Mandibular Overdenture Supported by Two or Four Unsplinted or Two Splinted Ti-Zr Mini-Implants: In Vitro Study of Peri-Implant and Edentulous Area Strains.

Clinical indications for the newly released Ti-Zr (Roxolid®) alloy mini-implants (MDIs) aimed for overdenture (OD) retention in subjects with narrow alveolar ridges are not fully defined. The aim of this study was to analyze peri-implant and posterior edentulous area microstrains utilizing models of the mandible mimicking a "real" mouth situation with two (splinted with a bar or as single units) or four unsplinted Ti-Zr MDIs. The models were virtually designed from a cone beam computed tomography (CBCT) scan of a convenient patient and printed. The artificial mucosa was two millimeters thick. After MDI insertion, the strain gauges were bonded on the oral and vestibular peri-implant sites, and on distal edentulous areas under a denture. After attaching the ODs to MDIs, the ODs were loaded using a metal plate positioned on the first artificial molars (posterior loadings) bilaterally and unilaterally with 50, 100, and 150 N forces, respectively. During anterior loadings, the plate was positioned on the denture's incisors and loaded with 50 and 100 N forces. Each loading was repeated 15 times. The means with standard deviations, and the significance of the differences (two- and three-factor MANOVA) were calculated. Variations in the MDI number, location, and splinting status elicited different microstrains. Higher loading forces elicited higher microstrains. Unilateral loadings elicited higher microstrains than bilateral and anterior loadings, especially on the loading side. Peri-implant microstrains were lower in the four-MDI single-unit model than in both two-MDI models (unsplinted and splinted). Posterior implants showed higher peri-implant microstrains than anterior in the four-MDI model. The splinting of the two-MDI did not have a significant effect on peri-implant microstrains but elicited lower microstrains in the posterior edentulous area. The strains did not exceed the bone reparatory mechanisms, although precaution and additional study should be addressed when two Ti-Zr MDIs support mandibular ODs.

New insights into the structural properties of κ-(BEDT-TTF)2Ag2(CN)3 spin liquid.

Here, the first accurate study is presented of the room-temperature and 100 K structures of one of the first organic spin liquids, κ-(BEDT-TTF)2Ag2(CN)3. It is shown that the monoclinic structure determined previously is only the average one. It is shown that the exact structure presents triclinic symmetry with two non-equivalent dimers in the unit cell. But surprisingly this does not lead to a sizeable charge disproportionation between dimers. The difference from the analogue compound κ-(BEDT-TTF)2Cu2(CN)3 which also presents a spin liquid phase is discussed in detail. The data provided here show the importance of the anionic layer and in particular the transition metal position in the process of symmetry breaking. The possible impact of the symmetry breaking, albeit weak, on the spin-liquid mechanism and the influence of various disorders on the physical properties of this system is also discussed.

Effects of Curing Modes on the Microhardness of Resin-modified Glass Ionomer Cements.

OBJECTIVE: This study evaluated the effects of curing modes on surface microhardness of visible light-cured resin-modified glass ionomer cements (VLC RMGIC) and a giomer after different storage periods in comparison to auto-cured resin-modified glass ionomer cements (AC RMGIC). MATERIALS AND METHODS: The following materials were used: VLC RMIC: Fuji II LC Improved, Photac Fil Quick Aplicap, AC RMGIC: Fuji Plus, Fuji VIII and Giomer: Beautifil II. The measurements of microhardness were performed using a Vickers test (100 g loads were applied for 10 s) in the following time intervals: immediately after the recommended cure and after 1, 7 and 14 days of immersion in distilled water. Five samples (d=4 mm, h=2 mm) were prepared for each combination of curing mode and tested material. RESULTS: After 14 days, an improvement of microhardness was evident in all tested materials. The full factorial ANOVA identified a highly significant (p<0.001) effect of the factors "material", "time" and "curing mode ("low", "soft", "high") for the light-cured materials Beautifil II, Fuji II LC and Photac Fil Quick. There was a statistically significant difference in the microhardness between different material types (Beautifil II˃Fuji II LC˃Photac Fil Quick˃Fuji Plus˃Fuji VIII) and curing modes (low ˂soft ˂high). CONCLUSIONS: Material type had the greatest impact on microhardness, followed by the factor of time, while curing modes showed a considerably smaller influence on microhardness of the light-cured materials.

The effects of extended curing time and radiant energy on microhardness and temperature rise of conventional and bulk-fill resin composites.

OBJECTIVES: To investigate radiant energy, microhardness, and temperature rise in eight resin composites cured with a blue or violet-blue curing unit, using a curing protocol which exceeded manufacturer recommendations. MATERIALS AND METHODS: Cylindrical composite specimens (d = 8 mm, h = 2 or 4 mm, n = 5 per experimental group) were light-cured for 30 s. Light transmittance through specimens was recorded in real time to calculate radiant energy delivered to the specimen bottom. Vickers microhardness was used to evaluate the polymerization effectiveness at depth. Temperature rise at the bottom of the specimens was measured in real time using a T-type thermocouple. RESULTS: Radiant energy delivered from the blue and violet-blue curing unit amounted to 19.4 and 28.6 J/cm2, which was 19 and 13% lower than specified by the manufacturer. Radiant energies at bottom surfaces (0.2-7.5 J/cm2) were significantly affected by material, thickness, and curing unit. All of the composites reached 80% of maximum microhardness at clinically relevant layer thicknesses. The benefit of using the higher-irradiance violet-blue curing unit was identified only in composites containing alternative photoinitiators. Temperature rise during curing ranged from 4.4 to 9.3 °C and was significantly reduced by curing with the lower-intensity blue curing unit and by increasing layer thickness. CONCLUSION: Curing for 30 s, which can be regarded as extended considering manufacturer specifications, produced radiant energies which are in line with the recommendations from the current scientific literature, leading to adequate curing efficiency and acceptable temperature rise. CLINICAL RELEVANCE: Extended curing time should be used to minimize concerns regarding undercuring of composite restorations.