Repair of fractured framework: scanning electron microscopy and energy dispersive X-ray spectroscopy

Fractured metal prostheses can be analyzed for possible causes of failure using scanning electron microscopy (SEM). In this study, fractography is used to determine the cause of the failure and whether repair is practical. Energy-dispersive x-ray spectroscopy (EDS) is used to determine composition of the fractured prosthesis so that a repair process can be recommended. The technique is presented for the repair of a titanium framework for an implant-supported overdenture based on the analysis data.     

Adhesion of endodontic sealers: scanning electron microscopy and energy dispersive spectroscopy

The microscopic details of the debonded interfaces between endodontic sealers and dentin or gutta-percha were assessed in this study. Dentin, conditioned with 37% H3PO4 for 30 s, 25% citric acid for 30 s, 17% EDTA for 5 min, or a rinse with 10 ml of distilled H2O (control), and gutta-percha surfaces were coated with freshly mixed sealer: Grossman's sealer, Apexit, Ketac-Endo, AH Plus, RoekoSeal Automix, or RoekoSeal Automix with an experimental primer. The surfaces were pressed together and the sealers were allowed to set. After tensile bond strength testing, the morphological aspects of the fractured surfaces were assessed by scanning electron microscopy and energy dispersive spectroscopy. The energy dispersive spectroscopy successfully traced sealer components to the debonded surfaces. Some of the sealers penetrated into the dentinal tubules when the dentin surface had been pretreated with acids. However, these sealer tags remained occluding the tubules after bond failure in some instances only (Grossman's sealer, RoekoSeal Automix with an experimental primer, AH Plus/EDTA). Penetration of the endodontic sealers into the dentinal tubules when the smear layer was removed was not associated with higher bond strength.     

Gingival pigmentation beneath a metallic crown: light and electron microscopic observations and energy dispersive X-ray analysis

Light and electron microscopic studies and energy dispersive X-ray analysis disclosed that the essential cause of gingival discoloration following the placement of a metallic crown, was marked deposition of melanin pigment. Deposition of melanin pigment was observed in epithelial cells, on basement membranes, and in fibroblasts, macrophages and among intercellular ground substance of the proprial layer. Brown or dark brown colored granules were observed in the deep portion of the proprial layer. Some metallic elements as silver and sulfur were detected. It was presumed that these materials were dental metals accidentally implanted in gingival tissues during the therapeutic procedure. The deposition of melanin pigment closely corresponded with mucosal tissue where these materials were present in the deep portion of the proprial layer. These findings suggested that these materials influenced the physiological metabolism of melanin and induced its pathological deposition in the proprial tissue.     

Gingival pigmentation beneath a metallic crown: light and electron microscopic observations and energy dispersive X-ray analysis.

Light and electron microscopic studies and energy dispersive X-ray analysis disclosed that the essential cause of gingival discoloration following the placement of a metallic crown, was marked deposition of melanin pigment. Deposition of melanin pigment was observed in epithelial cells, on basement membranes, and in fibroblasts, macrophages and among intercellular ground substance of the proprial layer. Brown or dark brown colored granules were observed in the deep portion of the proprial layer. Some metallic elements as silver and sulfur were detected. It was presumed that these materials were dental metals accidentally implanted in gingival tissues during the therapeutic procedure. The deposition of melanin pigment closely corresponded with mucosal tissue where these materials were present in the deep portion of the proprial layer. These findings suggested that these materials influenced the physiological metabolism of melanin and induced its pathological deposition in the proprial tissue.     

Quantitative and qualitative elemental analysis of different nickel-titanium rotary instruments by using scanning electron microscopy and energy dispersive spectroscopy

This study was designed to determine if the alloy composition shares an influence with the geometric design on the physical behavior of nickel-titanium rotary endodontic instruments. ProTaper, HERO, and K3 files were selected. After sterilized and cleaning with alcohol, surface analysis was performed using energy dispersive spectroscopy. Measurements were performed on the active part and on the shank. SEM images of fractured instruments were also obtained and assessed. All three types of instruments were composed mainly of Nickel (54.3%, SD +/- 0.8) and Titanium (45.2%, SD +/- 0.9). SEM images revealed similar aspect with the presence of Kirkendall voids regularly distributed in the alloy. The results indicate that the difference in properties and behavior of these three endodontic rotary shaping instruments is solely related to the respective geometric characteristics of the instrument design.     

