Use of micro-computed tomography and scanning electron microscopy with energy-dispersive spectroscopy to distinguish natural white spot enamel lesions from sound enamel in human premolars.

PURPOSE: The aim of the present study was to develop a novel method for distinguishing white spot lesions (WSLs) from sound enamel in human premolars using micro-computed tomography (micro-CT) and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), and to examine differences in surface morphology, chemical composition, and mineral density (MD) between these two areas. METHODS: Fourteen premolars with natural WSLs on the enamel surface of the crowns were examined. After sectioning the teeth, each specimen containing WSLs adjacent to intact enamel was examined for MD, surface morphology, and atomic percentages (At%) of chemical components using micro-CT and SEM/EDS, respectively. Differences between these areas of the same specimen were analyzed statistically using paired t-test. RESULTS: SEM images highlighted increased roughness and irregularity in the lesion area. EDS analysis revealed significant reductions in calcium (Ca), phosphorus (P), fluorine (F), chlorine (Cl), and sodium (Na) levels at the lesion surface in comparison to intact enamel (P < 0.05). The decreases in the MD of the lesions were statistically significant in comparison to sound enamel (P < 0.05). CONCLUSION: These findings provide standard measurements for evaluating the essential characteristics of WSLs and intact enamel, being vital for assessment of treatment outcomes and development of innovative biomaterials for management of hypo-mineralized enamel lesions.

Iontophoresis effects of two-step self-etch and total-etch systems on dentin permeability and sealing of composite restoration under simulated pulpal pressure.

BACKGROUND: Studies demonstrated the bond strength enhancement and the decrease in degradation of the adhesive interface after applying either self-etch adhesives or two-step, etch-and-rinse adhesives under an electric field. However, the presence of dentinal fluid driven by the pulpal pressure in vivo is a profounding factor affecting both the sealing ability and bond strength of adhesives. This study aimed to evaluate the effect of three-step etch-and-rinse and two-step self-etch adhesives when applied with iontophoresis under simulated pulpal pressure on the permeability of dentin, resin infiltration, and the sealing ability of resin composite. METHODS: The experiments were done on 32 recently extracted premolars, randomly assigned into four groups (n = 8) according to two adhesive systems (SBMP and SE), applied following the manufacturer's instructions (control) for two groups or with iontophoresis for the others (SBMPi and SEi). For the iontophoresis, the anodal current was applied at 75 µA for 20 s through the cavity electrode during the bond. The fluid flow rate of dentin was recorded after cavity preparation (smear-layer-covered dentin; T1), bonding (T2), and composite restoration (T3) during the maintained pulpal pressure of 20 mm Hg. The flow rates were expressed as a percentage relative to the initial smear-layer-covered value for each specimen. Results were analyzed using repeated measures ANOVA. Scanning electron microscopy (SEM) was performed to observe the resin/dentin interface. RESULTS: There were no significant increases in the mean flow rates from T1 to T3 in the SBMP (P = 0.355), while these changes in the SE were significant between T1 (100%) and T2 (166.77%) and T1 and T3 (221.16%) (P = 0.002; one-way RM ANOVA; Holm-Sidak test). For the iontophoresis groups, the mean flow rates decreased significantly from T1 to T2 and T1 to T3 of both SBMPi (T2 = 86.43, and T3 = 79.53; P < 0.001) and SEi groups (T2 = 87.96, and T3 = 81.48; P = 0.004). The iontophoresis of both adhesives produced the optimal resin infiltration with improved quality of the hybrid layer and resin tags. CONCLUSIONS: SBMP bonded with or without iontophoresis performed better sealing ability than SE under the same condition. Both adhesives applied with anodal iontophoresis significantly decreased the dentin permeability, contributing to the improved resin infiltration.

Time-course of the effect of potassium oxalate in the treatment of hypersensitive dentine in man.

OBJECTIVE: Investigate the cause of hypersensitive dentine (HD) by recording the time course of changes in dentine sensitivity, sensory threshold to electrical stimulation (ET) and pulpal blood flow (PBF) following tubular occlusion using in vitro and clinical experiments. DESIGN: Nineteen teeth with HD and 13 with normal dentine from 8 participants were evaluated, and the intensity of any pain produced by various stimuli was recorded at different times after oxalate treatment. The participants used a visual-analogue scale (VAS) to indicate the intensity of any pain. The ET and PBF were recorded at the same times. RESULTS: Preliminary in vitro experiments showed that oxalate treatment had no effect on the method used to record PBF, and blocked the treated tubules immediately after application. Considering teeth with HD, a decrease in the median VAS evoked by all forms of stimulation was observed at all post-treatment times, except immediately after treatment (p < 0.05), while the treatment produced no significant effect in teeth with normal dentine. No significant changes in ET or PBF was observed in any of the groups. CONCLUSIONS: The effect of oxalate in relieving the symptoms of HD is not only due to a reduction in the intensity of stimulation of sensory receptors sensitive to fluid flow in the dentinal tubules, but also to a reduce in the sensitivity of the receptors that respond to dentine stimulation. There was no evidence that acute pulpitis or central sensitization to pain, which would be associated with changes in PBF or ET, contributes to HD.

