The invention relates to a method, system and a device for assessing the risk for periodontitis progression or for developing periodontitis, and a method, system and a device for prognosticating the outcome of a treatment procedure for treating periodontitis, on the basis of a risk score calculated on the basis of weight factors, which may be associated with numerical values, assigned to a plurality of measures corresponding to a plurality of predictors promoting periodontitis comprising host predictors, local predictors, and systemic predictors for periodontitis progression or for developing periodontitis for a patient. The invention provides among other things an objective tool that allows for preventive measures to be taken in time before severe and often irreversible damage caused by periodontitis has occurred, by taking into account the most important risk predictors promoting periodontitis, and in particular takes into account the synergy between these predictors. The invention also relates to a computer readable storage medium, on which there is stored a computer program comprising computer code adapted to perform one or more of the above-mentioned methods, and furthermore such a computer program.