Overview
Both restorations replace an entire arch of teeth with a fixed bridge screwed onto implants. The number of implants is a clinical decision driven by anatomy, bone quality, opposing dentition, and the prosthesis design — not by marketing.
At a glance: All-on-4 vs All-on-6 (or All-on-8)
This table summarises the most common decision factors. Every row is expanded in the sections that follow.
| Factor | All-on-4 | All-on-6 (or All-on-8) |
|---|---|---|
| Number of implants | 4 per arch | 6 (sometimes 8) per arch |
| Placement strategy | Two anterior axial + two posterior tilted (~30–45°) | Typically all axial; may need sinus lift or short implants posteriorly |
| Bone graft / sinus lift often required? | Often avoidable in the maxilla | More commonly needed for posterior implants |
| Distribution of bite force | Concentrated; cantilevers extend distally | Spread across more pillars; shorter cantilevers |
| Bridge cantilever length | Longer | Shorter or eliminated |
| Total surgical time | Shorter | Longer; often more grafting |
| Cost | Lower | Higher |
| Salvageability if one implant fails | Tighter — losing one of four is significant | More forgiving — losing one of six can often be managed without losing the prosthesis |
| Long-term evidence | Mature, including 10–18 yr cohorts | Mature, with broad use historically |
Why number of implants matters biomechanically
A fixed full-arch bridge is a beam supported on pillars. With four pillars, the rear of the bridge cantilevers behind the most distal implant. With six pillars, the bridge can extend further and the cantilevers are shorter, which reduces leverage and stress at the rear implants. In patients with strong bite forces, bruxism, or opposing fixed dentition, this stress matters.
Anatomy drives the decision in the upper jaw
The maxillary sinus expands downward after tooth loss, often leaving insufficient bone for axial posterior implants. All-on-4 was specifically designed to angulate the rear implants forward of the sinus, frequently avoiding sinus grafting[1]. All-on-6 in the maxilla often requires sinus lift procedures to place posterior axial implants[3][4].
What the long-term outcomes look like
Long-term All-on-4 cohorts report high survival of both implants and prostheses across 10–18 years[1][2]. All-on-6 protocols have similarly mature data. Across the literature, both approaches are clinically successful in appropriately selected patients; the comparative trials show small differences and no clear universal winner.
When four implants are sufficient
- Adequate anterior bone, limited posterior bone, sinus close to the ridge.
- Patient wishes to avoid sinus lift / extensive grafting.
- Moderate bite forces, no severe bruxism.
- Cost or surgical burden is a meaningful constraint.
When six (or more) implants are preferable
- Heavy bite forces, bruxism, or opposing fixed natural dentition.
- Adequate posterior bone, or willingness to undergo sinus lift.
- Desire to shorten cantilevers and reduce stress on individual implants.
- Long-term resilience valued over minimising surgery.
How to decide
There is rarely a universally correct answer. The right choice depends on the condition of the surrounding teeth and bone, your medical history, your budget, your tolerance for surgery, and what you want the result to feel and look like ten years from now. Bring this comparison to a consultation and ask the clinician to explain — in your specific case — why one option is being recommended over the other.
Frequently asked questions
Scientific references
- 1. Maló P, de Araújo Nobre M, Lopes A, Ferro A, Nunes M. (2019). The All-on-4 treatment concept for the rehabilitation of the completely edentulous mandible: A longitudinal study with 10 to 18 years of follow-up. Clin Implant Dent Relat Res. 21(4):565-577. View source
- 2. Soto-Peñaloza D, Zaragozí-Alonso R, Peñarrocha-Diago M, Peñarrocha-Diago M. (2017). The all-on-four treatment concept: Systematic review. J Clin Exp Dent. 9(3):e474-e488. View source
- 3. Pjetursson BE, Tan WC, Zwahlen M, Lang NP. (2008). A systematic review of the success of sinus floor elevation and survival of implants inserted in combination with sinus floor elevation. J Clin Periodontol. 35(8 Suppl):216-40. View source
- 4. Starch-Jensen T, Aludden H, Hallman M, Dahlin C, Christensen AE, Mordenfeld A. (2018). A systematic review and meta-analysis of long-term studies (≥5 years) on maxillary sinus floor augmentation. Int J Oral Maxillofac Surg. 47(1):103-116. View source