In vitro study of the Nd : YAG laser effect on human dental enamel: Optical and scanning electron microscope analysis

Objective: the Nd:YAG laser irradiation of dental enamel was evaluated in enamel demineralization experiments in a Streptococcus mutans culture media. Summary Background Data: Previous studies had shown that a continuous wave Nd:YAG laser at an energy of approximately 67 mJ may induce an increased acid resistance in human dental enamel when exposed to severe demineralization conditions. Methods: Enamel windows of 3 x 4 cm in the buccal surface were irradiated with a continuous wave Nd:YAG laser at a wavelength of 1,064 Ecm using energy densities of from 83.75 to 187.50 J/cm(2), Enamel windows of 3 x 4 cm on the lingual surface served as control (without the laser irradiation). The enamel windows were then exposed to a Streptococcus mutans culture media at a temperature of 37 degrees C for 15 and 21 days. The laser effects and demineralization were examined both by optical microscopy and scanning electron microscopy (SEM), Results: A comparison between the lased and the unlased windows of enamel showed fusion and recrystalization of the enamel and increased acid-resistance in all groups irradiated with the Nd:YAG laser, on the other hand, the 3 x 4 delimited enamel surfaces from the control group (not irradiated with the Nd:YAG laser) showed 100% deminerization, Conclusions: These findings are consistent with the finding that laser irradiation of dental results in significant reduction of the effective solubility of enamel mineral.

Micro-Shear Bond Strength of Different Adhesives to Human Dental Enamel

The aim of this study was to evaluate the micro-shear bond strength of 5 adhesive systems to enamel, one single-bottle acid-etch adhesive (O), two self-etching primers (P) and two all-in-one self-etching adhesives (S). Method: Sixty premolar enamel surfaces (buccal or lingual) were ground flat with 400- and 600-grit SiC papers and randomly divided into 5 groups (n=12), according to the adhesive system.. SB2 - Single Bond 2 (O); CSE - Clearfil SE Bond (P); ADS - AdheSE (P); PLP - Adper Prompt L-Pop (S); XE3 - Xeno III (S). Tygon tubing (inner diameter of 0.8mm) restricted the bonding area to obtain the resin composite (Z250) cylinders. After storage in distilled water at 37 degrees C for 24h and thermocycling, micro-shear testing was performed (crosshead speed of 0.5mm/min). Data were submitted to one-way ANOVA and Tukey test (a=5%). Samples were also subjected to stereomicroscopic and SEM evaluations after micro-shear testing. Mean bond strength values (MPa +/- SD) and the results of Tukey test were: SB2: 36.36(+/- 3.34)a; ADS: 33.03(+/- 7.83)a; XE3: 32.76(+/- 5.61)a; CSE: 30.61(+/- 6.68)a; PLP: 22.17(+/- 6.05)b. Groups with the same letter were not statistically different. It can be concluded that no significant difference was there between SB2, ADS, XE3 and CSE, in spite of different etching patterns of these adhesives. Only PLP presented statistically lower bond strengths compared with others. J Clin Pediatr Dent 35(3): 301-304, 2011

Effect of time in hardness test on artificially demineralized human dental enamel

A cross-sectional microhardness (CSMH) test was carried out in human dental enamel exposed to a demineralizing solution in order to evaluate two different times of indentation in sound tissue and artificially induced caries. Twenty caries-free extracted human molars had one of their smooth surfaces sectioned and the enamel surface was isolated with nail polish except for an area of 6 mm2. These specimens were submitted to artificially induced enamel caries on a lactate buffer containing 0.1 ppm fluoride (F) during 28 days. All specimens were bisected to create groups A and B in which CSMH test was performed employing a Knoop indenter with a 25g load for 5 or 10 s, respectively. Student's paired t-test (p<0.05) was used to determine statistically significant differences between group A and B in 7 depths. There were no significant differences between any of the analyzed depths. Since the present experiment showed no significant difference when comparing indentations made with a 25 g load during either 5 or 10 s in different depths, this method can be used with either one of the time intervals tested without compromising a CSMH test on artificially demineralized human enamel.

