Influence of Staining Solution and Bleaching on Color Stability of Resin Used for Caries Infiltration.

OBJECTIVE: The objective of this study was to evaluate the color stability of Icon-infiltrated white spot lesions after staining and the bleaching effect on the infiltrated and stained surfaces. METHODS AND MATERIALS: Enamel-dentin specimens (N=30, 5 × 5 × 3 mm, 1-mm enamel + 2-mm dentin thickness) were prepared from bovine incisors and randomly allocated into three groups (n=10): control, demineralized, and infiltrated. Artificial enamel subsurface lesions were created using 50 mL of 0.05 M acetate buffer solution. Specimens were produced by Icon application in enamel caries-like lesions, according to the manufacturer's instruction. Baseline color readings were assessed using a spectrophotometer, and CIE L*a*b* measurements of each specimen were performed using a white background. To simulate extrinsic dietary staining, specimens were placed into a 4-mL coffee infusion, three times daily for 15 minutes, for 14 days. After the staining procedure, color measurements were performed again. Then, bleaching procedures were performed using 16% carbamide peroxide gel for four hours daily for 21 days, and a final color assessment was performed. To compare the baseline and final measurements, t-test was used (α =0.05). The statistical comparison between the groups was performed using the one-way analysis of variance and Tukey tests (α =0.05). RESULTS: Coffee staining provided a significant reduction of L* values and an increase of a* and b* in all groups (control, decayed, and infiltrated). The bleaching procedure provided a significant increase in L* and decrease of a* and b* values in all groups. There was no significant difference in ΔE values between decayed and infiltrated groups before bleaching, and after bleaching, the infiltrated group showed the lowest ΔE values. CONCLUSION: It can be concluded that enamel infiltrated with Icon presents significant alteration of color after staining when compared with sound enamel. However, if there is discoloration of the infiltrant, the bleaching treatment can be used successfully.

Influence of chemical degradation on the surface properties of nano restorative materials.

OBJECTIVES: The aim of this in vitro study was to investigate the effect of chemical degradation on the surface roughness (Ra) and hardness (Knoop hardness number [KHN]) of nano restorative materials. METHODS: Disc-shaped specimens (5-mm diameter; 2-mm thick) of Filtek Z350 and TPH Spectrum composites and the Vitremer and Ketac Nano light-curing glass ionomer cements were prepared according to the manufacturers' instructions. After 24 hours, polishing procedures were performed and initial measurements of Ra and KHN were taken. The specimens were divided into 12 groups (n=10) according to material and storage media: artificial saliva, orange juice, and Coca-Cola. After 30 days of storage, the specimens were reevaluated for Ra and KHN. The pH values of the storage media were measured weekly. Data were tested for significant differences by repeated-measures three-way analysis of variance and Tukey tests (p<0.05). RESULTS: Composites were found to present lower roughness values and higher hardness values than the ionomeric materials under all storage conditions. After degradation, the KHN of all experimental samples decreased significantly, while the Ra of the ionomeric materials increased, depending on the media, with a markedly negative impact of Coca-Cola and orange juice. There was no difference among the storage media for Filtek Z350 with regard to the KHN values. Nanofillers did not show any influence on the roughness and hardness of resin-modified glass ionomer cements and resin composites concerning their degradation resistance.

Finite element analysis of stress distribution in intact and porcelain veneer restored teeth.

UNLABELLED: The aim of this study was to investigate the stress distribution generated in a veneer restoration of an upper central incisor compared to intact teeth using the finite element analysis after applying a lingual buccal loading at the incisal edge. METHODS: Two models were developed: one model contained enamel, dentine, cementum, periodontal ligament, cortical and trabecullar bones, and the other model was a veneer restoration; both models were developed using MSC/Nastran software (MacNeal-Schwendler Corporation, Los Angeles, CA, USA) as the pre- and post-processor. A 10-N load was applied at the incisal edge from the lingual to the buccal side to simulate oral conditions in this area (protrusion). RESULTS: Von Mises stresses were then analysed for three different regions: A-B (enamel elements under the veneer or second enamel layer), A'-B' (buccal enamel and/or veneer element layer) and C-D (lingual enamel elements layer). A higher stress mode was observed for both models at the lingual cervical region. CONCLUSIONS: The presence of a veneer restoration on the incisors is a good alternative to mimic the behaviour of enamel under protrusion loading conditions. The use of veneers to replace enamel during rehabilitations is recommended.

Biodegradation and abrasive wear of nano restorative materials.

The purpose of this study was to evaluate the biomechanical degradation of two nanofilled restorative materials (a resin-modified glass ionomer, Ketac N100 and a composite, Filtek Z350), compared with conventional materials (Vitremer and TPH Spectrum). Twenty specimens obtained from each material were divided into two storage groups (n=10): relative humidity (control) and Streptococcus mutans biofilm (biodegradation). After 7 days of storage, roughness values (Ra) and micrographs by scanning electron microscopy (SEM) were obtained. In a second experimental phase, the specimens previously subjected to biodegradation were fixed to the tooth-brushing device and abraded via toothbrushes, using dentifrice slurry (mechanical degradation). Next, these specimens were washed, dried, and reassessed by roughness and SEM. The data were submitted to repeated measures three-way analysis of variance (ANOVA) and Tukey tests (p<0.05). There was statistically significant interaction among factors: material, storage (humidity/biofilm), and abrasion (before/after). After biodegradation (S mutans biofilm storage), Ketac N100 presented the highest Ra values. Concerning bio plus mechanical challenge, TPH Spectrum, Ketac N100, and Vitremer presented the undesirable roughening of their surfaces, while the nano composite Filtek Z350 exhibited the best resistance to cumulative challenges proposed. The degraded aspect after biodegradation and the exposure of fillers after mechanical degradation were visualized in micrographs. This study demonstrated that the nanotechnology incorporated in restorative materials, as in composite resin and resin-modified glass ionomer, was important for the superior resistance to biomechanical degradation.