Enamel erosion control by strontium-containing TiO2- and/or MgO-doped phosphate bioactive glass.

OBJECTIVES: To evaluate the effect of strontium-containing titanium- and/or magnesium-doped phosphate bioactive glass on the control of dental erosion. MATERIALS AND METHODS: Fifty fragments of human enamel were divided into five groups: negative control, 45S5 bioglass, strontium-containing Ti-doped phosphate bioactive glass (PBG-Ti), strontium-containing Mg-doped phosphate bioactive glass (PBG-Mg), and strontium-containing Ti- and Mg-doped phosphate bioactive glass (PBG-TiMg). The specimens underwent cycles of erosive challenge twice daily for 5 days with 1 mL of citric acid for 2 min followed by 1 mL of the suspension with bioactive substances for 3 min. After the cycles, profilometry, roughness and microhardness testing, and scanning electron microscopy (SEM) were performed. The following statistical tests were used: one-way ANOVA (profile, roughness, and surface microhardness (%VMS) data variation), Tukey's HSD (%VMS), Games-Howell test (profilometry), Student's t test (roughness), and Pearson's correlation between the variables. RESULTS: The lower loss of enamel surface and lower %VMS was observed in the PBG-Mg and PBG-TiMg groups, and only the PBG-Mg group showed similar roughness between baseline and eroded areas (p > 0.05). On SEM micrographs, PBG-Ti and PBG-Mg groups showed lower apparent demineralization. CONCLUSION: All bioactive materials protected the enamel against erosion. However, strontium-containing phosphate bioactive glasses showed lower enamel loss, and the presence of Mg in these bioactive glasses provided a greater protective effect. CLINICAL RELEVANCE: Experimental strontium-containing phosphate bioactive glasses are effective in controlling enamel erosion. The results obtained in this study will guide the development of new dental products.

Performance of Dental Students in Shade Matching: Impact of Training.

OBJECTIVE: The present study evaluated the effect of training on dental students' ability for matching two different shade guides. MATERIALS AND METHODS: The study was conducted in 2012. The participants were 88 male and female undergraduate dental students from Brazil and Portugal, with or without previous color education and vision refractive errors (response rate of 73.33%). They were asked to match a pair set of the shade guides Vita Classical (VC) and Vitapan 3D Master (3DM), with a 20-minutes' rest between each match. The sets were assembled over a neutral gray background and under controlled light. About 7-10 days later, all participants watched a video lecture on color education and repeated the matching procedure. The percentage of matches was calculated and submitted to statistical analysis for the variables gender, geographic region, shade guide and previous color education (Mann-Whitney tests), vision refractive errors (Kruskal-Wallis), and training (Wilcoxon signed rank). All tests were performed at a confidence level of 95%. RESULTS: Training increased the percentage of matches for all groups, except for Portuguese and hyperopic individuals (VC and 3DM) and men (3DM). Previous color education affected VC shade matching before training. Gender, refractive errors, and geographic region did not affect shade matching ability. CONCLUSIONS: Previous education and training in color positively affected shade-matching ability of dental students on shade guide pairing tests. CLINICAL SIGNIFICANCE: The subjectivity of the visual method might not be a clinical concern in daily practice. The human eye can detect small differences in color and visualize the tooth with all its complex geometry, multilayered tissues, and secondary color parameters. Therefore, any color-matching task will be judged by the patient and/or other observers with consideration to this complexity. In other words, visual assessment is paramount to the success/failure of esthetic restorative procedures. The efficiency of the visual color method may be improved by color education through the development of professional color discrimination ability. This would make the students responsible for color selection, reproduction, and evaluation and lead to increased capability over a layperson observer receiving the restorative treatment. (J Esthet Restor Dent 29:E24-E32, 2017).

Effect of desensitizing agents on the microtensile bond strength of two-step etch-and-rinse adhesives to dentin.

