Higher Mineral Loss Research Articles

Validation of variants and structural parameters for mining systems for thin ore bodies

The current mining of thin and steeply dipping ore bodies features depth down to 700–1100 m below ground surface, increased dimension of various-purpose pillars and, as consequence, higher mineral loss and overall degradation of mining efficiency. In connection with this, it is urgent to find new mining systems as well as scientific approaches to validation of safe parameters of geotechnologies such that, depending on geological and geomechanical conditions, as well as on mineral value, minimize geotechnical risks and maintain competitiveness of production. The aim of this study is to determine safe parameters of open stoping technology for thin ore bodies in terms of the Irtysh complex ore mine. The key research methods are production planning and mathematical (numerical) stress–strain analysis and stability of structural elements in underground mines. The calculated parameters of pillars and stopes for open stoping ensure operating stoping in areas of steeply dipping or inclined ore bodies. Application of 3D mathematical modeling to geological and geomechanical conditions of an operating mine greatly expands the range of approaches and knowledge in complicated problem solving, which proves reliability and correctness of the results obtained for specific nonrecurring geotechnical situations.

Evaluation of an antibacterial orthodontic adhesive incorporated with niobium-based bioglass: an in situ study

This in situ study aimed to evaluate the antibacterial and anti-demineralization effects of an experimental orthodontic adhesive containing triazine and niobium phosphate bioglass (TAT) around brackets bonded to enamel surfaces. Sixteen volunteers were selected to use intra-oral devices with six metallic brackets bonded to enamel blocks. The experimental orthodontic adhesives were composed by 75% BisGMA and 25% TEGDMA containing 0% TAT and 20% TAT. Transbond XT adhesive (TXT) was used as a control group. Ten volunteers, mean age of 29 years, were included in the study. The six blocks of each volunteer were detached from the appliance after 7 and 14 days to evaluate mineral loss and bacterial growth including total bacteria, total Streptococci, Streptococci mutans, and Lactobacilli. Statistical analysis was performed using GLM model - univariate analysis of variance for microhardness and 2-way ANOVA for bacterial growth (p<0.05). The 20% TAT adhesive caused no difference between distances from bracket and the sound zone at 10-µm deep after 7 and 14 days. After 14 days, higher mineral loss was shown around brackets at 10- to 30-µm deep for TXT and 0% TAT adhesives compared to 20% TAT. S. mutans growth was inhibited by 20% TAT adhesive at 14 days. Adhesive with 20% TAT showed lower S. mutans and total Streptococci growth than 0% TAT and TXT adhesives. The findings of this study show that the adhesive incorporated by triazine and niobium phosphate bioglass had an anti-demineralization effect while inhibiting S. mutans and total Streptococci growth. The use of this product may inhibit mineral loss of enamel, preventing the formation of white spot lesions.

A PhD completed 5. Restoration survival in the composite resin age

The article describes studies aimed at investigating factors that can influence composite restoration survival in posterior teeth, focusing on the main reasons for failure of direct restorations - fracture and secondary-caries. Since direct composite resin restaurations seem to be more prone to secondary caries when compared to amalgam, one study was performed to evaluate the influence of materials on secondary caries lesion formation in situ. Also, in most clinical studies evaluating restoration survival, there is a tendency to focus on materials factors. Two retrospective clinical investigations, a meta-analysis with primary data of clinical studies and a systematic review were performed to assess the influence of patient-, materials-, and tooth-related variables in posterior composite restoration survival. Composite resins were not related with higher mineral loss when compared to amalgam. Tooth type, number of restored surfaces and patient-related factors like a high caries risk and occlusal wear were consistently found to influence composite resin restoration survival in posterior teeth, whereas materials factors were not consistently implicated with the survivalrate.

