The Investigation Of The Effect Of Pre-heating On The Properties Of Different Resin Composites.

Dental amalgam was commonly used for the dental defects in the past.But because of the grey color,poisonous and other shortcomings it has been gradually replaced by light-cured resin composite.Nevertheless,there are many deficiencies about resin composites,such as low mechanical properties which could reduce the resin life,residual monomer stimulation which could lead to pulp sensitivity,polymerization shrinkage and microleakage which could cause food debris,saliva and microbial invasion and the development of secondary caries and even lead to bond failure,prosthesis off.Therefore,how to make a more perfect performance of resin composite is a lot of academic research focus.Studies have shown that preheated resin composite can reduce its viscosity and improve the liquidity.The effect on the degree of conversion and the mechanical properties needs further study.Objectives: In this study,we compared the compressive strength,the micro Vickers hardness,the degree of conversion and the microleakage of the FiltekTMz350,Surefil,Solitaire 2,ESTELITEΣ,GRADIA DIRECT,BRILLIANT New Line and DENTEX at room temperature and pre-heated temperature respectively,which could provide the theoretical basis of clinical use for the preheated resin composite .Methods:There were two groups:room temperature group and preheated resin group. The room temperature resin composites were exposed 20s under LED curing light.The heated resin composites were heated to 600c in the incubator,then exposed 20s under LED curing light after 60s which was for the filling and shaping. We maked the samples which were demanded according to the testers.①5 specimens were prepared for the compressive strength of each material.After 24h storaged in the 370c distilled water,they were tested by the electronic universal testing machine.②There were also 5 hardness specimens and they were tested by the micro-Vickers hardness tester after 24h.③The seven different uncured resin composites were spread on KBr and placed in Fourier transform infrared spectrometer to record the absorption spectra.The cured resin composites were crushed, ground and pressed to paltes with KBr.Then they were also placed in infrared spectrometer to record the absorption spectra.We calculated the degree of conversion through the relative relationship of the internal standard peak(C···C)and the characteristic peak(C=C)before and after cured.④70 extracted teeth were collected.After preparing cavities,we filled them with the seven different resin composites at room temperature and pre-heated temperature respectively.Then the teeth were cut 3~4 slices labial-lingal direction along the long axis by the low speed diamond saw.We observed the penetration of dye alone the cavities wall under the stereoscopic microscope and scored them.We used the software SPSS 17.0 for the statistical analysis of all the result data with significance criteria of 0.05.Results:(1)There was no significant difference (p>0.05)between the room temperature group and the pre-heated group for the compressive strength and the Vickers hardness of FiltekTM Z350,Surefil,Solitaire 2,ESTELITEΣ,BRILLIANT New Line and DENTEX.But the strength and the hardness of the preheated GRADIA DIRECT were higher than the room temperature GRADIA DIRECT(p<0.05)(.2)In addition to GRADIA DIRECT and DENTEX,there was no significant difference (p>0.05)between the room temperature group and the preheated group for the degree of conversion of the other 5 resin composites.We couldn't get the degree of conversion of GRADIA DIRECT and DENTEX. (3)There was no difference between the room temperature group and the preheated group for the microleakage of ESTELITEΣand BRILLIANT New Line.The microleakage of the preheated FiltekTM Z350,GRADIA DIRECT and DENTEX decreased,but no significant difference with the room temperature group(p>0.05).The microleakage of the preheated Surefil and Solitaire 2 was significantly lower than the room temperature group(p<0.05).Conclusion:(1)Preteating can't significantly affect the compressive strength,hardness and the degree of conversion of FiltekTM Z350,Surefil,Solitaire 2,ESTELITEΣ,BRILLIANT New Line and DENTEX,but improve the strength and the hardness of GRADIA DIRECT significantly.(2)Preheating decrease the microleakage of Surefil,Solitaire 2 obviously and FiltekTM Z350,GRADIA DIRECT,DENTEX slightly, but no effect for ESTELITEΣand BRILLIANT New Line.(3)The effect of different resins by preheating varies in the degree.The effect of preheating on properties of seven different resins were measured. Different resins have different preheating sensitivity.In clinical application,we should consider the value of preheating synthetically according to the needs to get the best clinical results.