Rapid Communication: Argon Laser Polymerization of Composite: Blue Lines vs. Multilines

Measurement of solubility and water sorption of dental nanocomposites light cured by argon laser

Different parameters used for photoactivation process and also composition provide changes in the properties of dental composites. In the present work the effect of different power density of argon laser and filler loading on solubility (SL) and water sorption (WS) of light-cure dental nanocomposites was studied. The resin of nanocomposites was prepared by mixing bisphenol A glycol dimethacrylate (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) with a mass ratio of 65/35. 20 wt.% and 25 wt.% of nanosilica fillers with a primary particle size of 10 nm were added to the resin. Camphorquinone (CQ) and DMAEMA were added as photoinitiator system. The nanocomposites were cured by applying the laser beam at the wavelength of 472 nm and power densities of 260 and 340 mW/cm(2) for 40 sec. Solubility and water sorption were then measured according to ISO 4049, which in our case, the maximums were 2.2% and 4.3% at 260 mW/cm(2) and 20% filler, respectively. The minimum solubility (1.2%) and water sorption (3.8%) were achieved for the composite containing 25% filler cured at 340 mW/cm(2). The results confirmed that higher power density and filler loading decreased solubility of unreacted monomers and water sorption and improved physico-mechanical properties of nanocomposites.

Photopolymerization of dental resin as restorative material using an argon laser

The effect of the 488-nm wavelength of argon laser at different power densities and irradiation times on the degree of conversion (DC), temperature rise, water sorption, solubility, flexural strength, flexural modulus, and microhardness of bisphenole A glycol dimethacrylate and triethylen glycol dimethacrylate with a mass ratio of 75:25 was studied. Camphorquinone and N,N'-dimethyl aminoethyl methacrylate were added to the monomer as a photo initiator system. The DC% of the resin was measured using Fourier transform infrared spectroscopy. The maximum DC% (50%), which was reached in 20 s, and temperature rise because of the reaction (13.5 degrees C) were both higher at 1075 than 700 mW/cm(2). Water sorption and solubility were measured according to ISO4049, which in our case were 23.7 and 2.20 microg/mm(3) at 1075 mW/cm(2), respectively. A flexural modulus of 1.1 GPa and microhardness of 19.6 kg/mm(2) were achieved above the power density. No significant difference was observed (i.e., p>0.05) for water sorption and flexural strength at 700 and 1075 mW/cm(2).

The effect of irradiation wavelength bandwidth and spot size on the scraping depth and temperature rise in composite exposed to an argon laser or a conventional quartz-tungsten-halogen source

OBJECTIVES

The purpose of this study was to investigate the effect of the spectral distribution of the curing irradiation near the maximum excitation wavelength of the photo-initiator and the effect of the irradiation spot size on the scraping depth-of-cure and temperature rise in a resin composite for both an argon laser and a quartz-tungsten-halogen lamp.

METHODS

Using bandpass filters, the spectral outputs of an argon laser and a quartz-tungsten-halogen lamp were restricted to pass selected wavelengths on to a commercial camphorquinone-based resin composite and the depth-of-cure, using scraping methods, was measured. The temperature rise in composite was measured for some of the above-mentioned sources. The spot sizes for both sources were varied and the scraping depth was measured. Lateral curing or the extent of curing away from the focused spot was also measured.

RESULTS

For constant power density and exposure time, an irradiation spectral distribution closer to the photo-initiator excitation peak yielded a higher scraping depth than a broadband spectral distribution for both sources. Under similar conditions, the argon laser resulted in a lower temperature rise in the composite than the lamp. For the same total energy imparted to the resin composite, the scraping depth increased with reducing spot size of the curing irradiation. Furthermore lateral curing of the composite well beyond the irradiation spot size was observed.

SIGNIFICANCE

The spectral and spatial characteristics of the curing irradiation need to be carefully considered as these affect the scraping depth-of-cure and temperature rise in a resin composite.

Effects of argon laser curing on dentin shear bond strengths

Previous studies have demonstrated the ability of the argon laser to polymerize light-activated materials and improve enamel shear bond strengths. This study was conducted to evaluate the effects of the argon laser on dentin shear bond strengths of current dentin bonding systems. Argon laser (HGM Model 8) at 231 and 280 mW, 5 sec bonding agent, 10 sec composite, and a conventional curing light (Translux EC/Kulzer) at 10 sec bonding agent, 20 sec composite were used to polymerize samples of dentin bonding systems [Scotchbond Multi-Purpose Plus (3M) and Prime Bond (Dentsply/Caulk), both with TPH (Dentsply/Caulk) composite]. A flat dentin bonding site (600 grit) was prepared on the buccal surface of extracted human teeth. Twelve samples were made for each set of parameters for both laser and conventional light totaling 48 samples. Samples were stored in distilled water in light-proof containers for 24 h at 37 degrees C. Shear bond strengths (MPa) were determined for each sample on the Instron testing machine. Mean values were calculated for each set of data and ANOVA with Fisher PLSD were used for statistical analysis. The argon laser provided bond strengths that were 21-24% greater than those of the conventional curing light system.