Human dental enamel and dentin structural effects after Er:yag laser irradiation

Ideally projected to be applied on soft tissues, infrared lasers were improved by restorative dentistry to be used in hard dental tissues cavity preparations-namely enamel and dentin. This paper evidentiates the relevant aspects of infrared Erbium laser's action mechanism and its effects, and characterizes the different effects deriving from the laser's beams emission. The criteria for use and selection of optimal parameters for the correct application of laser systems and infuence of supporting factors on the process, such as water amount and its presence in the ablation process, protection exerted by the plasma shielding and structural factors, which are indispensable in dental tissues cavity preparation related to restorative technique, are subordinated to optical modifcations caused by the interaction of the energy dissipated by these laser light emission systems in the targeted tissue substrate. Clinical relevance: Differences in the action of infrared Erbium laser system in regard to the nature of the ablation process and variations on the morphological aspects observed in the super-fcial structure of the target tissue irradiated, may be correlated to the structural optical modifcations of the substrate produced by an interaction of the energy propagated by laser systems.

Synchrotron X-ray diffraction characterization of healthy and fluorotic human dental enamel

With the introduction of fluoride as the main anticaries agent used in preventive dentistry, and perhaps an increase in fluoride in our food chain, dental fluorosis has become an increasing world-wide problem. Visible signs of fluorosis begin to become obvious on the enamel surface as opacities, implying some porosity in the tissue. The mechanisms that conduct the formation of fluorotic enamel are unknown, but should involve modifications in the basic physical-chemistry reactions of demineralization and remineralisation of the enamel of the teeth, which is the same reaction of formation of the enamel's hydroxyapatite (HAp) in the maturation phase. The increase of the amount of fluoride inside of the apatite will result in gradual increase of the lattice parameters. The aim of this work is to characterize the healthy and fluorotic enamel in human tooth using Synchrotron X-ray diffraction. All the scattering profile measurements were carried out at the X-ray diffraction beamline (XRD1) at the Brazilian Synchrotron Light Laboratory-LNLS, Campinas, Brazil. X-ray diffraction experiments were performed both in powder samples and polished surfaces. The powder samples were analyzed to obtain the characterization of a typical healthy enamel pattern. The polished surfaces were analyzed in specific areas that have been identified as fluorotic ones. X-ray diffraction data were obtained for all samples and these data were compared with the control samples and also with the literature data. (c) 2012 Elsevier Ltd. All rights reserved.

Effects of Coffea arabica on Streptococcus mutans adherence to dental enamel and dentine

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Responses of human dental pulp cells after application of a low-concentration bleaching gel to enamel

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

AFM analysis of bleaching effects on dental enamel microtopography

The purpose of this in vitro study was to test a new methodology to evaluate the effects of 35% hydrogen peroxide agent on the microtopography of sound enamel using an atomic force microscope (AFM). The buccal sound surfaces of three extracted human lower incisors were used, without polishing the surfaces to maintain them with natural morphology. These unpolished surfaces were subjected to bleaching procedure with 35% hydrogen peroxide that consisted of 4 applications of the bleaching agent on enamel surfaces for 10 min each application. Surface images were obtained in a 15 mu m x 15 mu m area using an AFM. The roughness (Ra and RMS) and the power spectral density (PSD) were obtained before and after the bleaching treatment. As results we could inquire that the PSD analyses were very suitable to identifying the morphological changes on the surfaces, while the Ra and RMS parameters were insufficient to represent the morphological alterations promoted by bleaching procedure on enamel. The morphological wavelength in the range of visible light spectrum(380-750 nm) was analyzed, showing a considerable increase of the PSD with the bleaching treatment. (C) 2009 Elsevier B. V. All rights reserved.

Microbiopsies of Surface Dental Enamel as a Tool to Measure Body Lead Burden

Lead (Pb) poisoning is preventable but continues to be a public health problem in several countries. Measuring Pb in the surface dental enamel (SDE) using microbiopsies is a rapid, safe, and painless procedure. There are different protocols to perform these microbiopsies, but the reliability of dental enamel lead levels (DELL) determination is dependent upon biopsy depth (BD). It is established that DELL decrease from the outermost superficial layer to the inner layer of dental enamel. The aim of this study was to determine DELL obtained by two different microbiopsy techniques on SDE termed protocol I and protocol II. Two consecutive enamel layers were removed from the same subject group (n = 138) for both protocols. Protocol I consisted of a biopsied site with a diameter of 4 mm after the application of 10 l HCl for 35 s. Protocol II involved a biopsied site of 1.6 mm diameter after application of 5 l HCl for 20 s. The results demonstrated that there were no significant differences for BD and DELL between homologous teeth using protocol I. However, there was a significant difference between DELL in the first and second layers using both protocols. Further, the BD in protocol II overestimated DELL values. In conclusion, SDE analyzed by microbiopsy is a reliable biomarker in protocol I, but the chemical method to calculate BD in protocol II appeared to be inadequate for measurement of DELL. Thus, DELL could not be compared among studies that used different methodologies for SDE microbiopsies.

