In vitro study finds zirconia crown-abutment complexes remained intact after 1.2 million loading cycles, with no significant difference based on manufacturing method or restoration height
Zirconia-based screw-retained implant restorations demonstrated high load-bearing capacity and durability following cyclic loading, with no significant difference between additive and subtractive manufacturing methods, according to a new in vitro study published in The Journal of Prosthetic Dentistry.
The study evaluated zirconia crown-abutment complexes with different restoration heights and found that none of the specimens fractured during 1.2 million cycles of mechanical loading. During subsequent load-to-failure testing, the titanium-base abutments showed plastic deformation before crown fracture.
Researchers found no statistically significant effect of manufacturing method, crown height, or the interaction between the two on the maximum load-bearing capacity of the crown-abutment complexes.
Study Compared Additive and Subtractive Manufacturing
Additive manufacturing has increasingly been explored as an alternative to conventional subtractive techniques for producing implant-supported zirconia restorations.
However, limited evidence is available regarding how restoration height and fabrication method influence the mechanical performance of these restorations.
To investigate this, researchers evaluated screw-retained zirconia crown-abutment complexes manufactured using both additive and subtractive techniques after exposure to cyclic mechanical loading.
Zirconia Crowns Tested at Two Different Heights
The researchers used a mandibular model containing an implant positioned in the right first molar region. The model was digitally scanned and used to design implant-supported screw-retained crowns with heights of either 10 mm or 15 mm.
The restorations were fabricated from 3 mol% yttria-stabilized zirconia using either additive or subtractive manufacturing.
Five specimens were produced for each combination of manufacturing technique and crown height.
All zirconia crowns were cemented to identical titanium-base abutments using an autopolymerizing dental luting composite resin.
Specimens Underwent 1.2 Million Loading Cycles
The crown-abutment complexes were subjected to cyclic mechanical loading at a frequency of 1.7 Hz and a load of 98 N for 1.2 million cycles.
No crown failures occurred during the cyclic loading phase.
Following cyclic loading, all specimens underwent load-to-failure testing to determine the maximum load that could be sustained before failure of the crown-abutment complex.
The researchers analyzed the results using a two-way analysis of variance, with manufacturing method and crown height considered as the primary factors.
No Significant Effect of Manufacturing Method or Crown Height
During load-to-failure testing, the titanium-base abutments demonstrated plastic deformation before the zirconia crowns fractured.
As a result, the recorded maximum loads represented the overall load-bearing capacity of the crown-abutment complexes rather than the fracture resistance of the zirconia crowns alone.
No statistically significant effects were observed for manufacturing method, crown height, or the interaction between these factors, with all P values being at least 0.405.
Mean maximum loads ranged from 3,292 N to 3,810 N, while individual measurements ranged from 1,552 N to 5,335 N.
Zirconia Complexes Withstood Prolonged Mechanical Loading
Both additively and subtractively manufactured implant-supported screw-retained zirconia crown-abutment complexes remained intact throughout the 1.2 million loading cycles.
The maximum loads recorded during subsequent failure testing were higher than previously reported masticatory forces in the molar region.
These findings indicate that, under the specific laboratory conditions of this study, both manufacturing approaches produced zirconia crown-abutment complexes capable of withstanding substantial mechanical loading.
Clinical Relevance and Study Limitations
The findings suggest that additive manufacturing may provide mechanical performance comparable to subtractive manufacturing for the tested screw-retained zirconia implant restorations.
However, the study was conducted in vitro with a limited number of specimens. Laboratory loading conditions cannot fully reproduce the complex biological, mechanical, thermal, and functional environment of the oral cavity.
Therefore, clinical studies with longer follow-up and larger sample sizes will be needed to determine whether these findings translate into comparable long-term performance in patients.
Important Highlights
- Additively and subtractively manufactured zirconia crown-abutment complexes showed high load-bearing capacity in an in vitro study.
- No crown failure occurred during 1.2 million cyclic loading cycles.
- The study evaluated zirconia restorations with 10-mm and 15-mm heights.
- No statistically significant effect was found for manufacturing method, crown height, or their interaction (P ≥ .405).
- Mean maximum failure loads ranged from 3,292 N to 3,810 N.
- Abutments underwent plastic deformation before crown fracture during load-to-failure testing.
