The purpose of this study was to investigate the fracture resistance of crown-root fractured teeth repaired with dual-cured composite resin and horizontal posts. 48 extracted human premolars were assigned to control group and three experimental groups. Complete crown-root fractures were experimentally induced in all control and experimental teeth. In the control group, the teeth (n=12) were bonded with resin cement and endodontically treated. Thereafter, the access cavities were sealed with dual-cured composite resin. In composite resin core - post group (n=12), the teeth were endodontically treated and access cavities were sealed with dual-cured composite resin. In addition, the fractured segments in this group were fixed using horizontal posts. In composite resin core group (n=12), the teeth were endodontically treated and the access cavities were filled with dual-cured composite resin without horizontal posts. In bonded amalgam group (n=12), the teeth were endodontically treated and the access cavities were sealed with bonded amalgam. Experimental complete crown-root fractures were induced again on repaired control and experimental teeth. The ratio of fracture resistance to original fracture resistance was analyzed with Kruskal-Wallis test. The results showed that teeth in control and composite resin core - post group showed significantly higher resistance to re-fracture than those in amalgam core group (p < 0.05). The resistance to refracture was high in the order of composite resin - post group, control group, composite resin group and bonded amalgam group. Within the scope of this study, the use of horizontal post could be beneficial in increasing the fracture resistance of previously fractured teeth.

This study compared the microshear bond strength (µSBS) of light-cured and dual-cured composites to enamel bonded with three self-etching adhesives. Crown segments of extracted human molars were cut mesiodistally, and 1 mm thickness of specimen was made. They were assigned to three groups by used adhesives: Xeno group (Xeno III), Adper group (Adper Prompt L-Pop), and AQ group (AQ Bond). Each adhesive was applied to cut enamel surface as per manufacturer's instruction. Light-cured (Filtek Z 250) or dual-cured composite (Luxacore) was bonded to enamel of each specimen using Tygon tube.

After storage in distilled water for 24 hours, the bonded specimens were subjected to µSBS testing with a crosshead speed of 1 mm/minute. The mean µSBS (n = 20 for each group) was statistically compared using two-way ANOVA, Tukey HSD, and t test at the 0.05 probability level. The results of this study were as follows;

1. The µSBS of light-cured composite was significantly higher than that of dual-cured composite when same adhesive was applied to enamel.

2. For Z 250, the µSBS of AQ group (9.95 ± 2.51 MPa) to enamel was significantly higher than that of Adper goup (6.74 ± 1.80 MPa), but not significantly different with Xeno group (7.73 ± 2.01 MPa).

3. For Luxacore, the µSBS of Xeno group (5.19 ± 1.32 MPa) to enamel was significantly higher than that of Adper goup (3.41 ± 1.19 MPa), but not significantly different with AQ group (4.50 ± 0.96 MPa).