Limited Evidence Suggests a Single Implant Overdenture as an Alternative to Two-implant-Supported Mandibular Overdentures

Abstract

Selection Criteria: Hand and electronic searches were carried out independently for the PubMed, Embase, and CENTRAL databases by two investigators to identify prospective human studies published in English, between January 1980 and January 2014, reporting on mandibular implant overdentures (IODs) retained with un-splinted attachments. The last-performed search was January 8, 2015. Selections: Randomized controlled trials (RCTs), prospective cohort studies, case'control studies, and prospective case series were included. All reported on single and/or two mandibular IODs utilizing un-splinted attachments on two-piece microrough surface implants with a diameter of at least 3 mm, which had at least 1 year postloading follow-up. Data were extracted independently by the two investigators, who were blinded to each other's extraction. Disagreements were resolved by means of a consensus discussion presided over by third reviewer. The two included RCTs were assessed for risk of study bias using the Cochrane Collaboration's tool. Main Results: Thirty studies met the inclusion criteria for systematic review and qualitative synthesis (28 PCCS and 2 RCTs). Of the 2 RCTs, one had a 3-year follow-up and the other one had 5 years. The meta-analysis of the two RCTs comparing the single-IODs and two-IODs failed to demonstrate any significant risk differences (RDs) for the post-loading implant survival between the two modalities. The results revealed that one study1 slightly favored two-IODs (RD: 0.04, 95% confidence interval [CI]: 0.27, 0.19); while the other2 demonstrated a slight tendency toward single-IODs (RD: 0.08, 95% CI: 0.01, 0.14). However, the overall RD for implant survival for the two interventions was not significant (I2 5 36.6%, p = 0.209; RD: 0.05, 95% CI: -0.07, 0.18). Because the length of follow-up differed between the studies and there were many dropouts, a sensitivity analysis was performed that considered the dropouts as failures. The analysis revealed an inversion of the earlier tendencies. However, the overall RDs for implant survival in the sensitivity analysis still remained non-significant between the two studies (I2 5 57.7%, p = 0.124; RD: 0.07, 95% CI: 0.17, 0.32). Conclusions: The authors concluded that the post-loading implant survival for single implant overdenture was not significantly different from that of two-implant overdentures. However, before recommending the single-IOD as a definitive treatment modality, long-term observations are needed.