Bond strength of adhesive systems to human tooth enamel

The purpose of this study was to evaluate in vitro three adhesive systems: a total etching single-component system (G1 Prime & Bond 2.1), a self-etching primer (G2 Clearfil SE Bond), and a self-etching adhesive (G3 One Up Bond F), through shear bond strength to enamel of human teeth, evaluating the type of fracture through stereomicroscopy, following the ISO guidance on adhesive testing. Thirty sound premolars were bisected mesiodistally and the buccal and lingual surfaces were embedded in acrylic resin, polished up to 600-grit sandpapers, and randomly assigned to three experimental groups (n = 20). Composite resin cylinders were added to the tested surfaces. The specimens were kept in distilled water (37°C/24 h), thermocycled for 500 cycles (5°C-55°C) and submitted to shear testing at a crosshead speed of 0.5 mm/min. The type of fracture was analyzed under stereomicroscopy and the data were submitted to Anova, Tukey and Chi-squared (5%) statistical analyses. The mean adhesive strengths were G1: 18.13 ± 6.49 MPa, (55% of resin cohesive fractures); G2: 17.12 ± 5.80 MPa (90% of adhesive fractures); and G3: 10.47 ± 3.14 MPa (85% of adhesive fractures). In terms of bond strength, there were no significant differences between G1 and G2, and G3 was significantly different from the other groups. G1 presented a different type of fracture from that of G2 and G3. In conclusion, although the total etching and self-etching systems presented similar shear bond strength values, the types of fracture presented by them were different, which can have clinical implications.

Analysis of the effects of thermal cycling on the microtensile shear bond strength of a self-etching and a conventional pit and fissure sealants to dental enamel

Objective: To analyze the effects of thermal cycling on the microtensile shear bond strength of a self-etching and a conventional pit and fissure sealants to dental enamel. Material and Method: Twenty-four healthy human molars extracted for orthodontic reasons, were sectioned in the mesio-distal direction and divided into two groups (n=24) according to the sealant to be applied: GI - conventional sealant Climpro (3M/ESPE) and GII - self-etching sealant Enamel Loc (Premier Dental). The sealants were applied on flattened enamel in matrixes 1 mm in diameter, in accordance with the manufacturers' recommendations. The specimens were stored in distilled water at 37°C for 24 hours. After this, half the samples of both groups were submitted to 500 thermal cycles in 30s baths at temperatures between 5 and 55°C. Forty-eight hours after the samples were made, the microtensile shear test was performed in an Instron 4411 test machine, with a stainless steel wire with a cylindrical cross section of 0.2mm in diameter at a constant speed of 0.5mm/s. The bond strength values were submitted to ANOVA for 2 factors and the fracture patterns were examined under an optical microscope at 65X magnification. Results: Thermal cycling did not influence the bond strength of the two sealants. The conventional sealant Climpro presented a statistically higher microtensile shear bond strength (11.72MPa, 11.34MPa with and without cycling, respectively) than the self-etching sealant Enamel Loc (5.92MPa, 5.02MPa with and without cycling, respectively). Fracture pattern analysis showed the occurrence of 100% of adhesive failures for Enamel Loc, while the conventional sealant Climpro presented 95% of adhesive failures and 5% of mixed failures. Conclusion: The conventional sealant presented higher microtensile shear bond strength to dental enamel in comparison with the self-etching sealant. Thermal cycling did not affect the bond strength of the sealants used in this study. © 2011 Nova Science Publishers, Inc.

Effect of Er:YAG laser on CaF2 formation and its anticariogenic action on human enamel: An in vitro study

