Background/Objectives: After tooth removal the crest may close before the socket has mineralised, leaving a covered socket residuum (CSR). Third molars are usually removed in young patients, often prophylactically. We examined what former third molar sites contain years later. Methods: Retrospective single-centre study of bone removed at revision of a radiologically diagnosed CSR at former third molar sites, consisting of the bone lid covering the residuum and, where labelled separately, tissue from its depth. For every section the routine pathology report was coded for a leading finding, and the cells were classified independently by whole-slide AI analysis without knowledge of the report. Results: Eighty-three sections from 28 patients (median age 54 years) were analysed. Fifty-one (61.4%) carried a distinguishing finding (53.0% without haematopoietically active marrow), most often marrow fibrosis (14.5%), granulocytic inflammation or osteomyelitis (13.3%) and lymphoplasmacytic infiltrate (10.8%). Of 24 patients with more than one section, 13 showed different findings in different sections. Fibroblasts and inflammatory cells were inversely related (r = −0.979), and the diagnoses formed a gradient from fibroblast-rich avital bone and unremarkable marrow to lymphocyte-rich inflammation (Holm-adjusted p ≤ 0.0065 for fibroblasts, lymphocytes and neutrophils). Conclusions: In this cohort, more than half of the sections from former third molar sites were histopathologically altered, with findings that varied within the same patient. Third molar removal is bone surgery requiring asepsis, removal of the follicle and debridement of the socket, and filling the socket to prevent a residuum deserves controlled evaluation.