Desensitizers can be used to control postoperative sensitivity in adhesive restorations. The aim of this study was to evaluate the effect of desensitizing agents on the bond strength of two-step etch-and-rinse adhesive systems to dentin. Forty-two human molars were sectioned to obtain 3-mm-thick dentin discs. The discs were divided into three groups (n = 14 in each) - no-treatment control group (CT), and oxalic acid [BisBlock (BB)] and calcium phosphate [Desensibilize Nano-P (NP)] desensitizers - before the application of two adhesive systems [Adper Single Bond Plus (SB) and One-Step Plus (OSP)]. A nanoparticle composite resin was used to create a 3-mm-thick build-up. The specimens were stored in distilled water for 24 h before a microtensile bond-strength test was performed. The failure modes were determined using a stereomicroscope at 100 × magnification. Specimens were sectioned perpendicular to the interface for scanning electron microscopy analyses. The CT-SB group exhibited the highest bond strength, differing significantly from BB-SB and BB-OSP groups. Mixed failures were prevalent for all groups. Scanning electron microscopy revealed a continuous hybrid layer and resin tags in all groups. Dentin bond strength of etch-and-rinse adhesive systems was reduced by an oxalic acid desensitizer but was not affected by a calcium phosphate-containing desensitizer.

When adherence to CPAP fails, how do we treat workers with obstructive sleep apnea?

Aims: A cross-sectional study was designed to evaluate the effectiveness of a mandibular advancement device (MAD) with respect to respiratory and sleep parameters among miners with obstructive sleep apnea syndrome (OSAS) and primary snore. Methods: The target sample was composed by 102 Brazilian miners with a history of non-adherence to continuous positive airway pressure. All patients were treated with a MAD and underwent pre and post-treatment full-night polysomnography. Ethical approval and consents were obtained. Bivariate and logistic regression analyses were conducted. The level of statistical significance was set at 5%. Results: After the treatment with MAD, 71.8% of patients presented a decrease ≥ 50% in the basal apnea-hypopnea index (AHI), 51.2% presented an AHI < 5 events/h and 83.3% reached an AHI<10/h, whereas 22.5% did not show any changes and 7.5% of the sample presented an increase in the AHI (p<0.05). There was an increase in the mean SpO2 nadir (p<0.001) and in the baseline duration of the REM sleep stage (p<0.05). The MAD significantly decreased snore events (p<0.05). Multivariate analysis did not identify predictive factors related to therapy success (decrease ≥ 50% of AHI). However, basal AHI was a significant predictor related to the secondary endpoint (AHI<10/h) (OR= 1.06, IC 95%1.00-1.13, p=0.007). Conclusions: The MAD therapy showed significant improvements in AHI, minimum oxygen saturation, REM sleep and snoring.

Number of dental abutments influencing the biomechanical behavior of tooth‒implant-supported fixed partial dentures: A finite element analysis.

Background. Local or systemic issues might prevent installing a sufficient number of dental implants for fixed prosthetic rehabilitation. Splinting dental implants and natural teeth in fixed dentures could overcome such limitations. Therefore, this study aimed to evaluate the influence of the number of dental abutments in the biomechanics of tooth‒implant-supported fixed partial dentures (FPDs). The null hypothesis was that increasing the number of abutment teeth would not decrease the stress over the abutments and surrounding bone. Methods. Left mandibular lateral incisor, canine, premolars, and molars were reconstructed through computed tomography and edited using image processing software to represent a cemented fixed metal‒ceramic partial denture. Three models were set to reduce the number of abutment teeth: 1) lateral incisor, canine, and first premolar; 2) canine and first premolar; 3) the first premolar. The second premolar and first molar were set as pontics, and the second molar was set as an implant abutment in all the models. Finite element analyses were performed under physiologic masticatory forces with axial and oblique loading vectors. Results. After simulation of axial loads, the stress peaks on the bone around the implant, the bone around the first premolar, and prosthetic structures did not exhibit significant changes when the number of abutment teeth decreased. However, under oblique loads, decreasing the number of abutment teeth increased stress peaks on the surrounding bone and denture. Conclusion. Increasing the number of dental abutments in tooth‒implant-supported cemented FPD models decreased stresses on its constituents, favoring the prosthetic biomechanics.