Analysis of saliva samples from oncological patients treated with 5‐fluorouracil and leucovorin calcium by scanning electron microscopy with energy dispersive system

This work presents a chemical and morphological analysis of samples of saliva taken from patients who were under treatment with intravenous chemotherapy with 5‐fluorouracil and leucovorin calcium. Samples of saliva were extracted from fifteen patients during the three stages of the treatment: The initial stage (previous to the chemotherapy), the intermediate stage (during the chemotherapy), and the final stage (twenty‐one days after finishing the treatment). An amount of 50 μl was collected in each visit. Chemical contrast images were taken by means of scanning electron microscopy, and X‐ray characteristic spectra were obtained from all the studied samples by using an energy dispersive system from all the studied samples. Images that correspond to the intermediate stage showed important differences with respect to the initial and final stages. In addition, X‐ray spectra provided information about the present elements in saliva and their relative abundance allowed us to determine variations in the chemical composition. The backscattered electron images and X‐ray spectra from the intermediate stage showed clusters of crystals with fluorine content higher than those obtained in initial and final stages. This fact probably indicates the passage of metabolites of 5‐fluorouracil and leucovorin calcium from the plasma to the oral cavity. This finding enhances the hypothesis proposed by other authors about the secondary effects of the drugs on the stomatognathic system such as oral mucositis, dysgeusia, and xerostomia with or without hyposalivation.     

Effects of fast halogen and plasma arc curing lights on the surface hardness of orthodontic adhesives for lingual retainers

The aims of this study were to (1) identify the optimum cure times of 2 different lingual retainer adhesives with a conventional halogen, a fast halogen, and a plasma arc light by measuring Vickers surface hardness, and (2) determine whether different lights produce similar surface hardness values for the same adhesive resin material. The investigated plasma arc curing unit was the PowerPac (American Dental Technologies, Corpus Christi, Tex), and the fast halogen unit was the Optilux 501 (Kerr, Orange, Calif). A conventional curing unit, the Ortholux XT (3M Dental Products, St. Paul, Minn) was used as the control. Two orthodontic lingual retainer adhesives were used: Transbond Lingual Retainer (3M Unitek, Monrovia, Calif) and Light Cure Retainer (Reliance Orthodontic Products, Itasca, Ill). Concise (3M Dental Products) and diluted Concise were used as controls. Transbond Lingual Retainer was polymerized by the PowerPac light in 6 seconds, by the Optilux in 10 seconds, and by the conventional halogen light in 20 seconds. The minimum curing times for Light Cure Retainer adhesive were 15 seconds for PowerPac, 10 seconds for Optilux, and 40 seconds for conventional halogen. Surface hardness values for each resin did not differ significantly with different curing units. However, different adhesives demonstrated significantly different surface hardness values. Final Vickers surface hardness values (averaged across curing units) of Transbond Lingual Retainer, Concise, diluted Concise, and Light Cure Retainer were 62.8, 52.4, 46.0, and 40.4, respectively. Plasma arc or fast halogen units polymerize resin composite adhesive in much shorter times than do conventional curing units, without a significant loss in surface hardness. Therefore, these units are suggested for clinical use to save chairside time.     

Inter-crystallite nanoretention of self-etching adhesives at enamel imaged by transmission electron microscopy

The purpose of this in vitro study was to analyse the mode of action of self-etching adhesive systems when applied for resin-to-enamel bonding. Transmission electron microscopy was used to investigate the enamel-resin interface after application of non-rinsing self-etching adhesive systems based on phosphoric acid estered methacrylates (Clearfil Liner Bond 2, Clearfil SE Bond, Etch & Prime 3.0 and Resulcin AquaPrime) compared with conventional phosphoric acid etching and bonding (Heliobond). Non-decalcified ultrathin sections from the interface between enamel and self-etching adhesive systems revealed a 1.5-3.2-microm deep enamel surface layer characterized by a less-dense arrangement of enamel crystallites separated from each other by nanometer-sized spaces. A 1.5-3.2-microm wide, netlike resinous structure was observed in corresponding decalcified specimens, indicating that self-etching priming agents dissolve the peripheral and central part of the enamel crystallites, while simultaneously promoting inter- and intra-crystallite monomer infiltration. A similar pattern, but greater depth (6.9 microm) of enamel surface hybridization was found in the phosphoric acid-etched and bonded specimens. The nanoretentive interlocking between enamel crystallites and resin could explain the potential of self-etching adhesive systems in resin-to-enamel bonding despite the less distinct enamel etching pattern observed in scanning electron microscopy investigations.     

