Effect of different periods of calcium hydroxide dressing on the fracture resistance of root dentin.

The aim of this in vitro study was to evaluate the effect of different periods of intracanal calcium hydroxide (Ca[OH]) dressing application on the compressive strength of root dentin. The roots of 80 human mandibular premolars were prepared via the crown-down technique and randomly distributed into 1 control group (G) and 4 experimental groups (n = 16). The experimental groups were based on the length of intracanal Ca(OH) dressing use: 7 (G), 14 (G), 30 (G), or 90 (G) days. The prepared roots in the control group were left unfilled. The root canals in the experimental groups were dried, filled with the Ca(OH) dressing, and radiographed, and then the root canal entrance was sealed. All of the specimens were stored in saline solution at 37°C for the duration of their experimental period. After storage, the roots were sectioned with 2 cuts. The first cut was 1 mm below the cementoenamel junction, and the second was 6 mm apical to the first cut, creating 6-mm-long × 3-mm-diameter cylinders. At each test period, 4 specimens from G and all 16 specimens from the appropriate experimental group were submitted to compressive strength testing (1 mm/min). The groups demonstrated the following mean (SD) values of compressive strength: G, 174.41 (56.10) MPa; G, 161.29 (39.10) MPa; G, 130.27 (57.53) MPa; G, 167.88 (34.24) MPa; and G, 129.62 (31.46) MPa. Statistically significant differences among the groups were found (P = 0.007; analysis of variance and Tukey test, α = 5%), with a significant difference between G and both G and G (P < 0.05). There were no statistically significant differences (P > 0.05) among the mean compressive strength values of the experimental groups (7, 14, 30, and 90 days). The results indicated that the use of Ca(OH) as an intracanal medication for periods of 14 and 90 days reduced the fracture resistance of root dentin.