Chemical and morphological changes in human dentin after Er:YAGlaser irradiation: EDS and SEM analysis

The Effects of a Novel Nanohydroxyapatite Gel and Er: YAG Laser Treatment on Dentin Hypersensitivity

PURPOSE

This study evaluates the effects of a novel nanohydroxyapatite gel and Er: YAG laser on the surface roughness, surface morphology, and elemental content after dentin hypersensitivity treatments.

METHODS

Dentin discs (2 × 3 × 3 mm3) were prepared from 75 human molars. Out of 75 human molars, 50 were used to evaluate surface roughness and randomly divided into five groups: Group ID (intact dentin), Group DD (demineralized dentin), Group BF (fluoride varnish/Bifluorid 10), Group Lsr (Er: YAG laser-50 mJ, 0.50 W, 10 Hz), and Group NHA (nanohydroxyapatite-containing gel). Dentin hypersensitivity was stimulated by 35% phosphoric acid for 1 min (except Group ID). The surface roughness (Ra, μm) was measured via contact profilometry (n = 10). Out of the 75 sound human molars, 25 were used to evaluate the surface morphology and elemental content using scanning electron microscopy and energy-dispersive X-ray spectroscopy (n = 5). The data were statistically analyzed using Welsch ANOVA, Games-Howell, Kruskal-Wallis, and Dunn tests (p < 0.05).

RESULTS

Group Lsr showed significantly lower surface roughness than Group NHA and Group BF (p < 0.05). The SEM analysis indicated that most of the dentinal tubules were obliterated for Group NHA. Precipitant plugs with partially occluded dentinal tubules were observed for Group BF, while partially or completely occluded tubules with a melting appearance were detected for Group Lsr. The EDS analysis revealed that Group NHA and Group Lsr presented similar calcium and phosphorus amounts to Group ID. All dentin hypersensitivity treatment methods could provide promising results in terms of tubular occlusion efficiency. However, laser treatment resulted in smoother surfaces, which could help prevent dental plaque accumulation.

Micromorphology and analysis of dentin surfaces after preparation with Er:YAG laser and application of self-etch adhesive system with 10-MDP. A confocal laser scanning microscope study

AIM

The purpose of this study was to analyze and compare the micromorphology of the hybrid layer and the dentinal surface when the dentin was prepared with an Er:YAG laser or burs, and to find if there was any difference if the time of application of the self-etching primer on the dentin prepared with an Er:YAG laser was doubled.

Optical coherence tomography characterizes the roughness and thickness of the heterogeneous layer on cortical bone surface induced by Er:YAG laser ablation at different moisture contents

Background

As an innovative bone ablation tool, pulsed erbium: yttrium-aluminum-garnet (Er:YAG) laser is being used in clinical practice. It faces the same problems as traditional tools: the water content of bone usually changes with the position, while the amount of water spray in the process of laser irradiation is also uncertain. Real-time monitoring of the effects of laser bone ablation is necessary, but effective tools are still lacking. In this study, we examined the feasibility of rapidly and non-destructively evaluating the surface properties of bone after Er:YAG laser irradiation at different moisture contents by optical coherence tomography (OCT).

Methods

Bone specimens (n=90) collected from pig cortical bone were used in this study. All bone specimens had similar volume and surface characteristics after machining. To display the baseline level before Er:YAG laser ablation, a control group (n=10) without dehydration or Er:YAG laser ablation was examined with OCT, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy. The remaining specimens were randomly divided into four groups (n=20/group) with different moisture content: dried (Group 2 and Group 4) or not dried (Group 1 and Group 3). Pulsed Er:YAG laser (120 mJ/pulse, 20 Hz, 100 µs) was used for perpendicular irradiation with (Group 1 and Group 2) or without (Group 3 and Group 4) water spray. The treated specimens were subjected to SEM, EDX spectroscopy, OCT, and then processed for histological evaluation.

Results

After Er:YAG laser ablation, the melting effect was obvious in the SEM results of the dry groups and non-sprayed groups (Groups 2-4). EDX spectroscopy showed that the content of calcium and phosphorus and their ratios remained unchanged in the undried and with water spray group (Group 1) were the closest to the control group. Three-dimensional (3D) OCT could evaluate the depth and shape of ablation grooves. The roughness of the laser-ablated surface could be visualized by extracting the surface lines from cross-sectional OCT images. The results illustrated that the laser ablation with water spray could achieve a smoother surface. Furthermore, OCT results demonstrated that a layer with high image intensity was generated on the bone surface after laser irradiation. The thickness of these layers showed a correlation with whether or not the laser irradiation was sprayed with water. Histology showed that thin eosin-stained layers were created in all experimental groups, which matched well with OCT results of the layers with high image intensity. No denatured layer was observed in the non-irradiated areas of bone tissues.

Conclusions

OCT could rapidly and non-destructively visualize the bone surface before and after Er:YAG laser ablation at four different moisture contents. The morphology of ablation grooves, as well as the roughness and thickness of the heterogeneous layer on the bone surface, could be characterized quantitatively with good correlation with SEM and histology. This study will promote the development of OCT as an efficient and accurate tool for evaluating laser ablation of bone.

