Argon ion laser and halogen lamp activation of a dark and light resin composite: microhardness after long-term storage

Influence of cavity preparation with Er,Cr:YSGG laser and restorative materials on in situ secondary caries development

OBJECTIVE

The aim of this study was to evaluate the influence of cavity preparation and restorative materials containing fluorides in the prevention of secondary caries lesion development in situ.

METHODS

A total of 120 blocks obtained from human teeth were divided into two groups and standardized cavities were prepared using diamond burs (DB) or Er,Cr:YSGG-laser [20 Hz, 4.0W, 55% water, 65% air (LA)]. They were divided into three subgroups according to the restorative material (n=20): glass-ionomer cement (GI), resin modified glass-ionomer (RM) or composite resin (CR). Blocks were fixed in palatal intra-oral appliances worn in situ by 20 human volunteers, who dropped 20% sucrose solution eight times daily. After 21 days, blocks were removed and restorations were cross-sectioned to evaluate microhardness [Knoop hardness number (KHN)] underneath enamel surface from 30 to 200 μm. Factors "cavity preparation," "restorative materials," and "depth" were evaluated by three way ANOVA, followed by Tukey test (p<0.05).

RESULTS

The results showed lower microhardness in cavities prepared with DB than in cavities prepared with LA. At 30 μm, there were no statistical significant differences with regard to "cavity preparation" or "restorative materials" factors. In depth evaluation, the enamel microhardness progressively increased as a function of depth for the GI groups. In the groups prepared with LA at 60 μm/90 μm, there were no significant differences between GI and RM materials, whose microhardnesses were significantly higher than that of CR.

CONCLUSIONS

Cavity preparation using Er,Cr:YSGG laser increases caries resistance of enamel walls, and reduce caries lesion depth development regardless of fluoride presence in the restorative material. CR showed higher caries lesion development than GI, and RM showed intermediate results.

Interaction of LED light with coinitiator-containing composite resins: effect of dual peaks

OBJECTIVES

Recently the colour stability of composite resins has been an issue due to the emphasis on the aesthetics of restored teeth. The purpose of the present study was to investigate how dual-peak LED units affect the polymerization of coinitiator-containing composite resins.

MATERIALS AND METHODS

Five composite resins [coinitiator-containing: Aelite LS Posterior (AL), Tetric EvoCeram (TE), and Vit-l-escence (VI); only CQ-containing: Grandio (GD) and Filtek Z350 (Z3)] were light cured using four different light-curing units (LCUs). Among them, Bluephase G2 (BP) and G-light (GL) were dual-peak LED LCUs. Microhardness, polymerization shrinkage, flexural, and compressive properties were measured.

RESULTS

BP and GL had no consistent effect on the microhardness of AL, TE, and VI on the top and bottom surfaces of resin specimens. Among the specimens, AL and VI showed the least (9.86-10.41 μm) and greatest (17.58-19.21 μm) polymerization shrinkage, respectively. However, the effect of BP and GL on the shrinkage of specimens was not consistent. Among the specimens, GD showed the greatest flexural properties [strength (FS) and modulus (FM)] and TE showed the lowest flexural and compressive properties [strength (CS) and modulus (CM)]. In same resin product, maximum FS and CS differences due to the different LCUs were 10.3-21.0% and 3.6-9.2%, respectively. Furthermore, the influences of BP and GL on FS and CS were not consistent.

CONCLUSION

The tested dual-peak LED LCUs had no consistent synergic effect on the polymerization of coinitiator-containing composite resins as compared with QTH and single-peak LED LCUs.

CLINICAL SIGNIFICANCE

The dual-peak LED LCUs achieve a similar degree of polymerization in coinitiator-composite resins as QTH and single-peak LED LCUs did. Choice of LCU does not appear to be a determinant of the light curing of coinitiator-composite resins.

