Effect of different bleaching techniques on DNA damage biomarkers in serum, saliva, and GCF.

Bleaching agents containing a high concentration of H2O2 in the dental market lead to formation of reactive oxygen species, which have genotoxic effects. However, ozone bleaching, one of the most effective oxidants known, stimulates blood circulation and immune response and thus it has strong antimicrobial activity against viruses, bacteria, fungi, and protozoa. For these reasons, one of our hypothesis was ozone bleaching would reduce local and systemic DNA damage in the body. Hence, we aimed to determine the oxidative DNA damage biomarker levels in serum, saliva, and gingival crevicular fluid (GCF) by measuring 8-hydroxy-2'-deoxyguanosine (8-OHdG) after different bleaching methods.Forty-eight volunteers who requested dental bleaching were divided into three treatment groups (n = 16). Group 1: ozone bleaching with the ozone-releasing machine; Group 2: chemical bleaching with 40% hydrogen peroxide (H2O2) gel; Group 3: 40% H2O2 gel activated with the diode laser. Initial and post-operative (immediately after bleaching and two weeks later) color measurements were performed with a spectrophotometer. The color changes were calculated with the CIEDE2000 (ΔE 00) formula. 8-OHdG levels in serum, saliva, and GCF samples were determined with ELISA. All three treatments resulted in efficient and statistically similar bleaching. The 8-OHdG levels in the serum and saliva were not affected by all bleaching methods (p > 0.05), but a temporary increase was observed in the GCF for chemical and laser-assisted groups except the ozone group (p > 0.05). According to the findings, chemical and laser-assisted bleaching can affect DNA damage locally but not systemically. Bleaching with ozone may eliminate this local DNA damage.

The effect of post-cure heating on residual, unreacted monomer in a commercial resin composite.

OBJECTIVES: This paper examined the influence of post-cure temperature on the amount of unreacted monomer remaining in a commercial light-cured resin composite restoration following initial light-curing and subsequent post-cure heating. METHODS: Discs of composite were light-cured and then subjected to immediate post-cure heating (50, 75, 100, or 125 degrees C for 7 min) or were left unheated (control). They were then placed in a solvent for two weeks at 37 degrees C to extract the unreacted monomer. HPLC analysis was used to determine the amounts of TEGDMA, BIS-GMA, and ethoxylated BIS-GMA remaining after the different treatments. The amounts of each monomer leaching were compared using ANOVA with respect to the different curing treatments. RESULTS: Even the lowest post-cure heat treatment (50 degrees C) resulted in 80% reduction in remaining, unreacted TEGDMA, 75% reduction in BIS-GMA, and 77% lower ethoxylated BIS-GMA than the light-cured only control. Post-cure heating at 75 degrees C and above resulted in the lowest amount of each type monomer remaining uncured in the polymer and did not significantly decrease with an increase in post-cure temperature for the most part. SIGNIFICANCE: One of the main benefits of post-cure heating of resin composite restorations could be the enhancement of biocompatibility of these restorations as a result of the significant decrease in potentially leachable, unreacted monomer.

Effect of post-cure temperature and heat duration on monomer conversion of photo-activated dental resin composite.

OBJECTIVES: This research evaluated the relationship between post-cure heating temperature and duration on the monomer conversion of a commercial light-activated resin composite. METHODS: Disc-shaped composite specimens (10 x 1 mm) were initially light-cured and then submitted to one of the following post-cure. CONDITIONS: None (control), 50 degrees, 75 degrees, 100 degrees or 125 degrees C for 0.5, 1, 3, 5, or 7 min. After curing, specimens were stored in the dark at room temperature. Monomer conversion of all specimens was then determined using infrared spectroscopy. RESULTS: Post-cure temperature was 12 times more influential than was heal duration on the extent of resin cure. The extent of cure increased linearly with an increase in post-cure temperature. Post-cure specimens that were heated between 3 and 7 min demonstrated equivalent cure values. All post-cure healing conditions resulted in significantly higher cure values than the light-cured only control. SIGNIFICANCE: Physical properties of post-cure heated composites may change with respect to aging and water, but monomer conversion values of post-cure heated materials remain unaltered. Results of this study validate the use of relatively high temperatures for increasing the extent of monomer conversion. Such increases may lead to more biocompatible restorations.

Mass loss in urethane/TEGDMA- and Bis-GMA/TEGDMA-based resin composites during post-cure heating.

OBJECTIVES: This research examined weight loss of commercial UDMA/TEGDMA- and Bis-GMA/TEGDMA-based resin composites at a variety of post-cure temperatures. Weight loss profiles of individual monomer components were also tested at elevated temperature: Bis-GMA, ethoxylated Bis-GMA (EBis-GMA), urethane dimethacrylate (UDMA), and triethyleneglycol dimethacrylate (TEGDMA). METHODS: Disc-shaped composite specimens (1 x 5 mm, approximately 50 mg) were light-cured and then isothermally post-cure heated in a thermogravimetric analysis (TGA) unit at either 50 degrees, 75 degrees, 100 degrees, 125 degrees or 150 degrees C. A single specimen was made for each post-cure temperature for each product (a total of 10 discs). Individual monomer components were heated to 800 degrees C. Filler and organic phase weight percentages were determined by ashing cured composite in the TGA. Weight loss differences between resin systems at various post-cure temperatures were analyzed using linear regression. RESULTS: For each type of composite, loss of volatile component increased with both elevated post-cure temperature as well as duration of heat exposure. Using recommended post-cure temperature and time (125 degrees C for 7.5 minutes), there was no difference in weight loss profile between the two products: both exhibited 1.3% loss of resin component. After 10 min of heating, the Bis-GMA-based product always demonstrated a greater weight loss than the UDMA material. Weight loss could not be attributed to any specific monomer. SIGNIFICANCE: Specimen weight loss during post-cure heating may result in a depletion of leachable, unreacted material at the restoration surface, possibly enhancing material properties at that location. This decrease would also potentially reduce the biological impact of leachable materials. Loss of volatile components from post-cure heating would affect the accuracy of infrared spectroscopic techniques in determining monomer conversion values.