Bone Type and Zirconia Choice Both Move the Needle in All-on-4 Outcomes

The All-on-4 concept has become a mainstay for rehabilitating the edentulous arch, but how bone quality and prosthetic material choice interact to affect medium-term outcomes is less well documented in large, multicenter cohorts. This retrospective observational study followed 250 edentulous patients (125 maxillary, 125 mandibular) who received All-on-4 full-arch implant-supported prostheses between September 2018 and September 2021, for a mean follow-up of 3.6 years. Patients were categorized by bone type (Lekholm and Zarb Types 1-4), and the study tracked implant survival, peri-implant and prosthetic complications, insertion torque, implant stability quotient (ISQ), and patient-reported satisfaction (VAS), comparing metal-acrylic versus monolithic zirconia prostheses.

Across 1,000 implants, overall survival was 94.8%, but this masked a clear bone-quality gradient: survival was 98.3% in Type 1 (dense) bone versus only 89.1% in Type 4 (low-density) bone (p<0.05). Peri-implant complications — notably peri-implantitis and screw loosening — were also significantly more frequent in lower-density bone. On the prosthetic side, metal-acrylic restorations had roughly three times the complication rate of monolithic zirconia (26.9% vs 8.9%, p<0.001). Despite these technical differences, patient satisfaction remained high across all bone types (mean VAS 8.7/10), suggesting patients often don't perceive the complications clinicians are managing behind the scenes.

The clinical message for full-arch treatment planning is twofold: bone quality assessment should directly inform risk counseling and possibly protocol adjustments (e.g., closer follow-up, delayed loading, or additional implants) in Type 4 bone, and prosthetic material selection matters mechanically — monolithic zirconia held up better than metal-acrylic over the medium term in this cohort. The authors frame these as risk-informed planning considerations rather than absolute rules, appropriately noting the limits of a retrospective, medium-term design, but the sample size (1,000 implants across 250 patients, multiple centers) gives the associations real clinical weight for treatment planning discussions in complex full-arch cases.