Effects Of Cavity Lining With Three Repair Materials On The Microleakage Of Class Ⅱ Composite Resin Restorations

Objective: Composite resin material is widely used in the restoration of tooth caries due to its simple operation,non-toxicity,insulation,good appearance,and the ability to restore the tooth morphology.However,the composite resin occurs polymerization shrinkage during the curing process,when the shrinkage stress exceeds the bonding force,bonding interface is easy to be destroyed and will produce cracks,oral bacteria,food residue,saliva can easily through these cracks into the gaps,which may cause postoperative complications such as sensitivity and secondary caries.It is called the marginal microleakage and it can result in failure of filling treatment.Due to the lack of enamel in the molars gingival wall,microleakage is more likely to happen.How to reduce the microleakage of the gingival wall has been hot in current research.The purpose of this experiment is to observe effects of lining with three repair materials(3M Filtekt^TMZ350 flowable resin,3M Vitrebond,Constic flowable resin)on the microleakage of Class Ⅱ composite resin restorations and observe their gaps between fillings and teeth tissues by scanning electron microscopy in vitro study,meanwhile,comparing with the 3M Filtekt^TMZ350 universal resin directly filling group,which can provide a clinical basis for improving the treatment effect of molars class Ⅱ composite resin restorations.Methods:1 The 92 in total extracted healthy premolars were collected from The Department of Oral & Maxillofacial Surgery,Dental Hospital of Hebei Medical University,cleaned and preserved in the normal saline at 4℃.2 Teeth were divided randomly into A.B.C.D four groups（n=23）.Class Ⅱ cavities were prepared in ninety-two extracted premolars.The specimens in group A were only filled with 3M Filtekt^TMZ350 universalcomposite resin.In group B the cavities were lined with 1 mm thick 3M Filtek^TMZ350 flowable resin and followed by light curing,then filled with 3M Filtek^TMZ350 universal composite resin.In group C the cavities were lined with 1 mm thick 3M Vitrebond Class Ionomer and followed by light curing,then filled with 3M Filtek^TMZ350 universal composite resin.In group D the cavities were lined with 1 mm thick Constic flowable resin and followed by light curing,then filled with 3M Filtek^TMZ350 universal composite resin.3 All filled teeth were polished after 24 hours curing.All filled teeth were immersed in artificial saliva at 37℃ as constant temperature for 30 days.4 Temperature cycling test: the teeth stayed in cold water（0⁵℃）for 30 s and warm water（55⁶0℃）for 30 s in a cycle and repeated 500 times.5 After temperature cycling test,13 teeth were picked out randomly from each group for microleakage test,the remaining 10 teeth in each group were measured the gaps between fillings and teeth tissue by SEM.6 Recorded and graded microleakage on each tooth and gaps width between fillings and teeth tissue by SEM,then analyzed statistically.Results:1 The grades of four groups gained from stereomicroscope are significantly different by Wilcoxon Mann-Whitney test.Group B was the least,which showed statistical differences to other three groups（P<0.05）.Group C was the most,which showed statistical differences to group A and group B（P<0.05）.But there was no statistical difference between group C and group D,the same to group A and group D（P>0.05）.2 Through SEM observation,the gaps of group B and group D were smaller than other groups,but there was no statistical difference between them（P>0.05）.The gaps of group C were bigger than other groups,which showed statistical difference to other three groups（P<0.05）.The gaps of group A had statistical difference with other three groups（P<0.05）.Conclusions:1 The four ways of filling restorations for dente molars class Ⅱ caries all had a phenomenon of gingival wall microleakage,but there was somedifferences among them.2 Observed from the stereomicroscope,the group lined with 3M Vitrebond was less microleakage than the highest group lined with Constic flowable resin.The group lined with 3M Filtekt^TMZ350 flowable resin was the lowest one.3 Through SEM observation,the gap between Constic flowable resin and teeth was the largest,and the gaps between fillings and teeth in the group lined with 3M Vitrebond and 3M Filtekt^TMZ350 flowable resin were the smallest ones.