The Effect Of Endodontically Treated Teeth On The Bond Strengths,Post Materials And Convergence Angles

Teeth that were once considered nOnrestorable and extracted can now be treated endodontically and restored to function; however, restored pulpless teeth present unique problem. The most concerned questions are the fracture of the teeth and dislodgment of the prosthodontics. Successful fixed prosthodontic treatment depends on the ability of cemented cast restorations to resist dislodgrnent and strength to resist fracture from tooth preparation. The interaction of 3 primary factors appears to influence potential for dislodgment and fracture: (1) design of the tooth preparation, (2) selection of the post and fit of the casting, (3) nature of the cement. The influences of the convergence angles, types of post, shear bond strengths of the Super Bond on the fractured teeth were investigated in vittv. The first part of the study was to investigate the influence on the bond strengths of Super-Bond to the extracted teeth in the different conditions. Objective: To compare the shear bond strengths in different storage time and different conditions. Method: Divided 32 freshly extracted human teeth into 4 groups randomly, each group was 8 teeth. The first and second groups were stored in physiological saline, and the third and fourth groups were stored in the desiccator. The shear bond strengths were tested by use of the tensilometer. Result: Different shear bond strengths are investigated in different conditions when used Super Bond to bond the fractured tooth. The conditions included different time(I ,6 month) and storage(wet, dry). The values of the shear bond strengths were 17.96 ?.33~ 17.31 ?.72~ 17.O9?.86~ 13.11 ?1.65 (Mpa) respectively0 There were significant differences between the first three groups and the fourth group, but there were not significant differences among the first three groups. Conclusion: The conclusions can be drawn from this study are: (1) The shear bond strengths of Super Bond are over 17 Mpa in most conditions. (2) The wet of the teeth had an effect on the bond strengths. (3) The extraction time had little immfluence on the bond strengths when the teeth were stored in physiological saline after 1 month or 6 month. The second part of the study was to investigate the influence of different posts on the fractured teeth. Objective: To compare the failure loads of three types of post combined with two kinds of luting agents. Method: Divided 60 freshly extracted bovin teeth into 6 groups randomly, each group was 10 teeth. The first and second groups were placed with cast posts, the third and fourth groups were placed with prefabricated posts, and the fifth and sixth groups were placed with carbon fiber posts. The first, third, fifth groups were luted by zinc phosphate; and -4- Jr~1iiA~C the second, fourth, sixth groups were luted by Super-Bond, then to test the failure loads and observe the failure modes of each group. Result: æ…£he mean failure loads of each groups were 216.60?1.35 ~ 229.20 ?46.37 ~. 202.70?42.20.225.60 ?9.15~. ll0.30?3.50~. 135.90?5.03 Newtons respectively. The cast posts had the highest values among the three types of post; furthermore, the second group had the largest values among the six groups. The carbon fiber posts had the lowest values among the three types of post; furthermore, the fifth group had the lowest values among the six groups. There were significant diflerences between the carbon fiber posts groups and the...