New Resin-Based Bulk-Fill Composites: in vitro Evaluation of Micro-Hardness and Depth of Cure as Infection Risk Indexes

Abstract

The current in vitro study evaluated the Vickers hardness number (VHN) and hardness ratio of four bulk-fill composites (VisCalor bulk; Admira Fusion x-tra; x-tra fil; and GrandioSO x-tra-Voco, Cuxhaven, Germany) to assess the risk of bacterial colonization in comparison with standard composite materials. Thirty samples were prepared for each group. The VHN of both the external (top) and internal surface (bottom) was determined with a micro-hardness tester (200 g load for 15 s), and the hardness ratio was also calculated for each sample. Subsequently, storage in an acidic soft drink (Coca-Cola, Coca-Cola Company, Milano, Italy) was performed; for each group, 10 samples were stored for 1 day, while another 10 were stored for 7 days and the remaining 10 were kept in water as controls. A significant reduction in VHN was shown for all the groups when comparing the external versus internal side (P < 0.05), although the hardness ratio was greater than 0.80, resulting in an adequate polymerization. Regarding the acid storage, all the groups showed a significant decrease of VHN when compared with the controls, both after 1 day (P < 0.05) and after 7 days (P < 0.001). All the products showed adequate depth of cure without further risk of bacterial colonization. However, acid exposure negatively affected micro-hardness values, which might promote subsequent colonization.

Exposure of Biomimetic Composite Materials to Acidic Challenges: Influence on Flexural Resistance and Elastic Modulus

“…However, the acidic conditions of the oral cavity, such as the consumption of soft drinks or acidic foods and the presence of acidophile bacteria, constitute a danger not only for teeth but even for filling materials [ 34 ]. In particular, a recent study considering four of the five products tested in the present report (x-tra fil, GrandioSO x-tra, Admira Fusion x-tra, VisCalor bulk) stated that their microhardness is significantly reduced when stored in an acidic beverage, both for 1 day and for 1 week, with respect to the samples kept in water [ 14 ]. In the literature it has been supposed that, when exposed to low pH conditions, the filler of the resin tends to fall out and the matrix tends to decompose [ 35 ].…”

“…However, even restorative materials are subjected to the action of acids of the oral cavity with a corrosion and a subsequent alteration of their initial characteristics. For instance, in vitro microhardness has been shown to be significantly decreased after acidic exposure because of a degradation of the polymer network of the composite and the falling out of the resin, with an eventual risk of secondary decay [ 14 ].…”

Influence of the degree of conversion and Bis-GMA residues of bulk fill resins on tissue toxicity in an subcutaneous model in rats

“…26 Adequate light curing dramatically attenuates cell damage induced by monomers. 30 Therefore, despite the BF resins allowing application in a single increment, 20 there is a gradual decrease in DC in the deeper layers of the material, 31 thus we suggest caution in the use of BF resin with a large concentration of bis-GMA in very deep cavities (>2 mm). UDMA and TEGDMA are also cytotoxic, 22,24 however, light curing of the composite with higher UDMA content (Tetric N-Ceram, Filtek Z-350, Tetric N-Ceram Bulk Fill, Filtek Bulk Fill One) led to fewer monomer residues and toxicity.…”

“…Thus, corroborating the literature, there is a direct relationship between DC and the intensity of the inflammatory infiltrate. 19 DC reduction impairs the chemical and mechanical proprieties of BF resins, 20 and the high bioavailability of monomeric residues is strongly toxic to several cell types, 21 such as fibroblasts 22 and odontoblasts. 23 The direct contact of monomeric residues active apoptosis regulatory caspases causes toxicity and an inflammatory process, 24 as shown in Kerr® BF resin disks, negatively affecting pulp tissue, 25 following unbound composite diffusion through the dentine to the pulp.…”

Evaluation of the Milling Accuracy of Zirconia-Reinforced Lithium Silicate Crowns Fabricated Using the Dental Medical Device System: A Three-Dimensional Analysis

“…Indeed, it is important to manufacture a perfect prosthesis in order to avoid problems that may occur during the restoration of the dental prosthesis in the oral cavity. However, the most reliable method to protect the teeth is to prevent the initial formation of cavities in the oral cavity [ 16 ].…”