Effect of storage temperature on pH of in-office and at-home dental bleaching agents.

The aim of this study was to determine the pH of several commercially available in-office and at-home dental bleaching products stored at room temperature and refrigerated. The products were divided into in-office (n=09) and at-home (n=12) bleaching gels and submitted to two different temperatures, namely, room temperature (23 degrees C +/- 1 degree C) and refrigeration temperature (4 degrees C +/- 1 degree C). The pH was measured using a portable pH meter with a direct electrode, which was calibrated with standard buffer solutions at pH 4.0 and 7.0 and recalibrated for each new product. The pH of the dental bleaching products tested ranged from 2.39 +/- 0.10 to 6.52 +/- 0.09, and was found to vary significantly both with temperature and between bleaching agents. Most of the bleaching gels were found to be acidic, especially the in-office bleaching products, and the refrigerated at-home gels had the highest pH values. Thus, we conclude that the storage temperature affected the pH of the products tested.

Analysis of transmittance and degree of conversion of composite resins.

The objective of this study was to evaluate and correlate light transmittance (T), initial degree of conversion (IDC), and degree of conversion after 24 hr (DC24) for 22 composite resins (CR) for enamel and dentin use. The transmittance (n = 10) was measured with a spectrometer at a wavelength of 468.14 nm. The degree of conversion (DC; n = 5) was measured with Fourier Transform Near-Infrared Spectroscopy before polymerization, immediately after photoactivation, and 24 hr after photoactivation. Both sets of values are provided as percentages. ANOVA and Games-Howell (α = 5%) tests showed that Filtek Supreme Ultra gave the highest T values of all enamel CRs, while Esthet-X HD presented the lowest. Meanwhile, Venus diamond gave the highest values of all dentin CRs, while Esthet-X HD gave the lowest. For IDC and DC24, ANOVA showed differences between individual CRs and the two CR types (p < .0001). Despite the limitations of this study, it can be concluded that there was no correlation between T and either IDC or DC24 (p > .05); however, IDC and DC24 were strongly correlated (p < .05) by Pearson's correlation. That being said, as a higher DC reflects better mechanical properties, certain conclusions can be drawn about overall performance. The best IDC values were observed for the Opallis enamel resin and the Opallis and Premise dentin resins. Meanwhile, the best DC24 values were observed for the Opallis, Charisma, and Premise enamel resins and the Opallis and Premise dentin resins. Degree of conversion and light transmittance showed differences between composite resin types (enamel and dentin) and brands. It is important to know at the moment of composite choice taking into account mechanical and optical properties.

Fluorescence intensity of resin composites and dental tissues before and after accelerated aging: a comparative study.

This study quantitatively evaluated the fluorescence intensity of resin composites with different opacities and translucencies and determined changes in fluorescence after accelerated aging, using human enamel and dentin as controls. Six microhybrid and nanofilled composites, each in three different shades, were tested. Ten sound human incisors were used to obtain enamel and dentin specimens separately. Fluorescence measurements were obtained with a fluorescence spectrophotometer before (baseline) and after accelerated aging at 150 kJ energy for 120 hours. One-way analysis of variance (ANOVA) and Games-Howell multiple comparison tests were performed at a significance level of 0.05. Student's t-test was also used for comparison before and after aging. At baseline, there was no statistically significant difference (p>0.05) between the fluorescence intensity of dentin and any of the shades of Charisma or Opallis, Esthet-X dentin shade or Vit-l-escence enamel, or the translucent shades. After accelerated aging, all shades of the 4 Seasons, enamel and the translucent shades of Esthet-X had fluorescence intensities statistically similar to that of aged dentin (p>0.05). A significant reduction in fluorescence after aging (p<0.05) was observed for all the materials, except for human enamel and translucent Filtek Supreme XT. Accelerated aging reduced fluorescence in most of the composites evaluated.

