The Research On Effect Of Class Ⅱ Cavity Restored By Posterior Composite Resin With Flowable Liner

With the increasing demand for aesthetic dentistry and concerns regarding mercury toxicity,the popularity of posterior composite restoration has increased,and the posterior composite has the advantage of environmental protection and save tooth tissue as possible.Advances in filler technology have caused the wear rate of posterior composite restorations to approach that of amalgam restorations.Despite continuing improvements in resin-based composites,polymerization shrinkage remains a major drawback of polymerizable resins.Polymerization shrinkage generates stress within the composite that may lead to marginal gap formation,microleakage,postoperative sensitivity and secondary caries.Efforts to overcome these problems are directed towards improving treatment techniques and developing new materials.The use of an intermediate layer of flowable composite under hybrid or packable composites has been recommended to act as a stress-absorbing layer.It has been shown that a more elastic layer applied between the stiff cavity wall and the resin composite can absorb part of the interfacial stress generated during polymerization shrinkage.Recent microleakage tests of this technique have given contradictory results.Recently,a new technique called the modified incremental layering technique for restoring Classâ…¡composites restorations was presented.Accordingly,this in vito study compared Classâ…¡composite restorations either using flowable composite linings with the modified incremental layering technique or without flowable linings by evaluating cervical marginal microleakage and microtensile bond strength.2-year clinical performance of posterior composites with or without flowable linings was also evaluated.1.In vitro evaluation of gingival wall mieroleakage in packable and microhybrid conventional composite restorations with a flowable composite linerMethods:40 sound,caries free human mandibulary molar teeth were used.The teeth were randomly assigned into 4 groups of 8 teeth each.Classâ…¡cavities box were prepared in the mesial and distal aspects of each tooth,half with gingival margins in enamel and half with margins in dentin/cementum.In control groups,restoration was undertaken with packable alone(3M Filtek P60),conventional alone(3M Z250).In the experimental groups,restoration was undertaken with packable plus flowable liner(3M Filtek Flow) and conventional plus flowable liner.After restoration,the teeth were thermocycled 1,500 times,soaked in 2%methylene blue,sectioned and microleakage from the gingival margin scored.Statistical analysis was performed using Kruskal Wallis and Nemenyi tests.Results:There was significant difference between systems in terms of leakage scores at gingival margins.The lined groups showed significant reduction in microleakage at gingival margins. Conclusion:Leakage data support the use of flowable resin composite linings in Classâ…¡resin composite restorations.The conventional and packable resin composites tested were not associated with differences in microleakage.2.Influence of flowable composite lining on bond strength of classâ…¡composite restorationsMethods:20 sound,caries free human mandibulary molar teeth were used. Mesio-occlusal classâ…¡cavity preparations were made in each tooth.The prepared teeth were randomly divided into 4 groups of 5 teeth,according the combination of bonding agent(Single Bond(SB),Prime&Bond NT(NT)) and their respective manufacture packable composite(Filtek P60(P60) Surfil(SF) ) with or without flowable composite(FF).The FF layer was kept as thin as possible.Matckstick-shape samples through the bond interface were sectioned and subjected to micro-tensile bond test at va cross-head speed of 1.0 mm/min.Each fractured specimen was examined under stereo microscope.Results:Bond strength data were analyzed using one-way ANOVA test.No significant difference was found between bonds systems with or without flowable lining.Conclusion:There was no difference on bond strength of classâ…¡composite restorations with or without flowable lining.3.Clinical evaluation of posterior composite material in classâ…¡cavity restoration, lined or not lined with flowable compositesMethods:Total 144 molar teeth with classâ…¡caries were divided into four groups:the experimental group was restored with packable(3M Filtek P60) plus flowable liner(3M Filtek Flow),conventional(3M Z250) plus flowable liner.The control group was restored with packable alone,conventional alone.Patients were clinical reviewed after 1 week,1 year,2 year of treatment.Results:The lined groups showed lower post operation reaction at 1 week review and better cavity adaption.There were few secondary caries in lined groups.Conclusion It appears that clinical result is better when using flowable liner with posterior composite material in classâ…¡cavity restoration.