Effect Of Different Types Of Cements And The Timing Of Tooth Preparation On The Coronal Microleakage Of Fiber Post

Objective: The purpose of this study was to find the effect of different types of cements on the coronal microleakage of fiber post under the same tooth preparation timing and the effect of different tooth preparation timing on the coronal microleakage of fiber post, using the same cement.Materials and Method: 62 extracted human mandibular premolars with single root were involved in this experiment. After standard tooth treatment, Group 1,Group 2,Group 3 were cemented by resin modified glass ionomer cement Rely X luting,self-etch resin cement Panavia F and total-etch resin cement Paracore 5ml, respectively. Group 4 was not restored with a fiber post after post space preparation and Group 5 was treated without post space preparation. For Group 1,Group 2 and Group 3, each group was averagely divided into 3 subgroups: A, B, C and were prepared 15min,45min,90min after the cements mixed. After thermocycling and occlusal force cyclic loading, all the teeth were immersed in Indian ink, transparented, and observed under stereoscopic microscope. The scores were record according to Saunders method .Group 6,Group 7 and Group 8 were cemented by Rely X luting,Panavia F,Paracore 5ml, respectively. After thermocycling and occlusal force cyclic loading, each tooth was sectioned into two parts and observed at labels 2mm, 5mm, 8mm above the bottom of the fiber post with an SEM at magnification(×500). The length of hybrid layer of the mesial and distal surfaces was recorded.Result:1. Different types of cements had an effect on the coronal microleakage of fiber post under the same tooth preparation timing, Paracore 5ml caused the least while Rely X luting brought about the most. No statistical differences of the coronal microleakage of fiber post were found when the teeth preparation were carried out 15min,45min or 90min after the cements mixed.2. No obvious hybrid layer was found on the dentin-cement interface of Rely X luting group. Obvious microgaps were found in the inner cement and the interface between the cement and dentin. Microgaps seemed gradually smaller and smaller from the apical to the coronal part.3. Hybrid layer could be found on most of dentin-cement interfaces of Panavia F group, except 3 cases. However, no obvious resin tags or lateral adhesives were observed.4. Hybrid layer could be found on most of dentin-cement interface of Paracore 5ml group, except 1 case. Hybrid layer, resin tags and lateral adhesives were observed in the coronal and middle parts of fiber post.5. The hybrid layer became thicker and thicker from the apical to the coronal part in both Panavia F group and Paracore 5ml group, showing statistical differences.Conclusion:1. The resin modified glass ionomer cement causes the highest coronal microleakage of fiber post, followed by self-etch resin cement, while the total-etch resin cement brings about the lowest under the same tooth preparation timing.2. Different tooth preparation timing causes no significant effect on the coronal microleakage of fiber post when the cement has been completely set.