Search

The purpose of the present study was to evaluate the influence of height and length variations of alumina ceramics manufactured by stereolithography on deformations caused by the manufacturing process and on the 3D shrinkage ratio to control the final dimensions and improve the adaptation of stereolithographic ceramic dental prostheses. Two different U-shaped models were designed with variable heights or lengths. The specimens were manufactured by stereolithography and were scanned using a microtomographic device before and after the heat treatment. Dimensional variations were measured using inspection software. The number and surface of layers of alumina ceramic influenced the reliability of the stereolithography manufacturing but did not influence the 3D shrinkage ratio. The larger the layer surface, the larger the deformation of the ceramic. Dental ceramics manufactured by stereolithography with smallest layer surface are the most reliable. This helps in the selection of the build orientation. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate two agents for bonding denture bases and teeth manufactured either by stereolithography (SLA) or by the subtractive mixed technique. Methods: Two types of cylinders [small for the tooth resin and large for the base resin) were designed using CAD software according to the ANSI/ADA 15-2008 (R2013)] specification. For SLA manufacturing, 30 small cylinders were shaped with Denture Teeth resin and 30 large cylinders with Denture Base resin. For the mixed technique, 30 large cylinders were manufactured by SLA with V-print dentbase resin, and 30 small cylinders were milled with a CediTEC DT disk. Half the specimens were bonded with liquid Denture Base resin and half with CediTEC Primer and Adhesive, according to the manufacturers' protocols. Shear bond strength was measured using a universal testing machine. The failure mode was noted for all the specimens. Results: The shear bond strength values were not significantly different between the groups (P> 0.05). Specimens bonded with liquid Denture Base resin displayed cohesive failure (P> 0.05, Χ²= 0). Of the specimens bonded with CediTEC Primer and Adhesive, cohesive failures were observed with five specimens manufactured with the SLA technique and one specimen manufactured with the mixed technique (P> 0.05, Χ²= 3.33). The Chi-square test results were significant between groups with different bonding agents regardless of the technique used (P< 0.001). Within the limitations of the present study, even if the shear bond strength values were similar, the failure mode analysis suggests that the uncured liquid Denture Base resin may be more effective than the CediTEC Primer and Adhesive for bonding denture bases and teeth manufactured either by SLA or the mixed technique. [ABSTRACT FROM AUTHOR]

Purpose: This in vitro study evaluated the effect of sodium carbonate (Na2CO3) concentration on adhesion between two layers of irreversible hydrocolloid wash impression material. Methods: The first layer of irreversible hydrocolloid was brushed with three concentrations (0.1, 0.7, or 7.0 wt.%) of Na2CO.3. Irreversible hydrocolloid not brushed with Na2CO3 was used as a negative control. Adhesion between the two layers (bond strength and adhesion energy) was then evaluated using a traction test, and the fracture modes were identified. The results of traction test were analyzed with a one-way ANOVA followed by a Tukey post hoc test. Chi-square test was used for analyzed failure mode after testing (a= 0.05). Results: The bond strength (0.0340±005 MPa) and adhesion energy (60.240 *12.817 J.m-2) of the 0.7% Na2CO3 group were significantly higher than those of the other groups (P< 0.05). The 0.7% Na2CO3 group displayed only cohesive failure (x²= 16; P< 0.0001). [ABSTRACT FROM AUTHOR]

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]

The aim of this study was to evaluate the performance of ceramic, hybrid ceramic, and commercial plastic bloc root canal simulator (RCS) as preclinical training aids in the learning phase of endodontic treatments. A previously developed hydroxyapatite ceramic RCS was improved by adding epoxy resin to the ceramic matrix to more closely mimic the organic phase of dentin and to simulate the clinical situation as realistically as possible. The sintered hydroxyapatite ceramic RCS was vacuum infiltrated with epoxy resin, and the degree of infiltration was evaluated by methylene blue staining. The suitability of the resin-infiltrated ceramic simulator (CR) for preclinical endodontic training was compared to that of a non-infiltrated ceramic simulator (C) and a commercial epoxy bloc (P) using a cohort of 30 dental students at one dental school in France. The study was conducted in 2016. The students' perceptions following the required exercises using the CR, C, and P were scored using a questionnaire. The learning outcomes were also assessed by examining the canal preparations that the students performed on extracted teeth using a master cone try-in test. The vacuum process resulted in a good degree of resin infiltration into the ceramic. The questionnaire showed that the C and CR groups generally reported greater satisfaction, especially for radiographic visualizations, than the P group. The CR group had a higher score than the P group for tactile sensation. There was no significant difference among the three groups with respect to the canal preparations using extracted teeth. Resin infiltration improved the performance of the ceramic RCS, especially with respect to perception during root canal instrumentation. A larger scale student training investigation and an assessment by experienced endodontists are required to validate the model. [ABSTRACT FROM AUTHOR]

Purpose: To compare the effect of different treatments (heat capsule, ultrasound, and dual treatments) on the setting kinetics and maturation properties of a conventional GIC (EQUIA, GC) to that of standard setting. Methods: The optimal durations of the heat and ultrasonic treatments were determined by monitoring changes in the COO-/COOH ratio, surface hardness, and temperature within the samples. The influence of optimal treatments on the maturation properties of the GIC (microhardness, and 3-point flexural strength) were assessed using GIC samples incubated in artificial saliva for 24 hours, 1 month, and 3 months. Results: The optimal durations of the heat and ultrasonic treatments for accelerating setting were 5 minutes and 35 seconds, respectively. The dual treatment using the optimal conditions of the individual treatments further enhanced the setting kinetics. A temperature peak (49°C) within the GIC was detected during setting. Only the dual treatment increased the mechanical properties of the GIC after 24 hours compared to the control, while no significant difference was observed after 1 and 3 months. [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]