Effect of different surface treatments on the repair bond strength of indirect composites.

PURPOSE: To evaluate the tensile bond strength of indirect composites repaired with different surface treatments and direct composites. METHODS: 180 specimens were prepared with Targis, belleGlass HP and Sculpture indirect composites, light-activated and post-cured according to the manufacturers' recommendations. The specimens were stored in distilled water for 24 hours at 37 degrees C. The bonding surfaces were prepared with air abrasion, hydrofluoric acid or hydrofluoric acid followed by a neutralizing solution. All the treated surfaces were subject to the application of a silane and a bonding agent before the repair procedures with Tetric Ceram and Tetric Flow for the Targis specimens, Herculite XRV and Revolution for the belleGlass HP specimens and Sculp-It and Flow-It for Sculpture specimens. The tensile bond strength tests were carried out using a universal testing machine at cross-head speed of 0.5 mm/minute. The type of fracture was observed under a light microscope at x40 magnification. Data were analyzed by a two-way ANOVA and Tukey's post-hoc tests (P < 0.05). RESULTS: Targis showed a statistically higher repair bond strength than belleGlass HP and Sculpture, which were not significantly different from each other. Air abrasion increased the repair bond strength of belleGlass HP and Sculpture. For Targis, all the surface treatments resulted in similar repair bond strength. The different viscosity of repair composites did not affect the repair of indirect composites. Fractured surfaces showed mostly adhesive failures, mainly with hydrofluoric acid treatment.

Sorption and solubility of composites cured with quartz-tungsten halogen and light emitting diode light-curing units.

AIM: The objective of this study was to evaluate the effect of light polymerization on water sorption and solubility of hybrid composites. METHODS AND MATERIALS: Three composite resins were used to make discs cured with either quartz-tungsten halogen (QTH) or light emitting diode (LED) curing units. The specimens were stored in a desiccator at 37 degrees C and weighted to a constant mass, then immersed in deionized water for different periods of time, and reconditioned until achieving a constant mass. Sorption and solubility were calculated and subjected to analysis of variance (ANOVA) and Tukey tests (p<0.01). RESULTS: There were no statistically significant differences between the light sources. Water sorption increased with storage time for all the composites. The lowest sorption was observed for Herculite XRV, followed by Tetric Ceram, and Filtek Z250. Increased storage times reduced the solubility of Filtek Z250 but did not affect the solubility of Herculite XRV and Tetric Ceram. CONCLUSION: Water sorption and solubility of composites are not affected by the type of polymerization when the same intensity and exposure times are used. Thus, the differences found are probably related to the composition of the materials. CLINICAL SIGNIFICANCE: Water sorption and solubility of composites can lead to a shortened service life. However, these properties are not correlated to the type of polymerization.

In-office dental bleaching and enamel microabrasion for fluorosis treatment.

Recently, mostly as a result of drinking water fluoridation, the number of young patients affected by fluorosis increased considerably. This study describes a minimally invasive technique, using in-office dental bleaching (35% hydrogen peroxide) and enamel microabrasion (silicon carbide and 12% hydrochloric acid) to eliminate fluorosis like stains. The association of techniques was efficient and can be recommended as a good conservative alternative for the treatment of fluorosis affected teeth.

Effect of organic solvents compared to sandblasting on the repair bond strength of nanohybrid and nanofilled composite resins.

