Jozo Šutalo

Pulsed blue laser curing of hybrid composite resins

Clinical performance of light-curing composite restorations is greatly influenced by the quality of the curing-light. Currently used photopolymerization units have some important drawbacks, such as decreasing light output with time and distance, which results in a relatively low degree of conversion and shallow depth of cure, particularly of darker shades. Experiments with continuous argon laser polymerization showed overheating of the composite sample, as well as increased shrinkage of the material. In this study a pulsed laser, set at 468 nm (the maximum of the camphorquinone absorption coefficient), with 20-ns pulse duration, repetition rate of 10 Hz and energy of 10 mJ per pulse, was used as a light source. The aim of the study was to evaluate the effect of polymerization of light and dark shades of three different hybrid composites cured by pulsed laser at the surface and at 3.0 mm depth. The degree of conversion was measured by Fourier transform infrared spectroscopy (FTIR). Applying pulsed blue laser, significantly better results were obtained for both shades compared to standard polymerization values. Very weak dependence of the degree of conversion, between the surface measurements and those at 3.0 mm, were observed in the case of pulsed laser polymerization due to the piercing nanopulses and the monochromatic light at 468 nm.

Visualization of marginal integrity of resin-enamel interface by holographic interferometry

This study determined whether it was possible to detect deformations and fractures in dental hard tissues or in composite material from internal stresses using double-exposure holographic interferometry. On the proximal side of eight intact human permanent premolars, a direct Class II cavity was prepared and restored with a self-etching adhesive (Clearfil SE Bond) and Tetric Ceram, a resin composite. In five of the specimens, Tetric Flow was used as an elastic layer. The samples were illuminated using a helium-neon laser beam, and the holograms of samples were recorded using Agfa 10E75 photographic plates. Hologram reconstructions were captured with an 8-bit monochrome CCD camera and qualitatively analyzed. Deformations and fractures appeared as fringe patterns on all interferograms, where the distribution of fringes provided location information, while the density of fringes gave the amplitude information. Greater fringe densities were observed in samples treated without a flowable composite.

Measurement of the composite resin thickness variations using digital interferometry

Digital interferometry based device for measuring the thickness variations of the resin composite materials during blue light polymerization is described. The proposed device enables two types of quantitative measurements providing data for the total displacement and the dynamic behavior of displacement. The effect of the thermal expansion as well as polymerization shrinkage can be clearly resolved between different materials, curing lights and modes. The effectivness of our experimental device is illustrated with selected results obtained for a commercial dental material.

Temperature changes inside the molar pulp chamber and on the enamel and root surfaces induced by the CO2 laser beam, in vitro

The application of the CO2 laser continuous wave to hard dental tissue causes temperature changes on the impact area, on the adjacent area and inside the pulp chamber. The purpose of this study was to investigate the thermal effects induced by the CO2 laser continuous wave, and the temperature flow through adjacent areas. Forty healthy molars, 15 molars with class II amalgam restoration and 10 canines with cervical caries extracted for periodontal reasons were irradiated with laser beam. On the occlusal surface the class I preparation was made just beyond the dentine-enamel junction. Temperature changes were measured at the enamel, root surface and at the cross section of the previously prepared holes 3 mm in diameter which were made 2 mm above the bifurcation level.