Microhardness and elemental analysis of ion-releasing restoration/ dentin interface following enzymatic chemomechanical caries excavation.

BACKGROUND: This study was conducted to compare chemical, elemental and surface properties of sound and carious dentin after application of two restorative materials resin-modified glassionomer claimed to be bioactive and glass hybrid restorative material after enzymatic chemomechanical caries removal (CMCR) agent. METHODS: Forty carious and twenty non-carious human permanent molars were used. Molars were randomly distributed into three main groups: Group 1 (negative control) - sound molars, Group 2 (positive control) - molars were left without caries removal and Group 3 (Test Group) caries excavated with enzymatic based CMCR agent. After caries excavation and restoration application, all specimens were prepared Vickers microhardness test (VHN), for elemental analysis using Energy Dispersive Xray (EDX) mapping and finally chemical analysis using Micro-Raman microscopy. RESULTS: Vickers microhardness values of dentin with the claimed bioactive GIC specimens was statistically higher than with glass hybrid GIC specimens. EDX analysis at the junction estimated: Calcium and Phosphorus of the glass hybrid GIC showed insignificantly higher mean valued than that of the bioactive GIC. Silica and Aluminum mean values at the junction were significantly higher with bioactive GIC specimens than glass hybrid GIC specimen. Micro-raman spectroscopy revealed that bioactive GIC specimens showed higher frequencies of v 1 PO 4, which indicated high level of remineralization. CONCLUSIONS: It was concluded that ion-releasing bioactive resin-based restorative material had increased the microhardness and remineralization rate of carries affected and sound dentin. In addition, enzymatic caries excavation with papain-based CMCR agent has no adverse effect on dentin substrate.

Poly(N-isopropylacrylamide) based smart nanofibrous scaffolds for use as on-demand delivery systems for oral and dental tissue regeneration.

Stimuli-responsive domains capable of releasing loaded molecules, "on-demand," have garnered increasing attention due to their enhanced delivery, precision targeting, and decreased adverse effects. The development of an on-demand delivery system that can be easily triggered by dental clinicians might have major roles in dental and oral tissue engineering. A series of random graft poly(NIPAm-co-HEMA-Lactate) copolymers were synthesized using 95:5, 85:5, 60:40, and 40:60 ratios of thermosensitive NIPAm and HEMA-poly lactate respectively then electrospun to produce nanofibrous scaffolds loaded with bovine serum albumin (BSA). Cumulative BSA release was assessed at 25C and 37°C. To appraise the use of scaffolds as on-demand delivery systems, they were subjected to thermal changes in the form cooling and warming cycles during which BSA release was monitored. To confirm the triggered releasing ability of the synthesized scaffolds, the copolymer made with 60% NIPAm was selected, based on the results of the release tests, and loaded with bone morphogenetic protein-2 (BMP-2). The loaded scaffolds were placed with mesenchymal-like stem cells (iMSCs) derived from induced pluripotent stem cells (iPSCs), and subjected to temperature alterations. Then, the osteogenic differentiation of iMSCs, which might have resulted from the released protein, was evaluated after 10 days by analyzing runt-related transcription factor 2 (RUNX-2) osteogenic gene expression by the cells using real-time quantitative polymerase chain reaction (qRT-PCR). BSA release profiles showed a burst release at the beginning followed by a more linear pattern at 25°C, and a much slower release at 37°C. The release also decreased when the PNIPAm content decreased in the scaffolds. Thermal triggering led to a step-like release pattern in which the highest release was reported 30 min through the warming cycles. The iMSCs cultivated with scaffolds loaded with BMP-2 and exposed to temperature alteration showed significantly higher RUNX-2 gene expression than cells in the other experimental groups. The synthesized scaffolds are thermo-responsive and could be triggered to deliver biological biomolecules to be used in oral and dental tissue engineering. Thermal stimuli could be simulated by dental clinicians using simple means of cold therapy, for example, cold packs in intraoral accessible sites for specified times.

Effects of food-simulating solutions on the surface properties of two CAD/CAM resin composites.

Background: During clinical service, dental materials could experience chemical degradation due to exposure to different diet components which could affect their functions and longevity. So, the objective of this study was to investigate the effect of food simulating solutions on surface properties of two CAD/CAM dental resin composites. Material and Methods: Two CAD/CAM composites; a nano-hybrid and a resin nano-ceramic were machined into 2 mm plates then assessed at baseline for their surface roughness and microhardness. Each group was immersed into distilled water, ethanol and methyl ethyl ketone (MEK) for 15 days at 37oC. The surface properties were evaluated after one day, 10 and 15 days of immersion by a surface profilometer and Vickers microhardness tester, and finally the surface morphology was studied using scanning electron microscopy. Results: At baseline, there was no significant difference in roughness between Teric CAD and Lava Ultimate, however, Lava Ultimate was significantly harder than Tetric CAD. Aging in ethanol had no significant effect on roughness and hardness of both the materials. Yet, Lava Ultimate showed significantly higher roughness and hardness compared to Tetric CAD. Immersion in MEK resulted in a significant increase in roughness of Lava Ultimate at 10 and 15 days. Neverthless, it caused a significant decrease in hardness of Tetric CAD at 10 and 15 days and Lava Ultimate at 10 days. Finally, water immersion caused a significant increase of roughness Tetric CAD. Conclusions: Exposure to different storage media variably affected the surface properties of CAD/CAM machinable composites. Both materials showed greater stability in surface properties when being immersed in ethanol than MEK. Hence, the surface deterioration suggests the advisability of more research involving increased immersion periods and involvement of thermocycling changes. Key words:Food simulating solutions, chemical degradation, nano-hybrid CAD/CAM composite, resin nano-ceramic CAD/CAM material, surface roughness, micro-hardness, surface morphology.

Physico-mechanical properties and bacterial adhesion of resin composite CAD/CAM blocks: An in-vitro study.

Background: The recent introduction of CAD/CAM technology has been strongly impacting the workflow in dental clinics and labs. Among the used CAD/CAM materials, resin composite CAD/CAM blocks offer several advantages. The aim of this study was to evaluate the physico-mechanical properties and bacterial adhesion of a recently introduced nanoceramic hybrid material (Grandio Blocs) comparing it to a nanoceramic CAD/CAM material (Lava Ultimate). Material and Methods: A total of 82 specimens were prepared; 41 specimens from each material. For flexural strength testing, bar shaped specimens were sectioned from each material and flexural strength was evaluated using a three point bending test. For surface hardness, specimens with 2 mm thickness were prepared, polished and tested using Vickers micro-hardness tester. For wear evaluation, specimens were tested in a block on ring tribometer and the amount of weight loss was determined. A stylus profilometer was used to evaluate the surface roughness of disc shaped specimens in three directions. For the bacterial adhesion, the same specimens from the roughness test were used to evaluate the adhesion of Streptococcus mutans to the surface of each material after incubation for 24 hours. The correlation between surface roughness and bacterial adhesion was also investigated. Results: The nano-ceramic hybrid CAD/CAM material exhibited significantly higher flexural strength and surface hardness than the nano-ceramic CAD/CAM material. It also showed significantly lower surface roughness and surface bacterial adhesion and lower wear that was not significantly different. A positive correlation was found between surface roughness and bacterial adhesion of both materials. Conclusions: The nano-ceramic hybrid CAD/CAM material showed better physico-mechanical properties compared to the nano-ceramic CAD/CAM material which could be attributed to the use of nanohybrid filler system and an enhanced resin matrix structure. Key words:CAD/CAM blocks, nano-ceramic hybrid, flexural strength, wear, surface hardness, surface roughness, bacterial adhesion.