Diogo Rodrigues Cruvinel

Color stability of dental ceramics submitted to artificial accelerated aging after repeated firings

STATEMENT OF PROBLEM Color stability is an important factor to ensure the long-term clinical success of ceramic restorations. There is a lack of information on how color is affected by fabrication procedures, such as the number of firings. PURPOSE The purpose of this study was to evaluate the effects that the number of firings and type of substrate have on the color stability of dental ceramic submitted to artificial accelerated aging. MATERIAL AND METHODS Sixty specimens were fabricated: 30 metal ceramic (Verabond II + IPS d.SIGN) and 30 all-ceramic (IPS d.SIGN). Specimens were divided into 3 groups (n=10), and submitted to 2, 3, or 4 firings (+/-900 degrees C), respectively, according to the manufacturers instructions. Color readings were obtained with a spectrophotometer before and after artificial accelerated aging, and L*, a*, and b* coordinates and total color variation (Delta E) were analyzed (2-way ANOVA, Bonferroni, alpha=05). RESULTS For metal ceramic specimens, differences for the L* coordinates were significant (P<.05) only for the group submitted to 3 firings. With respect to the all-ceramic specimens, smaller L* coordinates were obtained for greater a* and b* coordinates, indicating that the greater the number of firings, the darker and more reddish/yellowish the specimen. All Delta E values, for all groups, were below 1.0. All-ceramic specimens submitted to 3 and 4 firings presented Delta E means differing statistically (P<.05) from those of the metal ceramic group. CONCLUSIONS The type of substrate and number of firings affected the color stability of the ceramic material tested. Artificial accelerated aging did not produce perceptible color stability changes (Delta E<1.0).

Color stability, surface roughness and microhardness of composites submitted to mouthrinsing action

Objective The purpose of this study was to evaluate the effect of mouth rinse solutions on color stability, surface roughness and microhardness of two composite resins. Material and Methods Fifty test specimens of each composite (Filtek Z250 and Z350; 3M ESPE) were made using a teflon matrix (12x2 mm). Color, surface roughness and Knoop microhardness baseline measurements of each specimen were made and specimens (n=10) were immersed in 5 mouth rinse solutions: G1: distilled water (control), G2: Plax Classic, G3: Plax alcohol-free; G4: Periogard, and G5: Listerine. Final measurements of color, roughness and microhardness were performed and the results submitted to statistical analysis (2-way ANOVA, Bonferronis test; p<0.05). Results The most significant color change was observed for Z250 when immersed in Listerine (p<0.05). Z350 showed greater color change when immersed in Plax alcohol-free (p<0.05), but with no significant difference for Listerine (p>0.05). With regard to roughness, both composites showed significant changes when immersed in Listerine in comparison with Plax alcohol-free (p<0.05). Microhardness of Z350 was shown to be significantly changed when the composite was immersed in Plax alcohol-free (p<0.05). Conclusion Composite changes depended on the material itself rather than the mouth rinse solution used.

Color stability, opacity and degree of conversion of pre-heated composites

OBJECTIVES To assess color stability and opacity associated with the degree of conversion of a pre-heated nanohybrid composite (Tetric N-Ceram, Ivoclar/Vivadent, Schaan, Liechtenstein). METHODS Twenty-seven specimens were prepared (n=9) using a Teflon matrix following storage of compules containing the composite at temperatures of 8°C, 25°C or 60°C. After photoactivation and polishing, baseline readings of six specimens were taken regarding their color and opacity (Spectrophotometer PCB 6807, Byk Gardner, Geretsried, Germany). Then, the specimens were submitted to artificial ageing for 384 h (C-UV, Adexim Comexim, São Paulo, SP, Brazil), after which the final readings were taken. Three specimens for each temperature were submitted to analysis of degree of conversion (Nicolet 380, Thermo Scientific, Waltham, MA, USA). The results were analysed by 1-way ANOVA/Tukey (p<0.05). RESULTS There was no significant difference in color stability and opacity variation amongst the temperatures evaluated. The composite pre-heated at 60°C had a higher degree of conversion (65.13%), with statistically significant difference compared to the other temperatures (p<0.05). CONCLUSIONS Composite pre-heating does not promote changes in the optical properties, despite the increase in the degree of conversion.

