Dimensional Changes of Glass Ionomers and a Giomer during the Setting Time

Application of Semipermanent Cements and Conventional Cement with Modified Cementing Technique in Dental Implantology

Objectives

The aim of this study was to evaluate the influence of artificial ageing on the retention force of original semipermanent cements, as well as the possibility of using conventional cements for semipermanent cementation with adequate modification of the cementing protocol.

Materials and methods

Forty CoCrMo alloy crowns were divided in four groups (each group n=10) and fixed with two semipermanent cements (resin-based and glass ionomer-based cements) and one conventional (zinc phosphate), using conventional and modified cementation techniques on titanium abutments. The samples were stored in humid conditions for 24 hours at 37°C and subjected to thermocycling (500 cycles) and mechanical cyclic loading (7 days, 3, 6, 9 and 12 months function simulation). The cast crowns were removed and the retention force was recorded.

Results

The highest initial retention force measured was for zinc-phosphate cement - conventional cementing (198,00±61,90 N), followed in descending order by zinc-phosphate cement - modified cementing technique (152,00±45,42 N), long term temporary cement - GC Fuji Temp LT (57,70±20,40 N), and semipermanent cement - Telio CS Cem Implant (56,10±18,68 N). After 12 months, the highest retention force measured was for zinc-phosphate cement - conventional cementing (88, 90±14, 45 N), followed by zinc-phosphate cement - modified cementing (48, 15±14,41N), semipermanent cement GC Fuji Temp LT (16,55±3,88 N) and Telio CS Cem Implant (15,55±5,52 N).

Conclusions

Zinc-phosphate cement - modified cementing technique and original semipermanent cements can be recommended for conditional permanent cementing of implant supported crowns.

Clinical relevance

The use of semipermanenet cements and zinc-phosphate cement - modified cementing technique provides a predictable retrievability of implant-supported crowns.

Retinal damage related to high-intensity light-emitting diode exposure: An in vivo study

INTRODUCTION

The objective of this investigation was to evaluate the effects of high-intensity light-emitting diode (LED) light from a curing device on the retinas of Wistar rats.

METHODS

Six male Wistar rats were used, and their ocular structures were the focus of this study. During the photostimulation of each animal, the right eye of the animal, considered the control sample, was covered with a removable polyvinyl chloride cap, and the contralateral eye, the experimental sample, was exposed to high-intensity LED light, 3200 mW/cm² (VALO Ortho; Ultradent Products, South Jordan, Utah) for 144 seconds from a distance of 30 cm. The animals were exposed to the LED light 3 times on the same day to investigate if any acute inflammatory changes in the retina occurred. Seven days after the photostimulation sessions, the animals were anesthetized and perfused with paraformaldehyde solution. After which, the eyes were resected and processed histologically. The histologic sections were analyzed stereologically and histomorphometrically to measure the parameters of the retina under investigation.

RESULTS

There was a statistically significant increase in total retinal volume in the experimental group because of the increased volume of the ganglion cell layers, inner plexiform layers, outer nuclear layers, and the cone and rod extensions. There was no statistically significant difference in terms of density. However, there was a statistically significant increase in the nuclear area of the cells in all the studied layers in the group exposed to high-intensity LED light. In addition, hyperchromatic cells that are suggestive of pyknosis were observed.

CONCLUSIONS

An acute but short protocol of exposure of high-intensity LED light to the eye caused morphometric alterations in the retinal structures, specifically in the nuclear area of the photosensitive cells.

Effects of ionizing radiation on surface properties of current restorative dental materials

To investigate the impact of radiotherapy on surface properties of restorative dental materials. A conventional resin composite-CRC (Aura Enamel), a bulk-fill resin composite-BFRC (Aura Bulk-fill), a conventional glass ionomer cement-CGIC (Riva self cure), and a resin-modified glass ionomer cement-RMGIC (Riva light cure) were tested. Forty disc-shaped samples from each material (8 mm diameter × 2 mm thickness) (n = 10) were produced according to manufacturer directions and then stored in water distilled for 24 h. Surface wettability (water contact angle), Vickers microhardness, and micromorphology through scanning electron microscopy (SEM) before and after exposition to ionizing radiation (60 Gy) were obtained. The data were statistically evaluated using the two-way ANOVA and Tukey posthoc test (p < 0.05). Baseline and post-radiation values of contact angles were statistically similar for CRC, BFRC, and RMGIC, whilst post-radiation values of contact angles were statistically lower than baseline ones for CGIC. Exposition to ionizing radiation statistically increased the microhardness of CRC, and statistically decreased the microhardness of CGIC. The surface micromorphology of all materials was changed post-radiation. Exposure to ionizing radiation negatively affected the conventional glass ionomer tested, while did not alter or improved surface properties testing of the resin composites and the resin-modified glass ionomer cement tested.

Fluoride-Releasing Restorative Materials: The Effect of a Resinous Coat on Ion Release

Objective

To determine the effect of two adhesive systems and a glass ionomer coating resin on fluoride release and concurrent pH changes over a period of 168 days.

Material and methods

Four restorative materials were investigated: a giomer Beautiful II, an “alkasite” material Cention, a conventional composite Filtek Z250, and a glass ionomer cement Fuji IX Extra. Light-cured composite specimens were coated using G-aenial Bond and Clearfil Universal Bond Quick. Glass ionomer specimens were coated using GC Fuji Coat LC. Uncoated specimens were used as references. Quantitative fluoride release and pH changes were measured after1 h, 24 h, 2 days, 7 days, 28 days, 84 days, and 168 days.

Results

The cumulative fluoride release after 168 days increased for uncoated specimens in the following order: Filtek Z250 < Beautifil II < Cention < Fuji IX Extra. A comparatively lower fluoride release was measured for the composites coated with Clearfil Universal Bond Quick, with cumulative values after 168 days increasing in the following order: Filtek Z250 < Beautifil II < Cention. The composites coated with G-aenial Bond showed lower fluoride release compared to the uncoated specimens, with cumulative values increasing in the following order: Filtek Z250 < Beautifil II < Cention. The composites coated with G-aenial Bond showed pH values in the acidic range (4.4-5.7) after 1 h and 24 h.

Conclusion

Fluoride release varied among the investigated restorative materials and depended on the use of dental adhesives and coatings. The pH of all materials, coating types and time points varied.

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.