KI estimation of small interfacial cracks in adhesive ceramic restorations

Objectives: Clinical failure of ceramic adhesive restorations is known to initiate at the interface. In predicting fatigue life, the evaluation of stress intensity factor of a crack initiating at the interface is important. However, evaluation of the stress intensity factor of a small crack in actual restoration geometry is computationally very difficult. The objective of this work is to develop an effective estimation method of stress intensity factor of a crack originating at an adhesive/ceramic interface.

Methods: A simplified trilayer (ceramic/adhesive/tooth substrate) with a half-penny crack located at the center of the bottom surface of the top layer is employed. The stress intensity factor at the crack tip is evaluated when indentation load is applied to the top surface. First, the stress distribution in the region of a crack is calculated from an identical structure without a crack. Second, the stress intensity factor as a function of crack size is obtained by employing a concept of local models developed in this work. The obtained results are compared against accurate stress intensity factors evaluated from a complete 3D finite element simulation with a crack.

Results: The validity of the proposed method is verified for practical dental material combinations and clinically relevant loads. For a crack smaller than 1/10 of the thickness of the top layer, the proposed method is found to be accurate within 2% error for most relevant clinical conditions.

Conclusion: Since the proposed method only requires stress calculation without a crack, no repetitive stress calculation is needed as crack size increases, and it can be utilized in all practical adhesive dental restorations.