The Effect Of Different Therapy Of Desensitization On The Microscopic Characteristic Of The Dentinal Surface And The Shear Bond Strength Of Resin Cements

Objective:In the fixed prosthesis for vital tooth.dental sensitivity always happen after tooth preparation or during adhesion process.Based on the requirement of painless dentistry, using dentin desensitizer or laser irradiation can decrease sensitivity during the adhension process of vital tooth.After desensitization of dentin surface,the interface status between dentin and cements will change and then effect the bond strength of restoration.The purpose of this experiment is to observe the microscopic characteristic of the dentin surface after using Gluma desensitizer or Nd:YAG laser and evaluate the effect of different treatments of dentin surface on the shear bond strength of three resin cements,which contains RelyXTMnicem, Panavia F and Super-Bond C&B.so as to provide theoretical basis for the choice of desensitization and resin cements.Methods:108 freshly extracted young human premolars were used for this study. The teeth were stored in 37℃normal saline after cleaning.27 teeth were randomly selected for SEM observation.the other 81 teeth were used for bond strength test. The buccal surfaces of 27 extracted teeth were flattened by means of a model TR-13 trimmer to expose an "3mm×3mm" dentin plane.27 teeth were divided into 3 groups with 9 in each group in a random manner:Group A in control group received no treatment.Group B was coated by Gluma desensitizer according to the operation guide. Group C was irradiated by Nd:YAG laser. Each groups were cleaved in buccolingual direction, dried and spray-gold, observation was performed with scanning electron microscope.One half of the samples were used to observe the characteristics of the dentin surface,the other were used to observe the characteristics of the profile feature,chose the position that adjoined the treatment surface to shoot. The tooth preparation of the buccal surface of 81 premolar was similar to the above,thus forming a standard plane of 3mm*3mm.The teeth were embedded with self-solidification resin.The buccal surface were exposed and bonded to the bottom surface of the mold with double-sided glue to ensure that it was parallel between the denin bonding surface and the resin undersurface. 81 teeth were divided into 3 groups with 27 in each group in a random manner:the grouping were similar to the above.Each group was divided into 3 subgroups. RelyXTMUnicem were applied in A1,B1,C1 groups, Panavia F were applied in A2,B2,C2 groups,and Super-Bond C&B were applied in A3,B3,C3 groups. The adhered posts to the teeth were completed in permanent strength by the same person. The test piece were preserved in 37℃water for 24h. The shear bond strength was measured and data was analyzed by SPSS 11.5 statistics software. Observe the type of fracture under stereoscopic microscope after the casting departed from the dental body.Results:1.The seal capability of different therapy of desensitization:the orifices of dentinal tubule were mostly occluded in Gluma samples under SEM. Dentinal tubule liquate and block or narrowing in Nd:YAG samples and pit were found in the region of irradiation.2.The shear bond strength of RelyXTMUnicem were obviously lower than Panavia F and Super-Bond C&B (P<0.05)3.After using Gluma desensitizer,The bond strength of Super-Bond C&B increased significantly. The bond strength of Super-Bond C&B increased significantly(P<0.05),(26.02±3.84)Mpa,while the bond strength of RelyXTMUnicem and Panavia F were uninfluenced (P>0.05)4.The bond strength of the three resin cements did not change after laser irradiation (P>0.05)Conclusions:1.Gluma desensitizer can block the orifices of dentinal tubule,while Nd:YAG laser can liquate the dentinal surface.Both of them were effective therapy of desensitization.2.Gluma desensitizer can increase the bond strength of Super-Bond C&B and it doesn't influence the the bond strength of RelyXTMUnicem and Panavia F. Gluma desensitizer can serve as desensitization before bonding of resin cements.3.Nd:YAG laser irradiation could not affect the bonding strength of the three resin cements,and it can also serve as desensitization before bonding of resin cements.