Four or six implants for a fixed full-arch bridge: what does the evidence show?

What immediate loading means in a full-arch plan

“All-on-4” and “All-on-6” describe a fixed full-arch restoration supported by four or six implants. They do not, by themselves, specify when the bridge is attached. In implant research, immediate loading generally means connecting a prosthesis within a short defined period after implant placement; study definitions vary. The 2019 maxillary review defined immediate as delivery by day seven. Some protocols use an interim bridge, while others describe immediate function with a definitive prosthesis. Healing and integration continue after the bridge is fitted, so “immediate” is a timing label, not proof that healing is complete. In the five-year guided-surgery trial, the team recorded insertion torque of 35–45 Ncm and fitted a provisional cross-arch bridge immediately; that is a description of that trial protocol, not a universal threshold or personal recommendation. [2] [4]

A four-implant plan may use posterior implants tilted to extend support and limit the back extension of the bridge. A six-implant plan uses two additional supports, but its practical value depends on bone volume, implant positions, the design and material of the bridge, bite forces, hygiene access and the maintenance plan. The number alone cannot determine suitability.

What comparative studies have found

The most directly relevant evidence now includes randomised trials as well as pooled studies. Their findings do not point to one universal winner: they examine different patients, implant layouts, prostheses and outcomes. A non-significant difference is not proof that two approaches are identical. A non-inferiority result applies only to the outcome, margin and protocol tested.

A five-year multicentre trial

Toia and colleagues reported a multicentre randomised clinical trial of 47 people rehabilitated with maxillary fixed complete dentures supported by four or six implants (233 implants in total). The primary question was whether four implants were non-inferior to six for radiographic marginal bone-level change after five years in function. Review visits were scheduled at years one, three and five. At visits, the fixed bridge was unscrewed; clinicians recorded plaque, bleeding on probing, pocket depth and keratinised mucosa width with a periodontal probe, took periapical radiographs, and provided maintenance care. The team also recorded survival, complications, treatment costs and satisfaction. [1]

Reported implant survival was 100% in the four-implant group and 99.3% in the six-implant group, with one early failure in the six-implant group. At five years, the trial found no significant marginal bone-level difference between groups and reported that four implants met the study’s non-inferiority criterion for this radiographic outcome. Both groups had prosthetic and biological complications; no peri-implantitis was reported. Technical complications were more frequent in the four-implant arm (16.6% versus 0%). The cost analysis favoured four implants for initial and total treatment cost. Satisfaction results varied by domain: four implants were preferred aesthetically and six functionally, particularly for speaking at earlier follow-ups. These findings do not mean that four implants are cheaper in every setting or that either group is complication-free.

The publisher abstract gives the sample and main results, but does not provide the numerical non-inferiority margin, confidence interval for the primary comparison, detailed allocation numbers by arm, or the satisfaction instrument and all time-specific scores. Those details should not be inferred from the abstract. The study was funded in part by Dentsply Sirona Implants; the disclosure reports speaker honoraria for Dr Toia, while the authors declared no conflicts of interest. The trial was registered as NCT02405169. [1]

An earlier guided-surgery trial of immediate function

Tallarico and colleagues randomised 40 people with edentulous maxillae to four or six implants placed with guided surgery and supporting an immediately loaded cross-arch fixed dental prosthesis. The trial followed participants for five years and assessed implant and prosthesis survival, complications, marginal bone loss and periodontal measures. No participant dropped out. Seven implants failed by the five-year examination: six in the six-implant group (5% of that group’s implants) and one in the four-implant group (1.25%); the between-group difference was not statistically significant (p=0.246). No prosthesis failed. Technical and biological complications did not differ significantly (p=0.501), although the authors described a trend towards more complications with four implants and more implant failures with six. Mean marginal bone loss from baseline to five years was 1.71 ± 0.42 mm for four implants and 1.51 ± 0.36 mm for six (mean ± standard deviation; p=0.12); periodontal parameters also showed no significant group differences. [2]

This small trial is directly relevant to immediate loading, but its non-significant results cannot establish equivalence. Its direction of numerical results also differs from the 2024 pooled review below, illustrating why one trial should not be treated as a rule for every patient.

A systematic review and meta-analysis of fixed maxillary prostheses

Sharaf and colleagues searched for studies comparing four- and six-implant support for fixed complete dentures in edentulous maxillae. Of 1,099 records retrieved, 53 studies reporting the relevant outcomes were included. Across studies, the mean follow-up was about 3.8 years. The pooled implant survival estimates were 98.5% (95% confidence interval 97.8%–99.1%) for four implants and 97.0% (95% CI 95.2%–98.4%) for six; the difference was not statistically significant (p=0.06). Prosthesis survival estimates were 99.8% (95% CI 99.1%–100.0%) and 99.6% (95% CI 99.3%–100.0%), respectively (p=0.37). Pooled marginal bone loss was higher in the four-implant group: 1.02 mm (95% CI 0.79–1.26) versus 0.46 mm (95% CI 0.20–0.72), p<0.01. [3]

