All-on-4® Treatment Concept for the Rehabilitation of the Completely Edentulous Mandible: A 7-Year Clinical and 5-Year Radiographic Retrospective Case Series with Risk Assessment for Implant Failure and Marginal Bone Level

BackgroundStudies are needed to evaluate long-term outcomes of the All-on-4 (R) treatment concept (Nobel Biocare AB) for rehabilitation of edentulous mandibles by assessing marginal bone levels and risk indicators for implant failure. PurposeTo evaluate 7-year clinical outcomes and 5-year radiographic outcomes of the All-on-4 treatment concept. Materials and MethodsThis retrospective case series included patients admitted for implant rehabilitations in the mandible, who were followed for 7 years clinically and 5 years radiographically. Primary outcome measures were cumulative prosthetic and implant survival using patient as the unit of analysis (Kaplan-Meier product limit estimator). Secondary outcome measure was marginal bone level (MBL) at 5 years. Variables associated with implant failure were analyzed using the Cox proportional hazards regression model to calculate hazard ratios (HRs) with 95% confidence intervals (CIs). Binary logistic regression was used to compute odds ratio (OR) with 95% CIs for variables associated with MBL 2.8mm at 5 years. ResultsA total of 324 patients (194 women, 130 men, average age=58.9 years) were rehabilitated with 1,296 implants supporting 324 full-arch fixed immediately loaded mandibular prostheses. Sixty-four patients (19.8%) were lost to follow-up. Prosthetic survival was 323/324 (99.7%), and 14 patients lost 18 implants, with an estimated cumulative survival rate of 95.4% at 7 years. Variables associated with implant failure were smoking (HR=5.28; 95% CI: 1.33, 20.91]) and the learning curve effect (0.69<HR<0.33 for more experienced levels). Mean MBL at 5 years was 1.81mm (95% CI: 1.70, 1.92), and smoking was associated with MBL 2.8mm (OR=2.4; 95% CI: 1.02, 5.62). ConclusionsThe high implant and prosthetic survival rates and excellent MBL outcome confirm the predictability and safety of the All-on-4 treatment concept over a longer term than previously reported.