Impact of restoration design and material on the mechanical behavior of implant-supported monolithic CAD-CAM single crowns: An in vitro study.

Purpose

To evaluate the effects of crown design and restorative material on screw loosening and load-bearing performance of monolithic single-implant restorations after cyclic loading.

Methods

Sixty implant-supported molar crowns were assigned to a conventional crown design (CCD; n=30), with a centrally positioned implant, or an alternative crown design (ACD; n=30), with a distally positioned implant and a premolar crown with cantilever. Each design was divided by restorative material (n=10): monochromatic zirconia (Zr_3), multilayer zirconia (Zr_3/5), and lithium disilicate (LS2). Crowns were fixed to titanium bases (35 Ncm) and underwent thermomechanical loading (98 N, 1,200,000 cycles). Occlusal load was applied centrally on CCD crowns and eccentrically on the cantilever in ACD groups. Reverse torque values before and after loading were recorded in Ncm, and reverse torque differences were calculated. Specimens were retightened (35 Ncm) and loaded to failure. Data were analyzed using two-way analysis of variance.

Results

No failures occurred during chewing simulation. ACD showed significantly lower reverse torque difference than CCD (6.72 ± 1.62 vs. 8.13 ± 1.70 Ncm; P = 0.002). CCD fracture loads were 6693 ± 738 N (Zr_3), 6969 ± 659 N (Zr_3/5), and 2330 ± 330 N (LS2). ACD-Zr_3/5 and ACD-Zr_3 showed abutment bending at 914.29 ± 212.92 N and 835.97 ± 70.91 N, respectively, while ACD-LS2 showed abutment bending followed by crown fracture at 1255.60 ± 195.88 N.

Conclusions

Within study limitations, ACD did not increase screw loosening compared with CCD after cyclic loading. All designs and materials tolerated loads exceeding typical physiological masticatory forces.