Optical clearing agents based on metallic and dielectric nanoparticles for caries diagnostic by optical coherence tomography.

OBJECTIVE: This study aimed to assess the effect of titanium dioxide (TiO2) and silver (Ag) nanoparticles dispersed in glycerol or water, serving as optical clearing agents nanocolloids (OCAs-NC), for improving optical coherence tomography (OCT) images and highlighting incipient lesions in ex vivo human teeth. MATERIALS AND METHODS: Twelve human teeth with incipient lesions were divided into seven groups according to the OCA-NC; they were subjected to G1 (air), G2 (glycerol), G3 (TiO2 0.1%), G4 (TiO2 0.01%), G5 (TiO2 0.001%), G6 (AgNO3 10%), and G7 (AgNO3 100%). The OCA-NC was applied to the occlusal surface, and two-dimensional images of the specimens were analyzed using OCT (930 nm central wavelength; 100 nm bandwidth; 5 mW output power; axial resolution of 7/5.3 µm in water and air, respectively; lateral resolution of 8 µm; and light penetration depth of 1.6 mm inside the sample). RESULTS: The findings demonstrated that the utilization of OCAs-NC containing metallic or dielectric nanoparticles (AgNO3 and TiO2) led to improved differentiation between sound and demineralized enamel on occlusal surfaces. Additionally, it enhanced the depth of image penetration when analyzing this hard tissue with OCT. CLINICAL RELEVANCE: In the current context of minimally invasive dentistry, the use of OCAs-NC in conjunction with OCT can provide clinicians with early diagnosis, allowing for the determination of less/more invasive therapies and consequently halting the disease before cavitation of dental tissues occurs.

The lingual enamel morphology and bracket shear bond strength influenced by Nd:YAG laser and aluminum oxide sandblasting preconditioning.

OBJECTIVES: This study aimed to investigate the influence of Nd:YAG laser and aluminum oxide sandblasting on the shear bond strength (SBS) of lingual brackets and to optically analyze the behavior of the enamel morphology. MATERIALS AND METHODS: Thirty-five bovines' incisors teeth were divided into 5 groups (n = 7), according to the surface preconditioning: G1, control group; G2, Nd:YAG laser; G3, laser + aluminum oxide sandblasting (Al2O3); G4, Al2O3; and G5, Al2O3 + laser. All groups had lingual brackets bonded and shear debonded after 72 h. SBS values were analyzed, and the enamel morphology was evaluated by optical coherence tomography (OCT) and scanning electron microscope (SEM), before and after preconditioning surface. The optical attenuation coefficient (α) analysis was obtained from OCT images. Data analysis used the ANOVA test, followed by post hoc Tukey, Kruskal Wallis, and post hoc Dunn tests (significance of 5%). RESULTS: The SBS values presented similarly among groups, but the value of α showed statistical difference (p-value = 0.0124) between G3 and G5 with the others. Optical analyses indicated a melting on the enamel that suffered laser irradiation for G2 and G5 and crystal surface disorganization for G4. Sandblasting partially removes the melting of the laser effect (G3). CONCLUSION: The sandblasting is a dispensable step for bonding lingual brackets, and the melting of the enamel after laser irradiation does not compromise the bracket adhesive resistance. CLINICAL RELEVANCE: The Nd:YAG laser became an interesting tool to prevent caries and decrease prevalence of white spot lesions in orthodontic treatments, without systemic effects in patients with genetic high risks of caries.

Optical coherence tomography as an auxiliary tool for the screening of radiation-related caries.

OBJECTIVE: The aim of this study was to evaluate the morphological alterations of radiation-related caries using optical coherence tomography. METHODS: Thirty-six extracted teeth from 11 patients who had undergone radiotherapy were sectioned in the sagittal axis in the center of the carious lesion, and 100 µm thick sections were obtained from each specimen. One sample from each tooth was investigated by an optical coherence tomography (OCT) system, and the results were compared with histological images from polarized light microscopy. RESULTS: In OCT dentin caries images, the demineralized area appeared as a white region, whereas the translucent zone appeared as a dark area, a similar pattern also seen in coronal caries. In noncavitated enamel lesions clinically observed as brown discoloration, the area of high porosity, and also the dark color, absorbs part of the light, resulting in a dark pattern. Finally, the involvement of dentin-enamel junction (DEJ) or cement-enamel junction (CEJ) could be clearly observed, when present and marked alterations along the CEJ could be noted, as junction continuity loss, gap formation, and mineral loss tissue. CONCLUSIONS: The OCT technique was able to characterize radiation-related caries, from a morphological point of view. Also demonstrated was its potential benefit for use in the clinical monitoring of radiation-related carious process.

Alternative methods for determining shrinkage in restorative resin composites.

OBJECTIVES: The purpose of this study was to evaluate polymerization shrinkage of resin composites using a coordinate measuring machine, optical coherence tomography and a more widely known method, such as Archimedes Principle. Two null hypothesis were tested: (1) there are no differences between the materials tested; (2) there are no differences between the methods used for polymerization shrinkage measurements. METHODS: Polymerization shrinkage of seven resin-based dental composites (Filtek Z250™, Filtek Z350™, Filtek P90™/3M ESPE, Esthet-X™, TPH Spectrum™/Dentsply 4 Seasons™, Tetric Ceram™/Ivoclar-Vivadent) was measured. For coordinate measuring machine measurements, composites were applied to a cylindrical Teflon mold (7 mm × 2 mm), polymerized and removed from the mold. The difference between the volume of the mold and the volume of the specimen was calculated as a percentage. Optical coherence tomography was also used for linear shrinkage evaluations. The thickness of the specimens was measured before and after photoactivation. Polymerization shrinkage was also measured using Archimedes Principle of buoyancy (n=5). Statistical analysis of the data was performed with ANOVA and the Games-Howell test. RESULTS: The results show that polymerization shrinkage values vary with the method used. Despite numerical differences the ranking of the resins was very similar with Filtek P90 presenting the lowest shrinkage values. SIGNIFICANCE: Because of the variations in the results, reported values could only be used to compare materials within the same method. However, it is possible rank composites for polymerization shrinkage and to relate these data from different test methods. Independently of the method used, reduced polymerization shrinkage was found for silorane resin-based composite.