Fracture resistance, trueness, and phase transformation of bar-reinforced and nonreinforced implant-supported fixed complete prostheses made of high-strength zirconia: An in vitro study.

STATEMENT OF PROBLEM: Implant-supported, fixed, complete arch zirconia prostheses have been widely used for edentulous patients; however, the reliability of bar-free designs remains uncertain. High-strength zirconia formulations may enable predictable restorations without bar reinforcement.

PURPOSE: The purpose of this in vitro study was to evaluate the trueness, fracture resistance, and phase transformation behavior of bar-reinforced and nonreinforced complete arch prostheses fabricated from conventional and high-strength zirconia.

MATERIAL AND

METHODS

Thirty standardized edentulous maxillary models with 6 implant analogs were assigned to 3 groups (n=10): bar-reinforced conventional zirconia (Katana; K-WB), nonreinforced conventional zirconia (Katana; K-NB), and nonreinforced high-strength zirconia (Ice Plus; ICP-NB). The frameworks were digitally designed, milled, sintered, polished, and glazed. The titanium bar was cemented after airborne-particle abrasion. All specimens underwent mastication simulation with thermocycling. Trueness was assessed by superimposing fabricated frameworks onto digital design datasets, phase transformation was analyzed by X-ray diffraction before and after aging, and fracture resistance was measured using a universal testing machine. Data were analyzed using 1-way ANOVA with post hoc tests for fracture strength and trueness and 2-way repeated-measures ANOVA for phase transformation (α=.05).

RESULTS

ICP-NB exhibited the highest mean ±standard deviation fracture resistance (1700 ±50 N), followed by K-WB (1550 ±45 N) and K-NB (900 ±40 N) (P<.05). ICP-NB showed better external trueness compared with both Katana groups (P<.05). In contrast, K-WB demonstrated the best marginal trueness (P<.05). After thermocycling, K-WB and K-NB exhibited significant tetragonal-to-monoclinic phase transformation, while ICP-NB maintained a predominantly tetragonal phase with minimal change (P>.05).

CONCLUSIONS

High-strength zirconia (ICP-NB) complete arch prostheses demonstrated favorable fracture resistance, high trueness, and better resistance to low-temperature degradation than conventional zirconia (K-WB, K-NB), suggesting they are a reliable alternative to bar-reinforced designs.