Gap formation in composite restorations : evaluation techniques, effect of photoactivation methods and relantionship with bond strength / Formação de fendas em restaurações de composito : tecnicas de avaliação, efeito de metodos de fotoavaliação e relação com a resistencia da união

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Gap formation in composite restorations has been characterized in this dissertation by way of evaluation techniques, modifying factors and the relationship between bond strength of the restorations and the dental structure. In Chapter 1 the objective was to compare the dye staining technique to Scanning Electron Microscopy (SEM) evaluation of gap formation in order to validate the dye technique. Twenty bovine incisors were selected and ground so as to expose a flat dentin area in which two circular cavities were prepared and restored using Filtek 2250 or Filtek Flow. The specimens were polished and replicas were obtained in epoxy resin. Replicas were observed in SEM to determine the percentage of gap fonnation in the margins of the restorations. In dye staining technique, the Caries Detector was applied on each restoration for 5 seconds. Digital images of the stained restorations were analyzed using Image Tool to determine gap percentage. Data were submitted to ANOVA and Pearson s correlation. Filtek Flow showed 35.54% and 33.52% of gap and Filtek 2250 showed 26.68% and 29.11%, when evaluated using SEM and Dye staining technique, respectively. There was no difference between the composites, regardless of the evaluation technique. There was a strong positive correlation (r=0.83) between the results obtained through the tested methods to assess marginal gap. This led to the conclusion that dye staining technique can be reliably employed to evaluate the gap fonnation in composite restorations. Chapter 2 aims at determining the effect of modulated photoactivation methods on gap fonnation of restorations using different composites. Sixty third molars were selected, sectioned (2 fragments) and ground so as to expose a flat enamel area in which a cavity was prepared. The specimens were distributed into twelve groups (n=10), according to the restorative composite (Filtek 2250, Herculite XRV, and Heliomolar) and the photoactivation method (Continuous Light, Soft-Start, Pulse Delay, and Intermittent Light) applied. Marginal adaptation test was conducted in the same way described before (dye staining technique). The specimens were then sectioned in 4 slices, all of which were stained, and the same evaluation procedure used to determine marginal adaptation was employed to evaluate internal gap fonnation. All restorations showed perfect sealing of the enamel outer margins. With regards to internal adaptation, modulated photoactivation methods showed a significant reduction on gap fonnation when compared under continuous light, regardless of the composite. Filtek 2250 showed the best internal adaptation, regardless of the photoactivation method. The interaction between restorative composite and photoactivation method was not significant. The conclusion was that modulated photoactivation methods decrease the internal gap formation of composite restorations and should thus be encouraged on clínical practice, regardless of the type of composite. In Chapter 3, the aim was to evaluate the relationship between bond strength and marginal and internal adaptation of composite restorations photocured by different methods. Bond strength was measured in conical cavities prepared in bovine incisors using push-out test (Instron). Marginal and internal adaptation testswere conducted in the same way as before (dye staining technique). For both tests, cavities were filled with Esthet X resin composite. The specimens were distributed into 5 groups (n= 1 O) according to photoactivation method: G 1 - continuous light; G2 low intensity continuous light; G3 - soft start; G4 - intermittent light; G5 - pulse delay. 14J was the standard energy dose. Data were submitted to ANOVA and Tukey s test. Regarding bond strength, G5 (7.2 MPa) was statistically superior to Gl (4.6 MPa). G2, G3 and G4 showed intermediate mean values, which were not different from each other or from G 1 or G5. Regarding marginal adaptation, there was no statistical difference among the groups. Internal adaptation results (that included dentin substrate) were the opposite of bond strength results. G5 (2.8%) showed a reduction on gap formation when compared to Gl (10.1%). In conclusion, it may be said that the modulated photocuring methods can increase bond strength while decreasing internal gap formation. An opposite relationship was observed regarding push-out bond strength and internal adaptation of composite restorations

ASSUNTO(S)

permanent materiais dentarios fotopolimerização adaptação marginal (odontologia) dental restoration restauração dentaria permanente composite resins resinas compostas photopolymerization dental materials marginal adaptation (dentistry)

ACESSO AO ARTIGO

Documentos Relacionados