The Comparative Study On Polymerization Shrinkage Properties And Degree Of Conversion Of Ten Kinds Of Resin-Composites

Objectives:Light-cured resin-composites have become the most widely used oral filling materials because of their advantages of good aesthetic property,biocompatibility and clinical operability.However,the resin-composites will undergo polymerization shrinkage during the polymerization process,which can lead to microleakage,secondary caries,marginal coloration of fillings,postoperative sensitivity and even treatment failure.Therefore,the use of low shrinkage resin-composites is of great significance to clinical practice.However,not all the monomer molecules of resin-composites will undergo polymerization reaction and convert into polymers during the polymerization process,and there are many unpolymerized residual monomers in the products.The degree of polymerization of resin-composites is usually expressed by the degree of conversion of monomers.The resin-composites with high degree of conversion have good mechanical properties,physical properties and biological properties due to sufficient polymerization.In this experiment,the polymerization shrinkage properties and degree of conversion of ten kinds of light-cured resin-composites were compared,and the relative influencing factors were discussed.Methods:In this experiment,10 commercial light-cured resin-composites including Filtek Z250(Z2),Filtek P60(P6),Surefil(SF),Kalore(KA),Admira Fusion(AF),CLEARFIL MAJESTY Posterior(CMP),Premisa(PR),Tetric N-Ceram Bulk Fill(TNC),Filtek One Bulk Fill(OBF)and X-tra Fil(XF)were selected.Five specimens were prepared for each material and cured under the light intensity of 650 mW/cm~2.The polymerization shrinkage properties of resin-composites were measured by laser ranging sensor method.Volumetric shrinkage,the maximum shrinkage rate and time to reach gel point of each resin-composite were obtained through real-time dynamic monitoring.Fourier transform infrared spectroscopy(FTIR)was utilized to measure the degree of conversion.Results:Experimental results showed that the values of volumetric shrinkage,the maximum shrinkage rate,gel point time and degree of conversion of ten kinds of light-cured resin-composites were significantly different(P<0.01).The volumetric shrinkage values varied from 1.30%to 2.12%and were in descending order of TNC>SF≈Z2≈P6≈OBF≈XF>PR≥KA≥AF≈CMP.The maximum shrinkage rate values ranged from 5.20μm/s to 21.57μm/s and were in descending order of TNC>XF≈P6>Z2≥KA≈OBF≈SF≈PR≥AF>CMP.The gel point time values were from 3.20 s to 4.30 s and in descending order of OBF≈PR≈XF>P6≈Z2≈TNC≈AF≈SF≈KA≈CMP.The degree of conversion values ranged from 54.18%to 86.87%and were in descending order of AF>CMP≥OBF≥PR>KA≈XF>P6≈SF≈Z2≈TNC.Conclusions:Ten kinds of light-cured resin-composites showed significant differences in polymerization shrinkage properties and degree of conversion,which was closely related to the composition and content of organic matrix and inorganic filler.The resin-composites containing nanofillers presented higher degree of conversion than the resin-composites containing microfillers.Some resin-composites having lower polymerization shrinkage and higher degree of conversion were beneficial for various clinical applications.