Laura Emma Rodríguez-Vilchis

Morphological and Structural Changes on Human Dental Enamel After Er:YAG Laser Irradiation: AFM, SEM, and EDS Evaluation

OBJECTIVE The purpose of this study was to evaluate, using atomic force microscopy (AFM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), the morphological and structural changes of the enamel after irradiation with the Er:YAG laser. BACKGROUND DATA A previous study showed that subablative Er:YAG laser irradiation produced undesirable morphological changes on the enamel surface, such as craters and cracks; however, the enamel acid resistance was not increased. METHODS Fifty-two samples of human enamel were divided into four groups (n = 13): Group I was the control (no laser irradiation), whereas Groups II, III, and IV were irradiated with the Er:YAG 100 mJ (12.7 J/cm(2)), 100 mJ (7.5 J/cm(2)), and 150 mJ (11 J/cm(2)), respectively, at 10 Hz with water spray. The morphological changes were observed by AFM and SEM. The weight percentages (wt%) of calcium (Ca), phosphorus (P), oxygen (O) and chlorine (Cl) were determined in the resultant craters and their periphery using EDS. Kruskal-Wallis and Mann-Whitney U tests were performed (p ≤ 0.05) to distinguish significant differences among the groups. RESULTS The AFM images showed cracks with depths between 250 nm and 750 nm for Groups II and IV, respectively, and the widths of these cracks were 5.37 μm and 2.58 μm. The interior of the cracks showed a rough surface. The SEM micrographs revealed morphological changes. Significant differences were detected in Ca, P, and Cl in the crater and its periphery. CONCLUSIONS AFM observations showed triangular-shaped cracks, whereas craters and cracks were evident by SEM in all irradiated samples. It was not possible to establish a characteristic chemical pattern in the craters.

Acid resistance and structural changes of human dental enamel treated with Er:YAG laser.

OBJECTIVE The purpose of this study was to evaluate the acid resistance and structural changes in the enamel surface of permanent teeth after subablative Er:YAG laser irradiation in vitro. BACKGROUND DATA Er:YAG irradiation laser is expected to enhance acid resistance and to produce morphological changes on the enamel surface. METHODS One hundred twenty samples of human enamel were divided into four groups (n = 30): Group I was the control (no laser irradiation), and Groups II, III, and IV were irradiated with Er:YAG laser at 100 mJ (12.7 J/cm(2)), 100 mJ (7.5 J/cm(2)), and 150 mJ (11 J/cm(2)), respectively, at 10 Hz and with water spray. The samples were placed in an acid solution, and the released calcium was quantified by atomic absorption spectrometry. The weight percentages of calcium, phosphorus, oxygen, and chlorine on the enamel surface were determined by energy dispersive X-ray spectroscopy. The morphological changes were observed by scanning electron microscopy. One-way ANOVA and Kruskal-Wallis tests were performed (p <or= 0.05) to distinguish significant differences among groups. RESULTS The weight percentage of calcium in the samples obtained from EDS and the amount of calcium in the solution did not show any significant difference. All irradiated samples showed morphological changes on the enamel surface compared to the control group. CONCLUSIONS The results of this study suggest that acid resistance of enamel due to subablative Er:YAG laser irradiation on the samples did not increase as expected. Morphological microscopic changes included craters and cracks on the irradiated zones.

Evaluation of self-etching adhesive and Er:YAG laser conditioning on the shear bond strength of orthodontic brackets.

The purpose of this study was to evaluate the shear bond strength, the adhesive remnant index scores, and etch surface of teeth prepared for orthodontic bracket bonding with self-etching primer and Er:YAG laser conditioning. One hundred and twenty bovine incisors were randomly divided into four groups. In Group I (Control), the teeth were conditioned with 35% phosphoric acid for 15 seconds. In Group II the teeth were conditioned with Transbond Plus SEP (5 sec); III and IV were irradiated with the Er:YAG 150 mJ (11.0 J/cm2), 150 mJ (19.1 J/cm2), respectively, at 7–12 Hz with water spray. After surface preparation, upper central incisor stainless steel brackets were bonded with Transbond Plus Color Change Adhesive. The teeth were stored in water at 37°C for 24 hours and shear bond strengths were measured, and adhesive remnant index (ARI) was determined. The conditioned surface was observed under a scanning electron microscope. One-way ANOVA and chi-square test were used. Group I showed the significantly highest values of bond strength with a mean value of 8.2 megapascals (MPa). The lesser amount of adhesive remnant was found in Group III. The results of this study suggest that Er:YAG laser irradiation could not be an option for enamel conditioning.

