Marginal Discrepancy in Two CAD/CAM Zirconia Systems Subjected to Thermo Mechanical Cycling: A Stereomicroscopic Study
DOI:
https://doi.org/10.66838/J.Carcinog.23.1.1114-1122Keywords:
Zirconia; Dental Marginal Adaptation; Computer-Aided Design; Dental Ceramics; Materials Testing.Abstract
Background: Marginal adaptation constitutes a primary factor affecting the clinical longevity of all-ceramic fixed restorations. Despite the widespread clinical adoption of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP), concerns persist regarding its susceptibility to hydrothermal low-temperature degradation (LTD). Ceria-stabilized tetragonal zirconia/alumina nanocomposite (Ce-TZP/Al₂O₃; NANOZR) has been introduced as an alternative with potentially superior aging resistance.
Objectives: The purpose of the current research was to compare the marginal gap of NANOZR and Y-TZP all-ceramic crowns fabricated via CAD/CAM, prior to and following simulated thermo-mechanical aging.
Materials and Methods: Twenty-four full-coverage ceramic crowns were constructed on standardized epoxy-resin dies reproducing a mandibular first molar preparation (1.2 mm chamfer finish line; 1.5–2.0 mm occlusal reduction; 20° total occlusal convergence). Specimens were equally allocated to two groups (n = 12 each): Group I – NANOZR (Ce-TZP/Al₂O₃; Yamakin, Japan) and Group II – Y-TZP (Katana™; Kuraray Noritake, Japan). Each group was subdivided into aged (n = 6) and unaged (n = 6) subgroups. Thermo-mechanical aging was performed using a ROBOTA chewing simulator (150,000 cycles; 50 N; integrated thermocycling). Marginal gap measurements (20 points/crown) were obtained by stereomicroscopy at 45× and quantified using ImageJ software.
Results: Prior to aging, no significant inter-group difference was detected (p = 0.281). Following aging, Y-TZP demonstrated significantly greater marginal discrepancy than NANOZR (p = 0.035). Irrespective of material, thermo-mechanical aging significantly elevated overall marginal gap values (p < 0.0001). All recorded values remained below the 120 µm clinically acceptable threshold.
Conclusions: NANOZR exhibited superior marginal stability relative to Y-TZP following simulated oral aging, likely attributable to its nanocomposite alumina-reinforced microstructure conferring resistance to LTD. Both materials produced clinically acceptable marginal gaps under the conditions tested. Thermo-mechanical aging adversely affected marginal adaptation in both ceramic systems.