Altered adhesion of dental sealant to tooth enamel microscopically modified by Er:YAG laser irradiation: An in vitro study

Background and Aims

Er:YAG laser has become optional for enamel and dentin preparation for a decade. However, it is unclear if Er:YAG laser is acceptable for enamel conditioning prior to an application of a pit-and-fissure sealant. This in vitro study thus aimed to investigate shear bond strength of a sealant to enamel etched with Er:YAG laser, as well as to demonstrate an alteration of enamel surface after the laser was applied.

Materials and Methods

One hundred and twenty extracted human premolars were divided into 4 groups (N = 30 per group) in which the enamel surfaces were treated with 1) 37% phosphoric acid, 2) Er:YAG laser 80 mJ/pulse, 2 Hz, 3) Er:YAG laser 120 mJ/pulse, 10 Hz, and 4) Er:YAG laser 140 mJ/pulse, 2 Hz. Prior to sealant application. Shear bond strength was determined by using a universal testing machine. Statistical analysis was performed using One-way ANOVA. Modification of enamel surface after laser ablation was also investigated using scanning electron microscope.

Results

Phosphoric acid-etched enamel yielded the highest shear bond strength when bonded with a sealant. Ablation of enamel with Er:YAG laser did not significantly improve sealant bonding since it demonstrated lower shear bond strength, compared to acid-etched enamel. Despite the presence of cracks after Er:YAG laser application, dissolution of enamel substances was limited.

Conclusion

Our study has shown a reduced shear bond strength of dental sealant to an Er:YAG laser-irradiated enamel, compared with phosphoric acid-etched enamel.

Changes in deciduous and permanent dentinal tubules diameter after several conditioning protocols: In vitro study

Innovators conditioning protocols are emerged in permanent dentin, however for deciduous dentin the information is limited; the aim of this study was to evaluate in vitro diameter of deciduous and permanent dentinal tubules after several conditioning protocols. Eighty dentin samples were distributed in sixteen groups (n = 5 p/g) and dentin surface was conditioned as follow: G1D/G1P acid etching; G2D/G2P, self-etch adhesive; G3D/G3P, G4D/G4P, Er: YAG laser irradiation at 200 mJ-25.5 J/cm² and 300 mJ-38.2 J/cm² , at 10 Hz under water spray respectively; G5D/G5P, G6D/G6P, G7D/G7P, and G8D/G8P were irradiated under the same energy densities followed phosphoric acid or self-etch adhesive conditioning. The sample dentin of deciduous and permanent teeth was analyzed with scanning electron microscopy and tubule diameter was evaluated by Image Tools Scandium program. Data were subjected to one-way analysis ANOVA to compare among groups with a level of significance at p ≤ .05. For deciduous dentin, diameters were from 1.52 ± 0.32 µm in G3D to 3.88 ± 0.37 µm in G1D; narrowest and widest diameter, respectively (p < .000). While permanent dentin tubules exhibited diameters from 1.16 ± 0.16/1.19 ± 0.12 µm in G7P/G8P to 2.76 ± 0.28 µm in G6P; narrowest and widest diameter, respectively (p < .000). All dentin conditioning protocols produced more open dentin tubules (diameter size) in deciduous dentin than permanent, specific conditioning protocols are required for each tissue (deciduous or permanent dentin), since same protocol produced stronger effects on primary dentin, which is important for dental clinical success in children and adolescents.

Selective removal of carious lesion with Er:YAG laser followed by dentin biomodification with chitosan

The aim of this study was to evaluate the effect of Er:YAG laser for selective removal of carious lesion, followed by biomodification with chitosan gel where the subsurface microhardness, chemical composition, and morphological changes of the residual caries-affected dentin were examined. Artificial dentinal lesions were created by pH-cycling method (14 days) in 104 bovine specimens (5 × 5 mm). Specimens were randomly divided according to the carious removal method: bur (low-speed handpiece) or Er:YAG laser (250 mJ/4 Hz). Specimens were treated with 35% phosphoric acid and were subdivided into two groups according to dentin biomodification: without chitosan (control) and 2.5% chitosan. Forty specimens were restored with an adhesive system and composite resin. Subsurface microhardness tests were performed in sound dentin, caries-affected dentin, residual caries-affected dentin, and after the restoration. The other 64 specimens were subjected to SEM-EDS atomic analysis. Data were statistically analyzed (p < 0.05). After the Er:YAG laser excavation, the microhardness value of residual caries-affected dentin was higher (p < 0.05) than bur-treated dentin. A significant decrease in the amount of Ca, P, and Ca/P ratio was found after the removal of carious lesions with Er:YAG laser (p < 0.05). The biomodification with chitosan did not influence the microhardness and atomic percentage of Ca, P, and Ca/P ratio of residual caries-affected dentin (p > 0.05). SEM analysis showed morphological changes on residual caries-affected dentin (p > 0.05). The selective removal of carious dentin with Er:YAG laser increased microhardness of residual caries-affected dentin, changing its surface morphology and chemical composition. The biomodification with chitosan did not influence the structural and chemical composition of residual caries-affected dentin.