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

Sixty samples of human dentin were divided into six groups (n = 10) and were irradiated with Er:YAG laser at 100 mJ–19.9 J/cm2, 150 mJ–29.8 J/cm2, 100 mJ–35.3 J/cm2, 150 mJ–53.0 J/cm2, 200 mJ–70.7 J/cm2, and 250 mJ–88.5 J/cm2, respectively, at 7 Hz under a water spray. The atomic percentages of carbon, oxygen, magnesium, calcium, and phosphorus and the Ca‐to‐P molar ratio on the dentin were determined by energy dispersive X‐ray spectroscopy. The morphological changes were observed using scanning electron microscopy. A paired t‐test was used in statistical analysis before and after irradiation, and a one‐way ANOVA was performed (P ≤ 0.05). The atomic percent of C tended to decrease in all of the groups after irradiation with statistically significant differences, O and Mg increased with significant differences in all of the groups, and the Ca‐to‐P molar ratio increased in groups IV, V, and VI, with statistically significant differences between groups II and VI. All the irradiated samples showed morphological changes. Major changes in the chemical composition of dentin were observed in trace elements. A significant increase in the Ca‐to‐P ratio was observed in the higher energy density groups. Morphological changes included loss of smear layer with exposed dentinal tubules. The changes produced by the different energy densities employed could have clinical implications, additional studies are required to clarify them. Microsc. Res. Tech. 78:1019–1025, 2015.

Chemical Changes Associated with Increased Acid Resistance of Er:YAG Laser Irradiated Enamel

Background. An increase in the acid resistance of dental enamel, as well as morphological and structural changes produced by Er:YAG laser irradiation, has been reported. Purpose. To evaluate the chemical changes associated with acid resistance of enamel treated with Er:YAG laser. Methods. Forty-eight enamel samples were divided into 4 groups (n = 12). Group I (control); Groups II, III, and IV were irradiated with Er:YAG at 100 mJ (12.7 J/cm2), 200 mJ (25.5 J/cm2), and 300 mJ (38.2 J/cm2), respectively. Results. There were significant differences in composition of irradiated groups (with the exception of chlorine) and in the amount of calcium released. Conclusions. Chemical changes associated with an increase in acid resistance of enamel treated with Er:YAG laser showed a clear postirradiation pattern characterized by a decrease in C at.% and an increase in O, P, and Ca at.% and no changes in Cl at.%. An increased Ca/P ratio after Er:YAG laser irradiation was associated with the use of higher laser energy densities. Chemical changes produced by acid dissolution showed a similar trend among experimental groups. Stable or increased Ca/P ratio after acid dissolution was observed in the irradiated groups, with reduction of Ca released into the acid solution.

Influence of four systems for dental bleaching on the bond strength of orthodontic brackets.

OBJECTIVE To compare the influence of four systems for dental bleaching on the shear bond strength (SBS) of orthodontic brackets. MATERIALS AND METHODS One-hundred and fifty freshly extracted bovine teeth were randomly divided into five groups. In group I the teeth were untreated (control). In the remaining groups the teeth were bleached, as follows: group II: 38% hydrogen peroxide; group III: 10% carbamide peroxide; group IV: resin-based coating material (RBCM), Beauty Coat; and group V: RBCM, White Coat. In all groups the enamel was conditioned with a self-etching primer and brackets were bonded with composite resin. Samples were stored (37°C, 24 hours), tested, and statistically analyzed, with significance predetermined at P ≤ .05. The adhesive remnant index (ARI) was also evaluated and analyzed. RESULTS The SBS of group V (22.49 ± 5.34 MPa) was significantly higher than that of all other groups (I: 17.1 ± 5.11 MPa; II: 14.72 ± 5.42 MPa; III: 12.04 ± 5.29 MPa; and IV: 18.23 ± 5.58 MPa). In contrast, the SBS of group III was significantly lower than that of all groups (except group II). Significant differences in the ARI scores were present between groups. CONCLUSIONS The use of RBCM for dental bleaching before bonding orthodontic brackets did not reduce the SBS. In contrast, hydrogen and carbamide peroxides negatively affected the SBS. The SBS yielded after bleaching with carbamide peroxide was significantly lower.

Microhardness, Structure, and Morphology of Primary Enamel after Phosphoric Acid, Self-Etching Adhesive, and Er:YAG Laser Etching