Effect of the pulpal hydrostatic pressure on the morphological data of the fluid droplets emerging from dental enamel in human teeth.

Enamel fluid in human teeth plays an important role in the permeability and mechanical property of the enamel. It can be invetigated as fluid droplets at the enamel surface by using the replica technique. The experiments were done on 17 premolars of 10 subjects (aged 10-25 yrs) to be extracted during orthodontic treatment. Teeth were divided into 2 groups. In the first group (n = 11), the fluid accumulated on the mid buccal of the enamel surface was recorded with the impression material both in vivo and in vitro. In vitro replicas were obtained when the pressure in the pulp cavity held at 0, 20, 100, and 200 mmHg above atmospheric. They were examined by a scanning electron microscope. For the other group (n = 10), each tooth was prepared for fluid flow measurement during which the same set of pulpal pressures was applied as mentioned in the other study [1]. However, four teeth of 3 subjects were arranged for the recording of fluid conductance, while the replica impression at the mid buccal surface was also taken simultaneously under each of the applied pulpal pressure. This dataset describes subjects' baseline characteristics, including their corresponding records of the droplets' observations both in vivo and in vitro. Also, data of in vitro fluid flow measurements were detailed according to the applied pulpal pressure. The patterns of changes of the fluid flow rates and the droplets' numbers provided in this dataset can be used to validate tests of agents affecting the structure and permeability of the enamel.

In vivo and in vitro study of enamel fluid flow in human premolars.

OBJECTIVE: To investigate fluid flow through enamel in intact human premolars in vivo and in vitro by using the replica technique. DESIGN: The experiments were done on 17 premolars of 10 subjects (aged 10-25 yrs) to be extracted during orthodontic treatment. Teeth were divided into 2 groups. In the first group (n = 11), the fluid accumulated on the enamel surface was recorded with the impression material in the mid-buccal enamel both in vivo and in vitro. In vitro replicas were obtained when the pressure in the pulp cavity held at 0, +20, +100, and +200 mmHg. They were examined by a scanning electron microscope (SEM). For the second group (n = 10), each tooth was prepared for fluid flow measurement during which the pulpal pressures of +20, +100, +200, and +300 mmHg were applied. RESULTS: The mean number of droplets presented after the pressure had been raised to 200 mmHg is significantly greater than those observed at lower pressures, including those obtained from the same tooth in vivo. A significant linear relationship between these numbers and the pulpal pressures was found (p < 0.001). In vitro fluid conductance through the crown also increased significantly with increased pressure (p < 0.001). CONCLUSION: SEM evaluation of droplets distribution on enamel surface revealed that the presence of fluid transudation forced by pulpal pressure may influence the accumulation of enamel fluid on the tooth surface in vitro, similar to those observed in vivo.

Effect of dentinal fluid on enamel permeability under simulated pulpal pressure.

OBJECTIVE: To determine the effect of pulpal perfusion on the fluid flow through human tooth after different treatments at the enamel surface. Changes in mineral density along with fluid flow rate were also analyzed before and after etching. DESIGN: The experiments were carried out on 97 human premolars. Ringer's solution and distilled water (DW) were applied under pressure of 20 mm Hg to the pulpal cavity of tooth crowns in the Ringer's-perfused and water-perfused groups respectively. Fluid flow through each specimen was recorded before and 0, 30, 60, 180 min after treatments at the enamel surface. The treatments included DW, 0.2% sodium fluoride solution, 1.23% acidulated phosphate fluoride gel (APF), 2.26% fluoride varnish (FV), 37% phosphoric acid gel (Etch) and artificial saliva (AS). Mineral density of the enamel was evaluated using micro-computed tomography. RESULTS: In water-perfused group, fluid flow rates recorded after etching were significantly increased (p = 0.005) with the significant reduction of mineral density (p = 0.018) from baseline. A significant negative correlation was found (r = -0.78, p = 0.015). After FV, the percentage reduction from baseline was significant at 180 min (p = 0.003). In Ringer's-perfused group, etching immediately produced the greatest mean flow rate and subsequently returned to the baseline within 60 min after treatment (p < 0.001). There were approximately 40, 55, and 63% reductions of flow rates within 60 min after AS, APF and FV respectively. CONCLUSION: Under simulated pulpal pressure, enamel fluid involves the process of enamel remineralization, particularly after etching.

Effect of cavity depth on dentine sensitivity in man.

