Single versus Two Implants-assisted Mandibular Overdentures: A Finite Element Analysis Study

Abstract

Introduction: Single-implant Overdentures (1IODs) have gained popularity as a more economical protocol than Two-implant Overdentures (2IODs). However, concerns have existed about the longevity of using a single implant compared to two implants. Aim: To investigate the marginal bone loss and stress distribution around dental implants assisting 1IODs compared to 2IODs within five years of clinical service. Materials and Methods: This randomised clinical trial was conducted at the Department of Prosthetic Dental Sciences, College of Dentistry of Qassim University in the Kingdom of Saudi Arabia from June 2018 to September 2023. Total 40 completely edentulous male patients, aged 50 to 60 years, were blindly allocated to two groups. Group I included 20 patients who received two implants at the canines’ regions, and Group II included 20 patients who received one implant under their mandibular overdentures at the midline of the mandible. The implants in both groups were followed up immediately after loading, at six and 12 months, three years, and five years for probing depth, mobility, and vertical bone loss. Finite Element Analysis (FEA) was used for stress analysis around the implants. One-way Analysis of Variance (ANOVA) and Mann-Whitney tests were used for statistical analysis at a significance level of p<0.05. Results: Group II had significantly more fractures and required more new dentures than Group I. Specifically, 6 (37.5%) patients at three years and 8 (80%) patients at five years, compared to 2 (13%) patients at three years and 3 (20%) patients at five years in Group I. Additionally, Group II had more fractures at the metal housings in the denture base: 6 (37.5%) patients at the first year, followed by 11 (69%) patients at three years follow-up and 12 (75%) patients at five years, whereas in Group I, 2 (13%) patients in the first year, then at three years, 3 (20%) patients, and at five years, 5 (55%) patients. Regarding reattaching the O-ring to their metal housing, in Group II, 12 (75%) patients required this procedure at three years, and 15 (94%) patients at five years, whereas in Group I, 5 (33%) patients needed this procedure at three years, and 8 (53%) patients at five years. Comparison of the crestal bone loss showed that Group II had significantly more marginal bone loss than Group I. At three years, Group II had vertical bone loss of (3.97±0.16 mm) compared to (2.76±0.15 mm) of Group I, and at 5 years, Group II had (5.01±0.12 mm) compared to (3.41±0.14 mm) in Group I. FEA results revealed statistically significantly less stress concentration around implants in Group I (n=15, 100%) compared to implants in Group II (n=16, 100%), with maximum Von Mises values of 63.30 MPa and 129.94 MPa for vertical and inclined loading in Group I, respectively, and 89.32 MPa and 213.93 MPa for vertical and inclined loading in Group II, respectively. Conclusion: Single implants exhibited more vertical bone loss than two implants, starting three years into service, and their dentures required more repairs and replacements than twoimplant dentures, making their long-term use less economical.