Background. Phosphoric acid is the traditional etching agent; self-etching adhesives and Er:YAG laser are alternative methods. Knowledge of deciduous enamel etching is required. Aim. To evaluate primary enamel microhardness, structure, and morphology after phosphoric acid, self-etching, and Er:YAG laser etching. Design. Seventy primary incisors were assigned to five groups ( ): I (control), II (35% phosphoric acid), III (self-etching adhesive), IV (Er:YAG laser at 15 J/cm2), and V (Er:YAG laser at 19.1 J/cm2). Microhardness was evaluated by Vickers indentation. Chemical composition was analyzed by energy dispersive X-ray spectroscopy and morphological changes by scanning electron microscopy. One-way ANOVA, Kruskal–Wallis, Mann–Whitney , and Pearson bivariate correlation were employed ( ). Results. Vickers microhardness showed differences and no correlation with Ca/P ratio. Group II showed differences in carbon, oxygen, and phosphorus atomic percent and group V in Ca/P ratio. Morphological changes included exposed prisms, fractures, craters, and fusion. Conclusions. Enamel treated with phosphoric acid showed different chemical characterization among groups. Self-etching and Er:YAG laser irradiation at 19.1 J/cm2 showed similar microhardness and chemical characterization. Er:YAG laser irradiation at 15 J/cm2 maintained microhardness as untreated enamel. Er:YAG laser irradiation at 19.1 J/cm2 enhanced mineral content. Morphological retentive changes were specific to each type of etching protocol.

Structural Changes on Human Dental Enamel Treated with Er:YAG, CO2 Lasers and Remineralizing Solution: EDS Analysis

Rosalia Contreras-Bulnes1, Oscar Fernando Olea-Mejia2, Laura Emma Rodriguez-Vilchis1, Rogelio Jose Scougall-Vilchis1 and Claudia Centeno-Pedraza1 1Centro de Investigacion y Estudios Avanzados en Odontologia, Facultad de Odontologia de la Universidad Autonoma del Estado de Mexico 2Centro Conjunto de Investigacion en Quimica Sustentable UAEM-UNAM, Facultad de Quimica de la Universidad Autonoma del Estado de Mexico Mexico

Chemical Changes of Enamel Produced by Sodium Fluoride, Hydroxyapatite, Er:YAG Laser, and Combined Treatments

Occlusal pits and fissures of permanent molars are considered to have higher risk of developing caries. Enamel demineralization can be prevented by applying remineralizing agents, and their absorption increases with prior irradiation. This work evaluates the chemical changes produced by treating occlusal surfaces with sodium fluoride (NaF), hydroxyapatite-NaF-xylitol (HA-NaF-X), Er:YAG laser irradiation (L), and combinations thereof. Fifty enamel samples were randomly assigned to five groups ( ): NaF, HA-NaF-X, L, L + NaF, and L + HA-NaF-X. The chemical composition of human enamel was evaluated before (BT) and after (AT) treatment using energy-dispersive X-ray spectroscopy (EDS) and expressed in atomic percentages (at%). For combined treatment groups, the products were applied after laser irradiation. The statistical analyses included a paired t-test and ANOVA ( ). After treatment, a significant increase in F at% was observed in the NaF group (2.71 ± 1.41). The irradiated groups showed significant increases in Ca and P at% and the Ca/P ratio. The highest values occurred for L + NaF (30.44 ± 4.28 Ca at%, 11.97 ± 1.45 P at%, and 2.55 ± 0.22 Ca/P ratio). Er:YAG laser irradiation alone or in combined protocols increased the Ca and P content of dental enamel, in vitro.

Adhesion of Streptococcus mutans and Streptococcus sanguinis on Er:YAG Laser-Irradiated Dental Enamel: Effect of Surface Roughness

OBJECTIVE To determine surface roughness caused by Er:YAG laser irradiation and its effect on the increase in bacterial adhesion. BACKGROUND Er:YAG laser was proposed as a strategic device to reduce caries by its ability to generate chemical and structural changes in tooth enamel; in turn, it produces undesirable effects on the tooth surface that could increase its roughness and allow a greater accumulation of microorganisms. METHODS Eighty-four samples of human enamel were divided into seven groups (n = 12): G1_control (no laser irradiation); G2_100/H2O, G3_200/H2O, and G4_300/H2O were irradiated with Er:YAG laser (12.7, 25.5, and 38.2 J/cm2, respectively) under water irrigation. In addition, G5_100, G6_200, and G7_300 were irradiated with the energy densities described above and no water irrigation. Surface roughness measurements were recorded before and after treatment using a profilometer. Afterward, three samples per group were incubated in a microorganism suspension for the tetrazolium salt (XTT) assay. Biofilm morphology was observed using scanning electron microscopy and confocal laser scanning microscope. One-way analysis of variance and t-tests were performed for statistical analysis (p < 0.05). RESULTS There were no statistically significant differences in roughness values in the G5_100 group before and after treatment, but there were statistically significant differences observed in the other groups evaluated (p < 0.05). No significant differences in adhesion of both strains were detected in irradiated groups compared with G1_control. CONCLUSIONS The increase in roughness on dental enamel surfaces was proportional to the irradiation conditions. However, the increase in surface roughness caused by Er:YAG laser irradiation did not affect Streptococcus mutans and S. sanguinis adhesion.