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 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.

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.