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.

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.

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.

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.

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.

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.

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.