Evaluation of Post and Ferrule Preparations - A Methodological Approach

Objectives: Many laboratory studies relate to restoration of root filled teeth by means of posts, cores and ferrules. Often it is difficult to draw conclusions from these investigations due to experimental heterogeneity and lack of statistical power. This study utilized a standardized protocol to test load and mode of failure cores incorporating combinations of posts, ferrules or both. The protocol aimed to reduce experimental dispersion, minimize sample numbers, but maintain clinical relevance and statistical power.

Methods: 50 ivory root analogues consisting of 5 groups of 10 samples were prepared: Group 1 - all ivory core; Group 2 –post, no ferrule; Group 3 no ferrule, no post; Group 4 – post and 2 mm ferrule; Group 5 - 2 mm ferrule, no post.

Steel Paraposts cemented with Panavia EX were used in Groups 2 and 4. ParaCore® was the core material for groups 2 - 4. A custom jig produced core preparations of a standardized morphology, using a high-speed dental handpiece and burs. Crowns were cast in gold/ palladium alloy from duplicate wax patterns. Static loads 135° to their long-axes were applied on a UTM.

Results: Load- Displacement graphs were used to obtain mean load(N) at failure. Values for each group (standard deviations) were: Group 1= 281.74N (58.38); Group 2= 151.10N (32.94); Group 3= 52.99N (25.34); Group 4 = 277.81N (41.91), Group 5 = 204.68 (48.15). Anova and post hoc 95 % C.I. for combinations of independent t-tests were used. Mode of failure: Groups 1, 2, 4 = root fracture; Group 3= mainly crown fracture. Group 5= crown and root fracture.

Conclusions: The study demonstrated a simple, reproducible protocol for testing combinations of post and core designs. Despite efforts to reduce dispersion, a sample size of at least 20 per test group was required for a fully powered study.