bonding interfaces. A profilometer determined roughnesses of enamel surfaces after phosphoric acid etching, OV priming, or TNBU conditioning. SEM observed the corresponding surface morphology. NMR and X-ray photoelectron spectroscopy (XPS) characterized chemical bonding in hydroxyapatites (HAps) conditioned with the adhesives. Etch-and-rinse samples had significantly stronger bonding than self-etch samples (p < 0.05) irrespective of aging. The µTBS values for initial and aged OV were significantly higher than those of TNBU (p < 0.05). Aging did not significantly decrease µTBS for any sample except TNBU (p < 0.05), but it significantly aggravated nanoleakage. Etch-and-rinse processing resulted in less nanoleakage than self-etching; the OV samples leaked less than TNBU, both before and after aging. Phosphoric acid etching achieved the highest enamel surface roughness, followed by OV primer. Ca-O-P bonds in hydroxyapatite conditioned with TNBU, SBU, and CUBQ were confirmed by NMR, which showed similar results to XPS observations of conditioned hydroxyapatite powders except OV primer. The GPDM-based, two-step, self-etch adhesive can provide higher micromechanical retention potential, bond strength, and durability than the MDP-based universal adhesive in self-etch mode but lower performance than the MDP-based universal adhesive in etch-and-rinse mode. None of the tested adhesives could avoid nanoleakage after aging.

An evaluation of an airline cabin safety education program for elementary school children.

The knowledge, attitude, and behavior intentions of elementary school students about airline cabin safety before and after they took a specially designed safety education course were examined. A safety education program was designed for school-age children based on the cabin safety briefings airlines given to their passengers, as well as on lessons learned from emergency evacuations. The course is presented in three modes: a lecture, a demonstration, and then a film. A two-step survey was used for this empirical study: an illustrated multiple-choice questionnaire before the program, and, upon completion, the same questionnaire to assess its effectiveness. Before the program, there were significant differences in knowledge and attitude based on school locations and the frequency that students had traveled by air. After the course, students showed significant improvement in safety knowledge, attitude, and their behavior intention toward safety. Demographic factors, such as gender and grade, also affected the effectiveness of safety education. The study also showed that having the instructor directly interact with students by lecturing is far more effective than presenting the information using only video media. A long-term evaluation, the effectiveness of the program, using TV or video accessible on the Internet to deliver a cabin safety program, and a control group to eliminate potential extraneous factors are suggested for future studies.