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Stereolithography (SLA) ceramic crown frameworks are suitable for clinical use, but the impact of SLA build orientation has not been identified. The purpose of this in vitro study was to investigate the effect of 3 build orientations on the physical and mechanical properties and the microstructure of SLA alumina dental ceramics. The physical and mechanical properties and microstructures of 3 different oriented SLA alumina ceramics (ZX, ZY, and XY) were evaluated by visual observation, hydrostatic weighing (n=10/group), Weibull analyses (n=30/group), scanning electron microscopy, 3-point flexural strength (n=30/group), fracture toughness (indentation, single-edge-V-notched-beam) (n=4/group), and Vickers hardness (n=15/group) testing. The hydrostatic weighing, 3-point flexural strength, fracture toughness, and Vickers hardness testing data were statistically analyzed (α=.05). The minimum resting period of slurries between the polymerization of 2 layers was shorter for the ZY- and ZX-oriented specimens and increased with the layer surface. The density and Vickers hardness of the SLA-manufactured specimens were similar for all groups (P >.05). The 95% confidence intervals of the Weibull moduli of the ZX- and ZY-oriented specimens were higher than that of the XY-oriented specimens, with no overlap fraction. The ZY-oriented specimens displayed significantly higher 3-point flexural strength (P <.05) and fracture toughness as evaluated by the single-edge-V-notched-beam method than the ZX-oriented specimens (P <.05). They also displayed significantly higher 3-point flexural strength than the XY-oriented specimens (P <.05). The microstructural analysis showed that the texturing was heterogeneous and that the major axis of the large grains of alumina ran parallel to the orientation of the layers. The ZY orientation produced a reliable dental ceramic by SLA, with the shortest general manufacturing time and the highest mechanical strength when the layers were perpendicular to the test load surface. [ABSTRACT FROM AUTHOR]

Objectives The aim of this study was to compare the physical and mechanical properties of stereolithography (SLA)- manufactured alumina ceramics of different composition to those of subtractive- manufactured ceramics and to produce suitable dental crown frameworks. Methods The physical and mechanical properties of a control and six experimental SLA ceramics prepared from slurries with small (S) and large (L) particles (0.46 ± 0.03 and 1.56 ± 0.04 μm, respectively) and three dry matter contents (70%, 75%, 80%) were evaluated by dynamic rheometry, hydrostatic weighing, three3-point flexural strength measurements, and Weibull analyses, and by the micrometrics measurement of shrinkage ratio before and after the heat treatments. Results S75 was the only small particle slurry with a significantly higher viscosity than L70. The viscosity of the S80 slurry made it impossible to take rheological measurements. The viscosities of the S75 and S80 slurries caused deformations in the printed layers during SLA manufacturing and were excluded from further consideration. SLA samples with low dry matter content had significantly lower and densityflexural strengths. Only SLA samples with a large particle size and high dry matter content (L75 and L80) were similar in density and flexural strength to the subtractive- manufactured samples. The 95% confidence intervals of the Weibull modulus of the L80 ceramic were higher (no overlap fraction) than those of the L75 ceramic and were similar to the control (overlap fraction). The Weibull characteristics of L80 ceramic were higher than those of L75 ceramic and the control. SLA can be used to process suitable crown frameworks but shows results in anisotropic shrinkage. Significance The hH High particle size and dry matter content of the L80 slurry allowed made it possible to produce a reliable ceramic by SLA manufacturing with an anisotropic shrinkage, and a density, and flexural strength similar to those of a subtractive-manufactured ceramic. SLA allowed made it possible to build up a dense 3D alumina crown framework with controlled shape. Further studies on the marginal adaptation and shrinkage model of alumina crown frameworks will be required to optimize the process. [ABSTRACT FROM AUTHOR]

Statement of problem Direct optical impression systems requiring powder opacification are widely used in prosthodontics, but little information is available about the influence of the dentist on the quality of scan sprays used for computer-aided design and computer-aided manufacturing (CAD/CAM) impressions. Purpose The purpose of this study was to evaluate the influence of operator experience on scan spray homogeneity and thickness on tooth surfaces before direct optical impressions are made. Material and methods A total of 36 crown-prepared acrylic resin teeth were coated (Optispray) for direct optical impressions by 3 experienced dentists and 3 inexperienced dentists (n=18 teeth per group). The teeth were visually scored for coating homogeneity (1, heterogeneous; 2, average; 3, homogeneous). To determine the coating thickness (μm), the teeth were resin-embedded, cut, and polished. A stereomicroscope (×100 magnification) was used to examine 148 areas per tooth. The results were statistically analyzed with the nonparametric Spearman and Mann-Whitney tests (α=.05). Results Coating homogeneity was significantly higher ( P <.001) for the experienced group (92.41 ±6.65%) than for the inexperienced group (66.11 ±12.69%). Coatings were significantly thinner for the experienced group (43.1 ±14.09 μm) than for the inexperienced group (70.19 ±31.26 μm) for all crown areas ( P =.007). Coatings were 52 μm thinner for occlusal areas ( P <.001) for the experienced group than for the inexperienced group. Coatings were significantly thinner for buccal ( P =.015) and lingual surfaces ( P =.002) for the experienced group than for the inexperienced group. Coatings on cervical surfaces were significantly thinner for the experienced group (43.52 ±15.76 μm) than for the inexperienced group (63.45 ±29.93 μm) ( P =.035). Conclusions Experienced dentists achieved greater homogeneity and thinner coatings on crown-preparation surfaces than inexperienced dentists. [ABSTRACT FROM AUTHOR]