When to restore: Critical crack-size thresholds in human first premolars

Area of Science:

• Dental biomechanics
• Tooth fracture analysis
• Clinical dentistry

Background:

• Cracked teeth pose a clinical challenge, lacking clear treatment guidelines for asymptomatic early-stage cracks.
• Uncertainty exists regarding critical crack dimensions that compromise tooth integrity, hindering decisions between monitoring and intervention.

Purpose of the Study:

• To determine the impact of crack depth and width on human premolar strength and stress distribution.
• To establish critical crack size thresholds for guiding clinical treatment decisions.

Main Methods:

• Experimental compression tests on human first premolars with varying crack depths and widths.
• Finite element analysis (FEA) to simulate stress distribution and validate experimental findings.
• Statistical analysis (ANOVA, regression) to assess the influence of crack dimensions on ultimate strength.

Main Results:

• Crack depth was the dominant factor in reducing tooth strength; width was less significant at greater depths.
• Fractures predominantly initiated at crack tips (91%), unlike in sound teeth.
• The von Mises stress criterion accurately predicted cracked tooth behavior; critical thresholds for strength reduction were identified.

Conclusions:

• Increasing crack size, particularly depth, significantly compromises tooth strength.
• The von Mises stress theory is recommended for analyzing cracked teeth.
• Identified critical crack sizes offer actionable thresholds for timely restorative intervention.