Ana Karla Souza Braz

Evaluation of crack propagation in dental composites by optical coherence tomography

OBJECTIVES The purpose of this study was to image the sites of fracture initiation and slow crack propagation in a fiber reinforced composite, using the optical coherence tomography (OCT) technique. METHODS Bar specimens (2mm x 3mm x 25mm) of fiber reinforced composite were mechanically and thermally cycled to emulate oral conditions. The interior of these samples was analyzed prior to and after loading, using OCT. The device used was a home-built Fourier domain OCT setup working at 800 nm with 6 microm spatial resolution. RESULTS Intact specimens after load cycling were analyzed. It was clearly seen that OCT images provide an insight into crack propagation, which is not seen by the naked eye. SIGNIFICANCE By using OCT the possibility of analyzing the fracture propagation quantitatively, and in depth, was added, opening up possibilities to quantitative studies.

Evaluation of the integrity of dental sealants by optical coherence tomography

OBJECTIVES The purpose of the present research was to demonstrate images of failures into the structure of pit and fissure sealants using optical coherence tomography (OCT). METHODS Five human third molars were selected and the sealant ALPHA SEAL LIGHT/DFL was applied according to the manufacturer instructions. For evaluation of the structure of pit and fissure sealants, twenty OCT images of each tooth were performed before and after application of sealant. A total of 200 images were evaluated. A home built spectral OCT system used was operating in spectral domain (SD-OCT), at 840 nm and a measured spatial resolution of 10 μm. The system is based on the Michelson interferometer set-up and is controlled by the software OCT 800--Complex Square/LabView, that collects data and generates the image. The occlusal surfaces were scanned in a bucco-lingual direction and tomographic images parallel to long axis of tooth were obtained. After the achievement of the images by OCT, the crown of each tooth was sectioned in a occlusogingival direction (buccolingually). Images from each section were obtained and evaluated by an optical microscope. OCT and microscopic images were compared. RESULTS Representative images showed that OCT image provides the insight into sealant material. It was possible to clearly identify the internal structure of sealant and the subjacent enamel. Sealant and enamel are very well distinguished, and failures at the interior and at surface are well detected. SIGNIFICANCE OCT could generate images of the features of fissures, bubbles and failures in the adaptation of sealants, opening up possibilities in the future to monitoring sealant application and retention in short and long term.

In Vitro Tomographic Image of Human Pulp-Dentin Complex: Optical Coherence Tomography and Histology

INTRODUCTION Optical coherence tomography (OCT), a noninvasive imaging method, was used in this work to image the pulp-dentin complex. Pulp and dentin are integrally connected in the sense that physiologic and pathologic reactions in one of the tissues will also affect the other. METHODS An OCT system with 6-mum spatial resolution at 800 nm was used to image the pulp-dentin complex of in vitro samples. Five intact human maxillary premolars scheduled for surgical extraction were used in this in vitro study. The occlusal surfaces of teeth were polished with wet 600-, 1,000-, and 1,200-grit aluminum oxide abrasive paper perpendicular to the long axis of teeth, producing a plane on that surface. The images of pulp-dentin complex were taken by scanning the occlusal surface in a mesiodistal direction. The laser penetrated into the teeth structure and a tomographic image of pulp-dentin complex, parallel to the long axis of teeth, was obtained. Histological and OCT images were analyzed and compared. RESULTS The results showed the capability of the OCT technique to generate images of the boundaries of pulp and its relation to the dentin. It could be clearly seen that the OCT image provided the insight into dentinal substrate about 0.65-mm deep (corrected for the dentin refractive index). CONCLUSION OCT can be used in the future to prevent iatrogenic exposures of the pulp, complementing other existing methods, and will permit a more predictive prognosis of treatments.

Effectiveness of varnish with CPP-ACP in prevention of caries lesions around orthodontic brackets: an OCT evaluation

