Fracture Behavior of Premolars with Metal Crowns and Several Post-systems

Methods: Natural crowns of 44 human maxillary premolars were removed at the cemento-enamel junction. Canals were prepared with Gates Glidden drills up to size 4 to the full root length. Post spaces were prepared in the palatal canals (8 mm depth, 1.25 mm diameter). Roots were embedded in acrylic. Groups of 11 samples each were treated with (1) cast post-and-cores (Parapost XP, Wironium Plus), (2) prefabricated metal posts (Parapost XH), (3) prefabricated glass fiber posts (Parapost FiberWhite), (4) custom-made glass fiber posts (EverStick Post). Posts of Groups 2, 3 and 4 were cemented (Panavia F) and cores were made (Clearfil Photo Core). Full crown preparations were made with a parallelometer drilling device (ferrule 1.2 mm; chamfer 1 mm), metal crowns were fabricated (Wironium Plus) and placed with Panavia (post-and-cores and crowns in Group 1 with Phosphate cement). All specimens were thermocycled (6000x, 5-55 oC). Preloading was applied (up to 2500 N) using a static loading device under a loading angle of 30 degrees (5 mm/min.). Subsequently, periodontal ligament was simulated (silicone material) and the static load test was repeated. Failure modes were categorized in favorable and unfavorable failures.

Results: During the preloading, no failures occurred. Mean failure loads among the four groups in the repeated test ([1] 1845N, sd=595N; [2] 1718N, sd=636N; [3] 1812N sd=768N; [4] 1514N, sd= 529N) were not significantly different (One-way ANOVA, P=0.62). In 8 specimens (18%) no failures occurred. Unfavorable failures (73%) were root fractures and favorable failures (9%) were post-crown displacements. No differences in frequencies of unfavorable/ favorable failures were seen among the groups (Fisher Exact Test, P=0.76).

Conclusions: Results suggest that different posts have no influence on the fracture behavior of premolars restored with metal crowns.