Paulo Acioly M. dos Santos

Assessment of enamel damage after removal of ceramic brackets

INTRODUCTION Since the introduction of ceramic brackets, research has been performed to evaluate enamel damage caused during their removal. One problem in comparing treated and control groups is the absence of assurance that the surfaces were undamaged before the brackets were bonded and debonded, or that superficial treatment applied to the enamel could hinder damage detection. The aim of this in-vitro study was to evaluate enamel injuries during debonding of 3 types of ceramic brackets. METHODS Forty-five premolars, extracted for orthodontic purposes, were divided into 3 groups of 15. The enamel surfaces were photographed with a magnifying loupe (60 times) in an optical stereomicroscope (Stemi 2000-C, Zeiss, Oberkochen, Germany) with a digital camera. A different type of backet was bonded and debonded in each group: mechanical retention, mechanical retention with a polymer base, and chemical retention. After debonding, the surfaces were again photographed. The photographs were evaluated for quality of enamel surface according to a predetermined scale. The results were tested by method error and the chi-square test. RESULTS The damage evaluation comparing the same surface before bonding and after debonding showed no significant statistical difference between the mechanical retention group and the polymer base retention group. There was a significant statistical difference (P <0.05) for the chemical adhesion ceramic bracket group. CONCLUSIONS The difference between the enamel surfaces before bonding and after debonding brackets with chemical retention was statistically significant; bonding and debonding these brackets resulted in enamel damage.

Photo refractive intrinsic parameters measured in Bi12TiO20 crystal at λ=0.633 μm

Abstract This paper contains the experimental results from an application of anisotropic self-diffraction concepts in a simple holographic method which allows to obtain the diffusion transport length, quantum efficiency, and trap density, measured in the photorefractive Bi 12 TiO 20 crystal operated at λ=0.633 μm.

Recovering obliterated laser engraved serial numbers in firearms

An easy procedure for recovering obliterated firearms serial numbers, which are laser engraved is presented in this case report. For these serial numbers, the traditional recovering method using acid etching generally fails, once marking the serial number does not necessarily imply a deep permanent deformation of the crystalline array. The standard required mirror-like finish of the surface commonly can destroy any evidence of the original serial number, i.e., can destroy the heat affected zone (HAZ) of only few micra, if it is still present. It is shown in this report that relief polishing and reflected light stereomicroscopy can, in certain cases, successfully reveal obliterated serial numbers, originally marked by laser. The use of this procedure for recovering this type of obliterated serial number is illustrated and discussed with an example we have dealt with.

Photorefractive optical holographic correlation using a Bi12TiO20 crystal at λ=0.633 μm

Abstract This paper reports real time optical holographic correlation using the Bi 12 TiO 20 photorefractive crystal at λ=0.633 μm. The experiments were performed in the diffusion-only Bragg regime operation and are based on the anisotropic self-diffraction properties of the photorefractive material. The performance of the developed correlator is evaluated by means of the SNR concept. This system is simple and easy to control. The material employed here has high sensitivity and spatial resolution at low power HeNe laser light source illumination.

Holographic Fourier synthesis of dynamic Moiré-like patterns in the photorefractive Bi12TiO20 crystal

We propose and physically discuss a kind of holographic Fourier synthesis in the profile of dynamic Moire-like patterns. The interference patterns are obtained by progressively controlling the superposition of more than two dynamic sinusoidal phase gratings. It represents a new holographic optical nondestructive testing routine in real time for metrological purposes. The sinusoidal phase gratings with slightly different pitches are dynamically generated by photorefraction in the Bi 12 TiO 20 (BTO) crystal sample. The photorefractive holographic medium is used in anisotropic self-diffraction configuration and in a diffusion-only recording mechanism.

Dynamic holographic moiré patterns in photorefractive Bi 12 TiO 20 and small-angle measurements

A procedure for obtaining real-time holographic moirélike patterns and measuring small angles is proposed. Two rotated sinusoidal phase gratings are superposed, and the result represents a promising technique for making small-angle measurements in metrological applications. The experiments are performed with a diffusion-only recording mechanism in the photorefractive crystal Bi12TiO20 illuminated by lambda = 0.633 microm light from a He-Ne laser.

Identification of material properties using full-field and non contact measurements

In the present work, the Digital Image Correlation (DIC) measurement method is used to obtain the displacement field of specific regions of a cantilever beam under bending. These fields are used within an inverse analysis scheme in order to obtain the elasticity modulus of the beam material. The parameter estimation is performed by means of the minimization of an error function comprising of the difference between the displacement fields obtained from the experiment and from an appropriate mathematical model. The inverse problem is solved by means of the classical Levenberg-Marquardt nonlinear parameter estimation technique. The estimate obtained for the elasticity modulus is validated taking into account new experimental data obtained through modal analysis of another beam-like specimen which, in turn, is made of the same material as the original one.

An application of stereoscopy and image processing in forensics: recovering obliterated firearms serial number

We present an application of the use of stereoscope to recovering obliterated firearms serial number. We investigate a promising new combined cheap method using both non-destructive and destructive techniques. With the use of a stereomicroscope coupled with a digital camera and a flexible cold light source, we can capture the image of the damaged area, and with continuous polishing and sometimes with the help of image processing techniques we could enhance the observed images and they can also be recorded as evidence. This method has already proven to be useful, in certain cases, in aluminum dotted pistol frames, whose serial number is printed with a laser, when etching techniques are not successful. We can also observe acid treated steel surfaces and enhance the images of recovered serial numbers, which sometimes lack of definition.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.We present an application of the use of stereoscope to recovering obliterated firearms serial number. We investigate a promising new combined cheap method using both non-destructive and destructive techniques. With the use of a stereomicroscope coupkd with a digital camera and a flexible cold light source, we can capture the image of the damaged area, and with continuous polishing and sometimes with the help of image processing techniques we could enhance the observed images and they can also be recorded as evidence. This method has already proven to be useful, in certain cases, in aluminum dotted pistol frames, whose serial number is printed with a laser, when etching techniques are not successful. We can also observe acid treated steel surfaces and enhance the images of recovered serial numbers, which sometimes lack of definition.

Fourier synthesis of moire-like pattern intensity profile in photorefractive sinusoidal phase gratings superposition

Fourier synthesis of dynamic Moire-like patterns generation with square intensity profile obtained by the superposition of more than two dynamic sinusoidal phase gratings is described. The sinusoidal phase gratings of slightly different pitches are involved and occur in the photorefractive crystal Bi12TiO20 (BTO). This holographic dynamic medium has been used in anisotropic two wave mixing architecture in diffusion only recording mechanism.

Photorefractive holographic polarization fringe discrimination

In this work we show a real time holographic polarization fringes discrimination. It is based on the dynamic anisotropic diffraction properties that happen in cubic photorefractive crystals of the sillenite family.