The effect of tooth and foundation restoration heights on the load fatigue performance of cast crowns.

STATEMENT OF PROBLEM

In badly damaged teeth and teeth with short clinical crown heights, the placement of foundation restorations has been advocated to permit the development of retention and resistance form. However, there is little information on the effect of these foundation restorations on the clinical performance of the definitive restoration.

PURPOSE

The purpose of this study was to evaluate the load fatigue performance of teeth restored with posts and cores, with varying tooth heights, and to compare them with similar groups having no posts and cores. A secondary purpose was to determine whether a critical tooth height existed at which the placement of a foundation restoration resulted in no significant difference in the load fatigue performance.

MATERIAL AND METHODS

Three test groups (n=10) with prepared tooth heights of 2, 3, and 4 mm were tested. These were compared with another 3 groups with similar tooth heights that were restored with prefabricated titanium posts and core heights of 4, 3, and 2 mm, respectively. Cast complete crowns were then fabricated and cemented with zinc phosphate cement. A fatigue load of 58.8 N was applied at an angle of 135 degrees to the long axis of each crown-tooth specimen. The number of cycles to preliminary failure was determined. Significant differences in cycles to preliminary failure were assessed with 1-way ANOVA, followed by Tukey HSD tests (α=.05).

RESULTS

The group with the greatest preparation height (4 mm) and a 2-mm post-retained foundation had the highest number of cycles to preliminary failure (437,701), while the group with the shortest preparation height and no foundation had the lowest number of cycles (53,806). The Tukey HSD multiple comparison tests showed that for all 3 tooth heights, groups with foundation restorations had a significantly higher number of cycles to preliminary failure than those without foundation restorations.

CONCLUSIONS

For a given tooth height, teeth restored with foundation restorations had a significantly better load fatigue performance than those with no foundation restoration.