Abstract:

BACKGROUND: Post and core crowns are used in the clinic under some conditions, including root fractures, broken posts, and post-core detachment caused by large-scale dental caries and defects. Dentists mainly increase the retentive force by selecting a bonding material with stronger adhesion or by making a retentive groove parallel to the long axis on the surface of the core, but the effect is not obvious.

OBJECTIVE: To investigate the effect of different types of retentive grooves and two different adhesives on the retentive force after the post-core crown restoration.

METHODS: Sixty cobalt-chromium alloy metal crowns and post-core modules simulating the morphology of mandibular premolars were prepared. The axial cohesion angle of the cores was 8°. These crowns and post-core modules were randomly divided into six groups with 10 crowns/pieces per group. In the smooth group, there was no auxiliary retentive groove on the post-core surface. In the horizontal and vertical groups, there were retentive grooves with equal spacing parallel to (horizontal group) or perpendicular to (vertical group) the long axis of the post and core. In the oblique group, the retentive grooves were placed with an oblique angle of 45° with the long axis of the post-core. In the mesh group, the retentive grooves were at an oblique angle of 45° with the long axis of the post and core and crossed. In the point group, the retentive grooves were dot-shaped. In all six groups, glass ionomer cement and self-curing resin adhesive were used to bond post-and-core with crown. The retentive force in each group was tested by the tensile test, and the displacement change of three-dimensional finite element model during the same time was analyzed by the finite element analysis.

RESULTS AND CONCLUSION: (1) Regardless of whether it was bonded with glass ionomer cement or self-curing resin adhesive, the retentive force was highest in the mesh group and lowest in the point group. There was no interaction between adhesives and retentive grooves used to increase retentive force (F=0.26, P=0.91). The effect of different adhesives on retentive force was not significant (F=1.04, P=0.31). The effect of different auxiliary retentive grooves on retentive force was significant (F=14.74, P < 0.05). (2) When the same force was applied at the same time, the displacement of three-dimensional finite element model was smallest in the mesh group. (3) These results suggest that preparation of retentive grooves on the post-core surface can enhance the retentive force. Mesh-shaped retentive grooves provide the greatest retentive force. Different types of adhesives do not provide obviously different effect on the retentive force between the crown and the post and core.

Key words: post and core">,  , metal full crown">,  , retentive groove">,  , adhesive">,  , retentive force">,  , modulus">,  , three-dimensional finite element