Effect of cigarette smoke on color stability and surface roughness of dental composites

OBJECTIVE To evaluate the color stability and surface roughness of 3 dental composites subjected to cigarette smoke and brushing. METHODS Twenty specimens were prepared for each type of restorative material used: nanohybrid (Tetric N-Ceram); hybrid (Z250-3M ESPE) and silorane-based microhybrid (Filtek P90-3M ESPE), which were divided into 2 groups (n=10), according to the type of finishing/polishing received: Group 1 - papers with decreasing abrasive grit and Group 2 - polyester matrix (without polishing). After initial readouts of color (Easy Shade-VITA) and surface roughness (SJ-201P Mitutoyo), specimens were subjected to action of smoke from 20 cigarettes, (Marlboro Red-Philip Morris). After each cigarette, the samples were submitted to brushing in a standardised device. After this, final readouts were taken to calculate change in color (ΔE and ΔL) and roughness (ΔRa), which were statistically analysed (2-way ANOVA, Bonferroni, and Students-t tests respectively, p<0.05). RESULTS Tetric N-Ceram presented color change at clinically unacceptable levels (ΔE>3.3) when the polyester strip was used for finishing, a result differing (p<0.05) from those of the other composites, which presented no difference between them (p>0.05). Unpolished composites presented higher Ra values than those that were polished (p<0.05), with exception of the silorane based composite. CONCLUSION Absence of polishing increases cigarette capacity to stain composites and surface roughness of composites, with exception of the silorane based type.

Evaluation of radiopacity and microhardness of composites submitted to artificial aging

The purpose of this study was to assess the radiopacity and microhardness of different types of resin-based composites (RBC - hybrid; microhybrid; flowable; cement and polyacid modified) before and after being submitted to artificial accelerated aging. Fifty specimens (7 mm in diameter and 2 mm thick) were fabricated, 10 for each material. The specimens were light-cured and submitted to radiopacity and microhardness tests. After obtaining initial radiopacity and microhardness values, the specimens were taken to the artificial accelerated aging, and new measurement of radiopacity and microhardness of the samples was performed. Data were submitted to statistical analysis (Students t-test - p < 0.05). None of the materials studied showed changes in radiopacity after artificial accelerated aging. There was a significant decrease in microhardness for the microhybrid and polyacid-modified RBC´s. This study suggests that radiopacity remains unaltered after materials are submitted to artificial accelerated aging. Microhardness, however, may vary due to plasticization of the aged RBC matrix.

In vitro comparison of the radiopacity of cavity lining materials with human dental structures

Aim: To compare the optical densities (OD) of calcium hydroxide (CH) and glass ionomer cement with the same thicknesses of the dental structures. Materials and Methods: Eighteen specimens of each material, with thicknesses of 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 mm were made in a Teflon matrix. To compare the radiopacity of the materials with the dental structures, dental cuts of the first molars, increasing in thickness from 0.5 to 3.0 mm, were obtained. To standardize the radiographs, a transparent acrylic matrix (Standardizing Device) was developed and used. Thirty radiographs were taken, five for each tested material. Results: Statistical analysis (Two-way ANOVA - Bonferroni, P < 0.05) demonstrated that when the materials were compared, there was statistically significant difference between the ODs, only for the thickness of 1.0 mm (P < 0.05). Conclusion: The thickness of the material contributed to its radiopacity, and these materials had to be used in a thickness between 1.5 and 2.0 mm.

Effect of brushing and accelerated ageing on color stability and surface roughness of composites

OBJECTIVES The aim of this study was to evaluate the effect of brushing and artificial accelerated ageing (AAA) on color stability and surface roughness of aesthetic restorative materials. METHODS One hundred and twenty specimens (12 mm diameter × 2 mm thick), 40 of each material (n=8) were obtained using nanosized composite Z350 (3M ESPE), nanohybrid composite Tetric N-Ceram (Ivoclar Vivadent) and ceramic IPS e.max Ceram (Ivoclar Vivadent), as control. Initial color (Spectrophotometer PCB 6807) and surface roughness (Surfcorder SE 1700) readouts were taken and the samples were separated into five groups (n=8) and treated as follows: Group 1: mechanical brushing with dentifrice RDA* 68 (Colgate), Group 2: mechanical brushing with dentifrice RDA* 180 (Colgate Total Plus Whitening), Group 3: AAA, Group 4: AAA followed by mechanical brushing with dentifrice RDA* 68 and Group 5: AAA followed by mechanical brushing with dentifrice RDA* 180. Mechanical brushing was performed for 205 min and AAA for 480 h; new color and surface roughness readouts were taken. Data were statistically analyzed (two-way ANOVA repeated measures, Bonferroni test, p<0.05). RESULTS Dentifrice abrasiveness was not significant for color change and surface roughness. When submitted to AAA+brushing, the color stability of Tetric was statistically significant (p<0.05) with both dentifrices and with dentifrice RDA* 180 for Z350. The roughness was different (p<0.05) for Z350 when brushed with RDA* 68 after AAA. CONCLUSIONS Dentifrice abrasiveness did not interfere in the ability to remove stains and roughness from aged samples. However, staining is material-dependent. CLINICAL SIGNIFICANCE The abrasiveness of dentifrice does not change the color and surface roughness of the composites and does not help to remove surface stains from the aged samples.

