Preparation And Properties Of POSS Modified Dental Composite Resin

With development of aesthetics demand and conservtive treatment concept from bothdoctors and patients, composite resin has gradually replaced the silver amalgam, becomethe material of routine therapy in tooth defect directly treatment. However, the long-termclinical practice and investigation show that composite resin restoration still have highclinical failure rates, and shorter clinical service life than silver amalgam.This is mainlybecause high polymerization shrinkage and the shrinkage stress, lead to microleakage,secondary caries, resin loss, postoperative sensitive, dyeing, teeth crack and many otherproblems. In addition, the low strength and low wear resistance of composite resin alsoresult in resin fracture and abrasion. In order to solve these problems, scholars at domesticand abroad committed to develop new types monomer and inorganic filler. Although theseattempts on some properities obtained satisfactory results, there are also showed that thedecrease of other properities, such as polymerization shrinkage decrease concurrentmechanical strength decrease. Polyhedral oligomeric silsesquioxane (POSS) are a kind ofnano hybrid material, it has the nano structure, as well as the characteristics of both organic and inorganic. In this study we attempt to use the two kind of methyl acrylatePOSS which have same functional groups with resin matrix to modify dental compositeresin.Experiment one use two kinds of methyl acrylate POSS (MA-POSS and MI-POSS)with different mass fraction (1wt%,3wt%,5wt%,10wt%), added into the resinmatrix directly; while the experiment two mix the resin with solvent evaporation methodto solve the agglomeration problems in experiment one. Both two experiments observe theinfluence of different types and different mass fraction of POSS on fracture surfacemorphology, double bond conversion, volume shrinkage, flexural strength, flexuralmodulus and wear resistance.The result of experiment one show that MI-POSS has astrong tendency to aggregation, while MA-POSS showed low tendency towardaggregation. With increase of concentration of MI-POSS, the size and quantity ofaggregation increaseing, which result in decrease of flexural strength, flexural modulusand wear resistance. The addition of low concentration of MA-POSS improved themechanical, wear and shrinkage properties. However, resin with a higher MA-POSSconcentration showed lower mechanical, wear, indicating that there is a limited range inwhich the reinforcement properties of MA-POSS can operate. The result showed that3wt%of MA-POSS is a potential candidate for dental composite resin.Experiment two shows that solvent evaporation method obviously increase themiscibility of both MA-POSS and MI-POSS in resin matrix. For MA-POSS, resin of allconcentration have a uniform fracture surface.With the increase of the concentration ofMA-POSS, the flexural strength, flexural modulus, and wear resistance of resin compositeincrease. Compared with the experimental one, the performance of the resin wereincreased, the highest flexural strength reached the in5wt%, and reached the highestwhen adding method directly on the3wt%, it shows that mixed solvent method toimprove the dispersivity of the MA-POSS. Compared with the experimental one, theMA-POSS concentration at maximum flexural strength increased from3wt%to5wt%,which means the solvent evaporation method improve the dispersivity of the MA–POSS.For MI-POSS, the SEM and WAXD shows that MI-POSS aggregation still exist, however both the size and quantity are smaller than experiment one. The flexural strength,flexural modulus, wear resistance are higher than experiment one, but they are stilldecreased with the increase of the concentration of MI-POSS.Section two adopted the method of the pre-reaction (experiment3) and electrostaticspinning (experiment4) process MI-POSS, and then added into the resin. Both twoexperiments aim to improve MI-POSS dispersion in the resin matrix. The result ofexperiment three show that pre-reaction improve the dispersion of POSS obviously, theroughness fracture surface and mechanical properties of resin increased significantly.When the concentration of POSS under3wt%, the flexural strength and flexural modulusof the resin improve constantly. However, WAXD and SEM show that the resin of5wt%POSS formed a small amount of aggregation, result in decrease of flexural strength.Similar to the experiment of section one, the polymerization shrinkage of resin decreasedwith the concentration of POSS increase. Experiment4were successful synthesized fiberscontaining POSS by electrostatic spinning. The results show that the tendency ofpeoperities of composite resin reinforced with electrostatic spinning fiber similar to thepre-reaction method. However, compared with pre-reaction method, the flexural strengthcomposite resin reinforced with electrostatic spinning fiber of3wt%POSS improved10Mpa, and flexural modulus of5wt%POSS improved1Gpa,In conclusion, both POSS can obviously reduce the polymerization shrinkage ofcomposite resin; direct add MI-POSS or high concentration MA-POSS into resin matrixresult in POSS aggregation, causing the deterioration of mechanical properties. Thesolvent evaporation method can obviously improve the dispersion of MA-POSS in theresin, and can improve the mechanical properties and wear resistance of composite resin;however it is less reliable for MI-POSS.Both methods of pre-reaction and electrostaticspinning can improve the dispersion of the MI-POSS resin, while the mechanicalproperties of electrostatic spinning method higher than pre-reaction method.