The 53 included studies were not all head-to-head trials: the reviewers extracted outcomes reported for four-implant and six-implant groups across randomised and non-randomised studies, then pooled group-specific rates using random-effects methods. Some studies contributed data to both groups; others contributed to one group. The estimates therefore summarise a mixed evidence base rather than 53 direct four-versus-six randomised comparisons. The review found no statistically significant difference in pooled implant or prosthesis survival or technical/mechanical and biological complications. Its complication rates per 100 prostheses per year were numerically higher in the four-implant group, but not significantly so. Subgroup analyses associated CAD/CAM-milled frameworks and anteroposterior implant distribution with higher implant survival in the six-implant group; these cross-study subgroup findings do not prove that the framework or layout caused the difference. The authors accepted immediate, early and delayed loading, so the pooled results are not an immediate-loading-only estimate. Between-study variation, differences in follow-up and study design, and inconsistent reporting limit how precisely the pooled figures can predict an individual outcome. [3]

Loading time is a separate decision

The number of implants and the timing of the bridge are related planning choices, but evidence about one is not automatically evidence about the other. Abdunabi and colleagues reviewed controlled clinical trials of immediate versus early or conventional/delayed loading for implant-supported complete dentures in edentulous maxillae. Their search covered multiple databases through 17 January 2019. From 1,052 candidate records, four controlled trials met the criteria. The authors could not pool results because the studies were too heterogeneous. Two trials assessed patient satisfaction: one randomised trial found greater satisfaction with immediate than early loading at 12 months; a non-randomised study found greater satisfaction with immediate than conventional loading at three months, but not at 12 months. Three trials found no significant differences in implant success or prosthetic complications between loading schedules. The authors judged the evidence for differences to be weak and called for better trials. [4]

This review addresses loading schedules, not simply four versus six implants. Its mixed fixed and removable prosthesis eligibility and small evidence base mean its results should not be converted into a promise that a temporary fixed bridge can be fitted immediately in every case. The team’s assessment of initial stability, bone and soft-tissue conditions, implant distribution and the planned restoration remains central.

How to read survival, bone and complication figures

Implant survival asks whether the fixtures remain in place; prosthesis survival asks whether the bridge remains in service. A bridge may remain functional after an implant is lost, and repairs may occur without counting as prosthesis failure. Marginal bone level is measured radiographically around implants; it is not a direct measure of comfort, chewing ability or the whole treatment’s success. Complication counts can include events of different severity, and studies may count them per implant, person or prosthesis. Percentages from one denominator cannot be compared casually with another.

Follow-up also matters. A five-year result describes the people who entered and remained in that study under its maintenance arrangements. It does not establish lifetime performance, guarantee a result for someone with different anatomy or health, or show that routine review can be omitted. “No statistically significant difference” means that the study did not demonstrate a difference under its analysis; it does not show that a clinically meaningful difference is impossible.

Questions to settle with the treating clinical team

Ask which jaw and implant positions are proposed, why four or six supports suit the assessed anatomy, and what findings during surgery could change the plan. Clarify whether the first bridge is provisional or definitive, what material and back extension it uses, how it will be checked or repaired, and what cleaning, diet and review schedule apply. Ask who will provide follow-up and how problems will be managed if you are away from the clinic. The studies do not establish personal eligibility, a safe travel date or a point when follow-up can stop; those decisions require the responsible care team’s assessment.

For budgeting, compare the proposed treatment with the All-on-4 dental implant cost in Turkey and the All-on-6 cost in Turkey. If reviewing a listed option, read the All-on-4 dental implant package and All-on-6 dental implant package alongside the written plan. A price or package description does not establish that a research protocol, a particular bridge material or every review is included; confirm the scope and exclusions with the authorised healthcare partner. Just Clinic Istanbul is an independent marketing and lead-generation platform, not a healthcare provider or medical tourism intermediary. Enquiries may be shared with authorised healthcare partners with your consent.

References

1. Toia M, Moreira CS, Dias DR, Corrà E, Ravidà A, Cecchinato D. Fixed Full-Arch Maxillary Prostheses Supported by Four Versus Six Implants: 5-Year Results of a Multicenter Randomized Clinical Trial. Clinical Oral Implants Research. First published online 24 November 2024; 2025;36(3):298–313. doi: 10.1111/clr.14383. Trial registration: NCT02405169; PMID: 39581887. Publisher abstract and disclosures reviewed. Publisher record.
2. Tallarico M, Meloni SM, Canullo L, Caneva M, Polizzi G. Five-Year Results of a Randomized Controlled Trial Comparing Patients Rehabilitated With Immediately Loaded Maxillary Cross-Arch Fixed Dental Prosthesis Supported by Four or Six Implants Placed Using Guided Surgery. Clinical Implant Dentistry and Related Research. 2016;18(5):965–972. Published online 7 October 2015. doi: 10.1111/cid.12380. PMID: 26446912. Accessible author-hosted full text reviewed.
3. Sharaf MA, Wang S, Mashrah MA, Xu Y, Haider O, He F. Outcomes that may affect implant and prosthesis survival and complications in maxillary fixed prosthesis supported by four or six implants: A systematic review and meta-analysis. Heliyon. 2024;10(3):e24365. Published online 20 January 2024. doi: 10.1016/j.heliyon.2024.e24365. PMID: 38317918; PMCID: PMC10839890. PubMed abstract and indexed full-text sections/search-indexed article reviewed; direct PMC page presented CAPTCHA.
4. Abdunabi A, Morris M, Abi Nader S, de Souza RF. Impact of immediately loaded implant-supported maxillary full-arch dental prostheses: a systematic review. Journal of Applied Oral Science. 2019;27:e20180600. Online 25 July 2019; PubMed citation date 12 August 2019. doi: 10.1590/1678-7757-2018-0600. PMID: 31411262; PMCID: PMC9648956. Indexed full text and PubMed record reviewed.