The Effect Of Cyclic Mechanical Loading On The Microleakage Of Class â…  Cavity With Different Margin

Microleakage is one of the most important reason for the dental prosthesis off. After chewing, the marginal microleakage of the prosthesis is affected by temperature, chewing and saliva, et al. To analysis the effects of chewing, chewing sites and beveled margin on the microleakage of class I cavity filled with composite resins, this study used cyclic mechanical loading simulate the physiological chewing process to carry out related experiments.Purpose:1To explore the effects of different numbers of cyclic mechanical loading on the microleakage of tooth restoration interface.2To analysis the microleakage of different tooth restoration interface when different site of the tooth is subjected to the vertical loading force.3To explore the effects of beveled margin on the microleakage of tooth-restoration interface when the tooth received numbers of cyclic mechanical loading.Method:Selected140fresh dissociation teeth removed of Orthodontic reasons, which randomly were divided into2big groups of A and B according to different cavity margin designs. By different numbers of loading cycles(0or10000or120000cycles) and different loading sites (the cusp or the middle fovea or the interface), group A and B were divided into six small groups of A0、A1、A2、A3、A4、A5、A6and B0、 B1、B2、B3、B4、B5、B6, each group got10dissociation teeth.Group A was prepared with a single class1cavity while group B got a class1cavity with a beveled margin of1mm width and the angle is about45°. After both were filled with total-etch systems(3M Prime&BondNT) and combined resins(3M FiltekTM P60), Two groups were immersed in saline at37°for24hours and then entrapped with total-curing resins into a sample model of30mm*30mm*25mm.After thermal cycling of500times, each sample was received different number of loading cycles on different site according to groupings. Among them, groupAO and B0is as well as control groups. Then all sample teeth were immersed in1%methyl blue solution for24hours. In each small group,5sample teeth were sectioned longitudinally to obtain3pieces from buccolingual direction while the others from mesiodistal direction. All pieces were examined under metallurgical microscope. The microleakage is measured as the depth to which the dye has penetrated along the tooth-restoration interface.The experimental data was analyzed by One-way ANOVA, Multi-Factor Variance Analysis and The Independent-Sample T Test,etal with SPSS17.0statistical software. Result:1Cyclic mechanical loading increases the microleakage of different interfaces(p<0.05); But there is no significant difference (p>0.05) in the microleakage between groups with10000times of cyclic mechanical loading and groups with no cyclic mechanical loading; While the microleakage in groups with120000times of cyclic mechanical loading is larger than groups with10000times an with no cyclic mechanical loading (p<0.05)2The microleakage is different among groups of different loading sites with the same cavity margin design (p<0.05); The trend of the microleakage is the interface> the cusp and the middle fovea(p<0.05) after10000times of cyclic mechanical loading, while it is the interface> the cusp> the middle fovea (p<0.05) after120000times of cyclic mechanical loading.3The extent of microleakage is different among groups of different interface direction (p<0.05);the microleakage of buccal interface is larger than other interface directions when the loading site is on the interface or the cusp (p<0.05); While there is no significant difference among the groups of different interface direction when the loading site is on the middle fovea or there is no cyclic mechanical loading (p>0.05);There is an interaction effect on the microleakage between the loading site and the interface direction (p<0.05), and the microleakage of buccal interface is the largest one among groups with same numbers of cyclic mechanical loading and same margin design when the loading site is on the buccal interface (p<0.05)4There is no significant difference among groups with beveled or nonbeveled margin when there is no cyclic loading(p>0.05); After10000times of cyclic mechanical loading, the microleakage of buccal and lingual interfaces in groups with beveled margin is less than groups with nonbeveled margin (p<0.05);while there is no significant difference in mesial and distal interface directions between two different margin design groups (p>0.05); After120000times of cyclic mechanical loading, the microleakage on buccal interface in groups with different margin designs is the same (p>0.05) when the loading site is on the buccal interface.while on the other interface, where the microleakage is less in groups with beveled margin (p<0.05)Conclusion:1Cyclic mechanical loading increases the microleakage of tooth restoration interfaces, and the microleakage increased with the increase in the number of cyclic mechanical loading.2The microleakage is different among different site of tooth subjected to the vertical loading force; it is larger on the restoration interface where cyclic mechanical loading happens, while the middle of the restoration is loaded on, the microleakage is the same among different interface direction and less than that of other site been loaded on.3The beveled margin reduce the early microleakage of tooth restoration interface on class I cavity.