Effects of fluoride treatment on phosphoric acid-etching in primary teeth: an AFM observation

Effects of topical fluoride treatment on the bond strength of pit and fissure sealants: A systematic review

Background

This systematic review aimed to evaluate the available scientific evidence concerning the effects of topical fluoride treatment on the bond strength of pit and fissure sealants. Prevention of dental caries is one of the crucial issues in pediatric dentistry. Pit and fissure sealant and fluoride therapies are two caries prevention procedures that may be performed in one session. However, fluoride therapy may affect the bond strength of pit and fissure sealants.

Methods

An electronic search for in vitro studies published in English and Persian on topical fluoride therapy and the bond strength of pit and fissure sealants was performed via PubMed/ Medline, Web of Science, Google Scholar, Embase, and Scopus databases until May 2022. The articles were independently reviewed for quality by two reviewers. Textual data were analyzed manually, and the bond strength of sealants placed after fluoride application was compared with control groups.

Results

A total of 8482 articles were initially identified and reviewed by two independent reviewers, and 13 were selected for full-text evaluation. Finally, six articles were included in the systematic review. A total of 250 teeth were studied, 148 of which were in the case group (fluoride group) and 102 in the control group. Tensile and shear bond strengths were compared between groups in the studies.

Conclusion

In the studies in which the tooth surfaces were washed after applying fluoride, there was no change in the fissure sealant bond strength. However, in studies in which fluoride was not washed, the bond strength decreased significantly, independent of the fluoride type.

Review: Advanced Atomic Force Microscopy Modes for Biomedical Research

Visualization of biomedical samples in their native environments at the microscopic scale is crucial for studying fundamental principles and discovering biomedical systems with complex interaction. The study of dynamic biological processes requires a microscope system with multiple modalities, high spatial/temporal resolution, large imaging ranges, versatile imaging environments and ideally in-situ manipulation capabilities. Recent development of new Atomic Force Microscopy (AFM) capabilities has made it such a powerful tool for biological and biomedical research. This review introduces novel AFM functionalities including high-speed imaging for dynamic process visualization, mechanobiology with force spectroscopy, molecular species characterization, and AFM nano-manipulation. These capabilities enable many new possibilities for novel scientific research and allow scientists to observe and explore processes at the nanoscale like never before. Selected application examples from recent studies are provided to demonstrate the effectiveness of these AFM techniques.

Applying Pb2+ to probe the dissolution of carbonated hydroxylapatite by Enterobacter sp.: A new insight into the bioerosion of tooth mineral

Dental caries is one of the most common disorders in dentistry. Typically, it is caused by the dissolution of the tooth mineral due to cariogenic organisms. Bioapatite is vulnerable to acid-etching ascribed to a variety of substitutions. This study applied Pb²⁺ cations to probe the dissolution of synthetic carbonated hydroxylapatite (CHAp) in the acidic environment induced by Enterobacter sp. It indicated a decreasing tendency of crystallite size (from ∼400 nm to 10-20 nm) during gradual incorporation of carbonate (from 2.5 to 13.8 wt %). Meanwhile, the shape of CHAp crystals was transformed from elongated to plate-like. Addition of Enterobacter sp. enhanced P release from CHAp (especially for the CHAp with ∼8 wt % CO₃ ) around 10 times. Moreover, the bacterium provided a moderately acidic environment to cause more formation of stable pyromorphite over other Pb-minerals, for example, Pb₃ (PO₄ )₂ , and PbCO₃ . Then, transmission electron microscopy-energy dispersive X-Ray spectroscopy mapping successfully confirmed the Pb labeling on the newly formed phosphate mineral as Pb (with high-atomic weight) has strong signal under electron microscopy. This study therefore elucidated that Pb labeling has a bright future to explore the degradation of tooth mineral by microorganisms, as well as to evaluate the resistance of calcium phosphate dental restorative materials.

Effect of Fluoride Treatment on the Acid Resistance of Hydroxyapatite

The etching behavior of polycrystalline synthetic hydroxyapatite samples has been evaluated to explore the protective impact of fluoride on a tooth-like model system. Etching rates before and after fluoridation with a NaF solution at pH 6 were determined by atomic force microscopy. Despite a very low F concentration of ca. 0.2 atom % in the hydroxyapatite surface, a very strong effect on the acid resistance can be observed. Depending on the crystal orientation, etching in a NaAc buffer at pH 4.5 was completely inhibited for at least 5 min. The major part of the surface withstood etching even for more than 23 min. These results give new insights into how the amount of incorporated fluoride in hydroxyapatite correlates with its protective impact.