OBJECTIVE To evaluate the in vitro efficiency of applying varnish containing casein phosphopeptide (CPP) and amorphous calcium phosphate (ACP) in prevention of caries lesions around orthodontic brackets. MATERIALS AND METHODS For this purpose, brackets were bonded to the vestibular surface of bovine incisors, and eight groups were formed (n = 15) according to exposure of oral hygiene substances and enamel varnish: 1 (control) brushing only performed, 2 (control) brushing + use of mouth wash with fluoride, 3 Duraphat varnish application only (Colgate-Palmolive Ind. E Com. Ltda, São Paulo, SP, Brazil), 4 Duraphat + brushing, 5 Duraphat + brushing + mouth wash, 6 MI Varnish application (GC America, USA), 7 MI + brushing, and 8 MI + brushing + mouth wash. The experimental groups alternated between pH cycling and the procedures described and were kept in an oven at temperature of 37°C. Both brushing and immersion in solutions was performed in a time interval of 1 minute, followed by washing in deionized water three times a day for 28 days of experimentation. Afterwards, evaluation by optical coherence tomography (OCT) of the special type (Ganymede OCT/Thorlabs, Newton, USA) was performed. In each group, a scanning exam of the white spot lesion area (around the region where brackets were bonded) and depth measurement of caries lesions were performed. RESULTS Groups 1 and 3 were shown to differ statistically from groups 5, 6, 7, and 8 (p = 0.000). MI Varnish was shown to be more effective in diminishing caries lesion depth, compared with Duraphat, irrespective of being associated with brushing and mouth wash, or not. LIMITATIONS The major limitation of this study is that it is a study in which demineralization was obtained with the use of chemical products, and did not occur due to the presence of Streptococcus mutans and its acid byproducts. CONCLUSION Application CPP-ACP-containing varnish irrespective of being associated with brushing and mouthwash, or not, reduced depth of caries lesions around orthodontic brackets.

Optical coherence tomography for debonding evaluation: an in-vitro qualitative study.

INTRODUCTION The purpose of this research was to demonstrate the potential of the optical coherence tomography technique on the evaluation of changes and damages in the enamel structure caused by debonding and cleanup procedures. METHODS Twin metal and ceramic brackets were bonded to the labial enamel surfaces of 120 incisors; the brackets were debonded 24 hours later. The anterior surfaces of the teeth were scanned, and optical coherence tomography images were captured in 2-dimensional and 3-dimensional modes before and after debonding and cleanup. A commercial spectral domain optical coherence tomography system with a 5-μm axial spatial resolution was used. The system is based on the Michelson interferometer setup. It is connected to a preconfigured personal computer, and the images are captured with a scanner probe that controls the light beam position at the sample. A total of 960 images were evaluated. RESULTS The analysis of the 2-dimensional and 3-dimensional images obtained with optical coherence tomography allows observation and evaluation of adhesive remnants, enamel damage, and superficial aspects of enamel from different methods of adhesive remnant removal. The 2-dimensional optical coherence tomography analysis allows in-depth observation of the adhesive remnant layer. CONCLUSIONS Optical coherence tomography can be a powerful tool for academic and clinical applications for the evaluation of debonding procedures.

In situ gold nanoparticles formation: contrast agent for dental optical coherence tomography

In this work we demonstrate the potential use of gold nanoparticles as contrast agents for the optical coherence tomography (OCT) imaging technique in dentistry. Here, a new in situ photothermal reduction procedure was developed, producing spherical gold nanoparticles inside dentinal layers and tubules. Gold ions were dispersed in the primer of commercially available dental bonding systems. After the application and permeation in dentin by the modified adhesive systems, the dental bonding materials were photopolymerized concurrently with the formation of gold nanoparticles. The gold nanoparticles were visualized by scanning electron microscopy (SEM). The SEM images show the presence of gold nanospheres in the hybrid layer and dentinal tubules. The diameter of the gold nanoparticles was determined to be in the range of 40 to 120 nm. Optical coherence tomography images were obtained in two- and three-dimensions. The distribution of nanoparticles was analyzed and the extended depth of nanosphere production was determined. The results show that the OCT technique, using in situ formed gold nanoparticles as contrast enhancers, can be used to visualize dentin structures in a non-invasive and non-destructive way.

Fracture process characterization of fiber-reinforced dental composites evaluated by optical coherence tomography, SEM and optical microscopy

This study used optical coherence tomography (OCT) compared to scanning electron microscopy (SEM) and optical microscopy (OM) to evaluate qualitatively crack propagation and final fracture in restorative composite materials - Filtek Z250 and Filtek Z350 (3M ESPE) - with fiber reinforcement after cyclic loading. Samples were made using a split mold. Initially, 3-point bending tests were performed to determine the maximum force and tension at the fracture moment using samples without fiber reinforcement. Then, mechanical cycling tests were performed using samples with glass fiber embedded internally. The failures were analyzed using the 3 methods described before. OCT permitted good characterization of internal crack propagation of the dental composites, which, however, could not be visualized by either SEM or OM. OCT was proven to be laboratory research tool that is easy to use, does not require any specific preparation of the samples, and is less expensive than SEM.