BACKGROUND: This study evaluated the effect of different surface treatments on the repair bond strength of nanohybrid (Empress Direct) and nanofilled (Filtek Z350 XT) composite resins. MATERIALS AND METHODS: A total of 120 specimens of each material (7.5 x 4.5 x 3 mm) were prepared and polished with SiC paper. Half of the specimens were kept in water for seven days and the other half for six months; they were then divided into six groups according to the type of surface treatment: negative control (no treatment), Al2O3sandblasted, liquid acetone, acetone gel, liquid alcohol and alcohol gel. Following application of the silane coupling agent and the adhesive system, composite resin cylinders were fabricated on the specimens and light cured (20 seconds). The same composite resins were used for the repair. Additionally, ten intact specimens of each composite resin (without repair) were prepared (positive control). The specimens were then loaded to failure in the microshear mode. Three additional specimens were fabricated in each group, and the surface treatments were analyzed by atomic force microscopy, energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM). RESULTS: The nanofilled composite resin showed higher cohesive strength and repair bond strength than the nanohybrid composite resin. The aging process affected the repair bond strength of the nanofilled composite resin. Al2O3sandblasting was more efficient for the nanofilled composite resin and promoted greater surface roughness in both materials. The solvents demonstrated higher efficacy for the nanohybrid composite resin. CONCLUSION: The strengths resulting from the solvents were material dependent, and Al2O3sandblasting resulted in superior repair bond strength in both materials.

Shear bond strength of resin-modified glass ionomer cement with saliva present and different enamel pretreatments.

The purpose of this study was to evaluate the shear bond strength of resin-modified glass ionomer cement in a saliva-contaminated environment, using different enamel pretreatments. A total of 125 freshly extracted, bovine permanent inferior incisors were divided into five groups. Group I received 10% polyacrylic acid, moistened with saliva/Fuji Ortho LC (FOLC); group II received 37% phosphoric acid, moistened with saliva/FOLC; group III was moistened with saliva/ FOLC, without acid etching; group IV received 10% polyacrylic acid, not moistened with saliva/ FOLC; and group V was used as a control with 37% phosphoric acid/dry/Transbond XT. After the bonding procedures, all samples were thermocycled, tested in a shear mode on a testing machine, and the Adhesive Remnant Index was evaluated. One-way analysis of variance and Tukey's honestly significant difference (HSD) tests indicated that group V yielded the highest shear bond strength (4.09 MPa) but with no statistically significant difference from group II (3.88 MPa). There were no statistically significant differences between groups I, III, and IV (2.84, 2.90, and 3.22 MPa, respectively) (P > or = .05). In groups I, II, IV, and V, where enamel was etched, more than 50% of the samples showed that all material adhered to the teeth surfaces. This was opposed to group III, where the bond failure was mostly between the enamel interface and the bonding material. The results indicated that in a saliva-moistened environment, FOLC achieved higher shear bond strength when 37% phosphoric acid is used, with no statistically significant difference from Transbond XT.

Determinação das características físico-químicas e das miopatias do músculo Pectoralis major em frangos de corte criados em piso de plástico perfurado / Determination of the physical-chemical characteristics and myopathy of the Pectoralis major muscle in broiler chickens raised on perforated plastic floor

Esse estudo teve como objetivo avaliar a influência da criação de frangos de corte em pisos plásticos perfurados sobre a qualidade físico-química da carne e a incidência de miopatias peitorais. Para isso, os animais foram alojados em 14 box, em dois tratamentos, cama e piso, 25 animais por box. Para a capacidade de retenção de água as aves do tratamento piso apresentaram melhores resultados; no entanto, apresentaram maior perda de água por cocção. O músculo Pectoralis major dos animais criados no piso de plástico, apresentou menor valor de força de cisalhamento, entretanto, maior força de deformação. Para as miopatias, o peito dos frangos criados no piso de plástico apresentaram maior incidência de white striping, enquanto os que permaneceram na cama de casca de arroz apresentaram maior incidência de wooden breast. A criação de frangos de corte em pisos de plástico perfurados não influenciou as características físico-químicas da carne, bem como a incidência de miopatias peitorais.

