Non-axial loading of crowns supported by new fiber post systems

Objectives: to evaluate the behavior of non-circular fiber post and accessory posts in supporting non-axially loaded cast metal crowns. Concerns remains about fiber posts used under crowns connected to RPDs using frictional attachments: the hypothesis tested is that an increase in the emerging section of fiber posts doesn't affect the restoration survival rate. Methods: 4 groups: 1)non-circular fiber post concept Ellipson; 2) Fibercone secondary post system (two posts) coupled with one DT Lightpost Illusion #0.5; 3)conventional DT Lightpost Illusion #1; and 4) Macro-Lock Illusion #1, all from RTD, France. 48 single rooted, crownless human teeth were selected and endodontically treated. The canal shape was standardized using the Ellipson ultrasonic diamond tip (Suprasson P5 Newtron, Satelec, France) to obtain a non-circular section, then the teeth were randomly distributed to the 4 groups. PanaviaF and Photocore (Kuraray) were used as luting and core materials, respectively. Core was made using transparent shells. The specimens were prepared with chamfer margins and 1.5mm ferrule height. Cast metal crowns with 5mm off-set extensions were made using CrCo alloy (Vivi) and luted with Fuji Plus (GC). The crowns were subjected to 3.2 million cycles ranging from 100N to 150N under water irrigation. Kaplan-Meyer survival analysis was performed to compare the groups (α=.05). Results: the Fibercone acce ssory post group showed the highest survival rate (0.667), followed by Ellipson (0.583) and Macro-Lock (0.500) groups. Conventional DT post showed the lowest survival rate (0.333). The difference among the groups was not statistically significant (p=0.068). Conclusion: Since non-axial loading generates torsion forces, non-circular post design could better resist this type of stress. Although the number of the specimens is too low to reject the null hypothesis, the survival data suggest that complete crowns restored with accessory and non-circular fiber posts have a higher survival rate in comparison to conventional posts.