Practical applications of energy dispersive X-ray microanalysis in diagnostic oral pathology

Energy dispersive X-ray microanalysis is a powerful tool that can reveal the presence and relative quantities of elements in minute particles in biologic materials. Although this technique has been used in some aspects of dental research, it has rarely been applied to diagnostic oral pathology. The purpose of this paper is to inform practicing dentists and oral specialists about the diagnostic potential of this procedure by presenting three case reports. The first case involved the identification of flakes of a metallic material claimed by a 14-year-old girl to appear periodically between her mandibular molars. In the second case, a periodontist was spared a lawsuit when a freely mobile mass in the antrum of his patient was found to be a calcium-phosphorus compound not related to the periodontal packing that had been used. The third case involved the differential diagnosis of amalgam tattoo and graphite tattoo in a pigmented lesion of the hard palate mucosa. The results of the analyses were significant and indicate a role for this technique in the assessment of selected cases. Potential for wider use of energy dispersive X-ray microanalysis in diagnostic oral pathology exists as research progresses.     

Multifunctional modification of orthodontic adhesives with ZnO quantum dots

ObjectivesTo develop a multifunctional orthodontic adhesive (QDA) using ZnO quantum-dots (ZnQDs) as modifier and investigate the antibacterial capability, fluorescence property as well as biocompatibility and bonding property.MethodsZnQDs were synthesized using sol-gel method. XPS, XRD, FT-IR, HRTEM, SAED, DLS and spectrofluorimetry were used to characterize ZnQDs. ZnQDs were incorporated into Transbond XT adhesive paste with 20 %, 30 %, 40 % mass fraction, respectively, to form the multifunctional adhesives (QDAs). Antibacterial capability was evaluated with MTT kit, CFU count and Live/Dead Bacterial Staining Kit. Ultraviolet photography and spectrofluorimetry were used to confirm the fluorescence property of QDAs. Biocompatibility assay was performed on gingival fibroblasts and subcutaneous tissue of rats. Softening in solvent rate, shear bond strength and degree of conversion (DC) were measured.ResultsThe synthesized ZnQDs presented excellent crystallinity and fluorescence properties. MTT assay, CFU count and CLSM analysis indicated that QDAs had significant antibacterial activity compared with Transbond XT adhesive paste. CCK-8 assay and Live/Dead cell staining analysis denied the cytotoxicity of QDAs and histological analysis proved that QDAs all had no inflammatory irritation to subcutaneous tissue. Softening in solvent, shear bond strength and DC evaluations indicated that 20 % mixing ratio of ZnQDs could enhance the resistance to degradation without influencing the bond strength and DC. Ultraviolet photography and spectrofluorimetry analysis proved the fluorescence capability of QDAs.SignificanceZnQDs can impart antibacterial and fluorescence properties to orthodontic adhesives without affecting biocompatibility and bonding performance. QDAs can be multifunctional orthodontic adhesives to reduce bacterial adhesion around brackets and help orthodontists remove residual adhesives precisely when needed.     

Bacterial colonization associated with fixed orthodontic appliances. A scanning electron microscopy study.

This investigation was undertaken to assess bacterial plaque accumulation adjacent to orthodontic brackets. Experiments were carried out on 11 subjects who were scheduled for orthodontic treatment including extraction of two or four premolars. Metal brackets were bonded to the premolars to be extracted using macro-filled bonding composite. A conventional elastomeric ring was placed around one bracket and a steel ligature wire around the bracket on the contralateral tooth. The subjects were told to continue their normal oral hygiene regimen. Teeth were extracted at 1, 2, or 3 weeks after bracket bonding. Scanning electron microscopic (SEM) examination of brackets, excess composite, and buccal enamel revealed that mature plaque was present on excess composite at 2 and 3 weeks after bonding, whereas plaque on the gingival enamel surface was still at an early stage of development. The results demonstrate that excess composite around the bracket base is the critical site for plaque accumulation due to its rough surface and the presence of a distinct gap at the composite-enamel interface. The method of ligation does not appear to influence the bacterial morphotypes on both composite and enamel surfaces.     

