Microfracture mechanisms of composite resins containing prepolymerized particle fillers

Evaluation of Mechanical Properties of Newer Nanoposterior Restorative Resin Composites: An In vitro Study

Introduction:

Tooth coloured restorative materials are subjected to various physical, mechanical conditions in oral conditions. Many newer composites with improved physical and mechanical properties are introduced for clinical use. There are not many clinical studies on recent composites. The aim of this study was to compare the mechanical properties of five commercially available nano composite restorative materials.

Materials and Methods:

Specimens of five nano posterior composite SureFil SDR, ClearFil Majesty, Ever X, Tetric Evo Ceram bulk fill and Filtek Z350 were tested in the study. All samples were prepared According ISO 4049 and polymerized with a LED light for 40 seconds and subjected to mechanical tests for compressive strength, flexural strength, flexural modulous and nano hardness.

Statistical Analysis:

Results obtained were subjected to one way ANOVA and Turkey's post hoc test at significance (p <0.05).

Results:

There was significant differences among composites restorative resins tested. CFM Nano hybrid composite exhibited highest hardness values. Flexural strength, flexural modulous and hardness properties of Ever X and Z350 were almost similar. Compressive strength value of Ever X was high compared with other four composites. SDR exhibited least values when compared with other composites.

Conclusion:

Differences in compressive strength, hardness, flexural strength and modulous is due to differences in percentage and type of filler particles in all composite resin material tested.

Mechanical and structural characterization of discontinuous fiber-reinforced dental resin composite

OBJECTIVES

This study evaluated several fiber- and matrix related factors and investigated different mechanical properties of discontinuous i.e. short fiber-reinforced composite (SFRC) (everX Posterior, eXP). These were compared with three conventional composites, microfilled G-ænial Anterior (GA), nanofilled Supreme XTE (SXTE) and bulk-fill Filtek Bulk-Fill (FBF).

METHODS

Fracture toughness (KIC), flexural strength (FS), flexural modulus (FM), compressive strength (CS), diametral tensile strength (DTS), apparent horizontal shear strength (AHSS) and fracture work (Wf) were determined for each composite (n=8) stored dry or in water. SEM analysis of the fiber diameter (df) (n=6) and orientation (n=6) were performed. The theoretical critical fiber length (lfc) and the aspect ratio (l/d) of SFRC were calculated and the volume fraction of discontinuous fibers (Vf%) and the fiber length (lf) of SFRC were evaluated. The results were statistically analyzed with two-way ANOVA (α=0.05).

RESULTS

The mechanical properties of SFRC (eXP) were generally superior (p<0.05) compared with conventional composites. GA had the highest FM (p>0.05), whereas FBF had the highest AHSS (p<0.05). The fiber related properties Vf%, l/d, lf, lfc and df of eXP were 7.2%, 18-112, 0.3-1.9mm, 0.85-1.09mm and 17μm respectively. SEM results suggested an explanation to several toughening mechanisms provided by the discontinuous fibers, which were shown to arrest crack propagation and enable a ductile fracture. Water exposure weakened the mechanical properties regardless of material type. Wf was unaffected by the water storage.

CONCLUSION

The properties of this high aspect ratio SFRC were dependent on the fiber geometry (length and orientation) and matrix ductility.

CLINICAL SIGNIFICANCE

The simultaneous actions of the toughening mechanisms provided by the short fibers accounted for the enhanced toughness of this SFRC, which toughness value matched the toughness of dentin. Hence, it could yield an inherently uniform distribution of stresses to the hard biological tissues.

Fracture resistance of endodontically treated premolars with direct composite restorations

Purpose:

To determine the fatigue resistance and failure mode of endodontically treated premolars using direct composite resin restorations.

Materials and Methods:

Eighty-four human premolars were divided into seven groups of 12, prepared as follows: Intact teeth used in Group 1 as control, the second group covers the endodontically treated teeth, restored with direct onlays using Z250 composite resin, the next two groups (i.e. 3,4) were similar to the second group, but subjected to 1 and 2 million fatigue load cycles, respectively. Groups 5, 6, 7 were similar to groups 2, 3, 4, however, in these groups Tetric Ceram was used as the restorative material. All specimens were loaded using a Universal Testing Machine until fracture occurred. One-way Anova andTukey's HSD tests were used to analyze the data of onlay groups.

Results:

All specimens withstood the masticating simulation. The mean fracture strength for Goups 1 to 7 was: 1276.92, 1373.47, 1269/70, 486/35, 484/12, 1130/49, 1113/79 Newton, respectively. No statistically significant differences were found between the groups in fracture strength and failure mode.

Conclusions:

No statistically significant differences in fracture strength were found between sound teeth and composite onlays that were subjected to 1 and 2 million fatigue load cycles.