OBJECTIVE: To determine if dentine at the enamel-dentine junction (EDJ) in man is more sensitive to hydrostatic pressure stimuli then deeper dentine. DESIGN: Cavities (1mm diam.) were cut at the tips of the buccal and lingual cusps of 8 premolars in 3 subjects (ages: 22-25 years). Both cavities were initially deepened to expose the EDJ then one (the test cavity) was deepened in steps of 0.5mm to a maximum of 2.0 mm below the EDJ. The cavities were tested at each stage, before and after etching, with 5s, hydrostatic pressure stimuli between 400 mm above, and 400 mm below atmospheric. The intensity of any pain produced was recorded on a VAS scale and electrodes were placed in both cavities in an attempt to monitor any action potentials evoked in intradental nerves. RESULTS: In all the teeth, the intensity of the pain produced by a stimulus tended to increase as the cavity was deepened, as did the number of action potentials recorded (in 6 of the 8 teeth). The responses were greater from etched than unetched dentine, and negative pressures evoked greater responses than the corresponding positive pressures. CONCLUSION: There was no evidence that dentine close to the EDJ was more sensitive to hydrostatic pressure stimuli than deeper dentine. It may however be more sensitive to mechanical stimuli as it is more compliant.

Effects of bleaching on laser Doppler blood-flow signals recorded from human teeth in vitro.

OBJECTIVE: To determine if bleaching a tooth affects significantly laser Doppler recordings of pulpal blood flow that are made through the treated enamel and dentine. DESIGN: Recordings of blood flow (flux) were made with a laser-Doppler flow meter from the crowns of 14, recently extracted, human premolars while diluted blood was pumped at three different rates through a cannula that was inserted into the pulp cavity with its tip in the coronal pulp chamber. The recordings of flux were made before and after bleaching the crown with 38% hydrogen peroxide for 30min. The colour changes produced by bleaching were also measured with a digital spectrophotometer in 15 teeth. The effects of bleaching on both blood flow recordings and tooth colour were studied in 11 of the teeth. RESULTS: Both before and after bleaching, there was a linear relationship between blood perfusion rate and flux. After bleaching, the flux readings increased by an average of 46%, and were significantly increased in every tooth (P<0.001, Wilcoxon Signed Rank Test). There was no significant correlation between the changes in flux and the changes in tooth colour. CONCLUSION: A laser Doppler flow meter cannot be used to determine the effect of bleaching on pulpal blood flow in intact teeth.

Effect of different osmotic stimuli on fluid flow before and after self-etching adhesive application.

PURPOSE: To determine the in vitro dentinal fluid movement produced by various osmotic stimuli, and evaluate fluid movement across human dentin in response to the application of various osmotic stimuli before and after the application of self-etching adhesive (Clearfil S3 Bond). MATERIALS AND METHODS: The experiments were carried out on 10 extracted premolars. Each tooth was cut transversely below to the cementoenamel junction with a diamond disk and water coolant. Dentin was exposed at the tip of the buccal cusp by cutting a cavity and was etched with acid. The osmotic stimuli were solutions of saturated CaCl2, sugar syrup, chocolate, and sweet Thai dessert, used as osmotic test solutions, randomly applied to dentin.The fluid flow through dentin obtained after 15 s of application of each osmotic stimulus was measured before and after bonding with Clearfil S3 Bond single-dose. RESULTS: Before bonding procedures, CaCl2 produced peak rates of fluid flow that were significantly higher (p <0.001), when compared with normal saline, sugar syrup, chocolate, and sweet Thai dessert. During the applications of all osmotic stimuli, the amount of fluid movement across resin-bonded dentin was significantly lower than that without adhesives. There were no significant differences of fluid shifts across resin-bonded dentin obtained during the application of any osmotic stimuli. CONCLUSION: It appears that different osmotic stimuli produced different rates of outward fluid flow through dentin. Clearfil S3 Bond produced similar significant reductions of fluid movement in response to osmotic stimulation, irrespective of the chemical composition, or the osmotic pressure of stimuli.

Effects of potassium ions on dentine sensitivity in man.

OBJECTIVE: To determine the effect of applying 500 mmol/l KCl at a pressure of 150 mm Hg above atmospheric to exposed dentine on pain sensation evoked by probing and air blast stimuli in human subjects. DESIGN: The experiments were carried out on 14 pairs of premolars in 14 human subjects (aged 17-30 years). Dentine was exposed at the tip of the buccal cusp, etched with acid and covered with saline, then 500 mmol/l KCl in Ringer's was applied at a pressure of 150 mm Hg for 4 min. Mechanical probing and air-drying stimuli were performed before and 2, 10, 20, 30 min after applying the KCl solution. The subject indicated the intensity of any pain produced on a visual analogue scale (VAS). Pulpal blood flow was recorded with a laser Doppler flow meter. Exactly the same procedure was carried out on the contralateral tooth except that 500 mmol/l NaCl in Ringer's was used in place of the KCl solution. RESULTS: The pain responses to mechanical probing and air blast stimuli were significantly reduced during the first 10 min after applying the KCl but not the NaCl solution. Pulpal blood flow did not change significantly after either treatment. CONCLUSION: Potassium ions, when applied to exposed dentine at a pressure of 150 mm Hg above atmospheric, produced temporary block of impulse conduction in sensory nerve endings in the dentine or pulp.