Effect of open-sandwich vs. adhesive restorative techniques on enamel and dentine demineralization: an in situ study.

OBJECTIVES: To assess in situ the effect of different restorative techniques used with fluoride-releasing materials on enamel and dentine demineralization in the presence of a cariogenic challenge. METHODS: Thirty human molars were prepared for 60 Class V cavities, with enamel and dentine margins. The teeth were divided into four groups (n=15): L1 - open sandwich technique with a conventional glass ionomer cement (GIC), L2 - open sandwich technique with a resin-modified GIC, A1 - total-etch bonding with a fluoride-containing adhesive, A2 - total-etch bonding with a nonfluoride-containing adhesive. All the cavities were restored with a nanofilled composite. Fifteen volunteers used appliances containing one specimen from each group. The cariogenic challenge was carried out with a 20% sucrose solution 8×/day for 7 days. The specimens were sectioned for microhardness test and EDS analysis at different depths below the enamel and dentine margins (25, 50 and 100µm) and distances from the tooth-restoration interfaces (25 and 75µm). The data were analyzed by ANOVA and Games-Howell test (α=5%). RESULTS: Both GICs produced higher hardness in enamel at all depth-and-distance combinations, but only L1 produced higher hardness in dentine (p<0.05). L2 and A1 exhibited similar dentine hardness at 25µm distance for all depths (p>0.05). L1 demonstrated significantly higher amounts of calcium in dentine than the other groups, but had similar amounts in enamel to L2 and A1. CONCLUSIONS: The open sandwich technique using conventional GIC proved more effective in reducing enamel and dentine demineralization at depths of up to 100µm under a cariogenic challenge. CLINICAL SIGNIFICANCE: Conventional GICs should be considered the materials of choice for lining of cavities not having all margins in enamel, particularly using the open sandwich technique.

The effect of at-home bleaching and toothbrushing on removal of coffee and cigarette smoke stains and color stability of enamel.

BACKGROUND: The authors conducted a study to evaluate the stain removal ability of tooth bleaching and simulated toothbrushing after coffee and cigarette smoke staining and to determine the enamel susceptibility to restaining. METHODS: The authors used a colorimeter to determine the baseline color of 40 bovine labial enamel surfaces according to the Commission Internationale de l'Eclairage L*a*b* coordinates. They immersed one-half of the specimens in coffee and exposed one-half to cigarette smoke in a smoking machine. They took color measurements again and determined the color change from baseline (ΔE1) for each group. The authors divided each group into two subgroups and subjected the specimens to at-home bleaching (one hour per day for 21 days) or simulated toothbrushing (120 cycles per day for 21 days), followed by another color measurement (ΔE2). The authors repeated both staining procedures (that is, cigarette smoke and coffee) and followed them with a third color measurement (ΔE3). They analyzed the data by using a two-way analysis of variance and the Tukey test (α = 5 percent). RESULTS: Both staining procedures resulted in similar values for ΔE1. The specimens stained with coffee and cigarette smoke exhibited a significant reduction in color change after bleaching (P < .05). However, toothbrushing resulted in a significantly reduced color change only for cigarette smoke-stained specimens (P < .001). The discoloration in coffee-stained specimens increased after restaining, irrespective of the stain removal method (P < .05). CONCLUSIONS: The study results show that at-home bleaching removed both coffee and cigarette smoke staining. The restaining potential was greater for specimens stained with coffee than for those stained with cigarette smoke, regardless of the removal method used. CLINICAL IMPLICATIONS: Six percent hydrogen peroxide at-home bleaching was effective in removing stains caused by coffee or cigarette smoke. However, continued frequent consumption of coffee can increase the staining susceptibility of enamel.