Enamel sample preparation for AFM: Influence on roughness and morphology

Human dental enamel is organized by prisms that are structured between 3 and 6 µm in diameter. Determining the relationships between different treatments on the surface of enamel using ultrastructural analysis is the purpose of many in vitro experiments. Different sample pretreatments have been reported in the literature. Grinding and polishing are common procedures for enamel preparation. They provide a flat and standardized surface, which is imperative for the use of some techniques such as ATR-FTIR. However, for morphological analysis, SEM and AFM represent easier methods to measure and reduce the biological sample variation. Therefore, the objective of this study was to establish how different forms of enamel preparation can influence the advent of artifacts during ultrastructural observation, especially by AFM analysis. Four groups (n = 10) were tested: (a) without preparation; (b) polishing with a diamond paste; (c) grinding with decreasing granulations of silicon carbide papers; (d) grinding with polishing. Images were obtained using the Peak-Force Tapping mode. After the first images were obtained, all fragments were acid etched with 37% phosphoric acid for 30 seconds, rinsed for 60 seconds, and dried intensively. Upon grinding and polishing, the exposure of the inner enamel surfaces provided a less mineralized layer that was marked by scratches and a higher susceptibility to treatments. Moreover, using native enamel provided more valuable information on the surface and the roughness changes for clinical applications. In addition, phosphoric acid is an option for observing the prismatic arrangement after grinding and/or polishing changes the morphology. RESEARCH HIGHLIGHTS: The use of native enamel samples to investigate the effects of different treatments on surface should be preferred in research, when the technique allows it.

Effect of Fluoride and Simplified Adhesive Systems on the Bond Strength of Primary Molars and Incisors

The aim of this study was evaluate in vitro the influence of simplified adhesive systems (etch-and-rinse and self-etching) and 1.23% acidulated phosphate fluoride (APF) on the microshear bond strength (μ-SBS) of composite resins on primary molars and incisors. Forty primary molars and forty incisors vestibular enamel was treated with either the self-etching Clearfil SE Bond (CSE, Kuraray) or etch-and-rinse Adper Single Bond 2 (SB2, 3M/ESPE) adhesive system. Each group was subdivided based on the prior treatment of the enamel with or without the topical application of 1.23% APF. Thereafter, matrices were positioned and filled with composite resin and light cured. After storage in distilled water at 37 ± 1°C for 24 h, the specimens were submitted to μ-SBS in a universal testing machine. Kruskal-Wallis and Mann-Whitney tests (p < 0.05) showed that the prior application of 1.23% APF led to a significant reduction in bond strength. The type of adhesive exerted no significant influence bond strength. In the inter-group analysis, however, significantly bond strength reduction was found for the incisors when CSE was employed with APF. Adhesive failure was the most common type of fracture. The bond strength was affected by the prior application of 1.23% APF and type of tooth.

The effects of acid etching time on surface mechanical properties of dental hard tissues

The objective of this study was to evaluate the effect of etching time on the surface properties of dental hard tissues including enamel and dentin. For this purpose, samples were prepared using extracted human teeth and treated with 37% phosphoric acid for various length of time using the set protocol. The effects of etching time on surface roughness were assessed using non-contact surface roughness profilometer and surface hardness was measured using nanoindentation technique. All results were analyzed statistically using SPSS computer software. Within the limitation of this study, it was concluded that etching time influences on the surface properties of dental hard tissues particularly the enamel. Enamel surface properties such as roughness and hardness can be altered remarkable as a matter of few seconds. Prolonged etching time than recommended is likely to increase the surface roughness and decrease surface hardness; compromising the bond strength of adhesive materials in clinical applications.

Potential effects of tooth-brushing on human dentin wear following exposure to acidic soft drinks

This study used scanning electron microscopy and atomic force microscopy to examine the short-term potential effects of brushing time and the start-time of tooth-brushing after demineralization on primary dentin wear in vitro. Thirty-six noncarious primary central incisors were assigned to 12 experimental groups. Exposure to cola drinks was used to initiate the demineralization process. Three brushing times (5, 15 and 30 s) and four start-times of brushing (0, 30, 60 and 120 min) after an erosive attack were used for the abrasion process. Tooth-brushing the softened dentin surface led to increases in the open tubular fraction and microstructural changes on the dentin surface. Brushing immediately after exposure to cola resulted in the greatest irreversible dentin loss, whereas brushing 60 or 120 min after pretreatment resulted in the least irreversible dentin loss. However, brushing time had no effect on the irreversible loss of dentin wear. Based on these experimental results, tooth-brushing should be performed at least 60 min after consuming a cola drink to achieve the desired tooth cleaning and avoid the introduction of surface lesions on dentin.

Effects of extracorporeal shockwave therapy on nanostructural and biomechanical responses in the collagenase-induced Achilles tendinitis animal model

The aim of this study was to quantitatively investigate the effects of extracorporeal shockwave therapy (ESWT) on the nanostructure and adhesion force of collagen fibrils in a rat model of collagenase-induced Achilles tendinitis (CIAT) using histology and atomic force microscopy. A total of 45 rats were divided into experimental groups of three rats each: a control group, 27 CIAT rats with nine time points, and 15 ESWT rats with five time points. Progressive changes in nanostructure including the fibrillary diameter and D-periodicity, and biomechanical properties including the fibrillary adhesion forces in each healing phase were investigated over a 5-week period after collagenase injection. On postoperative day 3, CIAT rats showed granulomatous tissue associated with subacute inflammation, and a deterioration in nanostructure and mechanical properties compared to controls. On postoperative day 12, the ESWT group showed increased vascularity, fibroblastic activity, lymphocyte and plasma cell infiltration, dense histocytes, and disorganization of the fibers compared to the CIAT group. The ESWT group showed and improvement in nanostructure and mechanical properties compared to controls, while the CIAT group showed a deterioration in nanostructure and mechanical properties compared to controls. On postoperative day 26, the ESWT group showed 30% inflamed tissue and 70% fibrotic tissue, while the CIAT group showed chronic inflammation. By the end of the experiments, in both groups the changes had reversed and the tissues were similar in appearance to those in the control group. Following ESWT the deformed and irregular collagen network returned to a well-aligned normal collagen network nanostructure. These results suggest that ESWT may promote the healing response in Achilles tendinitis.