Secondary Caries Development in in situ Gaps next to Composite and Amalgam

This in situ study investigated the secondary caries development in dentin in gaps next to composite and amalgam. For 21 days, 14 volunteers wore a modified occlusal splint containing human dentin samples with an average gap of 215 µm (SD = 55 µm) restored with three different materials: Filtek Supreme composite, Clearfil AP-X composite and Tytin amalgam. Eight times a day, the splint with samples was dipped in a 20% sucrose solution for 10 min. Before and after caries development, specimens were imaged with transversal wavelength independent microradiography, and lesion depth (LD) and mineral loss (ML) were calculated. The LD and ML of the three restoration materials were compared within patients using paired t tests (α = 5%). In total 38 composite samples (Filtek n = 19 and AP-X n = 19) and 19 amalgam samples could be used for data analysis. AP-X composite presented the highest mean values of LD and ML of the three restorative materials. Amalgam showed statistically significantly less ML (Δ = 452 µm × vol%) than the combined composite materials (p = 0.036). When comparing amalgam to the separate composite materials, only AP-X composite showed higher ML (Δ = 515 µm × vol%) than amalgam (p = 0.034). Analysis of LD showed the same trends, but these were not statistically significant. In conclusion, amalgam showed reduced secondary caries progression in dentin in gaps compared to composite materials tested in this in situ model.

Contact with Fluoride‐Releasing Restorative Materials Can Arrest Simulated Approximal Caries Lesion

Previous studies have suggested that the presence of white‐spot lesion is very probable when adjacent surface is affected by cavitated lesions. This study evaluated the potential of different fluoride‐releasing restorative materials in arresting enamel white‐spot lesions in approximal surface in contact with them, in vitro (I) and in situ (II). White‐spot lesions were formed in 240 primary enamel specimens via pH‐cycling. They were put in contact with cylindrical blocks of 6 materials (n = 20): composite resin, 2 high‐viscous glass ionomer cements (HVGIC), resin‐modified GIC, resin‐modified nanoionomer, and polyacid‐modified resin. In both studies I and II, these settings were designed to simulate the contact point between the restoration and simulated approximal lesion. For study I, they were subjected to a new pH‐cycling cariogenic challenge for 7 or 14 days (n = 10). For study II, a randomized double‐blind in situ design was conducted in two phases (7/14 days) to promote cariogenic challenge. At the end of both studies, specimens were collected for mineral analysis by cross‐sectional microhardness. Higher mineral loss was observed for lesions in contact with resin (p &lt; 0.001). HVGICs were the most efficient in preventing mineral loss, whereas other materials presented an intermediate behavior. It is concluded that fluoride‐releasing materials can moderately reduce white‐spot lesions progression, and HVGIC can arrest enamel lesion in approximal surface in contact with them.

Mineral distribution and CLSM analysis of secondary caries inhibition by fluoride/MDPB-containing adhesive system after cariogenic challenges

Objective To evaluate the inhibition zone formation (IZ) and mineral distribution along the interface of adhesive systems either containing fluoride and antibacterial primer or not, after chemical and biological artificial caries challenges. Methods Forty-eight third molars were used. Artificial caries was developed with S. mutans in a 4 mm × 4 mm area of occlusal dentin surface. Carious dentin was removed and cavities were restored with Adper Scotchbond Multi-Purpose (SBM) and Clearfil Protect Bond (CPB) ( n = 24). Samples were submitted to secondary caries development by chemical (C) (acidic gel) or biological (B) ( S. mutans culture) methods for 5 days. Four groups were tested ( n = 12): (1) SC (SBM + C); (2) SB (SBM + B); (3) CC (CPB + C); (4) CB (CPB + B). The IZ and outer lesion (OL) formations were analyzed by confocal laser scanning microscopy (CLSM). The distribution of calcium (Ca) and phosphorus (P) content along the interface was analyzed by micro X-ray fluorescence spectrometer by energy-dispersive (μEDX). Results The frequency of IZ formation and mean values of IZ thickness differed among the groups. The CC group presented the lowest OL depth. μEDX analysis showed that CPB had the highest mineral loss by the biological method, but the lowest mineral loss by the chemical method. SC and SB groups showed intermediate values of mineral loss. Conclusion The mineral loss along the dentin/restoration interface was affected by the artificial caries method, and hybrid layer formation by adhesive systems used. The adhesive system containing fluoride and antibacterial primer did not prevent secondary caries formation.