Estudo da resistência coesiva de cimentos resinosos convencionais e autoadesivos / Study of the cohesive strength of conventional and selfadhesive resin cements

O presente estudo teve como objetivo avaliar a resistência coesiva e o módulo de elasticidade de cimentos resinosos à tração e compressão. Os 15 espécimes foram divididos em 3 grupos: G1: AllCem, G2: Rely X U100, G3: Rely X ARC e submetidos a dois testes mecânicos: tração e compressão. Foram obtidos os resultados de resistência e módulo de elasticidade à tração e compressão dos cimentos resinosos. Os resultados foram avaliados estatisticamente por meio da ANOVA e múltiplas comparações de Games-Howell. Para a tração, a ANOVA revelou diferenças significativas entre os valores médios segundo o cimento (p<0.05). O teste de múltiplas comparações de Games-Howell para a tensão de ruptura mostrou que o cimento resinoso Rely X U100 apresentou os menores valores (21.91 ± 4.97 MPa), seguido pelo AllCem (23.13 ± 5.51 MPa) e pelo Rely X ARC (36.10 ± 8.27 MPa), onde o Rely X ARC diferiu estatisticamente doRely X U100 e doAllCem. ORely X U100 e AllCemnão revelaram diferenças entre si (p<0.05). No teste de compressão, o cimento Rely X U100 também apresentou os menores valores (134.57 ± 48.93 MPa), seguido do Rely X ARC (145.64 ± 32.76 MPa) e AllCem (243.71 ± 29.75 MPa), onde os cimentos Rely X U100 e Rely X ARC diferiram estatisticamente do AllCem e não revelaram diferenças entre si (p<0.05). Concluiu-se que os cimentos resinosos duais convencionais estudados apresentaram maiores valores de resistência à tração quando comparados ao cimento resinoso dual autoadesivo. A resistência coesiva à compressão foi maior que à tração para todos os cimentos resinosos estudados (AU).

The aim of the present study was to evaluate the cohesive strength and elastic modulus of resin cements subjected to the tensile and compression strength. Fifteen specimens were divided into 3 groups: G1: Allcem, G2: Rely X U100, G3: Rely X ARC, and subjected to two mechanical testing: tensile and compression. Strength and elastic modulus results of tension and compression tests of resin cements were obtained. The results were statistically analyzed by ANOVA and multiple comparisons of Games-Howell. For tensile test, the ANOVA revealed significant differences between the mean values according to the cement (p <0.05). The test multiple Games-Howell comparisons for the break to tensile showed that the resin cement Rely X U100 showed the lowest values (21.91 ± 4.97 MPa), followed by Allcem (23:13 ± 5:51 MPa) and the Rely X ARC (36.10 ± 8.27 MPa ), where the Rely X ARC differed from Rely X U100 and Allcem. The Rely X U100 and Allcem revealed no differences (p<0.05). In the compression test, Rely X U100 cement also had the lowest values (134.57 ± 48.93 MPa), followed by Rely X ARC (145.64 ± 32.76 MPa) and Allcem (243.71 ± 29.75 MPa), where cement Rely X U100 and Rely X ARC differed from the Allcem and revealed no differences (p <0.05). It was concluded that conventional dual resin cements studied showed higher tensile strength when compared to the dual-cured self-adhesive cement. The cohesive compressive strength was greater than to tensile for all resin cements studied (AU).

Assessing the use of 35 percent sodium ascorbate for removal of residual hydrogen peroxide after in-office tooth bleaching.

