Evaluation of the sealing capability and morphological fit of prefabricated dowels and fiber-reinforced composite resin: An in vitro study.

STATEMENT OF PROBLEM: Prefabricated dowels do not always provide intraradicular sealing in the root canal dentin, and the lack of sealing predisposes the dowel to adhesive failure and debonding. It is unclear if fiber-reinforced composite resin dowels provide better sealing. PURPOSE: The purpose of this in vitro study was to evaluate the intraradicular sealing and morphological fit of prefabricated dowels and fiber-reinforced composite resin dowels in root canal dentin. The thickness of the resin cement layer and push-out bond strength were determined to assess their effects on the sealing of the dowels. MATERIAL AND METHODS: A total of 50 permanent maxillary central incisors were endodontically treated and divided into 2 subgroups (n=25). In one group, prefabricated dowels were cemented; in the second group, fiber-reinforced composite resin dowels were placed. The thickness of the resin cement layer was assessed in 3 different locations: coronal, middle, and apical of the root canal dentin with fluorescence confocal laser microscopy. The push-out bond strength was then determined, and intraradicular sealing observed by using scanning electron microscopy. RESULTS: Fiber-reinforced composite resin dowels showed a closer intraradicular fit and seal in the root canal dentin, and the morphology of the apical portion of the fiber-reinforced composite resin dowels showed a sealing area with the gutta percha in the apical portion. The mean thickness of the resin cement layer was significantly reduced for the fiber-reinforced composite resin dowels compared with the prefabricated dowels (P<.05) in the cervical area (197.0 µm versus 311.0 µm) and in the apical portion of the root canal (57.3 µm versus 131.6 µm). The mean push-out strength was higher for the fiber-reinforced composite resin dowels (22.98 N/mm2) than that for the prefabricated dowels (16.49 N/mm2) (P<.05). CONCLUSIONS: The morphological fit of fiber-reinforced composite resin dowels provides better intraradicular sealing in the cervical and apical portions, reducing the resin cement thickness. The increased push-out strength can therefore be assumed to result from increased frictional retention compared with prefabricated dowels.

Surface degradation and biofilm formation on hybrid and nanohybrid composites after immersion in different liquids.

PURPOSE: This study evaluated the association of surface degradation and formation of Streptococcus mutans (S. mutans) biofilm in resin-based composites (RBCs) after storage in different acidic liquids. METHODS: To evaluate microhardness and surface micromorphology, hybrid and nanohybrid RBC discs were stored in artificial gastric acid, cola drink, orange juice, artificial saliva, and distilled water for three intervals of 15 min per day for 7, 15, and 30 days. After 30 days of storage, surface roughness was analyzed, and the RBC discs were placed in a biofilm reactor inoculated with S. mutans to evaluate surface biofilm formation. RESULTS: As compared with nanohybrid RBCs, roughness and surface microhardness values were significantly lower (P < 0.05) for hybrid RBCs stored in artificial gastric acid, followed by specimens stored in cola drink and orange juice. Artificial gastric acid caused greater surface degradation, which increased the biomass of S. mutans on the surface of both RBC types. CONCLUSION: Surface degradation of hybrid and nanohybrid RBCs correlated with the pH of the liquid, while S. mutans biofilm formation was associated with increased surface roughness in hybrid RBCs.

RGD-functionalization of PLA/starch scaffolds obtained by electrospinning and evaluated in vitro for potential bone regeneration.

The engineering of bone tissues represents an area of opportunity for the development of new polymeric compounds. In this context, the objective of this work is the generation and evaluation in vitro of supports obtained from mixtures of starch with poly (lactic acid) (PLA), treated with arginine-glycine-aspartic acid peptides (RGD). For this, non-woven fibers of PLA with different starch content (0.0, 2.5, 5.0 and 10.0%wt) were obtained using the electrospinning technique. Then the physical absorption of RGD was carried out, with the aim of increasing the cellular adhesion of the polymeric material. Subsequently, in vitro biocompatibility tests were performed, and viability (LIFE/DEAD), proliferation (MTS assay) and cell adhesion were carried out with osteoblasts incubated for 48 h. Regarding biocompatibility results, only viable cells were found for all the compositions, and the biocompatibility of the materials was validated by the morphological analysis of the cultured cells, where extended cells were observed. Proliferation assays show that osteoblasts proliferate better on the surfaces of PLA and PLA with 5.0% starch scaffolds. Therefore, it is concluded that the scaffolds obtained by electrospinning of PLA with starch and functionalized with RGD are promising for its use in the regeneration of bone tissue.