Nanostructural investigation of frontalis sling biomaterial surfaces

This study examined the nanostructural surface of three frontalis sling biomaterials: autogenous fascia lata, preserved fascia lata and silicone rod. The morphological characteristics of the sling biomaterial surfaces were examined qualitatively and quantitatively by scanning electron microscopy and atomic force microscopy, respectively. The autogenous fascia lata showed well-arranged nanostructures of parallel fascia collagen fibrils with clear 67 nm axial periodicity, whereas the preserved fascia lata showed tangled nanostructures of damaged collagen fibril bundles. The silicone rod showed a substantial amount of debris with some scratches and the smoothest roughness compared with the other sling biomaterials, followed by preserved fascia lata. Autogenous fascia lata showed the highest surface roughness. The association between the roughness and cell adhesion suggests that the nanostructure of autogenous fascia lata biomaterials is the best for frontalis sling and that of the silicone rod biomaterials is the worst.

Short-term nanostructural effects of high radiofrequency treatment on the skin tissues of rabbits

The aim of this study is to quantitatively investigate the short-term effects of RF tissue-tightening treatment in in vivo rabbit dermal collagen fibrils. These effects were measured at different energy levels and at varying pass procedures on the nanostructural response level using histology and AFM analysis. Each rabbit was divided into one of seven experimental groups, which included the following: control group, and six RF group according to RF energy (20 W and 40 W) and three RF pass procedures. The progressive changes in the diameter and D-periodicity of rabbit dermal collagen fibrils were investigated in detail over a 7-day post-treatment period. The dermal tissues treated with the RF tissue-tightening device showed more prominent inflammatory responses with inflammatory cell ingrowth compared to the control. This effect showed more prominent with the passage of day after treatment. Although an increase in the diameter and D-periodicity of dermal collagen fibrils was identified immediately after the RF treatment, a decrease in the morphology of dermal collagen fibrils continued until post-operative day 7. Furthermore, RF treatment led to the loss of distinct borders. Increases in RF energy with the same pass procedure, as well as an increase in the number of RF passes, increased the occurrence of irreversible collagen fibril injury. A multiple-pass treatment at low energy rather than a single-pass treatment at high energy showed a large amount of collagen fibrils contraction at the nanostructural level.

Ultrastructural investigation of intact orbital implant surfaces using atomic force microscopy

This study examined the surface nanostructures of three orbital implants: nonporous poly(methyl methacrylate) (PMMA), porous aluminum oxide and porous polyethylene. The morphological characteristics of the orbital implants surfaces were observed by atomic force microscopy (AFM). The AFM topography, phase shift and deflection images of the intact implant samples were obtained. The surface of the nonporous PMMA implant showed severe scratches and debris. The surface of the aluminum oxide implant showed a porous structure with varying densities and sizes. The PMMA implant showed nodule nanostructures, 215.56 ± 52.34 nm in size, and the aluminum oxide implant showed crystal structures, 730.22 ± 341.02 nm in size. The nonporous PMMA implant showed the lowest roughness compared with other implant biomaterials, followed by the porous aluminum oxide implant. The porous polyethylene implant showed the highest roughness and severe surface irregularities. Overall, the surface roughness of orbital implants might be associated with the rate of complications and cell adhesion.

Changes in ultrastructure and properties of bracket slots after orthodontic treatment with bicuspid extraction

This study examined the effects of an orthodontic treatment using a bicuspid extraction on the surface roughness and mechanical properties of stainless steel (SS) brackets adjacent to the extraction space. Four experimental groups were employed; groups 1 and 2 used the Archist(®) SS brackets before and after the extraction treatment, respectively, and groups 3 and 4 used the Victory(®) SS brackets before and after the extraction treatment, respectively. The slot surfaces of the bracket were scanned in air at a resolution of 512 × 512 pixels with a scan speed of 0.8 line/s. The visco-elasticity of the bracket slot was determined from the force-distance curves of atomic force microscopy. The orthodontic treatment with bicuspid extraction led to a significant increase (p<0.0001) in surface roughness in both groups. In particular, the Archist(®) SS brackets showed more changes than the Victory(®) SS brackets (p<0.0005). However, there was no significant difference in properties of the Victory(®) and Archist(®) brackets between before and after treatment. This suggests that the orthodontic treatment with bicuspid extraction is more responsible for the changes in surface roughness than the properties of the brackets.