Efficacy of Adhesive Crowns to Restore Endodontically-treated Molars: A Micro-CT Study.

Purpose: To evaluate 3D interfacial behavior, occlusal wear, and fracture resistance of endodontically treated molars restored with a full-crown restoration made with 2 different CAD/CAM materials after chewing simulation. Materials and Methods: 24 sound molars were selected and endodontically treated, shaped with PathFile and ProTaper Next (Dentsply Sirona) and filled using a warm condensation technique. Then a standardized MOD cavity was prepared and a fiber post (Panavia Post, Kuraray) supported build-up was performed. A standardized preparation for a complete crown with chamfer margin was done. Samples were then divided into two groups, according to restorative material: G1: zirconia-reinforced lithium silicate (Celtra DUO, Dentsply); G2: cubic zirconia (Katana, Kuraray). Preparations were scanned with Cerec Omnicam and restorations were milled with Cerec MXCL. The restorations were then luted (Panavia V5, Kuraray) following the manufacturer's instructions. After 7 days, the following tests were performed: micro-CT scan (Skyscan, Bruker); optical scan (Sinergiascan, Nobimetal). Fatigue and fracture resistance testing was performed with a chewing simulator (CS4.4, SD-Mechatronik). Thereafter, static fracture was tested using a universal testing machine (Instron) with a 6-mm-diameter steel sphere crosshead welded to a tapered shaft and applied to the specimens at a constant speed of 0.5 mm/min and an angle of 30 degrees to the long axis of the tooth. The load was applied perpendicular to the triangular crest of the palatal cusp. Samples were loaded until fracture; the maximum breaking loads were recorded in Newton (N). Each sample was scanned, radiographically and optically, before and after chewing. Data were imported into Mimics after smoothing and region growing; only external gaps were considered in the analysis. The STL optimal quality masks obtained were imported into Geomagic software for noise removal and volume calculation. Interfacial gap progression and occlusal wear data, expressed in mm3, and fracture resistance, expressed in N, were collected and statistically analyzed with two-way ANOVA (α < 0.05). Results: G1 showed a mean gap size of 0.43 mm3, while G2 had 0.39 mm3. Two-way ANOVA showed that interfacial gaps were not influenced by the material employed (p = 0.0674). Concerning the wear rate, lithium silicate showed a much larger volume reduction in mm3 than cubic zirconia (p = 0.00001). Fracture resistance (G1 = 1351,52; G2 = 1136,43) was significantly influenced by the material employed (p = 0.0001). Conclusion: The obtained results showed that cubic zirconia seems to better perform in the restoration of endodontically treated molars. Further studies are necessary to confirm present data. [ABSTRACT FROM AUTHOR]