The Authors point out dental fields when a treatment error may cause considerable civil TMJ damages. Various damage kinds were examined and diagnosis standards to point them out were illustrated. Evaluation hypothesis using a table system when a sagittal mandibular excursion permanent deficit is present was suggested. The propose analysed the main percentages be bunded in Literature. The distance between upper and lower first bicuspid in maximum non forced mouth opening was considered as a necessary landmark to estimate the mandibular function deficit.