The Effect On Retention Of Glassfiber-reiforced Composites Post Of Pre-treatment On Root Canal Wall

bjective::To evaluate the effect of making undercut in root canal on the retention strength of fiberposts. Methods : 40 extracted human lower mandible premolars which have one root canal and were taken root canal therapy were randomly assigned to five group. Teeth were prepared the path of post normally(depth:8mm),then,make every Canal orifices at the same size(the long diameter is 3.22mm,the short diameter is 2.20mm).Make sure the root wall have no under-cut,and continuous smooth. The control group(group 1) , were inserted using the normal resin adhesive system. Group 2,3,4 were prepared undercut(0.3×1mm) after prepared the path of post,the distance between the undercut and root canal orifice is 2mm (Group 2),4mm(Group 3),6mm(Group 4) . Group 5 were prepared undercut in all the three location .A pull -out test was performed on each fiber posts to measure bond strengths . Results: 1. bond strengths: 207.9±12.60N(group 1),425.3±10.52N(group 2),432.4±9.68N(group 3),335.7±23.69N(group 4),426.4±12.71N(group 5). There were significant difference(P< 0.01)between group 1and group 2,3,4,5 . Concerning the experimental group,there were significant difference(P< 0.05) between group2,3,4 and group 5.2. The control group : Destruction was happened between the dentine and the resin adhesive system .The experimental group: Destruction was happened in resin adhesive system.Conclusion: 1. The retention strength of fiber posts was increased by making undercut in root canal.2. the retention strength of glassfiber-reiforced composites post which have undercut in superior segment of root canal was significantly greater than which have undercut in midpiece of root canal 3. The retention strength have no relation with the quantity of undercut.4.under-cut can make the damage interface change from the dentine and the resin adhesive system to resin adhesive system...