Dye-enhanced laser fluorescence detection of caries lesions around brackets

The aim was to evaluate the performance of DIAGNOdent [laser fluorescence(LF) and LFpen] devices enhanced by fluorescent dye in detecting mineral loss around brackets and comparing the inhibitory effect of bonding material on artificial demineralization, and to verify whether LF methods show the same trends of mineral loss. Brackets were bonded to premolar halves with Fuji Ortho LC, Transbond XT, and Ortho Glass LC cements (n = 15). The teeth were soaked in demineralizing solution (pH = 4.8) for 16 days. Mineral loss was calculated by atomic emission spectrometry, and lesions were measured with LF devices with dye [tetrakis N-methylpyridyl porphyrin (TMPyP)]. Groups were compared with regard to LF readings and mineral loss, and performance of caries detection was calculated. Higher mineral loss and LF-TMPyP values occurred in the resin group. LFpen-TMPyP readings were significantly higher in the demineralized groups. Correlation was observed between mineral loss and LF measurements. LF methods are capable of identifying lower demineralization around brackets bonded with resin-modified glass ionomer cements.

Inhibition of mineral loss at the enamel/sealant interface of fissures sealed with fluoride- and non-fluoride containing dental materials in vitro

Objective. In this in vitro study we evaluated the enamel mineral loss effect of fluoride-containing and non-fluoride-containing materials at different distances from the sealant margin, and verified the fluoride-releasing capability of these materials. Material and methods. Extracted molars were randomly assigned into nine groups (n=12): Concise (C), FluroShield (F), Helioseal Clear Chroma (H), Vitremer (V), Fuji II-LC (FII), Ketac Molar (KM), Fuji IX (FIX), Single Bond (SB), and Clearfil Protect Bond (CF). All groups were subjected to thermo and pH cycling. Enamel mineral loss was evaluated by cross-section micro-hardness analysis at distances: −100 µm, 0 µm, 100 µm, 200 µm. The mineral loss data were analyzed using a multi-factor ANOVA with split-plot design, and fluoride-released data were submitted to ANOVA and Tukey tests. Results. FIX demonstrated a lower mineral loss than C, F, and H, but did not differ from the SB, CF, V, FII, and KM groups, which also demonstrated no difference among them. C, F, H, and V presented the highest mineral loss, with no difference among them. V did not differ from the other groups (p>0.05). Regarding the different distances from the sealant margin, −100 µm presented the lowest mineral loss. FIX showed the highest fluoride release on the 7th and 14th days of evaluation, while CF showed high fluoride release only on the 7th day. Conclusion. Resin sealant did not prevent enamel mineral loss, contrary to glass-ionomer cement, which showed the highest capacity for fluoride release. It is not exclusively the presence of fluoride in a material's composition that indicates its capability to interfere with the development of enamel caries-like lesions.

Microflora associated with experimental root surface caries in humans

This study describes the microflora from actively progressing root surface caries lesions, in which mineral loss had been determined by quantitative microradiography. The caries lesions were produced experimentally in root surface specimens from human molars inserted in lower partial dentures carried for 3 months by six elderly individuals. A total of 780 bacterial isolates were identified from 13 plaque samples, collected with a punch technique, and six dentin samples. The composition of the microflora showed distinct individual differences. The microflora from plaque samples associated with the highest mineral loss was dominated by either Actinomyces viscosus or a combination of mutans streptococci (serotypes c, d, and f) and Lactobacillus species (L. casei and L. brevis). Plaque from root surfaces with less pronounced mineral loss harbored a more complex microflora comprising gram-positive rods, mutans streptococci, Streptococcus mitis biovar 1, Veillonella spp., gram-negative rods, and low numbers of lactobacilli. In the latter samples, individual variations in the proportions of mutans streptococci (serotypes c, d, and g), Actinomyces species (A. viscosus and A. naeslundii), and Veillonella parvula biotypes were observed. These findings suggest that certain species or combinations of species are more cariogenic than others and that dominance of single acidogenic species in particular is conducive to high caries activity.