Effect of fiber posts on stress distribution of endodontically treated upper premolars : finite element analysis

By means of a finite element method (FEM), the present study evaluated the effect of fiber post (FP) placement on the stress distribution occurring in endodontically treated upper first premolars (UFPs) with mesial–occlusal–distal (MOD) nanohybrid composite restorations under subcritical static load. FEM models were created to simulate four different clinical situations involving endodontically treated UFPs with MOD cavities restored with one of the following: composite resin; composite and one FP in the palatal root; composite and one FP in the buccal root; or composite and two FPs. As control, the model of an intact UFP was included. A simulated load of 150 N was applied. Stress distribution was observed on each model surface, on the mid buccal–palatal plane, and on two horizontal planes (at cervical and root-furcation levels); the maximum Von Mises stress values were calculated. All analyses were replicated three times, using the mechanical parameters from three different nanohybrid resin composite restorative materials. In the presence of FPs, the maximum stress values recorded on dentin (in cervical and root-furcation areas) appeared slightly reduced, compared to the endodontically treated tooth restored with no post; in the same areas, the overall Von Mises maps revealed more favorable stress distributions. FPs in maxillary premolars with MOD cavities can lead to a positive redistribution of potentially dangerous stress concentrations away from the cervical and the root-furcation dentin

Antibacterial and Antibiofilm Properties of Three Resin-Based Dental Composites against <i>Streptococcus mutans</i>

Antibacterial and antibiofilm properties of restorative dental materials may improve restorative treatment outcomes. The aim of this in vitro study was to evaluate Streptococcus mutans capability to adhere and form biofilm on the surface of three commercially available composite resins (CRs) with different chemical compositions: GrandioSO (VOCO), Venus Diamond (VD), and Clearfil Majesty (ES-2). Disk-shaped specimens were manufactured by light-curing the CRs through two glass slides to maintain a perfectly standardized surface topography. Specimens were subjected to Planktonic OD600nm, Planktonic CFU count, Planktonic MTT, Planktonic live/dead, Adherent Bacteria CFU count, Biomass Quantification OD570nm, Adherent Bacteria MTT, Concanavalin A, and Scanning Electron Microscope analysis. In presence of VOCO, VD, and ES2, both Planktonic CFU count and Planktonic OD600nm were significantly reduced compared to that of control. The amount of Adherent CFUs, biofilm Biomass, metabolic activity, and extracellular polymeric substances were significantly reduced in VOCO, compared to those of ES2 and VD. Results demonstrated that in presence of the same surface properties, chemical composition might significantly influence the in vitro bacterial adhesion/proliferation on resin composites. Additional studies seem necessary to confirm the present results

Flexural Properties of Three Novel 3D-Printed Dental Resins Compared to Other Resin-Based Restorative Materials

To evaluate the flexural strength and flexural modulus of three recently introduced 3D-Printed resins and compare them with the flexural properties of other well known, already commercialized, and extensively used resin based dental materials. Three 3D-printed dental resins, a fiber-reinforced epoxy resin, a heat-cured bis-acrylate-based composite resin, two conventional CAD/CAM PMMA, and a graphene-reinforced CAD/CAM PMMA, were selected for this study. Ten prismatic-shaped specimens (2 × 2 × 25 mm) were fabricated for each material (n = 10). All specimens underwent a three-point bending test using a universal testing machine and were loaded until fracture. Flexural strength (MPa) and flexural modulus (MPa) mean values were calculated and compared using the on ranks One-Way ANOVA test. Scanning electron microscope analysis of the 3D-printed resins was performed. Significantly different flexural properties were recorded among the tested materials. The fiber-reinforced epoxy resin exhibited the highest flexural strength (418.0 MPa) while, among the 3D-printed resins, the best flexural strength was achieved by Irix-Max (135.0 MPa). Irix-Plus and Temporis led to the lowest mean flexural strength values (103.9 MPa and 101.3 MPa, respectively) of all the CAD/CAM milled materials, except for the conventional PMMA by Sintodent (88.9 MPa). The fiber-reinforced epoxy resin also showed the highest flexural modulus (14,672.2 MPa), followed by the heat-cured bis-acrylate composite (10,010.1 MPa). All 3D-printed resins had a higher flexural modulus than the conventional PMMA materials. CAD/CAM fiber-reinforced epoxy resin excels in flexural strength, with Irix-Max showing promising flexural properties, which could encourage its use for permanent restorations. Caution is needed with Irix-Plus and Temporis due to their lower flexural strength compared to other traditional materials

In Vitro Mechanical Properties of a Novel Graphene-Reinforced PMMA-Based Dental Restorative Material

Recent studies suggest that the incorporation of graphene in resin-based dental materials might enhance their mechanical properties and even decrease their degree of contraction during polymerization. The present study aimed at comparing the three-point flexural strength (FS), the compressive strength (CS), and the Vickers hardness (VH) of a CAD/CAM poly-methylmethacrylate (PMMA)-based resin, a recently introduced graphene-reinforced CAD/CAM PMMA-based resin (G-PMMA), and a conventional dental bis-acryl composite resin (BACR). No significant differences (p &gt; 0.05) were detected among the materials in terms of flexural strength. On the other hand, a mean flexural modulus value of 9920.1 MPa was recorded in BACR group, significantly higher compared to the flexural modulus detected for G-PMMA (2670.2 MPa) and for conventional PMMA (2505.3) (p &lt; 0.05). In terms of compressive modulus (MPa) and compressive strength (MPa), BACR was significantly stiffer than PMMA and G-PMMA. Concerning VH measurements, a significantly increased hardness emerged comparing the BACR group (VH 98.19) to both PMMA and G-PMMA groups (VH 34.16 and 34.26, respectively). Based on the finding of the present study, the graphene-reinforced (PMMA)-based polymer herein tested was not superior to the conventional PMMA and seemed not able to be considered as an alternative material for permanent restorations, at least in terms of hardness and mechanical response to compressive stress. More research on the mechanical/biological properties of G-PMMAs (and on graphene as a filler) seems still necessary to better clarify their potential as dental restorative materials