Effects of different surface treatments and accelerated artificial aging on the bond strength of composite resin repairs

The purpose of the present study was to assess the bond strength of composite resin repairs subjected to different surface treatments and accelerated artificial aging. 192 cylindrical samples (CSs) were prepared and divided into 24 groups (n = 8). Half of the CSs were stored in water for 24 h, and the other half were subjected to C-UV accelerated aging for non-metallic specimens. The treatments were phosphoric acid + silane + adhesive (PSA); phosphoric acid + adhesive (PA); diamond bur + phosphoric acid + silane + adhesive (DPSA); diamond bur + phosphoric acid + adhesive (DPA); air abrasion + phosphoric acid + silane + adhesive (APSA); and air abrasion + phosphoric acid + adhesive (APA). The repair was performed and the specimens were again aged as described above. A control group (n = 8) was established and did not receive any type of aging or surface treatment. The specimens were loaded to failure in shear mode with a crosshead speed of 0.5 mm/min until fracture. Data were analyzed by one-way ANOVA/Tukey's test (p < 0.05). No statistically significant differences were found among DPSA, DPA, APSA, APA, and the control group. The aged PSA and PA achieved low bonding values and were statistically different from the control group, whereas the non-aged PSA and PA presented no statistically significant difference from the control group. Repairs with the proposed surface treatments were viable on both recent and aged restorations; however, phosphoric acid + adhesive alone were effective only on recent restorations.

Influence of nanometer scale particulate fillers on some properties of microfilled composite resin

The aim of this study was to evaluate the effect of different weight fractions of nanometer sized particulate filler on properties of microfilled composite resin. Composite resin was prepared by mixing 33 wt% of resin matrix to the 67 wt% of silane treated microfine silica particulate fillers with various fractions of nanometer sized fillers (0, 10, 15, 20, 30 wt%) using a high speed mixing machine. Test specimens made of the composites were tested with a three-point bending test with a speed of 1.0 mm/min until fracture. Surface microhardess (Vicker's microhardness) was also determined. The volumetric shrinkage in percent was calculated as a buoyancy change in distilled water by means of the Archimedes principle. The degree of monomer conversion (DC%) of the experimental composites containing different nanofiller fractions was measured using FTIR spectroscopy. Surface roughness (Ra) was determined using a surface profilometer. Nanowear measurements were carried out using a nanoindentation device. The water uptake of specimens was also measured. Parameters were statistically analysed by ANOVA (P < 0.05). The group without nanofillers showed the highest flexural strength and modulus, DC% and Ra value. The group with 30% nanofillers had the highest water uptake and volumetric shrinkage. No significant difference was found in Vicker's microhardness and the nanowear of the composites. The plain microfilled composite demonstrated superior properties compared to the composites loaded with nanofillers with the exception of surface roughness.

Influence of DPSS laser on polymerization shrinkage and mass change of resin composites

OBJECTIVES

This study evaluated the effectiveness of the diode-pumped solid state (DPSS) laser as a light source for light-curing dental resin composites.

BACKGROUND DATA

A DPSS laser of 473  nm may be useful because of its match with the absorption peak of camphorquinone (CQ), the photoinitiator.

MATERIALS AND METHODS

A DPSS laser (LAS) of 473  nm and a quartz-tungsten-halogen (QTH) light-curing unit (OP) were used as the light sources for light curing six different resin composites (four nanocomposites and two hybrid composites). Polymerization shrinkage and mass change (water sorption and solubility) were measured during and after light curing to determine the degree of polymerization. Mass change was evaluated by following the ISO 4049 standard.

RESULTS

According to the evaluation, the specimens light cured using LAS showed similar maximum polymerization shrinkage (12.3∼18.1  μm for LAS; 13.2∼16.2  μm for OP) and water sorption (11.4∼24.1  μg/mm(3) for LAS; 11.3∼22.8  μg/ mm(3) for OP) to the cases light cured using OP. The specimens light cured using LAS showed a significantly higher solubility than the cases light cured using OP (2.4∼6.6  μg/ mm(3) for LAS; 0.8∼1.6  μg/ mm(3) for OP). However, the maximum water sorption and solubility obtained from the specimens were lower than the values permitted by the ISO 4049 standard.

CONCLUSIONS

The results may suggest that the DPSS laser with an emission wavelength of 473  nm can be used as a light source for light-curing dental resin composites.