Retention strengths of five luting cements on prefabricated dowels after root canal obturation with a zinc oxide/eugenol sealer: 1. Dowel space preparation/cementation at one week after obturation

PURPOSE: This investigation examined the effect of 5 different cements on the retention strength of prefabricated endodontic dowels placed into root canals previously obturated with gutta percha and a zinc oxide/eugenol (ZOE) sealer. MATERIALS AND METHODS: Ninety-six single-rooted teeth were decoronated, filed, cleaned, sequentially shaped, and divided into 6 groups of 16 specimens each. Five of the groups were then obturated with gutta percha and a ZOE sealer. One group was not obturated and served as the control group. Dowel space preparation and dowel cementation for all groups were completed 1 week later. Ten-mm deep dowel spaces were prepared using size 6 Gates Glidden drills. Size 5 Paraposts were then cemented with 5 different cements: Panavia 21 for group 1 (unobturated controls) and group 2; Ketac-Cem glass ionomer for group 3; Fleck's zinc phosphate for group 4; Parapost (composite) Cement for group 5; and C&B Metabond 4-META for group 6. After 48 hours, the dowels were removed using a universal testing machine in tensile mode at 1 mm min(-1). RESULTS: The following results were found (all values in kg): group 1 (controls; Panavia 21) mean = 61.81, 95% CI = +/-8.65; group 2 (Panavia 21), mean=43.15, 95% CI = +/-7.81; group 3 (Ketac-Cem), mean =34.45, 95% CI = +/-4.93; group 4 (zinc phosphate), mean = 25.07, 95% CI = +/-5.03; group 5 (Parapost Cement), mean = 24.99, 95% CI = +/-5.35. None of the group 6 (C&B Metabond) specimens developed measurable bond strengths, so this group was excluded from parametric statistical analyses. An analysis of variance (ANOVA) showed a significant effect of group; pairwise multiple comparison procedures (Tukey test) showed that group 1 (controls) had significantly greater retention than all other groups (p <0.001); group 2 (Panavia 21) had significantly greater retention than groups 4 (zinc phosphate) and 5 (Parapost cement) (p <0.001). None of the other pairwise comparisons were statistically different. CONCLUSION: Paraposts cemented with Panavia 21 in unobturated root canals exhibited significantly higher retention than Paraposts luted with Panavia 21 and 4 different cements into dowel spaces prepared 1 week after obturation with gutta percha/ZOE sealer (p <0.001). Among the obturated groups, Panavia 21 cement (group 2) demonstrated significantly greater retention of Paraposts than zinc phosphate (group 4) and Parapost composite (group 5) cements (p <0.001). Ketac-Cem glass ionomer cement (group 3) had intermediate retention values that were not statistically different than those of groups 2, 4, and 5 (p >0.05). The 4-META cement, C&B Metabond, failed to polymerize.