The influence of multiple bonding on the bracket slot and its sliding friction.

Objective To discuss the changes of the slot size and its related indexes and their influence on the slot' sliding friction during multiple bonding.Methods Forty recently extracted human upper premolars were chosen.Ten brackets were bonded to these teeth;the brackets were then reconditioned three times by thermal process and electropolishing.Use SEM before and after multiple bondings to observe the change of the bracket base and the slot size,then the bracket index,the bracket engage index and the critical contact angle were tested.Results The base of the slot became more coarse;the slot size became wider,the bracket width became shorter,the bracket index and the bracket engage index decreased greatly,and the critical contact angle increased significantly(P 0.01).Conclusion During multiple bonding,the wearing of the slot base and the augmentation of the critical contact angle,which is due to the electropolishing,has disadvantages during the sliding between the bracket and archwire.