Effects of etchant on the nanostructure of dentin: an atomic force microscope study

Nanostructure evaluation of healthy and fluorotic dentin by atomic force microscopy before and after phosphoric acid etching

The aim was to characterize by atomic force microscopy (AFM) the nanostructure of human dentin surfaces affected by dental fluorosis (DF) before and after phosphoric acid etching. This study included 240 human dentin samples classified according to the severity of DF, which were divided into four groups using the Thylstrup-Fejerskov Index (TFI). Samples were analyzed by AFM before and after acid etching for 15, 30, and 60 s. The roughness (R(a)) for healthy dentin, and dentin with mild, moderate, and severe fluorosis were 440 nm, 442 nm, 445 nm, and 449 nm, respectively. After 15, 30, and 60 s of acid etching, all healthy and fluorotic dentin samples increased in roughness (p<0.05). The diameter of dentinal tubule orifices (D(t)) in healthy human dentin increased after acid etching for 60 s. We conclude that effective etching times are 15 s for healthy and mild dentin fluorosis, 30-s for moderately fluorosed dentin, and 45-60 s for severe fluorotic dentin.

Scanning acoustic microscopy investigation of frequency-dependent reflectance of acid- etched human dentin using homotopic measurements

Composite restorations in modern restorative dentistry rely on the bond formed in the adhesive-infiltrated acid-etched dentin. The physical characteristics of etched dentin are, therefore, of paramount interest. However, characterization of the acid-etched zone in its natural state is fraught with problems stemming from a variety of sources including its narrow size, the presence of water, heterogeneity, and spatial scale dependency. We have developed a novel homotopic (same location) measurement methodology utilizing scanning acoustic microscopy (SAM). Homotopic measurements with SAM overcome the problems encountered by other characterization/imaging methods. These measurements provide us with acoustic reflectance at the same location of both the pre- and post-etched dentin in its natural state. We have applied this methodology for in vitro measurements on dentin samples. Fourier spectra from acid-etched dentin showed amplitude reduction and shifts of the central frequency that were location dependent. Through calibration, the acoustic reflectance of acid-etched dentin was found to have complex and non-monotonic frequency dependence. These data suggest that acid-etching of dentin results in a near-surface graded layer of varying thickness and property gradations. The measurement methodology described in this paper can be applied to systematically characterize mechanical properties of heterogeneous soft layers and interfaces in biological materials.

Effect of fluoride pretreatment on primary and permanent tooth surfaces by acid-etching

This study observed the effect of fluoride application on a 37% phosphoric acid etching for 20 s of the enamel surfaces of primary and permanent teeth based on a clinical protocol employed in dental hospitals, through atomic force microscopy and scanning electron microscopy. Enamel samples were prepared from 84 exfoliated and noncarious teeth. Primary (groups 1-4) and permanent (groups 5-8) tooth samples were assigned randomly to one of eight groups based on the timing of acid-etching with 37% phosphoric acid after an acidulated phosphate fluoride (APF) treatment. Groups 1 and 5 received no fluoride application. Groups 2-4 and 6-8 were pretreated with fluoride and received acid-etching 2 weeks later (groups 2 and 6), 1 week later (groups 3 and 7), and immediately (groups 4 and 8). The acid-etching process led to a significant increase in roughness (p<0.0001), and the APF treatment led to a decrease in primary and permanent tooth surface roughness (p<0.005). An acid-etching procedure 2 weeks after performing an APF pretreatment might be recommended to obtain the maximum enamel adhesion of a resin composite.

Effects of probe pollutants on morphological and mechanical measurements of muscle and collagen fibers using atomic force microscopy

Because of the interaction between probes and samples, pollutants in buffer solution or in the air would easily bind to probes and make the probe polluted, which might influence the morphological and mechanical measurements with atomic force microscopy. The polluted probes might transfer the pollutants onto the samples and thus change the surface ultrastructure of samples, or collect the deviated feedback signals to make the phantasm images. The former process is irreversible even if a new probe is employed, and the latter one is a reversible process as long as changing the used/polluted probe. Effects of polluted probes on morphological and mechanical characteristics of insect flight muscle and rat tail tendon collagen I fibers had been discussed in this study, in which, we constructed a series of methods to avoid/reduce the collecting of phantasm images and deviated mechanical information, such as changing the scanning direction and scanning force, replacing the new probes, or cleaning the polluted probes.

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

The aim of this study was to examine the effect of fluoride application on 37% phosphoric acid-etching by atomic force microscopy (AFM) in primary tooth samples based on a clinical protocol used in a pediatric dental hospital. Enamel samples were prepared from 36 exfoliated and non-carious primary teeth. Primary tooth samples were randomly assigned to one of the four groups based on the timing of acid-etching with 37% phosphoric acid after an acidulated phosphate fluoride (APF) pre-treatment. Group 1 received no fluoride application, Group 2 was pre-treated with fluoride and then received acid-etching 2 weeks later. One week separated the fluoride treatment and the acid-etching in Group 3, while Group 4 received acid-etching immediately after the fluoride treatment. The vestibular enamel surfaces of each primary tooth sample were scanned in air at a resolution of 512 x 512 pixels and a scan speed of 0.8 line/s. On the enamel surfaces of the primary teeth after APF pre-treatment, debris were observed although the teeth were smoother than they were prior to APF. As a result, it was concluded that APF treatment is responsible for decreased primary tooth surface roughness. The enamel surfaces etched for 20s showed that acid-etching was effective not only in removing scratches and debris, but also for evaluating enamel rod characteristics. Primary tooth enamel surfaces after etching showed minute structures caused by the decreased hydroxyapatite nanoparticle space, compared to those before etching. Also, acid-etching showed significantly increased roughness effects (p<0.0001, n=9). Finally, as more time elapsed after APF pre-treatment, the roughness was decreased to a lesser degree (p=0.005, n=9). We suggest that primary teeth etching 2 weeks after APF pre-treatment used clinically in pediatric hospitals may be effective to obtain properly etched enamel surfaces.