Comparison of 4‐ or 6‐implant supported immediate full‐arch fixed prostheses: A retrospective cohort study of 217 patients followed up for 3–13 years

Abstract

Purpose: Choosing four or six implants to support immediate full-arch fixed prostheses (FAFPs) is still controversial worldwide. This study aims to analyze and compare the long-term results of All-on-4 and All-on-6. Materials and Methods:This retrospective cohort study enrolled 217 patients rehabilitated with 1222 implants supporting 271 FAFPs, including 202 prostheses supported by 4 implants (All-on-4 group) and 69 prostheses supported by 6 implants (All-on-6 group), and followed up for 3-13 years. Implant survival, prosthesis survival, complications, and implant marginal bone loss (MBL) were evaluated and compared between two groups. Patient characteristics including age, gender, jaw, opposite dentition condition, smoking habit, bruxism, bone quantity and quality, cantilever length (CL), prosthesis material, and oral hygiene were analyzed to assess their influence on the clinical results of the two groups. Six surgeons and three prosthodontists who performed FAFPs more than 5 years were invited for questionnaires, to assess patient-and clinician-related influences on implant number. Result:In general, All-on-4 group indicated no significant difference with All-on-6 group in the implant survival (implant-level: hazard ratio [HR] = 1.0 [95% confidence interval (CI): 0.8-1.2], P = 0.96; prosthesis-level: HR = 0.8 [95% CI: 0.3-1.8], P = 0.54), prosthesis survival (odds ratio [OR] = 0.8 [95% CI: 0.3-2.8], P = 0.56), biological complications (OR = 0.9 [95% CI: 0.5-1.8], P = 0.78), technical complications of provisional prosthesis (OR = 1.3 [95% CI: 0.7-2.3], P = 0.42), technical complications of definitive prosthesis (OR = 1.1 [95% CI: 0.6-2.2], P = 0.33) and the 1st, 5th, and 10th year MBL (P = 0.65, P = 0.28, P = 0.14). However, for specific covariates, including elderly patients, opposing natural/fixed dentition, smoking, bruxism, long CL, low bone density, and all acrylic provisional prostheses, All-on-6 was more predictable in some clinical measurements than All-on-4. The implant prosthodontists and the medium-experienced clinicians showed significant preference for Allon-6 (P < 0.05). Conclusion:Based on this study, the long-term clinical results showed no significant difference between All-on-4 and All-on-6 groups in general. However, for some Yan Zhang and Sha Li contributed equally to this study and should be considered co-first authors.

Biomechanical comparison of all-on-4 and all-on-5 implant-supported prostheses with alteration of anterior-posterior spread: a three-dimensional finite element analysis

“…Similar results of higher forces with decreasing number of supporting implants have been reported in an in vivo study (Duyck et al, 2000). A randomized controlled clinical trials showed no significant difference in the 5-year implant failure rate and marginal bone absorption between all-on-4 and all-on-6 (Tallarico et al, 2016), and the same result was reported in a recent 3-13-years retrospective cohort study (Zhang et al, 2022).…”

“…The orthogonal anisotropy simulation mainly affected the stress distribution of the implant-bone interface and had no significant effect on the stress values of the implant, abutment, and superstructure. To streamline the calculation of experimental findings, the mandible was presumed to possess isotropic characteristics in accordance with the prevailing approach adopted in previous studies (Macedo et al, 2017;Ozan and Kurtulmus-Yilmaz, 2018;Liu et al, 2019;Zhang et al, 2022;Cheng et al, 2023). Experimental strain gauge and theoretical stress analysis methods have demonstrated that assuming materials are linear, elastic, and isotropic results in an agreement between experimental and theoretical results (Huiskes, 1982).…”

“…As the geometry of the mandible model is very complex, this study used tetrahedral elements of arbitrary geometries of higher simulation accuracy and computational cost to mesh the mandibular models for subsequent numerical calculations. The mandible was hypothesized to be isotropic, each component of the model was assigned a value based on the mechanical properties in the relevant literature in Table 2 (Macedo et al, 2017;Ozan and Kurtulmus-Yilmaz, 2018;Liu et al, 2019;Zhang et al, 2022).…”

Comparative study between two different designs of four implants placement supporting mandibular overdenture: Review article

“…prostheses by using only four implants rather than six implants. (Zhang et al, 2023) It was stated that mandibular overdentures supported by four implants placed in the positions of the canines and molars improve and simplify anchorage systems based on conical copings. They added that the prosthesis stability results in psychologic comfort and masticatory performance similar to that of fixed prostheses but with hygienic, esthetic, and cost advantages.…”