Influence of resin-composite formulation on the intra-oral degradation : in vitro study / Influencia da formulação de resinas compostas na resistencia a degradação intra-oral : estudo in vitro

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Natural teeth, as well as restorations, are composed of materials that are subject to deterioration. Besides chemical, mechanical and thermo degradation, the formulation and post-cure composite’s network are dominant mechanism to determine the restoration’s longevity. The purpose of this study was to investigate the effect of material’s formulation, light-activation mode (LM) and storage condition (SC) on resin-composite’s resistance to chemical and/or mechanical degradation. The aims, methods and results of this study, composed of two chapters were: CHAPTER 1: to evaluate how the LM and the SC would affect the chemical degradation, through the softening test, of two nanohybrids; a 1st and a 2nd generation ormocer. Disk specimens (4 mm x 2 mm) were prepared from each material and light-activated by full-cure (F) and soft-start (S) modes. Four storage conditions were evaluated (n=5): group 1: immediately after cure, group 2: dry and dark, group 3: absolute ethanol and group 4: distilled water. Knoop hardness values (KHN) were measured immediately after cure and after immersion in the different SC for 24 hours. Two-way ANOVA with Tukey’s post-hoc test (p = 0.05) was used to compare KHN among each SC and between the two LM. The LM presented no significant effect on the softening test, in all groups. However, significant differences were observed among the SC. Absolute ethanol produced the higher softening effect in all materials tested. The 2nd generation ormocer was the more stable material when stored in water. LM did not affect the final KHN. CHAPTER 2: to investigate the effect of filler-particle size of resin-composites, undergoing toothbrush abrasion (TA), on three surface properties: surface roughness (SR), surface gloss (G) and color stability (CS). Four models and one commercial resin-composite and with varying filler-size from 100 to 1000 nm were examined. Six discs (10 mm x 2 mm) from each - 0.97). Filler size did not affect CS. product were mechanically polished. The samples were then submitted to 20,000 brushing strokes in a TA machine. SR parameters (Ra, Rt and RSm), G and CS (CIE-L*a*b*) were measured before and after TA. Changes in SR and G were analyzed by 2-way ANOVA, with Bonferroni post-hoc test. CS values were submitted to one-way ANOVA and Bonferroni post-hoc test (p=0.05). There was no statistically significant difference in CS. TA resulted in rougher and matte surfaces for all materials tested. Although the individual differences in SR among filler sizes were not always significant, the correlation showed a trend that larger filler sizes result in higher surface roughness after abrasion for Ra and Rt parameters (r = 0.95; r = 0.93, respectively). RSm showed an increase after TA for all resin-composites; however no significant correlation was detected. Initial G values ranged between 73 and 83 gloss units (GU) and were reduced after TA to a range of 8.5 to 64 GU. TA revealed significant modifications in surface roughness and gloss amongst the materials tested, that related to filler sizes. There was a significant correlation between gloss and roughness (Ra) (r = ) - 0.97). Filler size did not affect CS.

ASSUNTO(S)

surface properties resinas compostas escovação dentaria toothbrushing composite resins dentistica propriedades de superficie dentistry

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