The corrosion behaviour of AISI 420 martensitic stainless steel, frequently employed in dental prosthetics due to its mechanical strength and cost-effectiveness, necessitates a thorough and multidimensional investigation. While this steel offers advantageous machinability, its lower corrosion resistance compared to that of austenitic steels raises concerns, particularly when influenced by factors such as inclusions, residual stresses, and contamination from machining processes. This study aims to elucidate the causes of pitting corrosion on prosthetic keys fabricated from AISI 420. It highlights critical manufacturing stages, particularly washing and passivation processes, which are vital for mitigating corrosion risks. Experimental analyses revealed that corrosion initiation can be attributed to metal residues, inadequate passivation, and contaminated washing water. Furthermore, it was determined that the presence of rust is more closely associated with improper storage and drying practices than with inherent material defects. These findings underscore the importance of meticulous handling and verification of prosthetic components prior to packaging and highlight the need for standardised procedures during sterilisation in clinical settings. The outcomes of this research contribute significantly to enhancing the longevity and reliability of dental prosthetic applications, emphasising the necessity for technological interventions to prevent corrosion in clinical environments.

Background/Objectives: Endo-periodontal lesions (EPLs) represent complex pathological entities involving both periodontal and pulpal tissues, often implying diagnostic and therapeutic challenges. Limited evidence exists regarding the relationship between periodontal disease staging and grading and EPL subtype. The aim is to evaluate the clinical and statistical distribution of endo-periodontal lesions and investigate their association with periodontal stage and grade according to the European Federation of Periodontology (EFP) classification. Methods: An observational retrospective study was conducted in the Department of Periodontology, Faculty of Dental Medicine, Carol Davila University of Medicine and Pharmacy, Bucharest, Romania. Among 884 examined patients, 31 of them were diagnosed with EPLs and included in the analysis. Demographic variables, systemic conditions, affected tooth type, EFP stage and grade, and EPL type according to the Foce classification were recorded. Statistical analysis included Fisher’s exact test and univariable and multivariable binomial logistic regression models. Results: The mean age of the patients was 53.55 ± 9.42 years, with a nearly equal gender distribution. Most patients presented Stage III periodontitis (54.8%), Grade B periodontitis (71%), and EPL 3 (58.1%). Pluriradicular teeth were the most frequently affected (64.5%). The only statistically significant association identified was between EFP grading and EPL classification (p = 0.001). Grade B patients were significantly more likely to present EPL 3 than Grade C patients. Logistic regression analysis demonstrated that Grade B was a strong predictor of EPL 3 both in the univariable model (OR = 27.2; 95% CI: 2.712–272.828) and after adjustment for age and gender (OR = 32.676; 95% CI: 2.832–376.984). Neither age nor gender showed a significant association with EPL 3 occurrence. Conclusions: EPL 3 was the predominant lesion subtype in the study. EFP grading was significantly associated with EPL distribution, with Grade B emerging as an independent predictor of EPL 3. These findings suggest that periodontal disease progression may play a key role in the development and characterization of combined endo-periodontal lesions and highlight the importance of integrated periodontal–endodontic assessment in clinical practice.