Objective: The objective of this study was to evaluate the effect of Er: YAG laser on the formation of CaF2, after the application of acidulated phosphate fluoride (APF), and its influence on the anti-cariogenic action in human dental enamel. Background Data: Er:YAG laser was designed to promote ablation of the enamel. However, the possibility of using this energy to increase the enamel's resistance to caries has hardly been explored, and neither has its interaction with the use of fluorides. Materials and Methods: One hundred and twenty blocks of enamel were allocated to four groups of 30 blocks each: (1) C, control group; (2) Er:YAG, laser; (3) APF; and (4) Er:YAG+APF. Of these, 80 blocks were submitted to pH cycling for 14 days. In the other 40 blocks, fluoride (CaF2) was measured before cycling. After pH cycling, surface microhardness (SMH), microhardness in cross-section (converted to mineral contents % vol. min.), and fluoride after cycling (40 blocks) were also determined. Results: SMH decreased in all groups. The control group showed the highest decrease, and Er:YAG+APF showed the lowest decrease (p < 0.05). Groups APF and Er:YAG showed the same results (p > 0.05). Mineral content at depths 10, 20, and 40 μm was lower in the control and Er:YAG groups, and higher in groups APF and Er:YAG+APF. CaF2 (μgF/cm2) deposited before pH cycling was higher in the APF group when compared to the Er:YAG+APF group. Control and Er:YAG groups showed the lowest values (p > 0.05). Conclusion: It was concluded that Er:YAG laser influenced the deposition of CaF2 on the enamel and showed a superficial anti-cariogenic action, but not in depth.

FTIR and SEM analysis of CO2 laser irradiated human enamel

Objectives: Considering the enamel chemical structure, especially carbonate band, which has a major role in the caries prevention, the objective of the present study was to assess the chemical alterations on the enamel irradiated with CO2 laser by means of FTIR spectroscopy and SEM analysis. Design: The enamel surfaces were analysed on a spectrometer for acquisition of the absorption spectrum relative to the chemical composition of the control sample. The irradiation was conducted with a 10.6-mu m CO2 laser (0.55 W, 660 W/cm(2)). The carbonate absorption band at 1600-1291 cm(-1) as well as the water absorption band at 3793-2652 cm(-1) was measured in each sample after the irradiation. The water band was measured again 24-h after the irradiation. The band area of each chemical compound was delimited, the background was subtracted, and the area under each band was integrated. Each area was normalized by the phosphate band (1190-702 cm(-1)). Results: There was a statistically significant decrease (p < 0.05) in the water content after irradiation (control: 0.184 +/- 0.04; irradiated: 0.078 +/- 0.026), which increased again after rehydration (0.145 +/- 0.038). The carbonate/phosphate ratio was measured initially (0.112 +/- 0.029) and its reduction after irradiation indicated the carbonate loss (0.088 +/- 0.014) (p < 0.05). Conclusion: The 10.6-mu m CO2 laser irradiation diminishes the carbonate and water contents in the enamel after irradiation. (C) 2012 Elsevier Ltd. All rights reserved.

Effect of microstructure upon elastic behaviour of human tooth enamel

Tooth enamel is the stiffest tissue in the human body with a well-organized microstructure. Developmental diseases, such as enamel hypomineralisation, have been reported to cause marked reduction in the elastic modulus of enamel and consequently impair dental function. We produce evidence, using site-specific transmission electron microscopy (TEM), of difference in microstructure between sound and hypomineralised enamel. Built upon that, we develop a mechanical model to explore the relationship of the elastic modulus of the mineral-protein composite structure of enamel with the thickness of protein layers and the direction of mechanical loading. We conclude that when subject to complex mechanical loading conditions, sound enamel exhibits consistently high stiffness, which is essential for dental function. A marked decrease in stiffness of hypomineralised enamel is caused primarily by an increase in the thickness of protein layers between apatite crystals and to a lesser extent by an increase in the effective crystal orientation angle. © 2009 Elsevier Ltd. All rights reserved.

Differentially Expressed Protein Profile of Human Dental Pulp Cells in the Early Process of Odontoblast-like Differentiation In Vitro

Dental pulp cells (DPCs) are capable of differentiating into odontoblasts that secrete reparative dentin after pulp injury. The molecular mechanisms governing reparative dentinogenesis are yet to be fully understood. Here we investigated the differential protein profile of human DPCs undergoing odontogenic induction for 7 days. Using two-dimensional differential gel electrophoresis coupled with matrix-assisted laser adsorption ionization time of flight mass spectrometry, 2 3 protein spots related to the early odontogenic differentiation were identified. These proteins included cytoskeleton proteins, nuclear proteins, cell membrane-bound molecules, proteins involved in matrix synthesis, and metabolic enzymes. The expression of four identified proteins, which were heteronuclear ribonuclear proteins C, annexin VI, collagen type VI, and matrilin-2, was confirmed by Western blot and real-time realtime polymerase chain reaction analyses. This study generated a proteome reference map during odontoblast- like differentiation of human DPCs, which will be valuable to better understand the underlying molecular mechanisms in odontoblast-like differentiation.