Post-gel shrinkage,elastic modulus,and stress generated by orthodontic adhesives

Objectives:To measure post-gel shrinkage, elastic modulus, and flexural strength of orthodontic adhesives and to predict shrinkage stress using finite element analysis (FEA).Materials and Methods:The following 6 orthodontic adhesives were tested: Transbond XT (3M Unitek, Monrovia, Calif), Transbond Plus Color Change (3M Unitek), Greengloo (Ormco, Brea, Calif), Ortho Connect (GC America, Alsip, Ill), Trulock (RMO, Denver, Colo), GoTo (Reliance, Itasca, Ill). Post-gel shrinkage was measured using a biaxial strain gauge during light curing. Elastic modulus and flexural strength were measured with a 4-point bending test. Analysis of variance and Student-Newman-Keuls post hoc tests were used to compare the shrinkage, elastic modulus, and flexural strengths among the materials (α = .05). Shrinkage stresses caused by the post-gel shrinkage and elastic modulus values were calculated using a cross-sectional FEA of a metallic bracket bonded to an incisor.Results:Properties were highly different among the adhesives (P ≤ .0001). Transbond XT (0.38 ± 0.09 percent volumetric contraction) and GoTo (0.42 ± 0.05 percent volumetric contraction) had the lowest post-gel shrinkage; Transbond Plus Color Change had the highest (0.84 ± 0.08 percent volumetric contraction). OrthoConnect (6.8 ± 0.6 gigapascals) had the lowest elastic modulus; GoTo (28.3 ± 3.1 gigapascals) had the highest. Trulock (64.1 ± 8.2 megapascals) had the lowest flexural strength; Greengloo (139.1 ± 20.7 megapascals) had the highest. FEA showed that the highest shrinkage stresses were generated with Transbond Plus Color Change and the lowest with OrthoConnect.Conclusions:Post-gel shrinkage of orthodontic adhesives was comparable with restorative composites, which are known to create shrinkage stresses in restored teeth. FEA indicated that this shrinkage creates stresses in the adhesive and in the enamel around the brackets.     

A review of orthodontic cements and adhesives.

Dental cements and resins are used intraorally to secure fixed orthodontic devices. Although cements are still used, the popularity of resin and resin-cement hybrid materials is increasing because of their improved physical properties and low solubility in oral fluids. Some cements bond chemically to enamel, but bond strengths are low because cements are brittle and fracture cohesively. Resin adhesives penetrate micropores in etched enamel and mechanical retentions in orthodontic devices, resulting in higher bond strengths because resins are more fracture resistant than cements. Resins, however, do not bond well in the presence of moisture, and their attachment to surfaces is primarily mechanical. Hybridized materials combine the advantages of cements and resins but also have certain disadvantages. Optimal material selection and application require an understanding of the chemical differences and physical limitations of today's orthodontic cements, resins, and hybrid materials.     

Zinc and strontium analyses by energy dispersive X-ray fluorescence in human permanent teeth

The zinc and strontium content of enamel and dentine from humans aged 9-64 yr was analysed, after systematic sampling, by X-ray fluorescence. Relatively high levels of zinc were found in both hard tissues but there was no significant increase with age. Zinc content decreased significantly from outer to inner enamel and increased significantly again from peripheral to pulpal coronal and root dentine. The strontium content was significantly higher in enamel than in dentine; there was a significant increase with age in enamel but not in dentine. However, outer and inner enamel showed no significant difference in strontium content. Almost similar amounts of strontium were found in coronal and root dentine.     

Dentin thickness, hardness, and Ca-concentration vs bond strength of dentin adhesives.

The relationship between the tensile bond strength (TBS) and three dentin characteristics: remaining dentin thickness (RDT), Ca-concentration, and hardness, were investigated. Sixty-two extracted bovine incisors, divided into four groups, were prepared using 600-grit SiC paper to create flat dentinal surfaces. The materials tested in this study consisted of three commercially available and one experimental dentin bonding systems. The TBS and modes of failure were determined after storage for 24 h in 37 degrees C water. Then RDT, Ca-concentration, and hardness were measured. Data were statistically compared with TBS of each group. The mean bond strength of the commercial materials ranged from 2.5 +/- 0.9 MPa to 7.7 +/- 2.8 MPa. Correlations with Ca-concentration and RDT varied, depending on the product. The bond strength of the experimental material was 9.2 +/- 4.4 MPa and significantly correlated with RDT and hardness. With two of the dentin bonding agents, specimens showed a high number of cohesive fractures in dentin, 40% to 82%. It was concluded that the variability of TBS was influenced by dentinal characteristics in three of the four materials tested.     

The use of easily debondable orthodontic adhesives with ceramic brackets

We experimentally produced an easily debondable orthodontic adhesive (EDA) containing heat-expandable microcapsules. The purpose of this in vitro study was to evaluate the best debondable condition when EDA was used for ceramic brackets. Shear bond strengths were measured before and after heating and were compared statistically. Temperatures of the bracket base and pulp wall were also examined during heating. Bond strengths of EDA containing 30 wt% and 40 wt% heat-expandable microcapsules were 13.4 and 12.9 MPa, respectively and decreased significantly to 3.8 and 3.7 MPa, respectively, after heating. The temperature of the pulp wall increased 1.8-3.6°C after heating, less than that required to induce pulp damage. Based on the results, we conclude that heating for 8 s during debonding of ceramic brackets bonded using EDA containing 40 wt% heat-expandable microcapsules is the most effective and safest method for the enamel and pulp.