Color stability of modern composites subjected to different periods of accelerated artificial aging

The aim of this study was to evaluate the color stability of composites subjected to different periods of accelerated artificial aging (AAA). A polytetrafluorethylene matrix (10 x 2 mm) was used to fabricate 24 test specimens of three different composites (n=8): Tetric Ceram (Ivoclar/Vivadent); Filtek P90 and Z250 (3M ESPE), shade A3. After light activation for 20 s (FlashLite 1401), polishing and initial color readout (Spectrophotometer PCB 687; BYK Gardner), the test specimens were subjected to AAA (C-UV; Comexim), in 8-h cycles: 4 h exposure to UV-B rays at 50°C and 4 h condensation at 50°C. At the end of each cycle, color readouts were taken and the test ended when the mean value of ΔE attained a level ≥3.30. Tetric Ceram presented alteration in ΔE equal to 3.33 in the first aging cycle. For Filtek P90 and Z250, two (ΔE=3.60) and four (ΔE=3.42) AAA cycles were necessary. After each cycle, there was a reduction of luminosity in all the samples (ΔL). It was concluded that a short period of AAA was sufficient to promote clinically unacceptable color alteration in composites, and that this alteration was material-dependent.

Influence of finishing/polishing on color stability and surface roughness of composites submitted to accelerated artificial aging.

AIM To assess the influence of finishing/polishing procedure on color stability (ΔE ) and surface roughness (R(a)) of composites (Heliomolar and Tetric - color A2) submitted to accelerated artificial aging (AAA). MATERIALS AND METHODS Sixty test specimens were made of each composite (12 mm × 2 mm) and separated into six groups (n = 10), according to the type of finishing/polishing to which they were submitted: C, control; F, tip 3195 F; FF, tip 3195 FF; FP, tip 3195 F + diamond paste; FFP, tip 3195 FF + diamond paste; SF, Sof-Lex discs. After polishing, controlled by an electromechanical system, initial color (spectrophotometer PCB 6807 BYK GARDNER) and R(a) (roughness meter Surfcorder SE 1700, cut-off 0.25 mm) readings were taken. Next, the test specimens were submitted to the AAA procedure (C-UV Comexim) for 384 hours, and at the end of this period, new color readings and R(a) were taken. RESULTS Statistical analysis [2-way analysis of variance (ANOVA), Bonferroni, P < 0.05] showed that all composites demonstrated ΔE alteration above the clinically acceptable limits, with the exception of Heliomolar composite in FP. The greatest ΔE alteration occurred for Tetric composite in SF (13.38 ± 2.10) statistically different from F and FF (P < 0.05). For R(a), Group F showed rougher samples than FF with statistically significant difference (P < 0.05). CONCLUSION In spite of the surface differences, the different finishing/polishing procedures were not capable of providing color stability within the clinically acceptable limits.

Analysis of Stress and Fracture Strength of Zirconia Implants after Cyclic Loading

The aim of this study was to manufacture a new zirconia implant (Y-TZP) and to evaluate the fracture strength and stresses generated after cyclic loading compared to titanium implants. Thirty-three zirconia and titanium implants were fabricated. The stress generated around the implants was observed by photoelastic analysis. The implants were then separated into groups (n = 10): Control (no treatment), mechanical fatigue and thermomechanical fatigue. All groups were submitted to a single cantilever flexure test to measure the material fracture strength. The results (2-way ANOVA, Bonferroni test, p <.05) showed no statistically significant difference in the stresses generated between the zirconia and titanium implants. Titanium implants showed higher fracture strength than the zirconia implants, a property that was not altered by fatigue applied. It was concluded that stress distribution was similar for Zr and Ti and mechanical and thermomechanical fatigue had no influence on the fracture strength of the implants tested.