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Analysis of stresses in hard dental tissues generated by clinical application of retentive root canal posts.

INTRODUCTION
Exact adjustment of retentive posts to the length of root canals is an important prerequisite for the effectiveness of post systems.


AIM
To determine stresses generated in hard dental tissues of upper and lower canines by the application of root canal posts.


MATERIAL AND METHODS
The finite element method was used to create models of upper and lower canines. Loading by a vertical force of Pw = 24 N and a horizontal force of Pv = 15 N was investigated. Twenty two partial dentures and total overdentures in 17 patients were constructed and retained by devices for intraroot retention, placed in canine roots. 16 upper and lower canines were restored by steel posts and composite resin cores.


RESULTS AND DISCUSSION
Equivalent stresses were the greatest at the opening of the root canal. Their maximal values during horizontal loading (6.2 - 6.8 MPa) were several times as high as the values during vertical loading (1.0 - 1.1 MPa). The maximal equivalent stresses were in the range of 20 - 25 MPa, when the diameter of the root canal was 1.5 x 10(-3) mm smaller than the diameter of the post.


CONCLUSIONS
Stresses generated in canine roots with retentive posts during horizontal loading are greater than the stresses induced by vertical loading. Attempts for forceful placement of posts in insufficiently enlarged root canals produce stresses of considerable magnitude which could result in cracks and fractures of hard dental tissues.