A Study On The Microleakage Of Composite Resins

Light-cured composite resins are finding wider use in clinical practice because of their esthetic advantages,ease of use,improved bonding to tooth structure,and enhanced mechanical properties.It has a tendency to replace silver amalgam in the future.However,it is volume shrinkage of composite resins during polymerization reaction that influence filling effectiveness.During polymerization,it would develop higher setting stresses that lead to gaps between resin and cavity walls which may cause marginal microleakage.There are two influencing factors of polymerization shrinkage and microleakage.First is the nature of composite resins, including elastic modulus,flow ability,inorganic contents and so on. Second is clinical filling procedure,such as bonding systems, configuration factor,base material,curing rate,etc.Now the study about reducing microleakage is concentrate on improving performance of resins and clinical filling technique,and the latter is the major problem that clinician care about.The purpose of this study was to evaluate the microleakage of composite resins with different clinical technique in vitro,and estimate the filling effect of composite resins in vivo. PartⅠThe evaluation of the influencing factor of composite resins' microleakage in vitroExperiment one:Different bonding systems on microleakage of composite resins[Materials and Methods]Ⅰtype cavities were prepared on occlusal surface of 24 freshly extracted molars.Teeth were randomly divided into 2 groups:A.3M Adper Prompt self-etch bonding system;B.3M Adper Single Bond 2 total-etch bonding system.Filling composite resin was 3M Z250.After thermal cycling,all teeth were then immersed in basic fuchsine solution.Each sample was then longitudinally sectioned to obtain 3 pieces from buccolingual direction.These were examined under stereomicroscope,and the degree of microleakage was assessed as the ratio of the extent of dye penetration at the tooth restoration interface to the length of the wall.[Results]No significant difference(P＞0.05)in total microleakage was observed among two materials.But the group of Prompt showed much more microleakage at the enamel margins compared to Single Bond 2 (P＜0.05).[Conclusion]It could be concluded that the bonding effect of self-etch bonding system to enamel was poorer than that of total-etch.Experiment two:Different light curing modes on microleakage of composite resins[Materials and Methods]Ⅰtype cavities were prepared on occlusal surface of 48 freshly extracted molars.Teeth were randomly divided into 4 groups:A.Low intensity lights:300mW/cm~2×40s;B.High intensity lights:600mW/cm~2×20s;C.Soft-Start:100mW/cm~2×10s+600mW/cm~2×15s;D.Intermittent light:600mW/cm~2×40s,2s on,2s off.After thermal cycling,all teeth were then immersed in basic fuchsine solution. Each sample was then longitudinally sectioned to obtain 3 pieces from buccolingual direction.These were examined under stereomicroscope,and the degree of microleakage was assessed as the ratio of the extent of dye penetration at the tooth restoration interface to the length of the wall.[Results]There was no significant difference among four groups(P＞0.05).[Conclusion]Soft-start and intermittent light curing modes did not reduce the microleakage of composite resin(Z250).Experiment three:The microleakage of different composite resins with or without marginal bevels[Materials and Methods]Ⅰtype cavities were prepared on occlusal surface of 40 freshly extracted molars.Teeth were randomly divided into 4 groups:A.3M P60 without bevels;B.3M Z250 without bevels;C.3M P60 with bevels;D.3M Z250 with bevels.After thermal cycling,all teeth were then immersed in basic fuchsine solution.Each sample was then longitudinally sectioned to obtain 3 pieces from buccolingual direction. These were examined under stereomicroscope,and the degree of microleakage was assessed as the ratio of the extent of dye penetration at the tooth restoration interface to the length of the wall.[Results]No significant difference(P＞0.05)was observed among two materials(Z250 and P60).The teeth with bevels showed lower microleakage(P＜0.05).[Conclusion]Margin bevels could reduce the microleakage of composite resins. PartⅡClinical application of composite resins in the initial stage[Materials and Methods]60 teeth with dental defect were admitted for composite resins filling.The oral hygiene of the patients should be well without any serious systemic disease.Then the short period of clinical filling effect of composite resins were assessed by modified USPHS criteria after 6 months.[Results]Filling failed happened in two samples.The clinical effect of composite resins after 6 months was acceptable.[Conclusion]The short-term clinical curative effect of composite resins was satisfactory.