Evaluation of the fracture resistance of computer‑aided design/computer‑aided manufacturing monolithic crowns prepared indifferent cement thicknesses

Abstract

Introduction: The purpose of this study was to evaluate the fracture resistance of monolithic computer‑aided  design/computer‑aided  manufacturing (CAD/CAM) crowns that are prepared with different cement thickness.

Materials and Methods: For this investigation, a human maxillary premolar tooth was selected. Master model preparation was performed with a demand bur under water spray. Master die was taken to fabricate 105 epoxy resin replicas. The crowns were milled using a CEREC 4 CAD/CAM system (Software Version, 4.2.0.57192). CAD/CAM crowns were made using resin nanoceramic, feldspathic glass ceramic, lithium disilicate, and leucite‑reinforced ceramics. Each group was subdivided into three groups in accordance with three different cement thicknesses (30, 90, and 150 μm). Crowns milled out. Then RelyX™ U200 was used as a luting agent to bond the crowns to the prepared samples. After one hour cementations, the specimens were stored in water bath at 37°C for 1 week before testing. Seven unprepared and unrestored teeth were kept and tested as a control group. A universal test machine was used to assume the fracture resistance of all specimens. The compressive load (N) that caused fracture was recorded for each specimen. Fracture  resistance data were statistically analyzed by one‑way ANOVA and two‑factor interaction modeling test (α = 0.001).

Results: There are statistically significant differences between fracture resistances of CAD/CAM monolithic crown materials (P < 0.001). It is seen that cement thickness is not statistically significant for fracture resistance of CAD/CAM monolithic crowns (P > 0.001).

Conclusions: CAD/CAM monolithic crown materials affected fracture resistance. Cement thickness (30, 90, and 150 μm) was not effective on fracture resistance of CAD/CAM monolithic crowns.

Keywords: Cement thickness, fracture resistance, monolithic computer‑aided design/computer‑aided manufacturing crowns