Failure analysis of clinically failed all-ceramic fixed partial dentures using fractal geometry

Area of Science:

• Materials Science
• Biomaterials Engineering
• Dental Ceramics

Background:

• Zirconia-based fixed partial dentures (FPDs) are widely used in restorative dentistry.
• Veneer fractures are a common cause of FPD failure, impacting clinical success.
• Understanding the fracture mechanics of these veneers is crucial for improving FPD longevity.

Purpose of the Study:

• To compare the fracture toughness of veneer materials in clinically failed FPDs versus in vitro specimens.
• To identify potential causes of early failures in zirconia-based FPDs.
• To evaluate fractal analysis as a method for assessing fracture toughness in failed ceramic restorations.

Main Methods:

• Fracture toughness was determined using fractal analysis with a modified slit island technique.
• Fractal dimensional increment (D*) and fracture toughness (K(C)) were calculated.
• Paired t-test was used to compare fracture toughness values between clinically failed FPDs and laboratory specimens.

Main Results:

• No significant difference in fracture toughness was found between veneer materials in clinically failed FPDs and laboratory specimens (p>0.05).
• Average fracture toughness values were 0.5+/-0.05 MPam(1/2) for clinical failures and 0.6+/-0.1 MPam(1/2) for lab specimens.
• Potential failure reasons include occlusal overloading, stress corrosion, fatigue, and inadequate structural design.

Conclusions:

• Fractal analysis is a viable alternative for analyzing fracture origins in clinically failed ceramic restorations, particularly when fractography is not feasible.
• This technique can provide insights into the mechanical behavior of fractured dental ceramics.
• The findings suggest that material properties alone may not fully explain FPD failures, highlighting the role of design and functional stresses.