No abstract

Resin composite shades and resin composite polymerization performed with a distanced light tip are factors that can affect polymerization effectiveness. This in vitro study aimed to evaluate the influence of curing tip distance and resin shade on the microhardness of a hybrid resin composite (Z250-3M ESPE). Forty-five resin composite specimens were randomly prepared and divided into nine experimental groups (n = 5): three curing tip distances (2 mm, 4 mm, and 8 mm) and three resin shades (A1, A3.5, and C2). All samples were polymerized with a continuous output at 550 mW/cm(2). After 24 hours, Knoop microhardness measurements were obtained on the top and bottom surfaces of the sample, with a load of 25 grams for 10 seconds. Five indentations were performed on each surface of each sample. Results showed that bottom surface samples light-cured at 2 mm and 4 mm presented significantly higher hardness values than samples light-cured at 8 mm. The resin shade A1 presented higher hardness values and was statistically different from C2. The resin shade A3.5 did not present statistical differences from A1 and C2. For the top surface, there were no statistical differences among the curing tip distances. For all experimental conditions, the top surface showed higher hardness values than the bottom surface. It was concluded that light curing tip distance and resin shade are important factors to be considered for obtaining adequate polymerization.

The aim of this in vitro study was to evaluate the effect of different mouthwashes on superficial roughness and Knoop hardness of two resin composites. Eighty specimens (6 mm Ø and 2 mm height) were prepared and divided into eight experimental groups (n = 10) according to the resin composites (4 Seasons and Esthet X), and storage solutions (G1 - Distilled water; G2 - Colgate Plax Overnight; G3 - Colgate Plax Alcohol Free; and G4 - Colgate Plax Whitening). The initial hardness and roughness readings (T1) were measured and then the specimens were stored in 2 mL of mouthwash for 12 h (T2) and 24 h (T3). The data were analyzed with repeat-measures two-way ANOVA and Tukey's test (α = 5%). Regardless of the type of solution and time of exposure, there was no statistical difference for roughness between the resins (p = 0.44). G4 and G8 presented higher roughness means than G1, G3, G5 and G7, after 12 and 24 hours of immersion. For Knoop microhardness analysis, there was a significant reduction for all groups after 12 hours and 24 hours. We conclude that the mouthwashes containing hydrogen peroxide and/or alcohol decrease the microhardness of the resins tested; however, the mouthwash containing hydrogen peroxide had a higher deleterious effect on roughness.

Superficial stains and irregularities of the enamel are generally what prompt patients to seek dental intervention to improve their smile. These stains or defects may be due to hypoplasia, amelogenesis imperfecta, mineralized white spots, or fluorosis, for which enamel microabrasion is primarily indicated. Enamel microabrasion involves the use of acidic and abrasive agents, such as with 37% phosphoric acid and pumice or 6% hydrochloric acid and silica, applied to the altered enamel surface with mechanical pressure from a rubber cup coupled to a rotatory mandrel of a low-rotation micromotor. If necessary, this treatment can be safely combined with bleaching for better esthetic results. Recent studies show that microabrasion is a conservative treatment when the enamel wear is minimal and clinically imperceptible. The most important factor contributing to the success of enamel microabrasion is the depth of the defect, as deeper, opaque stains, such as those resulting from hypoplasia, cannot be resolved with microabrasion, and require a restorative approach. Surface enamel alterations that result from microabrasion, such as roughness and microhardness, are easily restored by saliva. Clinical studies support the efficacy and longevity of this safe and minimally invasive treatment. The present article presents the clinical and scientific aspects concerning the microabrasion technique, and discusses the indications for and effects of the treatment, including recent works describing microscopic and clinical evaluations.

This in vitro study evaluated the effectiveness of whitening dentifrices for the removal of extrinsic tooth stains. Twenty dental blocks (4 x 4 mm), including enamel and dentine, removed from freshly extracted bovine incisors, were randomly divided into 4 groups: G1 -distilled water, G2 -Colgate, G3 -Crest Extra Whitening and G4 -Rapid White. In all specimens, the dentin was covered with colorless nail polish, and the enamel was left exposed. Next, the specimens were immersed in a solution of black tea, which was changed every 24 h, for a period of 6 days. After this period, a photo-reflectance reading was taken (Time 1) with a spectrometer. The stained specimens were then submitted to linear brushing movements (5,000 cycles) using brushes (Oral B-Soft) coupled to an automatic toothbrushing machine, under a static axial load of 200 g and with a speed of 4 movements/second, at 37°C, with the dentifrice or water being injected every 60 s. When toothbrushing ended, a second photo-reflectance reading was taken (Time 2). The results were submitted to two-criteria analysis of variance (ANOVA) and to the Tukey test (α = 0.05). When the two times for a same group were compared, Time 2 presented the highest reflectance values with statistical difference only for G3 and G4. Among the dentifrices tested, only the Rapid White group differed from the control group, presenting the highest reflectance values. Only the whitening dentifrice Rapid White was effective for the removal of extrinsic stains.