Trueness, 3D Deviation, Time and Cost Comparisons Between Milled and 3D-Printed Resin Single Crowns.

The purpose of this in-vitro study was to compare trueness, 3D deviation, production time and costs of milled and 3D-printed resin single crowns. A total of 20 CAD-CAM resin single crowns were fabricated from 10 digital wax patterns designed on 10 tooth preparations available in a reference model. Standardized control linear measurements were performed with a CAD software. Each STL file was then used to fabricate two resins crowns - one milled and one 3D-printed. All crowns underwent physical linear measurements using a digital caliper. The crowns were then scanned using an intraoral scanner for assessing 3D deviation. Finally, time to produce a single crown, as well as costs and production rates of both methods were also compared. Both CAM methods did not present statistically significant differences in linear measurements, as compared to controls (P⟩.05). Furthermore, 3D-printed crowns had significantly greater deviations in cervical margins (P=.032) and occlusal surfaces (P=.041), as compared with milled crowns. Finally, 3D-printing took significantly longer to produce one single crown (P=.001), but with a cheaper and higher production rate than milling. These findings suggest that milling devices produce resin single crowns with smaller 3D deviations but more expensive costs, as compared with low-cost 3D printers.

Influence of Gingival Contour on Marginal Fit of CAD-CAM Zirconia Copings on Implant Stock Abutments.

PURPOSE: Intraoral scanning subgingival finish lines has been described as challenging. The purpose of this study was to assess the impact of gingival contour around margins of implant stock abutments on marginal fit of Computer-aided Design - Computer-aided Manufacturing (CAD-CAM) zirconia copings. This in-vitro study was conducted on 40 analogues of implant stock abutments that were embedded into individual phantoms composed by a resin block. All 40 phantoms underwent two intraoral scans - one with (test group) and one without artificial gingiva (control group) - using a closed system intraoral scanner. Zirconia copings were then digitally designed and milled, followed by high-speed sintering, before being analyzed for marginal adaptation and internal surface roughness with scanning electron microscopy. Statistically significant differences between groups were assessed with the Mann-Whitney test. Median marginal gap values were 149.78 µm (95% CI: 112.39-216.66) for the test group and 94.90 µm (95% CI: 83.89-107.74) for the control group. A statistically significant difference was found between groups (p=0.0001). However, there were no subjective differences between groups for internal surface roughness. Within the limitations of this study, the present findings suggest that a gingival contour one millimeter higher than the finishing line affects marginal adaptation of CAD-CAM zirconia copings.

External PIGE-PIXE measurements at the São Paulo 8UD tandem accelerator / Medidas externas do PIGE-PIXE em São Paulo 8UD acelerador tandem

An external PIGE-PIXE setup was installed on a beam line of the 8 MV tandem Pelletron accelerator of the Open Nuclear Physics Laboratory (LAFN). Proton beam energy was chosen in the 8-12 MeV range, sufficient to get an acceptable gamma ray yield but not so high as to prevent us from measuring X-rays. This also allowed the use of a thick aluminum exit window (0.5 mm) instead of the usual thin and sometimes fragile plastic windows. This external PIXE-PIGE system was used to analyze trace element concentrations in the enamel of human and animal teeth. The main interest was to find compatible human teeth substitutes for dentistry laboratory practice and chemical tests. In spite of their morpho-histological similarity, trace element concentrations in human and animal teeth have not yet been compared. Teeth from humans, cattle and swine collected primary at São Paulo region were analyzed. The elements Cu, K, Zn, Fe, Ti, Sr, V, Mn and Zr were detected by high energy external beam PIXE technique. Though preliminary, the results showed that the trace element concentrations observed in the enamel of human and swine are more similar to each other than to cattle teeth

[Dimensional changes of silver and gallium-based alloy]. / Alteração dimensional de amálgama de prata e liga à base de gálio.

Gallium-based dental alloys were created with the aim of solving the problem of toxicity of mercury. The material shows mechanical properties similar to those of dental amalgam, but researches point out two unfavorable characteristics: great corrosion and excessive post-setting expansion, and the latter is capable of cracking dental structures. The aim of this study was to evaluate, during 7 days, the in vitro dimensional alteration of a gallium dental alloy (Galloy, SDI, Australia), in comparison with a dental amalgam containing zinc (F400, SDI, Australia), as a function of the contact with saline solution (0.9% NaCl) during the setting period. The storage experimental conditions were: storage in dry environment, immersion in saline solution and contamination during condensation. Additionally, the effects of contamination during the trituration of dental amalgam and the effects of protecting the surface of the gallium alloy with a fluid resin were studied. Specimens were stored at 37 degrees C +/- 1 degree C, and measuring was carried out, sequentially, every 24 h during 7 days. When the gallium alloy was either contaminated or immersed, an expansion significantly greater than that observed in the other experimental conditions was noticed after 7 days. The application of a fluid resin to protect the surface of the cylinders was able to avoid the increase in expansion caused by superficial moisture. The amalgam alloy did not show significant dimensional alterations, except when it was contaminated during trituration.