Enamel Quality after Debonding: Evaluation by Optical Coherence Tomography

The aims of this study were to evaluate quantitatively the enamel fractures, adhesive remnants and bracket fragments on enamel after debonding of metal and ceramic brackets, and to quantify the layer of adhesive remnants in depth after two different cleanup procedures. Metal and ceramic brackets were bonded on 120 human incisors and then debonded using two different techniques with Side Cutter (SC) and Anterior Bracket Removal plier (ABR). After this, a high-speed tungsten carbide finishing bur or a low-speed tungsten carbide finishing bur was used. The debonded samples were submitted to enamel assessment with optical coherence tomography (OCT). In sequence, two different methods of removing the remaining adhesive (tungsten carbide burs at high and low speed) were performed and at the end of these procedures, the remaining adhesive layer was measured with OCT. The results demonstrated that enamel fractures were observed only in the samples bonded with ceramic brackets, and the type of pliers did not influence the incidence and extent of enamel damage. Moreover, the type of debonding technique (with side-cutting pliers or anterior bracket removal pliers) and the type of bracket did not influence the amount of adhesive remaining after debonding. The burs at low speed removed the remaining adhesive more effectively during cleanup procedures.

TiO2-coated fluoride nanoparticles for dental multimodal optical imaging

Core-shell nanostructures associated with photonics techniques have found innumerous applications in diagnostics and therapy. In this work, we introduce a novel core-shell nanostructure design that serves as a multimodal optical imaging contrast agent for dental adhesion evaluation. This nanostructure consists of a rare-earth-doped (NaYF4 :Yb 60%, Tm 0.5%)/NaYF4 particle as the core (hexagonal prism, ~51 nm base side length) and the highly refractive TiO2 material as the shell (~thickness of 15 nm). We show that the TiO2 shell provides enhanced contrast for optical coherence tomography (OCT), while the rare-earth-doped core upconverts excitation light from 975 nm to an emission peaked at 800 nm for photoluminescence imaging. The OCT and the photoluminescence wide-field images of human tooth were demonstrated with this nanoparticle core-shell contrast agent. In addition, the described core-shell nanoparticles (CSNps) were dispersed in the primer of a commercially available dental bonding system, allowing clear identification of dental adhesive layers with OCT. We evaluated that the presence of the CSNp in the adhesive induced an enhancement of 67% scattering coefficient to significantly increase the OCT contrast. Moreover, our results highlight that the upconversion photoluminescence in the near-infrared spectrum region is suitable for image of deep dental tissue.

Effectiveness of fluoride sealant in the prevention of carious lesions around orthodontic brackets: an OCT evaluation

Abstract Objective: This article aimed to evaluate in vitro the efficiency of Pro Seal fluoride sealant application in the prevention of white spot lesions around orthodontic brackets. Material and Methods: Brackets were bonded to the buccal surface of bovine incisors, and five groups were formed (n = 15) according to the exposure of teeth to oral hygiene substances and the application of enamel sealant: G1 (control), only brushing was performed with 1.450 ppm fluoride; G2 (control) brushing associated with the use of mouthwash with 225 ppm fluoride; G3, only Pro Seal sealant application was performed with 1.000 ppm fluoride; G4 Pro Seal associated with brushing; G5 Pro Seal associated with brushing and mouthwash. Experimental groups alternated between pH cycling and the procedures described. All specimens were kept at a temperature of 37 °C throughout the entire experiment. Both brushing and immersion in solutions were performed within a time interval of one minute, followed by washing in deionized water three times a day for 28 days. Afterwards, an evaluation by Optical Coherence Tomography (OCT) of the spectral type was performed. In each group, a scanning exam of the white spot lesion area (around the sites where brackets were bonded) and depth measurement of carious lesions were performed. Analysis of variance (ANOVA) was applied to determine whether there were significant differences among groups. For post hoc analysis, Tukey test was used. Results: There was statistically significant difference between groups 1 and 2 (p = 0.003), 1 and 3 (p = 0.008), 1 and 4 (p = 0.000) and 1 and 5 (p = 0.000). The group in which only brushing was performed (Group 1) showed deeper enamel lesion. Conclusion: Pro Seal sealant alone or combined with brushing and/or brushing and the use of a mouthwash with fluoride was more effective in protecting enamel, in comparison to brushing alone.