ABSTRACT This study presents the application of the Bayesian method to estimate the probability of critical marginal leakage in dental restorations. Aim of the study was to evaluate the effectiveness of the Bayesian method in estimating the probability of leakage associated with gap in the subsurface layers of composite restorations, based on observations of their surfaces. The study, involving the construction of a Bayesian network model and probabilistic inference, was based on the results of experimental research. These results were used to verify the a priori and a posteriori probabilities of damage to the tooth-restoration system in three zones of the tooth’s anatomical structure and across four load level intervals; using a Bayesian classifier, the study demonstrated the potential for diagnosing critical subsurface leaks. The results obtained show that surface fissure parameters can support the probabilistic diagnosis of leakage throughout the entire volume of the restorative filling, thereby assisting in clinical decision-making regarding the replacement of damage fillings KEYWORDS: sieci Bayesa; prognozowanie niezawodności; stomatologiczne rekonstrukcje materiałowe; nieszczelność brzeżna; obserwacje powierzchniowe i podpowierzchniowe