Abstract:
Purpose: This in vitro study evaluated fracture strengths and failure modes of thin occlusal onlays fabricated from direct resin composite, CAD/CAM polymer-infiltrated ceramic-network, and CAD/CAM lithium-disilicate glass ceramic under compressive loading. Materials and Methods: Forty extracted maxillary molars were prepared, including occlusal enamel and dentin removal, leaving two dentin slopes with peripheral enamel. Thirty teeth were restored with 0.6-mm-thick occlusal onlays using direct resin composite (Premise), CAD/CAM polymer-infiltrated ceramic-network (Vita Enamic), and CAD/CAM lithium-disilicate glass ceramic (IPS e.max CAD). Others were restored with IPS e.max CAD crowns. All restored teeth were loaded vertically by means of a universal testing machine. Fracture loading data were recorded in Newtons (N) and statistically analyzed by one-way analysis of variance and Games-Howell post hoc test (α = 0.05). The failure modes were classified, and correlations between fracture strength and failure mode were analyzed by Spearman’s rank-order test. Results: The fracture strengths (mean ± SD) were 1,949.59, 2,358.86, 2,438.66 and 2,870.44 N for IPS e.max CAD crowns, Vita Enamic occlusal onlay, Premise occlusal onlay and IPS e.max CAD onlays respectively. The IPS e.max CAD onlays showed significantly higher fracture strength than the IPS e.max CAD crowns (p < 0.05). No correlation between fracture strength and failure modes was found within each material. Conclusion: The fracture strength of all thin occlusal onlays were comparable. However, all restorations demonstrated higher fracture resistance than average force of mastication.