BACKGROUND: The authors conducted a study to quantify the amount of hydrogen peroxide remaining after in-office bleaching and to investigate the effectiveness of 35 percent sodium ascorbate (SA) on removal of the bleaching agent from dentin. METHODS: The authors sectioned 70 extracted human third molars to form 4×4×2-millimeter blocks of dentin and then categorized them into eight groups as follows: group 1, no bleaching; group 2, bleaching (35 percent hydrogen peroxide) and daily measurement; group 3, bleaching plus one application of 35 percent SA for 60 minutes; group 4, bleaching plus one application of SA for 10 minutes; group 5, bleaching plus two applications of SA for 10 minutes each; group 6, bleaching plus two applications of SA for five minutes each; group 7, bleaching plus three applications of SA for one minute each; and group 8, bleaching plus two applications of SA for one minute each. They quantified the amount of residual hydrogen peroxide by using a colorimetric assay with horseradish peroxidase and o-phenylenediamine dihydrochloride as the enzyme and substrate, respectively. RESULTS: The authors analyzed the data by using the Kruskal-Wallis test (α = .05). The results showed that no hydrogen peroxide remained after 120 hours in group 2 and at their respective measurement points in groups 5, 6, 7 and 8, whereas hydrogen peroxide had been removed only partially in groups 3 and 4. CONCLUSION: Two applications of 35 percent SA for one minute each produced the same result--complete removal of the bleaching agent--as that observed five days after tooth bleaching with 35 percent hydrogen peroxide without any application of SA. CLINICAL IMPLICATIONS: In an appropriate concentration, SA facilitates rapid elimination of residual peroxide up to two minutes after bleaching with 35 percent hydrogen peroxide. This finding suggests that clinicians can perform bonding procedures shortly after the bleaching procedure.

Colour stability and opacity of resin cements and flowable composites for ceramic veneer luting after accelerated ageing.

OBJECTIVES: Colour changes of the luting material can become clinically visible affecting the aesthetic appearance of thin ceramic laminates. The aim of this in vitro study was to evaluate the colour stability and opacity of light- and dual-cured resin cements and flowable composites after accelerated ageing. METHODS: The luting agents were bonded (0.2 mm thick) to ceramic disks (0.75 mm thick) built with the pressed-ceramic IPS Aesthetic Empress (n=7). Colour measurements were determined using a FTIR spectrophotometer before and after accelerated ageing in a weathering machine with a total energy of 150 kJ. Changes in colour (ΔE) and opacity (ΔO) were obtained using the CIE L*a*b* system. The results were submitted to one-way ANOVA, Tukey HSD test and Student's t test (α=5%). RESULTS: All the materials showed significant changes in colour and opacity. The ΔE of the materials ranged from 0.41 to 2.40. The highest colour changes were attributed to RelyX ARC and AllCem, whilst lower changes were found in Variolink Veneer, Tetric Flow and Filtek Z350 Flow. The opacity of the materials ranged from -0.01 to 1.16 and its variation was not significant only for Opallis Flow and RelyX ARC. CONCLUSIONS: The accelerated ageing led to colour changes in all the evaluated materials, although they were considered clinically acceptable (ΔE<3). Amongst the dual-cured resin cements, Variolink II demonstrated the highest colour stability. All the flowable composites showed proper colour stability for the luting of ceramic veneers. After ageing, an increase in opacity was observed for most of the materials.

Evaluation of frictional forces between ceramic brackets and archwires of different alloys compared with metal brackets.

The aim of this study was to evaluate, in vitro, frictional forces produced by ceramic brackets and arch wires of different alloys. Frictional tests were performed on three ceramic brackets: monocrystalline (Inspire ICE), polycrystalline (InVu), polycrystalline with metal slot (Clarity), and one stainless steel bracket (Dyna-Lock). Thirty brackets of each were tested, all with .022' slots, in combination with stainless steel and nickel-titanium wires .019' x .025', at 0 degrees and 10 degrees angulation, in artificial saliva. Arch wires were pulled through the slots at a crosshead speed of 10 mm/min. There were statistically significant differences between the groups of brackets and wires studied (p < .05). The polycrystalline brackets with metal slots had values similar to those of conventional polycrystalline brackets, and the monocrystalline brackets had the highest frictional forces. The nickel-titanium wires produced the lowest friction. The addition of metal slots in the polycrystalline brackets did not significantly decrease frictional values. Nickel-titanium wires produced lower friction than those of stainless steel.