Variable reduced metal support for collarless metal ceramic crowns: a new model for strength evaluation

Area of Science:

• Dental Materials Science
• Biomaterials Engineering
• Prosthodontics

Background:

• Metal-ceramic crowns are widely used in restorative dentistry.
• Collarless designs offer aesthetic advantages but raise concerns about porcelain support and fracture resistance.
• Understanding the mechanical behavior of unsupported porcelain is crucial for clinical success.

Purpose of the Study:

• To evaluate the strength and fracture resistance of simulated collarless metal-ceramic crowns with varying degrees of unsupported porcelain.
• To compare the performance of these crowns under different loading angles.

Main Methods:

• A novel specimen design was used to test simulated collarless metal-ceramic crowns.
• Crowns featured ceramic veneers with 0 mm, 1 mm, and 2 mm of unsupported porcelain extension.
• Specimens were subjected to load-to-failure testing at 90, 45, and 6 degrees.

Main Results:

• At a 90-degree angle, crowns with 1 mm and 2 mm unsupported porcelain showed compressive strength comparable to those with complete metal support.
• Fracture resistance significantly decreased at 45 and 6 degrees for all tested porcelain extensions.
• Differences in strength at oblique angles were highly significant (P < .001).

Conclusions:

• Collarless metal-ceramic crowns with up to 2 mm of unsupported porcelain can achieve similar axial strength to fully supported crowns.
• A 90-degree shoulder tooth preparation is critical for maintaining strength in these designs.
• Clinical application requires careful consideration of loading angles to prevent catastrophic fracture.