Fracture strength and three-dimensional marginal evaluation of biocompatible high-performance polymer versus pressed lithium disilicate crowns.

STATEMENT OF PROBLEM

Despite the acceptable physical properties of biocompatible high-performance polymer (BioHPP), little is known about the marginal accuracy and fracture strength of restorations made from this material.

PURPOSE

This in vitro study assessed the marginal and internal adaptation and fracture strength of teeth restored with lithium disilicate (LD) ceramics and BioHPP monolithic crowns.

MATERIAL AND METHODS

Twenty-four extracted premolars were prepared for complete coverage crowns and divided into 2 groups to receive pressed IPS e.max LD, or computer-aided design and computer-aided manufacturing (CAD-CAM) BioHPP monolithic crowns. After adhesive cementation, the marginal and internal adaptations of the restorations were evaluated by microcomputed tomography at 18 points for each crown. Specimens were subjected to 6000 thermal cycles at 5 °C and 55 °C and 200 000 load cycles of 100 N at a frequency of 1.2 Hz. The fracture strength of the restorations was then measured in a universal testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed via an independent-sample t-test (α=.05).

RESULTS

The mean ±standard deviation of marginal gap was 138.8 ±43.6 μm for LD and 242.1 ±70.7 μm for BioHPP groups (P=.001). The mean ±standard deviation value of absolute marginal discrepancy was 193.8 ±60.8 μm for LD and 263.5 ±97.6 μm for BioHPP groups (P=.06). The internal occlusal and axial gap measurements were 547.5 ±253.1 μm and 197.3 ±54.8 μm for LD (P=.03) and 360 ±62.9 μm and 152.8 ±44.8 μm for BioHPP (P=.04). The mean ±standard deviation of internal space volume was 15.3 ±11.8 μm³ for LD and 24.1 ±10.7 μm³ for BioHPP (P=.08). The mean ±standard deviation of fracture strength was 2509.8 ±680 N for BioHPP and 1090.4 ±454.2 MPa for LD groups (P<.05).

CONCLUSIONS

The marginal adaptation of pressed lithium disilicate crowns was better, while BioHPP crowns displayed greater fracture strength. Marginal gap width was not correlated with fracture strength in either group.