Microleakage is a biological phenomenon with several implications. The affective component patient hyperalgesia (pain/hypersensitivity) of dentin which is a function of episodic hydrodynan (fluid) movement. The effective component is the disease process which signals the dentin-pulp complex to respond by disposition of sclerotic and/or reparative dentin. Vital dentin is an extension the pulp, presenting the first line of response to the consequences of microleakage. Recent data has demonstrated a correlation between pulp response and material biocompatibility when microleakage is prevented. Dentin-pulp healing is ensured when a proper hermetic seal is provided to control prevent microleakage. A critical evaluation of various clinical procedures is discussed.